Title of Invention

NON-STICK COATING FOR ALUMINIUM COOKING VESSELS

Abstract

A non-stick coating for aluminum cooking vessels comprises an undercoat layer applied directly to the aluminum, a primer layer applied to the undercoat layer and a top finish layer applied to the primer layer. The primer layer is obtained from an aqueous dispersion of polytatrafluorethylene (PTFE) to which are added polyamide-imide resin (PAI) and tetrailuorethylene and poly (propyl vinyl ether) copolymer (PFA). The top finish layer is obtained from an aqueous dispersion of PTFE and the undercoat layer is obtained from a polyamide-imide resin (PAI) in solution in an organic solvent.

Full Text

The present invention concerns a non-stick coating for aluminum cooking vessels such as saucepans and trying pans. Most non-stick coatings, are based on polytetrafluorethylene (PTFE). To make such coating9 adhere to the surface of the aluminum the latter is usually etched with acid to create microcavities encouraging the adhesion of the PTFE coating or a surface roughness of approximately 12 microns is produced by mechanical treatment to enable the adhesion of a primer layer. A coating adhering to an aluminum substrate that has not received any chemical or mechanical treatment to roughen its surface is known from PCT application WO 91/02773. The coating described in this PCT application comprises an undercoat layer, a primer layer and a top finish layer. The undercoat layer is obtained from an aqueous phase containing a surfactant, Gilica, a polyamide-imide resin (PAD, polyphenylene sulfide or polyether sulrone. The primer layer is obtained from an aqueous dispersion of polytetrafluorethylene (PTFE) to which are added polyamido-imide resin !PAI) and tetrafluorethylene and poly (propyl vinyl ether) (PFA) copolymer. The top finish layer is obtained from an aqueous dispersion of PTFF. The above layers are all applied to the substrate by spraying in the aqueous phase. After drying, these layers are baked in an oven to sinter the coating. The undercoat layer has the drawback of requiring transformation of the organic phase of the PAI resin into the aqueous phase and the presence of surfactants. The aim of the prosent invention is to create a non-stick coating that shows excellent adhesion to aluminum substrates whether or not they have been mechanically or chemically treated to roughen their surface. Accordingly, the invention concerns a non-stick coating for aluminum cocking vessels comprising an undercoat layer applied directly to the aluminum, a primer layer applied to said undercoat layer and a top finish layer applied to said primer layer, said primer layer being obtained from an aqueous dispersion ot polytetrafluorethylene to which are added polyamide-imide resin and tetrafluorethylene and poly (propyl vinyl other) copolymer, said top finish Layer being obtained from an aqueous dispersion of FTFE and said undercoat layer being obtained from a polyaimide-imide resin in solution in an organic solvent. Tests have shown, surprisingly, that an undercoat layer of this kind containing an organic solvent adheres to the substrate just as well as the prior art aqueous phase undercoat layer. This undercoat layer does not require any complex transformation from an organic phase to the aqueous phase in the presence of surfactants and amides. The undorcoat layer may be obtained, from a mixture of polyamine-imide resin and polyphenylene sulfide. The organic solvent used in the undercoat layer is preferably selected from the following co:rpoun:ls: N-methylpyrrolidone, dimethylformamide or an NMF/xylene or DMF/xylene mixture. The undercoat layer may contain inert charges such as mineral pigments, metal flakes, alumina, quartz. The undercoat layer of the coating of the invention shows excellent adhesion to aluminum even if the surface of the latter has not boen subjected to any form of chemical or physical treatment other than degreasiny. In one version of the invention the primer layer and the top finish layer are applied by the silkscreening or roller coating process. The method of applying a non-stick coating by the silkscreening process and the attendant advantages are described in French patent 2 689 037 in the name of SEB S.A. In thiG case, the primer layer and the top finish layer also contain A thickening agent such as an acrylic resin. There follows one example or the composition (in parts by weight) of the undercoat layer of the coating of the invention. dry PAI (polyamide-imide) resin 30 N-methylpyrrolidone 230 xylene 0-10 pigment (mineral or carbon black) 0-25 aluminum flakes 0 - 4 0 The aluminum flakes encourage adhesion of the primer layer to the above undercoat layer. Their the latter a roughness equivalent to that of mechanical treatment and provides an armature for the