Decorative coating having increased IR reflection

Abstract

A coated glass or glass ceramic substrate includes a substrate with a surface area and a coating on that surface area. The coating includes a glass matrix and IR-reflecting pigments. The IR-reflecting pigments have a TSR value of at least 20%, as determined according to ASTM G 173. The coating, at a wavelength of 1500 nm, exhibits a remission of at least 35%, as measured according to ISO 13468.

Claims

1. A coated glass or glass ceramic substrate, comprising: a substrate with a surface area; and a coating on the surface area in a laterally patterned form with a layer thickness from 3 to 35 μm and covering at least 60% of an entirety of the surface area, the coating including a glass matrix and IR-reflecting pigments, wherein the IR-reflecting pigments have a TSR value of at least 20%, as determined according to ASTM G 173, wherein, at a wavelength of 1500 nm, the coating exhibits a remission of at least 35%, as measured according to ISO 13468, wherein the surface area has no other coating containing conductive oxides selected from a group consisting of indium tin oxide, fluorine tin oxide, aluminum zinc oxide, and antimony tin oxide, wherein the IR-reflecting pigments comprise particles with a size distribution having a d50 value in a range from 0.5 μm to 2 μm, and wherein the laterally patterned form comprises a raster or dot pattern.

2. The coated glass or glass ceramic substrate of claim 1, wherein the surface area has no other coating containing any conductive oxides.

3. The coated glass or glass ceramic substrate of claim 1, wherein the substrate has no other coating containing any conductive oxides.

4. The coated glass or glass ceramic substrate of claim 1, wherein at least 65% of the surface area is coated with the coating.

5. The coated glass or glass ceramic substrate of claim 1, wherein, in a wavelength range from 1500 nm to 2500 nm, the coating exhibits a remission of at least 35%, as measured according to ISO 13468.

6. The coated glass or glass ceramic substrate of claim 1, wherein the IR-reflecting pigments comprise particles having a specific surface area in a range from 1.1 to 8 m.sup.2/g.

7. The coated glass or glass ceramic substrate of claim 1, wherein the TSR value is at least 25%.

8. The coated glass or glass ceramic substrate of claim 1, wherein the IR-reflecting pigments are selected from a group consisting of a chromium containing iron oxide, a chromium containing hematite, a chromium containing spinel, and any combinations thereof.

9. The coated glass or glass ceramic substrate of claim 1, wherein the coating has a content of less than 500 ppm of conductive oxides.

10. The coated glass or glass ceramic substrate of claim 1, wherein the coating comprises closed pores.

11. The coated glass or glass ceramic substrate of claim 10, wherein the coating is resistant to temperatures greater than 400° C.

12. The coated glass or glass ceramic substrate of claim 10, wherein the coating is substantially inorganic.

13. The coated glass or glass ceramic substrate of claim 10, wherein, in a temperature range from 20° C. to 700° C., the coating and the substrate have coefficients of thermal expansion that do not differ from one another by more than 4*10.sup.−6/K.

14. The coated glass or glass ceramic substrate of claim 1, wherein the substrate is selected from a group consisting of a soda-lime glass, a borosilicate glass, and a thermally toughened glass.

15. The coated glass or glass ceramic substrate of claim 1, wherein the glass matrix comprises 8 to 70 wt % of bismuth oxide and/or 0.1 to 0 wt % of zinc oxide.

16. The coated glass or glass ceramic substrate of claim 1, wherein the glass matrix comprises a glass composition, in wt %: TABLE-US-00018 SiO.sub.2 30-75, Al.sub.2O.sub.3  0-25, B.sub.2O.sub.3  0-30, Li.sub.2O  0-12, Na.sub.2O  0-25, CaO  0-12, MgO  0-9, BaO  0-27, SrO  0-4, ZnO  0-35, Bi.sub.2O.sub.3  0-5, TiO.sub.2  0-10, ZrO.sub.2  0-7, As.sub.2O.sub.3  0-1, Sb.sub.2O.sub.3  0-1.5, F  0-3, Cl  0-1, and H.sub.2O  0-3.

17. The coated glass or glass ceramic substrate of claim 1, wherein the glass matrix comprises a glass composition, in wt %: TABLE-US-00019 SiO.sub.2 6-65, Al.sub.2O.sub.3 0-20, B.sub.2O.sub.3 0-40, Li.sub.2O 0-12, Na.sub.2O 0-18, K.sub.2O 0-17, CaO 0-17, MgO 0-12, BaO 0-38, SrO 0-16, ZnO 0-70, TiO.sub.2 0-5, ZrO.sub.2 0-5, B.sub.i2O.sub.3 0-75, CoO 0-5, Fe.sub.2O.sub.3 0-5, MnO 0-10, CeO.sub.2 0-3, F 0-3, Cl 0-1, and H.sub.2O 0-3.

18. The coated glass or glass ceramic substrate of claim 1, wherein the IR-reflecting pigments are present in the coating in a proportion from 15 to 55 wt % and/or wherein the glass matrix is present in the coating in a proportion of from 45 to 85 wt %.

19. The coated glass or glass ceramic substrate of claim 1, wherein the IR-reflecting pigments comprise at least a first and a second IR-reflecting pigment, wherein the second IR-reflecting pigment is selected from a group consisting of a cobalt chromite spinel, an indium manganese yttrium oxide, a niobium sulfur tin zinc oxide, a tin zinc titanate, a cobalt titanate spinel, and any combinations thereof, and/or the second IR-reflecting pigment is present in the coating in a proportion from 0.75 to 18.5 wt %.

20. The coated glass or glass ceramic substrate of claim 1, wherein the coating is directly on the surface area of the substrate.

21. The coated glass or glass ceramic substrate of claim 1, wherein the substrate is configured as a door of a cooking oven or a viewing window of a fireplace.

22. An oven door, comprising: an inner glass sheet; and an outer glass sheet, wherein the outer glass sheet is a coated glass or glass ceramic substrate comprising: a substrate with a surface area; and a coating on the surface area in a laterally patterned form with a layer thickness from 3 to 35 μm and covering at least 60% of an entirety of the surface area, the coating including a glass matrix and IR-reflecting pigments, wherein the IR-reflecting pigments have a TSR value of at least 20%, as determined according to ASTM G 173, wherein, at a wavelength of 1500 nm, the coating exhibits a remission of at least 35%, as measured according to ISO 13468, wherein the surface area has no other coating containing conductive oxides selected from a group consisting of indium tin oxide, fluorine tin oxide, aluminum zinc oxide, and antimony tin oxide, wherein the IR-reflecting pigments comprise particles with a size distribution having a d50 value in a range from 0.5 μm to 2 μm, and wherein the laterally patterned form comprises a raster or dot pattern.

