EP2139964A2 - Nonstick coating with improved hydrophobic properties - Google Patents

Abstract

This invention relates to a nonstick coating for a cooking utensil having improved properties of hydrophobicity and high-temperature resistance. This invention also relates to a cooking article comprising a basic element coated with such a coating, and a method for applying such a coating to a basic element.

Description

 Non-stick coating with improved hydrophobic properties.

The present invention generally relates to nonstick cookware coverings which exhibit improved properties of hydrophobicity and high temperature resistance.

In this field, enamel-based coatings are already known, but these do not guarantee good anti-adhesion, and require high vitrification temperatures (greater than 540 ^° C.). Sol-gel coatings, in particular those obtained by polymerization of silanes, are also known. But these do not allow to deposit a large thickness and usually faience for thicknesses of the order of 10 microns. In addition, their cohesion is completed only if also high temperatures are applied for long periods, for example temperatures above 400 ⁰ C for at least thirty minutes. On the other hand, this type of coating makes it possible to envisage a range of use in temperature greater than that of PTFE-based coatings, which can be up to 600 ^° C., instead of 300 ^° C. at most for coatings based on PTFE). This is, however, to the detriment of anti-adhesion.

Such coatings have the drawback of losing their hydrophobic properties after aggression which may degrade the surface of the coating, and in particular a chemical attack such as that caused by dishwashing detergents, or a mechanical aggression such as that caused by a too vigorous scrubbing of the coating with an abrasive pad, or exposure of the order of a few minutes at an extreme temperature. To remedy these problems, the Applicant has developed a non-stick coating obtained by sol-gel by polymerization of a composition based on at least one metal alkoxide and a colloidal metal oxide. The Applicant has surprisingly found that when a very small amount of silicone oil is added to such a composition, the sol-gel-formed coating from this composition is not only resistant to high temperature, but it is also able to withstand a passage of several minutes to the flame of a bunsen burner (whose temperature is above 600 ⁰ C), and then quickly find its hydrophobic character.

It is known to those skilled in the art to use silicone oil to make sol-gel coatings from a composition based on alkoxysilane and colloidal silica.

Thus, US patent application US 2006/0147829 describes a process for producing superhydrophobic coatings for self-cleaning surfaces, having a contact angle with water greater than 130 °. This method comprises a step of preparing nanoparticles (in particular silica nanoparticles) preferably having a size ranging from 1 nm to 100 nm, and a step of treating these particles with a hydrophobic agent and an additive, the hydrophobic agent being preferably based on silicon (silicone), and the additive being selected from inorganic and organic bases. These nanoparticles may be prepared by a process of wet synthesis, and in particular by sol-gel, from precursors comprising water, a solvent, in particular an alcohol, and a metal alkoxide such as, for example, tetramethoxysilane. (TMOS) or tetraethoxysilane

(TEOS). After formation of the nanoparticles, they are mixed directly with the hydrophobic agent and the additive, and allowed to react at a temperature of between 0 and 100 ^° C. The material thus obtained is applied on a substrate (in particular glass, plastics material, metal, ceramic or polymer or composite material) according to any technique for obtaining a coating from a liquid (by centrifugation, dipping, or by coating by brush or roller). Then, after application to the substrate, the coating is dried at a temperature between room temperature and 200 ^° C. The coating thus obtained has a hydrophobic surface, forming an angle of contact with water of more than 130 °, or even greater than 150 °.

However, nothing is said in US 2006/0147829 concerning the non-stick nature of the coating thus obtained, nor its ability to withstand high temperatures and its ability to regain a hydrophobic character after aggression of the surface of the coating. Furthermore, US 2006/0147829 does not indicate that the sol-gel coating is in the form of a continuous film having a thickness of at least 10 μm.

The subject of the present invention is therefore a non-stick coating having improved hydrophobic properties and resistant to high temperature, characterized in that it is in the form of a film having a thickness of at least 10 μm and consists of a sol-gel material comprising: - a matrix of at least one metal polyalkoxylate,

at least 5% by weight relative to the total weight of the coating of at least one colloidal metal oxide dispersed in said matrix, and at least one silicone oil.

The coating according to the invention is preferably free of PTFE.

Most of the hydrophobicity of the surface of the coating is provided by the metal polyalkoxylate and the silicone oil. Indeed, the metal polyalkoxylate has hydrophobic groups which are destroyed at high temperature during a flame. However, this disappearance of the hydrophobic character is momentary, since it is progressively compensated by the silicone oil trapped in the polyalkoxylate and whose surface migration in infinitesimal amounts favors the progressive reconstitution of the hydrophobic groups of the polyalkoxylate at the surface of the film.

It is observed that with a coating according to the invention comprising at least 0.1% by weight of silicone oil, the reconstitution of the hydrophobic character is sufficient at the time of a new firing. Indeed, the value of the static contact angle Θ of a drop of water deposited on the coating of the invention is of the order of 20 ° after thermal aggression type flame passage. This static contact angle value rises back to at least 75 ° C. after a process of reconstitution of the hydrophobic properties consisting of a reheating of the ambient temperature to 200 ^° C. over a period of at least 5 minutes, ie ie when the utensil is ready for a new cooking.

