Household articles with sol-gel non-stick coatings having a silica- and colloidal metal oxide-free finish layer

Abstract

The present invention therefore relates to a sol-gel finish for a non-stick coating on 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 relates generally to the technical field of household articles with surfaces coated with non-stick coatings. More particularly, the present invention applies to the technical field of cooking articles and non-stick coatings for cooking surfaces of electric cooking appliances. The present invention also relates to a method for manufacturing such articles. [Background technology]

[0002] It is known in the art of cooking articles that coatings with non-stick properties exist that are applied to metal substrates or supports (aluminum or aluminum castings, stainless steel, castings, etc.) of various chemistries.

[0003] More specifically, with regard to the interior surfaces of these cooking articles intended to receive food, PTFE-type fluorinated resin coatings have been valued for their excellent non-stick properties for over 50 years. In recent years, so-called "ceramic" coatings based on sol-gel chemistry have also emerged, which offer superior heat resistance and surface hardness to PTFE coatings while remaining easily cleanable.

[0004] The non-stick properties of these sol-gel coatings have been found to deteriorate over years of use of the cookware. Those skilled in the art know how to add silicone oil to compensate for this deterioration. However, the durability of these articles, particularly the retention of the non-stick properties, is limited and unsatisfactory for the user.

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

[0006] However, Applicant has found that colloidal or microsilica is detrimental to the durability of the non-stick coating, particularly after prolonged contact of the household article with boiling water, as it promotes hydrolysis of part of the sol-gel network, resulting in a degradation of the non-stick coating. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] French Patent No. 2576253 Summary of the Invention

[0008] The present invention aims to overcome the disadvantages posed by the technical problem of improving the durability of the non-stick properties of sol-gel coatings.

[0009] To this end, it is an object of the present invention to provide sol-gel non-stick coatings that improve the non-stick properties and durability of these coatings without altering their appearance properties over time.

[0010] The applicant has developed a finishing layer for a sol-gel anti-stick coating that overcomes the above-mentioned disadvantages. Surprisingly, the inventors have found that when the finishing layer is prepared without silica or colloidal metal oxides, i.e., without adding silica or colloidal silica, the coating exhibits a higher level of anti-stick performance after a boiling water aging test. Thus, the inventors have been able to overcome their technical preconceptions.

[0011] An advantage of the non-stick coating with a sol-gel finish according to the present invention is that household articles provided with such a coating will maintain their non-stick properties during use for a longer period than other sol-gel coatings. Users can maintain their articles for several more years. In addition to the obvious advantages from an economic and environmental point of view, this allows users to use less oil while significantly increasing the level of satisfaction during use.

[0012] Yet another advantage of the present invention is that the finish layer has optical properties that match appearance attributes during coating.

[0013] Another advantage of the present invention is that, surprisingly, satisfactory mechanical properties are maintained and it is suitable for culinary use. DETAILED DESCRIPTION OF THE INVENTION

[0014] Accordingly, the present invention relates to a sol-gel finish layer of a non-stick coating for a household article, said layer forming a cooking surface and being free of silica and colloidal metal oxides.

[0015] The term "layer" should be understood in the sense of the present invention to mean a continuous or discontinuous layer. A continuous layer (also called a monolithic layer) is an entire layer that completely covers the surface on which it is placed and forms a single flat area as a whole. A discontinuous layer (or non-monolithic layer) can comprise several parts and is therefore not a single whole.

[0016] The terms "base layer", "primer layer", "bonding layer", "bonding primer" are understood to mean all layers from the first layer applied directly to the substrate (which preferably adheres well to the substrate and gives the coating all its mechanical properties: hardness, scratch resistance) to the last layer before the first decorative layer.

[0017] "Finishing layer" (sometimes called "finish"), in the sense of the present invention, 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 (e.g., food). This finishing layer can come into contact with the food to be cooked on one of its surfaces, thus forming the cooking surface. This layer is preferably continuous and transparent, i.e., capable of transmitting all visible light. This finishing layer protects the underlying layers from abrasion and gives the coating its non-stick properties, while leaving the underlying layers fully visible.

[0018] "Coating" means all of the layers that cover and adhere to the metal substrate.

