Glass or glass-ceramic plate

Abstract

The present invention relates to a glass or glass-ceramic plate having a glass or glass-ceramic substrate coated with a coating based on a metal oxide, characterized in that the coating has a coverage of 25% to 90% and the coated plate has a roughness RSm of 300 μm or less, preferably 250 μm or less.

Description

[Technical field]

[0001] The present invention relates to glass or glass-ceramic plates. More specifically, it relates to glass or glass-ceramic plates intended to function as furniture surfaces and / or cooking surfaces, as well as to articles comprising such glass or glass-ceramic plates. [Background technology]

[0002] Glass-ceramic plates are traditionally used as cooking plates. They also find applications in areas where heat resistance is required, for example forming fireplace inserts. Recently, they are also used in other areas of daily life. Glass-ceramic plates can be used as furniture surfaces, in particular to form worktops, central islands, consoles, etc. The surface area occupied by glass-ceramic plates is larger than before in these new applications. In certain applications, glass plates can be an alternative to glass-ceramic plates, in particular for furniture covers and also for cooking plates under certain conditions. Depending on their application, glass or glass-ceramic plates can be provided with keys, touch-sensitive areas, buttons or other controls, and their surfaces are in all cases (even in the case of simple furniture surfaces) exposed to multiple contacts related to their use, which generally result in unsightly finger marks at the contact points and therefore may lead to repeated cleaning operations, especially if the plates are dark in color. These marks or stains can also lead to interference with other optional components of the article (heating elements, light sources, displays, etc.).

[0003] To avoid fingerprints on the surface of an article, it is known in certain fields to apply hydrophobic and oleophobic coatings that make it possible to limit the amount of liquid(s) (water, sebum) that adheres upon contact with a finger. However, such coatings must be applied to the entire surface to be protected and are not heat resistant, which creates problems for cooking plate type applications.

[0004] In the field of glass-ceramics, existing textures or coatings are generally not suitable for systematically solving the problem of finger marks. The most frequently used coatings are those selected to withstand high temperatures, such as enamels, which are used locally to create decorative patterns or to indicate, for example, heated areas, or paints, which are used in flat form rather as opacifiers. However, these conventional coatings generally do not prevent finger marks associated with the handling and use of the coated substrate. Enamels further locally reduce the mechanical strength of the glass-ceramic plate and can chip. Also, paints are not suitable for all heating modes of cooking plates due to their relatively low resistance, especially thermal resistance. It is also known to use other coatings, particularly based on thin metal layers deposited flat over most of the substrate surface, but such layers sometimes contribute to the problem of finger marks. Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention proposes an improved glass or glass-ceramic plate, in particular a glass or glass-ceramic plate intended to be used with one or more heating elements, such as cooking plates, or intended to function as a furniture surface, which makes it possible to limit the visibility of finger marks on its surface. The plate according to the invention has anti-finger mark properties without compromising the other properties desired for its use, in particular their ease of maintenance and cleaning, its mechanical strength, in particular its resistance to scratches and abrasions, and, optionally, its heat resistance. [Means for solving the problem]

[0006] The present invention relates to a plate having a glass or glass-ceramic substrate coated with a metal oxide based coating, in particular with aluminium oxide or mixed aluminium oxide, said coating having a coverage of 25% to 90% and wherein the plate, i.e. the coated substrate, has a roughness RSm of 300 μm or less, preferably 250 μm or less. [Brief description of the drawings]

[0007] [Figure 1] FIG. 1 shows an SEM image of a coating according to the invention. [Diagram 2] FIG. 2 shows an image of the sample taken with an optical microscope. [Diagram 3] FIG. 3 shows the corresponding image after image processing that allows the calculation of the coverage. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] The substrate is preferably a glass-ceramic substrate, in particular a lithium aluminosilicate glass-ceramic substrate. The chemical composition of the glass-ceramic substrate typically comprises (or consists essentially of) the following components within the ranges defined below, expressed in weight percentages, the sum of which is 97-100%: SiO252-75% Al2O318~27% Li2O 2.5~5.5% K2O 0~3% Na2O 0~3% ZnO 0~3.5% MgO 0~3% CaO 0~2.5% BaO 0~3.5% SrO 0~2% TiO21.2~5.5% ZrO20-3%.

