Glass and ceramic products, and methods for manufacturing such products.

Abstract

DEPCT68 Planar glass-ceramic products have a primary surface (first surface), a secondary surface (second surface), and... Of the two main surface edges, at least one surface of a glass-ceramic product has a textured appearance. The hybrid RMS mean square root roughness of the surface is between 4.4 degrees and 11 degrees fabrication. It also relates to the methods used in the production of such glass-ceramic products;

Description

Glass-ceramic article and method of manufacturing such an article

[0001] The invention relates to a flat glass-ceramic article comprising a textured surface which has anti-scratch, anti-adhesion properties for soiling, as well as an aesthetic surface appearance suitable for domestic use. It also relates to a method for manufacturing such a glass-ceramic article. 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 obtained by the heat treatment of a glass capable of forming a glass-ceramic, called "mother glass", in order to crystallize, in a controlled manner, crystals in its volume. This treatment by which a glass partially crystallizes is called "ceramization treatment" 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 fields for their aesthetic qualities and their physicochemical properties, including their low coefficient of thermal expansion and their resistance to thermal shock. They are particularly used in kitchen equipment, especially in the form of plates, for example as a cooking surface in cooking appliances, glass oven walls, and work surfaces in worktops, tables or furniture for the preparation of food products. In these applications, glass-ceramics are generally based on lithium aluminosilicate.

[0004] Depending on their uses, glass-ceramic items can be equipped with a number of accessories, such as controls, sensors and displays, which allow interaction between the user and the devices in which these items are incorporated.

[0005] For example, they may be provided with controls, such as sensitive or optical keys, for actuating and controlling various electrical and / or electronic devices such as heating and / or lighting means. They may also include displays, in particular luminous displays, for the projection, in particular in transmission, of cognitive luminous patterns (for example icons or numbers) representative of values ​​of certain operating parameters of these devices (for example the heating power of a heating device), or relating to the physicochemical state of the article (for example the signaling of a hot zone).

[0006] They can also be equipped with optical and / or thermal sensors allowing, for example, the detection of elements on their surface such as spilled liquid, or the measurement of the surface temperature of the item, and the warning of the user by an audible or visual signal via a display area.

[0007] Interactions, particularly tactile, between the surface of the glass-ceramic item and the user, and the handling of liquid or solid food substances and mechanical preparation instruments (for example, knife blades) cause the appearance of various unsightly traces at the points of contact with the surface, particularly fingerprints. They can also cause soiling such as remains of dried or burnt food substances on the surface of the item or scratches.

[0008] These marks and stains can lead to repeated cleaning by the user using abrasive products, which themselves can cause further scratches. These various problems are particularly significant on glass-ceramic items with dark, matte or glossy work surfaces.

[0009] In order to prevent fingerprints and stains and to limit the appearance or visibility of scratches, it is known to use various organic or inorganic coatings, textured or not, having hydrophobic or oleophobic properties. It is also known to alter the surface of the glass ceramic in order to obtain such properties.

[0010] JP 2007170754 NIPPON ELECTRIC GLASS CO [JP] 05.07.2007 describes a glass-ceramic article comprising a working surface having a roughness of between 0.1 µm and 20 µm in order to give it light-diffusing properties and a milky white appearance. This article is obtained using 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 using chemical etching so as to form a rough surface whose arithmetic roughness value is between 100 nm and 300 nm. The roughness obtained provides an anti-reflective effect.

[0012] WO 2013 / 190230 A1 EUROKERA [FR] 27.12.2013 describes a glass-ceramic article comprising a surface provided with a textured layer, in particular sol-gel. The texture is formed by regular patterns, in particular geometric patterns, the height of which is between 2 and 100 µm.

[0013] WO 2014 / 070869 A1 CORNING INC [US] 09.09.2013 describes a method for manufacturing a glass-ceramic article using chemical etching to modify the surface of the article to a depth of between 0.01 µm and 20 µm. The resulting roughness reduces the gloss.

[0014] WO 2016 / 138051 A1 CORNING INC [US] 01.09.2016 describes a method for manufacturing a glass-ceramic article using two successive chemical attacks so as to form a surface roughness whose average distance between the features of the rough pattern is between 0.5 µm and 25 µm, and their density is between 9,000 and 25,000 features per mm². The chemical attacks are carried out using acidic solutions based on hydrofluoric acid.

