Process for applying sol-GEL non-stick ceramic coatings to glazed surfaces

Abstract

The present invention concerns a method for coating metallic substrates (1), preferably steel, covered with: (2) an intermediate ceramic enamel layer (3) a siloxane-based polymeric primer layer (4) a non-stick Sol Gel ceramic layer The polymeric primer layer has the function of creating a strong adhesion between the intermediate ceramic enamel layer and the non-stick Sol Gel ceramic layer, effectively creating a stable and solid "bridge" between the two coatings, increasing wear resistance and improving the non-stick properties of the obtained articles.

Description

Technical Field

[0001] The present invention concerns a method for coating metallic substrates, preferably steel, and already coated or to be coated with an intermediate ceramic enamel layer with a non-stick ceramic layer, wherein said non-stick ceramic layer is adhered to said intermediate ceramic enamel substrate by the application of a siloxane-based polymeric primer.Prior Art

[0002] The ability to render surfaces of objects and articles non-stick has in fact opened the door to operational advantages, both in domestic and industrial fields, which are by no means negligible. Examples include industrial reactors implemented in chemical and biotechnological productions that present non-stick coatings on the internal surfaces of said reactors to prevent precisely the undesired adhesion of substrates, microorganisms, and bacteria. Even in domestic environments, as well as in catering, the use of utensils that inhibit / limit the sticking of cooked food to the containers used has become standard practice. Commonly, non-stick surfaces are obtained by applying compositions containing polytetrafluoroethylene (PTFE). The use of PTFE is however disadvantageous for a large series of reasons, including the release of toxic compounds (e.g., tetrafluoroethylene and trifluoroacetic acid) which are liberated due to material degradation during the high-temperature sintering process, high costs and energy consumption required for carrying out the process itself, inadequate hardness of the perfluorinated polymer, and, not least, the further production of harmful substances during prolonged overheating of the article. In an attempt to overcome the above-mentioned problems, research has promoted ceramic coatings as an alternative to PTFE. This non-stick ceramic surface coating, obtained through sol-gel processes, is commonly adhered onto an underlying ceramic enamel layer which normally itself covers a metallic base, usually steel. Common techniques for manufacturing non-stick articles employ a specific treatment to promote the anchoring of the non-stick coating onto the ceramic enamel, i.e., sandblasting (or micro-sandblasting).

[0003] This technique consists of repeatedly striking a metallic or ceramic surface with abrasive material in the form of microparticles such as, for example, sand grains or cast iron granules, which, projected at high speed, allow the removal of impurities, surface asperities, and protrusions, roughening the surface itself and promoting subsequent treatments such as, for example, the application of protective / non-stick layers.

[0004] Although sandblasting aims at obtaining surfaces largely free from defects, imperfections, and irregularities, it remains an expensive process, rather impactful from the perspective of industrial sustainability, and poorly controllable. In fact, in addition to the need to allocate substantial funds for the purchase of machinery or to budget significant maintenance and operational costs, sandblasting machines do not guarantee fine control of the uniformity of surface roughness. This therefore results in evident surface irregularities, whose defects can only be detected downstream of the sol-gel ceramic application and baking process. In other words, sandblasting is outlined as an industrial process that is unreliable, inconsistent in performance, only partially reproducible, especially in cases where a constant qualitative standard over time is required, and sometimes produces stochastic results.

[0005] Moreover, articles irreparably damaged by production defects, not meeting the quality standards required for market release, must be mandatorily classified as scrap and ultimately disposed of. It follows that, in addition to the waste of raw material itself, the amount of costs for disposal of defective pieces must also be considered.

[0006] For example, EP2620521 discloses a method for applying SOL-GEL coatings for domestic utensils, which provides for the successive application onto a metallic layer of an anti-corrosion layer, a binder, and a SOL-GEL non-stick layer. Furthermore, US5079073 discloses a process for applying a non-stick coating applied onto an underlying "undercoat" layer and a primer.

[0007] However, in the current state of the art, there is a recognized need for a non-stick coating process on enameled metallic articles that is efficient from a production point of view and at the same time capable of providing improved adhesion of the non-stick layer to the intermediate ceramic enamel layer.

[0008] Unless explicitly stated otherwise, the content of the present chapter is to be considered as an integral part of the detailed description that follows.Summary of the invention

[0009] For the purposes of the invention, a method has been devised to apply a non-stick ceramic layer on a metallic substrate, comprising the steps of: Preparing a metallic substrate coated on at least one face with a intermediate ceramic enamel layer, to be understood as consisting of enamel or ceramic frit; Applying an adhesion promotion layer at a temperature between approximately 20-60°C, preferably by spraying or dipping, on an upper surface of said intermediate ceramic enamel layer; Drying the adhesion promotion layer for a time between approximately 2-5 min and at a temperature between approximately 80-150°C, said temperature to be understood as the temperature of the metallic substrate; Applying a non-stick SOL GEL ceramic layer on the upper surface of the adhesion promotion layer; Baking at a temperature between approximately 120-320°C for a time between approximately 10-60 min.

