Household article comprising a sol-gel non-stick coating with a finish layer free of silica and of colloidal metal oxide

Abstract

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

Description

HOUSEHOLD ITEM INCLUDING A SOL-GEL NON-STICK COATING WITH A TOP LAYER FREE OF SILICA AND COLLOIDAL METAL OXIDE Technical field

[0001] The present invention relates generally to the field of household articles comprising a surface covered with a non-stick coating. More specifically, the present invention applies to the field of non-stick coatings for cooking surfaces of kitchen articles and electrical cooking appliances. The present invention also relates to a method of manufacturing such articles. State of the art

[0002] In the field of cookware, coatings with non-stick properties are known, applied to metal substrates or supports (aluminum, aluminum casting, stainless steel, cast steel, etc.) which are of various chemical natures.

[0003] More specifically, regarding the interior surfaces of these cookware intended to receive food, PTFE-type fluorinated resin coatings have been known for over 50 years, prized for their excellent non-stick properties. In recent years, so-called "ceramic" coatings, based on sol-gel chemistry, have also appeared on the market, offering superior thermal resistance and surface hardness to PTFE coatings, while retaining 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 a silicone oil to compensate for this decrease in non-stick properties. However, the durability of these items, particularly their non-stick properties, remains limited and unsatisfactory for the user.

[0005] In addition, to obtain good mechanical properties, it is widely known, and all sol-gel coating manufacturers do it, to add to their colloidal silica coating formulations to achieve a coating several microns thick without cracks, with high mechanical strength in all layers of the sol-gel coating, including the topcoat.

[0006] However, it has been noted by the Applicant that the addition of colloidal or micronic silica is unfavorable for the durability of the anti-adhesion, in particular after prolonged contact with boiling water of the household item, by promoting the hydrolysis of part of the sol-gel network, leading to a drop in the anti-adhesion. Summary of the invention

[0007] The present invention aims to overcome this drawback by addressing the technical problem of improving the durability of the anti-adhesion of the sol-gel coating.

[0008] To this end, the invention aims to provide sol-gel non-stick coatings having improved durability without long-term alteration of the non-stick characteristics and visual properties of these coatings.

[0009] The applicant has developed a topcoat for sol-gel non-stick coatings that overcomes the aforementioned drawbacks. Surprisingly, the inventors observed that the level of non-stick performance of the coating after the boiling water aging test is much higher when the topcoat is prepared without silica or colloidal metal oxide, i.e., no silica or colloidal metal oxide is added. Thus, the inventors were able to overcome a technical prejudice.

[0010] The advantages of a non-stick coating including this sol-gel topcoat according to the invention are that a household item with such a coating will retain its non-stick properties longer than other sol-gel coatings in use. The user will be able to keep their item for several additional years. In addition to the obvious gain from an economic point of view and environmentally friendly, the user will achieve a significantly improved level of satisfaction during use, while potentially using less fat.

[0011] Furthermore, another advantage of the invention is that the topcoat has optical properties compatible with the presence of visual attributes in the coating.

[0012] Furthermore, another advantage of the invention is that surprisingly satisfactory mechanical properties are retained and compatible with culinary use. Detailed description of the invention

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

[0014] The term "layer" is understood to mean, within the meaning of the present invention, a continuous or discontinuous layer. A continuous layer (or also called a monolithic layer) is a single whole forming a total flat area completely covering the surface on which it is placed. A discontinuous layer (or non-monolithic layer) may comprise several parts, thus not being a single whole.

[0015] The term "base coat", "primer coat", "bonding coat" or "bonding primer" means all the layers from the first layer applied directly to the support (it is preferable that this layer adheres well to the support and provides all its mechanical properties to the coating: hardness, scratch resistance) to the last layer before the first decorative layer.

[0016] For the purposes of the present invention, the term “finishing layer” means the final layer of the coating, i.e. the surface layer of the coating intended to be in contact with the external environment, for example food. The finishing layer is likely to be in contact by one of its faces with food to be cooked and thus forms a cooking surface. This layer is preferably continuous and transparent, i.e. it allows light to pass through over the entire visible area. This finishing layer allows perfect visibility of the lower layers, while protecting them from abrasion and giving the coating its non-stick properties.

[0017] “Coating” means all the layers covering the metal support and adhering to this support.

