JPH07201030A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium having high corrosion resistance and durability by disposing an undercoat layer contg. an antioxidant by coating on a nonmagnetic substrate and disposing a top coat layer contg. a compd. represented by a specified formula and perfluoropolyether having polar groups by coating on the undercoat layer. CONSTITUTION:This magnetic recording medium has an undercoat layer on the nonmagnetic substrate, a ferromagnetic metallic thin film as a magnetic layer on the undercoat layer and a top coat layer on the magnetic layer. The undercoat layer is a coating film contg. an antioxidant and the top coat layer is a coating film contg. a compd. represented by the formula and perfluoropolyether having polar groups. In the formula, A is a group selected from among phosphoric acid, phosphonic acid, phosphinic acid, carboxylic acid and esters of them, L is an alkylene, alkenylene or alkynylene and each of R1-R3 is F or a perfluoroalkyl.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium having a ferromagnetic metal thin film.

[0002]

2. Description of the Related Art A magnetic metal thin film type magnetic recording medium in which a ferromagnetic metal thin film is formed on a substrate by a vacuum thin film forming method such as vapor deposition or sputtering is not only high in coercive force and residual magnetic flux density but also magnetic. Since the thickness of the ferromagnetic metal thin film, which is a layer, is extremely thin, recording demagnetization and thickness loss are reduced. Also, the packing density of the magnetic material is increased. Therefore, high density recording becomes possible, and it becomes suitable for short wavelength recording.

As described above, the ferromagnetic metal thin film type magnetic recording medium has excellent characteristics, but the surface properties of the ferromagnetic metal thin film magnetic layer are easily affected by running properties and durability.
Therefore, it has been proposed to improve the surface properties of the magnetic layer by improving the surface properties of the non-magnetic support or substrate to improve the running property and durability (JP-A-60-179).
924). Furthermore, in addition to running performance and durability, with the progress of high-density recording and short-wavelength recording, the influence of surface properties on electromagnetic conversion characteristics cannot be ignored, and running performance, durability and electromagnetic conversion characteristics In order to satisfy both requirements, it has been proposed to provide an undercoat layer formed of an emulsion coating film or the like on a non-magnetic support (JP-A-2-265011).
No. 2, JP-A-2-267718, JP-A-2-26771
No. 9, JP-A-2-267720).

By providing the undercoat layer on the non-magnetic support as described above, electromagnetic conversion characteristics (Y-C / N), still durability, shuttle durability and the like are improved, but Such an undercoat layer alone cannot prevent invasion of moisture or oxygen into the magnetic layer. Therefore, storage stability such as corrosion resistance and durability is insufficient.

[0005]

SUMMARY OF THE INVENTION A main object of the present invention is to provide a magnetic recording medium excellent in storage stability, particularly a magnetic recording medium excellent in corrosion resistance and durability.

[0006]

The above object is achieved by the following items (1) to (8). (1) A magnetic recording medium having an undercoat layer on a nonmagnetic substrate, a ferromagnetic metal thin film magnetic layer on the undercoat layer, and a topcoat layer on the ferromagnetic metal thin film magnetic layer. 2. The magnetic recording medium as described in 1 above, wherein the undercoat layer is a coating film containing an antioxidant, and the topcoat layer is a coating film containing a compound represented by the following chemical formula 2 and perfluoropolyether having a polar group.

[0007]

[Chemical 2]

[In the chemical formula 2, A represents one of a phosphoric acid group, a phosphonic acid group, a phosphinic acid group, a carboxylic acid group and esters thereof. L represents an alkylene group, an alkenylene group or an alkynylene group. R ₁ and R ₂
And R ₃ each represent a fluorine atom or a perfluoroalkyl group. (2) The ratio of the compound to the perfluoropolyether in the topcoat layer, the compound / perfluoropolyether is 0.05 / 1 in weight ratio.
The magnetic recording medium of (1) above, which is ˜1 / 1. (3) The magnetic recording medium according to (1) or (2) above, wherein the thickness of the top coat layer is 10 to 50 A. (4) The magnetic recording medium according to any one of (1) to (3) above, wherein the content of the antioxidant in the undercoat layer is 15 wt% or more. (5) One of the above (1) to (4), wherein the undercoat layer further contains at least one kind of high hardness resin fine particles and ceramic fine particles, and the fine particles are dispersed in a binder. Magnetic recording medium. (6) The average particle size of the fine particles is 40 A or more, and the content of the binder in the undercoat layer is 20 wt.
% Or more and 2.5 to 11 million fine particles / m
The magnetic recording medium according to the above (5), which is contained at an areal density of m ² . (7) The magnetic recording medium according to (6), wherein the thickness of the undercoat layer corresponds to 20 to 50% of the average particle diameter value of the fine particles. (8) The magnetic recording medium according to any one of (1) to (7), wherein the strong magnetic metal thin film contains Co as a main component and is formed by an oblique deposition method.

[0009]

Specific Structure The specific structure of the present invention will be described in detail below.

The magnetic recording medium of the present invention is a so-called metal thin film type magnetic recording medium having a ferromagnetic metal thin film as a magnetic layer, specifically a magnetic tape, having an undercoat layer on a non-magnetic substrate. A ferromagnetic metal thin film magnetic layer is formed on this, and a top coat layer is further formed on this.

In the above, the undercoat layer contains an antioxidant, and the topcoat layer contains a compound represented by Chemical formula 2 (hereinafter, also referred to as "compound of Chemical formula 2") and a polar group-containing par. Fluoropolyether is included.