[0010] The advantages obtained consist mainly in the fact that it is possible to eliminate the mechanical pre-treatment steps from the coating process of the intermediate ceramic enamel layer, whether enamel or ceramic frit.Brief Description of Figures

[0011] The invention will be described below in at least one preferred embodiment solely for explanatory and non-limiting purposes of the scope of the present invention by means of the attached figures, namely: Figure 1: is a three-dimensional schematic representation of the layered structure of the non-stick article obtained according to the method of the invention; Figure 2: shows a cross-sectional schematic of a non-stick article obtained according to the method of the invention. Definitions

[0012] In the present document, the terms "approximately" or "around" as used herein when referring to a measurable value such as a quantity, a time duration, and the like, are intended to encompass variations of ±20%, ±10%, ±5%, ±1%, or ±0.1% from the specified value, where such variations are appropriate for performing the methods described. In the present document, the terms "comprises", "includes", "has", "having", "contains", "containing", "characterized by" or any variation of these terms are intended to cover a non-exclusive inclusion, subject to any limitation explicitly indicated. For example, a composition, a mixture, a process, or a method comprising a list of elements is not necessarily limited only to those elements but may include other elements not expressly listed or inherent to such composition, mixture, process, or method. In the present document, the terms "upper" and "lower" referring to the faces of a generic layer of a utensil, which by definition is identified as co-planar with the XY plane (Figure 1), refer to the relative position (along the Z axis) of one face with respect to the other; i.e., the "upper" face will be associated with a height value (along the Z axis) greater than that of the "lower" face. In the present document, the terms "upper" or "lower", as well as "overlying" or "underlying" referring to the layers of the article, which by definition is identified as co-planar with the XY plane (Figure 1), refer to the relative position (along the Z axis) of one layer with respect to the other; i.e., the "upper" (or overlying) layer will be associated with a height value (along the Z axis) greater than that of the "lower" (or underlying) layer. In the present document, the term "intermediate ceramic enamel layer" may refer to either a ceramic enamel layer or a ceramic frit layer. Detailed Description

[0013] The present invention concerns a method for the manufacturing of manufactures, articles, objects and utensils superficially coated with a non-stick ceramic layer, which is able to overcome the issues of the previously known technique raised and which can offer a plurality of manufacturing advantages with respect to the processes / methods currently in use or otherwise already known / described in the literature.

[0014] In particular, the method according to the invention allows coating an enamelled metal utensil (or coated with ceramic frit) with a non-stick ceramic sol-gel layer, without the necessity of performing a preliminary sandblasting / micro-sandblasting step (conventional treatment in the manufacturing processes of non-stick manufactures) of the ceramic enamel layer of the utensil in production.

[0015] Advantageously, the method according to the invention proposes applying an adhesion-promoting layer or polymeric primer on the surface of the ceramic enamel layer / ceramic frit layer.

[0016] More in detail, the invention concerns a method of industrial manufacturing of two coating layers, i.e. an intermediate ceramic enamel layer (ceramic enamel or ceramic frit) and a non-stick ceramic sol-gel layer, on manufactures having a metal substrate (e.g., steel) as a base, in which said method allows not having to perform the conventional surface roughening process operated by means of sandblasting, thanks to the application of a specific water-based adhesion-promoting polymeric primer, thus overcoming the technical limits connected to the sandblasting itself.

[0017] It has in fact been found that the application of the polymeric primer on the surface of the ceramic enamel layer allows regularising the surface itself in a more efficient manner compared to what can be obtained with a sandblasting process, ensuring a more accurate elimination of protrusions, defects and surface asperities and thus providing a more uniformly levelled surface.

[0018] Furthermore, the application of the polymeric primer according to the method of the present invention on a surface of an intermediate ceramic enamel layer functionalises the surface itself, activating it and increasing its reactivity towards the subsequent layering of the non-stick material consisting of a SOL GEL layer of ceramic nature.

[0019] In the present document, for simplicity of exposition reference will be made to a system of Cartesian XYZ axes (as illustrated in Figure 1) in which the longitudinal X axis, the transverse Y axis and the vertical Z axis are respectively the axis of longitudinal development, the axis of width development and the axis of height development of a generic non-stick manufacture made according to the method of the present invention.

[0020] The method for coating a metal substrate with a non-stick ceramic layer according to the present invention, with reference to Figure 2, comprises the steps of: Providing a metal substrate (1) coated on the upper face with an intermediate ceramic enamel layer (2); Applying an adhesion-promoting layer (3) at a temperature between approximately 20-60°C, preferably by spraying process or dipping process, on the upper surface of the intermediate ceramic enamel layer (2); Drying (flash off) the adhesion-promoting layer (3) for a time between approximately 2-5 min and at a temperature between approximately 80-150°C, said temperature being intended as the temperature of the metal substrate; Applying a non-stick SOL GEL ceramic layer (4) on the upper surface of the adhesion-promoting layer (3); said SOL GEL ceramic layer having a thickness between around 3-60 microns (µm); Baking at a temperature between around 120-320°C for a time between around 10-60 min.

[0021] Optionally, the method according to the invention may further comprise a preliminary coating step of said metal substrate (1) with said intermediate ceramic enamel layer (2).

[0022] Said preliminary coating step of the metal substrate (1) comprises the steps of: Removing from said metal substrate (1) oily contaminants and greasy residues coming by way of non-limiting example from stamping processes, padding or machining processes, preferably by spraying systems or dipping systems; Optionally pickling the metal substrate (1) for the removal of surface oxides; Rinsing the metal substrate (1), preferably with demineralised water; Drying the metal substrate (1); Applying the intermediate ceramic enamel layer (2) on the upper face of said metal substrate (1), preferably with spraying systems or dipping systems; Baking the intermediate ceramic enamel layer (2) at a temperature between approximately 450-900°C, for a time between 20-60 min.