[0018] The term "non-stick coating" is understood to mean, within the meaning of the invention, a coating comprising at least one layer, generally several layers: - a first layer applied directly to a support, often metallic, also called a primer or primer; it is preferable that this layer adheres well to the support and provides all its mechanical properties to the coating: hardness, scratch resistance; - possibly a layer comprising a decorative pigment composition; this layer is also called a decorative layer or decoration; - a finishing layer which is a surface layer; this layer leaves the decorative layer perfectly visible while protecting it from abrasion and giving the coating its non-stick properties.

[0019] The topcoat according to the invention is easily distinguishable from the layers on which it is deposited by sectional observations using a scanning electron microscope (SEM). The thickness of the topcoat is measured at 20 random points on the section of the coating. The average thickness of the topcoat is obtained by averaging these 20 measurements.

[0020] The topcoat according to the invention is free of colloidal silica or micronic silica or mixtures thereof. This means that it does not contain colloidal or micronic silica or mixtures thereof. No colloidal or micronic silica has been added to the topcoat.

[0021] Advantageously, the finishing layer according to the invention has a thickness of 1 to 15 μm, preferably 2 to 12 μm, more preferably 2 to 10 μm.

[0022] Advantageously, the first layer of the non-stick coating receives the finishing layer, which may be of a different chemical nature and comprise, as a binder, a binder which is heat-stable at at least 300°C.

[0023] According to a variant, the thermostable binder used in the layers of the non-stick coating, with the exception of the topcoat, may also be a binder thermostable at at least 300°C, and may advantageously be chosen from enamels, fluorocarbon resins or a mixture of fluorocarbon resins, alone or in a mixture with other thermostable resins, polyester-silicone resins, silicone resins, fluorosilicones, polybenzimidazoles (PBI), polyimides, and inorganic or organic-inorganic hybrid polymers synthesized by sol-gel method (sol-gel materials). The fluorocarbon resin may be polytetrafluoroethylene (PTFE), tetrafluoroethylene and perfluoropropylvinylether copolymer (PFA) or tetrafluoroethylene and hexafluoropropylene copolymer (FEP) or a mixture of these fluorocarbon resins.Other thermostable resins resistant to at least 200°C can be polyamide imide (PAI), polyethylene sulfide (PES), polyphenyl sulfide (PPS), polyether ketone (PEK), polyetherether ketone (PEEK) or silicone. Finally, it is possible to use a silicone resin or a polyester-silicone resin as a thermostable binder.

[0024] Preferably, all layers of the non-stick coating are obtained by sol-gel method.

[0025] For the purposes of the present invention, the term sol-gel coating is understood to mean a coating synthesized by sol-gel method from a sol-gel composition. The coating thus obtained may be either organo-mineral or entirely mineral. For the purposes of the present invention, the term sol-gel method means the synthesis principle comprising the transformation of a solution based on precursors in the liquid phase into a solid, by a set of chemical reactions (hydrolysis and condensation) at low temperature. The coating thus obtained may be either organo-mineral, or entirely mineral.

[0026] For the purposes of the present invention, the term organo-mineral coating means a coating whose network is essentially inorganic, but which includes organic groups, in particular due to the precursors used and the baking temperature of the coating or due to the incorporation of organic fillers.

[0027] For the purposes of the present invention, the term “fully mineral coating” means a coating based on a fully inorganic material, free of any organic group. Such a coating can be obtained by sol-gel method, generally with a baking temperature of at least 400°C, or from precursors of the metal alkoxylate type and / or precursors of the metal polyalkoxylate type, generally with a baking temperature which can be lower than 400°C.

[0028] The finishing layer according to the invention is obtained from a sol-gel composition. This composition comprises at least one sol-gel precursor, of the metal alkoxide precursor type. As a sol-gel precursor suitable for the finishing layer according to the invention, mention may be made of precursors of the metal alkoxylate type or sol-gel precursor of the metal polyalkoxylate type, mention may be made, among others, of aluminates, titanates, zirconates, vanadates, borates, polyalkoxysilanes and mixtures thereof. These compositions synthesized by the sol-gel route from precursors of the metal polyalkoxylate type, preferably have a hybrid network, generally of silica with grafted alkyl groups.

[0029] The sol-gel (SG) composition of the topcoat is generally obtained from a sol-gel (SG) mixture comprising at least one metal alkoxide precursor.

