Glass-ceramic article

Abstract

To provide a glass-ceramic article with a disc-shaped, transparent substrate consisting of a glass ceramic.SOLUTION: A substrate 102 has a first surface 110 as a usage surface and a second surface 112 opposite to the first surface, wherein the substrate has a transparency of at least 80%, the substrate has a shift in color coordinates of incident light of a CIE standard light source D65 in transmission from a=0.05 to a=3, a reflective coating 114 with a reflectivity Rvis in a visible spectral range of more than 30% is provided on the second surface, the coating has at least three layers, a first layer 104 and a second layer 106 are a silicon-containing and / or aluminum-containing nitride layer or oxide layer or oxynitride layer, and the first layer has a thickness of 5 nm to 250 nm, and a third layer 108 consists of chromium or molybdenum.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a glass-ceramic article having a disc-shaped transparent substrate made of glass-ceramic. Background technology

[0002] Glass ceramics, particularly transparent glass ceramics, have been known for many years. A variant of such glass ceramics, also known in the prior art, is lithium aluminum silicate (LAS) glass ceramics, which contain either high-quartz mixed crystal (HQMK) (also known as β-eucryptite) for particularly transparent materials or keatite mixed crystal (KMK) (also known as β-spodumene) for particularly translucent or opaque materials as the predominant crystalline phase. To produce such glass ceramics, starting glasses, so-called green glasses, are first prepared using methods typical for glass production. These green glasses are then converted into glass ceramics by heat treatment, i.e., ceramization. The transparent glass ceramics thus produced can be used in a variety of fields. In particular, such glass ceramics are used as cooking surfaces. Furthermore, such glass ceramics are used as viewing windows for fireplaces and baking ovens, as worktops, or as safety glass.

[0003] See, for example, the applicant's EP 2593409 or EP 817269 (Reissue), which describe such transparent glass-ceramics.

[0004] When used as a cooking surface, transparent glass ceramics are usually provided with an underside coating so that components located below the cooking surface, particularly induction coils and further electrical components, are no longer visible to the end user from above the cooking surface. In addition to shielding the components below the cooking surface, such underside coatings also serve an aesthetic purpose. Therefore, a variety of configurations of such underside coatings are known, differing from one another by color and properties.

[0005] Among other things, metallic reflective underside coatings based on stainless steel alloys are known here, as described for example in EP 2 801 556 B1.

[0006] Due to the nature of the system, slight variations in manufacturing parameters during the production of glass-ceramics, such as variations in composition, process parameters for the melting process, and ceramming parameters, can result in variations in the optical properties of transparent glass-ceramics. Typically, one of the most important optical properties of such transparent glass-ceramics is as color-neutral as possible, as manifested by, for example, a low saturation of CIE Standard Illuminant D65 light incident on the glass-ceramic. Color-neutral transmission here is synonymous with the colorfastness of the underside coating. For certain types of glass-ceramics, a color shift is particularly observed in the red spectral range, as manifested by, for example, a shift in the color coordinates of incident CIE Standard Illuminant D65 light to values ​​of a in the CIELab color space between 0.05 and 3.

[0007] Here, especially when using a metallic reflective undercoating, the color shift of the glass ceramic is easily noticeable compared to color-neutral transmission, since the reflected surroundings in the undercoating are reproduced in distorted colors.

[0008] Against this background, there is a need for undercoatings that make it possible to compensate for the saturation of the transparent glass-ceramics to which they are applied, particularly in the red range.

[0009] This problem is solved by the subject matter of claim 1 of the present application.

[0010] Preferred configurations of the invention are set out in the dependent claims.

