WO2019223952A1

WO2019223952A1 - Double sided coated glass substrate and method for making the same

Info

Publication number: WO2019223952A1
Application number: PCT/EP2019/060672
Authority: WO
Inventors: Daniel Decroupet
Original assignee: Agc Glass Europe; Agc Flat Glass North America, Inc.
Priority date: 2018-05-23
Filing date: 2019-04-25
Publication date: 2019-11-28

Abstract

The present invention concerns a process for preparing a double sided coated substrate that comprises heating a glass sheet provided with a first heat reflecting coating on one side, depositing a second heat reflecting on the opposite side by chemical vapor deposition or pyrolytic spray deposition, in particular wherein the first heat reflecting coating is provided by chemical vapor deposition and the second heat reflecting coating is deposited using chemical vapor deposition or pyrolytic spray deposition.

Description

Double sided coated glass substrate and method for making the same Technical Field

[0001] The present invention concerns a process for preparing a coated substrate that includes a first heat reflecting coating on one side of the glass substrate and a second heat reflecting coating on the opposite side of the glass substrate wherein the first heat reflecting coating is deposited using chemical vapor deposition and the second heat reflecting coating is deposited using chemical vapor deposition or pyrolytic spray deposition. The present invention also concerns coated glass substrates that include heat reflecting coatings on both sides of the substrate. In particular the present invention concerns coated glass substrates that include a first heat reflecting coating on one side of the glass substrate and a second heat reflecting coating on the opposite side of the glass substrate, wherein the first and second heat reflecting coatings comprise fluorine doped tin oxide layers.

Background Art

[0002] Glass substrates are used as oven doors, so that a user can see inside the oven. Such glass substrates are often provided with one or more heat reflecting coatings to limit heat low from the oven through the oven door. At least one such coating is included on a glass substrate on the side in contact with the interior atmosphere of the oven. This coating must be temperature stable and particularly resistant to chemical degradation and mechanical degradation. For particularly high insulating efficiency it is known to provide glass substrates for oven doors with heat reflecting coatings on both sides of the glass substrate.

[0003] A well-known process for providing a glass substrate with chemically and mechanically durable coatings heat reflecting coatings on one or both sides of the substrate is pyrolytic spray deposition. Typically a glass sheet is conveyed through spray deposition line where it is heated, then sprayed with a coating solution comprising compounds that upon thermal decomposition on the hot glass form a heat reflecting layer of fluorine doped tin oxide. Known drawbacks of pyrolytic spray coatings is their lack of thickness uniformity, which also affects the uniformity of the coated glass sheet’s emissivity, their high haze levels and non-uniform colors in reflection.

[0004] Chemical vapor deposition (CVD) is a process for deposition, among

others, heat reflecting coatings that are uniform and neutrally colored in reflection and that have a low emissivity and low haze levels. Typically a hot glass sheet is provided, either during production of the glass on a float glass line (online CVD) or by heating in a separate installation (offline CVD). It is then brought into contact with a gas phase comprising compounds that upon thermal composition on the hot glass form a heat reflecting layer of fluorine doped tin oxide. Generally one or more additional layers are formed by CVD on the glass sheet before the deposition of the fluorine doped tin oxide layer. This one or more additional layer is known as an iridescence suppressing layer that reduces the colors in reflection of the final heat reflecting coating and also helps obtaining a low level of haze. In the industrial CVD coating installations that operate on a glass float line, coating both sides is complicated and expensive. In order to deposit heat reflecting coatings on both sides of a glass substrate by CVD is generally necessary to coat one side first, then reheat the glass and coat the other side in a second step. This excludes the use of online CVD at least for the second heat reflecting coating.

Summary of invention

[0005] It is an object of the present invention to improve upon these

disadvantages and to provide a process for manufacturing a glass substrate on both sides with mechanically and chemically durable heat reflecting coatings, while improving the esthetical appearance and emissivity levels.

[0006] In the present invention heat reflecting coatings increase a coated

substrate’s reflectivity of infrared radiation in the at least part of the wavelength range from 700 nm to 21 pm.

[0007] According to a first aspect of the invention, this and other objects are

achieved by means of a process for making double sided coated glass sheets comprising, providing a first glass sheet, wherein the first glass sheet has one uncoated side and one coated side which is provided with a first heat reflecting coating,

conveying the first glass sheet into a coating apparatus,

heating the conveyed first and second glass sheets in the coating apparatus to a temperature comprised between 400 and 700°C, preferably between 550 and 650 °C,

depositing a second heat reflecting coating on the uncoated side of the first glass sheet,

cooling the first glass sheet,

conveying the first and second glass sheets out of the coating apparatus.

[0008] The inventors found that heating the first glass sheet bearing only the first heat reflecting coating could be heated in a horizontal conveying oven with the first heat reflecting coating in contact with the conveyor rolls. The second heat reflecting coating could be deposited by either chemical vapor deposition or by pyrolytic spray deposition. Pyrolytic spray deposition was less sensitive to deformation or buckling of the glass during heating due to the differences in emissivity of the first glass sheet’s sides where only one side bears the first heat reflecting coating. Alternately the first glass sheet could be conveyed in a vertical position through a coating apparatus, preferably heated with both convective and radiative heat sources for improved planarity. The second heat reflecting coating can then either be deposited using chemical vapor deposition of pyrolytic spray deposition.

[0009] Another aspect of the invention concerns a process for making double sided coated glass sheets comprising,

providing a first and a second glass sheet, wherein each first and second glass sheet has one uncoated side and one coated side which is provided with a first heat reflecting coating,

positioning the first and second glass sheets vertically, parallel to each other and spaced apart, with the first glass sheet’s coated side facing the second glass sheet’s coated side,

conveying the thus positioned first and second glass sheets into a coating apparatus,

depositing a second heat reflecting coating on the uncoated sides of the first and of the second glass sheet,

cooling the first and second glass sheets,

conveying the first and second glass sheets out of the coating apparatus.

