Glass ceramic article

Abstract

Flat glass-ceramic article for a cooking device, wherein the article comprises a first main surface, a second main surface and an edge and is characterized in that the whole or part of at least one of the two main surfaces has an intrinsic texturing whose hybrid square roughness Rdq is between 4.4° and 11°.

Description

TECHNICAL FIELD

[0001] The invention relates to a flat glass-ceramic article comprising a textured surface, which has scratch-resistant, dirt-repellent properties and an aesthetic surface appearance and is suitable for household use. TECHNICAL BACKGROUND

[0002] A glass-ceramic material is a composite material comprising an amorphous phase in which crystalline phases or crystals are dispersed. It is generally produced by heat-treating a glass suitable for forming a glass-ceramic, the so-called "mother glass," to allow crystals to crystallize in a controlled manner within its volume. This treatment, which partially crystallizes a glass, is called "ceramization" or simply "ceramization." The final physicochemical properties of the glass-ceramic depend on the composition of the mother glass and the ceramization treatment.

[0003] Glass-ceramics are valued in many areas for their aesthetic qualities and their physico-chemical properties, particularly their low thermal expansion coefficient and resistance to thermal shock. They are primarily used in kitchen appliances, especially in the form of panels, for example, as cooking surfaces in cooking appliances, as glass walls in ovens, and as work surfaces in countertops, work tables, or food preparation furniture. In these applications, glass-ceramics are typically based on lithium aluminosilicate.

[0004] Depending on their intended use, glass-ceramic items can be equipped with a range of accessories such as controls, sensors and displays that enable interaction between the user and the devices into which these items are incorporated.

[0005] For example, they may 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 devices. They may also include displays, in particular illuminated displays, for projecting, in particular by transmission, cognitive light patterns (e.g., symbols or numbers) representative of values ​​of certain operating parameters of these devices (e.g., the heat output of a heating device) or relating to the physical-chemical state of the article (e.g., signaling a hot zone).

[0006] They can also be equipped with optical and / or thermal sensors that allow, for example, to detect elements on their surface such as spilled liquid or to measure the surface temperature of the item and warn the user through an acoustic or visual signal via a display zone.

[0007] Interactions, especially tactile ones, between the surface of the glass-ceramic article and the user, as well as handling liquid or solid foods and mechanical preparation tools (e.g., knife blades), cause various unsightly marks at the points of contact with the surface, particularly fingerprints. They can also cause soiling such as dried or burnt food residue on the surface of the article or scratches.

[0008] These marks and soiling can cause the user to repeatedly clean the surface with abrasive cleaners, which can cause further scratches. These various problems are particularly significant for glass-ceramic items with dark, matte or glossy surfaces.

[0009] To prevent fingerprints and smudges, and to limit the appearance or visibility of scratches, various organic or inorganic, textured or non-textured coatings with hydrophobic or oleophobic properties are known to be used. It is also known to modify the surface of the glass-ceramic to achieve such properties.

[0010] JP 2007170754 NIPPON ELECTRIC GLASS CO [JP] July 5, 2007 describes a glass-ceramic article comprising a working surface with a roughness between 0.1 µm and 20 µm to impart light-diffusing properties and a milky-white appearance. This article is obtained by a combination of mechanical and chemical surface treatments.

[0011] WO 2011 / 137144 A1 CORNING INC [US] 03.11.2011 describes a method for manufacturing a glass-ceramic article by etching to form a rough surface with an arithmetic roughness value between 100 nm and 300 nm. The resulting roughness provides an anti-reflection effect.

[0012] WO 2013 / 190230 A1 EUROKERA [DE] December 27, 2013 describes a glass-ceramic article comprising a surface provided with a textured layer, in particular a sol-gel layer. The texture is formed by regular, in particular geometric, patterns whose height is between 2 and 100 µm.

[0013] WO 2014 / 070869 A1 CORNING INC [US] 09.09.2013 describes a process for manufacturing a glass-ceramic article by chemical etching such that the surface of the article is modified to a depth of between 0.01 µm and 20 µm. The resulting roughness contributes to reducing gloss.

[0014] WO 2016 / 138051 A1 CORNING INC [US] 01.09.2016 describes a method for producing a glass-ceramic article using two successive chemical etchings to form a surface roughness whose average distance between the features of the roughness pattern is between 0.5 µm and 25 µm and whose density is between 9000 and 25000 features per mm 2 Chemical etching is performed with acid solutions based on hydrofluoric acid.

[0015] WO 2018 / 093844 A1 CORNING INC [US] May 24, 2018 describes a process for producing a glass-ceramic article comprising a non-planar surface having an arithmetic roughness value between 10 and 2000 nm. The process includes a step of chemically etching the surface using a hydrofluoric acid solution. The surface roughness provides aesthetic effects, a lower gloss level, an anti-reflective effect, and a better haptic feel.

