Decoration for glass-ceramic items containing talc

Abstract

The invention relates to an enamel composition for a glass-ceramic article comprising glass and talc. In a second aspect, the invention relates to a method for obtaining said composition comprising mixing a glass frit and talc, and optionally attrition of the resulting mixture. The invention also relates to a glass-ceramic article comprising at least one substrate, such as a glass-ceramic plate, coated at least partially with an enamel composition according to the invention. Finally, the invention also relates to a method for obtaining said glass-ceramic article comprising supplying a glass-ceramic substrate, printing thereon an enamel composition according to the invention, and ceramicizing the entire substrate and enamel.

Description

Title of the invention: Decoration for a glass-ceramic article comprising talc

[0001] The present invention relates to the field of glass-ceramics. More specifically, it relates to a glass-ceramic article (or glass-ceramic article), intended in particular to cover or receive heating elements and / or intended to serve as a furniture surface, optionally in combination with heating elements. Such an article is, for example, a cooking plate, an oven door, a fireplace insert, a fire screen or even a central island for a kitchen or dining room.

[0002] By glass-ceramic article is meant an article based on a substrate made of glass-ceramic material, such as a glass-ceramic plate, said substrate possibly being provided with accessories or additional elements, decorative or functional. The article can designate both the substrate alone and that provided with additional equipment. Thus, the article can designate a cooking plate provided with a control panel and / or heating elements. Prior art

[0003] There are several commonly used glass-ceramic products, in particular glass-ceramic cooking plates, which are very popular with householders, appliance manufacturers and users. This success is explained in particular by the attractive appearance of these plates and their ease of cleaning.

[0004] A glass-ceramic is originally a glass, called precursor glass, mother glass or "green glass", whose specific chemical composition allows controlled crystallization to be caused by suitable heat treatments, called ceramization. This specific, partly crystallized structure gives the glass-ceramic unique properties.

[0005] There are currently different types of glass-ceramic plates, each variant being the result of significant studies and numerous tests, given that it is very difficult to make modifications to these plates and / or to the process for obtaining them without risking an adverse effect on the desired properties.

[0006] In particular, in order to be used as a cooking plate, a glass-ceramic plate must generally have a transmission in the wavelengths of the visible range that is both low enough to mask at least part of the underlying heating elements when at rest and high enough so that, depending on the type of heating, the user can visually detect the heating elements in working order for safety purposes. A glass-ceramic plate must have a high transmission in the wavelengths of the infrared range in the This is particularly the case for radiant hobs. It must also have sufficient mechanical strength for the area of ​​use of such hobs. In particular, to be used as a cooking hob, a glass ceramic hob must have good resistance to pressure as defined by standard EN 60335-2-6, but also to impacts.

[0007] The most common glass-ceramic hobs are dark in color, particularly black, brown or orange-brown. They are generally decorated on the upper side with enamel in order to delimit the cooking zones and the functional keys as well as to protect the glass-ceramic from the aggressions linked to its use. The use of black enamel is particularly attractive because it offers a low-contrast appearance with a black glass-ceramic hob.

[0008] An enamel is usually a mineral layer formed by firing an enamel composition comprising a glass frit and pigments.

[0009] Thus, enamels have properties of resistance to heat, abrasion, tearing and chemical attack that are much higher than usual decorative elements such as paint, which allows their use on glass-ceramic items, in particular cooking plates.

[0010] However, the pigmentation of enamels based on black pigments available on the market such as CoCrFeNi or CuCr spinel leads to shades with a brown tendency. Furthermore, for screened decorations, these enamels are likely to be marked by traces after cleaning the plate using a dry cloth. These disadvantages are particularly observed for enamels formulated from a DEC 146 glass frit as described in application FR 2701 473 AL

[0011] Furthermore, the accumulation of food deposits on an enameled glass ceramic can lead to enamel peeling off under the effect of temperature, in particular for enamels formulated from DEC 146 glass frit and more particularly for enamels made from IB2 glass frit as described in application FR 3 012 130 AL

[0012] Document FR 2 457 312 A1 describes self-cleaning coating compositions, in particular for the internal walls of an oven, comprising an oxidation catalyst, an oil and grease polymerization inhibitor and a binder in which the action of the oxidation catalyst allows self-cleaning by volatile oxidation of the oils and greases on the walls of an oven. According to this document, the oil and grease polymerization inhibitor makes it possible to lower the temperature at which self-cleaning occurs. Among these inhibitors is talc. This document therefore does not take into account any of the specificities linked to the use of talc in an enamel for a glass-ceramic hob such as the required mechanical properties or aesthetic considerations, in particular in terms of color.

