JPH08185619A - Magnetic recording medium and its production - Google Patents

Abstract

PURPOSE: To provide a magnetic recording medium with uniform low protrusions on the surface of the undercoat layer by interposing an undercoat layer made of a silica film contg. heat resistant fine particles between a nonmagnetic substrate and a magnetic layer. CONSTITUTION: This magnetic recording medium has a magnetic layer made of a ferromagnetic metallic thin film on one side of the nonmagnetic substrate 5 and an undercoat layer 1 made of a silica film contg. heat resistant fine particles 3 between the substrate 5 and the magnetic layer. Since uniform fine protrusions 4 can be formed on the surface of the undercoat layer 1 and thermal deterioration is not caused owing to the heat resistant silica film adopted as the layer 1, surface properties are further improved. Since the undercoat layer 1 is excellent in heat resistance, the surface properties of the formed layer 1 are maintained even after forming the ferromagnetic metallic thin film and this magnetic recording medium has very uniform low protrusions 4, does not cause thermal deterioration and ensures high electromagnetic transducing characteristics.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium having a ferromagnetic metal thin film as a magnetic layer, and in particular electromagnetic conversion by forming an undercoat layer having high heat resistance, smooth surface property and high tensile strength. The present invention relates to manufacturing a metal thin film magnetic recording medium having excellent characteristics.

[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, if the surface properties of the magnetic layer are made too smooth, the actual contact area increases and the lubricant applied to the surface causes adsorption to the mating member, making it very difficult to ensure running durability. For this reason, electromagnetic conversion characteristics are slightly sacrificed by applying fine particles and a binder to the surface of the base film for magnetic tape, and mechanically polishing the substrate to provide appropriate irregularities on the surface for hard disks. Assures running durability.

Japanese Unexamined Patent Publication No. 57-8921 discloses that a substrate provided with a metal or an oxide film is sputtered with Si.
A magnetic recording medium in which an O ₂ or glass film is formed and an oxide magnetic film is provided thereon by sputtering is disclosed to improve magnetic characteristics. In Japanese Patent Laid-Open No. 57-52646, S is contacted with the surface of a base material made of a polymer molding.
It discloses that a vapor deposition film of io is formed and at least a magnetic metal film is arranged on the SiO vapor deposition layer to improve the life characteristics. And, JP-A-59-207
No. 422 discloses that an average particle size of 3 to 3 is provided on a film base material.
A magnetic recording medium in which an undercoat layer having a thickness of 0.2 μm or more containing inorganic fine particles of 50 nm is provided and a ferromagnetic metal thin film is provided thereon is disclosed to improve the mechanical strength of the tape.

By the way, in order to achieve both electromagnetic conversion characteristics and running durability at a high level, it is ideal that the irregularities provided on the surface of the medium have a high density of protrusions having substantially the same height.

However, in recent magnetic recording media, there is a strong demand for high-density recording, and higher electromagnetic conversion characteristics are required. Therefore, the height of the protrusions tends to gradually decrease. In such a magnetic recording medium, low protrusions of about 10 nm to 20 nm must be uniformly formed, which makes it difficult to form the protrusions.

For example, in the case of a magnetic tape, the fine particles to be coated on the surface of the non-magnetic support must be ultrafine particles having a particle diameter of about 10 nm as described above. It is very difficult to coat such ultrafine particles having surface energy on a non-magnetic support without agglomerating. Even if this agglomeration is local, it is often of sufficient density to form an extra void between the head and the magnetic recording medium, and has a lower electromagnetic conversion characteristic than expected from the coated particle size. I can't get it.

On the other hand, even in a hard disk, it is difficult to uniformly form the above-mentioned low protrusions by a mechanical method. Therefore, the present inventors usually use 20 to 3 normally.
A study was carried out using fine particles having a size of about 0 nm, but forming an undercoat layer on the surface of the non-magnetic support in which the thickness of the dispersion layer was increased in order to reduce the influence of the particle size as much as possible.