[0023] The baking times and temperatures of the intermediate ceramic enamel layer (2) may vary as a function of the nature of the ceramic layer (2), of its thickness, and of the nature (e.g., melting temperature) of the metal of the metal substrate (1) as well as of the oven used, preferably constituted by a continuous oven. An expert in the field will be able to evaluate and establish the suitable / appropriate temperature and baking duration for the baking of the manufacture in production.

[0024] The intermediate ceramic enamel layer (2) has a thickness between 40-100 µm, preferably between 50-90 µm, more preferably between 60-80 µm.

[0025] The non-stick SOL GEL ceramic layer (4) has a thickness between 3-60 µm, preferably between 5-55 µm, 8-50 µm, 10-50 µm, 15-50 µm.

[0026] Preferably the adhesion-promoting layer (3) applied according to the method of the present invention and interposed between the intermediate ceramic enamel layer (2) and the non-stick ceramic layer (4) has a thickness between approximately 1-10 µm (micron), preferably between 2-9 µm, 3-8 µm, 4-7 µm, 3-9 µm, 4-9 µm, 2-8 µm, 2-7 µm.

[0027] Said adhesion-promoting layer (3) is constituted by a polymeric primer in the form of aqueous solution, said polymeric primer comprising organic compounds (or polymers), preferably of siloxane (silicone) nature, and inorganic compounds, preferably silicon salts, dissolved in water, thus forming a hybrid mixture, i.e. constituted by a combination of organic and inorganic components which, through chemical bonds or physical interactions, form a unique structure integrating typical properties of both components.

[0028] The adhesion-promoting layer (3) is capable of altering the chemical-physical properties of the underlying intermediate ceramic enamel layer (2), thus promoting adhesion between said intermediate ceramic enamel layer (2) and the non-stick ceramic layer (4). This occurs through the creation of chemical-mechanical bonds between the intermediate ceramic enamel layer (2) and the non-stick ceramic layer (4) mediated precisely by the polymeric primer. The aqueous solvent contained in the polymeric primer of the adhesion-promoting layer (3) allows the organic and inorganic components of said primer to be conveyed onto the compact surface of the intermediate ceramic enamel layer, thus creating a wet and uniformly adhered coating on said surface. Following the drying process (flash off), part of the substances will remain adhered / anchored on the upper face of the intermediate ceramic enamel layer, while others will be available to bond with the subsequently applied non-stick ceramic sol-gel.

[0029] The subsequent firing process of the non-stick ceramic sol-gel will be conducted at an appropriate temperature, for example between 120-320°C, preferably between 280 and 300°C, and will develop chemical reactions of consolidation and stabilization of the chemical bonds of the polymers between the intermediate ceramic surface (2) and the non-stick ceramic layer (4), ensuring optimal and strong adhesion. In some embodiments of the method according to the present invention, the metallic substrate (1) can be selected by way of non-limiting example from metallic substrates in copper, steel, stainless steel, aluminum, carbon steel, cast iron, their combinations and their alloys.

[0030] The intermediate ceramic enamel layer (2) can be selected by way of non-limiting example from the group comprising ceramic enamel layers, ceramic frit, porous ceramic frit.

[0031] According to the present invention, the non-stick ceramic layer (4) is obtained by a sol-gel process carried out by a reaction between an aqueous silica sol and an alkoxysilane compound. The conditions for obtaining a non-stick ceramic layer by SOL-GEL technique are, however, known to a person skilled in the art. Advantageously, the application of the polymeric primer as an adhesion-promoting layer between the intermediate ceramic enamel layer (2) and the superficial non-stick ceramic layer (4) allows an increase in wear resistance. In fact, the non-stick ceramic layer (4), being strongly anchored to the underlying layers by means of the polymeric primer, appears more resistant to scratching, damage, abrasion, and detachment of portions of material when used repeatedly in domestic, industrial, or private environments.

[0032] Advantageously, the method according to the present invention allows obtaining a coating with a non-stick ceramic layer, obtained by a sol-gel process, free from microcracks and other defects, which are causes of a high scrap rate of the manufactured articles.

[0033] Furthermore, the method according to the invention for the production of non-stick articles advantageously allows an increase in corrosion resistance of the metallic substrate, preferably steel, at the base of the article, and an improvement of non-stick and wear-resistant properties.

[0034] Advantageously, the polymeric primer implemented in the method according to the invention unexpectedly achieves a technical effect of homogenization of the imperfections (asperities, grooves, defects, rough areas, irregularities) of the upper surface of the intermediate ceramic enamel layer (2), which cannot be obtained with a sandblasting process (which, although it smooths the surface, simultaneously promotes mechanical roughening).

[0035] Not only that, the polymeric primer is further and surprisingly capable of supporting the bond strength between the underlying and overlying layers, i.e., between the intermediate ceramic enamel layer (2) and the non-stick ceramic layer (4).