[0015] WO 2018 / 093844 A1 CORNING INC [US] 24.05.2018 describes a method for manufacturing a glass-ceramic article comprising a non-planar surface having an arithmetic roughness value between 10 and 2000 nm. The method comprises a step of chemically etching the surface using a hydrofluoric acid solution. The surface roughness provides aesthetic effects, a reduced level of gloss, an anti-reflective effect and an improved haptic sensation.

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

[0017] There remains a need to improve the aesthetic appearance and mechanical resistance to scratching of the surfaces of glass-ceramic items, particularly for dark or black glass-ceramic items.

[0018] Such an article must have optical and physicochemical surface properties compatible with the applications for which it is intended, in particular applications in cooking appliances and / or as a worktop surface. More specifically, it must have anti-scratch, anti-grease, anti-adhesion of soiling and anti-light diffusion properties. It must also have an aesthetic surface appearance suitable for domestic use. Solution to the technical problem

[0019] According to a first aspect of the invention, there is provided a glass-ceramic article 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 hybrid quadratic roughness Rdq is between 4.4° and 11°. Advantageous embodiments are described below.

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

[0021] According to a second aspect of the invention, there is provided a method of manufacturing a glass-ceramic article according to the first aspect of the invention.

[0022] According to a third aspect of the invention, there is provided a cooking device comprising a glass-ceramic plate formed by a glass-ceramic article according to the first aspect of the invention.

[0023] 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 preparing food. Advantages of the invention

[0024] A remarkable advantage of the invention is that, when applied to dark or black glass-ceramic articles, it allows the achievement of a surface gloss level at 60° much lower than 30, or even lower than 25, and a clarity level lower than 23. The article then has a dark matt appearance, meeting the aesthetic requirements for domestic applications.

[0025] For certain advantageous embodiments, the level of blurring is less than 50%, or even 30%. The visibility of the light patterns transmitted by light displays on or through the surface of the glass-ceramic article remains clear for better visual comfort when said article is used in a cooking device.

[0026] Another advantage is that, in certain embodiments, the particular roughness of the glass-ceramic article, roughness intrinsic or inherent to the surface of the glass-ceramic article, does not alter the thermal and mechanical properties of said surface. It allows easy cleaning of any dirt and better resistance to metallic friction.

[0027] represents the evolution of the gloss at 60° of the surface of examples of glass-ceramic articles in accordance with the invention and of counter-examples as a function of their hybrid quadratic roughness.

[0028] represents the evolution of the clarity of the surface of examples of glass-ceramic articles in accordance with the invention and of counter-examples as a function of their hybrid quadratic roughness.

[0029] represents the evolution of the level of blurring of the surface of examples of glass-ceramic articles in accordance with the invention and of counter-examples as a function of their hybrid quadratic roughness.

[0030] represents the evolution of the degree of visibility of scratches on the surface of examples of glass-ceramic articles in accordance with the invention and of counter-examples as a function of their hybrid quadratic roughness and their average spacing roughness.

[0031] represents the evolution of the degree of visibility of metallic friction on the surface of examples of glass-ceramic articles in accordance with the invention and of counter-examples as a function of their average spacing roughness.

[0032] represents the evolution of the anti-adhesion index of soils on the surface of examples of glass-ceramic articles in accordance with the invention and of counter-examples as a function of their hybrid quadratic roughness.

[0033] represents the evolution of the degree of visibility of nail scratches on the surface of examples of glass-ceramic articles in accordance with the invention and of counter-examples as a function of their surface asymmetry factor. Detailed description of embodiments

[0034] Within the scope of the invention, reference is made to the following definitions and conventions.

[0035] Hybrid quadratic roughness, denoted Rdq, is understood to mean the quadratic mean of the local slopes of the surface roughness profile in the sampling length, as defined in section 4.4.1 of ISO 4287. Hybrid quadratic roughness, Rdq, is a dimensionless number. It can also be expressed in angle units, degrees or radians, using the usual trigonometric relationships in the calculation of slopes, in particular the arctan function. In the context of the present invention, it is expressed in degrees.

[0036] By spacing mean roughness, denoted Rsm, is meant the average of the widths of the profile elements in the sampling length, as defined in section 4.3.1 of ISO 4287. By width of a profile element is meant the length of the abscissa axis which is cut by the element, i.e. projection or hollow, of the profile, as defined in section 3.2.12 of ISO 4287. The values ​​are expressed in millimeters.

[0037] By asymmetry factor, Rsk, is meant the quotient of the average of the cubes of height values ​​by the cube of the maximum projection heights in the sampling length, as defined in section 4.2.3 of ISO 4287.

