JPH0762898B2 - Magnetic recording medium - Google Patents

Description

The present invention relates to a magnetic recording medium in which a ferromagnetic metal thin film such as Co—Ni, Co—Cr is formed on an organic polymer film, and particularly, curling and wrinkling are reduced. The present invention also relates to a magnetic tape or magnetic disk suitable for high-density recording, which has excellent dimensional stability.

[Background of the Invention]

As the density of magnetic recording, the recording medium is conventional gamma-Fe ₂ O
_From the so-called coating type magnetic recording medium in which magnetic powder fine particles typified by ₃ are kneaded with an organic binder and coated on a substrate,
Ferromagnetic metals mainly composed of Fe, Co, Ni, etc. are moving to a so-called continuous magnetic thin film medium formed on a substrate by a sputtering method, a vacuum deposition method or a plating method. This type of magnetic recording medium is described in, for example, Makoto Isozaki, Journal of The Institute of Electronics, Communication, 67 , No. 11, 1197 (1984).

In particular, recently, Co-Cr films have been vigorously studied as a medium for a perpendicular magnetic recording medium, which is expected to dramatically improve the recording density. Usually, in order to obtain excellent magnetic properties with this Co-Cr film, it is necessary to heat the substrate to 100 ° C or higher, and particularly to heat the substrate temperature to 200 ° C in the vacuum deposition method. Therefore, in order to produce a Co-Cr film medium for magnetic tapes or magnetic disks, a polyimide film with excellent heat resistance is used as the substrate in the vacuum deposition method, and sputtering with a slightly low substrate temperature is used. In the method, a polyethylene terephthalate film is mainly used. However, in a commercially available polyimide film or polyethylene terephthalate film, the coefficient of thermal expansion is considerably larger than the coefficient of thermal expansion of the deposited metal, and when the film is deposited while the film is heated, the difference in thermal expansion coefficient causes Curls and wrinkles occur, and the flatness of the recording medium is significantly impaired.

When actually used as a recording medium, the size of the recording medium itself changes due to fluctuations in the outside temperature. Therefore, it is necessary to widen the track width of recording that can cover it, and as a result, the recording density cannot be increased. Therefore, in order to realize a high density magnetic recording medium, a low thermal expansion resin material having excellent heat resistance is indispensable because of problems of dimensional stability and thermal stress with the magnetic thin film.

[Object of the Invention]

An object of the present invention is to match a metal magnetic thin film used as a magnetic recording medium such as Co-Cr with a thermal expansion coefficient in terms of a coefficient of thermal expansion, and a specific polymer film whose dimensional change due to fluctuations in outside temperature is extremely small is used as a substrate. The purpose of the present invention is to provide a magnetic tape or a magnetic disk that can be used for high density recording.

[Outline of Invention]

The magnetic recording medium of the present invention, which achieves the above-mentioned object, uses a low thermal expansion polymer film having a specific chemical structure and a linear thermal expansion coefficient (2.0 × 10 ^-5 k ^-1 or less) as low as that of a metal as a substrate. I am using. This organic polymer material is disclosed in Japanese Patent Application No. 59-
A low thermal expansion resin composed of unsaturated cyclic hydrocarbons or heterocycles such as polyimide shown in JP-A No. 180549 (see JP-A-61-60725) and having a bending angle of the molecular axis within 40 degrees. It is made of materials.

The low thermal expansion polymer of the present invention includes polyimide and polyoxadiazole.

The low thermal expansion resin material used in the present invention has one or more aromatic rings, and the aromatic rings have a structure that is easy to rotate about the molecular axis but is not flexible in other directions (the molecular structure is An aromatic group having a substantially linear shape in the range of 0 ± 40 ° around the molecular axis), characterized in that the polyimide molecule contains at least a uniaxially oriented portion.

The degree of orientation is preferably 0.07 or more in order parameter (S). In addition, S is shown by the following equation.