[0010] The process of the present invention provides the possibility to combine two different heat reflecting coatings on a single glass sheets. Furthermore it maintains a high level of productivity as two sheets of glass can be coated simultaneously with the second heat reflecting coating.

[0011] By positioning the first and second glass sheets vertically, parallel to each other and spaced apart, with the first glass sheet’s coated side facing the second glass sheet’s coated side, the first and second glass sheets, which have the same dimensions, essentially face each other. They may be spaced apart by at least 10 mm, at least 20 mm or even at least 30 mm and up to 10 cm, up to 20 cm and even up to 30 cm. The spacing being adapted to allow a certain deformation during the heating phase as well as circulation of hot atmosphere in between the glass sheets.

[0012] According to an embodiment of the present invention, the first heat

reflecting coating is provided on the glass sheets by chemical vapor deposition.

[0013] According to an embodiment of the present invention, the second heat reflecting coating is deposited on the uncoated sides of the first and second glass sheets by chemical vapor deposition or by pyrolytic spray deposition.

[0014] The present invention further relates to a glass sheet bearing on one side a first heat reflecting coating and bearing in the opposite side a second heat reflecting coating wherein the first heat reflecting coating is deposited by chemical vapor deposition and the second heat reflecting coating is deposited by chemical vapor deposition or by pyrolytic spray deposition. In particular the glass sheet may be a float glass sheet, having a tin side which is the side that was in contact with the tin bath in the float glass production process and an opposite side which is the air side. In particular the first heat reflecting coating may be deposited on the air side of the float glass sheet in particular by online CVD, that is during the production of the glass on the hot glass of a float glass production line.

[0015] Each of the first and second reflecting coating may in particular comprise a sequence of one or more layers. In particular each heat reflecting coating comprises at least one heat reflecting layer, in particular comprising tin oxide doped with fluorine (Sn0₂:F). Each heat reflecting coating may comprise one or more further layers, for instance to improve its durability or to improve its aesthetics particularly regarding haze and reflected colors.

[0016] It is noted that the invention relates to all possible combinations of features recited in the claims.

Brief description of drawings

[0017] This and other aspects of the present invention will now be described in more detail, with reference to the appended drawings showing various exemplifying embodiments of the invention.

[0018] FIG. 1 is a schematic cross-sectional view of double sided coated glass sheet according to an exemplifying embodiment of the present invention;

[0019] FIG. 2 is a schematic cross-sectional view of double sided coated glass sheet according to another exemplifying embodiment of the present invention.

[0020] FIG. 3 is a schematic cross-sectional side view of a coating apparatus according to an embodiment of the present invention.

[0021] FIG. 4 is a cross-sectional schematic representation of vertically arranged first and second glass sheets according to another exemplifying

embodiment of the present invention.

[0022] FIG. 5 is a schematic top down cross-sectional view of a coating

apparatus according to another embodiment of the present invention.

Description of embodiments

[0023] FIG. 3 shows a coating apparatus (308, not to scale) according to an

embodiment of the present invention. The coating apparatus (308) comprises a heating chamber (302), coating chambers (303, 304), and a cooling chamber (305). A glass sheet (300) provided with a first heat reflecting coating (301) is conveyed horizontally by conveyor rolls (309) into and through the coating apparatus (308). The first heat reflecting coating I sin contact with the conveyor rolls. Heating chamber (302) is provided with radiative and/or convective heating (not shown). Coating chambers (303, 304) are provided with spray coaters or CVD coaters (306, 307) and exhausting means (not shown) for created effluents. Cooling chamber (305) is provided with means, such as for example fans, for controlled cooling of the glass sheet.

[0024] According to an embodiment of the present invention, the first heat

reflecting coating is provided on the glass sheets by chemical vapor deposition. In particular providing the first heat reflecting coating

comprises providing at least one heat reflecting layer, in particular comprising tin oxide doped with fluorine by chemical vapor deposition.

[0025] The first heat reflecting coating may comprise a first heat reflecting layer which is a layer of tin oxide doped with fluorine, preferably with a fluorine content in the fluorine doped tin oxide of 0.5 to 3 atomic percent. The first heat reflecting layer may have a thickness in the range from 250 to

800nm, preferably from 300 to 450 nm, more preferably from 380 to 430 nm, and a hemispherical emissivity in the range from 0.09 to 0.25, preferably from 0.10 to 0.15. Alternately, the layers of tin oxide doped with fluorine may be thinner, having a thickness in the range from 50 to 250nm, in particular when the first heat reflecting coating is used for resistive heating.

[0026] FIG. 4 is a cross-sectional schematic representation of vertically arranged first (401) and second (402) glass sheets, wherein each first and second glass sheet has one uncoated side (404a, 404b) and one coated side which is provided with a first heat reflecting coating (403a, 403b). First (401) and second (402) glass sheets are positioned parallel to each other and spaced apart, with the first glass sheet’s coated side facing the second glass sheet’s coated side. First and second glass sheets are held in position for example by clamps (405) that are attached to an overhead conveying system (not shown). Alternately the vertically positioned glass sheets may be conveyed by a bottom conveyor, possibly stabilized in their vertical position by a top rail.

[0027] FIG. 5 shows a coating apparatus (508, not to scale) according to an

embodiment of the present invention. The coating apparatus (508) comprises a heating chamber (502), coating chambers (503, 504), and a cooling chamber (505). A first and a second glass sheet (500a, 500b) provided with a first heat reflecting coating (501a, 501 b) are positioned vertically, parallel to each other and spaced apart, with the first glass sheet’s coated side facing the second glass sheet’s coated side. Thus positioned first and second glass sheets (501a, 501b) are conveyed into and through the coating apparatus (508) by a conveyor (not shown).

