Alkaline earth alumino-borosilicate crack resistant glass
The present disclosure relates to glass articles for use as a touchscreen substrate or cover glass article for use in a portable electronic device, particularly an aluminoborosilicate glass being substantially free of alkalis, comprising at least 55 mol % SiO 2 , at least 5 mol % Al 2 O 3 and at least one alkaline earth RO component. The alkali-free aluminoborosilicate exhibits an Al 2 O 3 +B 2 O 3 to RO mol % ratio which exceeds 1 and an Al 2 O 3 to RO mol % ratio which exceeds 0.65. The aluminoborosilicate glasses disclosed herein exhibits high damage resistance as evidenced by a Vickers median/radial crack initiation load which is greater than than 1000 gf, as well as a high scratch resistance of at least 900 gf, as measured by the lack of the presence of lateral cracks when a load is applied by a moving Knoop indenter.
1. An alkaline earth aluminoborosilicate glass, the aluminoborosilicate glass being substantially free of alkali metals, comprising: 59-64 mol % SiO 2 ; 8-12 mol % Al 2 O 3 ; 11-19 mol % B 2 O 3 ; 2-7 mol % MgO, 1-8 mol % CaO, 1-6 mol % SrO and 0-6 mol % BaO, wherein Al 2 O 3 (mol %)+B 2 O 3 (mol %)/RO (mol %)>2.25 and Al 2 O 3 (mol %)/RO (mol %)>0.65.
2. The alkaline earth aluminoborosilicate glass of claim 1 which exhibits a Vickers median/radial crack initiation threshold of at least 1000 gf.
3. The alkaline earth aluminoborosilicate a glass of claim 1 which exhibits a Vickers median/radial crack initiation threshold of at least 1100 gf.
4. The alkaline earth aluminoborosilicate glass of claim 1 which exhibits a Vickers median/radial crack initiation threshold of at least 1300 gf.
5. The alkaline earth aluminoborosilicate glass of claim 1 which exhibits a scratch resistance of at least 900 gf, as measured by the lack of the presence of lateral cracks when a load is applied by a moving Knoop indenter.
6. The alkaline earth aluminoborosilicate glass of claim 1 wherein the glass exhibits a linear coefficient of thermal expansion (CTE) over the temperature range 0-300° C. which satisfies the relationship: 25×10 −7 /° C.≦CTE≦40×10 −7 /° C.
7. The alkaline earth aluminoborosilicate glass of claim 1 wherein the glass is substantially non-frangible.
8. The alkaline earth aluminoborosilicate glass of claim 1 , wherein the glass has a molar volume of at least 27.5 cm 3 /mol.
9. The alkaline earth aluminoborosilicate glass of claim 1 , wherein the aluminoborosilicate glass has a Young's modulus of less than about 75 MPa.