[In the formula, E is the elastic modulus of the sample, E ₀ is a homogeneous system (Free cure
After), E∞ is the elastic modulus at infinite stretching of about 4.0 × 10
¹¹ dyn / cm ² . ] Looking at the thermal expansion coefficient ratio (α / α _FREE ), the above S value and α
There is a correlation with / α _FREE, and α is about half when the S value is about 0.07 (7%). The inventors of the present application examined and confirmed the relationship between the polymer elastic modulus and the orientation. Note that α is the coefficient of thermal expansion of the sample, and α _FREE is the coefficient of thermal expansion of the homogeneous system (after free cure).

The gist of the present invention is as follows. That is, in the magnetic recording medium in which one or more metal thin film layers are formed on the surface of the organic polymer film, the main chain of the organic polymer film has a structure represented by the following formulas [1] to [7]. A magnetic recording medium having at least one unit and having a linear expansion coefficient of 2 × 10 ⁻⁵ k ⁻¹ or less.

In the formula, R is an alkyl group, a fluorinated alkyl group, an alkoxy group, a fluorinated alkoxy group, an acyl group or a halogen atom, 1 is 0 to 4, m is 0 to 2, n is 0 to 3, k
Is an integer of 0 to 3. ) The low thermal expansion resin material of the present invention has low thermal expansion property, high strength, high elasticity, and high heat resistance as compared with other polymers even if the molecular arrangement is random, but it is remarkably improved by performing some molecular orientation treatment. The property becomes remarkable.

Aromatic polymers such as polyphenylene generally have the drawback of being rigid but brittle.
_{O -, - S-, CH 2} P, -SO ₂ -, CF _{2 P} , Introducing a flexible bond such as the entire polymer is flexible. The bonding position of the aromatic ring is also o- or m.
-It becomes flexible when it is in the negative position. Polyimide is the same,
All of the currently industrialized polyimides have bonds selected from these. Therefore, a low thermal expansion polymer which can be used in the present invention has not been found.

The low thermal expansion polyimide can be obtained by homopolymerization of an aromatic aminodicarboxylic derivative or reaction of an aromatic diamine or aromatic diisocyanate with an aromatic tetracarboxylic acid derivative. The tetracarboxylic acid derivative includes ester, acid anhydride and acid chloride. The use of an acid anhydride is preferred for synthesis. The synthetic reaction is generally performed by N-methylpyrrolidone (NMP), dimethylformamide (DMF), dimethylacetamide (DMAC), dimethylsulfoxide (DMSO), dimethyl sulfate, sulfolane, butyrolactone, cresol, phenol, halogenation. It is carried out in a solution of phenol, cyclohexanone, dioxane or the like in the range of 0 to 200 ° C.

Specific examples of the aminodicarboxylic acid derivative used above include 4-aminophthalic acid, 4-amino-5-methylphthalic acid, 4- (p-anilino) -phthalic acid and 4-
Examples thereof include (3,5-dimethyl-4-anilino) phthalic acid and the like, or their esters, acid anhydrides and acid chlorides.

The following are mentioned as aromatic diamine used for this invention.

p-phenylenediamine, 2,5-diaminotoluene, 2,5
-Diaminoxylene, diaminodeurene (2,3,5,6-tetramethyl-p-phenylenediamine), 2,5-diaminobenzotrifluoride, 2,5-diaminoanisole, 2,5-diaminoacetophenone, 2 , 5-diaminobenzophenone, 2,5-diaminodiphenyl, 2,5-diaminofluorobenzene, benzidine, o-tolidine, m-tolidine, 3,3 ', 5,5'-tetramethylbenzidine, 3, 3 ′
-Dimethoxybenzidine, 3,3'-di (trifluoromethyl) benzidine, 3,3'-diacetylbenzidine, 3,
3'-difluorobenzidine, octafluorobenzidine, 4,4 "-diaminoterphenyl, 4,4-diaminoquaterphenyl.

Further, these diisocyanate compounds can be used as well.

