TEMPERED GLASS SUBSTRATE HAVING REDUCED IRIDESCENCE

Abstract

A process for the manufacture of a heat strengthened glass substrate, includes the application of a temporary layer including a polymer on a glass substrate including a glass sheet, then the application to the glass substrate coated with the temporary layer of a treatment for the heat strengthening of the glass including heating, leading to the removal of the temporary layer, and then cooling by blowing of air through nozzles. The glass substrate thus obtained exhibits a reduced level of iridescences.

Claims

1. A process for the manufacture of a heat strengthened glass substrate, comprising: applying a temporary layer comprising a polymer on a glass substrate comprising a glass sheet, then applying to the glass substrate coated with the temporary layer treatment for the heat strengthening of the glass comprising heating, leading to a removal of the temporary layer, and then cooling by blowing of air through nozzles.

2. The process as claimed in claim 1, wherein the heating is carried out at a temperature of greater than 550 C.

3. The process as claimed in claim 1, wherein the glass substrate exhibits, before application of the temporary layer, a normal emissivity of less than 10%.

4. The process as claimed in claim 1, wherein a normal emissivity of the substrate coated with the temporary layer is greater than a normal emissivity of the substrate before application of the temporary layer.

5. The process as claimed in claim 1, wherein the temporary layer has a thickness of between 1 and 100 micrometers.

6. The process as claimed in claim 1, wherein the glass substrate comprises a functional coating, the temporary layer being applied on the functional coating.

7. The process as claimed in claim 6, wherein the functional coating is of the low-e type or of the solar control type.

8. The process as claimed in claim 6, wherein the functional coating is deposited by cathode sputtering assisted by a magnetic field and wherein the temporary layer is directly in contact with the functional coating.

9. The process as claimed in claim 1, wherein the functional coating comprises at least one metal layer.

10. The process as claimed in claim 9, wherein the functional coating comprises a stack of thin layers comprising an alternation of x metal layers based on silver or on a metal alloy containing silver and of (x+1) antireflective coatings, each antireflective coating comprising at least one dielectric layer, each metal layer being positioned between two antireflective coatings, x being greater than or equal to 1.

11. The process as claimed in claim 6, wherein the functional coating comprises an upper layer chosen from nitrides, oxides or oxinitrides of titanium and/or of zirconium and/or of hafnium.

12. The process as claimed in claim 1, wherein the cooling produces a surface stress of the glass of greater than 40 MPa.

13. The process as claimed in claim 12, wherein the cooling is a heat tempering producing a surface stress of greater than 90 MPa.

14. The process as claimed in claim 1, wherein the polymer is a polymer of a (meth)acrylate.

15. The process as claimed in claim 14, further comprising: preparing a liquid composition comprising (meth)acrylate compounds chosen from monomers, oligomers, prepolymers or polymers comprising at least one (meth)acrylate functional group, applying the liquid composition on the glass substrate, then solidifying, by polymerization and/or crosslinking, the composition, so as to form the temporary layer.

16. The process as claimed in claim 15, wherein the liquid composition comprises less than 20% by weight of solvent and has a viscosity of between 0.05 and 5 Pa.Math.s at its application.

17. The process as claimed in claim 1, further comprising cutting up the glass substrate between the application of the temporary layer and the heating.

18. A line for the manufacture of heat strengthened glass substrates from glass substrates comprising a glass sheet, comprising, in the following order: a device for application to the glass substrates of a temporary layer comprising a polymer, a device for heating the glass substrates coated with the temporary layer, a device for blowing of air by nozzles over the heated glass substrates, a conveyor configured to convey the glass substrates from the first to the final device of the line.

19. The manufacturing line as claimed in claim 18, wherein the device for application of the temporary layer comprises: a device for deposition of a layer of a liquid composition comprising (meth)acrylate compounds on the glass substrates, a device for solidification, by polymerization and/or crosslinking, of the (meth)acrylate compounds, leading to the temporary layer.

20. The manufacturing line as claimed in claim 18, further comprising a device for the deposition of a functional coating before the device for application of a temporary layer.

21. The manufacturing line as claimed in claim 18, further comprising a device for cutting up the glass substrates between the device for application of a temporary layer and the heating device.

22. A heat strengthened glass sheet comprising a surface stress of greater than 40 MPa and comprising iridescences visible to the naked eye, the arithmetic mean of the retardation of which, measured with circular polarized light, is less than 50 nm.

