JP4518218B2 - Magnetic recording medium - Google Patents

Description

【００４８】
アルコキシシランとしては、具体的には、メチルトリエトキシシラン、ジメチルジエトキシシラン、フェニルトリエトキシシラン、ジフェニルジエトキシシラン、ジメチルジメトキシシラン、メチルトリメトキシシラン、フェニルトリメトキシシラン、ジフェニルジメトキシシラン、イソブチルトリメトキシシラン、デシルトリメトキシシラン等が挙げられる。
【００４９】
カーボンブラックの脱離率及び付着効果を考慮すると、メチルトリエトキシシラン、メチルトリメトキシシラン、ジメチルジメトキシシラン、イソブチルトリメトキシシラン、フェニルトリエトキシシランから生成するオルガノシラン化合物が好ましく、メチルトリエトキシシラン、メチルトリメトキシシランから生成するオルガノシラン化合物が最も好ましい。
【００５０】
オルガノシラン化合物の被覆量は、オルガノシラン化合物を被覆した芯粒子粉末に対し、Ｓｉ換算で０．０２〜５．０重量％であることが好ましく、より好ましくは０．０３〜４．０重量％であり、更により好ましくは０．０５〜３．０重量％である。
【００５１】
０．０２重量％未満の場合には、得られる黒色複合ヘマタイト粒子粉末の黒色度、体積固有抵抗値及びミリスチン酸吸着量を改良できる程度にカーボンブラックを十分付着させることが困難である。
【００５２】
５．０重量％を超える場合には、得られる黒色複合ヘマタイト粒子粉末にカーボンブラックを十分付着させることはできるが、効果が飽和しており必要以上に添加する意味がない。
【００５３】
本発明におけるポリシロキサンは、化２で表わされるポリシロキサン、化３で表わされる変成ポリシロキサン、化４で表わされる末端変成ポリシロキサンまたはこれらの混合物を用いることができる。
【００５４】
【化２】

【００５５】
【化３】

【００５６】
【化４】

【００５７】
カーボンブラックの脱離率及び付着効果を考慮すると、メチルハイドロジェンシロキサン単位を有するポリシロキサン、ポリエーテル変成ポリシロキサン及び末端がカルボン酸で変成された末端カルボン酸変成ポリシロキサンが好ましい。
【００５８】
ポリシロキサンの被覆量は、ポリシロキサンを被覆した芯粒子粉末に対し、Ｓｉ換算で０．０２〜５．０重量％であることが好ましく、より好ましくは０．０３〜４．０重量％であり、更により好ましくは０．０５〜３．０重量％である。
【００５９】
０．０２重量％未満の場合には、黒色度や体積固有抵抗値及びミリスチン酸吸着量を改良できる程度にカーボンブラックを十分付着させることが困難である。
【００６０】
５．０重量％を超える場合には、カーボンブラックを十分付着させることはできるが、効果が飽和しており必要以上に添加する意味がない。
【００６１】
本発明におけるカーボンブラック付着量の総量は、芯粒子粉末１００重量部に対し１〜６０重量部である。
【００６２】
１重量部未満の場合には、カーボンブラックの付着量が少ないため、優れた黒色度と低い体積固有抵抗値を有する黒色複合ヘマタイト粒子粉末を得ることが困難となる。
【００６３】
６０重量部を超える場合には、得られる黒色複合ヘマタイト粒子粉末の黒色度及び体積固有抵抗値の改善効果が飽和しており、必要以上に付着させる意味がない。
【００６４】
カーボンブラックが多量に付着、殊に、３０重量部を超えて付着されている場合には、ミリスチン酸吸着量が抑制された黒色複合ヘマタイト粒子粉末が得られる。即ち、芯粒子粉末１００重量部に対しカーボンブラック付着量が３０重量部以下の黒色複合ヘマタイト粒子粉末はミリスチン酸吸着量が０．３４ｍｇ／ｍ²以上であるのに対し、芯粒子粉末１００重量部に対し３０重量部を超えてカーボンブラックが付着されている黒色複合ヘマタイト粒子粉末（以下、多量のカーボンブラックが付着されている黒色複合ヘマタイト粒子粉末とする。）はミリスチン酸吸着量０．３ｍｇ／ｍ²以下である。
【００６５】
カーボンブラック微粒子粉末は、市販のファーネスブラック、チャンネルブラック等を使用することができ、具体的には、＃３０５０、＃３１５０、＃３２５０、＃３７５０、＃３９５０、ＭＡ１００、ＭＡ７、＃１０００、＃２４００Ｂ、＃３０、ＭＡ７７、ＭＡ８、＃６５０、ＭＡ１１、＃５０、＃５２、＃４５、＃２２００Ｂ、ＭＡ６００等（商品名：三菱化学株式会社（製））シースト９Ｈ、シースト７Ｈ、シースト６、シースト３Ｈ、シースト３００、シーストＦＭ等（商品名、東海カーボン株式会社（製））、Ｒａｖｅｎ １２５０、Ｒａｖｅｎ８６０、Ｒａｖｅｎ １０００、Ｒａｖｅｎ １１９０ＵＬＴＲＡ（商品名：コロンビヤン・ケミカルズ・カンパニー（製））、ケッチェンブラックＥＣ、ケッチェンブラックＥＣ６００ＪＤ（商品名：ケッチェンブラック・インターナショナル株式会社（製））、ＢＬＡＣＫ ＰＥＡＲＬＳ−Ｌ、ＢＬＡＣＫ ＰＥＡＲＬＳ １０００、ＢＬＡＣＫ ＰＥＡＲＬＳ ４６３０、ＶＵＬＣＡＮ ＸＣ７２、ＲＥＧＡＬ ６６０、ＲＥＧＡＬ ４００（商品名：キャボット・スペシャルティ・ケミカルズ・インク（製））等が使用できる。
【００６６】
ミリスチン酸吸着量の低減効果を考慮すれば、粉体ｐＨ値が９．０以下のカーボンブラック微粒子粉末を用いることが好ましく、具体的には＃３０５０、＃３１５０、＃３２５０、＃３７５０、＃３９５０、ＭＡ１００、ＭＡ７、＃１０００、＃２４００Ｂ、＃３０、ＭＡ７７、ＭＡ８、＃６５０、ＭＡ１１、＃５０、＃５２、＃４５、＃２２００Ｂ、ＭＡ６００等（商品名：三菱化学株式会社（製））シースト９Ｈ、シースト７Ｈ、シースト６、シースト３Ｈ、シースト３００、シーストＦＭ等（商品名、東海カーボン株式会社（製））、Ｒａｖｅｎ １２５０、Ｒａｖｅｎ ８６０、Ｒａｖｅｎ １０００、Ｒａｖｅｎ １１９０ＵＬＴＲＡ（商品名：コロンビヤン・ケミカルズ・カンパニー（製））、ＢＬＡＣＫＰＥＡＲＬＳ−Ｌ、ＢＬＡＣＫ ＰＥＡＲＬＳ １０００、ＢＬＡＣＫ ＰＥＡＲＬＳ ４６３０、ＲＥＧＡＬ ６６０、ＲＥＧＡＬ ４００（商品名：キャボット・スペシャルティ・ケミカルズ・インク（製））が好ましい。
【００６７】
更に、オルガノシラン化合物被覆層又は、ポリシロキサン被覆層へのより均一な付着処理を考慮すれば、ＤＢＰ吸油量が１８０ｍｌ／１００ｇ以下であるカーボンブラック微粒子粉末を用いることがより好ましく、具体的には＃３０５０、＃３１５０、＃３２５０、ＭＡ１００、ＭＡ７、＃１０００、＃２４００Ｂ、＃３０、ＭＡ７７、ＭＡ８、＃６５０、ＭＡ１１、＃５０、＃５２、＃４５、＃２２００Ｂ、ＭＡ６００等（商品名：三菱化学株式会社（製））シースト９Ｈ、シースト７Ｈ、シースト６、シースト３Ｈ、シースト３００、シーストＦＭ等（商品名、東海カーボン株式会社（製））、Ｒａｖｅｎ １２５０、Ｒａｖｅｎ ８６０、Ｒａｖｅｎ １０００、Ｒａｖｅｎ １１９０ＵＬＴＲＡ（商品名：コロンビヤン・ケミカルズ・カンパニー（製））、ＢＬＡＣＫ ＰＥＡＲＬＳ−Ｌ、ＢＬＡＣＫ ＰＥＡＲＬＳ １０００、ＢＬＡＣＫ ＰＥＡＲＬＳ ４６３０、ＲＥＧＡＬ ６６０、ＲＥＧＡＬ ４００（商品名：キャボット・スペシャルティ・ケミカルズ・インク（製））がより好ましい。
【００６８】
カーボンブラック微粒子粉末の平均粒子径は０．００２〜０．０５μｍが好ましく、より好ましくは０．００２〜０．０３５μｍ程度である。
【００６９】
カーボンブラック微粒子の平均粒子径が０．００２μｍ未満の場合には、カーボンブラック微粒子があまりに微細となるため、取扱いが困難となる。
【００７０】
０．０５μｍを超える場合には、カーボンブラック微粒子の粒子サイズが大きいため、アルコキシシラン被覆又はポリシロキサン被覆へ均一に付着させるために非常に大きな機械的せん断力等が必要となり、工業的に不利となる。
【００７１】
本発明におけるカーボンブラックは、付着量が多量である場合、殊に、芯粒子粉末１００重量部に対し３０重量部を超える場合には、必要により、層間が接着された少なくとも２層をアルコキシシランから生成するオルガノシラン化合物被覆又はポリシロキサン被覆に付着させてもよい。
【００７２】
カーボンブラックの脱離率や付着効果を考慮すると、本発明におけるアルコキシシランから生成するオルガノシラン化合物被覆又はポリシロキサン被覆に付着して形成されているカーボンブラックからなる層（以下、カーボンブラックの第１層という。）の付着量は、芯粒子粉末１００重量部に対し１〜３０重量部が好ましく、より好ましくは３〜２５重量部であって、本発明における上記第１層の表面に接着されて形成されているカーボンブラックからなる層（以下、カーボンブラックの第２層という。）の接着量は、芯粒子粉末１００重量部に対し１〜３０重量部、好ましくは５〜２５重量部である。
【００７３】
本発明におけるカーボンブラックからなる層の層間は、カーボンブラック同志を接着剤をで接着すればよい。層間を強固、且つ、均一に接着し、ミリスチン酸吸着量を抑制するためには、化５で表されるジメチルポリシロキサンが好ましい。接着剤の量は、芯粒子粉末１００重量部に対し、０．１重量部〜５重量部使用することができる。
【００７４】
【化５】