Preferably, the silicone oil is 0.1 to 6% by weight and more preferably 0.3 to 5% by weight of the total weight of the coating (dry state). Below 0.1% by weight of silicone oil, the reconstitution of the hydrophobic groups have disappeared during a flaming (600 ⁰ C) is smaller, the angle obtained being less than 62 °.

More preferably, the sol-gel material of the coating according to the invention comprises 0.5 to 2% by weight of silicone oil relative to the total weight of the dry coating. In this case, the initial static contact angle Θ of a drop of water deposited on such a coating is 95 °. This coating after a flame-type thermal attack has an angle of 20 °. After a reconstitution process comprising at least one temperature reheating step ambient at 200 ⁰ C over a period of at least 5 minutes, the static contact angle becomes greater than 75 ° when the utensil is ready for a new cooking.

The coating according to the invention may comprise a silicone oil or a mixture of silicone oils.

Silicone oils that can be used in the coating according to the invention include phenyl silicones, methyl-phenyl silicones and methyl silicones. If the coating according to the invention is used to be in contact with food, a food grade silicone oil, and in particular an oil chosen from methyl-phenyl silicones and methyl silicones of food grade, will preferably be chosen. Mention may be made, for example of methylphenyl silicone oils, of the non-food oils marketed by the company Wacker under the trade name Wacker Siliconol AP150 and by the company Dow Corning under the trade name DOW CORNING 550 fluid, as well as edible oils. marketed by WACKER AROO. Mention may be made, for example, of methyl silicone oils, the oil sold by RHODIA under the trade name RHODIA 47 V 350, the oil from WACKER 200 fluid, or the oil from TEGO ZV 9207. , which are food grade methylsilicone oils.

Preferably, use will be made of a silicone oil chosen from those mentioned above, with a molecular weight of at least 1000 g, which is non-reactive and has a viscosity of between 20 and 2000 mPa.s.

Advantageously, the matrix of the coating according to the invention comprises, as metal polyalkoxylate, a polyalkoxysilane, and in particular an amorphous polyalkoxysilane, an aluminate, a titanate, a zirconate, a vanadate, or their mixtures. In a preferred manner, the matrix of the coating according to the invention comprises a polyalkoxysilane and / or an aluminate so as to constitute a mixed matrix.

In a variant of the invention, coating of the matrix according to the invention is grafted with one or more organic groups selected from alkyl _Cl-C4 and phenyl groups. These groups are necessary to improve the hydrophobicity of the coating. Preferably, the matrix of the coating according to the invention is grafted with one or more methyl groups, which improve the hydrophobic character of the coating without hindering the formation of the inorganic network. In addition to the matrix of at least one metal polyalkoxylate, the non-stick coating according to the invention comprises at least 5% by weight, and preferably from 5 to 30% by weight relative to the total weight of the coating of at least one metal oxide. colloidal, which is preferably finely dispersed in the matrix. This metal oxide is generally in the form of aggregates, whose size is less than one micron, or even 300 or 400 nm.

The presence of colloidal metal oxide in the matrix of the coating according to the invention makes it possible to obtain a film of sufficient thickness, namely a thickness of at least 10 μm. If the thickness of the coating is less than 10 microns, a good cohesion of the formed film is not obtained. Preferably, the film has a thickness of between 10 and 80 μm, and better still between 30 and 70 μm so that the film thus formed is continuous, coherent and sufficient to absorb the roughness of the support.

As colloidal metal oxide that can be used in the non-stick coating according to the invention, there may be mentioned silica, alumina, cerium oxide, zinc oxide, vanadium oxide and zirconium oxide. The preferred colloidal metal oxides are silica and alumina.

Advantageously, the sol-gel material of the coating according to the invention may further comprise fillers for improving the cohesion of the formed coating film, and / or pigments, to impart color to the coating. In addition, the presence of fillers and / or pigments also has a beneficial effect on the hardness of the film.

As fillers that may be used in the coating according to the invention, there may be mentioned alumina, zirconia, mica, clays (such as montmorillonite, sepiolite, gypsite, kaolinite) and zirconium phosphate.

As pigments that can be used in the coating according to the invention, mention may be made especially of titanium dioxide, mixed oxides of copper-chromium-manganese, iron oxides, carbon black, pyralene red, aluminosilicates, metallic flakes and especially aluminum flakes.

Preferably, the fillers and / or the pigments are in the form of flakes, which has the advantage of improving the hardness of the non-stick coating. Preferably, the pigment and / or the fillers are of nanometric size, in order to improve their dispersion and their distribution in the coating, conferring on it a great regularity of performance.

The nonstick coating according to the invention can be used for coating the interior surface of a cooking utensil, but also as: coating of plates, grills or barbecue vats, coating of electric cooking equipment (crepe makers, waffle irons, grills table, raclette, fondue, rice cookers, jammers, breadmaker tanks, blender tanks and mixing blades for this equipment), furnace walls lining (electric, gas, microwave, steam ovens), - cookware coating (spatulas, ladles, forks, spoons), coating of handles or buttons of cookware).

The present invention also relates to a culinary article comprising a support coated with a coating according to the invention.

