WO2018186040A1

WO2018186040A1 - Ionic liquid, lubricant for magnetic recording medium and magnetic recording medium

Info

Publication number: WO2018186040A1
Application number: PCT/JP2018/006322
Authority: WO
Inventors: 信郎多納; 弘毅初田; 近藤　洋文; パンカジュバヘル
Original assignee: デクセリアルズ株式会社
Priority date: 2017-04-04
Filing date: 2018-02-21
Publication date: 2018-10-11

Abstract

Provided is an ionic liquid, characterized in containing a cationic component and an anionic component, and in that the cationic component comprises a group having a perfluoropolyether chain and a group having a hydroxyl group.

Description

Ionic liquid, lubricant for magnetic recording medium, and magnetic recording medium

The present invention relates to an ionic liquid, a lubricant for a magnetic recording medium, and a magnetic recording medium.

As the recording density of the magnetic disk increases, the gap between the head and the disk is becoming smaller year by year, and in recent years, the gap is on the order of several nm to sub-nm. For this reason, contact wear of the disk by the head is likely to occur, leading to a decrease in recording reliability.

Therefore, a carbon protective layer and a lubricant layer are provided on the hard disk (HD) surface to prevent contact wear. Generally, a perfluoropolyether (PFPE) having a polar functional group represented by a hydroxyl group represented by the following structural formula is used for the lubricant layer (see, for example, Patent Documents 1 and 2).

Such end-functionalized PFPE is known to exhibit high wear resistance, evaporation resistance, and scattering resistance even when the lubricant layer is thinned by adsorbing to the carbon protective layer. It is often used in HD (for example, see Non-Patent Document 1).

PFPE is known to exhibit high wear resistance even in a thin film at a monomolecular film level, but naturally it cannot be made thinner than a monomolecular film, and its thickness depends on the molecular weight of the PFPE used. To do. As the recording density is expected to increase further in the future, it is expected that the film thickness will be reduced and the molecular weight will be lowered. However, if the molecular weight is reduced, the heat resistance and scattering resistance are expected to be reduced. Has its limits.

In recent years, a recording system called a HAMR (Heat-Assist Magnetic Recording) system has been developed as a system for further improving the recording capacity and recording speed of a magnetic disk. In this HAMR method, recording capacity, speed, and reliability can be improved by locally heating a recording portion with near-field light and recording and reproducing a magnetic field while applying a thermal offset.
However, in this method, the disk is locally heated to around 200 ° C. (see Non-Patent Document 2). Therefore, the lubricant used in this method is required to have a thermal stability of 200 ° C. or higher (preferably 250 ° C. or higher in consideration of long-term durability). However, the above-mentioned PFPE has a problem that the thermal stability is insufficient.

Lubricant ionic liquid is one method for improving the thermal stability of the lubricant. For example, there is an example in which PFPE having an acid at the terminal is reacted with alkylamine to form an ammonium salt ionic liquid. This technique has been reported to exhibit excellent friction and lubrication properties while maintaining a high pyrolysis temperature.

By the way, the lubricant for HD is generally used for dip coating after being diluted with a fluorine-based solvent (for example, 2H, 3H-decafluoropentane (manufacturer: DuPont Mitsui (Vertell XF))). For example, see Patent Document 3). However, the above-mentioned ionic liquid has a problem that it cannot be uniformly applied due to poor solubility in these fluorinated solvents. Therefore, high fluorine-based solvent solubility is required to put an ionic liquid lubricant into practical use.

Furthermore, HD is required to have wear resistance that does not crash even if it is repeatedly worn. As one of the methods for improving the wear resistance, improvement of the fluidity of the lubricant is known (see Non-Patent Document 3 and Patent Document 4). It is known that the lubricant layer is thinned by pressure and contact as the head passes over the substrate. If the lubricant layer remains thin, the head tends to be worn when contact between the head and the disk occurs. That is, if the fluidity of the lubricant is poor or the lubricant is solid, the durability of the head is deteriorated. However, when the fluidity is high, the thinned lubricant can be restored by backfilling, and the wear resistance becomes high. For this reason, it is considered important that the recording medium is liquid at room temperature where it is used.

However, if these lubricant layers are liquid, there is a concern that it will be difficult to maintain reliability due to scattering by spin-off and transfer of lubricant to the head, and the bond rate will be improved to overcome this Is desired.

JP 2006-70173 A JP 2014-191847 A JP 2008-75000 A JP 2007-231056 A

This invention makes it a subject to solve the said various problems in the past and to achieve the following objectives. That is, the present invention provides an ionic liquid having a high bond rate despite excellent heat stability and wear characteristics, and further excellent solubility and fluidity in a fluorinated solvent, and a magnetic material using the ionic liquid. It is an object of the present invention to provide a recording medium lubricant and a magnetic recording medium using the magnetic recording medium lubricant.

Means for solving the problems are as follows. That is,
<1> having a cation component and an anion component;
The cation component is an ionic liquid having a group having a perfluoropolyether chain and a group having a hydroxyl group.
<2> The ionic liquid according to <1>, which is represented by the following general formula (1).

In the general formula (1), Rf represents a perfluoropolyether chain having a perfluoroalkyloxy chain having 1 to 4 carbon atoms as a repeating unit.
X represents either a single bond or a divalent linking group.
R ¹ represents an alkyl group having a hydroxyl group.
R ² and R ³ each independently represents an alkyl group having 1 to 4 carbon atoms (provided that R ² and R ³ are bonded to form a nitrogen-containing hydrocarbon ring having 2 to 8 carbon atoms). You may).
Z ⁻ represents the anion component.
<3> The ionic liquid according to any one of <1> to <2> represented by the following general formula (2).

In the general formula (2), R ¹ represents an alkyl group having a hydroxyl group. R ² and R ³ each independently represents an alkyl group having 1 to 4 carbon atoms (provided that R ² and R ³ are bonded to form a nitrogen-containing hydrocarbon ring having 2 to 8 carbon atoms). You may). m represents an integer of 0 to 10. n represents an integer of 2 to 10. p represents an integer of 1 to 20. Z ⁻ represents the anion component.
<4> The ionic liquid according to any one of <1> to <3>, wherein the anion component has a fluorinated hydrocarbon group.
<5> The <1> to <4>, wherein the anion component is represented by any one of the following general formula (I), the following general formula (II), the following general formula (III), and the following general formula (IV): Or an ionic liquid according to any one of the above.

In the general formula (I), x represents an integer of 0 to 7.
However, in the general formula (II), x1 and x2 each independently represents an integer of 0 to 8.
However, in the general formula (III), x3 represents an integer of 1 to 8.
In the general formula (IV), n represents an integer of 1 to 8.
<6> A magnetic recording medium lubricant containing the ionic liquid according to any one of <1> to <5>.
<7> The magnetic recording medium lubricant according to <6>, further including a fluorinated solvent.
<8> A nonmagnetic support, a magnetic layer on the nonmagnetic support, and the magnetic recording medium lubricant according to any one of <6> to <7> on the magnetic layer. A characteristic magnetic recording medium.

