Coating for the surface of a household item comprising a thermochromic pigment compound

Abstract

The present invention relates to a coating for the surface of a household item comprising a decoration (a) that comprises a thermochromic pigment compound of formula BiOA1-xBx (I) where: - A and B are selected from the group consisting of iodine, fluorine, chlorine and bromine; A and B are different from one another; and - x is between 0 and 1, the decoration (a) being in the form of a layer that exhibits a reversible variation in its optical and / or colorimetric properties when the coating comprising it is subjected, in whole or in part, to a variation in temperature 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.

Description

[0001] SURFACE COATING OF A HOUSEHOLD ARTICLE COMPRISING A THERMOCHROME PIGMENT COMPOUND

[0002] FIELD OF THE INVENTION

[0003] 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.

[0004] STATE OF THE ART

[0005] 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.

[0006] In the case of a cookware, good temperature control when cooking food is necessary for health and taste reasons (for example, when searing a steak on a grill or in a pan), but also to limit occasional overheating, which weakens the coating of the cookware and can cause the oils to smoke, thus releasing harmful fumes. Equipment that 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 energy input and therefore the environmental impact.

[0007] In the case of an iron or a hair straightener, temperature control helps to avoid the undesirable effects linked to the use of such items, such as breakage of hair or degradation of textile fibers, and also helps to avoid domestic accidents such as burns.

[0008] 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 made 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.

[0009] 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.

[0010] 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 repeated uses such as cooking food.

[0011] 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 (B12O3), from yellow-orange to red-orange (V2O5), from red-orange to very dark red (Fe?O3), etc.We can therefore see that, even if it is possible to achieve colors other than red, the perception of the thermochromic effect remains difficult and imprecise. 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 B12O3 (thermochromic) is combined with C0AI2O4 (thermostable, blue in color), in a ratio of 15:1, the pigments being bound by a potassium silicate. The coating containing this mixture is blue at room temperature and becomes 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.

[0012] From an industrial point of view, there remains a need to develop new coatings for household items comprising at least one layer of functional decoration to accompany and guide the user of the household item on which the coating in question is deposited.

[0013] DEFINITIONS

[0014] “Room temperature” means a temperature between 18 and 30°C.

[0015] The term "layer" is understood to mean, within the meaning of the present invention, a continuous or discontinuous layer. A continuous layer (or 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, thus not being a single whole.

[0016] 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.

[0017] 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. 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, one or more colors. A decor is clearly visible to the user with the naked eye and at a conventional distance from which the household item is used.

[0018] Overlapping layers are defined as partially or completely superimposed layers. These layers may be in the form of decoration with partially overlapping patterns, for example concentric discs.

[0019] "Adjacent layers" are understood to mean non-overlapping layers. These layers can be presented in the form of decoration with identical or different non-overlapping patterns, preferably distributed evenly.

[0020] The term "temperature reference pigment composition" means a composition comprising a pigment which, at a given temperature, indicates to the user that the optimum operating temperature has been reached. This indication is made by comparing the colours of the BiOAi-type pigment x B x (I) and the reference temperature pigment composition. Either the optimum use temperature is reached when the colours are identical, or the optimum use temperature is reached when the colours are visually very different.

[0021] The “temperature reference pigment composition” may include a pigment that has: the same color as the BiOAi-type pigment x B x (I) at the optimum temperature of use, or because this pigment has the same color at room temperature as the BiOAi- type pigment x B x (I) at the optimum temperature of use, and does not change color with temperature, or because this pigment has a different color at room temperature from that of the BiOAi- type pigment x B x (I) which evolves to the same color as the BiOAi- type pigment x B x (I) at the optimum operating temperature a color very different from that of the BiOAi- type pigment x B x(I) at the optimum use temperature, whether or not this pigment changes color with the change in temperature. 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.

[0022] The temperature reference pigment composition is thermochromic or thermostable.

[0023] For a household item that is not a cooking item, such as a hair straightener or an iron, the temperature reference pigment composition may be, for example, a normal use temperature reference pigment composition or a burn hazard indication pigment composition.

[0024] 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.

