Glass substrate for magnetic recording medium, magnetic recording medium, and method of manufacturing the same

Abstract

In a method of manufacturing a glass substrate for a magnetic recording medium for forming a predetermined roughness, a principal surface of the glass substrate is precisely polished by the use of polishing material containing free abrasive grain. Remaining stress distribution for a portion of a polishing trace due to the free abrasive grain is generated on the surface of the glass substrate. A surface process is performed for at least the principal surface of the glass substrate by the use of hydrosilicofluoric acid. A portion having relatively high remaining distortion in the generated remaining stress distribution is decided as an island portion. The glass substrate is heated after precisely polishing before performing the surface process by the use of the hydrosilicofluoric acid.

What is claimed is:  
     
         1 . A method of manufacturing a glass substrate for a magnetic recording medium for forming a predetermined roughness, comprising the steps of: 
 precisely polishing a principal surface of the glass substrate by the use of polishing material containing free abrasive grain,    generating remaining stress distribution for a portion of a polishing trace due to the free abrasive grain on the surface of the glass substrate,    performing a surface process for at least the principal surface of the glass substrate by the use of hydrosilicofluoric acid, and    deciding a portion having relatively high remaining distortion in the generated remaining stress distribution as an island portion,    the glass substrate being heated after precisely polishing before performing the surface process by the use of the hydrosilicofluoric acid.    
     
     
         2 . A method of manufacturing a glass substrate for a magnetic recording medium for forming a predetermined roughness, comprising the steps of: 
 precisely polishing a principal surface of the glass substrate by the use of polishing material containing free abrasive grain,    generating remaining stress distribution for a portion of a polishing trace due to the free abrasive grain on the surface of the glass substrate,    chemically strengthening at least the principal surface of the glass substrate, and    deciding a portion having relatively high remaining distortion in the generated remaining stress distribution as an island portion,    the glass substrate being heated by dipping the glass substrate in heated solvent after precisely polishing before chemically strengthening the surface.    
     
     
         3 . A method as claimed in  claim 2 , wherein: 
 the chemical surface process comprises either one of an etching process by the use of solution containing hydrofluoric acid, solution containing hydrosilicofluoric acid, and alkali solution.    
     
     
         4 . A method as claimed in any one of the claims  1  through  3 , wherein: 
 heating temperature in the heating process step falls within the range between 30° C. and 180° C.  
 
     
     
         5 . A method as claimed in any one of the claims  1  through  4 , wherein: 
 the heating process is carried out by the use of at least one selected from the group consisting of hot water, heated sulfuric acid, heated glycerin, and heated phosphoric acid.  
 
     
     
         6 . A method as claimed in any one of the claims  1  through  5 , wherein: 
 the glass substrate contains at least alkali metal oxide and alkali earth oxide, and  
 content of the alkali earth oxide is not exceeding 3 mol %.  
 
     
     
         7 . A method as claimed in  claim 6 , wherein: 
 the glass constituting the glass substrate contains SiO 2  between 58 and 75 weight %, Al 2 O 3  between 5 and 23 weight %, Li 2 O between 3 and 10 weight %, and Na 2 O between 4 and 13 weight % as main components.    
     
     
         8 . A method as claimed in  claim 7 , wherein: 
 the glass contains SiO 2  between 62 and 75 weight %, Al 2 O 3  between 5 and 15 weight %, Li 2 O between 4 and 10 weight %, Na 2 O between 4 and 12 weight %, and ZrO 2  between 5.5 and 15 weight % as main components, and    weight ratio of Na 2 O/ZrO 2  falls within the range between 0.5 and 2.0 while weight ratio of Al 2 O 3 /ZrO 2  falls within the range between 0.4 and 2.5.    
     
     
         9 . A method as claimed in any one of claims  1  through  7 , wherein: 
 the chemical strengthening process is carried out after the surface process due to the hydrosilicofluoric acid.  
 
     
     
         10 . A method of manufacturing a magnetic recording medium, wherein: 
 at least a magnetic layer is formed on the principal surface of the glass substrate manufactured by the method claimed in any one of claims  1  through  9 .    
     
     
         11 . A glass substrate for a magnetic recording medium for use in a load/unload system, wherein: 
 the glass substrate has a principal surface, and    surface roughness of the principal surface is specified by Rmax=3-15 nm, Ra=0.2-2.5 nm, and Rmax/Ra=3-15,    where Ra is representative of a center-line mean roughness, and Rmax is defined as a maximum height representative of a difference between a highest point and a lowest point.    
     
     
         12 . A glass substrate for a magnetic recording medium for use in a load/unload system, wherein: 
 the glass substrate has a principal surface, and    surface roughness of the principal surface is specified by Rp=1-7 nm, Ra=0.2-2.5 nm, and Rp/Ra=1-15,    where Ra is representative of a center-line mean roughness, and Rp is representative of a maximum height of a highest point.    
     
     
         13 . A magnetic recording medium having at least a magnetic layer on a glass substrate for use in a load/unload system, wherein: 
 the glass substrate has a principal surface, and surface roughness of the principal surface is specified by Rmax=3-15 nm, Ra=0.2-2.5 nm, and Rmax/Ra=3-15,    where Ra is representative of a center-line mean roughness, and Rmax is defined as a maximum height representative of a difference between a highest point and a lowest point.    
     
     
         14 . A magnetic recording medium having at least a magnetic layer on a glass substrate for use in a load/unload system, wherein: 
 the glass substrate has a principal surface, and    surface roughness of the principal surface is specified by Rp=1-7 nm, Ra=0.2-2.5 nm, and Rp/Ra=1-15,    where Ra is representative of a center-line mean roughness, and Rp is representative of a maximum height of a highest point.