JPH08325700A - Formation of silica protective film and production of magnetic recording medium - Google Patents

Abstract

PURPOSE: To obtain a silica protective film high in coating property and excellent in mechanical strength owing to low-temp. treatment by applying polysilazane on a magnetic metal thin film, irradiating the coating film with light to oxidize and polymerize the polysilazane and forming the protective film. CONSTITUTION: This magnetic recording medium has a magnetic film on at least one side of a nonmagnetic substrate, a polysilazane-contg. film is formed on the magnetic film, then the coating film is irradiated with light to oxidize and polymerize the polysilazane, and a silica protective film is formed. The thickness of the protective film is preferably controlled to 3-30μm, polysilazane dissolved in org. solvent is applied, a silica protective film having about 1μm thickness is obtained at a time, uniform film thickness is obtained by laminating the film in plural layers, and cracking is prevented after drying. IR, UV, various laser beams, etc., are used in the irradiation. When UV is used, a UV having <=200nm wavelength component is preferably used, and hence a even a small amt. of ozone generated in the irradiation contributes to the oxidation of polysilazane.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a protective film for improving the mechanical properties and corrosion resistance of the surface of a raw material, which method has a high film-forming property at a low temperature treatment and an excellent mechanical strength. It also relates to a method of manufacturing a magnetic recording medium using this silica protective film.

[0002]

2. Description of the Related Art As a magnetic recording medium such as a magnetic tape or a hard disk, a magnetic recording medium having a ferromagnetic metal thin film as a magnetic film suitable for high density recording has been put into practical use. A magnetic recording medium using such a ferromagnetic metal thin film as a magnetic film can easily achieve high magnetic energy and, at the same time, can achieve a very smooth surface property, so that the gap between the magnetic head and the magnetic recording medium can be reduced, resulting in a spacing loss. Is low and has high electromagnetic conversion characteristics.

However, these ferromagnetic metal thin film type magnetic films have lower abrasion resistance than conventional coating type magnetic films,
There was a large amount of wear due to sliding contact with the magnetic head and the like, and there was a problem in running durability. Therefore, a method of forming an inorganic oxide such as silica or zirconia or a protective film of carbon on the magnetic film to improve wear resistance is generally used.

Among the protective films as described above, the carbon protective film, which has been receiving the most attention recently, is formed by a vacuum film forming method such as a sputtering method or a chemical vapor deposition method (CVD), so that the film forming speed is low and There is a problem of lack of mass productivity.

Furthermore, the protective film formed by the vacuum film forming method does not have sufficient coverage, and pinholes are often generated when the substrate has a shape having complicated irregularities. In particular, this tendency becomes more remarkable as the thickness of the protective film becomes thinner, and in the case of a protective film having a film thickness of 20 nm or less like a protective film of a magnetic recording medium, there is a problem that the degree of improvement in corrosion resistance is low.

Further, when the protective film made of an inorganic oxide is also formed by the vacuum film forming method, there are the same problems as those of the above carbon protective film. As a method of solving this problem, there is a method of forming an inorganic oxide protective film by a sol-gel method. This method improves productivity, and by selecting an appropriate coating method, it is possible to form a pinhole-free protective film regardless of the shape of the substrate. Furthermore, by the sol-gel method, it is possible to prepare inorganic oxide protective films having various compositions such as silica, zirconia, alumina, titania and composite oxides thereof.

However, in the case of the sol-gel method, since the coating film (dry gel film) after coating and drying the sol solution is porous, in order to obtain a sufficiently dense film, it must be baked at a certain high temperature. However, heating at 500 ° C. or higher is required. Therefore, such a method requires a severe heat treatment even for a hard disk made on a metal or glass substrate, and is particularly difficult to apply to a flexible medium made on a plastic support.

Further, in the sol-gel method, an acid catalyst for adjusting the hydrolysis rate and the polymerization rate of the starting materials such as alkoxide is required to form a good silica film, which is the corrosion resistance of the magnetic film. However, there is a problem that it deteriorates and causes corrosion of manufacturing equipment.

[0009]

Therefore, according to the present invention,
Polysilazane, which is converted to silica by oxidation, is used to form a silica protective film by the coating method, but the conversion temperature of this polysilazane to silica by heating and oxidation is as high as 400 ° C or higher, and the temperature is lowered. Even the decomposition type has a conversion temperature of 250 ° C. or higher, and it is difficult to apply it to a plastic substrate or the like which is easily affected by heat.