[0016] WO 2021 / 121846 A1 EUROKERA [FR] 24.06.2021 describes a method for producing a glass-ceramic article by chemical etching. The surface of the glass-ceramic article has an arithmetic roughness value between 2 µm and 7 µm. SUMMARY OF THE INVENTIONTechnical problem

[0017] There is still a need to improve the aesthetic appearance and mechanical scratch resistance of the surfaces of glass-ceramic articles, especially for glass-ceramic articles of dark or black color.

[0018] Such an article must exhibit optical and physico-chemical surface properties compatible with its intended applications, particularly applications in cooking appliances and / or as a countertop surface. More specifically, it must exhibit scratch-resistant, grease-repellent, dirt-repellent, and anti-light-scattering properties. It must also exhibit an aesthetic surface appearance suitable for household use. Solution to the technical problem

[0019] According to a first aspect of the invention, a glass-ceramic article is provided comprising a first main surface, a second main surface, and an edge, characterized in that all or part of at least one of the two main surfaces has an intrinsic texturing whose root mean square hybrid roughness Rdq is between 4.4° and 11°. Advantageous embodiments are described below.

[0020] According to the invention, the rough texturing of the surface of the glass-ceramic article is intrinsic, i.e. the roughness of the surface results from the surface itself without the addition of a surface coating.

[0021] According to a further aspect of the invention, there is provided a cooking appliance comprising a glass-ceramic plate formed from a glass-ceramic article according to the first aspect of the invention. Advantages of the invention

[0022] A notable advantage of the invention is that, when used on dark-colored or black glass-ceramic articles, it enables a surface gloss level at 60° of well below 30 or even below 25 and a brightness level of below 23. The article then has a dark matte appearance that meets the aesthetic requirements for household applications.

[0023] In certain advantageous embodiments, the turbidity value is less than 50% or even 30%. The visibility of light patterns transmitted from illuminated displays onto or through the surface of the glass-ceramic article remains sharp, resulting in improved visual comfort when the article is used in a cooking appliance.

[0024] A further advantage is that, in some embodiments, the specific roughness of the glass-ceramic article, the intrinsic or inherent roughness of the surface of the glass-ceramic article, does not alter the thermal and mechanical properties of that surface. It allows for easy cleaning of possible contamination and is more resistant to metal abrasion. BRIEF DESCRIPTION OF THE DRAWINGS [ Fig. 1] shows the evolution of the gloss at 60° of the surface of examples of glass-ceramic articles according to the invention and of counterexamples as a function of their hybrid quadratic roughness. [ Fig. 2] shows the evolution of the brightness of the surface of examples of glass-ceramic articles according to the invention and of counterexamples as a function of their hybrid square roughness. [ Fig.3] shows the evolution of the haze value of the surface of examples of glass-ceramic articles according to the invention and of counterexamples as a function of their hybrid square roughness. [ Fig. 4] shows the evolution of the degree of visibility of scratches on the surface of examples of glass-ceramic articles according to the invention and of counterexamples as a function of their hybrid root mean square roughness and their mean pitch roughness. [ Fig. 5] shows the development of the degree of visibility of metal abrasions on the surface of examples of glass-ceramic articles according to the invention and of counterexamples as a function of their mean pitch roughness. [ Fig. 6] shows the evolution of the anti-stick index of dirt on the surface of examples of glass-ceramic articles according to the invention and counterexamples as a function of their hybrid square roughness. [ Fig.7] shows the evolution of the degree of visibility of scratches by nails on the surface of examples of glass-ceramic articles according to the invention and of counterexamples as a function of their surface asymmetry factor. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0025] In the context of the invention, reference is made to the following definitions and conventions.

[0026] Hybrid root mean square roughness, denoted by Rdq, is defined in Section 4.4.1 of ISO 4287 as the root mean square of the local slopes of the surface roughness profile within the sample length. The hybrid root mean square roughness, Rdq, is a dimensionless number. It can also be expressed in angular units, degrees, or radians, using the usual trigonometric relationships for calculating slopes, in particular the arctan function. For the purposes of the present invention, it is expressed in degrees.

[0027] Spacing mean roughness, denoted by Rsm, is defined in section 4.3.1 of ISO 4287 as the mean value of the widths of the elements of the surface roughness profile within the sample length. The width of a profile element, as defined in section 3.2.12 of ISO 4287, is the length of the abscissa axis intersected by the element, i.e., the elevation or depression, of the profile. Values ​​are given in millimeters.

