WO2024235819A1 - Glass-ceramic article with a ceramic decoration, method for producing a glass-ceramic article and ink for use in a method of this type - Google Patents

Abstract

The invention relates to a glass-ceramic article with a ceramic decoration, wherein the decoration has pigment particles embedded in a glass matrix, wherein the article has a glass-ceramic substrate with a first thermal expansion coefficient α1, wherein the decoration has a second thermal expansion coefficient α2, wherein the difference Δα between the expansion coefficients α1 and α2 is max. 6 ppm/K, preferably max. 4 ppm/K, particularly preferably max. 3 ppm/K, wherein the decoration has a layer thickness of 0.5 - 5 µm, wherein the decoration has a blurriness according to ISO 24790 of less than 100 µm, preferably less than 70 µm, particularly preferably less than 50 µm, and wherein the smoothness Sdq of the decoration has a value of lower than 25 µm/mm, preferably lower than 20 µm/mm, particularly preferably lower than 15 µm/mm. The invention also relates to a method for producing a glass-ceramic article and an ink for use in a method of this type.

Description

Glass-ceramic article with a ceramic decoration, method for producing a glass-ceramic article and ink for use in such a method

Description

The invention relates to a glass-ceramic article according to the preamble of claim 1, as well as a method for producing such an article and an ink for use in such a method.

Glass-ceramic articles are known in the prior art in various forms. A "glass-ceramic article" is understood to mean an article whose main component is a glass ceramic. Well-known examples of this are cooking surfaces made of glass ceramic. A large number of markings and other optical elements are usually applied to the top of such a cooking surface, with which, for example, the boundaries of cooking zones are indicated or control elements, in particular touch-sensitive sensor surfaces, are highlighted. The type of cooking surface or a manufacturer's logo can also be applied to the top of a cooking surface. Such markings and optical elements are referred to collectively below as "decor". Thus, a decoration in the sense of the present invention does not have a purely artistic content, but rather serves a technical purpose.

When a cooking surface is in use, such decorations are usually exposed to high thermal and mechanical stress. For example, there are massive local temperature differences in the area of the cooking zones or at their edges, which place high demands on the thermal expansion of such decorations. At the same time, the decorations are exposed to strong mechanical stress, for example when a piece of cookware is moved or when the hob is cleaned with an abrasive cleaner, which must not lead to abrasion of the decoration and thus a deterioration in the visual appearance of the hob.

In the state of the art, materials are often used to produce such decorations whose physical properties are similar to the substrate on which the decoration is applied, for example a plate made of glass ceramic. In particular, a glass frit is often used, which is mixed with pigment particles and other substances to produce an ink and applied to the substrate. When the ink is subsequently fired, the glass frit is melted and thus forms a glass matrix that is firmly bonded to the substrate and in which the pigment particles are embedded. With the appropriate choice of glass frit, a small difference in the thermal expansion coefficient can be achieved. between substrate and decor, so that detachment of the decor due to different thermal expansion between substrate and decor is avoided.

In the prior art, such decorations are usually applied using a screen printing process in which the ink is spread through a suitably structured screen using a squeegee, so that the ink is only deposited on the areas of the substrate specified by the screen. The decorations on substrates printed in this way often have a relatively rough surface, which has a negative effect on the mechanical resistance of the decoration. Furthermore, when a decoration is applied using screen printing, the specific shape of the decoration is specified by the corresponding screen. Changing the decoration is therefore only possible by replacing the screen, which is usually only possible by interrupting the printing process and time-consuming retooling of the printing device.

In contrast, the present invention is based on the object of specifying a glass-ceramic article with a ceramic decoration, which is characterized by high thermal and mechanical resilience and can preferably be produced by alternative printing methods, in particular inkjet printing methods (hereinafter also referred to as "inkjet"). Furthermore, a corresponding method for producing such an article and an ink for use in such a method are specified.