[0025] The present invention has at least one of the following advantages:

[0026] - the coating according to the invention has a thermochromic functionality with marked visibility, a contrasting color change over a targeted, precise and centered temperature range, for example around the cooking temperatures of food for a kitchen appliance;

[0027] - 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;

[0028] - the compound of type BiOAi- x Bx (I) has reversibility of its thermochromic properties, 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;

[0029] - the coating according to the invention has significant thermal stability during temperature increases, it is stable up to approximately 450°C;

[0030] - it is possible to modulate the color of the BiOAi- type compound x B x(I) depending on the nature of elements A and B and the value of x. By the expression "thermochromic semiconductor", it is necessary to understand, within the meaning of the present invention, a mineral or organic compound, which exhibits a reversible change of color during an increase in temperature. The progressive and reversible thermochromic character 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] For the purposes of the present invention, the term "pigment, pigment compound or thermochromic pigment composition" means a pigment, pigment compound or pigment composition which changes color depending on the temperature in a given temperature range, this change being reversible. This color change 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 within a given temperature range or which exhibits a change in hue when subjected to an increase in temperature within a given temperature range which is so slight that it is not visible to the user with the naked eye and at a conventional operating distance. By "the colors are identical" is meant indistinguishable by the user with the naked eye and at a conventional operating distance.

[0035] The term "household goods" means kitchenware and household appliances.

[0036] The household appliances referred to here are intended to produce heat.

[0037] The expression "cooking article" is understood to mean, within the meaning of the present invention, an object intended for cooking and being heated by an external heating system such as frying pans, saucepans, sauté pans, woks, barbecue grills. A cooking article is capable of transmitting the heat energy provided by this external heating system to a material or food in contact with said object.

[0038] The expression "object intended to produce heat" is understood to mean, 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.

[0039] “Fluoropolymer-based coating” means a coating that includes one or more fluoropolymer(s) in one or more of its layers.

[0040] 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 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.

[0041] For the purposes of the present invention, the term organo-mineral coating, layer or decoration means a coating, layer or decoration whose network is essentially inorganic, but which includes organic groups, in particular due to the precursors used and the cooking temperature of the coating.

[0042] For the purposes of the present invention, the term “fully mineral coating” means a coating, layer or decoration made of a completely 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 tetraethoxysilane (TEOS) type with a baking temperature which can be less than or equal to 400°C.

[0043] 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.

[0044] 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- x Bx (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, the decoration (a) being 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 whole, to a variation in temperature between a cold temperature and a hot temperature, the cold temperature being from 0°C to 40°C and the hot temperature being from 80°C to 400°C.

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

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

[0052] - Observe the change(s) in color of the decor (a) and, when present, of the decor (b), - Use said household item when the colors of the decor (a) and, when present, of the decor (b), respectively reach the colors defined in the instructions for use of said household item.

[0053] Another subject of the invention relates to the use of a pigmentary compound of formula BiOAi- x Bx (I) where:

[0054] - A and B are chosen from the group consisting of iodine, fluorine, chlorine and bromine,

[0055] - A and B are different from each other, and

[0056] - x is included from 0 to 1 in the surface coating of a household item as a temperature indicator.

[0057] Other aspects of the invention are as described below.

[0058] DESCRIPTION OF FIGURES

[0059] [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).

[0060] [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 primer 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).

[0061] In Figures 2A / B / C, the left views represent the decoration (A) and the other decoration (B) seen from above the household item (1) on the coated side. The right views represent the household item (1) shown in section.

[0062] DETAILED DESCRIPTION OF THE INVENTION

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

[0064] The inventors thus discovered that, surprisingly, bismuth oxyhalides of formula BiOAi- x B x (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 - x is from 0 to 1 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.

[0067] 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- x Bx (I) where:

[0068] - A and B are chosen from the group consisting of iodine, fluorine, chlorine and bromine,

[0069] - A and B are different from each other, and

[0070] - x is from 0 to 1, the decoration (a) being 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 whole, to a variation in temperature between a cold temperature and a hot temperature, the cold temperature being from 0°C to 40°C and the hot temperature being from 80°C to 400°C.

