Glass ceramic articles and methods of making such articles

Abstract

A planar glass ceramic article has 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 intrinsic texture having a mixed root mean square roughness (RMS) of 4.4 DEG to 11 DEG. The invention also relates to a manufacturing method for obtaining such a glass ceramic article.

Description

Technical Field

[0001] The present invention relates to planar glass-ceramic articles comprising a textured surface having anti-scratch, anti-staining properties and an aesthetically pleasing surface appearance suitable for domestic use. The present invention also relates to a method for making such a glass-ceramic article. Technical Background

[0002] Glass ceramic material is a composite material comprising an amorphous phase (a crystalline phase or crystals are dispersed therein). It is usually obtained by heat treating a glass suitable for forming glass ceramics (referred to as "mother glass") so that the crystals are crystallized in a controlled manner in its volume. This process of partially crystallizing the glass is called "ceramic treatment" or simply "ceramicization". The final physicochemical properties of glass ceramics depend on the composition and ceramic treatment of the mother glass.

[0003] Glass ceramics are popular in many fields for their aesthetic qualities and their physical / chemical properties, in particular their low coefficient of thermal expansion and their resistance to thermal shock. They are particularly used in kitchen appliances in the form of cooktops, for example as cooking surfaces in cooking appliances, glazed oven walls and working surfaces in tables, tables or furniture for preparing food. In these applications, glass ceramics are usually based on lithium aluminosilicates.

[0004] Depending on their use, glass-ceramic articles may be equipped with a variety of accessories, such as controls, sensors and displays, which enable the user to interact with the devices into which these articles 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 luminous displays, for projecting (in particular in a transmissive manner) certain operating parameter values ​​of these devices (such as the heating power of a heating device) or cognitive luminous patterns (such as icons or numbers) related to the physico-chemical state of the article (such as signaling a hot zone).

[0006] They may also be equipped with optical and / or thermal sensors in order, for example, to detect elements on their surface (such as spilled liquid) or to measure the surface temperature of the article and to warn the user by an acoustic or visual signal via a display area.

[0007] The interaction between the glass-ceramic surface and the user, especially the tactile interaction, as well as the handling of liquid or solid food substances and mechanical preparation tools (e.g. blades), leads to various unsightly marks, especially fingerprints, at the points of contact with the surface. They may also cause soiling, such as residues of dried or burnt food on the surface of the product, or scratches.

[0008] These marks and dirt may cause the user to repeatedly clean with abrasive products, which in turn may cause more scratches. These problems are particularly severe on glass ceramic products with dark, matte or glossy work surfaces.

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

[0010] JP 2007170754 NIPPON ELECTRIC GLASS CO [JP] filed on 05 July 2007 describes a glass ceramic article comprising a working surface having a roughness of 0.1 μm to 20 μm to impart light scattering 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] filed on November 03, 2011 describes a method for manufacturing a glass ceramic article using etching to form a rough surface with an arithmetic roughness value of 100 nm to 300 nm. The resulting roughness provides an anti-reflective effect.

[0012] WO 2013 / 190230 A1 EUROKERA [FR] filed on 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 a regular pattern, in particular a geometric pattern, the height of which is between 2 and 100 μm.

[0013] WO 2014 / 070869 A1 CORNING INC [US] filed on September 9, 2013 describes a method of manufacturing a glass ceramic article using etching to modify the surface of the article to a depth of 0.01 μm to 20 μm. The resulting roughness reduces the gloss.

[0014] WO 2016 / 138051 A1 CORNING INC [US] filed on September 1, 2016 describes a method for manufacturing a glass ceramic article using two consecutive chemical etchings to form a surface roughness, wherein the average distance between features of the roughness pattern is 0.5 μm to 25 μm and the density is 9,000 to 25,000 features / mm 2 . Chemical etching is performed using a hydrofluoric acid based acid solution.

[0015] WO 2018 / 093844 A1 CORNING INC [US] filed on May 24, 2018 describes a method for manufacturing a glass ceramic article comprising a non-planar surface having an arithmetic roughness value of 10 to 2000 nm. The method comprises the step of etching the surface with a hydrofluoric acid solution. The surface roughness provides aesthetic effects, reduced gloss, anti-reflective effects and improved tactile feel.