【００７５】
接着剤が０．１重量部未満の場合には、カーボンブラックからなる第２層を十分接着させることが困難となり、得られる黒色複合ヘマタイト粒子粉末のミリスチン酸吸着量を改良できない。
【００７６】
５重量部を超える場合には、カーボンブラックを十分付着させることはできるが、効果が飽和しており必要以上に添加する意味がない。
【００７７】
黒色複合ヘマタイト粒子粉末の粒子形状や粒子サイズは、芯粒子粉末の粒子形状や粒子サイズに大きく依存し、芯粒子粉末にほぼ相似する粒子形態を有し、芯粒子粉末よりも若干大きい粒子サイズを有している。
【００７８】
即ち、黒色複合ヘマタイト粒子粉末は、粒状のヘマタイト粒子粉末を芯粒子粉末とした場合には、粒子サイズが平均粒子径０．０８〜１．０μｍ、好ましくは平均粒子径０．０９〜０．７μｍ、より好ましくは平均粒子径０．１〜０．５μｍである。
【００７９】
針状のヘマタイト粒子粉末を芯粒子粉末とした場合には、平均粒子径（平均長軸径）が０．０８〜１．０μｍ、好ましくは０．０９〜０．７μｍ、より好ましくは０．１〜０．５μｍであって、軸比が２〜２０、好ましくは２．５〜１５、より好ましくは３〜１０である。
【００８０】
板状のヘマタイト粒子粉末を芯粒子粉末とした場合には、平均粒子径（板面径）が０．０８〜１．０μｍ、好ましくは０．０９〜０．７μｍ、より好ましくは０．１〜０．５μｍであって、板状比が２〜５０、好ましくは２．５〜２０、より好ましくは３〜１０である。
【００８１】
平均粒子径が０．０８μｍ未満の場合には、粒子の微細化による分子間力の増大により、磁性塗料の製造時におけるビヒクル中への分散が困難となり、得られる磁気記録媒体の表面平滑性、耐久性及び電磁変換特性が低下する。平均粒子径が１．０μｍを超える場合には、粒子の大粒子化に伴い着色力が低下するため、得られる磁気記録媒体の光透過率を低減することが困難となる。
【００８２】
黒色複合ヘマタイト粒子粉末の粒子形状が針状の場合、軸比が２０を超えると粒子相互間の絡み合いが多くなり、磁性塗料の製造時におけるビヒクル中での均一な分散が困難となり、表面平滑性、耐久性及び電磁変換特性に優れた磁気記録媒体を得ることが困難となる。
【００８３】
黒色複合ヘマタイト粒子粉末の粒子形状が板状の場合、板状比が５０を超えると粒子相互間のスタッキングが多くなり、磁性塗料の製造時におけるビヒクル中での均一な分散が困難となり、表面平滑性、耐久性及び電磁変換特性に優れた磁気記録媒体を得ることが困難となる。
【００８４】
黒色複合ヘマタイト粒子粉末のカーボンブラックの脱離率は２０％以下が好ましく、より好ましくは１０％以下である。カーボンブラックの脱離率が２０％を超える場合には、磁性塗料の製造時において、脱離したカーボンブラックによりビヒクル中での均一な分散が阻害されるため、表面平滑性、耐久性及び電磁変換特性に優れた磁気記録媒体を得ることが困難となる。
【００８５】
黒色複合ヘマタイト粒子粉末の黒色度は、芯粒子粉末として黒色ヘマタイト粒子粉末を用いた場合、上限値がＬ^*値で１９、好ましくは１８．５であり、芯粒子粉末としてヘマタイト粒子粉末を用いた場合、上限値がＬ^*値で２１、好ましくは２０．５である。Ｌ^*値が上限値を超える場合には、明度が高くなり、黒色度が十分とはいえず、得られる磁気記録媒体の光透過率を低減することが困難となる。黒色度の好ましい下限値はＬ^*値で１５程度である。
【００８６】
黒色複合ヘマタイト粒子粉末の体積固有抵抗値は、１×１０⁶Ω・ｃｍ以下であることが好ましく、より好ましくは１×１０¹Ω・ｃｍ〜５×１０⁵Ω・ｃｍ、更により好ましくは１×１０¹Ω・ｃｍ〜１×１０⁵Ω・ｃｍである。体積固有抵抗値が１×１０⁶Ω・ｃｍを超える場合は、得られる磁気記録媒体の表面電気抵抗値を十分に低減することが困難となる。
【００８７】
多量にカーボンブラックが付着されている本発明における黒色複合ヘマタイト粒子粉末は、ミリスチン酸吸着量が０．０１〜０．３ｍｇ／ｍ²であり、好ましくは０．０１〜０．２９ｍｇ／ｍ²、より好ましくは０．０１〜０．２８ｍｇ／ｍ²である。
【００８８】
ミリスチン酸吸着量が上記範囲である場合には、黒色複合ヘマタイト粒子粉末に吸着されるミリスチン酸が適量であるため、磁気記録層表面に浸み出すミリスチン酸吸着量の調整が容易であり、繰り返しのテープ使用に対して十分低い摩擦係数を長期間保つことが可能であり、優れた走行性を確保することができる。
【００８９】
黒色複合ヘマタイト粒子粉末のＢＥＴ比表面積値は、１．０〜２００ｍ²／ｇ、好ましくは２．０〜１５０ｍ²／ｇ、より好ましくは、２．５〜１００ｍ²／ｇである。ＢＥＴ比表面積値が１．０ｍ²／ｇ未満の場合には、粒子が粗大であったり、粒子相互間で焼結が生じた粒子粉末となっており、着色力が低下するため、得られる磁気記録媒体の光透過率を低減することが困難となる。ＢＥＴ比表面積値が２００ｍ²／ｇを超える場合には、粒子の微細化による分子間力の増大により、磁性塗料の製造時におけるビヒクル中への分散が困難となり、得られる磁気記録媒体の表面平滑性、耐久性及び電磁変換特性が低下する。
【００９０】
黒色複合ヘマタイト粒子粉末の粒子径の幾何標準偏差値は、１．８以下であることが好ましい。幾何標準偏差値が１．８０を超える場合には、存在する粗大粒子のため、磁性塗料の製造時におけるビヒクル中での均一な分散が困難となり、表面平滑性、耐久性及び電磁変換特性に優れた磁気記録媒体を得ることが困難となる。得られる磁気記録媒体の表面平滑性、耐久性及び電磁変換特性を考慮すれば、幾何標準偏差値は１．７以下がより好ましく、更により好ましくは１．６以下である。工業的な生産性を考慮すれば、粒子径の幾何標準偏差値の下限値は１．０１である。
【００９１】
カーボンブラックの付着厚みは、０．０４μｍ以下が好ましく、より好ましくは０．０２μｍ以下、更に好ましくは０．０１μｍ以下である。
【００９２】
本発明に係る磁気記録媒体の磁気記録層中に含まれる磁性粒子粉末としては、マグヘマイト粒子粉末、マグネタイト粒子粉末、マグヘマイトとマグネタイトとの中間酸化物であるベルトライド化合物粒子粉末等の磁性酸化鉄粒子粉末、該磁性酸化鉄粒子粉末にＦｅ以外のＣｏ、Ａｌ、Ｎｉ、Ｐ、Ｚｎ、Ｓｉ、Ｂ等の異種元素を含有させた磁性酸化鉄粒子粉末、これら磁性酸化鉄粒子にＣｏ等を被着させたＣｏ被着型磁性酸化鉄粒子粉末、鉄を主成分とする金属磁性粒子粉末、鉄以外のＣｏ、Ａｌ、Ｎｉ、Ｐ、Ｚｎ、Ｓｉ、Ｂ及び希土類金属等を含有する鉄合金磁性粒子粉末、Ｂａ，Ｓｒ又はＢａ−Ｓｒを含有する板状マグネトプランバイト型フェライト粒子粉末並びに該フェライト粒子粉末にＣｏ、Ｎｉ、Ｚｎ、Ｍｎ、Ｍｇ、Ｔｉ、Ｓｎ、Ｚｒ、Ｎｂ、Ｃｕ、Ｍｏ等の２価及び４価の金属から選ばれた保磁力低減剤の１種又は２種以上を含有させた板状マグネトプランバイト型フェライト粒子粉末等のいずれをも用いることができる。
【００９３】
なお、近年の磁気記録媒体の高密度記録化を考慮すれば、磁性粒子粉末としては、Ｃｏ被着型磁性酸化鉄粒子粉末、鉄を主成分とする金属磁性粒子粉末及び鉄以外のＣｏ、Ａｌ、Ｎｉ、Ｐ、Ｚｎ、Ｓｉ、Ｂ、希土類金属等を含有する鉄合金磁性粒子粉末等が好ましい。
【００９４】
磁性粒子粉末の粒子の形状は、針状はもちろん、紡錘状、米粒状、立方状、板状等のいずれであってもよい。ここで「針状」とは、文字通りの針状はもちろん、紡錘状や米粒状などを含む意味である。
【００９５】
磁性粒子粉末は、平均長軸径（板状粒子の場合は平均粒子径）が０．０１〜０．５０μｍ、好ましくは０．０３〜０．３０μｍであって、平均短軸径（板状粒子の場合は平均厚み）が０．０００７〜０．１７μｍ、好ましくは０．００３〜０．１０μｍであり、幾何標準偏差値は２．５以下、好ましくは１．０１〜２．３である。
【００９６】
また、粒子形状が針状の磁性粒子粉末の場合、軸比は３以上、好ましくは５以上であり、磁性塗料の製造時におけるビヒクル中への分散性を考慮すれば、その上限値は１５であり、好ましくは１０である。
【００９７】
粒子形状が板状の磁性粒子粉末の場合、板状比は２以上、好ましくは３以上であり、磁性塗料の製造時におけるビヒクル中への分散性を考慮すれば、その上限値は２０であり、好ましくは１５である。
【００９８】
磁性粒子粉末のＢＥＴ比表面積値は、１５ｍ²／ｇ以上であり、好ましくは２０ｍ²／ｇ以上である。磁性塗料の製造時におけるビヒクル中への分散性を考慮すれば、その上限値は１００ｍ²／ｇであることが好ましく、より好ましくは８０ｍ²／ｇである。
【００９９】
磁性粒子粉末の磁気特性は、針状磁性酸化鉄粒子粉末やＣｏ被着型針状磁性酸化鉄粒子粉末の場合、保磁力値が２５０〜１７００Ｏｅ、好ましくは３００〜１７００Ｏｅであって、飽和磁化値が６０〜９０ｅｍｕ／ｇ、好ましくは６５〜９０ｅｍｕ／ｇである。
【０１００】
鉄を主成分とする針状金属磁性粒子粉末又は針状鉄合金磁性粒子粉末の場合、保磁力値が８００〜３５００Ｏｅ、好ましくは９００〜３５００Ｏｅであって、飽和磁化値が９０〜１７０ｅｍｕ／ｇ、好ましくは１００〜１７０ｅｍｕ／ｇである。
【０１０１】
板状マグネトプランバイト型フェライト粒子粉末の場合、保磁力値が５００〜４０００Ｏｅ、好ましくは６５０〜４０００Ｏｅであって、飽和磁化値が４０〜７０ｅｍｕ／ｇ、好ましくは４５〜７０ｅｍｕ／ｇである。
【０１０２】
本発明に係る磁気記録媒体の磁気記録層中に含まれる結合剤樹脂としては、現在、磁気記録媒体の製造にあたって汎用されている塩化ビニル−酢酸ビニル共重合体、塩化ビニル−酢酸ビニル−無水マレイン酸共重合体、塩化ビニリデン、ポリウレタン樹脂、スチレン−ブタジエン共重合体、ブタジエン−アクリロニトリル共重合体、ポリビニルブチラール、ニトロセルロース等セルロース誘導体、ポリエステル樹脂、ポリブタジエン等の合成ゴム系樹脂、エポキシ樹脂、ポリアミド樹脂、ポリイソシアネート、電子線硬化型アクリルウレタン樹脂等とその混合物を使用することができる。
【０１０３】
また、各結合剤樹脂には−ＯＨ、−ＣＯＯＨ、−ＳＯ₃Ｍ、−ＯＰＯ₂Ｍ₂、−ＮＨ₂等の極性基（但し、ＭはＨ、Ｎａ、Ｋである。）が含まれていてもよい。磁性塗料の製造時における磁性粒子粉末及び黒色複合ヘマタイト粒子粉末のビヒクル中への分散性を考慮すれば、極性基として−ＣＯＯＨ、−ＳＯ₃Ｍを含有している結合剤樹脂が好ましい。
【０１０４】
本発明における磁気記録層の塗膜厚さは、０．０１〜５．０μｍの範囲である。０．０１μｍ未満の場合には、均一な塗布が困難で塗りむら等が生じやすくなるため好ましくない。５．０μｍを超える場合には、反磁界の影響のため、所望の電磁変換特性が得られにくくなる。好ましくは０．０５〜１．０μｍの範囲である。
【０１０５】
磁気記録層中の磁性粒子粉末と結合剤樹脂との配合割合は、磁性粒子粉末１００重量部に対して結合剤樹脂が５〜５０重量部、好ましくは６〜３０重量部である。
【０１０６】
結合剤樹脂が５０重量部を超える場合には、磁気記録層中の磁性粒子粉末が少なすぎるため、磁性粒子粉末の充填率が低下し、電磁変換特性が低下する。５重量部未満の場合には、磁性粒子粉末の量に対して結合剤樹脂が少なすぎるため、磁性塗料中で磁性粒子粉末が十分に分散されず、その結果、塗膜にした時に表面が十分平滑な塗膜が得られ難い。また、磁性粒子粉末が結合剤樹脂によって十分にバインドされないために、得られた塗膜はもろいものとなりやすい。
【０１０７】
磁気記録層中の磁性粒子粉末と黒色複合ヘマタイト粒子粉末との配合割合は、磁性粒子粉末１００重量部に対して黒色複合ヘマタイト粒子粉末が１〜３０重量部、好ましくは３〜２５重量部である。
【０１０８】
黒色複合ヘマタイト粒子粉末が１重量部未満の場合には、磁気記録層中に含有される黒色複合ヘマタイト粒子粉末が少なすぎるため、磁気記録媒体の耐久性が不十分となるとともに、磁気記録媒体の光透過率及び表面電気抵抗値を低減することが困難となる。黒色複合ヘマタイト粒子粉末が３０重量部を超える場合には、磁気記録媒体に十分な耐久性を付与できるとともに、磁気記録媒体の光透過率及び表面電気抵抗値を低減することができるが、磁気記録層中に非磁性成分が増加することになり、磁気記録媒体の高密度記録化に不利となる。
【０１０９】
磁気記録層中には、通常用いられる潤滑剤、研磨剤、帯電防止剤等が必要により含まれていてもよい。
【０１１０】
本発明に係る磁気記録媒体の非磁性基体材料としては、現在、磁気記録媒体に汎用されているポリエチレンテレフタレート、ポリエチレン、ポリプロピレン、ポリカーボネート、ポリエチレンナフタレート、ポリアミド、ポリアミドイミド、ポリイミド等の合成樹脂フィルム、アルミニウム、ステンレス等金属の箔や板及び各種の紙を使用することができ、その厚みは、その材質により種々異なるが、通常好ましくは１．０〜３００μｍ、より好ましくは２．０〜２００μｍである。
【０１１１】
磁気ディスクの場合、非磁性基体としてはポリエチレンテレフタレートが通常用いられ、その厚みは、通常５０〜３００μｍ、好ましくは６０〜２００μｍである。磁気テープの場合は、ポリエチレンテレフタレートの場合、その厚みは、通常３〜１００μｍ、好ましくは４〜２０μｍ、ポリエチレンナフタレートの場合、その厚みは、通常３〜５０μｍ、好ましくは４〜２０μｍ、ポリアミドの場合、その厚みは、通常２〜１０μｍ、好ましくは３〜７μｍである。
【０１１２】
本発明における非磁性下地層は、塗膜厚さが０．２〜１０．０μｍの範囲が好ましい。０．２μｍ未満の場合には、非磁性支持体の表面粗さを改善することが困難となり、スティフネスも不十分となりやすい。磁気記録媒体の薄層化及び塗膜のスティフネスを考慮すれば、より好ましくは０．５〜５．０μｍの範囲である。
【０１１３】
非磁性下地層における結合剤樹脂には、磁気記録層を形成する場合に用いた前記結合剤樹脂を使用することができる。
【０１１４】
非磁性下地層における非磁性粒子粉末と結合剤樹脂との配合割合は、結合剤樹脂１００重量部に対し、非磁性粒子粉末が５〜２０００重量部、好ましくは１００〜１０００重量部である。
【０１１５】
非磁性粒子粉末が５重量部未満の場合には、粒子粉末が少なすぎるため、塗膜にした時に、非磁性粒子粉末の連続分散した層が得られず、塗膜表面の平滑性及び基体のスティフネスが不十分となる。２０００重量部を超える場合には、結合剤樹脂の量に対して非磁性粒子粉末が多すぎるため、非磁性塗料中で非磁性粒子粉末が十分に分散されず、その結果、塗膜にした時に、表面が十分平滑な塗膜が得られ難い。また、非磁性粒子粉末が結合剤樹脂によって十分にバインドされないために、得られた塗膜はもろいものとなりやすい。
【０１１６】
尚、非磁性下地層に、通常の磁気記録媒体の製造に用いられる潤滑剤、研磨剤、帯電防止剤等が必要により結合剤樹脂１００重量部に対し０．１〜５０重量部程度含まれていてもよい。
【０１１７】
本発明における非磁性下地層用非磁性粒子粉末としては、通常磁気記録媒体用非磁性下地層に用いられる非磁性無機質粉末を使用することがでる。具体的には、ヘマタイト、含水酸化鉄、酸化チタン、酸化亜鉛、酸化スズ、酸化タングステン、二酸化ケイ素、α−アルミナ、β−アルミナ、γ−アルミナ、酸化クロム、酸化セリウム、炭化ケイ素、チタンカーバイト、窒化ケイ素、窒化ホウ素、炭酸カルシウム、炭酸バリウム、炭酸マグネシウム、炭酸ストロンチウム、硫酸カルシウム、硫酸バリウム、二硫化モリブデン、チタン酸バリウム等を単独又は組み合わせて用いることができ、殊に、ヘマタイト、含水酸化鉄、酸化チタン等が好ましい。
【０１１８】
なお、非磁性塗料製造時におけるビヒクル中での分散性改善のため、必要により、これら非磁性粒子粉末の粒子表面をアルミニウムの水酸化物、アルミニウムの酸化物、ケイ素の水酸化物、ケイ素の酸化物等で表面処理してもよく、また、得られる磁気記録媒体の光透過率、表面電気抵抗値、機械的強度、表面平滑性、耐久性等の諸特性改善のため、必要により、粒子内部にＡｌ，Ｔｉ，Ｚｒ，Ｍｎ，Ｓｎ，Ｓｂ等を含有させたりしてもよい。
【０１１９】
得られる非磁性下地層の表面平滑性を考慮すれば、非磁性粒子粉末の形状は針状が好ましい。ここで「針状」とは、文字どおりの針状はもちろん、紡錘状や米粒状などを含む意味である。
【０１２０】
非磁性粒子粉末の粒子サイズは、平均長軸径が０．０１〜０．３μｍであり、好ましくは０．０１５〜０．２５μｍ、より好ましくは０．０２〜０．２μｍである。
【０１２１】
本発明に係る磁気記録媒体は、フィラー材として粒子表面がアルミニウムの水酸化物等によって被覆されていない黒色複合ヘマタイト粒子粉末を用いた場合には、保磁力値が２５０〜４０００Ｏｅ、好ましくは３００〜４０００Ｏｅ、角形比（残留磁束密度Ｂｒ／飽和磁束密度Ｂｍ）が０．８５〜０．９５、好ましくは０．８６〜０．９５、塗膜の光沢度が１６５〜３００％、好ましくは１７０〜３００％、塗膜の表面粗度Ｒａが９．５ｎｍ以下、好ましくは２．０〜９．０ｎｍ、より好ましくは２．０〜８．５ｎｍ、塗膜の線吸収係数が１．３０〜５．００μｍ^-1、好ましくは１．３５〜５．００μｍ^-1、塗膜の表面電気抵抗値が１．０×１０⁹Ω／ｓｑ以下、好ましくは７．５×１０⁸Ω／ｓｑ以下、より好ましくは５．０×１０⁸Ω／ｓｑ以下である。
【０１２２】
フィラー材として、多量にカーボンブラックが付着されている黒色複合ヘマタイト粒子粉末を用いた場合には、上記諸特性を有することはもちろん、塗膜の線吸収係数が１．４０〜５．００μｍ^-1、好ましくは１．４５〜５．００μｍ^-1、塗膜の表面電気抵抗値が５×１０⁸Ω／ｓｑ以下、好ましくは２．５×１０⁸Ω／ｓｑ以下、より好ましくは１×１０⁸Ω／ｓｑ以下、摩擦係数が０．２５〜０．３０、好ましくは０．２５〜０．２９である。
【０１２３】
本発明に係る磁気記録媒体は、フィラー材として粒子表面がアルミニウムの水酸化物等によって被覆されている黒色複合ヘマタイト粒子粉末を用いた場合には、保磁力値が２５０〜４０００Ｏｅ、好ましくは３００〜４０００Ｏｅ、角形比（残留磁束密度Ｂｒ／飽和磁束密度Ｂｍ）が０．８５〜０．９５、好ましくは０．８６〜０．９５、塗膜の光沢度が１７０〜３００％、好ましくは１７５〜３００％、塗膜の表面粗度Ｒａが９．０ｎｍ以下、好ましくは２．０〜８．５ｎｍ、より好ましくは２．０〜８．０ｎｍ、塗膜の線吸収係数が１．３５〜５．００μｍ^-1、好ましくは１．４０〜５．００μｍ^-1、塗膜の表面電気抵抗値が１．０×１０⁹Ω／ｓｑ以下、好ましくは７．５×１０⁸Ω／ｓｑ以下、より好ましくは５．０×１０⁸Ω／ｓｑ以下である。
【０１２４】
フィラー材として、多量にカーボンブラックが付着されている黒色複合ヘマタイト粒子粉末を用いた場合には、上記諸特性を有することはもちろん、塗膜の線吸収係数が１．４５〜５．００μｍ^-1、好ましくは１．５０〜５．００μｍ^-1、塗膜の表面電気抵抗値が５×１０⁸Ω／ｓｑ以下、好ましくは２．５×１０⁸Ω／ｓｑ以下、より好ましくは１×１０⁸Ω／ｓｑ以下、摩擦係数が０．２１〜０．２６、好ましくは０．２１〜０．２５である。
【０１２５】
本発明に係る磁気記録媒体は、磁性粒子粉末として、鉄を主成分とする針状金属磁性粒子粉末又は針状鉄合金磁性粒子粉末を用いるとともに、フィラー材として粒子表面がアルミニウムの水酸化物等によって被覆されていない黒色複合ヘマタイト粒子粉末を用いた場合には、保磁力値が８００〜３５００Ｏｅ、好ましくは９００〜３５００Ｏｅ、角形比（残留磁束密度Ｂｒ／飽和磁束密度Ｂｍ）が０．８５〜０．９５、好ましくは０．８６〜０．９５、塗膜の光沢度が１９０〜３００％、好ましくは１９５〜３００％、塗膜表面粗度Ｒａが８．５ｎｍ以下、好ましくは２．０〜８．０ｎｍ、より好ましくは２．０〜７．５ｎｍ、塗膜の線吸収係数が１．３０〜５．００μｍ^-1、好ましくは１．３５〜５．００μｍ^-1、塗膜の表面電気抵抗値が１．０×１０⁹Ω／ｓｑ以下、好ましくは７．５×１０⁸Ω／ｓｑ以下、より好ましくは５．０×１０⁸Ω／ｓｑ以下である。
【０１２６】
フィラー材として、多量にカーボンブラックが付着されている黒色複合ヘマタイト粒子粉末を用いた場合には、上記諸特性を有することはもちろん、塗膜の線吸収係数が１．４０〜５．００μｍ^-1、好ましくは１．４５〜５．００μｍ^-1、塗膜の表面電気抵抗値が５×１０⁸Ω／ｓｑ以下、好ましくは２．５×１０⁸Ω／ｓｑ以下、より好ましくは１×１０⁸Ω／ｓｑ以下、摩擦係数が０．２５〜０．３０、好ましくは０．２５〜０．２９である。
【０１２７】
本発明に係る磁気記録媒体は、磁性粒子粉末として、鉄を主成分とする針状金属磁性粒子粉末又は針状鉄合金磁性粒子粉末を用いるとともに、フィラー材として粒子表面がアルミニウムの水酸化物等によって被覆されている黒色複合ヘマタイト粒子粉末を用いた場合には、保磁力値が８００〜３５００Ｏｅ、好ましくは９００〜３０００Ｏｅ、角形比（残留磁束密度Ｂｒ／飽和磁束密度Ｂｍ）が０．８５〜０．９５、好ましくは０．８６〜０．９５、塗膜の光沢度が１９５〜３００％、好ましくは２００〜３００％、塗膜表面粗度Ｒａが８．０ｎｍ以下、好ましくは２．０〜７．５ｎｍ、より好ましくは２．０〜７．０ｎｍ、塗膜の線吸収係数が１．３５〜５．００μｍ^-1、好ましくは１．４０〜５．００μｍ^-1、塗膜の表面電気抵抗値が１．０×１０⁹Ω／ｓｑ以下、好ましくは７．５×１０⁸Ω／ｓｑ以下、より好ましくは５．０×１０⁸Ω／ｓｑ以下である。
【０１２８】
フィラー材として、多量にカーボンブラックが付着されている黒色複合ヘマタイト粒子粉末を用いた場合には、上記諸特性を有することはもちろん、塗膜の線吸収係数が１．４５〜５．００μｍ^-1、好ましくは１．５０〜５．００μｍ^-1、塗膜の表面電気抵抗値が５×１０⁸Ω／ｓｑ以下、好ましくは２．５×１０⁸Ω／ｓｑ以下、より好ましくは１×１０⁸Ω／ｓｑ以下、摩擦係数が０．２１〜０．２６、好ましくは０．２１〜０．２５である。
【０１２９】
粒子表面がアルミニウムの水酸化物等によって被覆されていない黒色複合ヘマタイト粒子粉末をフィラー材とする本発明に係る磁気記録媒体の電磁変換特性値は、保磁力値が２５０Ｏｅ以上１２００Ｏｅ未満の磁性粒子粉末を用いた磁気記録媒体の場合、記録周波数４ＭＨｚにおける出力値が＋１．２ｄＢ以上、好ましくは＋１．７ｄＢ以上であり、保磁力値が１２００Ｏｅ以上４０００Ｏｅ以下の磁性粒子粉末を用いた磁気記録媒体の場合、記録周波数７ＭＨｚにおける出力値が＋１．２ｄＢ以上、好ましくは＋１．７ｄＢ以上である。
【０１３０】
粒子表面がアルミニウムの水酸化物等によって被覆されている黒色複合ヘマタイト粒子粉末をフィラー材とする本発明に係る磁気記録媒体の電磁変換特性値は、保磁力値が２５０Ｏｅ以上１２００Ｏｅ未満の磁性粒子粉末を用いた磁気記録媒体の場合、記録周波数４ＭＨｚにおける出力値が＋１．７ｄＢ以上、好ましくは＋２．２ｄＢ以上であり、保磁力値が１２００Ｏｅ以上４０００Ｏｅ以下の磁性粒子粉末を用いた磁気記録媒体の場合、記録周波数７ＭＨｚにおける出力値が＋１．７ｄＢ以上、好ましくは＋２．２ｄＢ以上である。
【０１３１】
粒子表面がアルミニウムの水酸化物等によって被覆されていない黒色複合ヘマタイト粒子粉末をフィラー材とする本発明に係る磁気記録媒体の耐久性は、走行耐久時間が、２４分以上、好ましくは２５分以上、より好ましくは２６分以上であって、ヘッド汚染がＢ又はＡ、好ましくはＡである。
【０１３２】
粒子表面がアルミニウムの水酸化物等によって被覆されている黒色複合ヘマタイト粒子粉末をフィラー材とする本発明に係る磁気記録媒体の耐久性は、走行耐久時間が２５分以上、好ましくは２６分以上、より好ましくは２７分以上であって、ヘッド汚染がＢ又はＡ、好ましくはＡである。
【０１３３】
本発明における上記黒色複合ヘマタイト粒子粉末は、下記の製造法によって得ることができる。
【０１３４】
芯粒子粉末のアルコキシシラン又はポリシロキサンによる被覆は、芯粒子粉末とアルコキシシラン溶液又はポリシロキサンとを機械的に混合攪拌したり、芯粒子粉末にアルコキシシラン溶液又はポリシロキサンを噴霧しながら機械的に混合攪拌すればよい。添加したアルコキシシランは、ほぼ全量が芯粒子粉末の粒子表面に被覆される。
【０１３５】
アルコキシシラン又はポリシロキサンを均一に芯粒子粉末の粒子表面に被覆するためには、芯粒子粉末の凝集をあらかじめ粉砕機を用いて解きほぐしておくことが好ましい。
【０１３６】
芯粒子粉末とアルコキシシラン溶液又はポリシロキサンとの混合攪拌や後述のカーボンブラック微粒子粉末と粒子表面にアルコキシシランから生成するオルガノシラン化合物又はポリシロキサンが被覆されている芯粒子粉末との混合攪拌をするための機器としては、粉体層にせん断力を加えることのできる装置が好ましく、殊に、せん断、へらなで及び圧縮が同時に行える装置がより好ましく、例えば、ホイール形混練機、ボール型混練機、ブレード型混練機、ロール型混練機を用いることができる。
【０１３７】
具体的には、ミックスマラー、シンプソンミル、サンドミル、マルチミル、ストッツミル、ウエットパンミル、コナーミル、ヘンシェルミキサー、リングマラー、回転ミル、振動ミル、加圧ニーダ、エクストルーダー及びスクリューミキサーを用いることができる。好ましくは、ミックスマラー、シンプソンミル、サンドミル、マルチミル、ストッツミル、ウエットパンミル、コナーミル、ヘンシェルミキサーであり、殊に、ミックスマラー、シンプソンミル、サンドミル、マルチミルがより好ましい。
【０１３８】
混合攪拌時における条件は、芯粒子粉末の粒子表面にアルコキシシランができるだけ均一に被覆されるように、線荷重は２〜２００ｋｇ／ｃｍ、好ましくは１０〜１５０ｋｇ／ｃｍ、より好ましくは１５〜１００ｋｇ／ｃｍ、処理時間は５〜１２０分、好ましくは１０〜９０分の範囲で処理条件を適宜調整すればよい。なお、攪拌速度は２〜２０００ｒｐｍ、好ましくは５〜１０００ｒｐｍ、より好ましくは１０〜８００ｒｐｍの範囲で処理条件を適宜調整すればよい。
【０１３９】
アルコキシシラン又はポリシロキサンの添加量は、芯粒子粉末１００重量部に対して０．１５〜４５重量部が好ましい。０．１５重量部未満の場合には、黒色度、体積固有抵抗値及びミリスチン酸吸着量を改善できる程度にカーボンブラックを付着させることが困難である。４５重量部を超える場合には、カーボンブラックを十分付着させることができるが、必要以上に添加する意味がない。
【０１４０】
次いで、芯粒子粉末の粒子表面にアルコキシラン又はポリシロキサンを被覆した後、カーボンブラック微粒子粉末を添加し、混合攪拌してアルコキシラン被覆又はポリシロキサン被覆にカーボンブラックを付着させた後、乾燥乃至加熱処理する。
【０１４１】
カーボンブラック微粒子粉末は、少量ずつを時間をかけながら、殊に５〜６０分間程度をかけて添加するのが好ましい。
【０１４２】
混合攪拌時における条件は、カーボンブラックが均一に付着するように、線荷重は２〜２００ｋｇ／ｃｍ、好ましくは１０〜１５０ｋｇ／ｃｍ、より好ましくは１５〜１００ｋｇ／ｃｍ、処理時間は５〜１２０分、好ましくは１０〜９０分の範囲で処理条件を適宜調整すればよい。なお、攪拌速度は２〜２０００ｒｐｍ、好ましくは５〜１０００ｒｐｍ、より好ましくは１０〜８００ｒｐｍの範囲で処理条件を適宜調整すればよい。
【０１４３】
カーボンブラック微粒子粉末の添加量は、芯粒子粉末１００重量部に対して１〜６０重量部である。１重量部未満の場合には、カーボンブラックの付着量が少ないため、優れた黒色度と低い体積固有抵抗値を有する黒色複合ヘマタイト粒子粉末を得ることが困難となる。６０重量部を超える場合には、得られる黒色複合ヘマタイト粒子粉末の黒色度及び体積固有抵抗値の改善効果が飽和しており、必要以上に付着させる意味がない。
【０１４４】
殊に、多量にカーボンブラックを付着させた黒色複合ヘマタイト粒子粉末を得る場合には、カーボンブラックを２回以上に分割して添加し、添加と付着を繰り返して行うことが好ましい。殊に、第１層を構成するカーボンブラック上に第２層を構成するカーボンブラック微粒子粉末を添加する場合には、添加に先立って、第１層を構成するカーボンブラック上に接着剤を接着しておくことがより好ましい。
【０１４５】
即ち、カーボンブラックの第１層が形成されている黒色複合ヘマタイト粒子粉末に接着剤を添加し、混合攪拌して接着した後、更にカーボンブラック微粒子粉末を添加し、混合攪拌して第１層のカーボンブラック上にカーボンブラックの第２層を接着すればよい。
【０１４６】
接着剤の混合攪拌時における条件は、カーボンブラックの第１層が形成されている黒色複合ヘマタイト粒子粉末表面へ接着剤が均一に接着するように、線荷重は２〜２００ｋｇ／ｃｍ、好ましくは１０〜１５０ｋｇ／ｃｍ、より好ましくは１５〜１００ｋｇ／ｃｍ、処理時間は５〜１２０分、好ましくは１０〜９０分の範囲で処理条件を適宜調整すればよい。なお、攪拌速度は２〜２０００ｒｐｍ、好ましくは５〜１０００ｒｐｍ、より好ましくは１０〜８００ｒｐｍの範囲で処理条件を適宜調整すればよい。
【０１４７】
接着剤の添加量は、芯粒子粉末に対し、０．１〜５重量部である。 ０．１重量部未満の場合には、カーボンブラックからなる第２層を十分接着させることが困難となる。５重量部を超える場合には、接着効果が飽和するため、必要以上に添加する意味がない。
【０１４８】
第２層のカーボンブラックの混合攪拌時における条件は、接着剤とカーボンブラックが均一に接着するように、線荷重は２〜２００ｋｇ／ｃｍ、好ましくは１０〜１５０ｋｇ／ｃｍ、より好ましくは１５〜１００ｋｇ／ｃｍ、処理時間は５〜１２０分、好ましくは１０〜９０分の範囲で処理条件を適宜調整すればよい。なお、攪拌速度は２〜２０００ｒｐｍ、好ましくは５〜１０００ｒｐｍ、より好ましくは１０〜８００ｒｐｍの範囲で処理条件を適宜調整すればよい。
【０１４９】
第２層を構成するカーボンブラックの添加量は、芯粒子粉末１００重量部に対して１〜３０重量部である。１重量部未満の場合には、カーボンブラックの総量が不十分となり、黒色度をより向上させ、且つ、体積固有抵抗値をより低減させることが困難となり、ミリスチン酸吸着量も改善されない。３０重量部を超える場合には、得られた黒色複合ヘマタイト粒子粉末の表面からカーボンブラックが脱離しやすくなり、その結果、ビヒクル中における分散性が低下する。
【０１５０】
本発明における黒色複合ヘマタイト粒子粉末は、芯粒子粉末にカーボンブラックを付着した後、乾燥乃至加熱処理する。乾燥乃至加熱工程における加熱温度は、通常４０〜２００℃が好ましく、より好ましくは６０〜１５０℃であり、加熱時間は、１０分〜１２時間が好ましく、３０分〜３時間がより好ましい。アルコキシシランは、この乾燥乃至加熱工程によりオルガノシラン化合物となる。
【０１５１】
芯粒子粉末は、必要により、アルコキシシランの溶液又はポリシロキサンとの混合攪拌に先立ってあらかじめ、粒子表面をアルミニウムの水酸化物、アルミニウムの酸化物、ケイ素の水酸化物及びケイ素の酸化物から選ばれる１種又は２種以上で被覆しておいてもよい。
【０１５２】
アルミニウムの水酸化物等による被覆は、芯粒子粉末を分散して得られる水懸濁液に、アルミニウム化合物、ケイ素化合物又は当該両化合物を添加して混合攪拌することにより、又は、必要により、混合攪拌後にｐＨ値を調整することにより、前記芯粒子粉末の粒子表面に、アルミニウムの水酸化物、アルミニウムの酸化物、ケイ素の水酸化物及びケイ素の酸化物から選ばれる１種又は２種以上を被着し、次いで、濾別、水洗、乾燥、粉砕する。必要により、更に、脱気・圧密処理等を施してもよい。
【０１５３】
アルミニウム化合物としては、酢酸アルミニウム、硫酸アルミニウム、塩化アルミニウム、硝酸アルミニウム等のアルミニウム塩やアルミン酸ナトリウム等のアルミン酸アルカリ塩等が使用できる。
【０１５４】
アルミニウム化合物の添加量は、ヘマタイト粒子粉末に対してＡｌ換算で０．０１〜５０重量％である。０．０１重量％未満である場合には、粒子表面に十分な量のアルミニウムの水酸化物等を被覆することが困難であり、効果的にカーボンブラックの脱離率を改良できない。５０重量％を超える場合には、被覆効果が飽和するため、必要以上に添加する意味がない。
【０１５５】
ケイ素化合物としては、３号水ガラス、オルトケイ酸ナトリウム、メタケイ酸ナトリウム等が使用できる。
【０１５６】
ケイ素化合物の添加量は、ヘマタイト粒子粉末に対してＳｉＯ₂換算で０．０１〜５０重量％である。０．０１重量％未満である場合には、粒子表面に十分な量のケイ素の酸化物等を被覆することが困難であり、効果的にカーボンブラックの脱離率を改良できない。５０重量％を超える場合には、被覆効果が飽和するため、必要以上に添加する意味がない。
【０１５７】
アルミニウム化合物とケイ素化合物とを併せて使用する場合には、ヘマタイト粒子粉末に対してＡｌ換算量とＳｉＯ₂換算量との総和で０．０１〜５０重量％が好ましい。
【０１５８】
次に、前記本発明に係る磁気記録媒体の製造法について述べる。
【０１５９】
本発明に係る磁気記録媒体は、常法により、非磁性支持体上に非磁性粒子粉末、結合剤樹脂及び溶剤を含む非磁性塗料を塗布、乾燥して非磁性下地層を形成し、該非磁性下地層上に磁性粒子粉末、結合剤樹脂、黒色複合ヘマタイト粒子粉末及び溶剤を含む磁性塗料を塗布して塗膜を形成した後、磁場配向することにより得ることができる。
【０１６０】
非磁性塗料及び磁性塗料の混練分散に当たっては、混練機は、例えば、二軸ニーダー、二軸エクストルーダー、加圧ニーダー、二本ロールミル、三本ロールミルなどが使用でき、分散機としては、ボールミル、サンドグラインダー、アトライター、ディスパー、ホモジナイザー、超音波分散機などを使用することができる。
【０１６１】
非磁性塗料及び磁性塗料の塗布にあたっては、グラビアコーター、リバースロールコーター、スリットコーター、ダイコーターなどを使用することができる。塗布したシートは、対向磁石配向、ソレノイド磁石配向等により磁場配向を行うことができる。
【０１６２】
溶剤としては、現在磁気記録媒体に汎用されているメチルエチルケトン、トルエン、シクロヘキサノン、メチルイソブチルケトン、テトラヒドロフラン及びその混合物等を使用することができる。
【０１６３】
溶剤の使用量は、非磁性粒子粉末又は磁性粒子粉末１００重量部に対してその総量で６５〜１０００重量部である。６５重量部未満では磁性塗料とした場合に粘度が高くなりすぎ塗布が困難となる。１０００重量部を超える場合には、塗膜を形成する際の溶剤の揮散量が多くなりすぎ工業的に不利となる。
【０１６４】
【本発明の実施の形態】
本発明の代表的な実施の形態は以下の通りである。
【０１６５】
芯粒子粉末、黒色複合ヘマタイト粒子粉末及びカーボンブラック微粒子粉末の各粒子粉末の平均粒子径は、電子顕微鏡写真を４倍に拡大した写真（×８０，０００）に示される粒子約３５０個について一定方向径をそれぞれ測定し、その平均値で示した。
【０１６６】
軸比は、平均長軸径と平均短軸径との比で示し、板状比は平均板面径と平均厚みとの比で示した。
【０１６７】
粒子径の幾何標準偏差値は、下記の方法により求めた値で示した。即ち、上記拡大写真に示される粒子径を測定した値を、その測定値から計算して求めた粒子の実際の粒子径と個数から、統計学的手法に従って、対数正規確率紙上の横軸に粒子径を、縦軸に所定の粒子径区間のそれぞれに属する粒子の累積個数( 積算フルイ下) を百分率でプロットした。そしてこのグラフから粒子の累積個数が５０％及び８４．１３％のそれぞれに相当する粒子径の値を読み取り、幾何標準偏差値＝（積算フルイ下８４．１３％における粒子径）／（積算フルイ下５０％における粒子径（幾何平均径）に従って算出した値で示した。幾何標準偏差値が１に近いほど、粒度分布が優れていることを意味する。
【０１６８】
比表面積値は、ＢＥＴ法により測定した値で示した。
【０１６９】
芯粒子粉末及び黒色複合ヘマタイト粒子粉末の内部や表面に存在するＭｎ量、Ａｌ量、及びＳｉ量並びにアルコキシシランから生成するオルガノシラン化合物、ポリシロキサン又はジメチルポリシロキサンに含有されるＳｉ量のそれぞれは「蛍光Ｘ線分析装置３０６３Ｍ型」（理学電機工業（株）製）を使用し、ＪＩＳＫ０１１９の「けい光Ｘ線分析通則」に従って測定した。
【０１７０】
黒色複合ヘマタイト粒子粉末に付着しているカーボンブラック量は、「堀場金属炭素・硫黄分析装置ＥＭＩＡ−２２００型」（（株)堀場製作所製）を用いて炭素量を測定することにより求めた。
【０１７１】
黒色複合ヘマタイト粒子粉末に付着しているカーボンブラックの脱離率（％）は、下記の方法により求めた値で示した。カーボンブラックの脱離率（％）が０に近いほど、粒子表面からのカーボンブラックの脱離量が少ないことを示す。
【０１７２】
黒色複合ヘマタイト粒子粉末３ｇとエタノール４０ｍｌを５０ｍｌの沈降管に入れ、２０分間超音波分散を行った後、１２０分静置し、比重差によって黒色複合ヘマタイト粒子粉末と脱離したカーボンブラックを分離した。次いで、この黒色複合ヘマタイト粒子粉末に再度エタノール４０ｍｌを加え、更に２０分間超音波分散を行った後１２０分静置し、黒色複合ヘマタイト粒子粉末と脱離したカーボンブラックを分離した。この黒色複合ヘマタイト粒子粉末を１００℃で１時間乾燥させ、前述の「堀場金属炭素・硫黄分析装置ＥＭＩＡ−２２００型」（株式会社堀場製作所製）を用いて炭素量を測定し、下記式に従って求めた値をカーボンブラックの脱離率（％）とした。
【０１７３】
カーボンブラックの脱離率（％）＝{（Ｗａ−Ｗｅ）／Ｗａ}×１００
Ｗａ：黒色複合ヘマタイト粒子粉末のカーボンブラック付着量
Ｗｅ：脱離テスト後の黒色複合ヘマタイト粒子粉末のカーボンブラック付着量
【０１７４】
ヘマタイト粒子粉末及び黒色複合ヘマタイト粒子粉末のそれぞれの黒色度は、試料０．５ｇとヒマシ油０．７ｍｌとをフーバー式マーラーで練ってペースト状とし、このペーストにクリアラッカー４．５ｇを加え、混練、塗料化してキャストコート紙上に６ｍｉｌのアプリケーターを用いて塗布した塗布片（塗膜厚み：約３０μｍ）を作製し、 該塗料片について、多光源分光測色計ＭＳＣ−ＩＳ−２Ｄ（スガ試験機（株）製）を用いて測定し、ＪＩＳ Ｚ ８７２９に定めるところに従って表色指数Ｌ^*値で示した。
【０１７５】
ここでＬ^*値は、明度を表わし、Ｌ^*値が小さいほど黒色度が優れていることを示す。
【０１７６】
ヘマタイト粒子粉末及び黒色複合ヘマタイト粒子粉末の各粒子粉末の体積固有抵抗値は、まず、粒子粉末０．５ｇを測り取り、ＫＢｒ錠剤成形器（株式会社島津製作所）を用いて、１４０Ｋｇ／ｃｍ²の圧力で加圧成形を行い、円柱状の被測定試料を作製した。
【０１７７】
次いで、被測定試料を温度２５℃、相対湿度６０％環境下に１２時間以上暴露した後、この被測定試料をステンレス電極の間にセットし、ホイートストンブリッジ（ＴＹＰＥ２７６８ 横河北辰電気株式会社製）で１５Ｖの電圧を印加して抵抗値Ｒ（Ω）を測定した。
【０１７８】
次いで、被測定（円柱状）試料の上面の面積Ａ（ｃｍ²）と厚みｔ₀（ｃｍ）を測定し、次式にそれぞれの測定値を挿入して、体積固有抵抗値（Ω・ｃｍ）を求めた。
体積固有抵抗値（Ω・ｃｍ）＝Ｒ×（Ａ／ｔ₀）
【０１７９】
黒色複合ヘマタイト粒子粉末に付着しているカーボンブラックの付着厚みは、透過型電子顕微鏡ＪＥＭ−２０１０（日本電子株式会社（製））を用いて加速電圧２００ｋＶの条件下で撮影した電子顕微鏡写真（×５００，０００）を１０倍に拡大した写真（×５，０００，０００）に写っている粒子の表面に付着しているカーボンブラックの平均的な厚み部分を実測し、該実測値を実際の付着厚みに換算し直した値で示した。
【０１８０】
ヘマタイト粒子粉末及び黒色複合ヘマタイト粒子粉末の各粒子粉末のミリスチン酸吸着量は、下記の方法によって求めた。ミリスチン酸吸着量が少ないほど、磁気テープとした時に脂肪酸が浸み出しやすく、摩擦係数の低減を図ることができる。
【０１８１】
まず、１４０ｍｌのガラスビンに１．５ｍｍφのガラスビーズ１００ｇ、被測定粒子粉末９ｇ及び被測定粒子粉末の表面を一層被覆するだけのミリスチン酸を含有するテトラヒドロフラン溶液４５ｍｌを加え、６０分間ペイントシェーカーで混合分散した。
【０１８２】
次に、この混合分散物を５０ｍｌの沈降管に取り出し、回転数１００００ｒｐｍで１５分間遠心分離を行い、固形部分と溶剤部分とを分離する。そして、溶剤部分に含まれるミリスチン酸濃度を重量法によって定量し、仕込みのミリスチン酸量との差し引きにより、固形部分に存在するミリスチン酸量を求め、これを粒子に対するミリスチン酸吸着量（ｍｇ／ｍ²）とした。
【０１８３】
塗料粘度は、塗料の２５℃における塗料粘度をＥ型粘度計（コーンプレート型粘度計）ＥＭＤ−Ｒ（株式会社東京計器製）を用いて２５℃におけるずり速度が１．９２ｓｅｃ^-1での見かけ粘度の値で示した。
【０１８４】
磁性粒子粉末及び磁気記録媒体の磁気特性は、「振動試料型磁力計ＶＳＭ−３Ｓ−１５」（東英工業（株）製）を使用し、最大外部磁場１０ｋＯｅにて測定した。
【０１８５】
磁気記録層の塗膜表面の光沢度は、「グロスメーターＵＧＶ−５Ｄ」（スガ試験機株式会社製）を用いて塗膜の４５°光沢度を測定して求めた。
【０１８６】
表面粗度Ｒａは、「ｓｕｒｆｃｏｍ−５７５Ａ」（東京精密（株）製）を用いてカレンダー後の塗布膜の中心線平均粗さを測定した値で示した。
【０１８７】
磁気記録媒体の光透過の程度は、「自記光電分光光度計ＵＶ−２１００」（株式会社島津製作所製）を用いて測定した光透過率の値を下記式に挿入して算出した線吸収係数で示した。線吸収係数は、その値が大きいほど、光を透しにくいことを示す。
【０１８８】
尚、光透過率の値を測定するにあたっては、上記磁気記録媒体に用いた非磁性支持体と同一の非磁性支持体をブランクとして用いた。
【０１８９】
線吸収係数（μｍ^-1）＝〔ｌｎ（１／ｔ）〕／ＦＴ
ｔ：λ＝９００ｎｍにおける光透過率（−）
ＦＴ：測定に用いた磁気記録媒体の塗膜組成物層の厚み（μｍ）
【０１９０】
電磁変換特性は、「ドラムテスターＢＸ−３１６８」（ベルデックス社製）を用いて相対速度５．８ｍ／ｓｅｃにおける４ＭＨｚ又は７ＭＨｚの各記録周波数における電磁変換出力値を基準テープに対する相対値として示した。
【０１９１】
基準テープは、後述する磁性塗料の組成のうち、黒色複合ヘマタイト粒子粉末を磁性粒子粉末１００重量部に対してアルミナ（商品名：ＡＫＰ−３０、住友化学株式会社製）７．０重量部に置き換えた以外は同様にして作製したものを基準テープとして用いた。
【０１９２】
耐久性は、「メディアデュラビリティテスターＭＤＴ−３０００」（Ｓｔｅｉｎｂｅｒｇ Ａｓｓｏｃｉａｔｅｓ社製）を用いて、相対速度１６ｍ／ｓｅｃ、負荷２００ｇにおける測定値で示した。
【０１９３】
ヘッド汚染は、「メディアデュラビリティテスターＭＤＴ−３０００」（Ｓｔｅｉｎｂｅｒｇ Ａｓｓｏｃｉａｔｅｓ社製）を用いて、相対速度１６ｍ／ｓｅｃ、負荷２００ｇにおいて、３０分間走行させた後のヘッド汚れを目視で観察し、４段階で評価した。Ａが最もヘッドの汚れが少ないことを示す。
Ａ：汚れなし
Ｂ：若干汚れ有り
Ｃ：汚れ有り
Ｄ：ひどい汚れ有り
【０１９４】
磁気記録媒体の摩擦係数は、磁気テープ面と金属面（アルミニウム鏡面）との摩擦力を引張試験機テンシロン（株式会社島津製作所製）を用いて測定し、果樹との比から求めた値で示した。
【０１９５】
塗布膜の表面電気抵抗値は、被測定塗布膜を温度２５℃、相対湿度６０％の環境下に１２時間以上曝した後、幅６．５ｍｍの金属製の電極に幅６ｍｍにスリットした塗布膜を置き、その両端に各１７０ｇのおもりを付け、電極に塗布膜を密着させた後、電極間に５００Ｖの直流電圧をかけて測定した値で示した。
【０１９６】
磁気記録媒体を構成する非磁性支持体、非磁性下地層及び磁気記録層の各層の厚みは、次の通りの測定手法によって測定した。
【０１９７】
「デジタル電子マイクロメーターＫ３５１Ｃ」（安立電気株式会社製）を用いて、先ず、非磁性支持体の膜厚（Ａ）を測定する。次に、非磁性支持体と該非磁性支持体上に形成された非磁性下地層との厚み（Ｂ）（非磁性支持体の厚みと非磁性下地層の厚みとの総和）を同様にして測定する。更に、非磁性下地層上に磁気記録層を形成することにより得られた磁気記録媒体の厚み（Ｃ）（非磁性支持体の厚みと非磁性下地層の厚みと磁気記録層の厚みとの総和）を同様にして測定する。そして、非磁性下地層の厚みは（Ｂ）−（Ａ）で示し、磁気記録層の厚みは（Ｃ）−（Ｂ）で示した。
【０１９８】
＜黒色複合ヘマタイト粒子粉末の製造＞
マンガン含有黒色ヘマタイト粒子粉末（粒子形状：粒状、平均粒子径０．３０μｍ、幾何標準偏差値１．４６、ＢＥＴ比表面積値３．６ｍ²／ｇ、Ｍｎ含有量１３．３重量％、黒色度Ｌ^*値２２．６、体積固有抵抗値２．０×１０⁷Ω・ｃｍ、ミリスチン酸吸着量０．７２ｍｇ／ｍ²）２０ｋｇを、凝集を解きほぐすために、純水１５０ｌに攪拌機を用いて邂逅し、更に、「ＴＫパイプラインホモミクサー」（製品名、特殊機化工業（株）製）を３回通してマンガン含有黒色ヘマタイト粒子粉末を含むスラリーを得た。
【０１９９】
続いて、このマンガン含有黒色ヘマタイト粒子粉末を含むスラリーを横形サンドグラインダー「マイティーミルＭＨＧ−１．５Ｌ」（製品名、井上製作所（株） 製）を用いて、軸回転数２０００ｒｐｍにおいて５回パスさせて、マンガン含有黒色ヘマタイト粒子粉末を含む分散スラリーを得た。
【０２００】
得られたマンガン含有黒色ヘマタイト粒子粉末を含む分散スラリーの３２５ｍｅｓｈ（目開き４４μｍ）における篩残分は０％であった。この分散スラリーを濾別、水洗して、マンガン含有黒色ヘマタイト粒子粉末のケーキを得た。このマンガン含有黒色ヘマタイト粒子粉末のケーキを１２０℃で乾燥した後、乾燥粉末１１．０ｋｇをエッジランナー「ＭＰＵＶ−２型」（製品名、（株）松本鋳造鉄工所製）に投入して、３０ｋｇ／ｃｍで３０分間混合攪拌を行い、粒子粉末の凝集を軽く解きほぐした。
【０２０１】
次に、メチルトリエトキシシラン１６５ｇを２００ｍｌのエタノールで混合希釈して得られるメチルトリエトキシシラン溶液を、エッジランナーを稼動させながら粒子の凝集を解きほぐした上記マンガン含有黒色ヘマタイト粒子粉末に添加し、６０ｋｇ／ｃｍの線荷重で２０分間混合攪拌を行った。なお、この時の攪拌速度は２２ｒｐｍであった。
【０２０２】
次に、カーボンブラック微粒子粉末Ｂ（粒子形状：粒状、平均粒子径０．０２２μｍ、幾何標準偏差値１．７８、ＢＥＴ比表面積値１３３．５ｍ²／ｇ、黒色度Ｌ^*値１４．６、ｐＨ値３．４、ＤＢＰ吸油量８４ｍｌ／１００ｇ）１９２５ｇを、エッジランナーを稼動させながら１０分間かけて添加し、更に３０ｋｇ／ｃｍの線荷重で３０分間混合攪拌を行い、メチルトリエトキシシラン被覆にカーボンブラックを付着させた。なお、この時の攪拌速度は２２ｒｐｍであった。
【０２０３】
得られた黒色複合ヘマタイト粒子粉末を、乾燥機を用いて８０℃で１２０分間熟成し、残留した水分、エタノール等を揮散させた。この黒色複合ヘマタイト粒子粉末は、電子顕微鏡観察の結果、平均長軸径が０．３１μｍ、幾何標準偏差値は１．４６であり、ＢＥＴ比表面積値は７．８ｍ²／ｇ、黒色度Ｌ^*値は１７．６、体積固有抵抗値は６．８×１０³Ω・ｃｍ、カーボンブラックの脱離率は７．８％であり、カーボンブラックの付着量が、１４．７８重量％（芯粒子粉末１００重量部に対して１７．５重量部に相当する）、メチルトリエトキシシランの被覆量はＳｉ換算で０．２２重量％であって、粒子表面のカーボンブラックの付着厚みは０．００２４μｍであった。電子顕微鏡観察の結果、カーボンブラックがほとんど認められないことから、カーボンブラックのほぼ全量が、メチルトリエトキシシランから生成するオルガノシラン化合物被覆に付着していることが認められた。
【０２０４】
比較のため、メチルトリエトキシシランを被覆することなく、マンガン含有黒色ヘマタイト粒子粉末とカーボンブラック微粒子粉末とを同様にエッジランナーで混合攪拌して得られた処理粒子粉末は、電子顕微鏡観察の結果、カーボンブラックがマンガン含有ヘマタイト粒子粉末の粒子表面に付着しておらず、両粒子粉末がバラバラに混在していることが認められた。
【０２０５】
＜非磁性下地層の製造＞
後出表９に示す非磁性粒子粉末１（種類：ヘマタイト粒子、粒子形状：紡錘状、平均長軸径０．１８７μｍ、平均短軸径０．０２４０μｍ、軸比７．８、幾何標準偏差値１．３３、ＢＥＴ比表面積値４３．３ｍ²／ｇ、体積固有抵抗値８．６×１０⁸Ω・ｃｍ、黒色度Ｌ^*値）１２ｇと結合剤樹脂溶液（スルホン酸ナトリウム基を有する塩化ビニル−酢酸ビニル共重合樹脂３０重量％とシクロヘキサノン７０重量％）及びシクロヘキサノンとを混合して混合物（固形分率７２％）を得、この混合物を更にプラストミルで３０分間混練して混練物を得た。
【０２０６】
この混練物を１．５ｍｍφガラスビーズ９５ｇ、追加の結合剤樹脂溶液（スルホン酸ナトリウム基を有するポリウレタン樹脂３０重量％、溶剤（メチルエチルケトン：トルエン＝１：１）７０重量％）、シクロヘキサノン、メチルエチルケトン及びトルエンとともに１４０ｍｌガラス瓶に添加し、ペイントシェーカーで６時間混合・分散を行って塗料組成物を得た。その後、潤滑剤を加え、更に、ペイントシェーカーで１５分間混合・分散した。
【０２０７】
得られた非磁性塗料の組成は、下記の通りであった。
【０２０８】

