Glass or glass ceramic substrate provided with a decorative coating and method for producing same

Abstract

Glass or glass ceramic substrates are provided that have a decorative coating. Methods for coating a glass or glass ceramic substrate with a decorative coating are also provided. In the method, a first, textured layer is applied which is filled with a further layer, so that a layer material of graded composition is formed.

Claims

1. A coated glass ceramic substrate, comprising: a substrate made of glass ceramic having a top surface and a bottom surface, the top surface being configured as a cooktop; a first layer on the bottom surface of the substrate, the first layer including pigment particles embedded in a glass flux, the first layer having a textured surface that has a maximum texture depth from 0.1 to 5 μm that is more than 40% of a maximum thickness of the first layer; and a second layer on the first layer, the second layer at least partially filling the textured surface of the first layer so that the second layer is merged into the first layer with components of the first and second layers being hardly distinguishable from one another in a scanning micrograph, wherein the first layer comprises pigments in a proportion of more than 50% by weight.

2. The coated glass ceramic substrate of claim 1, wherein the second layer is a polymeric layer.

3. The coated glass ceramic substrate of claim 2, wherein the polymeric layer includes colorants or pigments.

4. The coated glass ceramic substrate of claim 1, wherein the first and second layers form a gradient layer that is black.

5. The coated glass ceramic substrate of claim 1, wherein the second layer is selected from a group consisting of a polysiloxane, polysilsesquioxane, polyurethane, epoxy-functionalized silicone resin, polyester-functionalized silicone resin, and a sol-gel.

6. The coated glass ceramic substrate of claim 1, wherein the second layer comprises pigments in a proportion of more than 50% by weight.

7. The coated glass ceramic substrate of claim 6, wherein the pigment particles of the first layer comprise metal oxide particles, and wherein the first layer further comprises an inorganic material.

8. The coated glass ceramic substrate of claim 1, wherein the pigment particles of the first layer have a mean particle size of more than 0.25 μm.

9. The coated glass ceramic substrate of claim 1, wherein the first and second layers individually exhibit a lightness L in the Lab color space of more than 29.0, and wherein the first and second layers combined exhibit a lightness L of less than 28.0.

10. The coated glass ceramic substrate of claim 1, further comprising a further textured layer below the first layer.

11. The coated glass ceramic substrate of claim 10, wherein the further textured layer is omitted in at least one area.

12. The coated glass ceramic substrate of claim 1, wherein the first layer further comprises filler particles.

13. The coated glass ceramic substrate of claim 1, wherein the first layer has a closed porosity of less than 30%.

14. The coated glass ceramic substrate of claim 1, wherein the second layer has a gloss level of G1 according to EN ISO 2813 when viewed through the substrate from a side opposite the first and second layers.

15. A cooktop comprising the coated glass ceramic substrate of claim 1.

16. The cooktop of claim 15, comprising a display area and/or a hob, wherein the first and second layers are left out of the display area and/or the hob.

17. The coated glass ceramic substrate of claim 1, wherein the textured surface further comprises cracks, wherein the second layer at least partially fills the textured surface and the cracks so that the second layer is merged into the first layer.

18. The substrate of claim 1, wherein the substrate is made of a zero-expansion material.

19. A coated glass ceramic substrate, comprising: a substrate made of glass ceramic having a top surface and a bottom surface, the top surface being configured as a cooktop; a first layer on the bottom surface the substrate, the first layer including pigment particles embedded in a glass flux, the first layer having a textured surface that has a maximum texture depth from 0.1 to 5 μm that is more than 40% of a maximum thickness of the first layer; and a second layer on the first layer, the second layer at least partially filling the textured surface of the first layer so that the second layer is merged into the first layer with components of the first and second layers being hardly distinguishable from one another in a scanning micrograph, wherein the second layer is selected from a group consisting of a polysiloxane, polysilsesquioxane, polyurethane, epoxy-functionalized silicone resin, and polyester-functionalized silicone resin, wherein the first layer comprises pigments in a proportion of more than 50% by weight.