The present invention has been made in view of the above problems, and provides a method for forming a silica protective film which can be formed under low temperature conditions and is excellent in mechanical properties and corrosion resistance, and a method for manufacturing a magnetic recording medium using the same. It is intended to be provided.

[0011]

Means for Solving the Problems The method for producing a silica protective film of the present invention which achieves the above object is to form a coating film of polysilazane on a substrate and then irradiate the coating film with light to oxidize it.
Polymerization is performed to form a silica protective film.

Further, the method for producing a magnetic recording medium of the present invention has a magnetic film on at least one surface of a non-magnetic support, and after forming a coating film of polysilazane on the magnetic film, the coating film is formed on the coating film. It is characterized in that a silica protective film is formed by performing light irradiation to oxidize and polymerize.

As described above, according to the present invention, polysilazane is used as a starting material for forming a silica protective film, and a polysilazane solution prepared by dissolving the polysilazane in a solution is applied on a substrate or a magnetic film and dried. Irradiation is performed to oxidize and polymerize polysilazane to form a silica protective film.

Polysilazane is a silicon-containing polymer having a main chain structure of (-SiH ₂ -NH-) _n , and examples of actual structures thereof include the following. Such polysilazane can be synthesized, for example, by the method described in JP-B-63-16325.

[0015]

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Since this polysilazane becomes silica when oxidized in air, it can be used as a starting material for producing silica. The density of the polysilazane coating film, which is the precursor of the silica protective film, is higher than that of the dry gel film, which is the precursor of the sol-gel method, so that the volume change upon decomposition is small and cracks are less likely to occur. Therefore, it has features that the critical thickness of the silica film that can be formed by one coating is large, and that a relatively dense silica film can be obtained even at low temperature.

In particular, in the present invention, the polysilazane coating film is subjected to oxidation and polymerization reaction by irradiating it with light such as ultraviolet rays, so that the conversion temperature to silica is low and a good silica protective film can be obtained even at a low temperature close to room temperature. Along with this, as a material capable of forming the silica protective film, in addition to a material such as polyethylene terephthalate or polyethylene naphthalate that deforms at a relatively low temperature, various materials such as metal and glass can be prepared.

The thickness of the silica protective film to be formed is preferably 3 nm or more, and when the silica protective film having a thickness of 2 μm or more is formed, it is preferable to form the silica protective film having a thickness of about 1 μm by laminating a plurality of times. By doing so, a silica protective film having a uniform film thickness can be easily formed, and cracks after drying can be prevented.

When a silica protective film for a magnetic recording medium is formed, the silica protective film has a thickness of 3 nm to 30.
nm is preferable, and more preferably 5 nm to 20 nm. If it is thinner than this, the function as a protective film is not sufficiently exerted, and if it is thicker than this, the spacing between the head and the magnetic film increases and the reproduction output is lowered.

In the present invention, the polysilazane coating film is prepared by dissolving a solution of the above raw material in an organic solvent by a wire bar method, a gravure method, a spray method, a dip coating method, a spin coating method or the like. It may be dried after being applied to. At this time, the film thickness of polysilazane can be adjusted by adjusting the concentration of the coating liquid and the coating amount of the solution.

The solvent for dissolving polysilazane is xylene,
Toluene, benzene, THF and the like can be used, but alcohols such as ethanol cannot be used because they react with polysilazane.

Light to be applied to the polysilazane in the present invention includes infrared rays, ultraviolet rays, various laser beams, electron beams and the like. Explaining ultraviolet irradiation, the irradiation light source is not particularly limited, and general high-pressure mercury lamp, low-pressure mercury lamp, excimer lamp and the like can be used. However, it is preferable to use ultraviolet rays having a wavelength component of 200 nm or less in order to accelerate the oxidative polymerization of polysilazane. As such a light source, a low pressure mercury lamp having a component of 185 nm or an excimer lamp generating a wavelength of about 172 nm is used. And so on.

The atmosphere at the time of this ultraviolet irradiation may be an inert gas atmosphere or air, and it is considered that a small amount of ozone generated by the ultraviolet irradiation accelerates the oxidation of polysilazane.

As the non-magnetic support used in the method for producing a magnetic recording medium of the present invention, a polymer film can be used in the case of a flexible medium, and a glass substrate or an aluminum substrate can be used in the case of a rigid medium. In the case of a flexible medium, a film made of polyethylene terephthalate, polyethylene naphthalate, polyimide, polyamide, polyamideimide or the like having a thickness of 3 to 75 μm is preferable. Further, a fine powder (filler) may be contained inside or on the surface of the support, and the surface of the support may have irregularities.

