JP2021014417A - Ionic liquid, lubricant, and magnetic recording medium - Google Patents

Abstract

To provide an ionic liquid or the like which is excellent in thermal stability, solubility in a fluorine-based solvent, and fluidity, has a high bonding ratio, and is capable of forming a thin monomolecular film.SOLUTION: The ionic liquid comprises a cationic component and an anionic component. The cationic component is a quaternary ammonium cation. The quaternary ammonium cation has a first group bonded to a nitrogen cation and having a hydroxyl group and a fluorine atom, and a second group bonded to the nitrogen cation and having a hydroxyl group.SELECTED DRAWING: Figure 2

Description

The present invention relates to ionic liquids, lubricants, and magnetic recording media.

As the recording density of magnetic disks increases, the gap between the head and the disk is narrowing year by year, and in recent years, the gap has become on the order of several nm to subnm. Therefore, contact wear of the disc by the head is likely to occur, which is said to lead to a decrease in recording reliability.

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

It is known that such terminal-functionalized PFPEs 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 (see, for example, Non-Patent Document 1).

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

In recent years, a recording method called a HAMR (Heat-Assisted Magnetic Recording) method has been developed as a method for further improving the recording capacity and recording speed of a magnetic disk. In this HAMR method, the recording capacity, speed, and reliability can be improved by locally heating the recording site with near-field light and recording and reproducing the magnetic field while applying a thermal offset.
However, in this method, the disc is locally heated to around 200 ° C. (see Non-Patent Document 2). Therefore, the lubricant used in this method is required to have 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.

As a method for improving the thermal stability of a lubricant, there is an ionic liquefaction of the lubricant. For example, there is an example in which PFPE having an acid at the terminal is reacted with an alkylamine to form an ammonium salt-based ionic liquid. It has been reported that this technique exhibits excellent friction and lubrication properties while maintaining a high pyrolysis temperature.

By the way, the lubricant for HD is generally used for dip application after being diluted with a fluorine-based solvent [for example, 2H, 3H-decafluoropentane (manufacturer: Mitsui DuPont (Vertrel XF)), etc.] ( For example, see Patent Document 3). However, the above-mentioned ionic liquid has a problem that it is poorly soluble in these fluorine-based solvents and cannot be uniformly applied. Therefore, high fluorine-based solvent solubility is required for practical use of ionic liquid lubricants.

Further, the HD is required to have wear resistance that does not easily 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 becomes thin due to the pressure and contact when the head passes over the substrate. Then, if the lubricant layer remains thin, the head is likely to be worn when the head comes into contact with the disc. That is, if the fluidity of the lubricant is poor, or if the lubricant is solid, the durability of the head will be poor. However, when the fluidity is high, the thinned lubricant can be repaired by backfilling, and the wear resistance becomes high. Therefore, it is important that the recording medium is liquid at room temperature where it is used.

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

Japanese Unexamined Patent Publication No. 2006-70173 Japanese Unexamined Patent Publication No. 2014-191847 Japanese Unexamined Patent Publication No. 2008-75000 JP-A-2007-231056

B. Bushhan, Tribology and Mechanics of Magic Story Device, Springer (1996) Fuji Electric Technical Report 2012 vol. 85 no. 4 pp. 329-332 IDEMA Japan News No. 58, pp. 1-4

An object of the present invention is to solve the above-mentioned problems in the past and to achieve the following object. That is, the present invention uses an ionic liquid which is excellent in thermal stability, solubility in a fluorine-based solvent, and fluidity, has a high bond ratio, and can form a thin monomolecular film, and the ionic liquid. It is an object of the present invention to provide a lubricant and a magnetic recording medium using the lubricant.

The means for solving the above-mentioned problems are as follows. That is,
<1> It has a cation component and an anion component.
The cation component is a quaternary ammonium cation.
An ionic liquid characterized in that the quaternary ammonium cation has a first group bonded to a nitrogen cation and having a hydroxyl group and a fluorine atom, and a second group bonded to the nitrogen cation and having a hydroxyl group. Is.
<2> The hydroxyl group of the first group is bonded to the carbon atom at the end of the first group.
The ionic liquid according to <1>, wherein the hydroxyl group of the second group is bonded to a carbon atom at the end of the second group.
<3> The ionic liquid according to any one of <1> to <2>, wherein the molecular weight of the first group is 1,500 or less.
<4> The ionic liquid according to any one of <1> to <3> represented by the following general formula (1).
However, 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 is an alkylene group having 1 or more carbon atoms, an oxyalkylene group having 1 or more carbon atoms, a repetition of an oxyalkylene group having 1 or more carbon atoms, or a combination thereof.
Y represents either a single bond or a divalent group.
Y'represents either a single bond or a divalent group.
R ¹ and R ² each independently represent an alkyl group having 1 to 4 carbon atoms (however, R ¹ and R ² combine to form a nitrogen-containing hydrocarbon ring having 2 to 8 carbon atoms. You may).
R ³ is a (n + 1) -valent hydrocarbon group having 1 to 12 carbon atoms.
A is a hydroxyl group.
n is an integer of 1 or more.
Z ⁻ represents the anion component.
<5> The ionic liquid according to any one of <1> to <4> represented by the following general formula (1-1).
However, in the general formula (1-1), p represents an integer of 1 to 20. q represents an integer of 2 to 10. r represents an integer from 0 to 4. s represents an integer from 0 to 4.
R ¹ and R ² each independently represent an alkyl group having 1 to 4 carbon atoms (however, R ¹ and R ² combine to form a nitrogen-containing hydrocarbon ring having 2 to 8 carbon atoms. You may).
R ³ is a (n + 1) -valent hydrocarbon group having 1 to 12 carbon atoms.
A is a hydroxyl group.
n is an integer of 1 or more.
Z ⁻ represents the anion component.
<6> The ionic liquid according to any one of <1> to <5>, wherein the anion component has a fluorinated hydrocarbon group.
<7> The ionic liquid according to any one of <1> to <6> represented by any of the following general formulas (2) to (5).
However, in the general formula (2), n represents an integer of 0 to 8.
However, in the general formula (3), n represents an integer of 0 or more.
However, in the general formula (4), n represents an integer of 0 to 8.
However, in the general formula (5), n represents an integer of 1 or more.
<8> The lubricant is characterized by containing the ionic liquid according to any one of <1> to <7>.
<9> The lubricant according to <8>, which further contains a fluorine-based solvent.
<10> Magnetic characterized by having a non-magnetic support, a magnetic layer on the non-magnetic support, and the lubricant according to any one of <8> to <9> on the magnetic layer. It is a recording medium.