【０２０９】
得られた非磁性塗料の塗料粘度は３１０ｃＰであった。
【０２１０】
次いで、上記非磁性塗料を厚さ１２μｍのポリエチレンテレフタレートフィルム上にアプリケーターを用いて５５μｍの厚さに塗布し、次いで、乾燥させることにより非磁性下地層を形成した。
【０２１１】
得られた非磁性下地層の厚みは３．４μｍ、光沢は１９３％、表面粗度Ｒａは８．２ｎｍ、ヤング率（相対値）は１２３、線吸収係数は１．０１ｃｍ^-1、表面電気抵抗値は１．１×１０¹⁴Ω・ｃｍであった。
【０２１２】
＜磁気記録媒体の製造＞
Ｃｏ被着型針状マグネタイト粒子粉末（平均長軸径０．２３μｍ、軸比７．３、ＢＥＴ比表面積値３０．３ｍ²／ｇ、保磁力値７２６Ｏｅ、飽和磁化値８１．９ｅｍｕ／ｇ、Ｃｏ含有量２．２２重量％）１００重量部、塩化ビニル−酢酸ビニル共重合樹脂（商品名：ＭＲ−１１０、日本ゼオン（株）製）１０．０重量部、シクロヘキサノン２３．３重量部、メチルエチルケトン１０．０重量部、カーボンブラック微粒子粉末（三菱化学（株）製、平均粒子径２６ｎｍ、ＢＥＴ比表面積値１３０ｍ²／ｇ）１．０重量部と上記で得られた黒色複合ヘマタイト粒子粉末７．０重量部とをニーダーを用いて２０分間混練した後、該混練物にトルエン７９．６重量部及びメチルエチルケトン１１０．２重量部及びシクロヘキサノン１７．８重量部を添加して希釈し、次いで、サンドグラインダーによって３時間混合、分散させて混合分散物を得た。
【０２１３】
上記混合分散物に、ポリウレタン樹脂（商品名：ＴＩ−１０７５、三洋化成工業（株）製）の固形分１０．０重量部を含むメチルエチルケトン／シクロヘキサノンの１／１溶液３３．３重量部を添加して、更に３０分間サンドグラインダーを用いて混合・分散した後、目開き１μｍのフィルターで濾過して得られた濾過物にミリスチン酸１．０重量部及びブチルステアレート３．０重量部を含むメチルエチルケトン／トルエン／シクロヘキサノンの５／３／２溶液１２．１重量部及び三官能性低分子量ポリイソシアネート（商品名：Ｅ−３１、武田薬品工業（株）製）５．０重量部を含むメチルエチルケトン／トルエン／シクロヘキサノンの５／３／２溶液１５．２重量部を攪拌しながら混合して磁性塗料を製造した。
【０２１４】
得られた磁性塗料の組成は下記の通りであった。
磁性粒子粉末 １００重量部、
塩化ビニル−酢酸ビニル共重合樹脂 １０重量部、
ポリウレタン樹脂 １０重量部、
黒色複合ヘマタイト粒子粉末（フィラー材） ７．０重量部、
カーボンブラック微粒子粉末 １．０重量部、
ミリスチン酸 １．０重量部、
ステアリン酸ブチル ３．０重量部、
三官能性低分子量ポリイソシアネート ５．０重量部、
シクロヘキサノン ５６．６重量部、
メチルエチルケトン １４１．５重量部、
トルエン ８５．４重量部。
【０２１５】
得られた磁性塗料の塗料粘度は２，８１６ｃＰであった。
【０２１６】
得られた磁性塗料を前記非磁性下地層の上にアプリケーターを用いて１５μｍの厚さに塗布した後、磁場中において配向・乾燥し、次いで、カレンダー処理を行った後、６０℃で２４時間硬化反応を行い０．５インチ幅にスリットして磁気テープを得た。得られた塗膜の膜厚は３．４μｍであった。
【０２１７】
上記磁気テープの磁気特性は、保磁力値が７５４Ｏｅ、角型比（Ｂｒ／Ｂｍ）が０．８８であった。光沢度は１９４％、表面粗度Ｒａは６．８ｎｍ、線吸収係数は１．３６μｍ^-1、表面電気抵抗値は６．８×１０⁷Ω／ｃｍ²、電磁変換特性は、記録周波数４ＭＨｚにおける出力が＋２．３ｄＢであり、耐久性は走行耐久時間が２９．２分以上であって、ヘッド汚染がＡであった。
【０２１８】
なお、電磁変換特性を求めるための基準テープとして、後述する表１３に記載の基準テープ１を用いた。
【０２１９】
【作用】
本発明において最も重要な点は、磁気記録層に含有させるフィラー材として本発明における黒色複合ヘマタイト粒子粉末を用いた場合には、優れた耐久性と良好な電磁変換特性を有するとともに、より小さい光透過率とより低い表面電気抵抗値とを有する磁気記録媒体が得られるという事実である。
【０２２０】
本発明に係る磁気記録媒体が優れた耐久性と良好な電磁変換特性を有する理由について、本発明者はフィラー材として使用する黒色複合ヘマタイト粒子粉末の粒子表面から脱離するカーボンブラックが少ないことに起因して、系内におけるカーボンブラックによって、殊に磁性粒子粉末の分散が阻害されることがなく、また、粒子表面にカーボンブラックが付着していることにより粒子表面に凹凸が生じている黒色複合ヘマタイト粒子粉末が磁性粒子粉末の間に介在することによって、磁性粒子相互間の接触が抑制され、磁性粒子粉末が高充填されやすいためと考えている。
【０２２１】
なお、本発明における黒色複合ヘマタイト粒子粉末の粒子表面から脱離するカーボンブラックが少ない理由について、本発明者は、アルコキシシランを用いた場合には、ヘマタイト粒子粉末の粒子内部や粒子表面に含有されているＳｉ、Ａｌ、Ｆｅ等の金属元素とカーボンブラックが付着しているアルコキシシランが有しているアルコキシ基との間で、メタロキサン結合（≡Ｓｉ−Ｏ−Ｍ（但し、ＭはＳｉ、Ａｌ、Ｆｅ等のヘマタイト粒子に含まれている金属原子である。））が形成されることにより、カーボンブラックが付着しているオルガノシラン化合物がヘマタイト粒子粉末の粒子表面に強固に結合するためと考えている。
【０２２２】
また、ポリシロキサンを用いた場合には、カーボンブラックが付着しているポリシロキサンが有している各種官能基が、ヘマタイト粒子粉末の粒子表面へ強固に結合するためと考えている。
【０２２３】
本発明に係る磁気記録媒体の光透過率が小さい理由について、本発明者は、非磁性下地層を有しているとともに磁性層中に含有されている黒色複合ヘマタイト粒子粉末の黒色度が優れていることによるものと考えている。即ち、本発明における黒色複合ヘマタイト粒子粉末は、通常は微粒子粉末であることに起因して、凝集体として挙動するカーボンブラック微粒子粉末が、ヘマタイト粒子粉末の粒子表面にアルコキシシランから生成するオルガノシラン化合物又はポリシロキサンを介して均一且つ緻密に付着されることによって、カーボンブラックがより効果的に機能しているためと考えている。
【０２２４】
本発明に係る磁気記録媒体の表面電気抵抗値が小さい理由について、本発明者は、磁気記録層中に均一に分散している黒色複合ヘマタイト粒子粉末の粒子表面に均一且つ緻密に付着しているカーボンブラックが相互に接触しながら連綿と連なっていることによるものと考えている。
【０２２５】
本発明に係る磁気記録媒体の摩擦係数を低減できた理由について、本発明者は、磁性層中に含有される黒色複合ヘマタイト粒子粉末の粒子表面へのミリスチン酸の吸着が特定範囲内に抑制された結果、ミリスチン酸の適量が調整されながら長期に亘って磁気記録層表面に浸み出すことにより、潤滑剤としての機能が効果的に発揮できたものと考えている。
【０２２６】
本発明に係る磁気記録媒体の走行耐久性が優れている理由について、本発明者は、上記と同様の理由により、ミリスチン酸の適量が調整されながら磁気記録層表面に浸み出すことにより、安定した走行耐久性が得られたものと考えている。
【０２２７】
【実施例】
次に、実施例並びに比較例を挙げる。
【０２２８】
芯粒子１〜５
公知の製造方法で得られた各種のヘマタイト粒子粉末を準備し、上記発明の実施の形態と同様にして凝集が解きほぐされたヘマタイト粒子粉末を得た。
【０２２９】
このヘマタイト粒子粉末の諸特性を表１に示す。
【０２３０】
【表１】