As described above, by providing the undercoat layer and the topcoat layer so as to sandwich the ferromagnetic metal thin film magnetic layer above and below, it is possible to block moisture and oxygen from above and below the magnetic layer. It is possible to improve corrosion resistance and durability. In contrast,
Only one of the undercoat layer and the topcoat layer has insufficient corrosion resistance. In particular, when the undercoat layer only is provided and the topcoat layer is not provided, in addition to this, the friction characteristics are further deteriorated.

Further, even if the undercoat layer is provided, if the antioxidant is not included, the corrosion resistance becomes insufficient, and further, dropout due to storage increases.
If the anti-oxidation effect is not sufficient, this increase in dropout causes the ferromagnetic metal thin film to oxidize from the surface of the undercoat layer side, so the volume increases in the thickness direction of the thin film and expands, causing abnormalities on the magnetic layer surface. It is considered that this is due to the formation of the protrusion. Then, the abnormal protrusion on the surface of the magnetic layer formed in this manner causes dropout during sliding contact with the magnetic head, or the abnormal protrusion is peeled off,
The peeled portion or peeled material may cause dropout.

Further, even if the top coat layer is provided, if the compound of Chemical formula 2 is not contained, the corrosion resistance becomes insufficient, and the dropout due to storage increases for the same reason as in the case of the undercoat layer. That is, it is considered that the ferromagnetic metal thin film is oxidized from the surface of the topcoat layer side, so that the abnormal protrusion is formed on the surface of the magnetic layer as in the case of the undercoat layer.

Further, if the perfluoropolyether having a polar group is not contained, the friction characteristics are deteriorated.

It should be noted that JP-A-2-265011 describes that a protective layer containing a lubricant, an anticorrosive agent or the like may be formed in order to improve the corrosion resistance and running property of the ferromagnetic metal thin film. Has been done. However, it has not even been suggested to selectively use the compound of Chemical formula 2 and perfluoropolyether as in the present invention.

Next, the undercoat layer of the magnetic recording medium of the present invention will be described.

The undercoat layer contains an antioxidant.
As the antioxidant, a usual antioxidant is used.
Specifically, antioxidants classified as 1) phosphorus-based, 2) phenol-based, 3) amine-based, 4) organic acids, alcohols, ester-based, 5) quinone-based, 6) inorganic acids, inorganic chlorine Agents.

Further, a concrete example will be shown for each series.

1) As the phosphorus-based antioxidant, R of the phosphoric acid ester moiety contains an alkyl group, an alkylphenyl group, other ethylene oxide and propylene oxide, and the R is preferably C 1 to 26, and 1-22 are preferable. As the phosphate ester, mono, di,
Tri-type may be included, which may be rich in mono- or di-components, and tri-type may be cut. The phosphoric acid ester includes NH ₄ type, methacrylate type and acrylate type. Specifically, triphenyl phosphite, trioctadecyl phosphite, tridecyl phosphite,
Phosphorous acid esters such as trilauryl trithiophosphate, triphenyl phosphate, hexamethylphosphoric triamide, butyl phosphate, cetyl phosphate, butoxyethyl phosphate, 2-ethylhexyl phosphate, β-chloroethyl phosphate, butoxyethyl phosphate diethylamine salt , Di (2-
Ethylhexyl) phosphate, ethylene glycol acid phosphate, (2-hydroxyethyl) methacrylate phosphate, butyl hydroxymethacrylate phosphate, capryl hydroxymethacrylate phosphate, myristyl hydroxymethacrylate phosphate, stearyl hydroxymethacrylate phosphate, cetyl hydroxymethacrylate.
Phosphate, butylphenyl hydroxymethacrylate phosphate, amylphenylhydroxymethacrylate phosphate, nonylphenylhydroxymethacrylate phosphate and their acrylate types, other alcohols, and phenyl phosphates such as nonylphenyl, phosphoric acid such as vanadium acid phosphate Esters can be mentioned.

2) As the phenolic antioxidant,
2,6-di-tert-butyl-p-cresol, 2,6-di-tert-butyl-p-phenol, 2,4-di-methyl-
5-tert-butyl-phenol, butylhydroxyanisole, 2,2'-methylenebis (4-methyl-6-tert-butylphenol), 4,4'-butylidenebis (3-
Methyl-6-tert-butylphenol), 4,4'-thiobis (3-methyl-6-tert-butylphenol), tetrakis [methylene-3 (3,5-di-tert-butyl-4-)
Hydroxyphenyl) propionate] methane, 1,
1,3-tris (2-methyl-4-hydroxy-5-tert-butylphenyl) butane, dibutylhydroxytoluene, propyl gallate, nordihydroguaiaretic acid and the like. Radiation-curable types include monoglycol salicylate, 2,5-di-tert-butylhydroquinone, 2,4
-Methacrylate such as dihydroxybenzophenone, 2,4,5-trihydroxybutyrophenone and hydroquinone, and acrylate type.

3) As amine-based antioxidants, phenyl-β-naphthylamine, α-naphthylamine, N,
In addition to N'-di-tert-butyl-p-phenylenediamine, phenothiazine, N, N'-diphenyl-p-phenylenediamine, alkanolamines, phospholipids and the like can be mentioned. Radiation-curable amine-based ones such as dimethylaminoethyl methacrylate and acrylate can be mentioned as radiation-curable types.

4) Examples of the organic acid, alcohol and ester type antioxidants include sorbitol, glycerin, propylene glycol, adipic acid, citric acid and ascorbic acid, which may be radiation-curable.

5) Examples of the quinone type antioxidant include hydroquinone, tocopherol and the like, and of these, radiation curing type may be used.

6) Typical examples of the inorganic acid and inorganic salt antioxidants include phosphoric acid.