However, if the undercoat layer is thickened, a phenomenon of so-called "heat loss" occurs, in which large protrusions are formed in the magnetic layer, probably because the binder of the undercoat layer changes when the magnetic layer is formed by sputtering. was there.

[0010]

SUMMARY OF THE INVENTION The present invention is to provide a magnetic recording medium which has low and uniform protrusions on the surface of a non-magnetic support of the magnetic recording medium and which has both high electromagnetic conversion characteristics and running durability. It is a thing.

[0011]

The above object of the present invention is to:
In a magnetic recording medium having a magnetic layer made of a ferromagnetic metal thin film on at least one surface of a non-magnetic support, an undercoat layer made of a silica film containing heat-resistant fine particles is provided between the non-magnetic support and the magnetic layer. A magnetic recording medium characterized by having a coating solution containing the heat-resistant fine particles in a solution containing a silicon-containing compound on at least one surface of a non-magnetic support, and then forming the undercoat layer This can be achieved by the above-described method of manufacturing a magnetic recording medium, characterized in that the ferromagnetic metal thin film is formed by a vacuum film forming method.

The present invention is characterized in that a silica film containing heat-resistant fine particles is used as an undercoat layer, and uniform fine projections can be formed on the surface of the undercoat layer to improve the surface property of the magnetic layer. Furthermore, since a heat-resistant silica film is used as the undercoat layer, heat loss or the like does not occur, so that the surface property is further improved.

That is, in the magnetic recording medium of the present invention, since the undercoat layer made of a silica film containing heat-resistant fine particles has excellent heat resistance, the surface property of the prepared undercoat layer is after the formation of the ferromagnetic metal thin film. It is possible to obtain a magnetic recording medium which is maintained even in the above and has a very uniform and low protrusion.

The silica film in the magnetic recording medium of the present invention is used in a broad sense and refers to a film mainly composed of a compound composed of a silicon-oxygen bond network, but it is not always the amount of SiO ₂ . It does not have to be rational.
For example, the silica film may contain a hydroxyl group, an alkoxy group, an alkyl group, or the like. The method for producing such a silica film is not particularly limited, but it is preferably produced by a production method to which the sol-gel method described later is applied. Such a silica film can be easily prepared, and has a characteristic that it is excellent in heat resistance as compared with ordinary resins such as polyester resin. In other words, this silica film does not cause surface loss due to heat loss or oligomer precipitation even when the non-magnetic support is heated during the production of a ferromagnetic metal thin film, that is, during vacuum deposition or sputtering. The surface property of the layer can be maintained. In addition, even when the surface is smooth, it has the characteristic that blocking is less likely to occur, so in a medium in which a polymer film is used as the non-magnetic support, the non-magnetic support is wound without being affected by the back surface of the non-magnetic support. Even if it is stored in the taken roll state, the original surface property can be maintained.

In the present invention, bringing the silica film closer to the stoichiometric ratio SiO ₂ leads to an increase in hardness and a decrease in elasticity of the film.
If the elasticity is lowered, cracks may occur during the preparation of the undercoat layer such as drying or heat treatment or the subsequent handling, and attention is required especially when the non-magnetic support is a polymer film. Such a problem is that some of the SiO ₂ bonds are Si-
It is known that this can be solved by substituting R (R is an alkyl group) (for example, Proceedings of 1991 Annual Meeting of the Ceramic Society of Japan, page 95, etc.). The alkyl group is not particularly limited, and a methyl group, an ethyl group, a propyl group or the like can be used, but it is preferable to use an alkyl group having 8 or less carbon atoms in order to suppress a change in film thickness when the bond is decomposed. The number of alkyl groups bonded to one Si atom is 1 or 2, but the number of alkyl groups is preferably 1 in order to reduce the change in film thickness during decomposition. The content of Si atoms having an alkyl group in the silica film is not particularly limited, but it is 20 to 80 atom% in order to form a uniform and crack-free undercoat layer.
It is preferred that

The material of the heat resistant fine particles used in the undercoat layer of the present invention is not particularly limited as long as it has heat resistance, and any organic or inorganic material can be used. For example,
Examples of the organic substance include aromatic polyamide, polyimide, polysulfone, polyphenylene oxide and the like. Further, examples of the inorganic material include silica, alumina, titania, carbon and the like.