In a first aspect, the invention accordingly relates to a glass-ceramic article with a ceramic decoration, wherein the decoration has pigment particles embedded in a glass matrix. The article has a glass-ceramic substrate with a first thermal expansion coefficient en, wherein the decoration has a second thermal expansion coefficient 02. The difference Aa between the expansion coefficients c and ct2 is at most 6 ppm/K, preferably at most 4 ppm/K, particularly preferably at most 3 ppm/K. Furthermore, the decoration has a layer thickness of 0.5 - 5 pm, and a blurriness according to ISO 24790 of less than 100 pm, preferably less than 70 pm, particularly preferably less than 50 pm.

wobei z eine Erhebung der Dekoroberfläche über eine Referenzfläche beschreibt, wobei die Referenzfläche parallel zur Oberfläche des glaskeramischen Substrats aufgespannt ist und wobei A eine Teilfläche der Oberfläche des Dekors beschreibt. It is further provided that the smoothness Sdq of the decoration has a value of less than 25 pm/mm, preferably less than 20 pm/mm, particularly preferably less than 15 pm/mm, wherein the smoothness is calculated as follows:

where z describes an elevation of the decorative surface above a reference surface, the reference surface being spanned parallel to the surface of the glass-ceramic substrate and A describing a partial area of the surface of the decoration.

The limitation of the smoothness of the decoration to values of less than 25 pm/mm has the effect that the decoration offers a smaller area of attack for forces that act essentially parallel to the surface of the substrate and could therefore lead to the decoration detaching from the substrate. Consequently, the mechanical strength of the decoration is increased by the inventive design of the decoration.

The smoothness Sdq, which is described as a characteristic feature, describes the gradient of the decorative surface compared to the substrate surface, averaged over a reference surface A. The values x and y describe the width and length of a measuring window in the form of the reference surface A, while the height function z(x,y) describes the local elevation of the decoration above a reference surface, in particular the surface of the decoration. In particular, a measuring window with a size of 1.5 x 1.5 ^mm2 can be provided as the reference surface A, which lies completely within the decoration, i.e. does not include any unprinted areas of the substrate. The partial derivatives of the height function dz(x,y)/dx and dz(x,y)/dy indicate the gradient of the decorative surface in the x and y directions at each measuring point on the measuring surface A. These gradients per measuring point in the x and y directions are added quadratically and summed for each measuring point (x,y) on the measuring surface A. To calculate the average, the result obtained is then divided by the measuring area A and the square root is taken from the result.

A "ceramic decoration" is generally understood to mean a decoration whose main components are inorganic, non-metallic materials. The glass frit used, in which the pigment particles of the decoration are embedded after the glass frit has been melted in a firing process, is adapted in its mechanical and thermal properties to the properties of the substrate. In particular, it can be provided that the chemical composition of the glass frit is close to the chemical composition of the substrate, so that the substrate and decoration have approximately the same thermal expansion coefficients.

As previously stated, the decor also has a blurriness according to ISO 24790 of less than 100 pm, preferably less than 70 pm and particularly preferably less than 50 pm. The blurriness is a measure of the sharpness of the edges of a decor and indicates the distance over which the thickness of the decor at its edge decreases from its target thickness to a defined level. The previously described mechanical resistance of the decoration is further improved according to a further embodiment in that the scattering Sq of the decorative layer has a value of less than 250 nm, preferably less than 200 nm, wherein the scattering Sq of the decorative layer is calculated as follows:

J ^A wobei z einen Abstand der Dekoroberfläche von einer Referenzfläche beschreibt, wobei die Referenzfläche parallel zur Oberfläche des glaskeramischen Substrats aufgespannt ist und wobei A eine Teilfläche der Oberfläche des Dekors beschreibt. Sq =

J ^A where z describes a distance of the decorative surface from a reference surface, the reference surface being spanned parallel to the surface of the glass-ceramic substrate and A describing a partial area of the surface of the decoration.

The scattering of the decorative layer Sq according to the calculation rule described above provides a measure of the roughness of the surface of the decor. The values used in the calculation rule are defined analogously to the calculation of the smoothness of the decor Sdq described above. The value Sq represents the root mean square of the ordinate values z(x,y) of the decor within the reference area A and corresponds to the standard deviation of the roughness within the reference area A. Analogous to the previous considerations, a lower roughness of the surface of the decor also means that the decor offers only small attack surfaces for forces acting on the decor essentially parallel to the surface of the substrate, which further increases the mechanical resistance of the decor.