[0038] By intrinsic or inherent texturing of a surface of a glass-ceramic article, we mean the texturing of the glass-ceramic material of the article itself, devoid of any surface coating.

[0039] By glass-ceramic article is meant a composite material, preferably based on aluminosilicate, in particular based on lithium silicate, comprising an amorphous phase in which crystalline phases or crystals are dispersed. It is obtained by the heat treatment of a glass capable of forming a glass-ceramic, called "mother glass", in order to crystallize, in a controlled manner, crystals in its volume.

[0040] By "light transmission", TL, is meant the light transmission, noted TL, as defined and measured and / or calculated in the standard EN 410:1998.

[0041] By color difference, ΔE*, lightness or brightness, L*, and colorimetric coordinates a* and b*, we mean color difference, ΔE*, lightness or brightness, L*, and colorimetric coordinates a* and b* as defined in ISO / CIE 11664-4:2019.

[0042] By "60° gloss" is meant the specular gloss at 60° as described and measured in the standard EN ISO 2813:1999.

[0043] By "blur" is meant blur as defined and measured in ISO 14782:1999.

[0044] According to a first aspect of the invention, there is provided a planar glass-ceramic article 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 hybrid quadratic roughness Rdq is between 4.4° and 11°.

[0045] According to the first aspect of the invention, the glass-ceramic article is flat. It may comprise two substantially parallel main flat surfaces and four lateral surfaces substantially perpendicular to the two main faces, and may in particular be in the form of a glass-ceramic plate.

[0046] The “mother glass” for obtaining the glass-ceramic article can be of any suitable type. According to a preferred embodiment, the mother glass is based on lithium aluminosilicate comprising the following constituents within the weight limits defined in Table 1 below and expressed as mass percentages of the glass:

[0047] Table 1SiO258-75%Al2O316-25%Li2O2-4.5%Na2O0-2%K2O0-2%CaO0-4%MgO0-5%BaO0-5%Z nO0-5%SrO0-5%TiO21-6%ZrO20-3%P2O50-6%B2O30-2%Fe2O30-2%Cr2O30-2%CoO0-2%

[0048] As mentioned above, a remarkable advantage of the first aspect of the invention is to allow the production of a glass-ceramic article meeting the aesthetic requirements for domestic applications such as, for example, a hob or a worktop. In particular, in the case of an initially black or dark glass-ceramic article, the surface gloss level at 60° may be much lower than 30, or even lower than 25, and the clarity level lower than 23.

[0049] According to certain advantageous embodiments, the hybrid quadratic 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 by light displays on or through the surface of the glass-ceramic article remains clear for better visual comfort. The level of blur observed is then less than 50%, or even 30%.

[0050] According to other particular embodiments, the intrinsic texturing may further have an average spacing roughness Rsm greater than 0.2 mm, preferably greater than 0.27 mm. Such texturing makes it possible to increase the surface mechanical resistance and thus reduce the visibility of scratches.

[0051] It is common to use glass-ceramic items as cooking or work surfaces in kitchen appliances. In this type of application, when metal utensils such as pots or pans are moved across their surfaces, these can be particularly stressed. This movement can manifest itself in the form of metallic friction.

[0052] According to certain embodiments, the average spacing 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 have a high resistance to metallic friction, in particular to metallic friction linked to the movement of pans, as well as advantageous chemical and mechanical durability for repeated exposures to food products and heating cycles.

[0053] In addition to exposure to utensils and food products, the surfaces of glass-ceramic articles incorporated in kitchen equipment can also be subject to fingernail friction, particularly when users move their hands over the integrated control panels. According to certain embodiments, the intrinsic texturing can then have an asymmetry factor, Rsk, of less than -0.2, preferably less than -0.3, preferably less than -0.5. It was then surprisingly found that the visibility of traces formed by the movement of nails on the surface of the glass-ceramic article was then reduced.

[0054] The effects and advantages of the invention are particularly marked when the glass-ceramic article is weakly transmissive, poorly diffusing and dark in color (defined by the brightness L*), in particular black or dark brown in color. Preferably, the glass-ceramic article can remain suitable for the transmission display of luminous zones comprising cognitive luminous patterns representative of values ​​of certain operating parameters of associated electrical and / or electronic devices, or relating to the physicochemical state of the article, while masking the underlying elements.

[0055] In this sense, in a particular embodiment of the invention, the glass-ceramic article has a brightness L* of less than or equal to 25, preferably less than or equal to 20. It may also have, initially, that is to say when it is devoid of surface texture, a brightness L* of less than or equal to 25, preferably less than or equal to 20.