23. The oven door of claim 22, wherein the coating on the outer glass sheet faces towards the inner glass sheet.

24. The oven door of claim 22, further comprising an intermediate glass sheet between the inner and outer glass sheets, wherein the intermediate glass sheet is the coated glass or glass ceramic substrate.

25. The oven door of claim 24, wherein the surface area of the intermediate glass sheet has the coating on both sides of the intermediate glass sheet facing the inner and outer glass sheets.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee.

(2) The invention will now be described in more detail by way of exemplary embodiments and with reference to the figures, wherein:

(3) FIG. 1 is a schematic view showing an exemplary embodiment of a substrate coated according to the invention;

(4) FIG. 2 is a schematic view showing a comparative example of a coated substrate;

(5) FIG. 3 shows a graph of total transmittance spectra (measured according to ASTM D 1003) of several exemplary embodiments and one comparative example;

(6) FIG. 4 shows a graph of remission spectra (measured according to ISO 13468) of several exemplary embodiments and one comparative example;

(7) FIG. 5 shows a graph illustrating the shift in color coordinates of the coating depending on the coating composition;

(8) FIGS. 6 to 8 are schematic views illustrating the configuration of an oven door according to one embodiment of the invention and of comparative examples known from the prior art;

(9) FIG. 9 is a schematic view of the outer sheet of an oven door illustrating different degrees of coverage;

(10) FIGS. 10 and 11 are schematic views of the configuration of different oven doors;

(11) FIGS. 12 and 13 show thermal imaging camera photographs of an oven comprising a glass sheet coated according to the invention as an exemplary embodiment and of an oven comprising a conventionally coated glass sheet as a comparative example;

(12) FIG. 14 is a schematic diagram of the measurement setup for determining the surface temperature of the outer oven glass. By setting different temperatures, a pyrolysis process at 468° C. (875° F.) or a cooking process at 246° C. (475° F.) can be simulated.

(13) FIG. 15 is a schematic diagram of the measurement setup for determining the surface temperature of the outer oven glass during simulation of a cooking process at 450° C.;

(14) FIG. 16 is a graph of the temperature profile of the temperature of the outer oven glass of various exemplary embodiments and of the comparative example at an operating temperature of the oven of 475° F. (246° C.);

(15) FIG. 17 is a graph of the temperature profile of the temperature of the outer oven glass of various exemplary embodiments and of the comparative example at an operating temperature of the oven of 875° F. (468° C.);

(16) FIG. 18 is a graph illustrating the shift in color coordinates of the coating depending on the glass composition in the coating,

(17) FIG. 19 is a graph showing in-line transmittance profiles of various exemplary embodiments (23 to 27) and of the comparative example (22);

(18) FIG. 20 is a graph illustrating a schematic view of a substrate coated with a porous enamel as an exemplary embodiment, the porous enamel having largely isotropic pores;

(19) FIG. 21 is a schematic view of a substrate coated with a porous enamel as a further exemplary embodiment, the porous enamel having largely anisotropic pores;

(20) FIG. 22 is a graph showing the temperature profile of the measured maximum temperature of the outer oven glass of various exemplary embodiments which differ with regard to the porosity of the coating at an operating temperature of the oven of 450° C.; and

(21) FIG. 23 shows the averaged values of the temperature profiles of FIG. 22; and

(22) FIG. 24 is a graph of the measured profiles of maximum temperature of the outer oven door glass at an operating temperature of the oven of 450° C., for which the decorative layers of different layer thicknesses were applied prior to firing.

DETAILED DESCRIPTION

(23) FIG. 1 is a schematic side view showing an embodiment of a substrate coated according to the invention. In the illustrated exemplary embodiment, the coating 2 has been applied to one of the surfaces of substrate 1, while the other surface 110 of substrate 1 is not coated. Coating 2 is applied to the surface area of the substrate 1 shown in FIG. 1 in a laterally patterned manner, so that the substrate 1 has non-coated areas 120 on the coated surface 100 as well. Coating 2 may be applied in the form of a raster pattern or in the form of a dot pattern, for example. Degree of coverage of the substrate refers to the ratio of the coated surface to the entire surface 100.

(24) FIG. 2 shows a schematic view of a comparative example. Here, the entire surface of substrate 1 is provided with a coating 3 which includes conductive oxides, such as indium tin oxide. Thus, coating 3 is the IR-reflecting layer in the comparative example. Furthermore, a pigmented decorative layer 4 is applied on top of layer 3. However, in contrast to the exemplary embodiment shown in FIG. 1, layer 4 is merely a decorative layer.

(25) The making of the coated substrate as shown in FIG. 1 will now be explained in more detail below by way of an exemplary embodiment.

(26) For producing the coated substrate shown in FIG. 1, first a paste is provided comprising an IR-reflecting pigment, a glass powder, and a pasting medium. Table 1 lists several IR-reflecting pigments that have proven to be particularly advantageous. Pigment #5 is a comparative pigment.

(27) TABLE-US-00009 TABLE 1 IR-reflecting pigments and comparative example 5 Color Code BET Mean size TSR Pigment Composition Density (m.sup.2/g) (d50) (μm) (%) 1 CI Brown 29 - chromium iron oxide 5.2 1.9 1.1-1.6 25 1 2 CI Brown 29 - chromium iron oxide 5.4 2.9 0.97-1.2  27 2 3 CI Green 17 chromium green-black 5.2 2.7 1.1-1.4 25 hematite 4 CI Brown 29 - chromium iron oxide 5.1 3 1.11-1.3  29 3 5 CI Black 30 chromium iron nickel 5.3 3 1.1 13 black spinel

(28) For producing the glass powder or glass frit, the individual glass constituents are mixed, melted, and the molten glass is quenched, and a glass powder with the desired particle size and particle size distribution is obtained by grinding processes. The glass powder (layer-forming glass component) may have very different compositions. Numerous glass compositions are known, which cover a range of softening points from approximately 500° C. to 1000° C., adapted to the deformation temperature of the substrate to be coated.

(29) Table 2 shows some glass compositions or glass powders that have been found to be particularly advantageous.

