Glasses having improved drop performance

Abstract

Chemically strengthened glass articles exhibiting superior resistance to damage when dropped onto an abrasive surface. The strengthened glass article has a stress profile in which the compressive and tensile stresses within the article vary as a function of the thickness t of the glass article. The stress profile has a first region extending from the surface of the glass article to a depth d1 into the glass, wherein d1≤0.025t or ≤20 um and has a maximum compressive stress of at least about 280 MPa at the surface, a second region extending from a depth of at least d1 to a second depth d2 and having a local compressive stress maximum, and a third region extending from a third depth d3 in the glass to a depth of compression DOC, wherein d2≤d3 and DOC≥0.15t. A method of strengthening a glass article to provide resistance to damage when dropped is also provided.

1 . A method of strengthening a glass, the glass comprising first alkali cations and having a first surface, a second surface opposite the first surface, and a thickness t and a center at t/2, wherein the glass article has a stress profile comprising a first region extending from the first surface to a depth d 1  into the glass, wherein d 1 <0.025t and having a maximum compressive stress CS 1  at the surface, a second region extending from a depth of at least d 1  to a second depth d 2 , wherein d 2 ≤0.0625t and having a compressive stress maximum CS 2 , and a third region extending from a third depth d 3  in the glass to the depth of compression DOC, wherein the DOC≥0.15t, and wherein d 2 ≤d 3 , the method comprising:
 a. immersing the glass in a first ion exchange bath, the first ion exchange bath comprising a first alkali cation and a second alkali cation, wherein the first ion exchange bath comprises from about 20 wt % to about 30 wt % of at least one salt of the first alkali cation, the second alkali cation being different from the first alkali cation, wherein the second alkali cation from the ion exchange bath replace the first alkali cation in the glass article; 
 b. immersing the glass in a second ion exchange bath after immersing the glass article in the first ion exchange bath, the second ion exchange bath comprising the first alkali cation and the second alkali cation, wherein the second ion exchange bath comprises from about 60 wt % to about 80 wt % of at least one salt of the first alkali cation; and 
 c. immersing the glass in a third ion exchange bath after immersing the glass article in the second ion exchange bath, the second ion exchange bath comprising the first alkali cation and the second alkali cation, wherein the third ion exchange bath comprises from about 75 wt % to about 100 wt % of at least one salt of the second alkali cation. 
 
     
     
         2 . The method of  claim 1 , further comprising a thermal diffusion step following at least one of the step of immersing the glass article in the second ion exchange bath in the first ion exchange bath and the step of immersing, the thermal diffusion step comprising heating the glass to a temperature in a range from about 400° C. to about 500° C. 
     
     
         3 . The method of  claim 1 , wherein the thermal diffusion step comprises heating the glass for at least about 16 hours at the temperature. 
     
     
         4 . The method of  claim 1 , wherein the maximum compressive stress CS 1  is at least about 280 MPa. 
     
     
         5 . The method of  claim 1 , wherein the glass article comprises an alkali aluminosilicate glass. 
     
     
         6 . The method of  claim 5 , wherein the alkali aluminosilicate glass comprises at least about 4 mol % P 2 O 5 , wherein (M 2 O 3 (mol %)/R x O(mol %)) <1, wherein M 2 O 3 =Al 2 O 3 +B 2 O 3 , and wherein R x O is the sum of monovalent and divalent cation oxides present in the alkali aluminosilicate glass. 
     
     
         7 . The method of  claim 5 , wherein the alkali aluminosilicate glass comprises: from about 40 mol % to about 70 mol % SiO 2 ; from about 11 mol % to about 25 mol % Al 2 O 3 ; from about 2 mol % to about 15 mol % P 2 O 5 ; from about 10 mol % to about 25 mol % Na 2 O; from about 10 to about 30 mol % R x O, where R x O is the sum of the alkali metal oxides, alkaline earth metal oxides, and transition metal monoxides present in the glass. 
     
     
         8 . The method of  claim 1 , further comprising fusion forming the glass article. 
     
     
         9 . The method of  claim 1 , wherein 125 MPa≤CS 2 ≤250 MPa.