ION EXCHANGED GLASSES VIA NON-ERROR FUNCTION COMPRESSIVE STRESS PROFILES

• US 20130224492A1
• Filed: 02/21/2013
• Published: 08/29/2013
• Est. Priority Date: 02/29/2012
• Status: Active Grant

• Current Assignee: Corning Incorporated
• Original Assignee: Corning Incorporated
• Inventors: Bookbinder, Dana Craig, Fiacco, Richard Michael, Gross, Timothy Michael, Logunov, Stephan Lvovich
• Granted Patent: US 9,359,251 B2
• Time in Patent Office: Days
• US Class Current: 428/410
• CPC Class Codes: C03C 21/002 to perform ion-exchange between alkali ions C03C21/005 takes precedence
• CPC Class Codes: C03C 23/007 by thermal treatment
• CPC Class Codes: Y10T 428/315 Surface modified glass [e.g., tempered, strengthened, etc.]

Abstract

Glasses with compressive stress profiles that allow higher surface compression and deeper depth of layer (DOL) than is allowable in glasses with stress profiles that follow the complementary error function at a given level of stored tension. In some instances, a buried layer or local maximum of increased compression, which can alter the direction of cracking systems, is present within the depth of layer. Theses compressive stress profiles are achieved by a three step process that includes a first ion exchange step to create compressive stress and depth of layer that follows the complimentary error function, a heat treatment at a temperature below the strain point of the glass to partially relax the stresses in the glass and diffuse larger alkali ions to a greater depth, and a re-ion-exchange at short times to re-establish high compressive stress at the surface.

Claims

1. A glass having a surface and a thickness t, the glass comprising:

a first region under a compressive stress, the first region extending from the surface to a depth of layer DOL in the glass, wherein the compressive stress CS has a maximum CS₁ at the surface and varies with distance d from the surface according to a function other than a complementary error function; and

a second region under a tensile stress CT, the second region extending from the depth of layer into the glass.

2. The glass of claim 1, wherein the first region comprises:

a. a first segment, the first segment extending from the surface to a first depth d₁, wherein the depth d₁ is less than the depth of layer DOL, wherein the compressive stress CS in the first segment varies according to a first function; and

b. a second segment, the second segment extending from the first depth d₁ up to the depth of layer DOL, wherein the compressive stress CS in the second segment varies according to a second function, and wherein the first function is different than the second function.

3. The glass of claim 2, wherein the first function is a first complementary error function.

4. The glass of claim 3, wherein the second function is a second complementary error function or a diffusion tail.

5. The glass of claim 2, wherein the compressive stress has a local maximum CS₂ in the second segment.

6. The glass of claim 5, wherein CS₁>

CS₂.

7. The glass of claim 1, wherein the tensile stress CT, expressed in MPa, is greater than or equal to −

36.7 ln(t) (MPa)+48.7 (MPa).

8. The glass of claim 1, wherein the glass is an alkali aluminosilicate glass.

9. The glass of claim 1, wherein the maximum compressive stress CS₂ is at least about 400 MPa.

10. The glass of claim 1, wherein the depth of layer DOL is at least about 40 μ

m.

11. The glass of claim 1, wherein the glass is ion exchanged.

12. An ion exchanged glass having a surface and a thickness t, the glass comprising a first region under a compressive stress CS and extending to a depth of layer DOL in the glass, the first region comprising a first segment in which the compressive stress CS varies according to a first error function, the first segment extending from the surface to a first depth d₁, wherein the depth d₁ is less than the depth of layer DOL, and a second segment in which the compressive stress CS varies according to a second function, the second segment extending from the first depth d₁ up to the depth of layer DOL, wherein the first error function is different than the second function.

13. The ion exchanged glass of claim 12, further comprising a second region under a tensile stress CT, the second region extending from the depth of layer into the glass.

14. The ion exchanged glass of claim 13, wherein the tensile stress CT, expressed in MPa, is greater than or equal to −

36.7 ln(t) (MPa)+48.7 (MPa).

15. The ion exchanged glass of claim 12, wherein the second function is a second complementary error function or a diffusion tail.

16. The ion exchanged glass of claim 12, wherein the compressive stress has a local maximum CS₂ in the second segment.

17. The ion exchanged glass of claim 16, wherein the compressive stress CS has a maximum CS₁ at the surface, and wherein CS₁>

CS₂.

18. The ion exchanged glass of claim 12, wherein the compressive stress CS is at least about 400 MPa.

19. The ion exchanged glass of claim 12, wherein the depth of layer DOL is at least about 40 μ

m.

20. The ion exchanged glass of claim 12, wherein the glass is an alkali aluminosilicate glass.

21. A method of providing a glass with a compressive stress in a layer extending from a surface of the glass to a depth of layer in the glass, the method comprising:

ion exchanging the glass with a salt comprising first cations to a first compressive stress and a first depth of layer, wherein the first compressive stress varies with distance in the glass according to a complementary error function;

relaxing stresses within the glass and diffusing the first cations deeper into the glass; and

re-ion exchanging the glass with a salt comprising the first cations to a second compressive stress at the surface, wherein the compressive stress varies with distance according to a function other than the complementary error function.

22. The method of claim 21, wherein relaxing stresses within the glass and diffusing the first cations deeper into the glass comprises heating the glass at a temperature below a strain point of the glass.