【０２３１】
芯粒子６
芯粒子１の凝集が解きほぐされたマンガン含有黒色ヘマタイト粒子粉末２０ｋｇと水１５０ｌとを用いて、発明の実施の形態と同様にしてマンガン含有黒色ヘマタイト粒子粉末を含むスラリーを得た。得られたマンガン含有黒色ヘマタイト粒子粉末を含む再分散スラリーのｐＨ値を、水酸化ナトリウム水溶液を用いて１０．５に調整した後、該スラリーに水を加えスラリー濃度を９８ｇ／ｌに調整した。このスラリー１５０ｌを加熱して６０℃とし、このスラリー中に１．０ｍｏｌ／ｌのアルミン酸ナトリウム溶液２７２２ｍｌ（マンガン含有黒色ヘマタイト粒子粉末に対してＡｌ換算で０．５重量％に相当する）を加え、３０分間保持した後、酢酸を用いてｐＨ値を７．５に調整した。この状態で３０分間保持した後、濾過、水洗、乾燥、粉砕して粒子表面がアルミニウムの水酸化物により被覆されているマンガン含有黒色ヘマタイト粒子粉末を得た。
【０２３２】
この時の主要製造条件を表２に、得られたマンガン含有黒色ヘマタイト粒子粉末の諸特性を表３に示す。
【０２３３】
尚、表面処理工程における被覆物の種類のＡはアルミニウムの水酸化物であり、Ｓはケイ素の酸化物を表わす。
【０２３４】
【表２】

【０２３５】
【表３】

【０２３６】
芯粒子７〜１０
芯粒子粉末の種類、表面処理工程における添加物の種類及び量を種々変えた以外は、芯粒子６と同様にして表面処理済ヘマタイト粒子粉末を得た。
【０２３７】
この時の主要処理条件を表２に、得られた表面処理済ヘマタイト粒子粉末の諸特性を表３に示す。
【０２３８】
＜黒色複合ヘマタイト粒子粉末の製造＞
実施例１〜１２、比較例１〜４
芯粒子粉末の種類、アルコキシシラン、ポリシロキサン、シリコン化合物による被覆工程におけるアルコキシシラン、ポリシロキサン、シリコン化合物の有無、種類及び添加量、エッジランナーによる処理条件、カーボンブラック微粒子粉末の付着工程におけるカーボンブラック微粒子粉末の種類及び添加量、エッジランナーによる処理条件を種々変えた以外は、前記発明の実施の形態と同様にして黒色複合ヘマタイト粒子粉末を得た。実施例１〜１０の各実施例で得られた黒色複合ヘマタイト粒子粉末は、電子顕微鏡観察の結果、カーボンブラックがほとんど認められないことから、カーボンブラックのほぼ全量がアルコキシシランから生成するオルガノシラン化合物被覆又はポリシロキサン被覆に付着していることが認められた。
【０２３９】
尚、使用したカーボンブラック微粒子粉末Ａ乃至Ｆの諸特性を表４に示す。
【０２４０】
この時の主要処理条件を表５に、得られた黒色複合ヘマタイト粒子粉末の諸特性を表６に示す。
【０２４１】
実施例８〜１０の各実施例で使用されている添加物は、いずれもポリシロキサンである。「ＴＳＦ４８４」（商品名：東芝シリコーン株式会社（製））はメチルハイドロジェンポリシロキサンであり、「ＢＹＫ−０８０」（商品名：ビックケミー・ジャパン株式会社（製））は変成ポリシロキサンであり、「ＴＳＦ−４７７０」（商品名：東芝シリコーン株式会社（製））は末端カルボキシル変成ポリシロキサンである。
【０２４２】
【表４】

【０２４３】
【表５】

【０２４４】
【表６】

【０２４５】
＜多量のカーボンブラックが付着されている黒色複合ヘマタイト粒子粉末の製造＞
実施例１３
実施の形態で得られた黒色複合ヘマタイト粒子粉末５．０ｋｇをエッジランナー「ＭＰＵＶ−２型」（製品名、（株）松本鋳造鉄工所製）に投入して、３０ｋｇ／ｃｍで３０分間混合攪拌を行い、粒子粉末の凝集を軽く解きほぐした。
【０２４６】
次に、ジメチルポリシロキサン１００ｇを、エッジランナーを稼動させながら上記黒色複合ヘマタイト粒子粉末に添加し、６０ｋｇ／ｃｍの線荷重で４５分間混合攪拌を行って、表面にジメチルポリシロキサンが均一に接着されている黒色複合ヘマタイト粒子粉末を得た。
【０２４７】
次に、上記カーボンブラック微粒子粉末Ｂ８７５ｇを、エッジランナーを稼動させながら１０分間かけて添加し、更に６０ｋｇ／ｃｍの線荷重で３０分間、混合攪拌を行い、カーボンブラックから構成される第１層の表面にジメチルポリシロキサンを接着剤としてカーボンブラックからなる第２層を接着させて、黒色複合ヘマタイト粒子粉末を得た。
【０２４８】
得られた黒色複合ヘマタイト粒子粉末を、乾燥機を用いて１０５℃で６０分間乾燥処理を行った。この黒色複合ヘマタイト粒子粉末は、電子顕微鏡観察の結果、粒子径が０．３１μｍの粒状粒子粉末であった。幾何標準偏差値は１．４５であり、ＢＥＴ比表面積値は１０．５ｍ²／ｇ、黒色度Ｌ^*値は１７．１、体積固有抵抗値は３．１×１０²Ω・ｃｍ、ミリスチン酸吸着量は０．２６ｍｇ／ｍ²であって、カーボンブラック脱離率は７．９％であり、付着及び接着しているカーボンブラックの総量がＣ換算で２５．６８重量％（芯粒子粉末１００重量部に対して３５重量部に相当する）であって、ジメチルポリシロキサンの被覆量はＳｉ換算で０．７０重量％であって、粒子表面のカーボンブラックの付着厚みは０．００２７μｍであった。なお、電子顕微鏡観察の結果、カーボンブラックがほとんど認められないことから、カーボンブラックのほぼ全量がカーボンブラックの第１層に接着していることが認められた。
【０２４９】
実施例１４〜２５、比較例５〜１１
黒色複合ヘマタイト粒子粉末の種類、接着剤による処理工程における接着剤の種類、添加量及びエッジランナーによる処理条件、カーボンブラックの接着工程におけるカーボンブラック微粒子粉末の種類、添加量、エッジランナーによる処理条件を種々変化させた以外は、前記の実施例１３と同様にして多量のカーボンブラックが付着されている黒色複合ヘマタイト粒子粉末を得た。
【０２５０】
尚、実施例１４〜２５の各実施例で得られた黒色複合ヘマタイト粒子粉末は、電子顕微鏡観察の結果、カーボンブラックがほとんど認められないことから、カーボンブラックのほぼ全量がカーボンブラックの第１層に接着されていることが認められた。
【０２５１】
この時の主要処理条件を表７に、得られた黒色複合ヘマタイト粒子粉末の諸特性を表８に示す。
【０２５２】
【表７】

【０２５３】
【表８】

【０２５４】
＜非磁性下地層の製造＞
非磁性粒子１〜６
各種非磁性粒子粉末を用いて、前記発明の実施の形態と同様にして非磁性下地層を製造した。
【０２５５】
使用した非磁性粒子粉末１乃至６の諸特性を表９に示す。
【０２５６】
【表９】

【０２５７】
この時の主要製造条件及び得られた非磁性下地層の諸特性を表１０に示す。
【０２５８】
【表１０】

【０２５９】
＜基準テープの製造＞
基準テープ１〜６
各種非磁性下地層及び各種非磁性粒子粉末を用いて、前記発明の実施の形態と同様にして基準テープを製造した。
【０２６０】
各種磁性粒子粉末の諸特性を表１１に示す。
【０２６１】
【表１１】

【０２６２】
なお、磁性粒子３は板状磁性粒子粉末であり、表１１中の「平均長軸径」は、「板面径」を、「平均短軸径」は「厚み」を、「軸比」は「板状比」を意味する。
【０２６３】
この時の主要製造条件及び得られた基準テープの諸特性を表１２及び表１３に示す。
【０２６４】
【表１２】

【０２６５】
【表１３】

【０２６６】
＜磁気記録媒体の製造＞
実施例２６〜５０、比較例１２〜２２
磁性粒子粉末の種類、黒色フィラー材の種類及び添加量を種々変化させた以外は、本発明の実施の形態と同様にして磁気記録媒体を得た。
【０２６７】
磁気記録媒体の製造条件を表１４に、その諸特性を表１５乃至表１７に示した。
【０２６８】
【表１４】

