TWO-STEP METHOD FOR STRENGTHENING GLASS

• US 20120052271A1
• Filed: 08/17/2011
• Published: 03/01/2012
• Est. Priority Date: 08/26/2010
• Status: Abandoned Application

• Current Assignee: Corning Incorporated
• Original Assignee: Corning Incorporated
• Inventors: Gomez, Sinue, Lamberson, Lisa Ann, Morena, Robert Michael
• Application Number:
  US13/211,661
• Publication Number:
  US 20120052271A1
• Time in Patent Office: Days
• US Class Current: 428/213
• CPC Class Codes: C03C 21/002 to perform ion-exchange between alkali ions C03C21/005 takes precedence
• CPC Class Codes: C03C 2204/00 Glasses, glazes or enamels with special properties
• CPC Class Codes: C03C 3/091 containing aluminium
• CPC Class Codes: C03C 3/095 containing rare earths
• CPC Class Codes: C03C 3/097 containing phosphorus, niobium or tantalum
• CPC Class Codes: C03C 4/18 for ion-sensitive glass
• CPC Class Codes: Y10T 428/2495 Thickness [relative or absolute]
• CPC Class Codes: Y10T 428/315 Surface modified glass [e.g., tempered, strengthened, etc.]

Abstract

A method of strengthening an alkali aluminoborosilicate glass. A compressive layer extending from a surface of the glass to a depth of layer is formed by exchanging larger metal cations for smaller metal cations present in the glass. In a second step, metal cations in the glass are exchanged for larger metal cations to a second depth in the glass that is less than the depth of layer and increase the compressive stress of the compressive layer. Formation of the compressive layer and replacement of cations with larger cations can be achieved by a two-step ion exchange process. An alkali aluminoborosilicate glass having a compressive layer and a crack indentation threshold of at least 3000 gf is also provided.

Claims

1. A method of strengthening an alkali aluminoborosilicate glass, the method comprising the steps of:

a. providing the alkali aluminoborosilicate glass, the glass comprising alkali metal cations;

b. forming a compressive layer extending from a surface of the glass to a depth of layer, wherein the compressive layer is under a compressive stress; and

c. replacing at least a portion of the alkali metal cations in the compressive layer with a larger alkali metal cation to a second depth that is less than the depth of layer, wherein replacing the alkali metal cations in the compressive layer with the larger alkali metal cation increases the compressive stress.

2. The method of claim 1, wherein the step of forming the compressive layer comprises replacing lithium cations with sodium cations to the depth of layer of the glass.

3. The method of claim 2, wherein the step of forming the compressive layer comprises immersing the glass in a first ion exchange bath comprising a sodium salt.

4. The method of claim 3, wherein the first ion exchange bath further comprises a potassium salt.

5. The method of claim 1, wherein the step of replacing the alkali metal cations in the compressive layer with the larger alkali metal cation comprises replacing at least one of sodium cations and lithium cations with potassium cations within the second depth.

6. The method of claim 5, wherein the step of replacing the alkali metal cations in the compressive layer with the larger alkali metal cation comprises immersing the glass in a second ion exchange bath comprising a potassium salt.

7. The method of claim 1, wherein the step of providing the alkali aluminoborosilicate glass comprises providing an alkali aluminoborosilicate glass comprising:

50-70 mol % SiO₂;

5-15 mol % Al₂O₃;

5-20 mol % B₂O₃;

2-15 mol % Li₂O;

0-20 mol % Na₂O; and

0-10 mol % K₂O.

8. The method of claim 7, wherein the alkali aluminoborosilicate glass further comprises at least one of:

0-10 mol % P₂O₅;

0-5 mol % MgO;

0-1 mol % CeO₂; and

0-1 mol % SnO₂.

9. The method of claim 1, wherein the step of providing the alkali aluminoborosilicate glass comprises providing an alkali aluminoborosilicate glass having a crack initiation threshold of at least 1000 gf upon indentation with a Vickers indenter.

10. The method of claim 1, wherein, after replacing the alkali metal cations in the compressive layer with the larger alkali metal cation, the surface of the glass has a crack initiation layer threshold of at least 3000 gf upon indentation with a Vickers indenter.

11. The method of claim 1, wherein, after replacing alkali metal cations in the compressive layer with the larger alkali metal cation, the compressive stress is at least 500 MPa and the depth of layer is at least 50 μ

m.