final coating in the manner of a mechanical treatment. To this end, their dimensions must not exceed 25 microns. The above undercoat layer may be sprayed onto an aluminum disc that has merely been degreased or applied by the silkscreening process or any other conventional means. The undercoat layer is then dried to eliminate the organic solvent. The primer layer and the top finish layer are then applied in succession by the silkscreening process as described in French patent 2 6 89 037 or any other conventional means. The primer layer is mode up of an aqueous dispersion of PTFE to which has been added a PAI resin, a PFA dispersion and, in the case of application by the silkscroening or roller coating process, an acrylic rosin. The top finish layer applied after the prime, layer has dried is mada up of an aqueous dispersion of FTFE, mica flakes, a pigment such as carbon black ami, in the case of application by the silkscreening or roller coating process, a thickening agent such as an Acrylic resin. After drying the top layer, the three layers are baked simultaneously in an oven for 1' - 10' at approximately 400°C - 420°c. Tests show that the coating obtained in this way adhere perfectly to the support. When an aluminum disc is coated with these three layers by the silkscroening or roller coating process, for example, it can be formed after sintering into a Cooking vessel such as a saucepan, frying pan, cake tin, etc. without degrading the adhesion of the coating to the support. 1. A non-stick coating for aluminum cooking vessels comprising an undercoat layer applied directly to the aluminum, a primer layer applied to said undercoat layer and a top finish layer applied to said primer layer, said primer layer being obtained from an aqueous dispersion of polytetrafluorethylene (PTFE) to which are added polyamide-imide resin (PAD and tetrafluorethylene and poly (propyl vinyl ether) copolymer (PFA), said top finish layer being obtained from an aqueous dispersion of PTFE and said undercoat layer being obtained from, a polyamide-imide resin (PAT) in solution in an organic solvent. 2. The coating claimed in claim 1 wherein said undercoat layer is obtained from a mixture of polyamide imide resin (PAI) and polyphenylene sulfide. 3. The coating claimed in claim 1 or claim 2 wherein said organic solvent in selected from: N-methylpyrrolidone, dimethylformamide or an KMP/xylene or DMF/xylene mixture. 4. The coating claimed in any one of claims 1 to 3 wherein said undercoat layer further contains inert charges such as mineral pigments, metal flakes, alumina 5. The coating claimed in any one of. claims 1 to 4 wherein said undercoat layer has the following composition, in parts by weight: . dry PAI (polyamide-imide) resin 30 . N-methylpyrrolidone 230 . xylene 0-10 . pigment (mineral or carbon black) 0 - 25 . aluminum flakes 0 - 40 . PPS (polyphenylene sulfide) 0-30 6. The coating claimed 1n any one of claims 1 to 5 wherein said undercoat layer is applied to aluminum which has not been subjected to any chemical or physical treatment other than degreasing. 7. The coating claimed in any one of claims 1 to 6 wherein said primer and top finish layers are applied by the silkscreening or roller conting process. 8. The coating claimed in claim 7 wherein said primer and top finish layers further contain a thickening agent. 9. The coating claimed in any one of claims 4 to 7 wherein said undercoat layer contains aluminum flakes having dimensions less than or equal to 25 microns. 10. A non-stick coating composition for aluminium cooking vessels, substantially as herein described. 11. An aluminium cooking vessel with a non-stick coating, substantially as herein described. 12. A process for the manufacture of a non-stick coating composition for aluminium cooking vessel, substantially as herein described. A non-stick coating for aluminum cooking vessels comprises an undercoat layer applied directly to the aluminum, a primer layer applied to the undercoat layer and a top finish layer applied to the primer layer. The primer layer is obtained from an aqueous dispersion of polytatrafluorethylene (PTFE) to which are added polyamide-imide resin (PAI) and tetrailuorethylene and poly (propyl vinyl ether) copolymer (PFA). The top finish layer is obtained from an aqueous dispersion of PTFE and the undercoat layer is obtained from a polyamide-imide resin (PAI) in solution in an organic solvent.

Documents:

146-cal-1997-abstract.pdf

146-cal-1997-claims.pdf

146-cal-1997-correspondence.pdf

146-cal-1997-description (complete).pdf

146-cal-1997-form 1.pdf

146-cal-1997-form 2.pdf

146-cal-1997-form 3.pdf

146-cal-1997-form 5.pdf

146-cal-1997-priority document.pdf

146-cal-1997-specification.pdf

146-cal-1997-translated copy of priority document.pdf

62-cal-1997_abandoned_letter.pdf