Highly strengthened glass article
A strengthened glass sheet product as well as process and an apparatus for producing the product. The process comprises cooling the glass sheet by non-contact thermal conduction for sufficiently long to fix a surface compression and central tension of the sheet. The process results in thermally strengthened glass sheets having improved breakage properties.
1. A thermally strengthened glass sheet:
the glass sheet having a thickness, expressed in millimeters, of t, a length, expressed in millimeters, of l, and a width, expressed in millimeters, of w, t being less than l and less than w;
the glass sheet having a first major surface and a second major surface separated by the thickness t;
the glass sheet comprising a glass having a low temperature linear CTE, expressed in 1/° C., of α S CTE , a high temperature linear CTE, expressed in 1/° C., of α L CTE , an elastic modulus, expressed in GPa, of E, a strain temperature, expressed in units of ° C., of T strain , and a softening temperature, expressed in units of ° C., of T soft ;
the first major surface of the glass sheet having a roughness in the range of from 0.2 to 0.7 nm Ra over an area of 10 μm×10 μm and a thermally induced surface compressive stress of less than 800 MPa and greater than
P
1
(
h
)
*
t
(
P
2
(
h
)
+
t
)
·
E
·
[
T
strain
·
α
CTE
s
+
α
CTE
L
·
(
T
soft
-
T
strain
)
]
;
in units of MPa;
wherein P 1 is given by
910.2
-
259.2
·
exp
(
-
h
0.143
)
;
P 2 is given by
2.53
+
23.65
(
1
+
(
h
0.00738
)
1.58
)
;
and h is a constant greater than or equal to 0.0625.
2. The glass sheet according to claim 1 wherein h is greater than or equal to 0.063.
3. The glass sheet according to claim 1 wherein h is greater than or equal to 0.065.
4. The glass sheet according to claim 1 wherein h is greater than or equal to 0.07.
5. The glass sheet according to claim 1 wherein h is greater than or equal to 0.075.
6. The glass sheet according to claim 1 wherein h is greater than or equal to 0.08.
7. The glass sheet according to claim 1 wherein h is greater than or equal to 0.10.
8. The glass sheet according to claim 1 wherein h is greater than or equal to 0.15.
9. The glass sheet according to claim 6 , l and w each being at least 10.
10. The glass sheet according to claim 9 , wherein the ratio l/t and the ratio w/t each are equal to 10/1 or more.
11. The glass sheet according to claim 1 wherein the first major surface of the sheet is flat to 100 μm total indicator run-out (TIR) along any 50 mm or less profile of the first major surface.
12. The glass sheet according to claim 1 wherein the first major surface has a roughness in the range of from 0.2 to 0.4 nm Ra over an area of 10 μm×10 μm.
13. The glass sheet according to claim 12 wherein the first major surface has a roughness in the range of from 0.2 to 0.3 nm Ra over an area of 10 μm×10 μm.
14. The glass sheet according to claim 1 wherein the first major surface has a coating.
15. The glass sheet according to claim 1 wherein t is less than 2.
16. The glass sheet according to claim 13 wherein t is 1 or less.
17. The glass sheet according to claim 1 wherein t is 0.5 or less.
18. The glass sheet according to claim 1 wherein t is 0.28 or less.
19. The glass sheet according to claim 1 wherein the sheet exhibits a 50% cracking threshold at 5 Newtons or greater after a 15 second Vickers Hardness Test.
20. A thermally strengthened glass sheet according to claim 1 wherein the sheet has a thermally induced central tension less than 400 MPa and greater than
P
1
CT
(
h
CT
)
*
t
2
(
P
2
CT
(
h
CT
)
+
t
)
·
E
·
[
T
strain
·
α
CTE
s
+
α
CTE
L
·
(
T
soft
-
T
strain
)
]
;
in units of MPa;
wherein P 1CT is given by
910.2
-
259.2
·
exp
(
-
h
CT
0.143
)
;
P 2CT is given by
2.53
+
23.65
(
1
+
(
h
CT
0.00738
)
1.58
)
;
and h CT is a constant greater than or equal to 0.06.
21. The sheet according to claim 20 wherein h CT is greater than or equal to 0.10.
22. The glass sheet according to claim 1 wherein the glass has an annealing temperature, expressed in units of ° C., of T anneal and a surface fictive temperature measured on the first major surface of the glass sheet represented by Tfs when expressed in units of ° C.;
the glass sheet having a non-dimensional surface fictive temperature parameter θs given by (Tfs−T anneal )/(T soft −T anneal ),
wherein the parameter θs is in the range of from 0.50 to 0.9.
23. The glass sheet according to claim 22 wherein the parameter θs is in the range of from 0.60 to 0.9.
24. The glass sheet according to claim 1 , wherein the compressive stress at said first major surface is larger than 100 MPa.
25. The glass sheet according to claim 16 , wherein the compressive stress at said first major surface is larger than 150 MPa.
26. The glass sheet according to claim 1 , wherein the compressive stress at said first major surface is larger than 200 MPa.
27. The glass sheet according to claim 1 , wherein the central tension of the sheet is larger than 50 MPa.
28. The glass sheet according to claim 1 , wherein the central tension of the sheet is larger than 100 MPa.
29. The glass sheet according to claim 1 , wherein the surface fictive temperature measured on the first surface of the sheet is at least 75° C. above a glass transition temperature of the glass.
30. The glass sheet according to claim 25 , wherein the surface fictive temperature measured on the first surface of the sheet is at least 90° C. above a glass transition temperature of the glass.