JPH0971409A - Inorganic protecting film and magnetic recording material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an inorganic protecting film by adding fine particles into an oxidized film of a polysilazane coating film, having a reduced coefficient of friction during sliding on the surface of a protecting film, excellent in durability and corrosion resistance. SOLUTION: This inorganic protecting film is obtained by oxidizing a polysilazane coating film formed by coating to give an inorganic oxide film and adding fine particles to the film. The inorganic protecting film containing the fine particles in the inorganic oxide film is formed at least one face of a nonmagnetic substrate to give the objective magnetic recording medium. In the magnetic recording medium, preferably the magnetic layer is preferably a ferromagnetic metal thin film formed by a vacuum film-forming method. The thickness of the inorganic protecting film is >=3nm and <=30nm. The fine particles are an inorganic substance and have >=3 Mohs hardness, >=5nm and <=40nm particle diameters, especially >=5nm and <=20nm particle diameters. Particles of silica, alumina, zirconia, titania, chromium oxide, carbon black, polystyrene, etc., may be cited as the fine particle material used.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inorganic protective film which improves mechanical properties and abrasion resistance of a material surface. It also relates to a magnetic recording medium using this inorganic protective film.

[0002]

2. Description of the Related Art In magnetic recording media such as magnetic tapes and hard disks, magnetic recording media having a magnetic layer of a ferromagnetic metal thin film suitable for high density recording have been put into practical use. A magnetic recording medium using such a ferromagnetic metal thin film as a magnetic layer can easily achieve high magnetic energy, and at the same time, can achieve a very smooth surface property so that it has a small spacing loss and high electromagnetic conversion characteristics. There are features.

However, these ferromagnetic metal thin film type magnetic layers have a large wear due to sliding contact with a magnetic head or the like and have problems in running durability as compared with the conventional coating type magnetic layers. Therefore, a method of forming an inorganic oxide such as silica or zirconia or a protective film of carbon on the magnetic layer to improve wear resistance is generally used.

However, since the carbon protective film, which has received the most attention recently, is formed by a vacuum film forming method such as a sputtering method or a chemical vapor deposition method (CVD), the film forming rate is slow and the mass productivity is insufficient. There is.

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 there is a problem that the degree of improvement in corrosion resistance becomes lower 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. When the inorganic oxide protective film is also formed by the vacuum film forming method, it has the same problem as the carbon protective film. As a method of solving such a problem, there is a method of forming a protective film by a coating method. With such a coating method, the productivity is improved, and by selecting an appropriate coating method, it is possible to form a pinhole-free protective film regardless of the shape of the substrate. As such a method, there is a method of forming an inorganic oxide protective film by a sol-gel method (Japanese Patent Laid-Open Nos. 52-20804 and 7-161031).
No. 7-61032). Furthermore, by the sol-gel method, it is possible to prepare inorganic oxide protective films of various compositions such as silica, zirconia, alumina, titania and composite oxides thereof.

However, in this case, 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 high temperature to some extent, and preferably 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 considerably 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 deteriorates the corrosion resistance of the magnetic layer. There is also a problem of causing corrosion of manufacturing equipment.

As another method, there is known a method in which a polymer-dissolved solution is applied and dried, or a monomer-dissolved solution is applied and then polymerized by, for example, an electron beam to form a polymer protective film. (For example, JP-A-6-
(See Japanese Patent No. 50564). However, in this case, when the sliding member is a relatively hard material such as metal or ceramics, such as a magnetic recording medium, the cured film of the polymer lacks wear resistance and durability during sliding. There was a problem that it was inferior to.

Further, when the protective film is formed by such a coating method, the film has good coating properties by filling the recesses on the surface, a film with few pinholes can be obtained, and the surface can be smoothed. Because of this characteristic, the surface becomes too smooth, which may lead to an increase in the actual contact area during sliding and an increase in the friction coefficient. As the friction coefficient increases, the sliding contact surfaces are less likely to slip with each other, which may adversely affect the durability of both.

