Sol-gel coating with temperature indicator

Abstract

The present invention relates to a sol-gel coating on the surface of a household product, which comprises at least two decorations (a) and (b) arranged between or in its layers, (a) being a (Bi 1-x A x )(V 1―y M y ) A decoration comprising at least one thermochromic pigment composition in the form of particles consisting of an O4 type pigment and optionally additives, where x is 0 or between 0.001 and 0.999, y is 0 or between 0.001 and 0.999, A and M are selected from the group consisting of nitrogen, phosphorus, alkali metals, alkaline earth metals, transition metals, minor metals, semimetals or lanthanides, A and M being different from each other; (b) A decoration comprising a temperature-indicating pigment composition.

Description

[Technical Field]

[0001] The present invention relates to a sol-gel coating for a surface of a household product, preferably a cooking utensil, that has a functional temperature indicator with improved visibility. [Background technology]

[0002] The color of an object is not an actual physical matter, but rather the result of the simultaneous interaction of three factors: light beam or (light) source, observer (eyes -> vision), and the object itself (Figure 1).

[0003] Light is a wave with the special characteristic of propagating through a vacuum and transparent media. There are two types of light sources: primary sources are those that produce their own light (e.g., sunlight, fire, lamps, TVs, lasers), while secondary sources are ambient light: objects that scatter light from the primary source.

[0004] Light-receiving materials such as textiles, paper, foodstuffs, and coatings behave differently: they can allow light to pass through or prevent light from passing through if they are transparent, and therefore they are opaque.

[0005] If an object is opaque, it may be white, and in that case, it completely reflects the luminous energy. Conversely, if it is black, it completely absorbs the luminous energy. If it is gray (dark or light), it reflects some of the radiation and absorbs the rest.

[0006] This is the selective absorption of radiation at certain wavelengths in the visible light spectrum that characterizes the color of the material. Therefore, the remaining radiation not absorbed by the material is reflected and thus visible to the observer.

[0007] Therefore, the visual recognition of an object is related to the light that is modified by this object, transmitted, perceived by the eyes, and ultimately interpreted by the brain. The eyes can distinguish approximately 350,000 different colors.

[0008] In the eye, the cornea creates an image on the retina, the lens adjusts the focus, and the iris acts as a filter by dilating or constricting the pupil. Receptor components are found in the retina: cones and rods. Rods give us night vision, while cones (blue, green, and red) give us day vision, and they convert light signals into nerve signals.

[0009] In the field of household products, when a product is exposed to a heat source or heated, it is essential for the user of such product to monitor the temperature changes of the product during use.

[0010] In the case of cookware, good temperature control during food preparation is necessary for health and taste reasons (for example, to sear the surface of a steak on a grill or in a frying pan), while simultaneously limiting overheating, which can sometimes occur and damage the cookware coating. Materials that are less prone to overheating will have a longer lifespan. Food cooked at low temperatures will have healthier sensory characteristics. Furthermore, cooking at the correct temperature makes it possible to limit energy input and, therefore, environmental impact.

[0011] In the case of clothes irons or hair dryers, temperature control makes it possible to avoid adverse effects associated with the use of such products, such as weakening hair or degrading the quality of textile fibers, while simultaneously preventing household accidents such as burns.

[0012] French Patent No. 1388029 (Patent Document 1) describes a cookware equipped with a temperature indicator consisting of a temperature-sensitive component whose color reversibly changes as a function of temperature, the temperature indicator being incorporated into a non-stick coating, particularly a non-stick coating composed of polytetrafluoroethylene. A heat-stable pigment (i.e., an inorganic or organic compound that shows no or very little color change when exposed to a temperature increase within a given temperature range) can also be incorporated into the cookware as a reference to enable evaluation of the relative color change of the heat-stable indicator, and therefore the temperature change. However, in this invention, the heat-stable reference is not integrated with the non-stick coating and therefore cannot provide clear visibility of the relative change.

[0013] To solve these problems, the applicant has developed a temperature indicator based on thermochromic pigments, which is described in European Patent No. 1121576 (Patent Document 2). This temperature indicator is a decoration comprising at least two patterns, one based on a thermochromic iron oxide pigment that darkens as the temperature rises, and the other based on a thermochromic pigment that lightens very slowly as the temperature rises, comprising a blend of perylene red and black spinel. At a predetermined temperature (which can be set between 160°C and 220°C), the colors derived from the two patterns blend together, which serves as a means for the user to identify this predetermined temperature.

[0014] By using these two thermochromic pigments simultaneously in adjacent areas of decoration, it is possible to improve the visual perception of temperature changes on the cooking surface of cookware. However, this type of temperature indicator is still difficult for users to grasp at first, as both areas are red and have similar chromatic values ​​even at room temperature. Furthermore, the colors of the pattern blend within a temperature range of at least 50°C. This makes it difficult to read and evaluate temperature changes, especially for untrained individuals. As a result, users tend to ignore the information provided by this temperature indicator.

[0015] Therefore, we are interested in providing a temperature indicator that clearly changes color and / or optical properties while there is a temperature change, for example, by showing a distinctly different color in the case of a color-based temperature indicator.

[0016] The advantage of this invention is to provide consumers with improved readability, comprehension, and cognition. [Prior art documents] [Patent Documents]

[0017] [Patent Document 1] French Patent No. 1388029 [Patent Document 2] European Patent No. 1121576 [Overview of the Initiative]

[0018] The first subject of the present invention relates to a sol-gel coating for the surface of a household product, comprising at least two decorations (a) and (b) arranged between or within the layers of the coating.

[0019] (a)(Bi 1-x A x )(V 1―y M y ) A decoration comprising at least one thermochromic pigment composition in the form of O4 type pigments.

[0020] -x is either 0 or between 0.001 and 0.999. -y is either 0 or between 0.001 and 0.999. -A and M are selected from the group consisting of nitrogen, phosphorus, alkali metals, alkaline earth metals, transition metals, poor metals, metalloids, or lanthanides. -A and M are different from each other.

[0021] (b) Decoration comprising a temperature reference pigment composition.

[0022] Another subject of the present invention relates to a household product comprising a substrate completely or partially covered with a coating according to the present invention.

