JP2001160212A - Non-magnetic particle powder for non-magnetic base layer of magnetic recording medium and magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide acicular hematite particle powder suitable for non-magnetic particle powder for a non-magnetic base layer of a magnetic recording medium having improved surface smoothness. SOLUTION: The acicular hematite particle powder suitable for the non- magnetic particle powder for the non-magnetic base layer is mixed acicular hematite particle powder of large particle size acicular hematite particle powder having 0.10-0.30 μm average major axis and an aspect ratio of 3.0-9.5 and small particle size acicular hematite particle powder having a ratio of the average major axis to the major axis of the large particle size acicular hematite particle powder of 0.10-0.83 and an aspect ratio of 3.0-9.5. The mixing ratio of the large particle size acicular hematite particle powder to the small particle size acicular hematite particle powder is 20:80-40:60 in volume.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention provides a needle-like hematite particle powder suitable as a non-magnetic particle powder for a non-magnetic underlayer of a magnetic recording medium.

[0002]

2. Description of the Related Art In recent years, as long-term recording and miniaturization of video and audio magnetic recording / reproducing devices have progressed, the performance of magnetic recording media such as magnetic tapes and magnetic disks has been improved. There is an increasing demand for higher performance, higher output characteristics, especially improved frequency characteristics, and lower noise.

In particular, in recent years, the demand for higher image quality and higher image quality of video tapes has been increasing more and more, and the frequency of a carrier signal to be recorded has shifted to a short wavelength region as compared with conventional video tapes. As a result, the magnetization depth from the surface of the magnetic tape is extremely shallow.

[0004] In order to improve the high output characteristics of a magnetic recording medium, especially the S / N ratio, for a short wavelength signal, it is strongly required to make the magnetic recording layer thinner. In order to reduce the thickness of the magnetic recording layer, it is necessary to smooth the magnetic recording layer and reduce unevenness in thickness. To do so, the surface of the base film must also be smooth.

In general, a magnetic recording medium is formed by forming a magnetic recording layer containing magnetic particle powder and a binder resin on a non-magnetic support such as a base film and calendering the surface to perform a surface smoothing treatment. Smoothing is performed.

In recent years, as magnetic recording layers have become thinner, non-magnetic particles such as needle-like matite particles are dispersed in a binder resin on a non-magnetic support such as a base film. It has been proposed that a single underlayer (hereinafter, referred to as a “nonmagnetic underlayer”) be provided to solve problems such as deterioration of the surface properties of the magnetic recording layer and deterioration of the electromagnetic conversion characteristics. (JP-B-6-93297, JP-A-62-159338, JP-A-63-1)
87418, JP-A-4-167225, JP-A-4-325915, JP-A-5-73882, JP-A-5-182177.

In the case of a magnetic recording medium having a nonmagnetic underlayer, a nonmagnetic underlayer containing nonmagnetic particle powder and a binder resin, a magnetic particle powder and a binder resin are formed on a nonmagnetic support. A magnetic recording layer containing the magnetic recording layer is formed, and then calendering is performed to absorb unevenness of the non-magnetic support by the non-magnetic underlayer, thereby smoothing the surface of the magnetic recording layer. For example, Japanese Patent Application Laid-Open No. Hei 5-12650 discloses "...
... By providing the non-magnetic buffer layer, the non-magnetic layer immediately below is crushed as a buffer layer when the layer containing the hexagonal ferrite magnetic powder is subjected to the surface smoothing treatment. As a result, the lower layer (nonmagnetic layer?) Acts as an absorption layer, and the upper magnetic recording layer containing the hexagonal ferrite plate-like magnetic powder is smoothed. It is described.

In order to improve the surface smoothness of the non-magnetic underlayer, it is preferable to use acicular hematite particles which have excellent dispersibility and can be expected to improve the surface smoothness by calendering.

Conventionally, various attempts have been made on non-magnetic particle powder for a non-magnetic underlayer to improve various characteristics of a magnetic recording medium. 1) A flat inorganic powder and a needle-like inorganic powder are used. Magnetic recording medium having an intermediate layer containing
3882), 2) a magnetic recording medium containing a granular inorganic powder, carbon black, and a coarse third component powder as a non-magnetic underlayer (JP-A-5-217149); 3) a non-magnetic layer or a soft magnetic layer. A magnetic recording medium containing an oxide, a carbide and a nitride having a major axis diameter larger than that of a nonmagnetic powder or a soft magnetic powder in a magnetic layer and having a new Mohs hardness of 6 or more (JP-A-5-242455) 4) A magnetic recording medium in which a nonmagnetic underlayer contains two types of nonmagnetic powders having different average particle sizes (Japanese Patent Application Laid-Open No. 6-267059) is known.

[0010]

A needle-like hematite particle powder suitable as a non-magnetic particle powder for a non-magnetic underlayer of a magnetic recording medium having more excellent surface smoothness has been most demanded at present, but it has not been obtained yet. Not been.

That is, in the case of the above-mentioned known method 1), since the particle shape of the inorganic powder is different, the surface smoothing effect by the calendar treatment cannot be expected. Further, since the inorganic powder used has a coarse particle size of 0.4 to 3.0 μm, it is difficult to obtain a coating film having a smooth surface.

In the case of the known method 2), since the inorganic powder has a granular particle shape, the surface of the inorganic powder is poorly calendered, and the surface smoothing effect by the calendering treatment cannot be expected.

In the above method 3), the mixing ratio of the large-sized soft magnetic particles or non-magnetic particles to the small-sized soft magnetic particles or non-magnetic particles is 2: 98-18. :
82, because the content of the small particle size powder is too large,
The surface smoothing effect by the calendar treatment cannot be expected.

In the method 4), the two types of non-magnetic particles having different average particle diameters may be granular or different in particle shape. Can't expect.

Accordingly, the present invention provides a needle having excellent dispersibility suitable for a non-magnetic particle powder for a non-magnetic underlayer of a magnetic recording medium having excellent surface smoothness and capable of improving surface smoothness by calendering. It is a technical object to obtain powdery hematite particles.

[0016]

The above technical object can be achieved by the present invention as described below.