The heat-resistant fine particles are preferably monodispersed or uniform spherical particles close to the monodispersed fine particles, and the material is preferably surface-treated in order to facilitate dispersion in a solvent. The average particle size of heat-resistant fine particles is 15 nm to 100 nm
Is preferred, and 20 nm to 50 nm is particularly preferred. If the average particle size is smaller than this, the surface energy of the particles is high, and several agglomerates are easily formed when the non-magnetic support is coated and dried, and this agglomerate leads to a decrease in surface property. On the other hand, if the particle diameter is larger than this, it is necessary to thicken the silica film described later, but in this case, it becomes difficult to form a continuous film having a uniform film thickness and no defects.

Further, in the present invention, when the average particle diameter of the heat-resistant fine particles is anm, 15 nm ≦ a ≦ 100 nm, and when the thickness of the silica film is dnm, 0 ≦ (ad) ≦ 20 nm. Is preferable, and (ad) is particularly preferably about 10 nm. This is because, as described above, heat-resistant fine particles of about 15 nm to 100 nm, which are easy to disperse, are used, and the height of the protrusions is extremely low to form uniform protrusions. At the same time, since the silica film is relatively thick, it is possible to fill the protrusions and foreign substances originally existing on the non-magnetic support, and it is difficult to be affected by the surface property of the non-magnetic support. Here, the height of the protrusion means the distance h between the reference surface 2 of the undercoat layer 1 and the top of the protrusion 4 formed by the heat-resistant fine particles 3 formed on the undercoat layer, as shown in FIG. FIG. 1 schematically shows a cross section of the non-magnetic support 5 provided with the undercoat layer 1 cut in the longitudinal direction. The diameter r of the protrusions depends on the average particle diameter of the heat-resistant fine particles, the thickness of the undercoat layer and the film thickness of the undercoat resin adhered to the heat-resistant fine particles, but is usually 5 to 100 nm, preferably 10 to 10. Three
It is 0 nm.

The undercoat layer of the present invention is prepared by preparing a coating solution containing the heat-resistant fine particles in a solution containing a silicon-containing compound, and coating the coating solution on at least one surface of a non-magnetic support. Can be formed. The silicon-containing compound may be a polymer compound, but is preferably hydrolyzed,
A sol-gel method using a polymerizable compound is exemplified. Examples of the monomer include alkoxysilane, alkylalkoxysilane, silicon chloride, silazane, alkylsilicon chloride, and the like, preferably tetraalkoxysilane,
Alkyltrialkoxysilanes may be mentioned.

In the sol-gel method, the compound, an acid for controlling the rate of polymerization and hydrolysis, water and heat-resistant fine particles are dissolved in a solvent, coated on a non-magnetic support, dried, and optionally heat-treated. Can be created by Although an inorganic salt such as silicon chloride can be used as a raw material, it is not so preferable when it is used in a state where the heat treatment is insufficient because it may adversely affect the corrosion resistance.

Further, as described above, since an appropriate amount of tetraalkoxysilane is replaced with monoalkyltrialkoxysilane or dialkyldialkoxysilane to contain a Si-R bond, flexibility can be given to the film and cracking can be prevented. You can hold it down. The substitution ratio at this time is preferably 20 to 80 mol%, and more preferably 20 to 60 mol% of the tetraalkoxysilane before substitution.

The alkoxysilanes used in the present invention are tetramethoxysilane, tetraethoxysilane, tetra-n-silane.
Examples thereof include propoxysilane and tetra-i-propoxysilane. The number of carbon atoms of the alkoxy group is preferably 5 or less in order to facilitate hydrolysis. Examples of the compound having a Si-R bond include methyltriethoxysilane, ethyltriethoxysilane, n-propyltriethoxysilane, dimethyldiethoxysilane, and diethyldiethoxysilane. The alkyl group preferably has 8 or less carbon atoms. It is preferable that the number of alkyl groups in one molecule is 1 or 2.

