Protective coating for a body as well as process and plant unit for preparing protective coatings

The invention relates to a protective layer, in particular a hard-material layer with a high scratch resistance and heat resistance, and a method and an arrangement for the production of protective layers.

The invention relates more particularly to a protective layer for glass ceramic plates and a method and an apparatus for its coating, which is preferably used as cooking surfaces in cooking areas and on at least one side having a protective layer with a relative to the uncoated glass ceramics increased scratch resistance.

Modern hobs have a glass ceramic plate as a cooking surface, wherein the glass ceramic plate is typically flat, but may be two or three-dimensionally. There are both glass ceramic plates printed in writing or on the market that are undecorated or with thermally stable colors, eg ceramic colors, decorated. The cooking surface has individual cooking zones that are inductively heated by electrically powered radiant heaters, gas radiant heating elements or with alternative heating systems (eg DHS SCHOTT).

typically have a Mohs hardness glass ceramic plates with a hardness 5-6, the the comparable steels from which typically the cookware is made. The everyday use, ie parked or moving the cooking vessel and clean the cooking surfaces with abrasive cleaning agents and sponges or using a scraper, represents a high mechanical load on the hob, which can lead to cause wear on the hob.

In addition, the cooking surface is often used in cold condition as additional storage. Right here is an increased risk of formation of surface damage, for example by rough floors ceramic articles. All resulting surface damage lead over time to form a scratching of the surface, which is more or less conspicuous to the observer in accordance with the selected lighting. In addition, damage to the surface provide starting points for dirt. The ease of cleaning of the surface is limited, since the cleaning of contaminants from this damage is much more difficult. This effect is independent of whether the hob is transparent, colored or translucent.

The glass ceramic plates of the previous generation had an orange skin-like surface structure typical. Although these plates were scratched by the above-described operations, they offered a relatively small scratches conspicuous because of the additional surface structure. The surfaces of the glass ceramic plates are, however, over time become smoother and shinier, resulting from the aforementioned reasons to enhanced conspicuity scratches.

The <patcit id="pcit0001" dnum="EP0716270B1"><text>EP 716 270 B1 0</text></patcit> describes a cooking surface of glass ceramic, on top of which a decoration is provided, which has to avoid scratching or traces of a protective layer in the form of email flows or silicate coating with respect to the ceramic increased scratch resistance, this protective layer, the glass ceramic cooking surface is closed or possible printed covers closed, and this protective layer or directly on the glass ceramic surface a decoration. Preferably, the protective layer made of a dark material is formed. This protective layer, although the mechanical strength of the glass ceramic cooking surfaces is generally increased so that the use of the hob decreased scratches conspicuity against an unprotected cooking surface occurs, however, offer the disclosed solely in EP font Emailflüsse- or silicate protective layers not have optimum mechanical long-term protection. The disadvantage is that is that the protective layer itself constitutes a decor that is applied by screen printing. This decorative paints are generally based on the same rivers as the decor colors used for optical design. Regarding abrasion they are therefore subject to the same restrictions. The minimum dimension of such designs is in the order of 0.5 mm, which is visually striking in any case, and thus is designerisch disturbing, particularly if glasses or glass ceramics are desired with smooth surfaces.

Furthermore, the explanations do not allow any conclusion on how far the solution presented with the heater systems used is compatible. Especially the use of preferably dark materials as protective layer for glass ceramics with high IR transparency and radiant heaters is thus a restriction of the desired IR transparency and to sacrifice in de lead r Ankochperformance.

In the <patcit id="pcit0002" dnum="DE10000663A1"><text>DE 100 00 663 A1</text></patcit> a method and associated apparatus is described with which an optically transparent body with a scratch protection layer of Al₂O₃ over the entire surface provided by a modified PICVD process, such that a hard-material layer is formed, since it has been shown that with the known methods is to produce sufficiently hard, dense, scratch-resistant and temperature-resistant layer, in particular of alumina. A disadvantage is the great process complexity, especially when large-area coatings must be applied homogeneously. Previously inhomogeneities are not avoided, which also interferes with the visual appearance of the long term.