[0023] Another subject of the present invention relates to a method of using a household product according to the present invention, characterized by the following steps:

[0024] - heating the household product or placing it in the presence of an external heat source, -(Bi 1-x A x )(V 1―y M y )O4 type pigment and observing the color change of the temperature reference pigment composition, - using the household product when:

[0025] · the color of the (Bi 1-x A x )(V 1―y M y )O4 type pigment is the same as the color of the temperature reference pigment composition, or · the color of the (Bi 1-x A x )(V 1―y M y )O4 type pigment and the temperature reference pigment composition have reached the temperatures specified in the instructions for using the household product, respectively.

[0026] (Definition) "Room temperature" is understood to mean a temperature between 18 and 30 °C.

[0027] In the context of the present invention, "layer" should be understood to mean a continuous layer or a discontinuous layer. A continuous layer (also called a monolithic layer) is a single coherent solid mass that forms a complete covering of the surface on which it is placed. A discontinuous layer (or non-monolithic layer) is composed of a plurality of parts and is not a single entity as a whole.

[0028] The terms "primer coat," "adhesive layer," or "adhesive undercoat" should be understood to refer to all layers from the first layer applied directly to the support (preferably this layer adheres well to the support and provides the coating with all its mechanical properties: hardness, scratch resistance) to the last layer before the first decorative layer.

[0029] The term "finishing layer" or "finishing coating" should be understood to mean a continuous and transparent surface layer that protects it from mechanical damage and gives the coating its non-adhesive properties while allowing the decorative layer to remain fully visible.

[0030] "Decoration" or "decorative layer" should be understood to mean multiple continuous or discontinuous layers containing pigment compositions. Decoration takes the form of one or more patterns and one or more colors. Decoration is visible to the naked eye and directly to the user at the standard distance of use of household products.

[0031] "Overlapping layers" should be understood as layers that are partially or completely overlapped. These layers can be forms of decoration with partially overlapping patterns, such as concentric discs.

[0032] "Adjacent coatings" should be understood as meaning non-overlapping layers. These layers may exist in the form of decoration with identical or different, preferably uniformly distributed, non-overlapping patterns.

[0033] The term "temperature-referenced pigment composition" should be understood to mean a composition containing a pigment that can indicate to the user that a suitable temperature has been reached at a given temperature. This instruction is, for example, (Bi 1-x A x )(V 1―y M y This can be created by comparing the color of an O4 type pigment with that of a temperature reference pigment composition. The suitable operating temperature is reached when the colors become the same, or when the colors are visibly very different.

[0034] The "temperature-referenced pigment composition" may include a pigment having the following:

[0035] -At the suitable operating temperature, (Bi 1-x A x )(V 1―y M y ) It is the same color as O4 type pigment,

[0036] Because this pigment is suitable for use at the appropriate temperature (Bi 1-x A x )(V 1―y M y ) Is it because it has the same color as O4 type pigment at room temperature, and its color does not change with temperature?

[0037] Or, because this pigment is suitable for use at the appropriate temperature (Bi 1-x A x )(V 1―y M y ) Changes to the same color as O4 type pigment (Bi 1-x A x )(V 1―y M y This is because O4 type pigments have different colors at room temperature.

[0038] - Whether or not this pigment changes color due to temperature changes, at the suitable operating temperature, this (Bi 1-x A x )(V 1―y M y This is a very different color from O4 type pigments.

[0039] A suitable operating temperature is obtained when the color of the temperature reference pigment composition is the color shown in the user guide for a household product equipped with the coating of the present invention, or the color shown on the color scale provided to the user in the product.

[0040] The temperature-reference pigment composition is either thermally color-changed or thermally stable.

[0041] For household products that are not cooking appliances, such as hair straighteners or clothes irons, the temperature reference pigment composition may be, for example, a reference pigment composition indicating the normal operating temperature or the risk of burns.

[0042] For cooking utensils, the temperature reference pigment composition may be, for example, a reference pigment composition that indicates the cooking temperature or the risk of overheating.

[0043] The present invention has at least one of the following advantages:

[0044] - The coating according to the present invention has a thermochromic functionality that is intended to be accurate and has remarkable visibility in contrasting color changes over a desired temperature range, such as a range around the food cooking temperature for a cookware.

[0045] - A coating according to the present invention can provide good temperature control, for example, when cooking food, which is sometimes necessary to limit overheating that could damage the coating of cooking utensils for health and taste reasons.

[0046] -( Bi 1-x A x )(V 1―y M y O4-type compounds possess the reversibility of their thermochromic properties; that is, after their color changes due to heating, as the temperature decreases, the compound returns to its original state and color. This color change cycle (reversibility) repeats infinitely without losing its properties.

[0047] - The coating according to the present invention has substantially thermal stability during temperature rise and remains stable up to approximately 450°C.

[0048] In the context of this invention, "thermally color-shifting semiconductor" should be understood to mean an inorganic or organic compound that exhibits a reversible color change during an increase in temperature. The stepwise and reversible thermal color shifting properties of these semiconductor compounds are related to the reduction in the width of the semiconductor's band gap due to the expansion of the material. Indeed, the periodicity of the anion and cation network leads to an aggregation of energy levels into energy bands. The energy band filled with high energies is called the valence band, and the empty energy band with lower energies is called the conduction band. Between these two bands exists a band gap. The color of a semiconductor material can arise from the presence of charge transfer, which corresponds to the transfer of electrons from the valence band to the conduction band within the same atom, or more generally, from anion orbitals to cation orbitals (interatomic photon absorption).

[0049] In the fields where the present invention is considered applicable, household appliances such as clothes irons or hair dryers are typically used at temperatures in the range of 100°C to 300°C, preferably 100°C to 250°C, and in a particularly preferred manner, 100°C to 200°C.

[0050] In the fields where the present invention may be applied, in the case of cooking utensils, preferred conditions are obtained when the coating reaches a temperature suitable for cooking food, preferably including a temperature of 100 to 250°C.

[0051] In the context of this invention, "thermochromic pigment, thermochromic pigment compound, thermochromic pigment composition" should be understood to mean a pigment, pigment compound, or pigment composition whose color changes as a function of temperature within a desired temperature range, and the change is reversible. This color change is visible to the user with the naked eye and at a standard distance of use.