[0030] Preferably, a metal alkoxide chosen from the group consisting of: - precursors corresponding to the general formula Mi(OR1 )n, - precursors corresponding to the general formula M2(OR2)(n-1 )R2', and - precursors corresponding to the general formula Ms(OR3)(n-2)R3'2, with: R1, R2, R3 or R3' denoting an alkyl group, R2' denoting an alkyl or phenyl group, n being an integer corresponding to the maximum valence of the metals Mi, M2 or M3, Mi M2 or M3 designating a metal chosen from Si, Zr, Ti, Sn, Al, Ce, V, Nb, Hf, Mg B or Ln.

[0031] The sol-gel topcoat according to the invention is advantageously obtained from a sol-gel precursor which is a polyalkoxysilane. Preferably, the sol-gel precursor is an alkoxysilane chosen from the group consisting of methyltrimethoxysilane (MTMS), methyltriethoxysilane (MTES), dimethyldimethoxysilane, and mixtures thereof.

[0032] Preferably, the sol-gel precursor is methyltrimethoxysilane (MTMS).

[0033] Preferably, the sol-gel precursor of the topcoat is not tetraethoxysilane (TEOS). Furthermore, according to one variant, the sol-gel composition of the topcoat according to the invention is free of tetraethoxysilane (TEOS).

[0034] The sol-gel composition of the topcoat may further comprise a solvent, in particular a solvent comprising at least one alcohol. A solvent comprising at least one alcohol is hereinafter referred to as an “alcoholic solvent”.

[0035] An alcohol is preferably a C1-C6 alcohol. A C1-C6 alcohol is understood to be a saturated, linear or branched hydrocarbon chain containing 1 to 6 carbon atoms and comprising a hydroxyl group (-OH) attached to a carbon atom. Examples include ethanol, n-propanol, isopropanol.

[0036] The finishing layer according to the invention may further comprise a hydroxylated silicone oil.

[0037] Advantageously, the composition of the finishing layer is obtained by hydrolysis of the sol-gel precursor by adding water and an acid or basic catalyst, followed by condensation reaction leading to the production of a sol-gel non-stick coating composition.

[0038] The composition of the sol-gel topcoat may include an acid catalyst such as, for example, acetic acid, formic acid, citric acid, hydrochloric acid, tartaric acid or mixtures thereof.

[0039] The composition of the sol-gel topcoat may include a basic catalyst such as sodium hydroxide NaOH, potassium hydroxide KOH, ammonia Nh or mixtures thereof.

[0040] The composition of the sol-gel topcoat may further comprise a pigment filler. As pigment fillers that may be used in the context of the present invention, mention may in particular be made of coated or uncoated mica, titanium dioxide, mixed oxides (spinels), aluminosilicates, iron oxides, carbon black, perylene red, metallic flakes, pigments, thermochromic organic dyes or mixtures thereof.

[0041] The main effect of these pigment fillers is to provide color, and also to improve heat diffusion, improve the hardness (and durability) of the sol-gel non-stick coating and have lubricating properties.

[0042] The composition of the sol-gel topcoat may further comprise at least one inorganic filler. These are, for example, fillers chosen from boron nitride, molybdenum sulfide, graphite and mixtures thereof.

[0043] The composition of the sol-gel topcoat may further comprise at least one organic filler.

[0044] The finishing layer according to the invention described above can be used to cover a household item and obtain a sol-gel non-stick coating. Thus, the invention also relates to the use of a sol-gel finishing layer forming a cooking surface and being free of silica and colloidal metal oxide to cover a household item and obtain a non-stick coating.

[0045] The present invention also relates to 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 the support, and a second sol-gel finishing layer free of silica and colloidal metal oxide. Advantageously, the household article according to the invention is in particular a culinary article.

[0046] For the purposes of the present invention, the term household article means an object intended to meet the domestic needs of everyday life, in particular an article intended to receive heat treatment or intended to produce heat. In particular, it may be a culinary article or a household appliance.

[0047] By intended to receive a heat treatment, is meant within the meaning of the present invention an object which will be heated by an external heating system, in particular a culinary article such as frying pans, saucepans, sauté pans, woks, crepe pans, stew pots, cooking pots, casseroles, braising pans, daubières, barbecue grills, baking tins, fondue pots and which is capable of transmitting the heat energy provided by this external heating system to a material or food in contact with said object.

[0048] For the purposes of the present invention, the term "intended to produce heat" means a heating object having its own heating system, in particular a household appliance, such as electrical cooking appliances such as a saucepan.

