Method for preparing glass substrates for magnetic recording mediums

Abstract

A method for preparing a glass substrate for magnetic recording mediums comprises the steps of lapping a glass substrate, then chemically treating the glass substrate for strengthening to form a strengthening layer having a thickness of not less than 20 μm and polishing the chemically strengthened glass substrate so that not less than 10 μm of the strengthening layer on the main face is removed, while leaving not less than 10 μm of the strengthening layer on the main surface of the glass substrate. The method for preparing a glass substrate for magnetic recording mediums permits the easy preparation of such glass substrates having excellent flatness and excellent surface smoothness and also permits the marked improvement of the rate of machine operation and production efficiency.

What is claimed is:  
     
         1 . A method for preparing a glass substrate for magnetic recording mediums, consisting essentially of the steps of lapping a glass substrate, then chemically treating the glass substrate for strengthening to form a strengthening layer having a thickness of not less than 20 μm and polishing the strengthened glass substrate so that not less than 10 μm of the strengthening layer on the main face is removed, while leaving not less than 10 μm of the strengthening layer on the main surface of the glass substrate.  
     
     
         2 . The method of    claim 1    wherein the thickness of the strengthening layer is not less than 30 μm and wherein not less than 15 μm of the strengthening layer on the main face is removed, while leaving not less than 15 μm of the strengthening layer on the main surface of the glass substrate.  
     
     
         3 . The method of    claim 1    wherein the lapping step is a two-stage lapping step comprising first and second lapping stages.  
     
     
         4 . The method of    claim 3    wherein an abrasive material used in the lapping step has a particle size ranging from 10 to 30 μm for the first lapping stage and 5 to 15 μm for the second lapping stage.  
     
     
         5 . The method of    claim 1    wherein the chemically strengthening treatment comprising immersing the glass substrate in a mixed and fused salt.  
     
     
         6 . The method of    claim 1    wherein the glass substrate is an aluminosilicate glass material.