Glass or glass-ceramic product with a coating and ink for its manufacture

Abstract

Glass or glass-ceramic product with a substrate made of glass or glass-ceramics, wherein the substrate is provided on at least one side on at least a part of its surface with a substantially pigment-free coating, wherein the coating has at least a partially molten glass flux, wherein the surface of the coating has a mean square height Sq of at least 0.1 µm and at most 2.5 µm, and wherein the coating has a core height Sk of at least 1.0 µm to at most 10 µm.

Description

[0001] The invention relates to a glass or glass-ceramic product with a coating, as well as an ink for producing such a glass-ceramic product. State of the art

[0002] A wide variety of applications for glass and glass-ceramic products are known from the state of the art. In particular, the most prominent example of glass-ceramic products, particularly in the case of disc-shaped products, is their use as a cooking surface.

[0003] Glass ceramic cooktops are often equipped with functional coatings on their upper surfaces that fulfill various functions. For example, EP 2 964 854 B1 discloses coatings that protect such a glass ceramic cooktop from scratches by means of a layer of AlSiN deposited on the substrate. Furthermore, coatings are also known that are intended to prevent soiling of cooktops, particularly from fingerprints. WO 2023 / 099833 A1 is an example of this.

[0004] There have also been approaches in the recent past to prevent scratches on the surface of a substrate as well as the formation of fingerprints or, in general, soiling of the cooking surface. EP 4 077 231 A1 is again an example here. This document discloses a glass-ceramic article obtained by a process which comprises a heat treatment for ceramizing a glass suitable for forming a glass-ceramic and a chemical treatment of a surface of the glass before and / or after the heat treatment for ceramization, wherein the chemical surface treatment is carried out such that, after the heat treatment, the arithmetic mean roughness of the surface is between 2 µm and 7 µm. With regard to the chemical treatment of the surface, the use of an acid solution based on hydrofluoric acid is described in particular.

[0005] The use of hydrofluoric acid for etching glass and glass ceramics is already known, but it comes with a number of disadvantages. Firstly, the time required to etch glass or glass ceramics until the aforementioned roughness is achieved is comparatively long. Secondly, hydrofluoric acid is a very problematic substance to handle, requiring numerous safety measures to ensure both the protection of the environment and the safety of those working with it.

[0006] Against this background, there is a need in the state of the art for a solution by means of which a glass or glass-ceramic article can be provided with the least possible effort, both in terms of time and in terms of occupational safety, the surface of which is both insensitive to scratches and largely avoids the formation of fingerprints and other contamination. Disclosure of the invention

[0007] The above-stated object is achieved with respect to a glass or glass-ceramic product having the features of claim 1. Solutions regarding an ink to be used for producing such a glass-ceramic product are the subject of claim 17. Advantageous embodiments are the subject of the dependent claims.

[0008] In a first aspect, the invention relates to a glass or glass-ceramic product with a substrate made of a glass or a glass-ceramic, wherein the substrate is provided at least on one side on at least part of its surface with a substantially pigment-free coating, wherein the coating has an at least partially melted, preferably boron-containing glass flux, wherein the surface of the coating has a mean square height Sq of at least 0.1 µm and at most 2.5 µm, and wherein the coating has a core height Sk of at least 1.0 µm to at most 10 µm.

[0009] The term "essentially pigment-free" means that the coating contains less than 1% pigment by weight, i.e., consists of at least 99% glass flux. A "pigment" refers to particles that alter the transmission properties of the coating compared to a coating consisting exclusively of glass flux. In particular, such pigment particles can cause the coating to become colored or to exhibit reduced transmission.

[0010] An “at least partially melted” glass flow is a glass flow, i.e. a quantity of glass particles with a defined size distribution, in which at least some of the particles have melted and re-solidified and are therefore no longer present as particles in the shape and size they originally contained in the glass flow. Due to this melted portion of the particles, the particles of the glass flow are firmly bonded to form a layer. At the same time, the melted part of the glass particles also serves to create a bond to the substrate. The unmelted part of the glass particles means that the surface is not completely flat, which would be expected with a completely melted glass flow. Rather, the partial melting of the glass particles results in a defined surface roughness of the coating.

[0011] The surface roughness of a glass or glass-ceramic product according to the invention, expressed as the mean square height Sq of the surface, is at least 0.1 µm and at most 2.5 µm. The mean square height of the surface of the coating is calculated according to the following rule: Sq=1A∫∫AZ2(x,y)dxdy where A is the observed area of ​​the coating and z is the deviation of a measurement point at position (x,y) from the mean height of the coating. Particularly preferably, the mean square height Sq of the coating is greater than 0.2 µm, greater than 0.3 µm, greater than 0.4 µm, or particularly preferably greater than 0.5 µm.

[0012] A further parameter that describes the nature of the coating according to the invention is the core height Sk of the surface of the coating. The core height describes the height of the area within the surface material portion of the coating surface to which 100% of the equivalence line (also referred to as the equivalent line) of the surface material portion falls. This area is also referred to as the core surface. The surface material portion (also referred to as the “areal material portion”) describes over which height range of the surface of the coating which portion of the coating material falls in the area of ​​the surface in question. Effectively, each height within the surface of the coating is assigned the material portion of the surface that lies above this height.In a graphical representation of this curve, the ordinate represents the height within the surface of the coating, while the abscissa indicates the material fraction in % that falls on the area above this height.

[0013] The degree of equivalence is the secant of the surface material fraction curve with the lowest detectable slope (or the smallest gradient), the points of intersection of which with the surface material fraction curve are 40% apart from their abscissa. By extrapolating the degree of equivalence to abscissa values ​​of 0% and 100%, the corresponding ordinate values ​​can be determined, with the core height being the distance between these ordinate values. Accordingly, a low core height means a very compact and therefore resistant coating, since a large portion of the surface material is concentrated in a narrow area. The core height Sk of the coating can in particular also be 1.5 µm to 9 µm, 1.5 µm to 8 µm, 1.5 µm to 7 µm, 2 µm to 6 µm, or particularly preferably 2 µm to 5 µm.