As the tetracarboxylic acid derivative used in the present invention, pyromellitic acid, methylpyromellitic acid, dimethylpyromellitic acid, di (trifluoromethyl) pyromellitic acid, 3,
3 ', 4,4'-biphenyltetracarboxylic acid, 5,5'-dimethyl-3,3', 4,4'-biphenyltetracarboxylic acid, p
-(3,4-dicarboxyphenyl) benzene, acid anhydrides, acid chlorides, esters thereof and the like can be mentioned.

The polyimide has low thermal expansion, high strength, and high elasticity as compared with other polymers without particularly increasing the molecular height, but can exert its power remarkably by orienting the molecular chains. . For example, the molecular chains can be arranged by uniaxially or biaxially stretching a film-shaped molded product. It is known that aromatic polyimide generally has low thermal expansion, high elasticity, and high strength due to the orientation treatment, but its effect is quite small as compared with the above polyimide. The method of orienting the polymer chains is not only the stretching of a normal film with a stretching machine, but also the shrinkage due to the curing reaction or the volatilization of the solvent in the process of forming a polyimide molded body from polyimide or its precursor varnish. I can. That is, it is possible to orient the molecular chains by suppressing the shrinkage when the varnish is applied and cured. The amount of stretching due to curing shrinkage is very small as compared with the conventional stretching method, but with the polyimide of the present invention, even such an orientation treatment is sufficiently effective.

Further, in the case of stretching the film-shaped molded product, when trying to stretch a completely cured product, the glass transition temperature of polyimide is extremely high, so it must be stretched at a very high temperature, and it is also necessary to stretch at a high temperature. However, the intermolecular cohesive force is so strong that it is difficult to orient. In order to easily orient, it is preferable that the molecules are orientated by stretching in a state of containing a solvent to a certain degree or in the state of polyamic acid having a low glass transition temperature, and then completely cured.

The reason why the polyimide that can be used in the present invention behaves in a manner completely deviated from the conventional wisdom of conventional polymers is considered as follows. That is, the polyimide main chain of the present invention has a substantially linear structure. However, in the state of polyamic acid or polyimide varnish, it is solvated to form a random coil, and even if it is cured, a linear structure cannot be taken. This is,
It is considered that, when the alignment treatment is applied, the polyimide molecule can have the most stable linear structure.

