Plate comprising glass or vitroceramic, process for its production, as well as its use

Abstract

The invention relates in general to composite plates made of glass or glass-ceramic, in particular those that are at least partially coated with a layer, to a method for producing such plates and to their use.

Description

Area of ​​Experience

[0001] The invention relates generally to plates comprising glass or glass-ceramic, in particular those which are at least partially covered with a coating, a method for producing such plates and their use.

[0002] In particular, the invention relates to a plate comprising a glass or a glass ceramic, in particular a lithium aluminum silicate glass or a lithium aluminum silicate glass ceramic, comprising a coating.

[0003] Coated glass or glass-ceramic panels have been known for a long time and have been used for many years, for example, as cover plates for cooking appliances (also called "cooktops" or "cooking surfaces"). These panels are generally provided with at least one coating. For example, panels consisting of a volume-colored substrate are known, on which so-called cooking zone markings are applied to the user-facing side (also referred to as the "top" or "front"). The printing of logos is also known. Furthermore, panels consisting of a non-volume-colored substrate are also known, on which a so-called "underside coating" is applied. Depending on the exact design of such a panel, different coatings can be combined on different sides.

[0004] Printing processes are generally used as the preferred method for printing. The state of the art here is primarily screen printing, which allows for high throughput in the production of printed plates. However, a disadvantage is that these plates must always be printed identically, and different printing inks require different process steps.

[0005] As an alternative, inkjet printing has therefore become increasingly important. These methods offer greater flexibility in the production of such plates. For example, smaller production runs are now possible.

[0006] In practice, however, for reasons that are still unclear, it has been shown that the print quality in screen printing is generally better than in inkjet printing.

[0007] European patent application EP 3 346 876 A1 describes large-area worktops for a kitchen island with a minimum surface area of ​​0.7 m² and a flatness of less than 0.1% of the substrate diagonal. However, the quality of the printing is not addressed. Inkjet printing is not mentioned, nor is the surface roughness of the worktop, which is relevant to the quality of inkjet printing.

[0008] US patent application US 2019 / 128534 A2 describes a glass-ceramic worktop for kitchen furniture with a low flatness of less than 0.1% diagonally. However, the application does not mention print quality or inkjet printing. Nor does it address the surface roughness of this worktop, which is relevant to the quality of inkjet printing.

[0009] Japanese patent application JP 2015 / 176753 A describes polished surfaces of panels used as cooktops. However, the patent does not address the quality of any applied decoration; rather, it focuses on the reflectivity of the surfaces, their gloss, and the visual impression of an underside print.

[0010] US 2021 / 188701 A1 discloses coated glass-ceramic plates on at least two different sub-areas.

[0011] No state-of-the-art document addresses the improvement of print quality, especially in non-contact printing, such as inkjet printing.

[0012] Therefore, there is a need for glass or glass-ceramic plates that produce a good print image in a non-contact printing process, such as inkjet printing, as well as for a method to manufacture them. Task of Experience

[0013] The object of the invention is to provide plates comprising a substrate made of glass or glass-ceramic and at least one coating, which at least partially mitigate the problems of the prior art. Correspondingly, there is also a need for a method for manufacturing such plates. Summary of Experience

[0014] The object of the invention is achieved by the subject matter of the independent claims. Preferred and specific embodiments are found in the dependent claims as well as in the description and drawings of the present disclosure.

[0015] The disclosure therefore relates to a plate comprising glass or glass-ceramic with two opposing side surfaces and a circumferential edge surface, wherein the flatness of the plate is less than or equal to 0.1% of a lateral dimension and at least one side has a mean surface roughness Rz,mean of less than 0.5 µm in at least one region with a standard deviation of the surface roughness, σRz, of less than 0.1 µm, further comprising a coating arranged on at least two different sub-regions of the at least one region of the at least one side of the plate, wherein the at least two sub-regions are spaced at least 3 cm apart and wherein the raggedness of the coating in the two sub-regions differs from each other by a maximum of 10%.

[0016] Such a design offers a number of advantages.

[0017] The plate's simultaneously good flatness and roughness enable excellent print quality of the coating, for example, even in inkjet printing. This very good print quality is particularly evident in the so-called "raggedness" of the coating. Preferably, the raggedness can be determined according to ISO 24790.

[0018] Raggedness is a measure of the image quality of a printed image and describes, for example, edge sharpness. The method for determining raggedness is described below. Figs. 1 Explained in detail.

[0019] The flatness of the plate is less than or equal to 0.1% of a lateral dimension, preferably the largest lateral dimension, of the plate. For example, according to one embodiment, the corresponding lateral dimension of the plate can be the diagonal of a rectangular plate. The diagonal is generally understood here to be the surface diagonal of the plate, i.e., the diagonal of one of the main surfaces (or sides) of the plate.

[0020] In general, within the scope of this disclosure, a lateral dimension is understood to be one of the length dimensions of the plate. Within the scope of this application, a plate is generally understood to be a body whose dimensions in two spatial directions of a Cartesian coordinate system are at least one order of magnitude larger than in the third spatial direction, which is perpendicular to these first two directions. In other words, the thickness of a plate is at least one order of magnitude less than its length and width. The length and width of the plate define the principal surfaces (as opposed to the circumferential edge surfaces, which constitute only a small fraction of the total surface area of ​​the plate) for a generally rectangular plate. However, a lateral dimension within the meaning of this disclosure is, in particular, the surface diagonal, which within the scope of this application is also referred to as the diagonal.This refers to the largest lateral dimension of a generally rectangular plate. In the case of a non-rectangular plate, the diameter, for example, can take the place of length, width, or diagonal and be referred to as the corresponding lateral dimension.

