Chemically strengthened glass, and method for manufacturing the same

Abstract

The present invention relates to a chemically strengthened glass having a thickness of t [mm], and having a profile of a stress value CS x [MPa,] at a depth x [µm] from a surface of the glass, the stress value being measured by a scattered-light photoelastic stress meter, in which a second-order differential value CS x " of the stress value CS x in the profile satisfies the following expression within a range of CS x ≥0: 0<CS x "≤0.050.

1 - 7 . (canceled) 
     
     
         8 . A method of manufacturing a chemically strengthened glass, the method comprising:
 immersing a lithium-containing glass into a first molten salt composition comprising sodium ions and potassium ions to thereby perform first ion exchange; and   immersing the lithium-containing glass into a second molten salt composition comprising potassium ions and an additive to thereby perform second ion exchange,   wherein in the first molten salt composition, a concentration of potassium nitrate is higher than a concentration of sodium nitrate,   in the second molten salt composition, a concentration of potassium nitrate is 85 mass% or higher, and a mass ratio of sodium ions to lithium ions is 0 or higher and 15 or lower, and   the additive comprises either one of silicic acid or carbonate.   
     
     
         9 . The method of manufacturing a chemically strengthened glass according to  claim 8 , wherein the concentration of potassium nitrate in the first molten salt composition is higher than 50 mass%. 
     
     
         10 . The method of manufacturing a chemically strengthened glass according to  claim 8 , wherein the second molten salt composition comprises sodium nitrate whose concentration is higher than 0 mass% and 5 mass% or lower. 
     
     
         11 . The method of manufacturing a chemically strengthened glass according to  claim 8 , wherein the second molten salt composition comprises lithium ions whose concentration is 0.1 mass% or higher and 10 mass% or lower. 
     
     
         12 . The method of manufacturing a chemically strengthened glass according to  claim 8 , wherein in the first ion exchange, the first molten salt composition has a temperature of 380° C. or higher and 450° C. or lower. 
     
     
         13 . The method of manufacturing a chemically strengthened glass according to  claim 12 , wherein in the first ion exchange, the lithium-containing glass is immersed in the first molten salt composition for 0.5 hours or more and 8 hours or less. 
     
     
         14 . The method of manufacturing a chemically strengthened glass according to  claim 8 , wherein in the second ion exchange, the second molten salt composition has a temperature of 380° C. or higher and 450° C. or lower. 
     
     
         15 . The method of manufacturing a chemically strengthened glass according to  claim 14 , wherein in the second ion exchange, the lithium-containing glass is immersed in the second molten salt composition for an immersion time t2 [min] satisfying the following expression using a temperature T [°C] of the second molten salt composition:        -0   .38T+173<t2<-1   .4T+650       . 
     
     
         16 . The method of manufacturing a chemically strengthened glass according to  claim 8 , wherein the chemical strengthening is performed so that a tensile stress value CT 2  [MPa] of the chemically strengthened glass after the second ion exchange is a value corresponding to 50% to 93% of a tensile stress value CT 1  [MPa] of the chemically strengthened glass after the first ion exchange. 
     
     
         17 . The method of manufacturing a chemically strengthened glass according to  claim 8 , wherein a tensile stress value CT 1  [MPa] of the chemically strengthened glass after the first ion exchange satisfies the following expression using a thickness t [mm] of the chemically strengthened glass:            CT     1     >-120t+164       . 
     
     
         18 . The method of manufacturing a chemically strengthened glass according to  claim 8 , wherein the lithium-containing glass comprises, by mol% in terms of oxides:        52       to       75%       of           SiO       2;                   8       to       20%       of           Al     2       O   3     ;               5       to       16%       of           LiO     2     ;       and               8%       or       lower       of           NaO     2         . 
     
     
         19 . The method of manufacturing a chemically strengthened glass according to  claim 8 , wherein the additive comprises the silicic acid and the content of the silicic acid in the second molten salt is 0.1 mass% or higher and 3 mass% or lower. 
     
     
         20 . The method of manufacturing a chemically strengthened glass according to  claim 8 , wherein the additive comprises the carbonate and the content of the carbonate in the second molten salt is 2 mass% or lower. 
     
     
         21 . The method of manufacturing a chemically strengthened glass according to  claim 8 , wherein in the first ion exchange, the first molten salt composition has a temperature of 421° C. or higher and 450° C. or lower. 
     
     
         22 . The method of manufacturing a chemically strengthened glass according to  claim 8 , wherein in the second ion exchange, the second molten salt composition has a temperature of 380° C. or higher and 400° C. or lower.