That is, according to the present invention, the average major axis diameter is 0.10 to 0.10.
The ratio of the average major axis diameter to the average major axis diameter of the large-diameter acicular hematite particle powder having an axis ratio of 3.0 to 9.5 and the large-diameter acicular hematite particle powder is 0.30 μm. 0.1
A needle-like hematite particle powder mixed with a small-diameter needle-like hematite particle powder having an axial ratio of 3.0 to 9.5, and the large-diameter needle-like hematite particles; The mixing ratio of the powder and the small-sized acicular hematite particles is 20:80 to 40:60 in volume ratio, and is a nonmagnetic particle powder for a nonmagnetic underlayer of a magnetic recording medium. Invention 1).

Further, according to the present invention, the particle surface of the large-sized acicular hematite particle powder and / or the small-sized acicular hematite particle powder of the present invention has an aluminum hydroxide or an aluminum oxide. A non-magnetic particle powder for a non-magnetic underlayer of a magnetic recording medium, which is coated with a surface coating comprising at least one selected from the group consisting of hydroxides of silicon and oxides of silicon. ).

The present invention also provides a non-magnetic support, a non-magnetic underlayer containing a non-magnetic particle powder and a binder resin formed on the non-magnetic support, and a magnetic particle formed on the non-magnetic under layer. In a magnetic recording medium comprising a magnetic recording layer containing a powder and a binder resin, the non-magnetic particle powder is any one of the non-magnetic particle powders for non-magnetic underlayer according to the first and second aspects of the present invention. It is a magnetic recording medium characterized by the following.

The configuration of the present invention will be described in more detail as follows.

First, the nonmagnetic particle powder for a nonmagnetic underlayer according to the present invention will be described.

The nonmagnetic particle powder for a nonmagnetic underlayer according to the present invention has a large diameter needle having an average major axis diameter of 0.10 to 0.30 μm and an axial ratio of 3.0 to 9.5. The ratio of the average major axis diameter to the average major axis diameter of the powdery hematite particle powder and the large-diameter acicular hematite particle powder is 0.10 to 0.83, and the axial ratio is 3.0 to 9.5. It is a mixed needle-like hematite particle powder with a small particle-size needle-like hematite particle powder.

The particle shape of each acicular hematite particle powder in the present invention is acicular. Here, the term "needle-shaped" means a needle-like shape, a spindle shape, a rice grain shape, and the like, as well as a literal needle-like shape.

When the particle shape is other than a granular or plate-like acicular shape, it is difficult to obtain the effect of improving the surface smoothness by the calendering treatment which is the object of the present invention.

The axial ratio of the large-sized acicular hematite particles and the small-sized acicular hematite particles according to the present invention is as follows:
3.0 to 9.5. When the axial ratio is less than 3.0, it is difficult to obtain a coating film having sufficient strength. When the axial ratio exceeds 9.5, the entanglement of the particles in the vehicle increases, and the dispersibility may worsen or the viscosity may increase. In consideration of the strength of the obtained coating film and the dispersibility in the vehicle, the axial ratio of each acicular hematite particle powder is 3.5 to 3.5.
9.0 is preferred, and more preferably 4.0 to 8.5.

In the present invention, the ratio of the average major axis diameter of the small-sized acicular hematite particles to the average major axis diameter of the large-sized acicular hematite particles is 0.10 to 0.83. If the ratio of the average major axis diameter of the small-diameter acicular hematite particle powder is out of the above range, the effect of improving the surface smoothness by the calendar treatment cannot be obtained. Preferably it is 0.11-0.80, More preferably, it is 0.12-0.75.

The large-diameter acicular hematite particles according to the present invention have an average major axis diameter of 0.1 to 0.3 μm. Also,
It is preferable that the geometric standard deviation value of the major axis diameter is 1.50 or less, and the BET specific surface area value is 35 to 80 m ² / g.

When the large-diameter acicular hematite particle powder has an average major axis diameter of less than 0.10 μm, the filling state in the coating film becomes dense, so that it is difficult to obtain a surface smoothing effect by calendering. If it exceeds 0.30 μm, the particle size is too large, which may impair the surface smoothness of the coating film. Preferably it is 0.1-0.28 μm, more preferably 0.1-0.25 μm.

When the BET specific surface area value of the large-diameter acicular hematite particle powder exceeds 80 m ² / g, the filling state in the coating film becomes dense, so that it is difficult to obtain a surface smoothing effect by calendering. If it is less than 35 m ² / g, the particle size is too large, which is not preferable from the viewpoint of improving the surface smoothness of the coating film. Considering the surface smoothness of the obtained magnetic recording medium, the BE
T specific surface area value is more preferably between 35 and 75 ² / g, and even more preferably 35~70m ² / g.

When the geometric standard deviation of the major axis diameter of the large-sized acicular hematite particle powder exceeds 1.50, the particle size distribution is large and the presence of coarse particles impairs the surface smoothness of the coating film. There is. In consideration of the surface smoothness of the coating film, it is more preferably 1.48 or less, and still more preferably 1.4.
5 or less. In consideration of industrial productivity, the lower limit of the geometric standard deviation of the major axis diameter of the large-diameter acicular hematite particle powder is 1.01.

The average major axis diameter of the acicular hematite particles having a small particle diameter in the present invention is the ratio of the average major axis diameter of the acicular hematite particles having a small particle diameter to the average major axis diameter of the acicular hematite particles having a large particle diameter. Is in the range of 0.10 to 0.83, preferably 0.01 or more and less than 0.1 μm, more preferably 0.01 to 0.09 μm. When the average major axis diameter is less than 0.01 μm, dispersion in a vehicle becomes difficult due to an increase in intermolecular force due to fine particles. Also, the geometric standard deviation of the major axis diameter is 1.50 or less,
The BET specific surface area value is preferably from 70 to ²⁰⁰ m ² / g.