Heating chamber (502) is provided with radiative and/or convective heating (not shown). Coating chambers (503, 504) are provided with spray coaters or CVD coaters (506a, 506b, 507a, 507b), for simultaneously depositing coating layers on the uncoated sides of the first and second glass sheets, and exhausting means (not shown) for created effluents. Cooling chamber (505) is provided with means, such as for example fans, for controlled cooling of the glass sheets.

[0028] In certain embodiments of the present invention the first heat reflecting coating further comprises in a sequence starting from the glass sheet first one or more iridescence suppressing layers, followed by the first heat reflecting layer described above. The iridescence suppressing layer may be a single layer, for example comprising or essentially consisting of silicon oxy-nitride SiO_xN_y, SiSn_yO_x or silicon oxycarbide SiO_xC_y, x being less than 2, having a refractive index at a wavelength of 550nm in the range from 1.65 to 1.80 and a thickness in the range from 55 to 95 nm.

The stoichiometry and thickness of the single iridescence layer is adapted so as to reach the desired refractive index and suppression of reflected colors of the resulting first heat reflecting coating. The iridescence suppressing layer may be an iridescence suppressing double layer comprising a first layer, in a sequence from the glass, a first layer of titanium oxide or tin oxide, followed by a second layer of silicon oxide silicon oxycarbide SiO_xC_y, or silicon oxynitride SiO_xN_y wherein x is less than 2. The thickness of the an iridescence suppressing double layer‘s first layer is in the range from 5 to 30 nm, the thickness of its second layer is in the range from 15 to 40 nm.

[0029] In certain embodiments the iridescence suppressing layer is deposited directly on the glass.

[0030] In certain embodiments the first heat reflecting layer is deposited directly on the iridescence suppressing layer.

[0031] In a particular embodiment the first heat reflecting coating comprises in sequence starting from the glass an iridescence suppressing layer of SiOxCy, having a thickness in the range from 55 to 80 nm and a refractive index at a wavelength of 550nm in the range from 1.6 to 1.8, and a first heat reflecting layer of fluorine doped tin oxide, comprising 0.05 to 2 atomic % of fluorine, having a thickness in the range from 350 to 450 nm and a hemispherical emissivity in the range from 0.10 to 0.20.

[0032] In certain embodiments the first heat reflecting coating is deposited on the glass sheets by online CVD, that is directly on the hot glass provided by a glass float line. Online CVD is a particularly economic process for producing CVD layers on glass that have thickness variations of at most +/- 3%. The thickness variations may be determined from calculating the average thickness of at least 10 measurement points, that is the arithmetic mean thickness, and the standard deviation of the measurement values. The standard deviation of the thickness of the layers of the first heat reflecting coating deposited by CVD is not more than 3% of the average thickness, preferably not more than 1.5% of the average thickness.

Thicknesses may for example be measured by step profiler

measuremements or by X-ray fluorescence.

[0033] Optionally, the sequence of layers of the first heat reflecting coating,

starting from the glass, comprises after the first heat reflecting layer, a reflectance reduction layer comprising or essentially consisting of SiO_z with z less than or equal to 2, having a thickness in the range from 40 to 180 nm. The thickness of the reflectance reduction layer may be adjusted so as to reduce the reflectance of a glass sheet having one side coated with the first heat reflecting coating and one uncoated side to less than 11 %, in particular less than 9%, even less than 7%. The reflectance is measured on the coated side with illuminant D65 at a 8° observer angle.

[0034] A glass sheet having one side coated with the first heat reflecting coating and one uncoated side has a haze level of less than 1.3%, not more than 1.0, not more than 0.5%, in particular not more than 0.3%. The haze is measured according to ASTM standard D1003-11 with illuminant A2.

[0035] A glass sheet having one side coated with the first heat reflecting coating and one uncoated side in certain preferred embodiments has a neutral, greenish or blueish color of the reflected light. In particular the CIELAB color coordinates of the reflected light on the coated side of the glass sheet are, expressed by the color coordinates of a^*Rc and b^*Rc in reflection, is blueish, that is a^* < 0 and b^* < 5, in particular -10 < a^* < 0 and -10 < b ^* < 5, or -5 < a^* < -1 and -6 < b^* < 4. The color of the reflected light is expressed using CIELAB color coordinates a^* and b^* under illuminant D65 using 10° observer angle and measured on the coated side.

[0036] According to an embodiment of the present invention, depositing a second heat reflecting coating on the uncoated sides of the first and of the second glass sheet comprises, depositing, by chemical vapor deposition, in sequence starting from the glass, an optional CVD sub layer, in particular comprising one or more of tin oxide, titanium oxide and silicon oxide and a CVD main layer, in particular of fluorine doped tin oxide.

[0037] Figure 1 shows a cross section (not to size) of a glass sheet (100), bearing a first heat reflecting coating comprising, in sequence starting from the glass, an iridescence suppressing layer (111), a heat reflecting layer (112) and a reflection reducing layer (113) on one side and on the other side, in sequence starting from the glass, a first CVD sub layer (101) and a first CVD main layer (102).

[0038] According to an embodiment of the present invention, depositing by

chemical vapor deposition the CVD main layer comprises contacting the heated first and second glass sheet with a vapor comprising a source of tin, a source of fluorine and a source of oxygen. A layer of fluorine doped tin oxide is thus formed. All chemical vapor deposition is preferably performed at atmospheric pressure. For chemical vapor deposition, the following sources may be used: the source of tin may for example be chosen among tin tetrachloride, dimethyl tin dichloride, mono-butyl tin trichloride; the fluorine sources are for example hydrogen fluoride or trifluoro acetic acid; the oxygen sources may comprise one or more of carrier air, water, alcohols and/or ethylacetate.

