Strengthened glass articles and methods of making

Abstract

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 - 24 . (canceled) 
     
     
         25 . A method of making a strengthened glass article, the strengthened glass article being substantially non-frangible, the method comprising the steps of:
 a. providing a glass article, the glass article having a thickness t; and   b. creating a compressive stress CS to a depth of layer DOL in an outer region of the glass article to form the strengthened glass article, the compressive stress being sufficient to generate a central tension CT in a central region of the strengthened glass article such that CT(MPa)≦−38.7(MPa/mm)·ln(t)(mm)+48.2(MPa), and wherein the strengthened glass article is substantially non-frangible.   
     
     
         26 . The method of  claim 25 , wherein the step of creating the compressive stress CS in the outer region comprises exchanging a plurality of first metal ions in the outer region with a plurality of second metal ions so that the outer region comprises the plurality of the second metal ions, wherein each of the first metal ions has a first ionic radius and each of the second metal ions has a second ionic radius, the second ionic radius being greater than the first ionic radius, and wherein the presence of the second metal ions creates the compressive stress in the outer region. 
     
     
         27 . The method of  claim 26 , wherein at least one of the plurality of first metal ions and the plurality of second metal ions comprises alkali metal ions. 
     
     
         28 . The method of  claim 26 , wherein the plurality of first alkali metal ions comprises at least one of lithium ions, sodium ions, potassium ions, and rubidium ions, and wherein the plurality of second alkali metal ions comprises at least one of sodium ions, potassium ions, cesium ions, and rubidium ions. 
     
     
         29 . The method of  claim 26 , wherein the step of exchanging a plurality of first metal ions in the outer region with a plurality of second metal ions so that the outer region comprises the plurality of the second metal ions comprises immersing the glass article in a molten salt bath, the molten salt bath comprising the second metal ions. 
     
     
         30 . The method of  claim 26 , wherein the strengthened glass article comprises an alkali aluminosilicate glass. 
     
     
         31 . The method of  claim 25 , wherein CT=(CS·DOL)/(t−2 DOL), and wherein CS is expressed in MPa and DOL is expressed in mm. 
     
     
         32 . The method of  claim 25 , wherein −15.7(MPa/mm)·t(mm)+52.5(MPa)<CT(MPa)≦−38.7(MPa/mm)·ln(t)(mm)+48.2(MPa). 
     
     
         33 . The method of  claim 25 , wherein the strengthened glass article has a frangibility index of less than 3. 
     
     
         34 . The method of  claim 25 , 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. 
     
     
         35 . The method of  claim 25 , wherein the strengthened glass article is substantially non-frangible when subjected to a point impact sufficient to break the strengthened glass article. 
     
     
         36 . The method of  claim 30 , wherein the alkali aluminosilicate glass has a liquidus viscosity of at least 130 kpoise. 
     
     
         37 . The method of  claim 30 , wherein the alkali aluminosilicate glass is substantially free of lithium. 
     
     
         38 . The method of  claim 25 , wherein the outer region has a depth of at least 30 μm. 
     
     
         39 . The method of  claim 25 , wherein the compressive stress is at least about 600 MPa. 
     
     
         40 . The method of  claim 25 , 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.