Ion exchanged glasses via non-error function compressive stress profiles

Patent metadata

Field	Value
Publication number	US-9718727-B2
Application number	US-201514874849-A
Country	US
Kind code	B2
Filing date	Oct 5, 2015
Priority date	Feb 29, 2012
Publication date	Aug 1, 2017
Grant date	Aug 1, 2017

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.

First claim

The invention claimed is:

1. A glass having a surface and a thickness t of from 0.05 mm to 1.3 mm, 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 compressive stress CS 1 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, wherein CT, expressed in MPa, greater than −37.6 ln(t)(MPa)+48.7 (MPa), wherein the glass is not frangible and CT is defined by the equation CT=(CS 1 *DOL)/(t−(2*DOL)) with CS 1 being expressed in MPa, and with DOL and t being expressed in millimeters (mm).

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 d 1 , wherein the depth d 1 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 d 1 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 CS 2 in the second segment, wherein CS 1 >CS 2 .

6. The glass of claim 1 , wherein the glass is an alkali aluminosilicate glass having an alkali metal oxide concentration, wherein the alkali metal consists of Na or K.

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

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

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

10. An ion exchanged glass having a surface and a thickness t of from 0.05 mm to 1.3 mm, the glass comprising a first region under a compressive stress CS and extending to a depth of layer DOL in the glass and second region under a tensile stress CT, the second region extending from the depth of layer into the glass, wherein CT, expressed in MPa, greater than −37.6 ln(t)(MPa)+48.7 (MPa), the first region comprising a first segment in which the compressive stress CS has a maximum CS 1 at the surface and varies according to a first error function, the first segment extending from the surface to a first depth d 1 , wherein the depth d 1 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 d 1 up to the depth of layer DOL, wherein the first error function is different than the second function, wherein the glass is not frangible and CT is defined by the equation CT=(CS 1 *DOL)/(t−(2*DOL)) with CS 1 being expressed in MPa, and with DOL and t being expressed in millimeters (mm).

11. The ion exchanged glass of claim 10 , wherein the second function is a second complementary error function or a diffusion tail.

12. The ion exchanged glass of claim 10 , wherein the compressive stress has a local maximum CS 2 in the second segment, wherein CS 1 >CS 2 .

13. The ion exchanged glass of claim 10 , wherein the maximum compressive stress CS 1 at the surface is at least about 400 MPa.

14. The ion exchanged glass of claim 10 , wherein the depth of layer DOL is at least about 40 μm.

15. The ion exchanged glass of claim 10 , wherein the glass is an alkali aluminosilicate glass having an alkali metal oxide concentration, wherein the alkali metal consists of Na or K.

16. An ion exchanged glass having a surface and a thickness t of from 0.05 mm to 1.3 mm, the glass comprising a first region under a compressive stress CS and extending to a depth of layer DOL in the glass and second region under a tensile stress CT, the second region extending from the depth of layer into the glass, wherein CT, expressed in MPa, greater than −37.6 ln(t)(MPa)+48.7 (MPa), the first region comprising, a first segment in which the compressive stress CS has a maximum CS 1 and varies according to a first function, the first segment extending from the surface to a first depth d 1 , wherein the depth d 1 is less than the depth of layer DOL, and a second segment in which the compressive stress CS varies according to a second function and has a maximum CS 2 , the second segment extending from the first depth d 1 up to the depth of layer DOL, wherein the first function is different than the second function, wherein the glass is not frangible and CT is defined by the equation CT=[(CS 1 *d 1 )/(t−(2*d 1 ))]+[(CS 2 *(DOL−d 1 )/(t−(2*(DOL−d 1 )))] with CS 1 and CS 2 being expressed in MPa, and with DOL, d 1 , and t, being expressed in millimeters (mm).

17. The ion exchanged glass of claim 16 , wherein the maximum compressive stress CS 1 is at least about 400 MPa.

18. The ion exchanged glass of claim 16 , wherein the depth of layer DOL is at least about 40 μm.

19. The ion exchanged glass of claim 16 , wherein the glass is an alkali aluminosilicate glass having an alkali metal oxide concentration, wherein the alkali metal consists of Na or K.

Assignees

• Corning Inc

Inventors

• Bookbinder Dana Craig
• Fiacco Richard Michael
• Gross Timothy Michael
• Logunov Stephan Lvovich

Classifications

• C03C21/002 Primary

  to perform ion-exchange between alkali ions (C03C21/005 takes precedence) · CPC title

• Y10T428/315

  Surface modified glass [e.g., tempered, strengthened, etc.] · CPC title

• C03C23/007

  by thermal treatment · CPC title