More particularly, the present invention relates to a culinary article having improved hydrophobic properties, comprising a support having an inner surface that can receive food and an outer face to be disposed towards the heat source, characterized in that the inner face of the support is coated with a non-stick coating according to the invention. In an advantageous version of the culinary article according to the invention, the support is a hollow cap of a culinary article, having a bottom and a side wall rising from said bottom.

The support of the culinary article according to the invention is made of a material chosen from metals, wood, glass, ceramics and plastics.

As metallic supports that can be used in the process according to the invention, it is advantageously possible to mention supports made of anodized or non-anodized aluminum or of polished, sandblasted, brushed or micro-blasted aluminum alloy, and supports made of polished, sandblasted or brushed stainless steel or microbead, cast iron supports, iron supports, or hammered or polished copper supports. Finally, the present invention also relates to a method of producing a coating according to the invention on a support.

More particularly, the subject of the present invention is a method for applying to one of the faces of a support at least one non-stick coating according to the invention, characterized in that it comprises the following steps: a) preparation of a aqueous composition A comprising: 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) 0.05 to 3% by weight relative to the total weight of said aqueous composition A of at least one silicone oil. b) preparing a solution B comprising at least one metal alkoxide precursor, which is advantageously partially combined with a Bronsted or Lewis acid. c) mixing the solution B of metal alkoxide with the aqueous composition A to obtain a sol-gel composition (A + B) with 40 to 75% by weight of aqueous composition relative to the weight of the sol-gel composition (A) + B), so that the amount of colloidal metal oxide is 5 to 30% by weight of the sol-gel composition (A + B) in the dry state. d) applying on the support at least one layer of the sol-gel composition (A + B) having a thickness of at least 20 μm wet, then e) baking said layer at a temperature between 180 and 350 ⁰ C, to obtain a coating with improved hydrophobic properties. With regard to the preparation of the aqueous composition A, it is necessary to incorporate at least 5% by weight of at least one colloidal metal oxide with respect to the total weight of the composition A to form a film having after firing a thickness at least 10 microns. If on the other hand we have more than 30% by weight relative to the weight of the composition A, it is no longer stable.

The colloidal metal oxide of the aqueous composition A is as defined above, and preferably selected from colloidal silica and / or colloidal alumina.

The purpose of the presence of an alcohol-based solvent is to improve the compatibility of the aqueous composition A with the solution B of metal alkoxide.

It is however possible to work without solvent, but in this case the choice of polyalkoxylates is reduced to those with excellent compatibility with water. An excessive amount of solvent (greater than 20%) is possible, but unnecessarily generates volatile organic compounds, which is not favorable for the environment.

The solvent used in the aqueous composition A of the invention is preferably an oxygenated alcoholic solvent or an ether alcohol.

To produce on a support a non-stick coating according to the invention, it is necessary that the silicone oil is present in the aqueous composition in a proportion of 0.05 to 3% by weight relative to the total weight of the composition.

With a composition comprising 0.5 to 2% by weight of silicone oil, a coating according to the invention is obtained which has reconstitutable hydrophobic properties in the context of a process of culinary use. The silicone oil of the composition A is a food grade silicone oil defined above.

The aqueous composition A of the invention may also comprise fillers and / or pigments, which are as defined above.

The aqueous composition A of the invention may further comprise fumed silica, whose function is to control the viscosity of the sol-gel composition and / or the gloss of the dry coating. Regarding the preparation of the solution

B is preferably used as a precursor metal alkoxide selected from the group consisting of:

the precursors corresponding to the general formula Mi (ORi) _n , the precursors corresponding to the general formula

the precursors corresponding to the general formula M ₃ (OR ₃ ) (n-2) R 3 ^! 2, with:

R 1, R ₂ , R ₃ or R ₃ 'denoting an alkyl group, R ₂ ' denoting an alkyl or phenyl group, n being an integer corresponding to the maximum valence of the metals Mi, M ₂ or M ₃ ,

Mi M ₂ or M ₃ denoting a metal selected from Si, Zr, Ti, Sn, Al, Ce, V, Nb, Hf, Mg or Ln. Advantageously, the metal alkoxide of solution B is an alkoxysilane.

As alkoxysilanes that may be used in solution B of the process of the invention, mention may especially be made of methyltrimethoxysilane (MTMS), tetraethoxysilane (TEOS), methyltriethoxysilane (MTES) and dimethyldimethoxysilane, and mixtures thereof, the preferred alkoxysilanes being TEOS and MTMS.

According to an advantageous embodiment of the process of the invention, solution B may comprise a mixture of an alkoxylane as defined above and an aluminum alkoxide. The metal alkoxide precursor of the solution B is mixed with a mineral organic Lewis acid which represents 0.01 to 10% by weight of the total weight of the solution B. As acids usable for mixing with the precursor metal alkoxide, there may be mentioned in particular acetic acid, citric acid, ethyl acetoacetate, hydrochloric acid or formic acid.

The preferred acids according to the invention are organic acids, and more particularly acetic acid and formic acid.

After the preparation of the aqueous composition A and that of the precursor solution B, they are mixed together to form a sol-gel composition (A + B). The respective amounts of each of compositions A and B must be adjusted so that the amount of colloidal silica in the sol-gel composition is 5 to 30% by weight on a dry basis.