According to the present invention, the above-described problems can be solved, and the bond rate is high despite excellent thermal stability and wear characteristics, and further excellent solubility and fluidity in a fluorinated solvent. An ionic liquid, a magnetic recording medium lubricant using the ionic liquid, and a magnetic recording medium using the magnetic recording medium lubricant can be provided.

FIG. 1 is a sectional view showing an example of a hard disk according to an embodiment of the present invention. FIG. 2 is a cross-sectional view showing an example of a magnetic tape according to an embodiment of the present invention.

(Ionic liquid)
The ionic liquid of the present invention has an anion component and a cation component. That is, the ionic liquid is composed of the anion component and the cation component.

In order to provide an ionic liquid having a high bond rate despite being excellent in thermal stability and wear characteristics, and also in solubility and fluidity in a fluorine-based solvent, the present inventors have conducted intensive studies. went. As a result, in the ionic liquid having an anion component and a cation component, the cation component has a group having a perfluoropolyether chain and a group having a hydroxyl group, so that it has excellent thermal stability and wear characteristics. Furthermore, it has been found that an ionic liquid having a high bond rate can be obtained despite excellent solubility in a fluorine-based solvent and fluidity. The ionic liquid can be suitably used for a lubricant for magnetic recording media.

In the ionic liquid, the present inventors consider the reason why the bond rate is high in spite of excellent thermal stability and solubility in a fluorine-based solvent and excellent fluidity as follows. Yes.
The ionic liquid itself is excellent in thermal stability. Furthermore, when the cationic component has a perfluoropolyether chain, it has excellent wear characteristics and fluorine-based solvent solubility and has a low melting point. Due to the low melting point, the fluidity at room temperature (25 ° C.) is excellent. Furthermore, since the cation component has a hydroxyl group, the bond rate can be increased without reducing the fluorine-based solvent solubility and fluidity.

<Cation component>
The cationic component has a group having a perfluoropolyether chain and a group having a hydroxyl group.
The cation component is preferably a quaternary ammonium cation.

The quaternary ammonium cation is preferably a cation represented by the following general formula (1-1).

In the general formula (1), Rf represents a perfluoropolyether chain having a perfluoroalkyloxy chain having 1 to 4 carbon atoms as a repeating unit.
X represents either a single bond or a divalent linking group.
R ¹ represents an alkyl group having a hydroxyl group.
R ² and R ³ each independently represents an alkyl group having 1 to 4 carbon atoms (provided that R ² and R ³ are bonded to form a nitrogen-containing hydrocarbon ring having 2 to 8 carbon atoms). You may).

<< Perfluoropolyether chain or Rf >>
The molecular weight of the perfluoropolyether chain or Rf is not particularly limited and may be appropriately selected depending on the intended purpose, but is preferably 1,500 or less, more preferably 1,000 or less, and more preferably 600 or less. preferable. There is no restriction | limiting in particular as a lower limit of the molecular weight of the said perfluoro polyether chain or the said Rf, According to the objective, it can select suitably, For example, 300 etc. are mentioned.

The perfluoropolyether chain or Rf is not particularly limited and may be appropriately selected depending on the intended purpose, but is preferably a group represented by the following general formula (1-1-1).

However, in the general formula (1-1-1), m represents an integer of 0 to 10, and an integer of 0 to 6 is preferable. n represents an integer of 2 to 10 and is preferably an integer of 2 to 6.

<< X >>
The divalent linking group in X is not particularly limited and may be appropriately selected depending on the intended purpose. However, it preferably has an alkylene group having 2 or more carbon atoms, and an alkylene group having 2 to 10 carbon atoms is preferred. More preferably.

The divalent linking group may be a group used for synthesis reasons when introducing an Rf group into the nitrogen atom (N) of the cation represented by the general formula (1-1).

<< R ¹ >>
R ¹ represents an alkyl group having a hydroxyl group. The number of carbon atoms of the alkyl group is not particularly limited and may be appropriately selected depending on the intended purpose, but is preferably 1 to 18, more preferably 1 to 10, still more preferably 1 to 6, and even more preferably 2 to 4 Is particularly preferred.
The number of hydroxyl groups in R ¹ is not particularly limited and may be appropriately selected depending on the intended purpose, but is preferably 1 to 4, and more preferably 1 to 2.

<< R ² , R ³ >>
R ² and R ³ each independently represent an alkyl group having 1 to 4 carbon atoms (provided that R ² and R ³ are combined to form a nitrogen-containing hydrocarbon ring having 2 to 8 carbon atoms). May be formed).
Examples of the nitrogen-containing hydrocarbon ring having 2 to 8 carbon atoms include an alkyleneimine ring. Examples of the alkyleneimine ring include an aziridine ring, an azetidine ring, a pyrrolidine ring, a piperidine ring, and a hexamethyleneimine ring.

The quaternary ammonium cation is more preferably a cation represented by the following general formula (2-1).

However, in the general formula (2-1), R ¹ represents an alkyl group having a hydroxyl group. R ² and R ³ each independently represents an alkyl group having 1 to 4 carbon atoms (provided that R ² and R ³ are bonded to form a nitrogen-containing hydrocarbon ring having 2 to 8 carbon atoms). You may). m represents an integer of 0 to 10. n represents an integer of 2 to 10. p represents an integer of 1 to 20. Z ⁻ represents the anion component.

Examples of symbols in the general formula (2-1) are the same as those in the general formula (1-1) and in the general formula (1-1-1), and preferred embodiments are also the same. It is.
p may be, for example, an integer from 1 to 18, an integer from 1 to 16, or an integer from 1 to 10.
p is preferably an integer of 2 to 8, and more preferably an integer of 3 to 6.
Further, from the viewpoint of the bond rate, p is preferably an integer of 7 to 18, more preferably an integer of 8 to 16, and particularly preferably an integer of 9 to 15.

<Anion component>
The anion component is not particularly limited and may be appropriately selected depending on the intended purpose. However, from the viewpoint of solubility, it preferably has a fluorinated hydrocarbon group, and the following general formula (I) and the following general formula More preferably, it is represented by any one of (II), the following general formula (III), and the following general formula (IV). The fluorinated hydrocarbon group may be a fully fluorinated hydrocarbon group or a partially fluorinated hydrocarbon group.

However, in the general formula (I), x represents an integer of 0 to 7, preferably an integer of 0 to 3.
However, in the general formula (II), x1 and x2 each independently represents an integer of 0 to 8, preferably an integer of 1 to 8, and more preferably an integer of 1 to 4.
However, in the general formula (III), x3 represents an integer of 1 to 8, and an integer of 1 to 3 is preferable.
However, in the general formula (IV), n represents an integer of 1 to 8, and an integer of 1 to 4 is preferable.

The ionic liquid is preferably represented by the following general formula (1).

In the general formula (1), Rf represents a perfluoropolyether chain having a perfluoroalkyloxy chain having 1 to 4 carbon atoms as a repeating unit.
X represents either a single bond or a divalent linking group.
R ¹ represents an alkyl group having a hydroxyl group.
R ² and R ³ each independently represents an alkyl group having 1 to 4 carbon atoms (provided that R ² and R ³ are bonded to form a nitrogen-containing hydrocarbon ring having 2 to 8 carbon atoms). You may).
Z ⁻ represents the anion component.