[0019] By the term "non-stick coating" it is to be understood in the sense of the present invention to mean a coating comprising at least one layer, and generally several layers. - a first layer applied directly to the substrate, often metallic, also called bonding layer or bonding primer or primer layer; this layer preferably adheres well to the substrate and provides the coating with all its mechanical properties: hardness, scratch resistance. - an optional layer comprising a decorative pigment composition: this layer is also called decorative layer or decoration. - Surface layer, finish layer: this layer leaves the decorative layer fully visible while protecting it from abrasion and providing the coating with its non-stick properties.

[0020] The finish layer according to the present invention can be easily distinguished from the deposited layer by sectional observation under a scanning electron microscope (SEM). The thickness of the finish layer is measured at 20 random points on a section of the coating. The average thickness of the finish layer is obtained by averaging these 20 measurements.

[0021] The finish layer according to the present invention does not contain colloidal silica or microsilica or a mixture thereof, which means that it does not contain colloidal silica or microsilica or a mixture thereof. No colloidal or microsilica is added to the finish layer.

[0022] Advantageously, the finishing layer according to the invention has a thickness of between 1 and 15 μm, preferably between 2 and 12 μm, more preferably between 2 and 10 μm.

[0023] Advantageously, the first layer of the non-stick coating receives a finish layer which may have different chemical properties and which may comprise as binder a binder which has thermal stability at least at 300°C.

[0024] In one variant, the heat-stable binder used in the layers of the non-stick coating, excluding the top layer, can be a binder that is heat-stable at least at 300°C and is advantageously selected from enamel, fluorocarbon resins or mixtures of fluorocarbon resins, alone or in combination with other heat-stable resins, polyester-silicone resins, silicone resins, fluorosilicones, polybenzimidazole (PBI), polyimides, 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), tetrafluoroethylene-hexafluoropropene copolymer (FEP), or a mixture of these fluorocarbon resins. Another heat-stable resin that can withstand temperatures of at least 200°C can be polyamideimide (PAI), polyethylene sulfide (PES), polyphenyl sulfide (PPS), polyether ketone (PEK), polyether ether ketone (PEEK), or silicone. Finally, it is also possible to use silicone resins or polyester-silicone resins as heat-stable binders.

[0025] Preferably, all layers of the non-stick coating are obtained by a sol-gel process.

[0026] By sol-gel coating, in the sense of the present invention, it is understood to mean a coating synthesized by the sol-gel method from a sol-gel composition. The resulting coating is therefore either organic-inorganic (organo-mineral) or entirely inorganic. By sol-gel method, in the sense of the present invention, it is understood to mean a synthesis principle that involves the transformation of a solution based on precursors in a liquid phase into a solid by a series of chemical reactions (hydrolysis and condensation) at low temperature. The resulting coating is therefore either organic-inorganic or entirely inorganic.

[0027] Organic-inorganic coatings refer to coatings that are essentially inorganic, but also contain organic groups, in particular due to the precursors used and the curing temperature of the coating, or due to the inclusion of organic fillers, which are networks.

[0028] For the purposes of the present invention, an all-inorganic coating means a coating based entirely on inorganic materials, without any organic groups, such coatings being obtainable by sol-gel processes, generally curing at at least 400°C, or from precursors of the metal alkoxylate and / or metal polyalkoxylate type, generally at curing temperatures below 400°C.

[0029] The finishing layer according to the invention can be obtained from a sol-gel composition, which comprises at least one sol-gel precursor of the metal alkoxide precursor type. The sol-gel precursor suitable for the finishing layer according to the invention may be made from precursors of the metal alkoxylate type or metal polyalkoxylate type, and may also be made from alumina, titanates, zirconates, vanadates, borates, and mixtures thereof. These compositions are preferably synthesized by the sol-gel method from precursors of the metal alkoxylate type, which generally comprise a hybrid network of silica with grafted alkyl groups.

[0030] The sol-gel (SG) composition of the finish layer is generally obtained from a sol-gel (SG) mixture that includes a metal alkoxylate precursor.

