Mineral substrate enamelled thereon and method for its preparation

Abstract

Disclosed is a mineral substrate comprising, on at least one of its surfaces, an inorganic enamel capable of withstanding metal friction. The inorganic enamel has a total roughness less than or equal to 2 μm, and the edges of the inorganic enamel protruding from the surface of the glass-ceramic substrate have a topographic slope value, expressed as a percentage, less than or equal to 1.4%.

Description

Field of the Invention

[0001] The present invention relates to a mineral substrate comprising an inorganic enamel resistant to metal friction on at least one of its surfaces. The present invention also relates to a method for preparing such a substrate. Background of the Invention

[0002] Mineral substrates such as glass-ceramics or colored specialty glasses are popular in many fields because of their aesthetic qualities and their physical / chemical properties, particularly their low coefficient of thermal expansion and their thermal shock resistance.

[0003] They are particularly used in kitchen equipment, particularly in the form of flat substrates, such as cooking surfaces in cooking appliances, vitrified oven walls, and working surfaces in countertops, tables, or furniture for food preparation.

[0004] As an example, in kitchen equipment, glass-ceramics (composite materials containing an amorphous phase with crystalline phases dispersed therein) are mineral substrates that are very widely appreciated because of their very good thermal shock resistance, their very low coefficient of expansion, and their mechanical strength. As cooking surfaces and / or working surfaces in cooking appliances, they are typically based on lithium aluminosilicate and have a dispersion of crystalline phases based on β-quartz and / or β-spodumene in their amorphous matrix.

[0005] Depending on the desired use for the kitchen equipment, the mineral substrate can be combined with electrical and / or electronic devices such as heating and / or lighting devices, and / or be provided with a number of accessories such as controllers, sensors, and displays that allow interaction between the user and the device incorporating these substrates.

[0006] It is common to enamel the surface of the said mineral substrate for decorative purposes and / or to define certain functional zones, such as control, signaling, and / or heating zones for cooking appliances. Enameling is typically carried out using screen printing or inkjet printing methods.

[0007] In the field of mineral substrates used in cooking appliances and / or near cooking appliances, for reasons of durability and aesthetics, the enamel preferably adheres correctly to the substrate (on which it is deposited) and has significant resistance to the mechanical and / or chemical stresses it may undergo under the conditions of using the cooking appliance.

[0008] In particular, an enamel is generally sought that is capable of withstanding repeated exposure to food and / or chemical products as well as mechanical stresses (such as metal friction caused by the repeated movement of kitchen utensils such as pots or pans).

[0009] The prior art provides many examples of enamel compositions, mineral inks, and / or mineral pastes as well as examples of suitable enameling methods.

[0010] FR 2858974 A1 [SCHOTT AG [DE]] 25.02.2005 describes a glass-ceramic cooking surface which is provided with a strongly artificial black decorative effect that is not very rough.

[0011] WO 2016 / 008848 A1 [SCHOTT AG [DE]] 21.01.2016 describes a mineral ink suitable for printing a decorative effect on a glass-ceramic substrate having a low coefficient of thermal expansion. This mineral ink enables the obtaining of an enamel having better resistance to bending and chipping.

[0012] WO 2016 / 110724 A1 [FENZI SPA [IT]] 14.07.2016 describes a mineral ink composition for printing a decorative effect on a glass-ceramic substrate. This mineral ink enables the obtaining of an enamel that is chemically resistant to acids, alkalis and radiation, and mechanically resistant to abrasion and delamination.

[0013] EP 3067334 A1 [SCHOTT AG [DE]] 14.09.2016 describes a decorative enamel for a glass-ceramic substrate which enables the reduction of noise generated by the movement of kitchen utensils on the enamel surface.

[0014] WO 2019 / 219691 A1 [EUROKERA [FR]] 21.11.2019 describes a mineral ink for printing a glass-ceramic substrate. This ink enables the obtaining of an enamel that is resistant to food products, detergents, the combined effects of repeated exposure to these products and heating cycles, and temperatures above 800 °C used during the preparation of the glass-ceramic substrate. Summary of the Invention

[0015] Technical Problem

[0016] Metal friction associated with the repeated movement of kitchen utensils (such as pots or pans) on the surface of a mineral substrate in and / or near a cooking appliance causes metal marks or traces to appear on the decorative enamel. These metal marks or traces are typically metal particles that have been torn from the metal utensil under the influence of repeated friction of the metal utensil on the enamel and have been embedded in the surface of the substrate or the enamel. This phenomenon is particularly evident for soft light-colored metal utensils (such as pots or pans with aluminum or stainless-steel bottoms).

[0017] Over time, these embedded particles ultimately reduce the aesthetic appearance of the enamel, especially for enamel with a low contrast level to the mineral substrate (such as dark or black enamel on a dark or black mineral substrate). In the long run, this aesthetic degradation is not conducive to the positive perception of the product by customers.

[0018] On the other hand, with the development of the so-called "flexible" cooking surface, that is, a surface on which cooking utensils can be placed anywhere to heat them, or in other words, a surface without dedicated heating areas, the utensils move more frequently on the cooking surface. The aesthetic degradation caused by metal friction then becomes more obvious or occurs faster.

