JP2006190393A - Magnetic recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic recording medium which can maintain its contact and lubricity even in severe environments and keep the lubrication effect for a long period and is excellent in its traveling stability and durability realizing the temporally stable lubricating property. <P>SOLUTION: This magnetic recording medium 10 has at least a magnetic layer 2 formed on a non-magnetic base 1, and a lubricant is prepared by mixing two kinds of compounds of a specific chemical formula and retained on the outermost layer. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a high-density magnetic recording medium in which a magnetic layer composed of at least a ferromagnetic metal thin film is formed on a nonmagnetic support, and more particularly to a lubricant retained on the outermost layer. The structure and the combination are specified to improve the running performance, durability, and stability of the lubricating characteristics over time.

  Conventionally, magnetic recording media include ferromagnetic powders such as oxide magnetic powders and alloy magnetic powders, binders such as vinyl chloride-vinyl acetate copolymers, polyester resins, urethane resins, and polyurethane resins, and organic solvents. A so-called coating-type magnetic recording medium in which a magnetic layer is formed by applying a paint on a nonmagnetic support has been widely used.

  On the other hand, with the increasing demand for high-density recording and long-term recording, ferromagnetic metal magnetic materials such as Co, Co—Ni alloy, Co—Cr alloy, and Co—O are plated or vacuum thin film forming technology (vacuum deposition). Developed a so-called ferromagnetic metal thin film type magnetic recording medium in which a magnetic layer is formed by directly depositing on a non-magnetic support such as a polyester film or a polyimide film by a method, a sputtering method, an ion plating method, etc. It was. Such a ferromagnetic metal thin film type magnetic recording medium has been put to practical use in a consumer video format (8 mm Hi-8 format, DV format) or a commercial video format (DVCAM).

  Such a magnetic recording medium has superior magnetic properties such as coercive force and squareness ratio, as well as excellent electromagnetic conversion characteristics in a short wavelength region as compared with a coating type magnetic recording medium. Since it can be made very thin, the thickness loss during recording demagnetization and reproduction is extremely small, and there is no need to mix a binder, which is a nonmagnetic material, into the magnetic layer. It has many advantages such as being able to increase

  In general, the magnetic recording medium as described above is subjected to high-speed relative motion with the magnetic head in the process of recording and reproducing magnetic signals, and the running at that time must be performed in a smooth and stable state. First, it is important to reduce wear and damage due to contact with the magnetic head.

  However, the magnetic recording medium of the ferromagnetic metal thin film type has a very good smoothness on the surface of the magnetic layer due to its structure, so that the substantial contact area with the magnetic head is increased, and an adhesion phenomenon (so-called peeling). There have been many problems regarding durability and running properties, such as the tendency of the occurrence of the problem and the increase of the friction coefficient, and improvements have been demanded.

In view of such problems of the prior art, for example, it has been attempted to improve durability and running performance by applying a lubricant to the surface of a magnetic layer, that is, a ferromagnetic metal thin film. It is known that an organic fluorine compound is effective as a lubricant applied for such applications.
For example, in the past, “an ester compound of a perfluoropolyether having a hydroxyl group at a terminal and a long chain carboxylic acid or an ester compound of a perfluoropolyether having a carboxyl group at a terminal and a long chain alcohol is used as a lubricant. , “A magnetic recording medium that exhibits an excellent lubricating effect under any use conditions” (for example, see Patent Document 1 below), “a compound of a bifunctional perfluoropolyether having a carboxyl group at the terminal and an amine, or a terminal. By using a compound of a perfluoropolyether having a carboxyl group and an amine as a lubricant, a magnetic recording medium that exhibits an excellent lubricating effect under any use conditions ”(see, for example, Patent Document 2 below), “A ferromagnetic metal thin film is formed on a non-magnetic support, and perfluorocarbon is formed on the ferromagnetic metal thin film. Magnetic recording medium "(e.g., see Patent Document 3.), Characterized in that deposited the alkyl alcohol it has been proposed.
These prior arts have an effect that the lubricating effect can be maintained even under conditions from low temperature to normal temperature.

Japanese Patent Laid-Open No. 05-194970 JP 05-93059 A JP-A-62-256218

Incidentally, in a ferromagnetic metal thin film type magnetic recording medium, a carbon protective layer is generally formed on the magnetic layer in order to ensure superior durability.
This is a technology that has been put to practical use in the above-mentioned consumer video format DV tapes, DVCAM tapes that are business video formats, and AIT tapes that are used for tape streamers. is there.

  In the magnetic recording medium having such a configuration, when a lubricant is applied on the carbon protective layer in order to further improve durability and running performance, the energy on the surface of the carbon protective layer is the same as that of the ferromagnetic metal thin film. Since it is small in comparison, sufficient adsorbability with the lubricant cannot be ensured, and problems such as rapid deterioration in running performance and durability due to long-term use have become prominent.

  In other words, assuming the presence of a carbon protective layer, it was necessary to study the chemical structure of the lubricant itself in the future, but the adsorbing power of the various lubricants disclosed in the above-mentioned patent documents to the carbon protective layer However, it was difficult to maintain stable lubrication characteristics even when the vehicle was run many times.

  Conventionally, various studies have been made on lubricants having good adsorptivity to the carbon protective layer. However, a magnetic recording medium having a structure in which these known lubricant compounds are applied alone on the carbon protective layer. However, it has not been possible to satisfy the demand for maintaining stable magnetic characteristics even in the long-time use of a magnetic recording medium, which will be further required in the future.

  Therefore, in the present invention, in view of the conventional problems as described above, a lubricant suitable for a ferromagnetic metal thin film type magnetic recording medium in which a carbon protective layer is formed is particularly studied, under extremely severe use conditions. In addition, the adhesion and lubricity are maintained, the lubrication effect is maintained for a long time, and excellent lubrication characteristics can be maintained and exhibited even when running many times, and the running stability and durability are excellent. An object of the present invention is to provide a magnetic recording medium capable of exhibiting a stable lubricating characteristic over time, that is, running property even in a severe environment.

In the present invention, a magnetic recording medium in which at least a magnetic layer is formed on a nonmagnetic support, which is a perfluoropolyether having a hydroxyl group at the terminal represented by the following general formula (1) and a long-chain carboxylic acid An ester compound of a perfluoropolyether having a carboxyl group at the terminal represented by the following general formula (2) and a long-chain alcohol, and a bifunctional compound having a carboxyl group at the terminal represented by the following general formula (3) Of the compound of perfluoropolyether and amine, the compound of perfluoropolyether and amine having a carboxyl group at the terminal represented by the following general formula (4), and the perfluoroalkyl alcohol represented by the following general formula (5), At least one and a fluoroalkyldicarboxylic acid derivative represented by the following general formula (6) To provide a magnetic recording medium which lubricant is held in the outermost layer.
_{R1COOCH 2 Rf1CH 2 OCOR1 ··· (1} )
(In the general formula (1), Rf1 represents a perfluoropolyether chain, and R1 represents a hydrocarbon group or a fluorinated hydrocarbon group.)
R2OCORf2COOR2 (2)
(However, Rf2 represents a perfluoropolyether chain, and R2 is a hydrocarbon group or a fluorinated hydrocarbon group.)

  Rf3 represents a perfluoropolyether chain, and R3, R4, R5 and R6 are hydrocarbon groups or hydrogen.

  Rf4 represents a perfluoropolyether chain, and R11, R12, R13 and R14 are hydrocarbon groups or hydrogen.

C _j F _{2j + 1} (CH ₂ ) _k OH (5)
(However, j ≧ 4 and k ≧ 0.)

  However, in General formula (6), Rf group is group represented by following General formula (7).

  In General Formula (7), m = 2 to 20 and n = 4 to 18.

According to the present invention, a lubricant is produced by combining a compound having a specific chemical structure as described above, and this is applied onto the carbon protective layer, so that it has excellent adhesion even under extremely severe use conditions. Thus, lubricity was obtained, the lubrication effect could be maintained even when the vehicle traveled for a long time, and the running stability and durability were improved.
In particular, compared to the case where a single type of lubricant is used in the past, it has been possible to dramatically improve the stability of the lubricating characteristics over time in a harsh environment.

A specific embodiment of the magnetic recording medium of the present invention will be described in detail with reference to the drawings. This invention is not limited to the example shown below, A conventionally well-known structure and material can be added or substituted.
FIG. 1 shows a schematic configuration diagram of an example of the magnetic recording medium of the present invention.
In the magnetic recording medium 10, a magnetic layer 2 and a protective layer 3 made of a ferromagnetic metal thin film are formed on a nonmagnetic support 1, and a back coat layer 5 is formed on the main surface opposite to the magnetic layer forming surface. In addition, the lubricant layer 4 is held on the protective layer 3. Hereinafter, each component will be described.

As the nonmagnetic support 1, any material that is used as a support for ordinary magnetic recording media can be used. For example, polyesters such as polyethylene terephthalate and polyethylene naphthalate, polyolefins such as polyethylene and polypropylene, cellulose derivatives such as cellulose triacetate and cellulose diacetate, vinyl resins such as polyvinyl chloride and polyvinylidene chloride, polycarbonate, polyimide and polyamide And plastics such as polyamideimide, light metals such as aluminum alloy and titanium alloy, and ceramics such as glass.
As the nonmagnetic support 1, a rigid material such as an aluminum alloy plate or a glass plate may be applied. In this case, the surface of the nonmagnetic support 2 is subjected to alumite treatment or the like to form an oxide film or Ni-P. A film or the like may be formed, and the surface of the nonmagnetic support 2 may be subjected to a curing process.
The form of the nonmagnetic support 1 may be any of a film shape, a sheet shape, a disk shape, a card shape, a drum shape, and the like.