Rf in the general formula (1), ^X, exemplary of R 1, ^{R 2,} and exemplary ^{R 3} are, Rf in the general formula (1-1) in, ^X, R 1, ^{R 2,} and ^{R 3} The preferred embodiments are also the same.

The ionic liquid is more preferably represented by the following general formula (2).

In the general formula (2), R ¹ represents an alkyl group having a hydroxyl group. R ² and R ³ each independently represents an alkyl group having 1 to 4 carbon atoms (provided that R ² and R ³ are bonded to form a nitrogen-containing hydrocarbon ring having 2 to 8 carbon atoms). You may). m represents an integer of 0 to 10. n represents an integer of 2 to 10. p represents an integer of 1 to 20. Z ⁻ represents the anion component.

Exemplary ^R 1, ^{R 2,} and ^{R 3} in the general formula (2) is, ^R 1, ^{R 2} in the formula (1), and are the same as exemplified for ^{R 3,} a preferred embodiment also the same is there.
Examples of m, n, and p in the general formula (2) are the same as those of m, n, and p in the general formula (2-1), and preferred embodiments are also the same.

The ionic liquid of the present invention is a liquid at normal temperature (25 ° C.).
The melting point of the ionic liquid is preferably 25 ° C. or less, and more preferably 10 ° C. or less. The lower limit of the melting point of the ionic liquid is not particularly limited and may be appropriately selected depending on the intended purpose. However, the melting point of the ionic liquid is preferably −100 ° C. or higher.
The melting point can be determined, for example, by differential scanning calorimetry.
When the ionic liquid has a melting point of room temperature or lower, it becomes an ionic liquid having fluidity at room temperature.

(Lubricant for magnetic recording media)
The lubricant for a magnetic recording medium of the present invention contains an ionic liquid, and further contains other components as necessary.

The ionic liquid is the ionic liquid of the present invention.

<Other ingredients>
Examples of the other components include known lubricants, extreme pressure agents, rust inhibitors, solvents, and the like.

<< Known Lubricant >>
As the lubricant, the ionic liquid may be used alone or in combination with a conventionally known lubricant. Known lubricants include, for example, long chain carboxylic acids, long chain carboxylic acid esters, perfluoroalkyl carboxylic acid esters, carboxylic acid perfluoroalkyl esters, perfluoroalkyl carboxylic acid perfluoroalkyl esters, perfluoropolyether derivatives, and the like. Is mentioned.

<< extreme pressure agent >>
In order to maintain the lubricating effect under severe conditions, the magnetic recording medium lubricant may be used in combination with an extreme pressure agent at a blending ratio of about 30:70 to 70:30. The extreme pressure agent acts to prevent friction and wear by forming a reaction product film by reacting with the metal surface due to frictional heat generated when metal contact occurs partially in the boundary lubrication region. Is. As the extreme pressure agent, for example, any of a phosphorus extreme pressure agent, a sulfur extreme pressure agent, a halogen extreme pressure agent, an organometallic extreme pressure agent, a composite extreme pressure agent, and the like can be used.

<< rust preventive agent >>
The rust inhibitor may be any rust inhibitor that can be used as a rust inhibitor for this type of magnetic recording medium. For example, phenols, naphthols, quinones, heterocyclic compounds containing nitrogen atoms, oxygen atoms And heterocyclic compounds containing sulfur atoms, and the like. The rust preventive agent may be used as a lubricant, but a magnetic layer is formed on a nonmagnetic support, a rust preventive layer is applied thereon, and then a lubricant layer is applied. Thus, it may be applied in two or more layers.

<< Solvent >>
Examples of the solvent include organic solvents. Examples of the organic solvent include a fluorine-based solvent and an alcohol-based solvent. Examples of the alcohol solvent include isopropyl alcohol (IPA) and ethanol. Examples of the fluorine-based solvent include hydrofluoroethers [for example, C ₃ F ₇ OCH ₃ , C ₄ F ₉ OCH ₃ , C ₄ F ₉ OC ₂ H ₅ , C ₂ F ₅ CF (OCH ₃ ) C ₃ F ₇ , C ₅ H ₂ F ₁₀ ] and the like.
The fluorinated solvent may be a commercially available product. Examples of the commercially available products include Novec ^™ 7000, 7100, 7200, 7300, 71IPA manufactured by 3M, Vertrel XF, X-P10 manufactured by Mitsui DuPont Fluorochemical Co., Ltd., and the like.
These solvents may be used alone or in combination of two or more.

(Magnetic recording medium)
The magnetic recording medium of the present invention includes a nonmagnetic support, a magnetic layer, and the magnetic recording medium lubricant of the present invention, and further includes other members as necessary.
The magnetic layer is formed on the nonmagnetic support. That is, the magnetic layer is disposed on the nonmagnetic support.
The magnetic recording medium lubricant is formed on the magnetic layer. That is, the magnetic recording medium lubricant is disposed on the magnetic layer.

The lubricant can be applied to a so-called metal thin film type magnetic recording medium in which a magnetic layer is formed on the surface of a nonmagnetic support by a technique such as vapor deposition or sputtering. The present invention can also be applied to a magnetic recording medium having a configuration in which an underlayer is interposed between a nonmagnetic support and a magnetic layer. Examples of such a magnetic recording medium include a magnetic disk and a magnetic tape.

FIG. 1 is a cross-sectional view showing an example of a hard disk. This hard disk has a structure in which a substrate 11, an underlayer 12, a magnetic layer 13, a carbon protective layer 14, and a lubricant layer 15 are sequentially laminated.

FIG. 2 is a cross-sectional view showing an example of a magnetic tape. This magnetic tape has a structure in which a backcoat layer 25, a substrate 21, a magnetic layer 22, a carbon protective layer 23, and a lubricant layer 24 are sequentially laminated.

In the magnetic disk shown in FIG. 1, the nonmagnetic support corresponds to the substrate 11 and the underlayer 12, and in the magnetic tape shown in FIG. 2, the nonmagnetic support corresponds to the substrate 21. When a rigid substrate such as an Al alloy plate or a glass plate is used as the nonmagnetic support, an oxide film such as an alumite treatment or Ni-P film may be formed on the substrate surface to harden the surface. Good.

The

magnetic layers

13 and 22 are formed as a continuous film by a technique such as plating, sputtering, vacuum deposition, or plasma CVD. The

magnetic layers

13 and 22 include metals such as Fe, Co, Ni, Co—Ni alloys, Co—Pt alloys, Co—Ni—Pt alloys, Fe—Co alloys, Fe—Ni alloys, In-plane magnetization recording metal magnetic film made of Fe—Co—Ni alloy, Fe—Ni—B alloy, Fe—Co—B alloy, Fe—Co—Ni—B alloy, etc., Co—Cr alloy Examples thereof include perpendicular magnetic recording metal magnetic thin films such as thin films and Co—O thin films.

In particular, when an in-plane magnetization recording metal magnetic thin film is formed, a nonmagnetic material such as Bi, Sb, Pb, Sn, Ga, In, Ge, Si, or Tl is previously formed on the nonmagnetic support as the underlayer 12. In addition, metal magnetic materials are vapor-deposited or sputtered from the vertical direction, and these non-magnetic materials are diffused in the magnetic metal thin film to eliminate orientation and ensure in-plane isotropy and improve coercive force. You may do it.