This problem can be solved by increasing the surface roughness of the substrate and controlling the surface roughness of the protective film surface (see JP-A-61-229227 and JP-A-61-73227). In this case, the film thickness of the protective film of the convex portion, which becomes the contact portion during sliding, becomes thinner than the other portions, and the effect of improving the basic sliding characteristics of the protective film decreases. In particular, in the case of a magnetic recording medium, the thickness of the protective film serves as a gap between the head and the magnetic film and directly affects the electromagnetic conversion characteristics, and therefore the above-mentioned problems are particularly important.

[0010]

Therefore, according to the present invention,
The protective film of the inorganic oxide film formed by the oxide film of the polysilazane coating film has a feature that it can be formed at a relatively low temperature, has high strength and is effective as a protective film, and has good film forming property. It is intended to be used as a protective film for magnetic recording media, especially ferromagnetic metal thin films, where a strong and uniform film is required, but the film surface obtained with the film forming property is extremely smooth. Since it is possible, by smoothing the surface of the film, the actual contact area during sliding as described above increases and the friction coefficient increases,
The running durability of the sliding contact surface that comes into contact with and slides on the protective film may be deteriorated.

The present invention has been made in view of the above-mentioned problems, and it is independent of the shape of the substrate, has a reduced coefficient of friction during sliding of the surface of the protective film, and has improved durability and corrosion resistance. And a magnetic recording medium using the same.

[0012]

The inorganic protective film of the present invention, which has solved the above-mentioned problems, is characterized by containing fine particles in an inorganic oxide film formed by subjecting a polysilazane film formed by coating to oxidation treatment. Is.

In the magnetic recording medium of the present invention, the surface of the magnetic layer formed on at least one surface of the non-magnetic support is
It is characterized in that an inorganic protective film containing fine particles is formed in the inorganic oxide film.

In the above magnetic recording medium, preferably, the magnetic layer is a ferromagnetic metal thin film formed by a vacuum film forming method, and the inorganic protective film has a thickness of 3 nm or more and 30 nm or less. The fine particles are inorganic substances and have a Mohs hardness of 3 or more and a particle diameter of 5 nm or more and 40 nm or less, particularly 5 nm or more and 20 nm or less.

The inorganic oxide film in the above inorganic protective film is a silicon oxide film obtained by subjecting a polysilazane coating film to an oxidation treatment, and constitutes a continuous film in which a network in which silicon atoms and oxygen atoms are strongly bonded is formed.

The fine particles are inorganic fine particles made of oxides, nitrides, carbides or the like or organic fine particles made of organic substances, and the size and the content in the film differ depending on the function expected of the protective film for the object to be protected. I can't decide because I do. The addition of the fine particles (filler) forms unevenness on the surface of the protective film, reduces the actual contact area in sliding contact, and reduces the friction coefficient. Further, when the fine particles are made of a material harder than the inorganic oxide film, abrasion resistance is further improved, which is preferable.

Examples of usable fine particle materials include inorganic oxides such as silicon oxide (silica), aluminum oxide (alumina), zirconium oxide (zirconia), titanium oxide (titania) and chromium oxide, carbon black,
Examples thereof include particles of diamond-like carbon, carbon such as diamond, and organic substances such as polystyrene.

The diameter of the fine particles to be added is preferably about 1 to 3 times the film thickness of the inorganic oxide film in order to obtain a uniform surface, but even if it is smaller than the film thickness, unevenness should be created on the surface. Can be used because it is possible. The addition amount depends largely on the application and purpose, so it needs to be optimized.

For example, when it is added to the inorganic protective film of the magnetic recording medium, the diameter of the fine particles is 5 to 40 n as described above.
It is preferably about m, and more preferably about 5 to 20 nm. If the diameter of the fine particles is smaller than this range, the surface energy increases and aggregation easily occurs. Even if they can be dispersed in a solution, it is difficult to form irregularities. On the other hand, if the diameter of the fine particles is larger than this, the maximum thickness of the inorganic protective film increases, the gap between the head and the magnetic film increases, and the electromagnetic conversion characteristics due to spacing loss deteriorate, which is not preferable.

