Domestic article comprising sol-gel non-stick coating having finish layer free of silica and colloidal metal oxides

Abstract

The invention therefore relates to a sol-gel facing layer of a non-stick coating of a household article, said layer forming a cooking surface and being free of silica and colloidal metal oxides.

Description

Technical Field

[0001] The present invention generally relates to the field of household articles comprising a surface covered by a non-stick coating. More particularly, the present invention is applicable to the field of non-stick coatings for cooking surfaces of cooking articles and electric cooking utensils. The present invention also relates to a method for making such an article. Background Art

[0002] In the field of culinary products, it is known that coatings having non-stick properties are applied to metal substrates or supports (aluminium, aluminium castings, stainless steel, cast steel, etc.) of various chemical natures.

[0003] More specifically, for the interior surfaces of these cooking articles for containing food, PTFE-type fluorinated resin coatings have been known for more than 50 years and are valued for their excellent non-stick properties. In recent years, coatings based on sol-gel chemistry, called "ceramic" coatings, have also appeared on the market, which provide superior heat resistance and surface hardness to PTFE coatings while maintaining easy-to-clean properties.

[0004] It has been found that the non-stick properties of these sol-gel coatings decrease over time with the use of the cookware. It is known to those skilled in the art to add silicone oils to compensate for this decrease in non-stick properties. However, the durability of these products, and in particular their non-stick properties, is still limited and unsatisfactory for the user.

[0005] Furthermore, in order to obtain good mechanical properties, it is known that all sol-gel coating manufacturers add colloidal silica to their coating formulations in order to obtain coatings several microns thick without cracks and with high mechanical resistance in all layers of the sol-gel coating, including the finishing layer.

[0006] However, the Applicant has noticed that the addition of colloidal or microfine silica leads to a reduction in the non-stick coating by promoting the hydrolysis of part of the sol-gel network, thus detrimental to the durability of the non-stick coating, in particular after prolonged contact of household articles with boiling water. Summary of the invention

[0007] The object of the present invention is to overcome this disadvantage by solving the technical problem of improving the durability of the non-stick properties of sol-gel coatings.

[0008] To this end, it was an object of the present invention to provide a sol-gel non-stick coating which has an improved durability without the non-stick properties and the visual properties of these coatings changing over the long term.

[0009] The applicant has developed a finishing layer for sol-gel non-stick coatings that overcomes the above-mentioned disadvantages. Surprisingly, the inventors observed that when the finishing layer is prepared in the absence of silica or colloidal metal oxides, i.e. without the addition of silica or colloidal metal oxides, the level of non-stick performance of the coating after the boiling water aging test is much higher. Thus, the inventors were able to overcome technical prejudices.

[0010] The advantage of the non-stick coating according to the invention comprising the sol-gel finishing layer is that household articles with such a coating will retain their non-stick properties longer during use than with other sol-gel coatings. Users will be able to keep their articles for additional years. In addition to the obvious benefits from an economic and ecological point of view, users will obtain a significantly improved level of satisfaction during use, while potentially using less grease.

[0011] Furthermore, another advantage of the present invention is that the finishing layer has optical properties that are compatible with the visual attributes present in the coating.

[0012] Furthermore, another advantage of the present invention is that satisfactory mechanical properties are surprisingly maintained and it is compatible with culinary applications. DETAILED DESCRIPTION

[0013] The present invention therefore relates to a sol-gel finishing layer for a non-stick coating of household articles, said layer forming a cooking surface and being free of silica and colloidal metal oxides.

[0014] Within the meaning of the present invention, the term "layer" should be understood as a continuous or discontinuous layer. A continuous layer (also called an integral layer) is a single integral body that completely covers the entire flat area of ​​the surface on which it is placed. A discontinuous layer (or non-integral layer) may consist of several parts and is therefore not a single integral body.

[0015] The terms "base layer", "primer layer", "bonding layer" or "bonding primer" refer to all layers from the first layer applied directly to the carrier (preferably this layer adheres well to the carrier and provides the coating with all its mechanical properties: hardness, scratch resistance) to the last layer before the first decorative layer.

[0016] Within the meaning of the present invention, a finishing layer (sometimes called "finish") refers to the final layer of the coating, i.e. the surface layer of the coating intended to come into contact with the external environment, such as food. This finishing layer is able to come into contact with the food to be cooked through one of its faces and thus forms a cooking surface. This layer is preferably continuous and transparent, that is to say it can be passed through by light over the entire visible range. This finishing layer leaves perfect visibility of the underlying layers, while protecting them from wear and giving the coating its non-stick properties.

[0017] "Coating" refers to all layers covering the metal support and adhering to the support.