The roughness of the decorative layer is influenced by a number of properties of the decor. Among other things, a distribution of the components of the decor that is as homogeneous as possible and, in particular, a homogeneous distribution of the pigment particles within the decor contributes to a low roughness, as in this case local accumulations or clumps of pigment particles, which can lead to a local increase in the thickness of the decor and thus to an increase in the roughness and a reduction in the smoothness of the decor, are avoided.

A homogeneous distribution of the decoration and the pigment particles is also reflected in other parameters, which in particular describe the print quality of the decoration. According to another embodiment, the decoration has a raggedness according to ISO 24790 of no more than 20 pm, preferably no more than 10 pm. Raggedness refers to the fraying of edges or borders of the decoration, for example the local deviation of the edge of the decoration from the ideal geometry of the intended decoration that is actually to be achieved. A slight fraying of the contours of the decoration also helps to ensure that the decoration offers the smallest possible surface area for acting forces, so that a low level of raggedness also contributes to the mechanical resistance of the decoration. According to a further embodiment, a particularly homogeneous decorative layer is also achieved in that the particle size distribution of the pigment particles is D100 less than 5 pm, D90 less than 5 pm, preferably less than 2.5 pm, particularly preferably less than 1 pm and D50 less than 1 pm. As already described, this contributes to a high level of smoothness, low roughness and clean edge quality of the decoration, resulting in a high level of mechanical resistance of the decoration. The small size and the uniform size distribution of the pigment particles also contributes to the fact that low layer thicknesses of the decoration can be achieved, whereby the layers are very homogeneous and therefore particularly stable.

According to a further embodiment, the high mechanical resistance of the decoration is also shown in that the decoration, after carrying out an abrasion test using an abrasive medium with abrasive particles, preferably consisting of Al2O3 with a dso of 5-20 pm and a solids content of 30-35%, with a contact pressure on the decoration of 1 N/ ^cm2 after 500 strokes over a distance of 15 cm, exhibits an abrasion of less than 0.5 pm, preferably less than 0.3 pm. “Abrasion” is understood to mean the reduction in the thickness of the decoration as a result of the abrasion test. To carry out such an abrasion test, a cloth can be used, for example, as the carrier material for the abrasive medium, and a commercially available cleaning agent with the properties mentioned above can be used as the abrasive medium. When carrying out the abrasion test, the test is preferably carried out on a track with a width of approximately 2 cm. To pretreat the area to be tested, it is preferable to clean the area to be tested of dirt using another cleaner before carrying out the abrasion test and then dry it so that reproducible test conditions are established.

Such tests can also be carried out automatically, for example with the aid of a suitable test device such as the Elcometer 1720 Washability Tester. In particular, a test speed can be set that specifies the speed at which the abrasive medium is passed over the decoration to be tested. A test speed of around 35 to 40, in particular 37 test cycles or strokes per minute is preferably set.

The degree of abrasion is influenced, among other things, by the specific nature of the solid bodies in the abrasive medium that act as scouring particles. It is preferably provided that the scouring particles essentially have a size of 1 pm to 50 pm. In particular, the distribution of the grain sizes of the scouring particles can be such that D10 is about 1 pm, D50 about 9 pm and D90 about 30 pm. The scouring particles can They may consist, for example, of aluminium oxide, whereby the abrasive particles may be emulsified in a suitable carrier medium.

According to a further embodiment, it is further provided that the weight ratio of glass to pigment of the decoration is 1:0.15 or greater. A high proportion of glass compared to pigment in the decoration can have a positive effect on the surface quality of the decoration, since the glass portion essentially melts smoothly when the decoration is fired, thus promoting a smooth surface of the decoration. With a higher pigment portion, on the other hand, the surface would possibly be roughened by protruding pigment particles. As already described above, a high level of smoothness of the decorative surface has a very positive effect on the mechanical resistance of the decoration to mechanical stress.