The sol-gel composition (A + B) of the invention may be applied to the support by spraying or by any other method of application, such as by dipping, by pad, by brush, by roller, by spin coating or by by screen printing. However, in the context of a shaped object, the spraying, for example by means of a spray gun, has the advantage of forming a homogeneous and continuous film which, after firing, forms a continuous coating of uniform thickness and waterproof.

After application of the sol-gel composition (A + B) according to the invention, drying is generally carried out, preferably at 80 ^° C., for 3 minutes. The cooking takes place in a preferred mode at a temperature of between 220 and 280 ^° C.

According to an advantageous embodiment of the process of the invention, it also comprises, after the step of producing the first non-stick coating: the production of a decoration by application and then drying on at least a part of the first non-stick coating of a decorative composition comprising a thermostable binder resistant to at least 200 ^° C. and an optically non-transparent or thermochromic chemical substance, and then the production a second non-stick coating by application, then drying and firing on the decoration of at least one layer of sol-gel composition according to steps a) to c) of the process of the invention.

The method according to the invention may further comprise a step of depositing an enamel layer on the face opposite to that coated with a non-stick coating according to the invention, this step of depositing the enamel layer being carried out prior to that of the non-stick coating according to the invention.

In addition to the advantages mentioned above, the method according to the invention is particularly simple to implement and can easily be envisaged without disruption of conventional manufacturing processes of cookware.

The method according to the invention also has the advantage of being able to be implemented without the need for a prior mechanical or chemical treatment of the first face of the support intended to be coated by the first coating, which has a very clear advantage from an economic point of view but also ecological. Other advantages and features of the present invention will result from the description which follows, given by way of non-limiting example and with reference to the appended figures: FIG. 1 represents a schematic sectional view of a culinary article according to FIG. the invention according to a first variant embodiment, FIG. 2 represents a diagrammatic cross-sectional view of a culinary article holder according to the invention according to a second variant embodiment, FIG. 3 represents a diagrammatic sectional view of a culinary article holder conforming to FIG. invention according to a third variant embodiment,

FIG. 4 represents a diagrammatic cross-sectional view of a culinary article holder according to the invention according to a fourth variant embodiment, FIG. 5 represents a schematic sectional view of a culinary article holder conforming to FIG. the invention according to a fifth variant embodiment,

- Figure 6 shows a schematic sectional view of a culinary article holder according to the invention according to a sixth embodiment.

The identical elements shown in FIGS. 1 to 6 are identified by identical reference numerals.

FIG. 1 shows, as an example of a culinary article according to the invention, a pan 1 comprising a support 3 in the form of a hollow cap with a bottom 34 and a side wall 35 rising to from the bottom 34, and a gripping handle 6. The support 3 comprises an inner face 31 can receive food, and an outer face

32 to be disposed on the side of the heat source, such as a cooking plate or a burner.

In Figures 2 to 6, there is shown only the support 3 of the culinary article (or more exactly its bottom 34).

In Figures 1 to 3, the inner face 31 of the support 3 is covered by a non-stick coating according to the invention 2, said bottom coating.

In the variants illustrated in FIGS. 2 and 3, a decorative layer 4 covers the bottom coating 2 and consists of a sol-gel material comprising a matrix of at least one metal polyalkoxylate, at least 5% by weight relative to the total weight of the decoration of at least one colloidal metal oxide and at least one silicone oil. More particularly, in the variant illustrated in Figure 3, a second non-stick coating 5, said surface covers the decorative layer 4. This non-stick surface coating 5 is a non-stick coating 5 according to the invention. The variant illustrated in FIG. 4 differs from that illustrated in FIG. 3 in that the decoration 40 consists of a sol-gel material that does not comprise silicone oil. Indeed, the decoration 40 consists of a sol-gel material comprising a matrix of at least one metal polyalkoxylate and at least 5% by weight relative to the total weight of the decoration of at least one colloidal metal oxide.

The variant illustrated in FIG. 5 differs from that illustrated in FIG. 4 in that the non-stick base coating 20 covering the inner surface 31 of the support 3 also does not include silicone oil. Indeed, it is a bottom coating 20 made of a sol-gel material comprising a matrix of at least one metal polyalkoxylate and at least 5% by weight relative to the total weight of the non-stick surface coating at least one colloidal metal oxide.

The variant illustrated in FIG. 6 differs from that illustrated in FIG. 5, in that the decoration 4 consists of a sol-gel material comprising silicone oil, that is to say a layer of decoration. 4 according to that of the variant illustrated in FIG.

For the six embodiments, the decorative layers 4, 40 may be continuous layers partially covering the base layer 2, 20, or discontinuous layers, for example in the form of dots or elementary patterns.

Preferably, the decor 4 comprises a reversible thermochromic chemical substance, said decor partially covering said non-stick coating 2.

The thermochromic chemical substance mentioned above may be chosen from those which lighten with the rise in temperature. This is the case of perylene red linked to a black pigment. The chemical substance can also be chosen from those which darken with temperature. This is the case of ferric oxide Fe2O3.

