JPH11120534A - Magnetic record medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent deformation of a nonmagnetic support elution of the component by heat or cracking in a film forming process and to obtain a record medium having excellent characteristics at a low cost by forming a base coating layer comprising a polyamide imide resin on a nonmagnetic support and forming a ferromagnetic metal thin film by vacuum film forming method thereon. SOLUTION: When a polyamide imide resin is applied as a base coating layer on a nonmagnetic support, the coating liquid is prepared to have 0.5 to 10 wt.% concn. by using a general solvent containing no fluorine. such as 1/1 mixture solvent of γ-butyrolactone/cyclohexanone, 1/1 mixture solvent of tetrahydrofuran/cyclohexanone, 1/1 mixture solvent of ethanol/toluene, 1/1 mixture solvent of dioxane/cyclopentanone, tetrahydrofuran or N-methylpyrrolide. The coating liquid is applied by wire bar method, gravure method, spray method, dip coating method or spin coating method to form a film having 0.05 to 0.8 μm thickness after being dried.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a magnetic recording medium using a ferromagnetic metal thin film as a magnetic film.

[0002]

2. Description of the Related Art A magnetic recording medium such as a magnetic tape, a floppy disk or a hard disk is generally manufactured by a process of forming a magnetic film, a protective film and the like on a non-magnetic support. In such a magnetic recording medium,
Magnetic recording media using a ferromagnetic metal thin film formed by a vacuum film forming method such as a sputtering method or a vapor deposition method as a magnetic film have been put to practical use. A magnetic recording medium in which a magnetic film is formed by a sputtering method or a vapor deposition method as described above can easily obtain high magnetic energy, and can further easily smooth the surface of the magnetic film by smoothing the surface of the nonmagnetic support. It is suitable for a high-density recording material because it is possible to obtain a high electromagnetic conversion characteristic with a small spacing loss. In particular, the sputtering method can further increase the magnetic energy than the vapor deposition method, and is therefore used for a magnetic recording medium such as a hard disk which requires a high recording density.

On the other hand, a magnetic recording medium is required to have high reliability for sliding with a head. For example, running durability such as CSS characteristics of a hard disk and still durability of a vapor-deposited tape can be mentioned. In order to secure such durability, minute projections are formed on the surface of a non-magnetic support to reduce the contact area with the head. Reductions have been made.

However, in recent magnetic recording media, there is a strong demand for higher recording density, and higher electromagnetic conversion characteristics than in the past have been required. For this reason, the height of the projection provided on the surface of the non-magnetic support tends to be increasingly lower,
The height of the protrusion has become less than 20 nm.

For this reason, in a hard disk, the surface of a nonmagnetic support such as an aluminum substrate, a glass substrate, or a carbon substrate is mechanically or chemically polished to provide a very smooth substrate. In a magnetic tape on which a magnetic film is formed by vapor deposition, the surface of a polymer film such as a polyethylene terephthalate film or a polyethylene naphthalate film, which is a nonmagnetic support, is made very smooth, and spherical fine particles are coated thereon. In order to achieve higher-density recording, the height of the protrusions must be further reduced, or a mirror surface substrate having substantially no protrusions must be used.

[0006] In a case where a flexible polymer film such as a polyethylene terephthalate film or a polyethylene naphthalate film is used as a non-magnetic support as described above, such as a magnetic tape or a floppy disk,
In order to improve the recording density and the like, it is desirable to form a magnetic film made of a ferromagnetic metal thin film by a sputtering method or a vapor deposition method. However, such a polymer film has poor heat resistance. In the case where the film is formed by evaporating at a high vapor deposition rate, the polymer film or its surface is heated to cause surface degradation due to oligomer precipitation and the like, and the smooth surface property of the non-magnetic support, and hence the magnetic film A problem arises in that it is difficult to obtain a smooth surface property. Therefore, the following technology has been proposed to solve this problem.

One is a method using a heat-resistant resin as a material for a polymer film as a nonmagnetic support. As the heat-resistant resin to be used, a polyimide film or the like can be considered, but the polyimide film is generally expensive. In addition, it is technically difficult to produce and use a polyimide film which is very smooth and has good surface properties, and this method is not practical.