[0018] The term "non-stick coating" within the meaning of the present invention must be understood as comprising at least one, usually multiple, coating layers:

[0019] - a first layer applied directly to the support, which is usually metallic, also called bonding layer or bonding primer or primer layer; preferably, this layer adheres well to the support and provides the coating with all its mechanical properties: hardness, scratch resistance;

[0020] - a layer optionally comprising a decorative pigment composition; this layer is also called decorative layer or decoration;

[0021] - A finishing layer, which is the surface layer; this layer provides perfect visibility of the decorative layer, while protecting it from wear and giving the coating non-stick properties.

[0022] By cross-sectional observation under a scanning electron microscope (SEM), the finishing layer according to the present invention is easily distinguished from the layer on which the finishing layer is deposited. The thickness of the finishing layer is measured at 20 random points on the coating cross section. The average thickness of the finishing layer is obtained by averaging these 20 measurements.

[0023] The finishing layer according to the present invention does not contain colloidal silica or finely divided silica or a mixture thereof. This means that it does not contain colloidal or finely divided silica or a mixture thereof. Colloidal or finely divided silica is not added to the finishing layer.

[0024] Advantageously, the finishing layer according to the invention has a thickness ranging from 1 to 15 μm, preferably from 2 to 12 μm, more preferably from 2 to 10 μm.

[0025] Advantageously, the first layer of the non-stick coating receives a finishing layer, which may be of a different chemical nature and comprises as binder a binder that is thermally stable at least at 300° C.

[0026] According to a variant, the heat-stable binder used in the layer of the non-stick coating, in addition to the finishing layer, can also be a heat-stable binder at least at 300° C. and can be advantageously chosen from enamel, fluorocarbon resins or mixtures of fluorocarbon resins, alone or in a mixture with other heat-stable resins, polyester-silicone resins, silicone resins, fluorosilicone, polybenzimidazole (PBI), polyimide, and inorganic or organic-inorganic hybrid polymers synthesized by sol-gel (sol-gel materials). The fluorocarbon resin can be polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoropropyl vinyl ether copolymer (PFA) or tetrafluoroethylene-hexafluoropropylene copolymer (FEP) or a mixture of these fluorocarbon resins. Other heat-stable resins resistant to at least 200° C. can be polyamide-imide (PAI), polyethylene sulfide (PES), polyphenylene sulfide (PPS), polyetherketone (PEK), polyetheretherketone (PEEK) or silicone. Finally, silicone resins or polyester-silicone resins can be used as heat-stable binders.

[0027] Preferably, all layers of the non-stick coating are obtained by a sol-gel process.

[0028] Sol-gel coatings are understood within the meaning of the present invention to be coatings synthesized from sol-gel compositions by a sol-gel process. The coatings obtained can thus be organic-inorganic or completely inorganic. The sol-gel process is understood within the meaning of the present invention to be a synthesis principle involving the conversion of a solution based on liquid precursors into a solid by a set of chemical reactions (hydrolysis and condensation) at low temperatures. The coatings thus obtained can be organic-inorganic or completely inorganic.

[0029] An organic-inorganic coating is one whose network is essentially inorganic but which comprises organic groups, in particular as a result of the precursors used and the curing temperature of the coating or as a result of the incorporation of organic fillers.

[0030] For the purposes of the present invention, a "completely inorganic coating" is understood to mean a coating based on completely inorganic materials, without any organic groups. Such coatings may be obtained by a sol-gel process, generally with a curing temperature of at least 400° C., or from precursors of the metal alkoxide type and / or metal polyalkoxide type, generally with a curing temperature that may be less than 400° C.

[0031] The finishing layer according to the present invention is obtained from a sol-gel composition. The composition comprises at least one sol-gel precursor of the metal alkoxide precursor type. As sol-gel precursors suitable for the finishing layer of the present invention, metal alkoxide type precursors or metal polyalkoxide type sol-gel precursors can be mentioned, especially aluminates, titanates, zirconates, vanadates, borates, polyalkoxysilanes and mixtures thereof can be mentioned. These compositions synthesized by the sol-gel method from metal polyalkoxide type precursors preferably have a mixed network, usually silica with grafted alkyl groups.

[0032] The sol-gel (SG) composition of the finishing layer is generally obtained from a sol-gel (SG) mixture comprising at least one metal alkoxide precursor.

[0033] Preferably, the metal alkoxide is selected from the group consisting of:

[0034] - a precursor corresponding to the general formula M1(OR1)n,

[0035] - a precursor corresponding to the general formula M2(OR2)(n-1)R2', and

[0036] - a precursor corresponding to the general formula M3(OR3)(n-2)R3'2, wherein:

[0037] R1, R2, R3 or R3' represents an alkyl group,

[0038] R2' represents an alkyl group or a phenyl group,

[0039] n is an integer corresponding to the highest valence of the metal M1, M2 or M3,

[0040] M1, M2 or M3 represents a metal selected from Si, Zr, Ti, Sn, Al, Ce, V, Nb, Hf, Mg, B or Ln.