As the acid, hydrochloric acid, nitric acid, acetic acid or the like can be used.
The amount of acid added is usually 0.1 with respect to the alkoxide.
-20 mol%, preferably 1-10 mol%, and the amount of water added is usually 100-800 mol%, preferably 100-400 mol%, based on the alkoxide. However, when the amount of hydrochloric acid and water is large, the heat-resistant fine particles may be aggregated depending on the kind of the heat-resistant fine particles used. In such a case, the addition amount may be reduced to the lower limit amount capable of forming a uniform film, the solvent species may be appropriately selected, the fine particles may be fixed to a non-magnetic support, and the height of protrusions of the fine particles may be adjusted. It is necessary to separate the application of silica for this purpose and apply sequentially in this order. Then, the amount of the silicon compound in the first coating layer is changed to the second amount.
It is desirable to set it to 1/20 to 1/5 of that of the coating layer.

Examples of the solvent that can be used include organic solvents such as methanol, ethanol, isopropyl alcohol, methyl ethyl ketone, and cyclohexanone. However, the dispersibility of the heat-resistant fine particles also changes depending on the type of solvent, so care must be taken when selecting the solvent. is necessary.

In the present invention, the method of forming the undercoat layer on the non-magnetic support may be a wire bar method, a gravure method, a spray method, a dip coating method, a spin coating method, etc. It may be dried after being applied on the non-magnetic support by the above method. In this state, the undercoating film is inferior in mechanical strength, but even as it is, the undercoating film can sufficiently exhibit its function. Further, after this, in order to completely remove the volatile components present in the undercoat film, or in order to complete the silica film formation, a heat treatment may be carried out,
In this case, the temperature is preferably 500 ° C. or less, at which the flexibility of the undercoat film is maintained, and particularly preferably 150 ° C. to 300 ° C.

The non-magnetic support used in the present invention includes:
A polymer film can be used for a flexible medium, and a glass substrate or an aluminum substrate can be used for a rigid medium.
In the case of a flexible medium, a film of polyethylene terephthalate, polyethylene naphthalate, polyimide, polyamide, polyamideimide or the like having a thickness of 3 to 75 μm is preferable. Also, contains a filler inside the base,
A base surface having irregularities may be used.

For the ferromagnetic metal thin film forming the magnetic layer 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 present invention is particularly suitable for manufacturing a floppy disk using the sputtering method and does not cause the problem of heat loss. When the magnetic layer is formed by a continuous winding type vacuum deposition method capable of high-speed film formation, a conventionally known metal or alloy mainly containing cobalt can be mentioned as a composition, and specifically, Co or C
It is possible to use a film containing oxygen in a film obtained by vapor deposition of oNi, CoFe, etc. in an oxygen atmosphere. In particular, in order to improve the electromagnetic conversion characteristics, 90% or more, more preferably 95% or more, of the metal atoms constituting the magnetic layer is cobalt Co-O,
Alternatively, Co—Fe containing Co—O or the like is preferable. The thickness of the magnetic layer is preferably 100 to 300 nm, more preferably 120 to 200 nm.

The traveling speed in the oblique vapor deposition method is usually 20.
m / min or more, preferably 50 to 200 m / min. In the case of the oblique vapor deposition method, the degree of vacuum in the vapor deposition chamber is usually 5 × 10 ⁻⁵ torr or less, preferably 1 × 10 ⁻⁶ t.
It is less than orr. The heating means for the ferromagnetic metal is not particularly limited, but electron beam, induction heating, etc. may be mentioned.

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 making Hc of 1600 Oe at the speed of m / min,
From the vicinity of the minimum incident angle, it is 250 cc / min. Also,
In this case, the oxygen partial pressure is usually 1 × 10 ⁻⁵ torr to ⁵ ×.
It is 10 ^-4 torr.

