Coated article

Abstract

The invention relates to a coated article comprising a substrate made of glass or glass ceramic, wherein a scratch protection coating is applied on at least one surface of the substrate, wherein the substrate has a refractive index (n1) and wherein the scratch protection coating has an average refractive index (n2). According to the invention, the magnitude of the difference between the refractive indices Δn = |n1-n2| is less than 0.3, wherein the scratch protection coating consists of a composition (X) containing silicon dioxide and zirconium dioxide, wherein the proportion of zirconium in the metal and semi-conducting component in the composition (X) is 0.2 to 10 wt.%.

Description

[0001] Coated article

[0002] Description

[0003] The invention relates to a coated article, in particular a coated glass-ceramic substrate with a scratch-resistant coating.

[0004] Such coated articles are known in the art. In particular, with regard to scratch-resistant coatings, a variety of different approaches have been described in the past for producing such scratch-resistant coatings, particularly for cooking surfaces. For example,

[0005] DE 10 2007 033 338 B4 describes an approach for producing a scratch-resistant coating based on silicon nitride. Furthermore,

[0006] DE 10 2008 054 139 B4 discloses the use of a silicon oxynitride layer as a scratch protection layer, while the use of amorphous aluminum silicon nitride is known, for example, from DE 10 2013 102 221 B4.

[0007] The scratch-resistant coatings described in the aforementioned publications consistently exhibit very good mechanical and thermal properties. However, the demands placed on chemical and optical properties in various markets have increased in recent years, sometimes necessitating new developments. In particular, all of the coating materials mentioned above are medium to high-index coatings, which is why these scratch-resistant coatings can be optically perceived as an interference system under various lighting conditions and reflect color, especially under discontinuous lighting.

[0008] In contrast, the object of the present invention is to provide a coated article with a scratch-resistant coating which, in particular as a one-sided scratch-resistant coating on the coated substrate, appears almost invisible and at the same time has a high mechanical and chemical resistance.

[0009] In particular, when the scratch-resistant coating is used in conjunction with a glass-ceramic substrate, particularly for use as a cooking surface, the scratch-resistant coating should also withstand the conditions of induction and radiant heating, particularly during boil-over processes of different media such as beef stock, acetic acid, citric acid and salt water, without optical and physiochemical changes and permanently form a homogeneous protective layer.

[0010] This object is achieved with the coated article according to claim 1. Preferred embodiments are the subject of the dependent claims.

[0011] The invention relates to a coated article comprising a substrate, in particular a substrate made of glass or glass ceramic, wherein a scratch-resistant coating is applied to at least one surface of the substrate, in particular the upper side. The substrate has a refractive index m, while the scratch-resistant coating has an average refractive index n2. According to the invention, the absolute value of the difference between the refractive indices Δn = |m-n2| is less than 0.3, preferably less than 0.2, wherein the scratch-resistant coating consists of a composition X which contains silicon oxide (SiO2) and zirconium oxide (ZrO2), wherein the proportion of zirconium in the metallic and semiconducting component in the composition X is 0.2 to 10 wt. %, preferably 0.2 to 5 wt. %, particularly preferably 0.5 to 3 wt.

[0012] In this case, the composition X of the coating may contain other components besides zirconium oxide and silicon oxide. For example, if only silicon and zirconium are included as metallic and semiconducting components in the composition of the coating, the above-mentioned proportion of zirconium in the composition X is equivalent to the requirement:

[0013] 0.2 <(Zr / (Zr+Si)*100 <10, preferred

[0014] 0.2 < (Zr / (Zr+Si)*100 < 5, particularly preferably 0.5 < (Zr / (Zr+Si)*100 < 3, where Zr is the zirconium content in wt.% in the coating and where Si is the silicon content in wt.% in the coating. In the event that, according to one embodiment, further metallic and semiconducting components are contained in the composition X of the coating, the denominator of the above relations would have to be supplemented accordingly.

[0015] Surprisingly, it has been shown that doping a silicon oxide coating with zirconium can achieve a positive effect on improving mechanical resistance even with very low zirconium concentrations in the coating. By carefully selecting the zirconium concentration in the coating, the refractive index of the scratch-resistant layer can be adapted to the refractive index of the coated substrate. With a small difference in the refractive index between the substrate and the coating, the coating is almost indistinguishable from the substrate, since reflection of visible light at the interface between the substrate and the coating is virtually nonexistent due to the small difference in the refractive index.

