JPS619822A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To simplify the manufacturing process and to control easily the surface roughness by forming a ferromagnetic metallic thin film on a nonmagnetic supporting body with granular protrusions consisting of a high molecular latex formed on the surface to obtain a stable traveling property at the contact surface with a magnetic head, etc. CONSTITUTION:Polyesters such as polyethylene terephthalate can be exemplified as the material for a nonmagnetic supporting body, and the nonmagnetic supporting body can be used in the form of a film, etc. Metals such as iron and cobalt or an alloy of Co-Ni, Fe-Co, etd. can be exemplified as a ferromagnetic metallic material. Although granular protrusions are formed by coating a high molecular latex on the surface of the nonmagnetic supporting body, the density of particles is important, and the density of said granular protrusions formed on said nonmagnetic supporting body is preferably regulated to 1X10<6>-2X10<7>unit/ mm.<2>. The particle diameter of the dispersoid fine particles contained in the high molecular latex is preferably regulated in the range 300-1,000Angstrom . When the particle diameter is less than 300Angstrom , the durability is not practically improved, and the surface property is excessively deteriorated, when the diameter exceeds 1,000Angstrom .

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a so-called ferromagnetic metal thin film type magnetic material in which a ferromagnetic metal thin film is formed on a nonmagnetic support by vapor deposition, ion blasting, sputtering, etc. It is related to recording media.

[Background technology and its problems]

In the field of magnetic recording, higher recording densities and shorter wavelengths of recorded signals are progressing, and in response to this trend, metals such as iron, cobalt, and nickel are being used instead of conventional coating-type magnetic recording media. Ferromagnetic metal materials such as alloy materials such as Co-Ni alloys can be deposited using vacuum evaporation, sputtering, or ion fluorocarbon deposition methods.
2. Description of the Related Art A ferromagnetic metal thin film type magnetic recording medium has been proposed, which is formed by directly depositing on a nonmagnetic support such as a polyimide film or a polyester film using a vacuum thin film forming technique such as a thin film forming technique. In this type of magnetic recording medium, not only the coercive force Hc and the residual magnetic flux density Br are large, but also the thickness of the magnetic layer can be made extremely thin, so that the thickness during recording demagnetization and reproduction can be reduced. It has many advantages in terms of magnetic properties, such as extremely low loss and the ability to dramatically increase the packing density of magnetic materials because there is no need to mix an organic binder, which is a non-magnetic material, into the magnetic layer. Because of this, it is attracting attention.

By the way, in this ferromagnetic metal thin film type magnetic recording medium, since the ferromagnetic metal thin film that is the magnetic layer is produced by vacuum thin film formation technology, its surface has extremely excellent smoothness, resulting in a so-called mirror surface state. It has been known.

As described above, if the surface smoothness of the magnetic layer is good, it is advantageous in terms of spacing crosses, etc., but there is a risk that running properties and durability will be hindered. In other words, if the surface of the magnetic layer is too smooth, adhesion (so-called sticking) is likely to occur at the contact area with, for example, a magnetic head, guide post, rotating head cylinder, etc., and the actual contact area is reduced. Due to the large size, the coefficient of friction becomes large, resulting in extremely poor running performance and a concomitant reduction in durability.

Conventionally, in order to improve the runnability of the above-mentioned magnetic recording medium, the surface roughness of the non-magnetic support on which the ferromagnetic metal thin film is deposited has been controlled so that the surface properties of the magnetic layer are appropriate. Attempts are being made to do so. For example, JP-A-58-6
As described in Japanese Patent No. 8224, a mixture of a silicone resin or styrene-butadiene rubber and a water-soluble polymer material is applied onto a base film to form a continuous film, which is then stretched to form a so-called surface film. In the case of a worm-like shape, not only a coating process to form a film but also a stretching process to form protrusions is required, which complicates the manufacturing process and reduces productivity, as well as the resulting magnetic recording medium. It is difficult to say that the friction coefficient and durability of this material are sufficient.

Alternatively, as described in JP-A-58-68227, fine particles of calcium carbonate, titanium oxide, etc. are added to an aqueous emulsion of linear saturated polyester or silicone resin dissolved in a solvent, and this is applied. A granular shape in which the above-mentioned fine particles are localized on the base film,
Alternatively, it has been considered to improve the surface properties of the magnetic layer by forming a worm-like film, but in this case, it is difficult to uniformly disperse the fine particles and it is difficult to achieve uniform surface roughness. Not only is this difficult, but it is also difficult to control the surface roughness by adjusting the particle size of the fine particles.