In addition, an undercoat film is formed on a relatively inexpensive polymer film generally used for a conventional magnetic recording medium in which a magnetic film is formed by coating, for example, to improve the smoothness and heat resistance of the film. A method has been proposed.

For example, Japanese Patent Application Laid-Open No. 6-349042 discloses a method for producing a film having an appropriate surface property by providing a resin film containing fine particles on a polymer film having a relatively rough surface. . However, when the general resin binder used here is used, when the magnetic film is formed by the sputtering method, the surface property is significantly deteriorated due to thermal damage.

Japanese Patent Application Laid-Open No. 7-225934 discloses that
A method is disclosed in which polyethylene naphthalate is coated on polyethylene terephthalate to suppress oligomer precipitation due to heat. However, even when polyethylene naphthalate is used, when the film is heated to 200 ° C., which is the temperature condition in a general sputtering method, the surface properties are deteriorated due to the precipitation of oligomers and the like.

Further, Japanese Patent Application Laid-Open No. 63-188823 discloses an invention in which the surface properties of a support surface are improved by providing a polyimide coating layer in which inorganic fine particles are dispersed on a polyimide film. However, even with this method, a general-purpose solvent cannot be used as a solution for dissolving the coating solution, or the adverse effect of heat in a sputtering process when forming a magnetic film by sputtering cannot be sufficiently addressed.

Japanese Patent Application Laid-Open No. 6-208717 discloses that
A method of applying a polyamide resin or a polyimide resin having higher heat resistance on a polymer film is disclosed. When such a material is used, heat resistance that can withstand a sputtering method can be imparted to the film. However, polyamide resins and polyimide resins have low solubility in general-purpose solvents, and thus it is necessary to use solvents that are difficult to handle. In addition, even if the resin is soluble in a general-purpose solvent, it is difficult to dry the solvent sufficiently after coating, and the residual amount of the solvent in the coating film increases. Blocking, which causes adhesion, is likely to occur, and a residual solvent volatilized when forming the magnetic film may contaminate the inside of the vacuum chamber.

As a film having higher heat resistance, it is effective to form an inorganic film. For example, a silica film obtained by hydrolysis of a silane compound or a metal oxide film obtained from a metal alkoxide is formed. Can be considered. However, such an inorganic coating cannot cope with the thermal change of the non-magnetic support, and there is a problem that a crack occurs on the surface of the coating and a crack occurs in the magnetic film formed thereon.

[0014]

As described above, when a magnetic film composed of a ferromagnetic metal thin film is to be formed on a polymer film or the like as a support by a sputtering method or the like, the support and the magnetic film need to be combined. It is desirable to provide an undercoat film that has heat resistance between the surfaces, has a surface smoothness, does not generate cracks, and can be easily formed, but in the prior art, an undercoat film that can sufficiently satisfy them is provided. It was difficult to provide. In view of the above circumstances, the object of the present invention has a smooth surface property, and even when a magnetic film is produced by a sputtering method involving heating of a non-magnetic support, there is no deterioration in surface properties or generation of cracks, It is an object of the present invention to provide a magnetic recording medium that can easily and at low cost have a magnetic recording medium having an undercoat film that does not cause blocking.

[0015]

In order to solve the above problems, a magnetic recording medium according to the present invention is a magnetic recording medium having a magnetic film made of a ferromagnetic metal thin film on at least one surface of a nonmagnetic support. An undercoat film made of a polyamideimide resin is formed between the support and the ferromagnetic metal thin film.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, a polyamide-imide resin formed as an undercoat film on a non-magnetic support comprises:
Since it is composed of an imide bond and an amide bond, it has excellent heat resistance as compared with conventional polyester resins and polyamide resins and the like, and has a glass transition point of 250 ° C. or more. Therefore, even when the magnetic film is formed by the sputtering method at a substrate temperature of 200 ° C., no deformation occurs, so that a magnetic recording medium having a smooth surface can be easily manufactured.

The polyamideimide resin which can be used in the present invention is described in Nikkan Kogyo "Polyamide resin handbook".
And the like, a method of reacting a low molecular weight polyamide having an amino group at a terminal with an acid anhydride, a method of reacting a low molecular weight polyamic acid having an amino group at a terminal with dibasic chloride; It can be obtained by, for example, a method of reacting a trimellitic acid derivative with a diamine.