[0009] The substrate may also be a glass substrate, the composition of which is of the lithium aluminosilicate, borosilicate or aluminoborosilicate type.

[0010] The chemical composition of lithium aluminosilicate type glasses typically comprises (or consists essentially of) the following components, varying within the weight limits defined below: SiO249-75% Al2O315~30% Li2O 1~8% K2O 0~5% Na2O 0~5% ZnO 0-5% MgO 0~5% CaO 0~5% BaO 0~5% SrO 0~5% TiO20-6% ZrO20-5% B2O30-5%.

[0011] The chemical composition of borosilicate type glasses typically comprises (or consists essentially of) the following components, varying within the weight limits defined below: SiO2 70~85% B2O3 8-16% Al2O30-5% RO 0~10% K2O 0~2% Na2O 1-8%.

[0012] The chemical composition of aluminoborosilicate type glasses typically comprises (or consists essentially of) the following components, the sum of which is between 97 and 100%, varying within the weight limits defined below: SiO245~68% Al2O38-20% B2O34-18% RO 5-30% R2O 10% or less.

[0013] The expression "RO" denotes the alkaline earth oxides MgO, CaO, SrO, and BaO, and the expression "R2O" denotes the alkali metal oxides, in particular Na2O and K2O.

[0014] The expression "consisting essentially of" in the sense of the present invention means that the aforementioned oxides make up at least 95% by weight, or even 97% by weight, or even 99% by weight of the composition. Regardless of the composition of the plate, it usually comprises additives used for refining. The refining agents are typically selected from oxides of arsenic, antimony, tin and cerium, halogens and metal sulfides, in particular zinc sulfide. The amount of refining agent is usually less than or equal to 1% by weight, preferably between 0.1% and 0.6% by weight. The plate is generally largely colored. Thus, the composition generally comprises a coloring agent, in particular selected from vanadium oxide, iron oxide, cobalt oxide, cerium oxide, selenium oxide, chromium oxide or even nickel oxide, copper oxide and manganese oxide. In the case of a glass-ceramic plate, this is preferably a glass-ceramic colored with vanadium oxide. It may contain 0.01 to 0.5% by weight of vanadium oxide, optionally in combination with other dyes such as iron oxide, cobalt oxide, or manganese oxide.

[0015] Glass or glass ceramic substrates typically have a light transmittance of less than 65%, or even less than 40%, or even less than 20%, or even less than 10%. It is preferably less than 5%, especially in the case of glass ceramic substrates, especially glass ceramic substrates colored with vanadium oxide. The light transmittance is measured according to standard EN 410:2011 under illuminance D65, taking into account both direct transmittance and diffuse transmittance. It can be measured using a spectrometer with an integrating sphere.

[0016] The substrate is preferably a dark substrate, i.e. it has an L of less than 50, preferably less than 40, more preferably less than 30. * a * b * The lightness L is defined by the system * has.

[0017] The substrate is typically in the form of a plate having a thickness of 2 to 15 mm, in particular 3 to 10 mm, for example 4, 5, 6, 7 or 8 mm. The dimensions (length and width) of the plate depend on the application for which it is intended: it generally has a dimension of 20 cm to 120 cm, in particular for those applications in cooking appliances, but may have relatively large dimensions, such as a width that may range up to 120 cm, or even up to 180 cm, and a length of more than 200 cm, for worktop applications.

[0018] The substrate is preferably at most 50×10 -7 K -1 For glass substrates, it is typically 25×10 -7 ~45×10 -7 K -1 For glass-ceramic substrates, the absolute value of the expansion coefficient is typically 25×10 -7 K -1 Less than or even 15×10 -7 K -1 Less than or even 5×10 -7 K -1The linear thermal expansion coefficient is measured according to standard ISO 7991:1987 from 20 to 300°C.