When the magnetic layer is formed by the sputtering method, a conventionally known metal or alloy containing cobalt as a main component can be used. Specifically, Co--Cr and C are used.
o-Ni-Cr, Co-Cr-Ta, Co-Cr-P
t, Co-Cr-Ta-Pt, Co-Cr-Pt-S
i, Co-Cr-Pt-B, etc. can be used. In particular, in order to improve the electromagnetic conversion characteristics, Co-Cr-Ta, Co-Cr
-Pt is preferred. The thickness of the magnetic layer is preferably 10 to 300 nm.

Further, the ferromagnetic metal thin film may have a multi-layered structure or may have an underlayer and an intermediate layer in order to improve electromagnetic conversion characteristics. The underlayer can be formed by a usual vacuum film forming method, for example, vapor deposition, ion plating, sputtering, etc. Among them, sputtering is particularly preferable. Further, the kind of non-magnetic metal forming the underlayer is not particularly limited. Examples of the metal include Pt, Au, Ti,
Ta, W, Al, Cr, V, Cu, Ag, Au, etc. are mentioned. These metals can be used alone or in combination, but one containing Cu as a main component is particularly preferable.

The thickness of the underlayer is usually 50 to 500Å, preferably 100 to 300Å. The underlayer does not necessarily have to be uniformly provided on the entire surface of the non-magnetic support, and may be formed intermittently or in an island shape. When the underlayer is provided, the Hc of the magnetic layer is about 200 O compared with the case where the underlayer is not formed.
There is also an effect of improving e and reproducing output.

The formation of the magnetic layer subsequent to the formation of the underlayer is preferably more effective when continuously performed without breaking the vacuum state.

In the magnetic recording medium of the present invention, a protective layer may be provided on the ferromagnetic metal thin film, and this protective layer can improve running durability and corrosion resistance.
Examples of the protective layer include oxides such as silica, alumina, titania, zirconia, cobalt oxide and nickel oxide, nitrides such as titanium nitride, silicon nitride and boron nitride, carbides such as silicon carbide, chromium carbide and boron carbide, graphite, and An example of the protective layer is carbon such as regular carbon.

As the protective layer, a hard film having a hardness equal to or higher than that of the head material is preferable, and further, it is most preferable that it is hard to cause seizure during sliding and its effect is stable and lasts. An example of such a protective layer is a hard carbon film. The carbon protective film is plasma C
Amorphous created by VD method, sputtering method, etc.
It is a carbon film composed of graphite, a diamond structure, or a mixture thereof, and particularly preferably a hard carbon film generally called diamond-like carbon. This carbon film has a Vickers hardness of 1000 kg /
It is a hard carbon film of mm ² or more, preferably 2000 kg / mm ² or more. Further, its crystal structure is an amorphous structure and is non-conductive.

Although the diamond-like carbon protective film can be produced by sputtering or CVD, productivity,
From the viewpoint of quality stability and good abrasion resistance even with an ultra-thin film with a thickness of 10 nm or less, it is preferable to prepare by CVD. In particular, chemical species decomposed by high frequency plasma are accelerated by applying a bias voltage to the substrate. Preferably.

The carbon compound to be made into plasma, which is the material of the carbon protective film, is not particularly limited,
Hydrocarbon-based, ketone-based, alcohol-based compounds, particularly carbon-containing compounds such as alkanes such as methane, ethane, propane, butane, alkenes such as ethylene and propylene, and alkynes such as acetylene are preferable.

These film-forming substances are introduced into the plasma generator, but it is also possible to introduce an inert gas such as hydrogen or argon at the same time. In this case, a desirable mixed gas includes a hydrocarbon such as methane and argon. If the hard carbon protective film is thick, the electromagnetic conversion characteristics are deteriorated and the adhesion to the magnetic layer is deteriorated. If the hard carbon protective film is thin, abrasion resistance is insufficient. Therefore, the film thickness is 30 to 200Å
Is preferable, and particularly preferably 50 to 100Å.

The surface of the hard carbon protective film may be surface-treated with an oxidizing gas or an inert gas for the purpose of further improving the adhesion with the lubricant applied 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 add a lubricant or a rust preventive agent on the magnetic layer or the protective film.