[0049] The expression "electric cooking appliance" is understood to mean, within the meaning of the present invention, a heating object having its own heating system, such as an electric crepe maker, an electric raclette appliance, an electric fondue appliance, an electric grill, an electric griddle, an electric cooker, a bread maker, or an electric pressure cooking appliance.

[0050] The household article according to the invention comprises a support coated with a sol-gel non-stick coating. After heat treatment, the sol-gel coating adheres to the support of the household article according to the invention to form an article whose support is coated with a sol-gel coating.

[0051] Advantageously, the support of the household article may be made of inorganic material, such as glass or ceramic, or of organic material such as plastic, or of metallic material, or of terracotta.

[0052] Preferably, the support may be metallic and may be made of aluminum or aluminum alloy, anodized or not, possibly polished, brushed, sandblasted or microblasted, or of steel possibly polished, brushed, sandblasted or microblasted, or of stainless steel possibly polished, brushed, sandblasted or microblasted, or of cast steel, aluminum or iron, or of copper possibly hammered or polished.

[0053] Preferably, the support may be metallic and may comprise alternating layers of metal and / or metal alloy, or is a cap of cast aluminum, aluminum or aluminum alloys lined with an outer base of stainless steel. The metal support may be a two-layer or three-layer support, these multilayers being able to be obtained for example by co-rolling, by hot diffusion under load (solid state bonding) or by hot or cold impact bonding.

[0054] The glass suitable as a coating support for the household article according to the invention may be tempered borosilicate or glass-ceramic, which have the advantage of good mechanical strength and good resistance to thermal shocks. This type of support may be obtained from glassmakers who have mastered formulations, molding, and tempering. The molding operation and application of the coating composition may be separate, which may be advantageous for implementing a discontinuous process. A chemical or mechanical treatment of the surface may possibly be useful to obtain a reinforced bond between the sol-gel coating and the glass support.

[0055] Stoneware and ceramics may also be suitable as coating supports for the household item according to the invention. So-called "all-fire" ceramics generally use specific products, the shaping of which requires a lot of know-how. The advantage of these materials is that they can withstand high thermal shocks. These materials are preferably molded by gravity casting or by conventional or isostatic pressure for better productivity. The molding techniques allow for various shapes to be obtained, then the molded materials are dried and baked, for example, in stages up to 1400°C in 4 hours. These raw objects, also called shards (because they are not coated), have a certain interesting roughness linked to the molding and which it is preferable to control for the application of the sol-gel coating.

[0056] Advantageously, the support is a hollow metal cap which comprises a bottom and a side wall rising from the bottom, said cap having a concave inner face adapted to receive food and a convex outer face intended to be arranged towards the heating means or a heat source. Advantageously, the inner face or the bottom are coated with a sol-gel coating comprising successively, from the cap, at least two layers, the first sol-gel layer in contact with the cap or support, and the second sol-gel layer is a finishing layer free of silica or colloidal metal oxide.

[0057] Advantageously, the sol-gel non-stick coating of the household article according to the invention is arranged on at least one of the two faces of the support of the culinary article, preferably on the inner face in contact with the food. Optionally, the outer face of the support of the household article according to the invention is coated with a sol-gel coating, in this case the entire support of the culinary article is coated.

[0058] Preferably, the sol-gel non-stick coating of the household article according to the invention may be arranged on a support either in a single layer or in several layers superimposed on each other. The sol-gel coating may 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 may be applied according to the method described in French patent FR2576253. The term “decoration” or “decorative layer” means one or more continuous or discontinuous comprising a pigment composition. The decoration may be in the form of one or more patterns, one or more colors. A decoration is clearly visible to the user with the naked eye and at a conventional distance from which the household item is used.

[0059] The sol-gel non-stick coating covering the support of the household article according to the invention comprises at least two layers, a first sol-gel layer in contact with the support (primary layer), and a second sol-gel layer free of silica or colloidal metal oxide.

[0060] The first layer of the sol-gel non-stick coating of the household article according to the invention is also called a primer layer (sometimes referred to as a "bonding primer" or "primer"). This primer layer is intended to be in contact with the surface of the support of the article on which the coating will be deposited. Advantageously, this primer layer allows the successive layers of the coating to adhere to the support. In addition, the sol-gel non-stick coating of the household article according to the invention may also comprise an intermediate layer (sometimes referred to as a "midcoat") between the primer layer and the finishing layer.