20. The substrate of claim 19, wherein the substrate is made of a zero-expansion material.

21. A coated glass ceramic substrate, comprising: a substrate made of glass ceramic having a top surface and a bottom surface, the top surface being configured as a cooktop; a first layer on the bottom the substrate, the first layer including pigment particles embedded in a glass flux, the first layer having a textured surface comprising cracks; and a second layer on the first layer, wherein the second layer at least partially fills the textured surface and the cracks so that the second layer is merged into the first layer with components of the first and second layers being hardly distinguishable from one another in a scanning micrograph.

22. The substrate of claim 21, wherein the second layer is selected from a group consisting of polysilsesquioxane, polyurethane, epoxy-functionalized silicone resin, and polyester-functionalized silicone resin.

23. The substrate of claim 21, wherein the first layer further comprises filler particles made of glass spheres and/or hollow glass spheres.

24. The substrate of claim 21, wherein the substrate is made of a zero-expansion material.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

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

(2) FIG. 1 is a schematic cross-sectional view of the glass or glass ceramic of the present disclosure.

(3) FIG. 2 shows a schematic flow chart of the essential method steps.

(4) FIG. 3 shows photographs of different samples of coated glass ceramic substrates according to the present disclosure.

(5) FIG. 4 shows the spectral transmittance curve of a glass ceramic substrate coated with component A according to the embodiment of Example 1 of the invention.

(6) FIG. 5 illustrates the lightness value (L value) in the Lab system of the samples shown in FIG. 3.

(7) FIG. 6 illustrates the change in color location due to rear printing with different colors.

(8) FIG. 7 shows a scanning electron micrograph, from a top view, of a glass flux based coating material for the first layer which was baked at 680° C. at 1,000 times magnification.

(9) FIG. 8 shows a scanning electron micrograph, from the top view, of the glass flux based coating material of FIG. 7 at 5,000 times magnification.

(10) FIG. 9 shows a scanning electron micrograph, from the top view, of the glass flux based coating material of FIG. 7 at 100,000 times magnification.

(11) FIG. 10 shows a scanning electron micrograph, from a sectional view, of the glass flux based coating material of FIG. 7 at 50,000 times magnification.

(12) FIG. 11 shows a scanning electron micrograph, from a top view, of a first layer with a pigment content of 70%, which was baked at 725° C. at 20,000 times magnification.

(13) FIG. 12 shows a scanning electron micrograph, from a sectional view, of the first layer of FIG. 11 at 50,000 times magnification.

(14) FIG. 13 shows a scanning electron microscope cross-sectional view of a first layer with a pigment content of 65% baked at 680° C. at 10,000 times magnification.

(15) FIG. 14 shows a scanning electron microscope cross-sectional view of a first layer with a pigment content of 70% baked at 725° C. at 10,000 times magnification.

DETAILED DESCRIPTION

(16) The invention will now be described with reference to the drawings of FIGS. 1 to 14.

(17) FIG. 1 is a schematic cross-sectional view which serves to illustrate the effect of the invention.

(18) A coated glass or glass ceramic substrate 1 can be seen which consists of the substrate 2 and a gradient layer.

(19) The gradient layer comprises a first layer 3 applied using a glass flux, which layer contains more than 60% of pigment particles and small filler particles.

(20) Due to the presence of the pigment particles which form randomly distributed valleys and mountains, a textured surface is formed which is filled with a polysiloxane layer as a further layer 4. The further layer 4 also contains pigment particles. The gradient layer is used as a bottom surface coating, that means the viewer will look at the gradient layer from the side opposite layers 3 and 4.

(21) The gradient layer is preferably black and glossy.

(22) In more detail, layers may be applied as described in the examples below.

(23) The layer material used for the first layer has a composition according to component A, and the further layer has a composition according to component B.

(24) For the matrix material of component A, in particular crystalline and/or glassy inorganic materials can be used.