[0019] Finally, the accumulation of embedded metal particles, when it becomes particularly visible, leads users to clean the surfaces of the glass-ceramic substrate and the enamel more frequently and forcefully. These cleanings usually aim to make the visible metal imprints and traces disappear. However, the frequency and intensity of these cleanings have the negative result of causing early and significant damage to the enamel. This damage in turn degrades the aesthetic appearance of the decorative enamel and reduces the durability of the cooking surface.

[0020] Therefore, there is a need for a glass-ceramic substrate incorporating decorative enamel that can limit the appearance of metal imprints or traces.

[0021] Solution to the technical problem

[0022] According to a first aspect of the present invention, there is provided a mineral substrate (1001) according to claim 1, and the dependent claims are advantageous embodiments.

[0023] According to a second aspect of the present invention, there is provided a method for preparing a substrate according to the first aspect of the present invention.

[0024] Advantages of the present invention

[0025] A significant advantage of the present invention is a significant reduction in the number of visible metal imprints and traces generated by the repeated frictional action of metal utensils on the enamel. Compared with a glass-ceramic substrate incorporating standard enamel, this reduction can reach 50%, or even 70%, or more.

[0026] A second advantage is that a reduction in the number of visible metal imprints or traces is observed, especially for utensils made of metals with generally the lightest colors (such as aluminum or stainless steel).

[0027] A third advantage is that the reduction in the number of visible metal imprints and traces is particularly significant for decorative enamel with a low contrast level to the mineral substrate (such as dark or black enamel on a dark or black mineral substrate).

[0028] The fourth advantage is that the present invention is easy to implement and can be applied to any chemical composition of enamel.

[0029] Brief Description of the Drawings

[0030] Figure 1 is an orthographic schematic view of a mineral substrate containing enamel.

[0031] Figure 2 is an orthographic schematic view of a cross-section of a mineral substrate containing enamel.

[0032] Figure 3 is an example of the surface profile of an inorganic enamel on a mineral substrate according to the present invention.

[0033] Figure 4 is a schematic view of an example of a pattern formed by an inorganic enamel within the meaning of the present invention.

[0034] Figure 5 is a first example of a 3D representation of a topographic profile according to an embodiment of the present invention.

[0035] Figure 6 is a second example of a 3D representation of a topographic profile according to an embodiment of the present invention.

[0036] Figure 7 is a graph showing the total roughness as a function of the topographic slope according to an embodiment and a counterexample of the present invention.

[0037] Detailed Description of the Embodiments

[0038] Within the meaning of the present invention, "enamel" is understood to mean a vitreous or composite material that typically contains annealed frit, in which fillers, reagents, and / or coloring and / or structural pigments may optionally be dispersed.

[0039] Within the meaning of the present invention, "pattern" is understood to mean a discontinuous decorative grid with a coverage of the given surface of the mineral substrate covered by the pattern that is strictly less than 100%, preferably less than 90%.

[0040] Within the meaning of the present invention, the "coverage rate" of the enamel forming a pattern on a given surface of a mineral substrate is understood to mean the proportion of the given surface covered by the pattern. In other words, it corresponds to the ratio (expressed as a percentage) of the surface covered by the pattern on the given surface.

[0041] According to these last two definitions, a "solid" consisting of a uniform (i.e., continuous) grid and having a 100% coverage of the given surface of the mineral substrate is not a pattern. ​​​​​​​

[0042] In the context of the present invention, "ink coverage" refers to the ink coverage as known and defined in the field of inkjet printing. For a given individual ink, it corresponds to the number of actually printed pixels counted relative to the total number of printable pixels. In the case of inkjet printing, it can depend on the resolution of the printing device used.

[0043] In the context of the present invention, "topographical slope" is understood to refer to the current measured value of the gradient, which is defined as the tangent of the slope between two points on a surface at different elevations, or even as the tangent of the angle of gravity relative to a reference level (usually the horizontal line). This measured value is typically expressed as a percentage.

[0044] In the context of the present invention, "total roughness" is understood to refer to the total roughness designated as Rt as defined in section 4.1.5 of the ISO 4287:1997 standard. It is defined as the sum of the maximum profile peak height Zp and the maximum profile valley depth Zv over the sampling length of the profile.

[0045] As an illustrative example, referring to Figure 1 , the mineral substrate 1001 (such as those used as the surface of a cooking device) comprises the mineral substrate 1001 which is itself provided with an inorganic enamel 1002 on at least one of its surfaces. In Figure 1 , the enamel 1002 is shown in the form of lines forming a patterned portion. It can form any suitable pattern.

[0046] An example of the pattern is in the form of a square periodic pattern with sides of approximately 1.25 mm, having a thickness between 1 μm - 3 μm and a pitch of 0.75 mm. The coverage of the inorganic enamel on the surface of the substrate is 40%.

[0047] According to a first aspect of the present invention, referring to Figure 1 and in Figure 2 , the mineral substrate 1001 forms a pattern comprising an inorganic enamel 1002 on at least one of its surfaces, characterized in that:

[0048] - the inorganic enamel 1002 has a total roughness Rt of its surface 1002 - S of less than or equal to 2 μm, and

[0049] - the edges 1002a, 1002b of the inorganic enamel 1002 protruding from the surface 1001 - S of the mineral substrate 1001 have a topographical slope value expressed as a percentage of less than or equal to 1.4%.

