阅读说明：本技术 有机氟化合物、润滑剂以及磁性记录介质的处理方法 (Organic fluorine compound, lubricant, and method for treating magnetic recording medium ) 是由 渡边贤太郎 上田祥之 塙健三 于 2018-06-27 设计创作，主要内容包括：本发明的一形态的有机氟化合物其通式如下,(R-π-E-CH<Sub>2</Sub>-A-CH<Sub>2</Sub>-E’)<Sub>n</Sub>-π’-G (1B)(其中,n是2～5的整数,A是2价的全氟聚醚基,π是亚芳基(arylene group)或单键,R是烯基(alkenyl group)或炔基(alkyne group),E以及E’分别是独立的由化学式-O-CH<Sub>2</Sub>CH(OH)CH<Sub>2</Sub>O-所示的基、醚键或酯键,π’是苯脱去n+1个氢原子的基,G是包含富勒烯(fullerene)骨架的有机基,n个由通式R-π-E-CH<Sub>2</Sub>-A-CH<Sub>2</Sub>-E’-所示的基是相同或不同的基,n个π中的至少1个是亚芳基)。(One embodiment of the organofluorine compound of the present invention has the following general formula (R-. pi. -E-CH) 2 ‑A‑CH 2 ‑E’) n - π '-G (1B) (where n is an integer of 2 to 5, A is a perfluoropolyether group having a valence of 2, π is arylene (arylene group) or a single bond, R is alkenyl group or alkynyl group, E and E' are each independently represented by the formula-O-CH 2 CH(OH)CH 2 O-, an ether bond or an ester bond, π' is a radical of benzene deprived of n +1 hydrogen atoms, G is an organic radical comprising a fullerene skeleton, n are represented by the general formula R- π -E-CH 2 ‑A‑CH 2 The radicals indicated by-E' -are identical or different radicals, at least 1 of n π -s is an arylene radical).)

1. An organofluorine compound having the general formula,

(R-π-E-CH₂-A-CH₂-E’)_n-π’-G (1B)

(wherein n is an integer of 2 to 5, A is a 2-valent perfluoropolyether group,. pi.is an arylene group or a single bond, R is an alkenyl group or an alkynyl group, and E' are each independently represented by the formula

-O-CH₂CH(OH)CH₂O-

Wherein π' is a group from which n +1 hydrogen atoms have been removed, G is an organic group containing a fullerene skeleton,

n are represented by the formula

R-π-E-CH₂-A-CH₂-E’-

The radicals represented are identical or different radicals, at least 1 of the n π radicals being arylene).

2. The organofluorine compound according to claim 1,

the A is a linear chain group.

3. The organofluorine compound according to claim 1 or 2,

a plurality of the R's are the same.

4. The organofluorine compound according to any one of claims 1 to 3,

a plurality of said pi are the same.

5. The organofluorine compound according to any one of claims 1 to 4,

a plurality of the E's are the same.

6. The organofluorine compound according to any one of claims 1 to 5,

the number of carbon atoms of A is 1-100.

7. The organofluorine compound according to any one of claims 1 to 6,

said A having at least one group represented by the following general formula,

-(CF₂)_xO- (2)

(wherein x is an integer of 1 to 5).

8. The organofluorine compound according to claim 7,

the A contains 1 to 50 groups represented by the general formula (2) in which x is 1 or 2.

9. The organofluorine compound according to any one of claims 1 to 8,

the average formula weight of A is within the range of 250-6000.

10. The organofluorine compound according to any one of claims 1 to 9,

the fullerene skeleton of G is C₆₀Skeleton, C₇₀Skeleton, C₇₆Skeleton, C₇₈A skeleton, a higher carbon fullerene skeleton.

11. The organofluorine compound according to any one of claims 1 to 10,

is a compound represented by the following chemical formula.

12. A lubricant for use in a motor vehicle, which,

comprising the organofluorine compound according to any one of claims 1 to 11.

