JPH0520809B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a so-called ferromagnetic metal thin film type magnetic recording medium in which a ferromagnetic metal thin film is formed on a nonmagnetic support by vapor deposition, ion plating, sputtering, etc. . [Background technology and its problems] Traditionally, magnetic recording media have been made of r-Fe ₂ O 3 , Co-containing r-Fe 2 O ₃ , Co-containing r-Fe ₂ O ₃ ,
Fe ₃ O ₄ , Co-containing Fe ₃ O ₄ , r-Fe ₂ O ₃ and
Powder magnetic materials such as bertolide compounds of Fe ₃ O ₄ , bertolide compounds containing Co, oxide magnetic powders such as CrO ₂ , or alloy magnetic powders whose main components are Fe, Co, Ni, etc., are mixed with vinyl chloride and acetic acid. Coating-type magnetic recording media, in which magnetic recording media are dispersed in an organic binder such as a vinyl copolymer, polyester resin, or polyurethane resin, coated, and dried, have been widely used. In recent years, with the increasing demand for high-density magnetic recording,
Ferromagnetic thin-film magnetic recording media, in which a thin metal film made of ferromagnetic metal is directly deposited on a non-magnetic support using vacuum evaporation, sputtering, ion blating, or plating, have been attracting attention. There is. This ferromagnetic metal thin film magnetic recording medium has coercive force.
Not only does it have high Hc and residual magnetic flux density Br, but the thickness of the magnetic layer can be made extremely thin, so the thickness loss during recording demagnetization and reproduction is extremely small, and the magnetic layer is made of non-magnetic material. It has many advantages in terms of magnetic properties, such as the ability to increase the packing density of the magnetic material since it is not necessary to mix an organic binder. However, in this type of magnetic recording medium, since a vacuum evaporation method or the like is used as a means of forming the ferromagnetic metal thin film, the base film, which is a non-magnetic support, is susceptible to thermal damage. However, when the evaporated metal atoms recrystallize to form a thin film, they shrink and generate internal stress, which causes the ferromagnetic metal thin film to curl into a concave shape. When such curling occurs, the contact between the magnetic recording medium and the magnetic head becomes poor, resulting in a reduction in the reproduction output and the occurrence of irregular winding. Therefore, various methods have been proposed to eliminate the above-mentioned curls. For example, it is disclosed in JP-A-53-83706, JP-A-53-104204, etc. that stress is applied after a magnetic thin film is deposited to cause a type of crack in the magnetic thin film to relieve strain stress. . Further, it is disclosed in Japanese Patent Laid-Open No. 16032/1983 that stress is relaxed by subjecting the substrate to heat treatment to shrink the substrate side after the magnetic thin film is deposited. In addition, it has been proposed in Japanese Patent Application Laid-Open No. 56-1997 that stress can be alleviated by providing a back coat layer on the back side of the magnetic recording medium, that is, on the side opposite to the magnetic layer.
-11622, JP-A-56-16939, etc. However, none of these methods can prevent curling during film formation and has many drawbacks in terms of productivity and other aspects. Curling during film formation is also an extremely serious problem even when using other deposition methods other than vapor deposition, such as sputtering and ion plating, and a sufficient preventive measure has not yet been realized. In addition, in the case of the above-mentioned ferromagnetic metal thin film type magnetic recording medium, since the ferromagnetic metal that is the magnetic layer is manufactured using vacuum thin film formation technology, the surface thereof has extremely excellent smoothness, resulting in a so-called mirror surface state. It has been known. If the surface smoothness of the magnetic layer is improved in this manner, it is advantageous in terms of spacing loss, etc., but there is a risk that it may cause problems in terms of runnability and durability. In other words, if the surface of the magnetic layer becomes too smooth, adhesion (so-called sticking) will easily occur at the contact area with, for example, a magnetic head, guide post, rotating head cylinder, etc., and the actual contact area will be reduced. Since the friction coefficient is large, running properties are extremely deteriorated, and durability is also reduced accordingly. [Object of the Invention] The present invention has been proposed in view of the above-mentioned conventional situation, and is free from curling and provides stable running performance at the contact portion with magnetic heads, rotary head cylinders, etc. The object of the present invention is to provide a magnetic recording medium whose surface roughness can be easily controlled. [Means for solving the problem] That is, the present invention provides an emulsion with a glass transition point of 30°C or less and an emulsion with a glass transition point of 30°C or less on a non-magnetic support.
An emulsion with a temperature of 50°C or higher is applied, and the emulsion with a glass transition point of 30°C or lower is used as a continuous film, and granular protrusions made of the emulsion with a glass transition point of 50°C or higher are formed at 10×10 ⁴ pieces/mm ² to 2000×10 The present invention relates to a magnetic recording medium characterized in that an undercoat layer having a particle density of ⁴ particles/mm ² is formed, and a ferromagnetic metal thin film is formed on the undercoat layer. A magnetic recording medium according to the present invention is shown in FIG. In the figure, 1 is a non-magnetic support, 2 is a ferromagnetic metal thin film, 3 is a continuous film formed from an emulsion with a glass transition point (Tg) of 30°C or lower, and 4 is a continuous film formed of an emulsion with a glass transition point (Tg) of 50°C or higher. These are granular protrusions formed by emulsion. The undercoat layer of the magnetic recording medium according to the present invention is composed of an emulsion with a glass transition point (hereinafter referred to as Tg) of 30°C or lower and an emulsion with a Tg of 50°C or higher, and the emulsion with a Tg of 30°C or lower forms a continuous film 3, Also Tg50℃
The above emulsion forms granular protrusions 4. The continuous film 3 is softer than the ferromagnetic metal thin film 2 and the non-magnetic support 1, which are magnetic layers, and is used to disperse stress concentration generated between the ferromagnetic metal thin film 2 and the non-magnetic support 1 and to relieve the stress. It is possible to suppress the occurrence of curls. Moreover, the surface roughness of the surface of the ferromagnetic metal thin film 2 can be controlled by the granular projections 4, and the running properties of the magnetic recording medium can be improved. Furthermore, the durability of the magnetic recording medium can be improved by the undercoat layer. The thicker the continuous film 3 made of emulsion with a Tg of 30°C or less, the less the amount of curl. However, as the continuous film 3 becomes thicker, the surface smoothness deteriorates and Electromagnetic conversion characteristics deteriorate. Therefore, the film thickness of the continuous film 3 is