According to the present invention, the above-mentioned problems in the prior art can be solved, the thermal stability, the solubility in a fluorosolvent, the fluidity are excellent, the bond ratio is high, and a thin monomolecular film can be formed. An ionic liquid, a lubricant using the ionic liquid, and a magnetic recording medium using the lubricant can be provided.

FIG. 1 is a cross-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 anionic component and a cation component. That is, the ionic liquid is composed of the anion component and the cation component.

The present inventors have diligently studied in order to provide an ionic liquid which is excellent in thermal stability, solubility in a fluorine-based solvent, and fluidity, has a high bond ratio, and can form a thin monomolecular film. Was done. As a result, in the ionic liquid having an anionic component and a cation component, the cation component is a quaternary ammonium cation, and the quaternary ammonium cation is bonded to a nitrogen cation and has a hydroxyl group and a fluorine atom. By having a group and a second group that is bonded to the nitrogen ion and has a hydroxyl group, it is excellent in thermal stability, solubility in a fluorine-based solvent, and fluidity, and has a high bond ratio. We have found that an ionic liquid capable of forming a thin monomolecular film can be obtained. The ionic liquid can be suitably used as a lubricant, particularly a lubricant for a magnetic recording medium.

The present inventors explain the reasons why the ionic liquid is excellent in thermal stability, solubility in a fluorine-based solvent, and fluidity, has a high bond ratio, and can form a thin monomolecular film. I am considering it as follows.
The ionic liquid itself has excellent thermal stability. Further, since the quaternary ammonium cation which is a cation component has a first group having a fluorine atom, it has excellent fluorine-based solvent solubility and has a low melting point. Due to its low melting point, it has excellent fluidity at room temperature (25 ° C.). Further, since the cation component has a hydroxyl group, the bond ratio can be increased without lowering the fluorine-based solvent solubility and fluidity. In addition, each of the first group and the second group of the cation component has a hydroxyl group that easily binds to the base material, and as a result of these hydroxyl groups binding to the base material, the ionic liquid is attached to the surface of the base material. It is thought that the orientation becomes easier along the line, and a thin monolayer can be formed.

<Cation component>
The cation component is a quaternary ammonium cation.
The cation component has a first group having a hydroxyl group and a fluorine atom, and a second group having a hydroxyl group.
The first group is attached to the nitrogen cation in the quaternary ammonium cation.
The second group is attached to the nitrogen cation in the quaternary ammonium cation.
The hydroxyl group in the first group and the hydroxyl group in the second group mean an OH group bonded to a carbon atom.

<< First group >>
The first group has, for example, a perfluoropolyether chain having a perfluoroalkyloxy chain having 1 to 4 carbon atoms as a repeating unit.
The molecular weight of the first group 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 even more preferably 800 or less. The lower limit of the molecular weight of the first group is not particularly limited and may be appropriately selected depending on the intended purpose. Examples thereof include 400.
The numerical range indicated by using "~" in the present specification indicates a range including the numerical values before and after "~" as the lower limit value and the upper limit value, respectively. That is, the carbon number 1 to 4 means the carbon number 1 or more and 4 or less.

The molecular weight of the perfluoropolyether chain is not particularly limited and may be appropriately selected depending on the intended purpose, but is preferably 1,200 or less, and more preferably 600 or less. The lower limit of the molecular weight of the perfluoropolyether chain is not particularly limited and may be appropriately selected depending on the intended purpose. Examples thereof include 300.

<< Second group >>
The second group is, for example, a hydrocarbon group having one or more hydroxyl groups. The hydrocarbon group preferably has 1 to 12 carbon atoms, and more preferably 1 to 5 carbon atoms.