The surface roughness of the nonmagnetic support 1 may be controlled by forming at least one or more of predetermined protrusions such as mountain-shaped protrusions, wrinkle-shaped protrusions, and granular protrusions.
The surface properties of the magnetic layer 2 can be controlled by forming the protrusions on the nonmagnetic support 1, but at least two of these protrusions, in particular, on the nonmagnetic support 1 on which the mountain-shaped protrusions are formed. It was confirmed that the formation of wrinkle-like projections and granular projections significantly improved the durability and running performance.
In this case, the overall height of the protrusions is preferably in the range of 10 to 200 nm, and the density is preferably 1 × 10 ⁵ to 1 × 10 ⁷ pieces / mm ² .

The mountain-shaped protrusion can be formed by internally adding inorganic fine particles having a particle size of about 50 to 300 nm into the nonmagnetic support 1. The height of the mountain-shaped protrusions is preferably 10 to 100 nm from the nonmagnetic support 1, and the density of the mountain-shaped protrusions is preferably about 1 × 10 ⁴ to 1 × 10 ⁵ pieces / mm ² .
As the inorganic fine particles to be internally added to the nonmagnetic support 1 when forming the mountain-shaped protrusions, it is preferable to use calcium carbonate, silica, alumina or the like.

The wrinkled protrusions are formed by applying a diluted solution of a resin using a specific mixed solvent on the nonmagnetic support 1 and drying it. The height of the wrinkled protrusion is preferably 0.01 to 1 μm, and more preferably 0.03 to 0.5 μm. Moreover, it is preferable that the shortest space | interval between wrinkle-shaped protrusions is 0.1-20 micrometers.
Resins for forming wrinkled protrusions include polyesters such as polyethylene terephthalate and polyethylene naphthalate, polyamide, polystyrene, polycarbonate, polyacrylate, polysulfone, polyvinyl chloride, polyvinylidene chloride, polyvinyl butyral, polyphenylene oxide, phenoxy A simple substance such as a resin, a mixture or a copolymer can be used, and those having a soluble solvent are suitable.
Then, in a solution obtained by dissolving these resins in the good solvent at a resin concentration of 1 to 1000 ppm, a solvent which is a poor solvent for the resin and has a boiling point higher than the good solvent is added 10 to 100 times the amount of the resin. A thin layer having very fine wrinkle-like protrusions can be formed by applying the dried solution to the surface of the nonmagnetic support 1 and drying it.

The granular protrusions are formed by adhering organic ultrafine particles such as acrylic resin or inorganic fine particles such as silica and metal powder in a spherical or hemispherical form on the nonmagnetic support 1.
The height of the granular protrusions is preferably 5 to 50 nm, and the density of the granular protrusions is preferably 1 × 10 ^{6 to} 5 × 10 ⁷ pieces / mm ² .

The magnetic layer 2 can be formed by directly depositing a ferromagnetic metal material on the nonmagnetic support 1 by a so-called physical vapor deposition (PVD) method such as plating, sputtering, or vacuum deposition. That is, the magnetic layer 2 is made of a ferromagnetic metal material. The film thickness of the magnetic layer 2 formed by such a method is preferably 0.01 to 1 μm.
Examples of the ferromagnetic metal material forming the magnetic layer 2 include metals such as Fe, Co, and Ni, Co—Ni alloys, Co—Pt alloys, Co—Pt—Ni alloys, Fe—Co alloys, Fe -Ni alloy, Fe-Co-Ni alloy, Fe-Ni-B alloy, Fe-Co-B alloy, Fe-Co-Ni-B alloy, Co-Cr alloy or Pt, Al The thing containing metals, such as, is applicable.
The ferromagnetic metal thin film includes an in-plane magnetization film and a perpendicular magnetization film. In particular, when a Co—Cr alloy is used, a perpendicular magnetization film is formed.
When forming an in-plane magnetized film, an underlayer made of a low-melting point nonmagnetic material such as Bi, Sb, Pb, Sn, Ga, In, Ge, Si, or Tl is formed in advance on the nonmagnetic support 1. It is preferable to keep it.
When forming the magnetic layer by depositing or sputtering the above various metal magnetic materials from the vertical direction of the nonmagnetic support 1, the orientation of the ferromagnetic metal thin film can be improved by diffusing these low melting point nonmagnetic materials. This eliminates the in-plane isotropy and improves the antimagnetic property.

The protective layer 3 is formed on the magnetic layer 2 by, for example, depositing carbon by chemical vapor deposition (CVD) or the like.
The thickness of the protective layer 3 is preferably 2 to 100 nm, and more preferably 5 to 30 nm. If the film thickness is less than 2 nm, the running durability may not be sufficiently obtained. On the other hand, if the film thickness exceeds 100 nm, sufficient output may not be obtained when performing short wavelength recording due to spacing loss.

A predetermined support reinforcing layer (not shown) may be formed on the main surface opposite to the surface on which the magnetic layer 2 is formed.
The support reinforcing layer is made of, for example, a metal such as Mg, Al, Si, Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Ge, Zr, Nb, Mo, and W, or an alloy or oxide of these metals. It is preferable to form by.
As a forming method, a film forming method such as an evaporation method, a sputtering method, or an ion plating method can be applied, and a film thickness of about 20 to 500 nm is preferable.

The back coat layer 5 can be formed by applying a paint in which a binder resin and a powder component are mixed and dispersed in an organic solvent to a nonmagnetic support.
Here, as the binder resin used for the preparation of the coating material for the back coat, for example, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylate ester- Acrylonitrile copolymer, thermoplastic polyurethane elastomer, vinylidene chloride-acrylonitrile copolymer, butadiene-acrylonitrile copolymer, polyamide resin, polyvinyl butyral, cellulose derivative, polyester resin, phenol resin, epoxy resin, polyurethane curable resin, melamine resin , Alkyd resin, silicone resin, epoxy-polyamide resin, nitrocellulose-melamine resin, mixture of high molecular weight polyester resin and isocyanate prepolymer, methacrylate copolymer and diisocyanate Mixtures of bets prepolymer, mixture of polyester polyol and polyisocyanate, urea formaldehyde resin, mixture of a low molecular weight glycol / high molecular weight diols / triphenylmethane triisocyanate, polyamine resin, and mixtures thereof.
Alternatively, in order to improve the dispersibility of the powder component, a binder resin having a hydrophilic polar group may be used.
On the other hand, examples of the powder component include carbon-based fine powders for imparting conductivity and inorganic pigments added to control surface roughness and improve durability.
Examples of the carbon-based fine particles include furnace carbon, channel carbon, acetylene carbon, thermal carbon, and lamp carbon. Examples of the inorganic pigment include α-FeOOH, α-Fe ₂ O ₃ , Cr ₂ O ₃ , and TiO _2. ZnO, SiO, SiO ₂ , SiO ₂ .2H ₂ O, Al ₂ O ₃ , CaCO ₃ , MgCO ₃ , Sb ₂ O _{3 and the} like.

  Examples of the organic solvent for preparing the coating for the back coat layer include ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone, and ester solvents such as methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, and glycol acetate monoethyl ether. , Glycol ether solvents such as glycol dimethyl ether, glycol monoethyl ether and dioxane, aromatic hydrocarbon solvents such as benzene, toluene and xylene, aliphatic hydrocarbon solvents such as hexane and heptane, methylene chloride, ethylene chloride, tetrachloride General-purpose solvents such as chlorinated hydrocarbon solvents such as carbon, chloroform, ethylene chlorohydrin and dichlorobenzene can be applied.

The back coat layer 5 may be used with a known lubricant.
In this case, a lubricant may be internally added to the backcoat layer, or a lubricant may be deposited on the backcoat layer.
As the lubricant, any conventionally known lubricants such as fatty acids, fatty acid esters, fatty acid amides, metal soaps, aliphatic alcohols, and silicone-based lubricants can be used.

Next, the lubricant layer 4 that is a feature of the present invention will be specifically described.
[First example]
First, as a first example, an ester compound of a perfluoropolyether having a hydroxyl group at a terminal represented by the following general formula (1) and a long-chain carboxylic acid, and a fluoroalkyl dicarboxylic acid represented by the following general formula (6) A magnetic recording medium in which a lubricant containing an acid derivative is held in the outermost layer is produced.
_{R1COOCH 2 Rf1CH 2 OCOR1 ··· (1} )
(In the general formula (1), Rf1 represents a perfluoropolyether chain, and R1 represents a hydrocarbon group or a fluorinated hydrocarbon group.)

  However, in general formula (6), the Rf group can be unsubstituted or substituted, and can be a saturated or unsaturated fluorine-containing hydrocarbon group or hydrocarbon group. In particular, in general formula (7) below, It was confirmed that by specifying the group represented, high lubrication characteristics can be exhibited in the finally obtained magnetic recording medium, and excellent running durability and stability over time in a harsh environment can be realized.

  In General Formula (7), m = 2 to 20 and n = 4 to 18.

An ester compound of a perfluoropolyether having a hydroxyl group at the terminal and a long chain carboxylic acid represented by the general formula (1) can be easily synthesized by the following method.
For example, it can be obtained by reacting perfluoropolyether having a hydroxyl group at a terminal with carboxylic acid chloride using a base as a catalyst.
As the perfluoropolyether having a hydroxyl group at the terminal, those having a hydroxyl group at both terminals are preferable, and examples thereof include HOCH ₂ CF ₂ (OC ₂ F ₄ ) _p (OCF ₂ ) _q OCF ₂ CH ₂ OH and the like.
The perfluoropolyether having a hydroxyl group at the terminal is not limited to this, and p and q in the perfluoropolyether chemical formula each represent an integer of 1 or more.
The molecular weight of the perfluoropolyether having a hydroxyl group at the terminal is not particularly limited, but is preferably about 600 to 5,000 for practical use. If the molecular weight is too large, the effect of the end group as an adsorbing group is diminished, and at the same time, the perfluoropolyether chain becomes larger, so it is difficult to dissolve in existing hydrocarbon solvents. This is because the lubricating effect of the ether chain is lost.
In the perfluoropolyether having a hydroxyl group at the terminal, the perfluoropolyether chain may be partially hydrogenated. That is, a part (50% or less) of fluorine atoms in the perfluoropolyether chain may be substituted with hydrogen atoms. In this case, a partially hydrogenated perfluoropolyether may be used as the perfluoropolyether.