These acid anhydrides, pyromellitic acid-
1,4-dimethyl ester, pyromellitic acid tetramethyl ester, pyromellitic acid ethyl ester, 2,3
6,7-naphthalenetetracarboxylic dianhydride, 3,
3 ′, 4,4′-biphenyltetracarboxylic dianhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, 2,2 ′, 3,3′-biphenyltetracarboxylic dianhydride, 2,2 ', 6,6'-biphenyltetracarboxylic dianhydride; and the above-mentioned aromatic diamines of diamines are used.

As a solvent for synthesizing polyamic acid, dimethylformamide, dimethylacetamide, dimethylmethoxyacetamide, N-methylcaprolactam, dimethylsulfone, tetramethylenesulfone, N-acetyl-
2-Pyrrolidone and the like are used.

The application of the undercoat layer of polyimideamide on the nonmagnetic support can be carried out using a solvent in which polyimideamide is dissolved. Specifically, γ-butyrolactone / cyclohexanone = 1/1 mixed solvent, tetrahydrofuran / cyclohexanone = 1/1 mixed solvent,
Ethanol / toluene = 1/1 mixed solvent, dioxane /
Cyclopentanone = 1/1 mixed solvent, tetrahydrofuran, N-methylpyrrolidone. The concentration of the coating solution is 0.05 to 100% by weight, preferably 0.1% by weight.
It is 1 to 30% by weight, more preferably 0.5 to 10% by weight. The application can be performed by the same method as the application of the magnetic paint.

Further, the preferred thickness of the undercoat film of the present invention is 0.03 to 1.0 μm, more preferably 0.05 to 0.8 μm, after drying. 0.03 μm
If it is thinner, the adhesion cannot be secured, and the coating layer will fall off,
Causes increased dropouts. If the thickness is more than 1.0 μm, the adhesion can be secured, but the thickness of the entire magnetic recording medium is increased, which is disadvantageous in the case of thinning.

In the present invention, the polyamideimide resin formed as an undercoat film on the non-magnetic support has better solvent solubility and processability than the polyimide resin. For this reason, ethanol, toluene, cyclohexanone, excellent productivity because it can be dissolved in commonly used solvents that do not contain fluorine such as tetrahydrofuran,
Furthermore, the drying property after application is good. Therefore, even if it is continuously applied to a plastic film or the like and dried, no blocking or deterioration in surface properties occurs.

In the present invention, the polyamideimide resin formed as an undercoat film on the nonmagnetic support is a resin having an imide bond and an amide bond, and preferably has a structure excellent in heat resistance and solvent solubility. . Examples of such a resin include Viromax series manufactured by Toyobo.

The thicker the undercoating film is, the higher the smoothing effect is, and the undercoating film can be smoothed even with a substrate having a coarse roughness of the nonmagnetic support. May occur. On the other hand, if it is too thin, the smoothing effect is small, and the roughness of the nonmagnetic support directly appears. If it is too thin, the effect of heat resistance will decrease,
Damage to the nonmagnetic support and precipitation of oligomers and the like from the nonmagnetic support cannot be prevented. In order to obtain a mirror surface which is not affected by the protrusions of the non-magnetic support, the thickness is preferably 2 to 5 times the height of the protrusions of the non-magnetic support.

In the present invention, as a method for preparing an undercoat film by coating a polyamideimide resin on a nonmagnetic support, a solution obtained by dissolving a polyamide resin in an organic solvent such as ethanol or toluene may be prepared by a wire bar method, a gravure method, or the like. A method in which the composition is applied onto a non-magnetic support by a method such as a spray method, a dip coating method, and a spin coating method and then dried is used. Further, after that, the undercoat film is baked, if necessary, to accelerate the curing and improve heat resistance, solvent resistance, adhesion, and the like. The type of the coating solvent used at this time is determined by the structure of the polyamideimide resin, but a general hydrocarbon-based organic solvent such as ethanol, toluene and cyclohexanone can be used.