[0052] "Thermally stable pigments, thermally stable pigment compounds, and thermally stable pigment compositions" are understood to mean pigments, pigment compounds, or pigment compositions that do not exhibit a color change when exposed to a temperature increase within a desired temperature range, or that exhibit a color change when exposed to a temperature increase within a desired temperature range, but the color change is so small that it is not visible to the naked eye and at the standard distance used.

[0053] Preferably, the heat-stable pigment has a color difference ΔE of 10 or less between 25 and 200°C. * It has.

[0054] (Bi 1-x A x )(V 1―y M y ) The particle form consisting of O4 type pigments is the form of particles in a thermochromic pigment composition, (Bi 1-x A x )(V 1―y M y This means they are composed purely of O4 type pigments. Therefore, they are uncoated. Advantageously, they are coarse.

[0055] "Color identical" means that the user cannot distinguish the color change with the naked eye and at the standard viewing distance.

[0056] The term "household products" should be understood to mean cooking utensils and home appliances.

[0057] In this specification, the household appliances covered are those that are intended to generate heat.

[0058] In the context of this invention, "cooking utensil" should be understood to mean an object intended for cooking. For this purpose, it is an object that is to be subjected to heat treatment.

[0059] In the sense of the present invention, "object to be heat-treated" should be understood to mean an object that is heated by an external heating system such as a frying pan, sauce pot, multi-pan, wok, or barbecue grill, and that can transfer the thermal energy provided by this external heating system to materials or food in contact with the object.

[0060] In the sense of the present invention, “object intended to generate heat” should be understood to mean an object having its own heating system, such as a clothes iron, a hair straightener, a steam generator, a kettle, or an electrical appliance for cooking.

[0061] In the context of this invention, "sol-gel coating" should be understood as a coating synthesized from a solution based on a precursor in the liquid phase via a sol-gel route, which is converted into a solid by a single set of chemical reactions (hydrolysis and condensation). The coating thus obtained is either organic-inorganic or entirely inorganic.

[0062] In the context of this invention, "organic-inorganic coating" should be understood to mean a coating whose network is essentially inorganic, but which contains organic groups depending on the particles used and the curing temperature of the coating.

[0063] In the context of this invention, "completely inorganic coating" is intended to mean a coating made from completely inorganic materials that do not contain any organic groups. Such coatings can be obtained by a sol-gel route at a curing temperature of at least 400°C, or from a tetraethoxysilane (TEOS) precursor at a curing temperature of 400°C or less. [Brief explanation of the drawing]

[0064] [Figure 1] Figure 1 shows the factors that influence color. [Figure 2] Figure 2 shows a convergent sphere representing the CIELAB space. [Figure 3] Figure 3 is a diagram illustrating the energy band theory. [Figure 4] Figure 4 is a diagram showing the relationship between the forbidden zone (or gap) and the observed color. [Figure 5] Figure 5 is a general diagram of computer visualization methods. [Figure 6] Figure 6 shows the manufacturing process of a coating integrated with a temperature indicator. [Figure 7] Figure 7 shows diagrams representing different types of samples and a light booth setup + camera. [Figure 8] Figure 8 shows a comparison of pigments in powder form. [Figure 9] Figure 9 is a diagram of the pattern distribution. 9A represents adjacent patterns that do not overlap. 9B represents patterns that partially overlap. 9C represents patterns that overlap. [Modes for carrying out the invention]

[0065] The first subject of the present invention relates to a sol-gel coating of the surface of a household product comprising at least two decorations (a) and (b) arranged between or within the layers:

[0066] (a)(Bi 1-x A x )(V 1―y M y ) Decoration comprising at least a thermochromic pigment composition in a particle form consisting of O4 type pigments,

[0067] -x is either 0 or between 0.001 and 0.999.

[0068] -y is either 0 or between 0.001 and 0.999.

[0069] -A and M are selected from the group consisting of nitrogen, phosphorus, alkali metals, alkaline earth metals, transition metals, poor metals, metalloids, or lanthanides.

[0070] -A and M are different from each other.

[0071] (b) Decoration comprising a temperature reference pigment composition.

[0072] Preferably, in decoration (a) (Bi 1-x A x )(V 1―y M y The amount of O4 is 0.1 to 100% by weight, preferably 0.2 to 80% by weight, and more preferably 0.5 to 70% by weight, relative to the weight of the layer in a dry state.

[0073] Preferably, the amount of the temperature reference pigment composition in decoration (b) is 0.1 to 100% by weight, preferably 0.2 to 80% by weight, and more preferably 0.5 to 70% by weight, relative to the weight of the layer in a dry state.

[0074] The coatings of the present invention are organic-inorganic or entirely inorganic sol-gel coatings. Synthesized via a sol-gel pathway from metal polyalkoxylate precursors, these coatings generally have a hybrid network of alkyl-grafted silica. The sol-gel (SG) composition comprises at least one colloidal metal oxide and at least one metal alkoxide precursor.

[0075] The metal oxide is preferably a colloidal metal oxide selected from colloidal silica and / or colloidal alumina.

[0076] The metal alkoxide is preferably used as a precursor selected from the following group:

[0077] -General formula M1 (OR1) n The corresponding precursor,

[0078] -General formula M2 (OR2) (n-1) R 2’ The corresponding precursor, and

[0079] -General formula M3 (OR3) (n-2) R 3’2 The corresponding precursor, and:

[0080] R1, R2, R3, or R 3’ This indicates an alkyl group.

[0081] R 2’ This represents an alkyl group or a phenyl group.

[0082] n is the total number corresponding to the maximum valence of metal M1, M2, or M3.

[0083] M1, M2, or M3 represents a metal selected from Si, Zr, Ti, Sn, Al, Ce, V, Nb, Hf, Mg, or Ln.

[0084] Advantageously, the metal alkoxide in the sol-gel solution is an alkoxysilane.

[0085] Alkoxysilanes that can be used in the sol-gel solution of the method of the present invention may include, in particular, methyltrimethoxysilane (MTMS), tetraethoxysilane (TEOS), methyltriethoxysilane (MTES), dimethoxydimethylsilane, and mixtures thereof.