[0011] Disclosure of the Invention The present invention relates to a glass-ceramic article having a disc-shaped transparent substrate made of glass ceramic, the substrate having a first surface as a use surface and a second surface opposite the first surface as a bottom surface, and the substrate has a transparency of at least 80%. The substrate further exhibits, in transmission, a shift in color coordinates of incident light of CIE standard illuminant D65 from a=0.05 to a=3. The second surface of the substrate has a reflectance R in the visible spectral range. vis a reflective coating is applied, the reflective coefficient of which is greater than 30%, preferably greater than 40%, upon light incidence on the first surface, wherein the coating has at least three layers, the first of which, closest to the second surface, is a silicon- and / or aluminum-containing nitride, oxide, or oxynitride layer having a thickness of 5 nm to 250 nm, the second of which, the coating's furthest away from the second surface, is a silicon- and / or aluminum-containing nitride, oxide, or oxynitride layer, and the third layer, disposed between the first and second layers, is made of chromium or molybdenum.

[0012] With the aforementioned layer structure, it was surprisingly found that the use of a chromium or molybdenum layer allows sufficient compensation for the color shift through the substrate into the red range, while varying the thickness of the first layer, i.e., the layer located between the substrate and the third layer, allows fine adjustment of the color coordinates of the coating, thereby achieving an overall color-neutral appearance. Thus, the article according to the invention allows for flexibly adapting the layer thickness of the first layer to accommodate variations in the saturation of the transparent glass-ceramic substrate, so that a color-neutral reproduction of the article's surroundings is achieved by the reflection of the coating.

[0013] Here, reflectance in the visible spectral range is understood to be the ratio of the intensity of incident radiation to the intensity of radiation reflected by the coating in the wavelength range of 400 nm to 780 nm. A reflectance of more than 30% therefore means that for incident electromagnetic radiation of any wavelength between 400 nm and 780 nm, at least 30% of the incident light power is reflected by the coating.

[0014] The thickness of the second layer, which shields the third layer from the surroundings, contributes little to the reflective properties of the coating and essentially functions as a barrier layer. Therefore, the thickness of the second layer can be chosen relatively freely. However, from the standpoint of process control, it is advantageous to choose the thickness of the second layer to be equivalent to the thickness of the first layer.

[0015] In addition to the aforementioned properties of the coating, which allow compensation of red discoloration through the substrate, the described coating is distinguished by further advantageous properties, such as high durability under thermal load. Thus, even as a result of a thermal load in the form of a temperature of 250° C. for a period of 100 hours, a color shift ΔE of up to 1 occurs, and ΔE in the CIE-Lab color space is calculated according to the rule:

number

[0016] Furthermore, the coatings are insensitive to detergents and acid-containing media. Thus, the coatings do not show any visible change in their optical properties after 24 hours in contact with acetic or citric acid. The saturation shift ΔE after such exposure can also be adjusted to values ​​of less than 2, particularly less than 1, and particularly preferably less than 0.8.

[0017] The coating preferably further exhibits optical properties characteristic of a mirror, in particular in the form of a gloss index in the range of more than 700, preferably more than 750, particularly preferably more than 800, very particularly preferably more than 850 at a viewing angle of 20°, more than 400 at a viewing angle of 60° and more than 100 at a viewing angle of 85°, where the saturation in reflection c * is preferably less than 20, in particular less than 10, and the lightness of reflection L is preferably greater than 50, particularly preferably greater than 60, in particular greater than 70. Furthermore, the luminance of the scattering of the reflection of incident light of CIE Standard Illuminant D65 without gloss factor (SCE) at an observation angle of 10° is less than 10, preferably less than 5, in particular less than 3.

[0018] In addition to the aforementioned properties characteristic of a reflective surface, the coating further preferably has a haze, measured through the glass ceramic, of less than 4, in particular less than 2, which value changes only by ΔH<1, in particular ΔH<0.5, even as a result of thermal loading.

[0019] The reflective coating here preferably has semi-transparent properties, the average transmittance of the coating in the visible spectral range being 0.5 to 10%, preferably 1 to 5%, particularly preferably 2.5 to 4.5%.

[0020] Here, the reflectivity of the coating is preferably increased in the infrared spectral range and, according to a preferred embodiment, is greater than 50%, in particular greater than 70%, for wavelengths above 3000 nm, which has the advantage of protecting components arranged below the substrate, in particular electrical circuits, from heat radiation that may be emitted by food or cooking utensils present on the cooking surface, such as when using the article as a cooking surface.

