Patent GB-821956-A (GB)
Title: Process for coating metals and product thereof
Inventor: PRENTISS WILLIAM CASE
IPC: B05D7/16
Filed: 1956-08-07
Abstract: Metals are coated with an aqueous alkaline dispersion of pH 9-11 of a pigment and an alkali-metal, ammonium or volatile, watersoluble amine salt of a linear copolymer containing (a) acrylic, methacrylic or itaconic acid to the extent of 1/2 % to 5% and (b) one or more esters of acrylic or methacrylic acid, said copolymer having a Ti point of between 5 DEG  C. and 100 DEG  C., the ratio of pigment to binder being from 0.5 : 1 to 5 : 1, and subsequently baked at at least 250 DEG  F.  Suitable monomeric esters are alkyl methacrylates having alkyl groups of not more than 4 carbon atoms, tertamyl methacrylate, tert-butyl acrylate, tertamyl acrylate, and cyclohexyl or benzyl acrylate or methacrylate.  Other esters unsuitable by themselves as they form polymers with Ti points below 5 DEG  C. which may be copolymerized with the above esters or with acrylonitrile or methacrylonitrile include primary and secondary alkyl acrylates of which the alkyl groups have more than 2 carbon atoms, and primary and secondary alkyl methacrylates of which the alkyl groups have more than 6 carbon atoms.  Numerous such esters and combinations of esters are given.  At least 20% of weight of the pigment should be a corrosionpreventive pigment such as red lead, white lead, zinc oxide or iron oxide; the remainder may be extenders such as titanium dioxide and barytes.  The metals coated include iron and steel, which may be phosphatized, deoxidized steel, galvanized iron, aluminium, anodized aluminium, magnesium and copper and alloys thereof.  In the preparation of the copolymers, the monomers are suspended in water with a non-ionic polyethoxyethanol, a catalyst such as a perborate, percarbonate, persulphate or organic peroxide activated by a reducing agent such as a sulphite, and a source of polyvalent metal ions. After polymerization the mixture is cooled and rendered alkaline by the addition of ammonia, an amine, or an inorganic base, so neutralizing any free carboxylic groups.  Other constituents of the coating suspension may be thickening agents, e.g. sodium alginate, sodium or ammonium polyacrylate, or methyl cellulose; dispersing agents for the pigments; defoaming agents; humectants; bactericides; perfumes or deodorants; and auxiliary anti-corrosion compounds such as sodium benzoate, sodium dichromate, sodium nitrite or guanyl urea phosphate.  Examples are given of compositions containing (1) ethyl acrylate, methyl methacrylate and methacrylic acid, and an octyl phenoxypolyethoxyethanol, the polymerization catalyst being ammonium persulphate and sodium hydrosulphite, the alkali, ammonia, and the pigment a mixture of zinc oxide and either titanium dioxide or red iron oxide; (2) butyl acrylate, methyl methacrylate and acrylic acid, an octyl phenoxypolyethoxyethanol, catalysts and alkali as in Example (1), the pigment being titanium dioxide and white lead; (3) lauryl acrylate, methyl methacrylate, and methacrylic acid, and nonylphenoxypolyethoxyethanol and methylene bis-diamylphenoxypolyethoxyethanol, the catalyst being potassium persulphate, sodium hydrosulphite and a trace of ferrous sulphate, the alkali, ammonia and the pigment red lead; (4) ethyl acrylate, tert-butyl methacrylate and itaconic acid, octyl phenoxypolyethoxyethanol, catalyst and alkali as in Example (1), the pigment being titanium dioxide and zinc oxide; (5) benzyl acrylate and methacrylic acid and diamylphenoxypolyethoxyethanol, the catalyst consisting of ammonium persulphate, sodium metabisulphite and ferrous sulphate, the alkali, morpholine and ammonia and the pigment titanium dioxide and zinc oxide; and (6) dodecyl methacrylate, acrylonitrile and methacrylic acid, octyl phenoxy polyethoxyethanol and an emulsifier formed by reacting the condensate of diisobutyl phenol and formaldehyde with ethylene oxide, catalyst and alkali as in Example (1), and pigment, titanium oxide and zinc oxide.  All these coatings may be followed by a decorative top coat of lacquer or enamel based on cellulose derivatives, melamine-formaldehyde resins or alkyd resins.