Glass-ceramic article and method of manufacturing same - Patent Application 20070122997

Abstract

To improve the aesthetic appearance and mechanical scratch resistance of glass-ceramic surfaces, particularly of dark or black glass-ceramic articles. The present invention relates to a planar glass-ceramic article having a first major surface, a second major surface, and an edge. At least one of the two major surfaces of the glass-ceramic article has an inherent texture, and the inherent texture has a composite root-mean-square roughness RMS of 4.4° to 11°. The present invention also relates to a manufacturing method for obtaining the glass-ceramic article.

Description

[Technical Field]

[0001] The present invention relates to planar glass-ceramic articles with a textured surface that is scratch-resistant, stain-resistant, and has an aesthetic surface appearance suitable for domestic use. The present invention also relates to methods for making the glass-ceramic articles. [Background technology]

[0002] Glass-ceramic materials are composite materials containing a crystalline phase or an amorphous phase in which crystals are dispersed. They are generally obtained by heat-treating a glass suitable for forming a glass-ceramic, known as a "mother glass," to crystallize crystals in a controlled manner within its volume. This process, in which the glass is partially crystallized, is known as a "ceramming process" or simply "ceramming." The final physicochemical properties of the glass-ceramic depend on the composition of the mother glass and the ceramming process.

[0003] Glass ceramics are popular in many fields due to their aesthetic qualities and their physical / chemical properties, especially their low coefficient of thermal expansion and their thermal shock resistance. Glass ceramics are particularly used in kitchen equipment, especially in the form of cooktops, for example, as cooking surfaces in cooking appliances, glazed oven walls, and food preparation work surfaces, countertops, or work surfaces in furniture. In these applications, glass ceramics are generally based on lithium aluminosilicate.

[0004] Depending on its application, the glass-ceramic article can be equipped with several accessories, such as controls, sensors and displays, that allow interaction between the user and the device in which the article is incorporated.

[0005] By way of example, the glass-ceramic article can be equipped with controls, such as touch-sensitive or optical buttons, for operating and controlling various electrical and / or electronic devices, such as heating and / or lighting means. The glass-ceramic article can also be provided with a display device, in particular a light-emitting display device, for projecting, in particular through the glass-ceramic article, perceptible luminous patterns (e.g., icons or numbers) representing the value of certain operating parameters of these devices (e.g., heating power of a heating device) or related to the physicochemical state of the article (e.g., hot zone signaling).

[0006] The glass-ceramic article may also be equipped with optical and / or thermal sensors, for example, to detect elements on its surface, such as spilled liquids, or to measure the surface temperature of the article and alert the user by an audible or visual signal through an indication zone.

[0007] Interactions between the surface of a glass-ceramic article and a user, particularly tactile interactions, as well as handling of liquid or solid food substances and mechanical cooking implements (e.g., knife blades), can result in various unsightly marks, particularly fingerprints, appearing at the contact points with the surface. Glass-ceramic articles can also become soiled, such as dried or burnt food residues and scratches on the surface of the article.

[0008] These marks and stains lead users to repeatedly clean with abrasive products, which in turn can lead to further scratches. This problem is particularly acute in glass-ceramic products with dark, matte, or glossy textured surfaces.

[0009] It is known to use various hydrophobic or oleophobic, textured or non-textured, organic or inorganic coatings to prevent fingerprints and smudges and to limit the conspicuousness or visibility of scratches. It is also known to modify the surface of glass-ceramics to obtain such properties.

[0010] Japanese Patent Publication No. 2007170754, issued July 5, 2007, by Nippon Electric Glass Co., Ltd. (JP), describes a glass-ceramic article that includes a processed surface having a roughness of 0.1 μm to 20 μm to impart a light-scattering and milky appearance. The article is obtained using a combination of mechanical and chemical surface treatments.

[0011] WO 2011 / 137144, published November 3, 2011, by CORNING INC. [US], describes a method for producing a glass-ceramic article using etching to create a roughened surface having an arithmetic roughness value of 100 nm to 300 nm. The resulting roughness provides an anti-reflective effect.

[0012] WO 2013 / 190230, published by EUROKERA [FR] on December 27, 2013, describes a glass-ceramic article having a surface provided with a textured layer, in particular a sol-gel layer, where the texture is formed by a regular pattern, in particular a geometric pattern, having a height of 2 to 100 μm.

[0013] WO 2014 / 070869, published September 9, 2013, by CORNING INC. [US], describes a method for manufacturing a glass-ceramic article using etching to modify the surface of the glass-ceramic article to a depth of 0.01 μm to 20 μm. The resulting roughness reduces gloss.