[0050] Without being bound by the theory or practical considerations of the present invention, a possible explanation for the significant advantages provided by the present invention could be that, in the case of inorganic enamel, the synergistic effect between a total surface roughness of less than 2 μm and a topographical slope of less than 1.4% enables the improvement of the sliding of metal utensils, particularly soft metals, on the surface of the inorganic enamel, and thus reduces the risk of tearing off metal particles.

[0051] According to the foregoing definition, the topographical slope corresponds to the tangent value of the gradient of the edges 1002a, 1002b of the inorganic enamel 1002 (which forms a pattern protruding from the surface 1001-S of the mineral substrate 1001). In other words, referring to Figure 2 , which corresponds to the tangent value: height change / distance of the height change, that is, for the height difference h between the surface 1001-S of the mineral substrate 1001 and the upper surface 1002-S of the inorganic enamel 1002 divided by the ratio h / l of the distance l between the two points considered for this height difference. Expressed as a percentage, the ratio h / l is multiplied by 100.

[0052] The topographical slope of the organic enamel forming the pattern can vary depending on the method and parameters of its deposition on the surface of the mineral substrate, with the thickness of the organic enamel, its chemical composition, and / or the size of the particles of the mixture (such as a mixture of mineral frit and / or mineral pigment) used to form it, particularly their combination. However, these characteristics are not sufficient to individually define a given topographical slope value. In other words, two inorganic enamels with the same composition, which have been obtained with the same mixture and have the same thickness, can have different topographical slopes, depending on how they are deposited on the mineral substrate.

[0053] The upper surface 1002-S of the inorganic enamel 1002 is generally the largest surface and is substantially parallel to the surface 1001-S of the mineral substrate 1001.

[0054] The gradient angle (expressed in radians) is the angular representation of the topographical slope. The gradient angle α then corresponds to the value obtained by applying the inverse function of the tangent function (denoted as arctan or tan -1 ) to the ratio h / l, that is

[0055]

[0056] Multiplying this ratio by 180 / π allows the conversion of the angle to degrees.

[0057] The value of the topographic slope is preferably the arithmetic mean of individual topographic slope values measured at different locations or positions of the edges 1002a, 1002b of the inorganic enamel 1002 protruding on the surface 1001-S of the mineral substrate 1001.

[0058] The enamel forming the pattern generally has the function of a decorative and / or functional coating deposited on the surface of the mineral substrate, for decorative, signaling and / or delineation purposes, in particular for delineating certain functional zones, such as, for example, the heating and / or control zones of a cooking device or a worktop.

[0059] Various methods of over-enameling, also known as glazing or more simply decorative methods, and the compositions of mineral or enamel pastes, inks or coatings for the purposes of said over-enameling methods are known from the prior art, in particular in the field of enamels for mineral substrates such as glass-ceramics.

[0060] The enamel is generally obtained by heat-treating a paste, ink or mineral or ceramic coating deposited on the surface of the mineral substrate using a suitable method, such as, for example, by screen printing or inkjet printing.

[0061] The paste, ink or mineral or ceramic coating contains a solid mineral phase that is comminuted and dispersed in a somewhat viscous organic medium. This organic medium allows the solid phase to be applied using a suitable deposition method. It also has the function of suspending and / or dispersing the mineral phase to ensure its uniform and consistent distribution in the decorative, signaling and / or delineation zones.

[0062] The mineral substrate 1001 can be any mineral substrate capable of withstanding the stress of metal utensils, in particular a mineral substrate capable of being used in an environment where kitchen utensils are used, such as, for example, as the surface of a worktop and / or a device and / or a cooking unit.

[0063] In some embodiments, the mineral substrate 1001 can be a glass-ceramic substrate or a mineral glass substrate. By way of example, it can be any type of glass-ceramic suitable for use as the surface of a worktop and / or a device and / or a cooking unit, such as a lithium aluminosilicate-based glass-ceramic. It can also be any type of mineral glass, optionally tempered, suitable for the same applications, such as borosilicate or aluminosilicate glass.

[0064] According to the invention, the value of the total surface roughness of the inorganic enamel 1002 is less than or equal to 2 μm. For certain inorganic enamel compositions, lower total roughness values can be achieved. Thus, in certain advantageous embodiments, the value of the total surface roughness can be less than or equal to 1.5 μm, preferably less than or equal to 1 μm. It has been observed that a reduction in the total surface roughness can further reduce the visibility of metal imprints and traces.

[0065] According to the present invention, the topographic slope value of the edges 1002a, 1002b of the inorganic enamel 1002 protruding from the surface 1001-S of the glass-ceramic substrate 1001 is less than or equal to 1.4%. For certain inorganic enamel compositions 1002, lower values can be achieved. Thus, in certain advantageous embodiments, the value of the topographic slope can be less than or equal to 1.2%. It has been observed that the reduction of the topographic slope can further facilitate the sliding of the metal object or utensil on the inorganic enamel, and thus make it possible to further reduce the visibility of the metal imprints and traces.

[0066] Due to the reduction of the visibility of the metal imprints or traces allowed by the present invention, the thickness of the inorganic enamel can be advantageously reduced, because the need to compensate for the possible damage to the enamel caused by the embedding of metal particles and / or by repeated cleaning by the user is less important or even non-existent.