The drying is carried out in order to evaporate the solvent, and as a drying method, hot air drying, infrared drying and the like which are generally used can be used. The drying temperature at this time is preferably about 60C to 150C.

After the coating is dried, hot air heating, infrared heating, hot roller heating and the like can be used as a baking method for further promoting solvent removal and curing. The heating temperature at this time depends on the thickness of the coating film, the method of forming the magnetic film afterward, and the film forming temperature, but when it is around 1 μm, it is in the range of 80 ° C. to 250 ° C., preferably 100 ° C. to 200 ° C. It is. When the temperature is lower than this, the progress of the polymerization reaction is insufficient. On the other hand, when the temperature is too high, the nonmagnetic support may be deformed or productivity may be reduced. In addition to polymerization by heating, polymerization by ultraviolet irradiation, electron beam irradiation, or the like is also possible.

The undercoat film of the present invention may contain components other than the polyamideimide resin. Examples of such additives include heat-resistant fine particles (fillers) for providing irregularities on the surface, coupling agents for improving adhesion to the support, and rust preventives for preventing oxidation of the magnetic film.

Examples of heat-resistant fine particles for forming irregularities on the surface of the undercoat film of the present invention include inorganic oxides such as silica, alumina, titania, and zirconia, calcium carbonate, carbon, and polymers. The shape is preferably monodisperse and spherical. The particle size is selected depending on the thickness of the undercoat film, but is 10 to 1000 nm, preferably 20 to 100 nm. In the present invention, since the coating liquid is mainly an alcohol solution, an organosilica sol in which alcohol is dispersed or a silica sol in which an acidic aqueous solution is dispersed are particularly preferable.

The above-mentioned fine particles are internally added to the undercoat film or coated on the undercoat film to form fine irregularities on the surface, so that the electromagnetic conversion characteristics due to spacing loss are slightly reduced, but the running property and durability are reduced. Can be greatly improved. In this case, the height of the projection is 5 to 50 nm, preferably 10 to 50 nm.
30 nm. The density of the protrusions is 10 ⁵ to 10 ⁹ / m
m ² , preferably 10 ⁶ to 10 ⁸ pieces / mm ² . When the height of the projections is lower than this, or when the density is low, the effect of improving running performance and durability is small, and when the height of the projections is higher or the density is higher, the electromagnetic conversion characteristics decrease. Not preferred.

As the nonmagnetic support used in the present invention, a film of polyethylene terephthalate, polyethylene naphthalate, polyimide, polyamide, polyamide imide or the like having a thickness of 3 to 100 μm can be used. Further, a film containing a filler inside the film and having irregularities formed on the film surface may be used. In the case of a rigid medium, a glass substrate, an aluminum substrate or a carbon substrate can be used.

The undercoating film of the present invention is excellent in adhesion to the support, but when the adhesion is insufficient, the surface treatment of the support with an additive such as a silane coupling agent, oxygen plasma, argon plasma, ultraviolet light It is preferable to perform surface treatment such as irradiation, electron beam irradiation, and flame irradiation.

The ferromagnetic metal thin film serving as a magnetic film in the magnetic recording medium of the present invention can be formed by a conventionally known vacuum film forming method such as a vacuum evaporation method and a sputtering method. When the magnetic film is formed by a sputtering method, the composition includes a conventionally known metal or alloy mainly composed of cobalt, and specifically, Co-Cr, Co-Ni-Cr, Co-
Cr-Ta, Co-Cr-Pt, Co-Cr-Ta-P
t, Co-Cr-Pt-Si, Co-Cr-Pt-B, etc. can be used. In particular, to improve the electromagnetic conversion characteristics, Co
-Cr-Ta and Co-Cr-Pt are preferred. The thickness of the magnetic film is desirably 10 to 300 nm. In this case, it is preferable to provide a base film for improving the magnetostatic characteristics of the magnetic film. The base film may be composed of a conventionally known metal or alloy.
r, V, Ti, Ta, W, Si, etc. or alloys thereof can be used. Among them, Cr, Cr-Ti, Cr-V, Cr
-Si is particularly preferred. The thickness of this base film is 5n
m to 500 nm, preferably 10 nm to 200 n
m. When a magnetic film is formed by a sputtering method, it is preferable to form the film while the substrate is heated,
The temperature at that time is 150 to 200 ° C.

