Thermally tempered glass element and use thereof

Abstract

A thermally tempered glass element is provided made of glass with two opposite faces that are under compressive stress of at least 40 MPa. The glass has a working point at which the glass has a viscosity of 10.sup.4 dPa.Math.s of at most 1350° C. The glass has a viscosity versus temperature profile and a coefficient of thermal expansion versus temperature profile of the glass are such that a variable (750° C.−T.sub.13)/(CTE.sub.Liq−CTE.sub.Sol) has a value of at most 5*10.sup.6 K.sup.2. The CTE.sub.Liq is a coefficient of linear thermal expansion of the glass above a glass transition temperature T.sub.g, the CTE.sub.Sol is a coefficient of linear thermal expansion of the glass in a temperature range from 20° C. to 300° C., and the T.sub.13 is a temperature at which the glass has a viscosity of 10.sup.13 dPa.Math.s.

Claims

1. A thermally tempered glass element, comprising: glass with two opposite faces that are under compressive stress of at least 40 MPa, wherein the glass has a working point at which the glass has a viscosity of 10.sup.4 dPa.Math.s of at most 1350° C., wherein the glass has a viscosity versus temperature profile and a coefficient of thermal expansion versus temperature profile of the glass are such that a variable
(750° C.−T.sub.13)/(CTE.sub.Liq−CTE.sub.Sol) has a value of at most 5*10.sup.6 K.sup.2, wherein CTE.sub.Liq is a coefficient of linear thermal expansion of the glass above a glass transition temperature T.sub.g, wherein CTE.sub.Sol is a coefficient of linear thermal expansion of the glass in a temperature range from 20° C. to 300° C., wherein T.sub.13 is a temperature at which the glass has a viscosity of 10.sup.13 dPa.Math.s, and wherein the glass has a composition that is free of B.sub.2O.sub.3, and wherein the glass has a chemical resistance H, S, L of at least 2, 3, 3 or better, the chemical resistance being defined as hydrolytic class H according to ISO 719, acid class S according to DIN 12116, and alkali class L according to ISO 695.

2. The glass element of claim 1, wherein the coefficient of linear thermal expansion CTE.sub.Sol is in a range from 3.5*10.sup.−6 K.sup.−1 to 6*10.sup.−6 K.sup.−1.

3. The glass element of claim 1, wherein the coefficient of linear thermal expansion CTE.sub.Liq is in a range from 11*10.sup.−6 K.sup.−1 to 45*10.sup.−6 K.sup.−1.

4. The glass element of claim 1, wherein the glass has a density of at least 2.4 grams per cubic centimeter.

5. The glass element of claim 1, further comprising a coating on at least one of the two opposite faces.

6. The glass element of claim 5, wherein the coating is a glass flux-based coating.

7. The glass element of claim 5, wherein the coating has a coefficient of thermal expansion, CTE.sub.Coat, is adapted to the coefficient of thermal expansion CTE.sub.Sol of the glass so that an absolute value of a difference of thermal expansion coefficients, |ΔCTE|=|CTE.sub.Sol−CTE.sub.Coat|, is not more than 1 ppm/K.

8. The glass element of claim 7, wherein the difference is not more than 0.5 ppm/K.

9. The glass element of claim 7, wherein the difference is not more than 0.3 ppm/K.

10. The glass element of claim 1, further comprising a thickness between the two faces that is between greater than or equal to 2 mm and less than or equal to 5 mm.

11. The glass element of claim 1, further comprising a thickness between the two faces that is between greater than or equal to 3 mm and less than or equal to 5 mm.

12. The glass element of claim 1, wherein the composition, in percent by weight, comprises: TABLE-US-00005 SiO.sub.2 60-80, Al.sub.2O.sub.3  3-15, Li.sub.2O 0-5, Na.sub.2O  0-10, K.sub.2O 0-6, MgO 0-8, CaO  0-10, SrO 0-5, TiO.sub.2  .sup.   0-5, and ZrO.sub.2 0-9.

13. The glass element of claim 12, wherein the composition further comprises one more elements selected from a group consisting of refining agents, coloring agents, trace impurities inevitably contained in raw materials, and any combinations thereof, and wherein the one or more elements amount to a total of less than 2 wt %.

14. The glass element of claim 1, wherein the composition, in percent by weight, comprises: TABLE-US-00006 SiO.sub.2 63-75, Al.sub.2O.sub.3  8-21, Li.sub.2O 0-5, Na.sub.2O  0-14, K.sub.2O 0-5, MgO  0-12, CaO  0-18, SrO 0-5, TiO.sub.2  .sup.   0-5, and ZrO.sub.2 0-9.

15. The glass element of claim 14, wherein the composition further comprises one more elements selected from a group consisting of refining agents, coloring agents, trace impurities inevitably contained in raw materials, and any combinations thereof, and wherein the one or more elements amount to a total of less than 2 wt %.

16. The glass element of claim 1, wherein the composition, in percent by weight, comprises: TABLE-US-00007 SiO.sub.2 50-70, Al.sub.2O.sub.3  3-25, Li.sub.2O 0-8, Na.sub.2O 0-7, K.sub.2O 0-5, MgO 0-5, CaO 0-7, SrO 0-5, ZnO 0-3, TiO.sub.2 0-5, ZrO.sub.2  .sup.   0-5, and P.sub.2O.sub.5 0-5.

17. The glass element of claim 16, wherein the composition further comprises one more elements selected from a group consisting of refining agents, coloring agents, trace impurities inevitably contained in raw materials, and any combinations thereof, and wherein the one or more elements amount to a total of less than 2 wt %.