[0014] WO 2016 / 138051, published September 1, 2016 by CORNING INC [US], describes a method for manufacturing a semiconductor device having a coarse pattern with an average spacing between features of 0.5 μm to 25 μm and a density of 9,000 to 25,000 features / mm 2 A method for producing a glass-ceramic article is described that uses two successive chemical etches to create a surface roughness of 0.01 mm. The chemical etches are performed using a hydrofluoric acid-based acid solution.

[0015] WO 2018 / 093844, published May 24, 2018, by Corning Inc. (US), describes a method for producing a glass-ceramic article having a non-planar surface with an arithmetic roughness value of 10 to 2000 nm. The method includes etching the surface with a hydrofluoric acid solution. The surface roughness provides aesthetic benefits, reduced gloss, anti-reflective properties, and improved tactile feel.

[0016] WO 2021 / 121846, published by EUROKERA [FR] on June 24, 2021, describes a method for producing a glass-ceramic article using etching. The surface of the glass-ceramic article has an arithmetic roughness value of 2 μm to 7 μm. [Prior art documents] [Patent documents]

[0017] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007170754 [Patent Document 2] International Publication No. 2011 / 137144 [Patent Document 3] International Publication No. 2013 / 190230 [Patent Document 4] International Publication No. 2014 / 070869 [Patent Document 5] International Publication No. 2016 / 138051 [Patent Document 6] International Publication No. 2018 / 093844 [Patent Document 7] International Publication No. 2021 / 121846 Summary of the Invention [Problem to be solved by the invention]

[0018] There remains a need for improvements in the aesthetic appearance and mechanical scratch resistance of glass-ceramic surfaces, particularly of dark or black glass-ceramic articles.

[0019] The article must have optical and physicochemical surface properties that are suitable for the intended use, particularly in cooking appliances and / or as a worktop surface. More specifically, the article must be scratch-resistant, oil-repellent, stain-resistant, and anti-light-scattering. The article must also have an aesthetic surface appearance suitable for home use. [Means for solving the problem]

[0020] According to a first aspect of the present invention, there is provided a glass-ceramic article comprising a first major surface, a second major surface, and an edge, wherein all or part of at least one of the two major surfaces has an inherent texture, and the inherent texture has a composite root-mean-square roughness Rdq of 4.4° to 11°. Other advantageous embodiments are described below.

[0021] According to the present invention, the rough texturing is inherent to the surface of the glass-ceramic article, i.e., the surface roughness comes from the surface itself without any surface coating applied.

[0022] According to a second aspect of the present invention, there is provided a method for producing a glass-ceramic article according to the first aspect of the present invention.

[0023] According to a third aspect of the present invention, there is provided a cooking appliance comprising a glass-ceramic cooktop formed from a glass-ceramic article according to the first aspect of the present invention.

[0024] According to a fourth aspect of the invention, a glass-ceramic article according to the first aspect of the invention is used as all or part of a worktop for food preparation.

[0025] Advantages of the invention A significant advantage of the present invention is that when applied to dark or black glass-ceramic articles, it allows the achievement of surface gloss levels at 60° well below 30, or even below 25, and brightness levels below 23. The article then exhibits a dark, matte appearance that meets the aesthetic requirements of home applications.

[0026] In some advantageous embodiments, the haze level is less than 50%, or even 30%, such that the visibility of the light pattern transmitted on or through the surface of the glass-ceramic article by the light-emitting display device remains clear for improved visual comfort when the article is used in a cooking appliance.

[0027] Another advantage is that, in some embodiments, the particular roughness of the glass-ceramic article, inherent or intrinsic to the surface of the glass-ceramic article, does not alter the thermal and mechanical properties of the surface, allowing for easier removal of contamination and greater resistance to metal abrasion. [Brief explanation of the drawings]