23. The sheet as claimed in claim 22, wherein a percentage of its surface area exhibiting a retardation of less than 50 nm is greater than 60%.

24. The sheet as claimed in claim 1, comprising, on one of its main faces, a functional solar control coating comprising at least one metal layer, said coating having a thickness of between 100 and 300 nm.

Description

EXAMPLES 1 AND 2

[0072] Two glass sheets with a thickness of 6 mm and with dimensions of 800 mm600 mm, of Saint Gobain Glass CoolLite 154 II trademark, are taken. These two sheets exhibited, on one of their main faces, a functional coating of the solar control type made of a stack of thin layers successively comprising, from the glass, an alternation of two silver layers and of three antireflective coatings, each antireflective coating comprising several dielectric layers, including one made of Si.sub.3N.sub.4 and one made of ZnO, so that each silver layer is positioned between two antireflective coatings. The total thickness of this functional coating is between 150 and 200 nm.

[0073] On one of the sheets, a temporary layer is applied directly on the functional coating in the following way:

[0074] A liquid composition was prepared with mixtures of oligomers and of monomers, having at least one acrylate functional group sold by Sartomer: [0075] CN9276: tetrafunctional aliphatic urethane-acrylate oligomer, [0076] SR351: trimethylolpropane triacrylate, trifunctional acrylate monomer, [0077] SR833S: tricyclodecanedimethanol diacrylate, difunctional acrylate monomer.

[0078] The presence of the urethane-acrylate oligomer makes it possible to adjust the hardness and flexibility properties of the temporary protective layer. The temporary protective layer is subsequently cured by crosslinking with UV radiation. Irgacure 500, sold by BASF, as polymerization initiator, is added to the liquid composition. The acrylates and the initiator were present in the liquid composition in the following proportions, given as parts by weight:

TABLE-US-00001 TABLE 1 Acrylate oligomer CN9276 60 Trifunctional acrylate SR351 20 Difunctional acrylate SR833S 20 Initiator Irgacure 500 5

[0079] The liquid composition had a viscosity at 25 C. of 1.08 Pa.Math.s and was applied on the glass substrate by roll-to-roll coating. A thickness of between 10 and 20 m is obtained using speeds for the applicator roll of between 15 and 25 m/min. The temporary layer is cured by UV radiation provided by a mercury lamp with a power of 120 W. Under these conditions, the polymerization of the mixture of monomers and of oligomers is obtained within the thickness range from 10 to 20 m.

[0080] The emissivity of the glass substrate without a polymer layer (example 1, comparative) was 2.52%. The emissivity of the glass substrate with the polymer layer (example 2, according to the invention) was 56.9%. The emissivity is the normal emissivity (in the perpendicular direction) measured by the standard EN12898 of January 2001.

[0081] Heat strengthening of these two sheets is carried out by applying heating at 600 C. to them, followed by rapid cooling by blowing of air by nozzles which blow over the two main faces of the two sheets. The surface compression is subsequently measured at 60 MPa.

[0082] These substrates are subsequently observed with a circular polariscope (the substrates are placed between two polarizing filters). FIG. 1 shows these two substrates. In a), the substrate which had not received the temporary layer (example 1) exhibits a strong white mark in the central region.

[0083] The arithmetic mean of the retardations of these two sheets was measured by the method described in the paper by M. Illguth, M. Schuler and O. Bucak, 2015, The effect of optical anisotropies on building glass faades and its measurement method, Frontiers of Architectural Research, 4 pp. 119-126. A measurement per mm.sup.2 was carried out and then the arithmetic mean was calculated. The retardations were measured with circular polarized light. The results are collated in Table 2.

TABLE-US-00002 TABLE 2 Mean % of surface area with retardants retardation <50 nm Ex 1 (without polymer layer) 56.6 50% Ex 2 (with polymer layer) 33.2 80%

EXAMPLES 3 AND 4

[0084] The procedure as for Examples 1 and 2 is used, except that the heat strengthening is more intense because of faster cooling and leads to a surface compression of 110 MPa and that the observation is simply carried out in reflection with the naked eye. FIG. 2 shows these two substrates. In a), the substrate had not received the temporary layer and, in b), the substrate had received the temporary layer. The substrate which had not received the temporary layer shows much more marked iridescences.