[0016] It is generally known that pure ZrO2 exhibits good mechanical resistance. However, the disadvantage of using ZrO2 in coating solutions is that it has a very high refractive index of > 2.2, making it highly visible. For this reason, this material is also used, among other things, as a high-index layer in optical coating systems. A further disadvantage of using ZrO2 to coat a substrate is that the adhesion of such a coating is problematic, particularly under thermal stress (especially on decorative elements), and can lead to delamination.

[0017] Pure SiO2 is thermally very stable, but lacks good mechanical resistance, differing only slightly from uncoated glass or glass-ceramics in this respect. However, a coating of pure SiO2 on glass or glass-ceramics is comparatively unobtrusive in terms of optical properties.

[0018] However, it has surprisingly been shown that by adding only a very small amount of zirconium during the manufacturing process of a SiO2 coating, especially in a sputtering process involving co-sputtering of Si and Zr or using a SiZr alloy target, the mechanical properties of the resulting coating change significantly, while the optical properties of the coating remain virtually unchanged. Thus, by skillfully selecting the proportion of zirconium in the coating, the refractive index n2 of the scratch-resistant coating can be adapted to the refractive index m of the substrate, while simultaneously creating a mechanically and thermally robust scratch-resistant coating.

[0019] It has been shown that the refractive index of the coating, and thus the optical conspicuity of the coating, increases with the higher the proportion of zirconium in the coating. Furthermore, it was found that, above a threshold value for the zirconium content in the coating, the mechanical resistance to scratches in the coating visibly deteriorates with increasing zirconium content. The negative effect of poor adhesion of the coating to the substrate at high temperatures also becomes more significant with increasing zirconium content in the coating. For this reason, it is advantageous to keep the zirconium doping in the coating as low as possible.

[0020] In addition, the scratch protection coating according to the invention shows less conspicuity in the event of corrosion or changes due to thermal stress due to its low visibility in different lighting situations.

[0021] The coating according to the invention also exhibits excellent chemical resistance to various media, such as citric acid, acetic acid, and cleaning agents. When used as a protective coating for cooktops, the coating according to the invention also exhibits high resistance to boil-over media such as salt water.

[0022] When using a SiZr alloy target in a sputtering process to produce the coating, the composition of the sputtering target preferably corresponds to the composition ratios of the coating according to the invention with regard to the proportions of zirconium and silicon.

[0023] In principle, the coating can contain other components besides silicon oxide and zirconium oxide. These can be introduced into the coating, particularly during production of the coating by a sputtering process, through impurities in the target material. However, it is preferably provided that the coating consists of at least 95 wt. %, in particular 97 wt. %, or even 98 wt. % silicon oxide and zirconium oxide. The scratch-resistant coating is preferably applied over the entire area of ​​at least one of the surfaces of the substrate. However, it is also possible in principle for areas of the coated surface to be left out, so that the scratch-resistant coating does not extend into these areas.

[0024] In addition to the sputtering process mentioned above, other coating processes such as ion beam sputtering, vapor deposition or chemical vapor deposition (CVD) can be used to coat the substrate.

[0025] In a further development of the invention, it is further provided that the scratch-resistant coating has a Martens hardness of 3.5 to 7 GPa. The Martens hardness can be determined, for example, using the Martens hardness test method according to DIN EN ISO 14577. It has been shown that even with Martens hardnesses in the aforementioned range, a scratch-resistant coating according to the invention achieves a very good scratch-reducing effect.

[0026] The Martens hardness described above is relatively low compared to other scratch-resistant coatings based on hard material layers known in the prior art. Surprisingly, the effect of the coating according to the invention in reducing scratches is comparable to that of significantly harder coatings with Martens hardnesses of more than 7 GPa. This is related to other coating parameters that influence the mechanical resistance of the coating.