[0021] Advantageously, the mean surface roughness Rz,mean and the standard deviation of the surface roughness, σRz, are determined by measuring the roughness Rza at nine points on the plate, each spaced at least 5 cm apart, preferably at least 10 cm apart, and particularly preferably at least 15 cm apart, and then calculating the arithmetic mean and the standard deviation from these nine measurements. Particularly preferably, Rz is determined by measuring a line profile with a stylus profilometer and evaluating it according to ISO 4827.

[0022] This flatness is advantageous because it allows for a homogeneous application of the coating during printing, enabling the high-quality printing of even small and fine structures. Furthermore, it is beneficial because it can increase the buildability of a single plate. It has also been shown that such an arrangement can improve the visibility of displays. A uniform surface with minimal thickness variations in the plate largely minimizes differences in brightness. This is particularly advantageous with volume-dyed materials, where thickness variations have an exponential effect on the transmission properties.

[0023] This can be advantageously combined with the fact that the plate is not only very smooth, i.e., not very rough, and flat on at least one side, but that the two side surfaces are arranged parallel to each other. Therefore, it is also preferable in one embodiment that the side surfaces are arranged parallel to each other. An arrangement is considered parallel if the normal angles to the side surfaces enclose an angle of no more than 5° with each other, preferably no more than 2°, and most preferably, within the scope of usual manufacturing and measurement tolerances, 0°.

[0024] If one side of the plate is textured, the area formed by the tips of the bumps is used to determine the normal angle.

[0025] The inventors also assume that this method will generally improve the processing of the panels. The improved flatness and roughness also enhance the dimensional accuracy of the panels. This makes them easier to handle and allows them to be bonded more effectively, for example.

[0026] According to one embodiment, the plate can have a thickness between 2 mm and 6 mm. This is particularly advantageous for using the plate as a cover plate in a cooking appliance, because in this way a good compromise can be achieved between the smallest possible thickness, which is beneficial for boiling, and sufficient strength of the plate, which is essential for such an application and which increases with the plate thickness.

[0027] In general, the flatness and roughness of the plate according to the disclosure are advantageous for all coating types and processes. However, this is particularly advantageous for inkjet printing coatings.

[0028] The flatness of the substrate determines the minimum distance to the printhead in non-contact inkjet printing. It has been shown that, especially in non-contact printing processes, the distance between the printhead and the substrate being printed is crucial for a good print image. With a flatness of more than 0.1%, height differences of up to 600 µm are possible (for example, with a diagonal of 60 cm). This could mean that the distance between the printhead and the substrate is insufficient for the droplet to detach and fully form after exiting the printhead. This can be particularly critical with small distances between the printhead and the substrate, such as only 1 mm. While it would theoretically be possible to correct this by inline measurement of the distance between the plate and the printhead, adjusting the printhead height based on the measured distance, this is not always practical.This would, however, entail a significant amount of machinery. This can be cleverly avoided by the targeted use of flat and planar substrates.

[0029] The low flatness allows for the defined settling of droplets. This leads to better pressure control and reproducible droplet settling. This also enables improved resolution of printed images.

[0030] Especially in inkjet printing, maintaining a precise distance between the substrate and the printhead has proven crucial. Only then can the optimal droplet shape of the printing ink be guaranteed. Therefore, a minimum distance of approximately 1.5 mm between the printhead and the substrate is essential. Depending on the printing press, however, even smaller distances of, for example, 1 mm are possible. If this minimum distance is not maintained, the droplet shape cannot form optimally, or even approximately, a spherical shape.

[0031] If the distance between the printhead and the substrate is too great, the droplet can be deflected, causing it to land not on the intended spot on the substrate and / or resulting in the formation of so-called satellites. This leads to reduced edge sharpness and potentially even holes in the printed image.

[0032] Both of these factors result in an uneven and blurry print image. It is particularly problematic when different print images are applied to different areas of a substrate, and due to insufficient flatness and roughness, the print images appear with varying degrees of sharpness at different points on the plate.

[0033] According to one embodiment, the coating comprises a glass flux and / or is designed as an enamel. Preferably, the coating comprises a glass flux and / or is designed as an enamel and comprises at least one pigment. Particularly preferably, the at least one pigment does not comprise any pigment particles with a primary particle size, determined as the d50 value of the equivalent diameter, of more than 1.0 µm; most preferably, it does not comprise any pigment particles with a primary particle size, determined as the d90 value of the equivalent diameter, of more than 2.5 µm.

[0034] This design is particularly advantageous because coatings containing glass flux or enamel-like coatings are exceptionally thermally stable and adhere well to glassy surfaces such as glass or glass-ceramics. For example, such coatings can be designed to create a so-called "fusion reaction zone," allowing the coating, or the glass flux it contains, and the substrate material to form a strong bond during firing. This design also makes such coatings suitable for use as decorative surfaces on cooktops, for instance.Such surface decorations, which are used, for example, for printing logos or marking cooking zones, must withstand the sometimes very harsh cleaning conditions (with a so-called glass surface scraper) as well as the operating conditions (abrasion, for example, by moving cookware, sometimes under heat stress).

[0035] Within the scope of this disclosure, coatings comprising a glass flux are understood to be those coatings which have at least one glassy component, for example, produced from a paste comprising a glass powder. Within the scope of this disclosure, such coatings are also referred to as "enamel," particularly when the glass flux melts at least partially during firing.

[0036] In principle, it is possible for the coating applied to the substrate to consist solely of a glass flux. In this case, it can also be understood or referred to as a "glaze." However, it is generally possible, and may even be preferred, for the coating to include at least one pigment in addition to a glass flux, or to be designed as an enamel comprising at least one pigment. This increases the visibility of a marking, which can, for example, improve user safety when using a cooking appliance equipped with such a plate. Furthermore, depending on the type of pigment, the mechanical resistance of the coating can also be increased, for example, by using a particularly abrasion-resistant pigment.

