Annular glass plate, method for manufacturing glass substrate for magnetic disk, glass substrate for magnetic disk, and magnetic disk
An annular glass plate has an outer circumferential edge surface, an inner circumferential edge surface, and a thickness not larger than 0.6 mm. The outer circumferential edge surface and the inner circumferential edge surface are constituted by molten surfaces. The molten surfaces in the outer circumferential edge surface and the inner circumferential edge surface each have an arithmetic average surface roughness Ra not larger than 0.1 μm and the surface roughness of the molten surface in the inner circumferential edge surface is larger than the surface roughness of the molten surface in the outer circumferential edge surface. The molten surfaces in the inner circumferential edge surface and the outer circumferential edge surface do not bulge relative to both main surfaces of the annular glass plate.
1 . An annular glass plate that has an outer circumferential edge surface, an inner circumferential edge surface, and a thickness not larger than 0.6 mm,
wherein the outer circumferential edge surface and the inner circumferential edge surface each have an arithmetic average surface roughness Ra not larger than 0.1 μm and the surface roughness of the inner circumferential edge surface is larger than the surface roughness of the outer circumferential edge surface by at least 0.01 μm,
the inner circumferential edge surface and the outer circumferential edge surface do not bulge relative to both main surfaces of the annular glass plate, and
the surface roughness of the inner circumferential edge surface is not less than 0.02 um.
2 . The annular glass plate according to claim 1 , wherein
the outer circumferential edge surface and the inner circumferential edge surface are constituted by molten surfaces.
3 . The annular glass plate according to claim 1 , wherein
the main surfaces have an arithmetic average surface roughness Ra not larger than 0.3 nm.
4 . A magnetic disk comprising:
the annular glass plate according to claim 3 ; and
magnetic films formed on the main surfaces of the annular glass plate.
5 . An annular glass plate that has an outer circumferential edge surface, an inner circumferential edge surface, and a thickness not larger than 0.6 mm,
wherein the outer circumferential edge surface and the inner circumferential edge surface each have an arithmetic average surface roughness Ra not larger than 0.1 μm and the surface roughness of the inner circumferential edge surface is larger than the surface roughness of the outer circumferential edge surface,
the inner circumferential edge surface and the outer circumferential edge surface do not bulge relative to both main surfaces of the annular glass plate, and
the surface roughness of the inner circumferential edge surface is larger than the surface roughness of the outer circumferential edge surface by at least 0.01 μm.
6 . The annular glass plate according to claim 5 , wherein
the outer circumferential edge surface and the inner circumferential edge surface are constituted by molten surfaces.
7 . The annular glass plate according to claim 5 , wherein
the main surfaces have an arithmetic average surface roughness Ra not larger than 0.3 nm.
8 . A magnetic disk comprising:
the annular glass plate according to claim 7 ; and
magnetic films formed on the main surfaces of the annular glass plate.
9 . An annular glass plate that has an outer circumferential edge surface, an inner circumferential edge surface, and a thickness not larger than 0.6 mm,
wherein the outer circumferential edge surface has the arithmetic average surface roughness Ra not larger than 0.05 μm, the inner circumferential edge surface has an arithmetic average surface roughness Ra not larger than 0.1 μm, and the surface roughness of the inner circumferential edge surface is larger than the surface roughness of the outer circumferential edge surface by at least 0.01 μm,
the inner circumferential edge surface and the outer circumferential edge surface do not bulge relative to both main surfaces of the annular glass plate, and
the surface roughness of the inner circumferential edge surface is not less than 0.02 um.
10 . The annular glass plate according to claim 9 , wherein
the outer circumferential edge surface and the inner circumferential edge surface are constituted by molten surfaces.
11 . The annular glass plate according to claim 9 , wherein
the main surfaces have an arithmetic average surface roughness Ra not larger than 0.3 nm.
12 . A magnetic disk comprising:
the annular glass plate according to claim 11 ; and
magnetic films formed on the main surfaces of the annular glass plate.