JP2006202388A - Magnetic recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic recording medium wherein adhesion properties and lubricity are maintained even under a severe use condition and a lubricant effect is continued for a long time and which has excellent running properties, stability and durability and can exhibit stable lubricant characteristics over time. <P>SOLUTION: The magnetic recording medium 10 is provided, wherein at least a magnetic layer 2 is formed on a non-magnetic support body 1 and a lubricant formed by mixing plurality compounds having specific chemical formulas is retained in 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.
Conventionally, “a magnetic recording medium characterized in that a ferromagnetic metal thin film is formed on a non-magnetic support and a carboxylic acid perfluoroalkyl ester is deposited on the ferromagnetic metal thin film” (for example, (See Patent Document 1.), “A ferromagnetic metal thin film is formed on a nonmagnetic support, and a lubricating layer containing a perfluoroalkylcarboxylic acid ester and a fatty acid ester is deposited on the ferromagnetic metal thin film. Further, “a nonmagnetic support, a magnetic layer formed on the nonmagnetic support, made of a ferromagnetic metal material, and formed on the magnetic layer”. A lubricant layer containing a monoester monocarboxylic acid is formed on the protective film, and is used in a helical scan magnetic recording system using a magnetoresistive read head. Magnetic recording medium "(e.g., see Patent Document 3.) That we have been proposed.
These conventional techniques are said to have an effect that the lubricating effect can be maintained even under conditions from low temperature to normal temperature.

JP-A-62-256218 Japanese Examined Patent Publication No. 7-62904 JP 2002-92858 A

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 excellent running 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 comparatively small, the adsorptivity with the lubricant cannot be ensured sufficiently, and problems such as rapid deterioration of running performance and durability have become prominent when used for a long time.

  In other words, when it is assumed that there is a carbon protective layer, the necessity of studying the chemical structure of the lubricant itself has increased in the future. The adsorptive power to the layer is not yet sufficient, and it has been difficult to maintain a stable lubrication characteristic for a long time when traveling 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. In order to maintain stable magnetic properties even for long-term use of magnetic recording media, which will be required more in the future, and to maintain excellent magnetic properties even when stored for a long time in harsh environments The request was not satisfied.

  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, the carboxylic acid perfluoroalkyl ester represented by the following general formula (1), the following general formula (2): At least one of the perfluoroalkylcarboxylic acid ester shown and the fluorine-containing monoester monocarboxylic acid compound shown in the following general formula (3), and the fluoro shown in the following general formula (4) and general formula (5) Provided is a magnetic recording medium in which a lubricant containing at least one of alkyltricarboxylic acid carboxylic acid derivatives is held in an outermost layer.
R-COO- (CH ₂ ) _j C _k F _{2k + 1} (1)
(In the general formula (1), R is a hydrocarbon group, and j ≧ 0 and k ≧ 4.)
F (CF ₂ ) _a (CH ₂ ) _b COOR ′ (2)
(However, in the general formula (2), a ≧ 0, 25 ≧ a + b ≧ 6, and R ′ is a hydrocarbon group having 9 to 25 carbon atoms.)
_{R1CH (COOR2) CH 2 COOR3 ···} (3)
(In the general formula (3), R1 is an aliphatic alkyl group, an aliphatic alkenyl group or hydrogen, and R2 and R3 are a fluoroalkyl group, a fluoroalkenyl group, a fluoropolyether group or hydrogen.)
R 4 —CH (COOCH (COOH) CH ₂ COOH) CH ₂ COORf (4)
_{R4-CH (COORf) CH 2} COOCH (COOH) CH 2 COOH ··· (5)
(In the general formulas (4) and (5), R 4 is a saturated or unsaturated hydrocarbon group having 6 to 20 carbon atoms, and R f is a group represented by the following general formula (6). )

  In General formula (6), it is m + n = 6-25 and n = 3-9.

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 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, among the carboxylic acid perfluoroalkyl ester represented by the following general formula (1) and the fluoroalkyl tricarboxylic acid carboxylic acid derivatives represented by the following general formula (4) and general formula (5): It is assumed that the lubricant containing at least one of the above is held in the outermost layer.