(30) TABLE-US-00010 TABLE 2 Properties of the glass powders of different exemplary embodiments Glass No. Composition wt % 1 2 3 4 5 6 7 8 9 10 Li.sub.2O 0.1 0.2 3.1 0.8 4.4 1.3 4 3.1 4.4 Na.sub.2O 3.3 10.1 2.4 0.2 10 18.8 0.2 K.sub.2O 0.6 1.5 1.7 0.5 0 MgO 1.7 0.1 1 1.7 CaO 0.0 2.0 0.5 0.2 3 0.9 2 SrO 2.3 BaO 1.1 ZnO 9.6 28.0 3.4 0.1 8 8.5 2.2 B.sub.2O.sub.3 4.9 15.8 16.7 21.9 22.8 7.2 18 13.1 16.7 23.1 Al.sub.2O.sub.3 0.2 1.6 16.6 5.1 7.2 3.3 5 1 16.6 5.9 SiO.sub.2 27.0 36.0 54.4 63.4 56.0 21.2 50 50.9 54.3 57 P.sub.2O.sub.5 0.0 TiO.sub.2 2.2 5.2 0.1 1 6.3 ZrO.sub.2 0.8 1.3 2 0.5 1.1 SnO.sub.2 Bi.sub.2O.sub.3 52.0 0.1 10.0 64 9.4 F 0.2 0.9 2.2 Cl 0.8 0.5 Total 100 100 100 100 100.60 100 100 100 100.00 100 Properties glassy Transition temperature Tg ° C. ~480 550 430 474 445 490 536 578 478 Softening point SP (10.sup.7.6 dPa .Math. s) ° C. ~560 750 715 660 548 594 644 755 698 Thermal expansion α.sub.20/300 10.sup.−6/K ~12 4.40 4.1 4.8 7.3 8.6 9.7 4.4 4.8 Density g/cm.sup.3 ~2.9 2.40 2.21 2.41 4.52 2.48 2.69 2.41 2.43

(31) The glass powders listed in Table 2 have proven to be particularly advantageous with regard to processability during the process of making the coated substrate and also with regard to the optical, mechanical, and chemical properties of the corresponding coating.

(32) What is relevant, for example, in order to ensure good processability is the softening point (T.sub.SP_glass_powder) of the glass, since for flowing so as to smooth out, i.e. for producing the coating from the applied paste, the firing temperature has to equal at least the softening point SP of the glass powder. The softening point SP is the temperature at which the glass has a viscosity of 10.sup.7.6 dPa.Math.s. Depending on the geometry of the glass sheet and the heating process, deformations of glass substrates, for example, have been observed already clearly below their SP. The flowing of the glass component so as to smooth out into a layer is necessary to ensure the required chemical, physical, mechanical, and optical properties. Flowing so as to smooth out is also necessary for fixing the added pigments and other fillers or additives.

(33) Furthermore, properties such as chemical resistance to acids and bases or to hydrolytic attacks as well as cleanability and scratch resistance are important selection criteria. The glasses listed in Table 2 meet these requirements in a particularly advantageous manner.

(34) Coatings 1 to 8 listed in Table 3 were obtained from the pigments and glass powders listed in Tables 1 and 2. Example 9 is a comparative example.

(35) TABLE-US-00011 TABLE 3 Table 3: Exemplary embodiments 1 to 8 and comparative example Example 1 2 3 4 5 transparent transparent transparent transparent transparent floated soda- floated soda- floated soda- floated soda- floated soda- Substrate Unit lime glass lime glass lime glass lime glass lime glass LAYER COMPOSITION Glass (glass # 1 (80 vol %) 2 (80 vol %) 1 (90.5 vol %) 2 (80 vol %) 1 (80 vol %) from table 1) Pigment (pigment # 1 (20 vol %) 1 (20 vol %) 2 (9.5 vol %)  2 (20 vol %) 3 (20 vol %) from table 2) Coating screen screen screen screen screen printing printing printing printing printing Medium Pasting ratio weight 10:3.7 10:2.5 10:3.7 10:2.5 10:3.7 (powder:organics) Screen mesh 77 77 77 77 77 Firing laboratory laboratory laboratory laboratory laboratory oven oven oven oven oven Firing conditions ° C./min 680/15 680/15 680/15 680/15 680/15 temperature/time PROPERTIES OF COATED SUBSTRATE - SINGLE PRINT Sclerometer test 10N ok ok ok ok ok Tightness against ok ok ok ok ok ingress of fluids Layer thickness   11.7   11.3   13.0 13.7 15.3 [±1 μm) Optical thickness   2.8   4.5   3.0 4.8 3.0 Gloss (60°) 58 16 46 10 76 L*a*b* (SCE; on color 11.41/ 28.07/ 12.99/ 28.3/ 9.52/ side; black background) 2.99/0.38 0.66/−1.6 2.17/−0.15 0.47/−1.38 2.04/0.6 Temperature measured ° C.  101.4  107.5  107.5 106.7 103.8 after heating with IR lamp for 10 min PROPERTIES OF COATED SUBSTRATE - DOUBLE PRINT Sclerometer test 10N ok ok ok ok ok Tightness against ok ok ok ok ok ingress of fluids Layer thickness   28.0   25.0   25.7 24.7 27.7 [±1 μm) Optical thickness   5.4   4.9   5.7 4.85 6.01 Gloss 43 13 34 10 58 L*a*b* 13.68/ 28.38/ 15.17/ 28.43/ 11.93/ 2.41/0.24 0.56/−1.87 1.66/−0.54 0.44/−1.59 1.59/−0.31 Temperature measured ° C. 101  108  110  106.5 104.6 after heating with IR lamp for 10 min Example 6 7 8 9 transparent transparent transparent transparent floated soda- floated soda- floated soda- floated soda- Substrate Unit lime glass lime glass lime glass lime glass LAYER COMPOSITION Glass (glass # 2 (80 vol %) 1 (80 vol %) 2 (80 vol %) 1 (80 vol %) from table 1) Pigment (pigment # 3 (20 vol %) 4 (20 vol %) 4 (20 vol %) 5 (20 vol %) from table 2) Coating screen screen screen screen printing printing printing printing Medium Pasting ratio weight 10:2.5 10:3.7 10:2.5 10:3.1 (powder:organics) Screen mesh 77 77 77 43 Firing laboratory laboratory laboratory laboratory oven oven oven oven Firing conditions ° C./min 680/15 680/15 680/15 680/15 temperature/time PROPERTIES OF COATED SUBSTRATE - SINGLE PRINT Sclerometer test 10N ok ok ok ok Tightness against ok ok ok ok ingress of fluids Layer thickness 14.0 13.3 [±1 μm) Optical thickness   4.7 2.9 2.5 Gloss (60°) 15 84 82 L*a*b* (SCE; on color 29.4/ 10.01/ 14.69/ side; black background) 0.28/−1.51 1.87/−0.38 0.66/−2.41 Temperature measured ° C.  108.7 98.9 101.8 after heating with IR lamp for 10 min PROPERTIES OF COATED SUBSTRATE - DOUBLE PRINT Sclerometer test 10N ok ok ok ok Tightness against ok ok ok ok ingress of fluids Layer thickness   30.0 30.0 26.3 [±1 μm) Optical thickness   4.6 2.9 2.5 Gloss 4 65 58 L*a*b* 31.19/ 11.99/ 20.23/ 0.36/−1.21 1.52/−0.86 0.33/−2.78 Temperature measured ° C.  108.8 97.1 96.7 119  after heating with IR lamp for 10 min

