Powder mixture for teflon-free non-stick coating

Abstract

The invention relates to a powder mixture, dry or as a dispersion in a liquid, comprising powder particles of at least one polyaryletherketone (PAEK) polymer and optionally polyphenylene sulfide (PPS) polymer, it being possible to produce the powder mixture without the addition of fluorine or fluorine-containing compounds. The powder mixture comprises preferably at most 1000 ppb, preferably at most 100 ppb, particularly preferably at most 25 ppb total fluorides, measured by combustion ion chromatography (TOF-CIC). The invention also relates to a method for coating an object, in particular cooking and baking utensils, using the powder mixture, to the use of the powder mixture for achieving a technical effect, selected from a non-stick effect and corrosion protection, and to an object coated using the method.

Description

[0001]P2022,2070 WO N August 22, 2023 - 1 - Powder mixture for Teflon-free non-stick coating The present invention relates to a powder mixture for Teflon-free non-stick coating, a method for coating an object, in particular cooking and baking accessories, using the powder mixture, the use of the powder mixture to achieve a non-stick and sliding effect on an object, in particular on cooking and baking accessories, and an object, in particular cooking and baking accessories, coated by the method. PTFE coatings, which are usually applied as a triple coating for higher-quality cookware, i.e. in 3 layers with usually at least 2 baking steps, are prior art. First, a base layer, usually consisting of a binding resin dissolved in a solvent, for example PAI dissolved in NMP, is wet-sprayed, dried, and pre-crosslinked.Subsequently, a transition layer and a top layer are sprayed on wet-on-wet. The top layer essentially contains a fluoropolymer, usually PTFE. The entire coating is then baked for approximately 10 minutes at 420°C. These coatings can be modified with pigments and various fillers. The disadvantage is the use of fluoropolymers and the fact that the baking temperature is significantly higher than the decomposition temperature of PTFE, which can produce substances that are hazardous to health (PFAS). Furthermore, these coatings have the disadvantage of releasing toxic substances (PFAS) during use at high temperatures. So-called ceramic sol-gel coatings, which contain silicones to achieve the non-stick effect and are usually very brittle and not durable, are also known. P2022,2070 WO N 22.August 2023 - 2 - According to the EU regulation, the limit for PFAS in the EU is to be reduced to such an extent from 2024 that, from today's perspective, PTFE coatings ("Teflon") must be replaced as non-stick coatings. The object of the present invention is a universally applicable coating for objects, in particular for cookware and bakeware, without fluoropolymers and without the addition of fluorine. The above object is achieved by providing a powder mixture according to claim 1, a method according to claim 8, a use according to claim 10, and an object, in particular cooking and baking accessories, according to claim 12 or 13. Preferred embodiments are presented in the subclaims. According to the invention, the term "cooking and baking accessories" encompasses any object whose shape is suitable for holding food and subsequent cooking and baking. Therefore, in addition to pans, baking trays, baking pans, etc., as well as grill trays, grill containers, grill racks, etc.encompassed by the above term. In a first aspect of the invention, a powder mixture, dry or as a dispersion in a liquid, is provided which comprises powder particles of at least one polyaryletherketone (PAEK) polymer and optionally polyphenylene sulfide (PPS) polymer. The powder mixture according to the invention can be produced without the addition of fluorine or fluorine-containing compounds. This is particularly the case according to the invention if the P2022,2070 WO N August 22, 2023 - 3 - powder mixture does not exceed certain limit values ​​for total fluoride after combustion at 900°C - 1000°C in a moist, oxygen-rich atmosphere. The powder mixture therefore preferably comprises at most 1000 ppb, preferably at most 100 ppb, particularly preferably at most 25 ppb of total fluoride, measured by combustion ion chromatography (TOF-CIC).Specifically, to carry out the combustion ion chromatography (TOF-CIC) measurement method, samples of the powder mixture are placed in ceramic boats and introduced into a furnace, where pyrohydrolysis takes place at 900–1000 °C in a humid, O2-rich environment. Under these conditions, the samples are oxidized, the strong carbon-fluorine bond