Tempered glass and process for producing the same

1. A tempered glass comprising, in terms of mass percent,

SiO 2 : 60 to 80%;

Al 2 O 3 : 3 to 18%;

B 2 O 3 : 0 to 7%;

Li 2 O: 0.01 to 10%;

Na 2 O: 4 to 16%;

K 2 O: 0 to 15%; and

R′O (wherein R′O indicates a total content of alkaline earth metal oxides): 0 to 5%,

wherein a value of (Li 2 O)/(Na 2 O+K 2 O) in terms of molar ratio is within a range of 0.05 to 0.5,

wherein a surface of the tempered glass is treated to form a compressive stress layer, and

wherein a liquidus viscosity is 10 5.0 dPas or more.

2. A tempered glass comprising, in terms of mass percent,

SiO 2 : 60 to 80%;

Al 2 O 3 : 8 to 18%;

B 2 O 3 : 0 to 5%;

Li 2 O: 0.01 to 10%;

Na 2 O: 4 to 14%;

K 2 O: 0.01 to 10%; and

R′O (wherein R′O indicates a total content of alkaline earth metal oxides): 0 to 5%,

wherein a value of (Li 2 O)/(Na 2 O+K 20 ) in terms of molar ratio is within a range of 0.05 to 0.5,

wherein a surface of the tempered glass is treated to form a compressive stress layer, and

wherein a liquidus viscosity is 10 5.0 dPas or more.

3. The tempered glass according to claim 1 , which has a compressive stress layer of 300 MPa or more formed on a surface thereof, said compressive stress layer having a thickness of 5 μm or more.

4. The tempered glass according to claim 1 , wherein the tempered glass is made of a glass having a liquidus temperature of 1050° C. or less.

5. The tempered glass according to claim 1 , which has a non-polished surface.

6. The tempered glass according to claim 1 , which has a plate thickness of 1.5 mm or less.

7. A process for producing a tempered glass, comprising:

melting glass raw materials blended so as to have a glass composition within a range of, in terms of mass percent, SiO 2 : 60 to 80%, Al 2 O 3 : 3 to 18%, B 2 O 3 : 0 to 7%, Li 2 O: 0.01 to 10%, Na 2 O: 4 to 16%, K 2 O: 0 to 15% and R′O (wherein R′O expresses a total content of alkaline earth metal oxides): 0 to 5%, wherein a ratio of (Li 2 O)/(Na 2 O+K 2 O) in terms of molar ratio is within a range of 0.05 to 0.5, followed by forming them into sheet; and then

conducting an ion exchange process to form a compressive stress layer on a surface of said glass sheet,

wherein the glass has a liquidus viscosity of 10 5.0 dPas or more.

8. The process for producing a tempered glass according to claim 7 , wherein the glass raw materials are formed into sheet by an overflow downdraw process.

9. A glass comprising: in terms of mass percent,

SiO 2 : 60 to 80%;

Al 2 O 3 : 3 to 18%;

B 2 O 3 : 0 to 7%;

Li 2 O: 0.01 to 10%;

Na 2 O: 4 to 16%;

K 2 O: 0 to 15%; and

R′O (wherein R′O indicates a total content of alkaline earth metal oxides): 0 to 5%,

wherein a value of (Li 2 O)/(Na 2 O+K 2 O) in terms of molar ratio is within a range of 0.05 to 0.5, and

wherein a liquidus viscosity is 10 5.0 dPas or more.

10. The tempered glass according to claim 2 , which has a compressive stress layer of 300 MPa or more formed on a surface thereof, said compressive stress layer having a thickness of 5 μm or more.

11. The tempered glass according to claim 2 , wherein the tempered glass is made of a glass having a liquidus temperature of 1050° C. or less.

12. The tempered glass according to claim 2 , which has a non-polished surface.

13. The tempered glass according to claim 2 , which has a plate thickness of 1.5 mm or less.

14. The tempered glass according to claim 1 , wherein the liquidus viscosity is 10 5.3 dPas or more.

15. The tempered glass according to claim 2 , wherein the liquidus viscosity is 10 5.3 dPas or more.

16. The tempered glass according to claim 7 , wherein the liquidus viscosity is 10 5.3 dPas or more.

17. The tempered glass according to claim 9 , wherein the liquidus viscosity is 1 dPas or more.