[0021] In addition to the thickness of the first layer, the thickness of the third layer also influences the reflective properties of the coating. In order to achieve the optical properties described above, and in particular to also realize the compensation of the red shift through the substrate described at the beginning, the third layer according to one embodiment has a thickness of 5 to 50 nm, preferably 10 to 30 nm.

[0022] Here, the third layer is particularly preferably a pure molybdenum layer.

[0023] According to a further embodiment, it is further envisaged that the first layer is made of SiO, in particular aluminum-doped SiO. Preferably, the second layer is also made of SiO, in particular aluminum-doped SiO, so that the first and second layers can be produced by essentially the same method. The use of a first layer made of SiO or aluminum-doped SiO has the advantage that, in addition to simple production, such as by a sputtering process using an (aluminum-doped) Si target, it is already possible to fine-tune the color coordinates, in particular to shift the a-value, by slightly changing the layer thickness.

[0024] According to a preferred embodiment, the third layer is made of molybdenum, and MoSiO 2 is interposed between the third layer and the first layer. x It is further envisioned that a gradient layer of MoSiO 2 may be disposed between the second and third layers, with the molybdenum content in the gradient layer increasing toward the third layer. x It is further contemplated that such a gradient layer made of MoO may be disposed, again with the molybdenum content in the gradient layer increasing in the direction of the third layer. x The SiO-rich phase may result in self-passivation of the molybdenum. Therefore, the molybdenum content increases towards the metallic molybdenum layer. x / MoSiO x / Mo / MoSiO x / SiO x A layer system of the form MoSiO x Such an intermediate layer contributes to the heat resistance of the coating, as already mentioned at the beginning.

[0025] According to a further embodiment, the first layer is made of SiO 2 having a thickness of 5 to 200 nm, preferably 5 to 100 nm, particularly preferably 5 to 60 nm.x N y Similarly, in this regard, the second layer may also be made of SiO 2 in the thickness range described. x N y The use of silicon oxynitride is particularly advantageous here, since the refractive index of the corresponding layer can be reduced by increasing the oxygen content in the compound, thus reducing the change in the reflection color of the coating at different viewing angles.

[0026] According to a further embodiment, the coating is further free of MoO3. The formation of MoO3 can be avoided by judiciously selecting process parameters during the production of the third layer. For example, when the third layer is produced by sputtering, it may be assumed that the atmosphere during the sputtering process is kept oxygen-free. Avoiding MoO3 is advantageous, since MoO3 is suspected of being carcinogenic.

[0027] According to a further embodiment, it is further envisaged that the first and / or second layer of the coating is amorphous. Forming the first and / or second layer as an amorphous layer is particularly advantageous since there are no crystalline boundaries in the amorphous layer through which foreign components can diffuse into the layer. Such foreign components could otherwise alter the optical and mechanical properties of the coating.

[0028] In contrast, the third layer of the coating is usually formed as a crystalline metal layer.

[0029] As mentioned at the beginning, the article of the present invention is particularly intended for use as a cooking surface. In this regard, a further embodiment is envisioned in which an additional layer, particularly a colored layer in the form of a decoration, is disposed between the first layer and the second surface of the substrate. For example, this allows for the realization of cooking zone markings or operating elements that are visible to the end user. In addition to the colored decorative coating, the substrate may also have structured regions on which the coating is applied.

[0030] According to a further embodiment, it may be further assumed that the coating has voids and therefore does not cover the entire second surface. Such voids may be provided, for example, at positions where it is desired to arrange display elements below the substrate. Here, the coating may be partially removed, for example, by laser, or certain areas on the second surface of the substrate may already be masked by a shadow mask during the coating process and left correspondingly void during coating.

[0031] According to a preferred embodiment, the substrate is made of a lithium aluminum silicate glass ceramic that is free of arsenic and antimony except for unavoidable trace amounts. Such glass ceramics are particularly environmentally friendly. Instead of arsenic or antimony, which typically act as refining agents in transparent LAS glass ceramics, such glass ceramics may contain tin, which also acts as a refining agent but is virtually harmless to health.