[0041] The sol-gel finishing layer according to the invention is advantageously obtained from a sol-gel precursor which is a polyalkoxysilane. Preferably, the sol-gel precursor is an alkoxysilane selected from methyltrimethoxysilane (MTMS), methyltriethoxysilane (MTES), dimethyldimethoxysilane and mixtures thereof.

[0042] Preferably, the sol-gel precursor is methyltrimethoxysilane (MTMS).

[0043] Preferably, the sol-gel precursor of the finishing layer is not tetraethoxysilane (TEOS).Moreover, according to one variant, the sol-gel composition of the finishing layer according to the invention does not contain tetraethoxysilane (TEOS).

[0044] The sol-gel composition of the finishing layer may further comprise a solvent, in particular a solvent comprising at least one alcohol. The solvent comprising at least one alcohol is hereinafter referred to as an "alcohol solvent".

[0045] The alcohol is preferably a C1-C6 alcohol. A C1-C6 alcohol is understood to be a saturated, straight or branched hydrocarbon chain comprising 1 to 6 carbon atoms and containing a hydroxyl group (-OH) attached to a carbon atom. Examples include ethanol, n-propanol, isopropanol.

[0046] The finishing layer according to the present invention may further contain hydroxylated silicone oil.

[0047] Advantageously, the composition of the finishing layer is obtained by hydrolyzing the sol-gel precursor by adding water and an acid or base catalyst, which then leads to the production of a sol-gel non-stick coating composition by a condensation reaction.

[0048] The composition of the sol-gel finishing layer may include an acid catalyst, such as acetic acid, formic acid, citric acid, hydrochloric acid, tartaric acid or a mixture thereof.

[0049] The composition of the sol-gel finishing layer may include a base catalyst, such as sodium hydroxide NaOH, potassium hydroxide KOH, ammonia NH4 or a mixture thereof.

[0050] The composition of the sol-gel finishing layer may further comprise a pigment filler. As pigment fillers that can be used in the present invention, mention may be made in particular of coated or uncoated mica, titanium dioxide, mixed oxides (spinels), aluminosilicates, iron oxides, carbon black, perylene red, metal flakes, pigments, thermochromic organic dyes or mixtures thereof.

[0051] The primary function of these pigment fillers is to provide color, and in addition they also improve heat diffusion, improve the hardness (and durability) of the sol-gel nonstick coating, and have lubricating properties.

[0052] The composition of the sol-gel finishing layer may further include at least one inorganic filler. Such fillers are selected, for example, from boron nitride, molybdenum sulfide, graphite and mixtures thereof.

[0053] The composition of the sol-gel finishing layer may further include at least one organic filler.

[0054] The above-mentioned finishing layer of the present invention can be used to cover household articles and obtain a sol-gel non-stick coating. Therefore, the present invention also relates to the use of a sol-gel finishing layer forming a cooking surface and free of silica and colloidal metal oxides to cover household articles and obtain a non-stick coating.

[0055] The invention also relates to a household article comprising a support covered with a sol-gel non-stick coating, the coating comprising at least two layers, a first sol-gel layer in contact with the support, and a second sol-gel finishing layer free of silica and colloidal metal oxides. Advantageously, the household article according to the invention is in particular a cooking article.

[0056] For the purposes of the present invention, the term household article refers to an object intended to satisfy a household need of everyday life, in particular an article intended to receive a heat treatment or intended to generate heat. In particular, it can be a cooking article or a household appliance.

[0057] The object of the present invention is to provide an object, in particular a cooking product, such as a frying pan, a deep saucepan, a saucepan, a wok, a crepe pan, a stew pot, a cooking pot, a cast iron enamel pot, a stew pot, a casserole pot, a grill, a baking pan, a fondue pot, etc., which is heated by an external heating system and is capable of transferring the heat energy provided by the external heating system to a material or food in contact with the object.

[0058] For the purposes of the present invention, for generating heat is understood to mean a heating object having its own heating system, in particular a household appliance, for example an electric cooking appliance, such as a deep-fried pot.

[0059] In the context of the present invention, the expression "electric cooking appliance" should be understood as a heating object having its own heating system, for example an electric griddle, an electric raclette appliance, an electric fondue appliance, an electric grill, an electric griddle grill, an electric rice cooker, a bread maker or an electric pressure cooker.