When the magnetic film is formed by a vacuum deposition method, the composition may be a conventionally known metal or alloy mainly composed of cobalt, and specifically, Co, Co-Ni, Co
-Fe or the like is deposited in an oxygen atmosphere, and a film containing oxygen in the film can be used. In particular, in order to improve the electromagnetic conversion characteristics, Co-O which is cobalt is 90% by atom or more, more preferably 95% by atom or more of the metal atoms constituting the magnetic layer, and Co-Fe containing Co-O or the like is preferable. The thickness of the magnetic layer is desirably 100 to 300 nm,
More preferably, it is 120 to 200 nm. Further, the ferromagnetic metal thin film may have a multilayer structure to improve electromagnetic conversion characteristics, or may have a nonmagnetic underlayer or an intermediate layer.

In the magnetic recording medium of the present invention, a protective film may be provided on the ferromagnetic metal thin film. With this protective film, running durability and corrosion resistance can be further improved. Silica, alumina, titania,
Oxides such as zirconia, cobalt oxide and nickel oxide, nitrides such as titanium nitride, silicon nitride and boron nitride, silicon carbide, chromium carbide and carbides such as boron carbide;
Examples of the protective film include carbon such as graphite and amorphous carbon.

The carbon protective film is a carbon film made of an amorphous, graphite, diamond structure or a mixture thereof produced by a plasma CVD method, a sputtering method or the like, and particularly preferably a hard carbon film generally called diamond-like carbon. is there. This hard carbon film has a Vickers hardness of 1000 kg / mm ²
Above, preferably a hard carbon film of 2000 kg / mm ² or more. The crystal structure is an amorphous structure and is non-conductive.

This hard carbon protective film is made of methane, ethane,
Plasma C made from a carbon-containing compound such as an alkane such as propane or butane, an alkene such as ethylene or propylene, or an alkyne such as acetylene.
It can be formed by VD, a sputtering method using carbon as a target in a hydrogen or hydrocarbon atmosphere, or the like.

If the thickness of the hard carbon protective film is large, the electromagnetic conversion characteristics are deteriorated and the adhesion to the magnetic layer is reduced. If the thickness is small, the abrasion resistance is insufficient. 20n
m is preferable, and particularly preferably 5 to 10 nm.
Further, the surface of the hard carbon protective film may be subjected to a surface treatment with an oxidizing or inert gas for the purpose of further improving the adhesion with the lubricant provided on the hard carbon protective film.

In the magnetic recording medium of the present invention, in order to improve running durability and corrosion resistance, it is preferable to provide a lubricant or a rust inhibitor on the magnetic film or the protective film. As the lubricant, a hydrocarbon-based lubricant, a fluorine-based lubricant, an extreme pressure additive and the like can be used. Examples of the hydrocarbon-based lubricant include carboxylic acids such as stearic acid and oleic acid, esters such as butyl stearate, sulfonic acids such as octadecylsulfonic acid, phosphoric esters such as monooctadecyl phosphate, stearyl alcohol, oleyl alcohol and the like. Alcohols, carboxylic acid amides such as stearic acid amide, and amines such as stearylamine.

Examples of the fluorine-based lubricant include lubricants in which a part or all of the alkyl group of the hydrocarbon-based lubricant is substituted with a fluoroalkyl group or a perfluoropolyether group. Examples of the perfluoropolyether group include a perfluoromethylene oxide polymer, a perfluoroethylene oxide polymer, a perfluoro-n-propylene oxide polymer (CF ₂ CF ₂ CF ₂ O) _n , and a perfluoroisopropylene oxide polymer (CF ( CF ₃ ) CF
₂ O) _n or a copolymer thereof.

Examples of extreme pressure additives include phosphoric esters such as trilauryl phosphate, phosphites such as trilauryl phosphite, thiophosphites and thiophosphoric esters such as trilauryl trithiophosphite and the like. And sulfur-based extreme pressure agents such as dibenzyl sulfide.