A hard protective layer such as a carbon film, diamond-like carbon film, chromium oxide film, or SiO ₂ film may be formed on the surface of the

magnetic layers

13 and 22.

As a method for retaining the lubricant for the magnetic recording medium in such a metal thin film type magnetic recording medium, as shown in FIGS. 1 and 2, the surfaces of the

magnetic layers

13 and 22 and the carbon

protective layers

14 and 23 are used. A method of top-coating on the surface of the film. The coating amount of the magnetic recording medium lubricant is preferably 0.1 mg / m ² to 100 mg / m ² , more preferably 0.5 mg / m ² to 30 mg / m ² , and Particularly preferred is 5 mg / m ² to 20 mg / m ² .

Further, as shown in FIG. 2, in the metal thin film type magnetic tape, in addition to the metal magnetic thin film as the magnetic layer 22, a back coat layer 25 may be formed as necessary.

The back coat layer 25 is formed by adding a carbon-based fine powder for imparting conductivity to the resin binder and an inorganic pigment for controlling the surface roughness.

As another embodiment, the lubricant can be applied to a so-called coating type magnetic recording medium in which a magnetic coating film is formed as a magnetic layer by applying a magnetic paint to the surface of a nonmagnetic support. is there. In the coating-type magnetic recording medium, any conventionally known magnetic powder, resin binder and the like constituting the nonmagnetic support, the magnetic coating film, and the like can be used.

For example, as the nonmagnetic support, for example, a polymer support formed of a polymer material typified by polyesters, polyolefins, cellulose derivatives, vinyl resins, polyimides, polyamides, polycarbonates and the like. Examples thereof include a metal substrate made of aluminum alloy, titanium alloy, etc., a ceramic substrate made of alumina glass, etc., a glass substrate, and the like. Moreover, the shape is not limited at all, and any shape such as a tape shape, a sheet shape, or a drum shape may be used. Further, the non-magnetic support may be subjected to a surface treatment so as to form fine irregularities in order to control the surface property.

Examples of the magnetic powder include ferromagnetic iron oxide particles such as γ-Fe ₂ O ₃ and cobalt-coated γ-Fe ₂ O ₃ , ferromagnetic chromium dioxide particles, metals such as Fe, Co, Ni, and the like. Examples thereof include ferromagnetic metal particles made of an alloy containing hexagonal plate-like ferrite fine particles.

Examples of the resin binder include vinyl chloride, vinyl acetate, vinyl alcohol, vinylidene chloride, acrylic acid ester, methacrylic acid ester, styrene, butadiene, acrylonitrile, or a combination of these two or more, polyurethane Resins, polyester resins, epoxy resins and the like are exemplified. In these binders, a hydrophilic polar group such as a carboxylic acid group, a carboxyl group or a phosphoric acid group may be introduced in order to improve the dispersibility of the magnetic powder.

In addition to the magnetic powder and the resin binder, a dispersant, an abrasive, an antistatic agent, an antirust agent, and the like may be added to the magnetic coating film as an additive.

As a method for retaining the lubricant for the magnetic recording medium in such a coating-type magnetic recording medium, a method of internally adding the magnetic coating film forming the magnetic coating film formed on the nonmagnetic support. And a method of top-coating the surface of the magnetic layer, or a combination of both. Further, when the magnetic recording medium lubricant is internally added to the magnetic coating film, it is added in the range of 0.2 to 20 parts by mass with respect to 100 parts by mass of the resin binder.

In addition, when the magnetic recording medium lubricant is top-coated on the surface of the magnetic layer, the coating amount is preferably 0.1 mg / m ² to 100 mg / m ² , and 0.5 mg / m ^2. More preferably it is ˜20 mg / m ² . In addition, as a deposition method when top-coating the magnetic recording medium lubricant, the ionic liquid is dissolved in a solvent, and the obtained solution is applied or sprayed, or the magnetic recording medium is placed in this solution. What is necessary is just to immerse.
The solvent is preferably a fluorinated solvent. Examples of the fluorinated solvent include:
Hydrofluoroether _{_{_{_{[e.g., C 3 F 7 OCH 3,}}}} C 4 F 9 OCH 3, C 4 F 9 OC 2 H 5, C 2 F 5 CF (OCH 3) C 3 F 7, C 5 H 2 F 10 ] Etc.
The fluorinated solvent may be a commercially available product. Examples of the commercially available products include Novec ^™ 7000, 7100, 7200, 7300, 71IPA manufactured by 3M, Vertrel XF, X-P10 manufactured by Mitsui DuPont Fluorochemical Co., Ltd., and the like.

By using the magnetic recording medium lubricant according to the present invention, even when a thin lubricant layer is formed, a good lubricating action can be exerted to reduce the friction coefficient, and the thermal stability is high. Sex can be obtained. Further, this lubricating action is not impaired even under severe conditions such as high temperature, low temperature, high humidity, and low humidity.

Therefore, the magnetic recording medium to which the magnetic recording medium lubricant is applied, even when a thin lubricant layer is formed, exhibits excellent running performance, wear resistance, durability, etc. due to the lubricating action. Furthermore, thermal stability can be improved.

Hereinafter, specific examples of the present invention will be described. The present invention is not limited to these examples.

Example 1
<Synthesis of ionic liquid (1-D)>
An ionic liquid (1-D) having a fluorinated triethylene glycol (PFTEG) structure and a hydroxypropyl group in the cation portion and the anion portion being bis (nonafluorobutylsulfonyl) imide was synthesized by the following method.

<< Step 1-A >>
Synthesis of 3-bromopropyl tosylate (1-A)

In a flask equipped with a stirrer and a condenser tube, 55.0 g (396 mmol) of 3-bromo-1-propanol (maker: Wako Pure Chemical Industries), 114 g (599 mmol) of p-toluenesulfonyl chloride (maker: Tokyo Chemical Industry) 400 g of toluene (manufacturer: Wako Pure Chemical Industries) and 60.6 g (599 mmol) of triethylamine (manufacturer: Kanto Kagaku) as a base were stirred for 20 hours at room temperature. After stirring, the reaction solution was filtered and diethyl ether was added. The ether layer was washed with water and aqueous hydrochloric acid, and the solvent was removed with an evaporator. Thereafter, the obtained crude product was purified by silica gel column chromatography (hexane + acetone = (mass ratio) 9 + 1 → 3 + 1). After purification, the fraction was concentrated to obtain the desired product 3-bromopropyl tosylate (1-A) in a yield of 90%.