[0037] Suitable glass fluxes can, for example, have a composition based on SiO₂ and B₂O₃ or on Bi₂O₃ and SiO₂. "Based on" means that these components constitute at least 50 wt% of the composition.

[0038] Examples of glass fluxes based on SiO2 and B2O3 are mentioned below.

[0039] Two examples of suitable glass fluxes based on Bi 2 O 3 and SiO 2 are listed in the following table. Component Eq.-% Eq.-% SiO 19,9 16,1 B 2 O 3 12,2 9,6 Al 2 O 3 0,6 0,5 Na 2 O 5,3 4,3 K 2 O 0,14 0,17 ZnO 3,9 10,2 TiO 2,6 5,9 ZrO 3,3 2,6 SnO 0,12 5,6 Bi 2 O 3 50 42 HfO 0,07 0,05 Density [g / cm 3< 4,49 4,75 α 20–300 [ppm / K] 8,15 8,11 T g [°C] 487 495 E w [°C] 599 581 V to [°C] 830 889

[0040] In this context, a pigment is understood to be a coloring agent comprising solid particles. In particular, according to the present disclosure, the pigment can be designed as a ceramic coloring agent. Within the scope of this disclosure, "ceramic" refers to inorganic, non-metallic substances. This is advantageous because ceramic coloring agents possess high temperature resistance, which is essential for the applications addressed here.

[0041] It can also be advantageous if the primary grain size of the pigment particles, i.e., the particles encompassed by the colorant, is limited as described above. This is beneficial for coating by inkjet printing, preventing nozzle clogging. Furthermore, the use of fine pigment particles simplifies the printing of fine structures and can therefore be particularly advantageous here, because the high flatness and planarity of the plate according to the present disclosure now allows for the particularly good reproduction of such fine structures.

[0042] In particular, it is also possible for the plate to be designed as a plate with smooth surfaces on both sides, which specifically means that neither side of the plate has any texture. Plates with smooth surfaces on both sides can be particularly advantageous when high-resolution displays are to be positioned beneath the plate. The low roughness and surface roughness of the plate are especially well-suited for such a design and can therefore be effectively combined with a high-resolution display.

[0043] Alternatively, particularly in cases where exceptionally high board strength is required or advantageous, one side of the board can be smooth, while the opposite side is textured, with the coating applied to the smooth side. In this case, the textured side of the board serves as the underside. The textured surface can mitigate the impact of any mechanical damage to the glassy or glass-ceramic material on the board's strength, at least to some extent. This also facilitates handling the board.

[0044] According to one embodiment, the plate comprises a glass ceramic, wherein the glass ceramic preferably comprises at least one of the following features: The glass ceramic is volume-colored; the glass ceramic does not have a glassy surface zone on at least one side.

[0045] Designing the plate in such a way that it includes glass ceramic is particularly advantageous because glass ceramic, especially so-called lithium aluminum silicate glass ceramic, has high strength and low thermal expansion and therefore also sufficient resistance to temperature differences to be used particularly advantageously in cooking appliances.

[0046] Suitable glass ceramics can be produced using various refining agents. For example, glass ceramics refined with As2O3, Sb2O3, SnO2, CeO2 or combinations thereof are suitable.

[0047] For example, glass ceramics with the following composition in wt.% based on oxides are suitable: Component 1 2 3 4 Reach Al 2 O 3 21,23 21,35 21,30 20,47 20-23 As 2 O 3 0,59 0,00 0,01 0,00 0-1 BaO 1,65 1,57 1,70 1,71 1-2 CaO 0,23 0,32 0,39 0,32 0-1 CeO 0,00 0,00 0,22 0,22 0-0,5 Cr 2 O 3 0 0 0 0 0-0,1 CoO 0 0 0 0 0-0,1 Fe 2 O 3 0,11 0,09 0,10 0,07 0,01-0,3 K 2 O 0,14 0,12 0,14 0,24 0-1 The 2 O 3,65 3,90 3,94 3,62 3,0-4,5 MgO 0,43 0,67 0,58 0,58 0-1 MnO 0,02 0,02 0,00 0,14 0-0,5 MoO 3 0 0 0 0 0-0,4 Na 2 O 0,66 0,66 0,68 0,44 0-1 Nd 2 O 3 0 0 0 0 0-0,5 NiO 0 0 0 0 0-0,5 P 2 O 5 0,87 0,78 0,95 1,18 0-3 Sb 2 O 3 0,00 0,00 0,00 0,07 0-0,2 SiO 64,43 64,33 63,80 64,35 60-68 SnO 0,02 0,24 0,23 0,18 0-0,6 TiO 2,95 3,03 3,11 3,09 2-4 V 2 O 5 0,21 0,03 0,03 0,03 0-0,4 ZnO 1,19 1,25 1,23 1,61 0,5-3 ZrO 1,58 1,60 1,54 1,52 0,5 - 3

[0048] Such glass ceramics may also contain up to 2 wt% other components, especially in the form of impurities.

[0049] It can be advantageous for the glass-ceramic to be volume-colored. This is beneficial because in this way the glass-ceramic itself – particularly without the need for a masking layer on the side facing the user or away from them – is sufficiently opaque to shade components of a cooking appliance located behind the surface.

[0050] According to a further embodiment, the plate comprises a glass-ceramic, wherein the plate does not have a glassy surface zone on at least one side. It has been shown that a particularly flat and only slightly rough surface can be achieved on at least one side in this way. This can be achieved in particular if at least one side of the plate is ground and polished.

[0051] According to a further preferred embodiment of the plate, it features an improved character surround area haze. This value describes the number of defects or satellites of the printing ink droplet around the deposited droplet or the printed image. This value is improved in the plate according to the present disclosure, particularly due to the low roughness and high flatness of the plate. In this way, the droplets can be deposited uniformly in a non-contact process, and droplet deflection is also much less likely.