(36) FIG. 3 shows the transmittance profile of exemplary embodiments 1 to 4 and of one comparative example. Here, transmittance is the total transmittance as measured according to the ASTM D1003 standard. Curve 60 corresponds to exemplary embodiment 1, curve 61 to exemplary embodiment 2, curve 62 to exemplary embodiment 3, and curve 63 to exemplary embodiment 4. The coatings were applied by screen printing in a printing process using a screen with a mesh size of 77 threads per cm in a layer thickness ranging from 11 to 15 μm.

(37) Curve 5 represents the transmittance of comparative sample 9 and was applied using a screen with a mesh size of 43 threads per cm. Here, layer thickness was greater than that of the exemplary embodiments.

(38) It is apparent here that the exemplary embodiments exhibit a transmittance which is below the transmittance of the comparative example, in particular in the longer wavelengths range of 1500 nm and above. It has to be taken into account here that the layer thickness of the comparison sample was greater than the layer thickness of the exemplary embodiments. Therefore, it can be assumed that the difference in the transmittance values between the exemplary embodiments and the comparative example would be even more pronounced for layers of the same thickness. Furthermore, curves 60 to 63 reveal that the IR-reflecting pigment which is employed has a greater impact on transmittance than the glass composition of the glass matrix. The layers of transmittance profiles 60 and 61 differ in their glass composition, but they include the same pigment. The same applies to the layers of curves 62 and 63. Samples 60 and 62, on the other hand, have the same glass composition, but differ in the pigment that was used.

(39) FIG. 4 shows the remission versus wavelength profiles of samples 7 and 8 and of comparative example 9 from table 3. The remission profiles shown in FIG. 4 corresponds to total remission measured in compliance with the ISO 13468 measurement standard. Samples 7 and 8 differ in their glass composition, but include the same IR-reflecting pigment. Curves 71 and 73 represent exemplary embodiment 7 from Table 3, the individual layers differing in terms of layer thickness. Curve 71 corresponds to the remission profile of exemplary embodiment 7, the coating was applied by two printing processes using a screen with a mesh size of 77 threads per cm, and the layer has a thickness of 24 to 28 μm. The layer of curve 73 was applied by a single printing process and has a thickness of 11 to 15 μm. The same applies to the relationship between curves 72 and 74 which represent embodiment 8 from Table 3. The layer corresponding to the remission profile represented by curve 72 has a thickness of 24 to 28 μm, and the layer corresponding to the remission profile represented by curve 74 has a thickness of 11 to 15 μm. With these layer thicknesses, stresses relax even in the case of larger differences in thermal expansion without causing chipping or strength issues.

(40) What becomes clear from FIG. 4 is that the layers according to the invention exhibit a remission in the IR range, which is significantly higher than the remission of the comparative example, in particular in the range of 1500 nm and above which is relevant for remission of heat radiation at temperatures in the range from 200 to 475° C. Furthermore, it becomes clear that the glass composition also has an impact on remission in the IR range, this impact increasing with increasing layer thickness of the coating.

(41) FIG. 5 shows the influence of different pigments in the coating on the color coordinates of the coating as determined in compliance with measurement standard EN ISO 11664-4 using a D65 light source and measured on the colored side. Reference numeral 80 indicates the color coordinates of a coating according to exemplary embodiment 8 from the table. The coating was applied to the substrate by a simple printing process using a screen with a mesh size of 77 threads per cm with a nominal thread diameter of 55 μm and has a layer thickness of 11 to 15 μm. The color coordinates of sample 80 are shifted into the yellow color space. Compared to this, samples 81 and 82 show a slight yellow shift, in particular sample 81 shows a strong offset from sample 80 towards the neutral range. This shift in color coordinates is caused by adding a second IR-reflecting pigment. Table 4 shows the pigment compositions of coatings 80 to 82.

(42) TABLE-US-00012 TABLE 4 Pigment composition of the layers shown in FIG. 5 Percentage of Percentage of First IR- first IR second IR reflecting pigment in the Second IR pigment in the Sample pigment coating pigment coating 80 CI Brown 29-3 20 vol % — — (chromium iron oxide) 81 CI Brown 29-3 15 vol % CI Pigment Blue 5 vol % (chromium iron oxide) 86 (cobalt chromite blue-green spinel) 82 CI Brown 29-3 15 vol% CI Pigment Blue 5 vol % (chromium iron oxide) 36 (indium manganese yttrium oxide)

(43) FIG. 6 is a schematic view illustrating the arrangement of the glass sheets in a cooking oven door as known from the prior art. Here, the oven door comprises three thermally toughened glass sheets 8, 9, and 10, with glass sheet 8 being the outer sheet and 10 being the inner glass sheet. Thus, glass sheet 10 faces the interior of the oven and glass sheet 8 delimits the oven door to the outside.

(44) Sheets 8 and 9 have additional coatings 3, 4 on one or two of the surfaces of the glass substrate 1. In the present case, the outer sheet 8 has a two-layer coating on the side facing the interior of the oven, including a coating 3 comprising a transparent conductive oxide, and a decorative layer 4 deposited thereon. Decorative layer 4 is an enamel layer and contains a black or brown pigment in a glass matrix. Layer 4 functions as a purely decorative layer, backscattering of the heat radiation emanating from the oven's interior is only or almost exclusively caused by the oxide layer 3. The intermediate sheet 9 has an oxide layer 3 on both sides thereof, for increasing the backscattering of heat radiation into the oven's interior.

(45) FIGS. 7 and 8 are schematic views illustrating the glass sheet assemblies of ovens according to two exemplary embodiments of the invention. The glass substrate 1 without coating preferably exhibits a light transmittance Y of more than 5%, preferably more than 20%, and most preferably more than 80%, as measured using standard illuminant C/2°. Light transmittance Y is measured in the CIE color system. This value is valid regardless of the thickness of the substrate, which can usually be between 2 and 10 mm. The substrate material may be transparent, transparently stained by coloring oxides, or may have a translucent appearance caused by light scattering. In glass ceramic substrates or ceramic substrates, such light scattering may be caused by the presence of scattering crystals in the substrate material, for example.