Further describes <patcit id="pcit0003" dnum="WO9631995A"><text>WO 96/31995</text></patcit> an inductively heated glass or glass ceramic cooktop with integrated coil, on a hard material layer of Al₂O₃ is applied in a layer thickness between 50 and 200 microns by means of the technique of plasma spraying. The disadvantage here is that such thick layers are very rough and thus the use properties, such as pot abrasion, wear and cleaning performance are adversely affected. Furthermore, the appearance of the cooking surfaces changes completely with such a layer. The surface appears dull and gray.

By <patcit id="pcit0004" dnum="DE4201914A1"><text>DE 42 01 914 A1,</text></patcit> (= <patcit id="pcit0005" dnum="US5594231A"><text>US 5,594,231</text></patcit>) It is also known, scanning window made of glass or glass ceramic from installed in cash registers of supermarkets and other consumer markets sensing systems for detecting applied to the product packaging bar codes, on the top side to be provided with a transparent hard material layer, which in turn has a transparent lubricious coating is applied, to make this sampling wear resistant. As materials for the hard material layer include metal oxides such as Al₂O₃, ZrO₂, SnO₂, Y₂O₃ called. Particularly suitable amorphous deposited alumina is called. Just the amorphous deposition of the metal oxide favors here the desired improved hardness and sliding properties of the protective layer. The hard coatings described herein are suitable for applications in the room temperature range, but also change their properties at high temperatures, as are customary, for example, in cooking surfaces, which makes them unsuitable for use at high temperatures. A protective layer for cooking plates requires materials that are up to 800 ° C temperature resistant and withstand the high occurring between the glass ceramic and protective layer thermomechanical stresses assets.

By <patcit id="pcit0006" dnum="DE20106167U1"><text>DE 201 06 167 U1</text></patcit> has become known as a cooking surface that is provided with a transparent scratch-resistant layer that can be formed inter alia by a hard material coating a hob with a glass ceramic plate. As materials for this transparent layer such as aluminum oxide, zirconium oxide, yttrium oxide, tin oxide, indium oxide and combinations thereof are mentioned, inter alia, metal oxides. The deposition of the materials can be carried out according to this document, for example by the sol-gel technique, the CVD method, in particular by the PICVD method and by sputtering.

With the known processes for the production of hard coatings such as those described in the above-mentioned

Fonts <patcit id="pcit0007" dnum="DE4201914A1"><text>DE 42 01 914 A1,</text></patcit> and <patcit id="pcit0008" dnum="DE20106167U1"><text>DE 201 06 167 U1</text></patcit> are described, the layers are typically deposited amorphous or partly crystalline structure. Such layers may experience adverse changes in the hot areas or in the case of maximum thermal stress during prolonged use. Thus the layers can be in these areas discolored by thermally induced compaction or deteriorate by crystallization, with the result that the hot areas are visually striking. Further, there may be a roughening in the range of 1 to 1000 nm. The roughening itself may already cause an optical abnormality, the resulting wells in addition lead to a more difficult cleaning. The crystallization problems in the hot areas exacerbated mechanical failure of the scratch-resistant layer. In the crystallization changes the structure of the layer, so that cracks in the layer formed. Due to the loss of lateral cohesion layer offers no special protection from scratches more.

For example, zirconium oxide to impart a higher temperature resistance, it is known (G.Wehl et al., Proc. CVD VII, 536 (1979)) to add this so-called stabilizers of yttrium oxide, magnesium oxide or calcium oxide. However, if such a layer, produced by the known method, a low density, so that such a layer is porous. Zirconia-hard coatings are also from the publications <nplcit id="ncit0001" npl-type="s"><text>H. Tomaszewski ET AL: "yttria-stabilized zirconia thin films grown by reactive rf magnetron sputtering", THIN SOLID FILMS 287 (1996) 104-109</text></nplcit>. <nplcit id="ncit0002" npl-type="s"><text>H. Tomaszewski ET AL: "yttria-stabilized zirconia thin films grown by rf magnetron sputtering from oxide to target" THIN SOLID FILMS 293 (1997) 67-74</text></nplcit>. <nplcit id="ncit0003" npl-type="s"><text>DE Ruddell ET AL: "The effect of deposition parameters on the properties of yttria-stabilized zirconia thin films", THIN SOLID FILMS 45 (2003) 14-19</text></nplcit>. <nplcit id="ncit0004" npl-type="s"><text>B. HOBEIN ET AL: "DC sputtering of yttria-Stabilized Zirconia films for solid oxide fuel cell applications", JOURNAL OF THE EUROPEAN CERAMIC SOCIETY 21 (2001) 1843-1846</text></nplcit> and <nplcit id="ncit0005" npl-type="s"><text>DENUL ET AL: "Ion-assisted deposition of biaxially aligned YSZ layers on metal tape" PHYSICA C 351 (2001) 45-48</text></nplcit>. known. were in the publications, inter alia, glass, Alumimiumoxid and sapphire, silicon, metals, such as aluminum or iron-chromium alloys, nickel oxide, and various plastics as substrates. These substrates have in common that the glass-ceramic compared with a cooktop having significantly higher coefficient of thermal expansion.