[0028] [Figure 1] FIG. 1 shows the progression of surface gloss at 60° versus its composite root mean square roughness for examples and comparative examples of glass-ceramic articles consistent with the present invention. [Figure 2] FIG. 1 shows the progression of surface lightness versus its composite root mean square roughness for examples and comparative examples of glass-ceramic articles consistent with the present invention. [Figure 3] FIG. 2 shows the evolution of surface haze levels versus their composite root mean square roughness for examples and comparative examples of glass-ceramic articles consistent with the present invention. [Figure 4] FIG. 1 shows the progression of the degree of surface scratch visibility for example and comparative examples of glass-ceramic articles according to the present invention, based on their combined root mean square roughness and mean spacing roughness. [Figure 5]FIG. 1 shows the progression of the degree of visibility of metal rubbing marks versus their average spacing roughness for examples and comparative examples of glass-ceramic articles according to the present invention. [Figure 6] FIG. 2 shows the progression of the anti-adhesion index for soiling on the surfaces of examples and comparative examples of glass-ceramic articles according to the invention versus their composite root-mean-square roughness. [Figure 7] FIG. 1 shows the progression of the degree of visibility of fingernail scratches on the surfaces of examples and comparative examples of glass-ceramic articles according to the present invention versus their surface skewness. DETAILED DESCRIPTION OF THE INVENTION

[0029] In the context of the present invention, the following definitions and conventions are referred to.

[0030] The composite root mean square roughness is designated Rdq, which means the root mean square of the local slope of the surface roughness profile over the sampling length, as defined in ISO 4287, section 4.4.1. The composite root mean square roughness Rdq is a dimensionless number. It can be equally expressed in angular units of degrees or radians, using the usual trigonometric correlations, particularly the arctan function, to calculate the slope. In the present invention, it is expressed in degrees.

[0031] The mean spacing roughness is expressed as Rsm and refers to the average width of the surface roughness profile elements over the sampling length as defined in ISO 4287, section 4.3.1. The width of the profile element is to be understood as the length of the x-axis intersecting the profile element, i.e. the protrusion or recess, as defined in ISO 4287, section 3.2.12. The value is expressed in millimeters.

[0032] Skewness is expressed as Rsk, which refers to the ratio of the mean cube of the height values ​​by the cube of the maximum protrusion height over the sampling length, as defined in ISO 4287, section 4.2.3.

[0033] Inherent or inherent texturing on the surface of a glass-ceramic article refers to the texturing of the glass-ceramic material of the article itself, without any surface coating.

[0034] Glass-ceramic articles are composite materials, preferably aluminosilicate-based, and especially lithium silicate-based, containing a crystalline phase or an amorphous phase in which crystals are dispersed, obtained by heat-treating a glass suitable for glass-ceramic formation, known as a "mother glass," to crystallize the crystals in a controlled manner within its volume.

[0035] "Light transmittance" TL is to be understood to mean the light transmittance expressed as TL as defined, measured and / or calculated in standard EN 410:1998.

[0036] Color deviation ΔE * , brightness or luminance L * , and colorimetric coordinate a * and b * is the color deviation ΔE as defined in ISO / CIE 11664-4:2019 * , brightness or luminance L * , and colorimetric coordinate a * and b * Refers to...

[0037] "60° gloss" refers to specular gloss at 60° as described and measured in EN ISO 2813:1999.

[0038] "Haze" refers to haze as defined and measured in ISO 14782:1999.

[0039] According to a first aspect of the present invention, there is provided a planar glass-ceramic article comprising a first major surface, a second major surface, and an edge, wherein all or a portion of at least one of the two major surfaces has an inherent texture, and the inherent texture has a composite root-mean-square roughness Rdq of 4.4° to 11°.

[0040] According to a first aspect of the present invention, the glass-ceramic article is planar. The glass-ceramic article may have two substantially parallel planar major surfaces and four side surfaces substantially perpendicular to the two major surfaces, and may take the form of a glass-ceramic cooktop.

[0041] The "mother glass" of the glass-ceramic article may be of any suitable type. According to one preferred embodiment, the mother glass is based on lithium aluminosilicate containing the following components within the weight limits defined in Table 1 below and expressed as weight percentages relative to the glass:

[0042] [Table 1]

[0043] As mentioned above, a significant advantage of the first aspect of the present invention is that it makes it possible to obtain glass-ceramic articles that meet the aesthetic requirements for domestic applications, such as cooktops, worktops, etc. In particular, for glass-ceramic articles that are initially black or dark, the surface gloss level at 60° can be well below 30 or even below 25, and the brightness level can be below 23.

[0044] According to some advantageous embodiments, the composite root mean square roughness Rdq can be between 5.5° and 9°. It has been found that with a roughness Rdq within this range, the visibility of the light pattern transmitted on or through the surface of the glass-ceramic article by a light-emitting display device remains clear for improved visual comfort. This results in a haze level of less than 50%, or even 30%.

[0045] In certain other embodiments, the unique texture may further have a mean spacing roughness Rsm of greater than 0.2 mm, preferably greater than 0.27 mm. This type of texturing increases the mechanical strength of the surface, thereby reducing the visibility of scratches.

