Article having a non-stick coating

Abstract

The invention relates to an article, in particular cookware and bakeware, comprising a coating having a first and a second layer, wherein the second layer is a surface layer and comprises a polycondensate formed from a polymer selected from the group consisting of polyaryletherketone (PAEK) polymer, polyphenylene sulphide (PPS) polymer, and a combination thereof, wherein the second layer has a silicon content, measured by energy-dispersive X-ray spectroscopy (EDS), of at least 0.05 wt.%, preferably at least 0.1 wt.%, more preferably at least 0.5 wt.%, even more preferably at least 1 wt.%, even more preferably 1-10 wt.%, even more preferably 1-5 wt.%, even more preferably 1-3 wt.%, and particularly preferably 1-2 wt.%. The invention also relates to: a method for coating an article, in particular cookware and bakeware; a method for the metallic forming of the article; and the use of a coating composition, in particular a wet coating composition, in the method for coating the article.

Description

[0001] Item with non-stick coating

[0002] The present invention relates to an article, in particular cooking and baking accessories or parts for food processing as well as parts subject to sliding stress, with a coating comprising a polycondensate of a polymer selected from the group consisting of polyaryletherketone (PAEK) polymer, polyphenylene sulfide (PPS) polymer and a combination thereof, wherein the coating has a silicon content, measured by energy dispersive X-ray spectroscopy (EDS), of at least 0.05 wt.% and a method for coating an article, in particular cooking and baking accessories.

[0003] PTFE coatings are state of the art and are usually applied as a triple coating for higher quality cookware, i.e. in three layers, usually with at least two baking processes. First, a base layer, usually consisting of a binding resin dissolved in a solvent, e.g. 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, with the top layer essentially containing fluoropolymer, usually PTFE. The entire coating is then baked for around 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 (PEAS).Furthermore, these coatings have the disadvantage of releasing toxic substances (PEAs) when used at high temperatures. So-called ceramic sol-gel coatings, which contain silicones to achieve the non-stick effect, are also known. These coatings are usually very brittle and not durable.

[0004] According to EU regulations, the limit value for PEAS in the EU is to be reduced from 2024 onwards to such an extent that, from today's perspective, PTFE coatings ("Teflon") will have to be replaced as non-stick coatings.

[0005] Furthermore, according to EU regulations, bisphenols are to be banned from food contact from January 2025, which practically also results in a ban on PES (polyethersulfone).

[0006] EP 2319631 A1 describes a layer with a maximum of 20% thermoplastic in a Si-SiOx matrix, which first produces the Si matrix at a lower temperature and only in a second step melts the thermoplastics at temperatures above their liquidus temperature. Tests have shown that with this process, concentrations above 20% thermoplastic lead to a reduction in strength and substrate bonding. Furthermore, a coating produced in this way is an improved Si-SiOx coating, but its properties with regard to wear, alkali and acid resistance, and ductility do not come close to those of a high-temperature thermoplastic coating.

[0007] EP 3964300 A1 describes a coating consisting of PES, PPS, PEEK or mixtures of these. Our own tests have shown that the thermoplastics listed are not miscible with silicone resins or oils unless at least one thermoplastic component is soluble in the same solvent as the silicone resins or oils. In the absence of PES and solubility, the silicone components behave like release agents when the thermoplastic powder or granulate particles melt and prevent them from flowing smoothly. In addition, a silicone layer forms on the substrate surface, metal or previously applied thermoplastic layer during drying, which prevents sufficient adhesion between the layers. All of the exemplary embodiments in D1 contain PES, but not exclusively insoluble thermoplastics.In particular, tests have shown that the presence of thermoplastic components in the topmost layer, which is to be applied last, impairs both the non-stick effect and the adhesion of this layer to the underlying layer.

[0008] In particular, in a coating produced in this way, the thermoplastic particles lie on the surface with little bonding.

[0009] The object of the present invention is to provide a coated article, in particular coated cooking and bakeware, with an improved non-stick coating and a production process therefor.

[0010] The above object is achieved by providing an article, in particular a cooking and baking accessory, according to claim 1, a method according to claim 12, a method according to claim 27, and the use of a lacquer according to claim 28. Preferred embodiments are presented in the subclaims. According to the invention, the term cooking and baking accessory encompasses any article which, in terms of its shape, is suitable for holding foodstuffs and then cooking and baking them. Therefore, in addition to pans, the above term also includes baking trays, baking tins, etc., as well as grill trays, grill containers, grill racks, etc.

[0011] In a first aspect of the invention, an article is provided, in particular cooking and baking accessories, with a coating comprising a first and a second layer, wherein the coating has a surface layer and wherein the first and optionally the second layer comprise a polycondensate of a polymer selected from the group consisting of polyaryletherketone (PAEK) polymer, polyphenylene sulfide (PPS) polymer and a combination thereof, wherein the surface layer of the coating has a silicon content, measured by energy dispersive X-ray spectroscopy (EDS), of at least 0.05 wt.%, preferably at least 0.1 wt.%, more preferably at least 0.5 wt.%, even more preferably at least 1 wt.%, even more preferably 1-10 wt.%, even more preferably 1-5 wt.%, even more preferably 1-3 wt.% and particularly preferably 1-2 wt.%.

[0012] The article according to the first aspect may also comprise parts for food processing and sliding-stressed parts.

[0013] To measure the silicon content, test plates with the coatings are prepared in a size of approximately 2 x 2 cm.