The in <patcit id="pcit0009" dnum="US4920014A"><text>US 4920014</text></patcit> described method for producing such a layer of stabilized zirconia is trying to solve this problem by the etc., the layer is deposited by the CVD method and precisely adjusted process parameters such as temperature of the substrate, the time and duration of the supply of the reaction substances, that they only having one or two parallel oriented to the substrate surface crystal planes. Apart from a very high process complexity, have such crystalline layers still on a rough surface.

Whereas the scope of turbine technology is known that columnar grown layers have a particularly high resistance to rapid thermal alternating loads. So describes the<patcit id="pcit0010" dnum="US4321311A"><text>US 4321311</text></patcit> the use of a columnar grown ceramic layer as thermal protection for metal components of the turbine construction. The layers described herein, however, because of their coarse crystalline structures large roughness or porosity.

Rough and porous surfaces easily and are difficult to clean. They are also not optically clear transparent but severely scattered and not suitable for applications with visually appealing surfaces.

In other optically transparent bodies made of glass or glass ceramic, the high operating temperatures, such as fireplace door windows, oven doors for cleaning ovens, etc., the scratch protection problems are similar as in cooking surfaces.

The invention is based on the object to form the protective layer of a body such that it is scratch-resistant and wear-resistant, remains structurally stable under thermal loads and not changed optically as well as having a permanently smooth and visually appealing surface.

This object is achieved with a glass ceramic hob with a protective coating according to claims 1 to 15, a process according to claims 16 to 34 and a use of a device according to claims 35 to 41.

The protective layer according to the invention of a body has at least one hard material layer of a metal oxide and / or metal and / or metal carbide and / or Metalloxonitrid and / or metal carbonitride and / or Metalloxocarbonitrid, wherein at least one of these hard coatings has a morphologically dense column structure.

It is advantageous if these dense column structures are formed as crystalline columnar structures with at least a proportion of 50%, preferably with a proportion of more than 80% in the layer. This film morphology, the layer is particularly insensitive to mechanical and thermal stresses.

Hard coatings of metal oxide and / or metal and / or metal carbide and / or Metalloxonitrid and / or metal carbonitride and / or Metalloxocarbonitrid have a function of the process conditions varied layer morphologies and properties. The setting of process conditions that enable a columnar, preferably columnar crystalline growth of the layer in narrow column structures, these hard coatings obtained a dense, smooth and visually appealing surface and are structurally stable in mechanical and thermal stresses.

As crystalline generally refers to the state of solids with arrangement of their particles in a three dimensional space lattice with pronounced long-range order. The crystalline body, here the hard material layer may consist of many small, irregular crystallites or the lattice structure may continue through the entire layer. The is forming in the layer columns are closely spaced columns structures that predominantly form perpendicular to the substrate. The crystals have a priority on orientations that show little tendency to widen in columnar growth.

To achieve the lowest possible porosity of the protective layer and thus a possible low-clean roughness of its surface, the layer is preferably formed so that the lateral extent of the columns is less than 1 .mu.m. In a particularly advantageous embodiment, the lateral extent of the columns is less than 200 nm. The densely packed column structures also make it possible to achieve a largely unimpeded optical transmission and to avoid disruptive effects by light scattering.

Particularly suitable for transparent protective layers according to the invention are proving to hard coatings of silicon or metal oxides in temperature-stable crystal phase.

