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;
a value of m 1 represented by the following expression is −1.5 MPa/μm or larger and −0.2 MPa/μm or less, a value of m 2 represented by the following expression is 0 MPa/μm or less, and the value of m 2 is smaller than the value of m 1 :
m 1 =(CS 1 −CS 2 )/(DOL/4−DOL/2),
m 2 =CS 2 /(DOL/2−DOL); and
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.
2. 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.
3. The chemically strengthened glass according to claim 1 , having a ratio (m 1 /m 2 ) between the value of m 1 and the value of m 2 of less than 0.9.
4. The chemically strengthened glass according to claim 1 , wherein the value of m 1 is −1.5 MPa/μm or larger and −0.4 MPa/μm or less.
5. The chemically strengthened glass according to claim 1 , having an internal tensile stress value of less than 100 MPa.
6. The chemically strengthened glass according to claim 1 , wherein the value of m 3 is 150 MPa/μm or larger.
7. The chemically strengthened glass according to claim 1 , having a base composition comprising, in mass percentage on an oxide basis:
55-80% of SiO 2 ;
15-28% of Al 2 O 3 ;
0-10% of B 2 O 3 ;
2-10% of Li 2 O;
0.5-10% of Na 2 O;
0-10% of K 2 O;
0-10% of (MgO+CaO+SrO+BaO); and
0-5% of (ZrO 2 +TiO 2 ).
8. 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 depth of the compressive stress layer (DOL) is 100 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 −1.5 MPa/μm or larger and −0.2 MPa/μm or less, a value of m 2 represented by the following expression is 0 MPa/μm or less, and the value of m 2 is smaller than the value of m 1 :
m 1 =(CS 1 −CS 2 )/(DOL/4−DOL/2),
m 2 =CS 2 /(DOL/2−DOL).
9. The chemically strengthened glass according to claim 8 , 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.
10. The chemically strengthened glass according to claim 8 , having a ratio (m 1 /m 2 ) between the value of m 1 and the value of m 2 of less than 0.9.
11. The chemically strengthened glass according to claim 8 , wherein the value of m 1 is −1.5 MPa/μm or larger and −0.4 MPa/μm or less.
12. The chemically strengthened glass according to claim 8 , having an internal tensile stress value of less than 100 MPa.
13. The chemically strengthened glass according to claim 8 , having a value of m 3 represented by the following expression of 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.
14. The chemically strengthened glass according to claim 8 , having a base composition comprising, in mass percentage on an oxide basis:
55-80% of SiO 2 ;
15-28% of Al 2 O 3 ;
0-10% of B 2 O 3 ;
2-10% of Li 2 O;
0.5-10% of Na 2 O;
0-10% of K 2 O;
0-10% of (MgO+CaO+SrO+BaO); and
0-5% of (ZrO 2 +TiO 2 ).
15. A method for producing the chemically strengthened glass of claim 8 , the method comprising:
bringing a glass for chemical strengthening which comprises Li 2 O into contact with a metal salt comprising an Na ion to conduct an ion exchange;
subsequently bringing the glass into contact with a metal salt comprising an Li ion to conduct an ion exchange; and
then bringing the glass into contact with a metal salt comprising a K ion to conduct an ion exchange.
16. The method according to claim 15 , wherein the glass for chemical strengthening comprises, in mass percentage on an oxide basis:
55-80% of SiO 2 ;
15-28% of Al 2 O 3 ;
0-10% of B 2 O 3 ;
2-10% of Li 2 O;
0.5-10% of Na 2 O;
0-10% of K 2 O;
0-10% of (MgO+CaO+SrO+BaO); and
0-5% of (ZrO 2 +TiO 2 ).