Enameled mineral substrate and method of manufacturing such a substrate

Abstract

Mineral substrate comprising, on at least one of its surfaces, an inorganic enamel resistant to metallic friction. The inorganic enamel has a total roughness value of less than or equal to 2 µm, and the edge of the inorganic enamel protruding at the level of the glass-ceramic substrate has a topographic slope value, expressed as a percentage, of less than or equal to 1.4%.

Description

Title of the invention: Enameled mineral substrate and method for manufacturing such a substrate technical field

[0001] The present invention relates to a mineral substrate comprising, on at least one of its surfaces, an inorganic enamel resistant to metallic friction. It also relates to a method for manufacturing such a substrate. Technical background

[0002] Mineral substrates such as glass-ceramics or special colored glasses are appreciated in many fields for their aesthetic qualities and their physico-chemical properties, in particular their low coefficient of thermal expansion and their resistance to thermal shock.

[0003] They are particularly used in kitchen equipment, especially in the form of a flat substrate, for example as a cooking surface in cooking appliances, oven glass wall, and work surface in worktops, tables or work units for the preparation of food products.

[0004] By way of example, in kitchen equipment, glass-ceramics, composite materials comprising an amorphous phase in which crystalline phases are dispersed, are highly valued mineral substrates due to their excellent resistance to thermal shock, their very low coefficient of expansion, and their mechanical strength. Used as cooking surfaces and / or worktops in cooking appliances, they are generally lithium aluminosilicate-based with a dispersion of crystalline phases based on [3-quartz and / or [3-spodumene] in their amorphous matrix.

[0005] Depending on the intended use for kitchen equipment, mineral substrates can be associated with electrical and / or electronic devices such as heating and / or lighting means, and / or be equipped with a number of accessories, such as controls, sensors and displays, which allow interaction between the user and the devices in which these substrates are incorporated.

[0006] It is common practice to enamel the surface of mineral substrates for decorative purposes and / or to delineate certain functional areas such as control, signaling, and / or heating zones for cooking devices. Enameling is commonly carried out using screen printing or inkjet printing methods.

[0007] In the field of mineral substrates used in and / or near cooking devices, for reasons of durability and aesthetics, an enamel preferentially presents actually a correct adhesion to the substrate on which it is deposited as well as appreciable resistance to the mechanical and / or chemical stresses that it is likely to undergo under the conditions of use of the cooking devices.

[0008] In particular, enamels capable of withstanding repeated exposure to food and / or chemical products as well as mechanical stresses such as metallic friction caused by the repeated movement of kitchen utensils such as pots or pans are generally sought.

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

[0010] WO 2016 / 008848 Al [SCHOTT AG [DE]] 21.01.2016 describes a mineral ink suitable for printing decorations on low-expansion glass-ceramic substrates. This mineral ink produces enamels with improved resistance to bending and chipping.

[0011] WO 2016 / 110724 Al [FENZI SPA [IT]] 14.07.2016 describes a mineral ink composition for printing decorations on glass-ceramic substrates. This mineral ink produces enamels that are chemically resistant to acids, bases, and radiation, and mechanically resistant to abrasion and delamination.

[0012] EP 3067334 Al [SCHOTT AG [DE]] 14.09.2016 describes a decorative enamel for glass-ceramic substrates that reduces the noise generated by the movement of kitchen utensils on the surface of the enamel.

[0013] WO 2019 / 219691 Al [EUROKERA [FR]] 21.11.2019 describes a mineral ink for printing decorations on glass-ceramic substrates. This ink makes it possible to obtain enamels resistant to food products, detergents, the combined effects of repeated exposure to these products and heating cycles, and temperatures exceeding 800°C used during the manufacture of glass-ceramic substrates. Summary of the invention Technical problem

[0014] Metallic friction resulting from the repeated movement of cooking utensils such as pots or pans on the surface of mineral substrates in and / or near cooking appliances causes metallic marks or traces to appear on decorative enamels. These metallic marks or traces are generally metallic particles that, due to the repeated friction of the metal utensils on the enamels, have been detached from said metal utensils and have become embedded in the surface of the substrate or the enamels. This phenomenon is particularly pronounced for utensils made of light and soft metals such as pots or pans with aluminum or stainless steel bases.

[0015] Over time, these embedded particles eventually degrade the aesthetic appearance of the enamels, particularly enamels with low contrast against the mineral substrate, such as dark or black enamels on a dark or black mineral substrate. In the long term, such aesthetic degradation is detrimental to a positive perception of the product by customers.

