Coating the surface of a household article comprising a thermochromic pigment compound

Abstract

The present invention relates to a coating of the surface of a household article comprising a decoration (a) comprising a thermochromic pigment compound of formula BiOA1-xBx (I) where: - A and B are chosen from the group consisting of iodine, fluorine, chlorine and bromine, - A and B are different from each other, and - x is from 0 to 1.

Description

Title of the invention: Coating of the surface of a household article comprising a thermochromic pigment compound FIELD OF THE INVENTION

[0001] The present invention relates to a coating of the surface of a household article comprising a functional decorative layer serving as a temperature indicator, as well as articles comprising such a coating. STATE OF THE ART

[0002] In the household sector, it is essential for a user to visualize the evolution of the temperature of an item in use when the latter is subjected to a heat source or when it heats up.

[0003] In the case of a culinary article, good temperature control when cooking food is necessary for health and taste reasons (for example, to sear a steak on a grill or in a pan), but also to limit occasional overheating which weakens the coating of the culinary article and can cause the oils to smoke, thus releasing harmful fumes. Equipment which is less overheated will have a longer lifespan. Food cooked at a lower temperature will have healthier organoleptic characteristics. In addition, cooking at just the right temperature limits the energy input and therefore the environmental impact.

[0004] In the case of an iron or a hair straightener, temperature control makes it possible to avoid the undesirable effects linked to the use of such articles, such as, for example, the brittle effect on the hair or the degradation of textile fibers, and also makes it possible to avoid domestic accidents such as burns.

[0005] French patent FR 1388029 is known, which describes a cooking utensil provided with a thermal indicator consisting of a heat-sensitive body that changes color reversibly depending on the temperature, this thermal indicator being formulated in a non-stick coating, in particular consisting of polytetrafluoroethylene. A thermostable pigment (i.e. a mineral or organic compound, which exhibits a very slight change in color when subjected to an increase in temperature in a given temperature range) can also be incorporated into the cooking utensil as a control to allow an assessment of the relative change in color of the thermal indicator, and therefore of the change in temperature. However, in this invention, the thermostable control is not integrated into the non-stick coating and therefore does not provide clear visibility of the relative change in color.

[0006] To overcome these problems, the Applicant then developed a thermal indicator based on thermochromic pigments, described in European patent EP 1 121 576. This thermal indicator is a decoration comprising at least two patterns, one based on a thermochromic pigment of the iron oxide type which darkens with increasing temperature, the other based on a thermochromic pigment which lightens very slightly with increasing temperature comprising a mixture of perylene red and spinel black. It follows that at a pre-established temperature (which can be adjusted from 160°C to 220°C) a confusion of the colors of the two patterns is obtained, which is a means of identifying this pre-established temperature.

[0007] French patent FR 2891844 describes CuMoW oxides exhibiting reversible color changes under the effect of a temperature variation and / or under the effect of mechanical stress, for example a pressure of at least 105 Pa. However, these oxides for which the color variation is the consequence of a phase change are particularly sensitive to cyclability. Thus, after five cycles at most, it is no longer possible to find the metastable alpha phase responsible for the green coloring at low temperature. The interest of such a pigment as a colored thermal indicator is therefore nil in practice for use in repeated uses such as cooking food.

[0008] Furthermore, semiconductors (SC) are also known, the properties of which suggest a progressive change in color upon increasing the temperature following the sequence white-yellow-orange-red-black. The term thermochromic semiconductor (SC) is therefore understood to mean, within the meaning of the present invention, a semiconductor compound which exhibits a change in color upon increasing the temperature. The progressive and perfectly reversible thermochromic nature of these semiconductor compounds is linked to the reduction in the width of the forbidden band of the semiconductor due to the expansion of the material. In this temperature range, the color changes of the SC remain limited and not very marked and are limited to the following evolutions: from pale yellow to bright yellow (Bi2O3), from yellow-orange to red-orange (V2O5), from red-orange to very dark red (Fe2O3), etc.We can therefore see that, even if it is possible to achieve colours other than red, the perception of the thermochromic effect remains difficult and imprecise.

[0009] European patent EP 0 287 336 and European patent application EP 1 405 890 disclose the preparation of mixtures consisting of one or more thermochromic semiconductors and one or more stable pigments in order to obtain complex compositions with increased thermochromic properties. More particularly, in patent EP 1 405 890, bismuth oxide Bi2O3 (thermochromic) is combined with CoA12 O4 (thermostable, blue in color), in a ratio of 15:1, the pigments being linked by a potassium silicate. The coating containing this mixture is blue at room temperature and turns orange at 400°C. However, the implementation of bismuth oxide is not easy and sensitivity to hot oils has been demonstrated, leading to blackening of the pigment.

[0010] From an industrial point of view, there remains a need to develop new coatings for household articles comprising at least one layer of functional decoration making it possible to accompany and guide the user of the household article on which the coating in question is deposited. DEFINITIONS

[0011] “Room temperature” means a temperature between 18 and 30°C.

[0012] By the term “layer”, it is necessary to understand in the sense of the present invention a continuous or discontinuous layer. A continuous layer (also called a monolithic layer) is a single whole forming a total flat area completely covering the surface on which it is placed. A discontinuous layer (or non-monolithic layer) may comprise several parts, which are not therefore a single whole.

[0013] The term "primer coat", "bonding coat" or "bonding primer" means all the layers from the first layer applied directly to the support (it is preferable that this layer adheres well to the support and provides all its mechanical properties to the coating: hardness, scratch resistance) to the last layer before the first decorative layer.

[0014] The term "finishing layer" or "finish" means a continuous and transparent surface layer, this layer allowing perfect visibility of the decorative layer while protecting it from mechanical attack and being able to give the coating its non-stick properties.

[0015] The term "decor" or "decorative layer" means one or more continuous or discontinuous layers comprising a pigment composition. The decor may be in the form of one or more patterns, of one or more colors. A decor is clearly visible to the user with the naked eye and at a conventional distance from the household item.

[0016] “Overlapping layers” means partially or completely superimposed layers. These layers may be in the form of decoration with partially overlapping patterns, for example concentric discs.

[0017] “Adjacent layers” means non-overlapping layers. These layers may be in the form of decoration with identical or different non-overlapping patterns, preferably distributed uniformly.

[0018] The term "temperature reference pigment composition" means a composition comprising a pigment which, at a given temperature, makes it possible to indicate to the user that the optimum operating temperature has been reached. This indication is done by comparing the colors of the BiOAi XBX (I) type pigment and the temperature reference pigment composition. Either the optimal use temperature is reached when the colors are identical, or the optimal use temperature is reached when the colors are visually very different.

[0019] The “temperature reference pigment composition” may comprise a pigment which has: - the same color as the BiOA, XBX (I) type pigment at the optimal use temperature, • either because this pigment has the same color at room temperature as the BiOA] XBX (I) type pigment at the optimum usage temperature and does not change color with temperature, • either because this pigment has a different color at room temperature from that of the BiOAi XBX (I) type pigment which evolves to the same color as the BiOAi XBX (I) type pigment at the optimal use temperature - a color very different from that of the BiOAi XBX (I) type pigment at the optimal use temperature, whether or not this pigment changes color with the change in temperature.

[0020] The optimum use temperature can be achieved when the color of the temperature reference pigment composition corresponds to a color indicated in the user guide for the household article comprising the coating of the invention or to a color indicated on a color scale provided to the user with said article.

[0021] The temperature reference pigment composition is thermochromic or thermostable.

[0022] For a household item which is not a cooking item, such as a hair straightener or an iron, the temperature reference pigment composition may be, for example, a reference pigment composition for normal use temperature or for indicating a danger of burning.

[0023] For a culinary article, the temperature reference pigment composition may be, for example, a cooking temperature reference pigment composition or an indication of the risk of overheating.