[Purpose of the invention]

Therefore, the present invention was proposed in view of the above-mentioned conventional situation, and it provides stable running performance at the contact portion with the magnetic head, rotary head cylinder, etc., and the manufacturing process is simple. An object of the present invention is to provide a magnetic recording medium whose surface roughness can be easily controlled.

[Means for solving problems]

As a result of long-term intensive research to achieve the above-mentioned objectives, the present inventors have discovered that polymer latex is extremely effective in controlling the surface roughness of non-magnetic supports, and have completed the present invention. It is characterized in that a ferromagnetic metal thin film is formed on a non-magnetic support on which granular protrusions made of polymer latex with a particle size of 300 to 1000 A are formed on the surface. .

The magnetic recording medium to which the present invention is applied is a so-called ferromagnetic metal thin film type magnetic recording medium in which a ferromagnetic metal material is directly deposited on a nonmagnetic support and a ferromagnetic metal thin film is formed as a magnetic layer. .

Materials for the non-magnetic support include polyesters such as polyethylene terephthalate, polyolefins such as polyethylene and polypropylene, cellulose derivatives such as cellulose triacetate, cellulose diacetate, and cellulose acetate phthalate, polyvinyl chloride, polyvinylidene chloride, etc. Examples include plastics such as vinyl resin, polycarbonate, polyimide, and polyamideimide. Furthermore, the form of the non-magnetic support is as follows:
Any of film, tape, sheet, disk, card, drum, etc. may be used.

The above-mentioned ferromagnetic metal materials include iron Fe, cobalt CO,
Metal such as nickel N1 or Co-Ni alloy, Fe-
, Co alloy, Fe-Ni alloy, Co-Ni -Fe-B
Examples include alloys such as alloys.

The means for depositing the ferromagnetic metal material include vacuum evaporation,
Examples include the ion printing ink method and the sputtering method.

In the vacuum evaporation method, the ferromagnetic metal material is evaporated by resistance heating, high frequency heating, electron beam heating, etc. under a vacuum of 10 to 1 O-8 Torr, and the evaporated metal (ferromagnetic metal material) is deposited on the nonmagnetic support. It is roughly divided into oblique evaporation method and vertical evaporation method. In the above-mentioned oblique deposition method, the ferromagnetic metal material is obliquely deposited on a non-magnetic support in order to obtain a high coercive force. It also includes things that are done. In the above vertical deposition method, Bi and TA are deposited on a non-magnetic support in advance in order to improve deposition efficiency and productivity and to obtain high coercive force.

A base metal layer of Sb, Ga, Ge, etc. is formed in advance, and the ferromagnetic metal material is vertically deposited on the base metal layer. The above-mentioned ion brating method is also a type of vacuum evaporation method, in which DC glow discharge and RF glow discharge are caused in an inert gas atmosphere of IC-1O-8 TOrr, and the above-mentioned ferromagnetic metal is evaporated during the discharge. . In the above sputtering method, glow discharge is caused in an atmosphere mainly composed of argon gas at 10 to 10 Torr, and the generated argon ions are used to knock out atoms on the target surface. There are sputtering methods, high-frequency sputtering methods, and Macnetron sputtering methods that utilize Macnetron discharge.

In the magnetic recording medium according to the present invention, granular protrusions are formed by coating the surface of the non-magnetic support with polymer latex, and as a result, the ferromagnetic metal thin film deposited thereon is It is configured to improve surface properties.

The surface of the nonmagnetic support used here may be smooth, or may be made of, for example, silicone resin or styrene resin.
A mixture of butadiene rubber and a water-soluble polymeric material may be applied to form a continuous film, which is then stretched to form so-called worm-like protrusions on its surface.

The polymer latex used to form the above-mentioned granular protrusions is a colloidal sol containing an aqueous solvent as a dispersion medium and fine particles of a rubber-based polymer substance as a dispersoid. The dispersoid particles adhere to the non-magnetic support, and granular protrusions are uniformly formed.

Examples of such polymer latex include styrene-butadiene copolymer, styrene-isoprene copolymer, styrene-chloroprene copolymer, acrylonitrile-butadiene copolymer, (meth)acrylic acid ester polymer, or A latex containing fine particles such as a copolymer mainly composed of (meth)acrylic acid ester such as methyl methacrylate-phtadiene copolymer as a dispersoid can be used.