[0016] On the other hand, with the development of so-called "flexible" cooking surfaces—that is, surfaces on which cooking utensils can be freely placed for heating, or in other words, on which there are no dedicated heating zones—the utensils are moved more frequently across the cooking surface. The aesthetic degradation caused by metal-to-metal friction then becomes all the more pronounced or rapid.

[0017] Finally, the accumulation of encrusted metallic particles, when it becomes particularly visible, leads to more frequent and vigorous cleaning of the glass-ceramic substrate and glazes by users. These cleanings generally aim to remove visible metallic marks and traces. However, the frequency and intensity of these cleanings have the negative consequence of causing premature and significant damage to the glazes, which in turn degrades the aesthetic appearance of the decorative glazes and reduces the durability of the cooking surfaces.

[0018] There is therefore a need for a glass-ceramic substrate comprising a decorative enamel capable of limiting the appearance of metallic marks or traces. Solution to the technical problem

[0019] According to a first aspect of the invention, a mineral substrate (1001) is provided comprising on at least one of its surfaces an inorganic enamel (1002), characterized in that: - the inorganic enamel (1002) has a total surface roughness value (1002-S) less than or equal to 2 pm, and - the edge (1002a, 1002b) of the inorganic enamel (1002) protruding at the level of the surface (1001-S) of the mineral substrate (1001) has a topographic slope value, expressed as a percentage, less than or equal to 1.4%.

[0020] Other advantageous embodiments are described below.

[0021] According to a second aspect of the invention, a method for manufacturing a substrate according to the first aspect of the invention is provided. Advantages of the invention

[0022] A notable advantage of the invention is a significant reduction in the number of visible metallic marks and traces resulting from repeated rubbing of metal utensils on the enamel or enamels. This reduction can reach 50%, or even 70%. or more, compared to a glass-ceramic substrate comprising a standard enamel.

[0023] A second advantage is that the reduction in the number of visible metallic marks or traces is particularly noticeable for utensils made from the lightest common metals such as aluminum or stainless steel.

[0024] A third advantage is that the reduction in the number of visible metallic marks and traces is particularly noticeable for decorative enamels with a low level of contrast with the mineral substrate, such as dark or black colored enamels on a dark or black colored mineral substrate.

[0025] A fourth advantage is the ease of implementation of the invention with the possibility of applying it to any chemical composition of enamel. Brief description of the drawings

[0026] [Fig. 1] is a schematic orthographic representation of a mineral substrate comprising an enamel.

[0027] [Fig.2] is a schematic representation of the cross-section of a mineral substrate comprising an enamel.

[0028] [Fig.3] is an example of a surface profile of an inorganic enamel on a mineral substrate according to the invention. Detailed description of implementation methods

[0029] As an illustrative example, with reference to [Fig. 1], a mineral substrate 1001 such as those used as a surface for cooking devices comprises the mineral substrate 1001 itself provided on at least one of its surfaces with an inorganic enamel 1002. In [Fig. 1], the enamel 1002 forms a line. It can form any suitable pattern.

[0030] According to a first aspect of the invention, with reference to [Fig. 1] and [Fig. 2], a mineral substrate 1001 is provided comprising on at least one of its surfaces an inorganic enamel 1002, characterized in that: - Inorganic enamel 1002 has a total surface roughness value 1002-S less than or equal to 2 pm, and - the edge 1002a, 1002b of the inorganic enamel 1002 protruding at the level of the surface 1001-S of the mineral substrate 1001 has a topographic slope value, expressed as a percentage, less than or equal to 1.4%.

[0031] Without being a theoretical or practical consideration to which the invention should be reduced, a possible explanation of the remarkable advantage provided by the invention may be that the synergy, with regard to the inorganic enamel, between a total surface roughness of less than 2 pm, and a topographic slope of less than 1.4%, makes it possible to improve the sliding of metal utensils, in particular made of soft metal, on the surface of said inorganic enamel, and thus reduce the risk of tearing off metal particles.

[0032] By "total roughness" is meant the total roughness, denoted Rt, as defined in section 4.1.5 of ISO 4287:1997. It is defined as the sum of the greatest of the protrusion heights, Zp, of a surface profile and the greatest of the depths, Zv, of the profile over the evaluation length of the profile.

[0033] By "topographic slope" is meant the common measure of the gradient, defined as the tangent of the inclination between two points of a surface located at different altitudes, or as the tangent of the angle of gradient with respect to a reference level, generally the horizontal. This measure is generally expressed as a percentage.

[0034] More specifically, in the context of disclosure, the topographic slope corresponds to the tangent of the slope of the edge 1002a, 1002b of the inorganic enamel 1002 projecting onto the surface 1001-S of the mineral substrate 1001. In other words, with reference to [Fig. 2], it corresponds to the tangent of the difference in elevation divided by the distance of said difference in elevation, that is, to the ratio, h / 1, of the difference in altitude, 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 distance, l, between the two points considered for the difference in altitude. Expressed as a percentage, the ratio h / 1 is multiplied by 100.