[0014] A summary of the values ​​of the coating according to the invention with regard to the mean square height and the core height clearly shows that the coating according to the invention combines a comparatively rough or matte surface with a very compact coating structure. Consequently, the coating according to the invention is characterized by good properties with regard to the prevention of fingerprints and other contaminants, while at the same time offering high resistance to scratches and wear.

[0015] The coating contains only components that are harmless to health and can be produced in a simple and cost-effective manner.

[0016] The glass particles in the coating's glass flux can, in particular, be particles made of boron-containing glass. The use of boron-containing glass flux offers advantages, among other things, regarding the coating's resistance to thermal shock and also improves the coating's adhesion, particularly when the substrate is a glass ceramic. Furthermore, when using a boron-containing glass flux, it is possible to fire the coating during the ceramization of the substrate, i.e., the conversion of a glass substrate into a glass ceramic substrate. In this way, a separate firing of the coating (so-called secondary firing) during product manufacturing can be avoided.

[0017] The previously described matte appearance of the coating is also reflected in one embodiment by the coating having a gloss value of no more than 25, measured at an angle of 60°. This also helps prevent the formation of visible contamination on the coating, particularly in the form of fingerprints. For example, fingerprints are more visible on a surface the glossier the surface.

[0018] Two important and unique parameters of the coating according to the invention have already been discussed. However, the coating according to the invention also differs significantly from coatings known in the prior art with regard to other surface parameters.

[0019] Thus, according to one embodiment, it is further provided that the coating has a skewness Ssk of > 0. The degree of skewness (also referred to as skewness) of a surface provides information about whether the surface can be described more as a surface with grooves or valleys, or rather as a surface with peaks. In the case of a surface with a skewness > 0, i.e. a surface with grooves, by definition the frequency of areas in the height distribution of the surface that protrude above the mean height is smaller than the proportion of areas that lie below the mean height. Since this can only occur if the areas below the mean height are less frequent but significantly more pronounced in their height (or depth) than the areas above the mean height, this means that the surface can be described more by valleys and grooves than by protruding peaks.

[0020] The skewness can be calculated by summing the cubes of all height values ​​and dividing them by the cube of the mean square height Sq of the surface of the coating: Ssk=1Sq3[1A∫∫Az3(x,y)dxdy]

[0021] A skewness > 0, i.e., a surface with grooves instead of peaks, has the advantage that grooves are significantly more resilient than protruding peaks. Thus, significantly more material must be removed to reduce the depth of a groove in the coating than to reduce a peak. Consequently, a surface skewness > 0 is associated with a greater robustness of the surface finish, since the surface structure is less affected, even during abrasive cleaning processes, for example.

[0022] According to a further embodiment, it is further provided that the surface of the coating has a kurtosis Sku of > 3, particularly preferably > 3 and < 8. The kurtosis of a surface describes the sharpness of a surface profile and is calculated as follows: Sku=1Sq4[1A∫∫Az4(x,y)dxdy]

[0023] A Kurstosis value of Sku > 3 describes a surface that tends to have jagged edges rather than rounded edges. A surface with a more jagged surface structure than rounded edges has the advantage that, for example, when touch-sensitive controls are activated, there is a smaller contact area between the coating surface and the operator's finger. This effectively prevents the visibility of fingerprints or similar marks, as these are only located on the very narrow tips of the surface structures.

[0024] According to a further embodiment, the coating has a thickness of 2 to 10 µm. The thickness of the coating is selected such that sufficient stability of the coating is ensured, but at the same time the transmission properties of the substrate are influenced as little as possible by the coating. Furthermore, structures arranged beneath the coating remain clearly visible. The thickness of the coating is preferably at least 3 µm, more preferably at least 4 µm. Furthermore, the thickness of the coating is preferably at most 9 µm, more preferably at most 8 µm, and most preferably at most 7 µm.

[0025] According to a further embodiment, it is further provided that a pigmented decorative layer is arranged at least in sections between the substrate and the coating. The pigmented decorative layer is preferably applied directly to the substrate and can be produced in particular by inkjet printing or screen printing. When the glass or glass-ceramic product is used as a cooking surface, the decoration can, for example, be a cooking zone marking. By arranging the decoration below the coating, the decoration is protected from abrasion, for example as a result of cleaning the glass or glass-ceramic product. At the same time, however, due to the low thickness of the coating and the absence of pigment in the coating, the visibility of the decoration and in particular its edge sharpness is only slightly impaired.In principle, the decoration can also be fired together with the coating, which simplifies the production of the glass or glass-ceramic product.

[0026] According to a preferred embodiment, the contour line of the decorative layer arranged beneath the coating has a root mean square roughness Rq of at most 20 µm, preferably at most 15 µm, when viewed vertically through the coating in a direction parallel to the surface of the substrate. The contour line of the decorative layer describes the course of the transition between that area of ​​the surface of the substrate which is covered by the decorative layer and that area of ​​the surface of the substrate which is essentially free of the decorative layer. “Essentially free” is understood to mean an area in which the thickness of the decorative layer and thus the color effect of the decoration is at least 10%, but at most 25% of the maximum color effect of the decoration.The contour line is considered analogous to the contour of a surface's elevation profile, so that the parameters known for describing surface textures can be used to describe the contour line. Accordingly, the root mean square roughness Rq can be specified for the contour line, among other things. This essentially provides information about the root mean square of all ordinate values ​​z(x) of the contour line at different points x along a measurement distance of length l. The value Rq is calculated as follows: Rq=1l∫0lz2(x)dx In effect, the Rq value reflects the contour sharpness of the decorative element when viewed through the textured coating. The smaller the Rq value, the sharper the decorative element's contours are. This is particularly advantageous because it allows even very fine decorative elements to be perceived essentially unadulterated, even through the textured coating.