[0031] Preferably, the metal alkoxide precursor is -General formula M1 (OR1) n a precursor having -General formula M2 (OR2) (n-1) a precursor having R2', and -General formula M3 (OR3) (n-2) R3'2 may be selected from precursors having During the ceremony, -R1, R2, R3 or R3' represents an alkyl group; -R2' represents an alkyl or phenyl group; -n is an integer corresponding to the maximum valence of metal M1, M2, or M3; M1, M2 or M3 corresponds to a metal selected from Si, Zr, Ti, Sn, Al, Ce, V, Nb, Hf, Mg or Ln.

[0032] The sol-gel finish layer according to the invention is obtained from a sol-gel precursor, which is advantageously a polyalkoxysilane, preferably selected from the group consisting of methyltrimethoxysilane (MTMS), methyltriethoxysilane (MTES), dimethoxydimethylsilane, and mixtures thereof.

[0033] Preferably, the sol-gel precursor is methyltrimethoxysilane (MTMS).

[0034] Preferably, the sol-gel precursor of the finishing layer is not tetraethoxysilane (TEOS). Furthermore, in one variant, the sol-gel composition of the sol-gel finishing layer according to the invention does not contain tetraethoxysilane (TEOS).

[0035] The sol-gel composition of the finishing layer may further comprise a solvent, in particular a solvent comprising at least one alcohol, hereinafter referred to as "alcoholic solvent".

[0036] The alcohol is preferably a C1-C6 alcohol. A C1-C6 alcohol is a saturated, linear or branched hydrocarbon chain containing 1 to 6 carbon atoms and containing a hydroxyl group (-OH) attached to a carbon atom. Specific examples include ethanol, n-propanol, and isopropanol.

[0037] The finish layer of the present invention may further comprise a hydroxylated silicone oil.

[0038] Advantageously, the composition of the finishing layer can be obtained by hydrolysis of a sol-gel precursor by adding water and an acid or base catalyst, followed by a condensation reaction to produce the sol-gel non-stick coating composition.

[0039] The composition of the finishing layer may include an acid catalyst such as, for example, acetic acid, formic acid, citric acid, hydrochloric acid, tartaric acid, or mixtures thereof.

[0040] The composition of the finishing layer may include a base catalyst such as sodium hydroxide NaOH, potassium hydroxide KOH, ammonia NH4, or mixtures thereof.

[0041] The composition of the finishing layer may further comprise a pigment filler, which may be used in the context of the present invention and may in particular be coated or uncoated mica, titanium dioxide, mixed oxides (spinel), aluminosilicates, iron oxides, carbon black, perylene red, metal flakes, pigments, thermochromic organic dyes or mixtures thereof.

[0042] These pigment fillers have the primary effect of providing color, and also improve heat dispersion, increase the hardness (and durability) of the sol-gel non-stick coating, and have lubricating properties.

[0043] The composition of the finishing layer further comprises at least one inorganic filler, such as a filler selected from boron nitride, molybdenum disulfide, graphite, and mixtures thereof.

[0044] The composition of the sol-gel finish layer may further comprise at least one organic filler.

[0045] The finish according to the invention described above can be used to coat household items and obtain a sol-gel non-stick coating. The invention therefore also relates to the use of a silica- and colloidal metal oxide-free cooking surface-forming sol-gel finish to coat household items and obtain a non-stick coating.

[0046] The present invention also relates to a household product comprising a substrate coated with a sol-gel non-stick coating, said coating comprising at least two layers, a first sol-gel layer in contact with the substrate and a second sol-gel layer free of silica and colloidal metal oxides. Advantageously, the household product according to the invention is in particular a cooking article.

[0047] For the purposes of the present invention, the term "household item" means an object intended to meet the household needs of everyday life, in particular an item intended to undergo a heat treatment or to generate heat, in particular it may be a cooking item or a household appliance.

[0048] In the sense of the present invention, "objects intended to undergo a heat treatment" should be understood to mean frying pans, saucepans, sauté pans, woks, crepe pans, stewpots, cooking pots, cooking pots, cocottes, steaming pans, braising pots, barbecue grills, baking moulds, fondue pots and any object that can be heated by an external heating system and that is able to transfer the amount of heat provided by this external heating system to a material or food that comes into contact with said object.

[0049] In the sense of the present invention, "object intended to generate heat" should be understood to mean a heating object having its own heating system, such as a saucepan, in particular a cooking appliance.

[0050] In the sense of the present invention, "cooking appliance" should be understood to mean 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 plancha, an electric cooker, a bread maker, an electric pressure cooker.