Now, a method of manufacturing a magnetic recording medium in which a silica protective film is formed as a protective film for a magnetic film of a magnetic recording medium such as a magnetic tape or a magnetic disk having polyethylene terephthalate as a non-magnetic support will be described.

For the ferromagnetic metal thin film used as the magnetic film in the magnetic recording medium of the present invention, conventionally known vacuum film forming methods such as vacuum vapor deposition method and sputtering method can be used. The traveling speed in the oblique vacuum vapor deposition method is usually 20 m / min or more, preferably 50 to 200 m / min. In the case of this oblique vacuum vapor deposition method, the degree of vacuum in the vapor deposition chamber is usually 5 × 10 ⁻⁵ torr or less, preferably 1 × 10 ⁻⁶ torr or less. The means for heating the ferromagnetic metal is not particularly limited, but electron beam, induction heating, etc. may be mentioned.

When the magnetic film is formed by a continuous winding type vacuum deposition method capable of high-speed film formation, a conventionally known metal or alloy containing cobalt as a main component can be mentioned. , CoNi, CoFe, or the like may be deposited in an oxygen atmosphere to contain oxygen in the film. In particular, in order to improve the electromagnetic conversion characteristics, 90% or more, and more preferably 95% or more of the metal atoms constituting the magnetic film are Co-O that is cobalt, or C that contains Co-O.
O-Fe and the like are preferable. The thickness of the magnetic film is 100 to 30.
The thickness is preferably 0 nm, more preferably 120 to
It is 200 nm. Further, the electromagnetic conversion characteristics can be further improved by forming the magnetic film in a multilayer structure.

Oxygen gas during vapor deposition is the coercive force (H
Necessary to increase c). 1200 Oe to 200
It is preferable to adjust the oxygen amount so that it becomes 0 Oe.
The amount of oxygen in the magnetic film is 10 to 30%, preferably 15 to 2
5%, the amount of oxygen introduced during vapor deposition depends on the vapor deposition width and the transport speed. For example, a non-magnetic support having a width of 100 mm, 20
When a magnetic film is formed under the condition of Hc of 1600 Oe at a speed of m / min, it is 250 cc / min from the vicinity of the minimum incident angle. In this case, the oxygen partial pressure is usually 1 × 10 ⁻⁵ torr.
˜5 × 10 ⁻⁴ torr.

On the other hand, when the magnetic film is formed by the sputtering method, a conventionally known metal or alloy mainly containing cobalt can be mentioned as the composition. Specifically, Co--C is used.
r, Co-Ni-Cr, Co-Cr-Ta, Co-Cr
-Pt, Co-Cr-Ta-Pt, Co-Cr-Pt-
Si, Co-Cr-Pt-B, etc. can be used. In particular, in order to improve the electromagnetic conversion characteristics, Co-Cr-Ta, Co-C
r-Pt is preferred. The thickness of the magnetic film is 10 to 300 nm
Is desirable.

Also in this case, in order to improve the electromagnetic conversion characteristics, a multilayer structure may be provided, or an underlayer and an intermediate layer may be provided. By using Cr or this alloy as the underlayer, the electromagnetic conversion characteristics can be particularly improved. This film thickness is usually 30 to 300 nm.

In the magnetic recording medium according to the present invention, it is preferable that a top coat film containing a lubricant for improving friction characteristics and a rust preventive for improving corrosion resistance is present on the silica protective film. As the lubricant, known hydrocarbon lubricants, fluorine lubricants, extreme pressure additives and the like can be used.

As the hydrocarbon lubricant, stearic acid,
Carboxylic acids such as oleic acid, esters such as butyl stearate, sulfonic acids such as octadecyl sulfonic acid, phosphoric acid esters such as monooctadecyl phosphate, alcohols such as stearyl alcohol and oleyl alcohol, carboxylic acids such as stearic acid amide Examples thereof include acid amides and amines such as stearylamine.

Examples of the fluorine-based lubricant include lubricants in which a part or all of the alkyl groups of the above hydrocarbon-based lubricant are 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 },
Perfluoroisopropylene oxide polymer {(CF
(CF ₃ ) CF ₂ O) _n } or copolymers of these.

Examples of extreme pressure additives include phosphoric acid esters such as trilauryl phosphate, phosphorous acid esters such as trilauryl phosphite, thiophosphorous acid esters and thiophosphoric acid esters such as trilauryl trithiophosphite, Examples include 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 onto the silica protective film, the lubricants are 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 deposition method. Just do it. Preferably 1 to 30 mg / m ² as a coating amount of the lubricant, 2 to 20 mg / m ² is particularly preferred.