(25) Preferably, these basic glasses may be of siliceous origin, such as e.g. borosilicate glasses, fused silica glasses, zinc-silicate glasses, zinc-borosilicate glasses, bismuth-silicate glasses, bismuth-borosilicate glasses, alumosilicate glasses, soda-lime glasses, or borate, zinc-borate, bismuth-borate glasses, or phosphate glasses, and invert glasses.

(26) These may include, for example, glasses of the following composition:

(27) Borosilicate Glass: SiO.sub.2: 45-85 wt % B.sub.2O.sub.3: 5-30 wt % Al.sub.2O.sub.3: 2-20 wt % R.sub.2O: 2-20 wt, R.sub.2O representing alkali oxides RO: 0-10 wt %, RO representing alkaline earth oxides RO.sub.2: 0-5 wt %, RO.sub.2 representing TiO.sub.2 and/or ZrO.sub.2 ZnO: 0-15 wt %.

(28) Zinc-Borate Glasses: SiO.sub.2: 10-45 wt % B.sub.2O.sub.3: 5-30 wt % Al.sub.2O.sub.3: 0-10 wt % R.sub.2O: 0-10 wt %, R.sub.2O representing alkali oxides RO: 0-25 wt %, RO representing alkaline earth oxides RO.sub.2: 0-10 wt %, RO.sub.2 representing TiO.sub.2 and/or ZrO.sub.2 ZnO: 10-70 wt %.

(29) A coated glass or glass-ceramic substrate may be produced in detail with reference to the following examples:

Example 1

(30) Component A is applied to the bottom surface of a transparent glass ceramic plate of the type CERAN CLEARTRANS® (size 250×300 mm, thickness 4 mm) over the entire surface by screen printing (180 mesh screen), and is baked at 725° C. for 10 min in a continuous furnace. Component A comprises 35% of zinc-borosilicate glass (softening point T.sub.s of 575° C.) and 65% of a black pigment (Cu—Cr spinel; CuCr.sub.2O.sub.4), both components having a grain size of D50<5 μm.

(31) Component A baked in this manner has a layer thickness of 1.8 μm, a smooth haptic perception, is dense and non-porous (a dried water droplet can be wiped off), is gray (results of color measuring device Datacolor: L=29.9; a=−0.4; b=0.4), and semi-transparent (transmittance at 550 nm: 11%).

(32) In order to determine the scattering of the layer, a sample was measured in a spectrometer “Lambda 900” from company Perkin Ellmer, with and without Ulbricht sphere. At a wavelength of 550 nm, the transmittance was 11% with Ulbricht sphere and 1% without sphere, which means the sample exhibits a high level of scattered light.

(33) Subsequently, component B1 which forms the further layer is applied on component A by screen printing, also to the entire surface area.

(34) A black silicone paint is used as the component B1, for example that described in published patent application DE 10 2010 031 866 A1. This paint is printed using a 77 mesh screen, and is then dried at 200° C. for 45 min.

(35) The resulting component B1 has a layer thickness of 11 μm and is gray when printed alone (L=30.8; a=−0.25; b=−1.2).

(36) The gradient layer resulting from component A and component B1, however, is smooth, dense, deep black (L=26.7; a=−0.1; b=−0.7) and glossy when viewed through the glass ceramic (i.e. viewed from the upper side); transmittance in the entire visible range is 0% (transmission measurement with and without Ulbricht sphere). The spectrometer “Lambda 950” from company Perkin Ellmer was used to measure both the individual layer of component A and the gradient layer including components A and B1 in reflection. The difference in haze values is 5.5%, that means the reflection measurements confirmed that the layer consisting of component A has a high scattering power, while the gradient composite exhibits almost no scattering behavior.

(37) The gradient layer so produced, consisting of the materials of components A and B, meets the requirements for a cooktop with a short-term temperature load of up to 500° C.