[0014] Since the coatings are not electrically conductive, they are sputtered with gold. The samples are then analyzed using energy-dispersive X-ray spectroscopy (EDS). At least nine spectra are recorded on each sample surface, and the results are averaged. The analysis software of an EDS system typically outputs the measurement results in wt. %. These values ​​can be converted to atomic % by dividing them by the value for the respective atomic weight.

[0015] Energy-dispersive X-ray spectroscopy (also known as EDS, EDX, or EDXA) is a powerful technique that allows the user to analyze the elemental composition of a desired sample. The main operating principle of EDS is the ability of high-energy electromagnetic radiation (X-rays) to eject "nuclear" electrons (electrons not in the outermost shell) from an atom. This principle is known as Moseley's law, which states that there is a direct relationship between the frequency of the emitted light and the atomic number of the atom.

[0016] When these electrons are removed from the system, a gap remains that can be filled by a higher-energy electron, which releases energy as it relaxes. The energy released during this relaxation process is unique for each element in the periodic table, and so bombarding a sample with X-rays can be used to determine which elements are present and in what proportions.

[0017] EDS works with a series of three main parts: an emitter, a collector, and an analyzer. These parts are usually additionally equipped with an electron microscope such as an SEM or TEM. The combination of these three parts allows for analysis of both the number of X-rays released and their energy (compared to the energy of the originally emitted X-rays). The EDS data is displayed as a graph with KeV on the x-axis and peak intensity on the y-axis. The peak positions on the x-axis are converted by a computer program into the atoms for which the energy changes represent.

[0018] Preferably, the first layer does not contain silicon. This can be achieved by not using any ingredients containing silicon in the production of the first layer. This improves the adhesion between the first and second layers. Furthermore, the adhesion between the first layer and the article, in particular cooking and baking accessories, is also improved.

[0019] The advantage of the invention is that the positive properties regarding mechanical properties, wear resistance, and chemical resistance can be combined with excellent non-stick properties that are equal to and even superior to those of PTFE. In contrast, coatings made of silicone resins, elastomers, or sol-gel coatings are mechanically and chemically less resilient and quickly lose their non-stick properties.

[0020] The article can also be a sheet, a plate, etc. made of aluminum, steel or stainless steel, copper and other metals whose melting point is above 300 °C. The article can be coated on one or both sides. It is particularly advantageous that these can be subsequently formed, folded, drawn or embossed without the coating becoming detached from the substrate and without the second layer detaching or peeling off the first. The polycondensate is preferably made of at least one polymer with an average melt viscosity of more than 150 Pa.s, preferably 200-500 Pa.s, more preferably 300 to 500 Pa.s, and preferably also of a polymer with an average melt viscosity of 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.Using a polycondensate of at least one polymer with an average melt viscosity of more than 150 Pa.s improves adhesion to the object and between the layers. Using another polymer with an average melt viscosity of 150 Pa.s or less improves the leveling of the layer during production. Furthermore, the production of a sufficiently fine-particle (based on the solids content) dispersion is facilitated.

[0021] The article, in particular cooking and baking accessories, preferably has a contact angle of the coating against water of at least 90°, preferably at least 95°, particularly preferably 100° to 120°. In comparison, a coating with pure PAEK polymer has a contact angle of approximately 90° and a coating with polytetrafluoroethylene (PTFE) has a contact angle of approximately 100°. For the measurement, water droplets are placed on the coating and the contact angle is optically evaluated using a camera. The measurements are carried out according to the invention in accordance with DIN EN ISO 19403-2:2020-04. With the help of the coating according to the invention, very good non-stick properties can therefore be achieved, which can even exceed those of PTFE. The article, in particular the cooking and baking accessory, preferably comprises several partial layers. It is possible to vary the silicon content of the partial layers.Since a higher silicon content leads to improved coating hardness, the surface layer or near-surface layers preferably have a higher silicon content. The sublayers may also be indistinguishable, so that the coating appears as a single layer. In this case, in particular, the silicon content of the coating may increase toward the surface of the coating, regardless of the presence of sublayers.

[0022] The coating can preferably be produced without fluorine compounds. This is particularly the case according to the invention if the coating 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).

[0023] In detail, to carry out the combustion ion chromatography (TOF-CIC) measurement method, coating samples are filled into 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 by 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.

[0024] Preferably the coating is free of polyethersulfone (PES).

[0025] The preferred thermoplastics are suitable for continuous temperature use above 220 ° C, better 240 ° C, preferably selected from the group consisting of PAEK (more preferably PEEK, PEK, PEKK, PEKEKK and their copolymers), PPS and thermoplastic polyimide. These thermoplastics are technically insoluble and are therefore applied as a dispersion in water and / or organic solvents. Tests have shown that with these insoluble thermoplastics it is not possible to mix them with silicone oils or resins and achieve a smooth and problem-free application after subsequent drying. In addition, the non-stick effect of a coating produced in this way is poor, and this effect increases with increasing concentration of the thermoplastic. A layer applied as a mixture is also not suitable as a base layer because it does not provide sufficient adhesion to the substrate.

[0026] The present coating according to the invention provides a thermoplastic, ductile, and non-brittle coating with an additional non-stick effect. A metal substrate coated in this way can also be subsequently formed, bent, rolled, or embossed.