[0039] According to certain embodiments of the present invention a CVD sub layer is deposited by chemical vapor deposition for example of a layer of silicon oxy carbide by contacting the heated first and second glass sheet with a vapor comprising silane, ethylene and carbon dioxide. Alternately a CVD sub layer comprising mixed silicon tin oxide SiSn_xO_y, is deposited by contacting the heated first and second glass sheet with a vapor comprising a source of silicon and a source of tin and optionally a source of boron and/or a source of phosphorus. For the CVD sub layer the source of tin may be chosen among the same compounds as the source of tin for the CVD main layer. The source of silicon may be chosen among silane SiH₄ or silicon alkoxides, such as tetraethyl orthosilicate Si(OC2H5)4 . The addition of a boron and/or phosphorous CVD source may be necessary for reaching sufficient deposition yields. Suitable as boron source are boric acid, trimethyl borate, triethyl borate, tripropyl borate or tributyl borate, hexafluoroboric acid and mixtures of these compounds. Suitable

phosphorous sources are phosphoric acid and its dialkyl and trialkyl esters (methyl, ethyl, butyl and octyl), orthophosphoric acid and its alkyl esters (methyl, ethyl, butyl and octyl), linear and cyclic polyphosphates, or also mixtures of the phosphorus-containing compounds named above.

[0040] According to an alternate embodiment of the present invention, the second heat reflecting coating is deposited by pyrolytic spray deposition.

According to an embodiment of the present invention, depositing by pyrolytic spray deposition a second heat reflecting coating on the uncoated sides of the first and of the second glass sheet comprises depositing a first spray main layer comprising fluorine doped tin oxide by contacting the heated first and second glass sheets with a first spray main layer spray composition that comprises a spray source of tin, a spray source of fluorine, and a solvent. In particular the first spray main layer spray composition is free of any source of titanium.

[0041] In pyrolytic spray deposition a liquid composition is sprayed on a heated substrate. The heat of the substrate leads to the pyrolysis of the spray composition’s components at the surface of the substrate whereby a layer is formed.

[0042] In an embodiment of the present invention depositing the second heat reflecting coating comprises, before depositing the first spray main layer comprising fluorine doped tin oxide, depositing at least one first spray sub layer comprising at least one oxide chosen from the group consisting of tin oxide, titanium oxide and silicon oxide, by contacting the heated first and second glass sheets with a first spray sub layer spray composition that comprises a solvent and at least one of a spray source of tin, a spray source of titanium, and a source of silicon. The first spray sub layer spray composition may further comprise a source of fluorine and/or a source of oxygen.

[0043] In an alternate embodiment of the present invention, depositing the

second heat reflecting coating comprises, before depositing the first spray main layer comprising fluorine doped tin oxide, depositing at least one first spray sub layer comprising oxides of phosphorous, boron, silicon and tin, by contacting the heated first and second glass sheets with a first spray sub layer spray composition that comprises a solvent and at least a spray source of tin, a source of phosphorous, a source of boron, and a spray source of silicon.

[0044] In an embodiment of the present invention depositing the second heat reflecting coating comprises, after depositing the first spray main layer comprising fluorine doped tin oxide, depositing a second main spray layer comprising fluorine doped tin oxide having a fluorine content that is different from the first fluorine doped tin oxide, by contacting the heated first and second glass sheets with a second main layer spray composition that comprises a spray source of tin, a spray source of fluorine, and a solvent. In particular the second main layer spray composition is free of any source of titanium. [0045] Figure 2 shows a cross section (not to size) of a glass sheet (200), bearing a first heat reflecting coating comprising, in sequence starting from the glass, an iridescence suppressing layer (211), a heat reflecting layer (212) and a reflection reducing layer (213) on one side and on the other side, in sequence starting from the glass, a first spray sub layer (201), a first spray main layer (202) and a second spray main layer (203).

[0046] In an embodiment of the present invention depositing the second heat reflecting coating comprises after depositing the first spray sub layer and before depositing the first fluorine doped tin oxide comprising main layer, and/or after depositing the first fluorine doped tin oxide main layer and before depositing the second fluorine doped tin oxide main layer, reheating the first and second glass sheets to a temperature in the range from 400 to 700°C, preferably from 550 to 650 °C.

[0047] In an embodiment of the present invention the first spray sub layer spray composition comprises a spray source of tin, a spray source of fluorine a spray source of titanium, and a solvent. In particular the first spray sub layer spray composition may comprise a spray source of tin, present in an amount of 15 wt % to 50 wt %, based on the weight of the composition; a spray source of fluorine, present in an amount of 5 wt % to 30 wt %, based on the weight of the composition; a spray source of titanium, present in an amount of 2 wt % to 15 wt %, based on the weight of the composition; and a solvent.

[0048] In an embodiment of the present invention the first spray sub layer spray composition comprises a spray source of tin, a spray source of fluoride, a spray source of titanium, and a solvent. In a particular embodiment, the spray source of tin is a tin oxide. Suitable tin oxides can be dibutyl tin oxide or dioctyl tin oxide. Other tin oxides with straight chain carbons may be suitable as well. An alternate spray source of tin may be di-n- butyltin(IV) diacetate (DBTDA, (C₄H9)₂Sn(OCOCH3) ), a monoalkyl tin tricarboxylate (such as monobutyl tin acetate), dialkyl tin dicarboxylates (such as dibutyl tin acetate), trialkyl tin carboxylate (such as tributyl tin acetate) or mixtures of all the tin sources above. The source of tin may be present in the composition in an amount of 15 wt % to 50 wt %, based on the total weight of the composition, or any subranges therebetween.