As the carboxylic acid chloride base, either a commercially available product or a synthetic product can be used.
One long-chain carboxylic acid having an arbitrary structure can be applied, and the structure can be selected regardless of whether there is a branched structure, an isomer structure, an alicyclic structure, or an unsaturated bond.
The molecular weight is also arbitrary, but since it becomes difficult to dissolve in a normal hydrocarbon-based organic solvent as the molecular weight decreases, it is preferable that at least the alkyl group has 10 or more carbon atoms.

  The fluoroalkyldicarboxylic acid derivative represented by the general formula (6) can be synthesized by reacting a partially fluorinated alcohol and 1,2,3-propanetricarboxylic acid in an approximately equimolar amount.

  In the general formula (7) representing the Rf group, m and n are preferably m = 2 to 20 and n = 4 to 18, respectively, and more preferably m = 4 to 13, n = 4 to 10 is more preferable.

  Limiting the number of carbon atoms as described above is that when the number of carbon atoms constituting the alkyl group or fluorine-containing alkyl group (the sum of m and n) is not less than the lower limit of the above numerical range, the cohesion between hydrophobic groups is This is because it is effectively exhibited, exhibits a good lubricating action, and improves friction and wear durability. Moreover, the solubility with respect to the solvent of the lubricant consisting of the said carboxylic acid type compound is kept favorable as the carbon number is below the said upper limit.

Furthermore, in the lubricant in this example, the ester compound of a perfluoropolyether having a hydroxyl group at the terminal and a long-chain carboxylic acid shown in the general formula (1), and the fluoroalkyldicarboxylic acid of the general formula (6) When the mixing ratio with the derivative is 10:90 to 90:10 by weight, excellent lubrication characteristics are exhibited, and excellent lubrication characteristics are maintained even when the magnetic recording medium is used for a long time. It was confirmed that a magnetic recording medium having good durability over time and excellent durability could be obtained.
On the other hand, it was confirmed that when the lubricant was prepared in a range out of the above numerical range, the lubricating characteristics deteriorated especially after storage in a harsh environment, and the stability over time deteriorated.

Examples of the method for retaining the lubricant in the outermost layer of the magnetic recording medium include a method of top-coating the surface of the magnetic layer 2 and the surface of the protective layer 3.
The coating amount is preferably from ^{0.05mg / m 2 ~100mg / m 2} , and more preferably ^{0.1mg / m 2 ~50mg / m 2} .
If the coating amount is less than the above numerical range, the effect of lowering the friction coefficient and improving wear resistance and durability cannot be obtained sufficiently. If the coating amount is too large, the sliding member and the sliding part A sharpening phenomenon occurs between the two and the running performance deteriorates.

  Further, in the magnetic recording medium of this example, a rust inhibitor may be used in combination as necessary. As the rust inhibitor, any of those usually used as a rust inhibitor for this type of magnetic recording medium can be used. For example, phenols, naphthols, quinones, nitrogen-containing heterocyclic compounds, oxygen atoms And heterocyclic compounds containing sulfur atoms, and the like.

  By holding the lubricant of this example on the outermost surface on the magnetic layer side, excellent adhesion and lubricity can be maintained even under extremely severe use conditions, and the lubricating effect can be maintained over a long period of time. In addition, excellent running performance and durability of the magnetic recording medium were secured.

[Second example]
As a second example, an ester compound of a perfluoropolyether having a carboxyl group at the terminal represented by the following general formula (2) and a long chain alcohol, and a fluoroalkyldicarboxylic acid derivative represented by the following general formula (6) Thus, a magnetic recording medium in which a lubricant containing the above was held in the outermost layer was produced.
R2OCORf2COOR2 (2)
(However, Rf2 represents a perfluoropolyether chain, and R2 is a hydrocarbon group or a fluorinated hydrocarbon group.)

  However, in general formula (6), the Rf group can be unsubstituted or substituted, and can be a saturated or unsaturated fluorine-containing hydrocarbon group or hydrocarbon group. In particular, in general formula (7) below, It was confirmed that by specifying the group represented, high lubrication characteristics can be exhibited in the finally obtained magnetic recording medium, and excellent running durability and stability over time in a harsh environment can be realized.

  In General Formula (7), m = 2 to 20 and n = 4 to 18.

  The ester compound of a perfluoropolyether having a carboxyl group at the end and a long chain alcohol represented by the general formula (2) is, for example, a perfluoropolyether having a carboxyl group at the end and a predetermined alcohol in the presence of a catalyst. It can obtain by making it react. The molecular weight, the number of carbon atoms, and the like can be the same as in the above [First Example].

  The fluoroalkyldicarboxylic acid derivative represented by the general formula (6) can be synthesized by reacting a partially fluorinated alcohol and 1,2,3-propanetricarboxylic acid in an approximately equimolar amount.

  In the general formula (7) representing the Rf group, m and n are preferably m = 2 to 20 and n = 4 to 18, respectively, and more preferably m = 4 to 13, n = 4 to 10 is more preferable.

  Limiting the number of carbon atoms as described above is that when the number of carbon atoms constituting the alkyl group or fluorine-containing alkyl group (the sum of m and n) is not less than the lower limit of the above numerical range, the cohesion between hydrophobic groups is This is because it is effectively exhibited, exhibits a good lubricating action, and improves friction and wear durability. Moreover, the solubility with respect to the solvent of the lubricant consisting of the said carboxylic acid type compound is kept favorable as the carbon number is below the said upper limit.

Furthermore, in the lubricant in this example, an ester compound of a perfluoropolyether having a carboxyl group at the terminal and a long-chain alcohol shown in the general formula (2), and a fluoroalkyldicarboxylic acid of the general formula (6) When the mixing ratio with the derivative is 10:90 to 90:10 by weight, excellent lubrication characteristics are exhibited, and excellent lubrication characteristics are maintained even when the magnetic recording medium is used for a long time. It was confirmed that a magnetic recording medium having good durability over time and excellent durability could be obtained.
On the other hand, it was confirmed that when the lubricant was prepared in a range out of the above numerical range, the lubricating characteristics deteriorated especially after storage in a harsh environment, and the stability over time deteriorated.

Examples of the method for retaining the lubricant in the outermost layer of the magnetic recording medium include a method of top-coating the surface of the magnetic layer 2 and the surface of the protective layer 3.
The coating amount is preferably from ^{0.05mg / m 2 ~100mg / m 2} , and more preferably ^{0.1mg / m 2 ~50mg / m 2} .
If the coating amount is less than the above numerical range, the effect of lowering the friction coefficient and improving wear resistance and durability cannot be obtained sufficiently. If the coating amount is too large, the sliding member and the sliding part A sharpening phenomenon occurs between the two and the running performance deteriorates.

  Further, in the magnetic recording medium of this example, a rust inhibitor may be used in combination as necessary. As the rust inhibitor, any of those usually used as a rust inhibitor for this type of magnetic recording medium can be used. For example, phenols, naphthols, quinones, nitrogen-containing heterocyclic compounds, oxygen atoms And heterocyclic compounds containing sulfur atoms, and the like.

  By holding the lubricant of this example on the outermost surface on the magnetic layer side, excellent adhesion and lubricity can be maintained even under extremely severe use conditions, and the lubricating effect can be maintained over a long period of time. In addition, excellent running performance and durability of the magnetic recording medium were secured.

[Third example]
In the third example, a bifunctional perfluoropolyether having a carboxyl group at the terminal represented by the following general formula (3) and an amine compound, and a fluoroalkyldicarboxylic acid derivative represented by the following general formula (6): A magnetic recording medium in which the contained lubricant is held in the outermost layer is produced.

  In the general formula (3), Rf3 represents a perfluoropolyether chain, and R3, R4, R5 and R6 are hydrocarbon groups or hydrogen.

  However, in the general formula (6), the Rf group may be unsubstituted or substituted, and may be a saturated or unsaturated fluorine-containing hydrocarbon group or hydrocarbon group. In particular, the following general formula (7) It was confirmed that the magnetic recording medium finally obtained can exhibit high lubrication characteristics and can realize excellent running durability and stability over time.

  In the general formula (3), m = 2 to 20 and n = 4 to 18.

  The compound of the bifunctional perfluoropolyether having a carboxyl group at the terminal and the amine represented by the general formula (3) is obtained, for example, by thermally reacting the bifunctional perfluoropolyether having a carboxyl group at the terminal with an amine. .

The perfluoropolyether having a carboxyl group at the terminal is preferably one having carboxyl groups at both terminals, and examples thereof include HOOCCF ₂ (OC ₂ F ₄ ) _p (OCF ₂ ) _q OCF ₂ COOH.

The perfluoropolyether having a carboxyl group at the terminal is not limited thereto.
In the chemical formula, p and q both represent an integer of 1 or more.
The molecular weight of the perfluoropolyether having a carboxyl group at the terminal is not particularly limited, and is preferably about 600 to 5,000 for practical use.
If the molecular weight is too large, the effect of the end group as an adsorbing group is diminished, and at the same time, the perfluoropolyether chain becomes larger, so that it becomes difficult to dissolve in the existing hydrocarbon solvent. On the other hand, if the molecular weight is too small, the lubricating effect by the perfluoropolyether chain is lost.
In the perfluoropolyether having a carboxylic acid group at the terminal, the perfluoropolyether chain may be partially hydrogenated. That is, a part (50% or less) of fluorine atoms in the perfluoropolyether chain may be substituted with hydrogen atoms.
In this case, a partially hydrogenated perfluoropolyether may be used as the perfluoropolyether.

  The fluoroalkyldicarboxylic acid derivative represented by the general formula (6) can be synthesized by reacting a partially fluorinated alcohol and 1,2,3-propanetricarboxylic acid in an approximately equimolar amount.