[0071] Advantageously, the hot temperature is between 100°C and 300°C.

[0072] The room temperature color of the thermochromic pigment compound with the formula BiOAi- x Bx (I) depends on the choice of elements A and B as well as the value of x.

[0073] So :

[0074] - if x = 0 and if A represents iodine, the compound of formula BiOl appears red-orange at room temperature and becomes brown at 200°C;

[0075] - if x = 0 and A represents bromine, the compound of formula BiOBr is white at room temperature and becomes pale yellow at 200°C;

[0076] - 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;

[0077] - 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.

[0078] Advantageously, the thermochromic pigment compound of formula BiOAi- x B x (I) is: - the compound with x = 0 and A=l or A=Br;

[0079] - or the compound with x different from 0 and A= F or Cl and B=l;

[0080] - or the compound with x different from 0 and A=Br and B=l.

[0081] According to embodiments, the thermochromic pigment compound is not the compound of formula BiOAi- x B x (I) with x = 1 and B is a chlorine atom.

[0082] The thermochromic pigment compound with the formula BiOAi- x B x (I) may be in the form of uncoated particles, i.e. the particles are purely made of BiOAi- x B x (I).

[0083] Where applicable, the thermochromic pigment compound of formula BiOAi- x B x(I) may be in the form of core-shell type coated particles whose core is made up of BiOAi- particles x B x (I) and whose envelope is made up of one or more coating layers. The envelope can improve the stability of the core with respect to lipids and oils when hot.

[0084] The rate of the thermochromic pigment compound of formula BiOAi- x B x (I) in the decoration (a) may be comprised 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.

[0085] Decor (a) may comprise a mixture of compounds of formula BiOAi- x B x (I).

[0086] The decoration (a) may further comprise a thermochromic pigment compound different from the pigment compound of formula (I), preferably TiO?, Fe?O3, VO?, WO3, B12O3, B1VO4 or mixtures thereof, or a thermostable pigment compound.

[0087] 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.

[0088] The temperature reference pigment composition can be chosen from the group consisting of:

[0089] - Yellow pigments of titanium rutile type, - Yellow pigments derived from bismuth, for example selected from stabilized bismuth vanadates (Py184)

[0090] - Red pigments, for example selected from perylene red, iron oxide,

[0091] - Bismuth vanadate orange pigments (PO86)

[0092] - Zinc tin titanium orange pigment (PO82)

[0093] - Cerium sulfide orange pigment (PO75; PO78)

[0094] - Orange-yellow pigment of the antimony titanium chrome rutile type (PBr24)

[0095] - Orange-yellow pigment of tin and zinc rutile type (Py216)

[0096] - Orange-yellow pigment of niobium oxide tin zinc sulfide (Py227)

[0097] - Orange-yellow pigment of double oxides of tin and niobium and their mixtures.

[0098] 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.

[0099] According to one embodiment, each of the two decorations (a) and (b) is presented 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).

[0100] 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).

[0101] 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).

[0102] Decor (a) and decor (b) optionally comprise one or more fluoropolymers, may be sol-gel decors or may comprise an enamel, a lacquer, a condensed tannin, a thermoplastic polymer other than a fluoropolymer or a silicone resin. Decor (a) and decor (b) optionally comprise additives. Said additives are selected from the group consisting of solvents, thickeners, antifoam agents, pH adjusters, wetting agents and dispersants.

[0103] The additives are chosen to optimize the quality of the deposit on the polymer layer on which they are deposited.

[0104] Said solvents are preferably chosen from the group consisting of: water, alcohols, diols, glycols, esters.

[0105] Said thickeners are preferably chosen from the group consisting of acrylic-based or polyurethane-based copolymer, cellulose, fumed silica, silicone resin.

[0106] Said anti-foaming agents are preferably chosen from the group consisting of polysiloxane, modified polysiloxane, polyether-siloxane copolymer, amphiphilic polymers, silicone, aliphatic mineral oil.

[0107] The said pH adjusters are preferably chosen from the group consisting of Bronsted bases: ammonia, amines (triethylamine, triethanolamine, etc.), hydroxides (soda, potash, etc.), carbonates.