[0028] The asymmetry factor Rsk is, as defined in section 4.2.3 of ISO 4287, the quotient of the mean of the cubed heights and the cubed maximum elevation heights within the sampling length.

[0029] Intrinsic or inherent texturing of a surface of a glass-ceramic article means the texturing of the glass-ceramic material of the article itself without any surface coating.

[0030] A glass-ceramic article is a composite material, preferably based on aluminosilicate, in particular based on lithium silicate, with an amorphous phase in which crystalline phases or crystals are dispersed. It is obtained by heat-treating a glass, referred to as a "mother glass," suitable for forming a glass-ceramic, to allow controlled crystallization of crystals within its volume.

[0031] “Light transmittance” TL means the light transmittance, designated TL, as defined and measured and / or calculated in EN 410:1998.

[0032] Colour deviation ΔE*, lightness or luminosity L* and colorimetric coordinates a* and b* are colour deviation ΔE*, lightness or luminosity L* and colorimetric coordinates a* and b* as defined in ISO / CIE 11664-4:2019.

[0033] “60° gloss” means the specular gloss at 60° as described and measured in EN ISO 2813:1999.

[0034] “Turbidity” means turbidity as defined and measured in ISO 14782:1999.

[0035] According to a first aspect of the invention, a flat glass-ceramic article is provided having a first major surface, a second major surface and an edge, characterized in that all or part of at least one of the two major surfaces has an intrinsic texturing whose hybrid root mean square roughness Rdq is between 4.4° and 11°.

[0036] According to the first aspect of the invention, the glass-ceramic article is flat. It can comprise two substantially parallel, flat main surfaces and four side surfaces extending substantially perpendicular to the two main surfaces and can, in particular, be in the form of a glass-ceramic plate.

[0037] The "mother glass" used to manufacture the glass-ceramic article can be of any suitable type. According to a preferred embodiment, the mother glass is based on lithium aluminosilicate, which comprises the following components within the weight limits defined in Table 1 below, expressed as a percentage by weight of the glass: [Table 1] Table 1 SiO2 58-75 % Al2O3 16-25 % Li2O 2-4,5 % Na2O 0-2 % K2O 0-2 % CaO 0-4 % MgO 0-5 % BaO 0-5 % ZnO 0-5 % SrO 0-5 % TiO2 1-6 % ZrO2 0-3 % P2O5 0-6 % B2O3 0-2 % Fe2O3 0-2 % Cr2O3 0-2 % CoO 0-2 %

[0038] As already mentioned, a notable advantage of the first aspect of the invention is that it makes it possible to obtain a glass-ceramic article that meets the aesthetic requirements for household applications, such as a hob or worktop. Particularly in the case of an initially black or dark glass-ceramic article, the surface gloss level at 60°C may be significantly below 30 or even below 25, and the brightness level below 23.

[0039] According to certain advantageous embodiments, the hybrid root-mean-square roughness Rdq can be between 5.5° and 9°. It has been found that when the roughness Rdq is within this range, the visibility of light patterns transmitted from illuminated displays onto or through the surface of the glass-ceramic article remains sharp, resulting in improved visual comfort. The observed haze is then less than 50% or even 30%.

[0040] According to further specific embodiments, the intrinsic texturing may further have a mean pitch roughness Rsm of more than 0.2 mm, preferably more than 0.27 mm. Such texturing makes it possible to increase the mechanical surface resistance and thus reduce the visibility of scratches.

[0041] It's common to use glass-ceramic items as cooking or work surfaces in kitchen appliances. When metal utensils, such as a pot or pan, are moved across their surfaces during this type of use, they can be subjected to particular stress. This movement can manifest itself, particularly in the form of metal abrasion.

[0042] According to certain embodiments, the mean pitch roughness Rsm can be much greater than 0.27 mm, in particular greater than 0.4 mm. The glass-ceramic article can then very advantageously exhibit high resistance to metal abrasion, in particular metal abrasion associated with the movement of pots, as well as chemical and mechanical durability, which is advantageous during repeated contact with food and heating cycles.

[0043] In addition to contact with utensils and food, the surfaces of glass-ceramic items incorporated into kitchen appliances may also be exposed to fingernail friction, particularly when the user's hands move over built-in control panels. According to certain embodiments, the intrinsic texturing may then have an asymmetry factor Rsk of less than -0.2, preferably less than -0.3, preferably less than -0.5. Surprisingly, it was then found that the visibility of the marks caused by the movement of the nails on the surface of the glass-ceramic item was reduced.