[0016] WO 2021 / 121846 A1 EUROKERA [FR] filed 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. SUMMARY OF THE INVENTION

[0018] Technical issues

[0019] There remains a need to improve the aesthetic appearance and mechanical scratch resistance of glass-ceramic surfaces, particularly for dark or black glass-ceramic articles.

[0020] Such articles must have optical and physico-chemical surface properties compatible with their intended use, in particular in cooking appliances and / or as worktop surfaces. More specifically, they must have anti-scratch, anti-oil, anti-stain and anti-light scattering properties. They must also have an aesthetically pleasing surface appearance suitable for domestic use.

[0021] Solutions to technical problems

[0022] According to a first aspect of the present invention, a glass ceramic article is provided, comprising 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 texture, and the mixed root mean square roughness Rdq of the intrinsic texture is 4.4° to 11°. Other advantageous embodiments are described below.

[0023] According to the invention, the rough texturing is intrinsic to the surface of the glass-ceramic article, ie the surface roughness comes from the surface itself without the addition of any surface coating.

[0024] 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.

[0025] According to a third aspect of the present invention, there is provided a cooking device comprising a glass ceramic cooktop formed from the glass ceramic article according to the first aspect of the present invention.

[0026] According to a fourth aspect of the present invention, the glass-ceramic article according to the first aspect of the present invention is used as all or part of a work surface for food preparation.

[0027] Advantages of the present invention

[0028] A significant advantage of the present invention is that, when applied to dark or black glass-ceramic articles, it is able to achieve a surface gloss level at 60° that is much less than 30, or even less than 25, and a brightness level that is less than 23. The article thus has a dark matte appearance that meets the aesthetic requirements of household applications.

[0029] In some advantageous embodiments, the haze level is less than 50%, or even 30%.When the article is used in a cooking device, the visibility of the light pattern transmitted by the light emitting display on or through the surface of the glass ceramic article remains clear to improve visual comfort.

[0030] Another advantage is that, in some embodiments, the specific roughness of the glass-ceramic article (which is inherent to the surface of the glass-ceramic article) does not change the thermal and mechanical properties of the surface. It allows easy removal of any dirt and is more resistant to metal wear.

[0031] BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 The evolution of the surface gloss at 60° of the examples and comparative examples of glass-ceramic articles according to the invention based on their mixed RMS roughness is shown.

[0033] Figure 2 The evolution of the surface lightness of examples and comparative examples of glass-ceramic articles according to the invention based on their mixed RMS roughness is shown.

[0034] Figure 3 The evolution of the surface haze level of examples and comparative examples of glass-ceramic articles according to the present invention based on their mixed RMS roughness is shown.

[0035] Figure 4 The evolution of the surface scratch visibility of examples and comparative examples of glass-ceramic articles according to the invention based on their mixed RMS roughness and their mean pitch roughness is shown.

[0036] Figure 5 The evolution of the metal friction mark visibility of the examples and comparative examples of glass-ceramic articles according to the invention based on their average pitch roughness is shown.

[0037] Figure 6 The evolution of the anti-adhesion index of dirt on the surfaces of the examples and comparative examples of glass-ceramic articles according to the invention based on their mixed root mean square roughness is shown.

[0038] Figure 7 The evolution of the visibility of fingernail scratches on the surfaces of examples and comparative examples of glass-ceramic articles according to the invention as a function of their surface deflection is shown.

[0039] Detailed description of implementation plan

[0040] In the context of the present invention, reference is made to the following definitions and conventions.

[0041] The mixed root mean square roughness (expressed as Rdq) refers to the root mean square of the local slope of the surface roughness profile over the sampling length as defined in Section 4.4.1 of ISO 4287. The mixed root mean square roughness Rdq is a dimensionless number. It can also be expressed in units of angle (degrees or radians) using trigonometric relationships commonly used in slope calculations, in particular the inverse tangent function. For the purposes of the present invention, it is expressed in degrees.

[0042] The mean spacing roughness (denoted as Rsm) is the average value of the widths of the surface roughness profile elements in the sampling length as defined in section 4.3.1 of ISO 4287. The width of a profile element is understood to be the length of the x-axis that intersects a profile element (i.e. a protrusion or a depression) as defined in section 3.2.12 of ISO 4287. The value is expressed in millimeters.