[0027] According to a further preferred embodiment, the glass or glass-ceramic product has a decorative layer that is covered by the coating in a first partial region and not covered by the coating in a second partial region. The root mean square roughness Rq of the contour line of the decorative layer in the first partial region differs by only 10% at most, preferably 5% at most, from the root mean square roughness Rq of the contour line of the decorative layer in the second partial region.

[0028] Alternatively, the decoration can also be applied to the coating, which can simplify the production of the glass or glass-ceramic product. For example, the matte coating can be applied over a large area using a screen printing process, and the prepared glass or glass-ceramic product can then be decorated in a further step.

[0029] According to a further embodiment, the combination of decorative layer and coating has a thickness of at most 15 µm, preferably at most 12 µm, particularly preferably at most 10 µm.

[0030] It was already mentioned above that the coating is applied to at least part of the surface of the substrate. This means that the coating can certainly also have recesses, for example to create an area in which a display can be arranged. By creating a recess in the coating, i.e. an area of ​​the surface to which no coating is applied, the representation of the display can be improved compared to a full-surface coating. According to a further embodiment, however, it is provided that the coating is applied over the entire surface of one side of the substrate, which can simplify the production of the glass or glass-ceramic product.

[0031] As previously stated, the glass flux preferably contains boron. According to a preferred embodiment, the glass flux has the following composition in wt.% on an oxide basis: SiO2 75 - 85 Al2O3 0,1 - 5 B2O3 10 - 15 Na2O 1 - 5 K2O 0,1 - 1,5

[0032] A glass flux of this composition is particularly suitable for firing the coating during the ceramization of the substrate, which brings significant advantages with regard to the production of the glass or glass-ceramic product according to the invention.

[0033] According to a further embodiment, the substrate is disc-shaped and has a thickness between 2 mm and 6 mm, preferably between 3 mm and 5 mm, and particularly preferably a thickness of 4 mm. A "disc-shaped" substrate is understood to mean a substrate whose length and width are at least one order of magnitude greater than its thickness. In particular, the glass or glass-ceramic product can be a cooktop.

[0034] Different materials can be used as a substrate.

[0035] Thus, according to one embodiment, the substrate is transparent with a transmission τ vis of greater than 80%, preferably greater than 85%, and has a chroma c* of less than 10, in particular less than 8. The chroma c* is calculated according to the definition of the CIELab color system as c∗=a∗2+b∗2. In effect, it is a transparent and largely color-neutral substrate.

[0036] The composition of such a substrate in wt.% on an oxide basis can be selected, for example, as follows: SiO2 64 - 68 Al2O3 19 - 23 Li2O 3,2 - 4,2 MgO 0,2 - 1,0 Na2O + K2O 0,1 - 1,5 BaO 0 - 1,5 CaO + SrO 0 - 1,5 ZnO 1 - 2,5 TiO2 1,6 - 2,5 ZrO2 1,2 - 2,0 SnO2 0-0,5 Nd2O3 0,005 - 0,15 Fe2O3 0,001 - 0,03

[0037] Alternatively, according to a further embodiment, the substrate is volume-colored and has a transmission τ visof less than 10%. "Volume-colored" refers to a substrate that does not obtain its color from a coating, but rather contains elements within the material that contribute to the color of the material itself. Such volume coloration can be achieved, for example, by elements such as chromium, vanadium, or molybdenum that are added to the glass composition. For example, such a substrate can have the following composition in wt.% on an oxide basis: Li2O 3,0 - 4,2 Na2O+K2O 0,2 - 1,5 MgO 0 - 1,5 CaO+SrO+BaO 0 - 4 ZnO 0 - 2 B2O3 0 - 2 Al2O3 19 - 23 SiO2 60 - 69 TiO2 2,5 - 4 ZrO2 0,5 - 2 P2O5 0 - 3 SnO2 0,1 - <0,6 TiO2+ZrO2+SnO2 3,8 - 6 V2O5 0,01 - 0,06 Fe2O3 0,03 - 0,2

[0038] In a further alternative embodiment, it is further provided that the substrate is translucent with a transmission τ vis from 2% to 25% or opaque with a transmission τ visfrom 0.1% to 2%. In particular, this can be a glass-ceramic with a composition as previously described with reference to a transparent substrate, wherein the substrate can have a high volume fraction of keatite in the crystal phase. In the case of an opaque substrate, the coloration in the CIELab color space can furthermore be L* 85 - 97, a* of -1.5 - 0.5 and b* -6 - 0.5. Alternatively, in the case of a translucent substrate, the coloration of the substrate can be as follows: L* = 72 - 93, a* = -5.5 - 0, b* = -7 - 0.5 with a transmission of 2% to 10%, or alternatively: L* = 60 - 82, a* = -7.5 - -2, b* = -19 - -4.5 with a transmission of 10% to 25%.

[0039] Particularly when using a glass or glass-ceramic product according to the invention as a cooking surface, a further embodiment provides for the substrate to be made of a LAS glass-ceramic, i.e., a glass-ceramic made of lithium aluminum silicate. Such substrates have a very low thermal expansion coefficient and are highly resistant to temperature changes, making them particularly well-suited to the thermal requirements of a cooking surface.

[0040] According to a further embodiment, it is further provided that the substrate has at least one recess. In particular, such a recess can be an opening in the substrate through which an extractor (also referred to as a downdraft) can be integrated into the cooking surface when the substrate is used as a cooking surface. The coating on the substrate preferably extends to the edges of the recess, so that a seamless transition from the coated area into the recess is achieved. Such a recess in a substrate can be produced using a variety of methods, in particular by drilling, milling, waterjet cutting, or the like.