13. A method of processing a magnetic recording medium, comprising:

a step of coating the lubricant according to claim 12 on a magnetic recording medium; and

and a step of irradiating the lubricant onto the magnetic recording medium.

Technical Field

The present invention relates to an organofluorine compound, a lubricant, and a method for processing a magnetic recording medium.

Background

Perfluoropolyether (perfluoro polyethers) compounds have not only good heat resistance, chemical resistance, and oxidation resistance, but also a large viscosity index, and therefore change in fluidity (viscosity) is small in a wide temperature range from low temperature to high temperature, and good lubricity can be exhibited. Besides being nonflammable, perfluoropolyether compounds have properties such as low vapor pressure (vapor pressure), low evaporation loss (evaporative loss), low surface tension, and high electrical insulation, and hardly affect polymer materials such as rubber and plastics, and are known to exhibit high efficacy as lubricants in a very wide range. Therefore, perfluoropolyether compounds are widely used as lubricating oils for vacuum pump oils, lubricants for magnetic disks and belts, heat media, non-adhesive agents, and other applications.

As an example of using the perfluoropolyether group-containing organofluorine compound as the lubricant, a disk-like substrate used as a magnetic recording medium can be cited.

In general, a magnetic recording medium has a structure in which a recording layer or the like is stacked on a substrate, a protective layer of carbon or the like is formed on the recording layer, and a lubricant layer is formed on the protective layer. The protective layer can protect information recorded in the recording layer and improve the slidability of a magnetic head for reading data.

However, sufficient durability of the magnetic recording medium cannot be obtained by forming only the protective layer on the recording layer.

Therefore, an organofluorine compound lubricant having a perfluoropolyether group is usually applied to the protective layer to form a lubricant layer. This can suppress direct contact between the magnetic head and the protective layer, and can significantly reduce the frictional force of the magnetic head sliding on the magnetic recording medium, thereby improving durability.

As the lubricant used for the magnetic recording medium, for example, an organofluorine compound of the following chemical formula is known.

HOCH₂CF₂O(CF₂CF₂O)_p(CF₂O)_qCF₂CH₂OH (3)

(wherein p and q are each an integer of 1 or more.)

Examples of the organic fluorine compound include Fomblin (registered trademark) Zdol (manufactured by Solvay specialty Polymers).

Patent document 1 discloses a magnetic recording medium in which the above lubricant is applied to a protective layer.

Further, patent document 2 discloses a magnetic recording medium having a lubricant layer formed of an organic fluorine compound Fomblin ztiol (manufactured by Solvay Specialty Polymers) represented by the following chemical formula.

HOCH₂CH(OH)CH₂OCH₂CF₂O(CF₂CF₂O)_m(CF₂O)_nCF₂CH₂OCH₂CH(OH)CH₂OH (4)

(wherein m and n are integers, and the average molecular weight of the compound represented by the formula (4) is 500-5000.)

Further, patent document 3 discloses a magnetic recording medium in which a lubricant solution containing an organofluorine compound represented by chemical formula (5) and a solvent is applied to a protective layer.

(wherein p and q are each an integer of 1 or more.)

The organofluorine compounds used in the lubricants of the chemical formulas (3) to (5) all contain a linear perfluoropolyether group, but do not contain an aromatic ring in the molecule.

Further, patent document 4 discloses a magnetic recording medium having a lubricant layer formed of an organofluorine compound fombliam 2001 (manufactured by Solvay Specialty Polymers) represented by chemical formula (6).

(wherein p and q are each an integer of 1 or more.)

The organofluorine compound used in these lubricants has a phenyl group having a substituent in the molecule at the end of the linear perfluoropolyether group, and forms a ring with an oxygen atom group bonded to an adjacent carbon atom constituting the phenyl group through a methylene (methylene) group.