[0108] Said wetting agents and dispersants are preferably chosen from the group consisting of high molecular weight fatty acid derivatives, modified polyether, surfactants, modified polyacrylate.

[0109] 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).

[0110] According to a first embodiment, the household item 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.

[0111] According to a second embodiment, the decoration(s) are applied directly to the substrate. Preferably, the coating according to the invention comprises in the following order starting from one of the faces of the substrate of the household item: a primer layer, a decoration (a) or a decoration (a) and a decoration (b), and a finishing layer.

[0112] 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.

[0113] According to one embodiment, the topcoat(s) and, when present, the primer(s) comprise one or more fluoropolymers.

[0114] The fluoropolymer(s) may be in the form of powder or aqueous dispersion, or mixtures thereof.

[0115] 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.

[0116] 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).

[0117] 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.

[0118] According to this embodiment, the decorative layer(s) optionally comprise one or more fluoropolymers as described above. According to another embodiment, the finishing layer(s) and, when present, the primer layer(s) are sol-gel layers.

[0119] 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.

[0120] 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.

[0121] The metal oxide is preferably a colloidal metal oxide selected from colloidal silica and / or colloidal alumina.

[0122] Preferably, a metal alkoxide chosen from the group consisting of:

[0123] - precursors corresponding to the general formula Mi(0Ri) n ,

[0124] - precursors corresponding to the general formula M2(OR2)( n -i)R2', and

[0125] - precursors corresponding to the general formula M3(OR3)( n -2)R3', with:

[0126] Ri, R2, R3 or R3' denoting an alkyl group,

[0127] R2' denoting an alkyl or phenyl group, n being an integer corresponding to the maximum valence of the metals Mi, M2 or M3,

[0128] Mi M2 or M3 designating a metal chosen from Si, Zr, Ti, Sn, Al, Ce, V, Nb, Hf, Mg and Ln.

[0129] Advantageously, the metal alkoxide of the sol-gel solution is an alkoxysilane.

[0130] Examples of alkoxysilanes that can be used in the sol-gel solution include methyltrimethoxysilane (MTMS), tetraethoxysilane (TEOS), methyltriethoxysilane (MTES), dimethyldimethoxysilane, and mixtures thereof. Preferably, the alkoxysilanes MTES and TEOS will be used, as 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.

[0131] 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.

[0132] The aqueous composition A may further comprise a solvent, in particular a solvent comprising at least one alcohol.

[0133] The aqueous composition A may further comprise at least one silicone oil.

[0134] The aqueous composition A may further comprise a pigment.

[0135] The aqueous composition A may further comprise a mineral filler.

[0136] The aqueous composition A may also comprise fumed silica, the function of which is to regulate the viscosity of the sol-gel composition and / or the gloss of the dry coating.

[0137] The aqueous composition A typically comprises for a primer layer: i) 5 to 30% by weight relative to the total weight of the aqueous composition A of at least one colloidal metal oxide, ii) 0 to 20% by weight relative to the weight of the composition A of a solvent comprising at least one alcohol, iii) optionally 0.05 to 3% by weight relative to the total weight of said aqueous composition A of at least one silicone oil, iv) 5 to 30% of pigment, v) 2 to 30% of mineral filler.

[0138] The aqueous composition A typically comprises for a finishing layer: i) 5 to 30% by weight relative to the total weight of the aqueous composition A of at least one colloidal metal oxide, ii) 0 to 20% by weight relative to the weight of the composition A of a solvent comprising at least one alcohol, iii) optionally 0.05 to 3% by weight relative to the total weight of said aqueous composition A of at least one silicone oil, iv) 0.1 to 1% of metallic flakes.

[0139] 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.

[0140] Particular examples of acids suitable for mixing with the metal alkoxide precursor are acetic acid, citric acid, ethyl acetoacetate, hydrochloric acid or formic acid.

[0141] Solution B may further comprise a solvent, in particular a solvent comprising at least one alcohol.

[0142] Solution B may further comprise at least one silicone oil.

[0143] Solution B may additionally include metallic flakes.

[0144] 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.