【０２６９】
【表１５】

【０２７０】
【表１６】

【０２７１】
【表１７】

【０２７２】
【発明の効果】
本発明に係る磁気記録媒体は、磁気記録層中に添加するカーボンブラック量を可及的に少なくすることができることと黒色複合ヘマタイト粒子粉末自体の分散性が向上することともあいまって優れた耐久性と良好な電磁変換特性を有しており、しかも、非磁性下地層を有しているとともに、前述した通り、優れた黒色度と低い体積固有抵抗値を有する黒色複合ヘマタイト粒子粉末をフィラー材として用いていることに起因して、表面平滑であって、光透過率がより小さく、且つ、表面電気抵抗値がより低いものであるので、高密度記録用磁気記録媒体として好適である。
【０２７３】
フィラー材として、殊に、ミリスチン酸吸着量が抑制された黒色複合ヘマタイト粒子粉末を用いた本発明に係る磁気記録媒体は、上記諸特性を有することはもちろん、摩擦係数が小さく、走行耐久性が優れているので高密度記録用として好適である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a magnetic recording medium having excellent durability and good electromagnetic conversion characteristics, smooth surface, lower light transmittance, and lower surface electric resistance.
[0002]
[Prior art]
In recent years, as video and audio magnetic recording / reproducing devices have become smaller and lighter and have been recorded for a longer time, higher performance with respect to magnetic recording media such as magnetic tapes and magnetic disks, that is, higher density recording, higher durability, better The demand for new electromagnetic conversion characteristics is increasing.
[0003]
Magnetic recording media such as magnetic tapes and magnetic disks are subject to wear and tear on the magnetic recording layer due to recording and reproduction while in contact with the magnetic head, causing the magnetic head to become contaminated and thus causing deterioration of recording and reproduction characteristics. Therefore, there is a need for a highly durable magnetic recording medium with less wear than in the past.
[0004]
Conventionally, in order to improve the wear durability of a magnetic recording layer in a magnetic recording medium, alumina (Al ₂ O _Three ), Hematite (α-Fe ₂ O _Three ) And trichromium 2 chromium (Cr ₂ O _Three Attempts have been made to add various filler materials such as) to the magnetic layer.
[0005]
For example, alumina (Al ₂ O _Three ) Using α-Al in which an amorphous phase exists ₂ O _Three Recording medium (Japanese Patent Laid-Open No. 5-36059) and α-Al having specific crystallinity ₂ O _Three There is a magnetic recording medium using JP-A No. 7-244836. Hematite (α-Fe ₂ O _Three ) Using granular α-Fe ₂ O _Three Magnetic recording medium (Japanese Patent Laid-Open No. 61-194628), liquid hydrocarbon and α-Fe ₂ O _Three There is a magnetic recording medium using JP-A-54-70806. In addition, trichromium 2 chromium (Cr ₂ O _Three ) With needle-like Cr ₂ O _Three There is a magnetic recording medium using JP-A No. 62-112221.
[0006]
However, these filler materials have their own problems. Alumina is known to have poor dispersibility in a binder resin, and the electromagnetic conversion characteristics are significantly lowered as the amount added is increased. Hematite has relatively good dispersibility in the binder resin, but it needs to be added in a large amount in order to obtain sufficient durability. As a result, the filling rate of the magnetic particle powder decreases. For this reason, the electromagnetic conversion characteristics are deteriorated. Trichromium 2 chromium is not preferable in terms of environmental hygiene.
[0007]
In addition, these filler materials are generally known to increase in durability when the amount added increases, but the dispersibility of the magnetic particle powder in the vehicle decreases, resulting in a significant decrease in electromagnetic conversion characteristics. .
[0008]
Therefore, there is a strong demand for a magnetic recording medium that suppresses the decrease in dispersibility of the magnetic particle powder in the vehicle even when the filler material necessary for improving the durability is added. Has been.
[0009]
Further, in the video tape system that is currently widely used, the end detection mechanism of the magnetic recording medium is performed by detecting a transparent leader tape portion of the end portion with a sensor.
[0010]
However, in recent years, high-density recording has been demanded, and the magnetic particle powder used for this purpose has become finer, so that the light transmittance of the magnetic recording layer has increased, and as a result, there has been a risk of malfunctioning in the end detection. . Therefore, the magnetic recording portion is strongly required to have low light transmittance due to high blackness.
[0011]
Furthermore, when the surface electrical resistance value of the magnetic recording medium is large, an increase in the electrostatic charge amount is brought about, and at the time of manufacture and use of the magnetic recording medium, cutting chips and dust of the magnetic recording medium are used. And the like adhere to the surface of the magnetic recording medium, and as a result, the problem of an increase in dropout occurs. Therefore, it is strongly required to reduce the surface electric resistance value of the magnetic recording medium.
[0012]
The demand for higher performance of the magnetic recording medium is not limited, and if necessary, further improvement of physical properties such as runnability is strongly demanded.
[0013]
The runnability of the magnetic recording medium is generally such that the magnetic recording layer generally formed on the upper layer of the magnetic recording medium usually contains about 0.5 to 5% by weight of fatty acid such as myristic acid or stearic acid (hereinafter referred to as stearic acid). , "Myristic acid") is added, and the myristic acid is adjusted so that it gradually oozes out on the surface of the magnetic recording layer, thereby ensuring the slipperiness of the surface of the magnetic recording layer.
[0014]
If the amount of myristic acid that oozes out on the surface of the magnetic recording layer is too small, the traveling property of the magnetic recording medium cannot be secured, while the myristic acid is added so that the amount of myristic acid that oozes out increases. When added in a large amount, myristic acid is preferentially adsorbed on the surface of the magnetic particle powder dispersed in the magnetic recording layer, and the adsorption of the magnetic particle powder and the resin is inhibited. Dispersion inside becomes difficult. Furthermore, problems such as a decrease in magnetic properties of the magnetic recording medium due to an increase in the amount of myristic acid, which is a nonmagnetic component, and a decrease in strength of the magnetic recording medium due to the function of myristic acid as a plasticizer also arise.
[0015]
Recently, as the magnetic recording layer becomes thinner, the absolute amount of myristic acid that can be added decreases, and when the magnetic particle powder becomes finer and the BET specific surface area value increases as the recording density becomes higher, the magnetic particle Since the amount of myristic acid adsorbed on the particle surface of the powder increases, it is becoming increasingly difficult to adjust the leaching to the surface of the magnetic recording layer and ensure the traveling property of the magnetic recording layer.
[0016]
Therefore, as the thickness of the magnetic recording layer tends to become thinner and thinner, there is a strong demand for ensuring the runnability of the magnetic recording medium by adjusting the amount of myristic acid that oozes out on the surface of the magnetic recording layer. Has been.
[0017]
Conventionally, it is widely known that carbon black fine particle powder is used as a black filler material to be contained in a magnetic layer. Further, magnetic recording media using black titanium (TiO) (Japanese Patent Publication No. Sho 62-21185 and Japanese Patent Publication No. Sho 62-22179) and magnetic recording media using graphite fluoride (Japanese Patent Laid-Open No. Sho 56-156930). ) Etc.
[0018]
In the past, various attempts have been made to improve the substrate for forming a magnetic recording layer, to make the surface smooth and to increase the stiffness, as the magnetic recording layer is made thinner or the nonmagnetic support is made thinner. In addition, an underlayer (hereinafter referred to as “non-magnetic support”) in which a non-magnetic particle powder mainly composed of iron such as acicular hematite particle powder or acicular hydrous iron oxide powder is dispersed in a binder on a non-magnetic support such as a base film. At least one layer of “non-magnetic underlayer” has been provided and has already been put to practical use (Japanese Patent Publication No. 6-93297, Japanese Patent Laid-Open No. 62-159338, Japanese Patent Laid-Open No. 63). JP-A-187418, JP-A-4-167225, JP-A-4-325915, JP-A-5-73882, JP-A-5-182177, JP-A-5-347017, JP-A-6-60362. Gazette ).
[0019]
[Problems to be solved by the invention]
A magnetic recording medium having excellent durability and good electromagnetic conversion characteristics, smooth surface, smaller light transmittance and lower surface electric resistance value is currently most demanded. A magnetic recording medium that sufficiently satisfies these various characteristics has not yet been obtained.
[0020]
That is, in the magnetic recording medium using the filler material for magnetic recording media such as alumina, hematite, trichromium oxide, etc., which has been conventionally used, the amount of filler material to be added is increased in order to obtain durability. When increased, the electromagnetic conversion characteristics are greatly lowered, and a magnetic recording medium having excellent durability and good electromagnetic conversion characteristics cannot be obtained.
[0021]
In addition, when carbon black particle powder is used as the black filler material, since the blackness is excellent, it is possible to obtain a magnetic recording medium with low light transmittance, but from the poor dispersibility peculiar to carbon black particle powder. The dispersibility of the magnetic particle powder is reduced, and accordingly, adverse effects such as a decrease in electromagnetic conversion characteristics and a decrease in durability occur. This is described in Japanese Patent Application Laid-Open No. 4-139619, "... When a carbon black particle powder is added to produce a coating composition by kneading a binder resin and magnetic particle powder, a comparative example will be shown later. As described above, there is a problem in that the orientation and packing properties of the magnetic particle powder are lowered.
Furthermore, the carbon black particle powder has a bulk density of 0.1 g / cm. ^Three Since the powder was bulky and bulky, handling was difficult and workability was poor. In addition, problems from safety and hygiene such as carcinogenicity have been pointed out. ... "as described.
[0022]
Therefore, a black filler material is demanded as an alternative to the carbon black fine particle powder. However, the filler material such as alumina, hematite, and trichromium oxide is white in alumina, red in hematite, and green in trichromium oxide. , Both contribute less to the light transmittance reduction effect than black powder.
[0023]
The known black titanium is easily oxidized and is not sufficiently stable in air. Fluorinated graphite has poor dispersibility in the binder resin and often causes a decrease in electromagnetic conversion characteristics.
[0024]
Therefore, the present invention has excellent durability, good electromagnetic conversion characteristics, and smooth surface by being able to suppress deterioration of electromagnetic conversion characteristics even when a filler material necessary for improving durability is added. Therefore, it is an object of the present invention to provide a magnetic recording medium having a smaller light transmittance and a lower surface electric resistance value.
[0025]
[Means for solving the problems]
The technical problem can be achieved by the present invention as follows.
[0026]
That is, the present invention provides a nonmagnetic support, a nonmagnetic particle powder formed on the nonmagnetic support, a nonmagnetic underlayer containing a binder resin, a magnetic particle powder formed on the nonmagnetic underlayer, and a filler material. And a magnetic recording layer comprising a binder resin, the surface of the hematite particle powder is coated with an organosilane compound or polysiloxane produced from alkoxysilane, and the coating is 100 wt. A magnetic recording medium comprising a black composite hematite particle powder having an average particle diameter of 0.08 to 1.0 μm to which 1 to 60 parts by weight of carbon black is attached to a part thereof as the filler material. .
[0027]
The present invention also provides a nonmagnetic support, a nonmagnetic particle powder formed on the nonmagnetic support and a nonmagnetic underlayer containing a binder resin, a magnetic particle powder formed on the nonmagnetic underlayer, and a filler material. And a magnetic recording layer comprising a binder resin and selected from aluminum hydroxide, aluminum oxide, silicon hydroxide and silicon oxide as a lower layer on the particle surface of the hematite particle powder. 1 type or 2 types or more are coated, and the upper layer is coated with an organosilane compound or polysiloxane generated from alkoxysilane, and the coating is 1 to 60 parts by weight of carbon with respect to 100 parts by weight of the hematite particle powder. Using black composite hematite particle powder having an average particle size of 0.08 to 1.0 μm to which black is adhered as the filler material A magnetic recording medium according to symptoms.
[0028]
The configuration of the present invention will be described in detail as follows.
[0029]
First, the magnetic recording medium according to the present invention will be described.
[0030]
A magnetic recording medium according to the present invention includes a nonmagnetic support, a nonmagnetic underlayer formed on the nonmagnetic support, and magnetic particle powder, filler material, and binder resin formed on the nonmagnetic underlayer. And a magnetic recording layer.
[0031]
The magnetic recording medium according to the present invention is selected from hematite particle powder as a filler material, and if necessary, aluminum hydroxide, aluminum oxide, silicon hydroxide and silicon oxide on the particle surface of the particle powder. An organosilane compound or polysiloxane produced from alkoxysilane is coated on the surface of the core particle powder using the hematite particle powder coated with one or more kinds as a core particle powder, and the organosilane compound A black composite hematite particle powder having an average particle size of 0.08 to 1.0 μm in which carbon black is adhered to the coating or the polysiloxane coating is used.
[0032]
The black composite hematite particle powder in the present invention uses black hematite particle powder such as manganese-containing hematite particle powder containing 5 to 40% by weight of manganese based on the hematite particle powder or manganese-containing hematite particle powder as the core particle powder. Usually, since the hematite particle powder is red, considering the blackness of the resulting black composite hematite particle powder, black hematite particle powder such as manganese-containing hematite particle powder is preferable as the core particle powder.
[0033]
The core particle powder includes particles of various shapes, such as spherical, granular, octahedral, hexahedral, and polyhedral granular powders, acicular, spindle, and rice granular powders and plate granular powders. Etc.
[0034]
As for the particle size, in the case of granular particles such as spherical, granular, octahedral, hexahedral, and polyhedral, the average particle diameter is 0.075 to 0.95 μm, preferably 0.085 to 0.65 μm. Preferably it is 0.095-0.45 micrometer.
[0035]
In the case of needle-like powders such as needles, spindles, and rice grains, the average particle diameter (average major axis diameter) is 0.075 to 0.95 μm, preferably 0.085 to 0.65 μm, more preferably 0. 0.095 to 0.45 μm, and the axial ratio (ratio of average major axis diameter to average minor axis diameter) (hereinafter referred to as “axial ratio”) is 2 to 20, preferably 2.5 to 15, more preferably. Is 3-10.
[0036]
In the case of plate-like particle powder, the average particle diameter (average plate surface diameter) is 0.075 to 0.95 μm, preferably 0.085 to 0.65 μm, more preferably 0.095 to 0.45 μm. The plate ratio (ratio of average plate surface diameter to average thickness) (hereinafter referred to as “plate ratio”) is 2 to 50, preferably 2.5 to 20, and more preferably 3 to 10.
[0037]
When the average particle diameter of the core particle powder exceeds 0.95 μm, the resulting black composite hematite particles become coarse particles and the coloring power is reduced, so that it is difficult to reduce the light transmittance of the obtained magnetic recording medium. Become. When the particle size is less than 0.075 μm, aggregation is likely to occur due to an increase in intermolecular force due to particle miniaturization. Therefore, uniform coating treatment with alkoxysilane or polysiloxane on the particle surface of the core particle powder and carbon black fine particle powder A uniform adhesion process becomes difficult.
[0038]
When the particle shape of the core particle powder is needle-shaped, the entanglement between the particles increases when the axial ratio exceeds 20, and the surface of the particle of the core particle powder is uniformly coated with alkoxysilane or polysiloxane and the carbon black fine particles Uniform adhesion treatment with powder becomes difficult.
[0039]
When the particle shape of the core particle powder is plate-like, if the plate-like ratio exceeds 50, the stacking between the particles increases, and the surface of the particle of the core particle powder is uniformly coated with alkoxysilane or polysiloxane and carbon black Uniform adhesion treatment with fine particle powder becomes difficult.
[0040]
The blackness of the core particle powder is usually L in the case of black hematite particle powder. ^* The lower limit of the value exceeds 22, the upper limit is 28, preferably 26, and in the case of hematite particle powder, usually L ^* The lower limit of the value exceeds 22, and the upper limit is 38, preferably 36.
L ^* When the value exceeds the above upper limit, it is difficult to say that the blackness is sufficient, and it is difficult to obtain a black composite hematite particle powder excellent in blackness.
[0041]
The core particle powder has a BET specific surface area of 1.0 to 200 m. ² / G, preferably 2.0 to 150 m ² / G, more preferably 2.5 to 100 m ² / G. BET specific surface area value is 1.0m ² When the particle size is less than / g, the core particle powder is coarse or the particle powder is sintered between the particles, and the resulting black composite hematite particle powder is also coarse particle powder with reduced coloring power. Therefore, it is difficult to reduce the light transmittance of the obtained magnetic recording medium. BET specific surface area value is 200m ² / G exceeding, it is difficult to uniformly coat the surface of the core particle powder with alkoxysilane or polysiloxane and uniformly adhere with the carbon black fine particle powder due to the increase in intermolecular force due to finer particles. It becomes.
[0042]
The geometric standard deviation value of the particle diameter of the core particle powder is preferably 1.8 or less, more preferably 1.7 or less, and even more preferably 1.6 or less. When the geometric standard deviation value exceeds 1.8, due to the presence of coarse particle powder, uniform coating treatment with alkoxysilane or polysiloxane and uniform adhesion treatment with carbon black fine particle powder on the particle surface of the core particle powder It becomes difficult. Considering industrial productivity, the lower limit value of the geometric standard deviation value of the particle diameter is 1.01.
[0043]
The core particle powder according to the present invention may have one or more core particles whose surface is selected from aluminum hydroxide, aluminum oxide, silicon hydroxide, and silicon oxide (hereinafter referred to as “aluminum”). The coating may be coated with a hydroxide, etc.)), and the detachment of carbon black from the particle surface of the core particle powder is further reduced as compared with the case where it is not coated with a hydroxide of aluminum. Therefore, the dispersibility in the vehicle during the production of the magnetic coating material is further improved, and a magnetic recording medium having more excellent durability and electromagnetic conversion characteristics can be obtained.
[0044]
The coating amount of aluminum hydroxide, etc. is Al equivalent to the core particle powder, SiO ₂ Conversion or Al conversion amount and SiO ₂ The total amount with the converted amount is preferably 0.01 to 50% by weight.
[0045]
With the coating amount of 0.01 to 50% by weight, the carbon black desorption rate can be effectively reduced.
[0046]
The black composite hematite particle powder in the present invention coated with an aluminum hydroxide or the like has a particle size approximately the same as that of the black composite hematite particle powder in the present invention not coated with an aluminum hydroxide or the like, Geometric standard deviation value, BET specific surface area value, volume resistivity value and blackness L ^* Has a value.
[0047]
The organosilane compound (hereinafter referred to as “organosilane compound”) produced from the alkoxysilane in the present invention is an organosilane compound produced from the alkoxysilane represented by Chemical Formula 1 through a drying or heating step.
[Chemical 1]

[0048]
Specific examples of the alkoxysilane include methyltriethoxysilane, dimethyldiethoxysilane, phenyltriethoxysilane, diphenyldiethoxysilane, dimethyldimethoxysilane, methyltrimethoxysilane, phenyltrimethoxysilane, diphenyldimethoxysilane, isobutyltrimethoxysilane. Examples include methoxysilane and decyltrimethoxysilane.
[0049]
In view of the desorption rate and adhesion effect of carbon black, an organosilane compound produced from methyltriethoxysilane, methyltrimethoxysilane, dimethyldimethoxysilane, isobutyltrimethoxysilane, phenyltriethoxysilane is preferable, methyltriethoxysilane, Most preferred are organosilane compounds formed from methyltrimethoxysilane.
[0050]
The coating amount of the organosilane compound is preferably 0.02 to 5.0% by weight, more preferably 0.03 to 4.0% by weight in terms of Si, based on the core particle powder coated with the organosilane compound. And more preferably 0.05 to 3.0% by weight.
[0051]
When the amount is less than 0.02% by weight, it is difficult to sufficiently adhere carbon black to such an extent that the blackness, volume resistivity, and myristic acid adsorption amount of the resulting black composite hematite particle powder can be improved.
[0052]
If it exceeds 5.0% by weight, carbon black can be sufficiently adhered to the resulting black composite hematite particle powder, but the effect is saturated and there is no point in adding more than necessary.
[0053]
As the polysiloxane in the present invention, polysiloxane represented by Chemical Formula 2, modified polysiloxane represented by Chemical Formula 3, terminal modified polysiloxane represented by Chemical Formula 4 or a mixture thereof can be used.
[0054]
[Chemical 2]

[0055]
[Chemical 3]

[0056]
[Formula 4]

[0057]
In view of the carbon black elimination rate and the adhesion effect, polysiloxanes having methylhydrogensiloxane units, polyether-modified polysiloxanes, and terminal carboxylic acid-modified polysiloxanes whose ends are modified with carboxylic acids are preferred.
[0058]
The coating amount of polysiloxane is preferably 0.02 to 5.0% by weight, more preferably 0.03 to 4.0% by weight in terms of Si with respect to the core particle powder coated with polysiloxane. Even more preferably, it is 0.05 to 3.0% by weight.
[0059]
If it is less than 0.02% by weight, it is difficult to sufficiently adhere carbon black to such an extent that the blackness, volume resistivity, and myristic acid adsorption amount can be improved.
[0060]
If it exceeds 5.0% by weight, carbon black can be sufficiently adhered, but the effect is saturated and there is no point in adding it more than necessary.
[0061]
The total amount of carbon black attached in the present invention is 1 to 60 parts by weight with respect to 100 parts by weight of the core particle powder.
[0062]
When the amount is less than 1 part by weight, it is difficult to obtain a black composite hematite particle powder having excellent blackness and low volume resistivity because the amount of carbon black attached is small.
[0063]
When the amount exceeds 60 parts by weight, the effect of improving the blackness and volume resistivity of the obtained black composite hematite particle powder is saturated, and it is meaningless to attach more than necessary.
[0064]
When a large amount of carbon black is adhered, especially when it exceeds 30 parts by weight, a black composite hematite particle powder with suppressed myristic acid adsorption is obtained. That is, the black composite hematite particle powder having a carbon black adhesion amount of 30 parts by weight or less with respect to 100 parts by weight of the core particle powder has a myristic acid adsorption amount of 0.34 mg / m 2. ² In contrast to the above, black composite hematite particle powder to which more than 30 parts by weight of carbon black is attached to 100 parts by weight of core particle powder (hereinafter referred to as black composite hematite particle powder to which a large amount of carbon black is attached) Is the myristic acid adsorption amount 0.3 mg / m. ² It is as follows.
[0065]
As the carbon black fine particle powder, commercially available furnace black, channel black or the like can be used. Specifically, # 3050, # 3150, # 3250, # 3750, # 3950, MA100, MA7, # 1000, # 2400B , # 30, MA77, MA8, # 650, MA11, # 50, # 52, # 45, # 2200B, MA600, etc. (trade name: Mitsubishi Chemical Co., Ltd.) SEAST 9H, SEAST 7H, SEAST 6, SEAST 3H , Seest 300, Seest FM, etc. (trade name, Tokai Carbon Co., Ltd.), Raven 1250, Raven 860, Raven 1000, Raven 1190 ULTRA (trade name: Colombian Chemicals Company (product)), Ketjen Black EC, Ket Chain Black EC600 D (trade name: Ketchen Black International Co., Ltd.), BLACK PEARLS-L, BLACK PEARLS 1000, BLACK PEARLS 4630, VULCAN XC72, REGAL 660, REGAL 400 (trade name: Cabot Specialty Chemicals, Inc. ( Can be used).
[0066]
Considering the effect of reducing the amount of myristic acid adsorbed, it is preferable to use carbon black fine particle powder having a powder pH value of 9.0 or less, specifically, # 3050, # 3150, # 3250, # 3750, # 3950. , MA100, MA7, # 1000, # 2400B, # 30, MA77, MA8, # 650, MA11, # 50, # 52, # 45, # 2200B, MA600, etc. (trade name: Mitsubishi Chemical Corporation) 9H, Seast 7H, Seast 6, Seast 3H, Seast 300, Seast FM, etc. (trade name, Tokai Carbon Co., Ltd.), Raven 1250, Raven 860, Raven 1000, Raven 1190 ULTRA (trade name: Colombian Chemicals Company) (Manufactured)), BLACKPEARLS-L, BRAC K PEARLS 1000, BLACK PEARLS 4630, REGAL 660, and REGAL 400 (trade name: Cabot Specialty Chemicals, Inc.) are preferable.
[0067]
Furthermore, in consideration of more uniform adhesion treatment to the organosilane compound coating layer or the polysiloxane coating layer, it is more preferable to use carbon black fine particle powder having a DBP oil absorption of 180 ml / 100 g or less, specifically, # 3050, # 3150, # 3250, MA100, MA7, # 1000, # 2400B, # 30, MA77, MA8, # 650, MA11, # 50, # 52, # 45, # 2200B, MA600, etc. (trade name: Mitsubishi Chemical Co., Ltd.) SEAST 9H, SEAST 7H, SEAST 6, SEAST 3H, SEAST 300, SEAST FM, etc. (trade name, Tokai Carbon Co., Ltd.), Raven 1250, Raven 860, Raven 1000, Raven 1190 ULTRA ( Product Name: Colombian Chemicals Kang Pany (manufactured)), BLACK PEARLS-L, BLACK PEARLS 1000, BLACK PEARLS 4630, REGAL 660, REGAL 400 (trade name: Cabot Specialty Chemicals Inc. (manufactured)) are more preferable.
[0068]
The average particle diameter of the carbon black fine particle powder is preferably 0.002 to 0.05 μm, more preferably about 0.002 to 0.035 μm.
[0069]
When the average particle size of the carbon black fine particles is less than 0.002 μm, the carbon black fine particles become too fine, and handling becomes difficult.
[0070]
If it exceeds 0.05 μm, the particle size of the carbon black fine particles is large, so that a very large mechanical shearing force or the like is required to uniformly adhere to the alkoxysilane coating or polysiloxane coating, which is industrially disadvantageous. Become.
[0071]
In the case of carbon black in the present invention, when the amount of adhesion is large, particularly when it exceeds 30 parts by weight with respect to 100 parts by weight of the core particle powder, at least two layers with the layers bonded are optionally made of alkoxysilane. It may be attached to the resulting organosilane compound coating or polysiloxane coating.
[0072]
In consideration of the desorption rate and adhesion effect of carbon black, a layer composed of carbon black formed on the organosilane compound coating or polysiloxane coating formed from alkoxysilane in the present invention (hereinafter referred to as the first carbon black). The adhering amount of the layer is preferably 1 to 30 parts by weight, more preferably 3 to 25 parts by weight, based on 100 parts by weight of the core particle powder, and is adhered to the surface of the first layer in the present invention. The amount of adhesion of the formed carbon black layer (hereinafter referred to as carbon black second layer) is 1 to 30 parts by weight, preferably 5 to 25 parts by weight per 100 parts by weight of the core particle powder.
[0073]
What is necessary is just to adhere | attach carbon black with an adhesive agent between the layers of the layer which consists of carbon black in this invention. Dimethylpolysiloxane represented by Chemical formula 5 is preferred in order to firmly and uniformly bond the layers and suppress the myristic acid adsorption amount. The amount of the adhesive can be 0.1 to 5 parts by weight with respect to 100 parts by weight of the core particle powder.
[0074]
[Chemical formula 5]