[0027] The non-stick effect (tested using standard pancakes according to DIN EN 60350-2) of the coating according to the invention corresponded to the expectations for a non-stick effect for cookware without the addition of oil and without any fluorine components.

[0028] In particular, no fluorosurfactant is required to promote flow when producing the coating.

[0029] In addition, the coating according to the invention also passed the fried egg test, which is common for pan tests. This test is more difficult to pass than the test with standard pancakes.

[0030] To do this, after rinsing the non-stick surface in a household-standard manner, one egg is fried one after the other at 180-200°C without adding oil, if necessary with intermediate cleaning after 10 consecutively fried eggs. The coating according to the invention makes it possible to fry 50, 100, or more eggs one after the other and remove them cleanly. This is not possible with the designs according to documents EP 3964300 A1 and EP 2319631 A1 and allows for a greatly expanded range of applications.

[0031] There are no particular restrictions on the thickness of the coating. It can, for example, be up to 1 mm. However, for cookware and frying utensils, a maximum of 50 μm is sufficient, preferably a maximum of 40 μm, more preferably a maximum of 30 μm, and particularly preferably a maximum of 25 μm, and / or the second layer preferably has a thickness of a maximum of 100 μm, preferably for cookware and frying utensils a maximum of 20 μm, more preferably 1 to 15 μm, even more preferably 1 to 5 μm. In another embodiment, this can also have a thickness of 5 to 15 μm. The measuring method is carried out in accordance with the standard DIN EN ISO 2808: 2019-12. The stated layer thicknesses are average values ​​resulting from at least 3 measurements at one location and at least 3 different locations on a surface. The layer thickness is measured using a layer thickness measuring device, e.g. the “QNIX 4500” device from the manufacturer Automation Dr. Nix GmbH & Co KG.For magnetic substrates, the measurement is performed using a change in the magnetic field or the Hall effect (DIN EN ISO 2178, ASTM B499, ASTM D7091). For non-magnetic substrates, the measurement is performed using eddy current (DIN EN ISO 2360, ASTM D7091). The principles of measurement technology are observed (DIN 1319, Part 1 and Part 3).

[0032] Therefore, only a thin layer is needed to meet all the requirements of a non-stick coating for food contact. Currently, wear-resistant polytetrafluoroethylene (PTFE) coatings are commonly used in three layers with a layer thickness of approximately 50-60 μm. This coating significantly reduces material usage, volatile organic compounds (VOCs), and energy consumption, in addition to completely avoiding per- or polyfluoroalkyl compounds (PEAS).

[0033] Preferably, the coating also comprises a dry lubricant selected from the group consisting of polyamide-imide (PAI), polyimide (PI), graphite, MOS2, boron nitride (hexagonal modification; α-boron nitride), and a mixture thereof, or a decomposition product thereof that may be formed during heating and baking of the coating. This can further improve the cohesion of sublayers and wear resistance.

[0034] Preferably, the first layer comprises thermoplastics, and the second layer is free of thermoplastics. This achieves improved adhesion between the layers. Preferably, the second layer is a surface layer created by heating a silicone oil applied to the first layer.

[0035] Preferably, the second layer is a polycondensate of a thermoplastic-free polymer comprising particles selected from the group consisting of silicon particles, silicon dioxide particles and a combination thereof.

[0036] Preferably , a further layer is applied to the second layer , which is a surface layer produced by heating a silicone oil applied to the second layer .

[0037] Preferably, the article optionally comprises a further thermoplastic-free and silicon-free layer between the first and second layers.

[0038] Preferably, the last layer applied represents an impregnation of the previously applied layers.

[0039] Preferably, the first layer applied, consisting of temperature-resistant thermoplastics, preferably those with a permanent resistance of more than 220 °C, or a mixture thereof, does not contain any Si, SiO2, silicone resin or silicone oil. This layer can be applied several times, even in different compositions, to achieve a greater layer thickness. With the last layer, applied once or several times, selected from the group consisting of silicon particles, their oxides, silicone oil or silicone resin, the concentration of silicon and its oxides in the underlying thermoplastic layer is then increased in a tempering process, if possible above the glass transition temperature of at least one of the thermoplastics used. This preferably results in a concentration gradient of

[0040] Silicon and its oxides increasingly towards free

[0041] surface and decreasing towards the coated substrate.

[0042] In a second aspect of the invention, a method is provided for coating an article, in particular cooking and baking accessories, with a coating comprising a first and a second layer, wherein the coating has a surface layer, comprising the following steps:

[0043] 1) Production of a first layer comprising a) application of a powder mixture, dry or as a dispersion in a liquid, comprising powder particles comprising a polymer selected from the group consisting of polyaryletherketone (PAEK) polymer, polyphenylene sulfide (PPS) polymer and a combination thereof, to the article, in particular the cooking and baking accessory, wherein the application is preferably carried out electrostatically, in a fluidized bed sintering process or as a dispersion in liquid, in particular water; b) in the case of dispersion, complete removal of the liquid; c) heating the powder mixture to form a polycondensate; and d) baking the polycondensate above the liquidus temperature of the polycondensate;