[0086] Preferably, alkoxysilanes MTES and TEOS will be used because they have the advantage of not containing a methoxy group. Indeed, methoxy hydrolysis leads to the formation of methanol in the sol-gel composition, which is of a certain class of toxicity and requires additional precursors during application. In contrast, hydrolysis of the ethoxy group produces only ethanol, which is a more preferred class, and therefore the requirements for sol-gel coatings are less restrictive.

[0087] The formation of the sol-gel coating consists of mixing an aqueous composition A containing a colloidal metal oxide with a solution B containing a metal alkoxide. The mixing is preferably carried out with the aqueous composition in a ratio of 40-75% by weight relative to the weight of the sol-gel composition (A+B), and the amount of colloidal metal oxide is such that, in a dry state, it represents 5-30% by weight of the sol-gel composition (A+B).

[0088] Aqueous composition A may also include a solvent, in particular a solvent containing at least one alcohol.

[0089] Aqueous composition A may also contain at least one silicone oil.

[0090] Aqueous composition A may also contain a pigment.

[0091] Aqueous composition A may also include inorganic fillers.

[0092] Aqueous composition A may also contain fumed silica, whose function is to adjust the viscosity of the sol-gel composition and / or the gloss of the dry coating.

[0093] Aqueous composition A typically includes the following for use as a primer:

[0094] i) At least one colloidal metal oxide in an amount of 5 to 30% by weight relative to the total weight of aqueous composition A;

[0095] ii) A solvent containing at least one alcohol in an amount of 0 to 20% by weight relative to the weight of composition A;

[0096] iii) Optionally, at least one silicone oil in an amount of 0.05 to 3% by weight relative to the total weight of the aqueous composition A,

[0097] iv) 5-30% pigment,

[0098] v) 2-30% inorganic filler.

[0099] Aqueous composition A typically includes the following for a finishing coat:

[0100] i) At least one colloidal metal oxide in an amount of 5 to 30% by weight relative to the total weight of aqueous composition A;

[0101] ii) A solvent containing at least one alcohol in an amount of 0 to 20% by weight relative to the weight of composition A;

[0102] iii) Optionally, at least one silicone oil in an amount of 0.05 to 3% by weight relative to the total weight of the aqueous composition A,

[0103] iv) 0.1-1% metallic glitter.

[0104] Solution B may contain a Brønsted or Lewis acid. Advantageously, the metal alkoxide precursor in solution B is mixed with an organic or inorganic Lewis acid in an amount of 0.01 to 10% by weight of the total weight of solution B.

[0105] Specific examples of acids that can be used with mixtures of metal alkoxide precursors include acetic acid, citric acid, ethyl acetoethyl, hydrochloric acid, or formic acid.

[0106] Solution B may also contain a solvent, particularly a solvent containing at least one alcohol.

[0107] Solution B may also contain at least one silicone oil.

[0108] Solution B may also contain metallic glitter.

[0109] According to an advantageous embodiment of the method of the present invention, solution B may comprise a mixture of one of the alkoxysilanes specified above and an aluminum alkoxide.

[0110] A and M will be different from each other in the following cases:

[0111] -A is an alkali metal, which can be selected from Li, Na, K, Rb, and Cs.

[0112] -M is an alkali metal, which can be selected from Li, Na, K, Rb, and Cs.

[0113] -A is an alkaline earth metal, which can be selected from Be, Mg, Ca, Sr, and Ba.

[0114] -M is an alkaline earth metal, which can be selected from Be, Mg, Ca, Sr, and Ba.

[0115] -A is a transition metal, which can be selected from Sc, Ti, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Ta, W, and Ir.

[0116] -M is a transition metal, which can be selected from Sc, Ti, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Ta, W, and Ir.

[0117] -A is a poor metal, which can be selected from Al, Zn, Ga, In, and Sn.

[0118] -M is a poor metal, which can be selected from Al, Zn, Ga, In, and Sn.

[0119] -A is a metalloid, which can be selected from B, Si, Ge, and Sb.

[0120] -M is a metalloid, and it can be selected from B, Si, Ge, and Sb.

[0121] -A is a lanthanide, which can be selected from La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.

[0122] -M is a lanthanide, which can be selected from La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.

[0123] Preferably, A and M are different from each other and are B and / or Mg.

[0124] In one embodiment, decorations (a) and (b) each exist in the form of non-overlapping, adjacent patterns. For example, each decoration is represented by different geometric patterns that are uniformly distributed across the entire surface and alternate with one another (see Figure 9A).

[0125] In another embodiment, the two decorations (a) and (b) partially overlap. For example, each decoration is represented by different geometric patterns that are uniformly distributed across the entire surface and where they partially overlap (see Figure 9B).

[0126] Preferably, the two decorations (a) and (b) overlap, one of the decorations is a continuous layer and the other decoration covers it in the form of a pattern, or the two decorations (a) and (b) exist as an overlapping pattern (see Figure 9C).

[0127] Preferably, (Bi 1-x A x )(V 1―y M y O4 type pigments exhibit the morphology of monoclinic scheelite crystals at room temperature.

[0128] The decoration may optionally include additives.

[0129] The aforementioned additive is selected from the group consisting of solvents, thickeners, anti-foaming agents, pH adjusters, wetting agents, and dispersants.

[0130] The solvent is preferably selected from the group consisting of water, alcohol, diol, glycol, and ester.

[0131] The thickening agent is preferably selected from the group consisting of acrylic acid-based copolymers or polyurethane-based copolymers, cellulose, fumed silica, and silicone resins.

[0132] The anti-foaming agent is preferably selected from the group consisting of polysiloxane, modified polysiloxane, polyethersiloxane copolymer, amphiphilic polymer, silicone, and aliphatic inorganic oil.

[0133] The pH adjusting agent is preferably selected from the group consisting of Brønsted bases: ammonia, amines (such as triethylamine and triethanolamine), hydroxides (such as sodium hydroxide and potassium hydroxide), and carbonates.

[0134] The wetting agent and dispersant are preferably selected from the group consisting of high-molecular-weight fatty acid derivatives, modified polyethers, surfactants, and modified polyacrylates.