[0044] The effects and advantages of the invention are particularly pronounced when the glass-ceramic article has low transmission, low scattering, and a dark color (defined by the luminosity L*), in particular a black or dark brown color. Preferably, the glass-ceramic article may further be suitable for the transmission display of luminous zones comprising luminous recognition patterns representing the values ​​of certain operating parameters of associated electrical and / or electronic devices or relating to a physicochemical state of the article, while the underlying elements are concealed.

[0045] In this sense, in a particular embodiment of the invention, the glass-ceramic article has a luminosity L* of less than or equal to 25, preferably less than or equal to 20. Initially, ie when it has no surface texture, it may also have a luminosity L* of less than or equal to 25, preferably less than or equal to 20.

[0046] A dark-colored glass-ceramic article may initially, ie when it has no surface texture, have an opacity factor of less than 100 and advantageously more than 93, in particular to enable display by transmission through underlying sources in one embodiment of the invention or display by projection.

[0047] The opacity factor is determined by the formula f = 100 - ΔE*, where ΔE* is the color deviation. The color deviation ΔE* can be determined by measuring the changes in the brightness L* and the colorimetric parameters a* and b* of the top surface of the article upon reflection in the CIELAB color space when it is placed on an opaque black background and then placed on an opaque white background. The color deviation ΔE* can be calculated using the following formula: ΔE* = ((LN*-LB*) 2 + (aN*-aB*) 2 + (bN*-bB*) 2 )½, where LB*,aB*,bB* are the brightness and color coordinates of the first measurement on a white background and LN*,aN*,bN* are those of the second measurement on a black background.

[0048] A black glass-ceramic article may initially, i.e. when it has no surface texture, have a luminosity L* of less than 10, a haze of less than 30% and a light transmittance TL of less than 10% under standard illuminant D65.

[0049] Preferably, the dark-colored glass-ceramic article initially, ie when it has no surface texture, has an a* parameter value between -0.2 and 1.6 and a b* parameter value between -1 and 0.6.

[0050] A glass-ceramic article according to the first aspect of the invention enables light patterns transmitted from luminous displays onto or through the rough surface to remain sharp to improve visibility to the user.

[0051] According to some preferred embodiments, the 60° gloss of the glass-ceramic article may be less than 20, preferably less than 10. These gloss levels are particularly advantageous for the aesthetic appearance of the glass-ceramic surface, especially if it is dark-colored or black.

[0052] In some embodiments, the glass-ceramic article may further comprise at least one light source for the illuminated display by projection or transmission onto the surface, which then forms the screen. The display may, for example, be an LED display, in particular a seven-segment display for displaying alphanumeric characters.

[0053] The glass-ceramic article can be manufactured by a process comprising the following steps: - a heat treatment for ceramising a glass suitable for forming a glass-ceramic, and - a chemical treatment of a surface of the glass before and / or after the heat treatment for ceramization, wherein the chemical surface treatment is carried out in such a way that after the heat treatment the hybrid root mean square roughness value Rdq is between 4.4 and 11°, preferably between 5.5 and 9°.

[0054] According to certain advantageous embodiments, the method may further comprise a step of mechanical surface treatment by sandblasting prior to the chemical surface treatment.

[0055] The chemical surface treatment can be performed before and / or after the heat treatment for ceramization. According to a preferred embodiment, the chemical surface treatment is performed before the heat treatment for ceramization. It has been found that the scratch-resistant, grease-repellent, dirt-repellent, and light-scattering properties are thereby further improved.

[0056] The roughness is obtained by chemically treating the mother glass of the glass-ceramic article, i.e., before the heat treatment for ceramizing the mother glass, which allows the glass-ceramic article to be formed. The roughness values ​​are those of the rough surface of the glass-ceramic article after the ceramization treatment.

[0057] The glass suitable for forming a glass-ceramic is preferably based on aluminosilicate, in particular lithium aluminosilicate.

[0058] The type of chemical solution used for the treatment, the temperature of the treatment and its duration depend on the chemical composition of the material that forms the mother glass of the glass-ceramic article.

[0059] The process makes it possible to impart a roughness to the glass-ceramic article across its entire working surface. It is also possible to impart roughness to only part of the working surface of the glass-ceramic article. This property can be achieved, for example, by applying protective masks to the surface of the mother glass during chemical or mechanical surface treatment to protect certain areas of the surface.

[0060] In certain embodiments, the chemical surface treatment may be etching with a hydrofluoric acid-based solution. This embodiment is particularly advantageous for glass-ceramic articles based on aluminosilicate, especially lithium aluminosilicate.

[0061] According to some preferred embodiments, the chemical treatment may further comprise a precursor step, the so-called surface activation step, prior to the above-mentioned etching. This activation step may consist of etching using an acid solution comprising hydrochloric acid and hydrofluoric acid at room temperature for at least two minutes.