18. The glass element of claim 1, wherein the glass with two opposite faces is configured for a use selected from a group consisting of a door of a cooking chamber, a door of an electric oven, a door of an electric oven having a pyrolysis function, a cooking surface, a cover for a heating element, a cooking surface, a frying surface, a cover for a heating radiator, a grilling surface, a fireplace window, a carrier sheet, a furnace lining, a solar device, a pharmaceutical device, a medical device, a furnace lining for chemical or physical coating processes, a chemically resistant laboratory equipment, a substrate for high temperature applications, a substrate for extreme low temperature applications, a combustion furnace window, a heat shield for hot environment, a cover for a radiator, an IR radiator, an IR radiator appliance, a reflector, a floodlight, a projector, a video projector, a photocopier, thermo-mechanical load device, a night vision device, a wafer substrate, UV protection substrate, a housing component, an electronic device housing, a cover glass, a mobile phone cover glass, a laptop computer cover glass, a scanner cover glass, a facade panel, a fire protection glazing, and a ballistic protection component.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Below, for a description of the invention in more detail, reference will be made to the accompanying figures. In the figures, the same reference numerals designate the same or equivalent elements.

(2) FIG. 1 shows a conventional thermally tempered glass element with measured values of prestress after a pyrolysis cycle;

(3) FIG. 2 shows a top plan view of a glass element according to the invention, which is provided with a coating in one area; and

(4) FIG. 3 shows a sectional view of the glass element of FIG. 2 taken along line 3-3.

DETAILED DESCRIPTION

(5) FIG. 1 shows the outline of a glass element for an oven. The glass pane is made of a borosilicate glass according to the comparative example of the above table. The glass element or the glass pane was subjected to a temperature treatment corresponding to the temperature load after two pyrolysis cleaning cycles.

(6) The numbers in the oval fields indicate the residual prestress measured at the location of the respective field. As can be seen, prestress, i.e. compressive stress, is still quite high at the edge of the pane, with more than 50 MPa, but decreases significantly towards the center. In the center of the pane only 17 MPa are left. Thus, the prestress drops to less than half of the original value after only a short time.

(7) FIG. 2 schematically illustrates a glass element 1 according to the invention, here shown with a coating applied in a surface area 2 of the glass element 1, by way of example. FIG. 2 shows a top plan view of the glass element 1, while FIG. 3 shows a sectional side view along section line 3-3.

(8) The glass element 1 according to the invention has been thermally tempered and has two opposite faces 11 and 12 that are under compressive stress, the compressive stress being at least 40 MPa. Furthermore, the working point, i.e. the temperature T.sub.4 at which the glass of which the glass element 1 is made has a viscosity of 10.sup.4 dPa.Math.s, is at most 1350° C. The glass exhibits a viscosity versus temperature profile and a coefficient of thermal expansion versus temperature profile such that the variable
(750° C.−T.sub.13)/(CTE.sub.Liq−CTE.sub.Sol)
has a value of at most 5*10.sup.6 K.sup.2, wherein CTE.sub.Liq is the coefficient of linear thermal expansion of the glass above the glass transition temperature T.sub.g, CTE.sub.Sol is the coefficient of linear thermal expansion of the glass in a temperature range from 20° C. to 300° C., and T.sub.13 is the temperature at which the glass has a viscosity of 10.sup.13 dPa.Math.s.

(9) The coefficient of thermal expansion CTE.sub.Sol of the glass in the temperature range from 20° C. to 300° C. is preferably in a range from 3.5*10.sup.−6 K.sup.−1 to 6*10.sup.−6 K.sup.−1.

(10) Furthermore preferably, the glass is selected so that in its softened state, i.e. above glass transition temperature T.sub.g, the glass has an expansion coefficient CTE.sub.Liq in a range from 11*10.sup.−6 K.sup.−1 to 45*10.sup.−6 K.sup.−1.

(11) According to a further embodiment of the invention, the glass element is distinguished by the fact that the glass has a density of at least 2.4 grams per cubic centimeter.

(12) According to a further embodiment of the invention, the glass element 1 has a thickness between at least 2 mm and at most 5 mm, preferably between greater than or equal to 3 mm and less than or equal to 5 mm.

(13) According to yet another embodiment of the invention, the glass exhibits chemical resistance H, S, L of at least 2, 3, 3 or better, the chemical resistance being defined as hydrolytic class H according to ISO 719, acid class S according to DIN 12116, and alkali class L according to ISO 695.

(14) Furthermore, according to a further embodiment of the invention the glass element 1 may be provided with a coating in at least one surface area 2 thereof, as illustrated by way of example here. Preferably, such a coating is a glass flux-based coating, also known as enamel.

(15) According to a preferred embodiment of the invention, the coefficient of thermal expansion of the coating CTE.sub.Coat is adapted to the coefficient of thermal expansion CTE.sub.Sol of the glass element so that an absolute value of the difference of the thermal expansion coefficients,
|ΔCTE|=|CTE.sub.Sol−CTE.sub.Coat|,
is not more than 1 ppm/K, preferably not more than 0.5 ppm/K, and more preferably not more than 0.3 ppm/K.

(16) However, more generally, without being limited to the example shown in FIG. 2, the glass element 1 may as well be provided without such a coating.

LIST OF REFERENCE NUMERALS

(17) 1 Glass element 11, 12 Faces of glass element 2 Coated area of the glass element