The above lubricants are used alone or in combination of two or more. As a method of applying these lubricants on a magnetic film or a protective film, a lubricant is dissolved in an organic solvent and applied by a wire bar method, a gravure method, a spin coating method, a dip coating method, or a vacuum evaporation method. What is necessary is just to make it adhere. The amount of the lubricant to be applied is 1 to 30 mg / m ^2.
Preferably, 2 to 20 mg / m ² is particularly preferred.

Examples of the rust preventive usable in the present invention include nitrogen-containing heterocycles such as benzotriazole, benzimidazole, purine and pyrimidine, and derivatives having an alkyl side chain introduced into the mother nucleus, benzothiazole, 2-mercapto. And nitrogen- and sulfur-containing heterocycles such as benzothiazole, tetrazaindene ring compounds and thiouracil compounds, and derivatives thereof. The tetrazaindene ring compounds that can be used for such purposes include the following.

[0044]

Embedded image

Here, R is a hydrocarbon group selected from an alkyl group, an alkoxy group and an alkylamide group.
Particularly preferably, it has 3 or more and 20 or less carbon atoms, and in the case of alkoxy, R of ROCOCH ₂ — is C ₃ H ₇ —, C ₆
H _13- , phenyl or, in the case of an alkyl group, C ₆ H
_{13 -, C 9 H 19 -} , C 17 H 35 - , and the like, in the case of alkylamide RNHCOCH ₂ - of R phenyl, C ₃
H ₇ -, and the like. Further, examples of the thiouracil ring compound include the following.

[0046]

Embedded image

Here, R is a hydrocarbon group having 3 or more carbon atoms.

The present invention will be described below with reference to examples. Example 1 A polyamideimide resin (MT5050 manufactured by Toyobo Co., Ltd.) was dissolved in a mixed solvent of ethanol and toluene on a polyethylene naphthalate film having a maximum projection roughness of 0.01 μm and a thickness of 63 μm, and applied at a solid concentration of 10% by weight. A liquid was prepared. After applying this solution by the gravure coating method,
By drying at 00 ° C., an undercoat film having a thickness of 1 μm was prepared. Next, the coating film was heated at 170 ° C. for 20 seconds to perform curing and desolvation treatment. This film was formed in a sputtering apparatus by a DC magnetron sputtering method at a substrate temperature of 150 ° C. by a DC magnetron sputtering method to form a 60 nm Cr-Ti underlayer film, and then to form a 30 nm Co-Cr-Pt magnetic film. Next, this film was set in a plasma CVD apparatus, and a hard carbon protective film having a thickness of 20 nm was formed on the magnetic film by a plasma CVD method using ethylene as a raw material. Next, a perfluoropolyether-based lubricant (FOMBLIN manufactured by Ausimont) is formed on the protective film.
Z-DOL) with a fluorinated solvent (FC manufactured by Sumitomo 3M)
-77) was applied by a dip coating method to form a lubricating film having a thickness of 2 nm. This base film, magnetic film,
The protective film and the lubricating film were formed on both sides of the film. Then, this sample was punched into a 3.7-inch magnetic disk shape to produce a floppy disk.

Example 2 A polyamideimide resin (AT8020 manufactured by Toyobo Co., Ltd.) was dissolved in a mixed solvent of tetrahydrofuran and cyclohexanone on a polyethylene naphthalate film having a maximum projection roughness of 0.01 μm and a thickness of 63 μm, and the solid content concentration was 10% by weight. Was prepared. After this solution was applied by a gravure coating method, it was dried at 100 ° C. to prepare an undercoat film having a thickness of 1 μm. Next, the coating film is heated at 170 ° C. for 20 seconds,
Curing and solvent removal were performed. A base film, a magnetic film, a protective film, and a lubricating film were formed thereon in the same manner as in Example 1 to prepare a sample.