The hydroxyl group of the first group is bonded to the carbon atom at the end of the first group, and the hydroxyl group of the second group is bonded to the carbon atom at the end of the second group. Is preferable. The cation component has a hydroxyl group that easily binds to the base material in each of the first group and the second group, and as a result of these hydroxyl groups binding to the base material, the ionic liquid is oriented along the surface of the base material. It is thought that this will facilitate the formation of a thin monolayer. Then, the hydroxyl group of the first group is bonded to the carbon atom at the terminal of the first group, and the hydroxyl group of the second group is bonded to the carbon atom at the terminal of the second group. It is considered that the ionic liquid is more easily oriented along the surface of the base material, and a thinner monomolecular film can be formed.
Here, the carbon atom at the end of the first group and the second group is an atom bonded to a nitrogen cation in the first group and the second group as one end, and the atom at the one end. It refers to the carbon atom farthest from the one end among the carbon atoms of the chain having the longest connection among the plurality of chains connected by a covalent bond.

<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 is preferable to have a fluorinated hydrocarbon group, and the following general formula (2) and the following general formula are used. (3), it is more preferable that it is represented by any of the following general formula (4) and the following general formula (5). The fluorinated hydrocarbon group may be a fully fluorinated hydrocarbon group or a partially fluorinated hydrocarbon group.
However, in the general formula (2), n represents an integer of 0 to 8, and an integer of 0 to 3 is preferable.
However, in the general formula (3), n represents an integer of 0 or more, an integer of 0 to 8 is preferable, and an integer of 0 to 3 is more preferable.
However, in the general formula (4), n 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 (5), n represents an integer of 1 or more, an integer of 1 to 8 is preferable, and an integer of 1 to 4 is more preferable.

The ionic liquid is preferably represented by the following general formula (1).
However, 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 is an alkylene group having 1 or more carbon atoms, an oxyalkylene group having 1 or more carbon atoms, a repetition of an oxyalkylene group having 1 or more carbon atoms, or a combination thereof.
Y represents either a single bond or a divalent group.
Y'represents either a single bond or a divalent group.
R ¹ and R ² each independently represent an alkyl group having 1 to 4 carbon atoms (however, R ¹ and R ² combine to form a nitrogen-containing hydrocarbon ring having 2 to 8 carbon atoms. You may).
R ³ is a (n + 1) -valent hydrocarbon group having 1 to 12 carbon atoms.
A is a hydroxyl group.
n is an integer of 1 or more, and an integer of 1 or more and 3 or less is preferable.
Z ⁻ represents the anion component.

<< 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 1,200 or less, more preferably 600 or less. The lower limit of the molecular weight of the perfluoropolyether chain or Rf is not particularly limited and may be appropriately selected depending on the intended purpose. Examples thereof include 300.

The perfluoropolyether chain or the Rf is not particularly limited and may be appropriately selected depending on the intended purpose, but a group represented by the following general formula (1-A) is preferable.
However, in the general formula (1-A), q represents an integer of 2 to 10, and an integer of 2 to 6 is preferable. r represents an integer of 0 to 4, and an integer of 0 to 2 is preferable. s represents an integer of 0 to 4, and an integer of 0 to 2 is preferable. * 1 represents a bond that binds to X. * 2 represents a bond that binds to Y'.

<< X >>
X is an alkylene group having 1 or more carbon atoms, an oxyalkylene group having 1 or more carbon atoms, a repetition of an oxyalkylene group having 1 or more carbon atoms, or a combination thereof.
As the alkylene group having 1 or more carbon atoms, an alkylene group having 1 to 20 carbon atoms is preferable, and an alkylene group having 2 to 6 carbon atoms is more preferable.
The number of carbon atoms of the oxyalkylene group is preferably 1 to 4.
The number of repetitions of the oxyalkylene group may be, for example, 2 to 10 or 2 to 5.

<< Y >>
Y represents either a single bond or a divalent group.
Examples of the divalent group include esters (-COO-), secondary amides (-NHCO-), sulfones (-SO _3- ) and the like.

Since X and Y are for binding the Rf chain to the nitrogen cation, their structure is not particularly limited and can be appropriately selected depending on the intended purpose.

<<Y'>>
Y'represents either a single bond or a divalent group.
Examples of the divalent group include esters (-COO-), secondary amides (-NHCO-), sulfones (-SO _3- ) and the like.

Since Y'is for directly or indirectly binding a hydroxyl group to the Rf chain, its structure is not particularly limited and can be appropriately selected depending on the intended purpose.

<< R ¹ and R ² >>
R ¹ and R ² each independently represent an alkyl group having 1 to 4 carbon atoms. However, R ¹ and R ² may be combined to form a nitrogen-containing hydrocarbon ring having 2 to 8 carbon atoms.
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.
If R ¹ and R ² have the above structure, the effect of the present invention is not further impaired. Further, when R ¹ and R ² are independently alkyl groups having 1 to 4 carbon atoms, and when R ¹ and R ² are bonded to each other to form a nitrogen-containing hydrocarbon ring having 2 to 8 carbon atoms. The case is not so structurally different that the effect of the present invention is different.

<< R ³ >>
R ³ is a (n + 1) -valent hydrocarbon group having 1 to 12 carbon atoms.
The hydrocarbon group preferably has 1 to 6 carbon atoms, and more preferably 1 to 4 carbon atoms.

The ionic liquid is more preferably represented by the following general formula (1-1).
However, in the general formula (1-1), p represents an integer of 1 to 20, and an integer of 2 to 6 is preferable. q represents an integer of 2 to 10, and an integer of 2 to 6 is preferable. r represents an integer of 0 to 4, and an integer of 0 to 2 is preferable. s represents an integer of 0 to 4, and an integer of 0 to 2 is preferable.
R ¹ and R ² each independently represent an alkyl group having 1 to 4 carbon atoms (however, R ¹ and R ² combine to form a nitrogen-containing hydrocarbon ring having 2 to 8 carbon atoms. You may).
R ³ is a (n + 1) -valent hydrocarbon group having 1 to 12 carbon atoms.
A is a hydroxyl group.
n is an integer of 1 or more.
Z ⁻ represents the anion component.