is broken, and the vapors are passed through an absorption solution containing Ar. The HF produced during the combustion of organic fluorine dissociates in the absorption solution to form H+ and F- ions. The samples of the absorption solution, which also contains an internal standard for calibrating the analytical results, are then transferred to an ion chromatograph for analysis, where fluoride is measured. Surprisingly, the powder mixture according to the invention is particularly suitable for coating objects, in particular cooking and baking equipment.The non-stick effect (tested using standard pancakes according to DIN EN 60350-2) of the coating produced using the powder mixture according to the invention met the expectations for a non-stick effect for cookware without the addition of oil and without any fluorine components. In particular, when using the powder mixture according to the invention to produce the P2022,2070 WO N August 22, 2023 - 4 - coating, no fluorosurfactant is required to promote leveling. A further advantage is that only one, and relatively thin, layer is needed to meet all the requirements of a non-stick coating for food contact. According to the state of the art, wear-resistant polytetrafluoroethylene (PTFE) coatings are currently common in three layers with a layer thickness of approximately 50 - 60 µm. With the present coating of approximately20 -30 µm, the use of materials, the use of volatile organic compounds (VOCs) and the use of energy can be significantly reduced in addition to the complete avoidance of per- or polyfluorinated alkyl compounds (PFAS). The powder mixture preferably comprises at least two polymers, wherein powder particles comprising the first polymer have a mass-related grain size distribution D50, measured by static image analysis according to ISO 13322-1:2014, which is at most 70 µm, preferably at most 60 µm, more preferably at most 50 µm, even more preferably at most 40 µm, in particular at most 30 µm, and powder particles comprising the second polymer have a mass-related grain size distribution D50, measured by static image analysis according to ISO 13322-1:2014, which is at most 30 µm, preferably 25 µm, more preferably at most 20 µm, even more preferably at most 15 µm, in particular preferably 10 µm.This can increase the mechanical resistance. This could be achieved by adding PEK and / or PEKK. Even smaller mass-related concentrations of the second polymer of at least 2 wt. %, preferably at least 5 wt. %, particularly preferably at least 10 wt. %, showed a wear-reducing effect. Conversely, by adding PPS in quantities of up to 80 wt. %, 90 wt. %, or 95 wt. %, a further reduction in the baking temperature during production of the coating and a further improvement in the non-stick effect of the produced coating could be measured. The powder mixture is preferably in the form of a dispersion, and the liquid in the dispersion preferably comprises water.The powder mixture preferably comprises at least two PAEK polymers, or at least one PAEK polymer and one PPS polymer, wherein the PAEK polymers are preferably selected from the group consisting of polyetheretherketone (PEEK), polyetherketone (PEK), polyetherketoneketone (PEKK), and polyetherketoneetherketone (PEKKEK). The polymers preferably have different melting temperatures and / or preferably different melt viscosities. The average melt viscosity of at least one polymer is preferably at most 150 Pa.s, preferably at most 120, more preferably at most 100 Pa.s, or especially preferably at most 90 Pa.s, measured according to ISO 11443 at 400°C. This makes the flow on heating for polycondensation on a surface to be coated significantly smoother. The non-stick effect of the coated surface is thereby improved. This applies even if P2022,2070 WO N 22.August 2023 - 6 - if the particles are large relative to the layer thickness (e.g., 25 µm grain size D50 for a 25 µm layer thickness). Preferably, the powder mixture also comprises an element from the group consisting of polyamide-imide (PAI), polyimide (PI), graphite, MoS2, and a mixture thereof. This can further improve wear resistance. In a second aspect of the invention, a method for coating articles, in particular cooking and baking accessories, is provided.The process comprises the following steps: - applying the powder mixture according to the invention to the article, in particular to the cooking and baking accessory, wherein the application is preferably carried out electrostatically, by fluidized-bed sintering, or as a dispersion in liquid, in particular water; - in the case of dispersion, completely removing the liquid; - heating the powder mixture to