JPS60138722A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a recording medium for high density recording which has high heat resistance and excellent surface smoothness and has a ferromagnetic metallic layer particularly as a vertical magnetic recording medium by forming a soln. of specific polyimide by a casting method into a film and providing magnetic layers on one or both surfaces thereof. CONSTITUTION:The polyimide which is expressed by the formula (R is a compd. contg. aromatic hydrocarbon and n is >=1 integer) and withstands use even at >=200 deg.C, for example, biphenyl tetracarboxylic dianhydride and arom. diamine are thoroughly imidized in a solvent to prepare a polyimide soln. The soln. is formed into a film by a casting method and the film having good surface smoothness of <=0.02mu surface roughness is obtd. with the lack of water due to condensation. Two layers of Fe-Ni layer and Co-Cr layer are formed on one or both surfaces of the film by which a vertical magnetic recording medium is produced. The excellent magnetic recording medium which has large adhesion force between the film and the magnetic layer and decreases spacing loss is thus obtd. without deposition of oligomer on the film surface.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention is directed to a magnetic recording medium that can be used as a tape or a 2-P disk that can be used for external memory of /4-sonal computers, word processors, etc., and for video and audio equipment. It's about the medium.

(Conventional structure and its problems) In order to achieve even higher development as a magnetic recording medium than the conventional one,
Emphasis has been placed on increasing recording density in order to increase recording capacity and downsize devices.

The main challenges for magnetic recording media aimed at increasing recording density are thinning the magnetic layer, increasing coercive force, smoothing the surface of the magnetic layer, and achieving perpendicular magnetic recording.

In order to achieve these goals, we have developed video tapes and audio tapes in which a Co-Ni alloy is deposited in a thin film on one side of a polyethylene terephthalate (hereinafter abbreviated as PET) film, and /J-Malloy (J-Malloy) on one or both sides of a PET film. A perpendicular magnetic recording medium has been proposed in which two thin film layers, an Fe--Ni layer and a Co--Cr layer, are formed by sputtering or electron beam evaporation. In this case, in order to expand the recording frequency of the tape and increase the recording density while obtaining sufficient output, a magnetic layer with a large coercive force is required.

In order to increase the coercive force of the Co-Cr+Co-N1 thin film, it is effective to increase the temperature during vapor deposition or sputtering. However, PET film has a low heat distortion temperature and cannot be used in a high temperature atmosphere.

PET 74 lum also allows sputtering or vapor deposition even at relatively high temperatures if a heat-treated temporary magnetic thin film is provided, but oligomers precipitate from within the PET film, reducing the adhesion of the magnetic layer. In addition, especially when forming a Co-Cr thin film, if the electron pure evaporation method is used, the temperature of the evaporation atmosphere must be high (over 200°C).
ET film has drawbacks such as not being applicable.

There is a polyimide represented by the following formula as a film that can sufficiently withstand use even at temperatures above 200°C.

R is a compound containing an aromatic hydrocarbon. n is an integer of 1 or more.

This film is produced by polymerizing tetracarboxylic dianhydride and aromatic diamine in a polar solvent to form a solution of polyamic acid represented by the following formula.

R is a compound containing an aromatic hydrocarbon. n is an integer of 1 or more This is formed into a film by a casting method and condensed by heat treatment in the same manner as the solvent is removed to form a polyimide. In this method, condensed water is generated, which tends to create voids and irregularities on the bottom surface of the film, resulting in a surface roughness of 0.2 μm. Generally, in order to improve the surface smoothness of the magnetic layer, it is necessary to have good surface smoothness of the branch film. It has the disadvantage that it cannot achieve the full roughness, has poor contact with the head, increases cisbasing loss, and makes it difficult to achieve a recording density of 20 pits/inch or higher.

(Purpose of the Invention) The present invention eliminates the above-mentioned drawbacks of the conventional technology, and enables the deposition of thin magnetic materials at high temperatures and achieves a lower recording density by using a support film with excellent surface smoothness. The present invention provides a magnetic recording medium that can be expanded.

(Structure of the Invention) In order to achieve this object, the magnetic recording medium of the present invention obtains a solution of a polyimide of the following formula, where n is an integer of 1 or more, dissolved in a solvent, on a non-magnetic support by a casting method. It is composed of a film and a magnetic layer provided on one or both sides of the film.

(Description of Examples) Examples of the present invention will be described below. ◎Example: Biphenyltetracarboxylic dianhydride and aromatic diamine are completely imidized in a solvent to form a polyimide solution. This priimide solution was formed into a film, the solvent was removed by heat treatment, and a 50μ film having the structure shown by the following formula was formed.
A polyimide film with a thickness of m was used. (Polyimide film "Ubilex" manufactured by Ube Kojin Co., Ltd.) This polyimide film is formed after polyimide conversion, so there is no generation of condensed water during film formation, and the surface smoothness with a surface roughness of 0.02 μm or less is achieved. The whole agency did it.

Next, a perpendicular magnetic recording medium was prototyped using a continuous DC magnetron Z9 vine method, in which two layers, a permalloy (Fe--Ni) layer and a Co--Cr layer, were provided on both sides of this film. The sputtering conditions were explained in 1.

Next, a two-layer perpendicular magnetic recording medium was experimentally produced using a similar method using other support films and compared.

The prototype perpendicular magnetic recording medium was evaluated for appearance, adhesion of the magnetic layer to the support, and punched into 5.25-inch diameter FDs (floppy disks), and recorded and reproduced using a known auxiliary pole excitation type head. The table shows the results of measuring the head output, the number of dragouts, the recording density, and the perpendicular coercive force of the Co--Cr layer.

As described above, according to this example, by using a polyimide film having the structure of the following formula as a support that can be made into a solution even after polyimidization, it has excellent heat resistance and surface smoothness, so it can be used at high temperatures. It is possible to sputter under
By increasing the perpendicular coercive force of the magnetic layer, it is possible to increase the output and improve the recording density. Further, it is thought that there is no precipitation of oligomers, etc., and the adhesion of the magnetic layer is also good.

(Effects of the Invention) As described above, the present invention uses a solution of a polyimide represented by the following formula dissolved in a solvent as a non-magnetic support of a magnetic recording medium consisting of a non-magnetic support and a magnetic layer. This film has high heat resistance and excellent surface smoothness, and it is possible to form a thin magnetic layer using electron beam evaporation or sputtering at high temperatures, making it possible to maintain the magnetic layer. It is possible to improve the magnetic force, reduce the surface roughness of the magnetic layer, and increase the recording density, and the practical effects are impressive.

Claims (1)

[Claims] The following formula R dissolved in a solvent is a compound containing an aromatic hydrocarbon. n:=an integer of 1 or more. A magnetic recording medium characterized by having a magnetic layer on one or both sides of a film-like non-magnetic support obtained by casting a polyimide solution represented by the above.