[0035] The upper surface 1002-S of the inorganic enamel 1002 is generally the most extensive surface and substantially parallel to the surface 1001-S of the mineral substrate 1001.

[0036] The angle of inclination, expressed in radians, is an expression of the topographic slope in the form of an angle. The angle of inclination, a, then corresponds to the value obtained by applying to the ratio h / 1 the inverse function, denoted arctan or tan ', of the tangent function, i.e.

[0037] a=tan'($)

[0038] Multiplying this ratio by 180 / rr allows the angle to be converted into degrees.

[0039] The value of the topographic slope is preferably the arithmetic mean of the values ​​of the individual topographic slopes measured at different places or different locations of the edge 1002a, 1002b of the inorganic enamel 1002 protruding on the surface 1001-S of the mineral substrate 1001.

[0040] By "enamel" is meant a vitreous or composite material generally comprising an annealed glass frit in which fillers, agents and / or colouring and / or structuring pigments may optionally be dispersed.

[0041] An enamel generally functions as a decorative and / or functional coating deposited on the surface of a mineral substrate for the purposes of decoration, signaling and / or delimitation, particularly of certain functional areas such as, for example, the heating and / or control areas of cooking devices or worktops.

[0042] Various enameling processes, also called glazing or simply decoration, and the compositions of the mineral or ceramic pastes, inks or paints used for the purposes of said enameling processes are known from the prior art, particularly in the field of enamels for mineral substrates such as glass-ceramics.

[0043] An enamel is generally obtained by heat treatment of a paste, ink or mineral or ceramic paint deposited on the surface of a mineral substrate using a suitable method, for example, by screen printing or inkjet printing.

[0044] The mineral or ceramic paste, ink, or paint comprises a finely divided mineral solid phase dispersed in a more or less viscous organic medium. The organic medium allows the application of the solid phase using the appropriate deposition method. It also acts as a suspending and / or dispersing agent for the mineral phase to ensure its homogeneous and uniform distribution within the area to be decorated, marked, and / or delineated.

[0045] The mineral substrate 1001 can be any mineral substrate that can be subjected to stress by metal utensils, in particular a mineral substrate that can be used in an environment in which metal kitchen utensils are used, for example as a worktop surface and / or of a cooking device and / or of a cooking unit.

[0046] In certain embodiments, the mineral substrate 1001 may be a glass-ceramic substrate or a mineral glass substrate. By way of example, it may be any type of glass-ceramic suitable for use as a worktop surface and / or cooking appliance and / or cabinet surface, such as lithium aluminosilicate-based glass-ceramics. It may also be any type of mineral glass, possibly tempered, suitable for the same applications, such as borosilicate or aluminosilicate glasses.

[0047] According to the invention, the total surface roughness value of the inorganic enamel 1002 is less than or equal to 2 pm. For certain inorganic enamel compositions, lower total roughness values ​​can be achieved. Thus, in some advantageous embodiments, the value of said total surface roughness can be less than or equal to 1.5 pm, preferably less than or equal to 1 pm. It has been found that a reduction in the total surface roughness can further reduce the visibility of metallic marks and traces.

[0048] According to the invention, the topographic slope value of the edge 1002a, 1002b of the inorganic enamel 1002 protruding at the surface 1001-S of the substrate vi- The topographic slope of ceramic 1001 is less than or equal to 1.4%. For certain inorganic enamel compositions 1002, lower values ​​can be achieved. Thus, in some advantageous embodiments, the value of said topographic slope can be less than or equal to 1.2%. It has been observed that a decrease in the topographic slope can further facilitate the sliding of metallic objects or utensils on the inorganic enamel, and thus allow for a more significant reduction in the visibility of metallic marks and traces.

[0049] Thanks to the reduction in the visibility of metallic traces and marks made possible by the invention, the thickness of the inorganic enamel can be advantageously reduced since the need to compensate for possible enamel degradation caused by the encrustation of metallic particles and / or repeated cleaning by users is less important, or even non-existent.

[0050] Thus, in certain embodiments, the thickness of the inorganic enamel 1002 can advantageously be between 1.5pm and 3.5pm, or even between 1.5pm and 2pm.

