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 90 ) at a portion of 90 μm deep from a glass surface being 25 MPa or more, and

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°,

wherein the chemically strengthened glass

provides a depth of a compressive stress layer (DOL) being 50 μm or more when a glass sheet having a thickness of 1 mm which has a matrix composition of the chemically strengthened glass and has been gradually cooled from a temperature T° C., which is 30° C. to 50° C. higher than a glass transition temperature, to (T−300)° C. at 0.5° C./minute, is subjected to an ion exchange treatment for one hour with a molten salt at 400° C. composed of KNO 3 , NaNO 3 , or a mixed salt of KNO 3 and NaNO 3 , and

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 0 to 5% of B 2 O 3 , from 0 to 3% of P 2 O 5 , from 3 to 20% of Li 2 O, from 0 to 10% of Na 2 O, from 0 to 4% of K 2 O, from 0 to 10% of MgO, from 0.1 to 3% of CaO, from 0 to 3% of SrO, from 0 to 3% of BaO, from 0 to 10% of ZnO, from 0 to 1% of TiO 2 , and from 0 to 2% of ZrO 2 .

2. The chemically strengthened glass according to claim 1 , satisfying ΔCS 100-90 (unit: MPa/μm) being 0.4 or more,

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

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

3. The chemically strengthened glass according to claim 2 , wherein ΔCS 100-90 (unit: MPa/μm) is 4.0 or less.

4. The chemically strengthened glass according to claim 1 , satisfying ΔCS DOL-20 (unit: MPa/μm) being 0.4 or more,

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

Δ CS DOL-20 =CS DOL-20 /20.

5. The chemically strengthened glass according to claim 4 , wherein ΔCS DOL-20 (unit: MPa/μm) is 4.0 or less.

6. 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.

7. 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.

8. The chemically strengthened glass according to claim 1 , having a surface compressive stress value being 300 MPa or more.

9. The chemically strengthened glass according to claim 1 , wherein the depth of a compressive stress layer (DOL) is 100 μm or more.

10. The chemically strengthened glass according to claim 1 , wherein the thickness t is 0.9 mm or less.

11. The chemically strengthened glass according to claim 1 , having an area Sc (MPa·μm) of a compressive stress layer being 20,000 MPa·μm or more.

12. The chemically strengthened glass according to claim 1 , satisfying a value Sc/t (MPa) obtained by dividing an area Sc (MPa·μm) of a compressive stress layer by the thickness t (μm) being 28 MPa or more.

13. The chemically strengthened glass according to claim 1 , wherein the depth of a compressive stress layer (DOL) is 115.1 μm or more and 173.2 μm or less.

14. The chemically strengthened glass according to claim 1 , having a compressive stress value (CS 90 ) at a portion of 90 μm deep from a glass surface being 25 MPa or more and 60.2 MPa or less.

15. The chemically strengthened glass according to claim 1 , satisfying a number of fragments generated within a size of 25 mm×25 mm being 12 or less and 2 or more 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°.

16. The chemically strengthened glass according to claim 1 , satisfying an average crack height (unit: mm) being 300 mm or more in an on-sand drop test carried out 5 to 10 times, wherein, each time, a sample of the chemically strengthened glass (50 mm×50 mm×0.8 mm in thickness) attached to a hard Nylon-made mock plate (50 mm×50 mm×18 mm in thickness, weight: 54 g) by a sponge double-sided tape (50 mm×50 mm×3 mm in thickness) is dropped, chemically strengthened glass facing downward, from a predetermined height (drop height) onto a SUS plate (15 cm×15 cm) on which 1 g of silica sand is scattered, wherein the drop height is initially 10 mm and is increased by 10 mm until a height at which the sample is cracked (crack height) is determined.

17. The chemically strengthened glass according to claim 1 , satisfying an average crack height (unit: mm) being 313 mm or more and 509 mm or less in an on-sand drop test carried out 5 to 10 times, wherein, each time, a sample of the chemically strengthened glass (50 mm×50 mm×0.8 mm in thickness) attached to a hard Nylon-made mock plate (50 mm×50 mm×18 mm in thickness, weight: 54 g) by a sponge double-sided tape (50 mm×50 mm×3 mm in thickness) is dropped, chemically strengthened glass facing downward, from a predetermined height (drop height) onto a SUS plate (15 cm×15 cm) on which 1 g of silica sand is scattered, wherein the drop height is initially 10 mm and is increased by 10 mm until a height at which the sample is cracked (crack height) is determined.

18. The chemically strengthened glass according to claim 1 , which satisfies N0/Nh being 1.8 or more, wherein N0 is a value obtained by converting a value on an outermost surface in an Na ion concentration profile in a sheet thickness direction of the chemically strengthened glass measured by Electron Probe Micro Analyzer (EPMA) to Na 2 O (% by weight), and Nh is a value obtained by converting a central value of sheet thickness in an Na ion concentration profile in a sheet thickness direction of the chemically strengthened glass measured by EPMA to Na 2 O (% by weight).

19. The chemically strengthened glass according to claim 1 , which satisfies ΔCS 30-0 (unit: MPa/μm) being 20 or less,

wherein ΔCS 30-0 is calculated according to the following expression using a surface compressive stress (CS) and a compressive stress value (CS 30 ) at a portion of 30 μm deep from the glass surface,

Δ CS 30-0 =( CS−CS 30 )/(30−0).

20. A method for manufacturing the chemically strengthened glass according to claim 1 , comprising performing at least two stages of ion exchange treatments on the glass, wherein KNO 3 concentration in a molten salt to be used in a first-stage ion exchange treatment is 60% by weight or more and NaNO 3 concentration in a molten salt to be used in a second-stage ion exchange treatment is 5% by weight or more.