(46) In a preferred embodiment, the substrate material consists of a silicate glass (SiO.sub.2 content >40 wt %). Advantageously, a float glass sheet made of commercially available soda-lime glass is used as the substrate, here. Such soda-lime glass sheets are available in different qualities, depending on the iron content. Most preferably, the soda-lime glass sheet is thermally toughened. In a further preferred embodiment, the float glass sheet is made of borosilicate glass, such as, for example, float glass types BOROFLOAT® 3.3, or BOROFLOAT® 4.0 from SCHOTT AG.

(47) The exemplary embodiment shown in FIG. 7 differs from the configuration shown in FIG. 6 in that the coating of the outer glass sheet 8 comprises only one layer 2. Layer 2 contains an IR-reflecting pigment with a TSR value of at least 20% and a remission of at least 35% at a wavelength of 1500 nm. Here, layer 2 not only functions as a decorative layer, but also provides for efficient backscattering of the heat radiation into the interior of the oven, so that an additional layer 3 with transparent conductive oxides can be dispensed with. FIG. 8 shows a refinement of the invention in which the oxide layers 3 on the intermediate sheet 8 have also been replaced by the layer 2 according to the invention.

(48) Measurements have revealed that a substrate coated according to the invention is outstandingly suitable for use as the outer glass sheet of an oven door that comprises a plurality of glass sheets. For this purpose, a substrate coated accordingly was installed in an oven as the outer glass sheet, and the surface temperature was determined on the outer surface of the glass sheet (FIG. 14). The respective surface temperatures of the glass sheets were determined using an IR camera from Fluke, and a corresponding IR thermal image was recorded at intervals of one minute. The distance between the thermal imaging camera and the outer sheet of the oven door was 203.2 cm. The corresponding temperatures were determined from the thermal images obtained in this way. In the test setup, the oven volume was 28.317 l, or 5.3 ft.sup.3. The measurements were taken for an oven internal temperature of 875° F. (468° C.), and 475° F. (246° C.) in each case. In addition, comparative measurements were performed, in which a glass substrate with an enamel coating 4 including a conventional black pigment was used as the outer glass sheet.

(49) FIG. 15 illustrates a laboratory measurement setup. Here, the respective surface temperatures of the glass sheets were determined using a pyrometer 39 (impac, IE 120/82L), the focal point was placed on the outer surface of the decorated glass sheet, and a respective measured value was recorded every minute. The distance of the pyrometer 39 to the outer glass sheet of the oven door was 50 cm. The volume of the oven was 30×12×12 cm in the test setup. The distance from the decorated glass sheet to the oven was 2 cm, the opening of the oven had a diameter of 3 cm. The measured sheets were coated over the entire surface thereof.

(50) FIG. 9 is a schematic view showing the coverage of the outer sheet of the exemplary embodiment with the respective decorative layer. The outer sheet has dimensions of 29.0 by 20.1 inches. In the peripheral area of the sheet, the respective decorative coating was applied in the form of a full-surface frame 15, the frame 15 leaving a viewing area 16 with dimensions of 20 by 9.75 inches. In this viewing area 16, the decorative layer is applied in the form of a raster pattern 17. In addition, comparative measurements were performed, in which a glass substrate with an enamel coating 4 including a conventional black pigment was used as the outer sheet.

(51) FIGS. 10 and 11 are schematic views showing the respective configuration of the oven door of the exemplary embodiment (FIG. 10) and of the comparative example (11). In both cases, the non-coated side of the substrate faces outwards. In each case, both the intermediate and the inner sheets of the oven door are coated with a coating 3 on one surface thereof. Coating 3 comprises transparent conductive oxides.

(52) Once the respective sheets had been installed, the oven was brought to an operating temperature of 246° C. or 468° C., respectively, and the temperature was determined at several points on the outer surface of the outer glass sheet of the oven.

(53) FIG. 12 shows the photograph of a thermal imaging camera of an outer oven door comprising an outer glass sheet according to the invention, after an operating time of 180 minutes while the oven was heated to 468° C. Here, the comparatively high temperatures at the upper edge of the door and in the middle near the lower edge area can be explained by heat loss due to the experimental setup and also arise in the photograph of a thermal imaging camera of the comparative example as shown in FIG. 13.

(54) FIG. 14 schematically shows a variant of a measurement setup for determining the outside temperature of the oven door. Here, a typical household oven with a volume of 28.3171 or 5.3 ft is heated to 246° C. (maximum operating temperature in cooking mode) or to 468° C. (maximum operating temperature in pyrolysis mode). In this measurement setup, the oven door comprises three sheets, the inner two glass sheets each having a low-E coating 3. The coatings 3 are deposited on the surfaces of the two inner glass sheets facing one another. In the examined exemplary embodiments, the outer glass sheet had a coating 2 comprising an IR-reflecting pigment, and the coating 2 was applied to the surface of the glass sheet facing the interior of the oven. The respective surface temperatures of the glass sheets were determined using an IR camera 28 from Fluke, and a respective IR thermal image was recorded at intervals of one minute. The distance between the thermal imaging camera and the outer sheet of the oven door was 203.2 cm. The corresponding temperatures were determined from the thermal images obtained in this way. The volume of the oven was 28.317 l, or 5.3 ft.sup.3, in the test setup.

(55) FIG. 15 schematically shows a measurement setup for determining the surface temperatures of a coated glass sheet under laboratory conditions. In this case, a laboratory oven 31 is heated to a temperature of 450° C. The oven has an opening with a diameter of 3 cm. The glass sheet 1 with the coating 2 to be measured is placed at a distance of 3 cm from this opening with the coating 2 facing the opening of the oven. The surface temperature of the coated glass sheet 1 is determined using a pyrometer 34 (impac, IE 120/82L). The pyrometer 39 is arranged behind the decorated glass substrate 30 to be measured and at a distance of 50 cm from the glass sheet 1 to be measured.

(56) FIG. 16 and FIG. 17 show temperature profiles of the outer surface of several oven doors as a function of operating time, the individual oven doors only differing in the coating of the outer glass sheet. The surface temperatures were determined using the measurement setup shown in FIG. 14, the oven temperature was 246° C. (FIG. 16) and 468° C. (FIG. 17), respectively.

(57) Curve 11 represents the comparative example shown in FIGS. 10 and 12. Curves 12 to 15 and 18 and 19 represent different exemplary embodiments which differ in terms of their pigment content, degree of coverage, and the pattern of the applied decorative coating, and which will be described in Table 5.