[0046] Glass-ceramic articles are commonly used as cooking or work surfaces in kitchen appliances. In this type of application, these surfaces can be particularly stressed when metal cooking utensils, such as pots and pans, are moved over the surface of the glass-ceramic article. These movements can take the form of, among other things, metal friction.

[0047] According to certain embodiments, the average spacing roughness Rsm can be much greater than 0.27 mm, and in particular greater than 0.4 mm, whereby the glass-ceramic article can very advantageously exhibit high resistance to metal friction, particularly that associated with the movement of a frying pan, as well as favorable chemical and mechanical durability against repeated exposure to food and heating cycles.

[0048] In addition to exposure to cooking utensils and food, the surface of a glass ceramic article incorporated into a kitchen appliance may also be subject to rubbing by fingernails, particularly as a user's hands move over the incorporated control panel. In this case, according to some embodiments, the unique texture may have a skewness Rsk of less than -0.2, preferably less than -0.3, and most preferably less than -0.5. Surprisingly, this reduces the visibility of marks caused by fingernail movement on the surface of the glass ceramic article.

[0049] The glass-ceramic article has low transmittance, low scattering, and a deep color (brightness L * The effects and advantages of the present invention are particularly pronounced when the glass-ceramic article is black or dark brown in color, as defined by the formula (I), and preferably conceals underlying elements while remaining suitable for transmissive display of luminescent zones, including perceptible luminescent patterns that represent the value of certain operational parameters of associated electrical and / or electronic devices or that are related to the physicochemical state of the article.

[0050] In this sense, in certain embodiments of the present invention, the glass-ceramic article has a brightness L of 25 or less, preferably 20 or less. * The glass-ceramic article also has an initial brightness, L * , i.e., the luminance L when the article does not have a surface texture * can have:

[0051] The dark glass-ceramic article, in its initial state, i.e. when it has no surface texture, can have an opacity coefficient of less than 100 and advantageously greater than 93, which in particular allows said viewing in transmission by an underlying light source or projection display device in one embodiment of the invention.

[0052] The opacity factor is given by the formula f=100-ΔE * where ΔE * is the color deviation. Color deviation ΔE *is the lightness L of the upper surface of the article when the article is placed on an opaque black background and then on an opaque white background. * and colorimetric parameter a * and b * The color deviation ΔE can be evaluated by measuring in reflection with the CIELAB colorimetric system. * is expressed by the following formula ΔE * =((LN * -LB * ) 2 +(aN * -aB * ) 2 +(bN * -bB * ) 2 ) 1 / 2 where LB * , aB * , bB * are the lightness and colorimetric coordinates of the first measurement on a white background, and LN * , aN * , bN * are the lightness and colorimetric coordinates of the second measurement on a black background.

[0053] The black glass-ceramic article has a brightness L of less than 10 in its initial state, i.e., when the article has no surface texture. * , haze of less than 30%, and light transmission TL of less than 10% under illuminant D65.

[0054] Preferably, the dark glass-ceramic article has an a of -0.2 to 1.6 in the initial state, i.e., when the article has no surface texture. * parameter values, and b from -1 to 0.6 * It has a parameter value.

[0055] The glass-ceramic article according to the first aspect of the present invention allows the light pattern transmitted by a light-emitting display device onto or through a roughened surface to remain sharp for improved visual comfort for the user.

[0056] According to some preferred embodiments, the 60° gloss of the glass-ceramic article can be less than 20, preferably less than 10. These gloss levels are particularly advantageous for the aesthetic appearance of the glass-ceramic surface, especially when the glass-ceramic surface is dark or black.

[0057] Thus, according to some embodiments, the glass-ceramic article may further comprise at least one light source for a light-emitting display by projection or transmission onto the surface, where the surface forms a screen. The display may, for example, be a light-emitting LED display, in particular a seven-segment display for displaying alphanumeric characters.

[0058] According to a second aspect of the present invention, there is provided a method for producing a glass-ceramic article, the method comprising: - subjecting the glass to a ceramizing heat treatment capable of forming a glass-ceramic; - chemically treating the surface of said glass before and / or after said ceramizing heat treatment; wherein the chemical surface treatment is carried out in such a way that the composite root mean square roughness value Rdq after heat treatment is 4.4 to 11°, preferably 5.5 to 9°.

[0059] According to some advantageous embodiments, the method may further comprise a step of mechanical surface treatment by sandblasting prior to the chemical surface treatment.