[0041] According to a further embodiment, it is further provided that a light source arranged at a distance of 0.5 mm below the glass or glass-ceramic product produces a halo of at most 1.2, preferably at most 1.15, with a substrate thickness of 4 mm. More preferably, a light source arranged at a distance of 1.75 mm below the glass or glass-ceramic substrate produces a halo of at most 1.4, preferably at most 1.3, with a substrate thickness of 4 mm. The said distance refers to the distance between the top side of the light source and the underside of the substrate. A "halo" is understood to be a measure of the distortion of the perception of a light source when transmitted through the substrate and the coating arranged on the substrate.

[0042] For this purpose, the intensity profile of the light source recorded by a camera in the absence of the glass or glass-ceramic product is compared with an intensity profile recorded through the glass or glass-ceramic product at a defined distance between the light source and the underside of the substrate using the same camera with an identical arrangement of camera and light source. The underside of the substrate is preferably smooth so that as little scattering as possible occurs on the underside of the substrate. To evaluate the scattering behavior, the half-widths of the measured intensity profiles with and without substrate above the light source are compared. The halo value is calculated from the quotient of the half-width with substrate divided by the half-width without substrate.Accordingly, with a value of 1, the substrate with the coating arranged above the light source does not influence the measured intensity distribution. However, with values ​​greater than 1, scattering behavior of the coated substrate can be observed.

[0043] For example, the following process can be used to produce a glass-ceramic product as described above, which process comprises the following steps: a. Providing a glass substrate, b. Applying a layer of an ink comprising a glass flux and a printing medium to at least a portion of a surface of the substrate, wherein the application is preferably carried out by screen printing, c. Ceramicizing the coated substrate

[0044] In the process, both the substrate is ceramized, i.e., converted from glass to glass-ceramic, and the coating is fired in a single process step (c). Consequently, a separate step for firing the coating can be eliminated, which significantly simplifies the production of the glass or glass-ceramic product.

[0045] To ceramize the coated substrate, the following procedure can be used: a) Heating from room temperature to 680°C within 23 minutes, b) Temperature increase within 19 minutes from 680°C to 800°C, c) Temperature increase from 800°C to 918°C (maximum temperature) within 24 minutes d) Maintain the maximum temperature for 10 minutes e) Cooling to 800°C within 20 minutes, f) Rapid cooling to room temperature within less than 150 minutes.

[0046] Alternatively, ceramization can be carried out as follows: a) Rapid heating from room temperature to 740°C in 20 to 26 minutes, especially 24 minutes, b) Temperature increase from 740°C to 825°C in 12 to 18 minutes, especially 14 minutes, c) Temperature increase from 825°C to 930°C (maximum temperature) in 4 to 8 minutes, especially 6 minutes, d) Maintain the maximum temperature for 4 to 8 minutes, especially 6 minutes, e) cooling to 800°C within 8 to 16 minutes, in particular within 10 minutes, f) Rapid cooling to room temperature.

[0047] The coating is preferably applied by screen printing, with a screen with a mesh thickness of 140-31 to 54-64 being used for screen printing. A screen with a mesh thickness of 77-55 has proven particularly advantageous. The screen used can also have areas in which no glass flux is transferred to the substrate, so that recesses in the coating can be easily created. In particular, a screen can be used that creates a fine structure in the coating, whereby the area coverage of the coating, i.e. the ratio of coated to uncoated surface in the coated area of ​​the substrate, is less than 100%. This can, for example, create patterns in the coating that further reduce the visibility of scratches or surface contamination.The area occupancy rate should preferably not fall below 80%.

[0048] It can further be provided that a decorative layer is applied to the substrate before the coating is applied to the substrate, with the coating then being applied at least in sections to the decorative layer. The decorative layer can be applied to the substrate, in particular, using an inkjet printing process. Alternatively, however, it can also be provided that the decorative layer is applied after process step b, i.e., arranged on the coating.

[0049] As previously stated, the substrate can also have a recess, for example, for integrating an extractor fan. Such a recess is preferably introduced into the substrate before the substrate is coated. In this case, the coating can subsequently be applied to the substrate up to the edge of the recess, so that the coating is not affected by the recess manufacturing process. However, it is also possible to introduce the recess into the already coated substrate after ceramization.

[0050] In a further aspect, the invention relates to an ink for producing a glass or glass-ceramic product as described above, wherein the ink comprises a boron-containing glass flux and a printing medium, wherein the glass flux has a grain size of D 10 greater than 1 µm and D 90 less than 20 µm, preferably D 90less than 15 µm. The printing medium is preferably a medium containing dipropylene glycol monomethyl ether as a solvent, which is particularly advantageous in terms of its biocompatibility. Alternatively, a printing medium based on naphtha can be used as a solvent.

[0051] The glass flux is preferably particles of a borosilicate glass, the glass preferably having the following composition in wt.% on an oxide basis: SiO2 75 - 85 Al2O3 0,1 - 5 B2O3 10 - 15 Na2O 1 - 5 K2O 0,1 - 1,5

[0052] According to a further embodiment, the ratio of glass flow to printing medium in the ink is between 10:15 and 10:5, which has a particularly advantageous effect on the printing properties of the ink.

[0053] The invention will be described in more detail below with reference to the figures, without limitation. Like reference numerals designate like or similar elements.

[0054] They show: Fig. 1: schematic representations of different embodiments of an exemplary glass or glass-ceramic product, Fig. 2: a schematic representation of an exemplary process for producing an exemplary glass-ceramic product Fig. 3: a representation of a surface profile of a matte surface as a comparison example, Fig. 4: a histogram of an exemplary grain size distribution of a glass flux for producing a coating, Fig. 5: a perspective view of the surface profile of a glass flux from Fig. 4 manufactured coating, Fig. 6: a representation of the surface profile along a line within the Fig. 5 shown surface Fig. 7: a histogram of another exemplary grain size distribution of a glass flux for producing a coating, Fig. 8: a perspective view of the surface profile of a glass flux from Fig. 7 manufactured coating, Fig. 9: a representation of the surface profile along a line within the Fig. 8 shown surface, Fig. 10 and Fig. 11: a representation of a decoration arranged below the coating in a plan view of an exemplary glass-ceramic product and a contour line of the decorative layer derived therefrom, Fig. 12: an example measurement setup for determining a halo value.