[0145] According to this embodiment, the decorative layer(s) are optionally sol-gel layers as described above.

[0146] 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.

[0147] 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.

[0148] THERMOPLASTIC POLYMERS

[0149] 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.

[0150] PAEK

[0151] 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.

[0152] Other aromatic thermoplastic polymers

[0153] As aromatic thermoplastic polymer(s), examples 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.

[0154] Heterocyclic thermoplastic polymers

[0155] Examples of heterocyclic thermoplastic polymers suitable according to the invention are polyetherimides (PEI), polyimides (PI), polyamideimides (PAI) and polybenzymidazole (PBI), or mixtures thereof.

[0156] 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.

[0157] 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.

[0158] According to another embodiment, the finishing layer(s) and, when present, the primer layer(s) comprise one or more silicone resins.

[0159] SILICONE RESINS

[0160] 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.

[0161] This crosslinking can be done by thermal activation, or chemical activation using a catalyst, such as platinum.

[0162] 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.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.

[0163] 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.

[0164] 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-polyester resin (copolymers), methyl-phenyl silicone-polyester resin (copolymers), silicone-alkyd resin (copolymers), modified silicone resin and mixtures thereof.

[0165] Silicone resins can be obtained from precursors, notably chosen from: a silicone hydride, a silicone resin comprising at least one vinyl group (-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.

[0166] The silicone resin forms a network that can be made up 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. Table 1

[0167] 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.

[0168] 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 group, in particular phenyl, different natures of R being able to be present on the same macromolecule.

[0169] Organopolysiloxanes can be either linear or slightly branched (majority of D groups), or branched or highly branched (majority of T and Q groups). Linear or lightly 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 substantially 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.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.

[0170] 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.

[0171] All these reactive functions are present on each organopolysiloxane in number of at least one and can be present in number of 2, 3, or more ... as much as the molecular structure allows. Silicone oils containing 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.

[0172] 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.

[0173] 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 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.

[0174] Polymer 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 copolymer, MQ resin hydride, and the like, as well as combinations thereof.Polymeric precursors reacting by hydrolysis-polycondensation, whether 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 alkoxysilanes and their oligomers, and all similar macromolecules and their mixtures.

[0175] 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.

[0176] 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.

[0177] Silicone oil-type organopolysiloxane precursors can be considered additives if they are added in small amounts (typically between 0.1 and 5% dry) to the overall formulation of a layer, independently of other components for the formation of the solid organopolysiloxane polymer.

[0178] Crosslinking may require a catalyst:

[0179] - 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 tin dibutyl laurate.

[0180] - In the case of crosslinking of organopolysiloxanes by hydrosylilation, the addition of 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.

[0181] A crosslinking agent, for example carrying Si-H bonds, may be present.

[0182] According to this embodiment, the decorative layer(s) optionally comprise one or more silicone resins as described above.

[0183] It is preferable that the different layers of the coating are compatible with each other. However, it is not essential that the different layers be 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.

[0184] 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.

[0185] The color change of the pigment of formula BiOA(i- X )B x(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.

[0186] 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.

[0187] Examples of household items that can be used in the context of the present invention include fryer tanks, skillets or pots for fondue or raclette, the tank of a fryer or bread machine, the bowl of a blender, the plates of a hair straightener and the soleplates of an iron. 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.

[0188] The primer(s) may include a bonding resin, particularly when the substrate is mechanically treated.

[0189] 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.

[0190] The presence of PAI, PES, PPS polymer resins allowing adhesion to metal substrates, such as aluminum or stainless steel, can cause yellowing of the coating.

[0191] A variant of the decor formulation comprising a thermochromic pigment of formula BiOAi- x Bx then consists of integrating a source of copper into the composition of the decoration in order to preserve the original color of the pigment.

[0192] The copper source can be incorporated into the wet composition of the decoration during a preliminary step of grinding the thermochromic pigment before adding a fluoropolymer, for example, or can simply be added to the wet composition of the decoration as an additive. Copper sources include copper oxide CuO and sodium gluconate.

[0193] 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.

[0194] 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.