According to a further embodiment, the high quality of a decoration according to the invention is shown in particular in that the decoration has a partial geometry, wherein the partial geometry has a line width of at most 0.5 mm, preferably at most 3 mm, particularly preferably at most 1 mm.

In a further aspect, the invention relates to a method for producing a glass-ceramic article according to one of the preceding claims, comprising the steps:

• Providing the glass-ceramic substrate,

• Determining a target decoration to be applied to the substrate, wherein the target decoration is divided into a grid of regularly arranged pixels,

• Applying an ink pixel by pixel to positions on the substrate corresponding to the pixels of the desired decoration by means of a printing device, in particular an inkjet printer, and

• Burning the ink onto the substrate.

The glass-ceramic substrate is preferably a plate made of glass-ceramic, which is intended in particular for use as a hob. Both colored and uncolored, transparent substrates can be used.

The target decor can be determined in particular by automatically reading a storage medium. The target decor can have different types of decor. For example, a target decor can consist of line patterns and flat printed areas. Furthermore, the target decor can also include areas that have certain geometric patterns. The target decor is specified in the form of a regular grid, in particular, with a Color value, in particular a gray value, is specified. The target decor can also be derived from a precursor graphic, which does not necessarily have to be in raster form. In a previous step, it can also be provided that a graphic that is initially in a different format, for example a vector graphic, is converted into a raster graphic and then interpreted as the target decor.

The subsequent pixel-by-pixel application of the ink to the substrate is preferably carried out by moving a corresponding print head of the printing device, which is designed in particular as an inkjet printer, to a point on the substrate that corresponds to the raster point of the desired decoration. A defined amount of ink is then applied to the substrate at the corresponding position in accordance with the specified operating parameters of the printing device. The resulting print image can be adapted to individual requirements by varying the operating parameters of the printing device accordingly.

Once all the pixels of the desired decoration have been transferred to the substrate, the ink is then burned onto the substrate. Burning means that the ink is exposed to a temperature that causes the glass portion of the ink to melt. This can also cause volatile components of the ink to evaporate. By melting the glass, the pigment particles are firmly embedded in the resulting glass matrix. Burning can take place at a baking temperature of preferably < 1200 °C, more preferably < 900 °C, even more preferably < 850 °C, even more preferably < 800 °C, in particular < 750 °C and preferably a baking time in the range of 2 min to 5 h, more preferably 5 min to 1 h, in particular 10 to 15 min.

According to one embodiment, the quality of the decoration or the print image achieved and the homogeneity of the layer produced thereby are improved in that the method further comprises modifying the target decoration, wherein the modification of the target decoration includes selectively deleting pixels from the target decoration. “Deleting pixels” is to be understood in this case as changing the corresponding information at a colored raster point, i.e. a raster point at whose corresponding position on the substrate ink is to be applied, so that no ink is applied to the substrate. In effect, the pixel itself is not deleted, but the color information is changed to “not printed”.

For example, such deletion of pixels can be provided for an area that is to be printed on a large area, i.e. ink is to be applied to the corresponding position on the substrate for all pixels in a larger area. In this case, For example, the homogeneity of the resulting layer and thus the mechanical resistance of the decoration can be increased if a certain percentage of the corresponding pixels are deleted. Furthermore, the general printed image can also be improved in this way.

When using an inkjet printer, printing is usually done line by line. This means that the print head of the inkjet printer moves over all positions on the substrate that are next to each other in a line in the target decoration, with a corresponding amount of ink being applied to corresponding positions on the substrate where a color value is specified according to the target decoration. When the print head has moved over all points in a line, the procedure is repeated for an adjacent line. According to one embodiment, the printing process itself can be accelerated by applying the ink to a plurality of pixels arranged next to each other in a row at the same time. In this way, several lines of the target decoration can effectively be transferred to the substrate at the same time with a single pass of the print head, which can significantly shorten the overall duration of the printing process. It can be particularly preferred that the transfer of the target decoration is transferred to the substrate by means of a single pass of the print head, i.e. all lines of the target decoration are printed simultaneously.

