Damage resistant, chemically toughened protective cover glass

Abstract

The invention is directed to a high strength, chemically toughened protective glass article, the glass article having a high damage tolerance threshold of at least 1500 g as measured by the lack of radial cracks when the load is applied to the glass using a Vickers indenter; preferably greater than 2000 g s measured by the lack of initiation of radial cracks when the load is applied to the glass using a Vickers indenter

We claim: 
     
         1 . A high strength, chemically toughened protective glass article, said protective glass article having a thickness less than or equal to 2.0 millimeters, a high damage tolerance threshold of at least 6000 g as measured by the lack of the presence of radial cracks when the load is applied to the glass using a Vickers indenter, and a compressive stress greater than 600 MPa. 
     
     
         2 . The glass article according to  claim 1 , wherein said the glass of said cover glass is selected from the group consisting of alkali containing aluminosilicate glasses, alkali containing aluminoborosilicate glasses, alkali containing borosilicate glasses and alkali containing glass-ceramics. 
     
     
         3 . The glass article according to  claim 1 , wherein the composition of the glass of said article comprising, before any ion exchange to chemically strengthen, 64 mol %≦SiO 2 ≦68 mol %; 12 mol %≦Na 2 O≦16 mol %; 8 mol %≦Al 2 O 3 ≦12 mol %; 0 mol %≦B 2 O 3 ≦3 mol %; 2 mol %≦K 2 O≦5 mol %; 4 mol %≦MgO≦6 mol %; and 0 mol %≦CaO≦5 mol %, 0-0.5% (As 2 O 3 ,SnO 2 ); wherein: 66 mol %≦SiO 2 +B 2 O 3 +CaO≦69 mol %; Na 2 O+K 2 O+B 2 O 3 +MgO+CaO+SrO>10 mol %; 5 mol %≦MgO+CaO+SrO≦8 mol %; (Na 2 O+B 2 O 3 )—Al 2 O 3 ≦2 mol %; 2 mol %≦Na 2 O—Al 2 O 3 ≦6 mol %; and 4 mol %≦(Na 2 O+K 2 O)—Al 2 O 3 ≦10 mol %. 
     
     
         4 . The glass article according to  claim 1 , wherein the composition of the glass of said article comprising, before any ion exchange to chemically strengthen, 64-68% SiO 2 , 10-12% Al 2 O 3 , 0-2% B 2 O 3 , 12-15% Na 2 O, 2-4% K 2 O, 5-7% MgO, >0-1% CaO, 0-0.5% (As 2 O 3 , SnO 2 ), 0-1% (Sb 2 O 3 , SnO 2 ), and >0-1% TiO 2 . 
     
     
         5 . The article according to  claim 1 , wherein said article has a strength of 200 MPa or greater after blasting the surface of said article with SiC grit according to ASTM Method C158. 
     
     
         6 . The article according to  claim 1 , wherein said article has a strength of 300 MPa or greater after blasting the surface of said article with SiC grit according to ASTM Method C158. 
     
     
         7 . The article according to  claim 1 , wherein the surface of said article has been chemically toughed to a depth of at least 40 μm.