[0056] A dark-colored glass-ceramic article may initially have, that is to say when it is devoid of surface texture, an opacity factor of less than 100, and advantageously greater than 93, in particular to allow said display in transmission by underlying sources in one embodiment of the invention or a display by projection.

[0057] The opacity factor is determined by the formula f = 100 - ΔE* where ΔE* is the color difference. The color difference ΔE* can be evaluated by measuring, in reflection, the variations in lightness L* and colorimetric parameters a* and b* of the upper surface of the article when it is placed on an opaque black background and then when it is placed on an opaque white background, in the CIELAB colorimetric system. The color difference ΔE* can be calculated according to the following formula, ΔE* = ((LN*-LB*)² + (aN*-aB*)² + (bN*-bB*)²)½, LB*,aB*,bB* being the lightness and colorimetric coordinates of the first measurement on a white background and LN*,aN*,bN* being those of the second measurement on a black background.

[0058] A black-coloured glass-ceramic article may initially present, i.e. when it is devoid of surface texture, a brightness L* of less than 10, a haze of less than 30%, and a light transmission TL of less than 10% under illuminant D65.

[0059] Preferably, the dark-colored glass-ceramic article initially has, that is to say when it is devoid of surface texture, a parameter value a* of between -0.2 and 1.6 and a parameter value b* of between -1 and 0.6.

[0060] A glass-ceramic article according to the first aspect of the invention allows light patterns transmitted by light displays onto or through the rough surface to remain clear for improved viewing comfort for the user.

[0061] According to certain 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, in particular when the latter is dark or black in color.

[0062] Also, according to certain embodiments, the glass-ceramic article may further comprise at least one light source for light display by projection or transmission onto the surface then forming a screen. The display may, for example, be an LED-type light display, in particular a seven-segment display for displaying alphanumeric characters.

[0063] According to a second aspect of the invention, there is provided a method for manufacturing a glass-ceramic article comprising the following steps:- a heat treatment for ceramizing a glass capable of forming a glass-ceramic, and- a chemical treatment of a surface of said glass before and / or after said heat treatment for ceramizing, the chemical surface treatment being carried out so that after the heat treatment, the hybrid quadratic roughness value Rdq is between 4.4 and 11°, preferably between 5.5 and 9°.

[0064] According to certain advantageous embodiments, the method may further comprise, before the chemical surface treatment, a step of mechanical surface treatment by sandblasting.

[0065] The chemical surface treatment can be carried out before and / or after the ceramic heat treatment. According to a preferred embodiment, the chemical surface treatment is carried out before the ceramic heat treatment. It has been found that the anti-scratch, anti-greasy trace, anti-adhesion of soiling and anti-light diffusion properties are thus further improved.

[0066] According to the invention, the roughness is obtained using a chemical surface treatment of the mother glass of the glass-ceramic article, i.e. before the heat treatment of ceramization of the mother glass allowing the glass-ceramic article to be formed. The roughness values ​​are therefore those of the rough surface of the glass-ceramic article after the ceramization treatment.

[0067] The glass capable of forming a glass-ceramic may preferably be based on aluminosilicate, in particular lithium aluminosilicate.

[0068] The nature of the chemical solution used for treatment, the treatment temperature and its duration depend on the chemical composition of the material forming the mother glass of the glass-ceramic article.

[0069] The method according to the second aspect of the invention makes it possible to impart roughness to the glass-ceramic article over its entire working surface. It is also possible to impart roughness to only a part of the working surface of the glass-ceramic article. This characteristic can be obtained, for example, by applying protective masks to the surface of the mother glass during the chemical and / or mechanical surface treatment so as to create savings on certain areas of said surface.

[0070] In some embodiments, the chemical surface treatment may be a chemical etch using a hydrofluoric acid solution. These embodiments are particularly advantageous for aluminosilicate-based glass-ceramic articles, particularly lithium aluminosilicate.

[0071] According to certain preferred embodiments, the chemical treatment may further comprise a preliminary step, called a surface activation step, before the aforementioned chemical etching. This activation step may consist of a chemical etching using an acid solution comprising hydrochloric acid and hydrofluoric acid at room temperature for at least two minutes.

[0072] The mass content of hydrofluoric acid in the acid solution can advantageously be between 1% and 70% by mass. Generally, if the mass content is less than 1%, the duration of the chemical surface treatment is quite long and not very advantageous in industrial applications. If the mass content is greater than 20%, the chemical surface treatment may be too rapid and difficult to control. The temperature of the solution is preferably less than 40°C, or even 30°C, in order to avoid the chemical surface treatment being too rapid and difficult to control.