[0024] The present invention has at least one of the following advantages:

[0025] - the coating according to the invention has a thermochromic functionality with a marked visibility, a contrasting color change over a temperature range targeted, precise and centered, for example around food cooking temperatures for a kitchen appliance;

[0026] - the coating according to the invention can provide good temperature control, for example when cooking food, which is necessary for health and taste reasons, but also for safety reasons and to limit occasional overheating which weakens the coating;

[0027] - the compound of type BiOAi XBX (I) exhibits reversibility of its properties thermochromic, that is to say that after a change of color under the action of heat the compound returns to its initial state, and to its initial color, when the temperature decreases; this cycle of color change (reversibility) can be repeated infinitely without loss of its properties;

[0028] - the coating according to the invention has significant thermal stability during temperature increases, it is stable up to about 450°C;

[0029] - it is possible to modulate the color of the compound of type BiOAi XBX (I) according to the nature of elements A and B and the value of x.

[0030] The expression "thermochromic semiconductor" is understood to mean, within the meaning of the present invention, a mineral or organic compound which exhibits a reversible change in color upon increasing temperature. The progressive and reversible thermochromic nature of these semiconductor compounds is linked to the reduction in the width of the forbidden band of the semiconductor due to the expansion of the material. Indeed, the periodicity of the network of anions and cations leads to the gathering of energy levels into energy bands. The filled energy band with the highest energy is called the valence band and the empty energy band with the lowest energy is called the conduction band. Between these two bands, there is a forbidden band called the gap.The color of a semiconductor material can come from the presence of a charge transfer which corresponds to the passage of an electron either from a valence band to a conduction band on the same atom, or commonly from the orbital of an anion to the orbital of a cation (interatomic photonic absorption).

[0031] In the fields of application envisaged for the present invention, a household appliance of the iron or hair straightener type is typically used in a temperature range of 100°C to 300°C, preferably 100 to 250°C, particularly preferably 100 to 200°C.

[0032] In the fields of application envisaged for the present invention, in the case of a culinary article, the optimal conditions are reached when the coating reaches a temperature suitable for cooking food, preferably between 100 and 250°C.

[0033] By "pigment, pigment compound or thermochromic pigment composition" is meant, within the meaning of the present invention, a pigment, a pigment compound or a pigment composition which changes color depending on the temperature in a given temperature range, this change being reversible. This change in color is visible to the user with the naked eye and at a conventional operating distance.

[0034] The term "thermostable pigment, pigment compound or pigment composition" means a pigment, pigment compound or pigment composition which does not exhibit a change in color when subjected to an increase in temperature in a given temperature range or which exhibits a change in shade when subjected to an increase in temperature in a given temperature range which is so low that it is not visible to the user with the naked eye and at a conventional operating distance.

[0035] By "the colors are identical" we mean indistinguishable by the user with the naked eye and at a conventional viewing distance.

[0036] The expression "household article" means kitchen articles and household appliances.

[0037] The household appliances referred to here are intended to produce heat.

[0038] By the expression "culinary article", it is necessary to understand within the meaning of the present invention an object intended for cooking and to be heated by an external heating system such as pans, saucepans, sauté pans, woks, barbecue grills. A culinary article is capable of transmitting the heat energy provided by this external heating system to a material or food in contact with said object.

[0039] By the expression "object intended to produce heat", it is necessary to understand within the meaning of the present invention a heating object having its own heating system such as irons, hair straighteners, steam generators, kettles or electrical appliances intended for cooking.

[0040] The term “fluoropolymer-based coating” means a coating which comprises one or more fluoropolymer(s) in one or more of its layers.

[0041] For the purposes of the present invention, the term sol-gel coating, sol-gel layer or sol-gel decoration means a coating, layer or decoration synthesized by sol-gel method from a solution based on precursors in liquid phase, which transforms into a solid by a series of chemical reactions (hydrolysis and condensation), at low temperature. The coating, layer or decoration thus obtained can be either organo-mineral or entirely mineral.

[0042] By organo-mineral coating, layer or decoration, is meant, within the meaning of the present invention, a coating, a layer or a decoration whose network is essentially inorganic, but which contains organic groups, in particular due to the precursors used and the baking temperature of the coating.

[0043] For the purposes of the present invention, the term “fully mineral coating” means a coating, layer or decoration made of a fully inorganic material, free of any organic group. Such a coating can also be obtained by sol-gel method with a baking temperature of at least 400°C, or from precursors of the tetraethoxy-silane (TEOS) type with a baking temperature which can be less than or equal to 400°C.

[0044] By functional decoration, it is understood, within the meaning of the present invention, a decoration making it possible to guide the user of the article in its use. The field targeted is primarily that of culinary articles, but the present invention can also relate to any other type of surface, such as the soleplate of an iron, the plates of a hair straightener, or even a cover of a household appliance. Statement of the invention

[0045] A first subject of the invention relates to a coating of the surface of a household article comprising a decoration (a) comprising a thermochromic pigmentary compound of formula BiOAi XBX (I) where:

[0046] - A and B are chosen from the group consisting of iodine, fluorine, chlorine and bromine,

[0047] - A and B are different from each other, and

[0048] - x is from 0 to 1.

[0049] Another subject of the invention relates to a household article comprising a substrate, preferably metallic, covered in whole or in part with a coating according to the invention.

[0050] Another object of the invention relates to a method of using a household article according to the invention, characterized by the following steps:

[0051] - Heating or placing in the presence of an external heating source said household item,

[0052] - Observe the change(s) in color of the decoration (a) and, when present, decor (b),

[0053] - Use said household item when the colors of the decor (a) and, when it is present in the decor (b), respectively reach colors defined in the instructions for use of said household item.

[0054] Another subject of the invention relates to the use of a pigmentary compound of formula BiOAi XBX (I) where:

[0055] - A and B are chosen from the group consisting of iodine, fluorine, chlorine and bromine,

[0056] - A and B are different from each other, and

[0057] - x is from 0 to 1

[0058] in the coating of the surface of a household article as a temperature indicator.

[0059] Other aspects of the invention are as described below. DESCRIPTION OF FIGURES

[0060] [Fig. 1] represents a sectional view of an example of coating of the surface of a household article (1) comprising a metallic substrate (2), said coating comprising a decoration (a), a primer layer (3a) and a finishing layer (3b).

[0061] [Fig.2] represents an example of coating the surface of a household article (1), comprising a metallic substrate (2), said coating comprising a decoration (a) and another decoration (b), a primary layer (3a) and a finishing layer (3b), the decoration (a) and the other decoration (b) being: - in the form of adjacent non-overlapping patterns (Figure 2A); - in the form of partially overlapping patterns (Figure 2B); - in the form of overlapping patterns (Figure 2C).

[0062] In Figures 2A / B / C, the left-hand views represent the decoration (A) and the other decoration (B) seen from above the household item (1) on the coated side. The right-hand views represent the household item (1) shown in section. DETAILED DESCRIPTION OF THE INVENTION

[0063] The inventors have developed coatings meeting the expressed needs.

[0064] The inventors thus discovered that, surprisingly, bismuth oxyhalides of formula BiOAi XBX (I) where:

[0065] - A and B are chosen from the group consisting of iodine, fluorine, chlorine and bromine,

[0066] - A and B are different from each other, and

[0067] - x is from 0 to 1

[0068] are thermochromic pigment compounds within the meaning of the present invention, that is to say that they change color depending on the temperature in a given temperature range, this change being reversible and visible to the user with the naked eye and at a conventional operating distance.

[0069] A first subject of the invention relates to a coating of the surface of a household article comprising a decoration (a) comprising a thermochromic pigmentary compound of formula BiOAi XBX (I) where:

[0070] - A and B are chosen from the group consisting of iodine, fluorine, chlorine and bromine,

[0071] - A and B are different from each other, and

[0072] - x is from 0 to 1.