[0067] Thus, in certain embodiments, the thickness of the inorganic enamel 1002 can be advantageously between 1.5 μm and 3.5 μm, or even between 1.5 μm and 2 μm.

[0068] For the inorganic enamel 1002 having a low contrast level with the mineral substrate 1001, the metal imprints and traces thereof are significantly reduced, regardless of whether it has a dark appearance, particularly a black appearance, or a light appearance, such as a white appearance. Thus, in a particularly advantageous embodiment, the relative luminance difference ΔL*, which is defined as the difference between the luminance L*(enamel / substrate) measured in reflection of the inorganic enamel 1002 on the mineral substrate 1001 and the luminance L*(substrate) measured in reflection of the mineral substrate 1001 without the inorganic enamel 1002, is at most 50, preferably at most 35. It can particularly be between 2 and 45, optionally between 5 and 35, and these values correspond to an inorganic enamel 1002 having a relatively low contrast with respect to the mineral substrate 1001.

[0069] The relative luminance difference ΔL* can also be expressed in the form of the following equation:

[0070]

[0071] The term "luminance" is understood to refer to the luminance expressed as L*, as defined and measured in the ISO 11664-4 standard. The luminance of the mineral substrate 1001 (expressed as L*(substrate)) is measured in reflection. The luminance of the inorganic enamel 1002 deposited on the mineral substrate 1001 (expressed as L*(enamel / substrate)) is measured in reflection.

[0072] In a cooking appliance or worktop, a mineral substrate having a low contrast difference with inorganic enamel is generally a substrate with a dark appearance, optionally black, weak light transmittance, and low scattering. Also in certain embodiments, the light transmittance Tl of the mineral substrate 1001 is at most 17%, preferably not more than 10%, or even not more than 5%. A black mineral substrate (such as non-opaque standard black glass-ceramics) has a light transmittance of less than 5%, particularly between 0.2% and 2%.

[0073] "Light transmittance" is understood to refer to the light transmittance expressed as Tl as defined and measured in section 4.2 of standard EN410:1999 using light source D65 and a standard observer.

[0074] In certain specific embodiments, for a black mineral substrate, the luminance L*(substrate) of the mineral substrate 1001 measured in reflection can further be less than or equal to 5, preferably less than or equal to 2. A black mineral substrate (such as, for example, the glass-ceramics sold by Eurokera under the name or has such a luminance level.

[0075] One of the advantages of the present invention is to facilitate the sliding of metal utensils, particularly soft metals, on the surface of the inorganic enamel, and thus reduce the risk of tearing off metal particles.

[0076] In an advantageous embodiment, the coefficient of friction (also known as the static and / or kinetic coefficient of friction) of the surface of the mineral substrate (1001) provided with the inorganic enamel (1002) is at most 0.30, preferably at most 0.25. A mineral substrate according to the present invention having such a static and / or kinetic coefficient of friction value generally has optimal performance in reducing the number of visible metal imprints and marks generated by the repeated friction action of the metal utensils.

[0077] The coefficient of friction is understood to refer to the static and / or kinetic coefficient of friction as defined in standards ASTM D1894, ISO 8295:1995, and ISO 15359:1999.

[0078] The static coefficient of friction is defined as the ratio between the static frictional force (i.e., the force required to initiate the slip of one surface on another) and the force applied perpendicularly to the two surfaces to maintain their contact and sliding.

[0079] The kinetic coefficient of friction is defined as the ratio between the kinetic frictional force (i.e., the force required to maintain the slip of one surface on another) and the force applied perpendicularly to the two surfaces to maintain their contact and sliding.

[0080] The static and / or dynamic coefficient of friction of the surface of the mineral substrate (1001) provided with the inorganic enamel (1002) is understood to mean the static and / or dynamic coefficient of friction that can be measured on the surface of the mineral substrate (1001) on which the inorganic enamel (1002) is present).

[0081] The mineral substrate 1001 according to any of the described embodiments can advantageously be used as the surface of a cooking device (in particular an induction cooking device with a so-called "flexible" surface) or a workbench (in particular a workbench in furniture equipment such as a table or a work cabinet for food preparation).

[0082] According to a second aspect of the present invention, there is provided a method for preparing a mineral substrate 1001 according to any one of the foregoing embodiments, the method comprising the step of depositing an inorganic enamel 1002 by inkjet printing a mineral ink onto the mineral substrate 1001, wherein the ink coverage is at least 45% and at most 85%, and the weight percentage of the solid portion in the mineral ink for inkjet printing is at most 40% of the mineral ink.

[0083] By way of illustrative example, for an inkjet printing task at 800 dpi, the number of printable pixels on a one-square-inch square pattern is 640,000 pixels. For a given single ink, if only 200,000 pixels are actually printed, the ink coverage (for this given single ink) is 200,000 / 640,000, or expressed as a percentage 31.5%.

[0084] If multiple individual inks are used, such as inks of different colors, the ink coverage is the sum of the ink coverages of each of these individual inks.

[0085] The viscosity of the ink (usually between 20 Pa·s and 100 Pa·s) and the volume of the ink droplets (usually between 12 pL and 84 pL) can also affect the ink coverage. Very fluid inks and / or large-volume droplets can result in a greater coverage of the printed surface, particularly by covering those peripheral pixels actually printed by the inkjet printing device at the selected resolution. These parameters are typically taken into account by the inkjet printing device when the ink coverage is defined.