Advantageously, the decoration may comprise at least two motifs, one of the units containing a chemical substance that clears with temperature, such as, for example, perlylene red bonded to a black pigment, and the other pattern containing a chemical substance. which darkens with the rise in temperature, for example ferric oxide Fe2O3. Thus, the contrast achieved between the two pigments makes it possible to better distinguish the temperature change. If the above chemical compounds are used in each of the patterns of the decoration (a pattern comprising Fe 2 O 3 ferric oxide and the other motif comprising perylene red associated with a black pigment), a very marked contrast is observed between the two. patterns from 200 ⁰ C, that is the optimum temperature for frying or red roast.

In a particularly advantageous version of this embodiment, the bottom release coating comprises non-optically transparent fillers and / or pigments, and the surface release coating comprises neither fillers nor pigments or comprises fillers and / or pigments. optically transparent, and the decor includes a thermostable binder resistant to minus 200 ° C and a reversible thermochromic chemical.

Such an article has the combined advantages of being both hydrophobic, even after passing through the flame, and of being able to inform a user about the temperature of the cooking surface of a culinary article.

Indeed, since the top layer of non-stick coating according to the invention is transparent, the color change of the thermochromic substance of the decor is visible through the top layer of non-stick coating.

The color change described above allows the user to be warned both that the culinary article is hot, and therefore presents a risk of burning, and secondly that the surface of the article has reaches the correct temperature for its use.

The outer face of the culinary article, opposite to the inner face intended to receive food, may also be coated with a non-stick coating according to the invention, pigmented or not, or a lacquer based on one or more Silicone polyester resins, or enamel, or any other flame resistant coating.

The following examples illustrate the invention without, however, limiting its scope.

In the examples, unless otherwise indicated, all amounts are given in grams.

EXAMPLES

products

Aqueous composition A

Colloidal metal oxide

colloidal silica in the form of 30% aqueous solution of silica, sold by the company Clariant under the trade name Klebosol,

colloidal silica in the form of 30% aqueous solution of silica, sold by Grace Davison under the trade name Ludox,

colloidal alumina in the form of a 5% aqueous solution marketed by DGTec.

Solvent

- methanol,

- ethanol, - isopropanol,

2- (2-Butoxyethoxy) -ethanol (Butylcarbitol).

Food grade methyl silicone oil silicone oil marketed by the company Dow Corning under the trade name "Dow Corning 200 Fluid", and having a viscosity of 30OcSt, food grade methyl silicone oil sold by the company TEGO under the trade name "TEGO ZV 9207 ".

pigments

mineral black pigment marketed by Ferro under the trade name FA 1260, a mineral black pigment marketed by Ferro under the trade name FA 1220, ultramarine blue pigment sold by the company Holliday pigments, under the name "CM13",

perylene red pigment marketed by BASF,

- white titanium dioxide pigment marketed by Kronos.

loads

Powdered alumina marketed by the company ALCAN under the trade name CAHPF 1000, and nanometric flake alumina dispersed in a 40% aqueous phase marketed by the company Baikowski,

Alumina powder sold by the company Baikowski under the trade name "DF 1000",

Zirconium phosphate (ZrP) marketed by Rhodia,

- Clay BENTONITE type SE3010 sold by Sud Chemie.

Solution B

precursors

- methyltrimethoxysilane (MTMS) corresponding to the formula Si (OCHs) ₃ CH ₃ , tetraethoxysilane (TEOS) corresponding to the formula Si (OC ₂ Hs) ₄ .

Acid

- formic acid,

- acetic acid.

tests

- hardness evaluated with a Mohs scale: the coating is subjected to the action of materials of different hardness representing the levels of the Mohs hardness scale. The hardness of the coating is expressed by the highest value of the material not scratching it.

anti-adhesion evaluated by means of the carbonized milk test according to standard NF D 21-511

- flame resistance: the coating is subjected to the action of the flame of a Bunsen burner for 30 seconds, it is cooled by quenching with cold water, then the contact angle is measured.

hydrophobicity: measurement of the contact angle of a drop of water on the coating with a GBX Digidrop type goniometer.

EXAMPLE 1 Preparation of an aqueous composition A1 according to the invention

A first aqueous composition Al according to the invention was produced, which is shown in Table 1:

Table 1

EXAMPLE 2 Preparation of an aqueous composition A2 according to the invention

A second aqueous composition A2 according to the invention was produced, which is shown in Table 2:

Table 2

EXAMPLE 3 Preparation of an aqueous control composition A3 without silicone oil

A first aqueous control composition A3 without a silicone oil was produced. This composition is presented in Table 3:

Table 3

EXAMPLE 4 Preparation of an aqueous control composition A4 without silicone oil

A second aqueous control composition A4 without silicone oil was made, which is shown in Table 4: Table 4:

EXAMPLE 5 Preparation of an A5 Aqueous Composition Incorporating Colloidal Alumina

An aqueous composition A5 was made, which is shown in Table 5:

Table 5:

EXAMPLE 6 Preparation of a solution B1 based on MTMS

A first solution B1 according to the invention is produced by mixing 99.6 g of MTMS with 0.4 g of formic acid, giving a solution containing 0.4% by weight of acid in the MTMS.