In the general formula (7) representing the Rf group, m and n are preferably m = 2 to 20 and n = 4 to 18, respectively, and more preferably m = 4 to 13, n = 4 to 10 is more preferable.
Limiting the number of carbon atoms as described above is that when the number of carbon atoms constituting the alkyl group or fluorine-containing alkyl group (the sum of m and n) is not less than the lower limit of the above numerical range, the cohesion between hydrophobic groups is This is because it is effectively exhibited, exhibits a good lubricating action, and improves friction and wear durability. Moreover, the solubility with respect to the solvent of the lubricant consisting of the said carboxylic acid type compound is kept favorable as the carbon number is below the said upper limit.

Further, in the lubricant in this example, a bifunctional perfluoropolyether having a carboxyl group at the terminal represented by the general formula (3) and an amine compound, and a fluoroalkyldicarboxylic acid represented by the general formula (6) When the mixing ratio with the derivative is 10:90 to 90:10 by weight, excellent lubrication characteristics are exhibited, and excellent lubrication characteristics are maintained even when the magnetic recording medium is used for a long time. It was confirmed that a magnetic recording medium having good durability over time and excellent durability could be obtained.
On the other hand, it was confirmed that when the lubricant was prepared in a range out of the above numerical range, the lubricating characteristics deteriorated especially after storage in a harsh environment, and the stability over time deteriorated.

Examples of the method for retaining the lubricant in the outermost layer of the magnetic recording medium include a method of top-coating the surface of the magnetic layer 2 and the surface of the protective layer 3.
The coating amount is preferably from ^{0.05mg / m 2 ~100mg / m 2} , and more preferably ^{0.1mg / m 2 ~50mg / m 2} .
If the coating amount is less than the above numerical range, the effect of lowering the friction coefficient and improving wear resistance and durability cannot be obtained sufficiently. If the coating amount is too large, the sliding member and the sliding part A sharpening phenomenon occurs between the two and the running performance deteriorates.

  Further, in the magnetic recording medium of this example, a rust inhibitor may be used in combination as necessary. As the rust inhibitor, any of those usually used as a rust inhibitor for this type of magnetic recording medium can be used. For example, phenols, naphthols, quinones, nitrogen-containing heterocyclic compounds, oxygen atoms And heterocyclic compounds containing sulfur atoms, and the like.

  By holding the lubricant of this example on the outermost surface on the magnetic layer side, excellent adhesion and lubricity can be maintained even under extremely severe use conditions, and the lubricating effect can be maintained over a long period of time. In addition, excellent running performance and durability of the magnetic recording medium were secured.

[Fourth example]
In the fourth example, a lubricant containing a perfluoropolyether having a carboxyl group at the terminal represented by the general formula (4) and an amine compound, and a fluoroalkyldicarboxylic acid derivative represented by the general formula (6) Is produced on the outermost layer.

  Rf4 represents a perfluoropolyether chain, and R11, R12, R13 and R14 are hydrocarbon groups or hydrogen.

  However, in general formula (6), the Rf group can be unsubstituted or substituted, and can be a saturated or unsaturated fluorine-containing hydrocarbon group or hydrocarbon group. In particular, in general formula (7) below, It was confirmed that by specifying the group represented, high lubrication characteristics can be exhibited in the finally obtained magnetic recording medium, and excellent running durability and stability over time can be realized.

  In General Formula (7), m = 2 to 20 and n = 4 to 18.

  The general formula (4) is an ester of a perfluoropolyether having a carboxyl group at one end and an amine. About a raw material and a synthesis method, it shall follow the said 3rd example and detailed description is abbreviate | omitted.

  The fluoroalkyldicarboxylic acid derivative represented by the general formula (6) can be synthesized by reacting a partially fluorinated alcohol and 1,2,3-propanetricarboxylic acid in an approximately equimolar amount.

  In the general formula (7) representing the Rf group, m and n are preferably m = 2 to 20 and n = 4 to 18, respectively, and more preferably m = 4 to 13, n = 4 to 10 is more preferable.

  Limiting the number of carbon atoms as described above is that when the number of carbon atoms constituting the alkyl group or fluorine-containing alkyl group (the sum of m and n) is not less than the lower limit of the above numerical range, the cohesion between hydrophobic groups is This is because it is effectively exhibited, exhibits a good lubricating action, and improves friction and wear durability. Moreover, the solubility with respect to the solvent of the lubricant consisting of the said carboxylic acid type compound is kept favorable as the carbon number is below the said upper limit.

Further, in the lubricant in this example, the mixing ratio of the perfluoropolyether having a carboxyl group at the terminal and the amine compound represented by the general formula (4) and the fluoroalkyldicarboxylic acid derivative represented by the general formula (6) Has a weight ratio of 10:90 to 90:10, excellent lubrication characteristics are exhibited, and excellent lubrication characteristics can be maintained even when a magnetic recording medium is used for a long period of time. It was confirmed that a magnetic recording medium having excellent mechanical stability and excellent durability could be obtained.
On the other hand, it was confirmed that when the lubricant was prepared in a range out of the above numerical range, the lubricating characteristics deteriorated especially after storage in a harsh environment, and the stability over time deteriorated.

Examples of the method for retaining the lubricant in the outermost layer of the magnetic recording medium include a method of top-coating the surface of the magnetic layer 2 and the surface of the protective layer 3.
The coating amount is preferably from ^{0.05mg / m 2 ~100mg / m 2} , and more preferably ^{0.1mg / m 2 ~50mg / m 2} .
If the coating amount is less than the above numerical range, the effect of lowering the friction coefficient and improving wear resistance and durability cannot be obtained sufficiently. If the coating amount is too large, the sliding member and the sliding part A sharpening phenomenon occurs between the two and the running performance deteriorates.

  Further, in the magnetic recording medium of this example, a rust inhibitor may be used in combination as necessary. As the rust inhibitor, any of those usually used as a rust inhibitor for this type of magnetic recording medium can be used. For example, phenols, naphthols, quinones, nitrogen-containing heterocyclic compounds, oxygen atoms And heterocyclic compounds containing sulfur atoms, and the like.

  By holding the lubricant of this example on the outermost surface on the magnetic layer side, excellent adhesion and lubricity can be maintained even under extremely severe use conditions, and the lubricating effect can be maintained over a long period of time. In addition, excellent running performance and durability of the magnetic recording medium were secured.

[Fifth example]
In the fifth example, a lubricant containing a perfluoroalkyl alcohol represented by the following general formula (5) and a fluoroalkyldicarboxylic acid derivative represented by the following general formula (6) is held in the outermost layer.
C _j F _{2j + 1} (CH ₂ ) _k OH (5)
(However, j ≧ 4 and k ≧ 0.)

  However, in general formula (6), the Rf group can be unsubstituted or substituted, and can be a saturated or unsaturated fluorine-containing hydrocarbon group or hydrocarbon group. In particular, in general formula (7) below, It was confirmed that by specifying the group represented, high lubrication characteristics can be exhibited in the finally obtained magnetic recording medium, and excellent running durability and stability over time can be realized.

  In General Formula (7), m = 2 to 20 and n = 4 to 18.

The carbon number k of the perfluoroalkyl group (—C _k F _{2k + 1} ) of the general formula (5) is preferably 4 or more, and more preferably 6 or more.

  The fluoroalkyldicarboxylic acid derivative represented by the general formula (6) can be synthesized by reacting a partially fluorinated alcohol and 1,2,3-propanetricarboxylic acid in an approximately equimolar amount.

  In the general formula (7) representing the Rf group, m and n are preferably m = 2 to 20 and n = 4 to 18, respectively, and more preferably m = 4 to 13, n = 4 to 10 is more preferable.

  Limiting the number of carbon atoms as described above is that when the number of carbon atoms constituting the alkyl group or fluorine-containing alkyl group (the sum of m and n) is not less than the lower limit of the above numerical range, the cohesion between hydrophobic groups is This is because it is effectively exhibited, exhibits a good lubricating action, and improves friction and wear durability. Moreover, the solubility with respect to the solvent of the lubricant consisting of the said carboxylic acid type compound is kept favorable as the carbon number is below the said upper limit.

Furthermore, in the lubricant in this example, the mixing ratio of the perfluoroalkyl alcohol represented by the general formula (5) and the fluoroalkyldicarboxylic acid derivative represented by the following general formula (6) is 10:90 by weight. -90: 10, excellent lubrication characteristics are exhibited, excellent lubrication characteristics can be maintained even when a magnetic recording medium is used for a long time, good temporal stability is obtained, and durability It was confirmed that a magnetic recording medium excellent in properties could be obtained.
On the other hand, it was confirmed that when the lubricant was prepared in a range out of the above numerical range, the lubricating characteristics deteriorated especially after storage in a harsh environment, and the stability over time deteriorated.

Examples of the method for retaining the lubricant in the outermost layer of the magnetic recording medium include a method of top-coating the surface of the magnetic layer 2 and the surface of the protective layer 3.
The coating amount is preferably from ^{0.05mg / m 2 ~100mg / m 2} , and more preferably ^{0.1mg / m 2 ~50mg / m 2} .
If the coating amount is less than the above numerical range, the effect of lowering the friction coefficient and improving wear resistance and durability cannot be obtained sufficiently. If the coating amount is too large, the sliding member and the sliding part A sharpening phenomenon occurs between the two and the running performance deteriorates.

  Further, in the magnetic recording medium of this example, a rust inhibitor may be used in combination as necessary. As the rust inhibitor, any of those usually used as a rust inhibitor for this type of magnetic recording medium can be used. For example, phenols, naphthols, quinones, nitrogen-containing heterocyclic compounds, oxygen atoms And heterocyclic compounds containing sulfur atoms, and the like.

  By holding the lubricant of this example on the outermost surface on the magnetic layer side, excellent adhesion and lubricity can be maintained even under extremely severe use conditions, and the lubricating effect can be maintained over a long period of time. In addition, excellent running performance and durability of the magnetic recording medium were secured.