(58) The raster pattern has a diameter of 1 mm (small holes) with a total degree of coverage of the layer of 64%, and a diameter of 2 mm (big holes) with a total degree of coverage of the layer of 67%. The reference door has a raster pattern with a diameter of 1.5 mm and a total degree of coverage of the layer of 63%

(59) Table 5 shows the layer compositions of the exemplary embodiments according to curves 12, 13, 14, 15, 18 and 19. Within the viewing area, the glass sheets have a dot pattern with round non-coated areas, also referred to as holes below. Dot raster patterns or dot patterns with different hole sizes were used.

(60) In the dot raster patterns with small holes, the non-coated areas, i.e. the holes in the coating, have a diameter of 1 mm. In this design variant, the outer surface of the glass sheet with the coating has a degree of coverage of 64%.

(61) In the case of dot raster patterns with large holes in the dot raster pattern, the holes or non-coated areas in the dot raster pattern have a diameter of 2 mm. Here, the outer surface of the glass sheet has a degree of coverage of 67%.

(62) In FIG. 16 and in FIG. 17, curve 12 is the temperature profile of sample 1 from table 5 with big holes in the deposited decorative raster pattern, curve 13 is the temperature profile of sample 10 from table 5, curve 14 is the temperature profile of sample 1 from Table 5 with small holes in the deposited decorative raster pattern, curve 19a (only in FIG. 16) corresponds to sample 9 from Table 5 with big holes in the deposited decorative raster pattern, curve 18 is the temperature profile of sample 4 from Table 5, and curve 19 is the temperature profile of sample 3 from table 5.

(63) TABLE-US-00013 TABLE 5 Exemplary/comparative examples for the temperature measurements of FIGS. 16 and 17 Example SAMPLE 1 SAMPLE 2 SAMPLE 3 SAMPLE 4 SAMPLE 5 SAMPLE 9 SAMPLE 10 transparent transparent transparent transparent transparent transparent transparent floated soda- floated soda- floated soda- floated soda- floated soda- floated soda- floated soda- Substrate Unit lime glass lime glass lime glass lime glass lime glass lime glass lime glass LAYER COMPOSITION Glass (glass # 2 (80 vol %) 2 (60 vol %) 2 (70 vol %) 2 (80 vol %) 2 (70 vol %) 2 (82.5 vol %) 2 (82.5 vol %) from table 1) Pigment (pigment # 4 (20 vol %) 4 (40 vol %) 4 (30 vol %) 3 (20 vol %) 3 (30 vol %) 4 (17.5 vol %) 3 (17.5 vol %) from table 2) Coating screen screen screen screen screen screen screen printing printing printing printing printing printing printing Medium Pasting ratio wt % 10:3.1 10:3.1 10:3.1 10:3.1 10:3.1 10:3.1 10:3.1 (powder:organics) Viscosity (immersion-type cPoise 12,000 not 10,000 11,000 11,000 13,000 11,000 rotational viscometer) measured Screen mesh 77 77 77 77 77 77 77 Firing tempering tempering tempering tempering tempering tempering tempering furnace furnace furnace furnace furnace furnace furnace PROPERTIES OF COATED SUBSTRATE - SINGLE PRINT Sclerometer test 10N ok not ok (limit) ok (limit) ok ok (limit) ok ok Layer thickness [+/−1 μm) 15.0   14.0 14.5 15.5 11.0 17.0 16.0 Optical thickness 2.6   3.2 3.1 2.8 3.6 2.1 2.5 Gloss (60°) 11 3 14 2 L*a*b* (SCE; 25.6/ 8.04/ 11.2/ 25.8/ 10.1/ 28.6/ 26.9/ on glass side) 0.43/0.73 0.35/0.97 0.08/0.71 0.37/1.04 0.1/1.07 0.05/−0.48 0.12/−0.14 Temperature (Tmax) ° F. small holes: not big holes: big holes: big holes: big holes: measured after heating 155.8° F. measured 158.6° F. 159.7° F. 159.2° F. 159.0° F. for 180 min in oven big holes: test 162.7° F.

(64) For all samples, the temperature was measured in measuring area 15 (see FIGS. 12 and 13). Measuring area 15 is the surface area with the comparatively highest temperature.

(65) From FIG. 16 it is apparent that in the exemplary embodiments temperature rises sharply within the measuring area during an operating time of up to about 60 minutes, and after that the temperature does not or only slightly increases. For all the exemplary embodiments, the measured surface temperatures are below the corresponding temperatures of the comparative example.

(66) FIG. 17 shows the temperature versus time profile for an oven temperature of 468° C., i.e. for the pyrolysis mode of the oven, and thus simulates the temperature profile during a pyrolysis process. Here, again, the measured temperatures initially rise steeply within the first 60 minutes and then approach a largely constant value. This value is below the temperature of the comparative example for all of the exemplary embodiments. Even for an operating time of more than 160 minutes, the exemplary embodiments show a maximum temperature of less than 75° C. or less than 165° F. in the measurement area. Furthermore, from curves 12 and 14 it becomes obvious that coated glass sheets with a high degree of coverage will heat up less than corresponding glass sheets with a lower degree of coverage. Curve 12 represents a glass sheet having a raster pattern with which a higher degree of coverage can be achieved than with the glass sheet design with temperature profile 14.

(67) The glass sheets of curves 12 and 19 differ in terms of the pigment content in the coating. Curve 12 represents sample 1 and curve 19 represents sample 3 from table 5. Surprisingly, FIG. 17 shows that coatings with pigment contents of 20 vol % (curve 12) in the coating have a better temperature behavior than sample 3 (curve 19) with a pigment content of 30 vol %. This can be explained by the fact that when making such coatings with high pigment contents, the proportion of IR-reflecting pigments in the corresponding coating is so high that during the firing process a large part of the heat radiation is reflected in the paste by the IR-reflecting pigments and the heat is therefore not available to melt the glass powder or to form a uniform glass flux. This becomes also evident from the scratch resistance of the fired layers. With 30 vol % of pigment, a test with the 10 N sclerometer is just passed. This in turn may have an adverse effect on the optical properties of the layer. Also, homogeneity of the layer or its mechanical or chemical resistance may be adversely affected by an excessive pigment content in the coating. Therefore, preferably, the coating has a pigment content of 10 to 25 vol %, preferably 12 to 20 vol %.