[0062] The hydrofluoric acid mass content of the acid solution can advantageously range from 1 to 70 mass%. If the mass content is below 1%, the duration of the chemical surface treatment is generally quite long and not very advantageous for industrial applications. If the mass content is above 20%, the chemical surface treatment may be too rapid and difficult to control. The temperature of the solution is preferably below 40°C or even below 30°C to also avoid the chemical surface treatment being too rapid and difficult to control.

[0063] According to certain 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.

[0064] According to a further aspect of the invention, a cooking appliance is provided comprising a glass-ceramic plate formed from a glass-ceramic article according to any one of the embodiments of the first aspect of the invention.

[0065] Examples of heating elements for a cooking appliance can be radiant or halogen stoves or induction heating elements.

[0066] The glass-ceramic article according to the invention can be used as all or part of a worktop for food preparation. The worktop can, for example, be part of a piece of kitchen furniture or as a surface element of a cooking appliance, wherein the surface element serves to facilitate food preparation. Examples

[0067] The following examples and counterexamples were carried out using mother glasses for glass-ceramic panels as described in EP 0 437 228 A1 CORNING FRANCE [FR], July 17, 1991, and / or WO 2012 / 156444 A1 EUROKERA [FR], November 22, 2012, each marketed under the brand name KeraBlack Plus®. The panels are 6 mm thick.

[0068] The roughness was achieved by mechanical surface treatment of the mother glass by sandblasting and / or chemical surface treatment. These two treatments were performed before the heat treatment for ceramization. If mechanical treatment and chemical treatment are used, these two treatments are sequential, meaning that the mechanical treatment is performed before the chemical treatment.

[0069] The mechanical sandblasting treatment was carried out according to the parameters described in Table 2. [Table 2] Table 2 Type of abrasive grains Quartz, garnet or corundum Grain size 150 ≤ D90 ≤ 300 µm 100 ≤ D50 ≤ 200 µm Grain delivery rate 0.5 - 10 g / s Grain projection speed 1 - 50 m / s Pressure 0.5 - 5 bar, preferably between 2 bar and 4 bar Angle of incidence 45 - 90°

[0070] The chemical surface treatment was carried out with a hydrofluoric acid-based solution, the components of which are listed in Table 3. [Table 3] Table 3 concentration NH4F, HF 0 - 9 mol / L NaF, HF 0 - 0.065 mol / L KF, HF 0 - 0.013 mol / L HF 0.24 - 35 mol / L HCl 0 - 12 mol / L H2SO4 0 - 10 mol / L H2SiF6 0 - 0.12 mol / L SiO2 0 - 0.12 mol / L BaSO4 0 - 50 g / L

[0071] If the roughness is achieved by means of 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, wherein one of the components is selected from NH4F, HF; NaF, HF; and KF, HF.

[0072] To achieve different roughness values, the plate surfaces were exposed to hydrofluoric acid solutions with different pH values ​​by varying the proportions of their components within the limits specified in Table 3 and heating them to different temperatures between 20 °C and 50 °C. The plate surfaces were exposed for periods ranging from 1 min to 90 min.

[0073] For illustrative purposes, the conditions used to prepare some examples E1-E5 and some counterexamples CE1-CE4 are listed in Table 4 and Table 5, respectively. [Table 4] Table 4 E1 E2 E3 E4 E5 E6 Acid solution for chemical treatment HF (mol / L) 0,5 0,5 7,5 15 15 17,5 NH4F,HF (mol / L) 7 6,1 8,8 0 0 0 H2SiF6 (mol / L) 0,06 0 0,03 0,03 0,03 0,03 BaSO4 Yes no Yes no Yes no Temperature (°C) 20 20 40 50 50 50 Time (min.) 10 60 10 20 20 30 Chemical activation solution HCl (mol / L) 0,5 0,5 0,5 0,5 HF (mol / L) 0,05 0,05 0,05 0,05 Time (min.) 2 2 2 2 Temperature (°C) Ambient temperature Ambient temperature Ambient temperature Ambient temperature Ambient temperature Ambient temperature Mechanical treatment Type of abrasive grains Garnet 97-98% Garnet 97-98% Garnet 97-98% Grain size (µm) D90 = 264 D50 = 185 D90 = 264 D50 = 185 D90 = 264 D50 = 185 Pressure (bar) 2 2 2 [Table 5] Table 5 CE1 CE2 CE3 CE4 Acid solution for chemical treatment HF (mol / L) 1,5 7,5 10 12,5 NH4F,HF (mol / L) 5,3 8,8 0 0 H2SiF6 (mol / L) 0,06 0,03 0,03 0,03 BaSO4 no no no no Temperature (°C) 20 50 50 50 Time (min.) 20 30 20 20 Chemical activation solution HCl (mol / L) 0,5 0,5 0,5 HF (mol / L) 0,05 0,05 0,05 Time (min.) 2 2 2 Temperature (°C) Ambient temperature Ambient temperature Ambient temperature Ambient temperature Mechanical treatment Type of abrasive grains Garnet 97-98% Garnet 97-98% Garnet 97-98% Grain size (µm) D90 = 264 D50 = 185 D90 = 264 D50 = 185 D90 = 264 D50 = 185 Pressure (bar) 2 2 2

