Glass substrate

Abstract

The present invention is aimed to provide a method for producing a glass substrate with a thickness of not more than 200 μm, which is satisfied with the quality required for a substrate on which a thin-film electric circuit is formed, and a sheet glass substrate obtained according to this method. The present invention is concerned with a method for producing a glass substrate having a sheet thickness of from 10 to 200 μm, including a forming step of forming a molten glass into a ribbon shape in accordance with a down draw method, an annealing step of annealing the glass ribbon, and a cutting step of cutting the glass ribbon to give a glass substrate, wherein an average cooling rate in a temperature range of from the (annealing point +200° C.) to the (annealing point +50° C.) is controlled to the range of from 300 to 2,500° C./min.

1 .- 4 . (canceled) 
     
     
         5 . A glass substrate having a sheet thickness of from 10 to 200 μm, wherein a sheet thickness difference between a maximum sheet thickness and a minimum sheet thickness in the substrate is not more than 30 μm. 
     
     
         6 . The glass substrate according to  claim 5 , wherein a residual stress value thereof is not more than 2.5 nm. 
     
     
         7 . The glass substrate according to  claim 5 , wherein a warpage value thereof is not more than 200 μm. 
     
     
         8 . The glass substrate according to  claim 5 , wherein a thermal shrinkage ratio at the time of heating from ordinary temperature at a rate of 5° C./min, keeping at 450° C. for 10 hours and then cooling at a rate of 5° C./min is less than 300 ppm. 
     
     
         9 . The glass substrate according to  claim 5 , wherein an average surface roughness Ra thereof is not more than 0.3 nm. 
     
     
         10 . The glass substrate according to  claim 5 , which is composed of a glass comprising from 50 to 70% of SiO 2 , from 10 to 25% of Al 2 O 3 , from 1 to 15% of B 2 O 3 , from 0 to 10% of MgO, from 0 to 15% of CaO, from 0 to 15% of SrO, from 0 to 15% of BaO, and from 0 to 5% of Na 2 O in terms of percentage by mass. 
     
     
         11 . The glass substrate according to  claim 5 , which is used as a substrate for forming a thin-film electric circuit. 
     
     
         12 . The glass substrate according to  claim 5 , which is used as a substrate of a flexible display.