R-COO- (CH ₂ ) _j C _k F _{2k + 1} (1)
However, in the general formula (1), R is a hydrocarbon group, and j ≧ 0 and k ≧ 4.

R 4 —CH (COOCH (COOH) CH ₂ COOH) CH ₂ COORf (4)
_{R4-CH (COORf) CH 2} COOCH (COOH) CH 2 COOH ··· (5)

However, in the general formulas (4) and (5), R4 is a saturated or unsaturated hydrocarbon group having 6 to 20 carbon atoms.
Rf can be a saturated or unsaturated fluoroalkyl group having 6 to 25 carbon atoms and 4 to 10 carbon atoms of fluorinated alkyl. In particular, Rf can be a group represented by the following general formula (6). By specifying, it was confirmed that the finally obtained magnetic recording medium can exhibit high lubrication characteristics, and can realize excellent running durability and stability over time in a severe environment.

  In General formula (6), it is m + n = 6-25 and n = 3-9.

The hydrocarbon group R in the general formula (1) may be linear or branched, and may be either saturated or unsaturated.
Furthermore, the hydrocarbon group R may be an aryl group or a perfluorohydrocarbon group. 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.

On the other hand, the carbon number k of the perfluoroalkyl group (—C _k F _{2k + 1} ) is preferably 4 or more, more preferably 6 or more.

Carboxylic acid perfluoroalkyl esters can be easily synthesized, for example, by a reaction between the corresponding acid chloride and a fluorine-containing alcohol (the following reaction formula (7)).
RCOCl + C _k F _{2k + 1} (CH ₂ ) _j OH → RCOO (CH ₂ ) _j (C _k F _{2k + 1} ) (7)

The acid chloride can be easily synthesized by chlorinating an aliphatic carboxylic acid with phosphorus pentachloride PCl ₃ or thionyl chloride SOCl ₂ .
In particular, aliphatic carboxylic acids having a small number of carbon atoms can be synthesized by chlorination with thionyl chloride SOCl ₂ .
The reaction formula is as shown in the following formula (8).
RCOOH → (PCl ₅ ) → RCOCl (8)

On the other hand, for the fluorine-containing alcohol C _k F _{2k + 1} (CH ₂ ) _j OH, for example, after chlorinating perfluorocarboxylic acid obtained by the Simmons method or the like in the presence of dimethylformamide (DMF), It can be easily synthesized by reduction.
The reaction formula is shown in the following formula (9).

SOCl ₂
C _k F _{2k + 1} COOH ----> C _k F _{2k + 1} CH ₂ OH (9)
DMF

Alternatively, a perfluoroalcohol _represented by the general formula C _k F _{2k + 1} (CH ₂ ) _j OH is also provided.

  Further, the fluoroalkyltricarboxylic acid derivatives represented by the above (4) and (5) are synthesized as shown in the following formulas (10) and (11), for example.

RCH (COCl) CH ₂ COORf + HOCH (COOH) CH ₂ COOH
→ R—CH (COOCH (COOH) CH ₂ COOH) CH ₂ COORf (10)
RCH (COORf) CH ₂ COCl + HOCH (COOH) CH ₂ COOH
→ R—CH (COORf) CH ₂ COOCH (COOH) CH ₂ COOH (11)

  The fluoroalkyltricarboxylic acid derivative can also be easily synthesized by reacting a partially fluorinated carboxylic acid chloride and malic acid in an approximately equimolar amount.

  The numerical range of m and n in the general formula (6) representing the Rf group is limited as described above because the number of carbon atoms constituting the alkyl group or the fluorine-containing alkyl group is not less than the lower limit of the numerical range. This is because the cohesive force between the hydrophobic groups is effectively exhibited, a good lubricating action is exhibited, and the friction / wear durability is improved. 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, at least one of the carboxylic acid perfluoroalkyl ester of the general formula (1) and the fluoroalkyltricarboxylic acid carboxylic acid derivative represented by the general formulas (4) and (5). When the heel mixing ratio is 10:90 to 90:10 by weight, excellent lubrication characteristics are exhibited, and excellent lubrication characteristics can be maintained even when the magnetic recording medium is used for a long time. Thus, it was confirmed that good temporal stability was obtained and a magnetic recording medium excellent in durability was 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, among the perfluoroalkylcarboxylic acid ester represented by the following general formula (2) and the fluoroalkyltricarboxylic acid carboxylic acid derivatives represented by the following general formula (4) and general formula (5), It is assumed that the lubricant containing at least one is held in the outermost layer.