[0195] Advantageously, the article according to the invention is an iron and the coating according to the invention covers all or part of its soleplate. Advantageously, the article is a culinary article, one of the faces of the support of which 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.

[0196] Preferably, said household item is a culinary item, preferably chosen from the group consisting of saucepan, frying pan, stewpan, wok, sauté pan, crepe pan, grill, griddle, raclette machine, pot, casserole dish, and said coating is intended to be placed in contact with food.

[0197] In the fields of application envisaged for the present invention, a heating article 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.

[0198] Another subject of the invention relates to a method of using a household article according to the invention, characterized by the following steps:

[0199] - Heat or place the said household item in the presence of an external heating source,

[0200] - Observe the color change(s) of the decor (a) and, when present, the decor (b),

[0201] - Use said household item when the colors of the decor (a) and, when present, of the decor (b), respectively reach the colors defined in the instructions for use of said household item.

[0202] The optimal conditions of use can be achieved when their colors are visually identical to the naked eye for the user at a conventional operating distance of the article according to the invention.

[0203] The instructions for use may indicate to the user the colors at which he can begin to use 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. TJ

[0204] Preferably, in the case of a culinary article, the optimum conditions are reached when the coating reaches a temperature suitable for cooking food, preferably between 100 and 250°C.

[0205] Another subject of the invention relates to the use of a pigmentary compound of formula BiOAi- x Bx (I) where:

[0206] - A and B are chosen from the group consisting of iodine, fluorine, chlorine and bromine,

[0207] - A and B are different from each other, and

[0208] - x is from 0 to 1. in the surface coating of a household item as a temperature indicator.

[0209] The color change of the pigment of formula BiOA(i- X )B x (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.

[0210] EXAMPLES OF ACHIEVEMENT thermochromic

[0211] Thermochromic pigment compounds of formula BiOAi- x B ximplemented according to the invention are: o BiOBr, o BiOBro,7lo,3, o BiOBro,4lo,6, o BiOl, and o BiOClo,slo,5.

[0212] 2: Integration of thermochromic in a black fluorinated non-stick coating

[0213] In order to offer the consumer a household item of the culinary type with a non-stick interior coating with a decoration to guide him in the cooking of food, the thermochromic pigment compounds of formula BiOAi- x B x having thermochromic properties are introduced into a non-stick coating comprising several layers: one or more layers of opaque colored primer; a decorative layer comprising a thermochromic pigment compound; one or more layers of translucent finishes. i. Preparation of the two primer layers

[0214] A first formulation based on aqueous dispersion of PTFE is prepared.

[0215] (a) Primary 1 / Formula 1a

[0216] Table 2

[0217] A second formulation based on aqueous dispersion of PTFE is prepared.

[0218] (b) Primary 2 / Formula 2a

[0219] Table 3

[0220] 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 dust-free. For better adhesion of the coating, the surface of the support is treated by sandblasting to increase its specific surface area.

[0221] 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 applying the next. ii. Preparation of the thermochromic decoration

[0222] Several pad printing pastes each containing a thermochromic compound of formula BiOAi- x Bx of Example 1 were prepared according to the formulation described below. Table 4

[0223] This paste is applied in the form of a decoration by pad printing on the dried primer layer. iii. Preparation of the finishing layer and baking

[0224] The top coat is done in the same way as the first coat of primer, the only difference being that it must remain transparent, so it does not include pigments but possibly glitter.

[0225] Table 5

[0226] Once all layers have been applied and dried, the article is fired at 430°C for 11 min. iv. Thermochromic properties of the decoration

[0227] The BiOBr compound is a pigment that is white at room temperature and yellow at 200°C. After its integration into the coating of cookware in the form of 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.

[0228] The compound BiOBro,7lo,3 is a pigment that is yellow-orange at room temperature and orange at 200°C. After its integration into the coating of cookware in the form of decoration, the decoration has a mustard tint at room temperature and a more orange tint when brought to 200°C. The decoration recovers a mustard tint after returning to room temperature.

[0229] Concerning the BiOBro.do.ô compound, after its integration into the coating of cookware 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.