[0019] The coating is preferably based on aluminum oxide, titanium oxide, niobium oxide, zirconium oxide or mixed oxides thereof, in particular on mixed aluminum oxides, more preferentially on aluminum oxide or on mixed aluminum oxides. "Based on" is understood to mean that the coating generally contains at least 50% by weight, preferably at least 60% by weight, or even 70% by weight or 80% by weight, or even 90% by weight, 95% by weight or 99% by weight of the oxide under consideration. In some cases, the coating may consist of this oxide, except for impurities.

[0020] The mixed aluminum oxide is preferably selected from binary or ternary aluminum oxides, in particular from mixed oxides of aluminum and titanium, mixed oxides of aluminum zirconium and mixed oxides of aluminum, titanium and silicon, preferentially from mixed oxides of aluminum and titanium and mixed oxides of aluminum, titanium and silicon. The coating preferably comprises at least 30% by weight, preferably at least 40% to 80% alumina, based on the total weight of the oxides. Interestingly, coatings based on mixed oxides of aluminum and titanium allow to maintain a relatively low transparency and a relatively high gloss, which is appreciated in particular for applications as countertops.

[0021] The coatings according to the invention are typically obtained by spraying a material based on metal oxides, in particular aluminium oxide or mixed aluminium oxides, in the form of a powder. These deposition methods consist of spraying the powder particles, preferably molten, at very high speeds. The particles that reach the surface to be coated break up in the form of droplets (splats).

[0022] The coating according to the invention is generally a discontinuous deposition. The coating is typically in the form of a surface distribution of solid droplets of a material based on a metal oxide, in particular aluminum oxide or mixed aluminum oxide, randomly distributed on the surface of the plate. This type of coating is typically obtained by thermal spraying, in particular by plasma spraying, by oxygen gas flame spraying or by high velocity thermal spraying, preferably by plasma spraying. As shown in FIG. 1, which shows an SEM image of a coating according to the invention, on a scale of several hundred microns (for example 500 μm), some areas are covered with droplets, which overlap or overlap, while other areas are not covered. The coverage is 25% or more, preferably 35% or more, and 90% or less, preferably 80% or less. The coverage is more preferably 30-70%, or even 40-60%. In certain embodiments, it can be 50% or less, in particular 35-50%, or 50% or more, in particular 60-90%. For the purposes of the present invention, "coverage" refers to the ratio, expressed as a percentage, of the surface of the plate that is actually covered by a surface dispersion of drops of aluminum oxide-based material or mixed aluminum oxide-based material to the total surface theoretically covered by the coating (surface of the plate on which the coating is deposited). The coverage is measured by analysis of images taken under an optical microscope, followed by image processing by thresholding and binarization. The coverage corresponds to the ratio of pixels that correspond to the coating (generally white pixels) to all pixels. The coverage is typically measured at a resolution of 0.9 mm 2 (Typically 1.1mm x 0.8mm) to 3.7mm 2 Measurements are taken over an area of ​​the coating (typically 2.3 mm x 1.6 mm) and ideally averaged over 3 to 10 areas.

[0023] The average diameter of the droplets is preferably 10 to 200 μm, more preferably 20 to 160 μm. The average diameter of the droplets is measured by image analysis from an optical microscope.

[0024] The plate according to the invention has a roughness Rsm of 300 μm or less, preferably 50 to 250 μm. The ratio Ra / Rsm is preferably 0.0030 or more, typically 0.1000 or less, more preferably 0.0030 to 0.0500, or even 0.0035 to 0.0100. It has a roughness Ra of generally 2.5 μm or less, preferably 2.0 μm or less, or even 1.5 μm or less, typically 0.3 μm or more. The roughness Rdq is preferably 3.0 at 25.0 °. The coated plate has a roughness Rz of preferably 3.0 μm or more, or even 3.5 μm or more, typically 20 μm or less, preferably 15 μm or less. The roughness Rt is typically 5 μm or more, preferably 15 μm or less, or 9 μm or less.