[0043] The skewness (denoted as Rsk) is the quotient of the mean of the cubes of the height values ​​in the sampling length as defined in ISO 4287, section 4.2.3, divided by the cube of the maximum protrusion height.

[0044] Intrinsic or intrinsic 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.

[0045] A glass-ceramic article is a composite material, preferably based on aluminosilicates, in particular on lithium silicates, which comprises an amorphous phase in which a crystalline phase or crystals are dispersed. It is obtained by heat treating a glass suitable for forming a glass-ceramic (called "mother glass") so that the crystals crystallize in a controlled manner in its volume.

[0046] “Light transmittance” TL is understood to mean the light transmittance as defined in standard EN 410:1998 and measured and / or calculated, denoted TL.

[0047] The color deviation ΔE*, lightness or brightness L*, and chromaticity coordinates a* and b* refer to the color deviation ΔE*, lightness or brightness L*, and chromaticity coordinates a* and b* as defined in ISO / CIE 11664-4:2019.

[0048] "60° gloss" refers to specular gloss at 60° as described and measured in EN ISO 2813:1999.

[0049] "Haze" means haze as defined and measured in ISO 14782:1999.

[0050] According to a first aspect of the present invention, a flat glass-ceramic product 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 texture, and the mixed root mean square roughness Rdq of the intrinsic texture is 4.4° to 11°.

[0051] According to a first aspect of the present invention, the glass ceramic article is planar, may comprise two substantially parallel planar main surfaces and four side surfaces substantially perpendicular to the two main surfaces, and may take the form of a glass ceramic cooktop.

[0052] The "mother glass" used for the glass-ceramic article can be of any suitable type. According to a preferred embodiment, the mother glass is based on lithium aluminosilicate, which contains the following components within the weight limits defined in Table 1 below and expressed as weight percentages of the glass:

[0053] [Table 1]

[0054] Table 1 <![CDATA[SiO2]]> 58-75％ <![CDATA[Al2O3]]> 16-25％ <![CDATA[Li2O]]> 2-4.5％ <![CDATA[Na2O]]> 0-2％ <![CDATA[K2O]]> 0-2％ CaO 0-4％ MgO 0-5％ BaO 0-5％ ZnO 0-5％ SrO 0-5％ <![CDATA[TiO2]]> 1-6％ <![CDATA[ZrO2]]> 0-3％ <![CDATA[P2O5]]> 0-6％ <![CDATA[B2O3]]> 0-2％ <![CDATA[Fe2O3]]> 0-2％ <![CDATA[Cr2O3]]> 0-2％ CoO 0-2％

[0055] As mentioned above, a significant advantage of the first aspect of the present invention is that it enables the achievement of glass-ceramic articles that meet the aesthetic requirements for use in household applications such as, for example, cooktops or countertops. In particular, in the case of glass-ceramic articles that are initially black or dark in color, the surface gloss level at 60° can be well below 30, or even below 25, and the lightness level can be below 23.

[0056] According to some advantageous embodiments, the mixed root mean square roughness Rdq can be 5.5° to 9°. It has been found that when the roughness Rdq is within this range, the visibility of the light pattern transmitted by the light-emitting display on or through the surface of the glass-ceramic article remains clear to improve visual comfort. This results in a haze level of less than 50%, or even 30%.

[0057] In other specific embodiments, the intrinsic texture may further have an average spacing roughness Rsm 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.

[0058] Glass ceramic articles are often used as cooking surfaces or worktops in kitchen equipment. In this type of application, these surfaces may be subject to particular stresses when metal utensils such as pots and pans move over their surfaces. These displacements may in particular take the form of metal friction.

[0059] 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 therefore very advantageously exhibit high resistance to metal friction (especially metal friction associated with the movement of the pan), as well as chemical and mechanical durability that is conducive to repeated exposure to food and heating cycles.