(38) In detail, component B1 may have a composition as follows: 60-80 wt % polydimethylsiloxane 10-40 wt % black pigment, in particular selected from the group comprising (Cr,Fe)(Ni,Mn) spinel; Cu(Cr,Fe,Mn).sub.2O.sub.4 spinel (black 28); Co(Cr,Fe).sub.2O.sub.4 (black 27); (Ni,Fe)(Cr,Fe)O.sub.4 spinel (black 30); (Fe,Mn).sub.2O.sub.3 (black 33); (Fe,Mn)(Fe,Mn).sub.2O.sub.4 spinel (black 26); and (Cu,Cr)O.sub.x (black 28) 5-15 wt % graphite with a D90 value between 5 and 20 μm. (both synthetic and non-synthetic).

Example 2

(39) Component A is applied to the bottom surface of a transparent glass ceramic plate of the type CERAN CLEARTRANS® (size 250×300 mm, thickness 4 mm) over the entire surface by screen printing and is baked in a continuous furnace at 750° C. for 15 min.

(40) Component A comprises 25% of borosilicate glass (T.sub.s of about 620° C.) and 75% of black pigment (Cu—Cr spinel), with grain sizes of D50<5 μm.

(41) Component A baked in this manner has a layer thickness of 1.6 μm, a smooth haptic perception, is dense (non-porous), dark gray (L=30.8; a=−0.4; b=0.2) and semi-transparent.

(42) Subsequently, component B2 is applied on component A by screen printing (77 mesh screen), likewise to the entire surface area, and is dried at 230° C. for 90 min. A gray silicone paint is used as the component B2. The resulting gradient layer including component A and component B2 is smooth, dense, opaque, and dark gray (L=30.1; a=−0.7; b=−0.8).

(43) The so produced plate with the gradient layer satisfies the requirements for a cooktop with a short-term temperature load of up to 500° C.

(44) In detail, component B2 may have a composition as follows: 60-80 wt % polydimethylsiloxane 10-20 wt % black pigment, in particular selected from the group comprising (Cr,Fe)(Ni,Mn) spinel; Cu(Cr,Fe,Mn).sub.2O.sub.4 spinel (black 28); Co(Cr,Fe).sub.2O.sub.4 (black 27); (Ni,Fe)(Cr,Fe)O.sub.4 spinel (black 30); (Fe,Mn).sub.2O.sub.3 (black 33); (Fe,Mn)(Fe,Mn).sub.2O.sub.4 spinel (black 26); and (Cu,Cr)O.sub.x (black 28) 10-20 wt % TiO.sub.2 (white pigment) 5-15 wt % graphite with a D90 value between 5 and 20 μm. (both synthetic and non-synthetic).

Example 3

(45) Component A is applied to the bottom surface of a transparent glass ceramic plate of the type CERAN CLEARTRANS® (size 250×300 mm, thickness 4 mm) over the entire surface by screen printing (180 mesh screen) and is then dried.

(46) Component A comprises 90% of borosilicate glass (T.sub.s of about 755° C.) and 10% of an effect pigment (Merck, type Xirallic®—crystal silver), mixed with screen printing medium.

(47) Subsequently, component B is applied onto component A by screen printing (140 mesh screen), also to the entire surface area, and is dried at 825° C. for 10 min.

(48) Component B comprises 30% of zinc-borosilicate glass (T.sub.s of about 575° C.) and 70% of a black pigment (Fe—Ni—Cr spinel), grain sizes D50<5 μm.

(49) A black silicone paint as described in Example 1 is used as a component C(=B1).

(50) This paint is printed using a 77 mesh screen, and is then dried at 230° C. for 45 min. The resulting gradient layer including components A, B, and C is smooth, dense, and, when viewed from the upper side, black with glitter effect.

(51) Component A may also be produced using borosilicate glasses of different composition with varying contents of effect pigments (e.g. 1-10%). In this way, the visual appearance may be changed, e.g. as black with gold glitter or black with stainless steel color glitter.

(52) The gradient layers so produced satisfy the requirements for a cooktop with a short-term temperature load of up to 500° C.