[0073] In 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.

[0074] According to a third aspect of the invention, there is provided a cooking device comprising a glass-ceramic hob formed by a glass-ceramic article according to any one of the embodiments of the first aspect of the invention.

[0075] Examples of heating elements for a cooking device may be radiant or halogen burners or induction heating elements.

[0076] According to a fourth aspect of the invention, a glass-ceramic article according to any of the embodiments of the first aspect of the invention may be used as all or part of a worktop for preparing food. The worktop may, for example, be part of a piece of kitchen furniture or as a surface element of a cooking device, said surface element having the function of allowing food to be prepared. Examples

[0077] The following examples and counter-examples were produced using mother glasses for glass-ceramic plates as described in EP 0 437 228 A1 CORNING FRANCE [FR] 17.07.1991 and / or WO 2012 / 156444 A1 EUROKERA [FR] 22.11.2012, and marketed respectively under the brand name KeraBlack Plus®. The thickness of the plates is 4 to 6 mm.

[0078] The roughness was obtained using a mechanical surface treatment of the mother glasses by sandblasting and / or a chemical surface treatment. These two treatments were carried out before the heat treatment of ceramization. When mechanical treatment and chemical treatment are used, these two treatments are successive, that is to say that the mechanical treatment is carried out before the chemical treatment.

[0079] The mechanical sandblasting treatment was carried out according to the parameters described in Table 2.

[0080] Table 2Nature of abrasive grainsSilica, garnet or corundumGrain size150 ≤ D90 ≤ 300 µm100 ≤ D50 ≤ 200 µmGrain flow rate0.5 - 10 g / sGrain projection speed1 - 50 m / sPressure0.5 – 5 bar, preferably between 2 bar and 4 barIncident angle45 - 90°

[0081] The chemical surface treatment was carried out using a hydrofluoric acid-based solution whose constituents are described in Table 3.

[0082] Table 3ConcentrationNH4F, HF0 – 9 mol / LNaF, HF0 – 0.065 mol / LKF, ​​HF0 – 0.013 mol / LHF0.24 – 35 mol / LHCl0 – 12 mol / LH2SO40 – 10 mol / LH2SiF60 – 0.12 mol / LSiO20 – 0.12 mol / LBaSO40-50 g / L

[0083] When the roughnesses are obtained using a mechanical surface treatment followed by a chemical surface treatment, the acid solution comprises at least one of the constituents listed in Table 2. When a chemical treatment alone is used, the acid solution may advantageously comprise at least two constituents listed in Table 2, one of the constituents of which is chosen from NH4F, HF; NaF, HF and KF, HF.

[0084] To obtain different roughness values, the surfaces of the plates were subjected to hydrofluoric acid solutions of different pH by varying the proportions of their constituents within the limits of Table 3, and by heating them to different temperatures between 20°C and 50°C. The surfaces of the plates were exposed for times ranging from 1 min to 90 min.

[0085] For illustrative purposes, the conditions used for the fabrication of certain examples, E1-E5, and certain counterexamples, CE1-CE4, are respectively indicated in Table 4 and Table 5.

[0086] Table 4E1E2E3E4E5E6Acid solution of chemical treatmentHF (mol / L)0.50.57.5151517.5NH4F,HF (mol / L)76.18.8000H2SiF6 (mol / L)0.0600.030.030.030.03BaSO4yesnoyesnoyesnoTemperature (°C)202040505050Time (min)106010202030Chemical activation solutionHCl (mol / L) 0.50.50.50.5HF (mol / L) 0.050.050.050.05Time (min) 2222Temperature (°C)AmbientAmbientAmbientAmbientAmbientAmbientMechanical treatmentNature of abrasive grains Garnet 97-98%Garnet 97-98%Garnet 97-98%Grain size (µm) D90 = 264D50 = 185D90 = 264D50 = 185D90 = 264D50 = 185Pressure (bar) 222

[0087] Table 5CE1CE2CE3CE4Acid solution of chemical treatmentHF (mol / L)1.57.51012.5NH4F,HF (mol / L)5.38.800H2SiF6 (mol / L)0.060.030.030.03BaSO4nonnonnonnonTemperature (°C)20505050Time (min)20302020Chemical activation solutionHCl (mol / L)0.50.50.5HF (mol / L)0.050.050.05Time (min)222Temperature (°C)AmbientAmbientAmbientAmbientMechanical treatmentNature of abrasive grains Garnet 97-98%Garnet 97-98%Garnet 97-98%Grain size (µm) D90 = 264D50 = 185D90 = 264D50 = 185D90 = 264D50 = 185Pressure (bar) 222

[0088] The values ​​of the different roughness parameters, Rdq, Rsm and Rsk were measured using a Mitutoyo SJ401 mechanical probe and evaluated according to ISO 4287 over an evaluation length of 4 mm to 12.5 mm and equipped with a stylus type “12AAC731”.