The low thermal expansion polyimides described above do not lose much of their properties when blended or copolymerized with significant amounts of non-low thermal expansion polymers. Although some of the polyimides of the present invention are mechanically brittle, it may be preferable to blend or copolymerize such polymers with a flexible, non-low thermal expansion polymer.
Polymers that can be blended or copolymerized include, for example, polyimides obtained from the following diamines and tetracarboxylic acid derivatives. Specific examples of the aromatic diamine include m-phenylenediamine, 4,4'-diaminodiphenylmethane, 1,2-bis (anilino) ethane, 4,4 '.
-Diaminodiphenyl ether, diaminodiphenyl sulfone, 2,2-bis (p-aminophenyl) propane,
2,2-bis (p-aminophenyl) hexafluoropropane, 3,3'-dimethyl-4,4'-diaminodiphenyl ether, 3,3'-dimethyl-4,4'-diaminodiphenylmethane, diaminotoluene , Diaminobenzotrifluoride, 1,4-bis (p-aminophenoxy) benzene, 4,4'-bis (p-aminophenoxy) biphenyl, 2,2-bis {4- (p-aminophenoxy) phenyl} propane, diaminoanthraquinone , 4,4'-bis (3-aminophenoxyphenyl) diphenyl sulfone, 1,3-bis (anilino) hexafluoropropane,
1,4-bis (anilino) octafluorobutane, 1,5-bis (anilino) decafluoropentane, 1,7-bis (anilino) tetradecafluoroheptane, general formula Or (R ₅ and R ₇ are divalent organic groups, R ₄ and R ₆ are monovalent organic groups, and p and q are integers greater than 1),
2-bis {4- (p-aminophenoxy) phenyl} hexafluoropropane, 2,2-bis {4- (3-aminophenoxy) phenyl} hexafluoropropane, 2,2
-Bis {4- (2-aminophenoxy) phenyl} hexafluoropropane, 2,2-bis {4- (4-aminophenoxy) -3,5-dimethylphenyl} hexafluoropropane, 2,2-bis {4- (4-aminophenoxy)
-3,5-Ditrifluoromethylphenyl} hexafluoropropane, p-bis (4-amino-2-trifluoromethylphenoxy) benzene, 4,4'-bis (4-amino-2-trifluoromethyl) Phenoxy) biphenyl,
4,4'-bis (4-amino-3-trifluoromethylphenoxy) biphenyl, 4,4'-bis (4-amino-2)
-Trifluoromethylphenoxy) diphenyl sulfone, 4,4'-bis (3-amino-5-trifluoromethylphenoxy) diphenyl sulfone, 2,2-bis {4-
Diamines such as (4-amino-3-trifluoromethylphenoxy) phenyl} hexafluoropropane,
And diisocyanates obtained by the reaction of these diamines with phosgene, such as tolylene diisocyanate, diphenylmethane diisocyanate, naphthalene diisocyanate, diphenyl ether diisocyanate, phenylene-1,3 There are aromatic diisocyanates such as diison cyanate. Further, examples of the derivative of tetracarboxylic acid include the following. Here, as an example of tetracarboxylic acid,
Of course, these ester compounds, acid anhydrides, and salt oxides can also be used. 2,3,3 ', 4'-tetracarboxydiphenyl, 3,3', 4,4'-tetracarboxydiphenyl ether, 2,3,3 ', 4'-tetracarboxydiphenyl ether, 3,3 ′, 4,4′-Tetracarboxybenzophenone,
2,3,3 ', 4'-tetracarboxybenzophenone, 2,3,
6,7-tetracarboxynaphthalene, 1,4,5,7-tetracarboxynaphthalene, 1,2,5,6-tetracarboxynaphthalene, 3,3 ', 4,4'-tetracarboxydiphenylmethane, 2, 2-bis (3,4-dicarboxyphenyl) propane, 2,2-bis (3,4-dicarboxyphenyl) hexafluoropropane, 3,3 ', 4,4'-tetracarboxydiphenyl sulfone, 3,4,9,10-Tetracarboxyperylene, 2,2-bis {4- (3,4-dicarboxyphenoxy)
Phenyl} propane, 2,2-bis {4- (3,4-dicarboxyphenoxy) phenyl} hexafluoropropane,
Examples include butanetetracarboxylic acid and cyclopentanetetracarboxylic acid. It is also possible to introduce a crosslinked structure or a ladder structure by modifying with a compound having a reactive functional group. For example, there are the following methods.

(I) A pyrrolone ring, an isoindoloquinazolinedione ring or the like is introduced by modification with a compound represented by the general formula (III).

Here, R'is a 2 + x valent aromatic organic group, and Z is NH.
It is a group selected from _two groups, a CONH ₂ group, and a SO ₂ NH ₂ group, and is in an ortho position with respect to an amino group. x is 1 or 2.

(Ii) Modification with an amine, diamine, dicarboxylic acid, tricarboxylic acid, or tetracarboxylic acid derivative having a polymerizable unsaturated bond to form a crosslinked structure during curing. As the unsaturated compound, maleic acid, nadic acid, tetrahydrophthalic acid, ethynylaniline and the like can be used.

(Iii) A network structure is formed by modifying with a phenolic hydroxyl group or an aromatic amine having a carboxylic acid and using a crosslinking agent capable of reacting with the hydroxyl group or the carboxyl group.

In the present invention, the adhesiveness is important when integrated with the low thermal expansion polyimide inorganic material. It is preferable to roughen the surface of the inorganic material or to perform surface treatment with a silane coupling agent, a titanate coupling agent, an aluminum alcoholate, an aluminum chelate, a zirconium chelate, aluminum acetylacetone, or the like. These surface treatment agents may be added to the low thermal expansion polyimide.