<< Step 1-B >>
Synthesis of 3-bromopropyl PFTEG (1-B)

In a flask equipped with a stirrer, a thermometer, and a condenser tube, 54.9 g (100 mmol) of fluorinated triethylene glycol monobutyl ether (PFTEG-OH) (manufacturer: FluoroChem) was synthesized in << Step 1-A >>. Then, 61.9 g (211 mmol) of 3-bromopropyl tosylate (1-A) and 105 g of metaxylene hexafluoride (manufacturer: Wako Pure Chemical Industries, Ltd.) as a solvent were introduced and stirred at room temperature. Thereafter, 27.9 g (202 mmol) of potassium carbonate (maker: Wako Pure Chemical Industries) and 2.30 g of a 55% aqueous solution of tetrabutylammonium hydroxide (manufacturer: Aldrich) were added, and the mixture was stirred at 80 ° C. for 7 hours. Water and Novec7100 (manufactured by 3M) were added to the reaction solution, liquid separation extraction was performed, and after washing with hydrochloric acid, the Novec layer was concentrated with an evaporator. The obtained crude product was purified by silica gel column chromatography (hexane → hexane + acetone = (mass ratio) 24 + 1). The obtained fraction was concentrated to obtain 3-bromopropyl PFTEG (1-B) represented by the above structural formula in a yield of 50%.

<< Step 1-C >>
Synthesis of bromide salt (1-C)

In a flask equipped with a stirrer, a thermometer, and a condenser tube, 0.87 g (8.4 mmol) of 3- (dimethylamino) -1-propanol (manufacturer: Tokyo Kasei Kogyo) and << Step 1-B >> Then, 7.00 g (10.5 mmol) of 3-bromopropyl PFTEG (1-B) synthesized in Step 1 was added, 8 g of acetonitrile was added as a solvent, and the mixture was heated to reflux for 6 hours.
The obtained mixture solution was evaporated with an evaporator, decanted with hexane and diethyl ether, and then concentrated again with an evaporator. Novec7100 (manufactured by 3M) was added to the resulting concentrated solution, filtered through a 0.2 μm membrane filter, and then dried under reduced pressure at 80 ° C. to obtain a bromide salt (1-C) represented by the above structural formula as 82. % Yield. About 95% of the synthesized bromide salt (1-C) was confirmed to be the target product from the results of LC-MS (ELSD) measurement.

<< Step 1-D >>
Synthesis of ionic liquid (1-D)

To a flask equipped with a stirrer and a condenser, 3.85 g (5.0 mmol) of bromide salt (1-C) and 50 g of water were added and stirred. Thereafter, a solution prepared by dissolving 3.65 g (6.2 mmol) of EF-N445 [bis (nonafluorobutanesulfonyl) imide lithium, manufacturer: Mitsubishi Materials Electronic Chemicals] in 20 g of water was introduced into the flask and stirred for 18 hours. . After stirring, the obtained ionic liquid layer was washed with water. Thereafter, vacuum drying was performed to obtain the target ionic liquid in a yield of 87%.
The target product is analyzed by LC-MS (ELSD), and it can be confirmed from LC that it consists only of the target anion and cation. From the MS results, the cation is M / z = 692, and the anion is M / z = It became 580, and it could identify with the target object.

(Example 2)
<Synthesis of ionic liquid (2-D)>
An ionic liquid (2-D) having a fluorinated triethylene glycol (PFTEG) structure and a diol structure in the cation part, and the anion part consisting of bis (nonafluorobutylsulfonyl) imide was synthesized by the following method.

<< Step 2-C >>
Synthesis of bromide salt (2-C)

In << Step 1-C >> of Example 1, 8.4 mmol of 3- (dimethylamino) -1-propanol was added to 3- (dimethylamino) -1,2-propanediol (manufacturer: Tokyo Chemical Industry) 8 The bromide salt (2-C) was obtained in a yield of 99%.

<< Step 2-D >>
Synthesis of ionic liquid (2-D)

The same procedure as in Example 1 << Step 1-D >> was performed except that 5.0 mmol of bromide salt (1-C) was changed to 5.0 mmol of bromide salt (2-C). An ionic liquid (2-D) was obtained with a yield of 80%.
The target product is analyzed by LC-MS (ELSD), and it can be confirmed from LC that it consists only of the target anion and cation. From the MS results, the cation is M / z = 708 and the anion is M / z = It became 580, and it could identify with the target object.

(Example 3)
<Synthesis of ionic liquid (3-D)>
The connecting part between the fluorinated triethylene glycol (PFTEG) structure and the ammonium cation was changed to hexamethylene, and the ionic liquid (3-D) consisting of bis (nonafluorobutylsulfonyl) imide as the anion part was obtained by the following method. Synthesized.

<< Step 3-A >>
Synthesis of 6-bromohexyl tosylate (3-A)

In a flask equipped with a stirrer and a condenser tube, 6-bromo-1-hexanol (maker: Tokyo Chemical Industry) 50.3 g (278 mmol), p-toluenesulfonyl chloride (maker: Tokyo Chemical Industry) 79.46 g (417 mmol) ), Toluene (maker: Wako Pure Chemical Industries) 401 g, and triethylamine (maker: Kanto Chemical) 42.2 g (417 mmol) as a base were added and stirred at room temperature for 25 hours. After stirring, the reaction solution was filtered and diethyl ether was added. The ether layer was washed with water and aqueous hydrochloric acid, and the solvent was removed with an evaporator. Thereafter, the obtained crude product was purified by silica gel column chromatography (hexane + acetone = (mass ratio) 9 + 1 → 3 + 1). After purification, the fraction was concentrated to obtain the desired 6-bromohexyl tosylate (3-A) in a yield of 82%.

<< Step 3-B >>
Synthesis of 3-bromohexyl PFTEG (3-B)

In << Step 1-B >> of Example 1, 100 mmol of fluorinated triethylene glycol monobutyl ether (PFTEG-OH) was replaced with 100 mmol of fluorinated triethylene glycol monomethyl ether (manufacturer: Apollo Scientific), and 3-bromo The same procedure was followed except that 211 mmol of propyl tosylate was replaced with 6-bromohexyl tosylate (3-A) to obtain 3-bromohexyl PFTEG (3-B) in a yield of 40%.

<< Step 3-C >>
Synthesis of bromide salt (3-C)

In << Step 1-C >> of Example 1, 3-bromopropyl PFTEG (1-B) 10.5 mmol was changed to 3-bromohexyl PFTEG (3-B) 10.5 mmol, yield 99 % Bromide salt (3-C) was obtained.

<< Step 3-D >>
Synthesis of ionic liquid (3-D)

The same procedure as in Example 1 << Step 1-D >> was performed except that 5.0 mmol of bromide salt (1-C) was changed to 5.0 mmol of bromide salt (3-C). An ionic liquid (3-D) was obtained with a yield of 86%.
The target product is analyzed by LC-MS (ELSD), and it can be confirmed from LC that it consists only of the target anion and cation. From the MS results, the cation is M / z = 584 and the anion is M / z = It became 580, and it could identify with the target object.

Example 4
<Synthesis of ionic liquid (4-D)>
An ionic liquid (4-D) having a fluorinated triethylene glycol (PFTEG) structure, a hydroxyethyl group, and a pyrrolidine ring in the cation portion, and the anion portion comprising bis (nonafluorobutylsulfonyl) imide is obtained by the following method. Synthesized.

<< Step 4-C >>
Synthesis of ionic liquid (4-C)

Except that 8.4 mmol of 3- (dimethylamino) -1-propanol was changed to 8.4 mmol of 1- (2-hydroxyethyl) pyrrolidine (Acros Organics) in << Step 1-C >> of Example 1. In the same manner, an ionic liquid (4-C) was obtained with a yield of 99%.

