Chemically strengthened glass and manufacturing method thereof
The present invention relates to a chemically strengthened glass having a thickness t (mm), in which a first-order derivative CS x ′ of a stress value CS x (MPa) is −4.7 or larger in a range of CS x ≥0 in a profile of the stress value CS x (MPa), in which the stress value CS x (MPa) is a function of depth x (μm) from a glass surface, and in which the stress value CS x (MPa) is measured by a scattered light photoelastic stress meter, and a manufacturing method thereof.
1. A chemically strengthened glass having a thickness t in mm, wherein a first-order derivative CS x ′ of a stress value CS x in MPa is −4.7 or larger in a range of CS x ≥0 in a profile of the stress value CS x in MPa,
wherein the stress value CS x in MPa is a function of a depth x in μm from a glass surface,
wherein the stress value CS x in MPa is measured by a scattered light photoelastic stress meter,
wherein a base composition of the chemically strengthened glass comprises, as represented by mol % based on oxides,
from 40 mol % to 75 mol % of SiO 2 ;
from 1 mol % to 20 mol % of Al 2 O 3 ; and
from 5 mol % to 35 mol % of Li 2 O; and
wherein a stress value CS 90 at a depth 90 μm from a glass surface satisfies the following inequality:
CS
90
/
{
CT
2
×
(
t
-
2
×
DOL
/
1
,
000
)
}
/
t
≥
1.62
wherein t is the thickness in mm, CT 2 is a maximum tensile stress in MPa and DOL is a compressive stress layer depth in μm.
2. The chemically strengthened glass according to claim 1 ,
wherein the stress value CS 90 at a depth 90 μm from the glass surface satisfies the following inequality:
CS
90
/
{
CT
2
×
(
t
-
2
×
DOL
/
1
,
000
)
}
/
t
≥
2.
wherein t is the thickness in mm, CT 2 is a maximum tensile stress in MPa and DOL is a compressive stress layer depth in μm.
3. The chemically strengthened glass according to claim 1 ,
wherein in the profile of the stress value CS x , a second-order derivative CS x ″ of the stress value CS x satisfies CS x ″≤0.050.
4. The chemically strengthened glass according to claim 1 ,
wherein a second-order derivative CS x ″ of the stress value CS x is greater than 0.
5. The chemically strengthened glass according to claim 1 ,
wherein the first-order derivative CS x ′ of the stress value CS x is 0 or smaller.
6. The chemically strengthened glass according to claim 1 ,
wherein in the profile of the stress value CS x in MPa, a stress value CS 0 at a glass outermost surface is 300 MPa or smaller.
7. The chemically strengthened glass according to claim 1 ,
wherein a maximum tensile stress CT 2 in MPa satisfies the following inequality:
CT
2
≤
19.5
/
(
t
/
2
-
DOL
/
1
,
000
)
,
wherein t is the thickness in mm and DOL is a compressive stress layer depth in μm.
8. The chemically strengthened glass according to claim 1 , wherein:
the chemically strengthened glass is a chemically strengthened glass obtained by a chemical strengthening of at least two steps; and
a maximum tensile stress CT 2 in MPa of the chemically strengthened glass is from 50% to 99% of a maximum tensile stress CT 1 in MPa of a chemically strengthened glass obtained after a first-stage chemical strengthening of the chemical strengthening of the at least two steps.