[0074] The values ​​of the different roughness parameters, Rdq, Rsm and Rsk, were measured using a Mitutoyo SJ401 mechanical caliper with a stylus type “12AAC731” and evaluated according to ISO 4287 over an evaluation length of 4 mm to 12.5 mm.

[0075] The gloss at 60°, the brightness L* and the haze value of the examples and counterexamples were measured and / or evaluated according to EN ISO 2813:1999, ISO / CIE 11664-4:2019 and ISO 14782:1999, respectively. The results are shown in Fig. 1, Fig. 2 and Fig. 3. Table 6 and Table 7 show the results of examples E1-E6 and counterexamples CE1-CE4. [Table 6] Table 6 E1 E2 E3 E4 E5 E6 Rsm (mm) 0,066 0,117 0,091 0,451 0,413 0,608 Rdq (°) 9,52 10,42 9,77 8,73 9,84 4,36 Rsk 0,97 -0,14 -0,31 -0,32 -0,26 -0,39 L* 21,1 21,9 20,5 14,6 16,2 2,2 Shine at 60° 0,8 2,1 1,9 4,7 4 12,1 [Table 7] Table 7 CE1 CE2 CE3 CE4 Rsm (mm) 0,126 0,354 0,395 0,399 Rdq (°) 13,97 16,55 17,32 14,74 Rsk -0,11 -0,19 -0,35 -0,14 L* 20,2 20,0 23,5 22,7 Shine at 60° 0,8 0,6 1,7 2,6

[0076] In Fig. 1, the inventive examples are located between the vertical lines L1 (Rdq = 4.4°) and L2 (Rdq = 11°), and in some advantageous embodiments also between the vertical lines L3 (Rdq = 5.5°) and L4 (Rdq = 9°). The counterexamples lie outside the area bounded by the vertical lines L1 and L2. The inventive examples all have a gloss level B at 60° of less than 20.

[0077] In Fig. 2, the examples according to the invention lie between the vertical lines L1 and L2, and in some advantageous embodiments also between the vertical lines L3 and L4. The counterexamples lie outside the range delimited by the vertical lines L1 and L2. The examples according to the invention all have a brightness or luminosity L* of less than 25, and in the examples between the vertical lines L3 and L4, even less than 20.

[0078] In Fig.3, the examples according to the invention lie between the vertical lines L1 and L2, and in some advantageous embodiments also between the vertical lines L3 and L4. The counterexamples lie outside the area delimited by the vertical lines L1 and L2. The examples corresponding to the embodiments of the invention all have a turbidity value F of less than 50%, and for the examples between the vertical lines L3 and L4, even less than 30%.

[0079] The examples and counterexamples were also subjected to various tests to evaluate scratch resistance and dirt repellency properties.

[0080] The scratch resistance was evaluated using the following protocol. The rough surface of the article was placed under a P240 silicon carbide grinding wheel at a pressure of approximately 5 N / cm 2In this state, the disc is then moved once over a distance of approximately 4 to 5 cm. The rough surface of the glass-ceramic article is then placed under white light with an intensity of 300 to 400 lux and viewed at a viewing angle of approximately 60°. The visibility of the scratches is evaluated using the following scale: 1: clearly visible scratches; 2: acceptable visible scratches; 3: barely visible scratches; 4: no visible scratches.

[0081] The results obtained for the examples and counterexamples are shown in Fig. 4. This graph shows the evolution of the mean scratch visibility degree d for each glass-ceramic article as a function of the root mean square hybrid roughness Rdq on the abscissa and the mean pitch roughness Rsm on the ordinate. The visibility degree d is represented by the size of the symbols.

[0082] In Fig. 4, the examples according to the invention lie between the vertical lines L1 and L2 and above the horizontal line H1 (Rsm = 0.2) or H2 (Rsm = 0.27). The examples correspond to certain advantageous embodiments between the vertical lines L3 and L4 and above the horizontal line H1 (Rsm = 0.2) or H2 (Rsm = 0.27). The counterexamples lie outside the area delimited by the vertical lines L1 and L2 and below or above the horizontal line H1.