< Prior Art document >

< patent document >

Patent document 1: japanese patent laid-open publication No. 62-66417

Patent document 2: japanese laid-open patent publication No. 9-282642

Patent document 3: japanese laid-open patent publication No. 2008-75000

Patent document 4: specification of U.S. Pat. No. 5055359

Disclosure of Invention

< problems to be solved by the present invention >

For example, in the case where an organofluorine compound containing a perfluoropolyether group is used as a lubricant on a disk-shaped substrate used for a magnetic recording medium, after a lubricant layer is formed on a protective layer, the lubricant needs to be fixed on the protective layer in order to prevent the lubricant from escaping with time.

In order to form a lubricant layer by adsorbing a lubricant on the protective layer, generally, the protective layer is nitrided.

The organofluorine compounds described in patent documents 1 and 2 have a hydroxyl group (hydroxy group) at the molecular end thereof, and the hydroxyl group and a nitrogen atom provided in the protective layer can form a hydrogen bond, whereby the organofluorine compounds can be adsorbed on the protective layer to form a lubricant layer.

On the other hand, it is considered that the number of steps can be reduced without nitriding the protective layer, which is advantageous in reducing the production cost. In general, a nitrogen atom having a large electronegativity (electronegativity) is added to a protective layer having carbon atoms and hydrogen atoms as main components, whereby an increase in polarity can be suppressed. Therefore, it is considered that the corrosion resistance to moisture in the air and the like is improved.

However, when the lubricant is applied to the protective layer which is not nitrided, since hydrogen bonds are not formed between the protective layer and the lubricant, a small amount of the lubricant adheres due to its high viscosity, but there is a problem that a lubricant layer having a sufficient thickness cannot be formed.

The protective layer is made of carbon atoms or diamond-like carbon (DLC) containing carbon atoms. It is known that a part of carbon atoms in DLC has sp²Hybrid orbitals, containing the same double bonds as the bonds between carbon atoms in graphite.

Here, it is conceivable that the lubricant is adsorbed on the protective layer that is not subjected to the nitriding treatment by pi-pi interaction (pi-pi interaction) with the adsorption site in the lubricant using the double bond.

The organofluorine compounds described in patent documents 3 and 4 have cyclic phosphazenes (cyclophosphazenes) and 1, 3-benzodioxols (1, 3-benzodioxols) at the ends, respectively, and these are cyclic structures alternately including single bonds and double bonds, and therefore, it seems that adsorption can be performed on a protective layer that has not been nitrided by pi-pi interaction.

However, since these cyclic structures include a ring other than an aromatic ring, the flatness of the cyclic structure is impaired. Therefore, the pi-pi interaction between these lubricants and the protective layer not subjected to nitriding treatment is not sufficient, and there is a problem that a lubricant layer having a sufficient thickness cannot be formed.

Therefore, if a lubricant whose terminal cyclic structure is composed of only aromatic rings and which can be regarded as substantially flat is used, the lubricant can be adsorbed on the protective layer which has not been nitrided by an effective pi-pi interaction.

On the other hand, when a lubricant layer is formed on a protective layer of a magnetic recording medium such as a magnetic disk, a part of the lubricant on the protective layer is scraped off every time a magnetic head jumps. As a result, the lubricant layer becomes gradually thinner, and there is a risk of eventually causing collision (crash). In order to suppress this phenomenon, the amount of the lubricant fixed on the protective layer must be higher than a prescribed ratio, that is, the bonding rate (bonded ratio) of the lubricant layer must be high.

The bonding ratio of the lubricant layer is a ratio of the lubricant remaining after the magnetic disk on which the lubricant layer is formed is immersed in a solvent and the lubricant that has not been fixed on the protective layer is washed away.

In this case, there is a problem that it is difficult to obtain a sufficient bonding ratio due to the pi-pi interaction that works when a lubricant having only a terminal cyclic structure consisting of only an aromatic ring is adsorbed on a protective layer that has not been nitrided.

In view of the above circumstances, an object of one aspect of the present invention is to provide an organofluorine compound that can form a lubricant layer having a sufficient thickness on a protective layer that has not been nitrided and can improve the bonding ratio of the lubricant layer.