[0075]
When the adhesive is less than 0.1 part by weight, it is difficult to sufficiently bond the second layer made of carbon black, and the myristic acid adsorption amount of the resulting black composite hematite particle powder cannot be improved.
[0076]
When the amount exceeds 5 parts by weight, carbon black can be sufficiently adhered, but the effect is saturated and there is no meaning to add more than necessary.
[0077]
The particle shape and particle size of the black composite hematite particle powder are greatly dependent on the particle shape and particle size of the core particle powder, have a particle shape almost similar to the core particle powder, and have a slightly larger particle size than the core particle powder. Have.
[0078]
That is, the black composite hematite particle powder has an average particle size of 0.08 to 1.0 μm, preferably an average particle size of 0.09 to 0.7 μm, when the granular hematite particle powder is a core particle powder. More preferably, the average particle size is 0.1 to 0.5 μm.
[0079]
When the needle-like hematite particle powder is used as the core particle powder, the average particle diameter (average major axis diameter) is 0.08 to 1.0 μm, preferably 0.09 to 0.7 μm, more preferably 0.1. The axial ratio is 2 to 20, preferably 2.5 to 15, and more preferably 3 to 10.
[0080]
When the plate-like hematite particle powder is used as the core particle powder, the average particle diameter (plate surface diameter) is 0.08 to 1.0 μm, preferably 0.09 to 0.7 μm, more preferably 0.1 to 0.1 μm. It is 0.5 micrometer, Comprising: Plate-like ratio is 2-50, Preferably it is 2.5-20, More preferably, it is 3-10.
[0081]
When the average particle size is less than 0.08 μm, the increase in intermolecular force due to the refinement of the particles makes it difficult to disperse in the vehicle during the production of the magnetic paint, and the surface smoothness of the resulting magnetic recording medium, Durability and electromagnetic conversion characteristics deteriorate. When the average particle diameter exceeds 1.0 μm, the coloring power decreases as the particle size increases, and it becomes difficult to reduce the light transmittance of the obtained magnetic recording medium.
[0082]
When the black composite hematite particle powder has a needle shape, if the axial ratio exceeds 20, the particles will be entangled with each other, making it difficult to uniformly disperse in the vehicle during the production of the magnetic coating material, resulting in surface smoothness. Therefore, it is difficult to obtain a magnetic recording medium excellent in durability and electromagnetic conversion characteristics.
[0083]
When the particle shape of the black composite hematite particle powder is plate-like, if the plate-like ratio exceeds 50, stacking between the particles increases, and it becomes difficult to uniformly disperse the vehicle in the production of the magnetic paint, and the surface smoothness It is difficult to obtain a magnetic recording medium having excellent properties, durability and electromagnetic conversion characteristics.
[0084]
The carbon black desorption rate of the black composite hematite particle powder is preferably 20% or less, more preferably 10% or less. When the desorption rate of carbon black exceeds 20%, the uniform dispersion in the vehicle is hindered by the desorbed carbon black during the production of the magnetic paint, so that the surface smoothness, durability and electromagnetic conversion It becomes difficult to obtain a magnetic recording medium having excellent characteristics.
[0085]
The blackness of the black composite hematite particle powder has an upper limit of L when black hematite particle powder is used as the core particle powder. ^* The value is 19, preferably 18.5. When hematite particle powder is used as the core particle powder, the upper limit is L ^* The value is 21, preferably 20.5. L ^* When the value exceeds the upper limit value, the brightness becomes high and the blackness is not sufficient, and it becomes difficult to reduce the light transmittance of the obtained magnetic recording medium. The preferred lower limit of blackness is L ^* The value is about 15.
[0086]
The volume resistivity of the black composite hematite particle powder is 1 × 10 ⁶ It is preferably Ω · cm or less, more preferably 1 × 10 ¹ Ω · cm to 5 × 10 ^Five Ω · cm, even more preferably 1 × 10 ¹ Ω · cm to 1 × 10 ^Five Ω · cm. Volume resistivity is 1 × 10 ⁶ When it exceeds Ω · cm, it is difficult to sufficiently reduce the surface electric resistance value of the obtained magnetic recording medium.
[0087]
The black composite hematite particle powder in the present invention to which a large amount of carbon black is attached has a myristic acid adsorption amount of 0.01 to 0.3 mg / m. ² And preferably 0.01 to 0.29 mg / m ² , More preferably 0.01-0.28 mg / m ² It is.
[0088]
When the amount of myristic acid adsorbed is within the above range, the amount of myristic acid adsorbed on the black composite hematite particle powder is an appropriate amount. Therefore, it is easy to adjust the amount of myristic acid adsorbed on the surface of the magnetic recording layer. It is possible to maintain a sufficiently low friction coefficient for a long period of time with respect to the use of the tape, and to ensure excellent running performance.
[0089]
The BET specific surface area value of the black composite hematite particle powder is 1.0 to 200 m. ² / G, preferably 2.0 to 150 m ² / G, more preferably 2.5 to 100 m ² / G. BET specific surface area value is 1.0m ² When the particle size is less than / g, the particles are coarse or become powder particles that are sintered between the particles, and the coloring power is reduced, so that the light transmittance of the resulting magnetic recording medium is reduced. It becomes difficult. BET specific surface area value is 200m ² / G exceeds the intermolecular force due to the finer particles, it becomes difficult to disperse the magnetic coating medium in the vehicle, and the surface smoothness, durability and electromagnetic conversion of the resulting magnetic recording medium are difficult. Characteristics are degraded.
[0090]
The geometric standard deviation value of the particle diameter of the black composite hematite particle powder is preferably 1.8 or less. When the geometric standard deviation value exceeds 1.80, the coarse particles present make it difficult to uniformly disperse in the vehicle during the production of the magnetic paint, and is excellent in surface smoothness, durability and electromagnetic characteristics. It is difficult to obtain a magnetic recording medium. Considering the surface smoothness, durability, and electromagnetic conversion characteristics of the obtained magnetic recording medium, the geometric standard deviation value is more preferably 1.7 or less, and even more preferably 1.6 or less. Considering industrial productivity, the lower limit value of the geometric standard deviation value of the particle diameter is 1.01.
[0091]
The adhesion thickness of carbon black is preferably 0.04 μm or less, more preferably 0.02 μm or less, and still more preferably 0.01 μm or less.
[0092]
The magnetic particle powder contained in the magnetic recording layer of the magnetic recording medium according to the present invention includes magnetic iron oxide particles such as maghemite particle powder, magnetite particle powder, and beltride compound particle powder that is an intermediate oxide between maghemite and magnetite. Powder, magnetic iron oxide particle powder containing different elements such as Co, Al, Ni, P, Zn, Si, B, etc. other than Fe, and depositing Co etc. on these magnetic iron oxide particles Co-coated magnetic iron oxide particle powder, metal magnetic particle powder containing iron as a main component, iron alloy magnetic particles containing Co, Al, Ni, P, Zn, Si, B and rare earth metals other than iron Plate, magnetoplumbite type ferrite particle powder containing Ba, Sr or Ba-Sr, and Co, Ni, Zn, Mn, Mg, Ti, Sn, Z to the ferrite particle powder Any one of plate-like magnetoplumbite-type ferrite particle powders containing one or more coercive force reducing agents selected from divalent and tetravalent metals such as Nb, Cu, and Mo is used. Can do.
[0093]
In consideration of recent high-density recording of magnetic recording media, the magnetic particle powder includes Co-coated magnetic iron oxide particle powder, metal magnetic particle powder containing iron as a main component, and Co and Al other than iron. Iron alloy magnetic particle powder containing Ni, P, Zn, Si, B, rare earth metal or the like is preferable.
[0094]
The particle shape of the magnetic particle powder may be any of a spindle shape, a rice grain shape, a cubic shape, a plate shape, etc. as well as a needle shape. Here, the “needle shape” means not only a literal needle shape but also a spindle shape or a rice grain shape.
[0095]
The magnetic particle powder has an average major axis diameter (average particle diameter in the case of plate-like particles) of 0.01 to 0.50 μm, preferably 0.03 to 0.30 μm, and an average minor axis diameter (plate-like particles). In this case, the average thickness) is 0.0007 to 0.17 μm, preferably 0.003 to 0.10 μm, and the geometric standard deviation value is 2.5 or less, preferably 1.01 to 2.3.
[0096]
Further, in the case of magnetic particle powder having a needle shape, the axial ratio is 3 or more, preferably 5 or more, and the upper limit is 15 considering the dispersibility in the vehicle during the production of the magnetic paint. Yes, preferably 10.
[0097]
In the case of magnetic particle powder having a plate-like particle shape, the plate-like ratio is 2 or more, preferably 3 or more, and the upper limit is 20 in consideration of the dispersibility in the vehicle during the production of the magnetic paint. , Preferably 15.
[0098]
The magnetic particle powder has a BET specific surface area of 15 m. ² / G or more, preferably 20 m ² / G or more. Considering the dispersibility in the vehicle during the production of the magnetic paint, the upper limit is 100 m. ² / G, more preferably 80 m ² / G.
[0099]
The magnetic properties of the magnetic particle powder are as follows: in the case of acicular magnetic iron oxide particle powder or Co-coated acicular magnetic iron oxide particle powder, the coercive force value is 250 to 1700 Oe, preferably 300 to 1700 Oe, and the saturation magnetization value Is 60 to 90 emu / g, preferably 65 to 90 emu / g.
[0100]
In the case of acicular metal magnetic particle powder or acicular iron alloy magnetic particle powder mainly containing iron, the coercive force value is 800 to 3500 Oe, preferably 900 to 3500 Oe, and the saturation magnetization value is 90 to 170 emu / g, Preferably it is 100-170emu / g.
[0101]
In the case of plate-like magnetoplumbite type ferrite particle powder, the coercive force value is 500 to 4000 Oe, preferably 650 to 4000 Oe, and the saturation magnetization value is 40 to 70 emu / g, preferably 45 to 70 emu / g.
[0102]
Examples of the binder resin contained in the magnetic recording layer of the magnetic recording medium according to the present invention include vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-anhydrous maleate, which are currently widely used in the production of magnetic recording media. Acid copolymers, vinylidene chloride, polyurethane resins, styrene-butadiene copolymers, butadiene-acrylonitrile copolymers, polyvinyl butyral, cellulose derivatives such as nitrocellulose, polyester resins, synthetic rubber resins such as polybutadiene, epoxy resins, polyamide resins , Polyisocyanates, electron beam curable acrylic urethane resins and the like and mixtures thereof can be used.
[0103]
In addition, each binder resin has —OH, —COOH, —SO. _Three M, -OPO ₂ M ₂ , -NH ₂ And the like (where M is H, Na, K). Considering the dispersibility of the magnetic particle powder and the black composite hematite particle powder in the vehicle during the production of the magnetic coating material, -COOH, -SO as polar groups _Three Binder resins containing M are preferred.
[0104]
The coating thickness of the magnetic recording layer in the present invention is in the range of 0.01 to 5.0 μm. When the thickness is less than 0.01 μm, uniform coating is difficult and uneven coating tends to occur. If it exceeds 5.0 μm, it is difficult to obtain desired electromagnetic characteristics due to the influence of the demagnetizing field. Preferably it is the range of 0.05-1.0 micrometer.
[0105]
The blending ratio of the magnetic particle powder and the binder resin in the magnetic recording layer is 5 to 50 parts by weight, preferably 6 to 30 parts by weight of the binder resin with respect to 100 parts by weight of the magnetic particle powder.
[0106]
When the binder resin exceeds 50 parts by weight, the magnetic particle powder in the magnetic recording layer is too small, so that the filling rate of the magnetic particle powder is lowered and the electromagnetic conversion characteristics are lowered. If the amount is less than 5 parts by weight, the binder resin is too small relative to the amount of the magnetic particle powder, so that the magnetic particle powder is not sufficiently dispersed in the magnetic paint, and as a result, the surface is sufficient when formed into a coating film. It is difficult to obtain a smooth coating film. Further, since the magnetic particle powder is not sufficiently bound by the binder resin, the obtained coating film tends to be brittle.
[0107]
The blending ratio of the magnetic particle powder and the black composite hematite particle powder in the magnetic recording layer is 1 to 30 parts by weight, preferably 3 to 25 parts by weight of the black composite hematite particle powder with respect to 100 parts by weight of the magnetic particle powder. .
[0108]
When the black composite hematite particle powder is less than 1 part by weight, the amount of black composite hematite particle powder contained in the magnetic recording layer is too small, so that the durability of the magnetic recording medium becomes insufficient and the magnetic recording medium It becomes difficult to reduce the light transmittance and the surface electric resistance value. When the black composite hematite particle powder exceeds 30 parts by weight, the magnetic recording medium can be provided with sufficient durability, and the light transmittance and surface electrical resistance of the magnetic recording medium can be reduced. The nonmagnetic component increases in the layer, which is disadvantageous for high density recording of the magnetic recording medium.
[0109]
The magnetic recording layer may contain a commonly used lubricant, abrasive, antistatic agent, and the like as necessary.
[0110]
As the non-magnetic substrate material of the magnetic recording medium according to the present invention, a synthetic resin film such as polyethylene terephthalate, polyethylene, polypropylene, polycarbonate, polyethylene naphthalate, polyamide, polyamideimide, and polyimide, which are currently widely used for magnetic recording media, Metal foils and plates such as aluminum and stainless steel and various papers can be used, and the thickness varies depending on the material, but is usually preferably 1.0 to 300 μm, more preferably 2.0 to 200 μm. .
[0111]
In the case of a magnetic disk, polyethylene terephthalate is usually used as the nonmagnetic substrate, and the thickness is usually 50 to 300 μm, preferably 60 to 200 μm. In the case of magnetic tape, in the case of polyethylene terephthalate, the thickness is usually 3 to 100 μm, preferably 4 to 20 μm. In the case of polyethylene naphthalate, the thickness is usually 3 to 50 μm, preferably 4 to 20 μm. The thickness is usually 2 to 10 μm, preferably 3 to 7 μm.
[0112]
The nonmagnetic underlayer in the present invention preferably has a coating thickness of 0.2 to 10.0 μm. If it is less than 0.2 μm, it is difficult to improve the surface roughness of the nonmagnetic support, and the stiffness tends to be insufficient. In consideration of thinning of the magnetic recording medium and stiffness of the coating film, the thickness is more preferably in the range of 0.5 to 5.0 μm.
[0113]
As the binder resin in the nonmagnetic underlayer, the binder resin used for forming the magnetic recording layer can be used.
[0114]
The blending ratio of the nonmagnetic particle powder and the binder resin in the nonmagnetic underlayer is 5 to 2000 parts by weight, preferably 100 to 1000 parts by weight of the nonmagnetic particle powder with respect to 100 parts by weight of the binder resin.
[0115]
When the nonmagnetic particle powder is less than 5 parts by weight, the amount of the particle powder is too small, so that when the coating is formed, a continuously dispersed layer of the nonmagnetic particle powder cannot be obtained. Stiffness is insufficient. When the amount exceeds 2000 parts by weight, the amount of the non-magnetic particle powder is too much with respect to the amount of the binder resin, so that the non-magnetic particle powder is not sufficiently dispersed in the non-magnetic coating material. It is difficult to obtain a coating film having a sufficiently smooth surface. Further, since the nonmagnetic particle powder is not sufficiently bound by the binder resin, the obtained coating film tends to be brittle.
[0116]
In addition, the nonmagnetic underlayer contains about 0.1 to 50 parts by weight of a lubricant, an abrasive, an antistatic agent, etc. used in the production of a normal magnetic recording medium, if necessary, with respect to 100 parts by weight of the binder resin. May be.
[0117]
As the nonmagnetic particle powder for a nonmagnetic underlayer in the present invention, a nonmagnetic inorganic powder usually used for a nonmagnetic underlayer for a magnetic recording medium can be used. Specifically, hematite, hydrous iron oxide, titanium oxide, zinc oxide, tin oxide, tungsten oxide, silicon dioxide, α-alumina, β-alumina, γ-alumina, chromium oxide, cerium oxide, silicon carbide, titanium carbide , Silicon nitride, boron nitride, calcium carbonate, barium carbonate, magnesium carbonate, strontium carbonate, calcium sulfate, barium sulfate, molybdenum disulfide, barium titanate, etc. can be used alone or in combination, especially hematite, hydrous hydroxide Iron, titanium oxide and the like are preferable.
[0118]
In order to improve dispersibility in the vehicle during the production of non-magnetic paints, the surface of these non-magnetic particle powders may be treated with aluminum hydroxide, aluminum oxide, silicon hydroxide, silicon oxidation as necessary. The surface of the magnetic recording medium may be surface treated with an object, etc., and the inside of the particle may be added as necessary to improve various properties such as light transmittance, surface electrical resistance, mechanical strength, surface smoothness, and durability of the obtained magnetic recording medium. Al, Ti, Zr, Mn, Sn, Sb or the like may be contained in the alloy.
[0119]
Considering the surface smoothness of the obtained nonmagnetic underlayer, the nonmagnetic particle powder preferably has a needle shape. Here, the “needle shape” means not only a literal needle shape but also a spindle shape or a rice grain shape.
[0120]
The average major axis diameter of the nonmagnetic particle powder is 0.01 to 0.3 μm, preferably 0.015 to 0.25 μm, more preferably 0.02 to 0.2 μm.
[0121]
In the magnetic recording medium according to the present invention, when a black composite hematite particle powder whose particle surface is not coated with aluminum hydroxide or the like is used as a filler material, the coercive force value is 250 to 4000 Oe, preferably 300 to 4000 Oe, squareness ratio (residual magnetic flux density Br / saturated magnetic flux density Bm) of 0.85 to 0.95, preferably 0.86 to 0.95, and glossiness of the coating film of 165 to 300%, preferably 170 to 300 %, The surface roughness Ra of the coating film is 9.5 nm or less, preferably 2.0 to 9.0 nm, more preferably 2.0 to 8.5 nm, and the linear absorption coefficient of the coating film is 1.30 to 5.00 μm. ^-1 , Preferably 1.35 to 5.00 μm ^-1 The surface electrical resistance value of the coating film is 1.0 × 10 ⁹ Ω / sq or less, preferably 7.5 × 10 ⁸ Ω / sq or less, more preferably 5.0 × 10 ⁸ It is below Ω / sq.
[0122]
When a black composite hematite particle powder to which a large amount of carbon black is attached is used as a filler material, the coating film has a linear absorption coefficient of 1.40 to 5.00 μm, as well as the above properties. ^-1 , Preferably 1.45 to 5.00 μm ^-1 The surface electrical resistance value of the coating film is 5 × 10 ⁸ Ω / sq or less, preferably 2.5 × 10 ⁸ Ω / sq or less, more preferably 1 × 10 ⁸ It is below Ω / sq and the friction coefficient is 0.25 to 0.30, preferably 0.25 to 0.29.
[0123]
The magnetic recording medium according to the present invention has a coercive force value of 250 to 4000 Oe, preferably 300 to 4000, when a black composite hematite particle powder whose particle surface is coated with an aluminum hydroxide or the like is used as a filler material. 4000 Oe, squareness ratio (residual magnetic flux density Br / saturated magnetic flux density Bm) of 0.85 to 0.95, preferably 0.86 to 0.95, and glossiness of the coating film of 170 to 300%, preferably 175 to 300 %, The surface roughness Ra of the coating film is 9.0 nm or less, preferably 2.0 to 8.5 nm, more preferably 2.0 to 8.0 nm, and the linear absorption coefficient of the coating film is 1.35 to 5.00 μm. ^-1 , Preferably 1.40 to 5.00 μm ^-1 The surface electrical resistance value of the coating film is 1.0 × 10 ⁹ Ω / sq or less, preferably 7.5 × 10 ⁸ Ω / sq or less, more preferably 5.0 × 10 ⁸ It is below Ω / sq.
[0124]
When a black composite hematite particle powder to which a large amount of carbon black is attached is used as a filler material, the coating film has a linear absorption coefficient of 1.45 to 5.00 μm, as well as the above properties. ^-1 , Preferably 1.50-5.00 μm ^-1 The surface electrical resistance value of the coating film is 5 × 10 ⁸ Ω / sq or less, preferably 2.5 × 10 ⁸ Ω / sq or less, more preferably 1 × 10 ⁸ Ω / sq or less, and the friction coefficient is 0.21 to 0.26, preferably 0.21 to 0.25.
[0125]
The magnetic recording medium according to the present invention uses, as the magnetic particle powder, acicular metal magnetic particle powder or acicular iron alloy magnetic particle powder containing iron as a main component, and a hydroxide whose particle surface is aluminum as a filler material. Is used, the coercive force value is 800 to 3500 Oe, preferably 900 to 3500 Oe, and the squareness ratio (residual magnetic flux density Br / saturated magnetic flux density Bm) is 0.85 to 0. .95, preferably 0.86 to 0.95, the gloss of the coating film is 190 to 300%, preferably 195 to 300%, and the coating film surface roughness Ra is 8.5 nm or less, preferably 2.0 to 8 0.0 nm, more preferably 2.0 to 7.5 nm, and the linear absorption coefficient of the coating film is 1.30 to 5.00 μm. ^-1 , Preferably 1.35 to 5.00 μm ^-1 The surface electrical resistance value of the coating film is 1.0 × 10 ⁹ Ω / sq or less, preferably 7.5 × 10 ⁸ Ω / sq or less, more preferably 5.0 × 10 ⁸ It is below Ω / sq.
[0126]
When a black composite hematite particle powder to which a large amount of carbon black is attached is used as a filler material, the coating film has a linear absorption coefficient of 1.40 to 5.00 μm, as well as the above properties. ^-1 , Preferably 1.45 to 5.00 μm ^-1 The surface electrical resistance value of the coating film is 5 × 10 ⁸ Ω / sq or less, preferably 2.5 × 10 ⁸ Ω / sq or less, more preferably 1 × 10 ⁸ It is below Ω / sq and the friction coefficient is 0.25 to 0.30, preferably 0.25 to 0.29.
[0127]
The magnetic recording medium according to the present invention uses, as the magnetic particle powder, acicular metal magnetic particle powder or acicular iron alloy magnetic particle powder containing iron as a main component, and a hydroxide whose particle surface is aluminum as a filler material. Is used, the coercive force value is 800 to 3500 Oe, preferably 900 to 3000 Oe, and the squareness ratio (residual magnetic flux density Br / saturated magnetic flux density Bm) is 0.85 to 0. .95, preferably 0.86 to 0.95, the glossiness of the coating film is 195 to 300%, preferably 200 to 300%, and the coating film surface roughness Ra is 8.0 nm or less, preferably 2.0 to 7 0.5 nm, more preferably 2.0 to 7.0 nm, and the linear absorption coefficient of the coating film is 1.35 to 5.00 μm. ^-1 , Preferably 1.40 to 5.00 μm ^-1 The surface electrical resistance value of the coating film is 1.0 × 10 ⁹ Ω / sq or less, preferably 7.5 × 10 ⁸ Ω / sq or less, more preferably 5.0 × 10 ⁸ It is below Ω / sq.
[0128]
When a black composite hematite particle powder to which a large amount of carbon black is attached is used as a filler material, the coating film has a linear absorption coefficient of 1.45 to 5.00 μm, as well as the above properties. ^-1 , Preferably 1.50-5.00 μm ^-1 The surface electrical resistance value of the coating film is 5 × 10 ⁸ Ω / sq or less, preferably 2.5 × 10 ⁸ Ω / sq or less, more preferably 1 × 10 ⁸ Ω / sq or less, and the friction coefficient is 0.21 to 0.26, preferably 0.21 to 0.25.
[0129]
The electromagnetic conversion characteristic value of the magnetic recording medium according to the present invention using the black composite hematite particle powder whose particle surface is not coated with aluminum hydroxide as a filler material is a magnetic particle powder having a coercive force value of 250 Oe or more and less than 1200 Oe. In the case of a magnetic recording medium using a magnetic recording medium using a magnetic particle powder having an output value at a recording frequency of 4 MHz of +1.2 dB or more, preferably +1.7 dB or more and a coercive force value of 1200 Oe or more and 4000 Oe or less. The output value at a recording frequency of 7 MHz is +1.2 dB or more, preferably +1.7 dB or more.
[0130]
The electromagnetic conversion characteristic value of the magnetic recording medium according to the present invention using the black composite hematite particle powder whose particle surface is coated with aluminum hydroxide as a filler material is a magnetic particle powder having a coercive force value of 250 Oe or more and less than 1200 Oe. In the case of a magnetic recording medium using a magnetic recording medium using a magnetic particle powder having an output value at a recording frequency of 4 MHz of +1.7 dB or more, preferably +2.2 dB or more and a coercive force value of 1200 Oe or more and 4000 Oe or less. The output value at a recording frequency of 7 MHz is +1.7 dB or more, preferably +2.2 dB or more.
[0131]
The durability of the magnetic recording medium according to the present invention using black composite hematite particle powder whose particle surface is not coated with aluminum hydroxide or the like as a filler material is such that the running durability time is 24 minutes or more, preferably 25 minutes or more. More preferably, it is 26 minutes or more, and the head contamination is B or A, preferably A.
[0132]
The durability of the magnetic recording medium according to the present invention using the black composite hematite particle powder whose particle surface is coated with aluminum hydroxide or the like as a filler material, the running durability time is 25 minutes or more, preferably 26 minutes or more, More preferably, it is 27 minutes or more, and the head contamination is B or A, preferably A.
[0133]
The black composite hematite particle powder in the present invention can be obtained by the following production method.
[0134]
The core particle powder is coated with alkoxysilane or polysiloxane by mechanically mixing and stirring the core particle powder and the alkoxysilane solution or polysiloxane, or mechanically while spraying the alkoxysilane solution or polysiloxane on the core particle powder. What is necessary is just to mix and stir. Almost all of the added alkoxysilane is coated on the particle surface of the core particle powder.
[0135]
In order to uniformly coat the alkoxysilane or polysiloxane on the surface of the core particle powder, it is preferable that the aggregation of the core particle powder is previously unraveled using a pulverizer.
[0136]
Mixing and stirring the core particle powder and the alkoxysilane solution or polysiloxane, and mixing and stirring the carbon black fine particle powder described later and the core particle powder coated with an organosilane compound or polysiloxane generated from alkoxysilane on the particle surface. As an apparatus for the purpose, an apparatus capable of applying a shearing force to the powder layer is preferable, and an apparatus capable of simultaneously performing shearing, spatula and compression is more preferable. For example, a wheel-type kneader, a ball-type kneader A blade-type kneader or a roll-type kneader can be used.
[0137]
Specifically, a mix muller, a simpson mill, a sand mill, a multi mill, a stots mill, a wet pan mill, a conner mill, a Henschel mixer, a ring muller, a rotating mill, a vibration mill, a pressure kneader, an extruder and a screw mixer can be used. Preferred are a mix muller, a simpson mill, a sand mill, a multi-mill, a stots mill, a wet pan mill, a conner mill, and a Henschel mixer. Particularly preferred are a mix muller, a simpson mill, a sand mill, and a multi-mill.
[0138]
The conditions during mixing and stirring are such that the line load is 2 to 200 kg / cm, preferably 10 to 150 kg / cm, more preferably 15 to 100 kg / cm so that the alkoxysilane is coated as uniformly as possible on the particle surface of the core particle powder. The treatment conditions may be appropriately adjusted within a range of cm and a treatment time of 5 to 120 minutes, preferably 10 to 90 minutes. In addition, what is necessary is just to adjust process conditions suitably in the range of stirring speed 2-2000rpm, Preferably 5-1000rpm, More preferably, it is 10-800rpm.
[0139]
The amount of alkoxysilane or polysiloxane added is preferably 0.15 to 45 parts by weight with respect to 100 parts by weight of the core particle powder. When the amount is less than 0.15 parts by weight, it is difficult to deposit carbon black to such an extent that the blackness, volume resistivity, and myristic acid adsorption amount can be improved. When the amount exceeds 45 parts by weight, carbon black can be sufficiently adhered, but there is no meaning to add more than necessary.
[0140]
Next, after coating the surface of the core particle powder with alkoxysilane or polysiloxane, add carbon black fine particle powder, mix and stir to adhere the carbon black to the alkoxylane coating or polysiloxane coating, and then dry or heat. To process.
[0141]
The carbon black fine particle powder is preferably added over a period of about 5 to 60 minutes while taking a small amount of time.
[0142]
The conditions during mixing and stirring are such that the linear load is 2 to 200 kg / cm, preferably 10 to 150 kg / cm, more preferably 15 to 100 kg / cm, and the treatment time is 5 to 120 minutes so that carbon black is uniformly attached. The treatment conditions may be appropriately adjusted within a range of preferably 10 to 90 minutes. In addition, what is necessary is just to adjust process conditions suitably in the range of stirring speed 2-2000rpm, Preferably 5-1000rpm, More preferably, it is 10-800rpm.
[0143]
The addition amount of the carbon black fine particle powder is 1 to 60 parts by weight with respect to 100 parts by weight of the core particle powder. When the amount is less than 1 part by weight, it is difficult to obtain a black composite hematite particle powder having excellent blackness and low volume resistivity because the amount of carbon black attached is small. When the amount exceeds 60 parts by weight, the effect of improving the blackness and volume resistivity of the obtained black composite hematite particle powder is saturated, and it is meaningless to attach more than necessary.
[0144]
In particular, when obtaining a black composite hematite particle powder to which a large amount of carbon black is adhered, it is preferable to add carbon black in two or more portions and repeat the addition and adhesion. In particular, when the carbon black fine particle powder constituting the second layer is added onto the carbon black constituting the first layer, an adhesive is bonded onto the carbon black constituting the first layer prior to the addition. It is more preferable to keep it.
[0145]
In other words, an adhesive is added to the black composite hematite particle powder on which the first layer of carbon black is formed, mixed and stirred, and then further added with carbon black fine particle powder. What is necessary is just to adhere | attach the 2nd layer of carbon black on carbon black.
[0146]
The conditions during the mixing and stirring of the adhesive are such that the linear load is 2 to 200 kg / cm, preferably 10 so that the adhesive is uniformly adhered to the surface of the black composite hematite particle powder on which the first layer of carbon black is formed. The processing conditions may be appropriately adjusted within a range of ˜150 kg / cm, more preferably 15 to 100 kg / cm, and a processing time of 5 to 120 minutes, preferably 10 to 90 minutes. In addition, what is necessary is just to adjust process conditions suitably in the range of stirring speed 2-2000rpm, Preferably 5-1000rpm, More preferably, it is 10-800rpm.
[0147]
The addition amount of the adhesive is 0.1 to 5 parts by weight with respect to the core particle powder. When the amount is less than 0.1 part by weight, it is difficult to sufficiently bond the second layer made of carbon black. If the amount exceeds 5 parts by weight, the bonding effect is saturated, so there is no point in adding more than necessary.
[0148]
The condition at the time of mixing and stirring the second layer of carbon black is such that the linear load is 2 to 200 kg / cm, preferably 10 to 150 kg / cm, more preferably 15 to 100 kg so that the adhesive and carbon black are uniformly bonded. / Cm, the treatment time may be 5 to 120 minutes, preferably 10 to 90 minutes. In addition, what is necessary is just to adjust process conditions suitably in the range of stirring speed 2-2000rpm, Preferably 5-1000rpm, More preferably, it is 10-800rpm.
[0149]
The amount of carbon black constituting the second layer is 1 to 30 parts by weight with respect to 100 parts by weight of the core particle powder. When the amount is less than 1 part by weight, the total amount of carbon black becomes insufficient, it becomes difficult to further improve the blackness and the volume resistivity, and the myristic acid adsorption amount is not improved. When the amount exceeds 30 parts by weight, carbon black tends to be detached from the surface of the obtained black composite hematite particle powder, and as a result, dispersibility in the vehicle decreases.
[0150]
The black composite hematite particle powder in the present invention is dried or heat-treated after carbon black is attached to the core particle powder. The heating temperature in the drying or heating step is usually preferably 40 to 200 ° C, more preferably 60 to 150 ° C, and the heating time is preferably 10 minutes to 12 hours, more preferably 30 minutes to 3 hours. Alkoxysilane becomes an organosilane compound by this drying or heating process.
[0151]
For the core particle powder, the surface of the particle is selected from aluminum hydroxide, aluminum oxide, silicon hydroxide and silicon oxide in advance of mixing and stirring with an alkoxysilane solution or polysiloxane, if necessary. You may coat | cover with 1 type, or 2 or more types.
[0152]
Coating with aluminum hydroxide or the like is performed by adding an aluminum compound, a silicon compound or both of the compounds to an aqueous suspension obtained by dispersing the core particle powder and mixing or stirring as necessary. By adjusting the pH value after stirring, one or more selected from the hydroxide of aluminum, the oxide of aluminum, the hydroxide of silicon and the oxide of silicon on the particle surface of the core particle powder. Apply, then filter, wash, dry and grind. If necessary, a deaeration / consolidation process may be further performed.
[0153]
As the aluminum compound, aluminum salts such as aluminum acetate, aluminum sulfate, aluminum chloride, and aluminum nitrate, and alkali aluminates such as sodium aluminate can be used.
[0154]
The addition amount of the aluminum compound is 0.01 to 50% by weight in terms of Al with respect to the hematite particle powder. When the amount is less than 0.01% by weight, it is difficult to coat a sufficient amount of aluminum hydroxide or the like on the particle surface, and the carbon black desorption rate cannot be improved effectively. If it exceeds 50% by weight, the coating effect is saturated, so there is no point in adding more than necessary.
[0155]
As the silicon compound, No. 3 water glass, sodium orthosilicate, sodium metasilicate and the like can be used.
[0156]
The amount of silicon compound added is SiO to hematite particle powder. ₂ It is 0.01 to 50% by weight in terms of conversion. When the amount is less than 0.01% by weight, it is difficult to coat a sufficient amount of silicon oxide or the like on the particle surface, and the carbon black desorption rate cannot be improved effectively. If it exceeds 50% by weight, the coating effect is saturated, so there is no point in adding more than necessary.
[0157]
When an aluminum compound and a silicon compound are used in combination, the equivalent amount of Al and SiO in the hematite particle powder are used. ₂ The total amount with the converted amount is preferably 0.01 to 50% by weight.
[0158]
Next, a method for manufacturing the magnetic recording medium according to the present invention will be described.
[0159]
In the magnetic recording medium according to the present invention, a nonmagnetic undercoat layer is formed by applying a nonmagnetic coating material containing a nonmagnetic particle powder, a binder resin and a solvent onto a nonmagnetic support and drying it by a conventional method. It can be obtained by applying a magnetic coating material containing magnetic particle powder, binder resin, black composite hematite particle powder and solvent on the undercoat layer to form a coating film and then orienting the magnetic field.
[0160]
In the kneading and dispersion of the non-magnetic coating material and the magnetic coating material, for example, a twin-screw kneader, a twin-screw extruder, a pressure kneader, a two-roll mill, a three-roll mill, etc. can be used. A sand grinder, an attritor, a disper, a homogenizer, an ultrasonic disperser, or the like can be used.
[0161]
A gravure coater, a reverse roll coater, a slit coater, a die coater, or the like can be used for applying the nonmagnetic paint and the magnetic paint. The coated sheet can be magnetically oriented by facing magnet orientation, solenoid magnet orientation, or the like.
[0162]
As the solvent, it is possible to use methyl ethyl ketone, toluene, cyclohexanone, methyl isobutyl ketone, tetrahydrofuran and a mixture thereof, which are currently widely used for magnetic recording media.
[0163]
The usage-amount of a solvent is 65-1000 weight part in the total amount with respect to 100 weight part of nonmagnetic particle powder or magnetic particle powder. If it is less than 65 parts by weight, the viscosity becomes too high when it is used as a magnetic coating material, making application difficult. When it exceeds 1000 parts by weight, the volatilization amount of the solvent when forming the coating film becomes too large, which is industrially disadvantageous.
[0164]
[Embodiments of the Invention]
A typical embodiment of the present invention is as follows.
[0165]
The average particle size of each particle powder of the core particle powder, black composite hematite particle powder, and carbon black fine particle powder is in a certain direction for about 350 particles shown in a photograph (× 80,000) obtained by enlarging the electron micrograph four times. Each diameter was measured and indicated by its average value.
[0166]
The axial ratio is indicated by the ratio between the average major axis diameter and the average minor axis diameter, and the plate ratio is indicated by the ratio between the average plate surface diameter and the average thickness.
[0167]
The geometric standard deviation value of the particle diameter was indicated by a value obtained by the following method. That is, the value measured for the particle size shown in the above enlarged photograph is calculated from the measured value, and the particle size is plotted on the horizontal axis on the log-normal probability paper according to a statistical method from the actual particle size and number of particles. The diameter was plotted on the vertical axis in terms of the cumulative number of particles belonging to each of the predetermined particle diameter sections (under the cumulative sieve) as a percentage. Then, from this graph, the particle diameter values corresponding to the cumulative number of particles of 50% and 84.13% are read, and the geometric standard deviation value = (particle diameter at 84.13% under accumulated fluid) / (under accumulated fluid). The value calculated in accordance with the particle diameter (geometric mean diameter) at 50% is shown, the closer the geometric standard deviation value is to 1, the better the particle size distribution.
[0168]
The specific surface area value was indicated by a value measured by the BET method.
[0169]
Each of the amount of Mn, Al, and Si present in the core particle powder and black composite hematite particle powder and the amount of Si contained in the organosilane compound, polysiloxane or dimethylpolysiloxane produced from alkoxysilane is Using a “fluorescence X-ray analyzer 3063M type” (manufactured by Rigaku Denki Kogyo Co., Ltd.), the measurement was performed in accordance with “General X-ray fluorescence analysis rules” of JISK0119.
[0170]
The amount of carbon black adhering to the black composite hematite particle powder was determined by measuring the amount of carbon using a “Horiba Metal Carbon / Sulfur Analyzer EMIA-2200 type” (manufactured by Horiba, Ltd.).
[0171]
The desorption rate (%) of carbon black adhering to the black composite hematite particle powder was indicated by the value obtained by the following method. The closer the carbon black desorption rate (%) is to 0, the smaller the amount of carbon black desorbed from the particle surface.
[0172]
3 g of black composite hematite particle powder and 40 ml of ethanol were placed in a 50 ml settling tube, subjected to ultrasonic dispersion for 20 minutes, and then allowed to stand for 120 minutes to separate the black composite hematite particle powder from the desorbed carbon black due to the difference in specific gravity. . Next, 40 ml of ethanol was again added to the black composite hematite particle powder, and after ultrasonic dispersion for 20 minutes, the mixture was allowed to stand for 120 minutes to separate the black composite hematite particle powder from the detached carbon black. This black composite hematite particle powder was dried at 100 ° C. for 1 hour, and the carbon amount was measured using the above-mentioned “Horiba Metal Carbon / Sulfur Analyzer EMIA-2200 type” (manufactured by Horiba Seisakusho Co., Ltd.). This value was defined as the carbon black desorption rate (%).
[0173]
Desorption rate of carbon black (%) = {(Wa-We) / Wa} × 100
Wa: Carbon black adhesion amount of black composite hematite particle powder
We: Carbon black adhesion amount of black composite hematite particle powder after desorption test
[0174]
The blackness of each of the hematite particle powder and the black composite hematite particle powder is kneaded with 0.5 g of a sample and 0.7 ml of castor oil with a Hoover-type Mahler to add a paste, and 4.5 g of clear lacquer is added to the paste. Then, an application piece (coating thickness: about 30 μm) was prepared by applying a 6 mil applicator on cast-coated paper, and the multi-light source spectrocolorimeter MSC-IS-2D (Suga Test Machine) Color index L according to the place defined in JIS Z 8729 ^* Indicated by value.
[0175]
Where L ^* The value represents lightness and L ^* It shows that blackness is excellent, so that a value is small.
[0176]
The volume resistivity of each particle powder of the hematite particle powder and the black composite hematite particle powder was first measured by measuring 0.5 g of the particle powder, and using a KBr tablet molding machine (Shimadzu Corporation), 140 Kg / cm. ² A cylindrical sample to be measured was prepared by performing pressure molding at a pressure of 1 m.
[0177]
Next, after the sample to be measured was exposed to a temperature of 25 ° C. and a relative humidity of 60% for 12 hours or more, the sample to be measured was set between the stainless steel electrodes, and Wheatstone Bridge (manufactured by TYPE 2768 Yokogawa Hokushin Electric Co., Ltd.) A resistance value R (Ω) was measured by applying a voltage of 15V.
[0178]
Next, the area A (cm) of the upper surface of the sample to be measured (cylindrical) ² ) And thickness t ₀ (Cm) was measured, and each measured value was inserted into the following equation to determine the volume resistivity (Ω · cm).
Volume resistivity (Ω · cm) = R × (A / t ₀ )
[0179]
The thickness of carbon black adhering to the black composite hematite particle powder was measured with an electron microscope photograph (×) using a transmission electron microscope JEM-2010 (manufactured by JEOL Ltd.) under an acceleration voltage of 200 kV. 500,000) is magnified 10 times (× 5,000,000), the average thickness of carbon black adhering to the surface of the particles is measured, and the measured value is actually attached. It was shown as a value converted back to thickness.
[0180]
The myristic acid adsorption amount of each particle powder of the hematite particle powder and the black composite hematite particle powder was determined by the following method. The smaller the amount of myristic acid adsorbed, the easier the fatty acid oozes out in the magnetic tape, and the friction coefficient can be reduced.
[0181]
First, 100 g of 1.5 mmφ glass beads, 9 g of measured particle powder, and 45 ml of a tetrahydrofuran solution containing myristic acid that only coats the surface of the measured particle powder are added to a 140 ml glass bottle and mixed and dispersed in a paint shaker for 60 minutes. did.
[0182]
Next, this mixed dispersion is taken out into a 50 ml sedimentation tube, and centrifuged at 10000 rpm for 15 minutes to separate the solid portion and the solvent portion. Then, the myristic acid concentration contained in the solvent part is quantified by a gravimetric method, and the amount of myristic acid present in the solid part is obtained by subtracting it from the amount of myristic acid charged. ² ).
[0183]
As for the paint viscosity, the shear rate at 25 ° C. is 1.92 sec using the E-type viscometer (cone plate type viscometer) EMD-R (manufactured by Tokyo Keiki Co., Ltd.). ^-1 It was shown by the value of the apparent viscosity at.
[0184]
The magnetic properties of the magnetic particle powder and the magnetic recording medium were measured using a “vibrating sample magnetometer VSM-3S-15” (manufactured by Toei Kogyo Co., Ltd.) with a maximum external magnetic field of 10 kOe.
[0185]
The glossiness of the coating surface of the magnetic recording layer was determined by measuring the 45 ° glossiness of the coating film using “Gloss meter UGV-5D” (manufactured by Suga Test Instruments Co., Ltd.).
[0186]
The surface roughness Ra was represented by a value obtained by measuring the center line average roughness of the coating film after calendar using “surfcom-575A” (manufactured by Tokyo Seimitsu Co., Ltd.).
[0187]
The degree of light transmission of the magnetic recording medium is a linear absorption coefficient calculated by inserting the value of light transmittance measured using “Self-recorded photoelectric spectrophotometer UV-2100” (manufactured by Shimadzu Corporation) into the following equation. Indicated. The larger the value of the linear absorption coefficient, the harder it is to transmit light.
[0188]
In measuring the value of light transmittance, the same nonmagnetic support as the nonmagnetic support used in the magnetic recording medium was used as a blank.
[0189]
Linear absorption coefficient (μm ^-1 ) = [Ln (1 / t)] / FT
t: Light transmittance at λ = 900 nm (−)
FT: thickness of the coating composition layer of the magnetic recording medium used for measurement (μm)
[0190]
For the electromagnetic conversion characteristics, an electromagnetic conversion output value at each recording frequency of 4 MHz or 7 MHz at a relative speed of 5.8 m / sec was shown as a relative value with respect to the reference tape using “Drum Tester BX-3168” (manufactured by Verdex). .
[0191]
The reference tape replaces the black composite hematite particle powder with 7.0 parts by weight of alumina (trade name: AKP-30, manufactured by Sumitomo Chemical Co., Ltd.) with respect to 100 parts by weight of the magnetic particle powder in the composition of the magnetic paint described later. A tape prepared in the same manner except that was used as a reference tape.
[0192]
The durability was shown as a measured value at a relative speed of 16 m / sec and a load of 200 g using “Media Durability Tester MDT-3000” (manufactured by Steinberg Associates).
[0193]
For head contamination, a “media durability tester MDT-3000” (manufactured by Steinberg Associates) was used to visually observe head contamination after running for 30 minutes at a relative speed of 16 m / sec and a load of 200 g. It was evaluated with. A indicates that the head is least dirty.
A: No dirt
B: Slightly dirty
C: Dirt
D: Severe dirt
[0194]
The friction coefficient of the magnetic recording medium is the value obtained from the ratio of the fruit tree by measuring the frictional force between the magnetic tape surface and the metal surface (aluminum mirror surface) using a tensile tester Tensilon (manufactured by Shimadzu Corporation). It was.
[0195]
The surface electrical resistance of the coating film is determined by coating the film to be measured for 12 hours or more in an environment of a temperature of 25 ° C. and a relative humidity of 60%, and then slitting the film to a width of 6.5 mm on a metal electrode with a width of 6.5 mm. The weight was measured by applying a DC voltage of 500 V between the electrodes after attaching a weight of 170 g to both ends and attaching the coating film to the electrodes.
[0196]
The thickness of each layer of the nonmagnetic support, the nonmagnetic underlayer and the magnetic recording layer constituting the magnetic recording medium was measured by the following measurement method.
[0197]
First, the film thickness (A) of the nonmagnetic support is measured using “Digital Electronic Micrometer K351C” (manufactured by Anritsu Electric Co., Ltd.). Next, the thickness (B) of the nonmagnetic support and the nonmagnetic underlayer formed on the nonmagnetic support (the sum of the thickness of the nonmagnetic support and the nonmagnetic underlayer) was measured in the same manner. To do. Further, the thickness (C) of the magnetic recording medium obtained by forming the magnetic recording layer on the nonmagnetic underlayer (the sum of the thickness of the nonmagnetic support, the thickness of the nonmagnetic underlayer, and the thickness of the magnetic recording layer). ) Is measured in the same manner. The thickness of the nonmagnetic underlayer is indicated by (B)-(A), and the thickness of the magnetic recording layer is indicated by (C)-(B).
[0198]
<Production of black composite hematite particle powder>
Manganese-containing black hematite particle powder (particle shape: granular, average particle diameter 0.30 μm, geometric standard deviation value 1.46, BET specific surface area value 3.6 m ² / G, Mn content 13.3% by weight, blackness L ^* Value 22.6, volume resistivity 2.0 × 10 ⁷ Ω · cm, Myristic acid adsorption amount 0.72 mg / m ² ) In order to break up the agglomeration, 20 kg was added to 150 liters of pure water using a stirrer, and further passed through “TK Pipeline Homomixer” (product name, manufactured by Tokushu Kika Kogyo Co., Ltd.) three times to contain manganese. A slurry containing black hematite particle powder was obtained.
[0199]
Subsequently, the slurry containing the manganese-containing black hematite particle powder was passed five times at a shaft rotation speed of 2000 rpm using a horizontal sand grinder “Mighty Mill MHG-1.5L” (product name, manufactured by Inoue Seisakusho Co., Ltd.). Thus, a dispersion slurry containing manganese-containing black hematite particle powder was obtained.
[0200]
The sieve residue in 325 mesh (aperture 44 μm) of the obtained dispersion slurry containing manganese-containing black hematite particle powder was 0%. The dispersion slurry was filtered and washed with water to obtain a cake of manganese-containing black hematite particles. After drying this manganese-containing black hematite particle powder cake at 120 ° C., 11.0 kg of the dried powder was put into an edge runner “MPUV-2 type” (product name, manufactured by Matsumoto Foundry), and 30 kg The mixture was stirred for 30 minutes at / cm to loosen the agglomeration of the particle powder.
[0201]
Next, a methyltriethoxysilane solution obtained by mixing and diluting 165 g of methyltriethoxysilane with 200 ml of ethanol was added to the above-mentioned manganese-containing black hematite particle powder that was released from the aggregation of particles while operating the edge runner, and 60 kg The mixture was stirred for 20 minutes with a linear load of / cm. The stirring speed at this time was 22 rpm.
[0202]
Next, carbon black fine particle powder B (particle shape: granular, average particle diameter 0.022 μm, geometric standard deviation value 1.78, BET specific surface area value 133.5 m) ² / G, blackness L ^* 1925 g (value 14.6, pH value 3.4, DBP oil absorption 84 ml / 100 g) was added over 10 minutes while running the edge runner, and further mixed and stirred for 30 minutes at a linear load of 30 kg / cm. Carbon black was deposited on the triethoxysilane coating. The stirring speed at this time was 22 rpm.
[0203]
The obtained black composite hematite particle powder was aged at 80 ° C. for 120 minutes using a dryer, and the remaining water, ethanol, and the like were volatilized. As a result of observation with an electron microscope, this black composite hematite particle powder has an average major axis diameter of 0.31 μm, a geometric standard deviation value of 1.46, and a BET specific surface area value of 7.8 m. ² / G, blackness L ^* The value is 17.6 and the volume resistivity value is 6.8 × 10 ^Three Ω · cm, carbon black desorption rate is 7.8%, carbon black adhesion amount is 14.78% by weight (corresponding to 17.5 parts by weight with respect to 100 parts by weight of core particle powder), The coating amount of methyltriethoxysilane was 0.22% by weight in terms of Si, and the adhesion thickness of carbon black on the particle surface was 0.0024 μm. As a result of observation with an electron microscope, almost no carbon black was observed, and it was confirmed that almost the entire amount of carbon black was adhered to the organosilane compound coating formed from methyltriethoxysilane.
[0204]
For comparison, the treated particle powder obtained by mixing and stirring manganese-containing black hematite particle powder and carbon black fine particle powder with an edge runner without coating with methyltriethoxysilane, as a result of electron microscope observation, It was confirmed that carbon black did not adhere to the particle surface of the manganese-containing hematite particle powder, and both particle powders were mixed apart.
[0205]
<Manufacture of nonmagnetic underlayer>
Nonmagnetic particle powder 1 shown in Table 9 below (type: hematite particles, particle shape: spindle shape, average major axis diameter 0.187 μm, average minor axis diameter 0.0240 μm, axial ratio 7.8, geometric standard deviation value 1 .33, BET specific surface area value 43.3 m ² / G, volume resistivity value 8.6 × 10 ⁸ Ω · cm, blackness L ^* Value) 12 g, a binder resin solution (vinyl chloride-vinyl acetate copolymer resin having sodium sulfonate group 30% by weight and cyclohexanone 70% by weight) and cyclohexanone were mixed to obtain a mixture (solid content 72%), This mixture was further kneaded with a plastmill for 30 minutes to obtain a kneaded product.
[0206]
This kneaded product was mixed with 95 g of 1.5 mmφ glass beads, an additional binder resin solution (polyurethane resin having a sodium sulfonate group 30 wt%, solvent (methyl ethyl ketone: toluene = 1: 1) 70 wt%), cyclohexanone, methyl ethyl ketone and toluene. The mixture was added to a 140 ml glass bottle and mixed and dispersed for 6 hours with a paint shaker to obtain a coating composition. Thereafter, a lubricant was added, and further mixed and dispersed for 15 minutes with a paint shaker.
[0207]
The composition of the obtained nonmagnetic coating material was as follows.
[0208]

