Chemically strengthened glass and method for producing same
A chemically strengthened glass having a compressive stress layer formed in a surface layer thereof according to an ion exchange method, in which a surface of the glass has polishing flaws, the glass has a texture direction index (Stdi) of 0.30 or more, a hydrogen concentration Y in a region to a depth X from an outermost surface of the glass satisfies the following relational equation (I) at X=from 0.1 to 0.4 (μm), and a surface strength F (N) measured by a ball-on-ring test is (F≥1400×t 2 ) relative to a sheet thickness t (mm) of the glass: Y=aX+b (I) in which meanings of respective symbols in the equation (I) are as follows: Y: hydrogen concentration (as H 2 O, mol/L), X: depth from the outermost surface of the glass (μm), a: −0.300 or more, and b: 0.220 or less.
1. A glass sheet, having a compressive stress layer formed in a surface layer thereof according to an ion exchange method,
wherein a surface of the glass sheet has polishing flaws,
the glass sheet has a texture direction index (Stdi) of 0.30 or more,
a surface strength F (N) of the glass sheet measured by a ball-on-ring test is at least a value of (1400×t 2 ), wherein t (mm) is a thickness of the glass sheet, and
a hydrogen concentration Y in a region to a depth X from a surface of the glass sheet satisfies relational equation (I) at X=from 0.1 to 0.4 (μm):
Y=aX+b (I)
wherein:
Y is the hydrogen concentration measured as H 2 O, (mol/L);
X is the depth from the surface of the glass sheet (μm);
a is −0.300 or more; and
b is 0.220 or less,
wherein the ball-on-ring test is conducted by:
placing the glass sheet on a stainless ring whose diameter is 30 mm and whose contact part has a roundness with a curvature radius of 2.5 mm;
applying a load on a center of the ring by the ball under a static loading condition, while a steel ball having a diameter of 10 mm is kept in contact with the glass sheet; and
measuring a BOR surface strength which is a fracture load (unit: N) at which the glass sheet is fractured and determining an average value of twenty measured values of the BOR surface strength as the surface strength F, provided that in a case where a fracture origin of the glass sheet is apart from a loading point of the ball by 2 mm or more, the obtained value is excluded from data for calculating the average value.
2. The glass sheet according to claim 1 , wherein the glass sheet is made of an aluminosilicate glass, an aluminoborosilicate glass or a soda-lime glass.
3. The glass sheet according to claim 1 , wherein the glass sheet has a texture aspect ratio (Str20) of 0.10 or more.
4. The glass sheet according to claim 1 , wherein a thickness of the glass sheet is 5 mm or less.
5. A method for producing the glass sheet as defined in claim 1 , the method comprising:
polishing a surface of a glass sheet comprising sodium;
bringing the glass sheet into contact with an inorganic salt comprising potassium nitrate, thereby performing ion exchange of a Na ion in the glass sheet with a K ion in the inorganic salt, after the polishing;
washing the glass sheet after the ion exchange;
subjecting the glass sheet to an acid treatment after the washing; and
subjecting the glass sheet to an alkali treatment after the acid treatment,
wherein the inorganic salt further comprises at least one salt selected from the group consisting of K 2 CO 3 , Na 2 CO 3 , KHCO 3 , NaHCO 3 , K 3 PO 4 , Na 3 PO 4 , K 2 SO 4 , Na 2 SO 4 , KOH and NaOH.
6. The method according to claim 5 , wherein the inorganic salt has an Na concentration of 500 ppm by weight or more.
7. The method according to claim 5 , wherein the inorganic salt contains K 2 CO 3 in an amount of 0.1 mol % or more.
8. The method according to claim 5 , further comprising washing the glass sheet after the acid treatment.
9. The method according to claim 5 , further comprising washing the glass sheet after the alkali treatment.
10. The method according to claim 5 , wherein a solution having a pH of less than 7 is used in the acid treatment.
11. The method according to claim 10 , wherein the solution having the pH of less than 7 is a weak acid.
12. The method according to claim 10 , wherein the solution having the pH of less than 7 is a strong acid.
13. The method according to claim 5 , wherein the acid treatment is performed at a temperature of 100° C. or lower.
14. The method according to claim 5 , wherein a time for performing the acid treatment is from 10 seconds to 5 hours.
15. The method according to claim 10 , wherein the solution having the pH of less than 7 has an acid concentration of from 0.1 wt % to 20 wt %.
16. The method according to claim 5 , wherein a solution having a pH of more than 7 is used in the alkali treatment.
17. The method according to claim 16 , wherein the solution having the pH of more than 7 is a weak base.
18. The method according to claim 16 , wherein the solution having the pH of more than 7 is a strong base.
19. The method according to claim 5 , wherein the alkali treatment is performed at a temperature of from 0 to 100° C.
20. The method according to claim 5 , wherein a time for performing the alkali treatment is from 10 seconds to 5 hours.
21. The method according to claim 16 , wherein the solution having the pH of more than 7 has an alkali concentration of from 0.1 wt % to 20 wt %.