[0044] 2) optionally producing a second or further layer on the first or lower layer, wherein sub-steps a) to d) are repeated, wherein optionally instead of sub-step a) a sub-step a) ' is carried out, wherein sub-step a) ' corresponds to sub-step a) , but a thermoplastic-free powder mixture is used, wherein the powder mixture optionally comprises particles selected from the group consisting of silicon particles, silicon dioxide particles and a combination thereof, wherein optionally after step 1d) or 2) a second or further layer comprising an organic silicon compound, preferably an element from the group consisting of silicone oil, polysiloxane resin, silicone elastomer and a mixture thereof is applied and cured between the glass transition temperature and the liquidus temperature of the first and optionally further layer(s),and wherein the silicon content of the surface layer of the second or further layer is controlled by one of the group consisting of silicon content in the powder mixture, silicon content in the layer comprising an organic silicon compound and a combination thereof such that the surface layer of the article has a silicon content, measured by energy dispersive X-ray spectroscopy (EDS), of at least 0.05 wt.%, preferably at least 0.1 wt.%, more preferably at least 0.5 wt.%, even more preferably at least 1 wt.%, even more preferably 1-10 wt.%, even more preferably 1-5 wt.%, even more preferably 1-3 wt.% and particularly preferably 1-2 wt.%.

[0045] The method is suitable for producing the article according to the first aspect and all preferred embodiments.

[0046] The layer comprising the organic silicon compound preferably has a thickness of at most 100 μm, preferably for cookware and frying utensils at most 20 μm, more preferably 1 to 15 μm, even more preferably 1 to 5 μm, or even immeasurable as an impregnation and not measurable as an extra layer. In another embodiment, it can also have a thickness of 5 to 15 μm. The measurement method was carried out as described above for measuring the thickness of the coating in the first aspect of the invention.

[0047] Preferably, 0.1 to 5 wt.%, preferably 0.5 to 2.5 wt.%, particularly preferably 1 to 2 wt.% of particles consisting of the group selected from silicon particles, silicon dioxide particles and a combination thereof are added.

[0048] Preferably, the particles consisting of silicon particles, silicon dioxide particles, and a combination thereof have a mass-related particle size distribution D50 of at most 1 μm, as measured by static image analysis according to ISO 13322-1:2014. The addition of macroscopic glass particles, for example, glass spheres or glass flakes with dimensions greater than 1 μm, can improve the mechanical resistance and hardness of the coating at elevated temperatures, but has a negative effect on the non-stick effect after wear / aging. The same applies to carbon fibers.

[0049] Preferably, the layer comprising the organic silicon compound has a thickness of at most 30 μm, preferably at most 20 μm, more preferably at most 15 μm, even more preferably at most 10 μm, particularly preferably at most 5 μm, most preferably 0 to 2 μm. The measurement method was carried out as described above for measuring the thickness of the coating in the first aspect of the invention.

[0050] Preferably, the uppermost free layer contains silicone oil dissolved in an organic solvent, for example xylene, in a concentration of at most 10 wt.%, more preferably at most 5 wt.%.

[0051] In another embodiment, the topmost, free layer contains a mixture of silicone oil and silicone resin, dissolved in a solvent at a concentration of no more than 5% by weight each. Methyl, phenyl, methylphenyl resin, and mixtures of different resins are suitable as silicone resins.

[0052] This top layer is preferably clear without pigmentation or contains a maximum of 5% by weight of inorganic pigments.

[0053] In another embodiment, a mixture of water and an organic solvent, for example isopropanol, is used for the top layer.

[0054] Additionally, the top layer may contain thickeners, defoamers, and wetting agents. The same applies to the dispersions of the underlying thermoplastic layer(s).

[0055] The baking temperature of this uppermost, thermoplastic-free layer(s) is below that of the underlying layers, preferably below the liquidus temperature of the thermoplastic or the mixture of thermoplastics, but above the glass transition temperature thereof, for example at 230°C.

[0056] The powder mixture preferably comprises at least two polymers, and powder particles comprising the first polymer preferably have a mass-related grain size distribution D50, measured by static image analysis in accordance with ISO 13322-1:2014, of at most 70 pm, preferably at most 60 pm, more preferably at most 50 pm, even more preferably at most 40 pm, in particular at most 30 pm, and powder particles comprising the second polymer preferably have a mass-related grain size distribution D50, measured by static image analysis in accordance with ISO 13322-1:2014, of at most 30 pm, preferably 25 pm, more preferably at most 20 pm, even more preferably at most 15 pm, in particular preferably 10 pm. (Since the thermoplastic layer is produced from insoluble powder particles in dispersion, the minimum layer thickness is based on the size of the powder grains.Particles as small as 10 μm (D50, defined and measured as above) are viable for industrial milling, resulting in a minimum layer thickness of 5 μm, preferably 10 μm. This can increase mechanical resistance. This could be achieved, for example, 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.%, demonstrated a wear-reducing effect.

[0057] Conversely, by adding PPS in amounts of up to 80 wt.%, 90 wt.%, or 95 wt.%, a further reduction in the baking temperature during coating production and a further improvement in the non-stick effect of the produced coating could be measured.

[0058] Preferably, the powder mixture is in the form of a dispersion, and the liquid comprises water. Preferably, the PAEK polymers are selected from the group consisting of polyetheretherketone (PEEK), polyetherketone (PEK), polyetherketoneketone (PEKK), and polyetherketoneetherketone (PEKKEK), and the powder mixture preferably comprises at least two PAEK polymers, or at least one PAEK polymer and PPS polymer.

[0059] Preferably, the at least two PAEK polymers, or at least one PAEK polymer and PPS polymer, have different melting temperatures.