[0073] The decoration (a) may be in the form of a layer exhibiting a reversible variation in its optical and / or colorimetric properties when the coating comprising it is subjected, in part or in total, to a temperature variation between a cold temperature and a hot temperature, the cold temperature being between 0°C and 40°C and the hot temperature being between 80°C and 400°C.

[0074] The color at room temperature of the thermochromic pigment compound of formula BiOAl-xBx (I) depends on the choice of elements A and B as well as the value of x.

[0075] Thus:

[0076] - if x = 0 and if A represents iodine, the compound of formula BiOI appears red- orange at room temperature and turns brown at 200°C;

[0077] - if x = 0 and A represents bromine, the compound of formula BiOBr is white at room temperature and turns pale yellow at 200°C;

[0078] - if A represents an atom of F, Cl, advantageously, B will be iodine. Thus according to the invention and depending on the iodine level, the compound will appear yellow at room temperature and will turn towards an orange color at 200°C or will be orange at room temperature and will turn towards redder shades depending on the value of x;

[0079] - if A represents a Br atom, advantageously, B will be iodine. Thus according to the invention and depending on the iodine level, the compound will appear yellow to orange at room temperature and will turn orange to red at 200°C.

[0080] Advantageously, the thermochromic pigment compound of formula BiOAi XBX (I) is:

[0081] - the compound with x = 0 and A=I or A=Br;

[0082] - or the compound with x different from 0 and A= F or Cl and B=I;

[0083] - or the compound with x different from 0 and A=Br and B=I.

[0084] The thermochromic pigment compound of formula BiOAi XBX (I) may be in the form of uncoated particles, i.e. the particles are purely composed of BiOAi XBX (I).

[0085] Where appropriate, the thermochromic pigment compound of formula BiOAi XBX (I) may be in the form of core-shell coated particles, the core of which is made up of BiOAi XBX (I) particles and the shell of which is made up of one or more coating layers. The shell may improve the stability of the core with respect to lipids and oils when hot.

[0086] The level of the thermochromic pigmentary compound of formula BiOAi XBX (I) in the decoration (a) may be from 0.1% to 100% by weight relative to the weight of said decoration in the dry state, preferably from 0.2% to 80% by weight, more preferably from 0.5% to 70% by weight and even more preferably from 10% to 50% by weight.

[0087] The decor (a) may comprise a mixture of compounds of formula BiOAi XBX (I).

[0088] The decoration (a) may further comprise a thermochromic pigment compound different from the pigment compound of formula (I), preferably TiO2, Fe2O3, VO2, WO3, Bi2O3, BiVO4 or their mixtures, or a thermostable pigment compound.

[0089] According to one embodiment, the coating of the surface of the household article comprises at least the decoration (a) as defined above and a decoration (b) arranged between or in its layers, said decoration (b) comprising a temperature reference pigment composition.

[0090] The temperature reference pigment composition may be chosen from the group consisting of:

[0091] - Yellow pigments of titanium rutile type,

[0092] - Yellow pigments derived from bismuth, for example selected from vanadates stabilized bismuth (Pyl84)

[0093] - Red pigments, for example selected from perylene red, iron oxide,

[0094] - Bismuth vanadate orange pigments (PO86)

[0095] - Zinc tin titanium orange pigment (PO82)

[0096] - Cerium sulfide orange pigment (PO75; PO78)

[0097] - Orange-yellow pigment of the antimony titanium chrome rutile type (PBr24)

[0098] - Orange-yellow pigment of tin and zinc rutile type (Py216)

[0099] - Niobium tin zinc sulfide orange-yellow pigment (Py227)

[0100] - Orange-yellow pigment of double oxides of tin and niobium

[0101] and mixtures thereof.

[0102] The temperature reference pigment composition rate in the decoration (b) may be from 0.1% to 100% by weight relative to the weight of said decoration in the dry state, preferably from 0.2% to 80% by weight, more preferably from 0.5% to 70% by weight.

[0103] According to one embodiment, each of the two decorations (a) and (b) is in the form of adjacent non-overlapping patterns. For example, each decoration is represented by different geometric patterns distributed uniformly over the entire surface and alternating with respect to each other (see Figure 2A).

[0104] According to another embodiment, the two decorations (a) and (b) are partially overlapping. For example, each decoration is represented by different geometric patterns distributed uniformly over the entire surface and partially overlapping (see Figure 2B).

[0105] Preferably, the two decorations (a) and (b) are overlapping, either because one of the two decorations is a continuous layer and the other decoration covers it in the form of patterns, or because the two decorations (a) and (b) are in the form of two overlapping patterns (see Figure 2C).

[0106] The decoration (a) and the decoration (b) optionally comprise one or more fluoropolymers, may be sol-gel decorations or may comprise an enamel, a lacquer, a condensed tannin, a thermoplastic polymer other than a fluoropolymer or a silicone resin.

[0107] The decoration (a) and the decoration (b) optionally comprise additives. Said additives are chosen from the group consisting of solvents, thickeners, anti-foam agents, pH adjusters, wetting agents and dispersants.

[0108] The additives are chosen in order to optimize the quality of the deposit on the polymeric layer on which they are deposited.

[0109] Said solvents are preferably chosen from the group consisting of: water, alcohols, diols, glycols, esters.

[0110] Said thickeners are preferably chosen from the group consisting of acrylic-based or polyurethane-based copolymer, cellulose, fumed silica, silicone resin.

[0111] Said anti-foaming agents are preferably chosen from the group consisting of polysiloxane, modified polysiloxane, polyether-siloxane copolymer, amphiphilic polymers, silicone, aliphatic mineral oil.

[0112] Said pH adjusters are preferably chosen from the group consisting of Bronsted bases: ammonia, amines (triethylamine, triethanolamine, etc.), hydroxides (soda, potash, etc.), carbonates.

[0113] Said wetting agents and dispersants are preferably chosen from the group consisting of high molecular weight fatty acid derivatives, modified polyether, surfactants, modified polyacrylate.

[0114] Preferably, the coating according to the invention comprises one or more finishing layers. The finishing layer(s) is (are) applied to the decoration (a) and, where appropriate, the decoration (b).

[0115] According to a first embodiment, the household article comprises a substrate, preferably metallic, and the coating according to the invention comprises one or more primer layers applied to said substrate. The decorations (a) and (b) are then applied to the last primer layer.

[0116] According to a second embodiment, the decoration(s) are applied directly to the substrate.

[0117] Preferably, the coating according to the invention comprises in the following order from one of the faces of the substrate of the household article: a primary layer, a decoration (a) or a decoration (a) and a decoration (b), and a finishing layer.

[0118] The decoration can be applied by any method well known to those skilled in the art, for example by pad printing, electrostatic powdering, spray spraying, screen printing, roller application or digital printing.

[0119] According to one embodiment, the finishing layer(s) and, when present, the primer layer(s) comprise one or more fluoropolymers.

[0120] The fluoropolymer(s) may be in the form of powder or aqueous dispersion, or mixtures thereof.

[0121] Advantageously, the fluoropolymer(s) is(are) chosen from the group comprising polytetrafluoroethylene (PTFE), copolymers of tetrafluoroethylene and perfluoropropylvinylether (PFA), copolymers of tetrafluoroethylene and hexafluoropropene (FEP), polyvinylidene fluoride (PVDF), copolymers of tetrafluoroethylene and polymethylvinylether (MVA), terpolymers of tetrafluoroethylene, polymethylvinylether and fluoroalkylvinylether (TFE / PMVE / FAVE), ethylene tetrafluoroethylene (ETFE), and mixtures thereof.

[0122] Advantageously, the fluoropolymer(s) may be chosen from polytetrafluoroethylene (PTFE), copolymers of tetrafluoroethylene and perfluoropropylvinylether (PFA), copolymers of tetrafluoroethylene and hexafluoropropene (FEP), a mixture of PTFE and PFA (PTFE / PFA), a mixture of PTFE and FEP (PTFE / FEP).