[0060] In addition to being exposed to utensils and food, the surface of the glass-ceramic ware incorporated into the kitchen equipment may also be subjected to fingernail friction, especially when the user's hand moves on the integrated control panel. According to some embodiments, the inherent texture can therefore have a skewness Rsk of less than -0.2, preferably less than -0.3, most preferably less than -0.5. Surprisingly, this reduces the visibility of the marks formed by the movement of the fingernail on the surface of the glass-ceramic ware.

[0061] The effects and advantages of the present invention are particularly significant when the glass-ceramic article is low-transmitting, low-scattering and dark-colored (defined by the lightness L*), especially black or dark brown. Preferably, the glass-ceramic article may still be suitable for a transmissive display of a luminous area containing a cognitive luminescent pattern while shielding the underlying elements, the cognitive luminescent pattern representing certain operating parameter values ​​of the relevant electrical and / or electronic equipment or relating to the physico-chemical state of the article.

[0062] In this sense, in a particular embodiment of the present invention, the glass-ceramic article has a brightness L* less than or equal to 25, preferably less than or equal to 20. It may also have an initial brightness (ie when it has no surface texture) with an L* of 25 or less, preferably 20 or less.

[0063] The dark-colored glass-ceramic article may initially—ie when it has no surface texture—have an opacity factor of less than 100 and advantageously greater than 93, in order in particular to enable the described transmission display or projection display by a light source from below in one embodiment of the invention.

[0064] The opacity factor is determined by the formula f=100-ΔE*, where ΔE* is the color deviation. The color deviation ΔE* can be evaluated in the CIELAB colorimetric system by measuring the changes in the lightness L* and the colorimetric parameters a* and b* of the upper surface of the article in reflection when the article is placed on an opaque black background and then when the article is placed on an opaque white background. The color deviation ΔE* can be calculated according to the following formula: ΔE*=((LN*-LB*) 2 +(aN*-aB*) 2 +(bN*-bB*) 2 )1 / 2, LB*, aB*, bB* are the lightness and chromaticity coordinates of the first measurement on a white background, and LN*, aN*, bN* are the lightness and chromaticity coordinates of the second measurement on a black background.

[0065] The black glass-ceramic article may initially - ie when it has no surface texture - exhibit a lightness L* of less than 10, a haze of less than 30% and a light transmittance TL of less than 10% under illuminant D65.

[0066] Preferably, the dark glass-ceramic article initially - ie when it has no surface texture - has an a* parameter value of -0.2 to 1.6 and a b* parameter value of -1 to 0.6.

[0067] The glass-ceramic article according to the first aspect of the present invention enables a light pattern transmitted by a light-emitting display on or through a rough surface to remain clear, so that the viewing comfort of a user is improved.

[0068] According to some preferred embodiments, the glass ceramic article may have a 60° gloss of 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 in color.

[0069] Thus, according to some embodiments, the glass-ceramic article may further comprise at least one light source for luminous display by projection or transmission on a surface, thus forming a screen. The display may for example be a luminous LED display, in particular a seven-segment display for displaying alphanumeric characters.

[0070] According to a second aspect of the present invention, there is provided a method for manufacturing a glass ceramic product, comprising the following steps:

[0071] - a ceramizing heat treatment of the glass capable of forming a glass-ceramic, and

[0072] - chemically treating the surface of the glass before and / or after the ceramizing heat treatment,

[0073] After the heat treatment, the chemical surface treatment is carried out in such a way that the combined root mean square roughness value Rdq is from 4.4° to 11°, preferably from 5.5° to 9°.

[0074] According to some advantageous embodiments, the method may further comprise, prior to the chemical surface treatment, a mechanical surface treatment step by sandblasting.

[0075] Chemical surface treatment can be carried out before and / or after the ceramic heat treatment. According to a preferred embodiment, chemical surface treatment is carried out before the ceramic heat treatment. It has been found that the anti-scratch, anti-oil, anti-stain and anti-light scattering properties are further improved.

[0076] According to the invention, the roughness is achieved by chemical surface treatment of the mother glass of the glass-ceramic article, ie before the ceramizing heat treatment of the mother glass to form the glass-ceramic article. The roughness values ​​are therefore those of the roughened surface of the glass-ceramic article after the ceramizing treatment.

[0077] Glasses suitable for forming glass ceramics may preferably be based on aluminosilicates, in particular lithium aluminosilicates.