Example 4

(53) A sol-gel paint (preparation described in published patent application WO2010/081531 A1) including 25% of effect pigment (Merck, type Iriodin®; particle size <25 μm) is applied to the bottom surface of a transparent glass ceramic plate of the type CERAN CLEARTRANS® (size 250×300 mm, thickness 4 mm) over the entire surface thereof by screen printing, 140 mesh screen, in form of geometric patterns and labeling, and is dried at 150° C. for 10 min to obtain a layer thickness of 8 μm. Subsequently, the gradient layer is produced in the manner as described in Example 1.

(54) The resulting plates are deep black (L=26.6; a=−0.2; b=−0.7) when viewed from the upper side (viewer side), with bright contrasting patterns, markings and lettering (L=63; a=−1.7; b=2.1).

(55) The plates thus produced meet the requirements for a cooktop with a short-term temperature load of up to 500° C.

Example 5

(56) Component A is applied to the bottom surface of a plurality of transparent glass ceramic plates of the type CERAN CLEARTRANS® (size 250×300 mm, thickness 4 mm) over the entire surface by screen printing (100 mesh screen), and is baked at 725° C. for 10 min.

(57) Component A comprises 35% of zinc-borosilicate glass (T.sub.s of about 575° C.) and 65% of a white pigment (TiO.sub.2), with grain sizes of D50<5 μm.

(58) Component A baked in this manner has a layer thickness of 3 μm, a smooth haptic perception, is dense (non-porous), beige (L=63.69; a=−0.3; b=5.61) and semi-transparent.

(59) Subsequently, components B1, B2, and B3 are applied to different plates over component A by screen printing, likewise to the entire surface area thereof and using a 77 mesh screen, and then are dried at 200° C. for 45 min.

(60) The resulting plate with the gradient layer including component A and component B1 is smooth, dense, and gray (L=48; a=−2; b=−3) when viewed from the upper side; the resulting plate with the gradient layer including component A and component B2 is smooth, dense, and light gray (beige gray) (L=59; a=−1.6; b=1.4). The resulting plate with the gradient layer including component A and component B3 is smooth, dense, and beige (significantly more opaque (less transparent) than component A alone) (L=69; a=−0.7; b=5.5). The plates with the gradient layers so produced satisfy the requirements for a cooktop with a short-term temperature load of up to 500° C.

(61) In detail, component B3 may have a composition as follows: 60-80 wt % of polydimethylsiloxane 0-40 wt % of TiO.sub.2 (white pigment) 0-10 wt % of effect pigment iriodin.

Example 6

(62) Component A is applied to the bottom surface of a transparent glass ceramic plate of the type CERAN CLEARTRANS® (size 250×300 mm, thickness 4 mm) over the entire surface thereof by screen printing, and is baked at 800° C. for 30 min.

(63) Component A comprises 70% of borosilicate glass (T.sub.s of about 820° C.) and 30% of a black pigment (Cr—Fe—Ni—Mn spinel), grain sizes of D50<5 μm.

(64) Component A baked in this manner has a layer thickness of 4.2 μm, a smooth haptic perception, is dense, non-porous, gray (L=33.1; a=−1; b=−0.9) and semi-transparent. Subsequently, component B1 is applied on component A by screen printing (77 mesh screen), likewise to the entire surface area thereof, and is dried at 200° C. for 90 min. The resulting gradient layer including component A and component B1 is smooth, dense, black (L=27.5; a=−0.2; b=−0.9) and glossy.

(65) It may occur that a bead of adhesive which is applied to the bottom surface, is visible from the upper side. Therefore, it is also possible to first apply component A of Example 1 and then the layers according to Example 6.

Example 7

(66) Component A is applied to the bottom surface of a transparent, non-ceramized glass plate of the type CERAN CLEARTRANS® (size 250×300 mm, thickness 4 mm) over the entire surface thereof by screen printing (180 mesh screen). Component A comprises 55% of borosilicate glass (T.sub.s of about 820° C.) and 45% of a black pigment (Cr—Fe—Ni—Mn spinel), grain sizes of D50<5 μm, mixed with screen printing medium.

(67) During ceramization of the substrate, component A is baked at the same time and thereafter has a layer thickness of 1.4 μm, a smooth haptic perception, is dense, non-porous, gray, and semi-transparent.