[0051] Metallic marks and traces are notably reduced for an inorganic enamel 1002 having a low level of contrast with the mineral substrate 1001, whether it is dark in appearance, in particular black in color, or light in appearance, for example white in color. Thus, in a particularly advantageous embodiment, the relative difference of luminance AL*, 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 inorganic enamel 1002, can be at most 50, preferably at most 35. It can in particular be between 2 and 45, possibly between 5 and 35, these intervals of values ​​corresponding to an inorganic enamel 1002 of fairly low contrast with respect to the mineral substrate 1001.

[0052] The relative difference in luminance AL* can also be expressed in the form of the following equation:

[0053] AL = | (L {email I substrate} - L (substrate)) |

[0054] The term "luminance" refers to luminance, denoted L*, as defined and measured in ISO 11664-4. The luminance of the mineral substrate 1001, denoted L*(substrate), is measured by reflection. The luminance of the inorganic enamel 1002 deposited on the mineral substrate 1001, denoted L*(enamel / substrate), is measured by reflection.

[0055] In cooking appliances or worktops, the mineral substrates with which inorganic glazes exhibit a low contrast difference are generally dark-looking substrates, possibly black in color, with low transmissivity and low diffusion. Also, in some embodiments, the light transmission, Tl, of the mineral substrate 1001 is at most 17%, preferably at most 10%, or even at most 5%. Black mineral substrates, such as standard black non-opalescent glass-ceramics, have a light transmission of less than 5%, in particular between 0.2% and 2%.

[0056] By "light transmission" is meant the light transmission, denoted Tl, as defined and measured in section 4.2 of standard EN 410:1999 with illuminant D65 and a standard observer.

[0057] In certain particular embodiments, a black mineral substrate, the luminance L*(substrate), measured in reflection, of said mineral substrate 1001 may in addition be less than or equal to 5, preferably less than or equal to 2. Black colored mineral substrates, such as, for example, glass-ceramics marketed under the name KeraBlack® or KeraBlack+® by the company Eurokera, exhibit such a level of luminance.

[0058] One of the advantages of the invention is to promote the sliding of metal utensils, in particular made of soft metal, on the surface of said inorganic enamel, and thus reduce the risk of tearing off metal particles.

[0059] In advantageous embodiments, the static and / or dynamic coefficient of friction of the surface of the mineral substrate (1001) provided with said inorganic enamel (1002) is at most 0.30, preferably at most 0.25. Mineral substrates according to the invention having such static and / or dynamic coefficient of friction values ​​generally exhibit the best performance in terms of reducing the number of visible metallic marks and traces under the effect of repeated friction of metal utensils.

[0060] By coefficient of friction, it is understood that the coefficient of static and / or dynamic friction is defined as defined in the standards ASTM D1894, ISO 8295:1995 and ISO 15359:1999.

[0061] The static friction coefficient is defined as the ratio between the static friction force, i.e. the force required to initiate a sliding movement of one surface on another, and the force applied perpendicularly to these two surfaces to maintain their contact and sliding.

[0062] The dynamic friction coefficient is defined as the ratio between the dynamic friction force, i.e. the force required to maintain a sliding motion of one surface on another, and the force applied perpendicularly to these two surfaces to maintain their contact and sliding.

[0063] By static and / or dynamic friction coefficient of the surface of the mineral substrate (1001) provided with said inorganic enamel (1002), it is understood to mean the static and / or dynamic friction coefficient as it can be measured on the surface of the mineral substrate (1001) on which the inorganic enamel (1002) is present.

[0064] A mineral substrate 1001 according to any one of the embodiments described can be advantageously used as a surface for a cooking device, in particular an induction-type cooking device with a so-called "flexible" surface, or for a work surface, in particular a work surface in furniture such as tables or work units for the preparation of food products.

[0065] According to a second aspect of the invention, a method for manufacturing a mineral substrate 1001 is provided according to any one of the embodiments described above, said method comprising a step of depositing an inorganic enamel 1002 by mineral inkjet printing on a mineral substrate 1001 in which the ink coverage is at least 45% and at most 85%, and the mass percentage of the solid fraction in the mineral ink used for inkjet printing is at most 40% of said mineral ink.

[0066] The term "ink coverage" refers to the ink coverage as known and defined in the field of inkjet printing. For a given unit of ink, it corresponds to the number of pixels actually printed out of the total number of printable pixels. Consequently, it will depend on the resolution of the device, for example, a printer, used to perform the inkjet printing.

[0067] By way of illustration, for an inkjet print job at 800 dpi, the number of printable pixels on a one-inch square pattern is 640,000 pixels. For a given unit ink, if only 200,000 pixels are actually printed, the ink coverage for that given unit ink is 200,000 / 640,000, or, expressed as a percentage, 31.5%.

[0068] If several individual inks are used, for example inks of different colors, the ink coverage is the sum of the ink coverages of each of these individual inks.