Formula (1-1) in the ^{R 1,} R 2, ^{R 3,} and n illustrated, which are the same as ^R 1 in general formula ^(1), R 2, ^{R 3,} and n, preferably The aspect is the same.

The ionic liquid of the present invention is a liquid at room temperature (25 ° C.).
The melting point of the ionic liquid is preferably 25 ° C. or lower, more preferably 10 ° C. or lower. 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, but the melting point of the ionic liquid is preferably −100 ° C. or higher.
The melting point can be determined by, for example, differential scanning calorimetry.
When the ionic liquid has a melting point of room temperature or lower, the ionic liquid becomes fluid at room temperature.

(lubricant)
The lubricant of the present invention contains an ionic liquid and, if necessary, other components.

The ionic liquid is the ionic liquid of the present invention.
A suitable use of the lubricant is, for example, a lubricant for a magnetic recording medium.

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

<< Known Lubricant >>
As the lubricant, the ionic liquid may be used alone, or may be used in combination with a conventionally known lubricant. Known lubricants include, for example, long-chain carboxylic acid, long-chain carboxylic acid ester, perfluoroalkylcarboxylic acid ester, carboxylic acid perfluoroalkyl ester, perfluoroalkylcarboxylic acid perfluoroalkyl ester, perfluoropolyether derivative and the like. Can be mentioned.

<< Extreme pressure agent >>
In order to maintain the lubricating effect under severe conditions, the lubricant may be used in combination with an extreme pressure agent at a blending ratio of about 30:70 to 70:30 by mass ratio. When a metal contact occurs partially in the boundary lubrication region, the extreme pressure agent reacts with the metal surface by the frictional heat associated therewith to form a reaction product film, thereby performing a friction / wear prevention action. It is a thing. As the extreme pressure agent, for example, a phosphorus-based extreme pressure agent, a sulfur-based extreme pressure agent, a halogen-based extreme pressure agent, an organometallic extreme pressure agent, a composite type extreme pressure agent, or the like can be used.

<< Rust inhibitor >>
The rust preventive may be any one that can be usually used as a rust preventive for this type of magnetic recording medium. For example, phenols, naphthols, quinones, heterocyclic compounds containing nitrogen atoms, and oxygen atoms. Examples thereof include a heterocyclic compound containing a sulfur atom and a heterocyclic compound containing a sulfur atom. The rust preventive may be mixed and used as a lubricant, but a magnetic layer is formed on a non-magnetic support, a rust preventive layer is applied on the upper portion, and then a lubricant layer is applied. As such, the coating may be divided into two or more layers.

<< Solvent >>
Examples of the solvent include organic solvents and the like. 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 fluorine-based solvent may be a commercially available product. Examples of the commercially available products include Novec ^TM 7000, 7100, 7200, 7300, 71IPA manufactured by 3M, Vertrel XF and XP10 manufactured by Mitsui-DuPont Fluorochemical Co., Ltd.
These solvents may be used alone or in combination of two or more.

(Magnetic recording medium)
The magnetic recording medium of the present invention has a non-magnetic support, a magnetic layer, the lubricant of the present invention, and, if necessary, other members.
The magnetic layer is formed on the non-magnetic support. That is, the magnetic layer is arranged on the non-magnetic support.
The lubricant is formed on the magnetic layer. That is, the lubricant is arranged 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 non-magnetic support by a method such as vapor deposition or sputtering. It can also be applied to a magnetic recording medium having a structure in which a base layer is interposed between a non-magnetic support and a magnetic layer. Examples of such a magnetic recording medium include magnetic disks and magnetic tapes.

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, a base layer 12, a magnetic layer 13, a carbon protective layer 14, and a lubricant layer 15 are sequentially laminated.

Further, FIG. 2 is a cross-sectional view showing an example of the magnetic tape. This magnetic tape has a structure in which a back coat 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 non-magnetic support corresponds to the substrate 11 and the base layer 12, and in the magnetic tape shown in FIG. 2, the non-magnetic support corresponds to the substrate 21. When a rigid substrate such as an Al alloy plate or a glass plate is used as the non-magnetic support, even if an oxide film such as alumite treatment or a Ni-P film is formed on the surface of the substrate to harden the surface. Good.

The magnetic layers 13 and 22 are formed as a continuous film by techniques such as plating, sputtering, vacuum deposition, and plasma CVD. Examples of the magnetic layers 13 and 22 include metals such as Fe, Co, and Ni, Co—Ni alloys, Co—Pt alloys, Co—Ni—Pt alloys, Fe—Co alloys, and Fe—Ni alloys. In-plane magnetization recording metal magnetic film composed of Fe-Co-Ni based alloy, Fe-Ni-B based alloy, Fe-Co-B based alloy, Fe-Co-Ni-B based alloy, etc., and Co-Cr based alloy. Vertical magnetization recording metal magnetic thin films such as thin films and Co—O thin films are exemplified.