[0060] The chemical surface treatment can be carried out before and / or after the ceramification heat treatment. According to a preferred embodiment, the chemical surface treatment is carried out before the ceramification heat treatment. It has been found that the scratch resistance, oil repellency, stain resistance and light scattering prevention properties are further improved.

[0061] According to the present invention, the roughness is achieved by chemical surface treatment of the mother glass of the glass-ceramic article, i.e., before the mother glass is subjected to a ceramming heat treatment to form the glass-ceramic article, and therefore the roughness value is that of the roughened surface of the glass-ceramic article after the ceramming treatment.

[0062] Glasses suitable for forming glass-ceramics may preferably be aluminosilicate-based, in particular lithium aluminosilicate.

[0063] The type of chemical solution used in the treatment, the treatment temperature, and its duration depend on the chemical composition of the material that forms the mother glass of the glass-ceramic article.

[0064] The method according to the second aspect of the present invention allows the glass-ceramic article to be roughened over its entire working surface. It is also possible to roughen only a portion of the working surface of the glass-ceramic article. This feature can be achieved, for example, by applying a protective mask to the surface of the mother glass during the chemical and / or mechanical surface treatment to create a resist in specific areas of the surface.

[0065] In some embodiments, the chemical surface treatment may be a chemical etch using a hydrofluoric acid-based solution. These embodiments are particularly advantageous for aluminosilicate-based glass-ceramic articles, especially lithium aluminosilicate.

[0066] According to some preferred embodiments, the chemical treatment may further include a preliminary step known as a surfactant activation step prior to the aforementioned chemical etching, which may be a chemical etching using an acid solution containing hydrochloric acid and hydrofluoric acid for at least 2 minutes at room temperature.

[0067] The strength of hydrofluoric acid in the acid solution may advantageously be 1% to 70% by weight. Generally speaking, if the mass strength is less than 1%, the time required for chemical surface treatment is quite long, which is not very advantageous for industrial applications. If the mass strength is higher than 20%, the chemical surface treatment may become too rapid and difficult to control. To prevent the chemical surface treatment from becoming too rapid and difficult to control, the temperature of the solution is preferably less than 40°C, or even 30°C.

[0068] According to some advantageous embodiments, the hydrofluoric acid solution comprises sodium fluoride, potassium fluoride, ammonium fluoride, barium sulfate, silicic acid, hexafluorosilicic acid, hydrochloric acid and / or sulfuric acid, alone or in combination.

[0069] According to a third aspect of the present invention, there is provided a cooking appliance comprising a glass-ceramic cooktop formed by a glass-ceramic article according to any one of the embodiments of the first aspect of the present invention.

[0070] Examples of heating elements in the cooking appliance may be radiant or halogen heaters or induction heating elements.

[0071] According to a fourth aspect of the present invention, a glass-ceramic article according to any one of the embodiments of the first aspect of the present invention can be used as all or part of a worktop for food preparation. The worktop may for example be part of a kitchen piece of furniture or a surface element of a cooking device, said surface element having the function of enabling food preparation. [Example]

[0072] The following examples and comparative examples are based on the mother glass of the glass-ceramic cooktops described in European Patent Application No. 0 437 228 of July 17, 1991 to CORNING FRANCE [FR] and / or in WO 2012 / 156444 of November 22, 2012 to EUROKERA [FR] or sold under the trade name KeraBlack Plus®. The cooktops have a thickness of 4 to 6 mm.

[0073] The roughness was obtained by mechanical surface treatment of the mother glass using sandblasting and / or chemical surface treatment. These two treatments were carried out before the ceramization heat treatment. When mechanical and chemical treatments were used, these two treatments were carried out consecutively, i.e., the mechanical treatment was carried out before the chemical treatment.

[0074] Mechanical sandblasting was carried out according to the parameters listed in Table 2.

[0075] [Table 2]

[0076] Chemical surface treatment was carried out using a hydrofluoric acid-based solution, the components of which are listed in Table 3.

[0077] [Table 3]

[0078] If the roughness is obtained by a mechanical surface treatment followed by a chemical surface treatment, the acid solution comprises at least one of the components listed in Table 2. If only a chemical treatment is used, the acid solution may advantageously comprise at least two components listed in Table 2, one of which is selected from NHF,HF; NaF,HF and KF,HF.

[0079] To obtain different roughness values, the plate surfaces were subjected to hydrofluoric acid solutions of different pH values, the proportions of their components being varied within the limits of Table 3, and they were heated to different temperatures between 20°C and 50°C. The cooktop surfaces were exposed for periods ranging from 1 minute to 90 minutes.