[0123] Preferably, the fluoropolymer(s) may represent from 10 to 99% by mass, preferably from 50 to 98% by mass, of the total dry mass of the coating composition.

[0124] According to this embodiment, the decorative layer(s) optionally comprise one or more fluoropolymers as described above.

[0125] According to another embodiment, the finishing layer(s) and, when present, the primer layer(s) are sol-gel layers.

[0126] Sol-gel layers are organo-mineral or entirely mineral layers. These layers are synthesized by sol-gel method from metal alkoxide precursors, have a hybrid network, generally of silica with grafted alkyl groups.

[0127] According to this embodiment, the sol-gel layers are obtained from a sol-gel (SG) composition comprising at least one metal oxide, preferably a colloidal metal oxide chosen from colloidal silica and / or colloidal alumina and at least one precursor of metal alkoxide type, preferably an alkoxysilane chosen from the group consisting of methyltrimethoxysilane (MTMS), tetraethoxysilane (TEOS), methyltriethoxysilane (MTES), dimethyldimethoxysilane, and mixtures thereof.

[0128] The metal oxide is preferably a colloidal metal oxide chosen from colloidal silica and / or colloidal alumina.

[0129] Preferably, a metal alkoxide chosen from the group consisting of:

[0130] - precursors corresponding to the general formula Mi(0Ri)n>

[0131] - the precursors corresponding to the general formula M2(OR2)(n -i)R2', and

[0132] - the precursors corresponding to the general formula M3(OR3)(n 2)R3', with:

[0133] Ri, R2, R3 or R3' denoting an alkyl group,

[0134] R2' denoting an alkyl or phenyl group,

[0135] n being an integer corresponding to the maximum valence of the metals Mb M2 or M3j

[0136] Mi M2 or M3 designating a metal chosen from Si, Zr, Ti, Sn, Al, Ce, V, Nb, Hf, Mg and Ln.

[0137] Advantageously, the metal alkoxide of the sol-gel solution is an alkoxysilane.

[0138] As alkoxysilanes that can be used in the sol-gel solution, mention may in particular be made of methyltrimethoxysilane (MTMS), tetraethoxysilane (TEOS), methyltriethoxysilane (MTES), dimethyldimethoxysilane, and mixtures thereof.

[0139] Preferably, the alkoxysilanes MTES and TEOS will be used, because they have the advantage of not containing methoxy groups. Indeed, the hydrolysis of methoxy leads to the formation of methanol in the sol-gel formulation, which, given its toxic classification, requires additional precautions during application. Conversely, the hydrolysis of ethoxy groups only generates ethanol, which has a more favorable classification and therefore less restrictive usage requirements for the sol-gel coating.

[0140] The formation of a sol-gel layer consists of mixing an aqueous composition A comprising the colloidal metal oxide and a solution B comprising the metal alkoxide. The mixing is advantageously carried out in a ratio of 40 to 75% by weight of the aqueous composition relative to the weight of the sol-gel composition (A + B), so that the quantity of colloidal metal oxide represents 5 to 30% by weight of the sol-gel composition (A + B) in the dry state.

[0141] The aqueous composition A may further comprise a solvent, in particular a solvent comprising at least one alcohol.

[0142] The aqueous composition A may further comprise at least one silicone oil.

[0143] The aqueous composition A may further comprise a pigment.

[0144] The aqueous composition A may further comprise a mineral filler.

[0145] The aqueous composition A may also comprise fumed silica, the function is the regulation of the viscosity of the sol-gel composition and / or the gloss of the dry coating.

[0146] The aqueous composition A typically comprises for a primer layer:

[0147] i) 5 to 30% by weight relative to the total weight of the aqueous composition A of at least one colloidal metal oxide,

[0148] ii) 0 to 20% by weight relative to the weight of composition A of a solvent comprising at least one alcohol,

[0149] iii) optionally 0.05 to 3% by weight relative to the total weight of said aqueous composition A of at least one silicone oil,

[0150] iv) 5 to 30% pigment,

[0151] v) 2 to 30% mineral filler.

[0152] The aqueous composition A typically comprises for a finishing coat:

[0153] i) 5 to 30% by weight relative to the total weight of the aqueous composition A of at least one colloidal metal oxide,

[0154] ii) 0 to 20% by weight relative to the weight of composition A of a solvent comprising at least one alcohol,

[0155] iii) optionally 0.05 to 3% by weight relative to the total weight of said aqueous composition A of at least one silicone oil,

[0156] iv) 0.1 to 1% of metallic flakes.

[0157] Solution B may further comprise an acid in Bronsted or Lewis terms. Advantageously, the metal alkoxide precursor of solution B is mixed with an organic, mineral Lewis acid which represents 0.01 to 10% by weight of the total weight of solution B.

[0158] Particular examples of acids which can be used for mixing with the metal alkoxide precursor are acetic acid, citric acid, ethyl acetoacetate, hydrochloric acid or formic acid.

[0159] Solution B may further comprise a solvent, in particular a solvent comprising at least one alcohol.

[0160] Solution B may further comprise at least one silicone oil.

[0161] Solution B may further comprise metallic flakes.

[0162] According to an advantageous embodiment of the process of the invention, solution B may comprise a mixture of one of the alkoxysilanes as defined above and an aluminum alcoholate.

[0163] According to this embodiment, the decorative layer(s) are optionally sol-gel layers as described above.

[0164] According to other embodiments, the different layers of the coating (decoration, finish, primer) may comprise, instead of fluoropolymers or materials synthesized by sol-gel method, an enamel, a lacquer, a condensed tannin, a thermoplastic polymer other than a fluoropolymer or a silicone resin.

[0165] According to one embodiment, the topcoat(s) and, when present, the primer coat(s) comprise one or more aromatic thermoplastic polymers other than a fluoropolymer, one or more heterocyclic thermoplastic polymers or mixtures thereof.

[0166] THERMOPLASTIC POLYMERS

[0167] Advantageously, the thermoplastic polymer(s) is / are chosen from the group consisting of aromatic thermoplastic polymer(s) such as polyaryletherketone(s) (PAEK), poly(arylethersulfones) (PAES), poly(arylene sulfides) (PAS) or poly(phenylene oxide) (PPO), liquid crystal polymers, heterocyclic thermoplastic polymers and mixtures thereof.

[0168] PAEK

[0169] Advantageously, the polyaryletherketone(s) (PAEK) is (are) chosen from the group consisting of: polyetherketones (PEK), polyetheretherketone (PEEK), polyetherketoneketones (PEKK), polyetheretherketoneketones (PEEKK) and polyetherketoneetherketoneketones (PEKEKK), particularly preferably is (are) PEEK.

[0170] Other aromatic thermoplastic polymers

[0171] As aromatic thermoplastic polymer(s), examples which are suitable according to the invention are poly(phenylene oxide) (PPO), poly(arylethersulfone) polymer (PAES), and in particular polyethersulfone (PES), polyphenylene ether sulfone (PPSU), poly(arylene sulfides) (PAS) and in particular polyphenylene sulfide (PPS), liquid crystal polymers and mixtures thereof.

[0172] Heterocyclic thermoplastic polymers

[0173] As heterocyclic thermoplastic polymers, examples suitable according to the invention are polyetherimides (PEI), polyimides (PI), polyamideimides (PAI) and polybenzymidazole (PBI), or mixtures thereof.