[0135] Preferably, a coating according to the present invention comprises one or more finishing layers that are advantageously applied over the decoration. Preferably, these finishing layers are sol-gel layers, as defined above.

[0136] According to the first embodiment, the coating according to the present invention comprises one or more undercoat layers applied to a substrate. Thereafter, decoration is applied to the final undercoat layer.

[0137] Preferably, the coating according to the present invention comprises, in the following order from one side of the surface of the base material of the cookware: a primer layer, two decorative layers (a) and (b), and a finish layer.

[0138] According to the second embodiment, the decoration is applied directly onto the substrate. This means that the decoration is in contact with the substrate.

[0139] Decoration can be applied by methods well known to those skilled in the art, such as screen printing or pad printing.

[0140] Preferably, x and y are 0, i.e., the present invention relates to the use of bismuth vanadium (BiVO4). Advantageously, BiVO4 pigments in the form of monoclinic scheelite crystals are used at room temperature.

[0141] Bismuth vanadium is a yellow inorganic compound with the composition BiVO4, widely used due to its color properties and lack of toxicity. Recorded in the International Color Index database as QI Pigment Yellow 184, it is sold, in particular, by Heubach (Vanadur®), BASF (Sicopal®), FERRO (Lysopac), or Bruchsaler Farbenfabrik (Brufasol®).

[0142] This compound has become the subject of much research due to its intense color and thermochromism. Many synthetic routes can be considered to produce BiVO4 nanoparticles, such as sol-gel synthesis, thermal decomposition of precursors, hydrothermal and solvothermal synthesis, and vapor deposition. However, hydrothermal synthesis can be complex from a mechanical standpoint due to the simultaneous formation of stable and unstable phases in the case of rapid heating in a pressurized autoclave. Due to the numerous phases of the product obtained by hydrothermal synthesis and the complexity of the phase diagram, it is difficult to form and stabilize one or the other phase of the crystallographic phase.

[0143] A second, more commonly used synthesis route is the solid-phase sintering method. This has the advantage of easily obtaining large quantities of highly crystalline powder at low cost. Thus, BiVO4 particles can be obtained by annealing a mixture of bismuth and vanadium salts through a high-temperature sintering process. The resulting microstructure (particle size, morphology, crystallinity) and any impurity elements may consequently affect the band gap of BiVO4, as well as its initial color and / or thermochromism.

[0144] The temperature reference pigment composition is selected from the following group:

[0145] -Titanium rutile yellow pigment, - For example, a bismuth-derived yellow pigment selected from bismuth vanadate (Py184), - For example, a red pigment selected from perylene red or iron oxide, - Bismuth oxyhalide orange pigment (PO85), - Bismuth vanadate orange pigment (PO86), - Titanium zinc orange pigment (PO82), - Cerium sulfide orange pigment (PO75; PO78), -Chromium antimony titanium yellow-orange rutile pigment (PBr24), - Tin and zinc yellow-orange rutile pigment (Py216), - Zinc tin sulfide, niobium oxide, yellow-orange pigment (Py227), - Tin and niobium composite oxide yellow-orange pigment, - and mixtures thereof.

[0146] Advantageously, the coating according to the present invention has (Bi in the coating) 1-x A x )(V 1―y M y )ΔE of O4 type pigment * However, between room temperature and 150°C, it is 11 or greater, and ΔE * It is characterized by being defined by the composition of the CIELAB color space, CIE1976.

[0147]

number

[0148] L1 * a1 * , and b1 * The L of the compound at room temperature is * a * b * Characterize the values.

[0149] L2 * a2 * , and b2* characterizes the L value of the said compound at 150°C. * a * b * value.

[0150] Preferably, the (Bi 1-x A x )(V 1―y M y )O4 type pigment has a ΔE of 13 or more, particularly preferably 15 or more, in the said coating between room temperature and 150°C. * having.

[0151] Advantageously, the coating according to the invention is characterized in that the ΔE of the (Bi 1-x A x )(V 1―y M y )O4 type pigment in the said coating is 15 or more between room temperature and 200°C, and the ΔE * is defined by the composition CIE1976 in the CIELAB color space. * is characterized by.

[0152]

Number

[0153] L1 * , a1 * , and b1 * characterize the L * a * [[ID=​​​​​​​​​​​​​​​​​​​​​​​​​​​​​) The O4 type pigment, between room temperature and 200°C, in the coating, has a ΔE of 17 or more, and in a particularly preferred manner, a ΔE of 20 or more. * It has.

[0156] Advantageously, the color change ΔE as a function of temperature * The evolution is linear. Preferably, this linear solution has a slope consisting of 0.05 to 0.1, preferably 0.1 or more.

[0157] Colors are measured and then characterized using color classification. This classification is only possible if the colors are defined numerically and this conversion can be done using a color space.

[0158] "A color space is a three-dimensional mathematical model that represents a set of colors that can be perceived, used, or reproduced by humans or devices." Numerous spaces exist, each with its own unique distribution of colors and precise coordinates (e.g., the RGB space widely used by television systems, or the CIELAB space, which takes into account the logarithmic response of the eye).

[0159] The CIELAB color space works to characterize the colors of different surfaces. This space is L * a * b * The values ​​(Figure 2) can be represented according to the three orthogonal axes of the geometric model. Therefore, each color is clearly identified and has its own L * a * b * Having coordinates:

[0160] -L * This represents brightness along an axis expressed as a percentage, or from black: 0 to white: 100. -a * The axis ranges from green: -120 to red: +120. -b * The axis ranges from blue: -120 to yellow: +120.

[0161] These coordinates, unique to each color, result in a difference in brightness ΔL. * , tone difference ΔH *, or color difference ΔE * It becomes possible to calculate several parameters like these.

[0162] The parameter we are interested in in this invention is the color difference ΔE, which represents the measurement of the distance between two different colors placed in CIELAB space. * The color difference ΔE is... * It has no units.

[0163] [Table 1]

[0164] (Composition of color tones and color deviations and differences)

[0165] Thermochromism is defined as the ability of a compound to change color as a function of the temperature in question.

[0166] The BiVO4 compound is yellow at room temperature, and its color changes continuously as the temperature rises, ranging from orange to beyond red.