The oxidation treatment of the polysilazane film is a heat treatment, a light irradiation treatment, a treatment of contacting with active oxygen or ozone, and a silicon oxide film (silica protective film) is formed by this oxidation treatment.

[0021]

According to the present invention as described above, a fine protective film function is obtained by the inorganic protective film, and fine particles are contained in the inorganic oxide film, so that fine irregularities are formed on the surface of the inorganic protective film. The friction coefficient of the surface of the coating decreases and the increase of the friction coefficient due to the increase of the actual contact area due to the formation of the protective film is prevented, and the appropriate sliding property is given to provide durability suitable for the intended use of the material. It becomes an inorganic protective film having.

Further, by forming the inorganic protective film with a polysilazane coating film, the productivity and the corrosion resistance superior to those of the vacuum film forming method such as the sputtering method are achieved, and the sol-gel starting from alkoxysilane is used. It is possible to form an inorganic protective film that is dense and has high mechanical strength at a lower temperature than the method. Further, since polysilazane is used as a starting material, an acid catalyst is not required as in the sol-gel method, so that the corrosion resistance of the magnetic recording medium is impaired and the corrosion of the manufacturing apparatus can be prevented. Furthermore, not only glass and metal, but also plastic substrates such as polyethylene terephthalate, non-magnetic supports, polymer coatings, magnetic layers, etc. are formed with an inorganic protective film on materials that may be deformed or decomposed by the application of heat. It becomes possible. The inorganic protective film thus formed has excellent mechanical strength and gas shielding properties, and therefore has a hard coat, an anticorrosive film, an antiblocking film,
It can be used for various purposes such as insulating film.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in more detail below with reference to embodiments of the inorganic protective film of the present invention.

The inorganic protective film of this example is formed by forming a coating film of polysilazane containing fine particles (filler) on the surface of a substrate (object to be protected), and then subjecting this coating film to an oxidation treatment to form an inorganic oxide. The inorganic protective film (hereinafter referred to as silica protective film) having fine particles contained in the (silicon oxide) film and having irregularities on the surface is formed.

The above 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.

[0026]

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Since this polysilazane becomes silicon oxide when oxidized in air, it can be used as a starting material for forming a silica protective film. Then, as compared with the sol-gel method and the like described above, the density of the polysilazane coating film that is the precursor of the silica protective film is higher than that of the dry gel film that is the precursor in the sol-gel method, so the volume change when decomposed Less and less likely to crack. 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.

Particularly, in the oxidation treatment of the polysilazane coating film, the conversion temperature is 400 ° C. or higher when it is converted to silicon oxide by heating, and 250 ° C. or higher for the easily decomposable type, which is affected by the heat of the plastic substrate. For those that are susceptible to ultraviolet rays, the oxidation reaction is performed by irradiation with light such as ultraviolet rays or contact with active oxygen or ozone, the conversion temperature to silicon oxide is low, and a good silica protective film can be obtained even at low temperatures near room temperature. To be 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 a plurality of laminations. By doing so, a silica protective film having a uniform film thickness can be easily formed, and cracks after drying can be prevented.

When used as a silica protective film of a magnetic recording medium, the thickness of the silica protective film is 3 nm to 3 nm.
0 nm is preferable, and more preferably 5 nm to 20 nm.
It is. If it is thinner than this, the function as a protective film is not sufficiently exhibited, and if it is thicker than this, the spacing between the head and the magnetic layer is increased and the reproduction output is lowered.

As a method for producing the above polysilazane coating film, a solution obtained by dissolving the above raw materials in an organic solvent is applied onto the magnetic layer by a method such as a wire bar method, a gravure method, a spray method, a dip coating method, a spin coating method or the like. After doing
Just dry. 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.