[0013] Document FR 2 858 974 A1 addresses the problem of the brown color of enamels based on black pigments. According to this document, this coloring is due to the zinc oxide present in the flux, reacting chemically during firing with the surface of commercially available black pigments. In order to solve this problem, this document proposes the use of an enamel based on a colorless frit and a black pigment coated with glass in a weight proportion of 0% to 10%. This solution, however, has the disadvantage of requiring special implementation, complicating the enamel manufacturing process and resulting in additional costs.

[0014] There therefore remains a need for easily accessible glaze compositions for glass-ceramic articles having a black coloring and satisfactory mechanical properties, in particular in that the glazes obtained do not mark during their use, for example in contact with nails or a dry cloth, and allow cleaning of food deposits resulting in reduced tearing. Statement of the invention

[0015] The present invention aims to meet these needs by proposing such enamel compositions. As is apparent from the present text, the inventors have demonstrated that the incorporation of talc in enamel compositions makes it possible to obtain black-colored enamels which do not mark during their use and which have better resistance to tearing.

[0016] The invention is completely surprising from the tribology point of view because talc has a very low hardness, unlike, for example, the pigments usually used in enamels.

[0017] Furthermore, talc has the advantage of being an abundant and inexpensive raw material.

[0018] This solution is easily transposable to existing enamel formulations since it does not require any significant change in the manufacturing process and does not lead to a significant increase in their cost.

[0019] Thus, according to a first aspect, the invention relates to an enamel composition for a glass-ceramic article comprising glass and talc.

[0020] An enamel composition can designate an enamel before firing as well as after firing. Thus, by "glass" is meant to designate in an enamel composition according to the invention, before firing, a glass frit and after firing, a glass matrix obtained by melting the glass frit. The enamels according to the invention are typically obtained by firing above 850°C and preferably above 900°C. Brief description of the drawings

[0021] Other features and advantages of the present invention will become apparent from the following: description made below, with reference to the attached drawings which illustrate examples of embodiment, without any limiting character. In the figures:

[0022] [Fig.l] is a colorimetric diagram presenting the data relating to examples 1 to 4 according to the invention and to comparatives 1 and 2, this diagram comprises two parts: a first part in 2 dimensions according to the colorimetric coordinates a* and b*, schematically divided into 4 coloring domains (yellow, red, blue and green) and a second part according to 1 dimension, represented by the coordinate L* of the samples, representative of the luminosity of the shade of the sample, that is to say that the closer L* is to 0, the darker the sample has.

[0023] [Fig.2] shows photographs of samples of glazed ceramic hobs, illustrating scores of 0, 2 and 4 for the so-called "fingerprint" test set out in the examples of the application.

[0024] [Fig.3] presents the results obtained for examples 1 to 4 according to the invention for this same test.

[0025] [Fig.4] shows photographs of comparison 3 and example 5 according to the invention following the tear-off test set out in the examples of the application.

[0026] Description of embodiments of the invention

[0027] In a particular embodiment, the enamel composition according to the invention comprises a glass frit and talc. According to this embodiment, the composition according to the invention may further comprise an organic medium.

[0028] Said organic medium allows the desired viscosity to be set for application to the substrate and allows bonding with the substrate. This medium, chosen to ensure good suspension of the particles (frit and talc) and which must be consumed at the latest during firing of the enamel, can be any organic medium or binder usually used in traditional enamel compositions and can in particular comprise solvents, diluents, oils such as pine oils and other vegetable oils, resins such as acrylic resins, petroleum fractions, film-forming materials such as cellulosic materials, etc.

[0029] In particular, an organic medium suitable for the present invention may comprise at least one compound chosen from glycols and pine oils. Preferably, said organic medium comprises at least one glycol such as 2-(2-bu-toxyethoxy)ethanol or 2-butoxyethanol.