[0032] The invention will now be explained in more detail, without being limited thereto, with reference to the drawings, in which like reference numerals indicate the same or similar elements. [Brief explanation of the drawings]

[0033] [Figure 1] 1 is a schematic diagram of an exemplary glass-ceramic article having an underside coating. [Figure 2]2 is a schematic diagram of a further exemplary glass-ceramic article having a gradient layer in the underside coating. FIG. [Figure 3] 1 is a reflectance spectrum of an exemplary coating. [Figure 4] 1 is an XRD spectrum of an exemplary coating. [Figure 5] Angular dependence of color shift due to exemplary coatings for observation angles of 0° and 20°. [Figure 6] Angular dependence of color shift due to exemplary coatings for observation angles of 45° and 60°.

[0034] In the following, similar or identical features are identified with the same reference numerals.

[0035] 1 shows a schematic diagram of an exemplary glass-ceramic article 100 according to one embodiment of the present invention, which may be used, among other things, as a cooking surface. The glass-ceramic article 100 comprises a transparent glass-ceramic substrate 102 having an upper surface 110 and a lower surface 112. Here, the upper surface 110 faces a user as a use surface when the article 100 is used as a cooking surface, while the lower surface 112 faces away from the user. Here, the substrate may comprise, among other things, a lithium aluminum glass ceramic. Such a substrate may be, among other things, a 10 -6 K -1 It is distinguished by high heat resistance and low thermal expansion, which is expressed by a low CTE (coefficient of thermal expansion) of less than 1000 . A "transparent" substrate is understood here to be a substrate having a transmittance of at least 80% over the entire visible spectral range.

[0036] Transparent LAS glass ceramics often exhibit a slight shift in the color coordinates of incident light as it passes through the glass ceramic. In particular, tin-refined transparent LAS glass ceramics can exhibit a slight reddish tint. This reddish tint can be explained, for example, by the shift in the color coordinates of incident light for CIE Standard Illuminant D65 from a = 0.05 to a = 3 as it passes through the substrate 102. Here, the incident light is assumed to be completely achromatic, i.e., has an a value of 0.

[0037] The lower surface 112 of the substrate 102 is provided with a reflectance R vis A coating 114 is applied that has a reflectivity R of greater than 30%. vis is understood to mean that 30% of the incident light power in the spectral range from 400 nm to 780 nm is reflected by the layer.

[0038] In the illustrated embodiment, the coating 114 is constructed from three sub-layers 104, 106, and 108, where the first of these layers, layer 104, is disposed directly on the lower surface 112 of the substrate 102 and serves as a barrier layer. Here, the first layer 104 may be, for example, silicon oxide (SiO), silicon nitride (SiN), silicon oxynitride (SiO x N y ) In addition, aluminum-based oxides, nitrides or oxynitrides are also considered as barrier layers. Such layers can be applied to the substrate 102 by, for example, sputtering. The thickness of the first layer 104 can be between 5 nm and 250 nm.

[0039] A further layer 108, referred to as the third layer, is applied to the first layer 104. The third layer 108 is made of chromium or, preferably, molybdenum and can likewise be produced by a sputtering method. The third layer 108 preferably has a layer thickness of 5 nm to 50 nm, in particular 10 nm to 30 nm. If molybdenum is used as the material for the third layer 108, the third layer is particularly preferably free of molybdenum trioxide (MoO), which can be achieved by correspondingly adapting the production parameters.

[0040] A further barrier coating is applied to the third layer 108, which will be referred to hereinafter as the second layer 106. Here, the second layer 106, like the first layer, may consist of a silicon-based or aluminum-based oxide, nitride or oxynitride. Here, in particular, the first layer 104 and the second layer 106 may have essentially the same composition and comparable layer thicknesses.