Next, a method for producing the magnetic recording medium of the present invention will be described below.
First, a ferromagnetic metal thin film is formed as the magnetic layer 2 on one main surface of the nonmagnetic support 1 by a vacuum thin film forming technique such as a vacuum deposition method, an ion plating method, or a sputtering method.
Next, the protective layer 3 is formed on the magnetic layer 2 by, for example, a PVD method such as sputtering or a CVD method.
Next, the lubricant layer 4 is formed on the protective layer 3 by top-coating the predetermined lubricant described in [First Example] to [Fifth Example]. The magnetic recording medium 10 is produced by forming the backcoat layer 5 as necessary.

First, a method for forming the magnetic layer 2 will be specifically described.
For example, when the magnetic layer 2 is formed by a vacuum deposition method, the ferromagnetic metal material is evaporated by resistance heating, high-frequency heating, electron beam heating, etc. under a vacuum of 1 × 10 ⁻⁶ to 1 × 10 ⁻² Pa. An evaporated metal (ferromagnetic metal material) is deposited on the magnetic support. In vacuum deposition, oblique deposition is generally used in which the ferromagnetic metal material is obliquely deposited on a nonmagnetic support in order to obtain a high coercive force. Furthermore, in order to obtain a higher coercive force, vacuum deposition may be performed in an oxygen atmosphere.
When a magnetic layer is formed by an ion plating method which is a kind of vacuum deposition, a DC glow discharge or an RF glow discharge is caused in an inert gas atmosphere of 1 × 10 ⁻² to 1 × 10 ⁻¹ Pa, and the discharge is performed. The ferromagnetic metal material is evaporated therein, and the evaporated metal (ferromagnetic metal material) is deposited on the nonmagnetic support.
When a magnetic layer is formed by sputtering, glow discharge is caused in an atmosphere mainly composed of argon gas of 0.1 to 10 Pa, and atoms on the target surface are knocked out by the generated argon gas ions, and then on the nonmagnetic support. This atom is deposited. Specific examples of the sputtering method include direct current bipolar and tripolar sputtering methods, high frequency sputtering methods, and magnetron sputtering methods using magnetron discharge.

Next, a method for forming the protective layer 3 will be described.
For example, when the protective layer 3 is formed by the CVD method, first, a hydrocarbon gas or a mixed gas of a hydrocarbon gas and an inert gas is introduced into a vacuum vessel, and then maintained at a pressure of about 10 to 100 Pa. Then, a protective layer 3 is formed on the magnetic layer 2 by generating a plasma of hydrocarbon gas by discharging in a vacuum vessel.
The discharge type may be either an external electrode type or an internal electrode type, and the discharge frequency can be determined experimentally. Further, by applying a voltage of 0 to -3 kV to the electrode disposed on the nonmagnetic support 1 side on which the magnetic layer 2 is formed, the hardness of the protective layer 3 can be increased and the adhesion can be improved. .
As the hydrocarbon gas used as the material of the protective layer 3, methane, ethane, propane, butane, pentane, hexane, heptane, octane, ethylene, acetylene, propene, butene, pentene, benzene and the like can be used.

  The method for forming the lubricant layer 4 has been described in detail in the above [First Example] to [Fifth Example]. As the back coat layer, a material that has been applied as a conventionally known back layer for a magnetic recording medium can be used, and it can be formed by coating and drying.

Specific examples of the present invention will be described below, but the present invention is not limited to these examples.
[Example A]
The lubricant produced in this example corresponds to the lubricant produced in [First Example] above.
(Sample preparation)
1 Synthesis of ester compound of perfluoropolyether having hydroxyl group at terminal and long chain carboxylic acid of general formula (1) Perfluoropolyether having hydroxyl group at terminal HOCH ₂ CF ₂ (OC ₂ F ₄ ) _p (OCF ₂ ) _Q OCF ₂ CH ₂ OH (molecular weight: 2000, where p and q in the chemical formula each represents an integer of 1 or more) and triethylamine which is twice the molar ratio with this perfluoropolyether and Was dissolved in an organic solvent, and a 2-fold equivalent of stearic acid chloride was further added dropwise to the solution over 30 minutes.
After completion of the dropwise addition, the mixture was stirred for 1 hour and then heated to reflux for 30 minutes.
After cooling, it was washed with distilled water and dilute hydrochloric acid aqueous solution in this order, and again with distilled water until the washing solution became neutral.
Next, the organic solvent was removed, and the resulting compound was purified using silica gel column chromatography to obtain an ester compound. This is referred to as Compound A1.
Next, in the same manner as Compound A1, four types of compounds A2 to A5, which are ester compounds of a perfluoropolyether having a hydroxyl group at the terminal and a long-chain carboxylic acid, were synthesized.
Table 1 below shows Rf1 and R1 in the general formula (1) of the perfluoropolyether having a hydroxyl group at the terminal used for producing each compound.
Moreover, p, q, n in Table 1 represents an integer of 1 or more.

2 Synthesis of fluoroalkyldicarboxylic acid derivative 59.0 g of 11- (perfluorooctyl) undecanol of alcohol containing Rf group and 17.6 g of 1,2,3-propanetricarboxylic acid were mixed in 500 mL of toluene, and 3 The mixture was heated at reflux for a period of time and reacted as follows.
After completion of the reaction, toluene was removed by filtration, and the reaction product was purified by recrystallization.
CF ₃ (CF ₂ ) ₇ (CH ₂ ) ₁₁ OH
+ HOOCCH ₂ CH (COOH) CH ₂ COOH
→ CF ₃ (CF ₂ ) ₇ (CH ₂ ) ₁₁ OCOCH ₂ CH (COOH) CH ₂ COOH
+ H ₂ O
That is, the reaction solution is filtered to separate a solid reaction product from toluene, and the reaction product is dissolved in 500 ml of 2-propanol (IPA) heated to 60 ° C., and then insoluble matter is removed by filtration. The filtrate was collected and concentrated.
This concentrate was dissolved in 500 mL of n-hexane heated to 60 ° C., and then cooled with ice to precipitate the target product as crystals.
The crystals were collected by filtration to obtain a purified target product.
Compounds A6 to A10 corresponding to the general formula (6) were prepared by changing the Rf group.
Table 2 below shows the structures of Rf of compounds A6 to A10.

3 Production of Sample Tape Next, a magnetic tape was produced as a magnetic recording medium.
First, a 7.0 μm-thick polyethylene terephthalate film, which is a non-magnetic support, is coated with Co by an oblique vapor deposition method using the vacuum deposition apparatus described above to form a ferromagnetic metal thin film that becomes a 180 nm thick magnetic layer. Formed.
Next, a carbon protective layer having a thickness of 8 nm serving as a protective layer was formed on the magnetic layer using a magnetron sputtering apparatus.
Next, a 0.5 μm-thick backcoat layer made of carbon and polyutalene resin was formed on the surface opposite to the magnetic layer forming surface of the polyethylene terephthalate film.
Next, on the surface of the carbon protective layer of the nonmagnetic support having the ferromagnetic metal thin film and the carbon protective layer formed on one main surface side and the back coat layer formed on the other main surface side as described above, Each of the compounds shown in 1) and a mixture of the compounds dissolved in a hexane solvent were applied to give a coating amount of 5 mg / m ² to obtain a magnetic recording medium.
Each of these magnetic recording media was cut into a width of 6.35 mm to prepare 17 types of sample tapes of Examples A1 to A13 and Comparative Examples A1 to A4.

4. Evaluation of characteristics Next, characteristics of 17 types of sample tapes of Examples A1 to A13 and Comparative Examples A1 to A4 were evaluated.
Here, durability and running performance were evaluated, and specifically, friction coefficient, still durability, and shuttle durability were evaluated.
The environmental conditions at the time of evaluating these were the conditions that seemed to be the strictest conditions after examination by the present inventors.

(1) Friction coefficient measurement method The friction coefficient was measured by controlling the environmental conditions in the thermostatic chamber to a temperature of 40 ° C. and a humidity of 80% RH, and running each sample tape in the thermostatic bath for 100 passes. The numerical value at the 100th pass of the friction travel was used as the friction coefficient.

(2) Still durability measurement method Still durability was evaluated in a thermostatic bath at -5 ° C, and a commercially available digital video camcorder (manufactured by Sony Corporation, model name: DVC-VX1000) was used. The time until the reproduction output dropped by 3 dB was measured.

(3) Shuttle durability measurement method Shuttle durability is controlled by controlling the environmental conditions in the thermostatic chamber to a temperature of 40 ° C. and a humidity of 20% RH, and a commercially available digital video camcorder (manufactured by Sony Corporation, model name) : DVC-VX1000), each sample tape was run for 100 pass shuttle, and after 100 passes, how much dB the reproduction output dropped from the initial output was evaluated.
These evaluations were performed immediately after the lubricant was applied and after each sample tape was stored for 1 month in an environment of temperature 45 ° C. and humidity 80% RH.
The initial durability and running results immediately after applying the lubricant are shown in Table 4 below, and the durability and running results after storage for 1 month are shown in Table 5 below.

  From the results of Tables 4 and 5 above, a combination of an ester compound of a perfluoropolyether having a hydroxyl group at the terminal of the general formula (1) and a long chain carboxylic acid and a fluoroalkyldicarboxylic acid derivative of the general formula (6) In Examples A1 to A11 using the lubricant contained, the friction coefficient, still durability, and shuttle durability are extremely little deteriorated under various usage conditions such as high temperature and high humidity, high temperature and low humidity, or low temperature. It was found that very good results were obtained.

On the other hand, in Comparative Examples A1 to A4 using only an ester compound of a perfluoropolyether having a hydroxyl group at a terminal and a long-chain carboxylic acid, or only a fluoroalkyldicarboxylic acid derivative, all are high temperature and high humidity, high temperature and low humidity, low temperature, etc. It was found that the friction coefficient, the still durability, and the shuttle durability were greatly deteriorated under various use conditions, and good results could not be obtained.
In particular, it has been found that deterioration related to still durability and shuttle durability after storage for one month becomes large.