(68) Subsequently, component B1 is applied on component A by screen printing (77 mesh screen), likewise to the entire surface area thereof, and is dried at 200° C. for 90 min. The resulting gradient layer including component A and component B1 is smooth, dense, and glossy black.

Example 8 (Comparative Example)

(69) Component B1 is applied to the bottom surface of a transparent glass ceramic plate of the type CERAN CLEARTRANS® (size 250×300 mm, thickness 4 mm) over the entire surface thereof by screen printing (77 mesh screen) and is then dried at 200° C. for 90 min. Component B1 obtained in this manner has a layer thickness of 20 μm and is dark gray black. When this plate is subjected to a thermal load of 500° C. it discolors (becomes lighter). Massive cracks are produced in the silicone layer, where the light is scattered more strongly. The resulting color difference between the undamaged silicone layer and the silicone layer damaged by thermal action is not acceptable, i.e. the requirements for a cooktop are not met. Hence, the material of component B1 is not suitable for a single layer coating.

Example 9

(70) Component A is applied to the bottom surface of a transparent glass ceramic plate of the type CERAN CLEARTRANS® (size 250×300 mm, thickness 4 mm) over the entire surface thereof by screen printing (140 mesh screen), and is baked at 725° C. for 10 min. Component A comprises 40% of zinc borosilicate glass (T.sub.s of about 575° C.) and 30% of a blue pigment (Co—Al—Cr spinel) and 30% of a green pigment (Co—Zn—Ti—Cr spinel), grain sizes D50<5 μm.

(71) Component A baked in this manner has a layer thickness of 2.1 μm, a smooth haptic perception, is dense and non-porous, turquoise, and semi-transparent.

(72) Subsequently, component B2 which forms the further layer is applied on component A by screen printing, likewise to the entire surface area thereof.

(73) A gray silicone paint is used as the component B2. This paint is printed using a 54 mesh screen, and is then dried at 230° C. for 45 min.

(74) The resulting gradient layer consisting of component A and component B2 is smooth, opaque turquoise, and glossy.

(75) The gradient layer so produced comprising the materials of component A and component B2 meets the requirements for a cooktop with a short-term temperature load of up to 500° C.

Example 10

(76) Component A is applied to the bottom surface of a heat-resistant borosilicate glass of the type Borofloat 33 of a thickness of 3 mm over the entire surface by screen printing (100-40 mesh screen). Component A comprises 40% of bismuth-borosilicate glass (T.sub.s of about 600° C.) and 60% of a black pigment (Cu—Cr spinel). Baking is performed at 680° C. for 10 min. The resulting layer is almost black, dense, and has a layer thickness of 3.4 μm.

(77) A black silicone paint is used as the component B1, for example that described in published patent application DE 10 2010 031 866 A1. This paint is printed using a 77 mesh screen, and is then dried at 200° C. for 45 min.

(78) The resulting gradient layer including component A and component B1 is smooth, dense, and glossy black.

Example 11

(79) In the examples mentioned, additional substrates were printed with the semi-transparent component A and baked. Then one half of the substrate was printed on the rear so as to become opaque (as described in the examples above), and the other half was printed on the rear with a transparent pigment-free silicone resin and then dried. Even with the transparent rear printing, the display below the plate is not visible in the off state, but when switched on the display is easy to read. In order to keep the color contrast as small as possible between the opaque part and the semi-transparent display area, the transparent silicone resin was also colored with organic dyes, e.g. in Example 1 with black dye Orasol® RLi, or in Example 9 with phthalocyanine-based dyes.

Further Optional Embodiments

(80) For cooktop applications, for example, in addition to the bottom surface the upper surface may also be decorated.

(81) The invention enabled to provide a deep black coating of high temperature resistance, consisting of components A (first layer) and B (further layer).