[0051] The household product according to the present invention comprises a substrate coated with a sol-gel non-stick coating. After heat treatment, the sol-gel coating is applied to the substrate of the household product according to the present invention to form an article in which the substrate is coated with a sol-gel coating.

[0052] Advantageously, the support of the household item may be made from an inorganic material such as glass or ceramic, or from an organic material such as plastic, or from a metallic material or from terracotta.

[0053] Preferably, the support may be metallic and may be made of aluminium or an aluminium alloy, optionally polished, honed, sandblasted or microblasted, anodised or not, or optionally polished, polished, sandblasted or microblasted steel, or optionally polished, polished, sandblasted or microblasted stainless steel, or cast steel, aluminium or iron, or optionally hammered or polished copper.

[0054] Preferably, the support may be metal, may comprise alternating layers of metal and / or metal alloy, or may be an aluminum, aluminum or aluminum alloy chip cast with an outer base of stainless steel. The metal support may be a two- or three-layer support, these multiple layers being obtained, for example, by co-lamination, thermal diffusion under load (solid-state bonding) or hot or cold impact bonding.

[0055] Glasses suitable as coating substrates for household products according to the present invention may be tempered borosilicate glasses or glass ceramics, which have the advantage of good mechanical properties and good resistance to thermal shock. Substrates of this type may be obtained from glass manufacturers who have mastered the composition, shaping, and tempering techniques. The shaping and application of the coating composition may be separate, which may be advantageous for discontinuous applications. Chemical or mechanical surface treatment of the surface may be useful to obtain a strong bond between the sol-gel coating and the glass substrate.

[0056] Stoneware and ceramics can be suitable as coating substrates for household items according to the present invention. Ceramics known as "all-fire" generally use special manufacturing processes, requiring extensive know-how for molding. The advantage of these materials is their resistance to high temperature shocks. These materials are preferably molded by gravity casting or standard or isostatic pressing for good productivity. The molding techniques allow for the production of various shapes, after which the molding material is dried and fired, for example, at temperatures up to 1400°C for 4 hours. These raw objects, called shards (because they are not coated), have an interesting roughness relative to the molding, which is favorable for controlling the application of the sol-gel coating.

[0057] Advantageously, it is a hollow metal cup with a bottom and a side wall rising from the bottom, said cup having a concave inner surface for receiving the food product and a convex outer surface intended for placement towards a heating means or a heat source. Advantageously, the inner surface or bottom of the cup is provided with a sol-gel coating layer comprising at least two layers, successively, a first sol-gel layer in contact with the cup or support and a second sol-gel layer being a finishing layer free of silica or colloidal metal oxides.

[0058] Advantageously, the sol-gel non-stick coating of the household product according to the invention is disposed on one of the two surfaces of the support of the culinary product, preferably on the inner surface in contact with food. Optionally, the outer surface of the support of the household product according to the invention is coated with the sol-gel coating, in which case the entire support of the culinary product is coated.

[0059] Preferably, the sol-gel non-stick coating of the household product according to the invention is disposed on the support either in one layer or in multiple layers superimposed on one another. The sol-gel coating, especially if it comprises a decoration, can be in continuous or discontinuous form. Preferably, the decoration can be applied by screen printing or pad printing. In particular, the decoration can be applied according to the method described in Patent Document 1. The term "decoration" or "decorative layer" is understood to mean 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 the normal use distance of the household product.

[0060] The sol-gel non-stick coating for coating a household product substrate according to the present invention comprises at least two layers: a first sol-gel layer in contact with the substrate (primary layer), and a second sol-gel layer that does not contain silica or colloidal metal oxides.

[0061] The first layer of the sol-gel non-stick coating for household products according to the present invention is called the primary layer (sometimes also referred to as "bonding primary" or "primary"). This primary layer is intended to contact the surface of the substrate on the article on which the coating is disposed. Advantageously, this primary layer can adhere successive layers of the coating to the substrate. Furthermore, the sol-gel non-stick coating for household products according to the present invention may comprise an intermediate layer (sometimes referred to as a "midcoat") between the primary layer and the finish layer.

[0062] Advantageously, 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.