Among the above antioxidants, 1) phosphorus-based,
Among 2) phenol type, 3) amine type and 4) organic acid, alcohol and ester type, alcohol type and the like are particularly preferable. Specifically, 1) phosphorus-based triphenyl phosphite, (2
-Hydroxyethyl) methacrylate phosphate,
Myristyl hydroxymethacrylate phosphate,
Stearyl hydroxymethacrylate phosphate,
Triphenyl phosphate, 2) As a phenol type, 2,6-di-tert-butyl-
p-cresol, 2,6-di-tert-butyl-p-phenol, monoglycol salicylate acrylate, 3) phenothiazine, dimethylaminoethyl methacrylate as an amine type, and 4) sorbitol, propylene glycol as an alcohol type. Etc.

Further, among these, 1) phosphorus is
Good affinity with the magnetic layer, such as methyl ethyl ketone,
It is particularly preferable in that it is easily dissolved in a frequently used solvent such as toluene and cyclohexanone and is easy to handle in the manufacturing process.

The content of the antioxidant in the entire undercoat layer is preferably 15 wt% or more, more preferably 20 wt% or more. With such a content, the corrosion resistance is improved. On the other hand, if the content is too small, the present invention becomes ineffective. On the other hand, if the amount is too large, the content of other composition components is lowered, which is not preferable, so the upper limit is usually set to about 60 wt%.

The undercoat layer in the present invention preferably contains at least one of high hardness resin fine particles and ceramic fine particles.

By including such fine particles,
The surface property of the magnetic recording medium can be improved, and the magnetic recording medium can be excellent in running property, durability, and electromagnetic conversion characteristics.

Such fine particles have an average particle size of 4
0A or more, preferably 40 to 500A, more preferably 50 to 400A, and particularly preferably 100 to 350A. When the average particle size becomes small, the friction coefficient of the surface of the magnetic recording medium becomes high, the durability running property deteriorates, and the tape sticks to the running guide or the rotating cylinder during running. The maximum value of the average particle diameter depends on the surface density of the fine particles, the material of the fine particles to be used, the content of the antioxidant and the binder, and the thickness of the undercoat layer, which will be described later. If it becomes too high, the smoothness deteriorates and the electromagnetic conversion characteristics are likely to deteriorate.

These fine particles may be in the form of granules or crushed pieces, and the shape thereof is spherical, hemispherical, elliptical, needle-shaped, spindle-shaped, rod-shaped, plate-shaped, star-shaped or the like. There is no particular limitation as long as it may be in any of the shapes described above, or it may be indefinite. The average particle diameter in the above means the diameter of the fine particles after being mixed with the undercoat layer coating material described below and applied on the non-magnetic support in the thickness direction of the undercoat layer. That is, in general, fine particles having a spherical shape or a star shape have an average maximum particle diameter substantially equal to the average particle diameter. On the other hand, the fine particles having a hemispherical shape, an elliptical shape, a needle shape, a spindle shape, a rod shape, or a plate shape have a major axis and a minor axis, and may also have a thickness. When the major axis length (that is, the maximum particle diameter) of the particles having these shapes is sufficiently larger than the thickness of the undercoat layer, the non-magnetic support surface and the major axis are almost coated by coating on the non-magnetic support. Orient to be parallel. Therefore, in the particles having such a shape, the diameter of the fine particles after coating on the non-magnetic support in the thickness direction of the undercoat layer differs depending on the shape of the fine particles, but it means the minor axis length or thickness. . In such a case, the major axis length (maximum particle size) is not particularly limited, but is usually about 10 times or less the minor axis length or the thickness.

As the material of the fine particles used in the present invention, ceramics and high hardness resin are preferable as described above.
Of these, preferred ceramics have a hardness of 1000 kg / mm ² when expressed by Vickers hardness.
That's about it. Specific examples of preferable ceramics include alumina, silica, zirconia, magnesia, boron nitride and titanium nitride.

The high-hardness resin has a Tg higher than room temperature, is water-insoluble, has a weight average molecular weight Mw of about 100,000 to 300,000, and has a ratio of the weight average molecular weight Mw to the number average molecular weight Mn, Mw. / Mn = 3 or less, particle size distribution ±
It is preferably about 10%. Further, it is preferable that impurities such as a polymerization initiator contained in such a high hardness resin are 5 wt% or less.

Specific examples of preferable materials for the high hardness resin include acrylic resin, carbonate resin,
Among the styrene-based resins, ABS (acrylonitrile-butadiene-styrene) resins, divinylbenzene-based resins and phenol-based resins, those satisfying the above conditions can be mentioned.

Among these fine particles, silica, alumina, acrylic resin, carbonate resin and the like are particularly preferable because they are easy to handle, can easily obtain particles having a narrow particle size distribution, and are inexpensive and suitable for mass production.

Usually, only one kind of these fine particles is used.
You may use 2 or more types together.

The content of such fine particles may be determined by the surface density (particles / mm ² ) in the undercoat layer. The surface density of fine particles is 250 to 11 million /
mm ² , preferably 4 to 7 million pieces / mm ² , and more preferably 550 to 6.5 million pieces / mm ² . If the surface density of the fine particles becomes too low or too high, the coefficient of friction will increase and the durability running performance will decrease. The surface density of the fine particles may be measured with a scanning electron microscope (SEM).

The specific amount of the fine particles to be added to the undercoat layer coating material is determined by preparing a coating material in which the amount of the fine particles to be added is changed and obtaining the relationship between the addition amount and the areal density in advance. It can be determined experimentally.

The undercoat layer contains an antioxidant,
Although the above fine particles are dispersed in a binder, preferably a resin binder, the resin binder used at this time may be any of a thermoplastic resin, a thermosetting resin and a radiation curable resin, or a mixture thereof.