[0030] The proportion of medium in the composition ready to be deposited may be between 40% and 60% by weight of said composition, preferably between 45% and 55% by weight. The enamel composition before deposition on a glass-ceramic substrate is therefore generally in the form of a stable liquid-solid mixture, of pasty consistency, of viscosity adapted to the deposition process, in particular adapted to a screen printing deposit.

[0031] In another embodiment, the enamel composition according to the invention comprises a vitreous matrix and talc.

[0032] A composition according to the invention may comprise talc in a content ranging from 5% to 40% by weight, in particular from 7% to 35% by weight and preferably from 10% to 30% by weight relative to the total weight of the enamel.

[0033] A composition according to the invention may comprise less than 1% by weight of pigments, for example less than 0.5% by weight, in particular less than 0.1% by weight of pigment relative to the total weight of the enamel and preferably the enamel is free of pigment.

[0034] Thus, the present invention can simplify the composition of an enamel since a black enamel can be obtained by simply mixing a glass frit and talc, without adding pigment. However, a usual formulation of a black enamel may require the use of additional pigments in addition to black pigments in order to compensate for certain shade nuances.

[0035] An enamel composition according to the invention can be obtained from a mixture of glass frit and talc having a D90 of less than 20 pm, in particular less than 15 pm and preferably less than 10 pm.

[0036] That is to say that, in this case, 90% of the particles constituting the mixture of glass frit and talc have a diameter of less than 20 pm, in particular less than 15 pm and preferably less than 10 pm.

[0037] As demonstrated in the examples below, the inventors have observed that a reduction in the diameter of the particles, i.e. the particle size, constituting said mixture reinforces the effects of the invention. Thus, an enamel composition comprising a glass frit and talc with a fine particle size as described in the preceding paragraph, makes it possible to obtain an even darker enamel coloration and an enamel even less likely to be marked than an equivalent enamel composition having a higher particle size.

[0038] In a particular embodiment of the invention, the composition according to the invention comprises glass of the following composition SiO2: 35-50% B2O3: 23-30% A12O3: 10-22% Li2O: 1-3% Na2O: 0-3% K2O: 2-5% Li2O + Na2O + K2O: < 8% CaO: 1-5% CaO + MgO + ZnO + BaO + SrO: < 7% TiO2: 0-2% ZrO2: 0-5% the proportions being expressed as weight percentages relative to the total weight of glass.

[0039] Such a glass composition corresponds to a glass frit called “DEC146” and is described in application FR 2 701 473 A1. For an enamel composition according to the invention containing a glass of composition as described above, among the effects of the invention described above, the addition of talc makes it possible to particularly improve the resistance to marks of the enamel.

[0040] According to this embodiment, the glass may have a coefficient of thermal expansion less than or equal to 60.107 K1, in particular less than or equal to 56.107 K1.

[0041] Still according to this embodiment, the glass may have a softening temperature Tl greater than 650°C, in particular greater than 680°C.

[0042] Also according to this embodiment, the composition according to the invention may comprise talc in a content ranging from 15% to 40% by weight, in particular from 17% to 35% by weight and preferably from 20% to 30% by weight relative to the total weight of the enamel.

[0043] In another embodiment of the invention, the enamel composition comprises glass of the following composition, the proportions being expressed as weight percentages relative to the total weight of glass: SiO2 45-60%, preferably 50-58%, A12O3 12-22%, preferably 15-19%, B2O312-22%, preferably 15-19%, Li2O 0-5%, preferably >0-5%, Na2O 0-2%, K2O > 2%, CaO 0-4%, preferably 0-2%, MgO 0-4%, preferably > 0-4%, ZnO 0-4%, preferably > 0-4%, BaO 0-4%, preferably > 0-4%, ZrO2 0-4%, in particular 0-2% and preferably > 0-2% TiO2 0-1%, preferably 0-0.5% the sum of the proportions of the oxides CaO + MgO + BaO + SrO + ZnO furthermore being less than or equal to 10% and preferably between 2 and 8%.

[0044] Such a glass composition corresponds to a glass frit called “IB2” and is described in application FR 3 012 130 A1. For an enamel composition according to the invention containing a glass of composition as described above, among the effects of the invention described above, the addition of talc makes it possible to particularly improve the resistance to tearing of the enamel.

