GLASS SHEET WITH ENAMEL REFLECTING INFRARED RADIATION

Abstract

A glass sheet includes a tempered mineral glass substrate bearing, on one of its faces, a low-emissivity transparent coating and, on this coating, an enamel layer containing one or more ceramic pigments, the enamel layer covering only a portion of the low-emissivity layer and leaving another part thereof free. At least 50% by weight, preferably at least 80% by weight, and in particular at least 95% by weight of the ceramic pigments are chosen from ceramic pigments that reflect near-infrared radiation (NIR) having a reflectance at 1000 nm, determined according to the standard ASTM E 903, at least equal to 40% and a lightness L* of less than 30. It also relates to a process for manufacturing such a sheet and to an oven or refrigerator door containing such a sheet.

Claims

1. A glass sheet comprising: a tempered mineral glass substrate bearing, on one of its faces, a low-emissivity transparent coating and, on the coating, an enamel layer containing one or more ceramic pigments, the enamel layer covering only a portion of the low-emissivity layer and leaving another part thereof free, wherein at least 50% by weight of the ceramic pigments are chosen from ceramic pigments that reflect near-infrared radiation (NIR) having a reflectance at 1000 nm, determined according to the standard ASTM E 903, at least equal to 40% and a lightness L* of less than 30.

2. The glass sheet as claimed in claim 1, wherein the total content of ceramic pigments of the enamel layer is between 20% and 40% by weight, relative to the total weight of the enamel layer.

3. The glass sheet as claimed in claim 1, wherein the lightness L* of the ceramic pigments reflecting the NIR radiation is between 1 and 20.

4. The glass sheet as claimed in claim 1, wherein the ceramic pigment or pigments reflecting the NIR radiation are chosen from the group formed by CI Pigment Black 27, CI Pigment Black 28, CI Pigment Black 30, CI Pigment Green 17, CI Pigment Brown 29, CI Pigment Brown 35, Al- and Ti-doped chromium oxide hematite, chromium-free manganese, bismuth, strontium and/or vanadium oxide spinel.

5. The glass sheet as claimed in claim 1, wherein the pigment or pigments reflecting the NIR are chosen from iron chromites and iron nickel chromites.

6. The glass sheet as claimed in claim 1, wherein the enamel layer has a thickness of between 5 m and 40 m.

7. The glass sheet as claimed in claim 1, wherein the enamel layer covers the peripheral portion of the low-emissivity layer close to the edge of the tempered mineral glass sheet.

8. The glass sheet as claimed in claim 1, wherein the pigments reflecting the NIR are formed of particles having a mean diameter of between 500 nm and 10 m.

9. The glass sheet as claimed in claim 1, wherein the enamel layer has a reflectance at 1000 nm (measured according to ASTM E 903) of greater than 13%.

10. The glass sheet as claimed in claim 1, wherein the low-emissivity layer has an emissivity, determined according to the standard ISO 10292:1994 (Annex A), of between 0.01 and 0.30.

11. An oven door comprising: at least one of the glass sheet as claimed in claim 1.

12. The oven door as claimed in claim 11, wherein the oven door is a glazing having multiple sheets and, when the oven door is fitted to an oven, the low-emissivity layer faces toward a cavity of the oven.

13. The oven door as claimed in claim 12, wherein a sheet made of borosilicate glass or made of soda-lime glass coated with a low-emissivity layer is placed between the glass sheet and the cavity of the oven, thus separating the glass sheet from the cavity of the oven.

14. A refrigerator door comprising: at least one of the glass sheet as claimed in claim 1.

15. A process for manufacturing a glass sheet as claimed in claim 1, the process comprising: providing a mineral glass substrate bearing, on at least one of its faces, a low-emissivity transparent coating; applying, on a portion only of the low-emissivity transparent coating, a pigmented glass paste comprising a glass frit and one or more ceramic pigments, at least 50% by weight of the ceramic pigments being chosen from ceramic pigments that reflect near-infrared radiation (NIR) having a reflectance at 1000 nm, determined according to the standard ASTM E 903, at least equal to 40% and a lightness L* of less than 30; irradiating the glass sheet thus obtained by means of NIR radiation sources so as to heat the glass sheet to a temperature close to a softening point of the glass sheet; and thermal tempering of the glass sheet.

16. The glass sheet as claimed in claim 1, wherein at least 95% by weight of the ceramic pigments are chosen from ceramic pigments that reflect near-infrared radiation (NIR) having a reflectance at 1000 nm, determined according to the standard ASTM E 903, at least equal to 40% and a lightness L* of less than 30.

17. The glass sheet as claimed in claim 2, wherein the total content of ceramic pigments of the enamel layer is between 35% and 38% by weight, relative to the total weight of the enamel layer.

18. The glass sheet as claimed in claim 3, wherein the lightness L* of the ceramic pigments reflecting the NIR radiation is between 2 and 10.

19. The glass sheet as claimed in claim 6, wherein the enamel layer has a thickness of between 10 m and 15 m.

20. The glass sheet as claimed in claim 8, wherein the pigments reflecting the NIR are formed of particles having a mean diameter of between 700 nm and 3 m.

Description

EXAMPLE

[0055] Two glass pastes are prepared having the composition by weight indicated in the table below

TABLE-US-00001 According Comparative to the invention Frit 50% 50% IR-reflective pigment (FeCr) 30% Standard black pigment (CuCr) 30% Solvent + polymer 20% 20%

[0056] These two pastes are screenprinted in the form of a frame at the edge of a soda-lime glass substrate (dimensions 50 cm50 cm) bearing on each of its faces a coating (SGG EkoVision II) having an emissivity of 0.2 and which is formed of the following series of layers: Glass//Si.sub.3N.sub.4/SiO.sub.2/ITO/Si.sub.3N.sub.4/SiO.sub.2/TiOx.

[0057] The viscosity of the pastes is around 80 poise and the thickness of the layers is around 27 m. The printed substrates are then dried in an infrared furnace at a temperature of around 130 C. until the complete evaporation of the organic solvent.

[0058] The two glass sheets are then brought over a period of 4 minutes to a temperature of 670 C. by means of electrical resistors emitting infrared radiation having wavelengths up to around 5 m, then cooled abruptly using a stream of cold air.

[0059] FIG. 1 shows the reflection spectrum of the UV-visible-IR radiation of the enamel containing the standard black pigment and of the enamel containing the black pigment that reflects IR radiation.

[0060] When the comparative glass sheet is subjected to a fragmentation test is according to the standard standard EN 1250-1, it is observed that the pieces of glass are significantly smaller in the zone covered by the black enamel than in the zone covered only by the low-emissivity coating. The difference in size between the zones is such that the glass sheet is judged to not comply with the fragmentation test.

[0061] When the enamelled glass sheet according to the invention is subjected to the same fragmentation test according to the standard EN 1250-1, the pieces of glass in the zones covered by the enamel have dimensions similar to those observed in the zones not covered by the enamel. FIG. 2 shows a photo of such a glass sheet according to the invention after fragmentation according to the standard EN 1250-1.