GLASS SUBSTRATE FOR MAGNETIC DISK AND MAGNETIC DISK

摘要

A magnetic-disk glass substrate has a circular center hole, a pair of main surfaces and an edge surface. The edge surface has a side wall surface and chamfered surfaces interposed between the side wall surface and the main surfaces, and a roundness of an edge surface on an outer circumferential side is 1.5 μm or less. Also, a midpoint A between centers of two least square circle respectively derived from outlines in a circumferential direction respectively obtained at two positions spaced apart by 200 μm in a substrate thickness direction on the side wall surface on the outer circumferential side, and centers B and C respectively derived from a respective one of two chamfered surfaces on the outer circumferential side in the substrate thickness direction, are located such that a sum of respective distances between A and B, and A and C, is 1 μm or less.

主权项

1. A magnetic-disk glass substrate having a circular hole at a center, the magnetic-disk glass substrate comprising:
a pair of main surfaces; and an edge surface, the edge surface having a side wall surface and chamfered surfaces interposed between the side wall surface and the main surfaces, a roundness of the edge surface on an outer circumferential side being 1.5 μm or less, and when outlines in a circumferential direction are respectively obtained at two positions spaced apart by 200 μm in a substrate thickness direction on the side wall surface on the outer circumferential side, and a midpoint between centers of two least square circles respectively derived from the outlines is given as a midpoint A, and when outlines in the circumferential direction are respectively obtained at positions that are located at centers of the two chamfered surfaces on the outer circumferential side in the substrate thickness direction, and among centers of least square circles derived from the outlines, a center derived from one chamfered surface is given as a center B, and a center derived from the other chamfered surface is given as a center C, a sum of a distance between the midpoint A and the center B and a distance between the midpoint A and the center C being 1 μm or less.