Glass substrate for magnetic recording medium, production method thereof, and magnetic recording medium using the substrate

Abstract

The present invention provides a production method of a glass substrate for magnetic recording medium having an inner diameter and an outer diameter comprising an edge polishing step of a glass substrate. In one embodiment of the production method, it has the edge polishing step in which the inner or outer diameter of the glass substrate is chucked, in a single disk process, and the edge surface of the outer or inner diametral side of the glass substrate is polished using a polishing tape or a grindstone. Further, the present invention relates to a magnetic recording medium using the glass substrate. The production method of a glass substrate of the present invention can perform a polishing of edge surface in a high-quality without generating a defect on the surface of the glass substrate. The present invention can provide a superior magnetic recording medium by using the glass substrate.

What is claimed is:  
     
         1 . A production method of a glass substrate for magnetic recording medium having an inner diameter and an outer diameter comprising an edge polishing step of a glass substrate, 
 wherein said edge polishing step is a step in which said inner diameter of said glass substrate is chucked, in a single disk process, and an edge surface of the outer diametral side of said glass substrate is polished using a polishing tape or a grindstone.    
     
     
         2 . A production method of a glass substrate for magnetic recording medium having an inner diameter and an outer diameter comprising an edge polishing step of a glass substrate, 
 wherein said edge polishing step is a step in which said outer diameter of said glass substrate is chucked, in a single disk process, and an edge surface of the inner diametral side of said glass substrate is polished using a polishing tape or a grindstone.    
     
     
         3 . A production method of a glass substrate for magnetic recording medium having an inner diameter and an outer diameter comprising steps of: 
 (a) forming a shape of a disk-shaped glass substrate having a center hole,    (b) performing edge polishing of said disk-shaped glass substrate, and    (c) performing surface finishing of said disk-shaped glass substrate,    wherein said edge polishing step, the step (b), is a step in which said inner diameter of said glass substrate is chucked, in a single disk process, and an edge surface of the outer diametral side of said glass substrate is polished using a polishing tape or a grindstone.    
     
     
         4 . A production method of a glass substrate for magnetic recording medium having an inner diameter and an outer diameter comprising steps of: 
 (a) forming a shape of a disk-shaped glass substrate having a center hole,    (b) performing edge polishing of said disk-shaped glass substrate, and    (c) performing surface finishing of said disk-shaped glass substrate,    wherein said edge polishing step, the step (b), is a step in which said outer diameter of said glass substrate is chucked, in a single disk process, and an edge surface of the inner diametral side of said glass substrate is polished using a polishing tape or a grindstone.    
     
     
         5 . A production method of a glass substrate for magnetic recording medium having an inner diameter and an outer diameter comprising an edge polishing step of a glass substrate, 
 wherein said edge polishing step comprises a step in which said inner diameter of said glass substrate is chucked, in a single disk process, and an edge surface of the outer diametral side of said glass substrate is polished using a polishing tape or a grindstone; and a step in which said outer diameter of said glass substrate is chucked in a single disk process, and said edge surface of the inner diametral side of said glass substrate is polished using a polishing tape or a grindstone.    
     
     
         6 . A production method of a glass substrate for magnetic recording medium having an inner diameter and an outer diameter comprising steps of: 
 (a) forming a shape of a disk-shaped glass substrate having a center hole,    (b) performing edge polishing of said disk-shaped glass substrate, and    (c) performing surface finishing of said disk-shaped glass substrate,    wherein said edge polishing step, the step (b), comprises a step in which said inner diameter of said glass substrate is chucked, in a single disk process, and an edge surface of said outer diametral side of said glass substrate is polished using a polishing tape or a grindstone; and a step in which said outer diameter of said glass substrate is chucked, in a single disk process, and said edge surface of said inner diametral side of the glass substrate is polished using a polishing tape or a grindstone.    
     
     
         7 . The production method of a glass substrate for magnetic recording medium as claimed in any one of  claims 1  to  6 , wherein said edge polishing step is a step for polishing by polishing tape containing abrasive particles selected from the group consisting of diamond, aluminum oxide, cerium oxide, silicon carbide, and colloidal silica.  
     
     
         8 . The production method of a glass substrate for magnetic recording medium as claimed in  claim 7 , wherein said edge polishing step is a step of polishing by a wet method using a slurry.  
     
     
         9 . The production method of a glass substrate for magnetic recording medium as claimed in  claim 7 , wherein said edge polishing step is a step of polishing by a dry method without using a slurry.  
     
     
         10 . The production method of a glass substrate for magnetic recording medium as claimed in  claim 8 , wherein said edge polishing step is a step for polishing while dropping a slurry containing abrasive particles selected from the group consisting of diamond, aluminum oxide, cerium oxide, silicon carbide, and colloidal silica.  
     
     
         11 . The production method of a glass substrate for magnetic recording medium as claimed in  claim 8 , wherein said edge polishing step is a step for polishing while dropping water or an aqueous solution not containing abrasive particles selected from the group consisting of water, an aqueous solution of alkali which is pH adjusted with alkali, and an aqueous solution containing a surface-active agent.  
     
     
         12 . The production method of a glass substrate for magnetic recording medium as claimed in any one of  claims 1  to  6 , wherein said edge polishing step is a step for polishing using a polishing tape made of a material selected from polyurethane, polyester and nylon not containing abrasive particles while dropping water or an aqueous solution not containing abrasive particles selected from the group consisting of water, an aqueous solution of alkali which is pH adjusted with alkali, and an aqueous solution containing a surface-active agent.  
     
     
         13 . The production method of a glass substrate for magnetic recording medium as claimed in any one of  claims 1  to  6 , wherein said edge polishing step is a step for polishing using a polishing tape made of a material selected from polyurethane, polyester and nylon not containing abrasive particles while dropping a slurry containing abrasive particles selected from the group consisting of diamond, aluminum oxide, cerium oxide, silicon carbide, and colloidal silica.  
     
     
         14 . The production method of a glass substrate for magnetic recording medium as claimed in any one of  claims 1  to  6 , wherein said edge polishing step is a step for polishing using a grindstone containing a material selected from the group consisting of diamond, aluminum oxide, cerium oxide, silicon carbide, and colloidal silica.  
     
     
         15 . The production method of a glass substrate for magnetic recording medium as claimed in  claim 14 , wherein said edge polishing step is a step for polishing while dropping water or an aqueous solution not containing abrasive particles selected from the group consisting of water, an aqueous solution of alkali which is pH adjusted with alkali, and an aqueous solution containing a surface active agent.  
     
     
         16 . The production method of a glass substrate for magnetic recording medium as claimed in  claim 14 , wherein said edge polishing step is a step for polishing while dropping a slurry containing abrasive particles selected from the group consisting of diamond, aluminum oxide, cerium oxide, silicon carbide, and colloidal silica.  
     
     
         17 . A glass substrate for magnetic recording medium produced by the production method according any one of  claims 1  to  6 .  
     
     
         18 . A magnetic recording medium comprising at least a magnetic layer, a protective layer and a liquid lubricating layer are formed on a substrate and said substrate is the glass substrate for magnetic recording medium as claimed in claim  17 .