[0025] The roughnesses RSm, Ra, Rdq, Rz and Rt are defined in the conventional manner according to the standard ISO 4287:1997. It goes without saying that the characteristic roughness parameters of the present invention are measured on a surface that is coated with a coating according to the present invention. RSm represents the mean width of the elements of the roughness profile, which corresponds to the average value of the width of the elements of the profile within the sampling length. Ra represents the average deviation of the roughness profile, which corresponds to the arithmetic mean of the absolute values ​​of the deviations between successive peaks and valleys within the sampling length. Rdq represents the mean squared gradient of the roughness profile, which corresponds to the mean squared value of the local gradient within the sampling length. Rz represents the maximum height of the roughness profile, which corresponds to the sum of the maximum protruding height of the roughness profile and the maximum valley depth of the roughness profile within the sampling length. Rt represents the total height of the roughness profile, which corresponds to the sum of the maximum protruding height of the roughness profile and the maximum valley depth of the roughness profile within the evaluation length. The roughnesses RSm, Ra, Rdq, and Rz are measured over a sampling length of 0.8 mm, and the roughness Rt is measured over an evaluation length of 4 mm using a contact roughness tester, such as a Mitutoyo SJ-401 roughness tester.

[0026] In some embodiments, the coating has a coverage of 30-70%, preferably 40-60%, and the plate has a roughness RSm of 250 μm or less, a roughness Ra of less than 1.5 μm, and a ratio Ra / RSm of 0.003-0.01. Indeed, it has been observed that these embodiments, apart from reducing the visibility of finger marks, provide the glass or glass-ceramic plate with improved mechanical properties (improved scratch resistance and / or reduced visibility of scratches) and do not generate excessive haze, thus ensuring good visibility of the display placed under the plate.

[0027] Another subject of the invention relates to a method for producing a glass or glass-ceramic plate as defined above, comprising depositing a metal oxide-based coating by thermal spraying on the surface of a glass or glass-ceramic substrate, characterized in that the surface of the substrate is at a temperature above 300° C. during the deposition of the coating.

[0028] The so-called thermal spraying methods are well known to those skilled in the art. They can in particular be plasma spraying, oxygen flame spraying or high velocity spraying (or HVOF: high velocity flame spraying). The particles of the powder to be sprayed are brought to a temperature above the melting temperature of the powder. The deposited droplets adhere to the substrate mainly by atomic diffusion at the substrate / droplet interface or mechanically by plastic deformation of the particles and to a lesser extent by van der Waals forces.

[0029] The coating according to the invention is preferably obtained by plasma spraying. The spraying parameters, such as power, total flow rate of plasma gas, composition of plasma gas, powder flow rate, linear speed of the torch and number of passes, are adjusted in a manner known to the skilled person, depending on the type of torch and the characteristics of the powder used, to generate a flow of molten particles at a suitable velocity, thereby obtaining a non-bursty, adhesive and low-cracking droplet spread and to obtain the coating according to the invention. For example, in the case of plasma spraying using a plasma torch of the Proplasma HP8 type sold by Saint-Gobain Coating Solutions, the power can be 30-65 kW, the total gas flow rate 40-80 L / min, the powder flow rate 0.5-15 g / min, the linear travel speed of the torch 1,000-5,000 mm / s, the advance pitch 3-15 mm and the number of passes 1-10. The powder flow rate, the linear movement speed of the torch, the advance pitch (the distance separating the two lines of movement of the torch) and the number of passes make it possible in particular to adjust the coverage and the roughness of the coating according to the invention.

[0030] The powder used in the process according to the invention is generally of the same nature as the desired coating, i.e. a metal oxide powder, in particular an aluminium oxide powder, or a mixed aluminium oxide, preferably selected from binary or ternary aluminium oxides, in particular mixed oxides of aluminium and titanium, and mixed oxides of aluminium, titanium and silicon.