Examples of the thermoplastic resin include polyester resins such as polyethylene glycol terephthalate, acrylic acid ester-acrylonitrile copolymers, methacrylic acid ester-ethylene copolymers, polyamide resins, polyvinyl butyral and cellulose derivatives (cellulose acetate). Butyrate, cellulose diacetate, cellulose triacetate, cellulose propionate, nitrocellulose, etc.) and amino resin thermoplastic resins. These may be used alone or in combination of two or more.

Examples of the thermosetting resin include phenol resin, epoxy resin, polyurethane curable resin, urea resin, melamine resin, alkyd resin, silicone resin, acrylic reaction resin, high molecular weight polyester resin and isocyanate prepolymer. Examples thereof include a mixture, a mixture of a methacrylate copolymer and a diisocyanate prepolymer, a urea formaldehyde resin and a polyamine resin. These may be used alone or in combination of two or more.

A cross-linking agent may be used in combination with such a resin, and as the cross-linking agent, various polyisocyanates,
Particularly, diisocyanate can be used, and one or more kinds of tolylene diisocyanate, hexamethylene diisocyanate, and methylene diisocyanate are particularly preferable.
These cross-linking agents are particularly preferably used as a cross-linking agent modified to have a plurality of hydroxyl groups such as trimethylolpropane or an isocyanurate-type cross-linking agent in which 3 molecules of a diisocyanate compound are bonded, and functional groups contained in the resin, etc. To crosslink the resin. The content of the cross-linking agent is preferably 10 to 30 parts by weight with respect to 100 parts by weight of the resin.

To cure such a thermosetting resin, generally 12 to 4 at 50 to 70 ° C. in a heating oven.
It may be heated for 8 hours.

As the radiation curable resin, a resin obtained by curing a radiation curable compound is also suitable. Specific examples of the radiation curable compound include maleic anhydride type, urethane (meth) acryl type, epoxy (meth) acryl type, polyester (meth) acryl type, polyether (meth) acryl type, polyurethane (meth) acryl. Type, unsaturated prepolymers such as polyamide (meth) acrylic type; ether (meth) acrylic type, urethane (meth) acrylic type, epoxy (meth) acrylic type, phosphate ester (meth) acrylic type, aryl type and hydrocarbon type And other polyfunctional monomers. These may be used alone or in combination of two or more. In the case of radiation curing, the dose of radiation is preferably 1 M to 5 M Rad in terms of this dose, since electron beam (EB) is usually used as the radiation.

Among these resins, it is preferable to mix a thermoplastic resin and a thermosetting resin such as a polyester resin such as polyethylene glycol terephthalate and an epoxy resin, and the mixing ratio is thermoplastic resin / thermosetting resin. The curable resin is preferably in the range of 3/1 to 1/1. When the resin thus mixed is used, a curing treatment may be performed in order to maintain appropriate flexibility of the undercoat layer. Control is performed under the condition that the non-magnetic support does not curl using any of the above resins.

The content of the resin binder as described above is preferably 20 wt% or more of the undercoat layer, and more preferably 25 wt% or more. With such a content, the bondability of each component in the undercoat layer is improved. The optimum content of the binder may be determined from the specific gravity of the fine particles used. When the content of the binder is small, the effect of fixing the fine particles and the antioxidant decreases, which causes the particles, the antioxidant, and the magnetic layer to be lost due to running, and the dropout increases. Also,
If the content is too large, the content of other composition components contained in the undercoat layer is reduced, and the effects of those components are reduced. Therefore, the upper limit of the content is usually about 60 wt% or less of the undercoat layer.

The undercoat layer in the present invention is formed by using a coating material in which a predetermined amount of an antioxidant, preferably the above-mentioned fine particles, and a resin binder, if necessary, is contained in a predetermined amount of solvent.

The solvent used in this case is not particularly limited and may be appropriately selected in consideration of the solubility and compatibility of the binder and other composition components. For example, acetone, methyl ethyl ketone, methyl isobutyl ketone, ketones such as cyclohexanone, aromatic hydrocarbons such as toluene, xylene, ethylbenzene, esters such as ethyl formate, ethyl acetate, butyl acetate, methanol, ethanol, isopropanol, butanol, etc. Alcohols, ethers such as isopropyl ether, ethyl ether and dioxane, furans such as tetrahydrofuran and furfural, and diluents and solvents such as dimethylformamide and vinylpyrrolidone. These solvents may be used as a single solvent or a mixed solvent thereof. Further, the content of the solvent in the undercoat layer and the mixing ratio of the solvent are not particularly limited, and may be appropriately determined in consideration of the composition of the coating material, the preparation method or the coating method, and the like, these composition components and the solvent, etc. There is also no particular limitation on the method of mixing.

The coating method for forming a coating film using the above-mentioned coating material is not particularly limited and may be gravure coating, reverse coating, die nozzle coating, etc., but the surface after drying In consideration of smoothness, reverse coating, die nozzle coating and the like are preferable.

After forming a coating film using the above-mentioned coating material, in the case of a thermosetting resin, it may be thermally cured under the same conditions as described above, and in the case of a radiation curable resin, under the same conditions as above. It can be radiation-cured.

The thickness of the undercoat layer after curing and drying is
It is 20 to 50%, preferably 35 to 45% of the average particle diameter value of the fine particles used. By keeping the relationship between the thickness of the undercoat layer and the average particle diameter of the fine particles as described above,
Due to the fine particles, excellent surface properties of the magnetic layer are obtained, and excellent electromagnetic conversion characteristics and durability running properties are obtained. When the undercoat layer is too thick, the added fine particles are embedded in the undercoat layer in many portions, and the effect of improving the durability and running property cannot be obtained. On the other hand, if it is too thin, the Rmax value becomes too large, the surface properties of the magnetic layer deteriorate, the electromagnetic conversion characteristics deteriorate, and the content of the antioxidant decreases, so that the antioxidant effect on the magnetic layer decreases. Storability decreases.
Further, regardless of the average particle diameter of the fine particles used, if the undercoat layer is too thick, the non-magnetic support tends to curl due to the drying treatment after coating, which becomes an obstacle during the formation of the ferromagnetic metal thin film layer. The thickness is usually 200 A or less, preferably 150 A or less, because it is easy and the thickness of the magnetic recording medium becomes too thick.