[0027] Accordingly, in a further development of the invention, the scratch-resistant coating has a modulus of elasticity (E-modulus for short) of less than 150 GPa, preferably less than 100 GPa. The corresponding coating is therefore relatively well deformable compared to scratch-resistant layers known from the prior art, which are rather brittle with moduli of elasticity of more than 250 GPa. Accordingly, avoiding scratches with such an exemplary coating is not only based on the fact that the high hardness of the coating prevents particles from penetrating the coating, causing inelastic deformation or localized damage to the coating. Rather, the penetration of particles into the coating can be partially accepted, since any deformation of the coating caused thereby can be essentially elastic and is therefore reversible and does not lead to the formation of scratches.

[0028] According to a further embodiment, it is further provided that the layer thickness of the scratch protection coating is between 500 nm and 3000 nm, preferably 800 - 2000 nm, particularly preferably 1200 - 1800 nm.

[0029] It has already been stated above that the scratch-resistant coating according to the invention exhibits high thermal resistance. Accordingly, according to a further embodiment, the scratch-resistant coating exhibits a color shift (also referred to as color difference) ΔE of less than 2, preferably less than 1, after exposure to temperatures exceeding 600°C for a period of more than 24 hours. Consequently, the scratch-resistant coating according to the example remains visually inconspicuous even after prolonged, intensive thermal exposure, since such a color shift is generally imperceptible to the human eye.

[0030] The color distance AE in the L*a*b* color space between the color locations (Li* ai*, bi*) and (l_2*, a2*, b2*) is calculated as follows:

[0031] According to a further embodiment, the friction value (also referred to as the coefficient of friction) of the scratch-resistant coating is 0.1 to 0.5. Such a low friction value is particularly advantageous when using the scratch-resistant coating according to the invention on a glass-ceramic substrate in the form of a cooking surface. Thus, a low friction value of the coating means that cookware can be moved more easily and with less resistance on the cooking surface. This is also accompanied by less noise when moving the cookware.

[0032] A coating's low coefficient of friction is usually directly related to its surface roughness. A low surface roughness, in turn, is beneficial for preventing scratches, as the surface offers only a small area of ​​contact for forces acting parallel to the coating's surface.

[0033] In principle, the coating according to the invention can exert the previously described effect even as a single layer on a surface of the substrate. However, according to a further embodiment, the scratch-resistant coating is part of a layered composite comprising at least two layers arranged on a surface of the substrate. Not all layers of the layered composite necessarily have to be designed to reduce scratches on the surface of the coating. Rather, the additional layers of the layered composite can also fulfill other functions and can differ from the scratch-resistant coating in their chemical composition and physical properties.

[0034] Accordingly, according to a further embodiment, a first of the further layers of the layer composite, which is arranged in the layer composite between the substrate and the scratch-resistant coating, is free of zirconium oxide. In particular, the first layer can consist solely of SiO2. In this case, the first layer can act as an adhesion promoter for the scratch-resistant coating and improve the adhesion of the scratch-resistant coating to the substrate, thus preventing detachment of the scratch-resistant coating from the substrate, for example, due to thermal stress.

[0035] In addition to configuring the scratch-resistant coating as a single layer, a further embodiment can also provide for the scratch-resistant coating to be composed of at least two layers, wherein a first of the layers of the scratch-resistant coating contains a zirconium content that differs from the zirconium content of a second of the layers of the scratch-resistant coating. The condition formulated at the outset, according to which the mean refractive index n2 of the scratch-resistant coating differs from the refractive index m of the substrate by a maximum of 0.3, in particular by a maximum of 0.2, refers in this case, with respect to the value n2, to the mean value of the refractive indices n2,i and n2,2 of the two layers of the scratch-resistant coating.

[0036] Particularly preferably, the individual layers of the scratch-resistant coating are each designed such that both layers each have a refractive index n2,i or n2,2 that deviates from the refractive index m of the substrate by less than 0.3, preferably less than 0.2. The difference in refractive index between the individual layers of the scratch-resistant coating should also be kept as small as possible in order to continue to avoid reflections of visible light even within the scratch-resistant coating. In principle, it is also possible for both layers of the scratch-resistant coating to be identical in their composition, but to be applied to the substrate in separate processes, in particular two passes of a sputtering process. More than two identical layers can also be provided in the scratch-resistant coating, in particular three or even four layers.