[0083] In the area bounded by the vertical lines L1 and L2 and above the horizontal line H1 (Rsm = 0.2), 90% of the inventive examples exhibit a visibility level of at least 2, i.e., the visibility of the scratches is at least acceptable or not visible at all. Above the horizontal line H2 (Rsm = 0.27), all samples exhibited a visibility level of at least 2, and more than 50% exhibited a visibility level of more than 3.

[0084] The metal abrasion resistance of the examples and counterexamples was evaluated according to the following protocol. First, the surface of the enameled area of ​​the glass-ceramic hob is rubbed successively with several metal elements, such as coins and metal and / or enamel pots, using a reciprocating motion. The surface is then cleaned with various commercially available cleaning agents specifically developed for cleaning cooktops, such as those sold under the VitroClen® or CIF® brands. The deterioration of the enamel surface is assessed visually on a scale of 0 to 20; grade 0 corresponds to complete deterioration of the surface, and grade 20 corresponds to a complete absence of deterioration. In other words, the higher the grade, the more resistant the surface to metal abrasion.

[0085] The results obtained for the examples and counterexamples are shown in Fig. 5. This graph shows, for each glass-ceramic article, the evolution of the mean value of the degree d of the visibility of the metal abrasion as a function of the mean pitch roughness Rsm.

[0086] In Fig. 5, the examples according to the invention lie to the right of the vertical line L5 (Rsm = 0.2) or, in certain advantageous embodiments, to the right of the vertical line L6 (Rsm = 0.27). The examples according to the invention exhibit a metal abrasion visibility rating of more than 9, which can be considered acceptable. Preferably, the mean pitch roughness can be selected to be greater than 0.4 to achieve a visibility rating of more than 12 for applications requiring a certain degree of metal abrasion resistance.

[0087] The soil-resistant properties were evaluated using the following protocol. The glass-ceramic article is first placed in a cooking appliance where its work surface serves as the cooking surface. It is then subjected to a cycle of four consecutive soiling and cleaning operations, each comprising a soiling and a cleaning step. This cycle of four operations is repeated eight times. After these eight repetitions, the surface of the article is manually cleaned with a sponge soaked in a commercially available detergent specifically designed for cleaning cooktops, such as the detergent sold under the brand names VitroClen® or CIF®.

[0088] In the first step, the soiling step consists of pouring rice cooking water onto the glass-ceramic item and then placing a pot filled with water on top. The pot is heated to 100°C for two minutes. The pot is then allowed to cool to room temperature. Once room temperature is reached, the temperature is raised again to 100°C for two minutes, and the pot is then allowed to cool. At the end of the soiling step, after the water in the pot has cooled to room temperature, the item is cleaned using a scrubbing sponge soaked in water and detergent (dishwashing liquid). The cleaning process is repeated four times.

[0089] In the second step, the soiling step consists of pouring cooking oil onto the surface of the glass-ceramic item and then placing a pot filled with cooking oil on top, heating the pot to a temperature of at least 200°C for three minutes. The pot is then allowed to cool to room temperature. At the end of the soiling step, after the water in the pot has cooled to room temperature, the item is cleaned using a scrubbing sponge soaked in water and detergent (dishwashing liquid).

[0090] The third step, the soiling step, involves pouring tomato paste onto the surface of the glass-ceramic item and then placing a pot filled with water on top, which is heated to at least 100°C for two minutes. The pot is then allowed to cool to room temperature. At the end of the soiling step, after the water in the pot has cooled to room temperature, the item is cleaned using a scrubbing sponge soaked in water and detergent (dishwashing liquid).

[0091] In the fourth step, the soiling step, milk is poured onto the surface of the glass-ceramic item and then a pot filled with water is placed on top, heated to at least 100°C for two minutes. The pot is then allowed to cool to room temperature. At the end of the soiling step, after the water in the pot has cooled to room temperature, the item is cleaned using a scrubbing sponge soaked in water and detergent (dishwashing liquid).

[0092] The degree of soiling is rated on a scale of 1 to 4, depending on how easily the surface can be cleaned. Grade 0 corresponds to a completely cleanable surface; after cleaning, no or only minimal traces remain on the surface. Grade 4 corresponds to an uncleanable surface: traces remain after cleaning.

[0093] The results for the examples and counterexamples are in Fig. 6. This graph shows, for each glass-ceramic article, the evolution of the mean value of the degree d of the visibility of metal abrasion as a function of the hybrid root mean square roughness Rdq.

[0094] In Fig. In Figure 6, the examples corresponding to certain advantageous embodiments lie between vertical lines L3 and L4. According to these advantageous embodiments, the corresponding examples consistently exhibit a soiling level below 3, which is acceptable for use in household kitchen appliances such as cooking appliances or countertops.