[0086] "Mineral ink" is understood to mean a mineral ink suitable for depositing enamel by inkjet printing. Mineral inks are typically in the form of a suspension or colloidal dispersion of finely divided solid mineral phases in a usually organic liquid phase. The solid mineral phase of the colloidal suspension typically comprises a frit and optionally a mineral pigment.

[0087] The mineral ink has a density, viscosity and surface tension compatible with the inkjet printing method. The values of these parameters depend on the inkjet printing equipment used and affect the quality of the decorative pattern obtained.

[0088] The particles forming the solid mineral phase usually have a size in the micron range, or even in the submicron range. The liquid phase mainly contains a solvent, usually an organic solvent. The type and amount of the solvent partly affect the rheological properties, surface tension and drying behavior of the mineral ink. A dispersant can also be added to prevent flocculation and / or sedimentation of the solid phase, and a surfactant can be added to adjust the surface tension of the mineral ink.

[0089] The weight ratios of the organic solvent, dispersant, surfactant and frit can be adjusted so that the properties of the mineral ink are suitable for the equipment used for inkjet printing. The organic solvent usually accounts for 80% by weight of the mixture of the organic solvent, dispersant and surfactant of the mineral ink. The type and amount of the organic solvent can be adjusted according to the technical and preparation limitations of the inkjet printing equipment used.

[0090] In order to form an enamel using the mineral ink deposited by inkjet printing, the temperature at which the mineral ink is dried can be between 25°C and 180°C. The firing heat treatment temperature of the precursor glass for enameling can be equal to or greater than 650°C. Preferably, this temperature does not exceed 1100°C.

[0091] The organic solvent can be an organic compound that is liquid at room temperature or a mixture of organic compounds that are liquid at room temperature, and the organic compound contains at least one alcohol functional group.

[0092] The choice of the organic compound containing the alcohol functional group depends on the method and / or equipment used for inkjet printing. If the deposition of the mineral ink on the mineral substrate is slow, it is advantageous to use a solvent or a mixture of solvents having a low saturation vapor pressure under the pressure and temperature conditions of the method and / or equipment. In other words, under standard temperature and pressure conditions, in order to prevent the solvent or the solvent mixture from evaporating too fast, its boiling point can be higher.

[0093] Non-limiting examples of organic solvents are: methylene glycol, ethylene glycol, propylene glycol, butylene glycol, methanol, ethanol, propanol, butanol, glycol ethers such as propylene glycol methyl ether or dipropylene glycol methyl ether.

[0094] The dispersant is preferably a copolymer or a mixture of copolymers containing at least one acid functional group. The dispersant enables the prevention of flocculation and / or sedimentation of the solid phase. It preferably accounts for 3-7% by weight, up to 10% by weight, of the total mass percentage of the organic solvent, dispersant, and surfactant. Alkyl ammonium salts of copolymers containing one or more acid functional groups are non-limiting examples of the dispersant.

[0095] The surfactant is preferably a polyether or a mixture of polyethers. It preferably accounts for 0.05% to 0.5% by weight of the total mass percentage of the organic solvent, dispersant, and surfactant.

[0096] The mineral ink may not contain a dyed mineral pigment. Alternatively, it may contain a mineral pigment to provide a hue or color to the enamel. The mineral pigment enables the adjustment of the color of the mineral ink and the enamel. The mineral pigment may be based on metal oxides and / or metals or metal alloys (capable of oxidizing during the heat treatment of the mineral ink to form enamel). Non-limiting examples of the mineral pigment are titanium oxide, cerium oxide, cobalt oxide, iron oxide, zirconium oxide, manganese oxide, spinel, or doped alumina.

[0097] In one embodiment, the D90 of the particle size distribution of the solid portion of the mineral ink is at most 2 μm, preferably between 1 μm and 2 μm. The D90 is calculated from the particle size distribution determined by the laser diffraction method according to the ISO 13320:2009 standard. It corresponds to the size of the particles that account for 90% of the total volume of the particles in the mixture. In other words, 90% of the volume of the particles in the mixture of frit and mineral pigment consists of particles having a size of at most 2 μm, preferably between 1 μm and 2 μm. In an advantageous embodiment, the surface tension of the mineral ink is about 26 mN / m at 25 °C. It has been found that a mineral ink having a surface tension of about 26 mN / m at 25 °C can facilitate the obtaining of an inorganic enamel on a mineral substrate according to the first aspect of the present invention.

[0098] All the described embodiments, whether they relate to the first aspect or the second aspect of the present invention, can be combined with each other. Examples

[0099] In four examples E1, E2, E3, and E4 of the mineral substrate according to the present invention, three different inorganic enamels A, B, and C were deposited on (KB+) glass-ceramic plates sold by Eurokera S.N.C.

[0100] Enamel A is a black enamel containing 60%-70% frit F (the composition of which is described in Table 1), 15-20% of a mixed oxide of cobalt and silicon, and 15-20% of a mixed oxide of iron, chromium, cobalt, and nickel.

[0101] Enamel B is a dark gray enamel formed from a mixture of 75% by mass of Enamel A and 25% by mass of an enamel containing 70-75% frit F (the composition of which is described in Table 1) and 25-30% titanium oxide.