[0052] The present disclosure also relates to a method for manufacturing a plate according to an embodiment of the present disclosure. The method comprises the steps: Providing a plate comprising a glass or a glass-ceramic. In particular, the plate may comprise a lithium-aluminum-silicate glass or a lithium-aluminum-silicate glass-ceramic. Preferably, the plate has a thickness between 2 mm and 6 mm. The plate is particularly plate-shaped, i.e., with two opposing, preferably parallel, side surfaces and a circumferential edge surface.Grinding at least one side of the plate, polishing at least one side of the plate, preferably the side that was previously ground, printing on at least one side of the plate, preferably the side that was previously ground and / or polished, on at least two different sub-areas of the at least one area of ​​the at least one side of the plate, such that a coating is arranged in these at least two different sub-areas, wherein the at least two sub-areas are spaced at least 3 cm, preferably at least 9 cm, and particularly preferably at least 15 cm apart. Preferably, the printing can be carried out by means of a non-contact printing process, preferably by means of inkjet printing. Baking of the coating.

[0053] Firing can be carried out using a variety of known methods. For example, firing can take place in a furnace, particularly a furnace for the thermal tempering of glass or for the ceramicization of glass ceramics. Tunnel furnaces can also be used for this purpose. Firing temperatures can exceed 650 °C, 700 °C, or even 750 °C.

[0054] In addition, optical methods such as laser irradiation, especially using CO2 lasers, flash lamps ("Photonic Flash Sintering") or short-wave infrared radiation (KIR emitters) can also be used.

[0055] Furthermore, the method according to embodiments can be carried out, for example, by printing on so-called green glass. This is then transformed into a glass-ceramic during the firing process (so-called primary firing).

[0056] However, it may be preferable to print on a glass-ceramic surface that has already been ground and polished before ceramization. It is also possible, and may even be preferable, to perform the grinding and polishing steps only after the glass-ceramic conversion. This can be advantageous because it ensures high dimensional accuracy of the plate. During ceramization, the necessary temperatures can cause changes in the glass-ceramic's dimensions (e.g., shrinkage), which could reduce the high surface quality and the plate's beneficial flatness. Furthermore, the surface roughness may increase during ceramization due to oxidizing impurities and / or the adaptation of the softening glass to the substrate.This can be avoided if the surface properties of the slab are adjusted by grinding and polishing only after the ceramic coating has been applied. In this case, the coating is then fired on in a so-called secondary firing, which allows for lower temperatures than the primary firing.

[0057] According to one embodiment of the method, the coating comprises a glass flux and / or is designed as an enamel. Preferably, the coating comprises a glass flux or is designed as an enamel and further comprises at least one pigment, wherein the at least one pigment particularly preferably does not comprise any pigment particles with a primary particle size, determined as the d50 value of the equivalent diameter, of more than 1.0 µm, and most preferably does not comprise any pigment particles with a primary particle size, determined as the d90 value of the equivalent diameter, of more than 2.5 µm.

[0058] According to one embodiment, the plate comprises a glass, in particular a green glass, and the firing of the coating takes place during a ceramicization step in which the glass is transformed into a glass ceramic.

[0059] According to another preferred embodiment, the plate comprises a glass ceramic, and the coating is fired on in a secondary firing.

[0060] The present disclosure also relates to the use of a plate according to embodiments and / or manufactured by a method according to an embodiment as a cooking surface. For the purposes of this disclosure, a cooking surface is understood to be a plate used as a cover plate in a cooking appliance. Such a cooking surface can also be referred to synonymously as a hotplate. For the purposes of this disclosure, a cooking appliance is understood to be a device for preparing food by heating, in particular a so-called cooktop on which cookware is placed. Examples

[0061] The invention will be further explained below using examples and comparative examples. Example 1

[0062] A volume-dyed, ceramized glass-ceramic material (600* 600 mm 2< ) was subjected to a two-stage ablation process.

[0063] The first step was a coarse grinding process using a rotating pad (d = 15 cm) impregnated with a CeO₂ suspension. The d₅₀ value of the abrasive grains was between 2 and 2.5 µm. The process was continued until the flatness of the plate was less than 0.1% of the plate's diagonal – in this case, less than 600 µm.

[0064] After achieving the target flatness value, the initial roughness was reduced by local heating using a CO2 laser with a spatial wavelength range of 100 until a roughness of RZ,mean of less than 0.5 µm was obtained.

[0065] The polished surface was printed with a secondary firing fluid using an inkjet printer. The ink was fired in a 45-minute firing process at a maximum temperature of 750°C.

[0066] The print or the printed image subsequently shows a very slight deviation in print quality across the plate (raggedness for lines with a width of 300 µm at 22.26 µm).

[0067] The composition of the plate can be found in the following table: Component Eq.-% The 2 O 3,74 Al 2 O 3 21,29 SiO 65,21 TiO 3,64 ZrO 0,90 SnO 0,28 As 2 O 3 Cr 2 O 3 0,0035 P 2 O 5 0,052 MnO 0,021 Na 2 O 0,56 K 2 O 0,41 MgO 0,31 CaO 0,44 BaO 1,31 ZnO 1,58 V 2 O 5 0,0026 MoO 3 0,046 Fe 2 O 3 0,089 α 50-700 α 20-700 0,14 * 10 -6< / K α 25-700

[0068] The composition of the glass flux can be found in the following table: Component Eq.-% SiO 47,5 B 2 O 3 19 Al 2 O 3 2 The 2 O 4 Na 2 O 7,5 K 2 O 4 CaO 1 BaO 2 ZnO 8,75 TiO 3,8 Sb 2 O 3 0,2

[0069] The printing ink used was composed as follows: Glasfluss 1 2.98 Eq.-% Black Pigment CuCr 2 O 4 1.05 Eq.-% White pigment TiO 0.87 Wt.-% Dipropylenglycolmethylether 62.71 Wt.-% Additive 1 2.09 Gew.-% Additive 2 0.30 Eq.-%

[0070] Additive 1 is poly(oxy-1,2-ethanediyl), α-methyl-w-phosphate. Additive 2 is polyether-modified polymethylsiloxane.