form a polycondensate; and - baking the powder mixture above the melting temperature of the polymers. The baking temperature (substrate temperature) is preferably at most 60°C, preferably at most 50°C, more preferably at most 40°C, even more preferably at most 30°C, and especially preferably at most 20°C above the liquidus temperature of the polycondensate. Tests have shown that the non-stick effect improved with decreasing baking temperature and became too poor at excessively high baking temperature. P2022,2070 WO N 22.August 2023 - 7 - Preferably, the process, in particular in the step of heating the powder mixture to form a polycondensate, is carried out without using a fluorosurfactant. In a third aspect of the invention, the use of the powder mixture for coating objects, in particular cooking and baking accessories, to achieve a technical effect selected from the group consisting of a non-stick effect, tested using standard pancakes (DIN EN 60350-2), electrical insulation of at least 1 V, preferably at least 2 V, more preferably at least 3 V, even more preferably at least 4 V, particularly preferably at least 5 V, measured in 5% saline solution of the coated inner surface of the object, in particular the cooking and baking accessory, to ensure sufficient corrosion protection of the metallic substrate of the object, in particular the cooking and baking accessory, and a combination thereof.In a fourth aspect of the invention, an article, in particular a cooking and baking accessory, is provided, which has a coating produced by the method according to the second aspect of the invention. The average thickness of the coating is preferably at most 50 µm, preferably at most 40 µm, more preferably at most 25 µm, particularly preferably at most 25 µm. The invention is explained in more detail below with reference to exemplary embodiments and the associated figures. P2022,2070 WO N August 22, 2023 - 8 - The figures serve solely to better understand the invention and are only schematic and not true to scale. The invention is also not intended to be limited to the exemplary embodiments. Identical or equivalent parts are provided with the same reference numerals.Figure 1 shows a schematic cross-section of cooking and baking accessories with an applied dispersion layer. Figure 2 shows a cooking and baking accessory with a coating according to the invention. Figure 3 shows a coating process sequence based on various process steps. Figure 4 shows a flow diagram for coating using a dispersion process. An object to be coated or an area of ​​the cooking and baking accessory to be coated represents the substrate SU to be coated. The surface to be coated can first be subjected to a chemical and / or mechanical activation treatment. This can be done by mechanical roughening, for example using a sandblaster, or by etching with acids, alkalis, or by plasma or laser treatment.A correspondingly pretreated surface has additional chemical / physical bonding sites, is clean and free of grease, and, if roughened, has a larger surface area, which leads to better adhesion of the coating to be applied. P2022,2070 WO N August 22, 2023 - 9 - A layer DS of a dispersion is then applied to this surface. The dispersion contains all components of the coating in a finely divided and, if possible, homogeneous particle size distribution, dispersed in a solvent or solvent mixture. An application method is selected that is suitable for producing a desired layer thickness. The average particle size (D50) of the solids contained in the dispersion corresponds at most to the desired layer thickness for the coating, but is preferably selected to be lower. Figure 1 shows a substrate SU coated in this way with an applied dispersion layer DS.After carrying out a temperature program during which the substrate provided with the dispersion layer DS or the cooking and baking accessory is heated to a temperature above the melting point of the thermoplastic(s) contained in the dispersion, a homogeneous coating BS is obtained that is pore-free and thus dense and exhibits good mechanical cohesion and good adhesion to the substrate SU. Figure 2 shows the finished cooking and baking accessory. It is possible to apply the coating to only a portion of the surface. The remaining area not to be coated can be masked, or an application method for the dispersion can be selected that can differentiate between different surface areas, for example, brushing or printing. Masking can also be achieved using a shadow mask while spraying the dispersion.This shadow mask can also be in the form of a film that is applied to the surface of the substrate SU and leaves out