Durable glass ceramic cover glass for electronic devices

摘要

The invention relates to glass articles suitable for use as electronic device housing/cover glass which comprise a glass ceramic material. Particularly, a cover glass comprising an ion-exchanged glass ceramic exhibiting the following attributes (1) optical transparency, as defined by greater than 90% transmission at 400-750 nm; (2) a fracture toughness of greater than 0.6 MPa·m1/2; (3) a 4-point bend strength of greater than 350 MPa; (4) a Vickers hardness of at least 450 kgf/mm2 and a Vickers median/radial crack initiation threshold of at least 5 kgf; (5) a Young's Modulus ranging between about 50 to 100 GPa; (6) a thermal conductivity of less than 2.0 W/m° C., and (7) and at least one of the following attributes: (i) a compressive surface layer having a depth of layer (DOL) greater and a compressive stress greater than 400 MPa, or, (ii) a central tension of more than 20 MPa.

主权项

1. An article suitable as a cover glass for a portable electronic device, the article comprising a glass ceramic, the glass ceramic having a primary crystalline phase of transparent spinel or transparent mullite and exhibiting:
a. optical transparency of greater than 60%, as defined by the transmission of light over the range of from 400-750 nm through 1 mm of the glass ceramic; b. colorlessness, as defined by having the values of L*≧90; 0.1≧a*≧−0.1; and 0.4≧b*≧−0.4 on the CIE 1976 Lab color space as measured in transmission through 1 mm of glass ceramic; c. at least one of the following attributes:
(i) a fracture toughness of greater than 0.60 MPa·m1/2; (ii) a 4-point bend strength of greater than 350 MPa;(iii) a Vickers hardness of at least 450 kgf/mm2;(iv) a Vickers median/radial crack initiation threshold of at least 5 kgf;(v) a Young's Modulus ranging between 50 to 100 GPa; and(vi) a thermal conductivity of less than 2.0 W/m° C.; and d. at least one of the following attributes:
(i) a compressive surface layer having a depth of layer (DOL) greater than or equal to 20 μm and a compressive stress greater than 400 MPa, or,(ii) a central tension of more than 20 MPa.