In a further aspect, the invention relates to an ink for use in a method according to one of claims 8 to 10, wherein the ink comprises pigment particles, glass particles (also referred to as "glass frit"), a solvent, a dispersant and a wetting additive, characterized in that the ink is free of binders. A binder is usually used so that the structural fidelity and layer morphology of the ink applied to the substrate is maintained until the glass particles melt. However, it has been shown that omitting a binder in the ink has a positive effect on the resulting printed image and in particular on the durability of a corresponding decoration.

An example composition of the ink is as follows:

Pigment particles 0.1 - 5% by volume

glass particles 10 - 20 Vol-%

Solvent 70 - 85 Vol-%

dispersant 0.5 - 5 Vol-%

wetting additive 0.1 - 5 vol-%

The pigment particles preferably have a grain size of 0.2 - 2.5 pm, with D10 preferably being 0.2 - 0.3 pm, D50 0.6 - 0.9 pm and D90 1.3 - 1.7 pm. A suitable solvent can be selected from water, alcohols, ethers such as glycol ethers, lactates, acetates, aldehydes, ketones, aromatic hydrocarbons, oils and fatty acid derivatives. Commercially available products can also be used, such as solvents from Johnson Matthey (e.g. high-boiling paste oils such as JM 850-63 or JM 650-63); Dowanol DB (diethylene glycol n-butyl ether from Dow Chemical) or the like. Mixtures of two or more of these compounds are also possible. Preferred examples include, but are not limited to, polyethylene glycol, ethylene glycol monobutyl ether, dipropylene monoglycol ether, 1-methoxy-2-propanol and diethylene glycol n-butyl ether, and commercially available solvents can also be used.

According to the invention, a wide range of dispersants can be used. These are, for example, selected from the group consisting of lecithin, phosphoric acid esters, amine salts, polyester styrene resins, xylene, castor oil, 3-acryloxypropyltrimethoxysilane, polycarboxylic acids, polycarboxylic acid polyesters, polyacrylates, polyamides, polyamine amides, esters, micronized polyethylene wax, polyethylene glycol, silicones, alkoxysilanes, hybrid polymers, organically modified metal alkoxides, high molecular weight copolymers with pigment-affine groups, block copolymers, graft copolymers and mixtures thereof. Commercially available dispersants are also used, for example from TEGO or Byk, such as TEGO® Dispers, TEGO® VariPlus, TEGO® ViscoPlus, Bykumen ®, Disperbyk®, BYK®, Anti-Terra® U, K-Sperse XD, Efka, Texaphor® or the like. Organically modified metal alkoxides are particularly preferred, such as 3-methacryloxypropyltriethoxysilane (MPTES), 3-methacryloxypropyltrimethoxysilane (MPTMS), 3-glycidoxypropyltriethoxysilane (GPTES), 3-glycidoxypropyltrimethoxysilane (GPTMS), Dynasylan VTMO, isooctyltriethoxysilane or 7-octenyltrimethoxysilane, as well as commercial dispersing additives from Byk and TEGO. Mixtures can also be used. In the present invention, the dispersant is also referred to as a dispersing additive, which supports the distribution of the glass frit and/or the additives in the solvent.

Commercially available products such as TEGO® Dispers, TEGO® Wet, TEGO® TWIN, BYK® can be used as wetting additives.

The glass particles preferably have the following composition:

45 - 85 wt.% SiO2, 2 - 20 wt.% AI2O3, 0 - 23 wt.%, preferably 0 - 18 wt.% B2O3, 0 wt.% Bi2O3, 0 - 15 wt.%, more preferably 1 - 15 wt.%, even more preferably 1 - 9 wt.% alkali oxides, 0 - 18 wt.% alkaline earth oxides,

0 - 7 wt.% ZnO,

0 - 3 wt.% TiO2,

0 - 5 wt.% ZrO2, and 0 - 2 wt.% halides.