F (CF ₂ ) _a (CH ₂ ) _b COOR ′ (2)

  However, in the general formula (2), a ≧ 0, 25 ≧ a + b ≧ 6, and R ′ is a hydrocarbon group having 9 to 25 carbon atoms.

R 4 —CH (COOCH (COOH) CH ₂ COOH) CH ₂ COORf (4)
_{R4-CH (COORf) CH 2} COOCH (COOH) CH 2 COOH ··· (5)

However, in the general formulas (4) and (5), R4 is a saturated or unsaturated hydrocarbon group having 6 to 20 carbon atoms.
Rf can be a saturated or unsaturated fluoroalkyl group having 6 to 25 carbon atoms and 4 to 10 carbon atoms of fluorinated alkyl. In particular, Rf can be a group represented by the following general formula (6). By specifying, it was confirmed that the finally obtained magnetic recording medium can exhibit high lubrication characteristics, and can realize excellent running durability and stability over time in a severe environment.

  In General formula (6), it is m + n = 6-25 and n = 3-9.

The perfluoroalkylcarboxylic acid ester of the general formula (2) can be easily synthesized by reacting perfluoroalkylcarboxylic acid with the corresponding alcohol.
In the perfluoroalkyl carboxylic acid ester, the perfluoroalkyl carboxylic acid moiety preferably has 6 or more carbon atoms. When this carbon number is less than 6, the lubricating effect is insufficient.
The same applies to the number of carbon atoms of the hydrocarbon group in the ester portion, and the number of carbon atoms of the hydrocarbon group R ′ in the general formula is preferably 1 to 25 and more preferably 9 to 25. preferable.
This is because if the number of carbon atoms of the hydrocarbon group R ′ is less than 9, the lubricating effect is insufficient, and if it exceeds 25, it is difficult to dissolve in the solvent.
The hydrocarbon group R ′ may be a long-chain alkyl group, or a branched alkyl group or an alkylene chain having a double bond.

  Further, the fluoroalkyltricarboxylic acid derivatives represented by the above (4) and (5) are synthesized as shown in the following formulas (10) and (11), for example.

RCH (COCl) CH ₂ COORf + HOCH (COOH) CH ₂ COOH
→ R—CH (COOCH (COOH) CH ₂ COOH) CH ₂ COORf (10)
RCH (COORf) CH ₂ COCl + HOCH (COOH) CH ₂ COOH
→ R—CH (COORf) CH ₂ COOCH (COOH) CH ₂ COOH (11)

  The fluoroalkyltricarboxylic acid derivative can also be easily synthesized by reacting a partially fluorinated carboxylic acid chloride and malic acid in an approximately equimolar amount.

  The numerical range of m and n in the general formula (6) representing the Rf group is limited as described above because the number of carbon atoms constituting the alkyl group or the fluorine-containing alkyl group is not less than the lower limit of the numerical range. This is because the cohesive force between the hydrophobic groups is effectively exhibited, a good lubricating action is exhibited, and the friction / wear durability is improved. 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, at least one of the perfluoroalkylcarboxylic acid ester of the general formula (2) and the fluoroalkyltricarboxylic acid carboxylic acid derivative represented by the general formulas (4) and (5) When the mixing ratio of 10:90 to 90:10 by weight is used, excellent lubrication characteristics are exhibited, and excellent lubrication characteristics can be maintained even when the magnetic recording medium is used for a long time. It was confirmed that good temporal stability was obtained and a magnetic recording medium having excellent durability was 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]
As a third example, among the fluorine-containing monoester monocarboxylic acid compound represented by the following general formula (3) and the fluoroalkyltricarboxylic acid carboxylic acid derivatives represented by the following general formula (4) and general formula (5) It is assumed that the lubricant containing at least one of the above is held in the outermost layer.