[0069] The viscosity of the ink, typically between 20 and 100 Pa·s, and the volume of the ink droplets, typically between 12 and 84 pL, can also influence the ink coverage. A very fluid ink and / or a large droplet volume can result in greater coverage of the printed surface, particularly by covering peripheral pixels beyond those actually printed by the inkjet printing device at the selected resolution. These parameters are generally taken into account by the inkjet printing device when setting the ink coverage.

[0070] By "mineral ink" is meant a mineral ink suitable for deposition of enamels by inkjet printing. A mineral ink is generally in the form of a suspension or colloidal dispersion of a finely divided mineral solid phase in a generally organic liquid phase. The mineral solid phase of the colloidal suspension generally comprises a glass frit and possibly a mineral pigment.

[0071] Mineral ink has a density, viscosity, and surface tension compatible with inkjet printing methods. The values ​​of these parameters depend on the inkjet printing devices used and determine the quality of the decorative patterns obtained.

[0072] The grain size of the mineral solid phase is generally micrometric, or even sub-micrometric. The liquid phase mainly comprises a solvent, generally organic. The type and quantity of solvent partly determine the rheological properties, surface tension, and drying behavior of the mineral ink. It is also possible to add a dispersing agent to prevent flocculation and / or sedimentation of the solid phase, as well as a surfactant to adjust the surface tension of the mineral ink.

[0073] The mass proportions of the organic solvent, dispersing agent, surfactant, and glass frit can be adjusted so that the properties of the mineral ink are suitable for the inkjet printing device used. The organic solvent can generally represent 80% by weight of the mixture of organic solvent, dispersing agent, and surfactant in the mineral ink. The type and quantity of organic solvent can be adjusted according to the technical constraints of the inkjet printing device used and production requirements.

[0074] To form an enamel using mineral ink deposited by inkjet printing, the temperature at which the mineral ink is dried can be between 25 and 180°C. The heat treatment temperature for firing the enameled precursor glass can be equal to or greater than 650°C. Preferably, the temperature does not exceed 1100°C.

[0075] The organic solvent may be a liquid organic compound at room temperature or a mixture of liquid organic compounds at room temperature comprising at least one alcohol functional group.

[0076] The choice of the organic compound containing an alcohol functional group depends on the method and / or device used for inkjet printing. If the deposition of the mineral ink onto the mineral substrate is slow, it is advantageous to use a solvent or solvent mixture with a low saturated vapor pressure under the pressure and temperature conditions of use of the method and / or device. In other words, under standard temperature and pressure conditions, in order to prevent the solvent or solvent mixture from evaporating too rapidly, its boiling point can be higher.

[0077] Non-limiting examples of organic solvents include: methylene glycol, ethylene glycol, propylene glycol, butylene glycol, methanol, ethanol, propanol, butanol, glycol ethers such as propylene methyl ether glycol or dipropylene glycol methyl ether.

[0078] The dispersing agent is preferably a copolymer or a mixture of copolymers comprising at least one acidic functional group. The dispersing agent prevents flocculation and / or sedimentation of the solid phase. It preferably represents 3 to 7%, with a maximum of 10%, by weight of the sum of the mass percentages of the organic solvent, the dispersing agent, and the surfactant. Alkylammonium salts of a copolymer comprising one or more acidic functional groups are non-limiting examples of dispersing agents.

[0079] The surfactant is preferably a polyether or a mixture of polyethers. It preferably represents 0.05% to 0.5% by weight of the sum of the mass percentages of the organic solvent, the dispersing agent and the surfactant.

[0080] The mineral ink may not contain any coloring mineral pigment. Alternatively, it may contain a mineral pigment to impart a tint or color to the enamel. The mineral pigment allows the color of the mineral ink and the enamel to be adjusted. The mineral pigment may be based on metal oxides and / or metals or metal alloys that are capable of oxidizing during the heat treatment of the mineral ink to form the enamel. Non-limiting examples of mineral pigments include titanium oxide, cerium oxide, cobalt oxide, iron oxide, zirconium oxide, manganese oxide, spinels, or doped aluminas.

[0081] In one embodiment, the D90 of the particle size distribution of the solid fraction 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 laser granulometry methods according to ISO 13320:2009. It corresponds to the size of the particles that represent 90% of the total particle volume of the mixture. In other words, 90% of the particle volume of the glass frit and mineral pigment mixture consists of particles having a size of at most 2 µm, preferably between 1 and 2 µm.

[0082] In an advantageous embodiment, the surface tension of the mineral ink is approximately 26 mN / m at 25°C. It has been observed that a mineral ink with a surface tension around 26 mN / m at 25°C can facilitate the application of an inorganic enamel to a mineral substrate in accordance with the first aspect of the invention.