<< Step 4-D >>
Synthesis of ionic liquid (4-D)

The same procedure as in Example 1 << Step 1-D >> was performed except that 5.0 mmol of bromide salt (1-C) was changed to 5.0 mmol of ionic liquid (4-C). The ionic liquid (4-D) was obtained with a yield of 86%.
The target product is analyzed by LC-MS (ELSD), and it can be confirmed from LC that it consists only of the target anion and cation. From the MS results, the cation is M / z = 704 and the anion is M / z = It became 580, and it could identify with the target object.

(Example 5)
<Synthesis of ionic liquid (5-D)>
An ionic liquid (5-D) having a fluorinated triethylene glycol (PFTEG) structure and a hydroxypropyl group in the cation part and nonafluorobutanesulfonate in the anion part was synthesized by the following method.

<< Step 5-D >>
Synthesis of ionic liquid (5-D)

The same procedure as in Example 1 was performed except that 6.2 mmol of EF-N445 was replaced with 6.2 mmol of nonafluorobutanesulfonic acid potassium salt (Tokyo Chemical Industry) in << Step 1-D >> of Example 1. The product was obtained in 98% yield. The target product is analyzed by LC-MS (ELSD), and it can be confirmed from LC that it consists only of the target anion and cation. From the MS results, the cation is M / z = 692, and the anion is M / z = 299, and it was identified as the target product.

(Comparative Example 1)
<Synthesis of ionic liquid (6-D)>
An ionic liquid (6-D) having no hydroxypropyl group, having a fluorinated triethylene glycol (PFTEG) structure in the cation portion, and having an anion portion consisting of bis (nonafluorobutylsulfonyl) imide is obtained by the following method. Synthesized.

<< Step 6-C >>
Synthesis of bromide salt (6-C)

In Example <<<< Step 1-C >>, except that 8.4 mmol of 3- (dimethylamino) -1-propanol was changed to 8.4 mmol of triethylamine (manufacturer: Tokyo Kasei Kogyo), Example 1 The same operation was performed to obtain a bromide salt (6-C) with a yield of 53%.

<< Step 6-D >>
Synthesis of ionic liquid (6-D)

The same procedure as in Example 1 << Step 1-D >> was performed except that 5.0 mmol of bromide salt (1-C) was changed to 5.0 mmol of bromide salt (6-C). An ionic liquid (6-D) was obtained with a yield of 60%.
The target product is analyzed by LC-MS (ELSD), and it can be confirmed from LC that it consists only of the target anion and cation. From the MS results, the cation is M / z = 690, and the anion is M / z = It became 580, and it could identify with the target object.

(Comparative Example 2)
<Synthesis of ionic liquid (7-D)>
An ionic liquid (7-D) having no fluorinated triethylene glycol (PFTEG) structure, having an octedecyl group and a hydroxypropyl group in the cation portion, and the anion portion comprising bis (nonafluorobutylsulfonyl) imide, The method was synthesized.

<< Step 7-C >>
Synthesis of bromide salt (7-C)

In << Step 1-C >> of Example 1, 10.5 mmol of 3-bromopropyl PFTEG (1-B) was changed to 10.5 mmol of 1-bromooctadecane (manufacturer: Tokyo Kasei Kogyo) to carry out the reaction. . After completion of the reaction, reprecipitation purification was performed in hexane to obtain a bromide salt (7-C) in a yield of 92%.

<< Step 7-D >>
Synthesis of ionic liquid (7-D)

The same operation as in Example 1 << Step 1-D >> was performed except that 5.0 mmol of bromide salt (1-C) was changed to 5.0 mmol of bromide salt (7-C). The ionic liquid (7-D) was obtained with a yield of 81%.
The target product is analyzed by LC-MS (ELSD), and it can be confirmed from LC that it consists only of the target anion and cation. From the MS results, the cation is M / z = 356 and the anion is M / z = It became 580, and it could identify with the target object.

(Comparative Example 3)
<Z-TETRAOL>
Fomblin Z-TETRAOL (manufacturer: Solvay Specialty Polymers, the following structural formula) (molecular weight of about 2000) was used.

(Example 6)
<Synthesis of ionic liquid (8-D)>
An ionic liquid (8-D) having a fluorinated triethylene glycol (PFTEG) structure, a hydroxyethyl group, and a pyrrolidine ring in the cation part, and the anion part comprising bis (nonafluorobutylsulfonyl) imide is obtained by the following method. Synthesized.

<< Step 8-A >>
Synthesis of 12-bromododecyl tosylate (8-A)

In a flask equipped with a stirrer and a condenser tube, 50.1 g (189 mmol) of 12-bromo-1-dodecanol (maker: Tokyo Chemical Industry), 55.2 g (289 mmol) of p-toluenesulfonyl chloride (maker: Tokyo Chemical Industry) 280 g of toluene (maker: Wako Pure Chemical Industries) and 29.4 g (291 mmol) of triethylamine (maker: Kanto Kagaku) as a base were stirred for 23 hours at room temperature. After stirring, the reaction solution was filtered and diethyl ether was added. The ether layer was washed with water and aqueous hydrochloric acid, and the solvent was removed with an evaporator. Thereafter, the obtained crude product was purified by silica gel column chromatography (hexane + acetone = (mass ratio) 19 + 1 → 9 + 1). After purification, the fraction was concentrated to obtain the desired 12-bromododecyl tosylate (8-A) in a yield of 93%.

<< Step 8-B >>
Synthesis of 12-bromododecyl PFTEG (1-B)

In a flask equipped with a stir bar, thermometer, and condenser, fluorinated triethylene glycol monobutyl ether (PFTEG-OH) (manufacturer: FluoroChem) 33.0 g (60 mmol), synthesized in << Step 8-A >> Then, 50.3 g (120 mmol) of 12-bromododecyl tosylate (8-A) and 72 g of metaxylene hexafluoride (manufacturer: Wako Pure Chemical Industries, Ltd.) as a solvent were introduced and stirred at room temperature. During the stirring, 16.6 g (120 mmol) of potassium carbonate (maker: Wako Pure Chemical Industries) and 3.04 g of tetrabutylammonium hydroxide 55% aqueous solution (maker: Aldrich) were added, and the mixture was heated and stirred at 80 ° C. for 6 hours. Water and Novec7100 (manufactured by 3M) were added to the reaction solution, liquid separation extraction was performed, and after washing with hydrochloric acid, the Novec layer was concentrated with an evaporator. The obtained crude product was purified by silica gel column chromatography (hexane + acetone = (mass ratio) 97 + 3 => 96 + 4). The obtained fraction was concentrated to obtain 12-bromododecyl PFTEG (8-B) in a yield of 50%.

<< Step 8-C >>
Synthesis of bromide salt (8-C)

In a flask equipped with a stirrer, a thermometer, and a condenser, 1-pyrrolidineethanol (manufacturer: Tokyo Chemical Industry) 1.40 g (12 mmol) and 12-bromododecyl synthesized in << Step 8-B >> 11.95 g (15.0 mmol) of PFTEG (8-B) was added, 10 g of acetonitrile was added as a solvent, and the mixture was heated to reflux for 8 hours.
The obtained mixture solution was evaporated with an evaporator, decanted with hexane and diethyl ether, and directly used in << Step 8-D >>. About 98% of the synthesized bromide salt (8-C) was confirmed to be the target product from the results of LC-MS (ELSD) measurement.