It is desirable that the thickness is 1 μm or less. In addition, for the granular protrusions 4 made of emulsion with a Tg of 50°C or more, the particle density is important, and the granular protrusions 4 are formed on the surface of the undercoat layer at about 100,000 to 20 million pieces/mm ² . It is desirable to be present. If the density of the granular projections 4 is less than 100,000 pieces/mm ² , no improvement in durability can be expected, and if it exceeds 20 million pieces/mm ² , the image quality will deteriorate. Further, the particle size of the dispersoid particles contained in the emulsion is preferably within the range of 300 to 1000 Å. The above particle size is 300Å
If it is less than 1000Å, no improvement in durability can be expected.
Exceeding this will reduce the image quality. Examples of emulsions with a Tg of 30°C or less include polyvinyl acetate emulsion, polyacrylic acid ester emulsion, polyurethane emulsion, styrene-butadiene copolymer emulsion, polyisoprene emulsion, acrylonitrile-butadiene copolymer emulsion, etc. Can be mentioned. In addition, as an emulsion with a Tg of 50℃ or higher,
Examples include polystyrene emulsion, poly-α-methylstyrene emulsion, polyvinyl chloride emulsion, polymethyl methacrylate emulsion, and polyacrylonitrile emulsion. Materials for the non-magnetic support 1 include polyesters such as polyethylene terephthalate, polyolefins such as polyethylene and polypropylene, cellulose derivatives such as cellulose triacetate, cellulose diacetate, and cellulose acetate butyrate, polyvinyl chloride, polyvinylidene chloride, etc. Examples include plastics such as vinyl resin, polycarbonate, polyimide, and polyamideimide. The nonmagnetic support may be in any form such as a film, tape, sheet, disk, card, or drum. Materials for the ferromagnetic metal thin film 2 include Fe, Co,
Metals such as Ni or Co-Ni alloy, Fe-Co alloy,
Fe-Ni alloy, Fe-Co-Ni alloy, Fe-Co-B alloy, Co-Ni-Fe-B alloy or these with Cr,
Examples include those containing metals such as Al. The means for depositing the ferromagnetic metal thin film material is as follows:
Examples include a vacuum evaporation method, an ion plating method, and a sputtering method. The above vacuum evaporation method is
The ferromagnetic metal material is evaporated by resistance heating, high frequency heating, electron beam heating, etc. under a vacuum of 10 ^-4 to 10 ^-8 Torr, and the evaporated metal (ferromagnetic metal material) is deposited on the non-magnetic support 1. It is broadly divided into oblique deposition method and vertical deposition method. The above-mentioned oblique vapor deposition method is a method in which the above-mentioned ferromagnetic metal material is obliquely vapor-deposited on the non-magnetic support 1 in order to obtain a high coercive force. It also includes things that are done. In the vertical evaporation method described above, in order to improve the evaporation efficiency and productivity, and to obtain high coercive force,
A base metal layer such as Bi, Sb, Pb, Sn, Ga, In, Cd, Ge, Si, Tl, etc. is formed in advance, and the above-mentioned ferromagnetic metal material is vertically deposited on this base metal layer. . The above-mentioned ion plating method is also a type of vacuum evaporation method, and involves generating DC glow discharge and RF glow discharge in an inert gas atmosphere of 10 ^-4 to ^{10 -3} Torr, and evaporating the above-mentioned ferromagnetic metal during the discharge. It is something. The above sputtering method is 10 ^-3 ~
A glow discharge is generated in an atmosphere mainly composed of argon gas at 10 ^-1 Torr, and the generated argon ions are used to knock out atoms on the target surface. , high-frequency sputtering method, and magnetron sputtering method using magnetron discharge. In addition, in order to improve the running properties of magnetic recording media,
It is also possible to form a lubricant layer on the surface of the ferromagnetic metal thin film 2 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 the lubricant applied is 1 to 1000 mg/ ^m2 . is preferable. Fatty acids include lauric acid, myristic acid,
Those having 12 or more carbon atoms such as palmitic acid, stearic acid, behenic acid, oleic acid, linoleic acid, and linolenic acid can be used. Fatty acid esters include 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 bis stearic acid amide, etc. Can be used. Metal soaps include Zn, Pb, lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, oleic acid, linoleic acid, linolenic acid, etc.
Salts with Ni, Co, Fe, Al, Mg, Sr, Cu, etc., salts of sulfonic acids such as lauryl, palmitin, myristyl, stearyl, behenyl, oleyl, linole, linolenic, etc. and the above metals, etc. can be used. As the aliphatic alcohol, cetyl alcohol, stearyl alcohol, etc. can be used. As paraffin, saturated hydrocarbons such as n-nonadecane, n-tridecane, n-docosane, etc. 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. Examples of fluorosurfactants include salts of perfluoroalkylcarboxylic acids and perfluoroalkylsulfonic acids with Na, K, Mg, Zn, Al, Fe, Co, Ni, etc., perfluoroalkyl phosphate esters, and perfluoroalkyl phosphates. Alkyl betaines, perfluoroalkyltrimethylammonium salts, perfluoroethylene oxide, perfluoroalkyl aliphatic esters, etc. can be used. [Examples] Specific examples of the present invention will be described below, but it goes without saying that the present invention is not limited to these examples. Example 1 A polyvinyl acetate emulsion with a glass transition point of 29°C and a polyvinyl acetate emulsion with a glass transition point of 105 and a particle size of 300 Å were placed on a 12 μm thick polyethylene terephthalate film.
℃ polymethyl methacrylate emulsion diluted with a mixture of water and normal propyl alcohol containing 60 ^% by weight of normal propyl alcohol. Film thickness is 200
An undercoat layer of Å was formed. Next, cobalt Co was obliquely evaporated onto the undercoat layer using a vacuum evaporation device at an incident angle of 50° to 90°, and the film thickness was approx.
A sample tape with a 1300 Å ferromagnetic metal thin film was created. Example 2 On a polyethylene terephthalate film with a thickness of 12 μm, a polyacrylate emulsion with a glass transition point of 0°C and a polystyrene emulsion with a particle size of 300 Å and a glass transition point of 100°C were mixed with 60% by weight of n-propyl alcohol. Water contained
A diluted solution of normal propyl alcohol mixture was applied to form an undercoat layer with a polystyrene particle density of 4 million particles/mm ² and a continuous film thickness of 200 Å. Next, a sample tape was prepared in the same manner as in Example 1. Example 3 A polyester emulsion with a glass transition temperature of -20°C and a polyester emulsion with a particle size of 300 Å and a glass transition temperature of 100°C were placed on a polyethylene terephthalate film with a thickness of 12 μm.
A polystyrene emulsion diluted with a n-propyl alcohol mixture was applied to form an undercoat layer with a polystyrene particle density of 5 million particles/mm ² and a continuous film thickness of 200 Å. Next, a sample tape was prepared in the same manner as in Example 1. Comparative example Cobalt Co was obliquely evaporated onto a 12 μm thick polyethylene terephthalate film at an incident angle of 50° to 90° using a vacuum evaporator to form a ferromagnetic metal thin film with a thickness of approximately 1300 Å, and a sample tape was created. did. When the amount of curl, still characteristics, and image quality of the sample tapes obtained in the above-mentioned Examples and Comparative Examples were measured, the results shown in the following table were obtained. The amount of curl was measured by the amount indicated by h in Figure 2 on a 1/2 inch wide magnetic recording medium, and the still characteristics were measured by recording a 4.2MHz video signal on a sample tape, and the playback output was attenuated to 50%. It was measured as the time until.