the areas of the surface to be coated. After the dispersion layer DS has been applied, the film can be removed and, for example, peeled off, with the areas of the dispersion layer DS applied over it also being peeled off. Figure 3 shows a variant of the process with which a greater layer thickness can be achieved despite a smaller particle diameter of the solids contained in the dispersion. For this purpose, after the first dispersion layer DS1 has been applied, as shown in Figure 3a, at least the solvent is removed; alternatively, the first dispersion layer is additionally pre-compacted accordingly by a heat treatment. In a second step, the dispersion coating is repeated and a second dispersion layer DS2 is applied.If necessary, this layer can also be pre-compacted and the coating step repeated again. Finally, as shown in Figure 3c, the structure of dispersion layers consisting of several partial layers is brought to a temperature above the melting point of the thermoplastic in a final step, whereby a completely compacted, pore-free, closed coating BS is obtained on the substrate SU. A composition suitable for application by dispersion methods and also friction-reduced according to the invention contains, for example, solids in the following weight proportions: 100 weight percent PEEK P2022,2070 WO N August 22, 2023 - 11 - Color additives can be added if necessary. It is possible to apply one or more layers. The solids are optionally dispersed with auxiliaries in a solvent, which can be water or is advantageously miscible or mixed with water, e.g.Alcohol and in particular isopropanol. The dispersion mixture then contains approximately 30 percent by weight of the above-mentioned solids. In Figure 4, the process sequence just described is shown more clearly using a flow diagram. The process comprises, as step 1, the production and preparation of the powder mixture. For this purpose, the ingredients, which are selected from thermoplastic polymer, filler and dry lubricant, are either brought to a suitable particle size, preferably by grinding and / or by subsequent sorting according to the grain size in accordance with the desired narrowest possible grain size distribution. In parallel, in step 2, the solvent is prepared, which is preferably harmless to the environment and health, preferably water-based and in particular consists of a mixture of alcohol and water, e.g. isopropanol and water.An advantageous solvent composition contains, for example, 25 to 75 weight percent isopropanol in water. A solvent containing approximately 25-50 weight percent isopropanol in water is particularly preferred. In step 3, the dispersion is prepared by adding the solvent to the prepared powder mixture, maintaining a solids content of preferably 20 to 50 weight percent. To improve dispersion stability, known dispersion aids can be added in small amounts. In step 4, the surface of the article is coated, for example by spraying, dipping, brushing, printing, or spin-coating. The aim is to achieve the most homogeneous layer thickness possible for the dispersion layer, and any areas of the surface not to be coated are omitted from the coating.In step 5, the solvent is removed, preferably by evaporation, which can optionally be assisted by negative pressure or elevated temperature, for example, 80°C. In the next step 6, the cooking and baking utensil with the applied dried dispersion layer is converted into a homogeneous coating by heating and melting the thermoplastics, and the cooking and baking utensil is then cooled again. Following this step 6, a finished coating can be obtained at point 7. According to a variant V1 of the process, it is possible to repeat steps 4 to 7 directly after step 5. A second variant V2 follows step 6, whereby after melting the first dispersion layer, a new dispersion layer is applied (step 4) and compacted accordingly (steps 5 to 7). P2022,2070 WO N 22.August 2023 - 13 - According to a third variant V3 of the method, after producing a first coating according to step 6, a second partial coating layer, different from the first coating, is applied. For this purpose, a further dispersion is produced according to process steps 1 to 3, and the cooking and baking accessories are coated with it according to steps 4 to 6. Here, too, the method according to variants V1 and V2 can be modified by repeating individual process steps or individual process step sequences in order to achieve a desired layer thickness. In particular, when using finely divided particles for the dispersion, a particularly homogeneous coating can be obtained, which, due to the small particle diameter, makes multiple coatings advantageous