[0055] Fig. 1 shows schematic representations of different embodiments of an exemplary glass or glass-ceramic product 100. Fig. 1 a) the simplest case, in which a coating 104 is applied directly to a surface 106 of a disc-shaped substrate 102 made of glass or glass ceramic. The coating has a rough surface 114 with a mean square height Sq in the range from 0.1 µm to 2.5 µm and a core height Sk of the coating 104 of 1.5 µm to 10 µm, whereby the coating 104 has a matte appearance. Initially, no further coating, in particular in the form of a decoration, is provided between the coating 104 and the substrate 102. The substrate 102 is preferably a lithium aluminum silicate glass ceramic (LAS glass ceramic), which is particularly well suited for applications as a cooking surface due to its generally low thermal expansion coefficient. The substrate 102 can be a transparent, translucent, or opaque material.Furthermore, the substrate 102 may be substantially colorless or volume-colored.

[0056] In the illustrated embodiment, the coating 104 is applied to the upper side of the substrate 102, which would face the user when the product 100 is used as a cooking surface and on which, for example, cookware would be placed. Fig. 1, no further coating is shown on the underside 116 of the substrate 102 in any of the embodiments, such an additional underside coating is not fundamentally excluded. Rather, particularly in the case of a transparent substrate 102, the use of a bottom coating that is as opaque as possible in addition to the top coating 104 is advantageous, for example, to conceal electronic components arranged beneath the substrate 102.

[0057] The dimensions of the Fig. The elements shown in Figure 1 are greatly exaggerated for clarity and, in particular, are not realistic in their relationship. For example, a preferred thickness for substrate 102 would be 4 mm, while coating 104 preferably has a thickness in the range of 2 to 10 µm. Likewise, the length of substrate 102 is shown only as an example, and typically the thickness of substrate 102 would be at least an order of magnitude smaller than its length.

[0058] In the Fig. 1 b) shows a further embodiment of the glass or glass-ceramic product 100, in which a further coating 108 in the form of a decoration is additionally applied to the surface 106 of the substrate 102. In the illustrated embodiment, the decoration 108 is completely covered by the coating 104 and thus protected against external influences. By directly applying the decoration 108 to the generally very smooth surface 106 of the substrate 102, a high degree of edge sharpness of the decoration 108 can be ensured, while at the same time the rough surface 114 of the coating 104 gives the glass or glass-ceramic product 100 an overall matte appearance. The decoration 108 can be, for example, cooking zone markings, manufacturer logos, or other markings.In addition to the embodiment shown here, in which the decoration 108 is completely covered by the coating 104, it would also be possible within the scope of the invention for the decoration 108 to be only partially covered by the coating 104, i.e. for there to be areas of the decoration 108 that are exposed.

[0059] Although in the Fig. 1 a) and Fig. 1 b) the coating 104 is shown as a full-surface coating of a surface 106 of the substrate 102, it is also conceivable in principle that the coating 104 extends only over a part of the surface 106 of the substrate 102 and thus regions exist in which the coating 104 has recesses. This case is shown in the Fig. 1 c). In the embodiment shown here, which is based on the embodiment of Fig. 1 b), the coating 104 has a recess 110 in the center of the illustration, in which the surface 106 of the substrate 102 is exposed. Such a recess 110 can be taken into account, in particular, during the production of the coating 104 by leaving out the corresponding area when printing the coating 104 onto the surface 106 of the substrate 102, for example by appropriately masking the substrate 102 or by appropriately designing a screen for applying the coating 104 using a screen printing process.

[0060] Such a recess 110 can be particularly advantageous when display devices 112, for example in the form of seven-segment displays or full-color displays, are arranged beneath the substrate 102. Image reproduction from such display devices 112 would be distorted upon transmission through the coating 104 due to their rough surface. However, this can be avoided by a corresponding recess in the coating 104.

[0061] The Fig. Figure 2 shows a schematic representation of an exemplary method for producing an exemplary glass-ceramic product 100. In a first method step 200, a glass substrate 102 is provided, which may already have been cut to the desired dimensions for the final product. Furthermore, a pretreatment of the surface 106 of the substrate 102 to be coated can also be performed here, for example, by polishing the surface 106 to achieve the smoothest, most even surface 106 possible.

[0062] In a second method step 202, an ink comprising a glass flux and a printing medium is then applied to at least a portion of the surface 106 of the substrate 102. The glass flux preferably has a grain size of D 10 greater than 1 µm and D 90 less than 20 µm, preferably D 90less than 15 µm. In principle, any printing method suitable for processing a glass flux with the specified grain size can be used to apply the ink to the surface 106 of the substrate 102. However, the application of the ink by means of a screen printing method is particularly preferred. A screen printing method has the advantage that, on the one hand, large-area coatings can be produced with little effort, while, by appropriately designing the screen used, specific areas in the coating 104 can be left out. In this way, for example, structures such as those previously described with reference to the Fig. 1 c) are generated.

[0063] The screen used for screen printing should always be selected according to the printing medium and the glass flow. However, it has proven particularly advantageous to use a 140-31 mesh screen when using a printing medium based on naphtha as the solvent.

[0064] In a third process step 204, the printed substrate 102 is then ceramized. For this purpose, the following ceramization program can be used, for example, which, however, is provided merely as an example and should not be understood as a limitation. g) Heating from room temperature to 680°C within 23 minutes, h) Temperature increase within 19 minutes from 680°C to 800°C, i) Temperature increase from 800°C to 918°C (maximum temperature) within 24 minutes j) Maintain the maximum temperature for 10 minutes k) Cooling to 800°C within 20 minutes, l) Rapid cooling to room temperature within less than 150 minutes.