In particular, when forming an in-plane magnetization recording metal magnetic thin film, a non-magnetic material such as Bi, Sb, Pb, Sn, Ga, In, Ge, Si, or Tl is previously formed as the base layer 12 on the non-magnetic support. In addition, the metallic magnetic material is vaporized or sputtered from the vertical direction to diffuse these non-magnetic materials into the magnetic metal thin film, eliminating the orientation, ensuring in-plane isotropic property, and improving the coercive force. You may do so.

Further, a hard protective layer such as a carbon film, a diamond-like carbon film, a chromium oxide film, or a SiO ₂ film may be formed on the surfaces of the magnetic layers 13 and 22.

As a method of holding the lubricant in such a metal thin film type magnetic recording medium, as shown in FIGS. 1 and 2, the top surface is on the surfaces of the magnetic layers 13 and 22 and the surfaces of the carbon protective layers 14 and 23. There is a method of coating. The coating amount of the lubricant is ^{preferably 0.1mg / m 2 ~100mg / m 2} , more preferably ^{0.5mg / m 2 ~30mg / m 2} , 0.5mg / m 2 It is particularly preferably ~ 20 mg / m ² .

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

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

Further, 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 coating material to the surface of a non-magnetic support. is there. In the coating type magnetic recording medium, any conventionally known magnetic powder, resin binder, or the like constituting the non-magnetic support or the magnetic coating film can be used.

For example, as the non-magnetic support, for example, a polymer support formed of a polymer material such as polyesters, polyolefins, cellulose derivatives, vinyl resins, polyimides, polyamides, polycarbonate and the like. Examples thereof include a metal substrate made of an aluminum alloy, a titanium alloy, etc., a ceramics substrate made of an alumina glass, a glass substrate, and the like. Further, the shape is not limited in any way, and any shape such as a tape shape, a sheet shape, a drum shape, or the like may be used. Further, the non-magnetic support may be surface-treated so as to form fine irregularities in order to control its surface property.

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

Examples of the resin binder include polymers such as vinyl chloride, vinyl acetate, vinyl alcohol, vinylidene chloride, acrylic acid ester, methacrylic acid ester, styrene, butadiene, and acrylonitrile, or copolymers obtained by combining two or more of these, polyurethane. Examples thereof include resins, polyester resins, and epoxy resins. Hydrophilic polar groups such as carboxylic acid groups, carboxyl groups, and phosphoric acid groups may be introduced into these binders 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, a rust preventive, and the like may be added to the magnetic coating film.

As a method of holding the lubricant in such a coating type magnetic recording medium, a method of internally adding the lubricant in the magnetic layer constituting the magnetic coating film formed on the non-magnetic support, the magnetic layer. There is a method of top-coating the surface of the above, or a combination of both. When the lubricant is internally added to the magnetic coating film, it is added in the range of 0.2 parts by mass to 20 parts by mass with respect to 100 parts by mass of the resin binder.

Further, in the case of top coat the lubricant on the surface of the magnetic layer preferably has an applied amount is ^{0.1mg / m 2 ~100mg / m 2} , 0.5mg / m 2 ~20mg / m and more preferably ^2. When the lubricant is top-coated, the ionic liquid may be dissolved in a solvent and the obtained solution may be applied or sprayed, or a magnetic recording medium may be immersed in the solution. ..
As the solvent, a fluorine-based solvent is preferable. 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 and C ₅ H ₂ F ₁₀ ] And so on.
The fluorine-based solvent may be a commercially available product. Examples of the commercially available products include Novec ^TM 7000, 7100, 7200, 7300, 71IPA manufactured by 3M, Vertrel XF and XP10 manufactured by Mitsui-DuPont Fluorochemical Co., Ltd.

By using the lubricant of the present invention, even when a thin lubricant layer is formed, a good lubricating action can be exhibited to reduce the friction coefficient, and high thermal stability can be obtained. Can be done. Further, this lubrication 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 lubricant is applied exhibits excellent running performance, wear resistance, durability, etc. even when a thin lubricant layer is formed, and further improves thermal stability. Can be made to.

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)>
The following ionic liquids (1-D) were synthesized by the following methods.

<< Process 1-A >>
Synthesis of 3-Bromopropyl Tosylate (1-A)

In a flask equipped with a stirrer and a cooling tube, 72.1 g (519 mmol) of 3-bromo-1-propanol (manufacturer: Aldrich), 114 g (598 mmol) of p-toluenesulfonyl chloride (manufacturer: Tokyo Chemical Industry), toluene. (Manufacturer: Wako Pure Chemical Industries, Ltd.) 390 g and triethylamine (manufacturer: Kanto Chemical Co., Inc.) 59.5 g (588 mmol) were added as a base, and the mixture was stirred at room temperature for 21 hours. After stirring, the reaction solution was filtered, diethyl ether was added, the ether layer was washed with water and hydrochloric acid water, and the solvent was removed with an evaporator. Then, 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 give the desired 3-bromopropyltosylate (1-A) in 88% yield.