In the present invention, in order to further reduce the thermal expansion coefficient, increase the elastic modulus, or control the fluidity,
It is also possible to mix powders of inorganic, organic or metallic materials, fibers, polyester strands and the like.

Although some of the polymers of the present invention are mechanically brittle, it is often preferable to blend or copolymerize such polymers with flexible, non-low thermal expansion polymers.

For example, (i) some of them exhibit low thermal expansion and are mechanically brittle, but blending or copolymerizing a flexible polymer results in a significantly tough polymer, (ii)
When used as a coating film, it is difficult to adhere to metals and inorganic substances, but siloxane skeleton is introduced,
There are many merits, such as that the adhesiveness can be significantly improved by introducing an alkoxysilane group, and (iii) the thermal expansion coefficient is made to match the inorganic substance of the partner to be composited.

Conventionally, aromatic polymers such as polyphenylene generally have the drawback of being rigid but brittle, and in the main chain, -O
−, −S−, CH _{2 P} , CF _{2 P} , -SO _2- , Such as introducing a flexible bond, having no linearity, or introducing an o-bond or m-bond aromatic ring. It is always no exaggeration to say that all of the heat-resistant polymers industrialized to date contain these bonds. Therefore, the low thermal expansion polymer as in the present invention has not been discovered, and the magnetic recording medium as in the present invention has not been found.

Example of Invention

 Hereinafter, the present invention will be described in detail with reference to examples.

Example 1 A polyimide film having the following chemical structure was prepared from its precursor, polyamic acid varnish, by a casting method. After casting the varnish on a polypropylene carrier, the film was dried at 120 ° C. for 10 minutes. After peeling from the carrier, pull the film from the front, back, left and right so that it does not cause curing shrinkage of the film, 120 → 3
A polyimide film was made by passing through a tunnel furnace of 50 ℃ / 20 minutes, 350 ℃ / 5 minutes, 350 ℃ → room temperature / 20 minutes.

[However, The film thickness is a smooth film with a thickness of 50 μm, and its linear thermal expansion coefficient is 0.9 × 10 ^-5 k ^{-1 in} the longitudinal direction and 1.0 in the lateral direction.
It was x 10 ^-5 k ^-1 .

The polyimide film thus obtained is 100 mm x 70 mm
1 was cut out, and both ends were fixed with stainless steel fittings 2 as shown in FIG. 1, the film 1 was uniformly pulled by applying a tension of about 3 kg / cm ² , and the film 1 was placed in a vacuum deposition apparatus. After setting the vacuum in the bell jar to 1 × 10 ^-6 Torr, heat the film from the backside of the film with the heater 5 to increase the film temperature to 200.
The temperature was kept at 0 ° C. and the Co—Cr alloy was evaporated by using the electron beam heating type vapor deposition source 4 to form a Co—Cr film having a Cr composition of 23% by weight and a film thickness of 0.35 μm.

The curl size of the Co—Cr vapor deposition film thus produced was determined by measuring the radius of curvature. As a result, the Co-Cr thin film was slightly curved inward. Its radius of curvature is
It was 290 mm.

Next, the film was turned upside down, and a magnetic thin film was similarly vapor-deposited on the back side so that the film thickness was almost the same. as a result,
The curvature of the film was almost eliminated, and a smooth double-sided vapor deposition film was obtained.

Examples 2 to 5 and Comparative Examples 1 to 3 Various polyimide films were prepared in the same manner as in Example 1. The thermal expansion coefficient of the obtained film is as shown in the table.

Also, as in Example 1, first, a Co—Cr film was vapor-deposited on only one surface. After vapor deposition, the film was cooled to room temperature, the film was taken out, and the degree of curvature thereof is also shown in Table 1. Those with a coefficient of thermal expansion of around 1.0 × 10 ^-5 k ^-1 were almost flat, but those with a smaller coefficient of curvature slightly curved with the Co-Cr film inside, and those with a larger coefficient had the opposite curve. did. And, it can be seen that the degree of curling is extremely large in the polyimide film of 2.5 × 10 ^-5 k ^-1 or more.

