Base plate for magnetic recording disc
AssigneeHitachi, Ltd.
InventorsNobuo Nakagawa, Yoshiki Kato, Katsuo Abe, Takao Edamura, Takao Nakamura
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Abstract
A base plate for magnetic recording disc is produced by coating thin metal layers containing no impurities for forming defects by an anodizing treatment on one or both sides of a discoid substrate made of a metal such as aluminum or an aluminum alloy or from a plastic by a dry process, and anodizing the thin metal layers so as to form anodized film from the surfaces of the thin metal layers to a certain depth while the portions contacting to the substrate are retained not anodized.
Claims14
A base plate for a magnetic recording disc comprising a light, durable, smooth-surfaced discoid substrate, a thin metal layer formed on at least one side of the substrate, and an anodized layer formed from the surface of said at least one thin metal layer to a depth of at least one-half of the thickness of the thin metal layer by an anodizing treatment, said at least one thin metal layer containing no element which produces surface pin-hole defect portions on the anodized layer formed by the anodizing treatment and being formed by a dry process using, as a vapor source or a target, (a) aluminum having a purity of at least 99.999%;
- (b) magnesium having a purity of at least 99.999%;
- or (c) an aluminum-magnesium alloy in which aluminum has a purity of at least 99.999% in an amount of 90.0 to 99.9% by weight and magnesium has a purity of at least 99.999% in an amount of 10.0 to 0.1% by weight.
A base plate for a magnetic recording disc which is produced by coating at least one thin metal layer by a dry process containing no impurities for forming pin-hole defects with an anodizing treatment on at least one side of a light, durable, smooth-surfaced discoid substrate, and by anodizing the at least one thin metal layer so as to form anodized film from the surface of the thin metal layer to a depth of at least one-half of the thickness of the thin metal layer being anodized while portions of the at least one metal layer contacting the substrate are retained not anodized, said at least one thin metal layer being produced by using as a vapor source or a target:
- (a) aluminum having a purity of at least 99.999%;
- (b) magnesium having a purity of at least 99.999%;
- or (c) an aluminum-magnesium alloy in which aluminum has a purity of at least 99.999% in an amount of 90.0 to 99.9% by weight and magnesium has a purity of at least 99.999% in an amount of 10.0 to 0.1% by weight.
Dependencies are inferred from the claim text.