EXAMPLE 7 Preparation of a Solution B2 Based on MTMS A second B2 solution according to the invention is produced by mixing 59.7 g of MTMS with 0.3 g of acetic acid, giving a solution of 0.5% by weight of acid in the MTMS.

EXAMPLE 8 Preparation of a solution B3 based on MTMS and TEOS

A third solution B3 according to the invention is produced by mixing 50 g of MTMS, 9.5 g of TEOS and 0.5 g of acetic acid to give a 0.83% by weight solution of acid in the mixture of silanes.

EXAMPLE 9 Preparation of a sol-gel composition SG1 according to the invention

One carries out a sol-gel composition SGL according to the invention by adding 100 g of Al aqueous composition according to the invention 100 g of solution Bl. Were mixed in a planetary mixer for one hour maintaining a temperature below 60 ⁰ C, at the end of which is obtained a sol-gel composition according to the invention which is stored at room temperature. The composition SG1 is applied 48 hours after mixing. EXAMPLE 10 Preparation of a sol-gel SG2 composition according to the invention

A sol-gel composition SG2 according to the invention is produced by adding 100 g of aqueous composition A2 according to the invention to 60 g of solution B2. It is mixed in a planetary mixer for one hour while maintaining a temperature below 60 ^° C., at the end of which a sol-gel composition according to the invention is obtained which is stored at room temperature. The SG2 composition is applied 48 hours after mixing.

EXAMPLE 11 Preparation of a Sol-gel Composition Control SGO1

A sol-gel composition SGO1 according to the invention is produced by adding 100 g of aqueous composition A3 according to the invention to 100 g of solution B1. It is mixed in a planetary mixer for one hour while keeping a temperature below 60 ^° C. at the end of which is obtained a sol-gel composition according to the invention which is stored at room temperature. The composition SGO1 is applied 48 hours after mixing.

EXAMPLE 12 Preparation of a Control SGO2 Sol-gel Composition

A sol-gel SG02 composition according to the invention is produced by adding 100 g of aqueous composition A4 according to the invention to 60 g of solution B2. It is mixed in a planetary mixer for one hour while maintaining a temperature below 60 ^° C., at the end of which a sol-gel composition according to the invention is obtained which is stored at room temperature. The SG02 composition is applied 48 hours after mixing. EXAMPLE 13 Preparation of an aqueous composition SG3 according to the invention

A sol-gel composition SG3 according to the invention is produced by adding 100 g of aqueous composition A2 according to the invention to 60 g of solution B3. It is mixed in a planetary mixer for one hour while maintaining a temperature below 60 ^° C., at the end of which a sol-gel composition according to the invention is obtained which is stored at room temperature. The SG3 composition is applied 30 hours after mixing.

Example 14: Preparation of an aqueous composition SG4 according to the invention.

A sol-gel composition SG4 according to the invention is produced by adding 100 g of aqueous composition A5 according to the invention to 100 g of solution B2. It is mixed in a planetary mixer for one hour while maintaining a temperature below 60 ^° C., at the end of which a sol-gel composition according to the invention is obtained which is stored at room temperature. The SG4 composition is applied 24 hours after mixing.

The SG-SG sol-gel compositions of the invention as well as the control sol-gel compositions SGO1 and SG02 are summarized in Table 5 below.

Table 6

EXAMPLE 15: Production of Sol-Gel Coatings on an Aluminum Support

It is applied to the gun on a shot or sanded aluminum support, so as to form the sol-gel compositions of Examples 1 to 14, according to the following cycle:

- Application on the support of a layer of sol-gel composition (A + B) with a wet thickness of 40 to 70 microns, - drying for 3 minutes at 80 ⁰ C, and

- cooling at room temperature

It is possible to apply this cycle several times, the number of cycles being determined by the desired final thickness. At the end of the application cycle (s) / drying, it is heated for 18 minutes at 280 ^° C. This gives a coating having a dry thickness of between 30 and 70 microns, which is smooth, black and glossy.

The non-stick coatings according to the invention R1 to R4 are the coatings obtained from the sol-gel compositions according to the invention SG1 to SG4 respectively. The control non-stick coatings RO1 and R02 are the coatings obtained from the sol-gel compositions evmeneve _I oins SGO1 and SG02 respectively.

The properties of the various coatings obtained by applying each of the sol-gel compositions of Examples 1 to 14 are summarized in Table 7 below.

Table 7.) ₍₎ secun _i

The coatings R1 to R4 according to the invention have a hardness of between 3 and 4 Mohs, an excellent anti-adhesion (100 points in the carbonized milk test: standard NF D 21-511), and a good resistance to flame (no change of appearance after 30 seconds in direct contact with the Bunsen burner flame). The contact angle of a drop of water on the coatings R1 to R4 is respectively 93 and 96 ° (before passing to the flame). For the coatings R1 to R4, a drop in hydrophobicity is observed just after the flame has passed through the film (despite the unchanged appearance): the contact angle becomes less than 30 °. But at the end of the reconstitution process (at least 5 minutes at 200 ^° C.), angles greater than 75 ° are observed for the coatings R1 to R4.

