Pfas-free non-stick coating

Abstract

In order to provide a PFAS-free coating for improving the non-stick properties of a surface of an article which overcomes the disadvantages of coatings known from the prior art, a non-stick coating is proposed according to the invention comprising a base layer baked onto the surface of the article and a top layer baked onto the base layer, wherein the base layer and the top layer are free of per- and polyfluoroalkyl substances, and wherein the base layer contains 30 to 100 % by weight of thermoplastic material in relation to the total weight of the baked-on base layer, characterised in that the top layer, in relation to the total weight of the baked-on top layer, contains at least 30 % by weight of thermosetting material, selected from the group consisting of polyamide-imide, polyimide, silicone polyester and combinations thereof, and at least 2.5 % by weight of silicone oil.

Description

[0001] PFAS-free non-stick coating

[0002] The present invention relates to a non-stick coating for improving the non-stick properties of an object's surface, wherein the non-stick coating is free of per- and polyfluorinated alkyl compounds. Furthermore, the invention relates to a process for producing the coating and to an object coated therewith.

[0003] Non-stick coatings are currently used for bakeware, cooking appliances, and small electrical appliances, such as electric grills, deep fryers, and egg cookers, as well as irons, hair straighteners, and razors. The most common coatings are based on fluoropolymers, such as PTFE.

[0004] However, in the European Union, products based on per- and polyfluoroalkyl substances (PFAS) are to be limited in the future. A PFAS-free alternative is sol-gel coatings, often colloquially referred to as ceramic coatings, such as the GREBLON-CK2 product from Weilburger Coatings GmbH.

[0005] A disadvantage of this technology is the poor formability of the coating. Ceramic coatings are therefore not suitable for applications where the product must be formed after coating.

[0006] EP 3 964 300 A1 describes a two-layer PFAS-free coating system based on thermoplastic polymers. The base layer, consisting of high-performance thermoplastic polymers such as polyethersulfone, is coated with a top layer, also made of such a polymer, mixed with silicone oil and possibly a silicone resin. The disadvantage of such a combination of two thermoplastics is that the coating softens again during use, at least when exposed to very high temperatures.

[0007] The present invention is therefore based on the object of providing a PFAS-free non-stick coating that overcomes the disadvantages of the prior art. According to the invention, a non-stick coating for improving the non-stick properties of a surface of an object is proposed, wherein the non-stick coating has a base layer baked on the surface of the object and a top layer baked on the base layer, wherein the base layer and the top layer are free of per- and polyfluorinated alkyl compounds, and wherein the base layer contains 30 to 100 wt. % thermoplastic, based on the total weight of the baked base layer, characterized in that the top layer contains at least 30 wt. % thermosetting plastic and at least 2.5 wt. % silicone oil, based on the total weight of the baked top layer.

[0008] The inventive combination of base and top layers offers a PFAS-free alternative with excellent non-stick properties, as demonstrated by the test results presented below. Furthermore, the present invention overcomes the disadvantage of thermoplasticity of prior art PFAS-free non-stick coatings based purely on thermoplastics.

[0009] PFAS-free non-stick coatings with the advantages of the invention are obtained when the base layer consists of 30 to 100 wt.% thermoplastic and the top layer consists of at least 30 wt.% thermosetting plastic and at least 2.5 wt.% silicone oil. Particularly good results are achieved when the base layer contains at least 40 or at least 50 wt.% thermoplastic, based on the total weight of the baked base layer, and / or the top layer contains at least 40, at least 50, or at least 60 wt.% thermosetting plastic, based on the total weight of the baked top layer.

[0010] The term "fired layer" is to be understood here to mean that the deposited material of the base layer or the top layer has been subjected to a temperature treatment of at least 100 °C. In certain embodiments, the temperature treatment takes place at at least 200 °C or even at least 300 °C.

[0011] The term "thermoplastic" refers to plastics that can be reversibly deformed when heated. "Reversible" means that the material can be reshaped after cooling and reheating. Thermoplastics with a temperature resistance of over 200°C, preferably over 250°C, are preferably used here. The term "duroplast" refers to plastics that can be deformed once when heated. "One-time" means that the material can no longer be reshaped after cooling and reheating. Thermoplastics with a temperature resistance of over 200°C, preferably over 250°C, are preferably used here.

[0012] The term "temperature resistance" in the context of the plastics used here means that the plastics must have a melting point above their temperature resistance. Furthermore, the plastics should remain essentially constant in their adhesion, color, and / or gloss properties after continuous exposure for up to 100 hours in this temperature range. The adhesion, color, and / or gloss values ​​determined after exposure should deviate by no more than 5% from the value measured before exposure.