Furthermore, when a Co-Cr film was vapor-deposited on the screen, the one with a small degree of curvature when vapor-deposited on one side returned to almost flat, but for all three types of comparative examples, the film was made into a film due to internal thermal stress. I've found that I can. This tendency increased as the coefficient of thermal expansion increased.

Example 7 The same polyimide film 1 as in Example 1 was used, the film temperature during vapor deposition was set to 200 ° C., and the film thickness was 0.5 μm by the vacuum vapor deposition method.
After forming the permalloy (Fe containing Ni-20 wt%) film 7 on both sides, a Co-Cr film 8 having a thickness of 0.2 .mu.m was formed on both sides to prepare a two-layer film medium. As a result, the sample was almost flat.

Then, fluorine-based lubricating oil 9 was applied to both surfaces of the sample to obtain a flexible magnetic recording medium having the cross-sectional structure shown in FIG. This was punched into the shape shown in FIG. 3 and housed in the jacket 11 to obtain a floppy disc having the shape shown in FIG. 4 and the sectional structure shown in FIG. In each figure, reference numeral 7 is a soft magnetic film, 8 is a perpendicular magnetization film, 9 is a lubricating oil layer, 10 is a magnetic medium, and 11 is a magnetic medium.
Is a jacket, and 12 is a lubricating oil liner.

Example 8 A Co—Cr film was deposited in the same manner as in Example 1 using a polyoxadiazole film having a thermal expansion coefficient of 1.2 × 10 ⁻⁵ k ⁻¹ and having the following chemical structure.

As a result of vapor deposition on one side, the film was slightly curved with the film inside. The radius of curvature was 250 mm.

[Effects of the Invention] The polymer used in the present invention has an excellent effect that the linear expansion coefficient is small, and the film hardly curls even when a magnetic film is formed. The medium can be obtained.

[Brief description of drawings]

FIG. 1 is a schematic diagram of an electron beam heating type vacuum evaporation apparatus used in an experiment of the present invention, FIG. 2 is a sectional view of a magnetic recording medium according to an embodiment of the present invention, and FIG. 3 is an external view of the magnetic recording medium. FIG. 4 is an external view of the floppy disc stored in the jacket, and FIG. 5 is a sectional view of the floppy disc. 1 ... Film, 2 ... Metal fitting, 4 ... Evaporation source, 5 ... Heater, 7 ... Permalloy film, 8 ... Co-Cr film, 9 ...
Lubricating oil layer, 10 …… Magnetic medium, 11 …… Jacket, 12 ……
Lubricating oil liner.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Koji Fujisaki 4026 Kuji Town, Hitachi City, Ibaraki Prefecture, Hitachi Research Institute, Ltd. (72) Inventor Takaei Ikeda 4026 Kuji Town, Hitachi City, Ibaraki Prefecture Hitachi Research Laboratory (72) Inventor Tokuyuki Kaneshiro 4026 Kuji-machi, Hitachi City, Ibaraki Prefecture Hitachi Research Institute, Ltd. (72) Inventor Kaetsu Yoshida 1-280, Higashi Koigakubo, Kokubunji, Tokyo Hitachi Central Research Laboratory, Ltd. (72) Inventor Norikazu Sekida 1-280 Higashi Koigakubo, Kokubunji City, Tokyo Metropolitan Research Laboratory, Hitachi, Ltd.

Claims (1)

[Claims] 1. In a magnetic recording medium in which one or more metal thin film layers are formed on the surface of an organic polymer film, the main chain of the organic polymer film is represented by the following formula [1].
To a magnetic recording medium having at least one of the structural units shown in [7] and having a linear expansion coefficient of 2 × 10 ⁻⁵ k ⁻¹ or less. (In the formula, R is an alkyl group, a fluorinated alkyl group, an alkoxy group, a fluorinated alkoxy group, an acyl group or a halogen atom, l is 0 to 4, m is 0 to 2, n is 0 to 3,
k is an integer of 0 to 3. )