[0083] All the embodiments described, whether they relate to the first or second aspect of the invention, can be combined with each other. Examples

[0084] In four examples E1, E2, E3 and E4 of mineral substrates according to the invention, three different inorganic enamels, A, B and C, are deposited on a KeraBlack+® (KB+) glass-ceramic plate marketed by Eurokera SNC

[0085] Enamel A is a black enamel comprising 60-70% of a glass frit F whose composition is described in table 1, 15-20% mixed oxide of cobalt and silicon and 15-20% mixed oxide of iron, chromium, cobalt and nickel.

[0086] Enamel B is a dark grey enamel formed from a mixture of 75% by mass of enamel A and 25% by mass of an enamel comprising 70-75% of a glass frit F whose composition is described in Table 1 and 25-30% of titanium oxide.

[0087] Enamel C is grey enamel formed from a mixture of 50% by mass of enamel A and 50% of an enamel comprising 70-75% of a glass frit F whose composition is described in Table 1 and 25-30% of titanium oxide.

[0088] [Tables] Table 1 Mass fraction (%) SiO2 35-50 Al2O3 15-25 Li2O 1.5-4 B2O3 22-32 Na2O 0-2 K2O 2-5 CaO 1-5 ZrO2 1-4

[0089] In Examples E1, E2, and E3, the inorganic enamels were produced according to a method in accordance with the second aspect of the invention, more particularly by mineral inkjet printing with an ink coverage, Te, of 55%. The solid fraction in the mineral ink is at most 40% by weight. The D90 of the particle size distribution of the solid fraction of the mineral ink is approximately 1.3–1.5 µm.

[0090] In example E4, the inorganic enamel was deposited by a non-standard screen printing method with a screen printing paste whose D90 of the particle size distribution of its solid fraction is approximately 1.6 pm.

[0091] In a first IEC counterexample not in accordance with the invention, the inorganic enamel A is deposited by a standard screen printing method on a KeraBlack+® (KB+) glass-ceramic plate marketed by the company Eurokera SNC. The D90 of the particle size distribution of the solid fraction of the screen printing paste is approximately 5.1 pm.

[0092] In a second counterexample CE2 not conforming to the invention, the inorganic enamel A is deposited by a mineral inkjet printing method onto a KeraBlack+® (KB+) glass-ceramic plate marketed by Eurokera SNC with an ink coverage, Te, of 40%. The D90 of the particle size distribution the solid fraction of the mineral ink is approximately 1.4 pm.

[0093] In examples E1, E4, and in the IEC counterexample, the enamels are deposited in the form of a periodic pattern of squares approximately 1.25 mm on each side, with a thickness of between 1 and 3 µm and spaced 0.75 mm apart. The coverage rate of the inorganic enamel on the substrate surface is 40%.

[0094] In examples E2 and E3 and counterexample CE2, the enamels are deposited in the form of random patterns with an enamel coverage rate on the substrate of approximately 25%.

[0095] The characteristics of examples El, E2, E3 and E4 and of counterexamples IEC and CE2 are summarized in Table 2.

[0096] [Tables2] Table 2 El E2 E3 E4 IEC CE2 Substrate KB+ KB+ KB+ KB+ KB+ KB+ Email ABCAAA Method Mineral inkjet Mineral inkjet Mineral inkjet Screen printing Screen printing Mineral inkjet Te 55% 55% 55% - - 40% D90 1.3-1.5 pm 1.3-1.5 pm 1.3-1.5 pm 1.6 pm 5.1 pm 1.4 pm

[0097] The light transmission of the mineral substrate alone, i.e., without inorganic enamel, was measured using a Perkin Elmer Lambda 950 spectrophotometer and in accordance with section 4.2 of EN 410:1999 with illuminant D65 and a standard observer. The light transmission, Tl, measured of the mineral substrate alone for examples E1, E2, E3 and E4, and the IEC and CE2 counterexamples, is approximately 1.5%.

[0098] Luminance, denoted L*, was measured in accordance with ISO 11664-4 using a BYK Gardner SPC008 spectrophotometer with an illumination angle of 45° and an observation angle of 0°.

[0099] The luminance of the mineral substrate alone, denoted L*(substrate), i.e. devoid of inorganic enamel, is measured in reflection on a white background, in this case a standard Chart 2810 background supplied by BYK Gardner (L*=92.07; a* = -0.75; b* = 4.91).

[0100] The luminance of the inorganic enamel deposited on the mineral substrate, denoted L*(enamel / substrate), is measured by reflection. The surface of the mineral substrate is completely covered by the inorganic enamel.

