Chemical reinforced glass substrate having desirable edge profile and method of manufacturing the same

Abstract

In a method of manufacturing a chemical reinforced glass substrate, consideration is previously made about a relationship between conditions of chemical reinforcement for a glass substrate and deformation caused by the chemical reinforcement at an edge portion of the glass substrate. The glass substrate is chemically reinforced on the basis of the relationship so that an edge profile is shaped into a desirable edge profile during the chemical reinforcement. The resultant chemical reinforced glass substrate is flat and smooth in a wide area and effective to improve a recording density and to avoid head crashes.

What is claimed is:  
     
         1 . A method of manufacturing a glass substrate for an information recording medium, the glass substrate having an edge portion adjacent to an outer and/or an inner peripheral side end, comprising the steps of: 
 previously finding a relationship between chemical reinforcement conditions and that profile variation at the edge portion of the glass substrate which results from chemical reinforcement; and    performing the chemical reinforcement of the glass substrate on the basis of the relationship to obtain a chemically reinforced glass substrate.    
     
     
         2 . A method of manufacturing a glass substrate for an information recording medium, the glass substrate having an edge portion adjacent to an outer and/or an inner peripheral side end, comprising the steps of: 
 previously finding a relationship between chemical reinforcement conditions and that profile variation at the edge portion of the glass substrate which results from chemical reinforcement;    deciding a profile on the edge portion by predicting the profile variation of the edge portion to obtain, as a glass substrate prior to chemical reinforcement, an glass substrate prior to chemical reinforcement which has a decided profile and which is not subjected to the chemical reinforcement; and    performing the chemical reinforcement of the glass substrate prior to chemical reinforcement to obtain the glass substrate which has a desired profile at the edge portion.    
     
     
         3 . A method as claimed in  claim 1 , wherein the chemical reinforcement performing step is performed on conditions such that the profile variation on the edge portion becomes small.  
     
     
         4 . A method as claimed in  claim 1 , wherein the chemical reinforcement performing step is performed under the chemical reinforcement condition such that a compressive stress layer formed on a surface layer of the glass substrate by the chemical reinforcement reaches to a depth between 3 and 100 μm and has a compressive stress of 1-15 kg/mm 2  and that a tensile stress caused by the chemical reinforcement within the glass substrate is not larger than 4.5 kg/mm 2 .  
     
     
         5 . A method as claimed in  claim 1 , wherein the chemical reinforcement condition defines a processing temperature and a processing time during the chemical reinforcement.  
     
     
         6 . A method as claimed in  claim 5 , wherein the processing temperature and the processing time fall with a range between 280° C. and 400° C. and a duration between 0.5 and 5 hours, respectively.  
     
     
         7 . A method as claimed in  claim 2 , the glass substrate prior to chemical reinforcement having a main surface chamfered and polished together with the edge portion adjacent to the outer and/or the inner peripheral side end, wherein the previously finding step previously finds, as the relationship, a relationship between a polishing condition of the main surface and an edge profile obtained on the basis of the polishing condition; wherein: 
 the deciding step obtains the glass substrate prior to chemical reinforcement by controlling the polishing condition of the main surface on the basis of the above-mentioned relationship between the polishing condition and the edge profile.    
     
     
         8 . A method as claimed in  claim 7 , wherein the polishing condition is determined such that the edge portion is polished to be put into a surface down state lowered relative to the main surface of the glass substrate.  
     
     
         9 . A method as claimed in  claim 8 , wherein the polishing condition determined for the surface down state is defined such that use is made about a soft polisher of a hardness between 60 and 80 (Asker-C) and a surface pressure to the glass substrate is kept at a range between 40 and 150 kg/cm 2  during polishing.  
     
     
         10 . A glass substrate which is subjected to chemical reinforcement and which is for use in an information recording medium, the glass substrate chemically reinforced having a main surface and an edge portion adjacent to an outer and/or an inner peripheral side end and contiguous to the main surface, the edge portion of the glass substrate which is chemically reinforced having a predetermined region defined by an edge profile which falls within ±0.35 μm in relation to a flat portion of the main surface determined as a reference surface (zero).  
     
     
         11 . A glass substrate as claimed in  claim 10 , the glass substrate being subjected to chemical reinforcement and defined as a glass substrate after chemical reinforcement, the main surface of the glass substrate after chemical reinforcement having a glide area which includes a recording area located inside of the glide area, the glide area having a glide outer periphery while the recording area has a recording area outer periphery inside the glide outer periphery and a flat area, wherein: 
 the edge profile chemically reinforced has, within an area extended from the glide outer periphery to an inside of the recording area, a ski-jumped point which is the highest point with respect to a reference surface (zero) defined by the flat area and which has a ski-jump value not greater than ±0.35 μm at the skl-jump point;    the edge profile also having, at a roll-off point defined by a position of the glide outer periphery, a roll-off value not greater than ±0.35 μm with respect to the reference surface.    
     
     
         12 . A glass substrate as claimed in  claim 10 , wherein the glass substrate chemically reinforced has a compressive stress layer within a surface layer which is caused by the chemical reinforcement and which has a depth between 3 and 100 μm and a compressive stress of 1-15 kg/mm 2 ; 
 the glass substrate chemically reinforced also having a tensile stress not greater than 4.5 kg/mm 2  within an inside of the glass substrate.  
 
     
     
         13 . A method of manufacturing an information recording medium from the glass substrate claimed in  claim 1 , further comprising the step of: 
 depositing a recording layer on the main surface of the glass substrate.    
     
     
         14 . An information recording medium manufactured from the glass substrate claimed in  claim 10 , further comprising a magnetic layer over the main surface.  
     
     
         15 . An information recording medium as claimed in  claim 14 , the information recording medium being a magnetic recording medium of a LUL drive type.