[0036] A further advantage consists in the fact that, with the method of the invention, both adhesion processes of the coating, "cross link" and "hard link", can be effectively activated, to be understood respectively as the formation of chemical bonds and chemical-mechanical bonds between the intermediate ceramic enamel layer (2) and the non-stick ceramic layer (4) mediated by the adhesion-promoting layer (polymeric primer).

[0037] The combination of the technical effects of surface leveling of the intermediate ceramic enamel layer (e.g., ceramic enamel) and of chemical-mechanical anchoring between said intermediate ceramic enamel layer (2) and the superficial non-stick ceramic layer (4), not derivable from the prior art, allows the improvement of the performance of the manufactured articles, extends their service life, and increases their safety of use.

[0038] In particular, with respect to the technical teaching of EP2620521A1, the adhesion-promoting layer is not applied directly to the metallic base substrate (1) but on the intermediate ceramic enamel layer (2). It is precisely the application of the primer on said intermediate ceramic enamel layer (2) that allows the non-stick ceramic layer (4) to be strongly anchored to the article, which, being the outermost layer, is predominantly affected by mechanical stimuli, abrupt thermal excursions, and washing.USES

[0039] The method according to the invention is suitable for coating metallic substrates, preferably steel, with non-stick ceramic coatings, obtained preferably by sol-gel technique, for the manufacture of utensils such as pots, pans, baking trays, food cooking containers, oven cavities, automotive sector, and household appliances.EXAMPLES

[0040] By way of non-limiting example of embodiment, a process according to the invention is described for the production of carbon steel pots with an internal coating formed by the following layers: a) intermediate ceramic enamel applied on the metallic substrate b) water-based polymeric primer c) non-stick ceramic sol-gel Phase 1 SUBSTRATE MOLDING WITH LUBRICATING OILS Phase 2 SPRAY SUBSTRATE PRETREATMENT Descrizione Prodotto Time min °C 2.1degreasingAlkaline3-560-802.2rinsingTap water1-1,5502.3rinsingTap water1-1,5r.t.2.4rinsingDemineralized water1-1,5r.t.2.5dryingHot air10-1580-1202.6coolingr.t. Phase 3 INTERMEDIATE WET ENAMEL BY IMMERSION Description Product Time seconds °C dry thickness in microns 3.1Immersionpowders such as silicas, metal oxides, and pigments mixed with water until a homogeneous suspension is obtained5-15r.t.3.2draining3-10r.t.Time minutes 3.3DryingHot air15-2080-1203.4Baking Baking curve Time minutes First StepRamp-up5-7230-300Second Steppeak3-4850-900Third StepRamp-down25-3040-5080-100 Phase4 SPRAY APPLICATION OF PRIMER Description Product Time minutes °C dry thickness in microns 4.1Spraying with Airmix guns or HVLPwater-based polymeric primer30-404.2DryingHot air3-580-1204.3Cooling40-503-5 Phase 5 SPRAY APPLICATION OF CERAMIC SOL-GEL Description Product Time minutes °C dry thickness in microns 5.1Spraying with Airmix guns or HVLPNon-stick ceramic sol-gel40-505.2BakingBaking curveFirst StepRamp-up8-15250Second StepPeak8-13280-310Third StepRamp-down8-153035-45

[0041] The present invention has been described according to preferred embodiments of realization, but equivalent variants can be conceived without departing from the scope of protection granted.

Examples

examples

EXAMPLES

[0040]By way of non-limiting example of embodiment, a process according to the invention is described for the production of carbon steel pots with an internal coating formed by the following layers:

a) intermediate ceramic enamel applied on the metallic substrate b) water-based polymeric primer c) non-stick ceramic sol-gel

Phase 1 SUBSTRATE MOLDING WITH LUBRICATING OILS Phase 2 SPRAY SUBSTRATE PRETREATMENT Descrizione Prodotto Time min °C 2.1degreasingAlkaline3-560-802.2rinsingTap water1-1,5502.3rinsingTap water1-1,5r.t.2.4rinsingDemineralized water1-1,5r.t.2.5dryingHot air10-1580-1202.6coolingr.t. Phase 3 INTERMEDIATE WET ENAMEL BY IMMERSION Description Product Time seconds °C dry thickness in microns 3.1Immersionpowders such as silicas, metal oxides, and pigments mixed with water until a homogeneous suspension is obtained5-15r.t.3.2draining3-10r.t.Time minutes 3.3DryingHot air15-2080-1203.4Baking Baking curve Time minutes First StepRamp-up5-7230-300Se...

Technical Field

[0001] The present invention concerns a method for coating metallic substrates, preferably steel, and already coated or to be coated with an intermediate ceramic enamel layer with a non-stick ceramic layer, wherein said non-stick ceramic layer is adhered to said intermediate ceramic enamel substrate by the application of a siloxane-based polymeric primer.Prior Art