[0065] Alternatively, ceramization can be carried out as follows: g) Rapid heating from room temperature to 740°C in 20 to 26 minutes, especially 24 minutes, h) Temperature increase from 740°C to 825°C in 12 to 18 minutes, in particular 14 minutes, i) Temperature increase from 825°C to 930°C (maximum temperature) in 4 to 8 minutes, in particular 6 minutes, j) Maintain the maximum temperature for 4 to 8 minutes, especially 6 minutes k) Cooling to 800°C within 8 to 16 minutes, within 10 minutes, l) Rapid cooling to room temperature.

[0066] During the ceramization of the substrate 102, after a nucleation phase during which crystallization nuclei are formed within the substrate 102, controlled crystal growth is stimulated by a further increase in temperature, whereby the glass substrate 102 is converted into a glass ceramic with defined mechanical and optical properties. Due to the high temperatures during ceramization, the glass flux located on the surface 106 of the substrate 102 also partially melts, while the printing medium of the ink evaporates essentially without residue. The molten glass flux bonds with the glass substrate 102, creating a very robust coating 104 on the surface 106 of the substrate 102 that is largely insensitive to mechanical stress.The unmelted part of the glass flow forms an uneven structure on the surface 114 of the coating 104, which brings about the surface parameters according to the invention.

[0067] The Fig. 3 a) shows a schematic representation of the height profile of a surface to explain the surface parameters according to the invention. The height z(x) of the surface above a zero line is shown in µm for each of the different points along a measuring section within the surface (x-axis). The zero line is arranged at a height for which the deviations of the local elevations of the surface from the zero line along the measuring section add up to zero. The two-dimensional case shown here was chosen solely to explain the surface parameters already named and described. However, the surface parameters used to describe the subject matter according to the invention are not actually determined along a single line within the surface, but rather from an observation of the entire surface, i.e., a three-dimensional representation of the surface.

[0068] Based on the Fig. To determine the mean square height Sq of the surface, all local deviations z(x) from the zero line are squared, summed, and divided by the length of the measurement section. The square root of this result is then taken. This effectively provides information about how much the surface deviates from the zero line on average, i.e., how rough the surface is. The larger this value, the rougher the surface.

[0069] To determine the core height Sk, first, for each height y on the ordinate axis, the portion of the surface that is higher than the considered y-value is determined. This portion is then entered as the surface material portion M on the abscissa axis. For example, in the surface of the Fig. 3 a) at a height of 8 µm a value of 0% is determined for the surface material fraction, since the surface does not deviate from the zero line by more than 8 µm. For a height of 6 µm a low single-digit fraction of the surface would already be determined which deviates from the zero line by more than +6 µm. By definition, in the representation shown the ordinate value 0 µm would be assigned a fraction of 50%, since the zero line divides exactly equal portions of the surface. In principle, however, a different zero line can also be chosen as the reference point here. At a value of -10 µm a value of more than 95% would already be determined for the surface material fraction M, whereas from an ordinate value of around -13 µm 100% of the surface lies above this value.

[0070] An exemplary distribution 300 of this type is shown in the Fig. 3 b). To determine the core height Sk from this distribution, the equivalence degree of the distribution 300 of the surface material fraction is determined in a first step. For this purpose, a region of the surface material fraction M, to which a surface material fraction ΔM of 40% applies, is shifted along the ordinate axis until the region is found within which the secant of the end points of the region ΔM with the curve 300 of the distribution of the surface material fraction has the lowest possible gradient. This is shown in the Fig. 3 b) shows, by way of example, three different regions with a respective width ΔM of 40%. For the first region ΔM1, the corresponding points s11 and s12 are plotted, which correspond to the region ΔM1 on the curve 300 of the surface material portion. These intersection points s11 and s12 result in the secant 301 of the curve 300 of the surface material portion for the first region ΔM1. Similarly, the secant 302 for the second region ΔM2 was determined from the intersection points s21 and s22, and the secant 303 for the third region ΔM3 was determined from the intersection points s31 and s32.

[0071] Of the curves 301, 302, and 303 shown, the middle curve 302 has the lowest detectable gradient. This curve 302 of the lowest gradient, which was determined according to the procedure outlined above, is also referred to as the equivalence degree. To determine the core height Sk, the equivalence degree is divided into area proportions of 0% (intersection with the abscissa axis) and 100% (intersection S 100 ) is extrapolated. From the intersection points of the equivalence degrees with the ordinate values ​​for the area proportions 0% and 100%, the core height Sk is then determined as the distance between these intersection points along the abscissa axis. A low core height is synonymous with a high material density of the surface, which in turn contributes to a high robustness of the surface against mechanical stress. For example, the core height Sk of the Fig. 3 a) shown surface 12.7 µm.

[0072] Another relevant parameter for describing the coating surface is the skewness (Ssk). As previously explained, skewness describes whether the surface can be described as a surface with peaks (positive skewness) or a surface with grooves (negative skewness). This is equivalent to the question of whether the surface deflections from the zero line tend to occur more frequently in positive or negative areas. Therefore, if there are more positions along the measurement path for which the ordinate value is positive, the skewness (Ssk) is also positive; if there are more positions along the measurement path for which the ordinate value is negative, the skewness (Ssk) is also negative.For two surfaces with identical values ​​for the mean square height Sq, the skewness value can be quite different, since the deflections above or below the mean surface height are calculated from the squared heights of the surface to determine the value Sq, and the direction of the deflections is not taken into account. For example, the surface of the . Fig. 3 a) has a skewness Ssk of -0.33, so it can be described as a surface with grooves.