As the rust preventive agent, benzotriazole,
Nitrogen-containing heterocycles such as benzimidazole, purine and pyrimidine, and derivatives in which an alkyl side chain is introduced into their mother nucleus, benzothiazole, 2-mercapton benzothiazole, tetrazaindene ring compound, nitrogen such as thiouracil compound and the like. Examples thereof include sulfur-containing heterocycles and derivatives thereof.

The tetrazaindene ring compound which can be used for such a purpose includes the compounds shown below.

[0038]

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Here, R is a hydrocarbon group selected from an alkyl group, an alkoxy group and an alkylamido group.
Particularly preferably, the number of carbon atoms is 3 or more and 20 or less, and in the case of alkoxy, R of ROCOCH ₂ — is C ₃ H ₇ —,
C ₆ H ₁₃ -, phenyl and the like, also in the case of alkyl _{groups, C 6 H 13 -, C} 9 H 19 -, C 17 H 35 - , and the like, in the case of alkylamide RNHCOCH ₂ - of R is phenyl, C ₃ H ₇ - and the like.

Further, examples of the thiouracil ring compound include those shown below.

[0041]

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[0042]

According to the present invention as described above, the polysilazane coating film formed on the substrate or the magnetic film is oxidized and polymerized by using light irradiation such as ultraviolet irradiation to convert the polysilazane into silica. A silica protective film is formed by using this method, which achieves higher productivity and corrosion resistance than vacuum film-forming methods such as sputtering methods, and is more compact and high-temperature machine than sol-gel method using alkoxysilane as a starting material. It is possible to create a silica protective film having strength.

Since polysilazane is used as a starting material, an acid catalyst is not required as in the sol-gel method.
It is possible to prevent the corrosion resistance of the magnetic recording medium from being impaired and prevent the corrosion of the manufacturing apparatus.

Particularly, since the conversion of polysilazane to silica is carried out by irradiation of light and the treatment temperature is lowered, a substrate or a non-magnetic support such as polyethylene terephthalate or polyethylene naphthalate which is deformable at a relatively low temperature is used. Even when used, a good silica protective film can be prepared.

As a result, not only glass and metal but also plastic substrates such as polyethylene terephthalate, non-magnetic supports, polymer coatings, magnetic films, and other materials that may be deformed or decomposed by the application of heat are protected by a silica protective film. Can be created. Since the silica protective film thus prepared has excellent mechanical strength and gas shielding property, it can be used for various purposes such as hard coat, anticorrosive film, antiblocking film, insulating film, smoothing film for uneven surface. it can.

[0046]

EXAMPLES The present invention will be described in more detail below by showing Examples and Comparative Examples of the present invention.

Example 1 As a non-magnetic support, a thickness of 1
A 0 μm polyester film was used, and spherical silica particles having an average particle diameter of 30 nm and tetraethoxysilane, methyltriethoxysilane, hydrochloric acid,
A solution containing water and cyclohexanone is applied by a wire bar method to form protrusions having a height of about 10 nm at 3 × 10 per 1 mm ^2.
An undercoat layer having ⁶ pieces was prepared.

Next, the non-magnetic support was brought into close contact with a rotary can cooled to 0 ° C. and conveyed, and cobalt was deposited on the undercoat layer in an oxygen-containing atmosphere so that the incident angle of the magnetic metal vapor stream with respect to the film was increased. Set to 45 °, 70nm
Was obliquely vapor-deposited twice to form a magnetic film made of a ferromagnetic metal film having a two-layer structure and a total thickness of 140 nm. The inclinations of the columnar crystals of magnetic metal forming the thin films of both layers were set to be the same.

Then, a m-xylene solution of polysilazane (manufactured by Tonen Co., Ltd.) was applied on the magnetic film by a wire bar method, and dried at 100 ° C. Subsequently, ultraviolet rays (center wavelengths 254 nm and 185 nm) generated from a low-pressure mercury lamp (Oak Seisakusho) in air were applied to the polysilazane coating film.
Was irradiated to decompose, oxidize and polymerize the polysilazane coating film and convert it to silica to form a silica protective film. At this time, the back surface of the sample corresponding to the ultraviolet ray irradiation portion was brought into close contact with a water-cooling roller and cooled. When the thickness of the obtained silica protective film was measured by observing an ultrathin section of TEM, the layer thickness was about 17 nm.