[0037] According to a further embodiment, it can further be provided that the scratch-resistant coating comprises at least three, in particular four or more layers, wherein the refractive indices of the layers differ from one another, and wherein the proportion of zirconium in a layer, and thus the refractive index of the layer, is higher the further the layer is removed from the substrate. In particular, it can be provided that a first of the layers, which is closest to the substrate in the scratch-resistant coating, is selected in terms of its zirconium content such that there is the smallest possible difference between the refractive index of this layer and the refractive index m of the substrate.The subsequent layers then preferably have zirconium contents and thus refractive indices that are only a short distance from the neighboring layers, so that the reflection of visible light between the individual layers is as low as possible. The layer of the scratch-resistant coating furthest from the substrate in the layer sequence is then preferably optimized in its zirconium content for high scratch protection.

[0038] Even if the scratch-resistant coating is already composed of multiple layers, it is still possible for the scratch-resistant coating to be part of a layered composite arranged on the substrate. In particular, it can also be provided that an intermediate layer consisting exclusively of SiO2 is arranged between the scratch-resistant coating and the substrate and acts as an adhesion promoter between the substrate and the scratch-resistant coating. However, in this case, this intermediate layer is not considered part of the scratch-resistant coating. Rather, only those layers that have a zirconium content within the limits described above can be included in the scratch-resistant coating.

[0039] It has already been stated that the layer thickness of the scratch-resistant coating is between 500 nm and 3000 nm, preferably 800-2000 nm, and particularly preferably 1200-1800 nm. For a scratch-resistant coating composed of multiple layers, the layer thickness mentioned here refers to the thickness of each individual layer within the scratch-resistant coating. Accordingly, particularly when the scratch-resistant coating is designed as a multi-layer structure, the overall thickness of the scratch-resistant coating can be greater than the previously mentioned values.

[0040] According to a further embodiment, it is further provided that the scratch-resistant coating has a light transmittance in the visible wavelength spectrum of more than 70%, in particular more than 75%, more than 80%, more than 85%, or even more than 90%. A high light transmittance of the scratch-resistant coating is particularly advantageous when the coated article has a transparent substrate and is intended for application scenarios in which the coated article should, for example, restrict an observer's view as little as possible. Applications as a viewing window or as a cover for display elements are conceivable, for example. The total transmittance of the coated article can also deviate significantly from the aforementioned light transmittance and is generally highly dependent on the light transmittance of the substrate and any additional coatings that may be present.

[0041] According to a further embodiment, the substrate is a disc-shaped glass ceramic. In particular, this can be a lithium aluminum silicate glass ceramic (LAS glass ceramic), especially in the form of a cooktop. The refractive index of such a glass ceramic is typically in the range of 1.5 to 1.6, in particular 1.55. Such a glass ceramic can, in principle, be both transparent and volume-colored.

[0042] In the context of the present disclosure, a pane is generally understood to mean a plate-shaped molded body. A glass pane (which may be coated or uncoated) is a pane comprising or made of glass. A molded body is plate-shaped if its spatial dimensions in one spatial direction of a Cartesian coordinate system are at least one order of magnitude smaller than the spatial dimensions in the two other spatial directions of the Cartesian coordinate system perpendicular to the first spatial direction. In other words, the thickness of the molded body is at least one order of magnitude smaller than its length and width. The two main areas or main surfaces of the pane, i.e. those whose size is determined by length and width, are also abbreviated to sides in the context of the present disclosure. In principle, the substrate can also be a curved pane.

[0043] In the case of a transparent glass ceramic, it can be provided, in particular, that the scratch-resistant coating is applied to the top side of the glass ceramic, while a largely opaque coating, a so-called underside decoration, is applied to the underside of the glass ceramic. In this case, the optical properties of the scratch-resistant coating according to the invention are particularly advantageous, since the color impression of the underside coating is not distorted by the scratch-resistant coating.

[0044] Alternatively, the substrate can also be made of borosilicate glass, aluminosilicate glass, soda-lime glass, or lithium aluminum silicate glass, whereby these can also be chemically or thermally tempered substrates.

[0045] Fields of application for such coated substrates include oven viewing windows, control panels, worktops, protective screens for the automotive sector, consumer electronics, mobile phones, watches or smartwatches.