As the lubricant, a known hydrocarbon lubricant,
Fluorine-based lubricants and extreme pressure additives can be used. Hydrocarbon lubricants include 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, stearyl alcohol,
Examples thereof include alcohols such as oleyl alcohol, 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 groups of the above hydrocarbon-based lubricant are substituted with a fluoroalkyl group or a perfluoropolyether group. As the perfluoropolyether group, perfluoromethylene oxide polymer, perfluoroethylene oxide polymer, perfluoro-n-propylene oxide polymer {(CF ₂ CF ₂ CF ₂ O) _n }, perfluoroisopropylene oxide polymer { (CF (C
F ₃ ) CF ₂ O) _n } or copolymers thereof.

As the extreme pressure additive, 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, and diphosphoric acid 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 for applying these lubricants on the magnetic layer or the 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. It may be attached.

The coating amount of the lubricant is 1 to 30 mg / m
2 is preferable and 2 to 20 mg / m 2 is particularly preferable.

Examples of the rust preventive agent usable in the present invention include nitrogen-containing heterocycles such as benzotriazole, benzimidazole, purine and pyrimidine, and derivatives in which an alkyl side chain is introduced into the mother nucleus thereof, benzothiazole and 2-mercapto. And nitrogen- and sulfur-containing heterocycles such as benzothiazole, tetrazaindene ring compounds, and thiouracil compounds, and derivatives thereof.

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

[0046]

Embedded image

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, also in the case of alkyl groups, C
_{6 H 13 -, C 9 H} 19 -, C 17 H 35 - can be mentioned, RNHCOCH ₂ in the case of the alkyl amide - is the R phenyl, C ₃ H ₇ - and the like.

Examples of the thiouracil ring compound include those shown below.

[0049]

Embedded image

[0050]

EXAMPLES The present invention will be described in more detail below by showing Examples and Comparative Examples of the present invention. Example 1 A solution of the following composition 1 containing spherical silica particles having an average particle diameter of 30 nm was applied on a polyethylene terephthalate film having a thickness of 10 μm by a wire bar method using a wire bar having a wire diameter of 0.04 mm to form heat-resistant fine particles as a film. After fixing on the surface, a solution of the following composition 2 was further applied thereon so that the layer thickness after drying would be 20 nm to form an undercoat layer. This undercoat layer has a height of about 10 due to heat-resistant fine particles of silica
The number of projections of nm was 3.5 × 10 ⁶ per 1 mm ² , and the number of projections having a height of 30 nm or more was 5 × 10 ³ .

[0051] Next, the non-magnetic support was brought into close contact with a rotary can cooled to 0 ° C. and conveyed, and cobalt was placed on the undercoat layer in an oxygen-containing atmosphere so that the incident angle of the magnetic metal vapor stream to the polyethylene terephthalate film was 45 °. So that 70
The film was obliquely vapor-deposited twice at a thickness of nm to form a two-layered ferromagnetic metal film having 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. After that, the following plasma CVD is performed on the magnetic layer.
The carbon protective layer was created by the method.

Methane was supplied as a raw material at a flow rate of 150 sccm, and argon was used as a carrier at a flow rate of 5 sccm.
It is supplied at a flow rate of 0 sccm, high-frequency power of 600 W is applied, and-
A direct current voltage of 400 V is applied, and a direct current voltage of +500 V is applied to the anode installed in the gas introduction part to accelerate the generated plasma to transfer diamond-like carbon to the magnetic layer surface at a transport speed of 5 m / min and a temperature of 20 ° C. To form a hard carbon protective layer.

The obtained carbon protective layer had a layer thickness of 8 nm, and it was confirmed by Raman spectroscopy that the carbon protective layer was diamond-like carbon. The Vickers hardness of the protective layer separately prepared by the same method was 2,200 kg / mm ² . The density of protrusions formed on the surface of the protective layer and having a height of 30 nm or more was 0.05 / μm ² . A back coat composed of carbon black and a resin binder was formed on the back surface of this base film by a wire bar method.

