CHEMICALLY STRENGTHENED GLASS

1 . A chemically strengthened glass having a first surface and a second surface facing the first surface, and having a compressive stress layer provided on the first surface and the second surface, wherein:

a depth of compressive stress DOL 1 (μm) of the first surface is larger than a depth of compressive stress DOL 2 (μm) of the second surface, and

a stress distribution in a sheet thickness direction of the chemically strengthened glass satisfies the following relational expression (1) and the following relational expression (3):

CT 1 /CT 2 ≦0.8  (1) and

CT 1 ×L 1/2 ≦30(MPa·mm 1/2 )  (3),

wherein:

CT 1 : a maximum value of a tensile stress (MPa) in a region where a depth from the first surface X is from x 0 to x 1 ,

CT 2 : a maximum value of a tensile stress (MPa) in a region where a depth from the first surface X is from x 2 to x L ,

x 0 : a depth (mm) from the first surface to a point at which a compressive stress turns first into a tensile stress in the stress distribution in the sheet thickness direction from the first surface to the second surface,

x L : a depth (mm) from the first surface to a point at which a compressive stress turns first into a tensile stress in the stress distribution in the sheet thickness direction from the second surface to the first surface,

x 1 =0.8 x 0 +0.2 x L (mm),

x 2 =0.2 x 0 +0.8 x L (mm), and

L=x L −x 0 (mm).

2 . The chemically strengthened glass according to claim 1 , wherein:

the depth of compressive stress DOL 1 (μm) of the first surface and the depth of compressive stress DOL 2 (μm) of the second surface satisfy the following relational expression:

DOL 1 ≧DOL 2 +3(μm).

3 . A chemically strengthened glass having a first surface and a second surface facing the first surface, and having a compressive stress layer provided on the first surface and the second surface, wherein:

a depth of compressive stress DOL 1 (μm) of the first surface is larger than a depth of compressive stress DOL 2 (μm) of the second surface,

in a stress distribution in a sheet thickness direction of the chemically strengthened glass, a tensile stress function CT n (X) (MPa) standardized in a depth X (mm) from the first surface satisfies the following relational expression (2) in a region of X=from x 1 to x 2 (mm), and

the stress distribution in the sheet thickness direction of the chemically strengthened glass satisfies the following relational expression (3):

CT n ( X )= a ( X/L 2 )+ b , wherein a≧ 3  (2) and

CT 1 ×L 1/2 ≦30(MPa·mm 1/2 )  (3),

wherein:

CT 1 : a maximum value of a tensile stress (MPa) in a region where a depth from the first surface X is from x 0 to x 1 ,

x 0 : a depth (mm) from the first surface to a point at which a compressive stress turns first into a tensile stress in the stress distribution in the sheet thickness direction from the first surface to the second surface,

x L : a depth (mm) from the first surface to a point at which a compressive stress turns first into a tensile stress in the stress distribution in the sheet thickness direction from the second surface to the first surface,

x 1 =0.8 x 0 +0.2 x L (mm),

x 2 =0.2 x 0 +0.8 x L (mm), and

L=x L −x 0 (mm).

4 . The chemically strengthened glass according to claim 3 , wherein:

the depth of compressive stress DOL 1 (μm) of the first surface and the depth of compressive stress DOL 2 (μm) of the second surface satisfy the following relational expression:

DOL 1 ≧DOL 2 +3(μm).

5 . The chemically strengthened glass according to claim 1 , wherein:

the chemically strengthened glass has a radius of curvature of 15000 mm or more.

6 . The chemically strengthened glass according to claim 1 , wherein:

the chemically strengthened glass has a radius of curvature of less than 15000 mm.

7 . The chemically strengthened glass according to claim 1 , which is a chemically strengthened curved glass substrate.

8 . The chemically strengthened glass according to claim 3 , wherein:

the chemically strengthened glass has a radius of curvature of 15000 mm or more.

9 . The chemically strengthened glass according to claim 3 , wherein:

the chemically strengthened glass has a radius of curvature of less than 15000 mm.

10 . The chemically strengthened glass according to claim 3 , which is a chemically strengthened curved glass substrate.