12. The method of claim 1, wherein the depth of layer is in a range from 70 μ

m up to 290 μ

m.

13. The method of claim 1, wherein the second depth is in a range from 5 μ

m up to 20 μ

m.

14. The method of claim 1, wherein the step of providing the alkali aluminoborosilicate glass comprises providing an alkali aluminoborosilicate glass sheet having a thickness of less than 2 mm.

15. A method of strengthening an alkali aluminoborosilicate glass, the method comprising the steps of:

a. providing the alkali aluminoborosilicate glass, the glass comprising lithium cations and sodium cations;

b. replacing lithium cations with sodium cations to form a compressive layer extending from a surface of the glass to a depth of layer, wherein the compressive layer is under a compressive stress; and

c. replacing sodium cations and lithium cations with potassium cations to a second depth that is less than the depth of layer, and wherein replacing the lithium cations and the sodium cations in the compressive layer with the potassium cations increases the compressive stress.

16. The method of claim 15, wherein the step of replacing the lithium cations with the sodium cations comprises immersing the glass in a first ion exchange bath, the first ion exchange bath comprising a sodium salt.

17. The method of claim 16, wherein the first ion exchange bath further comprises a potassium salt.

18. The method of claim 15, wherein the step of replacing sodium cations and optionally lithium cations with potassium cations comprises immersing the glass in a second ion exchange bath, the second ion exchange bath comprising a potassium salt.

19. The method of claim 15, wherein the step of providing the alkali aluminoborosilicate glass comprises providing an alkali aluminoborosilicate glass comprising:

50-70 mol % SiO₂;

5-15 mol % Al₂O₃;

5-20 mol % B₂O₃;

2-15 mol % Li₂O;

0-20 mol % Na₂O; and

0-10 mol % K₂O.

20. The method of claim 19, wherein the alkali aluminoborosilicate glass further comprises at least one of:

0-10 mol % P₂O₅;

0-5 mol % MgO;

0-1 mol % CeO₂; and

0-1 mol % SnO₂.

21. The method of claim 15, wherein the step of providing the alkali aluminoborosilicate glass comprises providing an alkali aluminoborosilicate glass having a crack initiation threshold of at least 1000 gf upon indentation with a Vickers indenter.

22. The method of claim 15, wherein, after replacing sodium cations and optionally lithium cations with potassium cations, the surface of the glass has a crack initiation layer threshold of at least 3000 gf upon indentation with a Vickers indenter.

23. The method of claim 15, wherein, after replacing sodium cations and optionally lithium cations with potassium cations, the compressive stress is at least 500 MPa and the depth of layer is at least 50 μ

m.

24. The method of claim 15, wherein the depth of layer is in a range from 70 μ

m up to 290 μ

m.

25. The method of claim 15, wherein the second depth is in a range from 5 μ

m up to 20 μ

m.

26. The method of claim 15, wherein the step of providing the alkali aluminoborosilicate glass comprises providing an alkali aluminoborosilicate glass sheet having a thickness of less than 2 mm.

27. An alkali aluminoborosilicate glass comprising lithium cations, sodium cations, and potassium cations, wherein the glass has a surface having a compressive layer extending from the surface to a depth of layer and is enriched in potassium cations to a second depth that is less than the depth of layer, and wherein the surface of the glass has a crack initiation layer threshold of at least 3000 gf upon indentation with a Vickers indenter.

28. The glass of claim 27, wherein the surface has a compressive stress of at least 500 MPa, and wherein the depth of layer is at least 50 μ

m.

29. The glass of claim 27, wherein the depth of layer is in a range from 70 μ

m up to 290 μ

m.

30. The glass of claim 27, wherein the second depth is in a range from 5 μ

m up to 20 μ

m.

31. The glass of claim 27, wherein the alkali aluminoborosilicate glass comprises:

50-70 mol % SiO₂;

5-15 mol % Al₂O₃;

5-20 mol % B₂O₃;

2-15 mol % Li₂O;

0-20 mol % Na₂O; and

0-10 mol % K₂O.

32. The glass of claim 31, wherein the alkali aluminoborosilicate glass further comprises at least one of:

0-10 mol % P₂O₅;

0-5 mol % MgO;

0-1 mol % CeO₂; and

0-1 mol % SnO₂.

33. The glass of claim 27, wherein the glass is a glass sheet having a thickness of up to 2 mm.