_{R1CH (COOR2) CH 2 COOR3 ···} (3)

  However, in general formula (3), R1 is an aliphatic alkyl group, an aliphatic alkenyl group, or hydrogen, and R2 and R3 are a fluoroalkyl group, a fluoroalkenyl group, a fluoropolyether group, or hydrogen.

R 4 —CH (COOCH (COOH) CH ₂ COOH) CH ₂ COORf (4)
_{R4-CH (COORf) CH 2} COOCH (COOH) CH 2 COOH ··· (5)

However, in the general formulas (4) and (5), R4 is a saturated or unsaturated hydrocarbon group having 6 to 20 carbon atoms.
Rf can be a saturated or unsaturated fluoroalkyl group having 6 to 25 carbon atoms and 4 to 10 carbon atoms of fluorinated alkyl. In particular, Rf can be a group represented by the following general formula (6). By specifying, it was confirmed that the finally obtained magnetic recording medium can exhibit high lubrication characteristics, and can realize excellent running durability and stability over time in a severe environment.

  In General formula (6), it is m + n = 6-25 and n = 3-9.

The carbon number of the fluoroalkyl group, fluoroalkenyl group or fluoropolyether group represented by R2 and R3 of the fluorine-containing monoester monocarboxylic acid compound represented by the general formula (3) is the same as that of the fluoroalkyl group and the fluoroalkenyl group. In the case, it is preferably 6-30, and more preferably 6-21.
Moreover, when it is a fluoro polyether group, it is preferable that the average molecular weight is 1000-6000, More preferably, it is 2000-4000.
By making the carbon number of the fluoroalkyl group or fluoroalkenyl group represented by R2 and R3 6-30, the solubility in the solvent becomes good, and the effect of reducing the friction coefficient, improving the wear characteristics and durability are improved. The effect appears surely.
When the fluoroalkyl group or fluoroalkenyl group represented by R2 and R3 has less than 6 carbon atoms, the alkyl group length is too short, and the effects of lowering frictional properties, improving wear properties and durability do not appear. There is.
On the other hand, when the number of carbon atoms of the fluoroalkyl group or fluoroalkenyl group represented by R2 and R3 exceeds 30, the solubility in a solvent may be reduced, and formation of the uniform lubricant layer 5 may be difficult.
Further, when the average molecular weight of the fluoropolyether group represented by R2 and R3 is 1000 or less, the lubricant is easily peeled off, and the wear characteristics and durability may not be improved. When the average molecular weight is 6000 or more, the head and the lubricating layer are liable to adhere, and the wear characteristics are deteriorated.

  The fluorine-containing monoester monocarboxylic acid compound can be easily synthesized, for example, by a reaction between a corresponding acid anhydride and a fluorine-containing alcohol.

  Further, the fluoroalkyltricarboxylic acid derivatives represented by the above (4) and (5) are synthesized as shown in the following formulas (10) and (11), for example.

RCH (COCl) CH ₂ COORf + HOCH (COOH) CH ₂ COOH
→ R—CH (COOCH (COOH) CH ₂ COOH) CH ₂ COORf (10)
RCH (COORf) CH ₂ COCl + HOCH (COOH) CH ₂ COOH
→ R—CH (COORf) CH ₂ COOCH (COOH) CH ₂ COOH (11)

  The fluoroalkyltricarboxylic acid derivative can also be easily synthesized by reacting a partially fluorinated carboxylic acid chloride and malic acid in an approximately equimolar amount.

  The numerical range of m and n in the general formula (6) representing the Rf group is limited as described above because the number of carbon atoms constituting the alkyl group or the fluorine-containing alkyl group is not less than the lower limit of the numerical range. This is because the cohesive force between the hydrophobic groups is effectively exhibited, a good lubricating action is exhibited, and the friction / wear durability is improved. 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, among the fluorine-containing monoester monocarboxylic acid compound of the general formula (3) and the fluoroalkyltricarboxylic acid carboxylic acid derivatives represented by the general formulas (4) and (5), When the mixing ratio with at least one is 10:90 to 90:10 by weight, excellent lubrication characteristics are exhibited, and excellent lubrication characteristics are obtained even when the magnetic recording medium is used for a long time. It was confirmed that a magnetic recording medium that could be maintained, had good stability over time, and had 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.