<< Step 8-D >>
Synthesis of ionic liquid (8-D)

To a flask equipped with a stirrer and a condenser, 5.97 g (6.6 mmol) of the bromide salt (8-C) synthesized in << Step 8-C >> and 25 g of water were added and stirred. Thereafter, a solution prepared by dissolving 9.05 g (15.4 mmol) of EF-N445 [bis (nonafluorobutanesulfonyl) imide lithium, manufacturer: Mitsubishi Materials Electronic Chemicals] in 30 g of water was introduced into the flask and stirred for 17 hours. . After stirring, the obtained ionic liquid layer was washed with water. Thereafter, drying under reduced pressure was performed to obtain the target ionic liquid in a yield of 65% (total from << Step 8-C >>). The target product was analyzed by LC-MS (ELSD), and it was confirmed that it consisted only of the target cation (M / z = 830) and the anion (M / z = 580).

(Example 7)
<Synthesis of ionic liquid (9-D)>
An ionic liquid (9-D) having a fluorinated triethylene glycol (PFTEG) structure, a hydroxyethyl group, and a pyrrolidine ring in the cation part and the anion part consisting of bis (nonafluorobutylsulfonyl) imide is obtained by the following method. Synthesized.

<< Step 9-B >>
Synthesis of 12-bromododecyl M-PFTEG (9-B)

In a flask equipped with a stirrer, a thermometer, and a condenser tube, 18 g (43 mmol) of 12-bromododecyl tosylate (8-A) synthesized in the same manner as << Step 8-A >>, fluorinated triethylene glycol monomethyl 8.6 g (22 mmol) of ether (M-PFTEG-OH) (manufacturer: FluoroChem) and 32 g of metaxylene hexafluoride (manufacturer: Wako Pure Chemical Industries) as a solvent were introduced and stirred at room temperature. During the stirring, 5.9 g (43 mmol) of potassium carbonate (manufacturer: Wako Pure Chemical Industries) and 1.09 g of a 55% aqueous solution of tetrabutylammonium hydroxide (manufacturer: Aldrich) were added, and the mixture was heated and stirred at 80 ° C. for 5 hours. Water and Novec7100 (manufactured by 3M) were added to the reaction solution, liquid separation extraction was performed, and after washing with hydrochloric acid, the Novec layer was concentrated with an evaporator. The obtained crude product was purified by silica gel column chromatography (hexane + acetone = (mass ratio) 97 + 3). The obtained fraction was concentrated to obtain 12-bromododecyl M-PFTEG (9-B) in a yield of 46%.

<< Step 9-C >>
Synthesis of bromide salt (9-C)

In a flask equipped with a stirrer, a thermometer, and a condenser tube, 1.03 g (7.9 mmol) of 1-pyrrolidinepropanol (manufacturer: Combi-Blocks) and << step 9-B >> were synthesized. Bromodecyl M-PFTEG (9-B) 6.43 g (10 mmol) was added, 7.5 g of acetonitrile was added as a solvent, and the mixture was heated to reflux for 8 hours.
The obtained mixture solution was evaporated with an evaporator, decanted with hexane and diethyl ether, and directly used in << Step 9-D >>. About 96% of the synthesized bromide salt (8-C) was confirmed to be the target product from the results of LC-MS (ELSD) measurement.

<< Step 9-D >>
Synthesis of ionic liquid (9-D)

To a flask equipped with a stirring bar and a condenser tube, 7.31 g (9.4 mmol) of bromide salt (9-C) synthesized in << Step 9-C >> and 20 g of water were added and stirred. Thereafter, a solution prepared by dissolving 12.5 g (21.2 mmol) of EF-N445 [bis (nonafluorobutanesulfonyl) imide lithium, manufacturer: Mitsubishi Materials Electronic Chemicals] in 35 g of water was introduced into the flask and stirred for 17 hours. . After stirring, the obtained ionic liquid layer was washed with water. Thereafter, drying under reduced pressure was performed to obtain the target ionic liquid in a yield of 45% (total from << Step 9-C >>). The target product was analyzed by LC-MS (ELSD), and it was confirmed that it consisted only of the target cation (M / z = 694) and the anion (M / z = 580).

<Evaluation>
The following evaluation was performed.

<< Solubility in Fluorinated Solvents >>
It added to the fluorine-type solvent so that a density | concentration might be 1 mass%, and it stirred, hold | maintaining at 25 degreeC. The solubility was evaluated according to the following evaluation criteria. The results are shown in Table 1.
As the fluorinated solvent, the following two commonly used for applying lubricant to hard disks were used.
Vertrel XF: Mitsui DuPont Fluorochemical Co., Ltd. Novec7100: 3M Co. Vertrel XF is 1,1,1,2,3,4,4,5,5,5-decafluoropentane (CAS- No. 138495-42-8).
Novec7100 is a hydrofluoroether represented by C ₄ F ₉ OCH ₃ (boiling point 61 ° C.).
〔Evaluation criteria〕
○: Dissolved in a fluorinated solvent and no precipitation even if left undisturbed ×: Insoluble in a fluorinated solvent, or precipitated if left undissolved even after temporarily dissolving

The samples of Examples 1 to 7 and Comparative Examples 1 and 3 were dissolved in both.
The sample of Comparative Example 2 did not dissolve at 1% by mass.

<< Measurement of thermal decomposition temperature >>
The weight loss with respect to temperature was measured by TG-DTA (manufacturer name: Seiko Instruments Inc., model number: EXSTAR6000), and the 5% weight loss temperature was defined as the thermal decomposition temperature. The measurement conditions were a heating rate of 10 ° C./min and an Air flow rate of 200 mL / min.
The results are shown in Table 2.

<< Measurement of melting point >>
The endothermic peak temperature was determined by DSC (manufacturer name: Seiko Instruments model number: EXSTAR6000), and this was used as the melting point. The measurement conditions were a heating rate of 10 ° C./min and an air atmosphere.
The results are shown in Table 2.

-Pyrolysis temperature-
Compared with Comparative Example 3 which is a nonionic liquid, the ionic liquids of Examples 1 to 7 and Comparative Examples 1 and 2 showed high heat resistance of 5% weight loss temperature of 300 ° C. or more.

-Melting point-
All of the ionic liquids of Examples 1 to 7 exhibited a melting point of room temperature (25 ° C.) or lower.

<< Friction characteristics >>
-Fabrication of lubricant-coated hard disk-
A magnetic disk having a cross-sectional structure as shown in FIG. 1 was produced. The lubricant solution used for dip coating was prepared using the solvents shown in Table 3. The lubricant solution was filtered using a syringe filter (0.2 μm). Further, the concentration of the ionic liquid in the lubricant solution was set to 0.2% by mass (the ionic liquid of Comparative Example 2 was dissolved in the addition of 0.2% by mass with respect to Vertrel XF).
The dip coating was performed by pulling up the magnetic disk from a glass container containing a lubricant solution at a speed of 50 mm / min.
The dependence of the dip concentration on the film thickness was investigated by systematically changing the dip concentration conditions for each lubricant. The film thickness was measured by ellipsometry (model number: M-2000, manufacturer: JA Woollam). The average thickness of the formed lubricant layer was adjusted to 10 mm by adjusting the dip concentration for each lubricant.