[0174] Advantageously, the thermoplastic polymer(s) is / are chosen from the group consisting of polyethersulfone (PES), polyphenylene ether sulfone (PPSU), polyamideimide (PAI), polyimide (PI), poly(phenylene oxide) (PPO), poly(arylene sulfide) (PAS), polyetherimide (PEI), polybenzymidazole (PBI), liquid crystal polymers (LCP), polyphenylene sulfide (PPS), polyarylether ketone (PAEK) including polyether ketone (PEK), polyether ether ketone (PEEK), polyether ketone ketone (PEKK), polyether ether ketone ketone (PEEKK), polyether ketone ether ketone ketone (PEKEKK) and mixtures thereof.

[0175] According to this embodiment, the decorative layer(s) optionally comprise one or more aromatic thermoplastic polymers other than a fluoropolymer, one or more heterocyclic thermoplastic polymers or their mixtures, the thermoplastic polymers being as described above.

[0176] According to another embodiment, the finishing layer(s) and, when present, the primer layer(s) comprise one or more silicone resins.

[0177] SILICONE RESINS

[0178] In the text of the description, the expression "#silicone resin#" is used interchangeably to refer to the silicone before its crosslinking or after its crosslinking. In the text of the description, the expression "silicone" designates an organopolysiloxane material. Crosslinking is the step which makes it possible to transform the silicone into an insoluble material, for example by polyaddition, polycondensation or dehydrogenation. Crosslinking is carried out from precursors which are generally silicone oils or resins, which crosslink to obtain a three-dimensional network forming a material called silicone resin, in the description.

[0179] This crosslinking can be done by thermal activation, or chemical activation using a catalyst, such as platinum.

[0180] The silicone resins can be obtained from precursors, advantageously soluble in a solvent or in emulsion in water, such as oils or crosslinkable resins, in particular chosen from: a silicone hydride, a silicone oil resin comprising at least one vinyl group (-CH=CH2), a silicone or silicone-polyester resin (copolymer) comprising at least one alkoxy group, for example methoxy or ethoxy, and / or a silicone or silicone-polyester resin (copolymer) comprising at least one alkoxy group, in particular ethoxy, or a hydroxy group and mixtures thereof. These precursors have the capacity to crosslink in order to obtain a silicone resin which is characterized by its insolubility and its substantially solid form.

[0181] Advantageously, these precursors are polymeric or oligomeric, either in the form of silicone oils with a variable degree of branching, or in the form of silicone resins with a variable degree of pre-crosslinking or copolymers of silicone resins such as silicone-polyester, silicone-alkyd, silicone-polyurethane, silicone-epoxy resins, or in the form of a mixture of silicone oils, silicone resins and copolymers of silicone resins. The silicon atoms may be substituted by alkyl (in particular methyl) or aryl (in particular phenyl) groups or mixtures thereof. The oils or resins preferably comprise one or more (2, 3 or more) hydroxy or alkoxy (in particular methoxy, ethoxy, butoxy) functional groups as substituents of silicon atoms.

[0182] Advantageously, the silicone resin(s), obtained after crosslinking their precursors, i.e. crosslinked, is / are chosen from the group consisting of methyl silicone and / or phenyl silicone and / or methyl-phenyl-silicone resins, methyl silicone-polyester resin (copolymers), phenyl silicone-polyester resin (copolymers), methyl-phenyl silicone-polyester resin (copolymers), silicone-alkyd resin (copolymers), modified silicone resin and mixtures thereof.

[0183] Advantageously, the silicone resin(s) is / are chosen from the group consisting of methyl silicone and / or phenyl silicone and / or methyl-phenyl-silicone resins, methyl silicone-polyester resin (copolymers), phenyl silicone resin- polyester (copolymers), methyl-phenyl silicone-polyester resin (copolymers), silicone-alkyd resin (copolymers), modified silicone resin and their mixtures.

[0184] The silicone resins can be obtained from precursors, notably chosen from: a silicone hydride, a silicone resin comprising at least one vinyl group

[0185] (-CH=CH2), a silicone-polyester resin (copolymer) comprising at least one methoxy group, and / or a silicone-polyester resin (copolymer) comprising at least one ethoxy group, and mixtures thereof.

[0186] The silicone resin forms a network which may consist of a combination of 4 simple organosiloxane units called M, D, T and Q depending on the degree of substitution by oxygen of the silicon atom, as described in the following table, where R is an organic substituent described below.

[0187] [Tables 1] | Structure Degree of substitution Symbol by i' oxygen 1 M $ —ORs-O— A 2 | DR 1 V * § —Ç-SpO-" 4 | Q

[0188] The organopolysiloxane material or polymer is obtained by crosslinking from precursors which can be monomeric or polymeric, or intermediately which can be oligomeric. The organopolysiloxane polymer can also be obtained from a mixture of these different kinds of precursors. When the network contains a higher number of T and Q units than D, the crosslinking density is higher. The distribution between the M, D, T and Q units depends on the chemical structure of the precursors, in particular on this M, D, T, Q distribution within the precursors.

[0189] The polymeric precursors are organopolysiloxanes. These macromolecules are formed from M, D, T, and / or Q units as described in the table, where R is independently an alkyl group, in particular methyl, or aryl, in particular phenyl, different natures of R being able to be present on the same macromolecule.

[0190] Organopolysiloxanes can be either linear or weakly branched (majority of D groups), or branched or highly branched (majority of T and Q groups). Linear or weakly branched organopolysiloxanes are generally liquid, more or less viscous at room temperature, and are called silicone oils. Branched or highly branched (pre-crosslinked) organopolysiloxanes form a network at the level of the individual macromolecule and are called silicone resins. At room temperature, the resins are essentially in solid form, or in liquid form, provided in particular that they have a fairly low molecular weight, in the form of a solution in a solvent or in the form of an aqueous emulsion. They can be copolymerized with organic polymers or oligomers not containing silicon, chosen in particular from polyesters, acrylics, alkyds, polyurethanes, epoxy resins.

[0191] When the crosslinking is a hydrolysis-polycondensation: it is carried out thanks to the reactive hydroxy or alkoxy functions, in particular methoxy, ethoxy or butoxy, present on the organopolysiloxane.

[0192] When the crosslinking is a polyaddition (or hydrosilylation): it is carried out by reaction between the reactive vinyl functions (-CH=CH2) present on one of the organopolysiloxanes and the reactive silyl hydride functions (Si-H) present on the other organopolysiloxane mixed with the first.

[0193] All these reactive functions are present on each organopolysiloxane in the number of at least one and can be present in the number of 2, 3, or more ... as much as the molecular structure allows. Silicone oils comprising at least one reactive function are called "reactive oils". The reactive functions can be found either at the end of the macromolecular chain (termination), or distributed over the chain.

[0194] Silicone-polyester resins in particular have silicone / polyester mass ratios of, for example, 90 / 10, 80 / 20, 70 / 30, 60 / 40, 50 / 50, 40 / 50, 30 / 70, 20 / 80, 10 / 90, advantageously between 80 / 20 and 50 / 50.

[0195] Linear PDMS silicone oils, pure or pre-emulsified in water, are characterized firstly by their molecular mass, which is a direct increasing function of the viscosity of the pure oil. They are then characterized by the presence or absence of reactive functions, for example hydroxyls on the silicon atoms (silanol), their number and their location on the molecular chain. For example, reactive oils with viscosities of between 50 and 20,000 mPa.s, and in particular between 300 and 5,000 mPa.s, can be used, having at least one reactive function, preferably at least 2, which can be placed at the end of the chain.

[0196] Polymeric precursors reacting by polyaddition may include, for example, polymethylhydrosiloxane, vinylmethylsiloxane, vinyl-terminated polydimethylsiloxane (PDMS), in particular linear, vinyl-terminated diphenylsiloxane-dimethylsiloxane copolymers, hydride-terminated polydimethylsiloxanes, hydride terminated polyphenylmethylsiloxanes, cyclic vinylmethylsiloxane, vinyl-MQ resin, trimethylsilyl terminated polymethylhydrosiloxane, trimethylsiloxane terminated dimethylsiloxane and methylhydrosiloxane copolymer, hydride MQ resin, and the like, as well as combinations thereof.