[0167] BiVO4 compounds are part of a family of semiconductor oxides: this category also possesses the color mechanism that underlies their thermochromic properties.

[0168] Indeed, semiconductor materials are characterized by energy band theory, which describes the interactions of atoms. This model assumes that core electrons are localized on the atom to which they belong, and therefore exist in discrete atomic orbitals, and thus do not appear on the model's energy bands. Valence electrons, on the other hand, can be delocalized through the crystal network of the solid, and they constitute the valence band. The conduction band is the first empty energy band that can be occupied by free electrons. The valence band and the conduction band are separated by a forbidden band, the width of which (also called the "gap") is equal to the energy difference between the energy levels in which the valence band and the conduction band are related (Figure 3).

[0169] The color of a semiconductor material is related to the width of the forbidden band that separates the valence band and conduction band of the material in question. This forbidden band is determined by electron transitions of the same or greater energy as the width of the forbidden band that gives rise to the material's color. A forbidden band width in the range of 1.7 eV to 3 eV creates colors ranging from black to white, and the color palette extends from pale yellow to red, thereby exceeding orange (red corresponds to low energy, and pale yellow corresponds to high energy) (Figure 4).

[0170] Under the influence of temperature, interatomic anion-cation bonds expand, reducing orbital overlap. This lowers the shared valence of the bands and, consequently, reduces the gap, after which electron movement is facilitated between the valence band and the conduction band between the two atoms.

[0171] Therefore, semiconductor materials are thermally color-degradable due to changes in the size of their crystal structure under the influence of rising temperature. If the crystal structure changes, the interactions within the network are not the same, and subsequently the width of the forbidden band changes, resulting in a change in color.

[0172] Many semiconductor materials decrease the width of their forbidden band when exposed to rising temperatures. This explains the color change of BiVO4 from yellow at room temperature to red when heated.

[0173] Another subject of the present invention relates to household products having a substrate, preferably metal, that is completely or partially covered by a coating according to the present invention.

[0174] (Bi 1-x A x )(V 1―y M y The color change of the O4 pigment is noticeable to the user, the product is hot, and therefore there is a risk of burns, while on the other hand, the surface of the product has reached a temperature suitable for its use.

[0175] Advantageously, the product support may be plastic, metal, glass, ceramic, or terracotta. Metal supports that can be used in the context of the present invention may, advantageously, include aluminum or aluminum alloys, anodized or unanodized, or polished, sandblasted or chemically treated aluminum or aluminum alloys, or polished, brushed or bead-blasted stainless steel, or cast iron, aluminum, or titanium, or hammered or polished copper supports.

[0176] Specific examples of household products that can be used in the context of the present invention include, in particular, frying pan bowls, fondue or raclette pans or pots, frying pans or bread maker bowls, mixer jars, straightening iron plates, and iron sole plates.

[0177] For better adhesion of the coating, the surface of the support can be treated to increase its particular surface area, for example by sandblasting, brushing, or chemical treatment. For aluminum, this treatment can be carried out by anodizing (creating a tubular alumina structure), chemical etching, sandblasting, etc. Other metal substrates can also be polished, sandblasted, brushed, or bead-blasted.

[0178] Advantageously, the product according to the present invention is a cooking utensil, and the coating according to the present invention completely or partially covers a substrate on a surface that receives food.

[0179] Advantageously, the product according to the present invention is a hair straightener, and the coating according to the present invention completely or partially covers its plates.

[0180] Advantageously, the product according to the present invention is a clothes iron, and the coating according to the present invention completely or partially covers its sole plate.

[0181] Advantageously, the product is a cookware in which one of the surfaces of the support is a concave inner surface that comes into contact with the food placed inside the cookware, and the other surface of the support of the cookware is a convex outer surface that comes into contact with the heat source.

[0182] Preferably, the appliance is a cooking appliance, preferably selected from the group consisting of saucepans, frying pans, stew pots, woks, multi-pans, crepe makers, grills, pracher grills, raclette grills, Marmite pots, or casserole dishes, and the coating will come into contact with food.

[0183] In the fields of application for the present invention, cooking utensil-type heated products or iron-type heated products are typically used in a temperature range consisting of 10°C to 300°C.

[0184] Another subject of the present invention is a method of using a household product according to the present invention, characterized by the following steps:

[0185] - To heat the household product or to place it in the presence of an external heat source. -( Bi 1-x A x )(V 1―y M y ) Observe the color changes of the O4 type pigment and the temperature reference pigment composition. -Use the household product in the following situations:

[0186] ·(Bi 1-x A x )(V 1―y M y )When the color of the O4 pigment and the temperature reference pigment composition are the same, ·(Bi 1-x A x )(V 1―y M y )When the color of the O4 pigment and the color of the temperature reference pigment composition have reached the temperature specified in the instructions for use of the household product.

[0187] The coating according to the present invention is (Bi 1-x A x )(V 1―y M y It contains at least two pigments, including an O4 type pigment and a temperature reference pigment composition.

[0188] The optimal conditions for use can be achieved when the colors of a product according to the present invention are visually identical to those of the user's naked eye at a standard distance for use. For example, a coating according to the present invention may contain BiVO4, which changes from yellow to orange between room temperature and the optimal operating temperature, and an orange, heat-stable bismuth oxyhalide.

[0189] Instructions for use may indicate to the user the color in which they may begin using a household product according to the present invention under optimal conditions. These instructions may exist, for example, in the form of a geometric pattern filled with a specific color or a gradient color bar (see, for example, the one in Figure 4). This pattern or bar serves as a comparative reference for the user who can approach the coated surface of the product according to the present invention.

[0190] Preferably, in the case of cooking utensils, the optimal conditions are obtained when the coating reaches a temperature suitable for cooking food, preferably a temperature consisting of 100 to 250°C. [Examples]

[0191] (Example 1): Pigment selection

[0192] The pigments used are inorganic compound powders:

[0193] Thermochromic pigments:

[0194] • BiVO4, the method described in Example 2, batches 2b and 2d, • Bi2VO3, Barista Fine Grade, sold by 5N Plus.

[0195] • Sicopal (registered trademark) Yellow K1120FG pigment, sold by BASF. • Bayferrox® 130 pigment, sold by Bayferrox.