(82) Layers were in particular provided with the following color values in the Lab color space:

(83) TABLE-US-00001 Layer L a B Component A 29.9 −0.4 0.4 Component B 30.8 −0.25 −1.2 A + B 26.7 −0.1 −0.7

(84) It is in particular apparent that the lightness L of the layer system consisting of components A and B is less than 27, whereas when applied alone component A has a lightness of 29.9 and component B has a lightness of 30.8. Thus, only a combination of the two components that make up the first layer and the further layer results in a deep black color appearance.

(85) FIG. 2 shows a schematic flow chart of the essential method steps.

(86) First, a glass ceramic substrate is provided, then a first layer is applied which consists of a layer material comprising metal oxide particles for pigmentation purposes and a glass flux material.

(87) This first layer is baked at a temperature of more than 600° C., so that a dense textured layer is produced.

(88) Then, a black silicone paint is applied as a further layer. This silicone paint is dried at a temperature below 500° C.

(89) FIG. 3 shows photographs of different samples of coated glass ceramic substrates. Samples 6, 8, and 9 are coated glass ceramic substrates having a dark coating such as available on the market.

(90) It can be seen that the visual appearance is rather greyish.

(91) Sample 7 is coated using a noble metal oxide. As can be seen, it has a brown-black color appearance. However, the application of such a coating is very expensive.

(92) Sample 5 has been coated using a method according to the invention.

(93) As can be seen, it has a deep black color appearance. Furthermore, the coating has a glossy reflective color appearance.

(94) FIG. 4 shows the spectral transmittance curve of a glass ceramic substrate coated with component A according to the embodiment of Example 1 of the invention.

(95) It can be seen that in the visible range spectral transmittance is less than 20%.

(96) FIG. 5 illustrates the lightness value (L value) in the Lab system of the samples shown in FIG. 3.

(97) It can be seen that sample 5 which is the coating applied according to the invention has the lowest L value, which is even lower than the L value of sample 7 in which a noble metal oxide was applied.

(98) Referring to FIG. 6, the change in color location due to rear printing with different colors will be explained.

(99) In this example, component A has a dark pigmentation.

(100) It can be seen that when used as a bottom surface coating (front view) a gray color appearance is obtained together with light pigmented component B2.

(101) FIGS. 7 to 10 show scanning electron micrographs of a glass flux based coating material for the first layer, which was baked at 680° C.

(102) A highly textured layer can be seen, which due to the added particles has the desired high degree of texturing as intended.

(103) FIG. 9 shows a micrographs with high magnification as compared to the scale illustrated in FIGS. 7 and 8.

(104) In FIG. 9 cracking in the baked layer can be seen. Surprisingly it has been found that this cracking has no significant visible impact on the visual appearance of the layer when the latter is combined with a further layer which fills the texture of the first layer.

(105) Moreover, cracking even appears to increase the temperature stability of the coating system.

(106) FIG. 10 shows a sectional view of the layer. It can be seen how the substrate merges into the coating, even the individual pigment particles are clearly visible. In the bottom of one valley, a significant cracking can be seen.

(107) FIGS. 11 and 12 show scanning electron micrographs of a first layer with a pigment content of 70%, which was baked at 725° C. The result is roughly comparable, although the texture depth of this layer is further increased.

(108) The sectional view of FIG. 12 illustrates particularly well that the layer is almost free of pores. Therefore, the layer material itself has a very low porosity after baking.

(109) The first layer should be baked so fast that a formation of a porous structure due to the added particles is largely avoided.

(110) FIGS. 13 and 14 show scanning electron microscope cross-sectional views of a layer material which has been filled with a silicone paint as the second layer.

(111) Here, FIG. 13 relates to the first layer with a pigment content of 65% baked at 680° C., and FIG. 14 relates to the first layer with a pigment content of 70% baked at 725° C.

(112) It can be seen in the scanning electron micrographs that the first layer is sealed and a fairly smooth surface is obtained.

(113) Furthermore, the components of the first and the further layer are hardly distinguishable in this scanning micrograph, the material gradually merges into one another.

(114) The invention permits, in a particularly simple and cost-effective manner, to produce high-temperature stable colored decorative coatings for cooktops.