[0013] According to the invention, the top layer contains, in addition to the thermosetting plastic, a portion of silicone oil. The term "silicone oil" refers here to unbranched diorganopolysiloxanes, whose chain structure is characterized by the general molecular formula [R1 R2SiO] nSilicone oils are clear liquids at room temperature (20 °C) with a molecular mass of up to 150,000 g / mol. In certain embodiments of the invention, particularly good results are achieved with silicone oils that have a kinematic viscosity at 20 °C of at least 100 mm 2 s' 1 The viscosity value is determined using a rotational viscometer in accordance with DIN EN ISO 3219.

[0014] In principle, all thermoplastics are suitable for the main component of the base layer. In certain embodiments, the proportion of thermoplastic is selected from the group of thermoplastics consisting of polyethersulfone (PES), polyphenylene ether sulfone (PPSU), liquid crystalline polymer (LCP), polyaryletherketone, polyetherketone (PEK), polyetheretherketone (PEEK), polyetherketoneketone (PEKK), polyphenylene sulfide (PPS), and combinations thereof.

[0015] The proportion of thermosetting plastic in the cover layer is selected from the group of thermosetting plastics consisting of polyamide-imide, polyimide, silicone-polyester, and combinations thereof. Particularly preferred embodiments include those in which the proportion of thermosetting plastic in the cover layer consists of at least 80% by weight, at least 90% by weight, or entirely of a polyamide-imide or a silicone-polyester. The thermosetting plastics “polyamide-imide” and “polyimide” are just as clearly and unambiguously defined for those skilled in the art as the thermoplastics mentioned above. The term “silicone-polyester” here refers to copolymers of low-molecular-weight, hydroxy-functional silicones with polyesters. The term “hydroxy-functional silicones” here refers to cross-linked polysiloxanes with terminal OH groups at the free chain ends.

[0016] In certain embodiments of the invention, particularly good results are achieved when the base layer contains 1 to 65 wt.% silicone resin, based on the weight of the fired layer. In specific embodiments, the proportion of silicone resin in the base layer is at most 50 wt.%, at most 30 wt.%, or at most 20 wt.%. The term "silicone resin" here refers to cross-linked polysiloxanes, in particular polymethylsiloxanes or polymethylphenylsiloxanes. In specific embodiments, the silicone resin is selected from a methylsilicone resin, a phenylsilicone resin, and / or a methylphenylsilicone resin.

[0017] As additional components in the base coat and / or top coat, additives selected from the group consisting of pigments, fillers, metallic particles, and combinations thereof may be included. The proportion of additives is preferably up to 20 wt.%, up to 25 wt.%, or up to 30 wt.%.

[0018] The dry film thickness of the base layer and / or the top layer can range from 1 to 25 μm. Dry film thickness refers to the layer thickness after baking. In particular embodiments of the invention, the dry film thickness of the base layer and / or the top layer is 2 to 8 μm, preferably 3 to 6 μm, and particularly preferably 4 to 5 μm.

[0019] The present invention also encompasses a method for applying a non-stick coating according to one of the preceding claims, wherein the method is characterized in that the base layer is applied to the surface of the article as a liquid lacquer or as a powder and is subsequently baked at a temperature in the range of 200 to 500°C. Baking is preferably carried out at a temperature of at least 250°C. The maximum temperature for the baking process is preferably 450°C. The base layer can also be built up by applying it twice or more times and optionally baking it in two or more layers.

[0020] After the base layer is baked, the top layer is applied as a liquid lacquer or powder to the baked base layer. This is followed by heat treatment at the aforementioned temperature ranges, preferably in the range of 200 to 400 °C, which firmly bonds the base and top layers to each other and to the coated surface of the object. The top layer can also be built up by applying it twice or more times and, if necessary, baking it in two or more layers.

[0021] The varnish used to form the base layer or top layer contains the thermoplastic or thermosetting plastic, preferably in the form of a dispersion or in dissolved form.

[0022] In certain embodiments, the surface of the article coated with the non-stick coating according to the invention consists of metal, preferably of ECCS (Electrolytic Chromium Coated Steel), FAL (hot-dip aluminized steel) or aluminum.

[0023] The coatings used to form the base and top coats can be applied either by a coil coating process, a rolling process or a casting process, and in certain embodiments of the invention, the non-stick coating is reshaped after the baking process.

[0024] In this way, a coated article is obtained which has a surface at least partially provided with a non-stick coating of the type according to the invention described above. The article is preferably a cooking, baking, or roasting utensil or a small electrical appliance. The aforementioned cooking, baking, or roasting utensils include, for example, pots, pans, roasters, baking dishes, baking trays, and the like. Small electrical appliances include, for example, rice cookers, waffle irons, sandwich makers, milk frothers, and the like. Furthermore, the non-stick coating according to the invention can also be advantageously used on surfaces of coffee machines, electric grills, deep fryers, hair straighteners, irons, egg cookers, or razors.