[0060] The household article according to the invention comprises a carrier coated with a sol-gel non-stick coating. After heat treatment, the sol-gel coating adheres to the carrier of the household article according to the invention to form an article whose carrier is coated with a sol-gel coating.

[0061] Advantageously, the support of the household article can be made of an inorganic material, such as glass or ceramic, or of an organic material, such as plastic, or of a metallic material, or of terracotta.

[0062] Preferably, the carrier may be metallic and may be made of (anodized or non-anodized, optionally polished, brushed, sandblasted or micro-sandblasted) aluminum or an aluminum alloy, or of (optionally polished, brushed, sandblasted or micro-sandblasted) steel, or of (optionally polished, brushed, sandblasted or micro-sandblasted) stainless steel, or of cast steel, cast aluminum or cast iron, or of (optionally hammered or polished) copper.

[0063] Preferably, the support may be metallic and may comprise alternating layers of metals and / or metal alloys, or a cover of cast aluminium, aluminium or aluminium alloy lined with a stainless steel outer base. The metal support may be a two-layer or three-layer support, these multiple layers being able to be obtained, for example, by co-lamination, by thermal diffusion under load (solid state bonding) or by thermal or cold shock bonding.

[0064] Glass suitable as a coating carrier for the household appliance according to the invention may be a tempered borosilicate or glass ceramic, which has the advantages of good mechanical strength and good thermal shock resistance. Carriers of this type are available from glass manufacturers who master formulation, molding and tempering. The molding operation and the application of the coating composition can be separated, which is advantageous for implementing a discontinuous process. Chemical or mechanical treatment of the surface may be used to obtain an enhanced bond between the sol-gel coating and the glass carrier.

[0065] Stoneware and ceramics may also be suitable as coating carriers for the household appliances of the present invention. Ceramics known as "all-fire" ceramics generally use specific products, and their shaping requires a lot of technical know-how. The advantage of these materials is that they can withstand high thermal shocks. For better productivity, these materials are preferably molded by gravity casting or by conventional or isostatic pressing. Molding techniques allow a variety of shapes to be obtained, and the molded material is then dried and fired, for example in stages up to 1400° C. within 4 hours. These raw objects, also known as shards (because they are not coated), have a certain interesting roughness associated with molding, and preferably control the application of sol-gel coatings.

[0066] Advantageously, the support is a hollow metal cover comprising a bottom and side walls rising from the bottom, said cover having a concave inner face suitable for receiving food and a convex outer face intended to be placed towards the heating means or heat source. Advantageously, the inner face or the bottom is coated with a sol-gel coating, which comprises, in sequence from said cover, at least two layers, a first sol-gel layer in contact with said cover or support, and a second sol-gel layer being a finishing layer free of silica or colloidal metal oxides.

[0067] Advantageously, the sol-gel non-stick coating of the household utensil according to the invention is provided on at least one of the two faces of the carrier of the cooking utensil, preferably on the inner face in contact with the food. Optionally, the outer face of the carrier of the household article according to the invention is coated with the sol-gel coating, in which case the entire carrier of the cooking article is coated.

[0068] Preferably, the sol-gel non-stick coating of the household article according to the invention can be arranged on a support in a single layer or in multiple layers superimposed on each other. The sol-gel coating can be in the form of a continuous or discontinuous layer, in particular if it comprises a decoration. Also preferably, the decoration is applied by screen printing or pad printing. In particular, the decoration can be applied according to the method described in French patent FR2576253. The term "decoration" or "decorative layer" refers to one or more continuous or discontinuous layers comprising a pigment composition. The decoration can be in the form of one or more patterns and one or more colors. The decoration is clearly visible to the user with the naked eye at a conventional distance from the use of the household article.

[0069] According to the present invention, the sol-gel non-stick coating covering the carrier of the household article comprises at least two layers, a first sol-gel layer (first layer) in contact with the carrier, and a second sol-gel layer free of silica or colloidal metal oxides.

[0070] The first layer of the sol-gel non-stick coating of the household article according to the invention is also referred to as a primer layer (sometimes referred to as a "bonding primer" or "primer"). This primer layer is intended to be in contact with the support surface of the article on which the coating will be deposited. Advantageously, this primer layer allows the adhesion of successive layers of the coating to the support. In addition, the sol-gel non-stick coating of the household article according to the invention may also include an intermediate layer (sometimes referred to as an "intermediate coating") between the primer layer and the finishing layer.

[0071] Advantageously, the composition of the first sol-gel layer may comprise a solution based on liquid precursors comprising a sol-gel precursor of the metal alkoxide type and / or a sol-gel precursor of the metal polyalkoxide type.