[0197] The polymeric precursors reacting by hydrolysis-polycondensation, whether they are silicone resins or silicone oils, may include, for example, poly(methylsilsesquioxanes), poly(propylsilsesquioxanes), poly(phenylsilsesquioxanes), polydimethylsiloxane (PDMS), trimethylsilyl-terminated polydimethylsiloxane (PDMS), hydroxyl-terminated polydimethylsiloxane (PDMS), silanol-terminated polydimethylsiloxane (PDMS), silanol-terminated polyphenylsiloxane (PDMS), silanol-terminated diphenylsiloxane-dimethylsiloxane copolymer, poly(2-acetoxyethylsilsesquioxanes), organo-modified alkoxy-silanes and their oligomers, and all similar macromolecules and their mixtures.

[0198] The organopolysiloxane material or polymer may also be obtained by crosslinking a mixture of one or more monomeric precursors and one or more polymeric precursors as described above, as well as one or more oligomeric precursors which may be linear, branched or cyclic. These oligomeric precursors have a lower molecular weight than the polymeric precursors. Polymeric and / or oligomeric precursors comprising a number of reactive functions as described above greater than 2, advantageously much greater than 2, may be added to the mixture as a “co-binder” in order to promote a high crosslinking density of the organopolysiloxane polymer finally obtained.

[0199] The monomeric, oligomeric and / or polymeric precursors, in particular silicone resins, copolymerized or not with an organic polymer, act as a polymeric binder in order to obtain the solid organopolysiloxane polymer combined with the thermoplastics of each layer.

[0200] Silicone oil type organopolysiloxane precursors can be considered as additives if they are added in small quantity (generally between 0.1 and 5% dry) in the whole formula of a layer, independently of the other components for the formation of the solid organopolysiloxane polymer.

[0201] Crosslinking may require a catalyst:

[0202] - In the case of crosslinking of organopolysiloxanes by hydrolysis- polycondensation, the formula may include a metal catalyst, such as, for example, metal complexes based on platinum, tin, zinc, zirconium and cerium, in particular platinum-cyclovinylmethyl-silxane complexes, tin ethylhexanoate, zinc ethylhexanoate, zirconium ethylhexanoate, cerium ethylhexanoate, and dibutyl tin laurate.

[0203] - In the case of the crosslinking of organopolysiloxanes by hydrosylilation, the addition a catalyst may be necessary: this may be, for example, platinum or a suitable platinum-based catalyst such as the Karstedt catalyst or the Ashbys catalyst.

[0204] A crosslinking agent, for example carrying Si-H bonds, may be present.

[0205] According to this embodiment, the decorative layer(s) optionally comprise one or more silicone resins as described above.

[0206] It is preferable that the different layers of the coating are compatible with each other. But it is not essential that the different layers are of the same nature. Thus, it is possible to have a silicone resin-based layer in the functional decoration layer, while the primer layer and / or the finishing layer is a sol-gel layer.

[0207] Another subject of the invention relates to a household article comprising a substrate, preferably metallic, covered in whole or in part with a coating as described above.

[0208] The change in color of the pigment of formula BiOA(i X)BX (I) allows the user to be warned on the one hand, that the article is hot and therefore presents a risk of burns and on the other hand that the surface of the article has reached the temperature suitable for its use.

[0209] The substrate of the household item may be made of plastic, metallic material, glass, ceramic or terracotta. As metal supports that can be used in the context of the present invention, mention may advantageously be made of supports made of anodized or non-anodized aluminum or aluminum alloy, or of polished, brushed or micro-blasted, sandblasted, chemically treated aluminum or aluminum alloy, or of polished stainless steel, or of cast iron or aluminum, or of hammered or polished titanium or copper.

[0210] Examples of household items that can be used in the context of the present invention include fryer tanks, frying pans or pots for fondue or raclette, the tank of a fryer or a bread machine, the bowl of a blender, the plates of a hair straightener and the soleplates of an iron.

[0211] For better adhesion of the coating, the surface of the support can be treated so as to increase its specific surface area, for example by sandblasting, brushing or chemical treatment; for aluminum this treatment can be done by anodization (creation of a tubular alumina structure), by chemical attack, by sandblasting, etc. Other metal substrates can also be polished, sandblasted, brushed, micro-blasted.

[0212] The primary layer(s) may comprise a bonding resin, in particular when the substrate is mechanically treated.

[0213] Preferably, the bonding resin(s) is (are) chosen from the group consisting of polyamide imides (PAI), polyether imides (PEI), polyamides (PA), polyimides (PI), polyetherketones (PEK), polyetheretherketones (PEEK), polyaryletherketones (PAEK), polyethersulphones (PES), and polyphenylene sulfide (PPS), polybenzimidazoles (PBI), tannins.

[0214] The presence of PAI, PES, PPS polymer type resins allowing adhesion to metal substrates, such as aluminum or stainless steel, can cause yellowing of the coating.

[0215] A variant of the formulation of the decoration comprising a thermochromic pigment of formula BiOAi XBX then consists of integrating into the composition of the decoration a source of copper in order to preserve the original color of the pigment.

[0216] The copper source can be integrated into the wet composition of the decoration during a preliminary step of grinding the thermochromic pigment before adding a fluoropolymer for example or can be simply added to the wet composition of the decoration as an additive. Among the sources of copper, we can cite copper oxide CuO and sodium gluconate.

[0217] Advantageously, the article according to the invention is a culinary article and the coating according to the invention covers all or part of the face receiving the food.

[0218] Advantageously, the article according to the invention is a hair straightener and the coating according to the invention covers all or part of its plates.

[0219] Advantageously, the article according to the invention is an iron and the coating according to the invention covers all or part of its soleplate.

[0220] Advantageously, the article is a culinary article of which one of the faces of the support constitutes a concave internal face intended to be in contact with food placed inside said article and the other face of the support of the article is a convex external face intended to be in contact with a heat source.

[0221] Preferably, said household item is a culinary item, preferably chosen from the group consisting of saucepan, frying pan, stewpan, wok, sauté pan, crepe maker, grill, griddle, raclette machine, pot, casserole dish, and said coating is intended to be placed in contact with food.

[0222] In the fields of application envisaged for the present invention, an article to be heated of the culinary article type or a heating article of the iron type is typically used in a temperature range of 10°C to 300°C.

[0223] Another subject of the invention relates to a method of using a household article according to the invention, characterized by the following steps:

[0224] - Heat or place in the presence of an external heating source said household item,

[0225] - Observe the color change(s) of the decoration (a) and, when present, decor (b),

[0226] - Use said household item when the colors of the decor (a) and, when it is present in the decor (b), respectively reach colors defined in the instructions for use of said household item.

[0227] The optimal conditions of use can be achieved when their colors are visually identical to the naked eye for the user at a conventional usage distance of the article according to the invention.

[0228] The instructions for use may indicate to the user the colors at which he can start using the household article according to the invention under optimal conditions. This indication will be presented for example in the form of geometric patterns filled with the appropriate colors or a gradient color bar. This pattern or bar serves as a comparative reference for the user who can bring it close to the coated surface of the article according to the invention.

[0229] Preferably, in the case of a culinary article, the optimal conditions are reached when the coating reaches a temperature suitable for cooking food, preferably between 100 and 250°C.

[0230] Another subject of the invention relates to the use of a pigmentary compound of formula BiOAi XBX (I) where:

[0231] - A and B are chosen from the group consisting of iodine, fluorine, chlorine and bromine,

[0232] - A and B are different from each other, and

[0233] - x is from 0 to 1.

[0234] in the coating of the surface of a household article as a temperature indicator.