[0046] Preferred embodiments of the invention are explained in more detail below with reference to the drawings. Figure 1 shows schematic representations of sectional views of exemplary coated articles,

[0047] Figure 2 is a graphical representation of the influence of the zirconium-to-silicon ratio on the refractive index and scratch reduction of an exemplary scratch protection layer,

[0048] Figure 3 Detailed images of the result of a scratch test for a coated and an uncoated substrate,

[0049] Figure 4 shows the refractive index curve of an exemplary scratch protection coating,

[0050] Figure 5 Measurement data of the Martens hardness of an exemplary scratch protection coating,

[0051] Figure 6 Measurement data of the Young’s modulus of an exemplary scratch protection coating, and

[0052] Figure 7 Measurement data of the coefficient of friction of an exemplary scratch protection coating.

[0053] In the following, similar or identical features are identified by the same reference symbols.

[0054] Figure 1 shows schematic representations of sectional views of exemplary coated articles 100 and 100', respectively. The coated articles 100, 100' each comprise a substrate 102 and a scratch-resistant coating 104 and 104', respectively. The substrates 102 may, in particular, be disc-shaped substrates made of a glass ceramic, in particular a LAS glass ceramic. The substrates 102 may be either transparent or bulk-colored.

[0055] Figure 1 shows two different variants of coated articles 100 and 100'. Figure 1 a) shows a substrate 102 with a scratch-resistant coating 104 on the top side of the substrate 102, wherein the scratch-resistant coating is formed by a single layer 106. The layer 106 can, for example, have a layer thickness of 500 nm to 3000 nm, preferably 800-2000 nm, particularly preferably 1200-1800 nm.

[0056] The layer 106 consists of a composition X, wherein the composition X contains silicon oxide (SiO2) and zirconium oxide (ZrC), wherein the proportion of zirconium in the metallic and semiconducting components in the composition X is 0.2 to 10 wt. %, preferably 0.2 to 5 wt. %, particularly preferably 0.5 to 3 wt. Such a coating can be applied to the surface of the substrate 102, for example, by sputtering. For example, co-sputtering of silicon and zirconium with the addition of oxygen as a reactive gas can be provided to produce the layer 106. Furthermore, it is also possible to produce such a layer 106 by using a SiZr alloy target in the sputtering process with the addition of oxygen as a reactive gas, wherein the composition ratios of the sputtering target preferably correspond to the composition of the layer 106 to be produced.

[0057] As already explained above, the substrate 102 is preferably a lithium aluminum silicate glass ceramic. Such glass ceramics typically have a refractive index m of approximately 1.55. As already explained above, the scratch-resistant coating 104, and thus the layer 106, has a refractive index n2 that deviates from the refractive index m of the substrate by a maximum of 0.3, in particular by 0.2. Accordingly, the layer 106 preferably has a refractive index of approximately 1.45. The small difference in refractive index between the substrate 102 and the layer 106 results in very low reflection of incident light at the interface between the layer 106 and the substrate 102. Accordingly, the layer 106 is optically almost indistinguishable from the substrate 102.

[0058] At the same time, layer 106 exhibits very good mechanical properties with regard to scratch prevention, which results from the doping of the layer, which consists essentially of SiO2, with a defined proportion of ZrO2. The effect of the doping with ZrO2 is explained below with reference to Figure 2.

[0059] Figure 2 shows a graphical representation of the influence of the zirconium-to-silicon ratio on the refractive index n and scratch reduction (in %) of an exemplary scratch-resistant coating. The horizontal axis shows the zirconium-to-silicon ratio in wt.%, based on the metal base, while the left vertical axis shows the scratch reduction in percent and the right vertical axis shows the refractive index of the resulting coating. The bar chart displays the respective measured values ​​of the scratch reduction, while the linearly connected measuring points indicate the refractive index of the corresponding coating. The two bars for each measuring point represent measured values ​​taken at different positions on the coating. To determine the scratch reduction, a test was selected in which sand was used as the abrasive medium.The specified percentage describes the reduction in the scratched area of ​​a coated substrate when performing the scratch test compared to an uncoated surface of the substrate.

