Glass for chemical strengthening, chemically strengthened glass, and method for producing chemically strengthened glass
A glass for chemical strengthening is a glass sheet containing, as expressed by mass percentage based on oxides, 60 to 75% of SiO 2 , 3 to 12% of Al 2 O 3 , 2 to 10% of MgO, 0 to 10% of CaO, 0 to 3% of SrO, 0 to 3% of BaO, 10 to 18% of Na 2 O, 0 to 8% of K 2 O, 0 to 3% of ZrO 2 , 0 to 0.3% of TiO 2 , 0.005 to 0.2% of Fe 2 O 3 , and 0.02 to 0.4% of SO 3 . The glass has a sheet thickness of 0.2 mm or more and 1.2 mm or less. A value of β-OH measured without polishing both front and back surfaces of the glass sheet is lower than a value of β-OH measured after polishing surface layers of both the front and back surfaces of the glass sheet by 50 μm or more each.
1. A glass sheet comprising, as expressed by mass percentage based on oxides:
60 to 75% of SiO 2 ,
3.6 to 9% of Al 2 O 3 ,
2 to 10% of MgO,
0 to 10% of CaO,
0 to 3% of SrO,
0 to 3% of BaO,
10 to 18% of Na 2 O,
0 to 8% of K 2 O,
0 to 3% of ZrO 2 ,
0 to 0.3% of TiO 2 ,
0.005 to 0.2% of Fe 2 O 3 , and
0.02 to 0.4% of SO 3 ,
wherein:
the glass sheet has a thickness of 0.2 mm or more and 1.2 mm or less,
a temperature for logη=2 of the glass sheet is 1520° C. or lower,
a temperature for logη=4 of the glass sheet is 1080° C. or lower, and
when the glass sheet is subjected to polishing so that surface layers of each of a front surface and a back surface of the glass sheet are polished by 50 μm or more, a value of β-OH measured before polishing is lower than a value of β-OH measured after, and a difference between the value of β-OH measured before polishing and the value of β-OH measured after polishing is 0.003 mm −1 or more.
2. The glass sheet according to claim 1 , wherein the glass sheet is formed by a float process.
3. The glass sheet according to claim 2 , wherein the surface layers of the front and back surfaces of the glass sheet are not polished away after the glass sheet is formed by the float process.
4. A chemically strengthened glass sheet obtained by chemically strengthening the glass sheet according to claim 1 .
5. The chemically strengthened glass sheet according to claim 4 , having a surface compressive stress of 600 MPa or more and a depth of compressive stress of 6 μm or more and 30 μm or less.
6. The chemically strengthened glass sheet according to claim 4 , having a surface compressive stress of 700 MPa or more and a depth of compressive stress of 8 μm or more and 20 μm or less.
7. A method for producing a chemically strengthened glass, comprising subjecting the glass sheet according to claim 1 to an ion-exchange treatment.
8. The glass sheet according to claim 1 , wherein a ratio of amounts of Na 2 O, K 2 O, Al 2 O 3 , as expressed by mass percentages based on oxides, (Na 2 O +K 2 O)/Al 2 O 3 , is 2.2 or more and 4 or less.