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 [Third 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 [Third 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.

  In the above [first example] to [third example], the carboxylic acid perfluoroalkyl ester represented by the general formula (1), the perfluoroalkyl carboxylic acid ester represented by the general formula (2), and At least one of the fluorine-containing monoester monocarboxylic acid compound represented by the general formula (3) and the fluoroalkyltricarboxylic acid carboxylic acid derivative represented by the general formula (4) and the general formula (5). Although the case where the contained lubricant is held in the outermost layer has been described, the present invention is not limited to the above examples, and the compounds of the general formulas (1) to (3) are appropriately mixed, and this and the general formula A lubricant may be prepared by combining (4) and (5) and held in the outermost layer. In this case, excellent adhesion and moisture can be obtained under extremely severe conditions. Sex is maintained long-term lubricating effect can be sustained over a, is exhibited over time to good stability, good running properties and durability was confirmed to be ensured.

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 carboxylic acid perfluoroalkyl ester of general formula (1) First, commercially available 2-perfluorohexylethyl is prepared, and triethylamine having a molar equivalent of 2-perfluorohexylethyl is an organic solvent. In this solution, oleic acid chloride equivalent to twice the molar ratio was further added dropwise over 30 minutes.
After completion of dropping, 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 the compound A1, four types of compounds A2 to A5, which are carboxylic acid perfluoroalkyl esters of the general formula (1), were synthesized. The structure of the compound is shown in Table 1 below.

2 Synthesis of fluoroalkyltricarboxylic acid derivatives of general formulas (4) and (5) Using C ₁₈ H ₃₇ CH (COCl) CH ₂ COO (CH ₂ ) ₂ (CF ₂ ) ₇ CF ₃ , malic acid and To react.
C ₁₈ H ₃₇ CH (COCl) CH ₂ COO (CH ₂ ) ₂ (CF ₂ ) ₇ CF ₃
+ HOCH (COOH) CH ₂ COOH
→ C ₁₈ H ₃₇ CH (COOCH (COOH) CH ₂ COOH) CH ₂ COO (CH ₂ ) ₂ C ₈ F ₁₇
+ HCl

According to the above reaction formula, 42.8 g of C ₁₈ H ₃₇ CH (COCl) CH ₂ COO (CH ₂ ) ₂ (CF ₂ ) ₇ CF ₃ and 6.7 g of malic acid HOCH (COOH) CH ₂ COOH in 500 mL of toluene. The mixture was mixed and heated to reflux for 3 hours.
After completion of the reaction, toluene was removed by filtration, and the reaction product was purified by recrystallization.
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 of general formulas (4) and (5)). This is designated as Compound A6.
Compounds A7 to A10 corresponding to the general formulas (4) and (5) were prepared by changing the Rf group and the R4 group.
Table 2 below shows the structures of the 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 shown in Tables 4 and 5, in Examples A1 to A11 using the lubricant containing a combination of a carboxylic acid perfluoroalkyl ester and a fluoroalkyltricarboxylic acid derivative, all are high temperature and high humidity, high temperature and low humidity. Alternatively, it was found that the friction coefficient, the still durability, and the shuttle durability were hardly deteriorated under various use conditions such as a low temperature, and very good results were obtained.

On the other hand, in Comparative Examples A1 to A4 using only a carboxylic acid perfluoroalkyl ester or only a fluoroalkyltricarboxylic acid derivative, the friction coefficient and the still durability under various use conditions such as high temperature and high humidity, high temperature and low humidity or low temperature. As a result, it was found that 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.