[0089] The 60° gloss, L* clarity and haze level 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, and. Table 6 and Table 7 show the results of examples E1-E6 and counterexamples CE1-CE4.

[0090] Table 6E1E2E3E4E5E6Rsm (mm)0.0660,1170,0910,4510,4130,608Rdq (°)9.5210,429,778,739,844.36Rsk0.97-0.14-0.31-0.32-0.26-0.39L*21,121,920,514,616,22.2Brightness @ 60°0.82,11,94,7412.1

[0091] Table 7CE1CE2CE3CE4Rsm (mm)0.1260.3540.3950.399Rdq (°)13.9716.5517.3214.74Rsk-0.11-0.19-0.35-0.14L*20.220.023.522.7Brightness @ 60°0.80.61.72.6

[0092] In the, the examples in accordance with the invention are located between the vertical lines L1 (Rdq = 4.4°) and L2 (Rdq = 11°), and, for certain advantageous embodiments between the vertical lines L3 (Rdq = 5.5°) and L4 (Rdq = 9°). The counter-examples are located outside the zone delimited by the vertical lines L1 and L2. The examples in accordance with the invention all have a brightness, B, at 60° of less than 20.

[0093] In the, the examples in accordance with the invention are located between the vertical lines L1 and L2, and, for certain advantageous embodiments, between the vertical lines L3 and L4. The counter-examples are located outside the zone delimited by the vertical lines L1 and L2. The examples in accordance with the invention all have a clarity or brightness, L*, of less than 25, or even less than 20 for the examples located between the vertical lines L3 and L4.

[0094] In the, the examples according to the invention are located between the vertical lines L1 and L2, and, for certain advantageous embodiments, between the vertical lines L3 and L4. The counter-examples are located outside the area delimited by the vertical lines L1 and L2. The examples according to said embodiments of the invention all have a blur level, F, of less than 50%, or even less than 30% for the examples located between the vertical lines L3 and L4.

[0095] The examples and counterexamples were also subjected to various tests to evaluate the anti-scratch and anti-adhesion properties of soils.

[0096] The anti-scratch property was evaluated using the following protocol. The rough surface of the article is placed under a P240 silicon carbide abrasive disc with a pressure of approximately 5 N / cm². The disc is then moved once in this state over a distance of approximately 4 to 5 cm. The rough surface of the glass-ceramic article is then placed under white illumination with a power of 300-400 lux and then observed from an observation angle of approximately 60°. The visibility of scratches is evaluated according to the following degree scale:

[0097] 1: very visible scratches;

[0098] 2: Acceptably visible scratches;

[0099] 3: barely visible scratches;

[0100] 4: no visible scratches.

[0101] The results obtained for the examples and counterexamples are shown in the figure. This graph represents, for each glass-ceramic article, the evolution of the average value of the degree, d, of visibility of the scratches as a function of the value of the hybrid quadratic roughness, Rdq on the abscissa and the average spacing roughness, Rsm, on the ordinate. The degree of visibility, d, is represented by the size of the figures.

[0102] In the, the examples according to the invention are located between the vertical lines L1 and L2, and above the horizontal line H1 (Rsm = 0.2) or H2 (Rsm = 0.27). The examples according 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 counter-examples are located outside the area delimited by the vertical lines L1 and L2, and below or above the horizontal line H1.

[0103] In the area delimited between the vertical lines L1 and L2, and above the horizontal line H1 (Rsm = 0.2), 90% of the examples in accordance with the invention have a degree of visibility of at least 2, i.e. the visibility of the scratches is at least acceptable, or they are not visible. Above the horizontal line H2 (Rsm = 0.27), all the samples have a degree of visibility of at least 2, and more than 50% greater than 3.

[0104] The resistance to metallic friction 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 a back-and-forth motion using several metallic objects such as coins and metal and / or enameled pans. The surface is then cleaned using different detergent products specially designed for cleaning hobs and commercially available, such as those marketed under the VitroClen® or CIF® brand. The degradation of the enameled surface is visually assessed on a scale of 0 to 20; degree 0 corresponds to total degradation of the surface and degree 20 corresponds to a total absence of degradation. In other words, the higher the degree, the more resistant the surface is to metallic friction.