[0071] Using this printing ink, a resulting effective linear coefficient of thermal expansion, α 20-300, eff , based on the glass particles and pigment particles encompassed by the printing ink, of 9.15 * 10 -6< / K is achieved. Example 2:

[0072] A volume-dyed, ceramized glass-ceramic material (600* 600 mm 2< ) was subjected to a two-stage ablation process.

[0073] The first step was a coarse grinding process using a rotating pad (d = 15 cm) impregnated with a CeO₂ suspension. The d₅₀ value of the abrasive grains was between 2 and 2.5 µm. The process was continued until the flatness of the plate was less than 0.1% of the plate's diagonal – in this case, less than 600 µm.

[0074] After achieving the target flatness value, further material was removed using Ion Beam Figuring (IBF) until a roughness of PZ,mean of less than 0.5 µm was obtained.

[0075] The polished surface was printed with a secondary firing fluid using an inkjet printer. The ink was fired in a 45-minute firing process at a maximum temperature of 750°C.

[0076] The print or the printed image subsequently showed a very low deviation in print quality across the plate (raggedness for lines with a width of 300 µm at 29.04 µm).

[0077] The composition of the glass-ceramic material used can be found in the following table: Component Eq.-% The 2 O 3,74 Al 2 O 3 21,29 SiO 65,21 TiO 3,64 ZrO 0,90 SnO 0,28 As 2 O 3 Cr 2 O 3 0,0035 P 2 O 5 0,052 MnO 0,021 Na 2 O 0,56 K 2 O 0,41 MgO 0,31 CaO 0,44 BaO 1,31 ZnO 1,58 V 2 O 5 0,0026 MoO 3 0,046 Fe 2 O 3 0,089 α 50-700 α 20-700 0,14 α 25-700

[0078] The composition of the glass flux used can be found in the following table: Component Eq.-% SiO 47,5 B 2 O 3 19 Al 2 O 3 2 The 2 O 4 Na 2 O 7,5 K 2 O 4 CaO 1 BaO 2 ZnO 8,75 TiO 3,8 Sb 2 O 3 0,2

[0079] The printing ink used was composed as follows: Glasfluss 1 2.98 Eq.-% Black Pigment CuCr 2 O 4 1.05 Eq.-% White pigment TiO 0.87 Wt.-% Dipropylenglycolmethylether 62.71 Wt.-% Additive 1 2.09 Gew.-% Additive 2 0.30 Eq.-%

[0080] Additive 1 is poly(oxy-1,2-ethanediyl), α-methyl-w-phosphate. Additive 2 is polyether-modified polymethylsiloxane. This results in a net effective linear coefficient of thermal expansion, α 20-300, eff, based on the glass and pigment particles contained in the printing ink, of 9.15 × 10⁻⁶ / K. Example 3:

[0081] A green glass material (600* 600 mm 2< ) was subjected to a two-stage ablation process.

[0082] The first step was a coarse grinding process using a rotating pad (d = 15 cm) impregnated with a CeO₂ suspension. The d₅₀ value of the abrasive grains was between 2 and 2.5 µm. The process was continued until the flatness of the plate was less than 0.1% of the plate's diagonal – in this case, less than 600 µm.

[0083] After achieving the target flatness value, the initial roughness was reduced by local heating using a CO2 laser with a spatial wavelength range of 100 µm until a roughness of RZ,mean of less than 0.5 µm was obtained.

[0084] The polished surface was printed with a secondary firing fluid using an inkjet printer. The ink was fired in a 45-minute firing process at a maximum temperature of 750°C.

[0085] The print or the printed image subsequently shows a very slight deviation in print quality across the plate (raggedness for lines with a width of 300 µm and for lines at 23.02 µm).

[0086] After printing, the substrate with the print was subjected to a ceramicization process and transformed into a glass ceramic. Comparative example 1

[0087] In comparison example 1, good flatness is present, but simultaneously poor, i.e., high, roughness. This leads to a significantly altered raggedness of the printed image, as shown below.

[0088] A volume-dyed, ceramized glass-ceramic material (600* 600 mm 2< ) was subjected to a single-stage ablation process.

[0089] This step involved coarse grinding with a rotating pad (d = 15 cm) impregnated with a CeO₂ suspension. The d₅₀ value of the abrasive grains was between 2 and 2.5 µm. The process was continued until the flatness of the plate was less than 0.1% of the plate's diagonal – in this case, less than 600 µm.

[0090] No further polishing was performed after the target flatness value was achieved. The average roughness (RZ,mean) was 0.7 µm.

[0091] The polished surface was printed with a secondary firing fluid using an inkjet printer. The ink was fired in a 45-minute firing process at a maximum temperature of 750°C.

[0092] The print or the printed image subsequently shows a deviation in print quality across the plate (raggedness for lines with a width of 300 µm at 45.3 µm).