〔Effect of the invention〕

As is clear from the description of the above examples, in the present invention, the undercoat layer is formed of an emulsion with a glass transition point of 30°C or lower and an emulsion with a glass transition point of 50°C or higher, so that curling is prevented. and control of surface roughness is achieved at the same time.
A magnetic recording medium with excellent running properties and excellent contact with a magnetic head can be obtained.

[Brief explanation of the drawing]

FIG. 1 is an enlarged sectional view of a main part showing the structure of a magnetic recording medium to which the present invention is applied, and FIG. 2 is a schematic sectional view illustrating a curled state of a ferromagnetic metal thin film type magnetic recording medium. 1...Nonmagnetic support, 2...Ferromagnetic metal thin film,
3... Continuous film (undercoat layer), 4... Granular protrusions (undercoat layer).

Claims (1)

[Claims] 1. An emulsion with a glass transition point of 30°C or lower and an emulsion with a glass transition point of 50°C or higher are coated on a non-magnetic support, and the emulsion with a glass transition point of 30°C or lower is used as a continuous coating.
10x granular projections made of emulsion at 50℃ or higher
1. A magnetic recording medium comprising: an undercoat layer having a particle density of 10 ⁴ particles/mm ² to 2000×10 ⁴ particles/mm ² ; and a ferromagnetic metal thin film formed on the undercoat layer.