Method of surface finish for glass substrate for magnetic disk and glass substrate for magnetic disk

Abstract

The invention is to obtain a glass substrate for information recording disk with satisfactory circular ring strength through minimizing of polished depth at chemical polishing without performing any chemical strengthening treatment. The surface roughness of the edge face of inner circumferential portion of a doughnut-shaped glass substrate for magnetic disk is regulated by mechanical polishing to 9 nm or less in terms of Rmax. Subsequently, the edge face of inner circumferential portion is subjected to chemical polishing so that the surface layer thereof as much as 2 [mu]m or more is polished off. By such unprecedented mirror finish of the surface roughness of the edge face of inner circumferential portion through mechanical polishing, a satisfactory circular ring strength can be attained even when the polished depth at chemical polishing is reduced to less than in the prior art. The polished depth of less than 5 [mu]m is satisfactory.

Description

technical field [0001] The present invention relates to a surface processing method of a glass substrate for magnetic disks used for hard disks and the like, and a glass substrate for magnetic disks. Background technique [0002] Damage to the end surface of the inner peripheral portion of the substrate that generates the maximum tensile stress during the operation of the magnetic disk is one of the factors affecting the mechanical strength of the glass substrate for the magnetic disk. Patent Document 1: JP-A-7-230621 discloses At least the end face of the inner peripheral part must be etched to achieve the specified surface roughness. When measured by a three-dimensional length measuring SEM, the roughness of the end surface of the inner peripheral part or the outer peripheral part of the glass substrate described in Patent Document 1 is at least four positions selected arbitrarily in the case of a reference length of 240 μm and an Ra cutoff wavelength of 80 μm. The averag...

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Problems solved by technology

And, as this etching amount (the depth of the surface layer grinding and removal produced by chemical grinding), for example, as described in Patent Document 1, it is necessary to control the etching depth in the range of 5 to 25 μm, preferably 10 to 30 μm ( 0039 paragraph), in the past, if the amount of etching was not increased to more than 10μm, it was impossible to obtain sufficient mechanical strength

[0009] However, if the amount of etching is increased to more than 10 μm, there will be problems of reduced processing dimensional accuracy and deviations in roundness, so it is desirable to control the amount of etching to less than 5 μm

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