In the following, preferred embodiments of the invention are explained in more detail with reference to the figures. In the figures:

Figure 1 is a schematic representation of an exemplary glass-ceramic article in the form of a hob,

Figure 2 is a representation of the surface profile of an exemplary decoration of the hob of Figure 1,

Figure 3 is a greatly enlarged view of the decoration,

Figure 4 is a detailed view of another exemplary decoration,

Figure 5 is a flow chart of an exemplary method, and

Figure 6 shows an exemplary representation for modifying a target geometry.

In the following, similar or identical features are identified with the same reference symbols.

Figure 1 shows a schematic representation of an exemplary glass-ceramic article in the form of a hob 100. Accordingly, the hob 100 consists of a plate made of a glass ceramic, which has, for example, dimensions HBT of 4x740x560mm ^3. In particular, this can be a colored glass ceramic.

Different types of decorations are usually applied to the top of such a hob, which serve different purposes. For this purpose, Figure 1 shows an example of a first variant of a top-side decoration in the form of a circular cooking zone boundary 102. Such a cooking zone boundary 102 can be used, for example, to indicate in which area of the cooking surface 100 a cooking utensil can be heated by inductive or radiation-based heating elements arranged under the hob. Such Cooking zone boundaries 102 are usually represented by comparatively thick contours and are exposed to strong mechanical stresses, for example when cooking utensils are moved beyond the cooking zone boundary 102.

A control panel 104 for controlling the hob 100 or the heating elements arranged under the hob 100 is indicated at the bottom in the middle. Such a control panel 104 can have a wide variety of different types of decorations. In addition to decorations applied over a large area, for example to represent adjustment ranges for a temperature control of the cooking surface 100, very fine decorations can also be provided in such an area, by means of which control symbols, in particular numbers and characters, are displayed.

A third variant of a decoration shown in Figure 1 is a pattern 106 that is applied largely over the entire surface and only has recesses in the area of the cooking zone boundaries 102 and the control panel 104. Such patterns 106 can be applied for purely aesthetic reasons, for example, and can contain colored elements in addition to different patterns. In particular, such a pattern 106 can also contain very finely printed elements that have a line width of 0.1 mm. Not shown in Figure 1 are further markings on the top of the hob 100 that indicate, for example, the manufacturer of the hob, the type of hob or other product-specific information. Such markings are usually arranged in the area of the corners of the hob 100.

The types of decorations described above are exposed to different types of stress during operation of such a cooking surface 100. A first type of stress is thermal stress, which results from the heating of the cooking surface 100 in certain areas. This creates locally different temperature gradients, which can lead to different thermal expansions of the substrate and the decoration, depending on the nature of the substrate and the decoration. In extreme cases, this can cause the decoration to detach from the substrate. However, this effect can be compensated for by adjusting the thermal expansion coefficient of the decoration to the thermal expansion coefficient of the substrate.

A second type of load is mechanical loading of the decoration. Such a load can occur during operation of the cooking surface 100 by moving cookware beyond the cooking zone boundaries 102. In this case, forces can act on the decoration that act essentially parallel to the surface of the substrate and can therefore also lead to the decoration detaching from the substrate. The same effect can also occur when cleaning the cooking surface with abrasive cleaning agents, since in this case a force also acts parallel to the substrate surface. As already described above, the resistance of the decoration to mechanical stress is increased according to the invention in particular by the smoothness Sdq of the surface of the decoration being less than 25 pm/mm, preferably less than 20 pm/mm, particularly preferably less than 15 pm/mm. The smoothness of the decorative surface describes the average gradient of the decorative surface, as described above. For this purpose, Figure 2 a) shows an example of the surface profile of an exemplary decoration of the hob in Figure 1, the surface profile being recorded using white light interferometry. The decoration shown in Figure 2 a) was produced using an inkjet printing process, which is described in more detail below. In comparison, Figure 2 b) shows a surface profile of a decoration that was produced using a screen printing process. The local deviation of the height z of the decoration from a reference surface is shown.