[0095] The scratch resistance of the examples and counterexamples was assessed by fingernail rubbing according to the following protocol. A fingernail is rubbed across the surface of the glass-ceramic article. The surface of the glass-ceramic article is then placed under white light illumination with an intensity of 300-400 lux and viewed at a viewing angle of approximately 60°. The visibility of scratches is assessed using the following scale: 1: clearly visible scratches; 0.66: visible scratches; 0.33: barely visible scratches; 0: no visible scratches.

[0096] The results for the examples and counterexamples are in Fig. 7. This graph shows, for each glass-ceramic article, the evolution of the mean value of the degree d of scratch visibility as a function of the asymmetry factor Rsk.

[0097] In Fig.In Figure 7, the examples according to the invention are located to the left of the vertical line L7 (Rsk = -0.2) or, in some advantageous embodiments, to the left of the vertical line L8 (Rsk = -0.3) or L9 (Rsk = -0.5). The counterexamples are located to the right of the vertical line L7.

[0098] Fingernail scratches in the examples according to the invention (Rsk < - 0.2) are barely visible or, if the Rsk is less than -0.5, even invisible.

[0099] These examples and counterexamples clearly show that a glass-ceramic article according to the invention and some of its advantageous embodiments have all the above-mentioned advantages. Reference listPatent literature JP 2007170754 NIPPON ELECTRIC GLASS CO [JP] 05.07.2007. WO 2013 / 190230 A1 EUROKERA [FR] 27.12.2013. WO 2011 / 137144 A1 CORNING INC [US] November 3, 2011. WO 2014 / 070869 A1 CORNING INC [US] September 9, 2013. WO 2016 / 138051 A1 CORNING INC [US] September 1, 2016. WO 2018 / 093844 A1 CORNING INC [US] May 24, 2018 WO 2021 / 121846 A1 EUROKERA [FR] 24.06.2021. EP 0 437 228 A1 CORNING FRANCE [FR] July 17, 1991 WO 2012 / 156444 A1 EUROKERA [FR] 22.11.2012. Non-patent literature Geometrical product specifications - Surface texture: Stylus method - Terms, definitions and characteristics of surface texture, International Standard ISO 4287:1997. Glass in building - Determination of luminous and radiation characteristics of glazing, European Standard EN 410:1998. Colorimetry - Part: CIE 1976 L*a*b* color space, International Standard ISO / CIE 11664-4:2019. Determination of the reflectometer value of coatings (except metallic coatings) at 20°, 60° and 85°, European standard ISO 2813:1999. Plastics - Determination of opacity of transparent materials ISO 14782:1999. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] JP 2007170754 [0010, 0099] WO 2011 / 137144 A1 [0011, 0099] WO 2013 / 190230 A1 [0012, 0099] WO 2014 / 070869 A1 [0013, 0099] WO 2016 / 138051 A1 [0014, 0099] WO 2018 / 093844 A1

[0015] WO 2021 / 121846 A1 [0016, 0099] WO 2012 / 156444 A1 [0067, 0099] Cited non-patent literature

[0000] ISO / CIE 11664-4 :2019 [0032, 0075, 0099] EN ISO 2813:1999 [0033, 0075] ISO 14782:1999 [0034, 0075]

Claims

[1] A flat glass-ceramic article for a cooking appliance, the article comprising a first major surface, a second major surface and a rim, and characterized by is that all or part of at least one of the two main surfaces has an intrinsic texturing whose hybrid root mean square roughness Rdq is between 4.4° and 11°. [2] Glass-ceramic article according to claim 1 such that the hybrid root mean square roughness Rdq is between 5.5° and 9°. [3] Glass-ceramic article according to one of claims 1 to 2, such that the intrinsic texturing has an average pitch roughness Rsm of more than 0.2 mm, preferably more than 0.27 mm. [4] Glass-ceramic article according to one of claims 1 to 3, such that it has a luminosity L* of less than or equal to 25, preferably less than or equal to 20. [5] Glass-ceramic article according to one of claims 1 to 4 such that the intrinsic texturing has an asymmetry factor Rsk of less than -0.2, preferably less than -0.3, preferably less than -0.

5. [6] Glass-ceramic article according to one of claims 1 to 5, such that the gloss at 60° is less than 20, preferably less than 10. [7] Glass-ceramic article according to one of claims 1 to 6, such that it further comprises at least one light source for luminous display by projection or transmission onto the work surface forming the screen. [8] Cooking appliance comprising a glass-ceramic plate formed by a glass-ceramic article according to any one of claims 1 to 7.

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