[0072] Preferably, the metal alkoxide is selected from the group consisting of:

[0073] - a precursor corresponding to the general formula M1(OR1)n,

[0074] - corresponds to the general formula M2(OR2)(n-1)R 2' precursors, and

[0075] - corresponds to the general formula M3(OR3)(n-2)R 3'2 A precursor of

[0076] R1, R2, R3 or R 3' represents an alkyl group,

[0077] R 2' represents an alkyl group or a phenyl group,

[0078] n is an integer corresponding to the highest valence of the metal M1, M2 or M3,

[0079] M1, M2 or M3 represents a metal selected from Si, Zr, Ti, Sn, Al, Ce, V, Nb, Hf, Mg, B or Ln.

[0080] Advantageously, the metal alkoxide of the sol-gel solution of the composition of the first layer is an alkoxysilane. The alkoxysilanes that can be used in the sol-gel solution of the method of the invention can especially include methyltrimethoxysilane (MTMS), tetraethoxysilane (TEOS), methyltriethoxysilane (MTES), dimethyldimethoxysilane and mixtures thereof.

[0081] Preferably, the first layer intended to be applied to the support may advantageously comprise methyltrimethoxysilane (MTMS) as sol-gel precursor.

[0082] Advantageously, the composition of the first sol-gel layer comprises at least one sol-gel precursor of the metal alkoxide type as described above and at least 2% by mass of at least one colloidal metal oxide dispersed in said composition, relative to the total mass of the composition.

[0083] Advantageously, the composition of the first sol-gel layer is obtained by hydrolyzing the sol-gel precursor by adding water and an acid or base catalyst, which then results in a sol-gel non-stick coating composition by a condensation reaction.

[0084] The composition of the first sol-gel layer may include an acid catalyst, such as acetic acid, formic acid, citric acid, hydrochloric acid, tartaric acid, or a mixture thereof.

[0085] The composition of the first sol-gel layer may include a base catalyst, such as sodium hydroxide NaOH, potassium hydroxide KOH, ammonia NH4 or a mixture thereof.

[0086] The composition of the first sol-gel layer may further comprise a pigment filler. As pigment fillers that can be used in the present invention, mention may be made in particular of coated or uncoated mica, titanium dioxide, mixed oxides (spinels), aluminosilicates, iron oxides, carbon black, perylene red, metal flakes, pigments, thermochromic organic dyes or mixtures thereof.

[0087] The primary function of these pigment fillers is to provide color and in addition to improving heat diffusion, improve the hardness (and durability) of the sol-gel nonstick coating and have lubricating properties.

[0088] The composition of the first sol-gel layer may further include at least one inorganic filler. Such fillers are selected, for example, from boron nitride, molybdenum sulfide, graphite and mixtures thereof.

[0089] The composition of the first sol-gel layer may further include at least one organic filler.

[0090] The composition of the first sol-gel layer may further include at least one reactive or non-reactive silicone oil, such as polydimethylsiloxane oil (PDMS oil).

[0091] The second layer of the sol-gel non-stick coating of the household article according to the invention is a sol-gel layer free of silicon dioxide and colloidal metal oxides.

[0092] Advantageously, the second layer of the sol-gel non-stick coating of the household article according to the invention does not contain colloidal silica or finely divided silica. Furthermore, according to a variant, the second sol-gel layer of the coating of the household article according to the invention does not contain tetraethoxysilane (TEOS). The sol-gel composition of the second layer does not contain colloidal metal oxides. Preferably, the sol-gel precursor of the second layer is not tetraethoxysilane (TEOS).

[0093] Preferably, the preferred sol-gel precursor for the second layer is methyltrimethoxysilane (MTMS).

[0094] Advantageously, the second sol-gel layer of the sol-gel non-stick coating of the household article according to the invention is a finishing layer having the same properties as the above-mentioned finishing layer.

[0095] Advantageously, the second sol-gel layer of the sol-gel non-stick coating of the household article according to the invention has a thickness of 1 to 15 μm, preferably 2 to 12 μm, more preferably 2 to 10 μm.

[0096] Advantageously, the composition of the second sol-gel layer may comprise a solution based on liquid precursors comprising a sol-gel precursor of the metal alkoxide type and / or a sol-gel precursor of the metal polyalkoxide type.

[0097] Preferably, the metal alkoxide is selected from the group consisting of:

[0098] - corresponds to the general formula M2(OR2)(n-1)R 2’ precursors, and

[0099] - corresponds to the general formula M3(OR3)(n-2)R 3’2 A precursor of

[0100] R2, R3 or R 3' represents an alkyl group,

[0101] R 2' represents an alkyl group or a phenyl group,

[0102] n is an integer corresponding to the highest valence of metal M2 or M3,

[0103] M2 or M3 represents a metal selected from Si, Zr, Ti, Sn, Al, Ce, V, Nb, Hf, Mg or Ln.