[0101] The relative luminance difference AL* is calculated using the following equation:

[0102] AL = | (L (email / substrate) - L (substrate)) |

[0103] The total surface roughness, Rt, of the inorganic enamel of each example El, E2, E3 and E4, and of the counterexamples IEC and CE2 was measured using a Mitutoyo SJ-400 mechanical probe according to section 4.1.5 of ISO 4287:1997.

[0104] The topographic slope, Pt, of the inorganic enamel protruding from the surface of the glass-ceramic substrate is calculated using a surface profile. The surface profile is measured using a Mitutoyo SJ-400 mechanical probe equipped with a non-Gaussian PC75 filter applied to the Wt parameter.

[0105] An illustrative example of surface profile measurement on an inorganic enamel on the surface of a mineral substrate according to the invention is shown in [Fig.3].

[0106] The profile measurement is taken on the edge of the enamel protruding from the surface of the mineral substrate over a length of 15 mm. The enamel has a polygonal geometric shape. The topographic slope, corresponding to the tangent of the difference in elevation between the surface of the mineral substrate and the so-called effective surface of the enamel, is calculated using the formula:

[0107] pf=|xl00

[0108] in which 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 / is the length of the difference in height.

[0109] On the same inorganic enamel, at least three topographic slope measurements are taken at different locations on the edge of the enamel protruding from the surface of the mineral substrate. An arithmetic mean value, Ptm, of the topographic slope is calculated from these at least three measurements.

[0110] The evaluation of the visibility of metallic friction was carried out using the following protocol. A stainless steel (hereinafter referred to as "stainless steel") or aluminum pan with a diameter of 20 cm and a weight of 3 kg is positioned at an angle on the mineral substrate coated with inorganic enamel, and then moved at a speed of approximately 0.40 m / s in 10 back-and-forth movements. The stainless steel pan has a Vickers hardness of 200 HV.

[0111] The level of marking of metallic friction is evaluated according to two different methods: a visual analysis evaluation method, and an image analysis evaluation method.

[0112] According to the first visual analysis method, the enamel degradation, D, is visually assessed on a scale of 0 to 5 at a distance of 60 cm under normal viewing conditions. A score of 5 corresponds to significant visibility of embedded metallic particles, and a score of 0 corresponds to a visible absence of metallic marks or traces. In other words, the lower the score, the less visible the traces or marks of metallic friction are to the naked eye.

[0113] According to the second method of evaluation by image analysis, a digital photographic image of a defined size area of ​​the enamel is first taken under the artificial light of 3 colour light-emitting diodes in a light box adapted for this purpose.

[0114] The digital photographic image is then subjected to digital image conversion processing into grey levels from which an average grey level value, Vm, is calculated.

[0115] This same operation was performed on an area of ​​the enamel that had undergone metallic friction and an area of ​​the enamel that had not undergone metallic friction. The difference AVm between the Vm values ​​obtained for each of these two areas was calculated. The higher the value of the parameter AVm, the greater the number of metallic particles embedded in the enamel.

[0116] Simultaneously, the same photographic image undergoes digital binarization processing, from which a visibility index, Iv, is calculated. This index is defined as the ratio of the number of pixels with the highest intensity, i.e., a value of 1, to the total number of pixels. The higher this ratio Iv, the greater the visibility of the metallic particles embedded in the enamel.

[0117] The image size is 3264x2448 pixels for an enamel analysis area size between 400,000 and 450,000 pixels. This corresponds to approximately 10x13 squares of the pattern for examples El, E4 and the IEC counterexample.

[0118] The static and dynamic friction coefficients, denoted Fs and Fd respectively, were measured according to ASTM D1894, ISO 8295:1995, and ISO 15359:1999 standards using an AFT friction coefficient measuring instrument marketed by Hanatek Instruments®. The friction head is a 36 mm diameter, 2 mm thick stainless steel washer, NFE 25.513, from Berner®. The measurements were performed with a friction head travel speed of 500 mm / min over a stroke length of 50 mm.

[0119] Before any friction coefficient measurement, the samples are pre-cleaned using Clin'Glass detergent marketed by Laboratoires Prodene Klint ®. Four measurements are taken on each sample and their average is calculated.

[0120] For these measurements, the inorganic enamel on the surface of the substrate has a random pattern for examples E2 and E3 and counterexample CE2, and a periodic pattern of squares of about 1.25mm on each side for example El, E4 and for counterexample CEI.

[0121] All the results are grouped in Table 3. The values ​​of the parameters D, AVm and Iv are reported for metal friction using a stainless steel (inox) and aluminum (alu) pan and are respectively annotated with the words "inox" and "aluminum".