[0093] The composition of the plate can be found in the following table: Component Eq.-% The 2 O 3,74 Al 2 O 3 21,29 SiO 65,21 TiO 3,64 ZrO 0,90 SnO 0,28 As 2 O 3 Cr 2 O 3 0,0035 P 2 O 5 0,052 MnO 0,021 Na 2 O 0,56 K 2 O 0,41 MgO 0,31 CaO 0,44 BaO 1,31 ZnO 1,58 V 2 O 5 0,0026 MoO 3 0,046 Fe 2 O 3 0,089 α 50-700 α 20-700 0,14 * 10 -6< / K α 25-700

[0094] The composition of the glass flux can be found in the following table: Component Eq.-% SiO 47,5 B 2 O 3 19 Al 2 O 3 2 The 2 O 4 Na 2 O 7,5 K 2 O 4 CaO 1 BaO 2 ZnO 8,75 TiO 3,8 Sb 2 O 3 0,2

[0095] The printing ink used was composed as follows: Glasfluss 1 2.98 Eq.-% Black Pigment CuCr 2 O 4 1.05 Eq.-% White pigment TiO 0.87 Wt.-% Dipropylenglycolmethylether 62.71 Wt.-% Additive 1 2.09 Gew.-% Additive 2 0.30 Eq.-%

[0096] Additive 1 is poly(oxy-1,2-ethanediyl), α-methyl-w-phosphate. Additive 2 is polyether-modified polymethylsiloxane.

[0097] Using this printing ink, a resulting effective linear coefficient of thermal expansion, α 20-300, eff , based on the glass particles and pigment particles encompassed by the printing ink, of 9.15 * 10 -6< / K is achieved. Comparative example 2

[0098] In comparison example 2, the plate has poor flatness but good, i.e., low, roughness. As shown below, this leads to poor raggedness of the printed image.

[0099] A volume-dyed, ceramized glass-ceramic material (600* 600 mm 2< ) was subjected to a one-stage ablation process.

[0100] No grinding process was performed to achieve flatness. The flatness was 789 µm.

[0101] The initial roughness of the plate was reduced by local heating using a CO2 laser with a spatial wavelength range of 100 µm until a roughness of RZ,mean of less than 0.5 µm was achieved.

[0102] The polished surface was printed with a secondary firing inkjet. Due to the surface's slight flatness, the printhead distance had to be adjusted during printing to prevent damage to the printhead. This resulted in the droplets generated in the printhead having varying path lengths to the substrate. The ink was then fired in a 45-minute curing process at a maximum temperature of 750°C.

[0103] The print or the printed image subsequently shows a deviation in print quality across the plate (raggedness for lines with a width of 300 µm at 62.8 µm).

[0104] The composition of the plate can be found in the following table: Component Eq.-% The 2 O 3,74 Al 2 O 3 21,29 SiO 65,21 TiO 3,64 ZrO 0,90 SnO 0,28 As 2 O 3 Cr 2 O 3 0,0035 P 2 O 5 0,052 MnO 0,021 Na 2 O 0,56 K 2 O 0,41 MgO 0,31 CaO 0,44 BaO 1,31 ZnO 1,58 V 2 O 5 0,0026 MoO 3 0,046 Fe 2 O 3 0,089 α 50-700 α 20-700 0,14 * 10 -6< / K α 25-700

[0105] The composition of the glass flux can be found in the following table: Component Eq.-% SiO 47,5 B 2 O 3 19 Al 2 O 3 2 The 2 O 4 Na 2 O 7,5 K 2 O 4 CaO 1 BaO 2 ZnO 8,75 TiO 3,8 Sb 2 O 3 0,2

[0106] The printing ink used was composed as follows: Glasfluss 1 2.98 Eq.-% Black Pigment CuCr 2 O 4 1.05 Eq.-% White pigment TiO 0.87 Wt.-% Dipropylenglycolmethylether 62.71 Wt.-% Additive 1 2.09 Gew.-% Additive 2 0.30 Eq.-%

[0107] Additive 1 is poly(oxy-1,2-ethanediyl), α-methyl-w-phosphate. Additive 2 is polyether-modified polymethylsiloxane.

[0108] Using this printing ink, a resulting effective linear coefficient of thermal expansion, α 20-300, eff , based on the glass particles and pigment particles encompassed by the printing ink, of 9.15 * 10 -6< / K is achieved. Description of Drawings

[0109] The invention will be further explained below with the aid of figures. These show Fig. 1 a schematic representation to explain the raggedness, Fig. 2 a top view of a schematic and not to scale plate according to one embodiment, and Figs. 3 and 4 side views of schematic and not to scale plates according to embodiments.

[0110] In Figs. 1 The principle of raggedness and its determination are explained using three schematic representations a), b) and c).

[0111] In Figs. 1a) and Figs. 1b) Two print images are shown, of which the one shown in Fig. 1a9 has only a slight raggedness and the one in Figs. 1b ) a high raggedness. "Raggedness" literally means "fragmentation" or "deterioration" and can be understood as a measure of the quality of a printed image, especially its edge sharpness. High raggedness means low edge sharpness, and vice versa.

[0112] In Figs. 1a) and Figs. 1b Enlargements of two "line prints" can be seen. Figs. 1b In the image with high "raggedness," individual droplets are still clearly visible in some places, as they did not blend sufficiently into a homogeneous print image. Edge sharpness is poor, and holes are visible in some parts of the print.

[0113] In contrast, the representation in Figs. 1a ), in which the map sharpness is obviously better - which in turn corresponds to a lower raggedness.

[0114] In Figs. 1c Figure 1 schematically shows an enlarged printed image of a "line". First, the area with a significant line width of 1 is selected, and a straight line is fitted to each of the line's edges. These two straight lines, representing the boundaries of the "ideal line", are shown in Figure 2. Figs. 1c ) are schematically represented as white lines on the black printed image.

[0115] Starting from these two lines, the standard deviation of the actual boundaries of the printed image on both sides from the ideal line is then determined, as described in Figs. 1c ) is shown schematically at point 2.

[0116] Raggedness is the arithmetic mean of the standard deviations on one side, here the "left", and the other, here the "right", side.

[0117] Preferably, the plate is designed such that the raggedness in the two sub-areas differs from each other by no more than 10%. Preferably, the ratio of the raggedness in one sub-area, R1, to the raggedness in the second sub-area, R2, i.e., the value R1 / R2, is between 0.5 and 2, preferably between 0.75 and 1.5, and particularly preferably between 0.9 and 1.1.