or necessary. Although the invention has been explained using only a few exemplary embodiments, it is not limited to these.Possible variations arise in particular from the appropriate selection of fillers and, if necessary, from mixtures of different fillers. The proportions of the coating components used are selected depending on the desired load on the coating. The same applies to the layer thicknesses, which are not limited to the examples given. The coating is advantageously applied to metallic surfaces, although the coating can also be applied to other surfaces such as ceramic, glass or suitable plastic. Examples P2022,2070 WO N August 22, 2023 - 14 - A pan coating was produced as follows: An aqueous dispersion with a solvent content of 25% and a solid content of 30% was prepared. The solid consisted of PEEK fromVictrex with a mean mass-related grain diameter D50 of 10 µm and a specified mean melt viscosity, measured according to ISO 11443 at 400°C, of ​​150 Pa.s (120–180 Pa.s). The substrate, in the form of an aluminum pan, was cleaned and degreased and then blasted. The Rz after blasting was approximately 20 µm (measured by scanning or non-contact optical roughness measurement). The aqueous PEEK dispersion was sprayed on using conventional spray guns, dried at approximately 50°C, and then baked at an oven temperature of 400°C. This resulted in an optically closed, pore-free surface with a roughness of approximately Rz 20 µm (measured by scanning or non-contact optical roughness measurement).However, the migration tests subsequently conducted to demonstrate compliance with the statutory limits revealed that the prescribed limits could not be met because the coating was too thin to adequately cover the metal substrate. In subsequent experiments, the curing temperature was increased in order to improve leveling by reducing the melt viscosity. Surprisingly, it was found that the non-stick effect decreased with increasing curing temperature. Conversely, the non-stick effect was improved by reducing the curing temperature. Surprisingly, a further test showed that the addition of a PEEK grade with a lower melt viscosity of 90 Pa.s leads to smoother, trouble-free leveling and an improved non-stick effect, even with a grain size D50 of 25 µm, which is the same as the desired layer thickness.In particular, the baking temperature could be reduced by 30°C, i.e. to an oven temperature of 370°C and a maximum substrate temperature of 360°C. The non-stick effect was tested using standard pancakes (DIN EN 60350-2). The non-stick effect of the coating produced in this way met the expectations for a non-stick effect for cookware without the addition of oil and without any fluorine components. In particular, the inventive coating also eliminates the need for a fluorosurfactant to promote flow. A further advantage is that only one, relatively thin layer is needed to meet all the requirements of a non-stick coating for food contact. According to the state of the art, wear-resistant PTFE coatings are currently three-layered with a layer thickness of approx. 50 – 60 µm. With the present coating of approx.With a thickness of 20-30 µm, the use of material, VOCs, and energy can be significantly reduced in addition to completely avoiding PFAS. A further test aimed to increase mechanical resistance. This was achieved by adding PEK and / or PEKK. Even small concentrations of 10, 5, or 2% showed a wear-reducing effect. By adding an element from the group consisting of polyamide-imide (PAI), polyimide (PI), graphite, MoS2, and a mixture thereof, wear resistance could be further improved. Conversely, by adding PPS in concentrations of up to 80, 90, or 95%, a further reduction in the curing temperature and a further improvement in the non-stick effect could be measured. Quite surprisingly, it was observed during the tests that the mixing of different polymer types increased the melting temperature after curing.This ensures that the coating of a pan does not become liquid. During use, a pan can reach a surface temperature of over 300°C, whereas the melting temperature of the coating of a reference pan, for example, is 340°C. This does not correspond to the concentration between the two temperatures of the two polymers involved, but rather to that of the higher-melting polymer or even higher. In particular, it was measured that a coating according to the invention, consisting of PEEK and PEK, did not become liquid up to 400°C and above. But even a coating consisting of PEEK and PPS, with a PPS concentration of 90%, did not become liquid up to 380°C, although the melting points of the individual polymers are 285 and 340°C.