As can be clearly seen in Figure 2 a), particularly in comparison to Figure 2 b), the surface of the decoration according to the invention does indeed have elevations that are comparable in amplitude to those of the decoration in Figure 2 b). However, the respective elevations are significantly wider and less sharply demarcated from their surroundings. Accordingly, the number of such elevations within the reference surface under consideration is also significantly lower, so that overall the average gradient of the surface in Figure 2 a) is reduced compared to Figure 2 b).

The described smoothness of the decoration is achieved, among other things, by using an inkjet printing process to produce the decoration. The composition of the ink used, in particular the pigment particles used, also has an influence on the surface quality of the decoration. As already explained above, it is particularly advantageous if the pigment particles have a particle size distribution with a D50 of less than 1 pm and D90 of less than 5 pm, preferably less than 2.5 pm, particularly preferably less than 1 pm. For this purpose, Figure 3 a) shows an example of an image of a decorative surface according to the invention using scanning electron microscopy, while Figure 3 b) shows an image of a decoration applied using screen printing technology for comparison. As can be clearly seen in Figure 3, the pigment particles used in the exemplary decoration in Figure 3 a) are significantly smaller and significantly more homogeneously distributed than the particles shown in Figure 3 b).

In addition to the described surface quality, a decoration according to the invention is also characterized by the quality of its edges or contours. For example, in the figure 4 shows a detailed view of another exemplary decoration or a partial area of an exemplary decoration with a line geometry. In this case, Figure 4 a) again shows an exemplary decoration which was produced using an inkjet printing process, while Figure 4 b) shows a decoration produced using screen printing for comparison. As can be seen in the comparison of the figures, the decoration in Figure 4 a) has less fluctuation in the edge profile or less fraying and therefore less raggedness than the decoration in Figure 4 b). The contour sharpness of the decoration in Figure 4 a), expressed by the degree of blurriness, is also greater than the contour sharpness of the decoration in Figure 4 b), which, as previously stated, has a positive effect on the mechanical durability of the decoration.

Figure 5 shows a flow chart of an exemplary method for producing a decoration as described above. In a first method step 200, a glass-ceramic substrate is provided. The substrate can in principle be either a volume-colored substrate or a transparent substrate. The provision of the substrate can in particular include a preparation of the surface of the substrate that is to be printed on subsequently. Such preparation can in particular include a pretreatment to remove dirt and deposits, such as production residues from previous processing steps. Furthermore, the provision can also include clamping the substrate in a corresponding carrier device so that the position of the substrate is firmly defined relative to a printing device and no unintentional displacement of the substrate occurs during the printing process.

In a second method step 202, which in principle can also take place in parallel to the first method step, a target decoration to be applied to the substrate is determined. Such "determination" can in particular include retrieving corresponding information from a storage medium. The target decoration is divided into a grid of regularly arranged pixels, and is therefore preferably processed as a raster graphic. The determination of the target decoration can also include the conversion of a precursor graphic, for example a vector graphic, into such a raster graphic.

Before the actual printing process, such a target decoration can be subjected to further pre-processing steps. For example, in step 204, the target decoration can be modified, whereby the modification of the target decoration includes a selective deletion of pixels from the target decoration. It has been shown that the print image can be significantly improved by a clever selection of the pixels of the target decoration to be deleted. Such a selective deletion of pixels is shown as an example in Figure 6. The Figure 6 a) shows a raster graphic of the letter "R" as the initial target decoration. In Figure 6 b), however, individual pixels have been deleted from the raster graphic, where "deleted" in this case means that the color information is changed to the value "not printed" at the corresponding positions of the raster graphic.

Again with reference to Figure 5, after determining and, if necessary, modifying the target decoration in step 206, the target decoration is transferred to the substrate. For this purpose, ink is applied pixel by pixel to positions on the substrate corresponding to the pixels of the target decoration using a printing device, in particular an inkjet printer. For this purpose, a corresponding print head of the inkjet printer is preferably moved to the corresponding position and, depending on the color information of the pixel corresponding to the position, a defined amount of ink is deposited on the substrate. The print head can in particular be moved over the substrate line by line. During such a passage over the substrate, according to one embodiment, the ink can also be applied simultaneously to a plurality of pixels arranged next to one another in a row, with such a "row" extending perpendicular to the direction of movement of the print head. Particularly preferably, a print head can also be designed in such a way that the entire decoration is applied to the substrate with a single passage of the print head over the substrate.