<< Process 1-B >>
Synthesis of 3-Bromopropyl PFTEG-OH (1-B)

In a flask equipped with a stir bar, a thermometer, and a condenser, 1H, 1H, 11H, 11H-dodecafluoro-3,6,9-trioxundecane-1,11-diol (PFTEG-DOL) (manufacturer: Wako Pure Chemicals) 25.3 g (61.6 mmol), 37.2 g (92.8 mmol) of 3-bromopropyl tosylate (1-A) synthesized in << Step 1-A >>, and metaxylene as a solvent. 62 g of hexafloride (manufacturer: Wako Pure Chemical Industries, Ltd.) was introduced, and the mixture was stirred at room temperature. During stirring, 12.8 g (92.5 mmol) of potassium carbonate (manufacturer: Wako Pure Chemical Industries, Ltd.) and 2.89 g of a 55 mass% aqueous solution of tetrabutylammonium hydroxide (manufacturer: Aldrich) were added, and the mixture was heated and stirred at 80 ° C. for 6 hours. It was. Water and Novec7100 (manufacturer: 3M) were added to this reaction solution, liquid separation extraction was performed, and then the solution was washed with hydrochloric acid, and then the Novec layer was concentrated with an evaporator. The obtained crude product was purified by silica gel column chromatography (hexane + acetone = (mass ratio) 17 + 3⇒3 + 1). The resulting fraction was concentrated to give 3-bromopropyl PFTEG-OH (1-B) in 17% yield.

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

In a flask equipped with a stir bar, a thermometer, and a cooling tube, 4.4 g (38 mmol) of 1-pyrrolidin ethanol (manufacturer: Tokyo Chemical Industry) and 3-bromo synthesized by << Step 1-B >> 5.6 g (19 mmol) of propyl PFTEG-OH (1-B) was added, 8 g of acetonitrile was added as a solvent, and the mixture was heated under reflux for 6 hours.
The obtained mixture solution was distilled off with an evaporator, decanted with hexane and diethyl ether, and then concentrated again with an evaporator. Novec7100 (manufacturer: 3M) was added to the obtained concentrate, filtered through a 0.2 μ membrane filter, dried under reduced pressure at 80 ° C., and a quaternary pyrrolidinium bromide salt (1-C) was obtained in a yield of 48%. I got it in. From the measurement results of LC-MS (ELSD), it was confirmed that about 72% of the synthesized bromide was the target product.

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

In a flask equipped with a stirrer and a cooling tube, 6.0 g (9.2 mmol) of a quaternary pyrrolidinium salt [bromide salt (1-C)] synthesized in << Step 1-C >> was placed therein. 20 g of water was added to the flask and the mixture was stirred. Then, a solution prepared by dissolving 17.7 g (30.1 mmol) of EF-N445 (bis (nonafluorobutanesulfonyl) imide lithium, manufacturer: Mitsubishi Materials Denshi Kasei) in 30 g of water was introduced into a flask and stirred for 16 hours. .. After stirring, the obtained ionic liquid layer was washed with water. Then, it was dried under reduced pressure, and the ionic liquid (1-D) of the target substance was obtained in a yield of 72%. The target product was measured by LC-MS (ELSD) and confirmed to have a purity of 98%.

(Comparative Example 1)
<Synthesis of ionic liquid (2-D)>
The following ionic liquids (2-D) were synthesized by the following methods.

<< Process 2-B >>
Synthesis of 3-Bromopropyl PFTEG (2-B)

In a flask equipped with a stir bar, a thermometer, and a cooling tube, in 54.9 g (100 mmol) of fluorinated triethylene glycol monobutyl ether (PFTEG-OH) (manufacturer: RoomoChem), << step 1-A >>. 61.9 g (211 mmol) of the synthesized 3-bromopropyl tosylate (1-A) and 105 g of metaxylene hexafluorolide (manufacturer: Wako Pure Chemical Industries, Ltd.) were introduced as a solvent, and the mixture was stirred at room temperature. During stirring, 27.9 g (202 mmol) of potassium carbonate (manufacturer: Wako Pure Chemical Industries, Ltd.) and 2.30 g of a 55 mass% aqueous solution of tetrabutylammonium hydroxide (manufacturer: Aldrich) were added, and the mixture was heated and stirred at 80 ° C. for 7 hours. .. Water and Novec7100 (manufacturer: 3M) were added to this reaction solution, liquid separation extraction was performed, and then the solution was washed with hydrochloric acid, and then 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 resulting fraction was concentrated to give 3-bromopropyl PFTEG (2-B) in 50% yield.

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

7.00 g (10.5 mmol), 1- of 3-bromopropyl PFTEG (2-B) synthesized in << Step 2-B >> in a flask equipped with a stir bar, a thermometer, and a cooling tube. 0.97 g (8.4 mmol) of (2-hydroxyethyl) pyrrolidine (manufacturer: Flas Organics) and 8 g (manufacturer: Kanto Chemical Co., Inc.) of acetonitrile were added, and the mixture was heated under reflux for 6 hours. The obtained mixture solution was distilled off with an evaporator, decanted with hexane and diethyl ether, and then concentrated again with an evaporator. Novec7100 (manufacturer: 3M) was added to the obtained concentrate, filtered through a 0.2 μ membrane filter, and dried under reduced pressure at 80 ° C. to obtain a bromide salt (2-C) in a yield of 99%. ..

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

In a flask equipped with a stirrer and a cooling tube, 3.9 g (5.0 mmol) of a quaternary pyrrolidinium salt [bromide salt (2-C)] synthesized in << Step 2-C >> was placed therein. 20 g of water was added to the flask and the mixture was stirred. Then, a solution of 3.65 g (6.2 mmol) of EF-N445 (bis (nonafluorobutanesulfonyl) imide lithium, manufacturer: Mitsubishi Materials Denshi Kasei) in 20 g of water was introduced into a flask and stirred for 18 hours. .. After stirring, the obtained ionic liquid layer was washed with water. Then, it was dried under reduced pressure, and the ionic liquid (2-D) of the target substance was obtained in a yield of 86%.

