GB1108063A - Coating articles - Google Patents

Abstract

A surface is coated with a layer of a substance which on thermal decomposition yields on acid product and leaves a solid residue, thermal decomposition of the layer then being effected, and thereafter an oxymethylene polymer coating is formed on the treated surface by fusion of particles of the polymer in contact with the surface. Suitable materials for forming the thermally decomposable layer are nitrocellulose, cellulose acetate, polyvinyl acetate and polyvinyl chloride, and may be applied in a suitable vehicle say by spraying, painting, or dipping, along with pigments, e.g. titanium dioxide, carbon, iron oxide and mixtures thereof, and metal powders; a catalyst which reduces the temperature at which the decomposition takes place e.g. tris-beta-chloroethyl phosphate; substances which facilitate the decomposition of the said catalyst e.g. a mineral acid such as nitric acid, an organic acid e.g. acetic acid or mixtures thereof; fire retardants such as organo-borates of formula: (RO)3B wherein R is an alkyl group having up to 10 carbon atoms e.g. tri-n-butyl, tri-ethyl and tri-propyl borate. The oxymethylene polymers may be homopolymers end capped by esterification or etherification, or preferably copolymers consisting predominantly of chains of oxymethylene groups containing dispersed along their groups having adjacent carbon atoms forming links in the polymer chains e.g. oxyethylene groups. Such copolymers e.g. those obtained by copolymerising trioxane and ethylene oxide or dioxolane are preferably subjected to treatment before use to eliminate terminal oxymethylene groups such that all or most of the terminal groups of the polymer molecules have adjacent carbon atoms. The polymers may be blended with chemical stabilizers such as an anti-oxidant and an agent to repress chain scission e.g. a bisphenol and a trivalent nitrogen containing compound such as cyanoguanidine, benzoguanidine, melamine, N, N', N"-tri-n-propyl-melamine. Articles coated may be of metal e.g. aluminium, aluminium alloys such as aluminium alloyed with 5 to 12% silicon, nickel, magnesium, tin chromium or titanium, iron and low and high carbon steels and other iron alloys e.g. those containing chromium, molybdenum, silica, manganese or titanium, brass, bronze, copper, zinc or magnesium; or of glass, ceramic and plastics e.g. thermosetting resins of the phenolic, urea and melamine type. The article may be heated while the polymer particles are brought into contact with it, by say interior circulation of a heating fluid or induction heating or the article may be preheated to a temperature above the melting point of the polymer. To improve the glass and reduce porosity, the coated article may be reheated. The coated article may then be coated again with polymer particles to build up the thickness of the coating and the coated articles then cooled or quenched in water. The polymer particles may be applied by spraying or in a fluidised bed process. In the Examples liquid compositions for applying the thermally decomposible substance to the surface comprise a blend of 1 to 4 parts of a composition comprising Ethanol, isopropanol, ethyl acetate, methyl ethyl ketone, n-propanol, n-butanol, methyl isobutyl ketone, toluene, xylene, titanium dioxide, carbon, nitrocellulose, and trisbeta-chloroethyl phosphate, with 1 part of: (a) a composition comprising ethanol, isopropanol, methyl ethyl ketone, n-propanol, n-butanol, methyl isobutyl ketone, toluene, m-xylene, 2-methyl-pentanol-4, tri-n-butyl borate, nitric acid, acetic acid; or (b) a composition comprising isopropanol, ethyl acetate, isopropyl acetate, benzene, n-propanol, n-butanol, methyl isobutyl ketone, toluene, n-butylacetate, p-xylene, m-xylene, xylene, tri-n-butyl borate, nitric acid, acetic acid. The articles treated in the Examples comprise a cold rolled steel strap, steel sheet, and an aluminium rectangle.