[0078] The type of chemical solution used for the treatment, the treatment temperature and its duration depend on the chemical composition of the material forming the parent glass of the glass-ceramic article.

[0079] The method according to the second aspect of the invention enables roughening of the entire working surface of the glass ceramic article. It is also possible to roughen only part of the working surface of the glass ceramic article. This feature can be achieved, for example, by applying protective masks to the mother glass surface during chemical and / or mechanical surface treatment to produce protective films (resists) on certain areas of the surface.

[0080] 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 aluminosilicates.

[0081] According to some preferred embodiments, before the chemical etching, the chemical treatment may further include a preliminary step called a surface activation step. The activation step may include chemical etching at room temperature using an acid solution containing hydrochloric acid and hydrofluoric acid for at least two minutes.

[0082] The hydrofluoric acid titer of the acid solution can advantageously be 1 wt % to 70 wt % by weight. Generally speaking, if the mass titer is less than 1%, the time required for chemical surface treatment is quite long and is not very advantageous for industrial applications. If the mass titer is higher than 20%, the chemical surface treatment may be too fast and difficult to control. The temperature of the solution is preferably lower than 40° C. or even 30° C. to prevent the chemical surface treatment from being too fast and difficult to control.

[0083] 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.

[0084] According to a third aspect of the present invention, there is provided a cooking device comprising a glass ceramic cooktop formed from the glass ceramic article according to any embodiment of the first aspect of the present invention.

[0085] Examples of heating elements for cooking devices may be radiant or halogen ovens or induction heating elements.

[0086] According to a fourth aspect of the present invention, the glass ceramic article according to any embodiment of the first aspect of the present invention can be used as all or part of a work surface for food preparation. The work surface can be, for example, a component of a kitchen furniture or a part of a surface element of a cooking device, the surface element having the function of enabling food preparation. Example

[0087] The following examples and comparative examples are based on mother glasses for glass ceramic cooktops as described in EP 0 437 228 A1 CORNING FRANCE [FR] filed on July 17, 1991 and / or WO 2012 / 156444 A1 EUROKERA [FR] filed on November 22, 2012, respectively under the trade names KeraBlack Sale. The thickness of this cooktop is 4 to 6mm.

[0088] The roughness is obtained by mechanical surface treatment and / or chemical surface treatment of the mother glass using sandblasting. These two treatments are carried out before the ceramic heat treatment. When mechanical treatment and chemical treatment are used, these two treatments are carried out continuously, i.e. the mechanical treatment is carried out before the chemical treatment.

[0089] Mechanical blasting was performed according to the parameters described in Table 2.

[0090] [Table 2]

[0091]

[0092] The chemical surface treatment was performed using a hydrofluoric acid based solution, the composition of which is described in Table 3.

[0093] [Table 3]

[0094] Table 3 concentration <![CDATA[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 <![CDATA[H2SO4]]> 0–10 mol / L <![CDATA[H2SiF6]]> 0–0.12 mol / L <![CDATA[SiO2]]> 0–0.12 mol / L <![CDATA[BaSO4]]> 0–50 g / L

[0095] When the roughness is obtained by mechanical surface treatment and subsequent chemical surface treatment, the acid solution contains at least one of the components listed in Table 2. When a separate chemical treatment is used, the acid solution may advantageously contain at least two of the components listed in Table 2, wherein one component is selected from NH4F, HF; NaF, HF and KF, HF.

[0096] To obtain different roughness values, the plate surface was subjected to hydrofluoric acid solutions of different pH values, the proportions of its components were varied within the range of Table 3 and heated to different temperatures ranging from 20° C. to 50° C. The cooktop surface was exposed for durations ranging from 1 minute to 90 minutes.

[0097] For illustrative purposes, the conditions used to make some Examples E1-E5 and some Comparative Examples CE1-CE4 are shown in Tables 4 and 5, respectively.

[0098] [Table 4]

[0099]

[0100]

[0101] [Table 5]

[0102]

[0103] The values ​​of the various roughness parameters Rdq, Rsm and Rsk were measured using a Mitutoyo SJ401 mechanical probe equipped with a "12AAC731" type stylus and evaluated according to ISO 4287 over an evaluation length ranging from 4 mm to 12.5 mm.

