PROCESS FOR OBTAINING A MATERIAL COMPRISING A GLASS SHEET

Abstract

A process for obtaining a material including a glass sheet, includes providing a glass sheet including a first face coated at least partly by an essentially mineral first coating, the face having at least one first zone and at least one second zone, the at least one first zone having a higher emissivity than that of the second zone, then applying, on at least one portion of the second zone, a sacrificial layer including a resin, then heat treating the coated glass sheet at a temperature of at least 550° C., during which step the sacrificial layer is removed by combustion.

Claims

1. A process for obtaining a material comprising a glass sheet, said process comprising: providing a glass sheet comprising a first face coated at least partly by an essentially mineral first coating, said first face having at least one first zone and at least one second zone, said at least one first zone having a higher emissivity than that of said second zone, then applying, on at least one portion of said second zone, a sacrificial layer comprising a resin, then heat treating said coated glass sheet at a temperature of at least 550° C., during which step said sacrificial layer is removed by combustion.

2. The process as claimed in claim 1, wherein the first coating is electrically conductive.

3. The process as claimed in claim 2, wherein the first coating comprises at least one metal or comprises at least one transparent conductive oxide.

4. The process as claimed in claim 1, wherein the first face is coated over at least one portion by an essentially mineral second coating.

5. The process as claimed in claim 4, wherein the second coating is an enamel containing pigments.

6. The process as claimed in claim 4, wherein one of the first and second coatings partially covers the other.

7. The process as claimed in claim 6, wherein the first coating is electrically conductive and covers a portion of the second coating which is an enamel containing pigments.

8. The process as claimed in claim 7, wherein the first coating comprises silver paste tracks.

9. The process as claimed in claim 6, wherein the second coating is an enamel containing pigments and partially covers the first coating which is electrically conductive.

10. The process as claimed in claim 1, wherein the first coating is an enamel containing pigments, in particular black pigments.

11. The process as claimed in claim 1, wherein the sacrificial layer consists of resin and of refractory or combustible mineral compounds.

12. The process as claimed in claim 1, wherein the heat treatment is a treatment for bending and/or tempering the glass sheet.

13. The process as claimed in claim 5, wherein the heat treatment is a treatment for pre-firing the enamel.

14. The process as claimed in claim 13, wherein the treatment for pre-firing the enamel is followed by a treatment for bending the glass sheet.

15. The process as claimed in claim 1, further comprising, after the heat treatment step, a lamination step, wherein the glass sheet is bonded to another glass sheet by a thermoplastic interlayer.

16. The process as claimed in claim 3, wherein the at least one metal is silver.

17. The process as claimed in claim 5, wherein the enamel containing pigments includes black pigments.

18. The process as claimed in claim 11, wherein the sacrificial layer consists of resin and of pigments.

Description

EXAMPLES

[0070] The following examples illustrate the invention in a nonlimiting manner.

Example 1

[0071] A glass sheet was coated by screenprinting, firstly over the whole of its first face with a black enamel coating, then over half of this enamel coating with a coating based on silver paste. The coated face of the glass sheet therefore comprised two zones, a first zone (coated only with enamel) having a higher emissivity than that of a second zone (coated both with the enamel and with the silver paste).

[0072] The glass sheet thus coated was then heat treated by being placed for a period of 180 seconds in a furnace heated to a temperature of 680° C. The change in the temperature of the glass (measured on the face opposite the first face) in the first zone (T1) and in the second zone (T2) was measured.

[0073] In tests 1A and 1B, a sacrificial layer was deposited over the whole of the first and second zones. For test 1A the sacrificial layer was a layer of a UV-crosslinking resin based on acrylates, having a thickness of around 10 μm whereas for test 1B the sacrificial layer was a layer of paint comprising around 50%, as solids, of an epoxy acrylate resin and carbon black, having a thickness after drying of around 5 μm. In a (comparative) test 1C, no sacrificial layer was deposited.

[0074] FIG. 1 presents the temperature difference T1−T2 as a function of the heating time (t, expressed in seconds).

[0075] The results show that the sacrificial layer makes it possible to greatly reduce the temperature difference, which is at most 10° C. as an absolute value, whereas this difference may range up to 80° C. in the absence of a sacrificial layer.

Example 2

[0076] A glass sheet was coated over the whole of its first face, by sputtering, with a low-emissivity coating based on TCO, comprising a layer of mixed indium tin oxide (ITO) flanked by thin layers of silicon oxide and nitride. Half of this low-emissivity coating was then coated by screenprinting with a black enamel coating.

[0077] The coated face of the glass sheet therefore comprised two zones, a first zone (coated with enamel) having a higher emissivity than that of the second zone (coated only with the low-emissivity coating).

[0078] The glass sheet thus coated was then heat treated by being placed for a period of 180 seconds in a furnace heated to a temperature of 680° C. The change in the temperature of the glass (measured on the face opposite the first face) in the first zone (T1) and in the second zone (T2) was measured.

[0079] In tests 2A and 2B, a sacrificial layer (respectively identical to the one used for tests 1A and 1B) was deposited over the whole of the first and second zones. In a (comparative) test 2C, no sacrificial layer was deposited.