[0049] The source of fluoride can be any compound that is miscible with the

source of tin and the other components in the first spray sub layer spray composition. In one embodiment, the source of fluorine is a carboxylic acid with a fluoride group. One suitable example is trifluoro-acetic acid. The source of fluorine can be present in an amount of 5 wt % to 30 wt %, based on the total weight of the composition, or any subranges

therebetween. Alternate sources of fluorine ar tin(ll) fluoride, ammonium fluoride NH₄F, ammonium bifluoride NH₄FHF or hydrogen fluoride.

[0050] The source of titanium can be, in one embodiment, a titanium alkoxide.

One suitable example is titanium isopropoxide Ti[OCH(CH3)2]4 . The source titanium of can be present in an amount of 2 wt % to 15 wt %, based on the total weight of the composition, or any subranges

therebetween.

[0051] The source of silicon can be, in one embodiment, a silicon alkoxide. One suitable example is tetraethyl orthosilicate Si(OC2H5)4. Other suitable sources of silicon are polydimethylsiloxanes with an average chain length of up to 100 monomer units as well as alkyl-modified derivatives as well as copolymers containing them, cyclic polydimethylsiloxanes, hexafluorosilicic acid or also mixtures of these compounds. The source of silicon can be present in an amount of 2 wt % to 30 wt % based on the total weight of the composition, or any subranges therebetween.

[0052] In an embodiment of the present invention the first spray sub layer spray composition is free of chlorine. Thereby the formation of defect inducing NaCI crystals by reaction of chlorine with sodium from the glass is avoided.

[0053] In certain embodiments of the present invention, the oxygen in the first spray sub layer oxide may be provided by oxygen present in the sources of tin, titanium and/or silicon, in the solvent, in the carrier gas, and/or by adding an oxidizer to the sub layer spray composition or the carrier gas, for instance chosen among oxidizing acids, such as nitric acid or sulfuric acid, or hydrogen peroxide, ozone, pure oxygen, or ammonium nitrate. [0054] The solvent makes up the remaining amount of the first spray sub layer spray composition. In one embodiment, the solvent can be a straight-chain or branched hydrocarbon, one example of which is ethanol. Other suitable solvents are alcohols such as methanol, isopropanol, and butanol, ketones such as acetone, methyl ethyl ketone, and methyl isobutyl ketone, esters such as ethyl acetate, and butyl acetate and/or water.

[0055] Each of the source of tin, the source of fluorine, the source of titanium, and the solvent must be selected so that there is no phase separation in the first spray sub layer spray composition. There should be no solid particulate in the first spray sub layer spray composition, nor should the first composition separate into two or more distinct liquid phases, as would be the case in an emulsion.

[0056] In an alternate embodiment of the present invention, a first spray sub layer spray composition comprises a solvent and at least a spray source of tin, an optional source of phosphorous, a source of boron, and a spray source of silicon. Suitable as boron source are boric acid, trimethyl borate, triethyl borate, tripropyl borate or tributyl borate, hexafluoroboric acid and mixtures of these compounds. Suitable phosphorous sources are phosphoric acid and its dialkyl and trialkyl esters (methyl, ethyl, butyl and octyl),

orthophosphoric acid and its alkyl esters (methyl, ethyl, butyl and octyl), linear and cyclic polyphosphates, or also mixtures of the phosphorus- containing compounds named above. Suitable sources of tin and of silicon are the same as those cited for the first spray sub layer hereinabove.

[0057] In this embodiment, the source of silicon can be present in an amount of 4 wt % to 35 wt % based on the total weight of the composition, the source of boron can be present in an amount of 1 wt % to 27 wt % based on the total weight of the composition, the source of tin can be present in an amount of 8 wt % to 43 wt % based on the total weight of the composition, the source of phosphorous can be present in an amount of 0 wt % to 35 wt % based on the total weight of the composition, and the solvent can be present in an amount of 30 to 86 wt % based on the total weight of the composition. [0058] In an embodiment of the present invention the first spray main layer spray composition comprises a spray source of tin, a spray source of fluorine, and a solvent, without (i.e., is free of) a spray source of titanium. In particular the first spray main layer spray composition may comprise a spray source of tin, present in an amount of 15 wt % to 50 wt %, based on the weight of the composition; a spray source of fluorine, present in an amount of 2 wt % to 15 wt %, based on the weight of the composition; and a solvent. The second composition may be free of titanium.

[0059] In an embodiment of the present invention, the first spray main layer spray composition comprises a spray source of tin, and a spray source of fluorine and is free of any source of titanium. As discussed below, this ensures that the second composition has a lower index of refraction than the first spray sub layer spray composition, and thus the first spray main layer will have a lower index of refraction than the first spray sub layer.

[0060] The source of tin in the first spray main layer spray composition can be similar to that in the first spray sub layer spray composition. The source of tin may be present in the second composition in an amount of 15 wt % to 50 wt %, based on the total weight of the composition, or any subranges therebetween. The chemistry of the second composition can be the same as that of the first composition, with the exception that the titanium source is absent in the second composition. Furthermore, the source of tin in the second composition can be chlorinated, because first spray sub layer provides a barrier between the first spray main layer and the glass sheet. Monobutyl tin chloride is particularly useful because its pyrolysis leaves no traces of carbon in the coating.

[0061] The source of fluoride in the first spray main layer spray composition can be similar to the first spray sub layer spray composition. In one

embodiment, the source of fluorine is a carboxylic acid with a fluoride group. In one embodiment, the source of fluorine is trifluoroacetic acid.