[0104] Advantageously, the metal alkoxide of the sol-gel solution of the second layer is an alkoxysilane. As preferred alkoxysilanes, mention may in particular be made of methyltrimethoxysilane (MTMS), methyltriethoxysilane (MTES), dimethyldimethoxysilane and mixtures thereof.

[0105] Preferably, the composition of the second sol-gel layer does not include tetraethoxysilane (TEOS) as a sol-gel precursor.

[0106] Another object of the present invention relates to a method for manufacturing a household article according to the present invention, comprising the following successive steps:

[0107] i. having a carrier comprising two opposing surfaces;

[0108] ii. shaping the carrier to obtain concave and convex surfaces;

[0109] iii. continuously applying the sol-gel coating composition to the concave surface of the support and then applying a finishing layer according to the present invention;

[0110] iv. applying heat treatment to the product obtained by step (iii) at a temperature of 200 to 400 ℃;

[0111] v. Obtaining a household article whose carrier is coated with a sol-gel non-stick coating.

[0112] Implementation of this process allows obtaining articles whose support is coated with a sol-gel nonstick coating.

[0113] The carrier implemented in steps (i) and (ii) is the carrier as described above.

[0114] Advantageously, the method according to the invention may further comprise, before step i), a step of surface treatment of the face of the support to be coated. The surface treatment may consist of a chemical treatment (in particular chemical stripping) or a mechanical treatment (for example sandblasting, brushing, corundum, shot peening) or other physical treatment (in particular by plasma) in order to produce a roughness of the support surface that will facilitate the adhesion of the sol-gel coating. Furthermore, the surface treatment may advantageously be preceded by a degreasing operation aimed at cleaning the surface.

[0115] Advantageously, before applying the composition according to step (iii), the support is optionally cleaned and heated. The heating temperature may be comprised between 40° C. and 80° C., this preheating preventing dripping during application.

[0116] Advantageously, step (iii) of the process according to the invention may comprise an intermediate drying step, which is carried out after application of the sol-gel coating composition and before application of the finishing layer.

[0117] The sol-gel coating composition can be applied to the substrate by spraying or by any other application means, for example by dipping, pad, brush, roller, inkjet, curtain coating, spin coating or screen printing. However, spraying, for example by spray gun, has the advantage of forming a uniform and continuous layer, which after curing forms an impermeable coating of uniform thickness.

[0118] In step (iii) of the process according to the invention, it can be applied to the support by screen printing, roller coating, inkjet coating, spray coating or curtain coating.

[0119] In step (iii) of the method according to the invention, it can be applied to the support by pyrolytic spraying, which involves spraying or atomizing in the form of droplets of a solution of the sol-gel coating composition. In step (iii) of the method according to the invention, it can also be applied to the support by flat coating technology, which on the one hand can significantly save coating consumption from an industrial point of view and on the other hand can eliminate the problem of spraying (or "overspraying") on the outside of the device.

[0120] Advantageously, step (iv) of the process according to the invention may be carried out at a temperature ranging from 200 to 400°C, in particular at a temperature ranging from 220 to 350°C, more particularly at a temperature ranging from 250 to 320°C, preferably at 300°C.

[0121] A drying step can be envisaged between steps (iii) and (iv). Any drying method is conceivable, drying in an oven, drying by UV or infrared radiation, plasma drying, open air drying or a combination of these heating methods.

[0122] This optional drying step can allow the solvent to evaporate and avoid the stresses associated with densifying / curing the coating.

[0123] According to another variant, it is considered that the method further comprises the following two consecutive steps between step iii) of applying the sol-gel coating composition to the support and step iv) of heat treatment:

[0124] iii-1) a step of pre-densifying the support thus coated, so as to obtain a sol-gel coating having a pencil hardness ranging from 4B to 4H; then

[0125] iii-2) a step of stamping the coated carrier until the final shape of the cooking vessel is obtained, wherein the inner face is capable of containing food and the outer face is intended to be arranged on the heat source side, the stamping face being the face provided with the sol-gel coating or the face opposite thereto. According to this variant, the shaping step ii) is omitted.

[0126] For the purposes of the present invention, "pencil hardness" is understood to mean the resistance of a coating or lacquer to surface scratches. This hardness therefore indirectly reflects the condensation state of the sol-gel. This pre-densification step of the sol-gel coating may advantageously consist of a drying step at a temperature between 20° C. and 150° C., and more particularly of forced drying in a conventional curing oven at a temperature between 80° C. and 150° C. Preferably, in this configuration of the method according to the invention with forced drying, the drying time may be comprised between 30 seconds and 5 minutes.