It has been found that layers according to the invention, in particular of zirconium oxide or mixed layers based on zirconium oxide, particularly for transparent, visually appealing, especially thermally stable highly protective layers are also suitable. By a suitable Abscheideprozedur a particularly thermally stable, dense crystalline column structure are produced, which is also scratch-resistant in a high degree. It is advantageous here that the zirconium oxide layers by the addition of other metal oxides such as yttrium oxide, calcium oxide, magnesium oxide, tantalum oxide, niobium oxide, scandium oxide, titanium oxide or an oxide from the group of Lanthanioid-oxides such as lanthanum oxide or cerium oxide, and combinations thereof, but in particular by the addition of 0.5 to 50 mol% Y₂O₃, Advantageously by the addition of 0.5 to 10 mol% Y₂O₃ and most optimally by adding 4 mol% Y₂O₃, In a high-temperature crystal phase can be stabilized such that it (up to max. 800 ° C) experienced at least in the relevant temperature range for cooking systems no temperature-dependent structural changes.

The protective layer of the invention can be the hard coatings hitherto described contain one or more hard coatings. In what order number and what materials they are formed, depends mainly on the further desired optical and / or mechanical demands on the protective layer.

The protective layers of the invention are to coat different body, which must have particularly high scratch resistance and temperature resistance, suitable. They also allow an appealing visual appearance and, depending on the layer material and transparency. They are particularly useful as protective coatings for glass, glass ceramic or body of other non-metallic crystalline materials, but not limited thereto.

Particularly advantageously, the protective layer for the coating of glass-ceramic cooking surfaces is. Here are requirements of high scratch resistance, temperature resistance and a visually appealing appearance are important, which are achieved by using the inventive coating.

With transparent protective layers the glass-ceramic cooking surfaces or other body to be coated can be additionally decorated below or within the protective layer. But Not Transparent and transparent protective layers may be additionally decorated on the protective layer.

The inventive method for coating a body with a protective coating according to the invention comprises essentially providing the body and the laminates in a vacuum system and coating the body by means of a reactive physical vapor deposition, said laminates are produced in atomic dimensions and additionally enriched energetically, so that form the growing crop, the layer mainly morphologically dense column structures, preferably crystalline column structures.

Another inventive method for coating a body of glass, glass ceramic or another non-metallic crystalline material, preferably for coating a cooking surface, with a protective layer according to the invention includes substantially the transferring of the body in a vacuum system immediately after its production and the provision of the layer materials and coating the body by means of a reactive physical vapor deposition process, whereby layer materials are produced in atomic dimensions and additionally energetically enriched, so that morphologically dense column preferably form predominantly structures, crystalline columnar structures of the growing crop of the layer.

The application of the layers by ion beam assisted ion beam sputtering leads to particularly high energy inputs. This method is the best way to define the morphology and crystal structure of the layer by tuning ion energy and intensity of the ion beam. The energy of the ions of the supporting ion beam lies between 1 to 2500 eV, preferably between 1 to 800 eV, and particularly preferably between 20 to 450 eV. The ion energy and the intensity of the assisting ion beam must be adjusted in each case such that the application rate of the laminates remains greater than the removal rate of the layer materials by the additional ion source. The ion beam assist can also be optionally interrupted temporarily.

The deposition of the layers is not limited to ion beam sputtering. Basically, all sputtering can be used. There are different ways to realize an ion bombardment of the growing layer, depending on the chosen technology. Considering the wide range of setting with respect to the intensity and the choice of ions (noble gases, oxygen, nitrogen, etc.) and the geometric arrangement of the ion source relative to the substrate to be coated, can be found by those skilled in this regard settings, be prepared with those inventive layers are. In processes using the magnetron, succeeds in producing inventive layers, for example through the use of a so-called "unbalanced magnetron", a pulsed magnetrons, a medium-frequency magnetron source with very high AC frequencies or by applying a negative bias voltage to the substrate. In these processes, the required ion bombardment of the growing layer is realized by extracting the ions from the plasma of the material source. Other measures by which this can be achieved, are state of the technology. It is also possible to combine different measures such that a particularly strong ion bombardment is achieved.

In addition, it may be advantageous, preferably metal oxide layers, in particular when stabilized zirconium oxide layers, at least one additional gas, for example nitrogen, to optimize the ablation rate in the production of the layer materials or to optimize the degree of ionization of the reactive gas and / or oxygen for the optimization of the oxidation feeding the layer into the vacuum system.

In addition, oxide layers due to the process may not have been made completely oxidized and therefore have a disordered crystal structure, are oxidized by a subsequent thermal treatment in an oxidizing atmosphere and healed it. The thermal treatment can be carried out in a recipient in which the coated body can be heated to temperatures up to 800 ° C, preferably to 400 ° C to 700 ° C.