In this example, the method of incorporating the fine particles is to coat the fine particles on a substrate in advance and then apply polysilazane on top of this, or use a solvent in which the fine particles do not react with polysilazane such as xylene or toluene. If it is dispersed, a method of directly adding it to the polysilazane solution and coating it can be mentioned.

As a method of oxidizing polysilazane by heating in this example, after coating polysilazane and fine particles on a substrate, 150 ° C. or higher in an atmosphere containing water and oxygen,
A method of maintaining the temperature at 200 ° C. or higher is preferable.

When the polysilazane coating film is exposed to a UV lamp, for example, the polysilazane coating film may be exposed to a UV lamp. Ultraviolet rays are preferable as the light source, and particularly a low-pressure mercury lamp or excimer lamp having a wavelength component of 200 nm or less such as 185 nm is preferable because the oxidation treatment time can be shortened.

Examples of the method of contacting with active oxygen or ozone include a method of contacting a polysilazane coating film with ozone, a method of contacting with oxygen plasma under reduced pressure, and a method of flame treatment in the atmosphere. The ozone to be brought into contact can be created by a general generator applying a discharge method, an ultraviolet ray irradiation method, or a radiation irradiation method. When ozone is used for the oxidation treatment, the concentration of ozone is not particularly limited, but 1 to 100 g / m ³ (5
00~50000ppm), preferably 5 to 50 g / m ³
(2,500 to 25,000 ppm). Oxidation treatment is possible with contact time with ozone of several seconds to several minutes.

When exposed to the above-mentioned light or contacted with active oxygen, it can be oxidized even when the substrate temperature is near room temperature, so that it can be used for a substrate having low heat resistance such as a plastic substrate. However, in order to improve the processing speed, it is preferable to heat the substrate, and the heating temperature is set within a range that does not affect the substrate or the like by deformation. For example, when polyethylene terephthalate or polyethylene naphthalate is used for the substrate, and when the polysilazane coating film provided on the front surface of the substrate is subjected to oxidation treatment while the back surface of the substrate is brought into close contact with the heating roller, heating to around 100 ° C affects the substrate. Therefore, the processing speed can be increased.

An embodiment will be described below in which the above inorganic protective film is applied as a protective film for a magnetic layer of a magnetic recording medium such as a magnetic tape or a magnetic disk having polyethylene terephthalate as a non-magnetic support. .

As the non-magnetic support used in the magnetic recording medium of this example, 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. Thickness 3 to 75 for flexible media
A film of polyethylene terephthalate, polyethylene naphthalate, polyimide, polyamide, polyamide-imide or the like having a thickness of 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.

For the ferromagnetic metal thin film forming the magnetic layer in the magnetic recording medium of this example, a conventionally known vacuum film forming method such as a vacuum vapor deposition method or a 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 layer is formed by a continuous winding type vacuum vapor deposition method capable of high-speed film formation, conventionally known metals or alloys 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 layer are Co—O that is cobalt, or C that contains Co—O.
O-Fe and the like are preferable. The thickness of the magnetic layer is 100 to 30.
The thickness is preferably 0 nm, more preferably 120 to
200 nm. Further, the electromagnetic conversion characteristics can be further improved by forming the magnetic layer into a multilayer structure.

Oxygen gas during vapor deposition has a 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 layer 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 layer is formed under the condition of Hc of 1600 Oe at a speed of m / min, the magnetic field 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 layer is formed by the sputtering method, a conventionally known metal or alloy mainly containing cobalt can be mentioned as a composition, specifically, Co--C.
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 layer 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 octadecylsulfonic acid, phosphoric esters such as monooctadecyl phosphate, alcohols such as stearyl alcohol and oleyl alcohol, and carboxylic acids such as stearamide. 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.

Examples of the tetrazaindene ring compound that can be used for such a purpose include those shown below.