[0002] The ability to render surfaces of objects and articles non-stick has in fact opened the door to operational advantages, both in domestic and industrial fields, which are by no means negligible. Examples include industrial reactors implemented in chemical and biotechnological productions that present non-stick coatings on the internal surfaces of said reactors to prevent precisely the undesired adhesion of substrates, microorganisms, and bacteria. Even in domestic environments, as well as in catering, the use of utensils that inhibit / limit the sticking of cooked food to the containers used has become standard practice. Commonly, non-stick surfaces are obtained by applying compositions containing polytetrafluoroethylene (PTFE). The use of PTFE is however disadvantageous for a large series of reasons, including the release of toxic compounds (e.g., tetrafluoroethylene and trifluoroacetic acid) which are liberated due to material degradation during the high-temperature sintering process, high costs and energy consumption required for carrying out the process itself, inadequate hardness of the perfluorinated polymer, and, not least, the further production of harmful substances during prolonged overheating of the article. In an attempt to overcome the above-mentioned problems, research has promoted ceramic coatings as an alternative to PTFE. This non-stick ceramic surface coating, obtained through sol-gel processes, is commonly adhered onto an underlying ceramic enamel layer which normally itself covers a metallic base, usually steel. Common techniques for manufacturing non-stick articles employ a specific treatment to promote the anchoring of the non-stick coating onto the ceramic enamel, i.e., sandblasting (or micro-sandblasting).

[0003] This technique consists of repeatedly striking a metallic or ceramic surface with abrasive material in the form of microparticles such as, for example, sand grains or cast iron granules, which, projected at high speed, allow the removal of impurities, surface asperities, and protrusions, roughening the surface itself and promoting subsequent treatments such as, for example, the application of protective / non-stick layers.

[0004] Although sandblasting aims at obtaining surfaces largely free from defects, imperfections, and irregularities, it remains an expensive process, rather impactful from the perspective of industrial sustainability, and poorly controllable. In fact, in addition to the need to allocate substantial funds for the purchase of machinery or to budget significant maintenance and operational costs, sandblasting machines do not guarantee fine control of the uniformity of surface roughness. This therefore results in evident surface irregularities, whose defects can only be detected downstream of the sol-gel ceramic application and baking process. In other words, sandblasting is outlined as an industrial process that is unreliable, inconsistent in performance, only partially reproducible, especially in cases where a constant qualitative standard over time is required, and sometimes produces stochastic results.

[0005] Moreover, articles irreparably damaged by production defects, not meeting the quality standards required for market release, must be mandatorily classified as scrap and ultimately disposed of. It follows that, in addition to the waste of raw material itself, the amount of costs for disposal of defective pieces must also be considered.

[0006] For example, EP2620521 discloses a method for applying SOL-GEL coatings for domestic utensils, which provides for the successive application onto a metallic layer of an anti-corrosion layer, a binder, and a SOL-GEL non-stick layer. Furthermore, US5079073 discloses a process for applying a non-stick coating applied onto an underlying "undercoat" layer and a primer.

[0007] However, in the current state of the art, there is a recognized need for a non-stick coating process on enameled metallic articles that is efficient from a production point of view and at the same time capable of providing improved adhesion of the non-stick layer to the intermediate ceramic enamel layer.

[0008] Unless explicitly stated otherwise, the content of the present chapter is to be considered as an integral part of the detailed description that follows.Summary of the invention

[0009] For the purposes of the invention, a method has been devised to apply a non-stick ceramic layer on a metallic substrate, comprising the steps of: Preparing a metallic substrate coated on at least one face with a intermediate ceramic enamel layer, to be understood as consisting of enamel or ceramic frit; Applying an adhesion promotion layer at a temperature between approximately 20-60°C, preferably by spraying or dipping, on an upper surface of said intermediate ceramic enamel layer; Drying the adhesion promotion layer for a time between approximately 2-5 min and at a temperature between approximately 80-150°C, said temperature to be understood as the temperature of the metallic substrate; Applying a non-stick SOL GEL ceramic layer on the upper surface of the adhesion promotion layer; Baking at a temperature between approximately 120-320°C for a time between approximately 10-60 min.

[0010] The advantages obtained consist mainly in the fact that it is possible to eliminate the mechanical pre-treatment steps from the coating process of the intermediate ceramic enamel layer, whether enamel or ceramic frit.Brief Description of Figures

[0011] The invention will be described below in at least one preferred embodiment solely for explanatory and non-limiting purposes of the scope of the present invention by means of the attached figures, namely: Figure 1: is a three-dimensional schematic representation of the layered structure of the non-stick article obtained according to the method of the invention; Figure 2: shows a cross-sectional schematic of a non-stick article obtained according to the method of the invention. Definitions

[0012] In the present document, the terms "approximately" or "around" as used herein when referring to a measurable value such as a quantity, a time duration, and the like, are intended to encompass variations of ±20%, ±10%, ±5%, ±1%, or ±0.1% from the specified value, where such variations are appropriate for performing the methods described. In the present document, the terms "comprises", "includes", "has", "having", "contains", "containing", "characterized by" or any variation of these terms are intended to cover a non-exclusive inclusion, subject to any limitation explicitly indicated. For example, a composition, a mixture, a process, or a method comprising a list of elements is not necessarily limited only to those elements but may include other elements not expressly listed or inherent to such composition, mixture, process, or method. In the present document, the terms "upper" and "lower" referring to the faces of a generic layer of a utensil, which by definition is identified as co-planar with the XY plane (Figure 1), refer to the relative position (along the Z axis) of one face with respect to the other; i.e., the "upper" face will be associated with a height value (along the Z axis) greater than that of the "lower" face. In the present document, the terms "upper" or "lower", as well as "overlying" or "underlying" referring to the layers of the article, which by definition is identified as co-planar with the XY plane (Figure 1), refer to the relative position (along the Z axis) of one layer with respect to the other; i.e., the "upper" (or overlying) layer will be associated with a height value (along the Z axis) greater than that of the "lower" (or underlying) layer. In the present document, the term "intermediate ceramic enamel layer" may refer to either a ceramic enamel layer or a ceramic frit layer. Detailed Description

[0013] The present invention concerns a method for the manufacturing of manufactures, articles, objects and utensils superficially coated with a non-stick ceramic layer, which is able to overcome the issues of the previously known technique raised and which can offer a plurality of manufacturing advantages with respect to the processes / methods currently in use or otherwise already known / described in the literature.