< means for solving the problems >

[1] An organofluorine compound represented by the following general formula,

(R-π-E-CH₂-A-CH₂-E’)_n-π’-G (1B)

(wherein n is an integer of 2 to 5, A is a perfluoropolyether group having a valence of 2,. pi.is an arylene group or a single bond, R is an alkenyl group or an alkynyl group, and E' are each independently represented by the formula

-O-CH₂CH(OH)CH₂O-

Wherein π' is a group from which n +1 hydrogen atoms have been removed, G is an organic group containing a fullerene skeleton, and n are represented by the formula

R-π-E-CH₂-A-CH₂-E’-

The radicals indicated may be identical or different, at least 1 of the n π radicals being arylene).

[2] The organofluorine compound according to the above [1], wherein A is a linear group.

[3] The organofluorine compound according to the above [1] or [2], wherein a plurality of R are the same group.

[4] The organofluorine compound according to any one of the above [1] to [3], wherein a plurality of π are the same group.

[5] The organofluorine compound according to any one of the above [1] to [4], wherein a plurality of E are the same group.

[6] The organofluorine compound according to any one of the above [1] to [5], wherein A has 1 to 100 carbon atoms.

[7] The organofluorine compound according to any one of the above [1] to [6], wherein A has at least one group represented by the general formula

-(CF₂)_xO- (2)

The group (wherein x is an integer of 1 to 5).

[8] The organic fluorine compound according to the above [7], wherein A comprises 1 to 50 groups represented by the above general formula (2) wherein x is 1 or 2.

[9] The organofluorine compound according to any one of the above [1] to [8], wherein the average formula weight of A is in the range of 250 to 6000.

[10]As described above [1]～[9]The organic fluorine compound according to any one of the above, wherein the fullerene skeleton of G is C₆₀Skeleton, C₇₀Skeleton, C₇₆Skeleton, C₇₈A skeleton, a higher carbon fullerene skeleton.

[11] The organofluorine compound according to any one of the above [1] to [10], which is a compound represented by the following chemical formula.

[12] A lubricant comprising the organofluorine compound according to any one of the above [1] to [11 ].

[13] A method for processing a magnetic recording medium, comprising the step of applying the lubricant according to [12] above to a magnetic recording medium; and irradiating the lubricant applied to the magnetic recording medium with ultraviolet rays.

< effects of the invention >

According to one aspect of the present invention, an organofluorine compound capable of forming a lubricant layer having a sufficient thickness on a protective layer that has not been nitrided and improving the bonding ratio of the lubricant layer can be provided.

Detailed Description

(organic fluorine Compound)

The organofluorine compound of the present embodiment is a compound represented by the following general formula,

(R-π-E-CH₂-A-CH₂-E’)_n-π’-G (1B)

(wherein n is an integer of 2 to 5, A is a 2-valent perfluoropolyether group,. pi.is an arylene group or a single bond, R is an alkenyl group or an alkynyl group, and E' are each independently represented by the formula

-O-CH₂CH(OH)CH₂O-

Wherein π' is a group from which n +1 hydrogen atoms have been removed, G is an organic group containing a fullerene skeleton,

n are represented by the formula

R-π-E-CH₂-A-CH₂-E’-

The groups represented may be the same or different groups, and at least 1 of n π is an arylene group).

In view of ease of synthesis, it is preferable that all of π of the compound represented by the formula (1B) be arylene. In addition, in view of ease of synthesis, n of the compound represented by the general formula (1B) is preferably 3.

Here, the perfluoropolyether group is a group in which a plurality of fluorocarbon groups are bonded by ether bonds.

Hereinafter, unless otherwise specified, the description will be given of the organofluorine compound of the present embodiment by using an organofluorine compound in which a plurality of π's are arylene groups.

The organic fluorine compound of the present embodiment has a perfluoropolyether group having a valence of 2 and an aryl (aryl) group in the molecule represented by the general formula

-E-CH₂-

The structure shown in the figure is combined with the connecting group, and the aryl is formed by directly combining alkenyl or alkynyl on an aromatic ring.