  From the above results, the effect of maintaining the initial characteristics even after long-term storage in a harsh environment is exhibited particularly by incorporating the fluoroalkyldicarboxylic acid derivative represented by the general formula (6) into the lubricant. It was confirmed that

  That is, a lubricant containing a combination of an ester compound of a perfluoropolyether having a hydroxyl group at a terminal and a long-chain carboxylic acid and a fluoroalkyldicarboxylic acid derivative is retained in the outermost layer, and under extremely severe use conditions. It is confirmed that the adhesion and lubricity of the magnetic recording medium can be maintained, the lubrication effect can be maintained for a long time, the stable lubrication characteristics can be maintained over time, and the good running performance and durability of the magnetic recording medium can be ensured. It was done.

Further, comparing the results of Examples A1 to A11 with the results of Examples A12 and A13, an ester compound of a perfluoropolyether having a hydroxyl group at the terminal of general formula (1) and a long-chain carboxylic acid, The mixing ratio with the fluoroalkyldicarboxylic acid derivative of the formula (6) is in the range of 10:90 to 90:10 in weight ratio, and in particular, the effect on the lubricating properties over time is remarkably improved. I found out.
That is, it has been found that by selecting a suitable mixing ratio of these and preparing a lubricant, stable lubricating characteristics can be maintained over a long period of time even under harsh usage environments.

[Example B]
The lubricant produced in this example corresponds to the lubricant produced in the above [second example].
(Sample preparation)
1 Synthesis of ester compound of perfluoropolyether having carboxyl group at terminal of general formula (2) and long chain alcohol First, perfluoropolyether having carboxyl group at terminal HOOCCF ₂ (OC ₂ F ₄ ) _m (OCF ₂ ) _j OCF ₂ COOH (molecular weight: 2000, where m and j in the chemical formula each represent an integer of 1 or more) is prepared, and this perfluoropolyether and stearyl alcohol having a molar ratio of twice are equivalent. Were heated to reflux in anhydrous toluene using a small amount of p-toluenesulfonic acid and concentrated sulfuric acid as catalysts. At this time, the reaction was carried out while removing generated water.
After completion of the reaction, toluene was removed, and the resulting compound was purified using silica gel column chromatography to obtain an ester compound. This is referred to as Compound B1.
Next, four types of compounds B2 to B4 of a perfluoropolyether having a carboxyl group at the terminal and a long-chain alcohol were synthesized in the same manner as in the compound B1. Table 6 below shows Rf2 and R2 in the general formula (2).
In Table 6, p, q, and n represent an integer of 1 or more.

2 Synthesis of fluoroalkyldicarboxylic acid derivative of general formula (6) 59.0 g of 11- (perfluorooctyl) undecanol of alcohol containing Rf group, 17.6 g of 1,2,3-propanetricarboxylic acid, The mixture was mixed in 500 mL of toluene, heated at reflux for 3 hours, and reacted as follows.
After completion of the reaction, toluene was removed by filtration, and the reaction product was purified by recrystallization.
CF ₃ (CF ₂ ) ₇ (CH ₂ ) ₁₁ OH
+ HOOCCH ₂ CH (COOH) CH ₂ COOH
→ CF ₃ (CF ₂ ) ₇ (CH ₂ ) ₁₁ OCOCH ₂ CH (COOH) CH ₂ COOH
+ H ₂ O
That is, the reaction solution is filtered to separate a solid reaction product from toluene, and the reaction product is dissolved in 500 ml of 2-propanol (IPA) heated to 60 ° C., and then insoluble matter is removed by filtration. The filtrate was collected and concentrated.
This concentrate was dissolved in 500 mL of n-hexane heated to 60 ° C., and then cooled with ice to precipitate the target product as crystals.
The crystals were collected by filtration to obtain a purified target product.
Compounds R6 to B10 corresponding to the general formula (6) were prepared by changing the Rf group.
Table 7 below shows structures of Rf of compounds B6 to B10.

3 Production of Sample Tape Next, a magnetic tape was produced as a magnetic recording medium.
First, a 7.0 μm-thick polyethylene terephthalate film, which is a non-magnetic support, is coated with Co by an oblique vapor deposition method using the vacuum deposition apparatus described above to form a ferromagnetic metal thin film that becomes a 180 nm thick magnetic layer. Formed.
Next, a carbon protective layer having a thickness of 8 nm serving as a protective layer was formed on the magnetic layer using a magnetron sputtering apparatus.
Next, a 0.5 μm-thick backcoat layer made of carbon and polyutalene resin was formed on the surface opposite to the magnetic layer forming surface of the polyethylene terephthalate film.
Next, on the surface of the carbon protective layer of the nonmagnetic support having the ferromagnetic metal thin film and the carbon protective layer formed on one main surface side and the backcoat layer formed on the other main surface side as described above, Each of the compounds shown in (1) or a mixture of compounds dissolved in a hexane solvent was applied to give a coating amount of 5 mg / m ² to obtain a magnetic recording medium.
Each of these magnetic recording media was cut into a width of 6.35 mm to prepare 17 types of sample tapes of Examples B1 to B13 and Comparative Examples B1 to B4.

4. Evaluation of characteristics Next, characteristics of 17 types of sample tapes of Examples B1 to B13 and Comparative Examples B1 to B4 were evaluated.
Here, durability and running performance were evaluated, and specifically, friction coefficient, still durability, and shuttle durability were evaluated.
The environmental conditions at the time of evaluating these were the conditions that seemed to be the strictest conditions after examination by the present inventors.
The measurement method and the evaluation conditions were the same as in [Example A] above. The initial durability and running results immediately after applying the lubricant are shown in Table 9 below, and the durability and running results after storage for 1 month are shown in Table 10 below.

  From the results of Table 9 and Table 10, the ester compound of a perfluoropolyether having a carboxyl group at the terminal of the general formula (2) and a long-chain alcohol was combined with the fluoroalkyldicarboxylic acid derivative of the general formula (6). In Examples B1 to B11 using the lubricant, the friction coefficient, the still durability, and the shuttle durability are very little deteriorated under various use conditions such as high temperature and high humidity, high temperature and low humidity, or low temperature, which are very good. It turns out that the result is obtained.

On the other hand, in Comparative Examples B1 to B4 using only a ester compound of a perfluoropolyether having a carboxyl group at the terminal and a long-chain alcohol, or a lubricant using only a fluoroalkyldicarboxylic acid derivative, all are hot and humid. It can be seen that the friction coefficient, still durability, and shuttle durability are greatly deteriorated under various use conditions such as high temperature and low humidity or low temperature, and good results cannot be obtained.
In particular, it has been found that deterioration related to still durability and shuttle durability after storage for one month becomes large.

  From the above results, the effect of maintaining the initial characteristics even after long-term storage in a harsh environment is exhibited particularly by incorporating the fluoroalkyldicarboxylic acid derivative represented by the general formula (6) into the lubricant. It was confirmed that

  That is, a lubricant containing a combination of an ester compound of a perfluoropolyether having a carboxyl group at its terminal and a long-chain alcohol and a fluoroalkyldicarboxylic acid derivative is retained in the outermost layer under extremely severe use conditions. It is confirmed that the adhesion and lubricity of the magnetic recording medium can be maintained, the lubrication effect can be maintained for a long time, the stable lubrication characteristics can be maintained over time, and the good running performance and durability of the magnetic recording medium can be ensured. It was done.

Moreover, comparing the results of Examples B1 to B11 with the results of Examples B12 and B13, an ester compound of a perfluoropolyether having a carboxyl group at the terminal of the general formula (2) and a long-chain alcohol; Regarding the mixing ratio with the fluoroalkyldicarboxylic acid derivative of the general formula (6), the effect on the lubricating characteristics over time is remarkably improved by setting the mixing ratio to the weight ratio of 10:90 to 90:10. I found out.
That is, a suitable mixing ratio of an ester compound of a perfluoropolyether having a carboxyl group at the terminal of the general formula (2) and a long-chain alcohol and a fluoroalkyldicarboxylic acid derivative of the general formula (6) is selected. It has been found that by preparing a lubricant, stable lubricating characteristics can be maintained over a long period of time even under severe use environments.

[Example C]
The lubricant produced in this example corresponds to the lubricant produced in the above [third example].
(Sample preparation)
1. Synthesis of a compound of a bifunctional perfluoropolyether having a carboxyl group at the terminal of the general formula (3) and an amine First, a bifunctional perfluoropolyether having a carboxyl group at the terminal HOOCCF ₂ (OC ₂ F ₄ ) _p (OCF ₂ ) _q OCF ₂ COOH (Molecular weight: 4000, where p and q in the chemical formula each represents an integer of 1 or more) 20 g was placed in a round bottom flask, and 3.6 g of octadecylamine was added.
Next, the mixture was heated and dissolved at 50 ° C., sufficiently stirred to be uniform, and then cooled to obtain a perfluoropolyetheramine salt. This is referred to as Compound C1.
Next, in the same manner as the compound C1, four types of compounds C2 to C5 including a bifunctional perfluoropolyether having a carboxyl group at the terminal and an amine were synthesized. Rf3, R3, R4, R5 and R6 of the general formula (3) are shown in Table 11 below.
In Table 11, p, q, and n each represent an integer of 1 or more.

2 Synthesis of fluoroalkyldicarboxylic acid derivative of general formula (6) As alcohol containing Rf group, 11- (perfluorooctyl) undecanol 59.0 g and 1,2,3-propanetricarboxylic acid 17.6 g The mixture was mixed in 500 mL, heated at reflux for 3 hours, and reacted as follows.
After completion of the reaction, toluene was removed by filtration, and the reaction product was purified by recrystallization.
CF ₃ (CF ₂ ) ₇ (CH ₂ ) ₁₁ OH
+ HOOCCH ₂ CH (COOH) CH ₂ COOH
→ CF ₃ (CF ₂ ) ₇ (CH ₂ ) ₁₁ OCOCH ₂ CH (COOH) CH ₂ COOH
+ H ₂ O
That is, the reaction solution is filtered to separate a solid reaction product from toluene, and the reaction product is dissolved in 500 ml of 2-propanol (IPA) heated to 60 ° C., and then insoluble matter is removed by filtration. The filtrate was collected and concentrated.
This concentrate was dissolved in 500 mL of n-hexane heated to 60 ° C., and then cooled with ice to precipitate the target product as crystals.
The crystals were collected by filtration to obtain a purified target product.
By changing the Rf group, compounds C6 to C10 corresponding to the general formula (6) were prepared.
Table 12 below shows the structure of Rf of compounds C6 to C10.