-test-
The friction characteristics were evaluated by measuring the friction coefficient with respect to the number of sliding times using the prepared sample under the following test conditions. The results are shown in Table 3.
[Test conditions]
Using an automatic friction measurement device (manufacturer: Kyowa Interface Science Co., Ltd., model number: Triboster TS-501), point contact (3 mm steel ball), weight: 15 g, speed: 1.7 mm / sec, distance: 20 mm, number of repetitions : 100 times).

The lubricants of Examples 1 to 7 and Comparative Examples 2 and 3 maintained a coefficient of friction of 0.20 or less even after 100 times of sliding.
As for Comparative Example 1, the initial friction was about the same as that of the example, but the coefficient of repeated friction after 100 times was 0.30 and did not show lubricity.

<< bond rate >>
The bond ratio is a numerical value indicating how much lubricant is fixed on the surface of the recording medium, and the values are the film thickness of the lubricant after coating and the film thickness of the lubricant after surface rinsing with a fluorine-based solvent. And is represented by the following equation.
(Bond rate) = 100 × (lubricant film thickness after rinsing with a fluorine-based solvent) / (lubricant film thickness before rinsing) [%]

Specific evaluation was performed as follows.
The surface of the lubricant-coated hard disk was rinsed with a fluorine-based solvent, and the film thickness of the lubricant before and after rinsing was measured.
The lubricant-coated hard disk was produced in the same manner as the method produced in the evaluation of wear characteristics, except that the concentration of the ionic liquid in the lubricant solution was 1.0% by mass. The lubricant film thickness was 10 mm.
Vertrel XF was used as the fluorinated solvent.
Rinsing was performed by immersing the disc in Vertrel XF for 3 minutes.
The film thickness was measured by ellipsometry (model number: M-2000, manufacturer: JA Woollam).
The case where UV irradiation was performed before rinsing was also evaluated. It is considered that photoelectrons are generated on the surface of the hard disk during UV irradiation and react with polar functional groups in the lubricant molecular structure. The UV irradiation was performed for 60 seconds at wavelengths of 185 nm and 253 nm and an intensity of 2 mW (254 nm).
The results are shown in Table 4.

Examples 1 to 7 and Comparative Example 3 showed a relatively good bond rate.
Comparative Example 1 had a relatively low bond rate of less than 25% even after UV 60 irradiation.
Note that Comparative Example 2 was not measured because it was not dissolved in Vertrel XF.

<< Comprehensive evaluation >>
The above evaluation results were ranked as follows, and further comprehensive evaluation was performed according to the following evaluation criteria. The results are shown in Table 5.
<Ranking>
[Food base solvent solubility]
○ Evaluation: Rank ○
× Evaluation: Rank ×
[Melting point]
25 ° C or less: Rank ○
Over 25 ° C: Rank ×
[Heat resistance (thermal decomposition temperature)]
300 ℃ or higher: Rank ○
Less than 300 ° C: Rank ×
(Abrasion resistance)
The coefficient of friction after 100 slides is 0.20 or less: Rank ○
Friction coefficient of 100 times of sliding is over 0.20: rank x
[Bond rate]
50% or more after 60 seconds of UV irradiation: Rank ◎
40% or more and less than 50% after UV irradiation for 60 seconds: Rank ○
30% or more and less than 40% after UV irradiation for 60 seconds: Rank △
Less than 30% after UV irradiation for 60 seconds: Rank x

[Evaluation criteria for comprehensive evaluation]
◎: Except for the bond rate, ○, and the bond rate is ◎
○: Other than the bond rate, and the bond rate is ○
Δ: Other than the bond rate, and the bond rate is Δ
X: 1 out of 5 evaluations is included. Xx: 2 or more out of 5 evaluations are included. In addition, in the comprehensive evaluation, ◎, ○, and Δ are acceptable levels.

The bond rate “−” of Comparative Example 2 was evaluated as equivalent to “×”.

Examples 1 to 7 showed good characteristics as ionic liquids having all of excellent thermal stability, excellent wear characteristics, excellent fluorine-based solvent solubility, excellent fluidity, and excellent bond ratio. In particular, Examples 6 and 7 had a very good bond rate.

The lubricant for magnetic recording medium of the present invention is excellent in thermal stability, wear characteristics and solubility in a fluorine-based solvent, and is also a liquid at room temperature and an excellent bond rate, so that a high recording density magnetic recording medium Can be suitably used.

DESCRIPTION OF SYMBOLS 11 Substrate 12 Underlayer 13 Magnetic layer 14 Carbon protective layer 15 Lubricant layer 21 Substrate 22 Magnetic layer 23 Carbon protective layer 24 Lubricant layer 25 Backcoat layer

Claims

A cationic component and an anionic component;
An ionic liquid, wherein the cationic component has a group having a perfluoropolyether chain and a group having a hydroxyl group.
The ionic liquid of Claim 1 represented by following General formula (1).

In the general formula (1), Rf represents a perfluoropolyether chain having a perfluoroalkyloxy chain having 1 to 4 carbon atoms as a repeating unit.
X represents either a single bond or a divalent linking group.
R 1 represents an alkyl group having a hydroxyl group.
R 2 and R 3 each independently represents an alkyl group having 1 to 4 carbon atoms (provided that R 2 and R 3 are bonded to form a nitrogen-containing hydrocarbon ring having 2 to 8 carbon atoms). You may).
Z − represents the anion component.
The ionic liquid in any one of Claim 1 to 2 represented by following General formula (2).

In the general formula (2), R 1 represents an alkyl group having a hydroxyl group. R 2 and R 3 each independently represents an alkyl group having 1 to 4 carbon atoms (provided that R 2 and R 3 are bonded to form a nitrogen-containing hydrocarbon ring having 2 to 8 carbon atoms). You may). m represents an integer of 0 to 10. n represents an integer of 2 to 10. p represents an integer of 1 to 20. Z − represents the anion component.
The ionic liquid according to any one of claims 1 to 3, wherein the anion component has a fluorinated hydrocarbon group.
5. The anion component according to claim 1, wherein the anion component is represented by any one of the following general formula (I), the following general formula (II), the following general formula (III), and the following general formula (IV). Ionic liquid.

In the general formula (I), x represents an integer of 0 to 7.
However, in the general formula (II), x1 and x2 each independently represents an integer of 0 to 8.
However, in the general formula (III), x3 represents an integer of 1 to 8.
In the general formula (IV), n represents an integer of 1 to 8.
A magnetic recording medium lubricant comprising the ionic liquid according to any one of claims 1 to 5.
Furthermore, the lubricant for magnetic recording media of Claim 6 containing a fluorine-type solvent.
A magnetic recording medium comprising: a nonmagnetic support; a magnetic layer on the nonmagnetic support; and the magnetic recording medium lubricant according to any one of claims 6 to 7 on the magnetic layer. .