Further, a back coat consisting of carbon black and a resin binder is formed on the back surface of the non-magnetic support by the wire bar method, and then the perfluoropolyether having hydroxyl groups at both ends is formed on the silica protective film. System lubricant (FOMBLIN Z-DOL manufactured by Montefluos Co., Ltd.) was dissolved in a fluorine-based solvent (ZS-100 manufactured by the same company) and applied by a wire bar method so that the coating amount was 20 mg / m ^2, and
Dried. This raw fabric was cut into a width of 8 mm to obtain a magnetic recording medium (magnetic tape) as a sample.

<Example 2> This example is an example in which the atmosphere during ultraviolet irradiation was an inert gas atmosphere. Example 1 was repeated except that the atmosphere during ultraviolet irradiation on the surface of the polysilazane coating was replaced with nitrogen gas. A sample was prepared in the same manner as in.

Comparative Example 1 This example is an example in which light irradiation is not performed, and a sample was prepared in the same manner as in Example 1 except that the step of irradiating the polysilazane coating film with ultraviolet rays was omitted.

Comparative Example 2 In this example, a protective film is formed by a sol-gel method without using polysilazane, and the ultraviolet irradiation atmosphere is atmospheric air. Hydrochloric acid was added to an ethanol solution of tetraethoxysilane in place of the polysilazane solution in Example 1 and stirred for 10 hours, and then this solution was applied onto a magnetic film and dried to obtain a silica gel precursor as a precursor of silica by a sol-gel method. Samples were prepared in the same manner as in Example 1 except for the above.

Comparative Example 3 In this example, a protective film is similarly formed by a sol-gel method, and the ultraviolet irradiation atmosphere is nitrogen gas. In Example 2, hydrochloric acid was added to an ethanol solution of tetraethoxysilane instead of the polysilazane solution and stirred for 10 hours, and then this solution was applied onto a magnetic film and dried to obtain a silica gel precursor as a precursor of silica by a sol-gel method. Samples were prepared in the same manner as in Example 2 except for the above.

Comparative Example 4 This example is an example in which the protective film is not formed. In the same manner as in Example 1, the lubricant is applied on the magnetic film having no silica protective film without applying polysilazane in Example 1. Then, a sample was prepared.

The following abrasion resistance test was performed on each of the samples (Examples 1 and 2 and Comparative Examples 1 to 4) prepared as described above.
Evaluation by a corrosion resistance test was performed. The evaluation results are shown in Table 1.

(1) Scratch Strength Test A load of 10 g was applied to a steel ball having a diameter of 4 mm, and the steel ball was slid back and forth on the sample for 30 mm at a speed of 10 mm / sec. I observed.
Then, the load was increased by 10 g, and the load in which scratches were generated was taken as the scratch strength. The maximum load was 120 g.

(2) Still Durability Test After recording a color bar using a VTR modified from an 8 mm VTR (manufactured by FUJIFILM Corporation), reproduction is performed in the still mode, and the durability until the output drops by 3 dB is used. Made durable. The environment is 23 ° C, the humidity is 5% RH, and the load is 2
It was set to 0 g / 8 mm. The maximum evaluation was 30 minutes.

(3) Sulfurous acid gas corrosion resistance test The sample was kept in air containing 1 ppm of sulfurous acid gas for 72 hours, and the surface of the sample was observed after the test. The environmental conditions at this time were 27 ° C. and humidity 80% RH. After the test, there was a slight amount of corrosion, but the magnetic film remained on almost the entire surface was evaluated as ◯, when the magnetic film was completely dissolved was evaluated as x, and between the two was evaluated as Δ.

[0060]

[Table 1]

As can be seen from Table 1 above, Examples 1 and 2 and Comparative Example 1 in which a protective film made of a polysilazane coating film was formed showed good corrosion resistance, but the ultraviolet irradiation treatment of Comparative Example 1 was not performed. Has insufficient conversion to silica and has lower abrasion resistance than Examples 1 and 2. From this, it was confirmed that a good silica protective film was formed by the low temperature treatment.

Claims (2)

[Claims] 1. A method for producing a silica protective film, which comprises forming a coating film of polysilazane on a substrate and then irradiating the coating film with light to oxidize and polymerize to form a silica protective film. 2. In a magnetic recording medium having a magnetic film on at least one surface of a non-magnetic support, after forming a coating film of polysilazane on the magnetic film, the coating film is irradiated with light to oxidize and polymerize. And a silica protective film are formed to perform a method of manufacturing a magnetic recording medium.