[0102] Enamel C is a gray enamel formed from a mixture of 50% by mass of Enamel A and 50% by mass of an enamel containing 70-75% frit F (the composition of which is described in Table 1) and 25-30% titanium oxide.

[0103] [Table 1]

[0104]

[0105]

[0106] In Examples E1, E2, and E3, inorganic enamel was developed according to the method of the second aspect of the present invention, more particularly by inkjet printing of a mineral ink (with an ink coverage Te of 55%). The solid portion in the mineral ink is at most 40% by weight. The D90 of the particle size distribution of the solid portion of the mineral ink is about 1.3-1.5 μm.

[0107] In Example E4, the inorganic enamel was deposited by a non-standard screen printing method using a screen printing paste (the D90 of the particle size distribution of the solid portion of which is about 1.6 μm).

[0108] In Comparative Example CE1 not according to the present invention, the inorganic Enamel A was deposited on a glass-ceramic plate called (KB+) sold by Eurokera S.N.C. by a standard screen printing method. The D90 of the particle size distribution of the solid portion of the screen printing paste is about 5.1 μm.

[0109] In Comparative Example CE2 not according to the present invention, the inorganic Enamel A was deposited onto a glass-ceramic plate called (KB+) sold by Eurokera S.N.C. by a method for printing a mineral ink, with an ink coverage Te of 40%. The D90 of the particle size distribution of the solid portion of the mineral ink is about 1.4 μm.

[0110] In Examples E1, E4 and in the counterexample CE1, the enamel is deposited in the form of a periodic pattern of squares with a side length of approximately 1.25 mm, a thickness between 1 μm and 3 μm and a spacing of 0.75 mm, as schematically shown in Figure 4 . The coverage of the inorganic enamel on the substrate surface is 40%.

[0111] In Examples E2 and E3 and the counterexample CE2, the enamel is deposited in the form of random cells, which has a coverage of approximately 25% on the substrate.

[0112] The characteristics of Examples E1, E2, E3 and E4 and counterexamples CE1 and CE2 are summarized in Table 2.

[0113] [Table 2]

[0114]

[0115]

[0116] The light transmittance of the bare mineral substrate (i.e., without inorganic enamel) was measured using a Perkin Elmer Lambda 950 spectrophotometer according to section 4.2 of the EN410:1999 standard with a light source D65 and a standard observer. For Examples E1, E2, E3 and E4 and counterexamples CE1 and CE2, the measured light transmittance Tl of the bare mineral substrate was approximately 1.5%.

[0117] The brightness (expressed as L*) was measured according to the ISO 11664-4 standard using a BYK Gardner SPC008 spectrophotometer at an illumination angle of 45° and an observation angle of 0°.

[0118] The brightness of the bare mineral substrate (i.e., without inorganic enamel) (expressed as L*(substrate)) was measured in reflection on a white background. In this case, the standard background 2810 was supplied by BYK Gardner (L* = 92.07; a* = -0.75; b* = 4.91).

[0119] The brightness of the inorganic enamel deposited on the mineral substrate (expressed as L*(enamel / substrate)) was measured in reflection. The surface of the mineral substrate was completely covered by the inorganic enamel.

[0120] The relative brightness difference ΔL* was calculated using the following equation:

[0121]

[0122] The total surface roughness Rt of the inorganic enamel of each of the examples E1, E2, E3, and E4 and the counterexamples CE1 and CE2 was measured using a Mitutoyo SJ-400 mechanical probe in accordance with section 4.1.5 of ISO standard 4287:1997.

[0123] The topographical slope Pt of the inorganic enamel protruding from the surface of the glass-ceramic substrate was calculated using a surface profile. The surface profile was measured using a Mitutoyo SJ-400 mechanical probe equipped with a PC75 non-Gaussian filter applied to the parameter Wt.

[0124] An illustrative example of the surface profile measurement on the inorganic enamel on the surface of the mineral substrate according to the present invention is shown in Figure 3 .

[0125] The profile was measured on the enamel edge protruding 15 mm in length from the surface of the mineral substrate. The enamel has a polygonal geometry. The topographical slope (which corresponds to the tangent value of the height change between the surface of the mineral substrate and the so-called effective surface of the enamel) was calculated using the following formula:

[0126]

[0127] where h is the height difference between the surface of the mineral substrate and the effective surface of the inorganic enamel and generally corresponds to the thickness of the enamel relative to the surface of the mineral substrate, and l is the length of this height change.

[0128] On the same inorganic enamel, at least three topographical slope measurements were made at different positions or different sites on the enamel edge protruding from the surface of the mineral substrate. The arithmetic mean Ptm of the topographical slope was calculated from these at least three measured values.

[0129] Figure 5 and Figure 6 are examples of 3D representations of the topographical profile, the topographical profile being measured on an example according to the present invention using a Taylor Hobson 3D surface profiler from AMETEK Inc., and from which surface profile measurements can be made.

[0130] The visibility of metal friction was evaluated using the following protocol. A pot made of stainless steel or aluminum with a diameter of 20 cm and a weight of 3 kg was placed inclined on the mineral substrate provided with the inorganic enamel and then moved at a speed of approximately 0.40 m / s in 10 back-and-forth movements. The stainless steel pot has a Vickers hardness of 200 HV.

[0131] ​The level of the metal friction imprint is evaluated according to two different methods: a visual analysis evaluation method and an image analysis evaluation method.