The organofluorine compound of the present embodiment contains an aromatic ring which can be regarded as substantially flat, and therefore, can be adsorbed on a protective layer which has not been nitrided by pi-pi interaction, and a lubricant layer having a sufficient thickness can be formed. In addition, since the alkenyl group or the alkynyl group is directly bonded to the aromatic ring, irradiation with ultraviolet rays can promote an unsaturated bond contained in the alkenyl group or the alkynyl group and sp of a material constituting the protective layer (for example, diamond-like carbon (DLC))²Strong bonds are formed between the hybridized carbon atoms. As a result, the lubricant layer can be sufficiently fixed to the protective layer, and the bonding ratio of the lubricant layer can be improved. The aromatic ring also contains an unsaturated bond and similarly has an effect of increasing the bonding ratio, but the effect of increasing the bonding ratio is not sufficient only with the aromatic ring.

A may be a linear group or a branched group, but is preferably a linear group. When A is a straight chain group, lubricity and solubility in a fluorine-based solvent can be improved.

The number of carbon atoms of A is preferably 1 to 100, more preferably 5 to 40. When the number of carbon atoms of a is 1 or more, the solubility of the organofluorine compound in the fluorine-based solvent increases, and thus the organofluorine compound is more easily applied. When the number of carbon atoms of a is 100 or less, the solubility of the organofluorine compound in a general organic solvent increases, and therefore, the structural change is more easily achieved by the organic reaction of the organofluorine compound.

A preferably has at least one group represented by the following general formula,

-(CF₂)_xO- (2)

(wherein x is an integer of 1 to 5).

This increases the solubility of the organofluorine compound in the fluorine-based solvent, and as a result, the organofluorine compound can be more uniformly coated.

Further, A more preferably contains 1 to 50 groups represented by the general formula (2) wherein x is 1 or 2. The perfluoropolyether group having the above structure can be industrially synthesized, and therefore, the perfluoropolyether group is easily obtained and is industrially advantageously used.

The average formula weight of A is preferably in the range of 250 to 6000, more preferably 280 to 3000. When the average formula weight of a is 250 or more, the solubility of the organofluorine compound in the fluorine-based solvent increases, and therefore the application of the organofluorine compound becomes easier. When the average formula weight of a is 6000 or less, the solubility of the organofluorine compound in a general organic solvent increases, and the structural change is more easily achieved by the organic reaction of the organofluorine compound.

R is preferably an alkenyl group having 2 to 4 carbon atoms or an alkynyl group having 2 to 4 carbon atoms.

Specific examples of R include an ethylene (vinyl) group, an aryl group, a 3-Buten-1-yl group (3-Buten-1-yl), a propargyl group and the like, and among them, a vinyl group, an aryl group and a propargyl group are particularly preferable.

E and E' are each independently a group represented by the following chemical formula, an ether bond or an ester bond,

-O-CH₂CH(OH)CH₂O-，

and ester bonds are preferred in view of ease of synthesis. The direction of the ester bond is not particularly limited, and the ester bond is preferably a group capable of constituting the general formula

R-π-COO-CH₂-

The orientation of the radicals shown.

In the organofluorine compound of the present embodiment, a plurality of R are preferably the same group. This can reduce the number of steps required for synthesis.

The pi is not particularly limited, and may include phenylene (phenylene) group, naphthylene (naphthylene) group and the like, and among them, 1, 4-phenylene and 1, 2-naphthylene are particularly preferable.

In the organofluorine compound of the present embodiment, it is preferable that a plurality of π groups are the same group. This can reduce the number of steps required for synthesis.

The group π' is not particularly limited, and may include phenylene and naphthylene, among which 2,4, 6-phenylene is particularly preferred.

In the organofluorine compound of the present embodiment, a plurality of E are preferably the same group. This can reduce the number of steps required for synthesis.

G is not particularly limited as long as it contains a fullerene skeleton and can be bonded to pi', and examples thereof include a group forming a pyrrolidine (pyrolidine) ring on the fullerene skeleton.