[0196] Thermally stable pigments (temperature-referenced pigments):

[0197] • Yellow 10C242 pigment, sold by Shepherd Color. • Yellow 6716B pigment, sold by FERRO.

[0198] These compounds may be used individually or in combination.

[0199] (Example 2): Method for synthesizing BiVO4 pigment according to the present invention

[0200] (Process 2.1) A 0.1M solution of ammonium vanadate in 1M nitric acid is stoichiometrically added to a 0.1M solution of bismuth nitrate in 1M nitric acid. The mixture is stirred overnight, filtered, washed with water, and then dried. The powder is then tempered at 450°C for 3 hours. Subsequently, bismuth nitrate is obtained in the form of a bright yellow powder with a monoclinic scheelite structure, characterized by X-ray diffraction analysis.

[0201] (Process 2.2) To a 0.4 M solution of bismuth nitrate in 1 M nitric acid, a stoichiometric amount of sodium metavanadate in powder form is added. The mixture is stirred at 80°C for 2 hours. The precipitate is then filtered and washed with water to obtain yellow BiVO4 in monoclinic scheelite form. The powder is then tempered at 500°C for 3 hours. The method is carried out at pH < 1 without the addition of an alkalizing agent. Therefore, monoclinic scheelite BiVO4 has a ΔE = 40 between room temperature and 200°C.

[0202] (Example 3): Fusion of the compound into the sol-gel coating

[0203] To provide consumers with a cooking appliance having a non-stick coating with a decoration guide and not burning on the inside during cooking, a compound with improved thermochromic properties has been introduced into the non-stick coating having several layers.

[0204] · Sol-gel primer · Thermochromic compound incorporated into the decoration · Thermostable compound incorporated into the second decoration · Sol-gel topcoat

[0205] (i. Preparation of primer and topcoat)

[0206] (Composition of primer with silicone oil: Cl1)

[0207] [Table 2]

[0208] (Composition of topcoat with silicone oil: F1)

[0209] [Table 3]

[0210] (Composition of primer without silicone oil: Cl2)

[0211] [Table 4]

[0212] (Composition of topcoat without silicone oil: F2)

[0213] [Table 5]

[0214] (ii. Preparation of thermochromic decoration) Prepare a pad printing paste containing a thermochromic pigment according to the composition described below, as described in Example 1.

[0215] (Composition of thermochromic decoration: DT1)

[0216] [Table 6]

[0217] (Composition of thermochromic decoration: DT2)

[0218] [Table 7]

[0219] (iii. Preparation of thermostability reference decoration)

[0220] Prepare a pad printing paste containing a thermostable pigment according to the composition described below, as described in Example 1.

[0221] (Composition of reference decoration: DR1)

[0222] [Table 8]

[0223] (Composition of reference decoration: DR2)

[0224] [Table 9]

[0225] (iv. Manufacture of temperature indicator integrated cooking appliance)

[0226] The pre-formed aluminum caps are degreased and dust-free beforehand. For better adhesion of the coating, the support surface is treated by sandblasting to increase the surface area. Subsequently, a primer layer is applied to the surface of the cap by spraying. This layer may be optionally dried. Then, a thermochromic decoration obtained from the composition described above is applied to the primer layer by pad printing and drying. A reference decoration is applied in pattern form on the thermochromic decoration by pad printing. After drying, the finish coat layer is applied by spraying over the three previous layers. The entire product is then cured at 250°C for 30 minutes.

[0227] (Example 4: A method for characterizing simple colors)

[0228] A light booth consisting of a closed enclosure equipped with controlled lighting is used. A camera is mounted directly on the booth and connected to photoprocessing software to obtain color-related features of the analyzed sample. The light booth is illuminated by a D50 light source (corresponding to sunlight).

[0229] The principle of this characterization is to position the material to be analyzed within the booth, take a photograph of it, and then use suitable software to extract color data from the photograph.

[0230] The obtained L1 * a1 * b1 * Depending on the value, the color difference (or color change) ΔE * However, the values ​​obtained at each temperature were relative to the reference temperature (RT=25℃) for the obtained sample, and ΔE * This is defined by the composition of the CIELAB color space, CIE1976.

[0231]

number

[0232] L1 * a1* , b1 * : Coordinates of the pigment's color at standard temperature (25°C or RT), or the coordinates of the reference pigment.

[0233] L2 * a2 * , b2 * : The color coordinates of the pigment at the selected temperature (25℃ / 100℃ / 150℃ / 180℃ / 200℃ / 250℃), or the coordinates of the selected pigment.

[0234] The following protocol has been developed, and it allows for optimal control of the following elements: direct heating in the booth is not possible (to avoid interfering with the atmosphere and camera), but the phase shift time is used to take pictures at the target temperature.

[0235] (i. device) - Thermometer with contact sensor - Stopwatch - Photo light booth -CANON EOS 13000D camera (CANON 28mm wide-angle lens) - Microscope slide -Data acquisition software: Capture One and Photoshop

[0236] (ii. Protocol for samples in powder form (Figure 7))

[0237] -Make three different piles (approximately teaspoons) of powder in the frying pan. - Flatten the pile of powder on a glass plate to ensure it has the same thickness and a flat, uniform surface. -Then, execute the same protocol as before.

[0238] (Example 5: Use of Results) (i. ΔE of the sample at several temperatures) * (Calculation)

[0239] For example, let's consider the pigment Fe2O3 in powder form.

[0240] L1 * a1 * b1 * Coordinates and the ΔE of Fe2O3 for each temperature shown below. * The result.

[0241] [Table 10]

[0242] Specific example at 100°C:

[0243]

number

[0244]

number

[0245] [Table 11]

[0246] (ii. Interpretation of graphs) ΔE calculated for each sample at different temperatures * The value is shown in the graph (ΔE * The formula f(temperature in degrees Celsius) allows us to visualize the evolution of color difference relative to color at room temperature.

[0247] The graph (Figure 8) shows the color change of each pigment in powder form.

[0248] All the pigments studied in this case exhibit a fairly linear color change as a function of temperature.