[0104] The 60° brightness, L* clarity and haze level of the examples and control examples 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 Figure 1 , Figure 2 and Figure 3 Tables 6 and 7 show the results of Examples E1-E6 and Comparative Examples CE1-CE4.

[0105] [Table 6]

[0106] 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 60° glossiness 0.8 2.1 1.9 4.7 4 12.1

[0107] [Table 7]

[0108] 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 60° glossiness 0.8 0.6 1.7 2.6

[0109] exist Figure 1 In the embodiment according to the invention, the examples are located between the vertical lines L1 (Rdq=4.4°) and L2 (Rdq=11°), and in some advantageous embodiments, between the vertical lines L3 (Rdq=5.5°) and L4 (Rdq=9°). The control examples are located outside the area defined by the vertical lines L1 and L2. The examples according to the invention all have a glossiness B at 60° of less than 20.

[0110] exist Figure 2 In the embodiment according to the invention, the embodiment is located between the vertical lines L1 and L2, and in some advantageous embodiments, between the vertical lines L3 and L4. The control example is located outside the area defined by the vertical lines L1 and L2. The embodiments in accordance with the invention all have a lightness or brightness L* less than 25, or even less than 20 for the embodiments located between the vertical lines L3 and L4.

[0111] exist Figure 3 In the embodiment of the invention, the examples are located between the vertical lines L1 and L2, and in some advantageous embodiments, between the vertical lines L3 and L4. The control examples are located outside the area defined by the vertical lines L1 and L2. The examples according to the embodiments of the invention all have a haze level F of less than 50%, or even less than 30% for the examples located between the vertical lines L3 and L4.

[0112] The Examples and Comparative Examples were also subjected to various tests to evaluate their anti-scratch and anti-stain properties.

[0113] The following protocol was used to evaluate the scratch resistance. 2The rough surface of the article is placed under a P240 silicon carbide grinding disc under a pressure of . The disc is then moved once in this state, a distance of about 4 to 5 cm. The rough surface of the glass ceramic article is then placed under white light illumination of 300-400 lux and observed at an angle of about 60°. The visibility of the scratches is scored according to the following grade degree:

[0114] 1: Highly visible scratches;

[0115] 2: Acceptable visible scratches;

[0116] 3; Almost invisible scratches;

[0117] 4: No visible scratches.

[0118] The results obtained for the examples and control examples are shown in Figure 4 The figure shows the evolution of the mean value of the scratch visibility d for each glass-ceramic product based on the value of the mixed root mean square roughness Rdq on the abscissa and on the value of the mean spacing roughness Rsm on the ordinate. The visibility d is represented by the size of the graph.

[0119] exist Figure 4 In the embodiment according to the invention, the embodiment is located between the vertical lines L1 and L2 and above the horizontal line H1 (Rsm=0.2) or H2 (Rsm=0.27). The embodiment complies with 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 control example is located outside the area defined by the vertical lines L1 and L2 and below or above the horizontal line H1.

[0120] In the area between the vertical lines L1 and L2 and above the horizontal line H1 (Rsm=0.2), 90% of the examples according to the invention had a visibility of at least 2, i.e. the visibility of the scratches was at least acceptable, or they were not visible at all. All samples above the horizontal line H2 (Rsm=0.27) had a visibility level of at least 2, and more than 50% had a visibility level greater than 3.

[0121] The metal rubbing resistance of the Examples and Controls was evaluated according to the following protocol. First, the surface of the enameled area of ​​the glass ceramic cooktop was rubbed back and forth continuously with a plurality of metal elements (e.g., coins and metal and / or enameled pans). The surface was then rubbed back and forth using a series of commercially available cleaning agents designed for cooktop cleaning (e.g., those sold under the trade name or The surface is cleaned with a glazed surface cleaner (those sold by ). The deterioration of the glazed surface is visually assessed on a scale of 0 to 20, where 0 corresponds to complete deterioration of the surface and 20 corresponds to the complete absence of deterioration. In other words, the higher the degree, the more resistant the surface is to metal friction.