[0060] Preferably, the two PAEK polymers, or at least one PAEK polymer and PPS polymer, have different melt viscosities, measured according to ISO 11443 at 400°C.

[0061] The average melt viscosity of at least one polymer is preferably more than 150 Pa.s, preferably 200-500 Pa.s, more preferably 300 to 500 Pa.s, measured according to ISO 11443 at 400°C. This primarily improves the adhesion of the second layer to the first layer. The average melt viscosity of at least one further polymer is preferably 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. 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 when the particles are large relative to the layer thickness (e.g. 25 pm grain size D50 for 25 pm layer thickness).

[0062] Preferably, the powder mixture comprises a

[0063] Dry lubricant from the group consisting of polyamideimide (PAI), polyimide (PI), graphite, MoS2, boron nitride (hexagonal modification; a-boron nitride) and a mixture thereof.

[0064] Preferably, the powder mixture comprises the dry lubricant in an amount of 0.1 to 20 wt.%.

[0065] Preferably, 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, particularly preferably at most 20°C above the liquidus temperature of the polycondensate.

[0066] The tests have shown that the non-stick effect improved with decreasing baking temperature and became too poor with too high baking temperature.

[0067] Preferably, the process, in particular in the step of heating the powder mixture to form a polycondensate, is carried out without using a fluorosurfactant.

[0068] Preferably, the layer comprising the organic silicon compound has a thickness of at most 30 μm after curing, preferably at most 20 μm, more preferably at most 15 μm, even more preferably at most 10 μm, and most preferably at most 5 μm. The measurement method was carried out as described above for measuring the thickness of the coating in the first aspect of the invention.

[0069] Preferably, the powder mixture is in the form of a dispersion and the liquid comprises water. Coated with the coating according to the invention

[0070] Metal surfaces can be subsequently deep-drawn, bent, pressed, rolled, embossed, and so on. It is therefore possible to subsequently manufacture products from coated flat blanks, round blanks, and so on by metallic forming, for example frying pans, baking trays, pots, cake and bread tins, and so on. A further aspect of the present invention is therefore directed to an article, in particular cooking and baking accessories, wherein the article has been further processed by metallic forming, preferably selected from the group consisting of deep drawing, bending, pressing, rolling, embossing, and a combination thereof. In addition, a further aspect is directed to a method comprising the step of metallic forming, preferably selected from the group consisting of deep drawing, bending, pressing, rolling, embossing, and a combination thereof, of the article.

[0071] The coating according to the invention can be applied as a dispersion by common painting processes, wherein at least the first layer is free of soluble substances such as PES, PAI etc., based on the coating finished after firing. A further aspect is therefore directed to the use of a paint, in particular wet paint, in the process according to the second aspect of the invention, wherein the paint, in particular wet paint, comprises a powder mixture, dry or as a dispersion in a liquid, comprising powder particles comprising a polymer selected from the group consisting of polyaryletherketone (PAEK) polymer, polyphenylene sulfide (PPS) polymer and a combination thereof. The invention is explained in more detail below with reference to exemplary embodiments and the associated figures.

[0072] The figures serve solely to facilitate a better understanding of the invention and are only schematic and not drawn to scale. The invention is not intended to be limited to the exemplary embodiments. Identical or equivalent parts are designated by the same reference numerals.

[0073] Figure 1 shows cooking and baking accessories with an applied dispersion layer in schematic cross-section according to a reference example,

[0074] Figure 2 shows cooking and baking accessories with coating according to a reference example,

[0075] Figure 3 shows a process sequence for coating using various process stages according to an embodiment of the process according to the invention,

[0076] Figure 4 shows a flow diagram for a coating using a dispersion process.

[0077] Figure 5 shows a section of a sample plate for EDS measurement

[0078] 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 involve mechanical roughening, for example using a sandblaster, or etching with acids, alkalis, or plasma or laser treatment. A suitably pre-treated surface has additional chemical / physical bonding points, is clean and free of grease, and, in the case of roughening, has a larger surface area, which leads to better adhesion of the coating to be applied.

[0079] A layer DS of a dispersion is then applied to this surface. This layer contains all the components of the coating in a finely divided and as homogeneous a particle size distribution as possible when dispersed in a solvent or solvent mixture. An application method is selected which 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 smaller. Figure 1 shows a substrate SU coated in this way with an applied dispersion layer DS.

[0080] After conducting a temperature program during which the substrate coated 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, exhibiting good mechanical cohesion and good adhesion to the substrate SU. Figure 2 shows the finished cooking and baking accessory according to a reference example.

[0081] It is possible to apply the coating only on one

[0082] part of the surface. The remaining area not to be coated can be covered or an application method for the dispersion is selected which can differentiate between different surface areas, for example painting or printing. The covering can also be achieved with a shadow mask while the dispersion is sprayed on. This shadow mask can also be in the form of a film which 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 e.g. peeled off, whereby the areas of the dispersion layer DS applied over it are also peeled off.

[0083] Figure 3 shows an embodiment of the method according to the invention in which the silicon content of the surface layer of the coating is controlled by the silicon content of the powder mixture for the second layer. For example, the powder mixtures of embodiments 1 or 2, which are specified below, can be used for this purpose. In embodiments 3 and 4, the organic silicon compound for the second layer can be solid or liquid. If the organic silicon compound in embodiments 3 and 4 is solid, it can be applied as a dispersion as in embodiments 1 and 2. If it is liquid, the liquid can be applied, optionally diluted in solvent.