[0249] "Very good" thermochromic pigments have a color difference of 40 or more ΔE between 25°C and 200°C. * The color difference ΔE as a temperature function having and having a slope of 0.2 or greater has *It exhibits a linear change.

[0250] A "good" thermochromic pigment has a color difference ΔE of 30-40 between 25°C and 200°C. * The color difference ΔE as a temperature function having and having a slope of 0.2 or greater has * It exhibits a linear change.

[0251] The "average" thermochromic pigment has a color difference ΔE of 10-30 between 25°C and 200°C. * The color difference ΔE as a temperature function has the following properties and a slope ranging from 0.05 to 0.2. * It exhibits a linear change.

[0252] "Thermally stable" pigments have a color difference of ΔE of 10 or less between 25°C and 200°C. * The color difference ΔE as a temperature function having and having a slope of 0.05 or less. * It exhibits a linear change.

Claims

1. A sol-gel coating for the surface of a household product comprising a primer layer, a finish layer, a decorative layer (a), and a decorative layer (b), wherein the decorative layer (a) and the decorative layer (b) are arranged between the primer layer and the finish layer, or within the primer layer or within the finish layer: The decorative layer (a) is (Bi 1-x A x ) (V 1―y M y ) O 4 The particles, in the form of type pigments, contain at least a thermochromic pigment composition, -x is either 0 or between 0.001 and 0.

999. -y is either 0 or between 0.001 and 0.

999. - A and M are selected from the group consisting of nitrogen, phosphorus, alkali metals, alkaline earth metals, transition metals, poor metals, metalloids, or lanthanides. - A and M are different from each other. The decorative layer (b) comprises a temperature reference pigment composition, The ΔE of the (Bi 1-x A x )(V 1―y M y )O 4 type pigment is 11 or more between the temperature in the range of 18 °C to 30 °C and the temperature of 150 °C, and ΔE * is defined by CIE1976 in the CIELAB color space and​​ [Math 1] L 1 * a 1 * , and b 1 * The value is L at a temperature range of 18°C ​​to 30°C for the pigment. * a * b * Characterize the values, L 2 * a 2 * , and b 2 * The value is the L of the pigment at 150°C. * a * b * A coating that characterizes a value.

2. The coating according to claim 1, characterized in that the decorative layer (a) and the decorative layer (b) exist in the form of non-overlapping adjacent patterns.

3. The coating according to claim 1, characterized in that the decorative layer (a) and the decorative layer (b) partially overlap.

4. The coating according to claim 1, characterized in that the decorative layer (a) and the decorative layer (b) exist in the form of two partially overlapping patterns.

5. The (Bi) in the coating 1-x A x ) (V 1―y M y ) O 4 ΔE of type pigments * The temperature range is 15 or more between 18°C ​​to 30°C and 200°C, and ΔE * This is defined by the composition of the CIELAB color space, CIE1976. [Math 2] L 1 * a 1 * , and b 1 * The value is L at a temperature range of 18°C ​​to 30°C for the pigment. * a * b * Characterize the values, L 2 * a 2 * , and b 2 * The value is the L of the pigment at 200°C. * a * b * Characterizing the values The coating according to any one of claims 1 to 4.

6. (Bi in the decorative layer (a) 1-x A x ) (V 1―y M y ) O 4 The coating according to any one of claims 1 to 5, wherein the amount of the coating, in a dry state, is 0.1 to 100% by weight relative to the weight of the coating.

7. The coating according to any one of claims 1 to 6, wherein the decorative layer (a) and the decorative layer (b) are applied by screen printing or pad printing.

8. (Bi 1-x A x ) (V 1―y M y ) O 4 The coating according to any one of claims 1 to 7, wherein the pigment exhibits the form of monoclinic scheelite crystals at temperatures in the range of 18°C ​​to 30°C.

9. The coating according to any one of claims 1 to 8, wherein x and y are 0.

10. The coating according to any one of claims 1 to 8, wherein A and / or M are alkali metals selected from Li, Na, K, Rb, and Cs, and A and / or M are different from each other.

11. The coating according to any one of claims 1 to 8, wherein A and / or M are alkaline earth metals selected from Be, Mg, Ca, Sr, and Ba, and A and / or M are different from each other.

12. The coating according to any one of claims 1 to 8, wherein A and / or M are transition metals selected from Sc, Ti, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Ta, W, and Ir, and A and / or M are different from each other.

13. The coating according to any one of claims 1 to 8, wherein A and / or M are poor metals selected from Al, Zn, Ga, In, and Sn, and A and / or M are different from each other.

14. The coating according to any one of claims 1 to 8, wherein A and / or M are metalloids selected from B, Si, Ge, and Sb, and A and / or M are different from each other.

15. The coating according to any one of claims 1 to 8, wherein A and / or M are lanthanides selected from La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, and A and / or M are different from each other.

16. The coating according to claim 1, comprising, in the following order from the surface of the substrate of a household product: one undercoat layer, two decorative layers, and a finish coat layer.

17. The coating according to any one of claims 1 to 16, wherein the sol-gel layer is obtained from a sol-gel (SG) composition comprising at least one metal oxide and at least one metal alkoxide precursor.

18. A household product comprising a substrate completely or partially covered with the coating according to any one of claims 1 to 17.

19. A cooking utensil comprising a substrate completely or partially covered with the coating according to any one of claims 1 to 17, wherein the coating covers a surface that receives food.

20. The cookware according to claim 19, wherein the base material is aluminum or an aluminum alloy, anodized or unanodized, polished, brushed or bead-blasted, sandblasted or chemically treated aluminum or an aluminum alloy, polished stainless steel, cast iron or aluminum, titanium, or hammered or polished copper.

21. The cooking utensil according to claim 19 or 20, wherein the cooking utensil is selected from the group consisting of a sauce pot, frying pan, stew pot, wok, multi-pan, crepe maker, grill, pracha grill, raclette grill, Marmite pot, or casserole dish, and the coating comes into contact with food.

22. The household product is a clothes iron, and the coating according to any one of claims 1 to 17 completely or partially covers the sole plate of the clothes iron, as described in claim 18.

23. The household product is a hair dryer for straightening hair, and the coating described in any one of claims 1 to 17 completely or partially covers the plates of the hair dryer for straightening hair, as described in claim 18.

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