The surface roughness after curing and drying of the undercoat layer is represented by Rmax according to JIS B 0601 and is 20.
It is preferably 0 to 500 A, more preferably 250 to 450 A. By providing the undercoat layer having such Rmax, excellent running properties and electromagnetic conversion characteristics can be obtained. If Rmax is too large, the electromagnetic conversion characteristics are likely to deteriorate, and if it is too small, the friction coefficient is high and the durability running property is likely to be deteriorated.

Next, the top coat layer will be described.

The top coat layer in the present invention contains the compound of Chemical formula 2 and a perfluoropolyether having a polar group.

The compound of Chemical formula 2 will be described. In formula 2, A is a phosphate group (-PO ₄ H _2), phosphonic acid groups (-
PO ₃ H ₂ ), phosphinic acid group (-PO ₂ H ₂ ), carboxylic acid group (-COOH) and their esters [-P
_{O 4 H (R), -} PO 4 (R) 2, -PO 3 H (R),
_{-PO 3 (R) 2, -PO} 2 H (R), - PO 2 (R)
₂ , -COOR; wherein R represents an alkyl group (methyl, ethyl, etc.). ] Is represented. Above all,
It is preferably one of a phosphoric acid group, a phosphonic acid group, a phosphinic acid group, a carboxylic acid group, and a methyl or ethyl monoester thereof.

L represents an alkylene group, an alkenylene group or an alkynylene group, which may be substituted with a fluorine atom or the like. The alkylene group, alkenylene group, and alkynylene group have 1 to 4 carbon atoms, and preferably have a straight chain structure. Specifically, -CH ₂ -, - CH _{2
-CH 2 -, - (CH 2} ) 3 -, - CH = CH -, - C
≡C- and the like can be mentioned as preferable ones.

R ₁ , R ₂ and R ₃ each represent a fluorine atom or a perfluoroalkyl group. The perfluoroalkyl group represented by R ₁ may be linear or branched and preferably has 1 to 3 carbon atoms, and specifically includes —CF _{3 and the} like. R ₁ is preferably —F, —CF ₃ or the like. The perfluoroalkyl group represented by R ₂ or R ₃ may be linear or branched and is preferably one having 1 to 5 carbon atoms, specifically —CF ₃ , — C ₂ F _5, -C
_{F (CF 3) 2, -C} (CF 3) 3 and the like are preferable. R
₂ and R ₃ include -F, -CF ₃ , -C ₂ F ₅ , and -C.
_{F (CF 3) 2, -C} (CF 3) 3 and the like are preferable, and _{-C 2 F 5, -CF (CF} 3) 2, -C (CF 3) 3 and the like are preferable. R ₂ and R ₃ are usually the same but may be different.

Specific examples of the compound of Chemical formula 2 are shown below. In the table, combinations of A, L and R _{1 to} R ₃ in Chemical formula 2 are shown.

[0060]

[Table 1]

The compounds of formula 2 may be used alone or in combination of two or more kinds.

In the compound of Chemical formula 2, the phosphoric acid group, which is a polar group, represented by A in the top coat layer is located on the side of the ferromagnetic metal thin film magnetic layer to enhance the adhesiveness to the magnetic layer.
On the other hand, it is considered that the fluorine-containing groups represented by R _{1 to} R ₃ are located on the surface side and block water or the like entering from the outside. Therefore, by using the compound of Chemical formula 2 in the top coat layer, the effect of significantly improving the corrosion resistance can be obtained.
Such an effect is obtained only by using the compound of Chemical formula 2, and is not obtained by using an ordinary rust preventive agent.

The perfluoropolyether having a polar group which is used in the top coat layer together with the compound of Chemical formula 2 is
It has a hydroxy group, an ester group, a carboxy group, etc. as a polar group, and a hydroxy group, an ester group, etc. are particularly preferable as the polar group, and those having a number average molecular weight of 3000 to 5000 are preferable. In this case, the polar group exists as a terminal group in the polymer, but in a linear polymer, for example,
The polar group may be present at both ends or one end. As this product, a commercially available product may be used as it is, for example, AM2001, Z-DOL (manufactured by Montedison),
SA1 and SY3 (manufactured by Daikin Industries, Ltd.) are trade names. Even if only one such compound is used, 2
You may use together 1 or more types.

The compound of formula 2 and the perfluoropolyether having a polar group in the top coat layer have a weight ratio of the compound of formula 2 / perfluoropolyether having a polar group of about 0.05 / 1 to 1/1. Should be

By using the compound of Chemical formula 2 and the perfluoropolyether having a polar group as described above, the corrosion resistance and the friction characteristics can be improved. Also,
There is no increase in dropout due to saving. In contrast,
If the amount of the compound of Chemical formula 2 is too small or the amount of the perfluoropolyether is too large, the corrosion resistance becomes insufficient and the dropout due to storage tends to increase. Further, if the amount of the compound of Chemical formula 2 is too large or the amount of the perfluoropolyether is too small, sticking during running may occur or high friction may be caused, so that the running property and the friction characteristics are likely to be deteriorated.

The top coat layer preferably contains only the compound of Chemical formula 2 and perfluoropolyether having a polar group, but in addition to this, the top coat layer contains a non-polar perfluoropolyether or a long-chain carboxyl group. An acid etc. may be contained.

Such a top coat layer is formed by using a coating material in which a predetermined amount of the compound of Chemical formula 2 and perfluoropolyether having a polar group are contained in a predetermined amount of solvent.