[0045] According to this embodiment, the composition according to the invention may comprise talc in a content ranging from 5% to 30% by weight, in particular from 7% to 20% by weight and preferably the enamel comprises talc in a content of from 10% to 20% by weight relative to the total weight of the enamel.

[0046] According to a second aspect, the invention relates to a process for obtaining an enamel composition according to the invention comprising the mixing of a glass frit and talc, and optionally the attrition of the mixture obtained for a period ranging from 5 minutes to 1 hour, in particular from 15 minutes to 45 minutes and preferably from 20 minutes to 40 minutes.

[0047] By "attrition" is meant grinding using a grinder or microgrinder by attrition, in particular in an alcoholic medium. Such a microgrinder may for example be the one sold under the reference "Attriteur PE075" by the company Netzsch.

[0048] Attrition makes it possible, from a mixture of glass frit and talc particles of known particle size, to reduce the latter, in particular with a view to obtaining a D90 of less than 20 pm, in particular less than 15 pm and preferably less than 10 pm.

[0049] According to a third aspect, the invention relates to a glass-ceramic article comprising at least one substrate, such as a glass-ceramic plate, said substrate being coated at least in part with an enamel composition according to the invention.

[0050] The substrate is generally a plate, in particular intended: • to be used with, in particular to cover or receive, at least one light source and / or one heating element, or • intended to serve as a furniture surface or fireplace insert.

[0051] Said substrate generally has a shape chosen from the following: rectangular, in particular square, circular and oval. It generally has: • a face facing the user in the position of use called the visible or external face which may correspond to the upper face in the position of use, • a second face, opposite the external face, called the internal face, generally hidden in the position of use, for example in a frame or furniture box which may correspond to the lower face in the position of use, and • a slice, called edge or thickness.

[0052] The upper or external face is generally flat but may also locally have at least one raised area and / or at least one hollow area and / or at least one opening and / or beveled edges. These variations in shape may constitute continuous variations of the plate.

[0053] The lower or internal face can also be flat and smooth or provided with studs.

[0054] The thickness of the glass-ceramic substrate is generally at least 2 mm, in particular at least 2.5 mm, and is advantageously less than 15 mm, in particular is between 3 and 15 mm, in particular between 3 and 8 mm or between 3 and 6 mm.

[0055] The substrate may be based on any glass-ceramic and advantageously has a coefficient of thermal expansion or “Coefficient of Thermal Expansion” (CTE), zero or almost zero, in particular lower in absolute value than 30.107 K1 between 20°C and 700°C, in particular lower than 15.107 K1, or even lower than 5.107 K 1 between 20 °C and 700 °C.

[0056] In particular, a substrate with a black or brown appearance is used, allowing, in combination with light sources placed beneath it, the display of luminous zones or decorations, while masking any underlying elements. It may in particular be based on a black vitroceramic comprising crystals of [3-quartz] structure within a residual vitreous phase, the absolute value of its coefficient of thermal expansion being advantageously less than or equal to 15.107 K1, or even 5.107 K1, such as the vitroceramic plates marketed under the name Kerablack+ by the company Eurokera.

[0057] It may in particular be a vitroceramic refined with arsenic, of composition as described in patent applications EP0437228, US5070045 or FR2657079, or a vitroceramic refined with tin, having an arsenic oxide content preferably less than 0.1%, for example of composition as described in patent application WO 2012 / 156444, or refined with sulfide(s) as described in patent application WO 2008 / 053110.

[0058] The substrate may, if appropriate, be coated with other coatings or layers with a functional and / or decorative effect, deposited in particular in areas other than the areas coated with the enamel according to the invention, such as usual patterns based on other enamels or a layer of opacifying paint on another part of the substrate, or at least one functional layer of the anti-scratch layer, anti-overflow layer, opacifying layer, etc. type.

[0059] The article according to the invention may further comprise, associated or combined with the substrate, at least one light source and / or at least one heating element chosen from radiant or halogen elements, atmospheric gas burners and induction heating means.

[0060] The light source can be integrated into or coupled to at least one display type structure(s), to an electronic control panel with sensitive keys and digital display, etc., and is advantageously formed of displays made up of diodes electroluminescent, more or less spaced, possibly associated with at least one optical guide.

[0061] The article according to the invention may further be associated with at least one additional functional element such as a frame, a connector, a cable or control elements.