[0025] The non-stick coating obtained according to the present invention meets the food contact requirements of Regulation EC 1935 / 2004 (in the version valid at the time of filing this application) and, with regard to the tested parameters, complies with the requirements of Section 31 of the German Food and Feed Code (LFGB) for the production of coatings for frying, cooking, and baking appliances, as well as thermally controlled small electrical appliances (in the version valid at the time of filing this application). When used as intended, the coating can be heated to temperatures up to 230 °C, and briefly (15 minutes) to 250 °C.

[0026] For the purposes of original disclosure, it is noted that all features as they become apparent to a person skilled in the art from the present description and the claims, even if they were specifically described only in conjunction with certain other features, can be combined both individually and in any combination with other features or groups of features disclosed herein, unless this has been expressly excluded or technical circumstances make such combinations impossible or pointless. A comprehensive, explicit presentation of all conceivable feature combinations is omitted here solely for the sake of brevity and readability of the description.

[0027] Furthermore, it should be noted that it is obvious to those skilled in the art that the following exemplary embodiments serve merely as examples of possible embodiments of the present invention. Those skilled in the art will therefore readily understand that all other embodiments that have the inventive features or combinations of features recited in the claims are also within the scope of protection of the invention. A comprehensive, explicit presentation of all conceivable embodiments within the scope of protection of the claims is omitted here solely for the sake of brevity and readability of the description.

[0028] The non-stick coating of Example 1 is two-layered, with

[0029] - the base layer contains 60 wt% polyphenylene sulfide, 12 wt% silicone polyester, 23 wt% spinel black and 5 wt% carbon black, and

[0030] - the top layer contains 72 wt% silicone polyester, 8.5 wt% silicone oil (polydimethylsiloxane), 17 wt% mica and 2.5 wt% carbon black.

[0031] The base coat is applied in liquid form to a grease-free ECCS sheet using a squeegee, baked for 60 seconds at 410 °C, and then cooled to room temperature. The dry film thickness of the base coat is 4 to 5 μm.

[0032] The topcoat varnish is applied to the dried base coat with a squeegee and baked for 45 seconds at 340 °C. The dry film thickness of the topcoat is 4 to 5 pm.

[0033] The non-stick coating of Example 2 is two-layered, with

[0034] - the base layer contains 75% by weight polyethersulfone, 10% methyl phenyl silicone resin, 7% by weight aluminum flakes, 7% by weight mica and 1% by weight carbon black, and the top layer contains 85% by weight silicone polyester and 4% by weight silicone oil (polydimethylsiloxane).

[0035] The base coat is applied in liquid form to a grease-free ECCS sheet using a squeegee, baked at 410 °C for 65 seconds, and then cooled to room temperature. The dry film thickness of the base coat is 4 to 5 μm.

[0036] The topcoat varnish is applied to the dried basecoat with a squeegee and baked for 45 seconds at 340 °C. The dry film thickness of the topcoat is 4 to 5 pm.

[0037] The non-stick coating of Example 3 is two-layered, with

[0038] - the base layer contains 85 wt% polyethersulfone, 10 wt% mica and 5 wt% carbon black, and

[0039] - the top layer contains 85% by weight polyamideimide, 10% methyl phenyl silicone resin and 5% by weight silicone oil (polydimethylsiloxane).

[0040] The basecoat coating is applied in liquid form to a grease-free ECCS sheet using a squeegee, baked for 65 seconds at 410 °C, and cooled to room temperature. The dry film thickness of the basecoat is 5 to 6 μm.

[0041] The topcoat varnish is applied to the dried basecoat with a squeegee and baked for 45 seconds at 340 °C. The dry film thickness of the topcoat is 3 to 4 pm.

[0042] The fluoropolymer-containing non-stick coating of Comparative Example 1 is single-layer and contains 78 wt% polyethersulfone, 4 wt% carbon black, 10 wt% PTFE, 8 wt% aluminum flakes.

[0043] The corresponding coating is applied in liquid form to a grease-free ECCS sheet using a squeegee and baked for 65 seconds at 410 °C. The dry film thickness is 8 pm.

[0044] The fluoropolymer-containing non-stick coating of Comparative Example 1 is single-layer and contains 64 wt% of a silicone-modified polyester, 4 wt% of a fumed silica, 3 wt% of aluminum flakes, 2 wt% of carbon black, 13 wt% of spinel black, and 2 wt% of silicone oil (polydimethylsiloxane).