[0132] According to the first visual analysis method, the degree of deterioration D of the enamel is visually evaluated according to a scale from 0 to 5 at a distance of 60 cm under normal observation conditions. Degree 5 corresponds to the significant visibility of the embedded metal particles, and degree 0 corresponds to the obvious absence of metal imprints or traces. In other words, the lower the degree, the fewer metal friction marks or imprints visible to the naked eye.

[0133] According to the second image analysis evaluation method, a digital photographic image of a defined area of the enamel is first taken under the artificial light of a 3-color light-emitting diode in a light box suitable for this purpose.

[0134] This digital photographic image is then subjected to digital processing to convert it into a grayscale image, from which the average value Vm of the grayscale level is calculated.

[0135] This same operation is performed on the enamel area that has undergone metal friction and on the enamel area that has not undergone metal friction. The difference ΔVm between the values Vm obtained for each of these two areas is calculated. The higher the value of the parameter ΔVm, the higher the number of metal particles embedded in the enamel.

[0136] In parallel, the same photographic image is the object of digital binarization processing, from which the visibility index Iv is calculated. The visibility index is defined as the ratio of the number of pixels with a higher intensity (i.e., having a value of 1) to the total number of pixels. The higher this ratio Iv, the higher the visibility of the metal particles embedded in the enamel.

[0137] For an enamel analysis area size included in 400,000 - 450,000 pixels, the image size is 3264×2448 pixels. For Examples E1, E4 and Counterexample CE1, this corresponds to approximately 10×13 squares of the pattern.

[0138] The static friction coefficient and the dynamic friction coefficient (denoted as Fs and Fd respectively) are measured on an AFT instrument for measuring the friction coefficient sold by Hanatek company according to standards ASTM D1894, ISO8295:1995 and ISO 15359:1999. The friction head is a stainless steel washer NFE25.513 with a diameter of 36 mm and a thickness of 2 mm from company. The measurement is carried out on the sample with a friction head moving speed of 500 mm / min over a stroke length of 50 mm.

[0139] Before any measurement of the friction coefficient, use the one from Laboratoires Prodene The Clin’Glass detergent sold is pre-cleaned. Four measurements are made on each sample and their average value is calculated.

[0140] For these measurements, for Examples E2 and E3 and Comparative Example CE2, the inorganic enamel on the substrate surface has a random pattern, and for Example E1, E4 and Comparative Example CE1, it has a periodic pattern of squares with a side length of approximately 1.25 mm.

[0141] All the results are collected in Table 3. The values of the metal friction parameters D, ΔVm and Iv for using stainless steel and aluminum pots are reported and annotated with "stainless steel" and "aluminum" respectively.

[0142] [Table 3]

[0143]

[0144]

[0145] The results in Table 3 show that for Examples E1, E2, E3 and E4 according to the present invention, the number of the metal imprints and traces and thus the visibility are reduced more than those of Comparative Examples CE1 and CE2. In fact, regardless of the parameters D, ΔVm and Iv, considering the friction using stainless steel or aluminum pots, for the examples according to the present invention, the values are lower. The values of the parameters ΔVm and Iv are reduced from 75% to 92%, which means that the visibility of the metal imprints and traces is reduced as much as possible.

[0146] The comparison of the results of Example E1 and Example E4 shows that when using the preparation method according to the second aspect of the present invention, the parameter values D, ΔVm and Iv are lower. The preparation method according to the present invention can thus obtain better performance than the screen-printing method in terms of reducing the visibility of the imprints and metal imprints. Using the screen-printing method is still feasible.

[0147] The comparison of the results of Examples E1, E2 and E3 shows that the visibility of the metal traces and imprints remains very low, even for inorganic enamels with a low contrast level with the mineral substrate, particularly for dark-colored inorganic enamels with a ΔL* less than 35, and particularly for black inorganic enamels with a ΔL* less than 15.

[0148] As an additional illustration of the features and advantages of the present invention, multiple embodiments derived from the prior art are repeated in the form of comparative examples, and their features are reported in Table 4.

[0149]

[0150] The counterexamples CE3 - CE8 are taken from EP3067334A1 [SCHOTT AG [DE]] 14.09.2016. The examples CE3 - CE5, on the one hand, and the counterexamples CE6 - CE8, on the other hand, each have three different enamel compositions (Farbe 1, Farbe 1a, and Farbe6). These two series of counterexamples are deposited according to two different patterns (Punkmuster 11 and Punkmuster 12).

[0151] The counterexamples CE7 and CE9 have the same enamel composition and are taken from FR 2858974 A1 [SCHOTT AG [DE]] 25.02.2005. For the sake of comparison, they are deposited according to two different patterns (Punkmuster11 and Punkmuster 12) taken from EP 3067334A1 [SCHOTT AG [DE]] 14.09.2016.

[0152] The counterexamples CE11 and CE12 have the compositions of Examples E1 and E2 of WO 2019 / 219691 A1 [EUROKERA [FR]] 21.11.2019, respectively. For the purpose of comparison, they are deposited according to a 0.6 - mm - wide line pattern with a 55% coverage.

[0153] The enamels of the counterexamples CE3 - CE12 can have the chemical composition and / or particle size of the mixtures (such as mixtures of mineral frit and / or mineral pigments) that have been used to form them, similar to Examples E1 - E4 according to the present invention.