When the BET specific surface area value of the small particle size acicular hematite particles exceeds 200 m ² / g, aggregation tends to occur due to an increase in intermolecular force due to finer particles. , The dispersibility in the vehicle decreases. When the BET specific surface area is less than 70 m ² / g, the small-sized needle-like hematite particles are coarse particles or particles in which sintering occurs between the particles. It is difficult to obtain a surface smoothing effect. Considering the surface smoothness of the obtained magnetic recording medium and the dispersibility in the vehicle, the BET specific surface area of the small-sized needle-like hematite particles is 75 to ²⁰⁰ m ² / g.
Is more preferable, and still more preferably 80 to ²⁰⁰ m ²
/ G.

If the geometric standard deviation of the major axis diameter of the small particle size acicular hematite particle powder exceeds 1.50, the particle size distribution is large and the dispersion in the vehicle becomes difficult due to the presence of ultrafine particles, The surface smoothness of the coating film may be impaired.
Considering the surface smoothness of the coating film, more preferably 1.4.
8 or less, still more preferably 1.45 or less. In consideration of industrial productivity, the lower limit of the geometric standard deviation of the major axis diameter of the large-diameter acicular hematite particle powder is 1.01.

The mixing ratio of the large-sized acicular hematite particles and the small-sized acicular hematite particles in the present invention is as follows:
The volume ratio is 20:80 to 40:60, preferably 2
5:75 to 35:65. When the volume ratio between the large-diameter acicular hematite particles and the small-diameter acicular hematite particles is out of the above range, the effect of improving the surface smoothness by the calendering treatment is reduced.

The effect of improving the surface smoothness by the calendering treatment increases as the axial ratio of the acicular hematite particles having a large particle diameter and the axial ratio of the acicular hematite particles having a small particle diameter become closer to each other. Therefore, it is desirable to approximate the axial ratio of both particle powders as much as possible.

The mixed acicular hematite particle powder according to the present invention may have, if necessary, a surface of a large-acicular acicular hematite particle powder and / or a small-accurate acicular hematite particle powder whose surface is aluminum hydroxide or aluminum oxide. At least one selected from a substance, a hydroxide of silicon and an oxide of silicon
It may be coated with a surface coating consisting of seeds.
Needle-like hematite particle powder whose particle surface is coated with a surface coating has good compatibility with a binder resin when dispersed in a vehicle, and a desired degree of dispersion is easily obtained.

The amount of the surface coating is such that aluminum hydroxide or aluminum oxide is converted to Al, silicon hydroxide or silicon oxide is converted to SiO ₂ with respect to the acicular hematite particles. Each is preferably 0.01 to 50% by weight. If the amount is less than 0.01% by weight, the effect of improving the dispersibility by the coating is hardly obtained. Considering the effect of improving dispersibility in the vehicle and industrial productivity, 0.05 to 20% by weight is more preferable.

When the aluminum compound and the silicon compound are used in combination, the total of the converted amount in Al and the converted amount in SiO ₂ is 0.01 to
50% by weight is preferred.

The acicular hematite particle powder coated with the surface coating according to the present invention has a particle size and a geometric standard deviation substantially equivalent to those of the acicular hematite particle powder according to the present invention not coated with the surface coating. Value, axial ratio and BET
It has a specific surface area value.

Next, the magnetic recording medium according to the present invention will be described.

The magnetic recording medium according to the present invention comprises a non-magnetic support, a non-magnetic underlayer formed on the non-magnetic support, and a magnetic recording layer formed on the non-magnetic under layer.

Examples of the non-magnetic support include polyethylene terephthalate, which is currently widely used for magnetic recording media,
Polyethylene, polypropylene, polycarbonate, polyethylene naphthalate, polyamide, polyamide imide, synthetic resin film such as polyimide, aluminum,
Metal foils and plates such as stainless steel and various types of paper can be used. The thickness varies depending on the material, but is usually preferably 1.0 to 300 μm, more preferably 2.0 to 300 μm.
２００200 μm.

In the case of a magnetic disk, polyethylene terephthalate is generally used, and its thickness is usually 50 to 300 μm, preferably 60 to 200 μm. In the case of a magnetic tape, polyethylene terephthalate, polyethylene naphthalate, polyamide or the like is used, and the thickness of polyethylene terephthalate is usually 3 to
100 μm, preferably 4 to 20 μm, and the thickness of polyethylene naphthalate is usually 3 to 50 μm, preferably 4 μm.
~ 20μm, the thickness of the polyamide is usually 2 ~ 10μm,
Preferably it is 3 to 7 μm.

The nonmagnetic underlayer according to the present invention comprises the nonmagnetic particle powder for a nonmagnetic underlayer according to the present invention or the nonmagnetic particle powder for a nonmagnetic underlayer coated with the surface coating according to the present invention, and a binder. Made of resin.

As the binder resin, at present, magnetic recording media
PVC-vinyl acetate commonly used in the manufacture of
Copolymer, urethane resin, vinyl chloride-vinyl acetate-
Maleic acid copolymer, urethane elastomer, butadier
-Acrylonitrile copolymer, polyvinyl butyral
, Cellulose derivatives such as nitrocellulose, polyester
Resin, synthetic rubber resin such as polybutadiene, epoxy
Resin, polyamide resin, polyisocyanate, electron beam hardening
Uses acrylic urethane resin and mixtures of these
can do. Also, each binder resin has -OH,-
COOH, -SO ₃M, -OPO₂M₂, -NH₂Etc.
Polar groups (where M is H, Na, K)
May be. Mixed needle-like hematite particle powder in the present invention
Considering the dispersibility in the final vehicle,
-COOH, -SO₃Binder resin containing M
Is preferred.

The mixing ratio of the mixed needle-like hematite particle powder and the binder resin in the present invention is such that the mixed needle-like hematite particle powder is 5 to 2,000 per 100 parts by weight of the binder resin.
Parts by weight, preferably 100 to 1000 parts by weight.

When the mixed acicular hematite particle powder is less than 5 parts by weight, the mixed acicular hematite particle powder in the non-magnetic paint is too small. Layer cannot be obtained, and the smoothness of the coating film surface and the strength of the coating film become insufficient. If the amount exceeds 2000 parts by weight, the mixed needle-like hematite particles are not sufficiently dispersed in the non-magnetic paint because the amount of the mixed needle-like hematite particles is too large with respect to the amount of the binder resin. When formed into a film, it is difficult to obtain a coating film having sufficient surface smoothness. Further, since the mixed needle-like hematite particle powder is not sufficiently bound by the binder resin, the obtained coating film tends to be brittle.