[0235] The change in color of the pigment of formula BiOA(i X)BX (I) allows the user to be warned on the one hand, that the article is hot and therefore presents a risk of burns and on the other hand that the surface of the article has reached the temperature suitable for its use. EXAMPLES OF ACHIEVEMENT

[0236] Example 1: Selection of thermochromic pigment compounds

[0237] The thermochromic pigmentary compounds of formula BiOAi XBX used according to the invention are: • BiOBr, • BiOBrojIos, • BiOBro^Ioe, • BiOI, and • BiOCIo,5I0,5.

[0238] Example 2: Integration of thermochromic pigment compounds into a black fluorinated non-stick coating

[0239] In order to offer the consumer a household item of the culinary item type with a non-stick interior coating provided with a decoration to guide him in the cooking of food, the thermochromic pigment compounds of formula BiOAi XBX having thermochromic properties are introduced into a non-stick coating comprising several layers: - one or more coats of opaque colored primer; - a decorative layer comprising a thermochromic pigment compound; - one or more layers of translucent finishes. i. Preparation of the two primary coats

[0240] A first formulation based on aqueous dispersion of PTFE is prepared.

[0241] (a) Primary 1 / Formula Ia

[0242] [Tables2] Component % by mass in the liquid formulation % by mass in the dry film aqueous dispersion fluorinated polymers 24 60 aqueous dispersion carbon black 4 4 colloidal silica 16 20 solvent-based dispersion adhesive resin 41 16 additives (base, wetting agents, etc.) 6 - Water 9 -

[0243] A second formulation based on aqueous dispersion of PTFE is prepared.

[0244] (b) Primary 2 / Formula 2a

[0245] [Tables3] Component % by mass in the liquid formulation % by mass in the dry film aqueous dispersion fluorinated polymers 48 88 aqueous dispersion carbon black 5 4 colloidal silica 3 3 solvent-based dispersion adhesive resin 19 5 additives (base, wetting agents, etc.) 12 - Water 13 -

[0246] Formulations 1a and 2a are filtered before being applied with a pneumatic gun to the inside of a preformed aluminum cap. This support is first at least degreased and dusted. For better adhesion of the coating, the surface of the support is treated by sandblasting so as to increase its specific surface area.

[0247] The primer is applied in at least one layer with a thickness of 5 to 50 microns. In the case of application in several layers, each layer is dried before application of the next. ii. Preparation of the thermochromic decoration

[0248] Several pad printing pastes each containing a thermochromic compound of formula BiOAi XBX of Example 1 were prepared according to the formulation described below.

[0249] [Tables4] % by mass in the pad printing paste Mass (g) after receipt it per 100g of paste % by mass in the dry decor dispersion BiOA! XBX 36.18 36.18 69.70 Water 15.08 - - Dispersant 3.02 - - Antifoam 0.60 - - Ammonia 1.57 - - Thickener 0.24 - - Binder 3.62 1.81 3.49 post-additi on PTFE dispersion 23.20 13.92 26.82 Ammonia 0.40 - - Solvent 8.00 - - Antifoam 2.00 - - Thickener 2.00 - - Water 3.50 - - Ammonia 0.60 - - Total 100.00 51.91 100.00

[0250] This paste is applied in the form of a decoration by pad printing on the dried primer layer. [0251 ] iii. Preparation of the top coat and baking

[0252] The finishing coat is made in the same way as the first primer coat, the only difference being that it must remain transparent, so it does not include pigments but possibly glitter.

[0253] [Tables5] Component % by mass in the liquid formulation % by mass in the dry film 1m aqueous dispersion fluorinated polymers 93 99 Flakes 1 1 additives (base, wetting agents, etc.) 3 - ethylene glycol 2 - Water 1 -

[0254] Once all the layers have been applied and dried, the article is baked at 430°C for 11 min. iv. Thermochromic properties of the decoration

[0255] The BiOBr compound is a pigment that is white at room temperature and yellow at 200°C. After its integration into the coating of a culinary article in the form of a decoration, the decoration has a white tint at room temperature and a pale yellow tint when brought to 200°C. The decoration recovers a white tint after returning to room temperature.

[0256] The BiOBrojIos compound is a pigment that is yellow-orange at room temperature and orange at 200°C. After its integration into the coating of a cookware item in the form of a decoration, the decoration has a mustard tint at room temperature and a more orange tint when it is brought to 200°C. The decoration recovers a mustard tint after returning to room temperature.

[0257] Concerning the BiOBro.Jo.e compound, after its integration into the coating of a culinary article in the form of decoration, it has an orange tint at room temperature and a reddish-brown tint at 200°C. The decoration recovers an orange tint after returning to room temperature.

[0258] The BiOI compound is a pigment that is red-orange in color at room temperature and brown at 200°C. After its integration into the coating of a culinary article in the form of a decoration, the decoration has a red-orange tint at room temperature and a brown tint at 200°C. The decoration recovers a red-orange tint after returning to room temperature.

[0259] The compound BiOClo.5Io.5 is a pigment that is orange at room temperature and brown-orange at 200°C. It can be integrated into the coating of culinary articles in the form of decoration.

[0260] Example 3: Variants of the thermochromic decoration composition in a black fluorinated non-stick coating

[0261] The primer layers of PTFE-based non-stick coatings may comprise resins of the PAI, PES, PPS polymer type allowing adhesion to metal substrates, such as aluminum or stainless steel, but which may cause yellowing.

[0262] A variant of the formulation of the decoration comprising a thermochromic pigment of formula BiOAi XBX then consists of integrating into the composition of the decoration a source of copper in order to preserve the original color of the pigment.

[0263] The copper source can be integrated into the pad printing composition of the decoration during a step of grinding the thermochromic pigment (i) or can be added to the composition (ii).

[0264] (i) co-grinding of the copper source with the pigment (Table 6):

[0265] A portion of the aqueous dispersion in the pad printing composition of Example 2 (Table 4) is replaced by copper oxide CuO.

[0266] [Tableauxô] % by mass in the pad printing paste Mass (g) after annealing per 100 g of paste % by mass in the dry or grinding decor BiOA! XBX 36.18 36.18 69.36 Water 15.08 - - Dispersant 3.02 - - Antifoam 0.60 - - Ammonia 1.57 - - CuO 0.64 0.64 1.23 Thickener 0.24 - - Binder 3.62 1.81 3.47 po st-addition PTFE Dispersion 22.55 13.53 25.94 Ammonia 0.40 - - Solvent 8.00 - - Antifoam 2.00 - - Thickener 2.00 - - Water 3.50 - - Ammonia 0.60 - - Total 100.00 52.16 100.00 (ii) post-addition of the copper source to the pad printing paste (Table 7): The source of copper oxide, in the form of copper gluconate (20%), is added to the

[0267]

[0268]

[0269]

[0270]

[0271]

[0272]

[0273]

[0274] pad printing paste from Example 2 (Table 4). [Tables 7] % by mass in the pad printing paste Mass (g) after annealing per 100g of paste % by mass in the dry decoration Pad printing paste of example 2 93.37 48.47 99.58 Copper source 6.63 0.20 0.42 Total 100 48.67 100.00 Example 4: Integration of thermochromic pigment compounds into a sol-gel coating In order to offer the consumer a cookware item with a non-stick interior coating and a decoration to guide them in their cooking, the compounds with improved thermochromic properties are introduced into a non-stick coating comprising several layers: • The sol-gel primary layer(s), • The thermochromic compound integrated into a decoration, • The sol-gel finishing coat(s). i. Preparation of primer and definition coats Primer formula with silicone oil: Cil [Tables 8] Aqueous Composition A Mass (grams) 30% Colloidal Silica 27.5 Distilled Water 7 Isopropanol 3 Silicone Oil 1 TiO2 12 Alumina 14 Acid Solution B MTES 35.1 Formic acid 0.4 TOTAL 100