[0031] The powders are typically of diameter D 10 is 3 to 20 μm, and the diameter D 90 The particle size is 20 to 75 μm. 10 , D 90 The number of powder particles is 10% and 90%, respectively, of the value D 10 , D 90 These are understood to have diameters less than 1 mm, as determined by laser diffraction methods.

[0032] The powder is preferably a dense-grained powder, i.e. a powder with a porosity of less than 1%, which is preferably a powder obtained from a melt process (melt milling), thereby improving the adhesion of the coating.

[0033] During the deposition of the coating according to the invention, the surface of the substrate is at a temperature of more than 300° C., preferably more than 360° C., for example between 400 and 800° C., or even between 450 and 700° C. For this purpose, the substrate is heated before and / or during the deposition step. In fact, it has been pointed out that the temperature of the substrate influences the roughness of the deposit obtained.

[0034] A heat treatment can also be carried out after deposition of the coating according to the invention in order to improve its adhesion. In particular, in the case of glass-ceramic plates, it may prove advantageous to deposit the coating on the mother glass, i.e. before the ceramming heat treatment, to take advantage of the beneficial effect of the heat treatment on the adhesion of the coating.

[0035] The plate according to the invention may, where appropriate, be coated with other functional coatings (anti-overflow layers, opacifying layers, etc.) and / or decorative coatings, in particular localized ones, typically with patterns based on enamel, etc. By way of example, the plate may have a localized coating of decorative enamel, generally on the same side as the coating according to the invention, generally above it (e.g. to form a pattern or a logo or to demarcate / indicate certain areas, in particular heated areas), and / or an opacifying layer over all or part of the face of the plate opposite the coating according to the invention (e.g. to hide internal elements arranged underneath the plate, etc.).

[0036] The plate according to the invention is used in various applications, for example as a worktop, in a cooking device, such as a cooking plate, in particular an induction cooking plate, in a fireplace insert, in a fireproof glazing or as a decorative element. The invention therefore also relates to an article, in particular a worktop, a cooking device, a fireplace insert, a fireproof glazing or a decorative element, comprising a glass or glass-ceramic plate as described above or obtainable by the method described above. It is preferably a cooking device. Regardless of the application, the plate according to the invention is such that in the use configuration, a coating according to the design is arranged on the surface of the plate facing the user.

[0037] The article according to the invention may also have internal elements with heating means, a display device and / or a control device. The display device may be a light source, in particular a light-emitting diode or an LCD screen, optionally associated with an optical filter or an optical guide. The heating means may be selected from radiative or halogen heating means, atmospheric gas burners and inductive heating means. The control device may be a touch-sensitive electronic control panel. The article may also be provided with (or associated with) additional functional element(s), such as a frame, stiffener(s), connector(s), cable(s), control element(s), etc. EXAMPLES

[0038] The invention is illustrated by the following non-limiting examples.

[0039] Dark glass-ceramic plates of the KeraBlack+ type sold by Eurokera were coated by plasma spraying with various aluminium oxide based coatings and mixed aluminium oxides. The deposition of the coatings was carried out on substrates heated to 400-720° C. with an HP 8 torch sold by Saint-Gobain Coating Solutions. The spray parameters for sample I1 were as follows: - Power: 53kW - Total plasma gas flow rate: 68L / min - Torch-substrate distance: 130mm - Powder flow rate: 2.5g / min - Torch linear speed: 3000mm / s - Forward pitch: 7mm - Number of passes: 1

[0040] Samples C1-C3 and I2-I5 are obtained identically to sample I1, except for certain spray parameters, in particular powder flow rate, torch linear velocity, and number of passes.

[0041] The aluminum oxide powder used is densely granulated (fused milled) and has the following characteristics:

[0042] [Table 1]

[0043] The coverage of the various coatings obtained was measured by image analysis taken with an optical microscope (Leica DMC 2900) followed by image processing using ImageJ software. This process consisted of using the software's threshold function (Threshold) by adjusting the grey level and binarizing the image, so that the droplets appear as white pixels and the uncoated surface appears as black. Figure 2 shows the images of the samples taken with an optical microscope, and Figure 3 shows the corresponding images after image processing that allows the calculation of the coverage.