The fullerene skeleton may be, for example, C₆₀Skeleton, C₇₀Skeleton, C₇₆Skeleton, C₇₈A skeleton and a higher fullerene skeleton, and the like. Among them, C is preferable₆₀And (3) a framework.

C₆₀Compared with other fullerene skeletons, the skeleton is easy to obtain a high-purity product industrially. Therefore, the purity of the organofluorine compound of the present embodiment can be improved, and excellent lubricity and smoothness can be obtained.

(method for synthesizing organic fluorine Compound)

The organofluorine compound of the present embodiment can be synthesized, for example, by the following synthesis method.

(Compound represented by the general formula (1B'))

First, a compound represented by the following general formula was synthesized,

R-π-E-CH₂-A-CH₂-OH (1B’)

(wherein A is a 2-valent perfluoropolyether group,. pi.is an arylene group, R is an alkenyl or alkynyl group, and E is represented by the formula

-O-CH₂CH(OH)CH₂O-

The indicated group, ether linkage or ester linkage).

[ case where E is an ether bond ]

For example, a compound represented by the general formula (1B') can be synthesized by deprotonating a conventional perfluoropolyether compound having a hydroxyl group at the end to produce an alkoxide (alkoxide) and cross-coupling (cross-linking) the alkoxide with an aryl halide (aryl halide) in the presence of a copper catalyst. The reaction is carried out without solvent by stirring with appropriate heating.

As the base, a generally common ionic base can be used, and examples thereof include potassium carbonate, cesium carbonate, potassium tert-butoxide (potassium tert-butoxide), and the like.

As the copper catalyst, for example, a catalyst produced from copper iodide (copper (i) iodide) and ethyl 2-cyclohexanone formate (ethyl 2-cyclohexanone carbonate) can be used.

The aryl halide is preferably an aryl halide in which an alkenyl group or an alkynyl group is directly bonded to an aromatic ring constituting an aryl group in advance.

Examples of the aryl halide include aryl iodide (aryl iodide), and among them, 4-aryliodobenzene (4-aryliodobenzene) is particularly preferable.

[ case where E is an ester bond ]

For example, a compound represented by the general formula (1B') can be synthesized by subjecting a conventional perfluoropolyether compound having a hydroxyl group at the end to an esterification reaction with an acid chloride (e.g., carboxylic acid chloride) under the presence of an alkali group. The reaction can be carried out in a solvent.

Alternatively, a perfluoropolyether compound having a carbonyl chloride (carbonyl chloride) group at the terminal thereof in the past and a compound having a hydroxyl group may be subjected to an esterification reaction in the same manner.

The solvent is not particularly limited as long as the perfluoropolyether compound can be dissolved, and examples thereof include a chlorine-containing solvent such as methylene chloride (dichloromethane), and a fluorine-containing solvent such as AK-225 (manufactured by asahi glass company).

As the base, a generally common inorganic base and an organic base can be used, and examples thereof include cesium carbonate, triethylamine (triethylamine), and diisopropylamine (diisopropyramine).

[ E is-O-CH₂CH(OH)CH₂Case of-O-]

For example, a compound represented by the general formula (1B') can be synthesized by subjecting a conventional perfluoropolyether compound having a hydroxyl group at the end to a cycloaddition reaction (cycloaddition reaction) with a compound having a glycidyloxy group directly bonded to an aromatic ring constituting an aryl group under a condition having a base. The reaction can be carried out in a solvent.

The solvent is not particularly limited as long as it can dissolve the perfluoropolyether compound having a hydroxyl group and the ionic base, and examples thereof include alcohols such as methanol and tert-butyl alcohol (tert-butyl alcohol), and polar solvents such as N, N-dimethylformamide (N, N-dimethylformamide).

As the base, a generally common ionic base can be used, and examples thereof include potassium carbonate, cesium carbonate, potassium tert-butoxide and the like.