(68) TABLE-US-00014 TABLE 6 Temperatures of the embodiments shown in table 5, as determined in cooking mode (246° F.) and pyrolysis mode (875° F.) Sample 1 3 4 9 10 Standard door Temperature measured near 105° F. — — 106° F. 100° F. 106° F. the edge after heating for 180 minutes at 475° F./246° C. Temperature measured in 101° F. — — 103° F. 96° F. 104° F. the center of the glass sheet after heating for 180 minutes at 475° F./246° C. Temperature measured near 142° F. 139° F. 140° F. 140° F. 139° F. 146° F. the edge after heating for 180 minutes at 875° F./468° C. Temperature measured in 147° F. 142° F. 146° F. 144° F. 146° F. 155° F. the center of the glass sheet after heating for 180 minutes at 875° F./468° C.

(69) Table 6 summarizes the results of the temperature measurements shown in FIGS. 16 and 17 and gives the surface temperature of the glass sheet after heating for a duration of 180 minutes at 246° C. and 468° C., respectively. Samples 1, 3, 4, 9, and 10 correspond to the samples 1, 3, 4, 9, and 10 listed in Table 5. The comparative sample is a standard oven door, i.e. with normal black pigments. Table 6 shows that the exemplary embodiments exhibit a better insulation effect than the standard door. For example, in the exemplary embodiments the surface temperature measured after 180 minutes at the operating temperature is below the corresponding temperature of the standard oven door in each case. This applies to a heating temperature of 475° F., or 246° C., which simulates the cooking mode, as well as for a heating temperature of 875° F., or 468° C., which corresponds to the temperature in pyrolysis mode. Thus, it can be concluded from Table 6 that the IR-reflecting coating according to the invention is at least equal in terms of its insulating effect to the conventional coatings with transparent conductive oxides.

(70) FIG. 18 shows the influence of different glass compositions in the coating on the color coordinates of the coating, as determined using a D65 light source and measured from the color side in compliance with the EN ISO 11664-4 measurement standard. The samples within zone 21 represent coatings with a zinc-based glass matrix, the samples within zone 20 include a bismuth containing glass matrix. It becomes clear from FIG. 18 that coatings with zinc-based glasses exhibit a shift to yellow color coordinates, while the coatings of regime 20 are shifted to blue color coordinates.

(71) FIG. 19 shows in-line transmittance profiles of several exemplary embodiments (23 to 27) and of the comparative example (22). For in-line transmittance, only the light that passes through the measurement sample at a forward scattering angle of 5° is directed onto the detector, which means that scattered components are not shown in the measurement curve. It is apparent, here, that the in-line transmittance of the exemplary embodiments is below the transmittance of comparative example 22. The substrates coated according to the invention preferably exhibit an in-line transmittance of not more than 0.01% for the wavelength range between 1.5 μm and 4.5 μm.

(72) FIGS. 20 and 21 schematically illustrate embodiments in which the coating 2 deposited on the glass 1 includes pores, 32 and 33, respectively. In both cases, these are closed pores. FIG. 20 shows an embodiment with largely spherical pores 32. Such pores may be obtained by using calcium carbonate as a blowing agent, for example. In contrast, the pores 33 shown in FIG. 21 have an elliptical cross-sectional shape and hence an anisotropic structure. Pores with such a shape may be obtained by using rice starch as a blowing agent, for example.

(73) The pores may be of different size and shapes, i.e., more generally, are not limited by the example schematically illustrated here and need not be spherical.

(74) TABLE-US-00015 Pore former Pore size (μm) Pore shape CaCO.sub.3   5-30 roundish Sodium hydrogen   5-30 roundish phosphates Rice starch 0.1-5 elongated Potato starch  10-15 ovoid potato-shaped Wheat starch   2-10 grain-shaped

(75) FIGS. 22 and 23 show temperature profiles of the outer surface of several oven doors as a function of operating time for different exemplary embodiments. The individual oven doors differed only in the coating of the outer glass sheet. For FIGS. 22 and 23, a laboratory oven was heated to a temperature of 450° C. and subsequently the surface temperature of the coated glass sheet was determined as a function of operating time using the measurement device shown in FIG. 15.

(76) FIG. 22 shows the maximum temperatures measured in this way, as a function of operating time of the oven. FIG. 23 shows a fit obtained by averaging (logistic curve fit with 3 parameters) of the temperature profiles shown in FIG. 22.

(77) Curves 13, 14, and 15 (as samples 1, 9, 10 also measured in the form of a printed oven door, see above) correspond to temperature profiles of exemplary embodiments in which the IR-reflecting coating is largely free of pores, and curves 34 to 37 are temperature profiles of embodiments with porous IR-reflective coatings.

(78) The individual exemplary embodiments are characterized in more detail in Table 7.

(79) TABLE-US-00016 TABLE 7 Characterization of the samples shown in FIGS. 22 and 23 Blowing Type of T.sub.max (° C.) Optical density L*a*b* (SCE; Pigment agent blowing after 1 h (glass side (coated side Gloss Sclerometer Sidolin test Curve (vol %) (vol %) agent at 450° C. facing upwards) facing upwards) (60°) (10N) (porosity) 13 20 0 N/A 47.6 2.6 34.63/0.45/−3.71 18.5 ok very good 14 17.5 0 N/A 46.9 2.1 36.04/0.44/−4.09 55.9 ok very good 34 17.5 20 CaCO.sub.3 43.8 2.2 34.63/0.45/−3.71 4.0 ok good 35 17.5 10 CaCO.sub.3 43.2 2.6 31.58/0.49/−3.56 17.5 ok good 36 17.5 20 rice starch 45.7 2.1 21.38/0.6/−1.75 41.0 ok very good 37 17.5 10 rice starch 45.4 2.6 18.56/0.65/−1.95 50.5 ok very good

(80) Samples 13 and 14 correspond to the exemplary embodiments shown in FIGS. 16 and 17. The coatings of these exemplary embodiments were produced without using blowing agents. Samples 34 to 37, by contrast, are porous coatings. For producing these coatings, blowing agents were used as listed in table 7, and therefore the coatings obtained in this way include closed pores. All of the temperature profiles shown in FIGS. 22 and 23 were obtained using the measurement setup shown in FIG. 15. The respective coating compositions were applied to the substrate by screen printing using a 77/55 T screen.

(81) From FIG. 23 it is apparent that even after the oven has been in operation for one hour at 450° C., the temperature determined on the outer surface of the glass sheet is below 50° C. With the exemplary embodiments 34 to 37 in which the IR-reflecting pigments are provided within an enamel that has closed pores, this maximum temperature can be further reduced. It is assumed that the pores within the coating represent structures on which the IR radiation can additionally be scattered.