3 Production of Sample Tape Next, a magnetic tape was produced as a magnetic recording medium.
First, a 7.0 μm-thick polyethylene terephthalate film, which is a non-magnetic support, is coated with Co by an oblique vapor deposition method using the vacuum deposition apparatus described above to form a ferromagnetic metal thin film that becomes a 180 nm thick magnetic layer. Formed.
Next, a carbon protective layer having a thickness of 8 nm serving as a protective layer was formed on the magnetic layer using a magnetron sputtering apparatus.
Next, a 0.5 μm-thick backcoat layer made of carbon and polyutalene resin was formed on the surface opposite to the magnetic layer forming surface of the polyethylene terephthalate film.
Next, on the surface of the carbon protective layer of the nonmagnetic support having the ferromagnetic metal thin film and the carbon protective layer formed on one main surface side and the back coat layer formed on the other main surface side as described above, Each of the compounds shown in (1) or a mixture of compounds dissolved in a hexane solvent was applied to give a coating amount of 5 mg / m ² to obtain a magnetic recording medium.
Each of these magnetic recording media was cut into a width of 6.35 mm to prepare 17 types of sample tapes of Examples C1 to C13 and Comparative Examples C1 to C4.

4. Evaluation of characteristics Next, characteristics of 17 types of sample tapes of Examples C1 to C13 and Comparative Examples C1 to C4 were evaluated.
Here, durability and running performance were evaluated, and specifically, friction coefficient, still durability, and shuttle durability were evaluated.
The environmental conditions at the time of evaluating these were the conditions that seemed to be the strictest conditions after examination by the present inventors.
The measurement method and the evaluation conditions were the same as in [Example A] above. The results of initial durability and running performance immediately after applying the lubricant are shown in Table 14 below, and the results of durability and running performance after storage for 1 month are shown in Table 15 below.

  From the results of Tables 14 and 15, a lubricant comprising a combination of a bifunctional perfluoropolyether having a carboxyl group at the terminal of the general formula (3) and an amine compound with a fluoroalkyldicarboxylic acid derivative of the general formula (6) In Examples C1 to C11 using the above, the friction coefficient, the still durability, and the shuttle durability are hardly deteriorated under various use conditions such as high temperature and high humidity, high temperature and low humidity, or low temperature, and very good results are obtained. I found that it was obtained.

On the other hand, in Comparative Examples C1 to C4 in which only a bifunctional perfluoropolyether having a carboxyl group at the terminal and an amine compound or a lubricant using only a fluoroalkyldicarboxylic acid derivative are used, high temperature and high humidity and high temperature and low humidity are used. Alternatively, it was found that the friction coefficient, the still durability, and the shuttle durability were greatly deteriorated under various use conditions such as low temperature, and good results could not be obtained.
In particular, it has been found that deterioration related to still durability and shuttle durability after storage for one month becomes large.

  From the above results, the effect of maintaining the initial characteristics even after long-term storage in a harsh environment is exhibited particularly by incorporating the fluoroalkyldicarboxylic acid derivative represented by the general formula (6) into the lubricant. It was confirmed that

  That is, a lubricant containing a combination of a bifunctional perfluoropolyether having a carboxyl group at the terminal of the general formula (3) and an amine compound and a fluoroalkyldicarboxylic acid derivative of the general formula (6) in the outermost layer. By maintaining it, adhesion and lubricity can be maintained even under extremely severe use conditions, and the lubrication effect can be maintained over a long period of time, and stable lubrication characteristics can be maintained over time. And it was confirmed that durability was ensured.

Further, when the results of Examples C1 to C11 and the results of Examples C12 and C13 are compared, the bifunctional perfluoropolyether having a carboxyl group at the terminal of the general formula (3) and the amine compound, and the general formula Regarding the mixing ratio of (6) with the fluoroalkyldicarboxylic acid derivative, the effect on the lubricating properties over time is particularly improved by setting the weight ratio in the range of 10:90 to 90:10. I found out.
That is, it has been found that by selecting these suitable mixing ratios and preparing the lubricant, stable lubricating characteristics can be maintained over a long period of time even under severe use environments.

Example D
The lubricant produced in this example corresponds to the lubricant produced in the above [fourth example].
(Sample preparation)
1 Synthesis of perfluoropolyether having a carboxyl group at the terminal of general formula (4) and an amine compound First, perfluoropolyether F (CF ₂ CF ₂ CF ₂ O) _m CF ₂ CF ₂ having a carboxyl group at the terminal 20 g of COOH (molecular weight: 1700, where m in the chemical formula represents an integer of 1 or more) was placed in a round bottom flask, and 3.2 g of octadecylamine was added.
Next, the mixture was heated and dissolved at 50 ° C., sufficiently stirred to be uniform, and then cooled to obtain a perfluoropolyetheramine salt. This is referred to as Compound D1.
Next, in the same manner as in the compound D1, four kinds of compounds D2 to D5 of a perfluoropolyether having a carboxyl group at the terminal and an amine were synthesized.
Table 16 below shows Rf4, R11, R12, R13, and R14 of the perfluoropolyether having a carboxyl group at the terminal of the general formula (4) and the amine compound. In Table 16, j, k, and m represent an integer of 1 or more.

2 Synthesis of fluoroalkyldicarboxylic acid derivative of general formula (6) 59.0 g of alcohol 11- (perfluorooctyl) undecanol containing Rf group and 17.6 g of 1,2,3-propanetricarboxylic acid in 500 mL of toluene The mixture was heated at reflux for 3 hours and reacted as follows.
After completion of the reaction, toluene was removed by filtration, and the reaction product was purified by recrystallization.
CF ₃ (CF ₂ ) ₇ (CH ₂ ) ₁₁ OH
+ HOOCCH ₂ CH (COOH) CH ₂ COOH
→ CF ₃ (CF ₂ ) ₇ (CH ₂ ) ₁₁ OCOCH ₂ CH (COOH) CH ₂ COOH
+ H ₂ O
That is, the reaction solution is filtered to separate a solid reaction product from toluene, and the reaction product is dissolved in 500 ml of 2-propanol (IPA) heated to 60 ° C., and then insoluble matter is removed by filtration. The filtrate was collected and concentrated.
This concentrate was dissolved in 500 mL of n-hexane heated to 60 ° C., and then cooled with ice to precipitate the target product as crystals.
The crystals were collected by filtration to obtain a purified target product.
Compounds D6 to D10 corresponding to the general formula (6) were prepared by changing the Rf group.
Table 17 below shows the structures of Rf of compounds D6 to D10.

3 Production of Sample Tape Next, a magnetic tape was produced as a magnetic recording medium.
First, a 7.0 μm-thick polyethylene terephthalate film, which is a non-magnetic support, is coated with Co by an oblique vapor deposition method using the vacuum deposition apparatus described above to form a ferromagnetic metal thin film that becomes a 180 nm thick magnetic layer. Formed.
Next, a carbon protective layer having a thickness of 8 nm serving as a protective layer was formed on the magnetic layer using a magnetron sputtering apparatus.
Next, a 0.5 μm-thick backcoat layer made of carbon and polyutalene resin was formed on the surface opposite to the magnetic layer forming surface of the polyethylene terephthalate film.
Next, on the surface of the carbon protective layer of the nonmagnetic support having the ferromagnetic metal thin film and the carbon protective layer formed on one main surface side and the backcoat layer formed on the other main surface side as described above, Each of the compounds shown in (1) or a mixture of compounds dissolved in a hexane solvent was applied to give a coating amount of 5 mg / m ² to obtain a magnetic recording medium.
Each of these magnetic recording media was cut into a width of 6.35 mm, and 17 types of sample tapes of Examples D1 to D13 and Comparative Examples D1 to D4 were produced.

4. Evaluation of characteristics Next, characteristics of 17 types of sample tapes of Examples D1 to D13 and Comparative Examples D1 to D4 were evaluated.
Here, durability and running performance were evaluated, and specifically, friction coefficient, still durability, and shuttle durability were evaluated.
The environmental conditions at the time of evaluating these were the conditions that seemed to be the strictest conditions after examination by the present inventors.
The measurement method and the evaluation conditions were the same as in [Example A] above. The results of initial durability and running performance immediately after applying the lubricant are shown in Table 19 below, and the results of durability and running performance after storage for 1 month are shown in Table 20 below.

  From the results of Table 19 and Table 20, a lubricant in which a perfluoropolyether having a carboxyl group at the end of the general formula (4) and an amine compound and a fluoroalkyldicarboxylic acid derivative of the general formula (6) is used is used. In Examples D1 to D11, the friction coefficient, the still durability, and the shuttle durability are hardly deteriorated under various use conditions such as high temperature and high humidity, high temperature and low humidity, or low temperature, and very good results are obtained. I found out that

On the other hand, in Comparative Examples D1 to D4 in which only the perfluoropolyether having a carboxyl group at the terminal and the amine compound or the lubricant using only the fluoroalkyldicarboxylic acid derivative are used, all of them are hot and humid, hot and humid or cold. It was found that the friction coefficient, the still durability, and the shuttle durability were greatly deteriorated under various use conditions such as, and good results could not be obtained.
In particular, it has been found that deterioration related to still durability and shuttle durability after storage for one month becomes large.

  From the above results, the effect of maintaining the initial characteristics even after long-term storage in a harsh environment is exhibited particularly by incorporating the fluoroalkyldicarboxylic acid derivative represented by the general formula (6) into the lubricant. It was confirmed that

  That is, a lubricant containing a combination of a perfluoropolyether having a carboxyl group at the terminal of the general formula (4) and an amine and a fluoroalkyldicarboxylic acid derivative of the general formula (6) is retained in the outermost layer. As a result, adhesion and lubricity can be maintained even under extremely severe use conditions, and the lubrication effect can be maintained over a long period of time, and the stable lubrication characteristics can be maintained over time. It was confirmed that the property was secured.