[0127] After step (v) of the process according to the invention, an article is obtained whose support is coated with the sol-gel coating.

[0128] After carrying out the method according to the invention, the total thickness of the coating may be between 1 and 200 μm, in particular between 2 and 100 μm, preferably between 2 and 80 μm.

[0129] EXAMPLES The objects, aspects and advantages of the invention will be better understood from the following description of particular embodiments of the invention given by way of non-limiting example.

[0130] Of course, the invention is in no way limited to the embodiments described and illustrated, which are provided merely as examples. Modifications remain possible, in particular from the point of view of the composition of the various elements or by substitution of technical equivalents, without departing from the scope of protection of the invention.

[0131] Example 1 According to the invention: Preparation of a coating with a black sol-gel primer and a shiny topcoat:

[0132] A black primer formulation (first coat) was prepared from a three component system: Part A, Part B, and Part C.

[0133] Part A is colloidal silica with a particle size less than 200 nm, which is optionally impregnated with a hydrophobic compound such as PDMS oil.

[0134] Part B introduces the reactive silane MTMS and the acid catalyst.

[0135] Part C includes pigments, fillers, solvents, wetting agents and PDMS oil.

[0136] It should be noted that PDMS oil can also be introduced into part B.

[0137] Example 1: Black Primer

[0138] [Table 1]

[0139] Components part Mass, in g. Colloidal silicon dioxide (30%) A 41.2 MTMS B 29.1 Acetic acid B 0.9 Isopropyl alcohol C 3.3 Butyl glycol C 0.9 Hydroxylated PDMS Oil C 1.2 Black pigment C 15.5 Micro Alumina C 7.8 Wetting Agents C 0.1 total 100

[0140] The finishing formulation (finishing layer or second layer) of the present invention is also prepared from a three-component system, except that there is only deionized water in Part A, and it does not contain colloidal silica.

[0141] Part B contains the reactive silane MTMS and an acid catalyst.

[0142] Part C includes solvent, wetting agent, glitter, and PDMS oil.

[0143] It should be noted that PDMS oil can also be introduced into part B.

[0144] Example 1: Glitter finishing layer according to the present invention

[0145] [Table 2]

[0146]

[0147]

[0148] The method is as follows:

[0149] Part A (colloidal silica for primer or deionized water for finish) was stirred with a shear blade at 1000 rpm, sufficient to obtain a clear vortex.

[0150] Part B is prepared separately by mixing the silane with the acid and then introducing into part A under stirring: The hydrolysis reaction of MTMS then starts and must continue for at least 2 hours.

[0151] Then, part C is added to this mixture by adding the components one by one, stirring constantly. It should be noted that it is also possible to premix all the components of part C separately before adding the paste to the A+B mixture after 2 hours of reaction.

[0152] Once all components were mixed, stirring was continued for 30 minutes before storing the formulation in a closed glass bottle.

[0153] In addition, regarding the mixing method, the components of Part C may be first introduced into Part A, stirred for 30 minutes, and then Part B may be introduced alone and mixed for 2 hours to perform a sol-gel reaction.

[0154] The mixture is then left at room temperature for 24 hours before application. The pot life of the formulation is at least 48 hours.

[0155] The mixture can also be stored in a refrigerator at 5°C: in this case, its shelf life increases to at least 72 hours.

[0156] The primary mixture was then filtered with a 50 micron filter before being sprayed onto a sandblasted and degreased and preformed aluminum support. The support was preheated to 55°C to avoid any dripping during coating.

[0157] The finish was then filtered through a 90 micron filter and applied over the wet primer layer.

[0158] Before applying the finish, a drying step of the primer can also be carried out at a temperature below 100°C, for example in cases where it is necessary to pad print a functional or non-functional decoration between two layers of the coating.

[0159] The dry thickness of the primer is 30 to 40 microns, and the dry thickness of the finish is 3 to 10 microns.

[0160] The sol-gel coating was cured at 300 °C with a gradual increase in temperature and maintained at 300 °C for 10 min.

[0161] Comparative Example 2: Preparation of a coating comprising a black sol-gel primer and a shiny topcoat layer having colloidal silica:

[0162] This comparative example used an MTMS-based formulation with the same composition and process as used for the primer layer in Example 1, but with a finish layer containing colloidal silica.

[0163] Comparative Example: Glitter Finish Layer Containing Silica

[0164] [Table 3]

[0165] Components part Mass, in g. Colloidal silicon dioxide (40%) A 38.9 MTMS B 41.3 Acetic acid B 2 Isopropyl alcohol C 7.8 Butyl glycol C 7.7 Hydroxylated PDMS Oil C 2 Mica glitter C 0.2 Wetting Agents C 0.1

[0166] The method of formulating the finish was no different than in Example 1.