As the solvent used in this case, a fluorine-based solvent or a mixed solvent containing the fluorine-based solvent as a main component (fluorine-based solvent 60 vol% or more) is preferable. As a fluorine-based solvent, E-90 (manufactured by Montesozin) or EFL
-150 (manufactured by Daikin Industries, Ltd.) and the like can be used.

The total content of the compound of Chemical formula 2 and the perfluoropolyether having a polar group in such a coating material for a top coat layer is 0.1 to 1 wt% with respect to the total amount of the solvent,
Further, it is preferable to set it to 0.2 to 0.5 wt%. By using such a solvent amount, it becomes easy to control the film thickness of the coating film, and a good coating film can be formed.

The coating method for forming the coating film is not particularly limited and may be any of gravure coating, reverse coating, die nozzle coating and the like.

After forming the coating film of the top coat layer, it is dried.

The thickness of the top coat layer is preferably 10 to 50A. With such a thickness, corrosion resistance is improved, and friction characteristics and durability are also improved. On the other hand, if the top coat layer is too thin, the effect of the present invention cannot be obtained, and if it is too thick, improvement of the effect cannot be expected and the problem of spacing loss tends to occur.

In the present invention, the ferromagnetic metal thin film magnetic layer formed on the undercoat layer is composed of Co or an alloy containing Co as a main component. As an alloy containing Co as a main component, Co-Ni, Co-Fe, Co-Cr, Co
-Ni-Cr, Co-Pt, Co-Ta-Cr, etc. are mentioned. In particular, a Co-Ni alloy containing Ni is preferable, and in particular, the molar ratio of Co is about 80% or more, and N is
An alloy containing i of 20% or less is preferable. If necessary, Cr may be contained in an amount of 10% or less, and various metals described in JP-A-63-10315 and other metal components may be contained.

Such a ferromagnetic metal thin film is formed by a vacuum thin film forming method. Among them, the vapor deposition method is preferable, and the oblique vapor deposition method is particularly preferable.

The oblique vapor deposition method is, for example, one or more stationary metal sources in which a non-magnetic substrate having a long film-shaped undercoat layer fed from a supply roll is fed along the surface of a rotating cooling drum. Is obliquely vapor-deposited and wound on a winding roll. When forming an alloy thin film, a metal source of an alloy may be used if the metal has a close melting point, and multi-source vapor deposition using a plurality of metal sources may be used for a material having a different melting point.

At this time, when the angle between the incident angle of the ferromagnetic metal component during film formation and the normal to the substrate is θ, θ changes, and vapor deposition is carried out within the range from the initial θmax to the final θmin. .
Further, θmax during the deposition of the ferromagnetic thin film is preferably 80 to 90 degrees, and θmin is preferably 10 to 60 degrees. Furthermore, it is preferable to form the film so that the easy axis of magnetization is in the direction of 30 degrees with respect to the non-magnetic support.

The incident angle of the vapor-deposited metal particles is θmax at the initial stage of vapor deposition.
To a final θ min, the columnar crystal grains of ferromagnetic metal, preferably containing Co as a main component, are grown in an arcuate direction on the surface of the undercoat layer on the non-magnetic substrate.
To align. When the magnetic layer has a multilayer structure, this step is repeated.

The magnetic layer may have a single ferromagnetic metal thin film or may have a multilayer structure of two or more layers.

Further, if necessary, a small amount of oxygen may be contained in the surface layer of each layer, or a non-magnetic layer may be interposed to improve the corrosion resistance and the like.

In particular, oxygen is contained in the surface layer (hereinafter referred to as "surface layer") of the ferromagnetic metal thin film, which is the uppermost layer of the magnetic layer, and the metal oxide constituting this thin film is contained. Is preferred. This makes the magnetic layer less likely to be oxidized. The surface layer containing such an oxide may be formed by controlling the oxygen partial pressure of the atmosphere during vapor deposition, and the thickness of the surface layer is preferably about 50 to 210 A from the surface. The average oxygen content in this surface layer is 40 to 70 at% in terms of magnetic properties and strength.
It is preferable that the content of the metal oxide is approximately, and the contained metal oxide does not necessarily have to satisfy the stoichiometric relationship.
If the oxygen content decreases, the oxidation resistance becomes insufficient,
This leads to a decrease in strength. On the other hand, if the amount is too large, the magnetic properties tend to deteriorate.

Such surface analysis may be performed by Auger spectroscopy or the like.

The total thickness of the magnetic layer is 1200 to 3000.
It is preferably about A. At this time, the balance between the output and the C / N is improved. If it is too thin, the output tends to decrease, and if it is too thick, the noise component increases and C / N tends to decrease.

In addition, the ferromagnetic metal thin film magnetic layer may be formed by a sputtering method, an ion plating method, or the like. In the sputtering method, a metal (including alloy) thin film is formed by discharging in an Ar atmosphere at a pressure of about 10 ⁻³ Torr. The ion plating method is basically the same as the vapor deposition method, and the evaporated metal or multi-component of metal is RF
A metal thin film is formed on the undercoat layer of the non-magnetic substrate which is ionized at a high frequency such as (radio wave) and biased. At this time, normally, a bias cannot be applied on the insulator, but it is possible to generate a bias potential by applying an alternating bias.

The material of the non-magnetic substrate used in the present invention is not particularly limited, and various films such as polyethylene terephthalate (PET), which can withstand the heat of forming the ferromagnetic metal thin film,
Various resins such as polyesters such as polyethylene naphthalate (PEN), polyimide, aramid, polysulfone and polyether ether ketone (PEEK) can be used.

In the present invention, it is preferable to form a back coat layer on the surface of the non-magnetic substrate opposite to the side surface on which the magnetic layer is formed. The composition of the back coat layer is not particularly limited, but may be the same as that of the undercoat layer.