[0230] The BiOl compound is a pigment that is red-orange at room temperature and brown at 200°C. After its integration into the coating of a cookware in the form of 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.

[0231] The BiOClo.slo.s compound is a pigment that is orange at room temperature and brown-orange at 200°C. It can be integrated into the coating of cookware as a decoration.

[0232] Example 3: Variants of thermochromic decor composition in a black fluorinated non-stick coating

[0233] The primer layers of PTFE-based non-stick coatings can include PAI, PES, PPS polymer resins that allow adhesion to metal substrates, such as aluminum or stainless steel, but can cause yellowing. A variant of the decor formulation including a thermochromic pigment of the formula BiOAi- x Bx then consists of integrating a source of copper into the composition of the decoration in order to preserve the original color of the pigment. The source of copper can be integrated into the pad printing composition of the decoration during a step of the grinding of the thermochromic pigment (i) or can be added to the composition (ii).

[0234] (i) co-grinding of the copper source with the pigment (Table 6): A part of the aqueous dispersion in the pad printing composition of Example 2 (Table 4) is replaced by copper oxide CuO.

[0235] Table 6

[0236] (ii) post-addition of the copper source to the pad printing paste (Table 7):

[0237] The source of copper oxide, in the form of copper gluconate (20%), is added to the pad printing paste of Example 2 (Table 4). Table 7

[0238] Example 4: Integration of thermochromic pigment compounds into a sol-gel coating

[0239] 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),

[0240] - The thermochromic compound integrated into a decor,

[0241] - The sol-gel finishing coat(s).

[0242] 7. Preparation of primer and topcoat coats

[0243] Primer formula with silicone oil: CI1

[0244] Table 8 Top coat formula with silicone oil: F1

[0245] Table 9

[0246] Silicone oil-free primer formula: CI2 Table 10

[0247] Silicone Oil-Free Top Coat Formula: F2

[0248] Table 11 ü. Preparation of the thermochromic decoration

[0249] A pad printing paste containing a thermochromic pigment as described in Example 1 is prepared according to the formulation described below. Thermochromic Decor Formula DT 1

[0250] Table 12

[0251] Thermochromic decoration formula: DT2 Table 13 iv. Production of a culinary item incorporating the temperature indicator

[0252] A preformed aluminum cap is first degreased and dusted. For better coating adhesion, the surface of the support is treated by sandblasting to increase its specific surface area. A primer layer is spray-coated onto the surface of the cap. This layer can be optionally dried. A thermochromic decoration from a formula described above is then applied to the primer layer by pad printing and then dried. A finishing layer is spray-applied over the two previous layers. The entire article 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- x B x (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, the decoration (a) being 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 whole, to a variation in temperature between a cold temperature and a hot temperature, the cold temperature being from 0°C to 40°C and the hot temperature being from 80°C to 400°C.

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 TiO?, Fe?O3, VO?, WO3, B12O3, B1VO4 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 presented in the form of two overlapping patterns.

7. Coating according to any one of the preceding claims, in which the level of the thermochromic pigment compound of formula BiOAi- x B x (I) in the decoration (a) is comprised 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. Coating according to any one of the preceding claims, 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. Coating according to any one of the preceding claims, where: x = 0 and A=l or A=Br or x is different from 0 and A= F or Cl and B=l or x is different from 0 and A=Br and B=l 11. A coating according to any preceding claim, said household item comprising a substrate, preferably metallic, and said coating comprising one or more primer layers applied to said substrate.

12. 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 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.

16. Coating according to any one of claims 8 to 13 in which the finishing layer(s) and, when present, the primer layer(s) are sol-gel layers.

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. Coating according to any one of claims 8 to 13 in which the finishing layer(s) and, when present, the primer layer(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, plancha, raclette machine, pot, casserole dish, 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: - Heat or place the said household item in the presence of an external heating source, - Observe the color change(s) of the decor (a) and, when present, the decor (b), - Use said household item when the colors of the decor (a) and, when present, of the decor (b), respectively reach the colors defined in the instructions for use of said household item.

27. Use of a pigment compound of formula BiOAi- x B x (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 included from 0 to 1 in the surface coating of a household item as a temperature indicator.

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