  That is, from the above results, the effect of maintaining the initial characteristics even after long-term storage in a harsh environment by containing the fluoroalkyltricarboxylic acid derivatives represented by the general formulas (4) and (5) in the lubricant. It was confirmed that

  That is, by holding a lubricant containing a combination of a carboxylic acid perfluoroalkyl ester and a fluoroalkyltricarboxylic acid derivative in the outermost layer, adhesion and lubricity can be maintained even under extremely severe conditions, and It was confirmed that the lubrication effect lasted for a long period of time, stable lubrication characteristics could be maintained over time, and good running properties and durability of the magnetic recording medium were ensured.

Further, comparing the results of Examples A1 to A11 with the results of Examples A12 and A13, the carboxylic acid perfluoroalkyl ester of general formula (1) and the fluoroalkyltricarboxylic acid of general formulas (4) and (5) Regarding the mixing ratio with the acid derivative, it has been found that the effect on the lubricating characteristics over time is remarkably improved by setting the mixing ratio to the acid derivative in the range of 10:90 to 90:10.
That is, by selecting a suitable mixing ratio of a carboxylic acid perfluoroalkyl ester and a fluoroalkyltricarboxylic acid derivative and preparing a lubricant, stable lubrication characteristics can be maintained over a long period even in harsh usage environments. I found what I could do.

[Example B]
The lubricant produced in this example corresponds to the lubricant produced in the above [second example].
(Sample preparation)
1 Synthesis of Perfluoroalkyl Carboxylic Acid Ester of General Formula (2) An ester reaction was performed using commercially available oleyl alcohol and perfluorohexanoic acid in toluene and p-toluenesulfonic acid as a catalyst.
After refluxing for 1 hour, water in the solvent was removed over 3 hours, and toluene was further removed using an evaporator under reduced pressure, followed by vacuum distillation to obtain an ester compound. This is referred to as Compound B1.
Next, in the same manner as the compound B1, four types of compounds B2 to B5, which are perfluoroalkylcarboxylic acid esters of the general formula (2), were synthesized.
The structures of compounds B1 to B5 are shown in Table 6 below.

2 Synthesis of fluoroalkyltricarboxylic acid derivatives of general formulas (4) and (5) Using C ₁₈ H ₃₇ CH (COCl) CH ₂ COO (CH ₂ ) ₂ (CF ₂ ) ₇ CF ₃ , malic acid and To react.
C ₁₈ H ₃₇ CH (COCl) CH ₂ COO (CH ₂ ) ₂ (CF ₂ ) ₇ CF ₃
+ HOCH (COOH) CH ₂ COOH
→ C ₁₈ H ₃₇ CH (COOCH (COOH) CH ₂ COOH) CH ₂ COO (CH ₂ ) ₂ C ₈ F ₁₇
+ HCl

According to the above reaction formula, 42.8 g of C ₁₈ H ₃₇ CH (COCl) CH ₂ COO (CH ₂ ) ₂ (CF ₂ ) ₇ CF ₃ and 6.7 g of malic acid HOCH (COOH) CH ₂ COOH in 500 mL of toluene. The mixture was mixed and heated to reflux for 3 hours.
After completion of the reaction, toluene was removed by filtration, and the reaction product was purified by recrystallization.
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 of general formulas (4) and (5)). This is designated as Compound B6.
Compounds R7 to B10 corresponding to the general formulas (4) and (5) were prepared by changing the Rf group and the R4 group.
Table 7 below shows the structures of the 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.

(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 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, in Examples B1 to B11 using a lubricant in which a perfluoroalkyl carboxylic acid ester and a fluoroalkyl tricarboxylic acid derivative are combined, all are various such as high temperature and high humidity, high temperature and low humidity or low temperature. It was found that the friction coefficient, the still durability, and the shuttle durability were extremely little deteriorated under the use conditions, and very good results were obtained.

On the other hand, in Comparative Examples B1 to B4 using a lubricant using only a perfluoroalkylcarboxylic acid ester or only a fluoroalkyltricarboxylic acid derivative, all are under various use conditions such as high temperature and high humidity, high temperature and low humidity or low temperature. It was found that the friction coefficient, still durability, and shuttle durability were greatly deteriorated, 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 by including the fluoroalkyltricarboxylic acid derivatives represented by the general formulas (4) and (5) in the lubricant. It was confirmed that

  That is, by applying the present invention and retaining a lubricant containing a combination of a perfluoroalkyl carboxylic acid ester and a fluoroalkyl tricarboxylic acid derivative in the outermost layer, adhesion and lubrication can be achieved even under extremely severe use conditions. Thus, it was confirmed that the lubrication effect was maintained for a long period of time, the stable lubrication characteristics could be maintained over time, and good running properties and durability of the magnetic recording medium were ensured.