[0084] In embodiments 1 to 4, a greater layer thickness can be achieved despite a smaller particle diameter of the solids contained in the dispersion. To this end, after applying the first dispersion layer DS1, as shown in Figure 3a, at least the solvent is removed; alternatively, the first dispersion layer is additionally pre-compacted by a temperature 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.Finally, as shown in Figure 3c, the structure of dispersion layers consisting of several sublayers is brought to a temperature above the melting point of the thermoplastic in a final step, whereby a fully compacted, pore-free, closed coating BS is obtained on the substrate SU.

[0085] A composition suitable for application by dispersion processes and also friction-reduced according to the invention contains, for example, solids in the following proportions by weight:

[0086] Example 1: Layer 1 (DS1): 100 weight percent PEEK; Layer 2 (DS2): 99 weight percent PEEK and 1 weight percent SiCt particles

[0087] Example 2: Layer 1 (DS1): 100 weight percent PEEK; Layer 2 (DS2): 50 weight percent PEEK, 49 weight percent PPS and 1 weight percent SiCt particles

[0088] Example 3: Layer 1 (DS1): 100% by weight

[0089] PEEK; Layer 2 (DS2): 100% by weight organic

[0090] Silicon compound embodiment 4: Layer 1 (DS1): 50 weight percent

[0091] PEEK and 49 weight percent PPS; Layer 2: 100

[0092] Weight percent organic silicon compound

[0093] The PEEK particles in embodiments 1 to 4 have a high molecular weight fraction (or first polymer) with an average melt viscosity of 300 to 500 Pa.s and a low molecular weight fraction (or second polymer) with an average melt viscosity of at most 90 Pa.s, measured according to ISO 11443 at 400°C. 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 30 pm, 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 10 pm.

[0094] The silicon dioxide particles in embodiments 1 and 2 have a mass-related grain size distribution D50 of 1 pm, measured by static image analysis according to ISO 13322-1:2014.

[0095] Color additives can be added if necessary. It is possible to apply one or more coats.

[0096] The solids are dispersed, if appropriate with the aid of auxiliary agents, in a solvent which may be water or, advantageously, is 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. The process sequence just described is shown more clearly in Figure 4 using a flow diagram. The process comprises, as step 1, producing and preparing the powder mixture. For this purpose, the ingredients which are selected from thermoplastic polymer, silicon or silicon dioxide particles, organic silicon compound (if present as a solid), filler and dry lubricant are either brought to a suitable particle size, preferably by grinding and / or by subsequent sorting according to grain size in accordance with a desired grain size distribution which is as narrow as possible.

[0097] In parallel, in step 2, the solvent is prepared, which is preferably environmentally and health-safe, 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 percent by weight of isopropanol in water. A solvent with approximately 25-50 percent by weight of isopropanol in water is particularly preferred.

[0098] 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 percent by weight. To improve dispersion stability, known dispersion aids can be added in small amounts.

[0099] In step 4, the surface of the object 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 left out of the coating.

[0100] In step 5, the solvent is removed, preferably by evaporation, which may optionally be assisted by vacuum or elevated temperature, for example 80°C.

[0101] In the next step 6, the cooking and baking accessories with the applied dried dispersion layer are converted into a homogeneous coating by heating and melting the thermoplastics and then the cooking and baking accessories are cooled down again.

[0102] Following this step 6, for embodiments 1 to 4, a finished coating can be obtained at point 7 after passing through one of the process variants VI to V3 (optionally also several times). In embodiments 1 and 2, the silicon content of the coating is controlled solely by the content of silicon dioxide particles in the powder mixture such that the coating of the article, in particular the cooking and baking accessory, has a silicon content, measured by energy-dispersive X-ray spectroscopy (EDS), of at least 0.05 wt.%, preferably at least 0.1 wt.%, more preferably at least 0.5 wt.%, even more preferably at least 1 wt.%, even more preferably 1-10 wt.%, even more preferably 1-5 wt.%, even more preferably 1-3 wt.% and particularly preferably 1-2 wt.%.

[0103] According to a variant VI of the process, it is possible to carry out steps 4 to 7 again 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).

[0104] According to a third variant V3 of the process, 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 used to coat the cooking and baking accessories according to steps 4 to 6. Here, too, the process according to variants VI and V2 can be modified by repeating individual process steps or individual process step sequences in order to achieve a desired layer thickness.

[0105] In embodiments 3 and 4 (powder mixture without silicon or silicon dioxide particles), the silicon content of the surface layer of the coating is controlled such that the surface layer has a silicon content, measured by energy dispersive X-ray spectroscopy (EDS), of at least 0.05 wt.%, preferably at least 0.1 wt.%, more preferably at least 0.5 wt.%, even more preferably at least 1 wt.%, even more preferably 1-10 wt.%, even more preferably 1-5 wt.%, even more preferably 1-3 wt.%, and particularly preferably 1-2 wt.%. In contrast, in embodiments 1 and 2, the same silicon content of the surface layer of the coating is achieved by controlling the silicon content of the powder mixture for the second layer (DS2). It is also possible to combine the principles from embodiments 1 / 2 with those from 3 / 4, i.e.to use both a silicon-containing powder mixture for the second layer and to apply a further layer comprising an organic silicon compound. In this case, the silicon content of the coating is controlled by both the silicon content in the powder mixture and the silicon content in the surface layer such that the coating of the article, in particular the cooking and baking accessory, has a silicon content, measured by energy-dispersive X-ray spectroscopy (EDS), of at least 0.05 wt.%, preferably at least 0.1 wt.%, more preferably at least 0.5 wt.%, even more preferably at least 1 wt.%, even more preferably 1-10 wt.%, even more preferably 1-5 wt.%, even more preferably 1-3 wt.% and particularly preferably 1-2 wt.%.