The thickness of the back coat layer is 25 to 2000A.
The degree. By providing such a back coat layer, running stability can be obtained.

In addition, the present invention aims to improve the adhesion between the non-magnetic support and the magnetic layer, if necessary, between the non-magnetic support and the magnetic layer in addition to the undercoat layer. You may add the structure of a base layer and another intermediate layer. Before forming the undercoat layer, the undercoat layer-forming surface of the non-magnetic support may be subjected to glow treatment using, for example, argon Ar or oxygen O _2, or pretreatment such as corona treatment. The same treatment may be applied to the surface of the undercoat layer before forming the ferromagnetic metal thin film layer.

[0088]

EXAMPLES The present invention will be described in more detail below by showing specific examples of the present invention.

Example 1 (1) A coating material for the undercoat layer having the following composition was prepared.

Undercoat layer coating material No. 1 polyethylene glycol terephthalate 0.2 parts by weight epoxy resin 0.1 parts by weight fine particles (silica: spherical: average particle size 250A) 0.2 parts by weight cyclohexanone / methyl ethyl ketone (weight ratio 1 /
1) 100 parts by weight of mixed solvent

Undercoat layer coating material No. 2 Undercoat layer coating material No. 1 was prepared in the same manner except that triphenyl phosphite was added as an antioxidant so as to correspond to 10% by weight of the undercoat layer.

Undercoat layer coating materials No. 3 to No. 5 In the undercoat layer coating material No. 2, the amount of triphenyl phosphite was 20 wt% of the undercoat layer, 30 wt% of the undercoat layer, and 30 wt% of the undercoat layer. 40 wt
A coating material for the undercoat layer was prepared in the same manner except that it was changed so as to correspond to each%. These paints are referred to as undercoat layer paints No. 3 to No. 5, respectively.

Undercoat layer coating material Nos. 7 to 17 In the undercoat layer coating material No. 4, the antioxidants were phenothiazine, triphenyl phosphate, myristyl hydroxymethacrylate phosphate, sorbitol, 2,6-di-third. Butylphenol, (2-hydroxyethylmethacrylate), stearylhydroxymethacrylate, monoglycol salicylate acrylate, 2,6-tert-butyl-p-cresol, dimethylaminoethylmethacrylate, propylene glycol A layer coating was prepared. Apply these paints in order to the undercoat layer paint N
o.7 to No. 17 (3 for the undercoat layer)
Addition amount corresponding to 0 wt%).

The above undercoat layer coating material No.
The addition amount of the fine particles in No. 1 to No. 17 is 600 in the area density
The amount was appropriately adjusted so that the amount added would be 10,000 pieces / mm ² .

(2) A top coat layer coating material having the following composition was prepared. Top coat layer coating material No. 1 polyfluoropolyether [polar group -OH, number of polar groups 1, number average molecular weight 3500, product name SA1 (manufactured by Daikin Industries, Ltd.)] 1 part by weight Fluorine-based solvent [E-90 (Montedison) Company)] 200 parts by weight

Top coat layer paint No. 2 Compound No. 2-1 (Chemical formula 2) 0.1 part by weight Fluorine-based solvent [E-90 (manufactured by Montedison Co.)] 200 parts by weight

Top coat layer paint No. 3 Compound No. 2-1 (Chemical formula 2) 0.1 parts by weight Polyfluoropolyether [polar group --OH, polar group number 1, number average molecular weight 3500, trade name SA1 ( Daikin Industries, Ltd.)] 1 part by weight Fluorine-based solvent [E-90 (Montedison Company)] 200 parts by weight

(3) A magnetic tape sample was prepared by combining the undercoat layer and the topcoat layer as shown in Tables 2-4.

Coating No. for undercoat layer was formed on a polyethylene terephthalate (PET) film having a thickness of 7 μm.
1 to No. 5 and No. 7 to No. 17 were used as shown in Tables 2 to 4, and an undercoat layer as shown in Table 2 was applied.
The coating was performed by the die nozzle coating method, and the coating film was dried after formation.

The surface roughness of the undercoat layer was determined as follows. The surface roughness is indicated by Rmax defined by JISB601.

A polyethylene terephthalate film having such an undercoat layer formed thereon was treated with 10 ⁻⁴ Pa of Ar.
In an atmosphere, let it out from the supply roll, move it around the rotating cylindrical cooling drum, and move it to 20 at% Ni-
A Co alloy was obliquely vapor-deposited to form a ferromagnetic metal thin film, which was wound on a winding roll.

Then, using this winding roll as a supply roll, a ferromagnetic metal is obliquely vapor-deposited in an incident direction intersecting the incident direction at the time of oblique vapor deposition with the normal line direction of the PET film sandwiched therebetween to form a two-layer structure. Magnetic layer was formed. The total thickness of the magnetic layer was 2000A.

In this case, when forming the surface layer of the ferromagnetic metal thin film as the uppermost layer, the oxygen partial pressure in the atmosphere was controlled so that the surface layer contained oxygen to form a metal oxide-containing surface layer. The thickness of the surface layer was 200 A from the surface, and the oxygen content in this surface layer was 65 at%. Such analysis was based on Auger spectroscopy.

Furthermore, a coating material for the top coat layer is formed on the magnetic layer.
Tables 2-4 using No. 1-No. 3 as shown in Tables 2-4
A top coat layer as shown in was applied. The coating was performed by a die nozzle coating method, and then dried. 30 more
A back coat layer of A (dry film thickness) was applied.

The above magnetic sample cut to a width of 8 mm was cut into 8 pieces.
A mm video deck (S900 manufactured by Sony Corporation) was loaded and the following evaluations were performed. The method for obtaining the surface roughness is also shown below.