The source of fluorine in the second composition can also be an inorganic fluoride. One suitable example is hydrofluoric acid. The source of fluorine in the second composition can be present in an amount of 2 wt % to 15 wt %, based on the total weight of the composition, or any subranges therebetween.

[0062] As with the first spray sub layer spray composition, the solvent for the first spray main layer spray composition can be a straight-chain or branched hydrocarbon such as ethanol. In one embodiment, the solvent in the first main layer spray composition may also be water. The solvent in the first spray main layer spray composition makes up the remainder of the first spray main layer spray composition. As with the first spray sub layer spray composition, the components of the first spray main layer spray

composition should be selected so that they are miscible with one another, do not induce any precipitate, or induce any phase separation.

[0063] According to certain embodiments of the present invention, the second main spray layer spray composition comprises a spray source of tin, a spray source of fluorine, and a solvent, in particular without (i.e., is free of) a source of titanium. The sources of tin and of fluorine as well as the solvent may be chosen among the same chemical components as for the first spray main layer spray composition and within the same

compositional ranges as for the first spray main layer spray composition. According to the present invention the second main spray layer spray composition is different from the first spray main layer spray composition.

[0064] In certain embodiments of the present invention, the oxygen in the first and/or second main spray layer oxides may be provided by oxygen present in the sources of tin, titanium and/or silicon, in the solvent, in the carrier gas, and/or by adding an oxidizer to the sub layer spray

composition or the carrier gas, for instance chosen among oxidizing acids, such as hypochloric acid, nitric acid or sulfuric acid, or hydrogen peroxide, ozone, pure oxygen, or ammonium nitrate.

[0065] In any embodiment of the present invention, heating and re-heating of the glass sheets may be performed by radiative or convective heating or by a combination of both radiative and convective heating. In particular heating and re-heating the glass sheets by a combination of both radiative and convective heating has the advantage of limiting heating gradients in the glass sheets that may be aggravated by differing emissivities of a glass sheet’s both sides.

[0066] In any embodiment of the present invention, cooling of the glass sheets is preferably performed with a controlled cooling rate so as to limit or avoid the formation of permanent strain in the glass sheets. Cooling of the glass may be performed by radiative and/or convective cooling. The combination of radiative and convective cooling allows for a higher cooling rate.

[0067] A glass sheet according to the invention is made of glass whose matrix composition is not particularly limited and may thus belongs to different glass categories. The glass may be a soda-lime-silicate glass, an alumino- silicate glass, an alkali-free glass, a boro-silicate glass, etc. Preferably, the glass sheet of the invention is made of a soda-lime glass or a boro-silicate glass.

[0068] According to an embodiment of the invention, the glass sheet has a

composition comprising, in a content expressed in percentages of the total weight of the glass:

Si0₂ 55 - 85%

AI2O3 0 - 30%

B2O3 0 - 20%

Na₂0 0 - 25%

CaO 0 - 20%

MgO 0 - 15%

K₂0 0 - 20%

BaO 0 - 20%.

[0069] In a preferred manner, the glass sheet has a composition comprising, in a content expressed in percentages of the total weight of the glass:

[0070] Si0₂ 55 - 78%

AI2O3 0 - 18%

B2O3 0 - 18%

Na₂0 5 - 20%

CaO 0 - 10%

MgO 0 - 10% K₂0 0 - 10%

BaO 0 - 5%.

[0071] In a more preferred manner, the glass sheet has a composition

comprising, in a content expressed in percentages of the total weight of the glass:

[0072] Si0₂ 65 - 78%

AI2O3 0 - 6%

B2O3 0 - 4%

CaO 0 - 10%

MgO 0 - 10%

Na₂0 5 - 20%

K₂0 0 - 10%

BaO 0 - 5%.

[0073] Such a soda-lime-type base glass composition has the advantages to be inexpensive even if it is less mechanically resistant as such.

[0074] Ideally, according to this last embodiment, the glass composition does not comprise B₂O3 (meaning that it is not intentionally added, but could be present as undesired impurities in very low amounts).

[0075] In an alternative manner, the glass sheet has a composition comprising, in a content expressed in percentages of the total weight of the glass:

[0076] Si0₂ 55 - 70%

AI2O3 6 - 18%

B2O3 0 - 4%

CaO 0 - 10%

MgO 0 - 10%

Na₂0 5 - 20%

K₂0 0 - 10%

BaO 0 - 5%.

[0077] Such an alumino-silicate-type base glass composition has the advantages to be more mechanically resistant but it is more expensive than soda-lime glass. [0078] Ideally, according to this last embodiment, the glass composition does not comprise B2O3 (meaning that it is not intentionally added, but could be present as undesired impurities in very low amounts).

[0079] According to an advantageous embodiment of the invention, combinable with previous embodiments on base glass composition, the glass sheet has a composition comprising a total iron (expressed in terms of Fe203) content ranging from 0.002 to 0.06 weight%. A total iron (expressed in the form of Fe203) content of less than or equal to 0.06 weight% makes it possible to obtain a glass sheet with almost no visible coloration and allowing a high degree of flexibility in aesthetic designs (for example, getting no distortion when white silk printing of some glass elements of smartphones). The minimum value makes it possible not to be excessively damaging to the cost of the glass as such, low iron values often require expensive, very pure, starting materials and also purification of these. Preferably, the composition comprises a total iron (expressed in the form of Fe₂03) content ranging from 0.002 to 0.04 weight%. More preferably, the composition comprises a total iron (expressed in the form of Fe203) content ranging from 0.002 to 0.02 weight%. In the most preferred embodiment, the composition comprises a total iron (expressed in the form of Fe203) content ranging from 0.002 to 0.015 weight%.