[0106] Fig. 5 shows a section of a sample plate with the coating according to the invention. The entire sample plate measures approximately 2 x 2 cm. Since the coatings are not electrically conductive, they are sputtered with gold before measurement. As shown in Fig. 5, at least nine spectra are recorded from each sample surface using an EDS measuring device. This yields values ​​for the silicon content in wt. %, which are then averaged.

[0107] In particular, when using fine particles for the dispersion, a particularly homogeneous coating can be obtained, which makes multiple coatings advantageous or even necessary due to the small particle diameters.

[0108] Protein testing was carried out to determine the anti-stick properties against

[0109] The test was carried out on egg white, specifically the whites of chicken eggs. The pan was manufactured according to Example 1. The pan was rinsed before the test and then baked at 300°C for 30 minutes. The pan was then heated on the stove to 190°C + / - 10°C, and an egg white was added and fried for approximately 2-3 minutes (until solid) without prior addition of oil or fat.

[0110] This test was repeated until the protein could no longer be removed without leaving residue.

[0111] A pan with a PEEK / PPS coating without Si failed this test, or only passed it a few times. In contrast, the pan according to the invention passed the test 20 to >100 times, depending on the design, and the higher the Si content, the higher the test rate.

[0112] However, a design with a single-layer pan with silicon or SiO2 had a reduced scratch resistance (cross-cut) and wore faster (Stiwatest).

[0113] Although the invention has been explained using only a few exemplary embodiments, it is not limited to these. Possible variations arise, in particular, through the appropriate selection of fillers and, if appropriate, through mixtures of different fillers. The proportions of the components of the coating are selected depending on the desired load of 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 it can also be applied to other surfaces such as ceramic, glass, or suitable plastic.

Claims

Patent claims 1. An article, in particular cooking and baking accessories, with a coating comprising a first and a second layer, wherein the coating has a surface layer and wherein the first and optionally the second layer comprise a polycondensate of a polymer selected from the group consisting of polyaryletherketone (PAEK) polymer, polyphenylene sulfide (PPS) polymer and a combination thereof, and wherein the surface layer of the coating has a silicon content, measured by energy dispersive X-ray spectroscopy (EDS), of at least 0.05 wt.%, preferably at least 0.1 wt.%, more preferably at least 0.5 wt.%, even more preferably at least 1 wt.%, even more preferably 1-10 wt.%, even more preferably 1-5 wt.%, even more preferably 1-3 wt.% and particularly preferably 1-2 wt.%.

2. Article, in particular cooking and baking accessory, according to claim 1, wherein the polycondensate is at least made of a polymer with an average melt viscosity of more than 150 Pa.s, preferably 200-500 Pa.s, more preferably 300 to 500 Pa.s, and preferably further made of a polymer with an average melt viscosity of 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.

3. Article, in particular cooking and baking accessories, according to one of claims 1 or 2, wherein the coating has a contact angle against water of at least 90°, preferably at least 95 ° , particularly preferably 100 to 120 ° , measured according to DIN EN ISO 19403-2 : 2020- 04 .

4. An article, in particular a cooking and baking accessory, according to any one of claims 1 to 3, wherein the coating comprises further partial layers in addition to the first and second layers and / or wherein the silicon content of the coating increases towards the surface of the coating.

5. Article, in particular cooking and baking accessories, according to one of claims 1 to 4, wherein the coating can be produced without fluorine compounds, 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).

6. An article, in particular a cooking and baking accessory, according to any one of claims 1 to 5, wherein the thickness of the coating is at most 50 pm, preferably at most 40 pm, more preferably at most 30 pm, particularly preferably at most 25 pm and / or wherein the second layer has a thickness of 5 to 20 pm, preferably 10 to 15 pm.

7. An article, in particular a cooking and baking accessory, according to any one of claims 1 to 6, wherein the first layer comprises thermoplastics and the second layer is free of thermoplastics. 8 . Article, in particular cooking and baking accessories, according to claim 7 , wherein the second layer comprises a by heating a surface layer created by applying silicone oil to the first layer.

9. An article, in particular a cooking and baking accessory, according to claim 7, wherein the second layer is a polycondensate of a thermoplastic-free polymer comprising particles selected from the group consisting of silicon particles, silicon dioxide particles and a combination thereof.

10. An article, in particular a cooking and baking accessory, according to claim 9, wherein a further layer is applied to the second layer, which is a surface layer produced by heating a silicone oil applied to the second layer.

11. An article, in particular a cooking and baking accessory, according to any one of claims 7 to 10, wherein the article optionally comprises a further thermoplastic-free and silicon-free layer between the first and second layers.

