Alkali-free glass substrate and process for producing the same

Abstract

The invention provides an alkali-free glass substrate small in the variation of the thermal shrinkage and a process for producing the same. An alkali-free glass substrate of the invention has an absolute value of a thermal shrinkage of 50 ppm or more when the alkali-free glass substrate is heated at a rate of 10° C./min from a room temperature, kept at a holding temperature of 450° C. for 10 hr and then cooled at a rate of 10° C./min.

1 . An alkali-free glass substrate, which has an absolute value of a thermal shrinkage of 50 ppm or more when the alkali-free glass substrate is heated at a rate of 10° C./min from a room temperature, kept at a holding temperature of 450° C. for 10 hr and then cooled at a rate of 10° C./min. 
     
     
         2 . The alkali-free glass substrate according to  claim 1 , which has a strain point of 630 to 655° C. and the absolute value of the thermal shrinkage of 60 ppm or more. 
     
     
         3 . The alkali-free glass substrate according to  claim 1 , which has a strain point of 655 to 680° C. and the absolute value of the thermal shrinkage of 50 ppm or more. 
     
     
         4 . The alkali-free glass substrate according to  claim 1 , which has a liquidus viscosity of 10 4.5  Pa·s or more. 
     
     
         5 . The alkali-free glass substrate according to  claim 1 , which is formed in accordance with an overflow down draw method. 
     
     
         6 . The alkali-free glass substrate according to  claim 1 , which comprises, by weight %, 50 to 70% of SiO 2 , 1 to 20% of Al 2 O 3 , 0 to 15% of B 2 O 3 , 0 to 30% of MgO, 0 to 30% of CaO, 0 to 30% of SrO and 0 to 30% of BaO. 
     
     
         7 - 17 . (canceled) 
     
     
         18 . An alkali-free glass substrate, which is produced by a process comprising melting and forming a glass raw material, wherein, in a cooling step during said forming, an average cooling rate in a temperature range from an annealing point to a temperature lowered by 100° C. from the annealing temperature is 300° C./min or more. 
     
     
         19 . An alkali-free glass substrate, which is produced by a process comprising melting and forming a glass raw material, wherein, in a cooling step during said forming, an average sheet drawing rate in a temperature range from an annealing point to a temperature lowered by 100° C. from the annealing temperature is 150 cm/min or more.