[0122] The results obtained for the examples and control examples are shown in Figure 5 The figure depicts the evolution of the mean value of the metal friction visibility d based on the mean spacing roughness Rsm for each glass-ceramic product.

[0123] exist Figure 5 , the embodiments consistent with the present invention are located to the right of the vertical line L5 (Rsm=0.2), or in some advantageous embodiments to the right of the vertical line L6 (Rsm=0.27). The embodiments according to the present invention have a metal friction visibility greater than 9, which can be considered acceptable. Preferably, the average pitch roughness can be selected to be greater than 0.4 in order to achieve a visibility greater than 12 for applications requiring a certain level of metal friction resistance.

[0124] The following protocol was used to evaluate the anti-staining properties. The glass ceramic article was first inserted into a cookware, wherein its working surface was used as a cooking surface. It was then subjected to four consecutive cycles of staining-cleaning operations, each operation comprising a staining step and a cleaning step. The cycle of four operations was repeated eight times. At the end of these eight repetitions, the glass ceramic article was soaked with a commercially available cleaning agent designed for cleaning cooktops (e.g., sold under the trade name or The surface of the article is manually cleaned using a sponge using a commercially available cleaning agent.

[0125] In a first operation, the soiling step consists of pouring cooking water over the glass ceramic ware, which is then covered with a pan filled with water, the temperature of which is raised to 100°C for two minutes. The pan is then allowed to cool naturally to room temperature. Once room temperature is reached, the temperature is again raised to 100°C for two minutes, and the pan is then allowed to cool naturally. At the end of the soiling phase, once the water in the pan has cooled to room temperature, the ware is cleaned using a scraper sponge impregnated with water and a detergent (dishwashing liquid). The cleaning is repeated four times.

[0126] In the second operation, the soiling step includes pouring cooking oil on the surface of the glass ceramic article, then covering the glass ceramic article with a pan filled with cooking oil, the temperature of the cooking oil being raised to at least 200° C. for three minutes. The pan is then allowed 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 article is cleaned using a spatula sponge impregnated with water and a cleaning agent (dishwashing liquid).

[0127] In a third operation, the soiling step consists of pouring ketchup on the surface of the glass ceramic ware, which is then covered with a pan filled with water, the temperature of which is raised to at least 100° C. for two minutes. The pan is then allowed 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 ware is cleaned using a spatula sponge soaked with water and a cleaning agent (dishwashing liquid).

[0128] In a fourth operation, the soiling step comprises pouring milk on the surface of the glass ceramic ware, then covering the glass ceramic ware with a pan filled with water, the temperature of the water being raised to at least 100° C. for two minutes. The pan is then allowed 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 ware is cleaned using a spatula sponge impregnated with water and a cleaning agent (dishwashing liquid).

[0129] The degree of soiling is assessed on a scale of 1 to 4, depending on the suitability of the surface for cleaning. Scale 0 corresponds to a completely cleanable surface: little or no residue remains on the surface after cleaning. Scale 4 corresponds to an uncleanable surface: traces remain after cleaning.

[0130] The results obtained for the examples and comparative examples are shown in Figure 6 The figure depicts the evolution of the mean value of the metallic friction visibility d based on the mixed RMS roughness Rdq for each glass-ceramic article.

[0131] exist Figure 6 , examples according to some advantageous embodiments are shown between vertical lines L3 and L4. According to these advantageous embodiments, conforming examples have a staining degree strictly below 3, which is acceptable for applications in household kitchen equipment such as cooking utensils or worktops.

[0132] The nail scratch resistance of the examples and control examples was evaluated according to the following protocol. The fingernail was rubbed on the surface of the glass ceramic article. The surface of the glass ceramic article was then placed under 300-400 lux white light illumination and observed at an angle of approximately 60°. The visibility of the scratches was scored according to the following grade:

[0133] 1: Highly visible scratches;

[0134] 0.66: visible scratches;

[0135] 0.33; Almost invisible scratches;

[0136] 0: No visible scratches.

[0137] The results obtained for the examples and control examples are shown in Figure 7The figure shows the evolution of the mean value of the scratch visibility d as a function of the skewness Rsk for each glass-ceramic article.