[0063] Preferably, the metal alkoxylate is selected from the following group: -General formula M1 (OR1) n a precursor having -General formula M2 (OR2) (n-1) a precursor having R2', and -General formula M3 (OR3) (n-2) R3'2 may be selected from precursors having During the ceremony, -R1, R2, R3 or R3' represents an alkyl group; -R2' represents an alkyl or phenyl group; -n is an integer corresponding to the maximum valence of the metals M1, M2, and M3, M1, M2 or M3 are selected from metals selected from Si, Zr, Ti, Sn, Al, Ce, V, Nb, Hf, Mg, B or Ln.

[0064] Advantageously, the metal alkoxylate of the sol-gel solution of the first layer composition is an alkoxysilane. The alkoxysilane used in the sol-gel solution may be made in particular from methyltrimethoxysilane (MTMS), tetraethoxysilane (TEOS), methyltriethoxysilane (MTES), dimethoxydimethylsilane, and mixtures thereof.

[0065] Preferably, the first layer to be applied to the support may advantageously comprise, as sol-gel precursor, methyltrimethoxysilane (MTMS).

[0066] Advantageously, the composition of the first sol-gel layer comprises at least 2% by weight of at least one sol-gel precursor of the metal alkoxylate type, as described above, relative to the total weight of at least one colloidal metal oxide dispersed in said composition.

[0067] Advantageously, the composition of the first sol-gel layer is obtained by adding water and an acid or base catalyst to hydrolyze the sol-gel precursor, followed by a condensation reaction to produce a sol-gel non-stick coating composition.

[0068] The composition of the first sol-gel layer may include an acid catalyst such as, for example, acetic acid, formic acid, citric acid, hydrochloric acid, tartaric acid, or mixtures thereof.

[0069] The composition of the first sol-gel layer may include a base catalyst such as, for example, sodium hydroxide NaOH, potassium hydroxide KOH, ammonia N3H4, or mixtures thereof.

[0070] The composition of the first sol-gel layer may further comprise pigment fillers, which may be used in the context of the present invention, in particular coated or uncoated mica, titanium dioxide, mixed oxides (spinel), aluminosilicates, iron oxides, carbon black, perylene red, metal flakes, pigments, thermochromic organic dyes or mixtures thereof.

[0071] These pigment fillers have the primary effect of providing color, and also improve heat dispersion, increase the hardness (and durability) of the sol-gel non-stick coating, and have lubricating properties.

[0072] The composition of the first sol-gel layer further comprises at least one inorganic filler, such as a filler selected from boron nitride, molybdenum disulfide, graphite, and mixtures thereof.

[0073] The composition of the first sol-gel layer may further comprise at least one organic filler.

[0074] The composition of the first sol-gel layer may further comprise at least one reactive or non-reactive silicone oil, for example, polydimethylsiloxane oil (PDMS oil).

[0075] The second layer of the sol-gel non-stick coating of the household product according to the present invention is a silica- and colloidal metal oxide-free sol-gel layer.

[0076] Advantageously, the second layer of the sol-gel non-stick coating of the household product according to the invention does not contain colloidal silica or microsilica. Furthermore, according to one variant, the second layer of the sol-gel non-stick coating of the household product according to the invention does not contain tetraethoxysilane (TEOS). The sol-gel composition of the second layer does not contain colloidal metal oxide. Preferably, the sol-gel precursor of the second layer is not tetraethoxysilane (TEOS).

[0077] Preferably, the sol-gel precursor of the second layer is methyltrimethoxysilane (MTMS).

[0078] Advantageously, the second layer of the sol-gel non-stick coating of the household product according to the invention is a finish layer having the same characteristics as the finish layer described above.

[0079] Advantageously, the second layer of the sol-gel non-stick coating of the household product according to the invention has a thickness of between 1 and 15 μm, preferably between 2 and 12 μm, more preferably between 2 and 10 μm.

[0080] 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.

[0081] Preferably, the metal alkoxylate is selected from the following group: -General formula M2 (OR2) (n-1) A precursor having R2', and -General formula M3 (OR3) (n-2) R3'2 may be selected from precursors having During the ceremony, -R1, R2, R3 or R3' represents an alkyl group; -R2' represents an alkyl or phenyl group; -n is an integer corresponding to the maximum valence of the metals M2 and M3, M2 or M3 is selected from a metal selected from Si, Zr, Ti, Sn, Al, Ce, V, Nb, Hf, Mg or Ln.