Moreover, when the result of Example D1-D11 and the result of Example D12, D13 are compared, the compound of perfluoropolyether and amine which have a carboxyl group at the terminal of the said General formula (4), and General formula (6) )) With the fluoroalkyldicarboxylic acid derivative, it is found that the effect on the lubricating properties over time is remarkably improved by setting the weight ratio to the range of 10:90 to 90:10. It was.
That is, it has been found that by selecting these suitable mixing ratios and preparing the lubricant, stable lubricating characteristics can be maintained over a long period of time even under severe use environments.

Example E
The lubricant produced in this example corresponds to the lubricant produced in the above [fifth example].
(Sample preparation)
1 Preparation of Perfluoroalkyl Alcohol of General Formula (5) A commercially available perfluoroalkyl alcohol was used.
Table 21 below shows five types of perfluoroalkyl alcohols (E1 to E5).

2 Synthesis of fluoroalkyldicarboxylic acid derivative of general formula (6) 59.0 g of alcohol 11- (perfluorooctyl) undecanol having Rf group and 17.6 g of 1,2,3-propanetricarboxylic acid in 500 mL of toluene The mixture was heated at reflux for 3 hours and reacted as follows.
After completion of the reaction, toluene was removed by filtration, and the reaction product was purified by recrystallization.
CF ₃ (CF ₂ ) ₇ (CH ₂ ) ₁₁ OH
+ HOOCCH ₂ CH (COOH) CH ₂ COOH
→ CF ₃ (CF ₂ ) ₇ (CH ₂ ) ₁₁ OCOCH ₂ CH (COOH) CH ₂ COOH
+ H ₂ O
That is, the reaction solution is filtered to separate a solid reaction product from toluene, and the reaction product is dissolved in 500 ml of 2-propanol (IPA) heated to 60 ° C., and then insoluble matter is removed by filtration. The filtrate was collected and concentrated.
This concentrate was dissolved in 500 mL of n-hexane heated to 60 ° C., and then cooled with ice to precipitate the target product as crystals.
The crystals were collected by filtration to obtain a purified target product.
Compounds R6 to E10 corresponding to the general formula (6) were prepared by changing the Rf group.
Table 22 below shows structures of Rf of compounds E6 to E10.

3 Production of Sample Tape Next, a magnetic tape was produced as a magnetic recording medium.
First, a 7.0 μm-thick polyethylene terephthalate film, which is a non-magnetic support, is coated with Co by an oblique vapor deposition method using the vacuum deposition apparatus described above to form a ferromagnetic metal thin film that becomes a 180 nm thick magnetic layer. Formed.
Next, a carbon protective layer having a thickness of 8 nm serving as a protective layer was formed on the magnetic layer using a magnetron sputtering apparatus.
Next, a 0.5 μm-thick backcoat layer made of carbon and polyutalene resin was formed on the surface opposite to the magnetic layer forming surface of the polyethylene terephthalate film.
Next, on the surface of the carbon protective layer of the nonmagnetic support having the ferromagnetic metal thin film and the carbon protective layer formed on one main surface side and the back coat layer formed on the other main surface side as described above, Each of the compounds shown in (1) or a mixture of compounds dissolved in a hexane solvent was applied to give a coating amount of 5 mg / m ² to obtain a magnetic recording medium.
Each of these magnetic recording media was cut into a width of 6.35 mm, and 17 types of sample tapes of Examples E1 to E13 and Comparative Examples E1 to E4 were produced.

4. Evaluation of characteristics Next, characteristics of 17 types of sample tapes of Examples E1 to E13 and Comparative Examples E1 to E4 were evaluated.
Here, durability and running performance were evaluated, and specifically, friction coefficient, still durability, and shuttle durability were evaluated.
The environmental conditions at the time of evaluating these were the conditions that seemed to be the strictest conditions after examination by the present inventors.
The measurement method and the evaluation conditions were the same as in [Example A] above. The results of initial durability and running properties immediately after applying the lubricant are shown in Table 24 below, and the results of durability and running properties after storage for 1 month are shown in Table 25 below.

  From the results of Table 24 and Table 25, in Examples E1 to E11 using a lubricant in which the perfluoroalkyl alcohol of the general formula (5) and the fluoroalkyldicarboxylic acid derivative of the general formula (6) are combined, However, it was found that the friction coefficient, the still durability, and the shuttle durability were hardly deteriorated under various use conditions such as high temperature and high humidity, high temperature and low humidity or low temperature, and very good results were obtained.

On the other hand, in Comparative Examples E1 to E4 using a lubricant using only perfluoroalkyl alcohol or only a fluoroalkyldicarboxylic acid derivative, the coefficient of friction was varied under various usage conditions such as high temperature and high humidity, high temperature and low humidity, or low temperature. As a result, it was found that the deterioration of the still durability and the shuttle durability was large, and good results could not be obtained.
In particular, it has been found that deterioration related to still durability and shuttle durability after storage for one month becomes large.

  From the above results, the effect of maintaining the initial characteristics even after long-term storage in a harsh environment is exhibited particularly by incorporating the fluoroalkyldicarboxylic acid derivative represented by the general formula (6) into the lubricant. It was confirmed that

  That is, the lubricant containing a combination of the perfluoroalkyl alcohol of the general formula (5) and the fluoroalkyldicarboxylic acid derivative of the general formula (6) is retained in the outermost layer, so that even under extremely severe use conditions. It was confirmed that the adhesion and lubricity were maintained, the lubrication effect was maintained for a long time, the stable lubrication characteristics could be maintained over time, and the good running and durability of the magnetic recording medium were ensured. .

Moreover, when the results of Examples E1 to E11 and the results of Examples E12 and E13 were compared, mixing of the perfluoroalkyl alcohol of the general formula (5) with the fluoroalkyldicarboxylic acid derivative of the general formula (6) Regarding the ratio, it has been found that the effect on the lubricating properties over time is remarkably improved by setting the weight ratio in the range of 10:90 to 90:10.
That is, it has been found that by selecting these suitable mixing ratios and preparing the lubricant, stable lubricating characteristics can be maintained over a long period of time even under severe use environments.

1 is a schematic cross-sectional view of an example of a magnetic recording medium of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Nonmagnetic support body, 2 ... Magnetic layer, 3 ... Protective layer, 3 ... Lubricant layer, 5 ... Backcoat layer, 10 ... Magnetic recording medium

Claims (8)

A magnetic recording medium having at least a magnetic layer formed on a nonmagnetic support,
An ester compound of a perfluoropolyether having a hydroxyl group at the terminal represented by the following general formula (1) and a long-chain carboxylic acid;
An ester compound of a perfluoropolyether having a carboxyl group at the terminal represented by the following general formula (2) and a long-chain alcohol;
A compound of a bifunctional perfluoropolyether having a carboxyl group at the terminal and an amine represented by the following general formula (3);
A compound of a perfluoropolyether having a carboxyl group at the terminal and an amine represented by the following general formula (4),
At least one of the perfluoroalkyl alcohols represented by the following general formula (5);
A magnetic recording medium characterized in that a lubricant containing a fluoroalkyldicarboxylic acid derivative represented by the following general formula (6) is held in the outermost layer.
_{R1COOCH 2 Rf1CH 2 OCOR1 ··· (1} )
(In the general formula (1), Rf1 represents a perfluoropolyether chain, and R1 represents a hydrocarbon group or a fluorinated hydrocarbon group.)
R2OCORf2COOR2 (2)
(However, Rf2 represents a perfluoropolyether chain, and R2 is a hydrocarbon group or a fluorinated hydrocarbon group.)

(However, Rf3 represents a perfluoropolyether chain, and R3, R4, R5 and R6 are hydrocarbon groups or hydrogen.)

(However, Rf4 represents a perfluoropolyether chain, and R11, R12, R13 and R14 are hydrocarbon groups or hydrogen.)

C _j F _{2j + 1} (CH ₂ ) _k OH (5)
(However, j ≧ 4 and k ≧ 0.)

(However, in the general formula (6), the Rf group is a group represented by the following general formula (7).)

(In General Formula (7), m = 2 to 20 and n = 4 to 18) An ester compound of a perfluoropolyether having a hydroxyl group at the terminal of the general formula (1) and a long-chain carboxylic acid;
2. The magnetic recording medium according to claim 1, wherein a mixing ratio with the fluoroalkyldicarboxylic acid derivative of the general formula (6) is 10:90 to 90:10 by weight ratio. An ester compound of a perfluoropolyether having a carboxyl group at the terminal of the general formula (2) and a long-chain alcohol;
2. The magnetic recording medium according to claim 1, wherein a mixing ratio with the fluoroalkyldicarboxylic acid derivative of the general formula (6) is 10:90 to 90:10 by weight ratio. A bifunctional perfluoropolyether having a carboxyl group at the terminal of the general formula (3) and an amine compound;
2. The magnetic recording medium according to claim 1, wherein a mixing ratio with the fluoroalkyldicarboxylic acid derivative of the general formula (6) is 10:90 to 90:10 by weight ratio. A perfluoropolyether having a carboxyl group at the terminal represented by the general formula (4) and an amine compound;
2. The magnetic recording medium according to claim 1, wherein a mixing ratio with the fluoroalkyldicarboxylic acid derivative of the general formula (6) is 10:90 to 90:10 by weight ratio. Perfluoroalkyl alcohol represented by the general formula (5);
2. The magnetic recording medium according to claim 1, wherein a mixing ratio with the fluoroalkyldicarboxylic acid derivative of the general formula (6) is 10:90 to 90:10 by weight ratio.   The magnetic recording medium according to claim 1, wherein the magnetic layer is a ferromagnetic metal thin film. The magnetic recording medium according to claim 1, wherein a protective layer made of carbon is formed as an outermost layer on the magnetic layer.

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