Strengthened glass articles and methods of making
A strengthened glass article having a central tension that is below a threshold value above which the glass exhibits frangible behavior. The central tension varies non-linearly with the thickness of the glass. The glass article may be used as cover plates or windows for portable or mobile electronic devices such as cellular phones, music players, information terminal (IT) devices, including laptop computers, and the like.
1. A strengthened glass article, the strengthened glass article having a thickness t and comprising:
a. an outer region, the outer region extending from a surface of the article to a depth of layer DOL within the article, wherein the outer region is under a compressive stress CS; and
b. an inner region, wherein the inner region is under a central tension CT, and wherein −15.7 (MPa/mm)·t(mm)+52.5 (MPa)<CT(MPa)≦−38.7 (MPa/mm)·ln(t)(mm)+48.2 (MPa).
2. The strengthened glass article of claim 1 , wherein the strengthened glass article is substantially non-frangible behavior when subjected to a point impact sufficient to break the strengthened glass article.
3. The strengthened glass article of claim 1 , wherein the strengthened glass article, when subjected to a point impact sufficient to break the strengthened glass article, has a frangibility index of less than 3.
4. The strengthened glass article of claim 1 , wherein the strengthened glass article is a sheet and the thickness t is in a range from about 0.2 mm up to about 2 mm.
5. The strengthened glass article of claim 4 , wherein the thickness is in a range from about 0.5 mm up to about 0.75 mm.
6. The strengthened glass article of claim 4 , wherein the thickness is in a range from about 0.9 mm up to about 2 mm.
7. The strengthened glass article of claim 1 , wherein the strengthened glass article comprises an alkali aluminosilicate glass.
8. The strengthened glass article according to claim 7 , wherein the alkali aluminosilicate glass comprises: 60-70 mol % SiO 2 ; 6-14 mol % Al 2 O 3 ; 0-15 mol % B 2 O 3 ; 0-15 mol % Li 2 O; 0-20 mol % Na 2 O; 0-10 mol % K 2 O; 0-8 mol % MgO; 0-10 mol % CaO; 0-5 mol % ZrO 2 ; 0-1 mol % SnO 2 ; 0-1 mol % CeO 2 ; less than 50 ppm As 2 O 3 ; and less than 50 ppm Sb 2 O 3 ; wherein 12 mol %≦Li 2 O+Na 2 O+K 2 O≦20 mol % and 0 mol %≦MgO+CaO≦10 mol %.
9. The strengthened glass article according to claim 7 , wherein the alkali aluminosilicate glass comprises: 5-50 wt % SiO 2 ; 2-20 wt % Al 2 O 3 ; 0-15 wt % B 2 O 3 ; 1-20 wt % Na 2 O; 0-10 wt % Li 2 O; 0-10 wt % K 2 O; and 0-5 wt % (MgO+CaO+SrO+BaO); 0-3 wt % (SrO+BaO); and 0-5 wt % (ZrO 2 +TiO 2 ), wherein 0≦(Li 2 O+K 2 O)/Na 2 O≦0.5.
10. The strengthened glass article of claim 7 , wherein the alkali aluminosilicate glass has a liquidus viscosity of at least 130 kpoise.
11. The strengthened glass article of claim 7 , wherein the alkali aluminosilicate glass is substantially free of lithium.
12. The strengthened glass article of claim 1 , wherein the outer region has a depth of at least 30 μm.
13. The strengthened glass article of claim 1 , wherein the compressive stress is at least about 600 MPa.
14. The strengthened glass article of claim 1 , wherein the strengthened glass article is a cover plate or a window for one of a portable electronic device, an information terminal device, and a display for a computer.
15. The strengthened glass article of claim 1 , wherein the outer region is strengthened by ion exchange.
16. The strengthened glass article of claim 1 , wherein CT=(CS·DOL)/(t−2 DOL), and wherein CS is expressed in MPa and DOL is expressed in mm.
17. A strengthened glass article, the strengthened glass article having a thickness t of less than about 2 mm and comprising:
a. an outer region; and
b. an inner region under a central tension CT, wherein CT(MPa)>−15.7 (MPa/mm)·t(mm)+52.5 (MPa), and wherein the strengthened glass article is substantially non-frangible when subjected to a point impact that is sufficient to break the strengthened glass article.
18. The strengthened glass article of claim 17 , wherein the strengthened glass article, when subjected to a point impact sufficient to break the strengthened glass article, has a frangibility index of less than 3.
19. The strengthened glass article of claim 17 , wherein the strengthened glass article is a sheet the thickness t is in a range from about 0.2 mm up to about 2 mm.
20. The strengthened glass article of claim 19 , wherein the thickness is in a range from about 0.5 mm up to about 0.75 mm.
21. The strengthened glass article of claim 19 , wherein the thickness is in a range from about 0.9 mm up to about 2 mm.
22. The strengthened glass article of claim 17 , wherein the strengthened glass article comprises an alkali aluminosilicate glass.
23. The strengthened glass article of claim 17 , wherein the strengthened glass article is a cover plate or a window for one of a portable electronic device, an information terminal device, and a display for a computer.
24. The strengthened glass article of claim 17 , wherein the outer region is strengthened by ion exchange.