CHEMICALLY STRENGTHENED GLASS

1 . A chemically strengthened glass comprising a first main surface, a second main surface opposite to the first main surface, and an end surface connecting the first main surface and the second main surface, wherein:

a compressive stress layer is provided in the first main surface and the second main surface;

an average sheet thickness t is from 0.06 to 0.25 mm; and

when the following bending test method is performed, a crack originating in at least one main surface of the first main surface and the second main surface is not formed:

(Bending Test Method)

a bending test method of disposing a first support board and a second support board in parallel so that a supporting surface of the first support board and a supporting surface of the second support board are opposed to each other,

arranging an end part of the chemically strengthened glass to be supported respectively by the first support board and the second support board,

while maintaining a distance between the supporting surface of the first support board and the supporting surface of the second support board at a distance D [mm] determined according to the following formula (1), displacing a position of the second support board relative to the first support board by 200 mm in a direction that is parallel to the supporting surface of the first support board and the supporting surface of the second support board and that does not change a curvature direction of the chemically strengthened glass, and

examining whether a crack is formed or not in the chemically strengthened glass curved between the first support board and the second support board, is performed:

D =( A×E×t /σ)+ t   (1),

D; the distance between the supporting surface of the first support board and the supporting surface of the second support board (unit [mm]),

A=1.198,

E; Young's modulus of the chemically strengthened glass (unit [MPa]),

T; the average sheet thickness of the chemically strengthened glass (unit [mm]), and

σ=200 (unit [MPa]).

2 . The chemically strengthened glass according to claim 1 , wherein the end surface of the chemically strengthened glass comprises a first inclined part tilting and extending to a second main surface side relative to the first main surface, a second inclined part tilting and extending to a first main surface side relative to the second main surface, and a curved surface part connecting the first inclined part and the second inclined part.

3 . The chemically strengthened glass according to claim 2 , wherein a cross-sectional shape of the curved surface part in a sheet thickness direction of the chemically strengthened glass is an arc shape.

4 . The chemically strengthened glass according to claim 2 , wherein a minimum radius of curvature of the curved surface part is 0.125 mm or less.

5 . The chemically strengthened glass according to claim 1 , wherein the surface compressive stress of the first main surface and the second main surface is from 400 to 1,000 MPa.

6 . The chemically strengthened glass according to claim 1 , wherein a depth of compressive stress layer of the first main surface and the second main surface is from 6 to 25 μm.

7 . The chemically strengthened glass according to claim 1 , wherein an internal tensile stress is 250 MPa or less.

8 . The chemically strengthened glass according to claim 1 , wherein a compressive stress layer is provided in the end surface.

9 . The chemically strengthened glass according to claim 1 , wherein a difference between a maximum value and a minimum value of the sheet thickness within a plane of the chemically strengthened glass is 0.03 mm or less.

10 . The chemically strengthened glass according to claim 1 , that contains, as represented by mol % based on oxides, from 0.8 to 4.5% of Al 2 O 3 .

11 . The chemically strengthened glass according claim 1 , that is for a photomask substrate.