[0167] The primary mixture was then filtered with a 50 micron filter before being sprayed onto a sandblasted and degreased aluminum support, preheated to 55°C to avoid any dripping during coating.

[0168] The finish was then filtered through a 90 micron filter and applied over the wet primer layer.

[0169] Before applying the finish, a drying step of the primer can also be carried out at a temperature below 100°C, for example in cases where it is necessary to pad print a functional or non-functional decoration between the two coats.

[0170] The dry thickness of the primer is 30 to 40 microns, and the dry thickness of the finish is 5 to 15 microns.

[0171] The sol-gel coating was cured at 300 °C with a gradual increase in temperature and maintained at 300 °C for 10 min.

[0172] Non-stick performance test results

[0173] As for the evaluation of the non-stick properties of the coatings, the "FAN" test protocol was used to judge the cleanability and soiling of the resulting sol-gel layers. The purpose of this test is to highlight the ease of cleaning of the different coatings (FAN, adapted to standard NF A 92-032). 5 different foods were cooked in an oven at 250°C for 30 minutes: milk + salt, Viandox, Pulco, egg yolk and tomato sauce were contacted in 5 calibrated cylinders.

[0174] Then, clean with a damp blue Scotch Brite sponge (abrasive side).

[0175] Each food was given a score of 1 (worst) to 5 (easiest to clean) based on the weight required to completely clean the food. Therefore, after addition, the coating had a total score of 5-25 points.

[0176] Non-stick performance when new:

[0177] The non-stick properties when new are already good for formulations with a finish comprising colloidal silica, so it is a considerable question to check whether this property when new is retained:

[0178] [Table 4]

[0179]

[0180] Thus, it should be noted that on the ceramic coatings prepared according to the present invention, the non-stick performance level remains high, FAN>20 points.

[0181] Non-stick properties after aging in boiling water able ：

[0182] To simulate aging due to boiling, the aging test was carried out in boiling water.

[0183] The test process is as follows:

[0184] - Wash the pot before testing with warm water, the yellow side of a sponge and detergent;

[0185] - Fill the product to three quarters of its volume with tap water and heat on a hot plate until boiling;

[0186] -When boiling, keep heating on and start timer for 2 hours;

[0187] - End of the test after 2 hours: Wash with warm water, using the yellow side of a sponge and detergent to remove any surface scale.

[0188] A FAN test was then performed to evaluate the level of non-stick performance of the coating.

[0189] [Table 5]

[0190]

[0191]

[0192] Thus, after the 2-hour boiling water aging test, a much higher level of non-stick performance was noted, while FAN remained at the same level as before aging.

Claims

1. A sol-gel finishing layer for a non-stick coating of a household article, said layer forming a cooking surface and being free of silica and colloidal metal oxides.

2. The finishing layer according to claim 1, characterized in that: It does not contain colloidal silicon dioxide or finely divided silicon dioxide or mixtures thereof.

3. The finishing layer according to any one of the preceding claims, obtained from a precursor which is an alkoxysilane selected from the group consisting of methyltrimethoxysilane (MTMS), methyltriethoxysilane (MTES), dimethyldimethoxysilane and mixtures thereof.

4. The finishing layer according to any one of the preceding claims, characterized in that It further includes hydroxylated silicone oil.

5. Use of a sol-gel finishing layer according to any one of claims 1 to 4 for covering household articles and obtaining a non-stick coating.

6. A household article comprising a support covered with a sol-gel non-stick coating, said coating comprising at least two layers, a first sol-gel layer in contact with said support, and a second sol-gel finishing layer free of silica and colloidal metal oxides.

7. The household product according to claim 6, wherein: The second layer does not contain colloidal silica or finely divided silica.

8. The household product according to any one of claims 6 and 7, characterized in that The second layer has a thickness of 1 to 15 μm, preferably 2 to 12 μm.

9. The household product according to any one of claims 6 to 8, characterized in that The carrier is a hollow metal cover comprising a bottom and side walls rising from the bottom, the cover having a concave inner face adapted to receive food and a convex outer face intended to be placed towards the heating device or heat source.

10. A method for manufacturing a household product, characterized in that It comprises the following consecutive steps: i. having a carrier comprising two opposing surfaces; ii. shaping the carrier to obtain concave and convex surfaces; iii. continuously applying a sol-gel coating composition to the concave surface of the support, and then applying a finishing layer according to any one of claims 1 to 4; iv. applying heat treatment to the product obtained by step (iii) at a temperature of 200 to 400 ℃; v. Obtaining a household article whose carrier is coated with a sol-gel non-stick coating.

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