[0080] For illustrative purposes, the conditions used to prepare some Examples E1-E5 and some Comparative Examples CE1-CE4 are set forth in Tables 4 and 5, respectively.

[0081] [Table 4]

[0082] [Table 5]

[0083] The values ​​of various roughness parameters Rdq, Rsm and Rsk were measured using a Mitutoyo SJ401 mechanical probe and evaluated in accordance with ISO 4287 over an evaluation length of 4 mm to 12.5 mm with a "12AAC731" type stylus.

[0084] 60° luminance, L * Clarity and haze levels were measured and / or evaluated in accordance with EN ISO 2813:1999, ISO / CIE 11664-4:2019, and ISO 14782:1999, respectively. The results are shown in Figures 1, 2, and 3, respectively. Tables 6 and 7 show the results for Examples E1 to E6 and Comparative Examples CE1 to CE4.

[0085] [Table 6]

[0086] [Table 7]

[0087] In Figure 1, the examples according to the invention are located between vertical lines L1 (Rdq = 4.4°) and L2 (Rdq = 11°), and in some advantageous embodiments between vertical lines L3 (Rdq = 5.5°) and L4 (Rdq = 9°). The comparative examples are located outside the area bounded by vertical lines L1 and L2. All examples according to the invention have a gloss B of less than 20 at 60°.

[0088] In Figure 2, examples according to the invention are located between vertical lines L1 and L2, and in some advantageous embodiments between vertical lines L3 and L4. Comparative examples are located outside the area bounded by vertical lines L1 and L2. All examples consistent with the invention have a brightness or luminance L below 25. * or even a lightness or luminance L of less than 20 for embodiments located between vertical lines L3 and L4. * It has.

[0089] 3, examples according to the present invention are located between vertical lines L1 and L2, and in some advantageous embodiments between vertical lines L3 and L4. Comparative examples are located outside the area bounded by vertical lines L1 and L2. All examples consistent with the embodiments of the present invention have a haze level F of less than 50%, or even less than 30% for examples located between vertical lines L3 and L4.

[0090] The examples and comparative examples were also subjected to various tests to evaluate their scratch resistance and stain resistance.

[0091] Scratch resistance was evaluated according to the following protocol: The rough surface of the article was scratched with a force of approximately 5 N / cm 2The glass-ceramic article is then placed under a P240 silicon carbide abrasive disc with a pressure of 0.01 mm. The disc is then moved once in this state over a distance of approximately 4-5 cm. The roughened surface of the glass-ceramic article is then placed under white light of 300-400 lux and observed at an angle of approximately 60°. The visibility of the scratches is scored according to the following scale of severity: 1: Highly visible scratches; 2: Acceptably visible scratches; 3: faint scratches; 4: No visible scratches.

[0092] The results obtained for the examples and comparative examples are shown in Figure 4. The graph shows the evolution of the mean value of the degree of scratch visibility d for each glass-ceramic article versus the values ​​of the combined root-mean-square roughness Rdq on the abscissa and the mean spacing roughness Rsm on the ordinate. The degree of visibility d is represented by the size of the diagram.

[0093] In Figure 4, examples according to the present invention are located between vertical lines L1 and L2 and above vertical line H1 (Rsm = 0.2) or H2 (Rsm = 0.27). Each example follows a specific advantageous embodiment between vertical lines L3 and L4 and above vertical line H1 (Rsm = 0.2) or H2 (Rsm = 0.27). Each comparative example is located outside the area bounded by vertical lines L1 and L2 and below or above horizontal line H1.

[0094] In the region between vertical lines L1 and L2 and above horizontal line H1 (Rsm=0.2), 90% of the examples according to the invention have a visibility level of at least 2, i.e., the visibility of scratches is at least acceptable or scratches are not visible at all. Above horizontal line H2 (Rsm=0.27), all samples have a visibility level of at least 2, and more than 50% of the samples have a visibility level greater than 3.

[0095] The resistance to metal abrasion of the examples and comparative examples was evaluated according to the following protocol: First, the surface of the enamel area of ​​the glass-ceramic cooktop was rubbed back and forth continuously with several metallic elements, such as a coin and a metal and / or enamel frying pan. The surface was then cleaned using a series of commercially available detergents specifically designed for cleaning cooktops, such as those sold under the VitroClen® or CIF® trademarks. The deterioration of the enamel surface was visually evaluated on a scale of 0 to 20, with 0 corresponding to complete surface deterioration and 20 corresponding to no deterioration at all. In other words, the higher the rating, the more resistant the surface was to metal abrasion.