[0209]
The obtained nonmagnetic paint had a paint viscosity of 310 cP.
[0210]
Next, the nonmagnetic paint was applied on a polyethylene terephthalate film having a thickness of 12 μm to a thickness of 55 μm using an applicator, and then dried to form a nonmagnetic underlayer.
[0211]
The thickness of the obtained nonmagnetic underlayer was 3.4 μm, gloss was 193%, surface roughness Ra was 8.2 nm, Young's modulus (relative value) was 123, and linear absorption coefficient was 1.01 cm. ^-1 The surface electrical resistance value is 1.1 × 10 ¹⁴ It was Ω · cm.
[0212]
<Manufacture of magnetic recording media>
Co-coated acicular magnetite particle powder (average major axis diameter 0.23 μm, axial ratio 7.3, BET specific surface area value 30.3 m ² / G, coercive force value 726 Oe, saturation magnetization value 81.9 emu / g, Co content 2.22 wt% 100 parts by weight, vinyl chloride-vinyl acetate copolymer resin (trade name: MR-110, Nippon Zeon Co., Ltd.) )) 10.0 parts by weight, cyclohexanone 23.3 parts by weight, methyl ethyl ketone 10.0 parts by weight, carbon black fine particle powder (manufactured by Mitsubishi Chemical Corporation, average particle size 26 nm, BET specific surface area 130 m) ² / G) After kneading 1.0 part by weight and 7.0 parts by weight of the black composite hematite particle powder obtained above using a kneader for 20 minutes, 79.6 parts by weight of toluene and 110. 1 parts of methyl ethyl ketone were added to the kneaded product. 2 parts by weight and 17.8 parts by weight of cyclohexanone were added for dilution, and then mixed and dispersed by a sand grinder for 3 hours to obtain a mixed dispersion.
[0213]
Add 33.3 parts by weight of a 1/1 solution of methyl ethyl ketone / cyclohexanone containing 10.0 parts by weight of a solid content of polyurethane resin (trade name: TI-1075, manufactured by Sanyo Chemical Industries, Ltd.) to the above mixed dispersion. Then, after mixing and dispersing for 30 minutes using a sand grinder, the filtrate obtained by filtering with a filter having an opening of 1 μm contains methyl ethyl ketone containing 1.0 part by weight myristic acid and 3.0 parts by weight butyl stearate. / Methyl ethyl ketone / toluene containing 12.1 parts by weight of 5/3/2 solution of toluene / cyclohexanone and 5.0 parts by weight of trifunctional low molecular weight polyisocyanate (trade name: E-31, manufactured by Takeda Pharmaceutical Co., Ltd.) A magnetic paint was prepared by mixing 15.2 parts by weight of a 5/3/2 solution of / hexahexanone with stirring.
[0214]
The composition of the obtained magnetic paint was as follows.
100 parts by weight of magnetic particle powder,
10 parts by weight of vinyl chloride-vinyl acetate copolymer resin,
10 parts by weight of polyurethane resin,
7.0 parts by weight of black composite hematite particle powder (filler material)
1.0 part by weight of carbon black fine particle powder,
1.0 part by weight myristic acid,
3.0 parts by weight of butyl stearate,
Trifunctional low molecular weight polyisocyanate 5.0 parts by weight,
56.6 parts by weight of cyclohexanone,
141.5 parts by weight of methyl ethyl ketone,
Toluene 85.4 parts by weight.
[0215]
The resulting magnetic paint had a paint viscosity of 2,816 cP.
[0216]
The obtained magnetic paint was applied on the non-magnetic underlayer to a thickness of 15 μm using an applicator, then oriented and dried in a magnetic field, then subjected to a calendar treatment, and then cured at 60 ° C. for 24 hours. Reaction was performed and slit to 0.5 inch width to obtain a magnetic tape. The film thickness of the obtained coating film was 3.4 μm.
[0217]
The magnetic properties of the magnetic tape were a coercive force value of 754 Oe and a squareness ratio (Br / Bm) of 0.88. The glossiness is 194%, the surface roughness Ra is 6.8 nm, and the linear absorption coefficient is 1.36 μm. ^-1 The surface electrical resistance value is 6.8 × 10 ⁷ Ω / cm ² As for the electromagnetic conversion characteristics, the output at a recording frequency of 4 MHz was +2.3 dB, the durability was a running durability time of 29.2 minutes or more, and the head contamination was A.
[0218]
In addition, the reference | standard tape 1 of Table 13 mentioned later was used as a reference | standard tape for calculating | requiring an electromagnetic conversion characteristic.
[0219]
[Action]
The most important point in the present invention is that, when the black composite hematite particle powder in the present invention is used as a filler material to be contained in the magnetic recording layer, it has excellent durability and good electromagnetic conversion characteristics, and has a smaller light The fact is that a magnetic recording medium having a transmittance and a lower surface electrical resistance value can be obtained.
[0220]
The reason why the magnetic recording medium according to the present invention has excellent durability and good electromagnetic conversion characteristics is that the present inventors have less carbon black desorbed from the particle surface of the black composite hematite particle powder used as the filler material. As a result, the black composite in which the dispersion of the magnetic particle powder is not particularly disturbed by the carbon black in the system, and the particle surface is uneven due to the carbon black adhering to the particle surface. It is considered that the hematite particle powder intervenes between the magnetic particle powders, so that the contact between the magnetic particles is suppressed and the magnetic particle powder is easily filled with a high amount.
[0221]
In addition, for the reason why the carbon black desorbed from the particle surface of the black composite hematite particle powder in the present invention is small, the present inventor, when using alkoxysilane, contains it in the particle interior of the hematite particle powder or the particle surface. Between the metal element such as Si, Al, Fe, etc. and the alkoxy group of the alkoxy silane to which the carbon black is attached, a metalloxane bond (≡Si—OM (where M is Si, Al , Fe, and other metal atoms contained in hematite particles.))) Is formed, so that the organosilane compound to which carbon black is adhered is firmly bonded to the particle surface of the hematite particle powder. ing.
[0222]
In addition, when polysiloxane is used, it is considered that various functional groups possessed by the polysiloxane to which carbon black is attached are firmly bonded to the particle surface of the hematite particle powder.
[0223]
Regarding the reason why the light transmittance of the magnetic recording medium according to the present invention is small, the present inventor has a blackness of the black composite hematite particle powder having a nonmagnetic underlayer and contained in the magnetic layer. I think it is due to That is, the black composite hematite particle powder in the present invention is usually a fine particle powder, so that the carbon black fine particle powder that behaves as an aggregate is formed from an alkoxysilane on the particle surface of the hematite particle powder. Alternatively, it is considered that carbon black functions more effectively by being uniformly and densely attached via polysiloxane.
[0224]
As for the reason why the surface electric resistance value of the magnetic recording medium according to the present invention is small, the present inventor has adhered uniformly and densely to the particle surface of the black composite hematite particle powder uniformly dispersed in the magnetic recording layer. This is thought to be due to the fact that carbon black is in continuous contact with each other.
[0225]
Regarding the reason why the friction coefficient of the magnetic recording medium according to the present invention can be reduced, the present inventor has suppressed the adsorption of myristic acid on the particle surface of the black composite hematite particle powder contained in the magnetic layer within a specific range. As a result, it is considered that the function as a lubricant can be effectively exerted by leaching out onto the surface of the magnetic recording layer over a long period of time while adjusting an appropriate amount of myristic acid.
[0226]
As for the reason why the running durability of the magnetic recording medium according to the present invention is excellent, the present inventor, for the same reason as described above, is stable by leaching to the surface of the magnetic recording layer while adjusting an appropriate amount of myristic acid. It is considered that the running durability was achieved.
[0227]
【Example】
Next, examples and comparative examples are given.
[0228]
Core particles 1-5
Various hematite particle powders obtained by a known production method were prepared, and hematite particle powders that were deagglomerated were obtained in the same manner as in the above-described embodiment.
[0229]
Table 1 shows various properties of the hematite particle powder.
[0230]
[Table 1]