[0082] Advantageously, the metal alkoxylate of the sol-gel solution of the second layer is an alkoxysilane, and preferred alkoxysilanes may be made of, in particular, methyltrimethoxysilane (MTMS), methyltriethoxysilane (MTES), dimethoxydimethylsilane, and mixtures thereof.

[0083] Preferably, the composition of the second sol-gel layer does not include tetraethoxysilane (TEOS) as a sol-gel precursor.

[0084] The present invention also relates to a method for producing a household product according to the invention, comprising the following successive steps: i. Having a support with two opposing surfaces ii. Shaping the support to obtain concave and convex surfaces iii. successively applying to the concave surface of the substrate a sol-gel coating composition followed by the finish layer of the present invention; iv. applying a heat treatment at a temperature comprised between 200 and 400°C to the article obtained from step (iii); v. Obtaining a household article coated with a sol-gel non-stick coating.

[0085] Application of this method results in household articles coated with a sol-gel non-stick coating.

[0086] The substrates subjected to steps (i) and (ii) are described above.

[0087] Advantageously, the method according to the invention may further comprise, before step (i), a step of surface treatment of the surface of the substrate to be coated. This surface treatment may consist of a chemical treatment (in particular chemical stripping) or a mechanical treatment (for example sandblasting, peeling, abrasives, shot blasting) or another physical treatment (in particular plasma) in order to create a roughness on the surface of the substrate, which will favor the adhesion of the sol-gel coating layer. The surface treatment may furthermore advantageously be preceded by a degreasing operation to clean the surface.

[0088] Advantageously, the support is optionally cleaned and heated before applying the composition according to step (iii). The heating temperature may be comprised between 40 and 80° C., this preheating preventing dripping during application.

[0089] Advantageously, step (iii) of the method according to the invention may comprise an intermediate drying step carried out after application of the sol-gel coating composition and before application of the finishing layer.

[0090] The sol-gel coating composition may be applied to the substrate by spraying or by another application mode such as dipping, pad, brush, ruler, ink jet, curtain, spin coating, screen printing, etc. However, spraying, for example by means of a gun, has the advantage of forming a uniform, continuous layer, which after curing forms a continuous, uniformly thick, impermeable coating.

[0091] The coating on the support is carried out in step (iii) of the process according to the invention by screen printing, ruler, ink jet, spraying or curtain.

[0092] The application onto the substrate can occur in step (iii) of the method according to the invention by pyrolytic spraying, which comprises spraying or atomization in the formation of droplets of a solution of the sol-gel coating composition. The application onto the substrate can occur in step (iii) of the method according to the invention by flat coating techniques, which, from an industrial point of view, allows for significant savings in coating consumption, while on the other hand, eliminates the problem of spraying on the outside of the article (or "overspray").

[0093] Advantageously, step (iv) of the process according to the invention may take place at a temperature of 200 to 400°C, in particular at a temperature of 220 to 350°C, more in particular at a temperature of 250 to 320°C, preferably at 300°C.

[0094] A drying step may be considered between steps (iii) and (iv). Any drying means may be considered, such as drying in an oven, drying by ultraviolet or infrared radiation, plasma drying, drying in open air, or a combination of these heating means.

[0095] This optional drying step allows the solvent to evaporate and avoids stresses associated with densifying / curing the coating.

[0096] In another variant, the method may further comprise the following two successive steps between step (iii) of applying the sol-gel coating composition to the substrate and step (iv) of heat treatment: iii-1) a pre-thickening step for coating a substrate and thus obtaining a sol-gel coating layer with a pencil hardness of 4B to 4H, followed by iii-2) pressing the coated support, having an inner surface capable of receiving food and an outer surface intended to be placed at the side of a heat source, until the final shape of the culinary item is obtained, the pressed surface being either the sol-gel coating layer or its opposite surface. According to this variant, the shaping step ii) is omitted.