[0096] The results obtained for the examples and comparative examples are shown in Figure 5. This graph shows the progression of the mean value of the degree of visibility of metal friction d against the mean spacing roughness Rsm for each glass-ceramic article.

[0097] In Figure 5, examples consistent with the present invention are located to the right of vertical line L5 (Rsm = 0.2), or in some advantageous embodiments, to the right of vertical line L6 (Rsm = 0.27). Examples according to the present invention have a metal rub visibility degree of greater than 9, which can be considered acceptable. Preferably, the average spacing roughness can be selected to be greater than 0.4, thereby achieving a visibility degree of greater than 12 for applications where some resistance to metal rub is required.

[0098] The stain resistance was evaluated according to the following protocol: The glass-ceramic article was first inserted into a cooking appliance, with its textured surface serving as the cooking surface. It was then subjected to a cycle of four consecutive stain-clean operations, each of which included a staining step and a cleaning step. This cycle of four operations was repeated eight times. At the end of these eight repetitions, the surface of the article was manually cleaned with a sponge impregnated with a commercially available detergent specifically designed for cleaning cooktops, such as those sold under the trade names VitroClen® or CIF®.

[0099] In the first operation, the soiling step consists of pouring rice cooking water onto the glass-ceramic article, then covering it with a frying pan filled with water and raising the temperature of the water to 100°C over a period of 2 minutes. The frying pan is then allowed to cool naturally to room temperature. Once room temperature is reached, the temperature is again raised to 100°C over a period of 2 minutes, and the frying pan is then allowed to cool naturally to room temperature. At the end of the soiling stage, as soon as the water in the frying pan has cooled to room temperature, the article is cleaned with a scraper sponge impregnated with water and detergent (cleaning liquid). The cleaning is repeated four times.

[0100] In the second operation, the soiling step involves pouring cooking oil onto the surface of the glass-ceramic article, then covering it with a frying pan filled with cooking oil and raising the temperature of the cooking oil to at least 200°C over a period of 3 minutes. The frying pan is then allowed to cool naturally to room temperature. At the end of the soiling step, as soon as the water in the frying pan has cooled to room temperature, the article is cleaned with a scraper sponge impregnated with water and detergent (cleaning liquid).

[0101] In the third operation, the soiling step consists of pouring tomato paste onto the surface of the glass-ceramic article, then covering it with a frying pan filled with water, and raising the temperature of the water to at least 100°C over a period of 2 minutes. The frying pan is then allowed to cool naturally to room temperature. At the end of the soiling stage, as soon as the water in the frying pan has cooled to room temperature, the article is cleaned with a scraper sponge impregnated with water and detergent (cleaning liquid).

[0102] In the fourth operation, the soiling step consists of pouring milk onto the surface of the glass-ceramic article, then covering it with a frying pan filled with water, and raising the temperature of the water to at least 100°C over a period of 2 minutes. The frying pan is then allowed to cool naturally to room temperature. At the end of the soiling stage, as soon as the water in the frying pan has cooled to room temperature, the article is cleaned with a scraper sponge impregnated with water and detergent (cleaning liquid).

[0103] The degree of contamination is rated on a scale of 1 to 4 according to the cleanability of the surface, with grade 0 corresponding to a completely cleanable surface, with little or no residue remaining on the surface after cleaning, and grade 4 corresponding to an uncleanable surface, with marks remaining after cleaning.

[0104] The results obtained for the Examples and Comparative Examples are shown in Figure 6. This graph shows the evolution of the mean value of the degree of visibility of metal friction d versus the combined root mean square roughness Rdq for each glass-ceramic article.

[0105] In Figure 6, examples according to some advantageous embodiments are shown between vertical lines L3 and L4. According to these advantageous embodiments, matching examples have a degree of contamination strictly below 3, which is acceptable for use in domestic kitchen equipment such as cooking appliances or worktops.

[0106] The fingernail scratch resistance of the examples and comparative examples was evaluated according to the following protocol: A fingernail is rubbed on the surface of the glass-ceramic article. The surface of the glass-ceramic article is then placed under white light of 300-400 lux and observed at an angle of approximately 60°. The visibility of scratches is scored according to the following degree scale: 1: Highly visible scratches; 0.66: visible scratches; 0.33: faint scratches; 0: No visible scratches.