[0080] According to another embodiment of the invention, in combination with previous embodiments on Fe203 content, the glass has a composition comprising chromium in a content such as : 0.0001 % £ Cr203 £ 0.06%, expressed in percentages of the total weight of glass. Preferably, the glass has a composition comprising chromium in a content such as : 0.002% < Cr₂03 £ 0.06%. This chromium content allows getting a glass with a higher IR transmission and it is thus advantageous when using the glass sheet in a touch panel using optical IR touch technologies like, for example, the Planar Scatter Detection (PSD) or Frustrated Total Internal Reflection (FTIR) (or any other technology requiring high transmission of IR radiation) in order to detect the position of one or more objects (for example, a finger or a stylus) on a surface of the glass sheet. [0081] According to a preferred embodiment, the glass sheet of the invention is a float glass sheet. The term“float glass sheet” is understood to mean a glass sheet formed by the float process, which consists in pouring the molten glass onto a bath of molten tin, under reducing conditions. A float glass sheet comprises, in a known way, a“tin face”, that is to say a face enriched in tin in the body of the glass close to the surface of the sheet. The term“enrichment in tin” is understood to mean an increase in the concentration of tin with respect to the composition of the glass at the core, which may or may not be substantially zero (devoid of tin).

Therefore, a float glass sheet can be easily distinguished from sheets obtained by other glassmaking processes, in particular by the tin oxide content which may be measured, for example, by electronic microprobe to a depth of ~ 10 pm.

[0082] According to another preferred embodiment, the glass sheet of the

invention is a glass sheet formed by a slot draw process or by a fusion process, in particular the overflow downdraw fusion process. These processes, in particular the fusion process produces glass sheets whose surfaces may reach superior flatness and smoothness necessary in some applications, but they are also more expensive than the float process for large scale glass production.

[0083] The glass sheet according to the invention may have a thickness of from 0.1 to 25 mm. Particularly for the use in oven doors the glass sheet according to the invention has preferably a thickness of from 1 to 6 mm, in particular from 2 to 4 mm.

[0084] According to an embodiment of the present invention the process for

making double sided coated glass sheets further comprises, after cooling the first and second glass sheets, heat strengthening or tempering the first and second glass sheets. In particular the first and second glass sheets are transferred from the coating apparatus after cooling down, for example to a temperature in the range between room temperature and 60°C, to a glass tempering line, where the first and second glass sheets are individually heat strengthened or tempered. [0085] The first heat reflecting coating may be provided with a temporary protective coating, that can be easily removed by washing. For instance the temporary protective coating may comprise zinc oxide and may be washed after deposition of the second heat reflecting coating by washing with an acidic aqueous solution.

[0086] The invention also relates to an oven door comprising a double sided coated glass sheet obtained by a process according to the present invention.

[0087] The double coated glass sheets obtained with the process of the present invention may have any one or more of the following properties:

Haze from 0.2 to 1.5%, (ASTM standard D1003-11 with illuminant A2), Light transmission 70 to 80%, ( percentage of incident light flux, illuminant D65/2°, transmitted by the double coated glass sheet), and

hemispheric emissivity from 0.05 to 0.30.

[0088] The present invention further concerns a coating apparatus for carrying out a process of the present invention, said coating apparatus comprising a first heating chamber, at least one coating chamber, for example two or three coating chambers, and a cooling chamber, further comprising a conveyor for positioning a first and second glass sheets vertically, parallel to each other and spaced apart, with the one side of the first glass sheet facing one side of the second glass and the first and second glass sheet into and throughout the coating apparatus. The conveyor may be for example a top conveyor with clamps for holding and positioning the first and second glass sheets. The conveyor may also be a bottom conveyor supporting and positioning the first and second glass sheets, possibly with the aid of a top rail. The coating apparatus may comprise additional heating chambers in between two coating chambers, or in between every two coating chambers.

[0089] Embodiments of the invention will now be further described, by way of examples only, together with some comparative examples, not in accordance with the invention. The following examples are provided for illustrative purposes, and are not intended to limit the scope of this invention. [0090] The person skilled in the art realizes that the present invention by no means is limited to the preferred embodiments described above. On the contrary, many modifications and variations are possible within the scope of the appended claims.

Examples

[0091] First and second glass sheets may for example be coated on one side by chemical vapor deposition with any one of the heat reflecting coatings A to of table 1.

[0092] Table 1

[0093] Glass sheets coated on one side with any coatings chosen among first heat reflecting coatings A to E and coated by spray pyrolysis with a second heat reflecting coating of Sn0₂:F (about 500nm thick) from a solution comprising mono butyl tin trichloride and NH₄HF showed a hemispheric emissivity between 0.08 and 0.15 at a haze level between 1 and 3%. They also showed more uniform colors in reflectance that a comparative double sided coated glass sheet coated by spray pyrolysis on both sides with a heat reflecting coating of Sn0₂:F (about 500nm thick).

Claims

Claim 1. Process for making double sided coated glass sheets comprising, in sequence,

a. providing a first and a second glass sheet, wherein each first and second glass sheet has one uncoated side and one coated side which is provided with a first heat reflecting coating,

b. positioning the first and second glass sheets vertically, parallel to each other and spaced apart, with the first glass sheet’s coated side facing the second glass sheet’s coated side,

c. conveying the thus positioned first and second glass sheets into a coating apparatus,

d. heating the conveyed first and second glass sheets in the coating apparatus to a temperature comprised between 400 and 700°C, preferably between 550 and 650 °C,

e. depositing a second heat reflecting coating on the uncoated sides of the first and of the second glass sheet,

f. cooling the first and second glass sheets,

g. conveying the first and second glass sheets out of the coating

apparatus.

