GB860299A - Improvements in or relating to coating and coating compositions comprising polytetraf - Google Patents

Abstract

Coating compositions comprise dispersions of a finely-divided polytetrafluoroethylene of particle size 0.1 to 3 microns, with the predominant proportion having a particle size of about one micron, and at least one thermosettable resin in a dispersing medium, in which the combined weight of polytetrafluoroethylene and the thermosettable resin is less than 25% of the weight of the dispersion, the said composition including a stabilizing agent of such nature and amount that when the dispersion is allowed to stand the polytetrafluoroethylene particles agglomerate to an extent such that they settle in 2 to 5 hours so as to leave a proportion of 1/5 to 9/10 of the depth of the dispersion as clear supernatant liquid. The thermosettable resins may be phenolic resins, e.g. condensates of cresol, resorcinol or butyl phenol with formaldehyde or furfural, optionally modified with rosin, rosin esters or alkyds; urea-formaldehyde resins; melamine-formaldehyde resins; alkyd resins, e.g. derived from maleic, fumaric, phthalic or adipic acids and a glycol, glycerol or sorbitol, optionally modified with phenolic resins, drying or semi-drying oils; epoxy resins, e.g. condensates of epichlorhydrin with bisphenols or other bifunctional hydroxyl - containing compounds, optionally modified with polyester resins, phenolic resins or fatty acids; polyurethanes, e.g. reaction products of polyesters and isocyanates such as 2,4-tolylene diisocyanate; thermosettable alkyl and alkyl-aryl silicones, e.g. methyl silicones, ethyl silicones and methylphenyl silicones; and petroleum or hydrocarbon resins. The thermosettable resins may contain fillers, colouring agents and driers. The stabilizers may be vinyl or cellulosic resins, e.g. polyvinyl acetate, polyvinyl chloride, polyvinyl alcohol, polyvinyl acetal, polyvinyl butyral, polyvinyl formal, vinyl chloride-vinyl acetate copolymers, cellulose acetate, cellulose nitrate, cellulose propionate, cellulose acetate butyrate, ethyl cellulose, methyl cellulose and carboxymethyl cellulose. The dispersing medium may comprise hydrocarbons, e.g. toluene and xylene; alcohols, e.g. n-butyl alcohol and ethanol; esters, e.g. ethylene glycol monoethyl ether acetate; and ketones, e.g. methyl isobutyl ketone. The dispersions may also contain surface active agents, e.g. stearyl dimethyl benzyl ammonium chloride, sodium dioctyl sulphosuccinate and polyoxyethylene lauryl ether. The compositions may be applied to metals, e.g. steel, brass and aluminium, wood, glass, plastics, rubber and leather, and the thermosetting resin thereafter cured at a temperature below that required to fuse thepolytetrafluoroethylene. U.S.A. Specifications 2,681,324 and 2,777,733 are referred to.ALSO:Substrates may be coated, e.g. by brushing, dipping or spraying, with compositions comprising dispersions of finely divided polytetrafluoroethylene of particle size 0.1 to 3 microns, with the predominant proportion having a particle size of about one micron, and at least one thermosettable resin in a dispersing medium, in which the combined weight of polytetrafluoroethylene and thermosettable resin is less than 25% of the weight of the dispersion, said composition including a stabilizing agent of such nature and amount that when the dispersion is allowed to stand the polytetrafluoroethylene particles agglomerate to an extent such that they settle in 2 to 5 hours so as to leave a proportion of one-fifth to nine-tenths of the depth of the dispersion as clear supernatant liquid, and the coatings thereafter cured at temperatures above that needed to cure the thermosettable resins but below that needed to fuse the polytetrafluoroethylene. The substrate may be metal, e.g. steel, brass or aluminium, wood, glass, plastics, rubber or leather. The thermosettable resins may be phenolic resins, e.g. condensates of cresol, resorcinol or butyl phenol with formaldehyde or furfural, optionally modified with rosin, rosin esters or alkyds; urea-formaldehyde resins; melamineformaldehyde resins; alkyd resins, e.g. derived from maleic, fumaric, phthalic or adipic acids and a glycol, glycerol or sorbitol, optionally modified with phenolic resins, drying or semidrying oils; epoxy resins, e.g. condensates of epichlorhydrin with bisphenols or other bifunctional hydroxyl-containing compounds, optionally modified with polyester resins, phenolic resins or fatty acids; polyurethanes, e.g. reaction products of polyesters and isocyanates such as 2,4-tolylene diisocyanate; thermosettable alkyl and alkyl-aryl silicones, e.g. methyl silicones, ethyl silicones and methyl phenyl silicones; and petroleum or hydrocarbon resins. The stabilizers may be vinyl or cellulosic resins, e.g. polyvinyl acetate, polyvinyl chloride, polyvinyl alcohol, polyvinyl acetal, polyvinyl butyral, polyvinyl formal, vinyl chloride-vinyl acetate copolymers, cellulose acetate, cellulose nitrate, cellulose propionate, cellulose acetate butyrate, ethyl cellulose, methyl cellulose and carboxy methyl cellulose. The dispersing medium may comprise hydrocarbons, e.g. toluene and xylene; alcohols, e.g. n-butyl alcohol and ethanol; esters, e.g. ethylene glycol monoethyl ethers acetate; and ketones, e.g. methyl isobutyl ketone. The dispersions may also contain surface-active agents, e.g. stearyl dimethyl benzyl ammonium chloride, sodium dioctyl sulphosuccinate and polyoxyethylene lauryl ether. The coatings have a low coefficient of friction, have electrical-insulating, abrasion- and corrosion-resistant properties, and will readily accept printing inks. U.S.A. Specifications 2,681,324 and 2,777,733 are referred to.