[0061] Advantageously, the composition of the first sol-gel layer may comprise a solution based on liquid phase precursors comprising sol-gel precursors of the metal alkoxylate type and / or sol-gel precursors of the metal polyalkoxylate type.

[0062] Preferably, a metal alkoxylate chosen from the group consisting of:

[0063] - precursors corresponding to the general formula Mi(ORi)n,

[0064] - precursors corresponding to the general formula M2(OR2)(n-1 )R2', and

[0065] - precursors corresponding to the general formula M3(OR3)(n-2)R32, with:

[0066] Ri, R2, R3 or R3' denoting an alkyl group,

[0067] R2' denoting an alkyl or phenyl group,

[0068] n being an integer corresponding to the maximum valence of the metals Mi, M2 or M3,

[0069] Mi M2 or M3 designating a metal chosen from Si, Zr, Ti, Sn, Al, Ce, V, Nb, Hf, Mg, B or Ln.

[0070] Advantageously, the metal alkoxylate of the sol-gel solution of the composition of the first layer is an alkoxysilane. As alkoxysilanes that can be used in the sol-gel solution, mention may in particular be made of methyltrimethoxysilane (MTMS), tetraethoxysilane (TEOS), methyltriethoxysilane (MTES), dimethyldimethoxysilane, and mixtures thereof.

[0071] Preferably, the first layer which is intended to be applied to the support may advantageously comprise methyltrimethoxysilane (MTMS) as a sol-gel precursor.

[0072] Advantageously, the composition of the first sol-gel layer comprises at least one sol-gel precursor of the metal alkoxylate type as described above and at least 2% by mass relative to the total mass of the composition of at least one colloidal metal oxide dispersed in said composition.

[0073] Advantageously, the composition of the first sol-gel layer is obtained by hydrolysis of the sol-gel precursor by adding water and an acid or basic catalyst, then by condensation reaction leading to the production of a sol-gel non-stick coating composition.

[0074] The composition of the first sol-gel layer may comprise an acid catalyst such as, for example, acetic acid, formic acid, citric acid, hydrochloric acid, tartaric acid or mixtures thereof.

[0075] The composition of the first sol-gel layer may include a basic catalyst such as sodium hydroxide NaOH, potassium hydroxide KOH, ammonia NH4 or mixtures thereof.

[0076] The composition of the first sol-gel layer may further comprise a pigmentary filler. As pigmentary fillers which can be used in the context of the present invention, there may be mentioned in particular coated or uncoated mica, titanium dioxide, mixed oxides (spinels), alumino-silicates, iron oxides, carbon black, perylene red, metallic flakes, pigments, thermochromic organic dyes or their mixtures.

[0077] The main effect of these pigment fillers is to provide color, and also to improve heat diffusion, improve the hardness (and durability) of the sol-gel non-stick coating and have lubricating properties.

[0078] The composition of the first sol-gel layer may further comprise at least one inorganic filler. These are, for example, fillers chosen from boron nitride, molybdenum sulfide, graphite and mixtures thereof.

[0079] The composition of the first sol-gel layer may further comprise at least one organic filler.

[0080] The composition of the first sol-gel layer may further comprise at least one reactive or non-reactive silicone oil, for example a polydimethylsiloxane oil (PDMS oil).

[0081] 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 silica and colloidal metal oxide.

[0082] Advantageously, the second layer of the sol-gel non-stick coating of the household article according to the invention is free of colloidal silica or micronic silica. Furthermore, according to a variant, the second sol-gel layer of the coating of the household article according to the invention is free of tetraethoxysilane (TEOS). The sol-gel composition of this second layer is free of colloidal metal oxide. Preferably, the sol-gel precursor of the second layer is not tetraethoxysilane (TEOS).

[0083] Preferably, the preferred sol-gel precursor of the second layer is methyltrimethoxysilane (MTMS).

[0084] 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 characteristics as the finishing layer described above.

[0085] 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.

[0086] Advantageously, the composition of the second sol-gel layer may comprise a solution based on liquid phase precursors comprising sol-gel precursors of the metal alkoxylate type and / or sol-gel precursors of the metal polyalkoxylate type.

