Glass for chemical strengthening

1. A glass for chemical strengthening, comprising, in mole percentage based on following oxides, 55% to 80% of SiO 2 , 3% to 16% of Al 2 O 3 , 0% to 12% of B 2 O 3 , 5% to 16% of Na 2 O, 0% to 4% of K 2 O, 0% to 15% of MgO, 0% to 3% of CaO, 0% to 18% of ΣRO, where R represents Mg, Ca, Sr, Ba or Zn, 0% to 1% of ZrO 2 , 0.01% to 0.2% of Co 3 O 4 , 0.05% to 1% of NiO, and 0.01% to 3% of Fe 2 O 3 , wherein a content ratio Co 3 O 4 /Fe 2 O 3 is 0.05 or more.

2. The glass for chemical strengthening according to claim 1 , further comprising 0.005% to 3% of a color correcting component comprising at least one metal oxide selected from the group consisting of oxides of Ti, Cu, Ce, Er, Nd, Mn and Se.

3. The glass for chemical strengthening according to claim 1 , further comprising 0.1% to 1% of TiO 2 .

4. The glass for chemical strengthening according to claim 1 , further comprising 0.1% to 3% of CuO.

5. The glass for chemical strengthening according to claim 1 , further comprising 0.005% to 2% of a color correcting component comprising at least one metal oxide selected from the group consisting of oxides of Ce, Er, Nd, Mn and Se.

6. The glass for chemical strengthening according to claim 1 ,

wherein the content ratio Co 3 O 4 /Fe 2 O 3 is 0.05 to 0.5.

7. The glass for chemical strengthening according to claim 1 ,

wherein a content ratio (SiO 2 +Al 2 O 3 +B 2 O 3 )/(ΣR′ 2 O+CaO+SrO+BaO+Fe 2 O 3 +Co 3 O 4 ) is 3 or more, where R′ represents Na, K or Li.

8. The glass for chemical strengthening according to claim 1 , further comprising 0.005% to 0.5% of SO 3 .

9. The glass for chemical strengthening according to claim 1 , further comprising 0.005% to 1% of SnO 2 .

10. The glass for chemical strengthening according to claim 1 ,

wherein a ratio of an absorption coefficient at a wavelength of 550 nm to an absorption coefficient at a wavelength of 600 nm, as calculated from a spectral transmittance curve of the glass and a ratio of an absorption coefficient at a wavelength of 450 nm to the absorption coefficient at the wavelength of 600 nm, as calculated from the spectral transmittance curve of the glass are both within a range of 0.7 to 1.2.

11. The glass for chemical strengthening according to claim 1 ,

wherein absolute values of variation ΔT (550/600) and variation ΔT (450/600) expressed by expressions (1) and (2) are 5% or less:

Δ T (550/600)(%)=[{ A (550/600)− B (550/600)}/ A (550/600)]×100  (1); and

Δ T (450/600)(%)=[{ A (450/600)− B (450/600)}/ A (450/600)]×100  (2)

where in the expression (1), A(550/600) is a ratio of an absorption coefficient at a wavelength of 550 nm to an absorption coefficient at a wavelength of 600 nm, as calculated from a spectral transmittance curve of the glass after 100-hour irradiation with light of a 400 W high-pressure mercury lamp, and B(550/600) is a ratio of an absorption coefficient at the wavelength of 550 nm to an absorption coefficient at the wavelength of 600 nm, as calculated from a spectral transmittance curve of the glass before irradiation with the light; in the expression (2), A(450/600) is a ratio of an absorption coefficient at a wavelength of 450 nm to the absorption coefficient at the wavelength of 600 nm, as calculated from the spectral transmittance curve of the glass after 100-hour irradiation with light of the 400 W high-pressure mercury lamp, and B(450/600) is a ratio of an absorption coefficient at the wavelength of 450 nm to the absorption coefficient at the wavelength of 600 nm, as calculated from the spectral transmittance curve of the glass before irradiation with the light.

12. The glass for chemical strengthening according to claim 1 ,

wherein an absolute value of a difference Δa* between chromaticity a* of reflected light by a D65 light source and chromaticity a* of reflected light by an F2 light source in an L*a*b* color system, the absolute value of a difference Δa* being expressed by expression (I), and an absolute value of a difference Δb* between chromaticity b* of reflected light by the D65 light source and chromaticity b* of reflected light by the F2 light source in the L*a*b* color system, the absolute value of a difference Δb* being expressed by expression (II), are both 1 or less:

Δ a*=a * value( D 65 light source)− a * value( F 2 light source)  (I); and

Δ b*=b * value( D 65 light source)− b * value( F 2 light source)  (II).

13. The glass for chemical strengthening according to claim 1 ,

wherein when an indentation is formed by using a Vickers indenter in a mirror-finished surface of a glass plate having a thickness of 1 mm made of the glass, a load of the Vickers indenter that causes a crack occurrence rate to be 50% is 150 gf or more.

14. A chemical strengthened glass obtained by chemically strengthening the glass according to claim 1 ,

wherein a depth of a surface compressive stress layer formed in a surface of the chemical strengthened glass is 30 μm or more, and a surface compressive stress of the surface compressive stress layer is 550 MPa or more.

15. The glass for chemical strengthening according to claim 1 ,

wherein the content ratio Co 3 O 4 /Fe 2 O 3 is 0.3 or less.