CHEMICALLY STRENGTHENED GLASS, METHOD FOR PRODUCING SAME, AND GLASS FOR CHEMICAL STRENGTHENING
A plate-like chemically strengthened glass having a compression stress layer on the surface of the glass, wherein the compressive stress value (CS 0 ) at the glass surface of is 500 MPa or more, the plate thickness (t) is 400 µm or more, the compressive stress depth of layer (DOL) is (t × 0.15) µm or more, the compressive stress values (CS 1 ) and (CS 2 ) when the depth from the glass surface is ¼ and ½, respectively, are 50 MPa or more, m 1 expressed by {m 1 = (CS 1 - CS 2 /(DOL/4 - DOL/2)} is -1.5 MPa/µm or more, m 2 expressed by {m 2 = (CS 2 /(DOL/2 - DOL)} is 0 MPa/µm or less, and m 2 is less than m 1 .
1 . A chemically strengthened glass having a sheet shape and having a compressive stress layer in a glass surface, wherein:
the glass surface has a compressive stress value (CS 0 ) of 500 MPa or higher;
a sheet thickness (t) is 400 µm or larger;
a depth of the compressive stress layer (DOL) is (t×0.15) µm or larger;
a compressive stress value (CS 1 ) measured at a point lying at a depth of ¼ of the DOL from the glass surface is 50 MPa or higher;
a compressive stress value (CS 2 ) measured at a point lying at a depth of ½ of the DOL from the glass surface is 50 MPa or higher; and
a value of m 1 represented by the following expression is -0.2 MPa/µm or less, a value of m 2 represented by the following expression is 0 MPa/µm or less, and a ratio (m 1 /m 2 ) between the value of m 1 and the value of m 2 is 0.25 or larger:
m
1
=
CS
1
−
CS
2
/
DOL
/
4
−
DOL
/
2
,
m
2
=
CS
2
/
DOL
/
2
−
DOL
.
.
2 - 5 . (canceled)
6 . The chemically strengthened glass according to claim 1 , having an internal tensile stress value of less than 100 MPa.
7 . The chemically strengthened glass according to claim 1 , wherein a value of m 3 represented by the following expression is 120 MPa/µm or larger, with respect to a compressive stress value (CS 3 ) measured at a point lying at a depth from the glass surface of 2.5 µm:
m
3
=
CS
0
−
CS
3
/
2.5
.
.
8 - 17 . (canceled)
18 . The chemically strengthened glass according to claim 7 , wherein the value of m 3 is 150 MPa/µm or larger.
19 . The chemically strengthened glass according to claim 7 , wherein the value of m 3 is 180 MPa/µm or larger.
20 . The chemically strengthened glass according to claim 7 , wherein the value of m 3 is 200 MPa/µm or larger.
21 . The chemically strengthened glass according to claim 7 , wherein the value of m 3 is 220 MPa/µm or larger.
22 . The chemically strengthened glass according to claim 7 , wherein the value of m 3 is 500 MPa/µm or less.
23 . The chemically strengthened glass according to claim 1 , having a maximum depth which gives the compressive stress value of 50 MPa or higher of (0.55×DOL)µm or larger with respect to the DOL.
24 . The chemically strengthened glass according to claim 1 , having a base composition comprising, in mass percentage on an oxide basis:
50-70% of SiO 2 ;
0-10% of B 2 O 3 ;
2-7% of Li 2 O;
0.5-6% of Na 2 O;
0-8% of K 2 O;
0-5% of (MgO+CaO+SrO+BaO); and
0-3% of (ZrO 2 +TiO 2 ).
25 . The chemically strengthened glass according to claim 24 , having a base composition comprising, in mass percentage on an oxide basis:
15-28% of Al 2 O 3 .