[0154] The enamels of the examples CE3 - CE8 are deposited according to the methods described in the documents from which they are extracted.

[0155] The total roughness and topographic slope of the counterexamples CE1 - CE3 are measured and / or determined according to the same methods as those used for Examples E1 - E4 and counterexamples CE1 and CE2. The results are reported in

[0156] Table 5, as Figure 7 shown.

[0157] Table 5 Rt (μm) Ptm (%) Figure 7 Symbol CE3 6 2.23 Hollow diamond CE4 3.62 2.26 Hollow diamond CE5 1.22 2.29 Hollow diamond CE6 5.25 2.17 Asterisk CE7 3.69 2.07 Asterisk CE8 1.03 2.08 Asterisk CE9 1.99 1.90 Hollow square CE10 1.86 2.29 Hollow square CE11 3.2 1.22 Hollow triangle CE12 1.14 1.68 Hollow triangle

[0158] In Figure 7In [description], embodiments E1 - E4 according to the present invention are represented by solid circular symbols, counterexamples CE3 - CE5 are represented by hollow diamonds, counterexamples CE6 - CE8 are represented by asterisks, counterexamples CE9 - CE10 are represented by hollow squares, and counterexamples CE11 and CE12 are represented by hollow triangles. As a visual guide, a total roughness value Rt of 2.00 μm and a topographic slope Ptm of 1.40% are represented by a vertical dashed line and a horizontal dashed line, respectively.

[0159] Figure 7 shows that only the embodiments according to the present invention are located in the region defined below the horizontal line and to the right of the vertical line. Counterexamples CE3 - CE12 are all outside this region. This figure thus clearly and unambiguously shows that only the embodiments according to the present invention have a total roughness Rt and a topographic slope value Ptm that are less than or equal to 2.00 μm and less than or equal to 1.4%, respectively.​

Claims

1. A mineral substrate (1001) comprising, on at least one of its surfaces, a patterned inorganic enamel (1002), Characterized in that: - the inorganic enamel (1002) has a total surface roughness Rt of less than or equal to 2 μm on its surface (1002-S), and - the edges (1002a, 1002b) of the inorganic enamel (1002) protruding from the surface (1001-S) of the mineral substrate (1001) have a topographic slope value expressed as a percentage of less than or equal to 1.4%.

2. The mineral substrate (1001) according to claim 1, such that the value of the total surface roughness is less than or equal to 1.5 μm.

3. The mineral substrate (1001) according to claim 1, such that the value of the total surface roughness is less than or equal to 1 μm.

4. The mineral substrate (1001) according to claim 1, such that the value of the topographic slope is less than or equal to 1.2%.

5. The mineral substrate (1001) according to claim 1, such that the thickness of the inorganic enamel (1002) is between 1.5 μm and 3.5 μm.

6. The mineral substrate (1001) according to claim 1, such that the thickness of the inorganic enamel (1002) is between 1.5 μm and 2 μm.

7. The mineral substrate (1001) according to claim 1, such that the relative luminance difference ΔL* is at most 50, which is defined as the difference between the luminance L*(enamel / substrate) measured in reflection of the inorganic enamel (1002) on the mineral substrate (1001) and the luminance L*(substrate) measured in reflection of the mineral substrate (1001) without the inorganic enamel (1002).

8. The mineral substrate (1001) according to claim 1, such that the relative luminance difference ΔL* is at most 35, which is defined as the difference between the luminance L*(enamel / substrate) measured in reflection of the inorganic enamel (1002) on the mineral substrate (1001) and the luminance L*(substrate) measured in reflection of the mineral substrate (1001) without the inorganic enamel (1002).

9. The mineral substrate (1001) according to claim 1, such that the luminance L*(substrate) measured in transmission of the mineral substrate is less than or equal to 5.

10. The mineral substrate (1001) according to claim 1, such that the light transmittance of the mineral substrate is at most 17%.

11. The mineral substrate (1001) according to claim 1, such that the light transmittance of the mineral substrate is at most 10%.

12. The mineral substrate (1001) according to claim 1, such that the light transmittance of the mineral substrate is at most 5%.

13. The mineral substrate (1001) according to claim 1, such that the static and / or dynamic coefficient of friction of the surface of the mineral substrate (1001) provided with the inorganic enamel (1002) is at most 0.

30.

14. The mineral substrate (1001) according to claim 1, wherein the static and / or dynamic coefficient of friction of the surface of the mineral substrate (1001) provided with the inorganic enamel (1002) is at most 0.

25.

15. The mineral substrate according to claim 1, wherein the mineral substrate is a glass-ceramic substrate or a mineral glass substrate.

16. A method for preparing a mineral substrate (1001) according to any one of claims 1 to 15, the method comprising the step of depositing an inorganic enamel (1002) by inkjet printing a mineral ink onto the mineral substrate (1001), wherein the ink coverage is at least 45% and at most 85%, and the weight percentage of the solid part in the mineral ink for inkjet printing is at most 40% of the mineral ink.

17. The preparation method according to claim 16, wherein the surface tension of the mineral ink is 26 mN / m at 25 °C.

18. Use of the mineral substrate (1001) according to any one of claims 1 to 15 as a surface of a cooking device or a workbench.

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