[0014] In particular, the method according to the invention allows coating an enamelled metal utensil (or coated with ceramic frit) with a non-stick ceramic sol-gel layer, without the necessity of performing a preliminary sandblasting / micro-sandblasting step (conventional treatment in the manufacturing processes of non-stick manufactures) of the ceramic enamel layer of the utensil in production.

[0015] Advantageously, the method according to the invention proposes applying an adhesion-promoting layer or polymeric primer on the surface of the ceramic enamel layer / ceramic frit layer.

[0016] More in detail, the invention concerns a method of industrial manufacturing of two coating layers, i.e. an intermediate ceramic enamel layer (ceramic enamel or ceramic frit) and a non-stick ceramic sol-gel layer, on manufactures having a metal substrate (e.g., steel) as a base, in which said method allows not having to perform the conventional surface roughening process operated by means of sandblasting, thanks to the application of a specific water-based adhesion-promoting polymeric primer, thus overcoming the technical limits connected to the sandblasting itself.

[0017] It has in fact been found that the application of the polymeric primer on the surface of the ceramic enamel layer allows regularising the surface itself in a more efficient manner compared to what can be obtained with a sandblasting process, ensuring a more accurate elimination of protrusions, defects and surface asperities and thus providing a more uniformly levelled surface.

[0018] Furthermore, the application of the polymeric primer according to the method of the present invention on a surface of an intermediate ceramic enamel layer functionalises the surface itself, activating it and increasing its reactivity towards the subsequent layering of the non-stick material consisting of a SOL GEL layer of ceramic nature.

[0019] In the present document, for simplicity of exposition reference will be made to a system of Cartesian XYZ axes (as illustrated in Figure 1) in which the longitudinal X axis, the transverse Y axis and the vertical Z axis are respectively the axis of longitudinal development, the axis of width development and the axis of height development of a generic non-stick manufacture made according to the method of the present invention.

[0020] The method for coating a metal substrate with a non-stick ceramic layer according to the present invention, with reference to Figure 2, comprises the steps of: Providing a metal substrate (1) coated on the upper face with an intermediate ceramic enamel layer (2); Applying an adhesion-promoting layer (3) at a temperature between approximately 20-60°C, preferably by spraying process or dipping process, on the upper surface of the intermediate ceramic enamel layer (2); Drying (flash off) the adhesion-promoting layer (3) for a time between approximately 2-5 min and at a temperature between approximately 80-150°C, said temperature being intended as the temperature of the metal substrate; Applying a non-stick SOL GEL ceramic layer (4) on the upper surface of the adhesion-promoting layer (3); said SOL GEL ceramic layer having a thickness between around 3-60 microns (µm); Baking at a temperature between around 120-320°C for a time between around 10-60 min.

[0021] Optionally, the method according to the invention may further comprise a preliminary coating step of said metal substrate (1) with said intermediate ceramic enamel layer (2).

[0022] Said preliminary coating step of the metal substrate (1) comprises the steps of: Removing from said metal substrate (1) oily contaminants and greasy residues coming by way of non-limiting example from stamping processes, padding or machining processes, preferably by spraying systems or dipping systems; Optionally pickling the metal substrate (1) for the removal of surface oxides; Rinsing the metal substrate (1), preferably with demineralised water; Drying the metal substrate (1); Applying the intermediate ceramic enamel layer (2) on the upper face of said metal substrate (1), preferably with spraying systems or dipping systems; Baking the intermediate ceramic enamel layer (2) at a temperature between approximately 450-900°C, for a time between 20-60 min.

[0023] The baking times and temperatures of the intermediate ceramic enamel layer (2) may vary as a function of the nature of the ceramic layer (2), of its thickness, and of the nature (e.g., melting temperature) of the metal of the metal substrate (1) as well as of the oven used, preferably constituted by a continuous oven. An expert in the field will be able to evaluate and establish the suitable / appropriate temperature and baking duration for the baking of the manufacture in production.

[0024] The intermediate ceramic enamel layer (2) has a thickness between 40-100 µm, preferably between 50-90 µm, more preferably between 60-80 µm.

[0025] The non-stick SOL GEL ceramic layer (4) has a thickness between 3-60 µm, preferably between 5-55 µm, 8-50 µm, 10-50 µm, 15-50 µm.

[0026] Preferably the adhesion-promoting layer (3) applied according to the method of the present invention and interposed between the intermediate ceramic enamel layer (2) and the non-stick ceramic layer (4) has a thickness between approximately 1-10 µm (micron), preferably between 2-9 µm, 3-8 µm, 4-7 µm, 3-9 µm, 4-9 µm, 2-8 µm, 2-7 µm.