Then, a perfluoropolyether type lubricant having a carboxyl group at both ends (FOMBLIN Z-DIAC manufactured by Montefluos Co.) on the carbon protective layer was dissolved in a fluorine solvent (ZS-100 manufactured by the same company) to prepare a wire bar. Method to obtain a coating amount of 10 mg / m 2 and dried. This raw fabric was cut into a width of 8 mm and incorporated into a cassette for 8 mm VTR to prepare a sample.

The following evaluation was performed on the samples prepared as described above. Surface protrusion state After forming the undercoat layer and after forming the magnetic layer and the protective layer, the protrusion state of the surface was observed using an atomic force microscope, and the protrusion density at a height of 30 nm or more from the reference plane was obtained. . Electromagnetic conversion characteristics Using a VTR modified from Sony EV-S900, recording / reproduction of a single wave having a frequency of 7 MHz was performed, reproduction output and noise were measured, and C / N was calculated. Friction coefficient for stainless steel In order to evaluate the running property, the magnetic recording medium and the stainless steel pole (material SUS420 are used in the environment of 23 ° C. and 70% RH.
J) is contacted with a tension (T ₁ ) of 20 g at a wrapping angle of 180 °, and the tension (T ₂ ) required to run the magnetic tape at a speed of 3.3 cm / sec is measured. The friction coefficient μ of the magnetic tape was obtained.

Μ = (1 / π) ln (T ₂ / T ₁ ) Breaking weight of the magnetic layer The tape was fixed at a length of 100 mm, and while gradually observing the surface with an optical microscope, the tape was gradually stretched and cracked. The load at which the occurrence of rupture was taken as the breaking load (g). Example 2 Example 1 was repeated except that a solution having the following composition 3 was applied instead of the composition 2 in Example 1 and the thickness of the undercoat layer was 30 nm.
A magnetic recording medium was prepared in the same manner as in.

[0057] -Example 3 Example 1 except that the solution of the following composition 4 was applied in place of the composition 2 in Example 1 and the thickness of the undercoat layer was set to 10 nm.
A magnetic recording medium was prepared in the same manner as in.

[0058] -Example 4 After coating the solution of the composition 1 in Example 1, the solution of the following composition 5 was apply | coated, and the undercoat layer with a layer thickness of 40 nm was created.

[0059] Example 5 Instead of the composition 1 in Example 1, the average particle size is 50 nm.
The following composition 6 containing the silica particles of was used, the following composition 5 was used in place of the composition 2, and an undercoat layer was formed to have a layer thickness of 40 nm.

[0060] -Example 6 Instead of the composition 1 in Example 1, an average particle diameter is 12 nm.
The following composition 7 containing the silica particles of was used to form an undercoat layer having a layer thickness of 2 nm without applying the solution of composition 2.

[0061] Example 7 Instead of the solution having the composition 1 in Example 1, the average particle size is 3
Using a solution having the following composition 10 containing 0 nm silica particles,
A solution having the following composition 11 was used in place of the solution having the composition 2 to form an undercoat layer having a layer thickness of 20 nm.

[0062] -Example 8 Instead of the solution of the composition 1 in Example 1, average particle diameter 3
Using a solution having the following composition 12 containing 0 nm silica particles,
A solution having the following composition 13 was used in place of the solution having the composition 2 to form an undercoat layer having a layer thickness of 20 nm.

[0063] -Example 9 Instead of the solution of the composition 1 in Example 1, average particle diameter 3
Using a solution having the following composition 16 containing 0 nm silica particles,
A solution having the following composition 17 was used in place of the solution having the composition 2 to form an undercoat layer having a layer thickness of 20 nm.

[0064] -Example 10 Instead of the solution of composition 1 in Example 1, average particle diameter 3
Using a solution having the following composition 16 containing 0 nm silica particles,
A solution having the following composition 17 was used in place of the solution having the composition 2 to form an undercoat layer having a layer thickness of 20 nm.