[0052]

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Here, R is a hydrocarbon group selected from an alkyl group, an alkoxy group and an alkylamido group.
Particularly preferably, it has 3 to 20 carbon atoms, 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.

[0055]

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[0056]

EXAMPLES Examples and comparative examples of the present invention will be shown below to evaluate the protective film characteristics thereof.

Example 1 As a non-magnetic support, a thickness of 1
A 0 μm polyester film was used, and a solution of tetraethoxysilane, methyltriethoxysilane, and hydrochloric acid dissolved in cyclohexanone was applied on the film by a gravure coating method and then dried to a thickness of 0.2 μm.
m undercoat layer was prepared. This produced a smooth support substantially free of protrusions.

This support was conveyed in close contact with a rotary can cooled to 0 ° C., and cobalt was coated on the undercoat layer in an oxygen-containing atmosphere so that the angle of incidence of the magnetic metal vapor flow on the film was 45 °. Then, oblique vapor deposition was performed twice with a thickness of 70 nm to form a magnetic layer of a ferromagnetic metal film having a total thickness of 140 nm and having a two-layer structure. The inclinations of the columnar crystals of magnetic metal forming the thin films of both layers were set to be the same.

Thereafter, a spherical monodisperse silica sol having an average particle diameter of 12 nm dispersed in toluene as fine particles was added to an m-xylene solution of polysilazane (manufactured by Tonen Co., Ltd.) on the magnetic layer, and this was applied by a gravure coating method. 10,
It was dried at 0 ° C.

The thickness of the obtained polysilazane coating film was measured by TE
Layer thickness of about 12n as measured by ultrathin section observation of M
m. When the surface of this coating film was observed by AFM, it was found that about 10 ⁶ projections with a height of 5 to 20 nm from the reference plane were observed.
Pieces / mm ^{2 were} formed.

Next, the back surface of the non-magnetic support was brought into close contact with a roller cooled to 20 ° C., and ultraviolet rays (185 nm + 254 n) generated from a low-pressure mercury lamp under a nitrogen atmosphere.
m) was applied to the polysilazane coating film on the surface for about 1 minute to decompose, oxidize and polymerize the polysilazane coating film and convert it to silica to form a silica protective film.

Further, a coating liquid consisting of carbon black, an abrasive (calcium carbonate) and a resin binder is applied to the back surface of the non-magnetic support by a wire bar method to give a thickness of 0.5 μm.
m back coat was created. Then, a perfluoropolyether-based lubricant having hydroxyl groups at both ends (FOMBLIN Z- manufactured by Montefluos Co., Ltd. was formed on the silica protective film.
A 2: 1 mixture of DIAC and Z-DOL) was dissolved in a fluorine-based solvent (ZS-100 manufactured by the same company), and coated 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 In this example, a sample was prepared in the same manner as in Example 1 except that the oxidation process of the polysilazane coating film was changed to the following oxygen plasma treatment.

In the oxygen plasma treatment, the raw material on which the polysilazane coating film is formed is set in a continuous winding type CVD apparatus,
After evacuating the vacuum chamber, RF power of 800 W was applied to a quartz torch having a high frequency excitation coil, oxygen gas was introduced into this torch at a flow rate of 200 mL / min, oxygen plasma was generated, and polysilazane coating was applied to this plasma. Membrane is about 30
The original fabric was conveyed so as to come into contact for seconds.

Example 3 This example is different from Example 1 except that the non-magnetic support was changed to aramid film and the polysilazane coating film was oxidized by heating at 200 ° C. for 1 hour. A sample was prepared in the same manner as in Example 1.

Comparative Example 1 This example is the same as Example 1 except that spherical monodisperse silica sol was not added to the polysilazane solution.
A sample was prepared in the same manner as in Example 1 except that a silica protective film formed of a polysilazane coating film having substantially no protrusions was formed. The number of protrusions with a height of 5 to 20 nm is 10 ⁴ /
It was mm ² .