(Comparative Example 2)
<Synthesis of ionic liquid (3-D)>
The following ionic liquid (3-D) was synthesized by the following method.

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

In << Step 2-C >>, 3-bromopropyl PFTEG (2-B) was changed to 1-bromooctadecane (manufacturer: Tokyo Chemical Industry), and 1- (2-hydroxyethyl) pyrrolidine (2-hydroxyethyl) pyrrolidine as a tertiary amine ( The reaction was carried out in the same manner as << Step 2-C >> except that the manufacturer: Pros Organics was changed to 3- (dimethylamino) -1-propanol (manufacturer: Tokyo Chemical Industry), and then hexane was used. Bromide salt (3-C) was obtained by reprecipitation and purification in (92% yield).

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

In << Step 2-D >>, the same operation as << Step 2-D >> was performed except that the bromide salt (2-C) was changed to the bromide salt (3-C), and the ionic liquid (3) was performed. -D) was obtained in a yield of 81%.

(Comparative Example 3)
<PFTEG-DOL>
As Comparative Example 3, 1H, 1H, 11H, 11H-dodecafluoro-3,6,9-trioxaundecane-1,11-diol (PFTEG-DOL, manufacturer: Wako Pure Chemical, molecular weight 440) was used.

(Comparative Example 4)
<PFPE>
As Comparative Example 4, a perfluoropolyether (PFPE, manufactured by Solvay, terminal hydroxyl group bifunctional product having a molecular weight of 2000: Z-DOL) was used.

<Evaluation>
The following evaluations were made.

<< Solubility in Fluorine Solvent >>
It was added to a fluorine-based solvent so that the concentration was 1% by mass, maintained at 25 ° C., and stirred. Solubility was evaluated according to the following evaluation criteria. The results are shown in Table 1.
As the fluorine-based solvent, the following two solvents, which are generally used for applying a lubricant to a hard disk, were used.
-Vertrel XF: Mitsui-DuPont Fluorochemical Co., Ltd. Vertrel XF is 1,1,1,2,3,4,5,5,5-decafluoropentane (CAS-No. 138495-42-). 8).
〔Evaluation criteria〕
◯: Dissolved in a fluorine-based solvent and no precipitation occurs even if left untreated ×: Insoluble in a fluorine-based solvent, or even if temporarily dissolved but left untreated, precipitation occurs

The samples of Example 1 and Comparative Examples 1, 3, and 4 were all soluble.
The sample of Comparative Example 2 did not dissolve in 1% by mass.

<< Measurement of pyrolysis temperature >>
The weight loss with respect to temperature was measured by TG-DTA (manufacturer name: Seiko Instruments Co., Ltd., 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 peak temperature of endothermic was determined by DSC (manufacturer name: Seiko Instruments model number: EXSTAR6000), and that 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-
The ionic liquids of Examples 1 and Comparative Examples 1 and 2 showed high heat resistance with a 5% weight loss temperature of 300 ° C. or higher.
Compared with Comparative Example 3, Example 1 showed high heat resistance and a low melting point, and also showed higher heat resistance than Comparative Example 4.

− Melting point −
Example 1 became a liquid at room temperature unlike Comparative Example 3 having the same PFPE (perfluoropolyether) molecular weight.

<< Bond rate >>
The bond ratio is a numerical value indicating how much the lubricant is immobilized 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. It is determined by and is expressed by the following equation.
(Bond ratio) = 100 x (lubricant film thickness after rinsing with a fluorosolvent) / (lubricant film thickness before rinsing) [%]

The specific evaluation was carried out as follows.
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 a fluorine-based solvent (Vertrel XF, manufactured by Mitsui-DuPont Fluorochemical Co., Ltd.). The lubricant solution was filtered using a syringe filter (0.2 μm).
The dip coating was performed by pulling up the magnetic disk from the glass container containing the lubricant solution at a speed of 50 mm / min.
The dip concentration was adjusted for each lubricant so that the average thickness of the formed lubricant layers was 10 Å.
The surface of the lubricant-coated hard disk was rinsed with a fluorine-based solvent (Vertrel XF, manufactured by Mitsui-Dupont Fluorochemical Co., Ltd.), and the film thickness of the lubricant before and after the rinse was measured.
Rinsing was performed by immersing the disc in Vertrel XF for 3 minutes.
The film thickness was measured by scanning ellipsometry (manufacturer: Five Bravo, model number: Mary-102).
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 the polar functional groups in the molecular structure of the lubricant react with them. UV irradiation was carried out at wavelengths of 185 nm and 253 nm, at an intensity of 2 mW (254 nm), for 60 seconds.
The results are shown in Table 3.

Example 1 and Comparative Examples 1 and 4 showed good and comparable bond rates.
In Comparative Example 3, the film thickness became zero probably because of volatilization. In Comparative Example 2, it was not measured because it did not dissolve in Vertrel XF.

<< Single molecule film thickness >>
The single molecule film thickness is the minimum film thickness required when the lubricant covers the surface of the base material, and is obtained by a method called the terrace flow method. A single molecule layer is formed by dipping the lubricant on half of the disc and diffusing the lubricant, and measuring the thickness with a scanning ellipsometry meter (manufacturer: Fibravo, model number: Mary-102). did.