[0060] As can be seen in Figure 2, with a very high proportion of zirconium in the coating (shown on the far left in Figure 2), the influence of the SiO2 in the coating is largely lost. Accordingly, such a coating exhibits a high refractive index of more than 2 and is therefore visually very noticeable on a substrate with a refractive index of around 1.5. At the same time, however, such a coating is mechanically very resistant and shows a significant reduction in scratches in a corresponding scratch test.

[0061] As the proportion of zirconium decreases and the proportion of silicon increases in the coating, the coating's protective effect against scratches is largely lost at a zirconium to silicon ratio of 2:1. A corresponding coating therefore shows no positive effect on scratch reduction compared to an uncoated substrate.

[0062] Surprisingly, however, increasing the SiO2 content in the coating reverses this trend, and the coating's protective effect against scratch formation increases again. In a defined doping range, which occurs approximately at a zirconium to silicon ratio of 1:11, a significant improvement in the protective effect occurs, achieving a percentage reduction in scratches that is almost comparable to a coating with a very high zirconium content.

[0063] Such a coating has a refractive index of around 1.5, which is very close to the refractive index of a substrate made of LAS glass ceramic. Accordingly, such a coating on a glass ceramic substrate is largely optically inconspicuous and almost undetectable to the naked eye. As an example, Figure 4 shows the curve of the refractive index n of an exemplary scratch-resistant coating with a zirconium content of 0.5% over the wavelength of the incident light. As can be clearly seen in Figure 4, the refractive index of such a coating is largely constant in the range of optically visible light (400 - 800 nm) and lies between 1.49 and 1.46. Consequently, no selective reflection of individual wavelengths takes place at the interface between coating 106 and substrate 102.Such a reflection could otherwise be perceived by an observer as a visually perceptible color impression, so that the coating would be optically distinguishable from the substrate.

[0064] In contrast, a coating consisting solely of SiO2 (far right in Figure 2) exhibits a refractive index that also differs only very slightly from the refractive index of a glass-ceramic substrate. However, such a coating has only a minimal effect on reducing scratches and is therefore largely unsuitable as a scratch-resistant coating.

[0065] Figure 3 shows exemplary detailed images of a coated substrate (Figure 3 b)) and an uncoated substrate (Figure 3 a)) after carrying out a previously described scratch test. The coating used for the substrate in Figure 3 b) was an inventive SiO2-based coating with a zirconium content of 2.95 wt. % and a silicon content of 97.04 wt. % and a layer thickness of 1300 nm, which was applied to one side of the substrate by means of a sputtering process. The substrate used is a LAS glass ceramic. As can be clearly seen in a comparison of Figures 3 a) and b), the coated substrate has a significantly lower number of scratches than the uncoated substrate in Figure 3 a), despite the same test conditions. In particular, a significant reduction in scratches that only extend over short distances is evident.

[0066] This property of the exemplary scratch-resistant coating is due, among other things, to the special combination of hardness and elasticity of the coating. Figure 5 shows example measurement data for the Martens hardness of an exemplary scratch-resistant coating with a proportion of 0.5 wt.% zirconium in the coating. The Martens hardness was determined in accordance with DIN EN ISO 14577 (2015-11). As can be clearly seen in Figure 5, the determined Martens hardness is in a range of approximately 4.2 GPa, with the Martens hardness changing only slightly with increasing indentation depth of the probe used for the measurement. This hardness is significantly lower than the hardness of scratch-resistant coatings known from the prior art, which sometimes have Martens hardnesses of well over 6 GPa.

[0067] However, the coating's strong scratch-reducing effect is also due to the fact that the coating's elastic modulus differs significantly from the elastic moduli of known hard-material-based scratch-resistant coatings. Figure 6 shows exemplary measurement data for the elastic modulus of the exemplary scratch-resistant coating, which also served as the basis for the measured values ​​in Figure 5. The coating exhibits an elastic modulus of just over 80 GPa. In comparison, conventional scratch-resistant coatings have a significantly higher elastic modulus of more than 250 GPa, making them significantly more brittle than the exemplary coating.

[0068] The prevention of scratches by the exemplary coating is therefore not based solely on preventing the penetration of abrasive particles into the coating. Rather, slight penetration of abrasive particles is partially accepted, since the resulting deformation of the coating is largely reversible due to the low modulus of elasticity and does not damage the coating itself.