[0044] The visibility of the finger mark on the coated samples was evaluated in comparison with an uncoated glass-ceramic reference sample according to the following protocol. Multiple fingerprints were performed on the coated samples and on the reference uncoated glass-ceramic. The observer's evaluation was performed on the same day as the application of the finger, under the same lighting conditions, using Daylight lighting at an angle of 60° to the normal in a SpectraLight III lighting booth sold by X-Rite. The results are shown in Table 2. (-) indicates the same visibility of the finger mark as that of the uncoated glass-ceramic. (+) indicates that the visibility of the finger mark is less than that of the uncoated glass-ceramic.

[0045] The results are summarized in Table 2. Samples I1 to I5 are examples according to the present invention, and Examples C1 to C3 are comparative examples.

[0046] [Table 2]

[0047] Samples I1-I5 have significantly improved anti-finger mark properties compared to samples C1-C3, which are no better than the uncoated reference glass-ceramic.

Claims

1. 1. A plate having a glass or glass-ceramic substrate coated with a metal oxide based coating, said coating having a coverage of 25% to 90%, said plate having a roughness RSm of 300 μm or less, preferably 250 μm or less.

2. 2. The plate according to claim 1, wherein the coating is obtained by thermal spraying.

3. 3. Plate according to claim 1 or 2, having a roughness Ra such that the ratio Ra / RSm is ≧0.0030.

4. 3. A plate according to claim 1 or 2, having a roughness Ra of 2.5 μm or less.

5. 3. Plate according to claim 1 or 2, wherein the coating has a coverage of between 30 and 70%.

6. 3. Plate according to claim 1 or 2, wherein the coating is based on aluminium oxide, titanium oxide, niobium oxide, zirconium oxide or mixed oxides thereof.

7. 3. Plate according to claim 1 or 2, wherein the coating is based on mixed aluminum oxide.

8. 3. Plate according to claim 1 or 2, wherein the coating is based on aluminium oxide, a mixed oxide of aluminium and titanium, a mixed oxide of aluminium and zirconium, or a mixed oxide of aluminium, titanium and silicon.

9. 3. Plate according to claim 1 or 2, wherein the substrate exhibits a light transmission of less than 65%, preferably less than 5%.

10. The substrate has a brightness L of less than 50, preferably less than 40, more preferably less than 30. ＊ 3. The plate according to claim 1 or 2, having:

11. The substrate comprises the following components, expressed in weight percent, within the ranges defined below: Yes ２ 52~75% Al ２ O ３ 18-27 Li ２ O 2.5~5.5%% K ２ O 0~3% Na ２ O0~3% ZnO 0 to 3.5% MgO 0-3% CaO 0-2.5% BaO 0-3.5% SrO 0-2% TO ２ 1.2~5.5% ZrO ２ 0~3% 3. The plate according to claim 1, which is a glass-ceramic substrate having a chemical composition comprising:

12. 3. Plate according to claim 1 or 2, characterized in that the substrate is a glass substrate, the composition of which is of the lithium aluminosilicate, borosilicate or aluminoborosilicate type.

13. The substrate comprises the following components, expressed as weight percent, within the ranges defined below: Yes ２ 70~85% B ２ O ３ 8~16% Al ２ O ３ 0~5% RO 0-10% K ２ [0~2% Na ２ O1~8% 13. The plate according to claim 12, which is a borosilicate type glass substrate having a chemical composition comprising:

14. A method for producing a glass or glass-ceramic plate according to claim 1 or 2, comprising depositing a metal oxide-based coating onto a surface of a glass or glass-ceramic substrate by thermal spraying, the surface of the substrate being at a temperature exceeding 300°C during deposition of the coating.

15. An article comprising a glass or glass-ceramic plate according to claim 1 or 2, the article having an internal element comprising a heating means, a display device, and / or a control device.

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