The coating thickness of the non-magnetic underlayer formed on the non-magnetic support is preferably 0.2 to 10 μm. If it is less than 0.2 μm, it becomes difficult to improve the surface roughness of the nonmagnetic support, and the strength tends to be insufficient. In consideration of the thickness of the magnetic recording medium and the strength of the coating film, the thickness of the coating film is more preferably 0.5 to 5 μm.

The non-magnetic underlayer may contain a lubricant, an abrasive, an antistatic agent and the like which are usually used for manufacturing a magnetic recording medium.

The nonmagnetic underlayer using the nonmagnetic particle powder according to the present invention in which the particle surface is not coated with the surface coating has a glossiness of the coating film of 175 to 300%, preferably 180 to 300%, More preferably 185 to 300%
And the coating film surface roughness Ra is 0.5 to 8.5 nm, preferably 0.5 to 8.0 nm, and the strength of the coating film is
Young's modulus (relative value) is 126 to 160, preferably 12
8 to 160, and the shrinkage of the coating film is 10 to 20%, preferably 11 to 20%.

The non-magnetic underlayer using the non-magnetic particle powder according to the present invention, in which the particle surface is coated with the surface coating, has a glossiness of the coating film of 180 to 300%, preferably 185 to 300%, It is more preferably 190 to 300%, the coating film surface roughness Ra is 0.5 to 8.0 nm, preferably 0.5 to 7.5 nm, and the strength of the coating film is Young's modulus (relative value). ) Is from 128 to 160, preferably 130
And the shrinkage of the coating film is 10.5 to 20%, preferably 11.5 to 20%.

The magnetic recording layer according to the present invention comprises magnetic particles and a binder resin.

As the magnetic particles, maghemite particles (γ-Fe ₂ O ₃ ) and magnetite particles ( Fe
Co-coated magnetic iron oxide particles obtained by coating Co or Co and Fe on magnetic iron oxide particles such as O _x .Fe ₂ O ₃ , 0 <x ≦ 1); Co-coated magnetic iron oxide particle powder containing different elements such as Co, Al, Ni, P, Zn, Si, B, and rare earth metals other than Fe in the particle powder, and acicular metal magnetism mainly composed of iron Particle powder,
Acicular iron alloy magnetic particle powder containing Co, Al, Ni, P, Zn, Si, B, rare earth metal, etc. other than iron, Ba, S
r or Ba-Sr-containing magnetoplumbite-type plate-like ferrite particles and Co, Ni, Z
n, Mn, Mg, Ti, Sn, Zr, Nb, Cu, Mo
One of coercive force reducing agents selected from divalent and tetravalent metals such as
Either a plate-like magnetoplumbite-type ferrite particle powder or the like containing two or more species can be used.

In view of recent short-wavelength recording and high-density recording, acicular metallic magnetic particles containing iron as a main component, Co, Al, Ni, P, Zn, Si, B, and rare earths other than iron Needle-like iron alloy magnetic particles containing a metal or the like are preferred.

The magnetic particle powder has an average major axis diameter (average major axis diameter in the case of plate-like particles) of 0.01 to 0.5 μm, preferably 0.03 to 0.3 μm. The particle shape of the magnetic particle powder is preferably acicular or plate-like. Here, the term "needle-shaped" means not only a needle-like shape in a literal sense but also a spindle-shaped or rice-grained shape.

When the magnetic particle powder has a needle shape, the axial ratio is 3.0 or more, preferably 5 or more, and the upper limit value is 15 in consideration of the dispersibility in the vehicle.
And preferably 10.

When the particle shape of the magnetic particle powder is plate-like, the plate-like ratio (ratio of the average major axis diameter of the particles to the average thickness of the particles) is 2 or more, preferably 3 or more, and the dispersibility in the vehicle is improved. Considering that, the upper limit is 20, and preferably 15.

The magnetic properties of the magnetic particles are as follows.
9.8 to 318.3 kA / m (500 to 4000 O
e), preferably 43.8 to 318.3 kA / m (55
0 to 4000 Oe) and the saturation magnetization value is 50 to 17
^{0Am 2 / kg (50~170emu / g} ), preferably 60~170Am ² / kg (60~170emu /
g).

In consideration of high-density recording and the like, the magnetic properties when using acicular metallic magnetic particles containing iron as the main component or acicular iron alloy magnetic particles as the magnetic particles are as follows. 63.7 to 278.5 kA / m (800 to 3500
Oe), preferably 71.6 to 278.5 kA / m (9
00-3500 Oe), and the saturation magnetization value is 90-170 Am
² / kg (90-170 emu / g), preferably 10
^{0~170Am 2 / kg (100~170emu / g} )
It is.

As the binder resin, the binder resin used for forming the nonmagnetic underlayer can be used.

The coating thickness of the magnetic recording layer provided on the non-magnetic underlayer is in the range of 0.01 to 5 μm. 0.01
When the thickness is less than μm, uniform application is difficult and phenomena such as uneven coating are likely to occur, which is not preferable. If it exceeds 5 μm, it becomes difficult to obtain desired electromagnetic conversion characteristics due to the influence of a demagnetizing field. Preferably 0.05 to 1 μm
Range.

The mixing ratio of the magnetic particle powder and the binder resin is such that the magnetic particle powder is 2 parts per 100 parts by weight of the binder resin.
It is 00 to 2000 parts by weight, preferably 300 to 1500 parts by weight.

A commonly used lubricant, abrasive, antistatic agent and the like may be added to the magnetic recording layer.