[0062] The article according to the invention has in particular good thermal resistance compatible with the use of various types of heating, and does not pose any maintenance or scratching problems, in particular abrasion as indicated previously, in particular compared to a vitroceramic article comprising a usual enamel.

[0063] According to a fourth aspect, the invention relates to a method for obtaining a glass-ceramic article according to the invention, comprising: a. providing a glass-ceramic substrate, b. printing, in particular by screen printing, on said substrate of an enamel composition according to the invention, and c. ceramizing the entire substrate and enamel, in particular the ceramization step comprises heating the entire substrate and enamel to a temperature of 650°C to 830°C, preferably for 5 to 90 minutes and then to a temperature of 850°C to 1100°C, preferably for 5 to 30 minutes.

[0064] The manufacture of glass-ceramic plates generally takes place as follows: in a melting furnace, the glass of the composition chosen to form the glass-ceramic is melted, then the molten glass is rolled into a standard ribbon or sheet by passing the molten glass between rolling rollers and the glass ribbon is cut to the desired dimensions. The plates thus cut are decorated with an enamel-based decoration deposited by screen printing or enamel jet, then ceramized in a manner known per se. Ceramization consists of firing the plates according to the chosen thermal profile to transform the glass into a polycrystalline material called glass-ceramic, whose coefficient of expansion is zero or almost zero and resistant to thermal shock of up to 700 °C.Ceramization generally comprises a step of progressively increasing the temperature, for example up to a so-called "nucleation plateau" temperature and for example between 650°C and 830°C, this step being able to last from 5 to 90 minutes. The temperature is then raised again to allow the growth of the crystals, up to a so-called "crystal growth plateau" temperature of for example between 850°C and 1100°C, preferably between 900°C and 1000°C, for opalescent and opaque glass-ceramics, maintained for example for 5 to 30 minutes. Finally, the plate undergoes rapid cooling to room temperature.

[0065] Where appropriate, the method also comprises a cutting operation, for example for example by water jet or mechanical tracing with a wheel, followed by a shaping operation, for example by grinding or beveling. Preferably, said cutting operation is carried out before ceramization.

[0066] The enamel is deposited on the glass-ceramic substrate before ceramization. This deposition is carried out by printing, for example by digital printing or by screen printing.

[0067] A screen printing process comprises the deposition, in particular using a doctor blade, of a pasty liquid on a substrate through meshes of a screen printing screen. The meshes of the screen are closed in the part corresponding to the areas of the substrate which must remain bare, so that the paste can only pass through the screen in the areas to be printed, according to a predefined pattern. The selective closing of the meshes is therefore done according to the negative of the pattern to be printed.

[0068] This selective sealing is generally carried out by applying a photocrosslinkable resin to the screen and then by exposing, using ultraviolet radiation, the parts of the screen to be sealed.

[0069] Selective exposure is, for example, achieved using LEDs emitting ultraviolet radiation, controlled by a computer so as to block the screen meshes according to a selected image file.

[0070] The mesh of the screen is chosen according to the viscosity and surface tension of the paste as well as according to the desired thickness for the layer resulting from the screen printing deposit.

[0071] The following examples are representative of the invention described above without, however, it being limited thereto. Examples

[0072] The following examples illustrate the results obtained with the glass-ceramic and enamel articles according to the present invention (examples 1 to 8) in comparison with reference examples relating to different prior glass-ceramic and enamel articles (comparatives 1 to 4). The compositions of the enamels included in these are detailed in the following tables 1 and 2 where the contents of each of the compounds are expressed as a percentage by weight, relative to the total weight of the enamel. The enamels were tested for two different types of frits: DEC 146 as described in application FR 2 701 473 A1 and IB2 as described in application FR 3012 130 A1, for IB2 two different particle sizes of glass frit were tested. [Tables 1] Comp. 1 Comp. 2 Comp. 3 Comp. 4 Glass Frit DEC 146 70 80 - - IB2 - - 100 100 Black Pigment 16 18 Blue Pigment 14 2 Attrition (min) 35 35 D90 (pm) 4.5 5 3.4 10.9 L* 6.54 7.11 0.58 0.56 a* 0.76 1.41 0.03 -0.01 b* -1.32 0.17 -0.49 -0.50 [Tables 2] Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7 Ex. 8 Fri® glass DEC 146 (D90<9.5 pm) 70 70 80 80 - - - ■ - ■ IB2 (D90=3.4 pm) " ■ 90 ■ - ■ IB2 (D90=10.9 pm) - - - - 90 70 80 Talc (DC8345 from Nonnàg GmbH) (D90=3Ô um) 30 30 20 20 10 10 30 20 Attrition (min) 35 - 35 120 120. 120 120 D90 (pm) - 9.6 8.4 4.7 4.9 6.3 6.3 L* 7.20 6.18 7.68 3.44 0.8 0.87 8.20 2.67 a* -0.20 <04 <33 <10 <01 <03 0.11 <01 b* -3.53 <04 -3.60 -3.57 ■0.6 <77 -2.12 -1.05