[0045] Since this coating is not suitable for deep-drawing, the corresponding coating is sprayed onto a grease-free ECCS sheet and baked for 30 seconds at 150 °C and then for another 15 minutes at 270 °C. The dry film thickness is 25 μm. Test results a) Deep-drawing

[0046] Round cups were drawn from the baked non-stick coatings according to the invention using an Erichsen deep-drawing testing machine (Model 212) to assess their deep-drawability. The surfaces of the deep-drawing testing machine that came into contact with the sheet during deep-drawing were previously cleaned and degreased with ethyl acetate. No detachment or loss of adhesion was observed for any of the non-stick coatings according to the invention. Furthermore, no surface color changes or abrasions were observed on any of the non-stick coatings according to the invention after forming. Thus, all coatings according to the invention have very good deep-drawability. b) Baking test

[0047] In order to assess the non-stick effect against cakes, sheets (14 x 9 cm) of the inventive embodiments and the comparative examples were coated.

[0048] The following dough recipe was used for the test cake:

[0049] Mix 200 g butter, 200 g sugar, 1 sachet of vanilla sugar, 4 eggs, 250 g flour and 1 sachet of baking powder into a homogeneous dough.

[0050] A convection oven is preheated to 180°C. 50 g of cake batter is poured onto the ungreased baking surface and baked for 15 minutes. The baking pan is removed from the oven and allowed to cool at room temperature for 5 minutes. Then, turn the baking pan upside down to remove the cake. Note how easily the cake can be removed from the pan. The amount of remaining residue is also noted. The baking pan is then hand-washed with dish soap and thoroughly dried. Its cleanability is assessed and recorded.

[0051] The assessment is based on the scales in Table 1 below. Table 1 The points for loosening the baked goods are multiplied by the points for removing the crumb layer, resulting in scores between 100 and 0 points (see Table 2 below).

[0052] Table 2

[0053] Table 2 shows the evaluation of the baking tests of the inventive and comparative examples examined. The values ​​in Table 2 show that, on average, good results were achieved in the baking test, comparable to the two comparative examples 1 and 2. The advantage of the coating according to the invention lies in the fact that the good non-stick properties are achieved without the need for PFAS in the coating.

Claims

Patent claims 1. A non-stick coating for improving the non-stick properties of a surface of an object, the non-stick coating comprising a base layer baked on the surface of the object and a top layer baked on the base layer, the base layer and the top layer being free of per- and polyfluorinated alkyl compounds, and the base layer containing, based on the total weight of the baked base layer, 30 to 100 wt.% thermoplastic, characterized in that the top layer contains, based on the total weight of the baked top layer, at least 30 wt.% thermosetting plastic, selected from the group consisting of polyamideimide, polyimide, silicone polyester and combinations thereof, and at least 2.5 wt.% silicone oil.

2. Non-stick coating according to claim 1, characterized in that the thermoplastic contained in the at least one base layer is selected from the group consisting of polyethersulfone (PES), polyphenylene ether sulfone (PPSU), liquid crystalline polymer (LCP), polyaryletherketone, polyetherketone (PEK), polyetheretherketone (PEEK), polyetherketoneketone (PEKK), polyphenylene sulfide (PPS) and combinations thereof.

3. Non-stick coating according to one of the preceding claims, characterized in that the proportion of thermosetting plastic in the cover layer consists of at least 80% by weight, at least 90% by weight or entirely of a polyamideimide or a silicone polyester.

4. Non-stick coating according to one of the preceding claims, characterized in that the silicone oil contained in the cover layer has a kinematic viscosity at 20 °C of at least 100 mm 2 s' 1 has.

5. Non-stick coating according to one of the preceding claims, characterized in that the base layer contains 1 to 65 wt.% silicone resin based on the weight of the baked layer.

6. Non-stick coating according to claim 5, characterized in that the silicone resin is a methylsilicone resin and / or phenylsilicone resin and / or a methylphenylsilicone resin.

7. Non-stick coating according to one of the preceding claims, characterized in that the base layer and / or the cover layer contains an additive which is selected from the group consisting of pigments, fillers, metallic particles and combinations thereof.

8. Non-stick coating according to one of the preceding claims, characterized in that the dry film thickness of the at least one base layer and / or the dry film thickness of the cover layer is 2 to 8 pm.

9. A method for applying a non-stick coating according to any one of the preceding claims, characterized in that the base layer is applied as a liquid lacquer or as a powder to the surface of the article and then baked at 250 to 440 °C, and that the top layer is then applied as a liquid lacquer or as a powder to the baked base layer and the layers are baked by subsequent heat treatment at 200 to 400 °C.

10. Method according to claim 9, characterized in that the surface of the object is made of metal.

11. A method according to any one of the preceding claims, characterized in that the paints used to form the base and top coats are applied by a coil coating process, a rolling process or a casting process.

12. Method according to one of the preceding claims, characterized in that the non-stick coating is reshaped after baking.

13. Coated article, in particular cooking, baking or roasting utensils or small electrical appliance, with a surface provided with a non-stick coating according to one of claims 1 to 7.

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