<Surface Roughness> Using a stylus-type surface shape measuring instrument, TALYSTEP system, manufactured by Taylor Hobson, measurement values were obtained by the method described in JIS B0601. The measurement conditions are: needle pressure: 5 mg, needle used: diamond, scan speed: 0.3 mm / 10 sec, scan length: 0.3 mm. Rmax was determined from the obtained results.

<Friction characteristics> By measuring the dynamic friction coefficient μ at the time of one pass in a pin friction tester of 180 °.

<Durability Friction Properties> By measuring μ at the time of 200 passes with a pin friction tester of 180 °.

<Corrosion resistance (oxidation resistance)> 60 ° C., 90% R
The amount of saturation magnetization φm after storage for 1 week in H was measured, and the difference from the initial φm was determined.

<Number of increase in dropout (DO)> 60
The sample was stored at 90 ° C. in a 90% RH atmosphere for 3 days, and the dropout (DO) after storage was measured. In addition, DO records the color bar signal on the test tape, and is manufactured by Shiba Soku VH01BZ.
The reproduction was performed using a mold dropout counter, and the number of times that the output decrease of −16 dB continued for 15 μsec or more in 60 seconds was measured and obtained. It should be noted that the number immediately after production was also measured to determine the number of increases due to storage.

The results are shown in Tables 2-4.

[0112]

[Table 2]

[0113]

[Table 3]

[0114]

[Table 4]

From the above results, the effect of the present invention is clear. The dropout was measured for the samples immediately after the production, but all samples were at a level without any problem immediately after the production. But in the comparison sample,
It was found that dropouts increase significantly by preservation.

Further, samples No. 7 to No. 23 in the table
When the output and C / N as electromagnetic conversion characteristics were examined as follows, the output was ± from the output of the standard tape.
0.5dB, C / N is ± 0.7dB from C / N of standard tape
Within the range, all were good.

<Output> Recording and reproduction were performed at a signal of 7 MHz using an S1500 deck manufactured by Sony Corporation, and the output was recorded on a standard tape [Hi-standard ME tape manufactured by TDK Corporation, P6-120 ( [For NTSC system]].

<C / N> 6 with spectrum analyzer
The ratio of the signals of MHz / 7MHz was compared to be C / N, and the value was compared with that of the same standard tape as above.

In the above, it was found that if the undercoat layer was too thick (more than 700 A), cupping was likely to occur and it was not suitable for use.

Further, in the samples No. 7 to No. 23 in the table, other compounds shown in Table 1 as the compound of Chemical formula 2 and two or more kinds of the compounds in Table 1 are used or a polar group is contained. When various samples were prepared using other compounds as the perfluoropolyether [for example, those having an ester group as a polar group] or two or more kinds of these compounds and evaluated in the same manner, equivalent results were obtained for each sample. It was Further, in the above, even if the weight ratio of the compound of Chemical formula 2 / perfluoropolyether having a polar group was set to 0.5 / 1, the same result was obtained according to each sample.

In sample No. 9, compound N
o A sample was prepared in the same manner except that an ordinary rust preventive agent (for example, dilauryl thiodipropionate) was used in place of 2-1 and the same evaluation was performed. Was inferior to (for example, Δφm
= 25%).

Example 2 In sample No. 9 of Example 1, a high hardness resin (acrylic resin: spherical: average particle size 2) was used instead of the silica fine particles.
50A) except that a sample is prepared in the same manner,
When evaluated in the same manner, the same result as that of Sample No. 9 was shown.

[0123]

EFFECTS OF THE INVENTION According to the present invention, the shelf life is excellent, and in particular, the dropout due to storage does not occur, and the corrosion resistance is excellent. Also, the durability is excellent and the electromagnetic conversion characteristics are also good.

Claims (8)

[Claims] 1. A magnetic field comprising an undercoat layer on a non-magnetic substrate, a ferromagnetic metal thin film magnetic layer on the undercoat layer, and a topcoat layer on the ferromagnetic metal thin film magnetic layer. In the recording medium, the undercoat layer is a coating film containing an antioxidant, and the topcoat layer is a coating film containing a compound represented by the following chemical formula 1 and perfluoropolyether having a polar group. . [Chemical 1] [In Chemical Formula 1, A represents one of a phosphoric acid group, a phosphonic acid group, a phosphinic acid group, a carboxylic acid group and esters thereof. L represents an alkylene group, an alkenylene group or an alkynylene group. R ₁ , R ₂ and R ₃
Each represent a fluorine atom or a perfluoroalkyl group. ] 2. The ratio of the compound to the perfluoropolyether in the topcoat layer, the compound / perfluoropolyether being 0.
The magnetic recording medium according to claim 1, which is 05/1 to 1/1. 3. The top coat layer has a thickness of 10 to 50.
The magnetic recording medium according to claim 1 or 2, which is A. 4. The content of the antioxidant in the undercoat layer is 15 wt% or more.
Any of the magnetic recording media. 5. The magnetic material according to claim 1, wherein the undercoat layer further contains at least one kind of high hardness resin fine particles and ceramic fine particles, and the fine particles are dispersed in a binder. recoding media. 6. The average particle size of the fine particles is 40 A or more, the content of the binder in the undercoat layer is 20 wt% or more, and the fine particles contain 2.5 million to 110.
The magnetic recording medium according to claim 5, wherein the magnetic recording medium is contained at an areal density of 0,000 particles / mm ² . 7. The magnetic recording medium according to claim 6, wherein the thickness of the undercoat layer corresponds to 20 to 50% of the average particle diameter value of the fine particles. 8. The magnetic recording medium according to claim 1, wherein the strong magnetic metal thin film contains Co as a main component and is formed by an oblique deposition method.