In the above-mentioned polymer latex, the adhesion strength of the dispersoid particles to the non-magnetic support is strong, and the particles form granular protrusions while maintaining the shape of the fine particles relatively well. Therefore, by controlling the particle size of the dispersoid fine particles of the polymer latex, the surface roughness of the non-magnetic support can be controlled, and the surface properties of the ferromagnetic metal thin film formed thereon can be controlled. can do. According to experiments conducted by the present inventors, it has been found that the particle size of the dispersoid particles contained in the polymer latex is preferably within the range of 300 to 100 OA. If the particle size is less than 300A, the durability of the resulting magnetic recording medium will hardly improve, and if the particle size exceeds 100OA, the surface properties will be too poor, for example, when used in a video cheap recorder, etc. , the image quality will deteriorate.

In addition, the particle density is important for the granular protrusions formed on the non-magnetic support, and the number of granular protrusions on the surface of the non-magnetic support is 1 million to 20 million pieces/mr1.
It is desirable that the diameter is about 1'. If the density of the granular protrusions is less than 1 million pieces/m+m2, no improvement in durability can be expected, and if the density exceeds 20 million pieces/mm2, the image quality will deteriorate.

On the other hand, water is usually used as a dispersion medium for the polymer latex, and it is diluted with water to control the density of the granular protrusions within the above-mentioned range. Since the non-magnetic support surface has poor wettability, it may be difficult to uniformly apply the polymer latex. Therefore, for example, 1) a method of lowering the surface tension of the dispersion medium by using a mixture of water and a water-soluble organic solvent such as alcohol as a dispersion medium, and 2) a method of using a surfactant having a perfluoroalkyl group such as C5FltSOaNa. 3) applying a surface treatment such as corona discharge to the surface of the non-magnetic support to improve the wettability of the surface, etc. to ensure uniform application. Good too.

In particular, it is effective to use a mixture of water and a water-soluble organic solvent as a dispersion medium, and in particular, a mixture of water and n-propyl alcohol (containing 60% by weight or more of n-propyl alcohol) can be used to achieve extremely uniform coating. can do. As the above-mentioned water-soluble organic solvent, it is necessary to use one that does not destroy the dispersion stability of the dispersoid fine particles, and for example, methanol, ethanol, n-7' alcohol, isopropyl alcohol, etc. can be used. If it exceeds butyl alcohol, the solubility with water decreases, which is not preferable.

By the way, as a method for forming the above-mentioned granular protrusions, for example, a method of dispersing and applying a resin solution in which a thermoplastic resin is dissolved in an organic solvent in a solvent in which this resin is difficult to dissolve can be considered. Since granular protrusions are formed by adhering fine particles of When attempting to form them, resin solution particles tend to fuse together, making it difficult to form desired granular protrusions.

On the other hand, when forming granular protrusions using the polymer latex described above, such inconvenience does not occur.

As mentioned above, by depositing a ferromagnetic metal thin film on a non-magnetic support with granular protrusions formed on the surface using polymer latex, a ferromagnetic metal thin film type magnetic recording medium with extremely excellent running properties can be created. However, in order to further improve the running properties of the magnetic recording medium, it is also possible to form a lubricant layer on the surface of the ferromagnetic metal thin film described above.

As the lubricant, fatty acids, fatty acid esters, fatty acid amides, metal soaps, aliphatic alcohols, paraffins, silicones, fluorine surfactants, etc. can be used, and the amount of lubricant applied is 1 to 10001n9/m". is preferred.

As the fatty acid, those having 12 or more carbon atoms such as lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, oleic acid, linoleic acid, and crucic acid can be used.

As the fatty acid ester, ethyl stearate, butyl stearate, amyl stearate, stearic acid monoglyceride, oleic acid monoglyceride, etc. can be used.

Examples of fatty acid amides include caproic acid amide, capric acid amide, lauric acid amide, palmitic acid amide, stearic acid amide, behenic acid amide, oleic acid amide,
linoleic acid amide, methylene bisstearic acid amide,
Ethylene bisstearamide, etc. can be used.

Examples of metal soaps include Zn and Pb such as lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, oleic acid, linoleic acid, and crucic acid.

Salts with Ni, Co, Fe, A#, Mg, Sr, Cu, etc., salts of sulfonic acids such as lauryl, palmityl, myristyl, stearyl, behenyl, oleyl, linole, rinne, and the above metals, and the like can be used.

As the aliphatic alcohol, cetyl alcohol, stearyl alcohol, etc. can be used.

As the paraffin, saturated hydrocarbons such as n-nonadecane, n-tridecane, and n-tocosan can be used.

As silicones, polysiloxanes in which hydrogen is partially substituted with alkyl groups or phenyl groups, and those modified with fatty acids, aliphatic alcohols, fatty acid amides, etc. can be used.