[0041] Particularly preferably, the first layer 104 and the second layer 106 consist of aluminum-doped silicon oxide or silicon oxynitride, in particular with a thickness of 5 nm to 60 nm. By varying the thickness of the first layer 104, the compensation of the red shift through the substrate 102 for light incident on the first surface 110 and reflected by the coating 114 in the layer composite of the described coating 114 can be adjusted. Thus, the color shift of light incident on the coating upon reflection at the coating 114 depends, inter alia, on the thickness of the first layer 104.

[0042] Here, the first layer 104 and the second layer 106 are preferably amorphous, while the third layer 108 is grown as crystalline.

[0043] 1 suggests that coating 114 completely covers underside 112 of substrate 102, it is entirely possible for coating 114 to have voids where underside 112 of substrate 102 is not coated. Such voids may be provided, for example, to allow display elements to be placed below substrate 102 such that the display elements are visible from above substrate 102 by an end user.

[0044] It may further be envisaged that a decorative coating is disposed between the first layer 104 and the substrate 102, thereby realising, for example, cooking zone markings. Furthermore, such decoration may also be disposed on the upper surface 110 of the substrate 102.

[0045] Below, exemplary embodiments of coatings produced in a magnetron sputtering system are listed in tables, where the layer systems, and likewise the layer thicknesses, are listed in the order "first layer 104 / third layer 108 / second layer 106".

[0046] [Table 1]

[0047] [Table 2]

[0048] [Table 3]

[0049] FIG. 2 shows a schematic diagram of a further exemplary glass-ceramic article 100. Here, the embodiment of FIG. 2 differs from the embodiment of FIG. 1 in that the first layer 104 and preferably also the second layer 106 are each composed of silicon oxide, particularly aluminum-doped silicon oxide. Furthermore, in the embodiment of FIG. 2, gradient layers 116 and 118 are disposed between the first layer 104 and the third layer 108, and between the second layer 106 and the third layer 108, respectively, and the gradient layers 116 and 118 are composed of molybdenum-(aluminum)-silicon oxide. Here, as indicated by the arrows in FIG. 2, the molybdenum content in each layer 116 or 118 increases toward the third layer 108. Thus, in the case of layer 116 formed between first layer 104 and third layer 108, the molybdenum content increases in the direction away from substrate 102 (downward in the diagram of FIG. 2), while in the case of layer 118 formed between second layer 106 and third layer 108, the molybdenum content increases in the direction toward substrate 102 (upward in the diagram of FIG. 2). Here, such gradient layers 116 and 118 in coating 114 contribute to the heat resistance of the coating.

[0050] 3 shows the reflectance spectrum of an exemplary coating 114, where the third layer 108 is made of molybdenum and has a thickness of 22 nm. Here, the first layer 104 and the second layer 106 are each formed as 60 nm thick barrier layers made of aluminum-doped silicon oxide. It can be seen that the spectral reflectance of the coating 114 is 30% to 50% across the entire visible wavelength range from 380 nm to 780 nm.

[0051] 4 shows an XRD spectrum of an embodiment of the coating 114 in which the third layer 108 is made of molybdenum, where the crystalline structure of the molybdenum layer is clearly visible in the spectrum, while the first layer 104 and the second layer 106 do not contribute to the spectrum due to their amorphous structure.

[0052] Figures 5 and 6 show the angular dependence of the color impression of an exemplary coating 114, where the first and second layers 104, 106 are made of aluminum-doped silicon oxide and the third layer 108 is made of molybdenum. Here, Figure 5a) shows the a and b values ​​of coating 114 for a viewing angle of 0°, Figure 5b) shows the corresponding values ​​for a viewing angle of 20°, Figure 6a) shows the corresponding values ​​for a viewing angle of 45°, and Figure 6b) shows the corresponding values ​​for a viewing angle of 60°. Individual measurement points were identified for different layer thicknesses of the first and second layers 104, 106, which varied from 20 nm to 180 nm. Here, the thickness of the third layer was 28 nm. 5a), 5b), 6a), and 6b), it becomes clear that the color coordinates of coating 114, which can be adjusted by appropriately selecting the layer thicknesses, differ only slightly for different viewing angles. Thus, for different viewing angles, it is possible to adapt the color shift of coating 114 over a wide range by simply changing the layer thicknesses of first layer 104 and second layer 106, and thus to adjust an overall, nearly color-neutral reflection in conjunction with substrate 102.