[0027] Said adhesion-promoting layer (3) is constituted by a polymeric primer in the form of aqueous solution, said polymeric primer comprising organic compounds (or polymers), preferably of siloxane (silicone) nature, and inorganic compounds, preferably silicon salts, dissolved in water, thus forming a hybrid mixture, i.e. constituted by a combination of organic and inorganic components which, through chemical bonds or physical interactions, form a unique structure integrating typical properties of both components.

[0028] The adhesion-promoting layer (3) is capable of altering the chemical-physical properties of the underlying intermediate ceramic enamel layer (2), thus promoting adhesion between said intermediate ceramic enamel layer (2) and the non-stick ceramic layer (4). This occurs through the creation of chemical-mechanical bonds between the intermediate ceramic enamel layer (2) and the non-stick ceramic layer (4) mediated precisely by the polymeric primer. The aqueous solvent contained in the polymeric primer of the adhesion-promoting layer (3) allows the organic and inorganic components of said primer to be conveyed onto the compact surface of the intermediate ceramic enamel layer, thus creating a wet and uniformly adhered coating on said surface. Following the drying process (flash off), part of the substances will remain adhered / anchored on the upper face of the intermediate ceramic enamel layer, while others will be available to bond with the subsequently applied non-stick ceramic sol-gel.

[0029] The subsequent firing process of the non-stick ceramic sol-gel will be conducted at an appropriate temperature, for example between 120-320°C, preferably between 280 and 300°C, and will develop chemical reactions of consolidation and stabilization of the chemical bonds of the polymers between the intermediate ceramic surface (2) and the non-stick ceramic layer (4), ensuring optimal and strong adhesion. In some embodiments of the method according to the present invention, the metallic substrate (1) can be selected by way of non-limiting example from metallic substrates in copper, steel, stainless steel, aluminum, carbon steel, cast iron, their combinations and their alloys.

[0030] The intermediate ceramic enamel layer (2) can be selected by way of non-limiting example from the group comprising ceramic enamel layers, ceramic frit, porous ceramic frit.

[0031] According to the present invention, the non-stick ceramic layer (4) is obtained by a sol-gel process carried out by a reaction between an aqueous silica sol and an alkoxysilane compound. The conditions for obtaining a non-stick ceramic layer by SOL-GEL technique are, however, known to a person skilled in the art. Advantageously, the application of the polymeric primer as an adhesion-promoting layer between the intermediate ceramic enamel layer (2) and the superficial non-stick ceramic layer (4) allows an increase in wear resistance. In fact, the non-stick ceramic layer (4), being strongly anchored to the underlying layers by means of the polymeric primer, appears more resistant to scratching, damage, abrasion, and detachment of portions of material when used repeatedly in domestic, industrial, or private environments.

[0032] Advantageously, the method according to the present invention allows obtaining a coating with a non-stick ceramic layer, obtained by a sol-gel process, free from microcracks and other defects, which are causes of a high scrap rate of the manufactured articles.

[0033] Furthermore, the method according to the invention for the production of non-stick articles advantageously allows an increase in corrosion resistance of the metallic substrate, preferably steel, at the base of the article, and an improvement of non-stick and wear-resistant properties.

[0034] Advantageously, the polymeric primer implemented in the method according to the invention unexpectedly achieves a technical effect of homogenization of the imperfections (asperities, grooves, defects, rough areas, irregularities) of the upper surface of the intermediate ceramic enamel layer (2), which cannot be obtained with a sandblasting process (which, although it smooths the surface, simultaneously promotes mechanical roughening).

[0035] Not only that, the polymeric primer is further and surprisingly capable of supporting the bond strength between the underlying and overlying layers, i.e., between the intermediate ceramic enamel layer (2) and the non-stick ceramic layer (4).

[0036] A further advantage consists in the fact that, with the method of the invention, both adhesion processes of the coating, "cross link" and "hard link", can be effectively activated, to be understood respectively as the formation of chemical bonds and chemical-mechanical bonds between the intermediate ceramic enamel layer (2) and the non-stick ceramic layer (4) mediated by the adhesion-promoting layer (polymeric primer).

[0037] The combination of the technical effects of surface leveling of the intermediate ceramic enamel layer (e.g., ceramic enamel) and of chemical-mechanical anchoring between said intermediate ceramic enamel layer (2) and the superficial non-stick ceramic layer (4), not derivable from the prior art, allows the improvement of the performance of the manufactured articles, extends their service life, and increases their safety of use.

[0038] In particular, with respect to the technical teaching of EP2620521A1, the adhesion-promoting layer is not applied directly to the metallic base substrate (1) but on the intermediate ceramic enamel layer (2). It is precisely the application of the primer on said intermediate ceramic enamel layer (2) that allows the non-stick ceramic layer (4) to be strongly anchored to the article, which, being the outermost layer, is predominantly affected by mechanical stimuli, abrupt thermal excursions, and washing.USES

[0039] The method according to the invention is suitable for coating metallic substrates, preferably steel, with non-stick ceramic coatings, obtained preferably by sol-gel technique, for the manufacture of utensils such as pots, pans, baking trays, food cooking containers, oven cavities, automotive sector, and household appliances.EXAMPLES