As the fluorosurfactant, perfluoroalkylcarboxylic acid and perfluoroalkylsulfonic acid and Na,
Salts with Mg, Zn, A, Fe, Co, Ni, etc., perfluoroalkyl phosphate esters, perfluoroalkyl betaines, perfluoroalkyltrimethylammonium salts,
Perfluoroethylene oxide, perfluoroalkyl aliphatic ester, etc. can be used.

〔Example〕

Next, specific examples of the present invention will be described, but it goes without saying that the present invention is not limited to these examples.

Example 1 A polymer latex containing styrene-butadiene copolymer particles having a particle size of 65 OA as a dispersoid was placed on a polyethylene terephthalate film with a thickness of 12 μm in a water-propyl alcohol mixture (70% by weight of n-propyl alcohol).
A coating solution diluted and dispersed in (containing) was applied to form granular protrusions at a density of about 800,000 pieces/m♂.

Next, a Co-4Ji alloy (Co content 80% by weight) was applied to the film on which the granular protrusions were formed in a vacuum evaporation apparatus.
, Ni content 20% by weight) was obliquely deposited to a thickness of 0.1 μm.
A ferromagnetic metal thin film was formed.

Furthermore, a lubricant was applied to the ferromagnetic metal thin film in the atmosphere, and the sample tape was cut into a width of 50% inch.

Example 2 A polymer latex containing styrene-butadiene copolymer particles with a particle size of 450λ as a dispersoid was placed on a polyethylene terephthalate film with a thickness of 12 μm using water-n-propyl alcohol mixture 1 (n-propyl alcohol 70 wt. %
A coating solution diluted and dispersed in (containing) was applied to form one granular protrusion at a density of about 5 million pieces/mm.

Next, a Co-Ni alloy (Co content: 80% by weight,
A ferromagnetic metal thin film having a thickness of 0.1 μm was formed by obliquely depositing Ni (Ni content: 20% by weight).

Furthermore, a lubricant was applied to the ferromagnetic metal thin film in the atmosphere, and the sample tape was cut into a width of 50% inch.

Comparative Example 1 A Co-Ni alloy (C) was deposited on a 12μ thick polyethylene terephthalate film in a vacuum deposition apparatus.

Ni content: 80% by weight, Ni content: 20% by weight) was obliquely deposited to form a ferromagnetic metal thin film with a thickness of 0.1 μm.

Next, a lubricant was applied to this ferromagnetic metal thin film in the atmosphere, and the sample tape was cut into a width of % inch.

Comparative Example 24 A coating solution in which titanium oxide particles with a particle size of 45 OA were diluted and dispersed in an aqueous binder solution was applied onto a polyethylene terephthalate film with a thickness of 12 μm, and granular protrusions were formed at a density of about 5 million pieces/mm2. did.

Next, a Co-Ni alloy (Co content: 80% by weight,
A ferromagnetic metal thin film having a thickness of 0.1 μm was formed by obliquely depositing N1 (N1 content: 20% by weight).

Furthermore, a lubricant was applied to the ferromagnetic metal thin film in the atmosphere, and the sample tape was cut into a width of 50% inch.

When the still image quality and friction coefficient of each of the sample tapes mentioned above were measured, the results shown in the following table were obtained. In addition, the still characteristics are 4.2M on the sample tape.
The H2 video signal is recorded, and the time taken for this playback output to attenuate to 50% is measured. The friction coefficient is the friction between the magnetic layer surface and IS stainless steel at a low tape speed (0-4 mm/see) and a load of 50 g. The coefficients were calculated.

Table 4 shows that the magnetic recording medium according to the present invention has excellent durability and runnability. On the other hand, the still characteristics of the sample tape of Comparative Example 2,
The reason for the poor image quality and friction coefficient is thought to be that the titanium oxide particles are poorly dispersed and partially aggregated on the base film.

〔Effect of the invention〕

As is clear from the description of the above embodiments, in the present invention, granular protrusions are formed on a non-magnetic support using polymeric latex, and a ferromagnetic metal thin film is deposited thereon. The surface properties of the ferromagnetic metal thin film have been significantly improved, making it possible to significantly improve running performance and durability.

Furthermore, the present invention is advantageous in terms of productivity, etc., since extra steps such as a stretching step are not required.

Claims (1)

[Claims] A magnetic recording medium characterized in that a ferromagnetic metal thin film is formed on a nonmagnetic support on which granular protrusions made of polymer latex with a particle diameter of 300 to 1000 Å are formed.