[0087] Preferably, a metal alkoxylate chosen from the group consisting of:

[0088] - precursors corresponding to the general formula M2(OR2)(n-1 )R2', and

[0089] - precursors corresponding to the general formula M3(ORs)(n-2)R3'2, with:

[0090] R2, R3 or R3' denoting an alkyl group,

[0091] R2' denoting an alkyl or phenyl group,

[0092] n being an integer corresponding to the maximum valence of the metals M2 or M3,

[0093] M2 or M3 designating a metal chosen from Si, Zr, Ti, Sn, Al, Ce, V, Nb, Hf, Mg or Ln.

[0094] Advantageously, the metal alkoxylate of the sol-gel solution of the second layer is an alkoxysilane. Preferred alkoxysilanes include methyltrimethoxysilane (MTMS), methyltriethoxysilane (MTES), dimethyldimethoxysilane, and mixtures thereof.

[0095] Preferably, the composition of the second sol-gel layer does not include tetraethoxysilane (TEOS) as sol-gel precursors.

[0096] The invention also relates to a method for manufacturing a household article according to the invention comprising the following successive steps: i. providing a support comprising two opposite faces; ii. shaping the support to obtain a concave face and a convex face; iii. successively applying to the concave face of the support a sol-gel coating composition then a finishing layer according to the invention; iv. applying to the article resulting from step (iii) a heat treatment at a temperature of 200 to 400°C; v. obtaining a household article whose support is coated with a non-stick sol-gel coating.

[0097] The implementation of this process makes it possible to obtain an article whose support is coated with a sol-gel non-stick coating.

[0098] The support implemented in steps (i) and (ii) is that described above.

[0099] Advantageously, the method according to the invention may further comprise, prior to step i), a step of surface treatment of the face of the support intended to be coated. This surface treatment may consist of a chemical treatment (chemical stripping in particular) or mechanical treatment (sandblasting, brushing, emery, shot blasting for example) or even physical treatment (in particular by plasma), in order to create a roughness of the surface of the support which will be favorable to the adhesion of the sol-gel coating layer. The surface treatment may also be advantageously preceded by a degreasing operation intended to clean the surface.

[0100] Advantageously, the support is optionally cleaned and heated before applying the composition according to step (iii). The heating temperature can be between 40 and 80°C, this preheating prevents dripping during application.

[0101] Advantageously, step (iii) of the method according to the invention may comprise an intermediate drying step which takes place after the application of the sol-gel coating composition and before the application of the finishing layer.

[0102] The sol-gel coating composition can be applied to the substrate by spraying or by any other application method, such as dipping, pad, brush, roller, inkjet, curtain, spin coating or screen printing. However, spraying, for example by means of a gun, has the advantage of forming a homogeneous and continuous layer, which, after curing, forms a continuous coating of regular and waterproof thickness.

[0103] The application to the support, in step (iii) of the process according to the invention, can take place by screen printing, roller, inkjet, spraying or curtain.

[0104] The application to the support, in step (iii) of the method according to the invention, can take place by pyrolysis spraying comprising spraying or nebulization in the form of droplets of solution of the sol-gel coating composition. The application to the support, in step (iii) of the method according to the invention, can also take place by flat coating techniques, which allow on the one hand a significant saving in coating consumption from an industrial point of view, and on the other hand the elimination of the problem of spraying outside the article (or "over spray" in English).

[0105] Advantageously, step (iv) of the process according to the invention can take place at a temperature of 200 to 400°C, in particular at a temperature of 220 to 350°C, more particularly at a temperature of 250 to 320°C, preferably at 300°C.

[0106] A drying step may be considered between steps (iii) and (iv). Any means of drying may be considered, oven drying, drying by ultraviolet or infrared radiation, plasma drying, open air drying or a combination of these heating means.

[0107] This optional drying step can allow solvents to evaporate and avoid the stresses associated with densification / baking of the coating.

[0108] According to another variant, it may be envisaged that the method further comprises, between step iii) of applying the sol-gel coating composition to the support and step iv) of heat treatment, the following two successive steps: iii-1) a step of pre-densification of the support thus coated to obtain a sol-gel coating layer having a pencil hardness in the range 4B to 4H; then iii-2) a step of stamping the coated support until the final shape of the culinary article is obtained, with an inner face capable of receiving food and an outer face intended to be arranged on the side of a heat source, the stamped face being able to be either the face provided with the sol-gel coating layer, or the face opposite it. According to this variant, step ii) of shaping is omitted.