[0053] The layer system of coating 114 is therefore advantageous in that the reflected color remains almost unchanged at various angles of incidence from 0 to 60°. The color coordinates are given in the Lab color space as follows: * = 5, preferably at most 3, particularly preferably at most 1 shift, ΔE * is calculated as follows:

number

[0054] For the example of a coating in the form of AlSiO2 / Mo / AlSiO2 with respective layer thicknesses of 60 / 28 / 60 nm, the color coordinates of the coating for the viewing angles listed above are, in the Lab color space: 0°: a=-2.5 / b=0.278 20°: a=-2.5 / b=0.181 45°: a=-2.6 / b=-0.15 60°: a=-2.5 / b=-0.4 It is adjusted as follows.

[0055] Therefore, only very small changes are observed for different observation angles, especially in the region of red shift (a value).

[0056] Although the present invention has been described based on the preferred embodiment, the present invention is not limited thereto and can be modified in various ways. [Explanation of symbols]

[0057] 100 Glass ceramic articles 102 Base material 104 First Layer 106 Second Layer 108 Third Layer 110 Top surface of base material 112 Bottom surface of base material 114 Coating 116 Gradient Layer 118 Gradient Layer

Claims

1. A glass-ceramic article (100) having a disk-shaped transparent substrate (102) made of glass ceramic, the substrate (102) having a first surface (110) as a use surface and a second surface (112) opposite the first surface (110) as a lower surface; the substrate (102) has a transparency of at least 80%; the substrate (102) exhibits, in transmission, a shift in color coordinates of incident light of CIE Standard Illuminant D65 from a=0.05 to a=3; The second surface (112) of the substrate (102) has a reflectance R ｖｉｓ a reflective coating (114) having a reflectivity of greater than 30%, preferably greater than 40%, upon light incident on said first surface (110); the coating (114) has at least three layers (104, 106, 108); a first of said layers (104) closest to said second surface (112) is a silicon-containing and / or aluminum-containing nitride, oxide or oxynitride layer having a thickness of 5 nm to 250 nm; a second layer (106) of the layers, which is located in the coating (114) farthest from the second surface (112), is a silicon-containing and / or aluminum-containing nitride layer, oxide layer, or oxynitride layer; a third layer (108) disposed between the first layer (104) and the second layer (106) and made of chromium or molybdenum; Articles (100).

2. The article (100) of any preceding claim, wherein the third layer (108) has a thickness of 5 to 250 nm, preferably 5 to 50 nm.

3. The first layer (104) is SiO ２ from, in particular, aluminum-doped SiO ２ The article (100) of claim 1 or 2, comprising:

4. The third layer (108) is made of molybdenum, and MoSiO is provided between the third layer (108) and the first layer (104). ｘ The article (100) of claim 3, further comprising a gradient layer (116) of molybdenum disposed thereon, the gradient layer (116) having an increasing molybdenum content in a direction toward the third layer (108).

5. The first layer (104) is a SiO layer having a thickness of 5 to 200 nm, preferably 5 to 100 nm, particularly preferably 5 to 60 nm. ｘ N ｙ The article (100) of claim 1 or 2, comprising:

6. The coating (114) is MoO ３ The article (100) of any one of claims 1 to 5, wherein the article (100) is free of:

7. The article (100) of any one of claims 1 to 6, wherein the first layer (104) and / or the second layer (106) of the coating (114) is amorphous.

8. 8. The article (100) according to claim 1, wherein a further layer, in particular a colored layer in the form of a decoration, is disposed between the first layer (104) and the second surface (112) of the substrate (102).

9. The article (100) of any one of claims 1 to 8, wherein the coating (114) has voids and does not completely cover the second surface (112).

10. The article (100) of any one of claims 1 to 9, wherein the substrate (102) comprises a lithium aluminum silicate glass ceramic that is free of arsenic and antimony except for unavoidable trace amounts.

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