[0118] Figs. 2Figure 1 is a schematic and not-to-scale representation of a plate 3 according to one embodiment. The plate 3 comprises a glass or a glass-ceramic. The glass can, in particular, be a lithium-aluminum-silicate glass; the glass-ceramic a lithium-aluminum-silicate glass-ceramic. Preferably, the plate 3 has a thickness between 2 mm and 6 mm. The plate has two opposing, preferably parallel, side surfaces, of which only side surface 31 is visible here, as well as the circumferential edge surface 33. The flatness of the plate 3 is less than or equal to 0.1% of a lateral dimension 5, which here is, by way of example, the diagonal of the rectangularly shaped plate 3. Preferably, the lateral dimension 5 under consideration can be the maximum lateral dimension of the plate 3; for example, the diameter of a circular plate 3.

[0119] On at least one side of the plate 3, here side 31, it has a mean surface roughness Rz,minel of less than 0.5 µm in at least one area, here area 311, with a standard deviation of the surface roughness, σRz, of less than 0.1 µm. Preferably, Rz,minel and the standard deviation of the surface roughness, σRz, are determined by measuring the roughness Rz at nine points on the plate 3, which are spaced at least 5 cm apart, preferably at least 10 cm apart, and particularly preferably at least 15 cm apart, and by determining the arithmetic mean and the standard deviation from these nine measurements, and wherein Rz is particularly preferably determined by measuring a line profile with a stylus instrument and evaluating it according to ISO 4827.

[0120] The roughness Rz is also referred to as roughness depth and indicates the maximum height difference along a center line on a defined measuring distance.

[0121] Furthermore, the plate 3 comprises a coating 5, which is arranged on at least two different sub-areas 3101, 3102 of the area 311 of at least one side 31 of the plate 3. Here, the coating 4 is designed as a cooking zone marking by way of example, specifically in the form of four rings applied to the side 31. The area 311 here includes, by way of example, one of these cooking zone markings.

[0122] In principle, it is possible that area 311 encompasses the entire surface of page 31. In particular, it is also possible that sub-areas 3101 and 3102 of area 311 relate to different cooking zone markings.

[0123] The raggedness of the coating 5 in the two sub-areas 3101 and 3102 differs by a maximum of 10% from each other, preferably the raggedness being determined according to ISO 24790.

[0124] Preferably, according to one embodiment, the coating 5 can be an inkjet printing coating.

[0125] The Figs. 3 Figure 1 shows a schematic and not-to-scale side view or section of a plate 3 according to one embodiment. The plate 3, comprising a glass or a glass-ceramic, in particular a lithium-aluminum-silicate glass or a lithium-aluminum-silicate glass-ceramic, preferably has a thickness d between 2 mm and 6 mm. The thickness of the plate 3 is generally understood to be the distance between the two side surfaces 31, 32 of the plate 3. The two side surfaces 31, 32 of the plate 3 are opposite each other and are preferably arranged as shown in the illustration. Figs. 3, arranged parallel to each other within the limits of measurement accuracy.

[0126] An arrangement is considered parallel if the normal angles to the side surfaces 31, 32 enclose an angle of no more than 5° with each other, preferably no more than 2° and most preferably within the range of usual manufacturing and measurement tolerances of 0°.

[0127] If one side 31, 32 of plate 3 is textured, the area formed by the tips of the studs is used to determine the normal angle. This is shown schematically below. Figs. 4 shown.

[0128] Further shown is in Figs. 3 the circumferential edge surface 33 of the plate 3.

[0129] At least the side 31, on which in particular the coating 5 is also arranged, has in at least one area 311 as described only a low mean roughness R z,mean of less than 0.5 µm with a standard deviation of the surface roughness, σ Rz of less than 0.1 µm.

[0130] Furthermore, the plate 3 comprises a coating 5, which is arranged on at least two different sub-areas 3101, 3102 of the at least one area 311. The at least two sub-areas 3101, 3102 are spaced at least 3 cm, preferably at least 9 cm, and particularly preferably at least 15 cm apart, wherein the raggedness of the coating 5 in the two sub-areas 3101, 3102 differs from each other by a maximum of 10%, wherein the raggedness is preferably determined according to ISO 24790.

[0131] It may be intended that side 32 is also designed as a very smooth and / or very flat surface. However, it is also possible, and may even be preferable, that only one side, here side 31, which faces the user or operator during the operation of a device such as a cooktop, has the particularly good roughness and flatness. In particular, it may be intended that area 311 of side 31 of plate 3 encompasses the entire surface of side 31, in other words, that the entire side 31 is designed as a very smooth, flat surface. In this way, it is possible to achieve consistently good print images across the entire surface of side 31, especially in a non-contact printing process such as inkjet printing.

[0132] If the side 32 of plate 3 opposite the top side 31 is not as smooth and flat as side 31, it may be provided that side 32 is, for example, textured. This can be advantageously combined, for instance, with plate 3 comprising a colored glass-ceramic, since in this case the textured surface is not visually obtrusive due to the inherent color of the glass-ceramic within plate 3. Such a design can be particularly advantageous if a particularly high strength of plate 3 is desired.