12. A method for coating an article, in particular cooking and baking accessories, with a coating comprising a first and a second layer, wherein the coating has a surface layer, comprising the following steps: 1 ) Production of a first layer comprising a ) application of a powder mixture, dry or as a dispersion in a liquid, comprising powder particles comprising a polymer selected from the group consisting of polyaryletherketone (PAEK) polymer, Polyphenylene sulfide (PPS) polymer and a combination thereof, onto the article, in particular 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; b) in the case of dispersion, complete removal of the liquid; c) heating the powder mixture to form a polycondensate; and d) baking the polycondensate above the liquidus temperature of the polycondensate; 2) optionally producing a second or further layer on the first or lower layer, wherein sub-steps a) to d) are repeated, wherein the powder mixture for the second or further layer optionally comprises particles selected from the group consisting of silicon particles, silicon dioxide particles and a combination thereof, optionally instead of sub-step a) a sub-step a) ' is carried out, wherein sub-step a) ' corresponds to sub-step a) , but a thermoplastic-free powder mixture is used, wherein optionally after step 1d) or 2) a second or further layer comprising an organic silicon compound, preferably an element from the group consisting of silicone oil, polysiloxane resin, silicone elastomer and a mixture thereof is applied and cured between the glass transition temperature and the liquidus temperature of the first and optionally further layers,and wherein the silicon content of the surface layer of the, Coating by one of the group consisting of Silicon content in the powder mixture, silicon content in the Layer comprising the organic silicon compound and a combination thereof, is controlled such that the surface layer of the coating of the article, in particular the cooking and baking accessory, has a silicon content, measured by energy dispersive X-ray spectroscopy (EDS), of at least 0.05 wt.%, preferably at least 0.1 wt.%, more preferably at least 0.5 wt.%, even more preferably at least 1 wt.%, even more preferably 1-10 wt.%, even more preferably 1-5 wt.%, even more preferably 1-3 wt.% and particularly preferably 1-2 wt.%.

13. The method according to claim 12, wherein the layer comprising the organic silicon compound has a thickness of at most 30 pm, preferably at most 20 pm, more preferably at most 15 pm, even more preferably at most 10 pm, particularly preferably at most 5 pm.

14. The method according to claim 12 or 13, wherein the powder mixture comprises 0.1 to 5 wt.%, preferably 0.5 to 2.5 wt.%, particularly preferably 1 to 2 wt.% of particles consisting of the group selected from silicon particles, silicon dioxide particles and a combination thereof.

15. The method according to any one of claims 12 to 14, wherein the particles consisting of the group selected from silicon particles, silicon dioxide particles and a combination thereof have a mass-related particle size distribution D50 of at most 1 pm, measured by static image analysis according to ISO 13322-1:2014.

16. Method according to one of claims 12 to 15, wherein the layer comprising the organic silicon compound has a thickness of at most 30 pm, preferably at most 20 pm, more preferably at most 15 pm, even more preferably at most 10 pm, particularly preferably at most 5 pm after curing.

17. Method according to one of claims 12 to 16, 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 pm, preferably at most 60 pm, more preferably at most 50 pm, even more preferably at most 40 pm, in particular at most 30 pm, 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 pm, preferably 25 pm, more preferably at most 20 pm, even more preferably at most 15 pm, in particular preferably 10 pm.

18. A method according to any one of claims 12 to 17, wherein the powder mixture is in the form of a dispersion and the liquid comprises water.

19. Process according to one of claims 12 to 18, wherein the PAEK polymers are preferably selected from the group consisting of polyetheretherketone (PEEK), polyetherketone (PEK), polyetherketoneketone (PEKK) and polyetherketoneetherketone (PEKKEK), and wherein the powder mixture preferably comprises at least two PAEK polymers, or at least one PAEK polymer and PPS polymer.

20. The method according to claim 19, wherein the at least two PAEK polymers, or at least one PAEK polymer and PPS polymer, have different melting temperatures.

21. The process according to claim 18 or 20, wherein the two PAEK polymers, or at least one PAEK polymer and PPS polymer, have different melt viscosities, measured according to ISO 11443 at 400°C.

22. The process according to any one of claims 12 to 21, wherein the average melt viscosity of at least one polymer is more than 150 Pa.s, preferably 200-500 Pa.s, more preferably 300 to 500 Pa.s, and preferably the average melt viscosity of at least one further 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.

23. The method according to any one of claims 12 to 22, wherein the powder mixture comprises a dry lubricant selected from the group consisting of polyamideimide (PAI), polyimide (PI), graphite, M0S2, boron nitride (hexagonal modification; a-boron nitride) and a mixture thereof.

24. The method of claim 23, wherein the powder mixture comprises the dry lubricant in an amount of 0.1 to 20 wt.%.

25. Article, in particular cooking and baking accessories, according to one of claims 1 to 11, wherein the article is a Sheet, plate etc. made of aluminum, steel or Stainless steel, copper and other metals whose melting temperature is above 300°C are coated on one or both sides.

26. An article, in particular a cooking and baking accessory, according to claim 25, wherein the article has been further processed by metallic forming, preferably selected from the group consisting of deep drawing, bending, pressing, rolling, embossing and a combination thereof.

27. A method comprising the step of metallically forming, preferably selected from the group consisting of deep drawing, bending, pressing, rolling, embossing and a combination thereof, an article according to claim 25.

28. Use of a paint, in particular wet paint, in the method according to one of claims 12 to 24, wherein the paint, in particular wet paint, comprises a powder mixture, dry or as a dispersion in a liquid, comprising powder particles comprising a polymer selected from the group consisting of polyaryletherketone (PAEK) polymer, polyphenylene sulfide (PPS) polymer and a combination thereof.

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