[0073] A comparable, statistical analysis of the surface texture is also possible with the further surface parameter considered here, the kurtosis Sku. The kurtosis is calculated from the sum of the fourth powers of the local height of the surface z(x), normalized over the measurement distance and further divided by the mean square height Sq to the fourth power. In effect, this considers how frequently a certain value z occurs along the measurement distance, regardless of its sign. For a value Sku = 3, the various values ​​for the surface height are normally distributed around the zero line. With a value for Sku of < 3, the surface tends to have a more rounded structure, while a value Sku > 3 indicates a more pointed, jagged surface structure. Fig. 3 a) has a kurtosis Sku of 2.77, thus showing a rather rounded surface structure.

[0074] In the following, two exemplary embodiments are used to describe how a coating with the previously described and claimed properties can be produced.

[0075] The Fig. Figure 4 shows a histogram of an exemplary grain size distribution of a glass flux used to produce a coating. The particles of the glass flux have the following composition in wt.% oxide basis: SiO2 81 B2O3 13 Al2O3 2 Na2O 3,5 K2O 0,5

[0076] To produce the glass flux, a glass melted according to the above composition is ground, whereby in this case, wet grinding was carried out with water. The glass flux produced in this way has a grain size distribution D 10 of 1.37 µm, D 90 of 17.02 µm and D 99 of 24.10 µm.

[0077] The resulting glass flux was then mixed with a screen printing medium based on dipropylene glycol monomethyl ether (DPM) as a solvent at a mixing ratio of 10:6 (glass flux to screen printing medium). The resulting ink was then screen-printed onto a ceramizable glass substrate using a 140-31 mesh screen and fired according to the previously described ceramization program.

[0078] The Fig. 5 shows a local section over an area of ​​about 1 mm 2 from the surface profile of the resulting coating in perspective view. The mean square height Sq of the resulting surface is 1.21 µm, the core height Sk is 3.1 µm, the skewness Ssk is 0.01, and the kurtosis Sku is 3.05. Furthermore, the surface has a mean arithmetic height Sa of 0.96 µm.

[0079] The mean arithmetic height Sa is calculated from the area A of the coating and the height z of the coating according to the following rule: Sa=1A∫∫A|z(x,y)|dxdy

[0080] Another example is Fig. 6 a representation of the surface profile along a line within the Fig. 5 shown surface.

[0081] The Fig. Figure 7 shows another histogram of an exemplary grain size distribution of a glass flux for producing a coating for an exemplary glass-ceramic product. The glass flux consists of the same material as the glass flux previously described with reference to Fig. 4. Also in the case of Fig. 7, the glass was ground by wet grinding, resulting in the grain size distribution shown. D 10 1.15 µm, D 90 14.72 µm and D 9919.89 µm. The resulting glass flux was mixed with a naphtha-based screen printing medium in a paste ratio of 10:12 and applied to the surface of a substrate using a 77-55 mesh screen, similar to the embodiment of the Fig. 4 and fired with the ceramization of the substrate.

[0082] The Fig. 8 shows a local section over an area of ​​about 1 mm 2 from the surface profile of the resulting coating in perspective view. The mean square height Sq of the resulting surface is 1.6 µm, the core height Sk is 3.9 µm, the skewness Ssk is 0.045, and the kurtosis Sku is 3.46. Furthermore, the surface has a mean arithmetic height Sa of 1.25 µm.

[0083] Another example is Fig. 9 a representation of the surface profile along a line within the Fig. 8 shown surface.

[0084] The Fig. Figure 10 shows, in Figure a), a black-and-white image of an exemplary glass-ceramic product with a colored decorative layer arranged beneath the coating. Such an image can be created, for example, using a light microscope. Due to the granular structure of the coating, the largely homogeneous decorative layer, and in particular the typically very sharp contour line 404 of the decoration, which represents the transition between the decorated area 402 and the undecorated substrate 400, appears blurred or frayed.

[0085] To describe the nature of the contour line 404, the concrete course of the contour line 404 can be determined from the representation of the Fig. 11 a). For this purpose, a grey value between 0 and 100 can be set as a limit value, for example the value 20, representing a colour effect of the decor between 0% and 100%. All measuring points whose grey values ​​are included in the display of the Fig. 11 a) are above or below the specified limit, the gray value 0 is assigned, while all measurement points with a gray value of 20 are assigned the value 100. In addition to a discrete limit, a range of limit values ​​can also be specified that are to be assumed as the contour line, for example, all gray values ​​between 15 and 20.

[0086] The result of this operation is shown schematically in the Fig. 11 b) for the upper half of the Fig. 11 a) shown section. As in the Fig. As can be seen in Figure 11 b), by applying a limit value to the gray values ​​of the measurement points, spots within the decoration, which are also caused by optical distortion by the structured coating, are sometimes interpreted as contour lines. Such points can either be manually removed from the display, or a range can be defined within which the contour line should be viewed, so that points outside this range are no longer considered.

[0087] In this way, a discrete contour line can be determined, as shown for example in the Fig. 11 a). Due to the optical distortions caused by the structured coating arranged over the decorative layer, it may happen that along the contour line, when viewing the contour line in an xz diagram, points exist on the x-axis for which there are two different points on the z-axis that lie on the contour line. Fig. 11 a) this is the case, for example, at point x1, since this point cannot be assigned a unique value z that lies on the contour line, since a straight line parallel to the z-axis through point x1 intersects the contour line at two points.

[0088] However, to determine the root mean square of all ordinate values ​​of the contour line, a curve is required that assigns only one value z(x) to each value x, so that in a further step, the curve must be converted into a correspondingly adjusted curve. This can be done either by assigning the highest value z(x) lying on the contour line to each point x to which several ordinate values ​​z(x) can be assigned. This is exemplified in the Fig. 11 b). Conversely, each point x can be assigned the lowest ordinate value z(x) on the contour line, as in Fig. 11 c).