[0073] Tables 1 and 2 also present several parameters specific to the enamels obtained and detailed below.

[0074] For each of the examples, a mixture is made between the glass frit and the pigments or the talc. Optionally, this mixture then undergoes grinding carried out using an attrition microgrinder (“Attritor PE075” from the company Netzsch) in alcoholic medium, containing zirconium oxide beads with a diameter of 1 mm (reference “Zetabeads Plus” from the company Netzsch).

[0075] The particle size of the mixture obtained, whether attrited or not, is then measured using a “Mastersizer 3000” reference laser particle sizer from Malvem.

[0076] The mixture is then screen printed on a Kerablack+ mother glass from Eurokera SNC and then fired according to a ceramization cycle at 930°C.

[0077] The colorimetric parameters L*, a* and b*, defined in the CIE colorimetric system, are evaluated in a known manner using in particular a Byk-Gardner Color Guide 45 / 0 colorimeter by reflection colorimetry.

[0078] All the colorimetric data of examples 1 to 4 according to the invention and of comparatives 1 and 2, all containing a DEC146 glass frit, are also presented in the colorimetric diagram of [Fig.l].

[0079] It is observed that comparisons 1 and 2, containing black and blue pigments, both have a colorimetry with a brown tendency, that is to say with an a* coordinate greater than 0.7, particularly marked for comparison 2.

[0080] Examples according to the invention 1 to 4, containing the same glass frit as comparative examples 1 and 2 but devoid of pigments, have a* coordinates varying little according to the quantity of talc and their particle sizes, situated between 0 and -0.3, resulting in a less brown shade than the enamels in comparisons 1 and 2.

[0081] In the same way, the b* coordinate of examples 1 to 4 according to the invention is stable, between -3.53 for example 1 and -4.04 for example 2, for which the attrition seems to cause a slight variation in the colorimetry towards more bluish tints.

[0082] Finally, it can be observed that attrition influences the brightness of the enamels. Indeed, by comparison between examples 1 and 2 or 3 and 4, a reduction in the L* coordinate is observed in the cases where attrition has been carried out. This effect is even more marked for example 4 which has a frit / talc ratio of 80 / 20.

[0083] The enamel compositions according to the invention therefore make it possible to obtain a satisfactory dark shade, in particular when they have a D90 less than or equal to 10 pm and / or a talc content of 20% by weight relative to the total weight of the enamel.

[0084] Concerning the enamel compositions containing IB2 glass frit, comparatives 3 and 4 consisting of 100% IB2 glass frit have a neutral black tint. Examples according to the invention 5 and 6 to 8 have the advantage of each having a colorimetry very close to those of the talc-free compositions to which they relate, that is to say, respectively, comparatives 3 and 4.

[0085] Tables 3 and 4 below present the tests carried out for each of the compositions presented above. [Tables 3] Comp. 1 Comp. 2 Comp. 3 Comp. 4 Rt (pm) 4.0 ± 0.4 2.7 ±0.5 1.2 ±0.2 2.2 ± 0.4 Ra {pm) 0.31 ±0.02 0.23 ±0.01 0.11 ±0.01 0.26 ±0.03 Gloss 60s 37.3 44.0 88.0 69 Nail mark test 7 0 0 Tear-off 7 5 4 3 [Tables 4] Ex. 1 Ex. Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. Ex. 8 Rt (pm) 5.6 ± 2.5 ± 6.2 ± 1.9 ± 1.2 ± 1.5 ± 3.1 ± 1.3 ± 0.5 0.2 0.4 0.3 0.4 0.2 0.4 0.4 Ra (pm) 0.74 0.24 1.80 0.16 0.12 0.14 0.28 0.13 ±; .LÉ ■ i.- _L ± 0.04 0.03 0.05 0.02 0.02 0.01 0.02 0.01 Gloss 60ù 33.4 60.1 51.0 83.0 88.0 81.0 32.0 78.0 'Nail mark test 1 0 1 0 0 0 1 0 Tear-off - 2 1 1 1 7