[0069] In addition to the design of the scratch-protection coating 104 as a single layer 106 applied to the substrate 102, as described above with reference to Figure 1 a), a further embodiment provides for the scratch-protection coating 104 to be part of a layer composite 108 arranged on a surface of the substrate 102. In particular, the scratch-protection coating 104 can also be constructed from several sublayers.

[0070] Such a case is illustrated by way of example in Figure 1 b). A layer composite 108 comprising a total of five layers is applied to the top side of the substrate 102, with the top four layers forming the scratch-resistant coating 104'. Furthermore, a further coating 110 is applied to the underside of the substrate 102, which may be configured, for example, as a decorative layer. Such an underside coating 110 is useful when the substrate 102 is a transparent material. In this case, the area beneath the substrate can be concealed by a suitable underside coating 110. When the coated article 100' is used as a cooking surface, the electronics arranged beneath the cooking surface can then be concealed, in particular.

[0071] In the embodiment according to Figure 1 b), an intermediate layer 112, which can consist in particular of pure SiO 2 , is further formed between the scratch-resistant coating 104' and the substrate 102. Such an intermediate layer 112 can act as an adhesion promoter between the substrate 102 and the scratch-resistant coating 104', in particular the bottom layer of the scratch-resistant coating, and improve the adhesion of the scratch-resistant coating 104' to the substrate 102. Such an intermediate layer 112 can also be advantageous in combination with a single-layer scratch-resistant coating 104, as shown in Figure 1 a).

[0072] The scratch-resistant coating 104' in Figure 1 b) is constructed from a total of four layers. It is fundamentally possible for the layers of the scratch-resistant coating 104' to be identical and to be applied to the substrate 102 in successive passes of a sputtering process under essentially identical conditions. However, it is also fundamentally possible for the individual layers of the scratch-resistant coating 104' to differ from one another, in particular with regard to their respective zirconium content. In particular, it can be provided that a bottommost layer 114 of the scratch-resistant coating 104' has a zirconium content that results in a refractive index n2,i of the layer 114 that differs only very slightly from the refractive index of the intermediate layer 112 or the refractive index m of the substrate.In particular, a refractive index difference An = |m-n2,i | can be set that is less than 0.1, in particular less than 0.05. In the bottom layer 114, a low scratch protection effect is therefore accepted in favor of a low refractive index difference An and thus low scattering at the interface between layer 114 and the intermediate layer 112 or the substrate 102.

[0073] A layer 116 following the bottom layer in the scratch-protection coating 104' can then again have a slightly increased proportion of zirconium compared to layer 114. Consequently, layer 116 would already have a slightly improved scratch-protection effect, while the refractive index n2,2 of the second layer differs only slightly from the refractive index n2,i of the bottom layer 114, and thus only a slight reflection of incident light occurs at the corresponding interface. Analogously, a layer 118 lying above layer 116 can then have an even higher proportion of zirconium and thus a further increased refractive index n2,3, while the topmost layer 120 of the scratch-protection coating can have a zirconium proportion that results in an optimized scratch-protection effect with a refractive index of layer 120 of n2,4.

[0074] The refractive indices of adjacent layers 114, 116, 118, and 120 in the scratch-protection coating 104' preferably differ by a maximum of 0.1, in particular by a maximum of 0.05. At the same time, the difference An = |m-n2| between the average refractive index n2 of the scratch-protection coating 104' and the refractive index m of the substrate 102 is a maximum of 0.3, in particular a maximum of 0.2, wherein, in a multilayer structure of the scratch-protection coating consisting of N layers, the average refractive index n2 of the scratch-protection coating 104' is calculated as follows:

[0075] Such a multi-layer structure of a scratch-resistant coating 104' can be realized in the course of a sputter coating, for example, by a sequence of several magnetrons, wherein the targets of the respective magnetrons each consist of an alloy which already contains silicon and zirconium in those mass ratios which are later also desired in the corresponding layers of the scratch-resistant coating 104'.