The magnetic recording medium according to the present invention uses the magnetic particle powder as the magnetic particle powder, and the non-magnetic underlayer according to the present invention, which is not coated with a surface coating as the nonmagnetic particle powder for the nonmagnetic underlayer. When non-magnetic particle powder is used, the coercive force value is 39.8 to 318.3 kA / m (5
00 to 4000 Oe), preferably 43.8 to 318.
3 kA / m (550-4000 Oe), squareness ratio (residual magnetic flux density Br / saturated magnetic flux density Bm) of 0.85-0.9
5, preferably 0.86 to 0.95, and the glossiness of the coating film is 1
65-300%, preferably 170-300%, the coating film surface roughness Ra is 9.0 nm or less, preferably 2.0-8.
5 nm, more preferably 2.0 to 8.0 nm, the Young's modulus is 128 to 160, preferably 130 to 160, the shrinkage of the coating film is 8.5 to 20%, preferably 9.0 to 20%,
More preferably, it is 9.5 to 20%.

The magnetic recording medium according to the present invention uses the above magnetic particle powder as the magnetic particle powder and is coated with a surface coating as the nonmagnetic particle powder for the nonmagnetic underlayer according to the present invention. When non-magnetic particle powder is used, the coercive force value is 39.8 to 318.3 kA / m (50
0 to 4000 Oe), preferably 39.8 to 318.3.
kA / m (550-4000 Oe), squareness ratio (residual magnetic flux density Br / saturated magnetic flux density Bm) of 0.85-0.95,
Preferably 0.86 to 0.95, and the glossiness of the coating film is 170
To 300%, preferably 175 to 300%, and the coating film surface roughness Ra is 8.5 nm or less, preferably 2.0 to 8.0 n.
m, more preferably 2.0 to 7.5 nm, and a Young's modulus of 1
30 to 160, preferably 132 to 160, and the shrinkage of the coating film is 9.0 to 20%, preferably 9.5 to 20%, more preferably 10.0 to 20%.

In consideration of high-density recording and the like, a needle-like metal magnetic particle powder or a needle-like iron alloy magnetic particle powder containing iron as a main component is used as the magnetic particle powder, and the surface is used as the non-magnetic particle powder for the non-magnetic underlayer. When using the non-magnetic particle powder for non-magnetic underlayer according to the present invention not coated with the coating,
The coercive force value is 63.7 to 278.5 kA / m (800 to 3
500 Oe), preferably 71.6 to 278.5 kA /
m (900-3500 Oe), squareness ratio (residual magnetic flux density B
r / saturation magnetic flux density Bm) is 0.87 to 0.95, preferably 0.88 to 0.95, and the glossiness of the coating film is 195 to 30.
0%, preferably 200-300%, coating film surface roughness Ra
Is 8.0 nm or less, preferably 2.0 to 7.5 nm, more preferably 2.0 to 7.0 nm, and the Young's modulus is 128 to
160, preferably 130 to 160, and the shrinkage of the coating film is 8.5 to 20%, preferably 9.0 to 20%, more preferably 9.5 to 20%.

As the magnetic particle powder, acicular metal magnetic particle powder containing iron as a main component or acicular iron alloy magnetic particle powder is used.
When the nonmagnetic particle powder for a nonmagnetic underlayer according to the present invention coated with a surface coating is used as the nonmagnetic particle powder for a nonmagnetic underlayer, the coercive force value is 63.7 to 27.
8.5 kA / m (800-3500 Oe), preferably 71.6-278.5 kA / m (900-3500 Oe)
e), squareness ratio (residual magnetic flux density Br / saturated magnetic flux density Bm)
Is 0.87 to 0.95, preferably 0.88 to 0.9
5. The glossiness of the coating film is 200 to 300%, preferably 20
5 to 300%, the coating film surface roughness Ra is 7.5 nm or less, preferably 2.0 to 7.0 nm, more preferably 2.0 to 7.0 nm.
6.5 nm, Young's modulus is 130 to 160, preferably 1
32-160, shrinkage of coating film is 9.0-20%, preferably 9.5-20%, more preferably 10.0-20%
It is.

Next, a method for producing the nonmagnetic particle powder for a nonmagnetic underlayer according to the present invention will be described.

The non-magnetic particle powder for a non-magnetic underlayer according to the present invention can be obtained by mixing a large particle acicular hematite particle powder and a small particle acicular hematite particle powder.

The large-diameter acicular hematite particle powder and the small-diameter acicular hematite particle powder in the present invention can be obtained by a usual method, for example, a ferrous salt and an alkali hydroxide aqueous solution, an alkali carbonate aqueous solution or An oxygen-containing gas such as air is passed through a suspension containing an iron-containing precipitate obtained by a reaction using any one of an aqueous solution of an alkali hydroxide and an alkali carbonate to generate goethite particle powder. Can be obtained by heat dehydration treatment in a temperature range of 550 to 850 ° C.

The control of the average major axis diameter is performed during the reaction of forming goethite particles by adding Ni, Zn, P, Si
And the like, or by controlling reaction conditions such as reaction temperature and reaction time.

In the present invention, an edge runner, a Henschel mixer, or the like can be used as a device for mixing the large-diameter acicular hematite particles and the small-diameter acicular hematite particles. As an edge runner,
"Sandmill" manufactured by Matsumoto Casting Iron Works, "Mix Muller" manufactured by Shinto Kogyo Co., Ltd., and the like.

The load of the mixing process is 147 to 784 N / c.
m (15 to 80 kg / cm) is preferred.

The mixing time is preferably from 10 to 120 minutes.

Before performing the mixing process, a homomixer
It is preferable to disperse the aggregation of the particles by a horizontal sand grinder or the like.

The non-magnetic particle powder for the non-magnetic underlayer coated with the surface coating according to the present invention is obtained by coating either the large-diameter acicular hematite particles or the small-diameter acicular hematite particles with the surface coating. After the treatment, to perform a mixing treatment, or to perform a large particle size acicular hematite particle powder and a small particle size acicular hematite particle powder separately after surface treatment with a surface coating, or to perform a large particle size It can be obtained by simultaneously treating the surface of the acicular hematite particle powder and the small-diameter acicular hematite particle powder with a surface coating and then performing a mixing treatment.

The surface treatment of the acicular hematite particles with the surface coating is carried out by dispersing an aluminum compound, an aqueous suspension obtained by dispersing the acicular hematite particle powder having a large particle diameter and / or the acicular hematite particle powder having a small particle diameter. By adding a silicon compound or both compounds and mixing and stirring, or if necessary, by adjusting the pH value after mixing and stirring, the particle surface of the acicular hematite particle powder is changed to a hydroxide of aluminum, aluminum hydroxide. , A hydroxide of silicon and one or more compounds selected from oxides of silicon, followed by filtration, washing with water, drying and pulverization. If necessary, a deaeration / consolidation treatment may be performed.