[0107] The results obtained for the Examples and Comparative Examples are shown in Figure 7. This graph shows the progression of the average value of the degree of scratch visibility d versus the skewness Rsk for each glass-ceramic article.

[0108] 7, examples consistent with the present invention are located to the left of vertical line L7 (Rsk=-0.2), or in some embodiments, to the left of vertical line L8 (Rsk=-0.3) or L9 (Rsk=-0.5). Comparative examples are located to the right of vertical line L7.

[0109] Nail scratches in embodiments consistent with the present invention (Rsk<-0.2) are barely visible, or even not visible when Rsk is less than -0.5.

[0110] These examples and comparative examples clearly demonstrate that glass-ceramic articles according to the present invention and some of its advantageous embodiments have all of the advantages discussed above.

[0111] List of References Patent documents Japanese Patent Publication No. 2007170754 issued on July 5, 2007 by Nippon Electric Glass Co., Ltd. [JP] International Publication No. 2013 / 190230 of December 27, 2013 by EUROKERA [EN] CORNING INC. [US], WO 2011 / 137144, dated November 3, 2011 CORNING INC. [US], WO 2014 / 070869, dated September 9, 2013 CORNING INC. [US], WO 2016 / 138051, September 1, 2016 CORNING INC. [US], International Publication No. 2018 / 093844, dated May 24, 2018 International Publication No. 2021 / 121846 of June 24, 2021 by EUROKERA [FR] European Patent Application Publication No. 0437228, dated July 17, 1991, by Corning France [FR] WO 2012 / 156444 of November 22, 2012 by EUROKERA [EN] Non-patent literature Product specifications - Surface finishing: Profile methods - Terminology, definitions and parameters for surface finishing, International Standard ISO 4287:1997 Determination of the luminous and solar properties of architectural glass-glazing, European Standard EN 410:1998 Colorimetric analysis-Part:CIE 1976 L * a * b * Color space, international standard ISO / CIE 116644:2019 Measurement of specular gloss of non-metallic coatings at 20°, 60° and 85°, European Standard ISO 2813:1999 Plastics - Determination of haze in transparent materials, International Standard ISO 14782:1999

Claims

1. 1. A planar glass-ceramic article for use in a cooking appliance, the article comprising a first major surface, a second major surface, and an edge, wherein all or a portion of at least one of the two major surfaces has an inherent texture, and the inherent texture has a composite root-mean-square roughness Rdq of 4.4° to 11°.

2. 2. The glass-ceramic article of claim 1, wherein the composite root mean square roughness Rdq is between 5.5° and 9°.

3. 3. The glass-ceramic article according to claim 1 or 2, wherein the unique texture has a mean spacing roughness Rsm of more than 0.2 mm, preferably more than 0.27 mm.

4. The glass-ceramic article has a brightness L ＊ 3. The glass-ceramic article of claim 1, wherein

5. 3. The glass-ceramic article according to claim 1 or 2, wherein the intrinsic texture has a skewness Rsk of less than −0.2, preferably less than −0.3, preferably less than −0.

5.

6. 3. The glass-ceramic article according to claim 1 or 2, having a 60° gloss of 20 or less, preferably less than 10.

7. 3. The glass-ceramic article of claim 1 or 2, wherein the glass-ceramic article further comprises at least one light source for luminescent display by projection or transmission onto a work surface forming a screen.

8. 1. A method of manufacturing a glass-ceramic article, the method comprising: - a ceramizing heat treatment of a glass capable of forming a glass ceramic; chemically treating the surface of said glass before and / or after said ceramming heat treatment; wherein the chemical surface treatment is carried out such that after heat treatment the composite root mean square roughness value Rdq is between 4.4° and 11°, preferably between 5.5° and 9°.

9. 9. The method of claim 8, wherein the method includes a mechanical surface treatment step by sandblasting prior to the chemical surface treatment.

10. 10. The method according to claim 8 or 9, wherein the chemical treatment step is carried out before the ceramming step.

11. 10. The method according to claim 8 or 9, wherein the chemical surface treatment is chemical etching with a hydrofluoric acid solution.

12. 12. The method of claim 11, wherein the hydrofluoric acid solution comprises sodium fluoride, potassium fluoride, ammonium fluoride, barium sulfate, hydrochloric acid, and / or sulfuric acid, alone or in combination.

13. A cooking device comprising a glass-ceramic cooktop formed from the glass-ceramic article of claim 1 or 2.

14. 3. Use of the glass-ceramic article according to claim 1 or 2 as all or part of a worktop for food preparation.

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