(82) The manifestation of this positive effect for the maximum surface temperature of the glass sheet depends on the shape of the pores. The blowing agent used in samples 36 and 37 was rice starch, while CaCO.sub.3 was used in samples 34 and 35. When rice starch is used as a blowing agent, anisotropic pores with an ellipsoidal cross section will preferably be formed, while the use of CaCO.sub.3 as a blowing agent leads to largely spherical pores.

(83) FIG. 23 shows that for the coated glasses 34 and 35 which have pores of spherical or largely spherical shape, the insulation effect is higher than for the coated glasses 36 and 37 that have a coating with ellipsoidal or rice-shaped pores.

(84) FIG. 23 moreover shows that the percentage of blowing agent in the paste has an impact on the IR reflection of the corresponding coating. Samples 34 and 35 only differ in their content of blowing agent. While the amount of blowing agent in the paste for producing coating 34 is 20 vol %, the corresponding paste for producing coating 35 contains only 10 vol % of CaCO.sub.3 as the blowing agent. Sample 35 exhibits a better insulation effect than sample 34, so that under comparable conditions and after an operating time of 180 minutes the maximum temperature of sample 35 is lower than the maximum temperature of sample 34 by 0.8° C.

(85) An excessive amount of blowing agents in the paste results in a formation of so many pores that they in part combine so that open pores are created. An indication of open pores is an uneven surface associated therewith. It is assumed here that closed pores promote IR reflectance.

(86) If the substrate is in the form of a transparent, non-volume-stained substrate, the barrier effect of the coating can, for example, be determined by a test in which a drop of a fluid medium such as water is applied to the coating and allowed to act for at least 10 seconds and is then wiped off, and the test is passed if the area of action of the drop is not discernable as such when the coating is viewed through the substrate.

(87) Such test procedures are generally known under the term visual inspection and are based on the relevant standards, such as DIN EN 1330-10, DIN 25435-2, and DIN EN 13018. In the present case, direct or indirect visual inspection by an inspecting person is preferred. In the case of direct visual inspection, the inspection is performed with a non-interrupted beam path between the eye of the inspecting person and the surface to be tested, whereas in the case of an indirect visual inspection, the beam path is interrupted by capturing the surface to be tested by suitable photo or video equipment. Furthermore, local visual inspection in compliance with DIN EN 13018 is preferred, which defines minimum illuminance, a distance to the surface to be tested, and a viewing angle of the inspecting person.

(88) The minimum illuminance employed for the inspection is at least 500 lx on the test surface from a distance of less than 600 mm. The viewing angle of the examiner is at least 30°. The examiner preferably satisfies the requirements set out in the relevant standards, such as DIN EN 13018 and EN 473.

(89) Such a test procedure is particularly preferred because it can be easily adapted to the respective fields of application of the coated glass or glass ceramic substrates. For example, the duration of exposure is usually chosen as a function of the considered fluid medium and may also be more than 10 seconds.

(90) For the purposes of the present disclosure, fluids preferably include liquids, in particular water, aqueous liquids, alcohols, liquids based on these liquids or liquids comprising these liquids, such as glass cleaning agents, and/or oils, and water vapor.

(91) A preferred procedure for carrying out a visual inspection by an inspecting person as explained above with the aim of determining water-tightness or moisture-tightness of a coating according to the present disclosure comprises the steps of: applying a liquid, in particular a drop thereof, onto a surface area of the coating of the substrate; allowing the liquid to act for a duration of 15 seconds; wiping off residual moisture of the liquid using a dry cloth; turning over the substrate so that the coating is disposed on the side of the substrate facing away from the inspecting person; and verifying, by visual inspection, whether a color change is recognizable in this area or in an area adjacent to this area, wherein

(92) a) the visual inspection is performed under daylight according to standard illuminant D65 or under lighting of an incandescent lamp, compact fluorescent lamp, fluorescent lamp, or light-emitting diode;

(93) b) illuminance is at least 500 lx at a distance of less than 600 mm from the coating, i.e. from the inspected area; and

(94) c) the viewing angle of the inspecting person is between 5° and 90°, preferably at least 30°, wherein when the coating is viewed through the substrate, the area of action of the drop is not disruptively noticeable and in particular not discernable as such.

(95) The visual inspection mentioned above, which is also referred to as a “Sidolin test” in the table above, comprises in particular the examination of whether a water mark and/or a water stain is visible from the side of the substrate opposite the coated side. In the test listed in the table above, glass cleaner was used as the test liquid.

(96) Here, a layer is characterized as very good, if it exhibits no color change on the front side nor on the rear side when inspected. A layer is characterized as good in the present case, if it exhibits no color change on the front side and shows a wipeable border on the rear side in the test. Another way of increasing IR reflectance of the coating is to increase layer thickness, for example by repeatedly applying the corresponding paste or suspension to the substrate.

(97) FIG. 24 shows the influence of the layer thickness of the applied coating on the IR reflectance thereof. Here, samples 14 (non-foamed coating as comparison sample), 34, and 38 were applied to the substrate by screen printing using a 77T screen. The coatings of samples 14 and 34 were applied in a single print, the coating of sample 38 was applied to the substrate as a double print, by two printing processes. Samples 34 and 38 differed only in the number of printing processes. It can be seen here that the maximum temperature can be reduced by more than 2° C. by increasing the layer thickness. Further measurement results are described in the table below which indicates the number of printing processes (single or double print) and the maximum temperature determined with the measurement setup shown in FIG. 15 on the outer surface of the glass sheet after 60 minutes of operation of the oven at a temperature of 450° C.

(98) TABLE-US-00017 T.sub.max (° C.) Percentage Percentage after 1 h Optical density L*a*b* Sample Number of pigment of blowing Blowing of heating (glass side (coated side Gloss Sclerometer Sidolin test ID of prints [vol %] agent [vol %] agent used at 450° C. facing upwards) facing upwards) (60°) (10N) (porosity) 34 1 17.5 20 CaCO.sub.3 43.8 2.2 34.63/0.45/−3.71 4.0 ok good  34a 2 17.5 20 CaCO.sub.3 41.3 3.2 36.04/0.44/−4.09 1.4 ok good 36 1 17.5 20 rice starch 45.7 2.1 21.38/0.6/−1.75 41.0 ok very good  36a 2 17.5 20 rice starch 45.2 4.2 23.49/0.42/−2.15 35.4 ok very good 37 1 17.5 10 rice starch 45.4 2.6 18.56/0.65/−1.95 50.5 ok very good  37a 2 17.5 10 rice starch 44.9 4.7 19.86/0.40/−2.38 48.9 ok very good