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. As the silicon compound, No. 3 water glass, sodium orthosilicate, sodium metasilicate and the like can be used.

Next, a method for manufacturing a magnetic recording medium according to the present invention will be described.

As the solvent used for forming the nonmagnetic underlayer and the magnetic recording layer, methyl ethyl ketone, toluene, cyclohexanone, and the like generally used for magnetic recording media are used.
Methyl isobutyl ketone, tetrahydrofuran and mixtures thereof can be used.

The amount of the solvent used is 65 to 1000 parts by weight in total with respect to 100 parts by weight of the particle powder. If the amount is less than 65 parts by weight, the viscosity becomes too high in the case of a paint, and application becomes difficult. If the amount exceeds 1000 parts by weight, the amount of the solvent volatilized when forming a coating film becomes too large, which is industrially disadvantageous.

[0082]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A typical embodiment of the present invention is as follows.
It is as follows.

The average major axis diameter and average minor axis diameter of the particles were determined by measuring the major axis diameter of about 350 particles shown in an electron micrograph (× 30,000) enlarged four times in the vertical and horizontal directions, respectively. And the minor axis diameter were measured, and the average value was shown.

The axial ratio is the ratio between the average major axis diameter and the average minor axis diameter, and the plate ratio is the ratio between the average major axis diameter and the average thickness.

The particle size distribution of the major axis diameter of the particles was shown by a value obtained by the following method.

That is, a value obtained by measuring the major axis diameter of the particles shown in the above enlarged photograph is calculated on the logarithmic normal probability paper from the actual major axis diameter and the number of particles calculated from the measured values according to a statistical method. The horizontal axis represents the major axis diameter, and the vertical axis represents the percentage of the cumulative number of particles (under the integrated screen) belonging to each of the predetermined major axis diameter sections. Then, the value of the major axis diameter corresponding to each of 50% and 84.13% of the number of particles is read from this graph, and the geometric standard deviation value = 8
The value was calculated according to the major axis diameter at 4.13% / the major axis diameter (geometric mean diameter) at 50% below the integrated screen.
The closer the geometric standard deviation value is to 1, the better the particle size distribution of the particles.

The specific surface area was indicated by a value measured by the BET method.

The amount of Al and the amount of Si present inside the particles of the acicular hematite particle powder and the magnetic particle powder and on the surface of the particles were measured using a “fluorescent X-ray analyzer 3063M” (manufactured by Rigaku Corporation). And JIS K0119, "General rules for X-ray fluorescence analysis".

The paint viscosity was measured at 25 ° C. using an E-type viscometer EMD-R (manufactured by Tokyo Keiki Co., Ltd.), and the shear rate D was 1.92 sec.
^It was shown by the value at ^-1 .

The glossiness of the coating surface of the nonmagnetic underlayer and 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.). Was.

The surface roughness Ra is “Surfcom-57
The center line average roughness of the coating film was measured using “5A” (manufactured by Tokyo Seimitsu Co., Ltd.).

The strength of the coating film was measured by measuring the Young's modulus of the coating film using “Autograph” (manufactured by Shimadzu Corporation) and determining the Young's modulus of a commercially available video tape “AV T-120 (manufactured by Victor Company of Japan, Ltd.)”. It was expressed as a relative value to the rate. The higher the relative value, the better the strength of the coating film.

The thickness of each of the non-magnetic support, the non-magnetic underlayer, and the magnetic recording layer constituting the magnetic recording medium was measured by the following measuring method.

Digital electronic micrometer K351C
First, the film thickness (A) of the nonmagnetic support is measured using (manufactured by Anritsu Electric Co., Ltd.). Next, the thickness (B) of the nonmagnetic support and the nonmagnetic underlayer formed on the nonmagnetic support
(Sum of the thickness of the nonmagnetic support and the thickness of the nonmagnetic underlayer)
Is measured in the same manner. 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 shown by (B)-(A), and the thickness of the magnetic recording layer is shown by (C)-(B).

The magnetic properties of the magnetic particle powder and the magnetic recording medium were measured using an external magnetic field of 795.8 kA / m using a “vibrating sample magnetometer VSM-3S-15” (manufactured by Toei Kogyo Co., Ltd.).
(10KOe).

The shrinkage ratios of the nonmagnetic underlayer and the magnetic recording medium coating film were respectively determined by the film thickness t ₀ of the dried coating film after coating.
(Μm) and the thickness t ₁ of the coating film after calendering the coating film.
(Μm) according to the following equation.

[0097]

[Number 1] shrinkage of the coating film _{(%) = {(t 0} -t 1) / t 0} × 100 t 0: Thickness t ₁ of the non-magnetic undercoat layer or a non-magnetic undercoat layer and magnetic recording layer: After Calendar Thickness of the nonmagnetic underlayer or the nonmagnetic underlayer after calendering and the magnetic recording layer

<Production of mixed needle-like hematite particle powder> Large-diameter needle-like hematite particle powder (particle shape: needle-like, average major axis diameter 0.151 μm, average minor axis diameter 0.0228 μm, axial ratio 6.6, 6 kg of small-diameter acicular hematite powder (particle shape: acicular, average major axis diameter 0.072 μm, average minor axis diameter 0.0109 μm), with a geometric standard deviation of 1.35 and a BET specific surface area of 51.9 m ² / g. , Axial ratio 6.6, geometric standard deviation 1.38, BET specific surface area 91.1 m ² / g) 14k
g with 150 liters of pure water using a stirrer to disperse the coagulation, and further pass through "TK pipeline homomixer" (product name, manufactured by Tokushu Kika Kogyo Co., Ltd.) three times to obtain a large particle size needle. A slurry containing powdery hematite particles and small-sized needle-like hematite particles was obtained.