[0080] FIG. 2 presents the temperature difference T1−T2 as a function of the heating time (t, expressed in seconds).

[0081] The results show that the sacrificial layer makes it possible to greatly reduce the temperature difference, which is at most 20° C. as an absolute value, whereas this difference may range up to 40° C. in the absence of a sacrificial layer.

Example 3

[0082] A glass sheet was coated by screenprinting, firstly over the whole of its first face with a black enamel coating, then over half of this enamel coating with a coating based on silver paste. The coated face of the glass sheet therefore comprised two zones, a first zone (coated only with enamel) having a higher emissivity than that of a second zone (coated both with the enamel and with the silver paste).

[0083] The glass sheet thus coated was then heat treated by being placed for a period of 180 seconds in a furnace heated to a temperature of 710° C. The change in the temperature of the glass (measured on the face opposite the first face) in the first zone (T1) and in the second zone (T2) was measured.

[0084] In a test 3A, a sacrificial layer was deposited by screenprinting on the second zone.

[0085] The screenprinted composition consisted of an organic medium and of black mineral pigments based on oxides of copper (37% by weight), of iron (17% by weight) and of manganese (46% by weight). The wet thickness was 15 μm. In this example, the heat treatment made it possible to remove the sacrificial layer by combustion of the resin, leaving the pigments on the surface of the glass.

[0086] In a (comparative) test 3B, no sacrificial layer was deposited.

[0087] FIG. 3 presents the temperature difference T1−T2 as a function of the temperature T1.

[0088] The results show that the sacrificial layer makes it possible to greatly reduce the temperature difference, which is at most 6° C. as an absolute value in the case of example 3A, whereas this difference may range up to more than 70° C. in the absence of a sacrificial layer.

Example 4

[0089] A glass sheet was coated by screenprinting, over a portion of its first face with a black enamel coating. The coated face of the glass sheet therefore comprised two zones, a first zone (coated with enamel) having a higher emissivity than that of a second (uncoated, therefore bare glass) zone.

[0090] Next, another uncoated clear glass sheet was positioned on the glass sheet thus coated in order to simulate the bending conditions with a view to the manufacture of a laminated windshield. The assembly was then heat-treated by being placed for a period of 180 seconds in a furnace heated to a temperature of 710° C. The change in the temperature of the glass in the first zone (T1) and in the second zone (T2) was measured using thermocouples placed between the two glass sheets.

[0091] In test 4A the zone not coated by the enamel (second zone) was previously coated by screenprinting with a composition consisting of an organic medium and black pigments, the composition being identical to that used in the context of example 3.

[0092] In the (comparative) test 4B, no sacrificial layer was deposited.

[0093] FIG. 4 presents the temperature difference T1−T2 as a function of T1.

[0094] The results show that the sacrificial layer makes it possible to greatly reduce the temperature difference at high temperature, since it is at most 15° C. as an absolute value in the case of example 4A, whereas this difference may range up to more than 35° C. in the absence of a sacrificial layer. When the temperature of the enamel reaches 500° C., the temperature difference is less than 5° C. in the case of example 4A versus 35° C. for the comparative example 4B.

Example 5

[0095] In a comparative test 5A a layer of black enamel (wet thickness of around 20 μm) having at its center an uncoated 150×130 mm.sup.2 camera zone was deposited by screenprinting on a first glass sheet having a thickness of 2.1 mm. After drying at 150° C. for 2 minutes, the enamel was pre-fired at 600° C. for 115 seconds, then the first glass sheet was coupled with a second glass sheet having a thickness of 2.1 mm so that the enameled face is on the side of the second glass sheet, the two glass sheets being held at a distance by positioning between them an interlayer powder providing a space of a few tens of micrometers, typically from 20 to 50 μm. The assembly was then subjected to a bending treatment at 610° C. for 340 seconds, then the two glass sheets were separated, washed in order to remove the interlayer powder, and finally laminated by means of a polyvinyl butyral (PVB) sheet. In the laminated glazing obtained, the enamel layer was therefore on face 2.

[0096] In the test according to the invention 5B, a sacrificial layer was deposited both on the black enamel layer and on the camera zone, before the pre-firing treatment. To do this, a composition consisting of an organic medium and black pigments, identical to the one used in examples 3 and 4, was deposited by screenprinting after drying the black enamel. The layer, having a wet thickness of the order of 6 to 8 μm, was dried at 150° C. for 2 minutes. The pre-firing treatment makes it possible to remove the sacrificial layer by combustion of the organic medium, leaving a layer of black pigments on the glass sheet.

[0097] The optical distortion in the camera zone was then measured using a Labscan machine sold by ISRA Vision with 1/2/0 filtering. The maximum horizontal distortion in the camera zone that was measured was 584 millidiopters in the case of comparative example 5A and 160 millidiopters in the case of example 5B.

[0098] The presence of a sacrificial layer during the pre-firing and bending therefore made it possible to substantially reduce the distortion in the camera zone.