[0133] Figs. 4Figure 3 shows a schematic, not-to-scale, side view of a plate 3 according to one embodiment. The plate 3 has a side 31 which exhibits very good flatness and a very low average roughness, i.e., it is very smooth. Side 31 is designed as the top surface, meaning it is intended to face the user during the operational use of a device for which the plate 3 serves as a cover plate (for example, a cooktop). On side 31 of the plate 3, the coating 4 is arranged in the two sub-areas 3101 and 3102 of the area 311, which exhibits at least good flatness and smoothness. This coating may have been applied, in particular, by a non-contact printing process, such as inkjet printing.For example, generally, without being limited to the specific example of plate 3 shown here, the coating 4 can be configured as a cooking zone marking, but also as a logo. In particular, the coating 4 can be configured as a glass flux-based coating or comprise a glass flux, or be configured as enamel. Furthermore, it is possible, and may even be preferred, that the coating 4 is configured as a glass flux-based coating (or comprises a glass flux) or as enamel and further comprises at least one pigment, in particular a ceramic pigment. The at least one pigment preferably does not comprise pigment particles with a primary particle size, determined as the d50 value of the equivalent diameter, of more than 1.0 µm, and most preferably does not comprise pigment particles with a primary particle size, determined as the d90 value of the equivalent diameter, of more than 2.5 µm.

[0134] Plate 3 is shown here in a schematic and not to-scale illustration of Figs. 4 The plate 3 is designed such that the side 32 opposite side 31 is textured. The two opposite sides 31 and 32 are designed to be parallel to each other. To determine this, it is shown schematically in Figs. 4 As shown, the normal angle to the two sides 31, 32 is determined, i.e., angles n31 and n32. In the case of a studded side 32, a surface 32a is used for this purpose, in the schematic section view of the Figs. 4 The line represented as a dashed line is determined by the points of the bumps. The normal angle to this surface is then taken as the normal angle n 32 of side 32.

[0135] How to interpret the schematic representation in Fig. 4As can be seen, the normals to the two sides 31, 32 are parallel to each other within the limits of measurement accuracy, so that sides 31, 32 are also parallel to each other within the limits of measurement accuracy. Reference symbol list 1 Line width 2 Deviation from the edge of the printed image 3 plate 31, 32 Side surfaces of the plate 32a Area measured on a studded plate or page 32 33 Circumferential edge surface 311 Section of page 31 3101, 3102 subsection of 311 4 coating 5 lateral dimension of 3 n 31 , n 32 Normal angles at 31, 32

Claims

1. Plate comprising glass or glass-ceramic, more particularly a lithium aluminium silicate glass or a lithium aluminium silicate glass-ceramic, preferably having a thickness of between 2 mm and 6 mm, having two mutually opposite, preferably parallel, side faces and a circumferential edge face, where the flatness of the plate is less than or equal to 0.1% of a lateral dimension, for example a diagonal, of the plate, and at least one side in at least one region has a mean surface roughness Rz,mean of less than 0.5 µm with a standard deviation of the surface roughness, σRz, of less than 0.1 µm, where preferably Rz,mean and the standard deviation of the surface roughness, σRz, are determined by measuring the roughness Rz at nine points on the plate, which are each at least 5 cm, preferably at least 10 cm and more preferably at least 15 cm apart from one another, and from these nine measurement values determining the arithmetic mean and the standard deviation, and where more preferably Rz is determined by measuring a line profile with a stylus device and with evaluation according to ISO 4827, and further comprising a coating which is disposed on at least two different subregions of the at least one region of the at least one side of the plate, where the at least two subregions are at least 3 cm, preferably at least 9 cm and more preferably at least 15 cm apart from one another and where the raggedness of the coating in the two subregions differs by not more than 10%, where preferably the raggedness is determined according to ISO 24790.

2. Plate according to Claim 1, where the coating is an inkjet print coating.

3. Plate according to either of Claims 1 and 2, where the coating comprises a glass flux and / or is embodied as enamel, preferably as coating comprising a glass flux and / or embodied as enamel and comprising at least one pigment, where more preferably the at least one pigment comprises no pigment particles having a primary grain size, determined as d50 of the equivalent diameter, of more than 1.0 µm, very preferably no pigment particles having a primary grain size, determined as d90 of the equivalent diameter, of more than 2.5 µm.

4. Plate according to any of Claims 1 to 3, where the plate is embodied as a plate smooth on either side, more particularly in the form such that no side of the plate has a nubbed embodiment, or where the plate is embodied in the form such that one side is smooth and the opposite side has a nubbed embodiment and where the coating is disposed on the smooth side of the plate.

5. Plate according to any of Claims 1 to 4, where the plate comprises a glass-ceramic, preferably having at least one of the following features: - the glass-ceramic has a volume-coloured embodiment, - the glass-ceramic comprises on the at least one side no vitreously embodied surface zone.

6. Process for producing a plate according to any of Claims 1 to 5, comprising the steps of: - providing a plate comprising a glass or a glass-ceramic, more particularly a lithium aluminium silicate glass or a lithium aluminium silicate glass-ceramic, preferably having a thickness of between 2 mm and 6 mm, having two mutually opposite, preferably parallel, side faces and a circumferential edge face, - grinding at least one side of the plate, - polishing at least one side of the plate, - printing at least one side of the plate on at least two different subregions of the at least one region of the at least one side of the plate, so that a coating is disposed in these at least two different subregions, where the at least two subregions are at least 3 cm, preferably at least 9 cm and more preferably at least 15 cm apart from one another, preferably printing by means of a contactless printing process, preferably by means of inkjet printing, - baking the coating.

7. Process according to Claim 6, characterized by at least one of the following features: - the coating comprises a glass flux and / or is embodied as enamel, preferably a coating comprising a glass flux and / or embodied as enamel and comprising at least one pigment, where more preferably the at least one pigment comprises no pigment particles having a primary grain size, determined as d50 of the equivalent diameter, of more than 1.0 µm, very preferably no pigment particles having a primary grain size, determined as d90 of the equivalent diameter, of more than 2.5 µm, - the plate comprises a glass, more particularly a green glass, and the baking of the coating takes place during a ceramization step in which the glass is transformed into a glass-ceramic, - the plate comprises a glass-ceramic, and the baking of the coating takes place in a secondary firing.

8. Use of a plate according to any of Claims 1 to 5 and / or produced in a process according to either of Claims 6 and 7 as a cooking surface.

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