[0065] Comparative Example 1 For comparison with the present invention, in Example 1, silica particles having an average particle size of 30 nm and a polyester resin were used as the undercoating liquid.
An undercoat layer having a layer thickness of 20 nm was prepared using a solution having the following composition 18 containing (Byron # 200 manufactured by Toyobo Co., Ltd.).

[0066] Comparative Example 2 For comparison with the present invention, silica particles having an average particle diameter of 13 nm and a polyester resin were used as the undercoating liquid in Example 1.
An undercoat layer having a layer thickness of 2 nm was prepared using a solution having the following composition 19 containing (Byron # 200 manufactured by Toyobo Co., Ltd.).

[0067] The results of evaluating the above samples are shown in Table 1.

[0068]

[Table 1] As is clear from the above examples, the magnetic tape recording medium to which the present invention is applied can form protrusions having a low and uniform height, and this surface property is deteriorated due to heat loss and the like even during the vapor deposition process. I can't. Therefore, high electromagnetic conversion characteristics can be obtained by the present invention.

Next, in order to examine the stability of the undercoat layer of the present invention against the sputtering method, a sputter magnetic disk was prepared under the following conditions. Example 11 An undercoat layer was formed on a polyimide film having a thickness of 50 μm in the same manner as in Example 1. The support provided with this undercoat layer was attached to a sputtering device, and the substrate temperature was heated to 200 ° C.
The vacuum was evacuated to 8 × 10 ⁻⁷ Torr. Then, after introducing argon gas to 3 × 10 ⁻⁵ Torr, DC
15 (Cr) non-magnetic underlayer by magnetron sputtering
A film having a thickness of 0 nm was formed, and subsequently, a Co ₇₄ Pt ₂₁ Cr ₅ alloy (magnetic layer) having a thickness of 30 mm was formed thereon. Then, this raw fabric was taken out from the vacuum chamber, a hard carbon protective layer and a lubricating layer were provided in the same manner as in Example 1, and this was punched into a 3.5-inch disk shape to obtain a sample.

Comparative Example 3 A magnetic disk was prepared in the same manner as in Example 11 except that the undercoat layer of Example 11 was changed to the undercoat layer of the polyester resin used in Comparative Example 1. With respect to the surface of the undercoat layer and the surface of the protective layer in Example 11 and Comparative Example 3 above, the projection density at a height of 30 nm or more was measured by an atomic force microscope in the same manner as in Examples 1 to 10 to examine the change in surface property. Table 2 shows the results.

[0071]

[Table 2]

[0072]

INDUSTRIAL APPLICABILITY According to the present invention, by providing an undercoat layer made of a silica film containing heat-resistant fine particles between the non-magnetic support and the magnetic layer, protrusions made of heat-resistant fine particles are formed on the surface of the non-magnetic support. It can be formed uniformly and uniformly, and even if an underlayer or a magnetic layer is formed by a sputtering method, a magnetic layer with an extremely good surface property can be obtained without causing heat loss, providing high electromagnetic conversion characteristics. A magnetic recording medium that can be obtained is obtained.

[Brief description of drawings]

FIG. 1 is a view schematically showing a cross section of a non-magnetic support provided with an undercoat layer when cut in the longitudinal direction.

[Explanation of symbols]

 1 Undercoat layer 2 Reference surface 3 Heat-resistant fine particles 4 Protrusions 5 Non-magnetic support

Claims (3)

[Claims] 1. A magnetic recording medium having a magnetic layer comprising a ferromagnetic metal thin film on at least one surface of a non-magnetic support, comprising a silica film containing heat-resistant fine particles between the non-magnetic support and the magnetic layer. A magnetic recording medium having the following undercoat layer. 2. A coating solution containing the heat-resistant fine particles in a solution containing a silicon-containing compound is applied to at least one surface of a non-magnetic support, and then a ferromagnetic metal is formed on the formed undercoat layer. The method of manufacturing a magnetic recording medium according to claim 1, wherein the thin film is formed by a vacuum film forming method. 3. The method for producing a magnetic recording medium according to claim 2, wherein the silicon-containing compound is at least one of tetraalkoxysilane and alkyltrialkoxysilane.