Comparative Example 2 This example is an example in which no oxidation treatment is applied, and a sample was prepared in the same manner as in Example 1 except that the step of oxidizing the polysilazane coating film was omitted.

Comparative Example 3 This example is an example of a protective film formed by a sol-gel method without using polysilazane. Hydrochloric acid was added to an ethanol solution of tetraethoxysilane instead of the polysilazane solution in Example 1 and stirred for 10 hours, and then a spherical monodispersed silica sol having a diameter of about 12 nm dispersed in methanol was added, and this solution was applied onto the magnetic layer. A dried gel film which is a precursor of silica was prepared by a sol-gel method of drying and drying, and a sample was prepared in the same manner as in Example 1 except for this. The thickness of the gel film in this case is about 12n
m, and the number of protrusions of ^{5 to} 20 nm is about 7 × 10 ⁵ pieces / mm
^{Was 2} .

<Comparative Example 4> In this example, a sample was prepared under the same conditions as in Comparative Example 3 except that 50 mol% of the tetraethoxysilane of Comparative Example 3 was replaced with methyltriethoxysilane. In this case, the number of protrusions of 5 to 20 nm is 7 × 10
^{It was 5} pieces / mm ² .

The samples prepared as described above (Example 1)
.About.3 and Comparative Examples 1 to 4) were evaluated by the following abrasion resistance test and friction coefficient measurement. 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 that is a modified 8 mm VTR (manufactured by Fuji Film Co., Ltd.), it is played back in the still mode, and the durability until the output drops by 3 dB is still. 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) Friction coefficient test with stainless steel guide pole Under the environment of temperature 23 ° C. and humidity 5% RH, stainless steel (SU
S420J) Wrap the sample around the guide pole 180
The sample was brought into contact with each other at 20 ° and a load of 20 g was applied to one end of the sample. Then, the other side of the sample is run while pulling a distance of 30 mm at a speed of 3.3 cm / sec, the tension T at this time is detected by a strain gauge, and the friction coefficient μ is μ = (1 / π) · In (T / 20). The coefficient of friction was evaluated by the value after running 10 times.

[0074]

[Table 1]

As can be seen from Table 1 above, Example 1 in which a polysilazane coating film was provided with an oxidized silica protective film
In Examples 1 to 3 and Comparative Example 1, good scratch strength is shown, but in Examples 1 to 3 containing fine particles, the unevenness of the surface reduces the friction coefficient to 0.30 to 0.31 and results in good still strength. While showing durability, Comparative Example 1 containing no fine particles has an extremely flat surface and a large friction coefficient of 0.45.

Further, in the case of the polysilazane coating film of Comparative Example 2 which was not subjected to the oxidation treatment, the conversion to silicon oxide was insufficient and the scratch strength and still durability were lower than those of Examples 1 to 3. In the protective films of Comparative Examples 3 and 4 by the sol-gel method, the scratch strength and the still durability are further reduced. As a result, it was confirmed that a silica protective film suitable for a magnetic recording medium was formed.

Claims (4)

[Claims] 1. An inorganic protective film comprising fine particles contained in an inorganic oxide film formed by oxidizing a polysilazane film formed by coating. 2. A magnetic recording medium having a magnetic layer on at least one surface of a non-magnetic support, wherein an inorganic protective film containing fine particles in an inorganic oxide film is formed on the surface of the magnetic layer. Magnetic recording medium. 3. The magnetic layer is a ferromagnetic metal thin film formed by a vacuum film forming method, and the inorganic protective film has a thickness of 3 nm.
Or more and 30 nm or less, and the fine particles are inorganic substances and have a Mohs hardness of 3 or more and a particle diameter of 5 nm or more and 4 or more.
The magnetic recording medium according to claim 2, which has a thickness of 0 nm or less. 4. The magnetic recording medium according to claim 2, wherein the inorganic oxide film is a polysilazane film formed by coating and subjected to an oxidation treatment.