Patent ID: 11955151
Assignee: HOYA CORPORATION
Field: Audio-visual technology (Electrical engineering)
Classification: CPC G | IPC G

Claim 0:
1. A substrate for a magnetic disk, the substrate comprising:
a substrate main body having two opposing main surfaces and an outer circumferential edge surface, the outer circumferential edge surface including a side wall surface, which is orthogonal to the main surfaces, and chamfered surfaces, which are disposed between the main surfaces and the side wall surface, the substrate main body being a glass substrate main body or an aluminum alloy substrate main body, the substrate main body having a disk shape; and
a film that is an alloy film containing Ni and P, and is provided on a surface of the substrate main body such that the film is formed continuously over the main surfaces, the chamfered surfaces, and the side wall surface of the substrate main body,
wherein the substrate has a thickness (T+D) of 0.520 mm or less, the thickness (T+D) being the sum of a thickness T of the substrate main body and a thickness D of the film formed on the main surfaces of the substrate main body,
the disk shape has an outer diameter of 90 mm or more,
a ratio D/T of the thickness D of the film to the thickness T of the substrate main body is 0.025 or more, and
a surface roughness maximum height Rz of the film formed on the outer circumferential edge surface of the substrate main body is smaller than a surface roughness maximum height Rz of the substrate main body at the outer circumferential edge surface of the substrate main body.