Comparatively, the control coatings RO1 and R02 have, for an equivalent hardness (between 3 and 4 Mohs), a low anti-adhesion (25 points in the carbonized milk test). In addition, the static contact angle of a drop of water on these control coatings is of the order of 73-75 ° before passing to the flame. After passing through the flame, the contact angles are smaller than those obtained with the coatings according to the invention (62-63 ° instead of 75-79 °).

Claims

1. Non-stick coating (2) having improved hydrophobic properties and resistant to high temperature, characterized in that it is in the form of a continuous film having a thickness of at least 10 microns and consists of a soil material gel comprising: a matrix of at least one metal polyalkoxylate, at least 5% by weight relative to the total weight of the coating of at least one colloidal metal oxide dispersed in said matrix, and at least one silicone oil. 2. Coating (2) according to claim 1, characterized in that the silicone oil represents 0.1 to 6% by weight, preferably 0.3 to 5% by weight, and more preferably 0.5 to 2% by weight. weight of the total weight of the coating (2). 3. Coating (2) according to claim 1 or 2, characterized in that the sol-gel material further comprises at least one filler and / or at least one pigment. 4. Coating (2) according to claim 3, characterized in that the pigment and / or the filler is in the form of flakes. 5. Coating (2) according to claim 3 or 4, characterized in that the pigment and / or the filler are of nanometric size. 6. Coating (2) according to any one of claims 1 to 5, characterized in that it is free of PTFE. 7. Coating (2) according to any one of claims 1 to 6, characterized in that the metal polyalkoxylate is a polyalkoxysilane. 8. Coating (2) according to claim 7, characterized in that the polyalkoxysilane is amorphous. 9. Coating (2) according to any one of claims 1 to 6, characterized in that the metal polyalkoxylate is an aluminate. 10. The coating according to claim 1, wherein the sol-gel material comprises a mixed matrix of polyalkoxysilane and aluminate. 11. Coating (2) according to any one of claims 1 to 10, characterized in that the matrix is grafted with at least one organic group selected from C ₁ -C ₄ alkyl groups and phenyl groups. 12. The coating (2) according to claim 11, characterized in that the organic group is a methyl group. 13. Coating (2) according to any one of claims 1 to 12, characterized in that the colloidal metal oxide is selected from the group consisting of silica, alumina, cerium oxide, oxide of zinc, vanadium oxide and zirconium oxide. 14. Coating (2) according to claim 13, characterized in that the colloidal metal oxide is colloidal silica. 15. The coating according to claim 3, wherein the filler is chosen from alumina, zirconia, mica, clays and zirconium phosphate. 16. Coating (2) according to any one of claims 3 to 15, characterized in that the pigment is selected from the group consisting of titanium dioxide, mixed oxides of copper-chromium-manganese, aluminosilicates, oxides of iron, carbon black, pyralene red, metallic flakes and thermochromic pigments. 17. Coating (2) according to any one of claims 1 to 16, characterized in that the film has a thickness of between 10 and 80 microns, preferably between 30 and 70 microns. 18. Coating (2) according to any one of claims 1 to 17, characterized in that the silicone oil is chosen from phenyl silicones, methyl-phenyl silicones and methyl silicones. 19. Coating (2) according to any one of claims 1 to 18, characterized in that the silicone oil is a food grade oil. 20. Culinary article (1) having improved hydrophobic properties, comprising a support (3) having an inner face (31) capable of receiving food and an outer face (32) to be disposed towards the heat source, characterized in that the inner face (31) is coated with a non-stick coating (2), said non-stick coating (2) having a coating as defined in claim 19. 21. Cooking item (1) according to claim 20, characterized in that the support (3) is a hollow cap having a bottom (34) and a side wall (35) rising from said bottom (34). 22. Culinary article (1) according to claim 20 or 21, characterized in that the support (3) is made of a material selected from metals, wood, glass, ceramics and plastics. 23. Culinary article (1) according to claim 22, characterized in that the support is a metal support anodized aluminum or not, or polished aluminum, brushed or micro-blasted, or stainless steel polished, brushed or micro-blasted, or cast iron , or hammered or polished copper. 24. Culinary article (1) according to any one of claims 20 to 23, characterized in that it further comprises a layer of a decoration (4) disposed on the non-stick coating (2) of the background, said decoration ( 4) being made of a sol-gel material comprising a matrix of at least one metal polyalkoxylate, at least 5% by weight relative to the total weight of the decoration of at least one colloidal metal oxide and at least one silicone oil . 25. Culinary article (1) having hydrophobic properties, comprising a support (3) having an inner face (31) capable of receiving food and an outer face (32) intended to be arranged towards the heat source, characterized in that it comprises: - a non-stick base coating (2, 20) disposed on the inner face (31) of the support (3), said wherein the non-stick coating (2, 20) is either a non-stick coating (2) as defined in claim 19 or a coating (20) made of a sol-gel material comprising a matrix of at least one metal polyalkoxylate and at least 5% by weight relative to the total weight of the surface non-stick coating of at least one colloidal metal oxide, - a decoration (4, 40) disposed on said non-stick coating (20), said decoration (4, 40) consisting of a sol-gel material comprising a matrix of at least one metal polyalkoxysilate and at least 5% by weight relative to the total weight of the decoration of at least one colloidal metal oxide, and a non-stick surface coating (5) as defined in claim 19 and arranged on the decorative layer (4), 26. The article of cooking according to claim 25, characterized in that the sol-gel material of the decor (4) further comprises at least one silicone oil. 27. Cooking item according to any one of claims 24 to 26, characterized in that the decoration (4, 40) further comprises at least one reversible thermochromic chemical substance. 