[0086] The total roughness measurements Rt and average Ra are obtained using a Mitutoyo Sj-400 roughness meter according to ISO 97 standard over an evaluation length of 4 mm at 5 points on flat areas of 5 cm on each side screen-printed on a 9x9 cm substrate.

[0087] Gloss measurements at 60° are carried out using a Byk-Gardner Spectro-Guide 45 / 0 Gloss colorimeter according to ISO 2813. The results of these measurements are expressed in gloss units, denoted "Gloss Unit" or GU. The higher the gloss value, the glossier the sample observed. Conversely, a lower value is representative of the matte character of a sample.

[0088] It is generally observed that the reduction in granulometry in talc-based enamels has the consequence of increasing the shine of the enamel and reducing its roughness.

[0089] The samples also underwent a so-called “nail trace” test, carried out on a solid surface of enamel, completely covering a glass-ceramic substrate. This test consists of moving the nail of the index finger over a distance of 5 cm. A score of 0 to 4 is then assigned to the sample according to the trace left on the flat area of ​​enamel. A score of 0 qualifies an enamel on which no trace is observed while a score of 4 corresponds to an enamel showing a very marked trace. [Fig.2] shows photographs of samples representative of scores 0, 2 and 4. A score of 0 or 1 meets consumer expectations in terms of sensitivity of enamels to traces, for example from a cloth. [Fig.3] shows the results obtained for examples 1 to 4 according to the invention.

[0090] It is therefore observed that while comparative enamels 1 and 2 have a score of 2 deemed unsatisfactory, the talc-based enamels, comprising the same glass frit, of examples according to the invention 1 to 4 have a lower score of 1 or even 0 for the enamels whose mixture of frit and talc has undergone attrition (examples 2 and 4). The presence of talc in these enamels therefore makes it possible to obtain for them a better performance with regard to sensitivity to traces.

[0091] Concerning the enamels containing an IB2 glass frit, those of comparative examples 3 and 4 already have a satisfactory rating. It should therefore be noted that the addition of talc makes it possible to maintain satisfactory sensitivity to traces.

[0092] The results presented above also demonstrate that the talc content has little impact on the sensitivity of the enamel to traces since equivalent results are obtained for examples 1 and 3 (respectively 20% and 30% by weight of talc), 2 and 4 (respectively 20% and 30% by weight of talc) and 6 and 8 (respectively 10% and 20% by weight of talc) according to the invention.

[0093] Furthermore, as observed by comparing examples 1 and 2 or 3 and 4 according to the invention, the reduction in particle size resulting from attrition makes it possible to obtain better performance in terms of sensitivity to traces of an enamel containing talc.

[0094] The tear-off test simulates the cleaning of the accumulation of burnt food on a glass-ceramic hob decorated with enamel. It is carried out on an inductor-heated area and consists of depositing, on the enamel at the level of the heating zone, a mixture made up of different foods (ground beef, cheese, sugar, eggs, milk, flour, tomato sauce, cornstarch, salt, pepper) and letting it burn for 10 min at a power corresponding to a hot spot of 420 °C. Said hot spot is the average of the measurements taken using a thermocouple on the underside of a saucepan and a thermal camera on the upper side placed after removing the saucepan from the glass-ceramic article. This step is repeated 5 times. After the 1st and 5th cycles, the vitroceramic surface is cleaned using a scraper, then a non-abrasive pad and a vitroceramic cleaning product. The extent enamel tearing is then observed and a score is given to the sample from 0 (no tearing) to 5 (tearing over the entire tested surface).

[0095] [Fig.4] shows for information purposes the results of the tear-off tests for comparison 3 and example 5 according to the invention.

