Chemically strengthened glass and method for manufacturing chemically strengthened glass

1. A chemically strengthened glass having a thickness t of 2 mm or less,

having a compressive stress value (CS 40 ) at a portion of 40 μm deep from a glass surface being 60 MPa or more, having a compressive stress value (CS 20 ) at a portion of 20 μm deep from the glass surface being 153 MPa or more, and having a surface compressive stress value (CS) being 450 MPa or more, and

satisfying ΔCS DOL-20 (unit: MPa/μm) being 1.07 or less,

wherein ΔCS DOL-20 is calculated according to the following expression using a compressive stress value CS DOL-20 at a depth closer to a glass surface side by 20 μm from DOL:

ΔCS DOL-20 =CS DOL-20 /20,

wherein the chemically strengthened glass has a matrix composition comprising, in terms of molar percentage on the basis of oxides, from 58 to 72% of SiO 2 , from 7 to 20% of Al 2 O 3 , from 3 to 15% of Li 2 O, from 0 to 10% of Na 2 O, from 0 to 8% of K 2 O, from 0 to 10% of MgO, from 0 to 3% of CaO, from 0 to 3% of SrO, from 0 to 3% of BaO, from 0 to 10% of ZnO, and from 0 to 4% of ZrO 2 .

2. The chemically strengthened glass according to claim 1 , satisfying a number of fragments generated within a size of 25 mm×25 mm being 20 or less in a fracture test according to an indenter indentation test under a condition of holding a load ranging from 5 kgf to 10 kgf for 15 seconds with a pyramidal diamond indenter having an indenter angle of a facing angle of 60°.

3. The chemically strengthened glass according to claim 1 , wherein the ΔCS DOL-20 (unit: MPa/μm) is 0.4 or more.

4. The chemically strengthened glass according to claim 1 , wherein the ΔCS DOL-20 (unit: MPa/μm) is 1.02 or less.

5. The chemically strengthened glass according to claim 1 , having a fracture stress value σa (bending strength, unit: MPa) being 150 MPa or more obtained by performing a four-point bending test under conditions of an under spun of 30 mm, an upper spun of 10 mm, and a crosshead speed of 0.5 mm/minute after the glass surface is flawed by pressing a diamond indenter (indenter angle of facing angle: 110°) thereto for 15 seconds at a load of 0.5 kgf.

6. The chemically strengthened glass according to claim 1 , having a fracture stress value σc (bending strength, unit: MPa) being 150 MPa or more obtained by performing a four-point bending test under conditions of an under spun of 30 mm, an upper spun of 10 mm, and a crosshead speed of 0.5 mm/minute after the glass surface is flawed by pressing a diamond indenter (indenter angle of facing angle: 110°) thereto for 15 seconds at a load of 2 kgf.

7. The chemically strengthened glass according to claim 1 , wherein the CS 40 is 200 MPa or less.

8. The chemically strengthened glass according to claim 1 , having a compressive stress value (CS 90 ) at a portion of 90 μm deep from the glass surface being 40 MPa or more.

9. The chemically strengthened glass according to claim 8 , wherein the CS 90 is 75 MPa or less.

10. The chemically strengthened glass according to claim 8 , satisfying ΔCS 100-90 (unit: MPa/μm) being 0.4 or more,

wherein ΔCS 100-90 is calculated according to the following expression using a compressive stress value (CS 90 ) at a portion of 90 μm deep from the glass surface and a compressive stress value (CS 100 ) at a portion of 100 μm deep from the glass surface,

ΔCS 100-90 =(CS 90 −CS 100 )/(100−90).

11. The chemically strengthened glass according to claim 10 , wherein the ΔCS 100-90 (unit: MPa/μm) is 4.0 or less.

12. The chemically strengthened glass according to claim 11 , wherein the ΔCS 100-90 (unit: MPa/μm) is 1.6 or less.

13. The chemically strengthened glass according to claim 1 , wherein the surface compressive stress value is 1500 MPa or less.

14. The chemically strengthened glass according to claim 1 , having a depth of a compressive stress layer (DOL) being 120 μm or more and 180 μm or less.

15. The chemically strengthened glass according to claim 1 , wherein the matric composition comprises, in terms of molar percentage on the basis of oxides, from 60 to 72% of SiO 2 , from 7 to 18% of Al 2 O 3 , from 0 to 3% of B 2 O 3 , from 0 to 3% of P 2 O 5 , from 6 to 13% of Li 2 O, from 3 to 10% of Na 2 O, from 0 to 2% of K 2 O, from 0 to 10% of MgO, from 0 to 0.2% of CaO, from 0 to 3% of SrO, from 0 to 3% of BaO, from 0 to 2% of ZnO, and from 0 to 2% of ZrO 2 .

16. The chemically strengthened glass according to claim 15 , wherein MgO is contained.

17. The chemically strengthened glass according to claim 15 , wherein the matrix composition comprises 0.5% or more of K 2 O.

18. The chemically strengthened glass according to claim 15 , wherein the content of Li 2 O is 10% or less.

19. The chemically strengthened glass according to claim 15 , wherein P 2 O 5 is contained.

20. The chemically strengthened glass according to claim 15 , wherein the matrix composition comprises 0.5% or more of ZrO 2 .