Subsequently, a slurry containing the large-diameter acicular hematite particle powder and the small-diameter acicular hematite particle powder was placed in a horizontal sand grinder “Mighty Mill MHG-1.
5L "(product name, manufactured by Inoue Seisakusho Co., Ltd.) and passed five times at a shaft rotation speed of 2000 rpm to obtain a dispersion slurry containing large-sized acicular hematite particles and small-sized acicular hematite particles. Obtained.

325 mesh of the obtained dispersion slurry
The sieve residue at (opening 44 μm) was 0%. 75 l of the dispersed slurry was filtered off with a filter press and washed with water to obtain cakes of large-diameter acicular hematite particle powder and small-diameter acicular hematite particle powder. Next, after drying the cake of the large-diameter acicular hematite particle powder and the small-diameter acicular hematite particle powder at 120 ° C., 8.0 kg of the dried powder was weighed, and the edge runner “M” was used.
PUV-2 type "(product name, manufactured by Matsumoto Casting Iron Works) and loaded at a load of 441 N / cm (45 kg / cm).
Mixing and stirring were performed for 0 minutes to obtain mixed needle-like hematite particle powder.

<Production of Nonmagnetic Underlayer> 12 g of the mixed needle-like hematite particle powder obtained above and carbon black fine particle powder (particle diameter 0.020 μm, BET specific surface area 1
13 m ^{2 /} g) 1.2 g and alumina particle powder as abrasive (particle size 0.22 μm, BET specific surface area value 15.8)
m ^{2 /} g) and binder resin solution (vinyl chloride-vinyl acetate copolymer resin 3 having sodium sulfonate group 3)
0% by weight and 70% by weight of cyclohexanone) and cyclohexanone, and kneaded at a solid content of 72% by weight using a plastmill for 30 minutes.

Next, the kneaded material was taken out, and 95 g of 1.5 mmφ glass beads were placed in a 140 ml glass bottle, and an additional binder resin solution (consisting of 30% by weight of a polyurethane resin having a sodium sulfonate group, 35% by weight of toluene, and 35% by weight of methyl ethyl ketone) Then, cyclohexanone, toluene and methyl ethyl ketone were added, and the mixture was mixed and dispersed with a paint shaker for 6 hours.

The composition of the obtained non-magnetic paint is as follows. Mixed needle-like hematite particle powder 100.0 parts by weight, vinyl chloride-vinyl acetate copolymer resin having sodium sulfonate group 10.0 parts by weight, polyurethane resin having sodium sulfonate group 10.0 parts by weight, cyclohexanone 57.7 Parts by weight, 144.2 parts by weight of methyl ethyl ketone, 86.5 parts by weight of toluene.

The viscosity of the obtained nonmagnetic paint was 435 c.
P.

Next, the obtained non-magnetic paint was applied to a thickness of 12 μm.
On a polyethylene terephthalate film having a thickness of 55 m, a non-magnetic underlayer was formed by applying the film to a thickness of 55 μm using an applicator and drying the film.

The coating thickness of the obtained nonmagnetic underlayer is 3.8
6 μm, gloss 193%, surface roughness Ra 6.1 nm,
The Young's modulus (relative value) was 131. The thickness of the nonmagnetic underlayer after the calendering treatment was 3.38 μm, and the compression ratio of the coating film was 12.4%.

<Manufacture of Magnetic Recording Medium> Needle-like metal magnetic powder containing iron as a main component (average major axis diameter 0.120 μm, average minor axis diameter 0.0185 μm, axial ratio 6.5, coercive force value 148.
8 kA / m (1870 Oe), saturation magnetization value 136 Am ²
/ Kg (136 emu / g)), 12 g of carbon black fine particle powder (particle diameter 0.028 μm, BET specific surface area value 240 m ² / g), and alumina particle powder (particle diameter 0.22 μm, BET ratio as abrasive) 0.84 g of a surface area value (15.8 m ^{2 /} g), a binder resin solution (comprising 30% by weight of a vinyl chloride-vinyl acetate copolymer resin having a sodium sulfonate group and 70% by weight of cyclohexanone) and cyclohexanone, Solids content 78
%, And kneaded using a plastmill for 30 minutes to obtain a kneaded material.

The kneaded material was placed in a 140 ml glass bottle for 1.5 times.
Add 95 g of mmφ glass beads, an additional resin binder solution (comprising 30% by weight of a polyurethane resin having a sodium sulfonate group, 35% by weight of toluene, and 35% by weight of methyl ethyl ketone) and cyclohexanone, toluene, and methyl ethyl ketone, and then use a paint shaker for 6 hours. And mixing and dispersion. Thereafter, a lubricant and a curing agent were added to the obtained coating composition, and the mixture was further mixed and dispersed with a paint shaker for 15 minutes.

The composition of the obtained magnetic paint is as follows. Acicular metal magnetic particle powder containing iron as a main component 100.0 parts by weight, abrasive (alumina particle powder) 7.0 parts by weight, carbon black fine particle powder 1.0 parts by weight, vinyl chloride having a sodium sulfonate group 10.0 parts by weight of vinyl acetate copolymer resin, 10.0 parts by weight of polyurethane resin having sodium sulfonate group, 1.0 part by weight of lubricant (myristic acid: butyl stearate = 1: 2), curing agent (polyisocyanate) 5.0 parts by weight, 62.5 parts by weight of cyclohexanone, 156.3 parts by weight of methyl ethyl ketone, 93.8 parts by weight of toluene.

The viscosity of the obtained magnetic paint was 5280 c.
P.

The obtained magnetic coating material was applied to a thickness of 15 μm on the substrate having the nonmagnetic underlayer using an applicator, and then oriented and dried in a magnetic field. At this time, the thickness of the magnetic layer was 1.13 μm, and the total thickness of the coating layer was 4.99 μm.

Next, after performing a calendar process, 60
A curing reaction was performed at 24 ° C. for 24 hours, and slit to 0.5 inch width to obtain a magnetic tape. The total thickness of the coating layer of the obtained magnetic tape was 4.45 μm, and the coercive force value was 158.4 kA / m.
(1990 Oe), squareness ratio 0.88, gloss 238
%, Surface roughness Ra was 5.4 nm, Young's modulus (relative value) was 135, and compression ratio of the coating film was 10.8%.