[0097] For the purposes of the present invention, pencil hardness is understood to mean the resistance of a coating or varnish to surface scratches. This hardness therefore directly reflects the progress of sol-gel condensation. This step prior to condensation of the sol-gel coating layer may advantageously consist of a drying step at temperatures comprised between 20°C and 150°C, and more particularly of forced drying in a standard oven at temperatures comprised between 80°C and 150°C. Preferably, in such an arrangement with forced drying of the method according to the invention, the drying time is comprised between 30 seconds and 5 minutes.

[0098] After step (v) of the method according to the invention, an article coated with a sol-gel coating is obtained.

[0099] The total thickness of the coating after carrying out the method according to the invention may be comprised between 1 and 200 μm, in particular between 2 and 100 μm, preferably between 2 and 80 μm. [Example]

[0100] The objects, aspects and advantages of the present invention will be better understood from the following description of specific embodiments thereof, illustrated by way of non-limiting examples.

[0101] Of course, the invention is not limited to the described and illustrated embodiments, which are provided only as examples: modifications are possible, particularly in terms of the configuration of the various elements or the substitution of technical equivalents, without departing from the scope of protection of the invention.

[0102] Example 1 According to the Invention: Preparation of a Coating with a Black Sol-Gel Primer and a Decorative Finish Layer

[0103] A black primer composition (first coating) was prepared from a three-component system: Part A, Part B, and Part C.

[0104] Part A is colloidal silica with particle size below 200 nm, which may optionally be filled with a hydrophobic compound such as PDMS oil.

[0105] Part B contains the reactive silane MTMS and an acid catalyst.

[0106] Part C includes pigments, fillers, solvents, wetting agents and PDMS oil.

[0107] PDMS oil can also be added in part B.

[0108] Example 1: Black Primer

[0109] [Table 1]

[0110] The finishing composition (finishing layer or second layer) according to the present invention can be prepared by a three-component system, except that part A is deionized water and it does not contain colloidal silica.

[0111] Part B contains the reactive silane MTMS and an acid catalyst.

[0112] Part C includes solvents, wetting agents, decorating agents and PDMS oil.

[0113] PDMS oil can also be added in part B.

[0114] Example 1: Decorative Finish Layer of the Present Invention

[0115] [Table 2]

[0116] The method is as follows.

[0117] Part A (colloidal silica for primer or deionized water for finish) was stirred with a shear blade at a speed of 1000 rpm to obtain a clear swirl.

[0118] Part B is prepared separately by mixing the silane with the acid and then pouring it into part A: the hydrolysis reaction of MTMS then begins and continues for at least 2 hours.

[0119] Part C is then added to this mixture, component by component, and stirred in. It is also possible to premix all the components of Part C before adding this paste into the A+B mixture after the 2 hour reaction.

[0120] Once all ingredients are mixed, stirring is continued for 30 minutes, after which the composition is stored in a closed glass bottle.

[0121] Regarding the mixing method, it is also possible to first introduce the ingredients of part C into part A and leave it to stir for 30 minutes, then introduce only part B and mix for 2 hours for the sol-gel reaction.

[0122] The mixture is then left at room temperature for 24 hours before application. The shelf life of this composition is at least 48 hours.

[0123] The mixture can be stored in the refrigerator at 5°C, in which case its shelf life increases to at least 72 hours.

[0124] The primary mixture is sandblasted and degreased, then filtered through a 50 micron filter before being applied by spraying onto a previously formed substrate, which is preheated to 55°C to avoid dipping during coating.

[0125] The finish layer is then filtered through a 90 micron filter and applied in a wet primer layer.

[0126] Before the application of the finish is carried out, for example if it is desired to pad print a functional or non-functional decoration between the two layers of coating, a step of drying the primer at a temperature below 100°C may be carried out.

[0127] The primer will have a dry thickness of 30-40 microns and the finish will have a dry thickness of 3-10 microns.

[0128] The sol-gel coating is cured at 300°C, gradually increased in temperature, and held at this temperature for 10 minutes.

[0129] Comparative Example 2: Preparation of a coating with a black sol-gel primer and a decorative finish layer with colloidal silica

[0130] This comparative example uses an MTMS-based formulation in the same composition and manner as Example 1 for the primary layer, but the top layer includes colloidal silica.

[0131] Comparative Example: Decorative Finish Layer Containing Silica

[0132] [Table 3]

[0133] The method for formulating the finish remains the same as in Example 1.