28. Cooking article according to any one of claims 24 to 27, characterized in that the decoration (4, 40) comprises at least two patterns, one of the units containing a thermochromic chemical substance which darkens with temperature, and the other pattern containing a chemical which clears with temperature. 29. Cooking item according to claim 28, characterized in that the chemical substance which darkens with the temperature is ferric oxide Fe2O3 and the chemical that clears with the temperature is perylene red associated with a black pigment. Culinary article according to one of claims 20 to 29, characterized in that the bottom release coating (2, 20) comprises non-optically transparent fillers and / or pigments, and the surface release coating (5, 50) does not include fillers or pigments or comprises optically transparent fillers and / or pigments. 31. Article of cooking according to any one of claims 20 to 30, characterized in that the outer face (32) of the support (3) is coated with a lacquer based on one or more silicone polyester resins or a enamel layer. 32. Cooking article according to any one of claims 20 to 30, characterized in that the outer face (32) of the support (3) is coated with a non-stick coating as defined in claim 19. 33. A process for applying at least one non-stick coating as defined in claim 19 to one of the faces of a support, characterized in that it comprises the following steps: a) preparation of an aqueous composition A comprising: 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) 0.05 to 3% by weight relative to the total weight of said aqueous composition A of at least a silicone oil, b) preparing a solution B comprising at least one metal alkoxide precursor; c) mixing the solution B of metal alkoxide with the aqueous composition A to obtain a sol-gel composition (A + B) with 40 to 75% by weight of aqueous composition relative to the weight of the sol-gel composition (A) + B), so that the amount of colloidal metal oxide is 5 to 30% by weight of the sol-gel composition (A + B) in the dry state; d) applying on the support at least one layer of the sol-gel composition (A + B) having a thickness of at least 20 μm in the wet state, then e) firing said layer at a temperature between 180 and 350 ⁰ C, to obtain a coating with improved hydrophobic properties. 34. Process according to claim 33, characterized in that the colloidal metal oxide is chosen from the group consisting of silica, alumina, cerium oxide, zinc oxide, vanadium oxide and zirconium oxide. 35. The method of claim 34, characterized in that the aqueous composition A comprises colloidal silica and / or colloidal alumina. 36. Process according to any one of claims 33 to 35, characterized in that the solvent of the composition A is an oxygenated alcoholic solvent or an ether-alcohol. 37. Process according to any one of claims 33 to 36, characterized in that the silicone oil is chosen from phenyl silicones, methyl-phenyl silicones and methyl silicones, and preferably from methyl-phenyl silicones and food grade methyl silicones. 38. Process according to any one of claims 33 to 37, characterized in that the metal alkoxide precursor of solution B is chosen from the group consisting of: the precursors corresponding to the general formula Mi (ORi) _n , the precursors corresponding to the general formula - the precursors corresponding to the general formula M ₃ (OR ₃ ) (n-2) R ₃ '2, with R 1, R ₂ , R ₃ or R ₃ ' denoting an alkyl group, R ₂ 'denoting an alkyl group, phenyl, n being an integer corresponding to the maximum valence of the metals Mi, M ₂ or M ₃ Mi M ₂ or M ₃ denoting a metal chosen from Si, Zr, Ti, Sn, Al, Ce, Nb Hf, Mg or Ln, 39. Process according to claim 38, characterized in that the metal alkoxide is an alkoxysilane. 40. Process according to claim 39, characterized in that the alkoxysilane is methyltrimethoxysilane (MTMS) or tetraethoxysilane (TEOS). 41. The method of claim 39 or 40, characterized in that solution B further comprises an aluminum alkoxide. 42. Process according to any one of claims 33 to 41, characterized in that the acid of solution B is formic acid or acetic acid. 43. Process according to any one of claims 33 to 42, characterized in that two layers of the sol-gel composition are applied to the support, in order to obtain a layer thickness after firing of 30 to 70 μm. 44. Process according to any one of claims 33 to 43, characterized in that, during step d), at least one layer of sol-gel composition (A + B) is applied to a structure having the shape a hollow cap of a culinary article (1) and defining said support (3). 45. Process according to any one of claims 33 to 44, characterized in that the support is made of a material chosen from metals, wood, glass, ceramics and plastics. 46. Process according to any one of claims 33 to 45, characterized in that it further comprises, after the step of producing the first non-stick coating: the production of a decoration by application and then drying on at least a part of the first non-stick coating of a decorative composition comprising a thermostable binder resistant to at least 200 ^° C. and an optically non-transparent or thermochromic chemical substance, then producing a second non-stick coating by application, then drying and cooking on decorating at least one layer of sol-gel composition according to steps a) to c) of the process as defined according to claim 34. 47. A method according to any one of claims 33 to 46, characterized in that it further comprises a step of depositing an enamel layer on the opposite side to that coated with a non-stick coating as defined according to claim 19, the step of depositing the enamel layer being performed prior to that of a non-stick coating.