[0105] The results obtained for the examples and counter-examples are shown in the. This graph represents, for each glass-ceramic article, the evolution of the average value of the degree, d, of visibility of metallic friction as a function of the average spacing roughness, Rsm.

[0106] In the, the examples according to the invention are located to the right of vertical line L5 (Rsm = 0.2) or, for certain advantageous embodiments, to the right of vertical line L6 (Rsm = 0.27). The examples according to the invention have a degree of visibility of metallic friction greater than 9, which can be considered acceptable. Preferably, the average spacing roughness can be selected greater than 0.4 in order to obtain a degree of visibility greater than 12 for applications requiring a certain level of resistance to metallic friction.

[0107] The soil anti-adhesion property was evaluated using the following protocol. The glass-ceramic item is first inserted onto a cooking device in which its working surface serves as a cooking surface. It is then subjected to a cycle of four successive soiling-cleaning operations, each comprising a soiling step and a cleaning step. This cycle of four operations is repeated eight times. After these eight repetitions, the surface of the item is cleaned manually with a sponge impregnated with a detergent specially designed for cleaning cooktops and available commercially, for example the detergent marketed under the brand name VitroClen® or CIF®.

[0108] In the first operation, the soiling step consists of pouring rice cooking water onto the vitroceramic item, then covering it with a pan filled with water whose temperature is raised to 100°C for two minutes. The pan is then left to cool naturally to room temperature. Once room temperature is reached, the temperature is raised again to 100°C for two minutes, then the pan is left to cool naturally. At the end of the soiling step, once the water in the pan has cooled to room temperature, the item is cleaned using a scouring sponge soaked in water and detergent (dishwashing liquid). The cleaning is repeated four times.

[0109] In the second operation, the soiling step consists of pouring cooking oil onto the surface of the glass-ceramic item, then covering it with a pan filled with cooking oil, the temperature of which is raised to at least 200°C for three minutes. The pan is then left to cool naturally to room temperature. At the end of the soiling step, once the water in the pan has cooled to room temperature, the cleaning step of the item is carried out using a scouring sponge soaked in water and detergent (dishwashing liquid).

[0110] In the third operation, the soiling step consists of pouring tomato paste onto the surface of the glass-ceramic item, then covering it with a pan filled with water heated to at least 100°C for two minutes. The pan is then left to cool naturally to room temperature. At the end of the soiling step, once the water in the pan has cooled to room temperature, the item is cleaned using a scouring sponge soaked in water and detergent (dishwashing liquid).

[0111] In the fourth operation, the soiling step consists of pouring milk onto the surface of the glass-ceramic item, then covering it with a pan filled with water heated to at least 100°C for two minutes. The pan is then left to cool naturally to room temperature. At the end of the soiling step, once the water in the pan has cooled to room temperature, the item is cleaned using a scouring sponge soaked in water and detergent (dishwashing liquid).

[0112] The degree of soiling is assessed on a scale of 1 to 4 according to the surface's suitability for cleaning. Degree 0 corresponds to a completely cleanable surface; no or few traces remain on the surface after cleaning. Degree 4 corresponds to a non-cleanable surface: traces remain after cleaning.

[0113] The results obtained for the examples and counter-examples are shown in the. This graph represents, for each glass-ceramic article, the evolution of the average value of the degree, d, of visibility of metallic friction as a function of the hybrid quadratic roughness, Rdq.

[0114] In the, the examples according to certain advantageous embodiments are located between the vertical lines L3 and L4. According to these advantageous embodiments, the compliant examples have a degree of soiling strictly less than 3, which is acceptable for applications in domestic kitchen equipment, such as cooking devices or worktops.

[0115] The resistance to fingernail scratches of the examples and counterexamples was assessed 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 illumination with a power of 300-400 lux and observed from an observation angle of approximately 60°. The visibility of the scratches is assessed according to the following scale of degrees:

[0116] 1: very visible scratches;

[0117] 0.66: visible scratches;

[0118] 0.33: barely visible scratches;

[0119] 0: no visible scratches.

[0120] The results obtained for the examples and counter-examples are shown in the figure. This graph represents, for each glass-ceramic article, the evolution of the average value of the degree, d, of visibility of scratches as a function of the asymmetry factor, Rsk.