Additionally it can be embedded into the recipient oxygen. Preferred are the partial pressures of oxygen, which can be adjusted between 10^-2 and 1000 mbar. The duration of the heat treatment should be between 1 minute and 10 hours are preferred, between 10 to 60 minutes.

Depending on the stage in the production chain, it may be necessary to subject the body to be coated prior to coating of a cleaning. A cleaning will not take place necessary if the coating directly adjoins the last step in the manufacture of a hot glass or glass-ceramic body, since there are at this point cleanest surfaces.

The cleaning of the articles to be coated may be accomplished by using at least one suitable cleaning bath with final drying in order to remove contaminants from the surface to be coated. Depending on the contamination occurring it may be necessary to use more than one cleaning bath and apply additional cleaning effects by a heating and / or ultrasonic excitation.

There is also the possibility of cleaning in a vacuum chamber by a plasma treatment with ions, the energy of which is preferably in the range from 1 to 2500 eV, preferably 50 to 1600 eV, and particularly preferably from 100 to 500 eV is to perform. Alternate embodiments for example, the bombardment of the substrate with ions from an ion source or "bathing" of the sample in the plasma of a glow discharge. A particularly intensive cleaning of the surface of impurities and adsorbates is achieved. Sensible Cleaning times range from a few seconds up to several minutes.

Moreover, it is advantageous to activate the surface of the body to be coated. The activation can also be in a vacuum chamber by a plasma treatment of the surface, as described before, occur. The cleaning and activation can be carried out in one process step, if necessary.

Prior to and during the coating of the body to be coated can be heated in the vacuum chamber to the process temperature, for example, by suitable heating elements in the vacuum chamber. The body temperature can be selected to process start between room temperature and 800 ° C, preferably between 50 ° C and 550 ° C, more preferably between 100 ° C and 350 ° C.

Furthermore, it may be desired to achieve an especially high surface quality of the coated body. For this purpose, in one or more polishing steps, which are adapted to the low surface roughness to a remaining R_aValue of 1 nm to improve the surface to be reworked again.

The coating of a body made of glass, ceramic or other non-metallic crystalline material, in particular a glass-ceramic cooking plate, with a protective layer, in particular with a protective coating according to the invention succeeds in accordance with the invention with a coating installation and a with it an entrance lock (2.2) and substrate transfer station (2.1 ) directly associated manufacturing facility (1) in which the body to be coated was prepared immediately before. The coating system comprises at least one coating chamber (4.1), which is a vacuum chamber, which a target (14) with the layer starting material, an excitation source for generating layer starting materials in atomic dimensions, a directed onto the substrate, supporting ion beam source (12), at least one process gas inlet valve (15) for supplying process gases to the vacuum chamber and shutter (7) as closable openings for supply and removal of the substrate to be coated (8).

The excitation source may be an ion beam excitation source (13) or a magnetron.

In an advantageous embodiment, the coating machine to a cleaning / activation chamber (3), which is a vacuum chamber and at least one purification / activation ion beam source (11) for cleaning and / or activating the substrate (8), between the inlet lock (2.2) and the coating chamber (4.1) is arranged and shutter (7) is connected to these.

For the production of protective layers with a plurality of individual layers of different layer starting materials it is possible to either replace the target in the coating chamber or to arrange accordingly further coating chambers (4.n). Alternatively, this coating chambers (4.n) can also be occupied with the same starting materials layer so as to coat a plurality of substrates at the same time and increase throughput.

For further optimization of metal oxide, it may be advantageous to post-treat in an oxygen atmosphere. For this purpose, the coating apparatus, an aftertreatment chamber (5), wherein this is also a vacuum chamber and at least one oxygen supply valve (16) and heating elements (9) and shutter (7) to the coating chamber (4.1) or a further coating chamber ( is 4.n) connected.

Preferably, the coating chambers include (4.1, 4.n) and the purification / activation chamber (3) heating elements (9) for heating the substrate (8) and realization of an optimum heating concept during the coating of the substrate (8).