[0109] For the purposes of the present invention, pencil hardness is understood to mean the resistance of coatings or lacquers to surface scratches. This hardness therefore indirectly reflects a state of progress of the sol-gel condensation. This step of pre-densification of the sol-gel coating layer may advantageously consist of a drying step at a temperature between 20°C and 150°C, and more particularly by forced drying at a temperature between 80°C and 150°C in a conventional curing oven. Preferably, in such a configuration with forced drying of the method according to the invention, the drying time may be between 30 seconds and 5 minutes.

[0110] After step (v) of the process according to the invention, an article is obtained whose support is coated with a sol-gel coating.

[0111] The total thickness of the coating after implementation of the method according to the invention may be between 1 and 200 μm, in particular between 2 and 100 pm, preferably between 2 and 80 pm.

[0112] EXAMPLES

[0113] The aims, aspects and advantages of the present invention will be better understood from the description given below of a particular embodiment of the invention presented by way of non-limiting example.

[0114] Of course, the invention is in no way limited to the embodiment described and illustrated, which has been given only as an example. Modifications remain possible, in particular from the point of view of the constitution of the various elements or by substitution of technical equivalents, without departing from the scope of protection of the invention.

[0115] Example 1 according to the invention Preparation of a coating having a black sol-gel primer and glittery top coat:

[0116] The black primer formulation (first coat) is prepared from a three-component system: Part A, Part B and Part C.

[0117] Part A is a colloidal silica, with a particle size less than 200nm, which can optionally be impregnated with a hydrophobic compound such as PDMS oil.

[0118] Part B incorporates the MTMS reactive silane and the acid catalyst.

[0119] Part C includes pigments, fillers, solvents, wetting agent, and PDMS oil.

[0120] It should be noted that PDMS oil can also be introduced into part B.

[0121] Example 1: black primary [Table 1]

[0122] The finish formulation (top coat or second coat) according to the invention is also prepared from a three-component system, except that in part A there is only demineralized water, and it is free of colloidal silica.

[0123] Part B includes the MTMS reactive silane and the acid catalyst.

[0124] Part C includes solvents, wetting agent, glitter, and PDMS oil.

[0125] It should be noted that PDMS oil can also be introduced into part B.

[0126] Example 1: Glittery topcoat according to the invention [Table 2]

[0127] The process is as follows:

[0128] Part A (colloidal silica for the primer or demineralized water for the finish) is stirred with a shearing blade and a speed of 1,000 rpm, sufficient to obtain a clear vortex.

[0129] Part B is prepared separately by mixing the silane with the acid, then introduced with stirring into part A: the MTMS hydrolysis reaction then begins, and must continue for at least 2 hours.

[0130] Then, part C is introduced into this mixture by incorporating the components one by one, still stirring. It should be noted that we can also pre-mix all the components of part C separately, before introducing this paste into the A+B mixture after the 2 hours of reaction.

[0131] Once all the components are mixed, stirring continues for 30 minutes, then the formulation is stored in a closed glass bottle.

[0132] Also note, in terms of the mixing process, that we can also first introduce the components of part C into part A, leave for 30 minutes of stirring, then introduce part B alone and mix for 2 hours for the sol-gel reaction.

[0133] The mixture is then left at room temperature for 24 hours before application. The shelf life of this formulation is at least 48 hours.

[0134] The mixture can also be stored in the refrigerator at 5°C: in this case, its shelf life is increased to at least 72 hours.

[0135] The primary mixture is then filtered with a 50 micron filter before being spray-applied onto a sandblasted, degreased, and previously shaped aluminum substrate. The substrate is preheated to 55°C to prevent any dripping during coating.

[0136] The finish is then filtered with a 90 micron filter, and applied over the wet primer coat.

[0137] A drying step at a temperature below 100°C of the primer before applying the finish can also be carried out, for example in the case where we wish to pad print a functional or non-functional decoration between the two layers of the coating.

[0138] The primer will have a dry thickness of 30 to 40 microns, and the finish will have a dry thickness of 3 to 10 microns.

[0139] The sol-gel coating is baked at 300°C, with a gradual rise and a 10-minute hold at this temperature of 300°C.

[0140] Comparative example 2: preparation of a coating including a black sol-gel primer and a glittery top coat with colloidal silica:

[0141] In this comparative example, the formulations based on MTMS are used, with the same composition and process as in example 1 for the primer layer, but with a finishing layer containing colloidal silica.