[0040] By way of non-limiting example of embodiment, a process according to the invention is described for the production of carbon steel pots with an internal coating formed by the following layers: a) intermediate ceramic enamel applied on the metallic substrate b) water-based polymeric primer c) non-stick ceramic sol-gel Phase 1 SUBSTRATE MOLDING WITH LUBRICATING OILS Phase 2 SPRAY SUBSTRATE PRETREATMENT Descrizione Prodotto Time min °C 2.1degreasingAlkaline3-560-802.2rinsingTap water1-1,5502.3rinsingTap water1-1,5r.t.2.4rinsingDemineralized water1-1,5r.t.2.5dryingHot air10-1580-1202.6coolingr.t. Phase 3 INTERMEDIATE WET ENAMEL BY IMMERSION Description Product Time seconds °C dry thickness in microns 3.1Immersionpowders such as silicas, metal oxides, and pigments mixed with water until a homogeneous suspension is obtained5-15r.t.3.2draining3-10r.t.Time minutes 3.3DryingHot air15-2080-1203.4Baking Baking curve Time minutes First StepRamp-up5-7230-300Second Steppeak3-4850-900Third StepRamp-down25-3040-5080-100 Phase4 SPRAY APPLICATION OF PRIMER Description Product Time minutes °C dry thickness in microns 4.1Spraying with Airmix guns or HVLPwater-based polymeric primer30-404.2DryingHot air3-580-1204.3Cooling40-503-5 Phase 5 SPRAY APPLICATION OF CERAMIC SOL-GEL Description Product Time minutes °C dry thickness in microns 5.1Spraying with Airmix guns or HVLPNon-stick ceramic sol-gel40-505.2BakingBaking curveFirst StepRamp-up8-15250Second StepPeak8-13280-310Third StepRamp-down8-153035-45

[0041] The present invention has been described according to preferred embodiments of realization, but equivalent variants can be conceived without departing from the scope of protection granted.

Examples

examples

EXAMPLES

[0040]By way of non-limiting example of embodiment, a process according to the invention is described for the production of carbon steel pots with an internal coating formed by the following layers:

a) intermediate ceramic enamel applied on the metallic substrate b) water-based polymeric primer c) non-stick ceramic sol-gel

Phase 1 SUBSTRATE MOLDING WITH LUBRICATING OILS Phase 2 SPRAY SUBSTRATE PRETREATMENT Descrizione Prodotto Time min °C 2.1degreasingAlkaline3-560-802.2rinsingTap water1-1,5502.3rinsingTap water1-1,5r.t.2.4rinsingDemineralized water1-1,5r.t.2.5dryingHot air10-1580-1202.6coolingr.t. Phase 3 INTERMEDIATE WET ENAMEL BY IMMERSION Description Product Time seconds °C dry thickness in microns 3.1Immersionpowders such as silicas, metal oxides, and pigments mixed with water until a homogeneous suspension is obtained5-15r.t.3.2draining3-10r.t.Time minutes 3.3DryingHot air15-2080-1203.4Baking Baking curve Time minutes First StepRamp-up5-7230-300Se...

Claims

1. A method for applying a non-stick ceramic layer to a metal substrate comprising the steps of: preparing a metal substrate (1) coated on at least one coating face with an intermediate ceramic enamel layer (2); applying an adhesion-promoting layer (3) at a temperature of approximately 20-60°C, preferably by spraying or dipping process, on a top surface of said intermediate ceramic enamel layer (2); drying the adhesion-promoting layer (3) for approximately 2-5 min at a temperature of approximately 80-150 °C, said temperature being understood to be the temperature of the metal substrate; applying a non-stick SOL GEL ceramic layer (4) on the upper surface of the adhesion-promoting layer (3); baking this non-stick SOL GEL ceramic layer, wherein said adhesion-promoting layer (3) is a polymeric primer in the form of aqueous solution comprising organic siloxane compounds and inorganic salts of silicon.

2. The method according to the preceding claim wherein the adhesion-promoting layer (3) has a thickness of approximately 1-10 µm.

3. The method according to any one of the preceding claims wherein the metal substrate (1) can be chosen from metal substrates made of copper, steel, stainless steel, aluminium, carbon steel, cast iron, combinations thereof and alloys thereof.

4. Method according to any one of the preceding claims wherein the intermediate ceramic enamel layer (2) can be chosen from ceramic enamel, ceramic frit, porous ceramic frit.

5. Method according to any one of the preceding claims wherein the intermediate ceramic enamel layer (2) has a thickness of approximately 10-100 µm.

6. Method according to any one of the preceding claims wherein said non-stick SOL GEL ceramic layer (4) has a thickness of approximately 3-80 microns (µm).

7. Method according to any one of the preceding claims further comprising a preliminary coating step of a coating face of said metal substrate (1) with an intermediate ceramic layer (2).

8. Method according to claim 8 wherein said preliminary coating step comprises the steps of: cleaning said coating face of said metal substrate (1) by removing oily contaminants and greasy residues from, preferably from stamping, padding or machining processes, preferably by spraying or dipping systems; optionally, pickling said metal substrate (1) to remove surface oxides; rinsing the metal substrate (1), preferably with demineralised water; drying the metal substrate (1); coating said coating face of said metal substrate (1) with said intermediate ceramic layer (2), preferably by spraying or dipping systems; baking said intermediate ceramic layer (2).

9. Method according to any of the preceding claims for the manufacture of utensils, pots, pans, lickers, food cooking containers, oven cavities, vehicle body parts, home appliances.

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