[0113]

The magnetic recording medium having a non-magnetic underlayer using the mixed acicular hematite particle powder according to the present invention has excellent surface smoothness because of the large particle acicular hematite particle powder and the small particle acicular hematite particle. Since the powders have the same particle shape and are acicular, the small-sized acicular hematite particles can easily enter the gaps between the large-sized acicular hematite particles. The present inventor believes that the film is easily compressed and the needle-like hematite particles are easily arranged in the same direction by the calendering treatment, so that a coating film having a smooth surface can be obtained.

[0114]

Next, examples and comparative examples will be described.

Starting materials 1 to 10: Hematite particle powder having the properties shown in Table 1 was prepared as hematite particle powder.

[0116]

[Table 1]

<Mixing Process> Examples 1 to 11, Comparative Examples 1 to 7: Types of large-diameter acicular hematite particle powder, types of small-diameter acicular hematite particle powder, volume ratio in mixing process and mixing process A mixed needle-like hematite particle powder was obtained in the same manner as in the embodiment of the invention except that the conditions were variously changed.

Table 2 shows the manufacturing conditions at this time.

[0119]

[Table 2]

<Surface Coating Treatment> Example 12: Starting material 13 kg and starting material 47 kg
(Type and blending ratio of the particles of Example 1) were contacted with 75 L of pure water using a stirrer to dissolve the agglomeration, and a dispersion slurry containing mixed needle-like hematite particles was obtained in the same manner as in the embodiment. . Next, the slurry was washed with water by a decantation method to obtain a slurry having a pH value of 6.0. To ensure accuracy, the slurry concentration at this point was confirmed.
It was 28 g / l. After adjusting the pH value to 10.5 using sodium hydroxide, the mixture was heated again while stirring, and
The temperature was adjusted to 0 ° C., 11 l of a 1.0 mol / l sodium aluminate solution (corresponding to 3.0% by weight in terms of Al with respect to the mixed needle-like hematite particles) was added to the slurry, and stirring was continued for 60 hours. After holding for one minute, the pH was adjusted to 8.0 using acetic acid.

Next, this slurry was separated by filtration with a filter press and washed with water to obtain a cake of mixed needle-like hematite particle powder.
Dried at 20 ° C.

8.0 kg of the obtained dry powder was weighed, and an edge runner “MPUV-2 type” (product name,
441 N / cm
(45 Kg / cm) for 20 minutes with stirring to disperse the aggregates of the particles to obtain mixed needle-like hematite particles having a particle surface coated with aluminum hydroxide.

In the obtained acicular hematite particles, the surface treatment amount of aluminum hydroxide was 2.91% by weight in terms of Al.

Examples 13 to 18: Coated with a surface coating in the same manner as in Example 12, except that the type and mixing ratio of each acicular hematite particle powder, and the type and amount of additives were variously changed. A mixed needle-like hematite particle powder was obtained.

Table 3 shows the manufacturing conditions at this time. In addition, the kind of the coating in Table 3 is such that A is aluminum hydroxide, S is
Is an oxide of silicon.

[0126]

[Table 3]

<Manufacture of Non-Magnetic Underlayer> Examples 19 to 36 and Comparative Examples 8 to 14: Non-magnetic underlayers were prepared in the same manner as in the embodiment of the present invention, except that the type of mixed needle-like hematite particles was variously changed. A magnetic underlayer was obtained.

Table 4 shows the manufacturing conditions and various characteristics of the obtained non-magnetic underlayer.

[0129]

[Table 4]

Magnetic particle powders (a) to (c): Acicular metal magnetic particle powders (a) to (c) having the properties shown in Table 5 were prepared as magnetic particle powders.

[0131]

[Table 5]

<Manufacture of Magnetic Recording Medium> Examples 37 to 54 and Comparative Examples 15 to 21: Except that the type of the nonmagnetic underlayer and the type of the magnetic particle powder were variously changed,
A magnetic recording medium was obtained in the same manner as in the above embodiment.

Tables 6 and 7 show the manufacturing conditions and various characteristics of the obtained magnetic recording medium.

[0134]

[Table 6]

[0135]

[Table 7]

[0136]

When the non-magnetic particle powder for a non-magnetic under layer according to the present invention is used, a non-magnetic under layer having excellent surface smoothness can be obtained. In this case, a magnetic recording medium having excellent surface smoothness can be obtained, so that it is suitable as a nonmagnetic particle powder for a nonmagnetic underlayer of a magnetic recording medium having a nonmagnetic underlayer.

As described above, the magnetic recording medium according to the present invention has excellent surface smoothness and is therefore suitable as a high-density magnetic recording medium.

Claims (3)

[Claims] 1. A large-diameter acicular hematite particle powder having an average major axis diameter of 0.10 to 0.30 μm and an axial ratio of 3.0 to 9.5, and the large-diameter acicular hematite particles. Needle ratio of the average major axis diameter to the average major axis diameter of the powder is 0.10 to 0.83, and the needle ratio is in the range of 3.0 to 9.5. Hematite particle powder,
In addition, the mixing ratio of the large-diameter acicular hematite particle powder and the small-diameter acicular hematite particle powder is 20:
Nonmagnetic particle powder for a nonmagnetic underlayer of a magnetic recording medium, wherein the ratio is 80 to 40:60. 2. The particle surface of the large-sized acicular hematite particle powder and / or the small-sized acicular hematite particle powder according to claim 1 has a hydroxide surface of aluminum, an oxide of aluminum or a surface of silicon. Non-magnetic particle powder for a non-magnetic underlayer of a magnetic recording medium, which is coated with a surface coating comprising at least one selected from hydroxides and oxides of silicon. 3. A nonmagnetic support, a nonmagnetic underlayer containing a nonmagnetic particle powder formed on the nonmagnetic support and a binder resin, and a magnetic particle powder and a binder formed on the nonmagnetic underlayer. 3. A magnetic recording medium comprising a magnetic recording layer containing a resin, wherein the nonmagnetic particle powder is the nonmagnetic particle powder for a nonmagnetic underlayer according to claim 1 or 2.