[0089] From the contour lines thus obtained, the root mean square value, which is equivalent to the root mean square roughness Rq, can be determined. It is also possible that for both contour lines the Fig. 11 b) and Fig. 11 c) the value Rq is determined in each case, and the mean of these two values ​​is taken as the actual value of the contour line. This allows a statement to be made about the extent to which an otherwise sharp contour line of a decoration is distorted by the structured coating deposited on the decoration.

[0090] In addition to the previously described value Rq, further parameters known from the analysis of surface properties can also be determined to characterize the contour line profile. For example, the two-dimensional parameters Sa, Ssk, and Sku previously described with reference to the surface quality 114 of the coating 104 of an exemplary glass or glass-ceramic product 100 can each be determined in one-dimensional form, i.e., Ra, Rsk, and Rku, for the contour line profile. The arithmetic mean roughness Ra of the contour line is preferably at most 15 µm, while the skewness Rsk is preferably less than zero. Further preferably, the kurtosis Rku of the contour line is greater than 3.

[0091] The Fig.13 shows an exemplary measurement setup for determining the halo value of an exemplary glass or glass-ceramic product 100. In a darkroom 500, a holder 504 is arranged on a vibration-damping base 502, on which holder 504 a light source 506 with an illuminant, for example a white seven-segment display, is arranged. The article 508 to be tested, in particular a disc-shaped substrate, can in turn be placed on the light source, wherein a defined distance between the illuminant and the underside of the article 508 can be created by spacers arranged between the article 508 and the light source 506. Above the article 508, perpendicular to the light source 506 or the illuminant used, a camera 512 with a lens 514 is arranged, which is focused on the surface of the illuminant.The camera 512 can, for example, be arranged at a distance of approximately 30 - 35 cm above the light source 506.

[0092] To determine the halo value, a zero measurement is performed in the absence of Article 508 and a measurement is performed with Article 508, with the image of the illuminant being recorded in grayscale in each case. From the images obtained in this way, and in particular the resulting intensity distribution curves for a cross-section through the recorded image, the halo value can then be determined as described above.

[0093] The surface parameters Sq, Sk, Ssk, Sku and Sa used and described herein are also described as examples in DIN EN ISO 25178-2:2023-09.

[0094] Although the present invention has been described using preferred embodiments, it is not limited thereto but can be modified in many ways. List of reference symbols 100 glass or glass-ceramic product 102 Substrat 104 Coating 106 Surface of the substrate 108 Decor 110 recess 112 Display device 114 Surface of the coating 116 Underside of the substrate 300 Distribution of the surface material share 301 secant 302 degrees of equivalence 303 secant QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] EP 2 964 854 B1

[0003] WO 2023 / 099833 A1

[0003] EP 4 077 231 A1

[0004]

Claims

[1] Glass or glass-ceramic product with a substrate made of a glass or a glass-ceramic, wherein the substrate is provided at least on one side on at least part of its surface with a substantially pigment-free coating, wherein the coating comprises an at least partially melted glass flux, wherein the surface of the coating has a mean square height Sq of at least 0.1 µm and at most 2.5 µm, and wherein the coating has a core height Sk of at least 1.0 µm to at most 10 µm. [2] A glass or glass-ceramic product according to claim 1, wherein the coating has a gloss value of at most 25 at a viewing angle of 60°. [3] Glass or glass-ceramic product according to claim 1 or 2, wherein the coating has a skewness Ssk of > 0. [4] Glass or glass-ceramic product according to one of the preceding claims, wherein the coating has a kurtosis Sku of > 3. [5] Glass or glass-ceramic product, the coating having a thickness of 2 to 10 µm. [6] Glass or glass-ceramic product according to one of the preceding claims, wherein a pigmented decorative layer is arranged at least in sections between the substrate and the coating. [7] Glass or glass-ceramic product according to claim 6, characterized by that the contour line of the decorative layer arranged beneath the coating has a root mean square roughness Rq of not more than 20 µm when viewed vertically through the coating in a direction parallel to the surface of the substrate. [8] Glass or glass-ceramic product according to claim 6 or 7, wherein the combination of decorative layer and coating has a thickness of at most 15 µm. [9] Glass or glass-ceramic product according to one of the preceding claims, wherein the coating is applied over the entire surface of one side of the substrate. [10] Glass or glass-ceramic product, wherein the glass flux has the following composition in wt% on an oxide basis: SiO2 75 - 85 Al2O3 0,1 - 5 B2O3 10 - 15 Na2O 1 - 5 K2O 0,1 - 1,5 [11] Glass or glass-ceramic product according to one of the preceding claims, characterized by that the substrate is disc-shaped and has a thickness between 2 mm and 6 mm, preferably between 3 mm and 5 mm, particularly preferably 4 mm. [12] Glass or glass-ceramic product according to one of the preceding claims, characterized by that the substrate is transparent with a transmission τ vis of greater than 80% and has a chroma c* of less than 10, in particular less than 8. [13] Glass or glass-ceramic product according to one of claims 1 to 11, characterized by that the substrate is volume-colored and has a transmission τ vis of 2% to 10%. [14] Glass or glass-ceramic product according to one of claims 1 to 11, characterized by that the substrate is translucent with a transmission τ vis from 2% to 25% or opaque with a transmission τ vis from 0.1% to 2%. [15] Glass or glass-ceramic product according to one of the preceding claims, characterized by that the substrate consists of a LAS glass ceramic. [16] Glass or glass-ceramic product according to one of the preceding claims, characterized by that a light source arranged at a distance of 0.5 mm below the glass or glass-ceramic product produces a halo of no more than 1.2 for a substrate thickness of 4 mm. [17] Ink for producing a glass or glass-ceramic product according to any one of claims 1 to 16, wherein the ink comprises a boron-containing glass flux and a printing medium, wherein the glass flux has a grain size of D 10 greater than 1 µm and D 90 less than 20 µm, preferably D 90less than 15 µm. [18] The ink of claim 17, wherein the ratio of glass flux to printing medium in the ink is between 10:15 and 10:5.

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