Example 3 A polyamideimide resin (MT5050 manufactured by Toyobo Co., Ltd.) was dissolved in a mixed solvent of ethanol and toluene on a polyethylene naphthalate film having a maximum projection roughness of 0.01 μm and a thickness of 63 μm, and the solid content concentration was 10% by weight. Was prepared. After applying this solution by the gravure coating method,
By drying at 00 ° C., an undercoat film having a thickness of 1 μm was prepared. Furthermore, spherical silica particles having a particle diameter of 25 nm
A coating solution containing 05% by weight was applied and dried at 100 ° C. to form projections on the surface of the undercoat film. Next, apply the coating 170
The mixture was heated at 20 ° C. for 20 seconds to perform curing and desolvation treatment. A base film, a magnetic film, a protective film, and a lubricating film were formed thereon in the same manner as in Example 1 to prepare a sample.

Comparative Example 1 A sample was prepared in the same manner as in Example 2 except that the undercoat film was not applied and the magnetic film was formed directly on polyethylene naphthalate.

Comparative Example 2 The composition of the coating solution was changed to a polyamide resin (M9 manufactured by Nippon Rilsan Co., Ltd.).
A sample was prepared in the same manner as in Example 1 except that the mixed solution of 95) was used.

Comparative Example 3 A sample was prepared in the same manner as in Example 1, except that the composition of the coating solution was changed to a solution in which N, N-dimethylacetamide of a low-temperature curing type polyimide resin (CT4112 manufactured by Toshiba Chemical Co., Ltd.) was dissolved.

Comparative Example 4 The composition of the coating solution was changed to a methyl ethyl ketone solution of a polyester resin (Vylon 200 manufactured by Toyobo Co., Ltd.).
A sample was prepared in the same manner as in Example 1.

The prepared samples were evaluated by the following evaluation methods. Evaluation method 1) Presence / absence of blocking after application and drying of undercoat film The presence / absence of sticking to the back surface of the film (with a coating film) was checked in the wound state. Samples that could be peeled without surface roughness were rated "excellent", adhesion was observed, and whitening due to surface roughness due to peeling and those completely adhered were "bad". 2) Surface properties The surface of the undercoat film after curing and the surface of the completed medium were observed with an optical microscope (100 times) to generate cracks,
Observation of the occurrence of a portion where the undercoating coating solution was not partially wetted, deterioration of the surface property due to the generation of oligomer due to heat, etc. was observed.

Table 1 shows the evaluation results.

As described above, in Examples using the present invention, it is possible to produce a medium having good surface properties without blocking after application of an undercoat and without causing cracks or surface roughness in a completed floppy disk. Was completed. on the other hand,
When a typical resin other than the present invention was used, blocking occurred after application of the undercoat, so that it was impossible to carry out further trial production. In Comparative Example 1 in which the magnetic film was formed directly on the non-magnetic support without applying the resin, surface roughness due to the precipitation of resin components such as oligomers from the non-magnetic support and cracks were observed in the magnetic film. A floppy disk with good surface properties could not be produced.

In Examples 1 to 3, after preparing a floppy disk, the surface thereof was scanned with a scanning electron microscope (SEM).
And an atomic force microscope (AFM). The maximum projection height was determined from data analysis of a three-dimensional profile obtained with an atomic force microscope, and the projection abundance was determined by counting from a photograph of a scanning electron microscope. In Examples 1 and 2, the protrusions of the nonmagnetic support were smoothed by the undercoat film, and the mirror surfaces were substantially free of protrusions. And the measured maximum protrusion height is R _max = 20 nm
Was extremely small. In Example 3, the projections having a height of 20 to 30 nm were formed with good dispersibility, and the density was 10 ⁷ / mm ² .

[0058]

By providing an undercoat layer made of a polyamideimide resin on a non-magnetic support, the non-magnetic support may be deformed, components may be eluted by heat, cracks, etc. in the film forming process under vacuum. A magnetic recording medium having excellent characteristics can be obtained relatively inexpensively without the occurrence of the problem.

Claims (3)

[Claims] In a magnetic recording medium having a magnetic layer formed on a nonmagnetic support, an undercoat film made of a polyamideimide resin is formed on at least one surface of the nonmagnetic support, and a vacuum film forming method is performed on the undercoat film. A magnetic recording medium characterized in that a ferromagnetic metal thin film formed by the method described in (1) is formed. 2. The magnetic recording medium according to claim 1, wherein the non-magnetic support is a flexible organic polymer resin film. 3. The magnetic recording medium according to claim 1, wherein the vacuum film forming method is a sputtering method.