Claim 2. Process for making double sided coated glass sheets according to claim 1 , wherein the first heat reflecting coating is a chemical vapor deposition coating that comprises in sequence from the glass an iridescence suppressing layer, a first heat reflecting layer comprising tin oxide doped with fluorine and an optional reflectance reduction layer.

Claim 3. Process for making double sided coated glass sheets according to claim 2, wherein the first heat reflecting layer has a thickness in the range from 50 to 800 nm, preferably from 300 to 450 nm.

Claim 4. Process for making double sided coated glass sheets according to claim 2 or claim 3, wherein the first heat reflecting layer has an average thickness in the range from 50 to 800 nm, preferably from 300 to 450 nm and a standard deviation of the thickness of not more than 3% of the average thickness.

Claim 5. Process for making double sided coated glass sheets according to claim 2 wherein the first heat reflecting coating comprises the glass an iridescence suppressing layer, chosen among an iridescence suppressing single layer of silicon oxycarbide or silicon oxynitrides and an iridescence suppressing double layer comprising in sequence starting from the glass a first layer of titanium oxide or tin oxide and a second layer of silicon oxide, silicon oxycarbide or silicon oxynitride.

Claim 6. Process for making double sided coated glass sheets according to claim 5, wherein the iridescence suppressing layer is an iridescence

suppressing single layer of silicon oxycarbide having a thickness in the range from 55 to 95 nm and a refractive index at a wavelength of 550nm in the range from 1.65 to 1.80.

Claim 7. Process for making double sided coated glass sheets according to claim 5, wherein the iridescence suppressing layer is an iridescence

suppressing double layer comprising in sequence starting from the glass a first layer of titanium oxide or tin oxide having a thickness in the range from 5 to 30nm and a second layer of silicon oxide, silicon oxycarbide or silicon oxynitrides having a thickness in the range from 15 to 40 nm.

Claim 8. Process for making double sided coated glass sheets according to any one of claims 1 to 7, wherein depositing a second heat reflecting coating on the uncoated sides of the first and of the second glass sheet, comprises depositing, by chemical vapor deposition, in sequence starting from the glass, an optional CVD sub layer, comprising one or more of tin oxide, titanium oxide and silicon oxide and a CVD main layer, comprising fluorine doped tin oxide.

Claim 9. Process for making double sided coated glass sheets according to any one of claims 1 to 7, wherein depositing a second heat reflecting coating on the uncoated sides of the first and of the second glass sheet, comprises depositing, by pyrolytic spray deposition, in sequence starting from the glass, an optional first spray sub layer, comprising one or more of tin oxide, titanium oxide and silicon oxide, a first spray main layer, comprising fluorine doped tin oxide, and an optional second main spray layer, comprising fluorine doped tin oxide.

Claim 10. Process for making double sided coated glass sheets according to claim 9, wherein depositing the first spray sub layer comprises contacting the heated first and second glass sheets with a first sub layer spray composition that comprises a solvent and at least one of a spray source of tin, a spray source of titanium, and a spray source of silicon and optionally comprises a spray source of fluorine and/or a source of oxygen.

Claim 11. Process for making double sided coated glass sheets according to claim 9, wherein the first spray sub layer comprises oxides of phosphorous, boron, silicon and tin and wherein depositing the first spray sub layer comprises contacting the heated first and second glass sheets with a first sub layer spray composition that comprises a solvent and at least a spray source of tin, a source of phosphorous, a source of boron, and a spray source of silicon.

Claim 12. Process for making double sided coated glass sheets according to any one of claims 9 to 11 , wherein depositing the first spray main layer comprises contacting the first and second heated glass sheets with a first main layer spray composition that comprises a spray source of tin, a spray source of fluorine, and a solvent and that is optionally free of any source of titanium.

Claim 13. Process for making double sided coated glass sheets according to any one of claims 9 to 12, wherein depositing the second spray main layer comprises contacting the first and second heated glass sheets with a second main layer spray composition that comprises a spray source of tin, a spray source of fluorine, and a solvent and that is optionally free of any source of titanium and that is different from the first main layer spray composition.

Claim 14. Process for making double sided coated glass sheets according to claim 10, wherein the first sub layer spray composition comprises a spray source of tin, present in an amount of 15 wt % to 50 wt %, based on the weight of the composition; a spray source of fluorine, present in an amount of 5 wt % to 30 wt %, based on the weight of the composition; a spray source of titanium, present in an amount of 2 wt % to 15 wt %, based on the weight of the composition and a solvent.

Claim 15. Process for making double sided coated glass sheets according to claim 12, wherein the first main layer spray composition comprises a spray source of tin, present in an amount of 15 wt % to 50 wt %, based on the weight of the composition; a spray source of fluorine, present in an amount of 2 wt % to 15 wt %, based on the weight of the composition and a solvent.

Claim 16. Process for making double sided coated glass sheets according to claim 12, wherein the second main layer spray composition comprises a spray source of tin, present in an amount of 15 wt % to 50 wt %, based on the weight of the composition; a spray source of fluorine, present in an amount of 2 wt % to 15 wt %, based on the weight of the composition and a solvent.

Claim 17. Process for making double sided coated glass sheets according to any one of claims 1 to 16 wherein after cooling down the first and second glass sheets are transferred from the coating apparatus, to a glass tempering line, where the first and second glass sheets are individually heat strengthened or tempered.

Claim 18. Oven door comprising a double sided coated glass sheet provided by any one of processes of claims 1 to 17.

Claim 19. Coating apparatus comprising a first heating chamber, at least one coating chamber and a cooling chamber, further comprising a conveyor for positioning a first and second glass sheets vertically, parallel to each other and spaced apart, with the one side of the first glass sheet facing one side of the second glass and the first and second glass sheet into and throughout the coating apparatus.