[0096] By comparison: • examples 2 and 4 according to the invention with comparison 1, • of example 5 according to the invention with comparison 3, • examples 7 and 8 according to the invention with comparison 4, It is observed that the addition of talc to a glass frit in an enamel makes it possible to obtain better resistance to tearing.

[0097] In particular, the peel strength of the enamels containing an IB2 glass frit, represented by comparisons 3 and 4, is significantly improved by the addition of talc, as observed in examples 5, 7 and 8.

Claims

Claims

1. Enamel composition for a glass-ceramic article comprising glass and talc.

2. Enamel composition according to the preceding claim, in which the talc is present in a content ranging from 5% to 40% by weight, in particular from 7% to 35% by weight and preferably from 10% to 30% by weight relative to the total weight of the enamel.

3. An enamel composition according to any preceding claim, comprising less than 1% by weight of pigments, for example less than 0.5% by weight, in particular less than 0.1% by weight of pigment relative to the total weight of the enamel and preferably the enamel is free of pigment.

4. Enamel composition according to any one of the preceding claims, wherein the enamel is obtained from a mixture of glass frit and talc having a D90 of less than 20 pm, in particular less than 15 pm and preferably less than 10 pm.

5. Enamel composition according to any one of the preceding claims, in which the glass is of the following composition SiO2: 35-50% B2O3: 23-30% A12O3: 10-22% Li2O: 1-3% Na2O: 0-3% K2O: 2-5% Li2O + Na2O + K2O: < 8% CaO: 1-5% CaO + MgO + ZnO + BaO + SrO: < 7% TiO2: 0-2% ZrO2: 0-5% the proportions being expressed as weight percentages relative to the total weight of glass.

6. Enamel composition according to the preceding claim, in which the glass has a coefficient of thermal expansion less than or equal to 60.107 K1, in particular less than or equal to 56.107 K *.

7. Enamel composition according to any one of claims 5 or 6, wherein the glass has a softening temperature TL above 650°C, in particular above 680°C.

8. Enamel composition according to any one of claims 5 to 7, comprising talc in a content ranging from 15% to 40% by weight, in particular from 17% to 35% by weight and preferably from 20% to 30% by weight relative to the total weight of the enamel.

9. Enamel composition according to any one of claims 1 to 4, wherein the glass is of the following composition, the proportions being expressed as weight percentages relative to the total weight of glass: SiO2 45-60%, preferably 50-58%, Al2O3 12-22%, preferably 15-19%, B2O312-22%, preferably 15-19%, Li2O 0-5%, preferably > 0-5%, Na2O 0-2%, K2O > 2%, CaO 0-4%, preferably 0-2%, MgO 0-4%, preferably > 0-4%, ZnO 0-4%, preferably > 0-4%, BaO 0-4%, preferably > 0-4%, ZrO2 0-4%, in particular 0-2% and preferably > 0-2% TiO2 0-1%, preferably 0-0.5% the sum of the proportions of the oxides CaO + MgO + BaO + SrO + ZnO being further less than or equal to 10% and preferably between 2 and 8%.

10. Enamel composition according to the preceding claim, comprising talc in a content ranging from 5% to 30% by weight, in particular from 7% to 20% by weight and preferably the enamel comprises talc in a content of from 10% to 20% by weight relative to the total weight of the enamel.

11. A method of obtaining an enamel composition according to any one of the preceding claims comprising mixing a glass frit and talc, and optionally attrition of the mixture obtained for a period ranging from 5 minutes to 1 hour, in particular from 15 minutes to 45 minutes and preferably from 20 minutes to 40 minutes.

12. A glass-ceramic article comprising at least one substrate, such as a glass-ceramic plate, said substrate being coated at least in part with an enamel composition according to any one of claims 1 to 10.

13. Method for obtaining a glass-ceramic article according to the preceding claim, comprising: a. the supply of a glass-ceramic substrate, b. printing, in particular by screen printing, on said substrate of an enamel composition according to any one of claims 1 to 10, and c. ceramization of the entire substrate and enamel, in particular the ceramization step comprises heating the entire substrate and the enamel to a temperature of between 650°C to 830°C, preferably for 5 to 90 minutes and then at a temperature of 850°C to 1100°C, preferably for 5 to 30 minutes.

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