[0231]
Core particle 6
A slurry containing manganese-containing black hematite particle powder was obtained in the same manner as in the embodiment of the present invention using 20 kg of manganese-containing black hematite particle powder in which the aggregation of the core particles 1 was unraveled and 150 l of water. The pH value of the redispersed slurry containing the resulting manganese-containing black hematite particle powder was adjusted to 10.5 using an aqueous sodium hydroxide solution, and then water was added to the slurry to adjust the slurry concentration to 98 g / l. 150 l of this slurry was heated to 60 ° C., and 2722 ml of a 1.0 mol / l sodium aluminate solution (corresponding to 0.5% by weight in terms of Al with respect to the manganese-containing black hematite particle powder) was added to the slurry. After maintaining for 30 minutes, the pH value was adjusted to 7.5 using acetic acid. This state was maintained for 30 minutes, followed by filtration, washing with water, drying and pulverization to obtain a manganese-containing black hematite particle powder whose particle surface was coated with an aluminum hydroxide.
[0232]
The main production conditions at this time are shown in Table 2, and various characteristics of the obtained manganese-containing black hematite particle powder are shown in Table 3.
[0233]
In the surface treatment step, the type of coating A is an aluminum hydroxide, and S represents a silicon oxide.
[0234]
[Table 2]

[0235]
[Table 3]

[0236]
Core particles 7-10
A surface-treated hematite particle powder was obtained in the same manner as the core particle 6 except that the kind of the core particle powder and the kind and amount of the additive in the surface treatment step were variously changed.
[0237]
The main treatment conditions at this time are shown in Table 2, and various properties of the obtained surface-treated hematite particles are shown in Table 3.
[0238]
<Production of black composite hematite particle powder>
Examples 1-12, Comparative Examples 1-4
Kind of core particle powder, alkoxysilane, polysiloxane, presence / absence of alkoxysilane, polysiloxane, silicon compound in the coating process with silicon compound, type and addition amount, treatment condition by edge runner, carbon black in adhesion process of carbon black fine particle powder A black composite hematite particle powder was obtained in the same manner as in the embodiment of the present invention, except that the type and amount of the fine particle powder and the processing conditions by the edge runner were variously changed. As for the black composite hematite particle powder obtained in each Example of Examples 1-10, since carbon black is hardly recognized as a result of observation with an electron microscope, an organosilane compound in which almost the entire amount of carbon black is generated from alkoxysilane. Adherence to the coating or polysiloxane coating was observed.
[0239]
Table 4 shows various characteristics of the carbon black fine particle powders A to F used.
[0240]
Table 5 shows the main treatment conditions at this time, and Table 6 shows the characteristics of the obtained black composite hematite particle powder.
[0241]
All the additives used in Examples 8 to 10 are polysiloxanes. “TSF484” (trade name: Toshiba Silicone Co., Ltd.) is methyl hydrogen polysiloxane, “BYK-080” (trade name: Big Chemie Japan Co., Ltd.) is a modified polysiloxane, “TSF-4770” (trade name: Toshiba Silicone Co., Ltd.) is a terminal carboxyl-modified polysiloxane.
[0242]
[Table 4]

[0243]
[Table 5]

[0244]
[Table 6]

[0245]
<Production of black composite hematite particle powder to which a large amount of carbon black is adhered>
Example 13
The black composite hematite particle powder (5.0 kg) obtained in the embodiment is put into an edge runner “MPUV-2 type” (product name, manufactured by Matsumoto Foundry Co., Ltd.) and mixed and stirred at 30 kg / cm for 30 minutes. The particle powder was agglomerated lightly.
[0246]
Next, 100 g of dimethylpolysiloxane was added to the black composite hematite particle powder while operating the edge runner, and the mixture was stirred for 45 minutes at a linear load of 60 kg / cm, so that the dimethylpolysiloxane was uniformly adhered to the surface. A black composite hematite particle powder was obtained.
[0247]
Next, 875 g of the above carbon black fine particle powder B is added over 10 minutes while the edge runner is operated, and further mixed and stirred for 30 minutes at a linear load of 60 kg / cm. A second layer made of carbon black was adhered to the surface using dimethylpolysiloxane as an adhesive to obtain black composite hematite particle powder.
[0248]
The obtained black composite hematite particle powder was dried at 105 ° C. for 60 minutes using a dryer. As a result of observation with an electron microscope, the black composite hematite particle powder was a granular particle powder having a particle diameter of 0.31 μm. Geometric standard deviation value is 1.45, BET specific surface area value is 10.5m ² / G, blackness L ^* The value is 17.1, and the volume resistivity is 3.1 × 10 ² Ω · cm, Myristic acid adsorption amount is 0.26 mg / m ² The carbon black desorption rate was 7.9%, and the total amount of carbon black adhered and adhered was 25.68% by weight in terms of C (35 parts by weight with respect to 100 parts by weight of the core particle powder). The coating amount of dimethylpolysiloxane was 0.70% by weight in terms of Si, and the adhesion thickness of carbon black on the particle surface was 0.0027 μm. As a result of observation with an electron microscope, almost no carbon black was observed, and it was confirmed that almost the entire amount of carbon black was adhered to the first layer of carbon black.
[0249]
Examples 14-25, Comparative Examples 5-11
The type of black composite hematite particles, the type of adhesive in the processing step with the adhesive, the amount added, and the processing conditions with the edge runner, the type of carbon black fine particle powder in the carbon black bonding step, the amount added, and the processing conditions with the edge runner A black composite hematite particle powder to which a large amount of carbon black was adhered was obtained in the same manner as in Example 13 except that various changes were made.
[0250]
In addition, since the black composite hematite particle powder obtained in each Example of Examples 14 to 25 shows almost no carbon black as a result of observation with an electron microscope, almost the entire amount of carbon black is the first layer of carbon black. It was observed that it was adhered to.
[0251]
Table 7 shows the main treatment conditions at this time, and Table 8 shows the characteristics of the obtained black composite hematite particle powder.
[0252]
[Table 7]

[0253]
[Table 8]

[0254]
<Manufacture of nonmagnetic underlayer>
Nonmagnetic particles 1-6
Using various nonmagnetic particle powders, nonmagnetic underlayers were produced in the same manner as in the above embodiments.
[0255]
Table 9 shows properties of the nonmagnetic particle powders 1 to 6 used.
[0256]
[Table 9]

[0257]
Table 10 shows the main manufacturing conditions and the characteristics of the obtained nonmagnetic underlayer.
[0258]
[Table 10]

[0259]
<Manufacture of reference tape>
Reference tape 1-6
A reference tape was manufactured using various nonmagnetic underlayers and various nonmagnetic particle powders in the same manner as in the above-described embodiment.
[0260]
Table 11 shows properties of various magnetic particle powders.
[0261]
[Table 11]

[0262]
The magnetic particle 3 is a plate-like magnetic particle powder. In Table 11, “average major axis diameter” is “plate surface diameter”, “average minor axis diameter” is “thickness”, and “axis ratio” is It means “plate ratio”.
[0263]
Tables 12 and 13 show the main production conditions and the characteristics of the obtained reference tape.
[0264]
[Table 12]

[0265]
[Table 13]

[0266]
<Manufacture of magnetic recording media>
Examples 26-50, Comparative Examples 12-22
A magnetic recording medium was obtained in the same manner as in the embodiment of the present invention, except that the type of magnetic particle powder, the type of black filler material, and the amount added were variously changed.
[0267]
Table 14 shows the manufacturing conditions of the magnetic recording medium, and Tables 15 to 17 show the characteristics.
[0268]
[Table 14]

[0269]
[Table 15]

[0270]
[Table 16]

[0271]
[Table 17]

[0272]
【The invention's effect】
The magnetic recording medium according to the present invention has excellent durability combined with being able to reduce the amount of carbon black added to the magnetic recording layer as much as possible and improving the dispersibility of the black composite hematite particle powder itself. In addition to having a non-magnetic underlayer and a black composite hematite particle powder having excellent blackness and low volume resistivity as a filler material. Due to the use, the surface is smooth, the light transmittance is lower, and the surface electrical resistance value is lower, so that it is suitable as a magnetic recording medium for high-density recording.
[0273]
As a filler material, in particular, the magnetic recording medium according to the present invention using the black composite hematite particle powder in which the amount of myristic acid adsorption is suppressed has the above-mentioned characteristics as well as a low friction coefficient and a running durability. Since it is excellent, it is suitable for high-density recording.

Claims (2)

A nonmagnetic underlayer comprising a nonmagnetic support, a nonmagnetic particle powder and a binder resin formed on the nonmagnetic support, and a magnetic particle powder, a filler material and a binder resin formed on the nonmagnetic underlayer In a magnetic recording medium comprising a magnetic recording layer, the surface of the hematite particle powder is coated with an organosilane compound or polysiloxane generated from alkoxysilane, and the coating is 1 to 100 parts by weight of the hematite particle powder. A magnetic recording medium comprising a black composite hematite particle powder having an average particle diameter of 0.08 to 1.0 μm to which 60 parts by weight of carbon black is adhered as the filler material. A nonmagnetic underlayer comprising a nonmagnetic support, a nonmagnetic particle powder and a binder resin formed on the nonmagnetic support, and a magnetic particle powder, a filler material and a binder resin formed on the nonmagnetic underlayer In a magnetic recording medium comprising a magnetic recording layer, one or two types selected from aluminum hydroxide, aluminum oxide, silicon hydroxide and silicon oxide as a lower layer on the particle surface of hematite particles The above is coated, and the upper layer is coated with an organosilane compound or polysiloxane generated from alkoxysilane, and 1 to 60 parts by weight of carbon black is adhered to 100 parts by weight of the hematite particle powder. Magnetic composite comprising black composite hematite particles having an average particle size of 0.08 to 1.0 μm as the filler material Media.