[0076] In addition to the previously discussed visual inconspicuousness and mechanical robustness of the exemplary scratch-resistant coatings 104 and 104', the scratch-resistant coatings 104 and 104' are also characterized by a very low coefficient of friction. Figure 6 shows measured data for the coefficient of friction of an exemplary scratch-resistant coating with a zirconium content of 0.5 wt.% in the coating, with the rotational speed plotted on the horizontal axis and the correspondingly determined coefficient of friction p indicated on the vertical axis. The coefficient of friction was determined in accordance with DIN EN 1071-13 (2010-07) using a pin-on-disc method. As can be seen from Figure 6, the coating in question has a coefficient of friction p of 0.15 to 0.3.Such a low coefficient of friction promotes the wear resistance of the scratch-resistant coating and simultaneously reduces noise when objects are pushed across the coating. This is particularly advantageous when the coated article 100 is used as a cooking surface, as it minimizes noise when cookware is moved across the cooking surface. The scratch-resistant coating described above can, in principle, be used in a variety of technical fields requiring a transparent scratch-resistant coating. In particular, it can be used for coating glass ceramics. However, it is also conceivable for other types of glass or ceramics to be coated with this coating.This coating is particularly advantageous for transparent substrates with underside decorations, since the scratch-resistant coating according to the invention does not distort the color impression of these underside decorations. Therefore, scratch-resistant coatings can be implemented for induction, radiation, and gas cooktops.

[0077] Furthermore, coating oven viewing panels, control panels, worktops, and protective screens for the automotive, consumer electronics, mobile phones, watches, and smartwatches sectors is also conceivable. The described scratch-resistant coating is particularly advantageous when displays or decorations require colorfast reproduction. The following materials are particularly suitable as substrate materials: borosilicate glass, aluminosilicate glass, lithium aluminosilicate glass, soda-lime glass, glass ceramics (transparent or opaque), preferably lithium aluminosilicate glass ceramics, even more preferably chemically or thermally toughened glasses, or even non-toughened glasses and glass ceramics, primarily non-toughened LAS glass ceramics.

Claims

Patent claims 1 . A coated article comprising a substrate made of glass or glass-ceramic, wherein a scratch-resistant coating is applied to at least one surface of the substrate, wherein the substrate has a refractive index m and wherein the scratch-resistant coating has an average refractive index n2, characterized in that the absolute value of the difference in the refractive indices An = |m-n2| is less than 0.3, wherein the scratch-resistant coating consists of a composition X which contains silicon oxide and zirconium oxide, wherein the proportion of zirconium in the metallic and semiconducting component in the composition X is 0.2 to 10 wt.%.

2. Coated article according to claim 1, characterized in that the scratch-resistant coating has a Martens hardness of 3.5 to 7 GPa.

3. Coated article according to claim 1 or 2, characterized in that the scratch-resistant coating has an elastic modulus of less than 150 GPa.

4. Coated article according to one of the preceding claims, characterized in that the layer thickness of the scratch-resistant coating is between 500 nm and 3000 nm.

5. Coated article according to one of the preceding claims, characterized in that the scratch protection coating has a color shift AE of less than 2 after a temperature load of more than 600°C over a period of more than 24 hours.

6. Coated article according to one of the preceding claims, characterized in that the coefficient of friction of the scratch-resistant coating is 0.1 to 0.

5.

7. Coated article according to one of the preceding claims, characterized in that the scratch-resistant coating is part of a layer composite of at least two layers.

8. Coated article according to claim 7, characterized in that a first of the further layers of the layer composite, which is arranged in the layer composite between the substrate and the scratch-resistant coating, is free of zirconium oxide.

9. Coated article according to one of the preceding claims, characterized in that the scratch-resistant coating is composed of at least two layers, wherein a first of the layers of the scratch-resistant coating contains a zirconium content which differs from the zirconium content of a second of the layers of the scratch-resistant coating.

10. Coated article according to one of the preceding claims, characterized in that the scratch-resistant coating comprises at least three layers, the refractive indices of the layers differing from one another, and the proportion of zirconium in a layer and thus the refractive index of the layer is higher the further the layer is away from the substrate.

11. Coated article according to one of the preceding claims, characterized in that the scratch-resistant coating has a light transmittance in the visible wavelength spectrum of more than 70%.

12. Coated article according to one of the preceding claims, characterized in that the substrate is a disc-shaped glass ceramic.

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