Further, comparing the results of Examples B1 to B11 with the results of Examples B12 and B13, the perfluoroalkylcarboxylic acid ester of the general formula (2) and the fluoroalkyl of the general formulas (4) and (5) Regarding the mixing ratio with the tricarboxylic acid derivative, it has been found that the effect on the lubricating characteristics over time is remarkably improved by setting the mixing ratio to the weight ratio in the range of 10:90 to 90:10.
That is, by preparing a lubricant by selecting a suitable mixing ratio of the perfluoroalkylcarboxylic acid ester of the general formula (2) and the fluoroalkyltricarboxylic acid derivatives of the general formulas (4) and (5), It was found that stable lubrication characteristics can be maintained over a long period of time even under severe usage conditions.

[Example C]
The lubricant produced in this example corresponds to the lubricant produced in the above [third example].
(Sample preparation)
1 Synthesis of fluorine-containing monoester monocarboxylic acid of general formula (3) 37 g of F (CF ₂ ) ₈ (CH ₂ ) ₁₀ OH and 15 g of isooctadecyl succinic anhydride are dissolved in 400 cc of toluene, and concentrated. A catalytic amount of sulfuric acid was added and refluxed for 3 hours.
After cooling, the reaction solution was washed with water, dried by adding magnesium sulfate, and concentrated.
After removing the raw material by column chromatography (silica gel / toluene), the eluent was changed to ethyl acetate, and the target product was collected.
Finally, by concentrating the ethyl acetate solution, 25 g of C ₉ H ₁₉ CH (C ₇ H ₁₅ ) CH ₂ CH (COOC ₁₀ H ₂₀ C ₈ F ₁₇ ) CH ₂ COOC ₁₀ H ₂₀ C ₈ F ₁₇ is obtained. It was.
This is referred to as Compound C1 for convenience.
Next, in the same manner as in the compound C1, four types of compounds C2 to C5, which are fluorine-containing monoester monocarboxylic acids represented by the general formula (3), were synthesized.
The structures of compounds C1 to C5 are shown in Table 11 below.

2 Synthesis of fluoroalkyltricarboxylic acid derivatives of general formulas (4) and (5) Using C ₁₈ H ₃₇ CH (COCl) CH ₂ COO (CH ₂ ) ₂ (CF ₂ ) ₇ CF ₃ , malic acid and To react.
C ₁₈ H ₃₇ CH (COCl) CH ₂ COO (CH ₂ ) ₂ (CF ₂ ) ₇ CF ₃
+ HOCH (COOH) CH ₂ COOH
→ C ₁₈ H ₃₇ CH (COOCH (COOH) CH ₂ COOH) CH ₂ COO (CH ₂ ) ₂ C ₈ F ₁₇
+ HCl

According to the above reaction formula, 42.8 g of C ₁₈ H ₃₇ CH (COCl) CH ₂ COO (CH ₂ ) ₂ (CF ₂ ) ₇ CF ₃ and 6.7 g of malic acid HOCH (COOH) CH ₂ COOH in 500 mL of toluene. The mixture was mixed and heated to reflux for 3 hours.
After completion of the reaction, toluene was removed by filtration, and the reaction product was purified by recrystallization.
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 of general formulas (4) and (5)). This is designated as Compound C6.
Compounds C7 to C10 corresponding to the general formulas (4) and (5) were prepared by changing the Rf group and the R4 group.
Table 12 below shows the structures of the compounds C6 to C10.

3 Production of Sample Tape Next, a magnetic tape was produced as a magnetic recording medium.
First, Co was deposited on a 7.0 μm-thick polyethylene terephthalate film, which is a nonmagnetic support, by an oblique vapor deposition method using a vacuum vapor deposition apparatus to form a ferromagnetic metal thin film serving as a magnetic layer having a thickness of 180 nm. .
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.