[0142] Comparative example: glittery topcoat containing silica [Table 3]

[0143] The process of formulating the finish does not differ from example 1.

[0144] The primary mixture is then filtered with a 50 micron filter before being applied by spray onto a sandblasted and degreased aluminum support, preheated to 55°C to avoid any dripping during coating.

[0145] The finish is then filtered with a 90 micron filter, and applied over the wet primer coat.

[0146] A drying step at a temperature lower than 100°C of the primer before applying the finish can also be carried out, for example in the case where we wish to pad print a functional or non-functional decoration between the two layers of coating.

[0147] The primer will have a dry thickness of 30 to 40 microns, and the finish will have a dry thickness of 5 to 15 microns.

[0148] The sol-gel coating is baked at 300°C, with a gradual rise and a 10-minute hold at this temperature of 300°C.

[0149] Anti-adhesion test results

[0150] Regarding the evaluation of the non-stick properties of the coatings, we use the "FAN" test protocol to judge the cleanability and staining of the sol-gel layers obtained. The objective of this test is to highlight the ease of cleaning (FAN, adaptation of the NF A 92-032 standard) of the different coatings. We place in contact, in 5 calibrated cylinders, 5 different foods with cooking at 250°C for 30 minutes in an oven: Milk + salt, Viandox, Pulco, egg yolk and Ketchup.

[0151] Then, clean with a blue Scotch Brite sponge (abrasive side) moistened is achieved.

[0152] Depending on the weight required to completely clean the food, each food is given a score from 1 (worst) to 5 (easiest to clean). The coating is then given an overall score, after addition, ranging from 5 to 25 points.

[0153] Non-stick when new:

[0154] The anti-adhesion when new was already good for the formulations with finish containing colloidal silica, it is therefore rather a question of checking that this property is retained when new: [Table 4]

[0155] It is therefore noted that the level of anti-adhesion remains high, with a FAN > 20 points, on the ceramic coating prepared according to the invention.

[0156] Anti-adhesion after aging in boiling water:

[0157] In order to simulate aging due to aqueous cooking, we carry out an aging test in boiling water.

[0158] The test procedure is as follows:

[0159] - wash the pan before testing with lukewarm water, sponge yellow side and detergent;

[0160] - filling with tap water, three-quarters of the volume of the article, and heating on an electric hotplate until boiling;

[0161] - when boiling, maintain heating and start the stopwatch for 2 hours;

[0162] - end of test after 2 hours: wash the item in lukewarm water, sponge yellow side and detergent to remove surface limescale.

[0163] We then carry out the FAN test to assess the level of non-stick properties of the coating. [Table 5]

[0164] We therefore note a much higher level of anti-adhesion after the 2-hour boiling water aging test, the FAN remains at the same level as before aging.

Claims

CLAIMS 1. Sol-gel finishing layer of a non-stick coating of a household article, said layer forming a cooking surface and being free of silica and colloidal metal oxide.

2. Finishing layer according to claim 1 characterized in that it is free from colloidal silica or micronic silica or their mixtures.

3. Topcoat according to one of the preceding claims, the sol-gel topcoat is obtained from a precursor which is an alkoxysilane chosen from the group consisting of methyltrimethoxysilane (MTMS), methyltriethoxysilane (MTES), dimethyldimethoxysilane, and mixtures thereof.

4. Finishing layer according to one of the preceding claims, characterized in that it further comprises a hydroxylated silicone oil.

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

6. 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 the support, and a second sol-gel finishing layer free of silica and colloidal metal oxide.

7. Household article according to claim 6 in which the second layer is free of colloidal silica or micronic silica.

8. Household article according to 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. Household article according to one of claims 6 to 8, characterized in that the support is a hollow metal cap which comprises a bottom and a side wall rising from the bottom, said cap having a concave inner face adapted to receive food and a convex outer face intended to be arranged towards the heating means or a heat source.

10. Method for manufacturing a household article, characterized in that it comprises the following successive steps: i. providing a support comprising two opposite faces; ii. shaping the support to obtain a concave face and a convex face; iii. successively applying to the concave face of the support a sol-gel coating composition then a finishing layer according to one of claims 1 to 4; iv. applying to the article resulting from step (iii) a heat treatment at a temperature of 200 to 400°C; v. obtaining a household article whose support is coated with a non-stick sol-gel coating.

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