[0122] [Tables3] Tab. 3 El E2 E3 E4 CEI CE2 E (pm) 1.7 1.8 1.9 1.7 1.7 2.7 Rt (pm) 1.0 1.0 1.2 1.2 4 1.14 Ptm(%) 0.95 0.86 1.05 1.12 2.2 D-60 x 3.5 5 1.5 D - alu 1 0 0 4 5 4 AVm - stainless steel (UA) 2.0 0 0 2.8 8.9 5.3 AVm - alu (UA) 2.0 0 0 3.8 8.0 4.3 Iv - stainless steel (%) 1.03 0 0 1.05 Iv - stainless steel (UA) 0.55 0 0 2.23 7.03 - AL* 13.3 31.0 45.0 8.8 7.2 12.3 Fs 0.23 0.13 0.19 0.20 0.52 0.16 Fd 0.17 0.10 0.40.10.15

[0123] The results in Table 3 show that the number, and therefore the visibility, of metallic marks and traces is lower for the examples E1, E2, E3, and E4 according to the invention than for the IEC and CE2 counterexamples. Indeed, regardless of the parameter, D, AVm, and Iv, considered for friction using a stainless steel (inox) or aluminum (alu) pan, the values ​​are lower for the examples according to the invention. The values ​​of the parameters AVm and Iv decrease by 75% to 92%, meaning that the visibility of the metallic marks and traces is reduced accordingly.

[0124] Comparing the results of Example E1 with those of Example E4 shows that the parameter values, D, AVm, and Iv, are lower when a manufacturing method conforming to the second aspect of the invention is used. The manufacturing method according to the invention therefore provides better performance, in terms of reducing the visibility of metallic marks and traces, than a screen-printing method. The use of a screen-printing method nevertheless remains possible.

[0125] Comparison of the results of examples E1, E2, and E3 shows that the visibility Metallic traces and marks remain very limited even for inorganic enamels with a low level of contrast with the mineral substrate, particularly dark in appearance with an AL* below 35, especially black in color with an AL* below 15.

Claims

Demands

1. Mineral substrate (1001) comprising on at least one of its surfaces an inorganic enamel (1002), characterized in that: - the inorganic enamel (1002) has a total surface roughness value (1002-S) less than or equal to 2 pm, and - the edge (1002a, 1002b) of the inorganic enamel (1002) protruding at the surface (1001-S) of the mineral substrate (1001) has a topographic slope value, expressed as a percentage, less than or equal to 1.4%.

2. Mineral substrate (1001) according to claim 1, wherein the value of said total surface roughness is less than or equal to 1.5 pm, preferably less than or equal to 1 pm.

3. Mineral substrate (1001) according to any one of claims 1 to 2, such that the value of said topographic slope is less than or equal to 1.2%.

4. Mineral substrate (1001) according to any one of claims 1 to 3, such that the thickness of the inorganic enamel (1002) is between 1.5pm and 3.5pm, or even between 1.5pm and 2pm.

5. Mineral substrate (1001) according to any one of claims 1 to 4, such that the relative difference in luminance AL*, defined as the difference between the luminance L*(enamel / substrate), measured by reflection, of the inorganic enamel (1002) on the mineral substrate (1001) and the luminance L*(substrate), measured by reflection, of the mineral substrate (1001) without inorganic enamel (1002), is at most 50, preferably at most

6. □ J. Mineral substrate (1001) according to any one of claims 1 to 5, such that the luminance L*(substrate), measured in transmission, of said mineral substrate is less than or equal to 5.

7. Mineral substrate (1001) according to any one of claims 1 to 6, wherein the light transmission of the mineral substrate is at most 17%, preferably at most 10%, or even at most 5%.

8. Mineral substrate (1001) according to any one of claims 1 to 7, such that the static and / or dynamic friction coefficient of the surface of said mineral substrate (1001) provided with said inorganic enamel (1002) is at most 0.30, preferably at most 0.

25.

9. Mineral substrate according to any one of claims 1 to 8, such that the mineral substrate is a glass-ceramic substrate or a mineral glass substrate.

10. Method of manufacturing a mineral substrate (1001) according to any one of claims 1 to 9, said method comprising a step of depositing an inorganic enamel (1002) by mineral inkjet printing onto a mineral substrate (1001) in which the ink coverage is at least 45% and at most 85%, and the mass percentage of the solid fraction in the mineral ink used for inkjet printing is at most 40% of said mineral ink.

11. Manufacturing method according to claim 10, wherein the surface tension of the mineral ink is approximately 26 mN / m at 25°C.

12. Use of a mineral substrate (1001) according to any one of claims 1 to 9 as a surface of a cooking device or worktop.

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