The specific evaluation was carried out as follows.
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 a fluorine-based solvent (Vertrel XF, manufactured by Mitsui-DuPont Fluorochemical Co., Ltd.). 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 0.1% by mass.
After immersing the lubricant solution in half of the magnetic disk, the magnetic disk was pulled up at a speed of 50 mm / min.
Then, after being air-dried, it was left at 25 ° C. until a monomolecular layer was formed by diffusing the lubricant into the unimmersed portion of the magnetic disk.
Regarding the terrace flow method, non-patent documents (GW Tyndall, T. Karis, M. S. Jon, Spreading Properties of Molecularly Thin, Perfluoropolyether, Films Tribol. The details are introduced in.
The results are shown in Table 4.

The single molecule film thickness of Example 1 was about one-third that of Comparative Example 4 and about half that of Comparative Example 1.
Since Comparative Example 3 was volatile, the single molecule film thickness could not be measured.
In Comparative Example 2, since it was not dissolved in Vertrel XF, it was not measured.

<< Summary >>
The above evaluation results were ranked below, and further summarized according to the following evaluation criteria. The results are shown in Table 5.
<Ranking>
[Fluid solvent solubility]
○ Evaluation: Rank ○
× Evaluation: Rank ×
[Melting point]
25 ° C or less: Rank ○
Over 25 ° C: Rank x
[Heat resistance (pyrolysis temperature)]
300 ° C or higher: Rank ○
Less than 300 ° C: Rank ×
[Bond rate]
40% or more after 60 seconds of UV irradiation: Rank ◎
30% or more and less than 40% after UV irradiation for 60 seconds: Rank ○
Less than 30% after 60 seconds of UV irradiation: Rank ×
[Single molecule film thickness]
Less than 10 Å: Rank A
10 Å or more and 15 Å or less: Rank B
Over 15 Å: Rank C

As described above, Example 1 achieved high heat resistance and thinning of the single molecule film thickness while maintaining the solubility of the fluorine-based solvent.
Although the result of Comparative Example 1 was also relatively good, the fact that the single molecule film thickness was ranked A was very excellent as compared with Rank B.

The ionic liquid of the present invention has excellent thermal stability, solubility in a fluorine-based solvent, and fluidity, has a high bond ratio, and can form a thin monomolecular film. Therefore, magnetic recording with a high recording density is possible. It can be suitably used as a medium.

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 (10)

It has a cation component and an anion component,
The cation component is a quaternary ammonium cation.
An ionic liquid characterized in that the quaternary ammonium cation has a first group bonded to a nitrogen cation and having a hydroxyl group and a fluorine atom, and a second group bonded to the nitrogen cation and having a hydroxyl group. .. The hydroxyl group of the first group is bonded to the carbon atom at the end of the first group.
The ionic liquid according to claim 1, wherein the hydroxyl group of the second group is bonded to a carbon atom at the end of the second group. The ionic liquid according to any one of claims 1 to 2, wherein the molecular weight of the first group is 1,500 or less. The ionic liquid according to any one of claims 1 to 3 represented by the following general formula (1).
However, 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 is an alkylene group having 1 or more carbon atoms, an oxyalkylene group having 1 or more carbon atoms, a repetition of an oxyalkylene group having 1 or more carbon atoms, or a combination thereof.
Y represents either a single bond or a divalent group.
Y'represents either a single bond or a divalent group.
R ¹ and R ² each independently represent an alkyl group having 1 to 4 carbon atoms (however, R ¹ and R ² combine to form a nitrogen-containing hydrocarbon ring having 2 to 8 carbon atoms. You may).
R ³ is a (n + 1) -valent hydrocarbon group having 1 to 12 carbon atoms.
A is a hydroxyl group.
n is an integer of 1 or more.
Z ⁻ represents the anion component. The ionic liquid according to any one of claims 1 to 4, which is represented by the following general formula (1-1).
However, in the general formula (1-1), p represents an integer of 1 to 20. q represents an integer of 2 to 10. r represents an integer from 0 to 4. s represents an integer from 0 to 4.
R ¹ and R ² each independently represent an alkyl group having 1 to 4 carbon atoms (however, R ¹ and R ² combine to form a nitrogen-containing hydrocarbon ring having 2 to 8 carbon atoms. You may).
R ³ is a (n + 1) -valent hydrocarbon group having 1 to 12 carbon atoms.
A is a hydroxyl group.
n is an integer of 1 or more.
Z ⁻ represents the anion component. The ionic liquid according to any one of claims 1 to 5, wherein the anionic component has a fluorinated hydrocarbon group. The ionic liquid according to any one of claims 1 to 6, wherein the anionic component is represented by any of the following general formulas (2) to (5).
However, in the general formula (2), n represents an integer of 0 to 8.
However, in the general formula (3), n represents an integer of 0 or more.
However, in the general formula (4), n represents an integer of 0 to 8.
However, in the general formula (5), n represents an integer of 1 or more. A lubricant containing the ionic liquid according to any one of claims 1 to 7. The lubricant according to claim 8, further containing a fluorine-based solvent. A magnetic recording medium comprising a non-magnetic support, a magnetic layer on the non-magnetic support, and the lubricant according to any one of claims 8 to 9 on the magnetic layer.