(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 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, in Examples C1 to C11 using a lubricant in which a fluorine-containing monoester monocarboxylic acid and a fluoroalkyltricarboxylic acid derivative are combined, 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 extremely little deteriorated under various use conditions, and very good results were obtained.

On the other hand, in Comparative Examples C1 to C4 using a lubricant containing only a fluorine-containing monoester monocarboxylic acid or a lubricant containing only a fluoroalkyltricarboxylic 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 usage 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 by including the fluoroalkyltricarboxylic acid derivatives represented by the general formulas (4) and (5) in the lubricant. It was confirmed that

  That is, by applying the present invention, a lubricant containing a combination of the fluorine-containing monoester monocarboxylic acid represented by the general formula (3) and the fluoroalkyltricarboxylic acid derivative represented by the general formulas (4) and (5) is most suitable. By holding it in the outer layer, 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. It was confirmed that running performance and durability were ensured.

Further, comparing the results of Examples C1 to C11 with the results of Examples C12 and C13, the fluorine-containing monoester monocarboxylic acid of the general formula (3) and the fluoro of the general formulas (4) and (5) It has been found that by setting the mixing ratio with the alkyltricarboxylic acid derivative in the range of 10:90 to 90:10 by weight, the effect on the lubricating characteristics over time is remarkably improved.
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.

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 (6)

A magnetic recording medium having at least a magnetic layer formed on a nonmagnetic support,
Carboxylic acid perfluoroalkyl ester represented by the following general formula (1),
Perfluoroalkylcarboxylic acid ester represented by the following general formula (2),
And at least one of fluorine-containing monoester monocarboxylic acid compounds represented by the following general formula (3):
A magnetic recording medium characterized in that a lubricant containing at least one of the fluoroalkyltricarboxylic acid carboxylic acid derivatives represented by the following general formula (4) and general formula (5) is held in the outermost layer. .
R-COO- (CH ₂ ) _j C _k F _{2k + 1} (1)
(In the general formula (1), R is a hydrocarbon group, and j ≧ 0 and k ≧ 4.)
F (CF ₂ ) _a (CH ₂ ) _b COOR ′ (2)
(However, in the general formula (2), a ≧ 0, 25 ≧ a + b ≧ 6, and R ′ is a hydrocarbon group having 9 to 25 carbon atoms.)
_{R1CH (COOR2) CH 2 COOR3 ···} (3)
(In the general formula (3), R1 is an aliphatic alkyl group, an aliphatic alkenyl group or hydrogen, and R2 and R3 are a fluoroalkyl group, a fluoroalkenyl group, a fluoropolyether group or hydrogen.)
R 4 —CH (COOCH (COOH) CH ₂ COOH) CH ₂ COORf (4)
_{R4-CH (COORf) CH 2} COOCH (COOH) CH 2 COOH ··· (5)
(In the general formulas (4) and (5), R 4 is a saturated or unsaturated hydrocarbon group having 6 to 20 carbon atoms, and R f is a group represented by the following general formula (6). )

(In General Formula (6), m + n = 6 to 25 and n = 3 to 9)   The mixing ratio of the carboxylic acid perfluoroalkyl ester of the general formula (1) and the fluoroalkyltricarboxylic acid carboxylic acid derivative of the general formula (4) and / or the general formula (5) is 10:90 to The magnetic recording medium according to claim 1, wherein the magnetic recording medium is 90:10.   The mixing ratio of the perfluoroalkylcarboxylic acid ester of the general formula (2) and the fluoroalkyltricarboxylic acid carboxylic acid derivative of the general formula (4) and / or the general formula (5) is 10:90 to The magnetic recording medium according to claim 1, wherein the magnetic recording medium is 90:10.   The mixing ratio of the fluorine-containing monoester monocarboxylic acid compound of the general formula (3) to the fluoroalkyltricarboxylic acid carboxylic acid derivative of the general formula (4) and / or the general formula (5) is 10: The magnetic recording medium according to claim 1, wherein the magnetic recording medium is 90 to 90:10.   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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