Depending on the design of the inkjet printer, the print image can be adapted to the respective requirements by varying a large number of operating parameters. In particular, parameters such as the speed of the print head during a pass, the distance of the print head from the substrate surface, or the amount of ink to be dispensed per pixel can be varied.

In a final process step 208, the applied ink is then burned onto the substrate. The decoration is preferably burned at a temperature that is sufficient to melt the glass particles of the ink used, but does not lead to a change in the substrate, in particular to a ceramization or melting of the substrate surface.

Claims

patent claims 1. Glass-ceramic article with a ceramic decoration, the decoration having pigment particles embedded in a glass matrix, the article having a glass-ceramic substrate with a first thermal expansion coefficient en, the decoration having a second thermal expansion coefficient ct2, the difference Aa between the expansion coefficients c and 02 being at most 6 ppm/K, preferably at most 4 ppm/K, particularly preferably at most 3 ppm/K, the decoration having a layer thickness of 0.5 - 5 pm, the decoration having a blurriness according to ISO 24790 of less than 100 pm, preferably less than 70 pm, particularly preferably less than 50 pm, and the smoothness Sdq of the decoration having a value of less than 25 pm/mm, preferably less than 20 pm/mm, particularly preferably less than 15 pm/mm, the smoothness being calculated as follows:

where z describes an elevation of the decorative surface above a reference surface, the reference surface being spanned parallel to the surface of the glass-ceramic substrate and A describing a partial area of the surface of the decoration. 2. Glass-ceramic article according to claim 1, characterized in that the scattering Sq of the decorative layer is a value of less than 250 nm, preferably less than 200 nm, wherein the scattering Sq of the decorative layer is calculated as follows:

where z describes a distance of the decorative surface from a reference surface, the reference surface being spanned parallel to the surface of the glass-ceramic substrate and A describing a partial area of the surface of the decoration. 3. Glass-ceramic article according to one of the preceding claims, characterized in that the decoration has a raggedness according to ISO 24790 of at most 20 pm, preferably at most 10 pm. 4. Glass-ceramic article according to one of the preceding claims, characterized in that for the particle size distribution of the pigment particles D100 less than 5 pm, D90 less than 5 pm, preferably less than 2.5 pm, particularly preferably less than 1 pm and D50 is less than 1 pm. 5. Glass-ceramic article according to one of the preceding claims, characterized in that the decoration, after carrying out an abrasion test using an abrasive medium with a solid content of 30-35% at a contact pressure on the decoration of 1 N/cm ^2, has an abrasion of less than 0.5 pm, preferably less than 0.3 pm, after 500 strokes over a distance of 15 cm. 6. Glass-ceramic article according to one of the preceding claims, characterized in that the weight ratio of glass to pigment of the decoration is 1:0.15 or greater. 7. Glass-ceramic article according to one of the preceding claims, characterized in that the decoration has a partial geometry, wherein the partial geometry has a line width of at most 0.5 mm. 8. A method for producing a glass-ceramic article according to any one of the preceding claims, comprising the steps: • Providing the glass-ceramic substrate, • Determining a target decoration to be applied to the substrate, wherein the target decoration is divided into a grid of regularly arranged pixels, • Applying an ink pixel by pixel to positions on the substrate corresponding to the pixels of the desired decoration by means of a printing device, in particular an inkjet printer, and • Burning the ink onto the substrate. 9. The method according to claim 8, characterized in that the method further comprises modifying the target decoration, wherein modifying the target decoration includes selectively deleting pixels from the target decoration. 10. Method according to claim 8 or 9, characterized in that the application of the ink for a plurality of pixels arranged next to one another in a row takes place simultaneously. 1 1. Ink for use in a method according to one of claims 8 to 10, wherein the ink comprises pigment particles, glass particles, a solvent, a dispersant and a wetting additive, characterized in that the ink is free of binders.