[0275] Topcoat formula with silicone oil: Fl

[0276] [Tables9] Aqueous Composition A Mass (grams) 40% Colloidal Silica 31 Distilled Water 8.5 Acetic Acid 1.6 Isopropanol 4 Silicone Oil 1 Acid Solution B MTES 40.5 Butyl Glycol 12.9 Pearlescent Glitter 0.5 TOTAL 100

[0277] Silicone oil-free primer formula: Cf2

[0278] [TableauxlO] Aqueous Composition A Mass (grams) 30% Colloidal Silica 27.5 Distilled Water 7 Isopropanol 3 TiO2 13 Alumina 14 Acid Solution B MTES 35.1 Formic Acid 0.4 TOTAL 100

[0279] Silicone oil-free topcoat formula: F2

[0280] [Tableauxll] Aqueous composition A Mass (grams) Colloidal Silica 40% 32 Distilled Water 8.5 Acetic Acid 1.6 Isopropanol 4 Acid Solution B MTES 40.5 Butyl Glycol 12.9 Pearlescent Glitter 0.5 TOTAL 100 ii. Preparation of the thermochromic decoration

[0281] A pad printing paste containing a thermochromic pigment as described in Example 1 is prepared according to the formulation described below. DTI thermochromic decor formula

[0282] [Tablesl2] Composition Mass (grams) Thermochromic pigment of formula BiOAi XBX (I) 30 Butyl glycol 25.7 Colloidal silica 15.4 Water 4 Acetic acid 0.7 Isopropanol 1.6 MTES 20.6 wetting agent 2 Sum 100 Thermochromic Decor Formula#: DT2

[0283] [Tables 13] Composition Mass (grams) Thermochromic pigment of formula BiOAi XBX (I) 30.0 Additive 4.7 Water 50.0 Propylene glycol 9.5 Acrylic thickener 3.8 Ammonia 2.0 Total 100

[0284]

[0285] iv. Production of a culinary item incorporating the temperature indicator A preformed aluminum cap is first degreased and dusted. For better adhesion of the coating, the surface of the support is treated by sandblasting to increase its specific surface area. A layer of primer is spray-coated onto the surface of the cap. This layer can be dried if necessary. A thermochromic decoration from a formula described above is then applied over the primer layer by pad printing and then dried. A finishing coat is applied by spray on the two previous layers. The entire item is then baked at 250°C for 30 minutes.

Claims

Claims

1. Coating of the surface of a household article comprising a decoration (a) comprising a thermochromic pigment compound of formula BiOAi XBX (I) where: - A and B are chosen from the group consisting of iodine, fluorine, chlorine and bromine, - A and B are different from each other, and - x is from 0 to 1.

2. Coating according to claim 1 comprising at least the decoration (a) as defined in claim 1 and a decoration (b) arranged between or in its layers, said decoration (b) comprising a temperature reference pigment composition.

3. Coating according to any one of the preceding claims in which the decoration (a) further comprises a thermochromic pigment compound different from the pigment compound of formula (I), preferably TiO2, Fe2O3, VO2, WO3, Bi2O3, BiVO4 or their mixtures or a thermostable pigment compound.

4. Covering according to claim 2 or claim 3 in which each of the 2 decorations (a) and (b) is in the form of adjacent non-overlapping patterns.

5. Covering according to claim 3 in which the 2 decorations (a) and (b) are partially overlapping.

6. Covering according to claim 3 in which the 2 decorations (a) and (b) are in the form of two overlapping patterns.

7. Coating according to any one of the preceding claims, in which the level of the thermochromic pigmentary compound of formula BiOAi XBX (I) in the decoration (a) is from 0.1% to 100% by weight relative to the weight of said decoration in the dry state, preferably from 0.2% to 80% by weight.

8. A coating according to any preceding claim, comprising one or more finishing layers.

9. Coating according to any one of the preceding claims, the decorations being applied by pad printing, electrostatic powdering, spray spraying, screen printing, roller application or digital printing.

10. A coating according to any preceding claim, wherein: x = 0 and A=I or A=Br or x is different from 0 and A= F or Cl and B=I or x is different from 0 and A=Br and B=I

11. A coating according to any preceding claim, said household article comprising a substrate, preferably metallic, and said coating comprising one or more primer layers applied to said substrate.

12. A coating according to claim 11, comprising in the following order from one of the faces of the substrate of the household article: a primer layer, a decoration (a) or a decoration (a) and a decoration (b), and a finishing layer.

13. Coating according to any one of claims 1 to 10, the decoration(s) being applied directly to the substrate.

14. A coating according to any one of claims 8 to 13 wherein the topcoat(s) and, when present, the primer(s) comprise one or more fluoropolymers.

15. The coating of claim 14, wherein the fluoropolymer(s) is(are) selected from the group consisting of polytetrafluoroethylene (PTFE), copolymers of tetrafluoroethylene and perfluoropropylvinylether (PFA), copolymers of tetrafluoroethylene and hexafluoropropene (FEP), polyvinylidene fluoride (PVDF), copolymers of tetrafluoroethylene and polymethylvinylether (MVA), terpolymers of tetrafluoroethylene, polymethylvinylether and fluoroalkylvinylether (TFE / PMVE / FAVE), ethylene tetrafluoroethylene (ETFE), and mixtures thereof.

16. A coating according to any one of claims 8 to 13 wherein the topcoat(s) and, when present, the primer(s) are sol-gel coats.

17. Coating according to claim 16, in which the sol-gel layers are obtained from a sol-gel (SG) composition comprising at least one metal oxide, preferably a colloidal metal oxide chosen from colloidal silica and / or colloidal alumina and at least one precursor of metal alkoxide type, preferably an alkoxysilane chosen from the group consisting of methyltrimethoxysilane (MTMS), tetraethoxysilane (TEOS), methyltriethoxysilane (MTES), dimethyldimethoxysilane, and mixtures thereof.

18. A coating according to any one of claims 8 to 13 wherein the topcoat(s) and, when present, the primer(s) comprise one or more silicone resins.

19. A coating according to any one of claims 8 to 13 wherein the topcoat(s) and, when present, the primer coat(s) comprise one or more aromatic thermoplastic polymers other than a fluoropolymer, one or more heterocyclic thermoplastic polymers or mixtures thereof.

20. Household article comprising a substrate, preferably metallic, covered in whole or in part with a coating according to any one of the preceding claims.

21. Household article according to claim 20, characterized in that it is a culinary article and in that the coating according to any one of claims 1 to 19 covers all or part of the face receiving the food.

22. Culinary article according to claim 21, the substrate being made of anodized or non-anodized aluminum or aluminum alloy, or polished, brushed or micro-blasted, sandblasted, chemically treated aluminum or aluminum alloy or polished stainless steel, or cast iron or aluminum, or hammered or polished titanium or copper.

23. Culinary article according to claim 22, said culinary article being chosen from the group consisting of saucepan, frying pan, stewpan, wok, sauté pan, crepe pan, grill, griddle, raclette machine, pot, casserole, and said coating is intended to be placed in contact with food.

24. Household article according to claim 20, characterized in that it is an iron and in that the coating according to any one of claims 1 to 19 covers all or part of the soleplate of said iron.

25. Household article according to claim 20, characterized in that it is a hair straightener and in that the coating according to any one of claims 1 to 19 covers all or part of the plates of said hair straightener.

26. Method of using a household article according to any one of claims 20 to 25, characterized by the following steps: - Heating or placing said household article in the presence of an external heating source, - Observing the change(s) in color of the decoration (a) and, when present, of the decoration (b), - Using said household article when the colors of the decoration (a) and, when present, of the decoration (b), respectively reach colors defined in the instructions for use of said household article.

27. Use of a pigment compound of formula BiOAi XBX (I) where: - A and B are selected from the group consisting of iodine, fluorine, chlorine and bromine, - A and B are different from each other, and - x is from 0 to 1 in the coating of the surface of a household article as a temperature indicator.

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