Stock material or miscellaneous articles – Composite – Of inorganic material
Patent
1983-06-14
1985-05-28
Robinson, Ellis P.
Stock material or miscellaneous articles
Composite
Of inorganic material
252 6254, 427 44, 427 541, 427128, 428900, 428522, 360134, 360135, 360136, G11B 570
Patent
active
045200793
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a magnetic recording medium and, more particularly, to a magnetic recording medium having a superior durability.
BACKGROUND ART
In order to enhance the durability of a magnetic recording medium, there has been employed a method, for example, of providing an improved binding of magnetic powder to a binder using binder having a high compatibility with the magnetic powder, thus improving dispersibility and packing properties to decrease the rubbing-off of the powder. In this method, it has been proposed that there be employed as a binder a polymer which is modified by the polymerization of its copolymeric ingredients highly compatible with the magnetic powder, thereby improving the binding property of the binder to the magnetic powder. This method, however, requires that all the copolymeric ingredients are capable of being polymerized. Even if this requirement is met, a binder containing a desired amount of copolymeric ingredients cannot be produced or a block copolymer is produced in the absence of a proper relative polymerization ratio, so that conditions of manufacture are significantly limited. This method is accordingly less valuable and less practical in industrial applications.
DISCLOSURE OF INVENTION
The object of the present invention is to provide a magnetic recording medium which has a superior durability by the employment of a binder comprising a modified polymer. The modified polymer binder to be employed in the present invention is produced by the modification of a polymer conventionally used as a binder for magnetic recording media through its graft polymerization with a polymerizable unsaturated compound containing a sulfonic group or a metal sulfonate group through irradiation. Such a binder may be produced by causing organic free radicals to be generated through exposure of a graph polymerizable polymer to radiation such as gamma rays, electron beams or the like, and thereafter allowing the free radicals to polymerize with the polymerizable unsaturated compounds. Thus, the polymer to be modified or a trunk polymer to be employed as a binder in the present invention can be any one which can generate free radicals upon being irradiated and which is not degraded by irradiation. It is to be noted that, since any organic material without exception can produce free radicals if radiation having a high penetrating power is used, and since a polymer likely to be degraded by such radiation can produce enough free radicals to react with the polymerizable unsaturated compound even if the radiation is applied in a small dose under conditions which control degradation, the kind of polymer which can be modified for use with this method extends over a wide range. As a polymer to which the aforementioned method can be applied, there may be mentioned preferably a polymer having a molecular weight ranging from about 10,000 to about 100,000, such as vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl propionate copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinyl propionate-vinyl alcohol copolymer, vinyl chloride-vinyl acetate-maleic acid copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylic ester-acrylonitrile copolymer, acrylic ester-vinylidene chloride copolymer, methacrylic ester-vinylidene chloride copolymer, methacrylic ester-styrene copolymer, thermoplastic polyurethane resin, phenoxy resin, polyvinyl fluoride, vinylidene chloride-acrylonitrile copolymer, butadiene-acrylonitrile copolymer, acrylonitrile-butadiene-acrylic acid copolymer, acrylonitrile-butadiene-methacrylic acid copolymer, polyvinyl butyral, cellulose derivative, styrene-butadiene copolymer, polyester resin, phenolic resin, epoxy resin, thermosetting polyurethane resin, urea resin, melamine resin, alkyd resin, urea-formaldehyde resin or a mixture thereof or the like.
The radiation to be used to irradiate the aforementioned polymer for the generation of free radicals may be, for example, gamma
REFERENCES:
patent: 4404253 (1983-09-01), Kohler
patent: 4407901 (1983-10-01), Miyatsuka
patent: 4411957 (1983-12-01), Tokuda
patent: 4415630 (1983-11-01), Kubuta
patent: 4420531 (1983-12-01), Tokuda
patent: 4444838 (1984-04-01), Yamada
Miyai Seiichi
Nakajima Kaoru
Robinson Ellis P.
Sony Corporation
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