After the coating of the substrate (8) and optionally after-treatment of the layer, the substrate (8) via an output gate (6.1) and substrate output unit (6.2) is guided out of the coating system. The exit lock (6.1) is connected via a shutter (7) to the last vacuum chamber in the processing chain. The invention will be explained in more detail further with reference to an embodiment. These shows<dl id="dl0001"><dt>Figure 1:</dt><dd>an ion beam sputtering system with an ion beam assist</dd></dl>With a shown in Figure 1 ion beam sputtering system, which operates with a supportive ion beam, may protective layers, especially transparent, visually pleasing, structurally and thermally stable scratch protection layers, for example, stabilized zirconium oxide, are applied to a ceramic hob.

Substrate transfer:

The substrate (8), for example, a CERAN plate for hobs with a dimension of 60 cm * 60 cm, is transferred immediately after its production, following the recent hot step of ceramization of the manufacturing facility (1) in the coating plant. The coater is a vertical system which enables a borderless coating of the substrates (8). The substrates (8) are transferred individually into the coating system.

After transfer of a substrate (8) in the substrate transfer station (2.1), this is closed and a pressure of &lt;1 mbar is set. Subsequently, the substrate (8) on a shutter (7) in the inlet lock (2.2) is transferred. The inlet lock (2.2) is evacuated, so that in this a pressure of &lt;10^-2 mbar is set. Generally, the further transfer of the substrate (8) from a processing unit to the next takes place within the sputtering on the shutter (7). The substrate is then transferred to the cleaning / activation chamber (3).

Substrate cleaning and activation:

The cleaning / and activation chamber (3) is also a vacuum chamber in which the heating elements (9) for heating the substrate (8) and cleaning / activation ion beam sources (11).

Purification need not be necessary, because the coating directly adjoins the last hot-step in the preparation. If necessary, can be carried out the cleaning of the substrate (8) in one step with the activation of the surface of the substrate (8).

The cleaning / activation chamber (3) is first on the process pressure &lt;5 * 10^-5 mbar evacuated and the substrate (8) is heated to a temperature to about 700 ° C. Since the substrate (8) was transferred immediately after the final hot step ceramization for coating, heating to these high temperatures with a much lower cost is possible, as in the known methods.

In the cleaning / activation chamber (3) argon ions now be fired at the surface of the substrate (8) with an energy of 400 eV for cleaning and activation. The substrate (8) while continuously moving forward at a speed of 3 cm / min. Subsequently, the substrate (8) is transferred into the coating chamber (4.1).

coating:

The first coating chamber (4.1) is also a vacuum chamber and is used to coat a first feedstock. If the coating comprises several layers of different starting materials or if the coating multiple substrates (8) are parallel, and further coating chambers (4.n) can follow.

In the first coating chamber (4.1) and the possibly required further coating chambers (4.n) each is a target (14) with the layer starting material, heaters (9), diaphragm (10), ion beam excitation source (13) and a supportive ion beam source (12).

With the heating elements (9), the substrate (8) is maintained at the desired process temperature. The film source material is metallic zirconium-yttrium in a ratio 92: 8, which is bombarded with a mixture of xenon and argon ions from the ion beam excitation source (13) with an ion energy of 1500 eV. At the same time is supplied through the process gas inlet valve (15) of oxygen so as to form a zirconium-yttrium oxide film on the substrate (8). The aperture (10) thereby define a coating window over the entire length (perpendicular to the substrate movement direction) of the substrate (8) having a width of 20 cm.

In addition, the substrate (8) is bombarded with argon ions having an ion energy of 100 eV of the supporting ion beam source (12). The substrate (8) is now coated by suitable movements to the coating window homogeneously with a layer thickness of 2 microns. After coating, the substrate (8) is transferred into the treatment chamber (5).

treatment:

The after-treatment chamber (5) is a vacuum chamber with heating elements (9) and an oxygen supply valve (16).

The substrate (8) is heated to temperatures&gt; 400 ° C and in the chamber is an increased oxygen partial pressure of&gt; 10^-2 mbar, in order to ensure a complete oxidation of the layer.

In principle it is also possible to carry out this post-treatment outside the coating unit. After treatment, the substrate (8) is passed into the exit lock (6.1), which is then vented to atmospheric pressure. About the substrate dispensing station (6.2) leaving the finished coated Sustrat (8), the coating plant.

The coated cooking surface thus obtained CERAN has a substantially increased scratch resistance compared to an uncoated hob. The coating is resistant to mechanical loads, structural stability when exposed to temperatures up to 800 ° C and has an appealing optical design.