[0121] In the, the examples in accordance with the invention are located to the left of vertical line L7 (Rsk = -0.2) or, for certain advantageous embodiments, to the left of vertical line L8 (Rsk = -0.3) or L9 (Rsk = -0.5). The counter-examples are located to the right of vertical line L7.

[0122] The nail scratches on the examples in accordance with the invention (Rsk < - 0.2) are barely visible, or even invisible when the Rsk is less than -0.5.

[0123] These examples and counter-examples clearly show that a glass-ceramic article in accordance with the invention, as well as with certain of its advantageous embodiments, has all the advantages mentioned above. List of references Patent literature

[0124] JP 2007170754 NIPPON ELECTRIC GLASS CO [JP] 05.07.2007.

[0125] WO 2013 / 190230 A1 EUROKERA [FR] 27.12.2013.

[0126] WO 2011 / 137144 A1 CORNING INC [US] 03.11.2011.

[0127] WO 2014 / 070869 A1 CORNING INC [US] 09.09.2013.

[0128] WO 2016 / 138051 A1 CORNING INC [US] 01.09.2016.

[0129] WO 2018 / 093844 A1 CORNING INC [US] 24.05.2018

[0130] WO 2021 / 121846 A1 EUROKERA [FR] 24.06.2021.

[0131] EP 0 437 228 A1 CORNING FRANCE [FR] 07.17.1991

[0132] WO 2012 / 156444 A1 EUROKERA [FR] 22.11.2012. Non-patent literature

[0133] Product specification – Surface conditions: Profile method – Terms, definitions and surface condition parameters, International Standard ISO 4287:1997.

[0134] Glass in buildings – Determination of luminous and solar characteristics of glazing, European standard EN 410:1998.

[0135] Colorimetry – Part: L*a*b* color space CIE 1976, International Standard ISO / CIE 11664- 4:2019.

[0136] Determination of specular gloss of non-metallic paint films at 20°, 60° and 85°, European Standard ISO 2813:1999.

[0137] Plastics — Determination of haze for transparent materials, International Standard ISO 14782:1999.

Claims

DEPCT681. Planar glass-ceramic products for cooking utensils, which consist of a primary surface, a secondary surface, and an edge, which are characterized by the fact that all or part of at least one of the two primary surfaces has a textured surface with a hybrid mean root square roughness Rdq between 4.4 degrees and 11 degrees.

2. Glass-ceramic products according to claim 1 until the hybrid mean root square roughness Rdq is between 5.5 degrees and 9 degrees.

3. Glass-ceramic products according to one of the Regarding claims 1 to 2, the product's internal texture exhibits an average roughness (Rsm) greater than 0.2 mm, or ideally greater than 0.27 mm.

4. Any glass-ceramic product under claims 1 to 3, where the product's luminance (L*) is less than or equal to 25, or ideally less than or equal to 20.

5. Any glass-ceramic product under claims 1 to 4, where the internal texture exhibits skewness (Rsk) less than -0.2, or ideally less than -0.3, or ideally less than -0.

5. 6.

7. Glass-ceramic products under any of the claims 1 through 5, until the gloss of 60 degrees is less than or equal to 20, if ideally less than 107. Glass-ceramic products under any of the claims 1 through 6, until the product is further incorporated with at least one light source for emitting light by projection or transmission onto the working surface for screen formation.

8. Methods for the manufacture of glass-ceramic products, in which the method incorporates the following steps: - heat treatment for ceramicization of glass capable of glass-ceramic formation and - chemical treatment of the surface of such glass before and / or after such heat treatment for ceramicization, in which the chemical surface treatment is carried out in such a manner that after the heat treatment, the hybrid mean root square roughness (Rdq) is between 4.4 degrees and 11 degrees, if ideally between 5.5 degrees and 9 degrees.

9. Methods under claim 8, until the method incorporates, before the chemical surface treatment, a step of mechanical surface treatment by sandblasting. 10.

11. Any of the methods under claims 8 to 9, until the chemical treatment procedure is carried out prior to the ceramicization procedure.

12. Any of the methods under claims 8 to 10, until the chemical surface treatment is chemical etching with a hydrofluoric acid solution.

13. Any of the methods under claim 11, until the hydrofluoric acid solution contains sodium fluoride, potassium fluoride, ammonium fluoride, barium sulfate, hydrochloric acid and / or sulfuric acid, alone or in combination.

14. Cooking equipment incorporating a glass-ceramic cooking hob formed by any of the glass-ceramic products under claims 1 to 7.

15. Use of any of the glass-ceramic products under claims 1 to 7 as the whole or as part of the upper surface of kitchen furniture for food preparation.

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