[0138] exist Figure 7 In the embodiment, the embodiment according to the present invention is located on the left side of the vertical line L7 (Rsk=-0.2), or in some advantageous embodiments on the left side of the vertical line L8 (Rsk=-0.3) or on the left side of L9 (Rsk=-0.5). The control example is located on the right side of the vertical line L7.

[0139] When Rsk is less than -0.5, the fingernail scratches on the embodiments consistent with the present invention (Rsk<-0.2) are barely visible, or even invisible.

[0140] These examples and comparative examples clearly show that the glass-ceramic articles according to the invention and according to some of its advantageous embodiments possess all the above-mentioned advantages.

[0141] References

[0142] Patent Literature

[0143] JP 2007170754 NIPPON ELECTRIC GLASS CO[JP]07 / 05 / 2007.

[0144] WO 2013 / 190230 A1 EUROKERA[EN]12 / 27 / 2013.

[0145] WO 2011 / 137144 A1 CORNING INC[US]11 / 03 / 2011.

[0146] WO 2014 / 070869 A1 CORNING INC[US]09 / 09 / 2013.

[0147] WO 2016 / 138051 A1 CORNING INC[US]09 / 01 / 2016.

[0148] WO 2018 / 093844 A1 CORNING INC[US]05 / 24 / 2018

[0149] WO 2021 / 121846 A1 EUROKERA[FR]06 / 24 / 2021.

[0150] EP 0 437 228 A1 CORNING FRANCE[FR]07 / 17 / 1991

[0151] WO 2012 / 156444 A1 EUROKERA[EN]11 / 22 / 2012.

[0152] Non-patent literature

[0153] Product specification-Surface finish:Profile method-Surface finishterms, definitions and parameters, international standard ISO 4287:1997.

[0154] Glass in building-Determination of luminous and solar characteristics of glazing, European standard EN 410:1998.

[0155] Colorimetry-Part: CIE 1976L*a*b*Color space, International Standard ISO / CIE 11664-4:2019.

[0156] Determination of specular gloss of non-metallic paint films at 20°, 60° and 85°, European Standard ISO 2813:1999.

[0157] Plastics-Determination of haze for transparent materials, international standard ISO14782:1999.

Claims

1. A planar glass-ceramic article for a cooking device, the 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 texture, and the mixed root mean square roughness Rdq of the intrinsic texture is 4.4° to 11°.

2. The glass-ceramic article according to claim 1, wherein the mixed root mean square roughness Rdq is 5.5° to 9°.

3. The glass-ceramic article according to any one of claims 1 to 2, wherein the intrinsic texture has an average spacing roughness Rsm greater than 0.2 mm, preferably greater than 0.27 mm. 4 . The glass-ceramic article according to claim 1 , wherein the glass-ceramic article has a lightness L* of less than or equal to 25, preferably less than or equal to 20.

5. The glass-ceramic article according to any one of claims 1 to 4, wherein the intrinsic texture has a skewness Rsk of less than -0.2, preferably less than -0.3, preferably less than -0.

5. 6 . The glass-ceramic article according to claim 1 , wherein the 60° glossiness is less than or equal to 20, preferably less than 10.

7. The glass-ceramic article according to any one of claims 1 to 6, further comprising at least one light source for luminous display by projection or transmission onto a working surface forming a screen.

8. A method for manufacturing a glass-ceramic product, the method comprising the following steps: - a ceramizing heat treatment of the glass capable of forming a glass-ceramic, and - chemically treating the surface of the glass before and / or after the ceramizing heat treatment, After the heat treatment, the chemical surface treatment is carried out in such a way that the combined root mean square roughness value Rdq is from 4.4° to 11°, preferably from 5.5° to 9°.

9. The method according to claim 8, so that, before the chemical surface treatment, it comprises a mechanical surface treatment step by sandblasting.

10. A method according to any one of claims 8 to 9, such that the chemical treatment step is performed before the ceramizing step.

11. The method according to any one of claims 8 to 10, wherein the chemical surface treatment is chemical etching using a hydrofluoric acid solution.

12. The method according to 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 according to any one of claims 1 to 7.

14. Use of a glass-ceramic article according to any one of claims 1 to 7 as all or part of a worktop for food preparation.

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