Claims

P2022,2070 WO N August 22, 2023 - 17 - Claims 1. A powder mixture, dry or as a dispersion in a liquid, comprising powder particles of at least one polyaryletherketone (PAEK) polymer and optionally polyphenylene sulfide (PPS) polymer, wherein the powder mixture can be prepared without the addition of fluorine or fluorine-containing compounds.

2. The powder mixture according to claim 1, wherein the powder mixture comprises at most 1000 ppb, preferably at most 100 ppb, particularly preferably at most 25 ppb, of total fluorides, measured by combustion ion chromatography (TOF-CIC). 3.Powder mixture according to claim 1 or 2, wherein the powder mixture comprises at least two polymers, and wherein powder particles comprising the first polymer have a mass-related grain size distribution D50, measured by static image analysis according to ISO 13322-1:2014, which is at most 70 µm, preferably at most 60 µm, more preferably at most 50 µm, even more preferably at most 40 µm, in particular at most 30 µm, and powder particles comprising the second polymer have a mass-related grain size distribution D50, measured by static image analysis according to ISO 13322-1:2014, which is at most 30 µm, preferably 25 µm, more preferably at most 20 µm, even more preferably at most 15 µm, particularly preferably 10 µm.

4. Powder mixture according to one of the preceding claims, wherein the powder mixture is in the form of a dispersion and the liquid comprises water. P2022,2070 WO N August 22, 2023 - 18 - 5. The powder mixture according to any one of the preceding claims, wherein the powder mixture comprises at least two PAEK polymers, or at least one PAEK polymer and PPS polymer, wherein the PAEK polymers are preferably selected from the group consisting of polyetheretherketone (PEEK), polyetherketone (PEK), polyetherketoneketone (PEKK), and polyetherketoneetherketone (PEKKEK).

6. The powder mixture according to claim 5, wherein the polymers have different melting temperatures.

7. The powder mixture according to claim 5 or 6, wherein the PAEK polymers have different melt viscosities, measured according to ISO 11443 at 400°C.

8. Powder mixture according to one of the preceding claims, wherein the average melt viscosity of at least one polymer is at most 150 Pa.s, preferably at most 120, more preferably at most 100 Pa.s, or particularly preferably at most 90 Pa.s, measured according to ISO 11443 at 400°C. 9.Powder mixture according to one of the preceding claims, wherein the powder mixture further comprises an element from the group consisting of polyamide-imide (PAI), polyimide (PI), graphite, MoS2, and a mixture thereof.

10. A method for coating an article, in particular cooking and baking accessories, comprising the following steps: - applying the powder mixture according to one of claims 1 to 9 to the article, in particular the cooking and. P2022,2070 WO N August 22, 2023 - 19 - Baking accessories, wherein the application is preferably carried out electrostatically, by fluidized-bed sintering, or as a dispersion in liquid, in particular water; - in the case of dispersion, complete removal of the liquid; - heating the powder mixture to form a polycondensate; and - baking the powder mixture above the melting temperature of the polymers.

11. The method according to claim 10, wherein the baking temperature (substrate temperature) is at most 60°C, preferably at most 50°C, more preferably at most 40°C, even more preferably at most 30°C, and most preferably at most 20°C above the liquidus temperature of the polycondensate.

12. The method according to claim 10 or 11, wherein the method, in particular in the step of heating the powder mixture to form a polycondensate, is carried out without using a fluorosurfactant. 13.Use of the powder mixture according to one of claims 1 to 9 for coating an article, in particular cooking and baking accessories, to achieve a technical effect selected from the group consisting of non-stick effect, tested by means of standard pancakes (DIN EN 60350-2), electrical insulation of at least 1 V, preferably at least 2 V, more preferably at least 3 V, even more preferably at least 4 V, particularly preferably at least 5 V, measured in 5% saline solution of the coated inner surface. P2022,2070 WO N August 22, 2023 - 20 - of the article, in particular the cooking and baking accessory, to ensure sufficient corrosion protection of the metallic substrate of the article, in particular the cooking and baking accessory, and a combination thereof.

14. Article, in particular cooking and baking accessory, comprising a coating produced by the method according to any one of claims 10 to 12.

15. Article, in particular cooking and baking accessory, according to claim 14, wherein the thickness of the coating is at most 50 µm, preferably at most 40 µm, more preferably at most 30 µm, particularly preferably at most 25 µm.

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