(Compound represented by the general formula (1B))

Next, the compound represented by the general formula (1B') was reacted with trifluoromethanesulfonic acid anhydride (Tf)₂O) to replace the hydroxyl group with OTf, a compound represented by the following general formula can be synthesized,

R-π-E-CH₂-A-CH₂-OTf (1B”)。

(Compound represented by the general formula (1B))

Then, the compound represented by the general formula (1B') is reacted with 2,4,6-trihydroxybenzaldehyde (2,4,6-trihydroxybenzaldehyde) in an aprotic polar solvent such as N, N-dimethylformamide under the presence of a base_N2, then reacting with N-methylglycine and C₆₀The fullerene reacts to synthesize a compound represented by the general formula (1B).

[ crude product ]

In each reaction, water or dilute hydrochloric acid is added to the reaction mixture, and if necessary, a fluorine-containing solvent such as AK-225 (manufactured by asahi glass corporation) is added as an extraction solvent to perform liquid separation (fractionation), and after drying the organic layer, the organic layer is filtered and concentrated by a rotary evaporator to obtain a crude product.

[ refining ]

The crude product can be used directly as a lubricant. When higher purity is required, the crude product can be used as a lubricant after refining it by silica gel column chromatography (silica gel column chromatography) or supercritical carbon dioxide fluid extraction, for example.

In the case of the supercritical carbon dioxide fluid extraction method, for example, the crude product is placed in a pressure vessel, and then liquefied carbon dioxide is introduced into the pressure vessel while maintaining the pressure and temperature in the pressure vessel, so that the carbon dioxide is brought into a supercritical fluid state, and the target compound is extracted and purified.

The temperature in the pressure vessel is preferably from 31 ℃ to 80 ℃. When the temperature in the pressure vessel is lower than 31 ℃, the liquefied carbon dioxide cannot be brought into a supercritical state, and when the temperature exceeds 80 ℃, the extraction power of the supercritical carbon dioxide is weakened.

The pressure in the pressure vessel is preferably 7.38MPa or more and 30MPa or less. If the pressure in the pressure vessel is less than 7.38MPa, the liquefied carbon dioxide cannot be brought into a supercritical state, and if it exceeds 30MPa, the apparatus must have a sufficient pressure resistance, and the price of the apparatus increases, resulting in an increase in the production cost.

(Lubricant)

The lubricant of the present embodiment contains the organofluorine compound of the present embodiment.

The lubricant of the present embodiment may be the organofluorine compound of the present embodiment, and may contain another organofluorine compound in addition to the organofluorine compound of the present embodiment.

The other organofluorine compound is not particularly limited, and for example, a generally common organofluorine compound which has been conventionally used as a lubricant can be used.

Examples of commercially available products of other organofluorine compounds include Fomblin (registered trademark) series (manufactured by Solvay Specialty Polymers Co., Ltd.).

In order to obtain good adsorption, the content of the organofluorine compound of the present embodiment in the lubricant is preferably 0.1 mass% or more, more preferably 1 mass% or more, and particularly preferably 10 mass% or more.

The lubricant of the present embodiment can be used by dissolving it in a solvent or dispersing it in a dispersion medium to form a solution or a dispersion, and then applying it on the surface of a magnetic recording medium such as a magnetic disk, if necessary.

The method of applying (the solution or dispersion of) the lubricant is not particularly limited, and for example, a spin coating (spin coating) method, a dip coating (dip coating) method, or the like can be used.

In the case where (a solution or dispersion of) a lubricant is applied to the surface of a magnetic recording medium by dip coating, for example, the magnetic recording medium is immersed in (a solution or dispersion of) a lubricant contained in an immersion-inoculated tank of a dip coating apparatus, and then the magnetic recording medium is taken out from the immersion-inoculated tank at a predetermined speed.

The content of the organofluorine compound of the present embodiment in the solution or dispersion of the lubricant is preferably 0.005 mass% or more.

Here, as described above, the ultraviolet line is preferably irradiated after (the solution or the dispersion of) the lubricant according to the present embodiment is applied. This makes it possible to form a lubricant layer having a sufficient thickness on the protective layer that has not been subjected to nitriding treatment, and to improve the bonding rate of the lubricant layer.