[0134] The primary mixture is then sandblasted and filtered through a 50 micron filter before being sprayed onto a degreased aluminum substrate and preheated to 55°C to avoid dipping during coating.

[0135] The finish is then filtered through a 90 micron filter and then applied in a wet primer layer.

[0136] Before the application of the finish is carried out, for example if it is desired to pad print a functional or non-functional decoration between the two layers of coating, a step of drying the primer at a temperature below 100°C may be carried out.

[0137] The primer will have a dry thickness of 30-40 microns and the finish will have a dry thickness of 5-15 microns.

[0138] The sol-gel coating is cured at 300°C, gradually increasing the temperature, and then held at this temperature for 10 minutes.

[0139] Non-adhesion test results

[0140] Regarding the non-adhesive properties of the coatings, the "FAN" test protocol is used to determine the cleanliness and staining of the resulting sol-gels. The purpose of this test is to focus on the ease of cleaning (FAN, NF A 92-032) of different coatings. Five foods are cooked in an oven at 250°C for 30 minutes, placed in calibrated cylinders in contact with: milk + salt, Viandox, Pulko, egg yolk and ketchup.

[0141] This is followed by cleaning with a damp blue Scotch-Brite sponge (abrasive side).

[0142] Each food item was assigned a score of 1 (worst) to 5 (easy to clean) depending on the weight required to completely clean the food item. Thus, after application, the coating was given an overall score ranging from 5 to 25 points.

[0143] Non-adhesion when new:

[0144] The new anti-adhesion properties are already good for compositions with a finish containing colloidal silica, and it is rather questionable to check this property when new.

[0145] [Table 4]

[0146] Therefore, it can be said that on the ceramic coating prepared according to the present invention, FAN>20 and a high level of non-adhesion is maintained.

[0147] Non-adhesion after aging in boiling water:

[0148] Aging tests were performed in boiling water to mimic cooking aging in water.

[0149] The test method is as follows.

[0150] Clean the frying pan before testing with lukewarm water, the yellow side of a sponge and detergent.

[0151] Fill the container three-quarters full with tap water and heat on an electric heater until boiling.

[0152] Once boiling, maintain heat and start a stopwatch for 2 hours.

[0153] After 2 hours of testing, the items are washed with lukewarm water, the yellow side of a sponge and detergent to remove any surface limescale.

[0154] The FAN test is then performed to evaluate the non-adhesive properties of the coating.

[0155] [Table 5]

[0156] Therefore, the higher level of non-adhesion after the 2-hour boiling water aging test is noteworthy, while FAN maintains the same level as before aging.

Claims

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

2. 2. The finishing layer of claim 1, characterized in that it does not contain colloidal silica or microsilica or mixtures thereof.

3. 3. The finishing layer of claim 1 or 2, wherein the sol-gel finishing layer is obtained from a precursor that is an alkoxysilane selected from the group consisting of methyltrimethoxysilane (MTMS), methyltriethoxysilane (MTES), dimethoxydimethylsilane, and mixtures thereof.

4. The finishing layer according to any one of claims 1 to 3, further comprising a hydroxylated silicone oil.

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

6. 1. A household article comprising a substrate coated with a sol-gel non-stick coating, the coating comprising at least two layers, a first sol-gel in contact with the substrate and a second sol-gel free of silica and colloidal metal oxides.

7. 7. The household article of claim 6, wherein the second layer does not include colloidal silica or microsilica or mixtures thereof.

8. 8. Household article according to claim 6 or 7, wherein the second layer has a thickness of 1 to 15 μm, preferably 2 to 12 μm.

9. 9. A household article according to any one of claims 6 to 8, characterized in that the support is a hollow metal cup with a base and a side wall rising from the base, said cup having a concave inner surface for receiving the food product and a convex outer surface intended to be placed towards the heating means or heat source.

10. A method for producing a household product, characterized in that it comprises the following successive steps: i. having a support with two opposing surfaces; ii. shaping the support to obtain a concave surface and a convex surface; iii. Successively applying to the concave surface of the substrate a sol-gel coating composition, followed by the finish layer according to any one of claims 1 to 4; iv. applying a heat treatment step at a temperature comprised between 200 and 400°C to the article obtained from step (iii); v. Obtaining household articles coated with a sol-gel non-stick coating.

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