GB842950A - Coating process - Google Patents

Abstract

A finely divided epoxy resin composition comprises a dry mixture of 100 parts of an epoxy resin obtained by reacting bisphenol A with epichlorohydrin, 8 parts of dicyandiamide, and 2 parts of a synthetic silica flatting agent. A varnish composition comprises as solvent equal parts by weight of methyl isobutyl carbinol, methyl isobutyl ketone, toluene, and xylene in which is dissolved 73,1% of the above epoxy resin, 24,4% of a liquid phenolic resin, 1% of polyvinyl butyral resin, and 1,5% of phosphoric acid. Both these compositions, as well as a composition comprising the former composition and a pulverulent plasticized cellulose acetate-butyrate, are used to coat fibre-glass-polyester moulded panels, aluminium rods, wood and fibre glass either by immersion or by the fluidized bed technique, (see Groups III and XV).ALSO:<PICT:0842950/III/1> A surface is coated by wetting with a liquid capable of holding a layer of powdered coating material contacting the surface with a fluidised bed of the powdered coating material consisting of a dense phase bounded by an upper free surface, and heating the applied coating. With paper surfaces, the liquid may be water or n-butyl alcohol. The liquid may also be a methyl ethyl ketone solution of the epoxy resin Epon 828 catalyzed with m-phenylenediamine or, where the coating particles are of this resin, methyl ethyl ketone itself. The liquid may chemically or physically combine with or act as a polymerization catalyst for the particles, e.g. diallyl phthalate with an unsaturated linear polyester containing maleic anhydride as a portion of the acid component or di-butyl phthalate with plasticized cellulose acetate-butyrate resin. The liquid may also be catalyzed monomers such as liquid styrene or diallyl phthalate which will polymerize in situ alone or cross-link with the particles. The liquid may be phosphoric acid in the case of metal surfaces. The liquid may also be a solvent or plasticizer for the surface, or may be a substance, e.g. diphenyl phthalate, requiring heating to liquefy it prior to application. A continuous ribbon of paper can be fed by rollers through the desired liquid bath, or metal or plastic castings may be fed through the bath on a continuous belt or conveyer. Other coatings for waterproofing and finishing may be applied, and the coated paper may be calendered. The surface may also be of cardboard, cartonboard, cloth, wood, glass, synthetic resin, heat-sensitive resin or fabric, or metal, including a metal of low melting point. As shown, a steel container 10 with an open top 11 is divided by the gas-pervious partition 14 into an upper chamber 12 containing the powdered coating material and a pressure chamber 13. The partition 14 may be of a refractory material composed of fused alumina grains bonded together with an aluminous glass at a high firing temperature. The fluidizing gas, which may be air, nitrogen or oxygen (where a chemical change is desired in the coated material) is supplied through a pipe 15 having a valve 16. The coated material may be heated in an oven or subjected to dielectric high frequency heating. The heat may cause the coating to polymerize. With an aqueous liquid, a wetting agent such as dioctyl sodium sulphosuccinate may be added. The liquid may contain a small amount of suspended material which will react or combine with the powdered material on subsequent heating and may be a dilute resin suspension or emulsion in water or an organic solvent. In Example 1, paper wetted with a mixture of 2-ethylhexanediol-1:3 and toluene is dipped in a fluidized bed of powdered plasticized cellulose acetate-butyrate, which adheres to both sides of the paper. The coated paper is dried at 450 DEG F. In Example 2, paper wetted with water is dipped in a fluidized bed of powdered polyethylene of molecular weight 10,000 or 20,000. Corresponding heating temperatures of 450 DEG F. and 500 DEG F. are employed. In Example 3, aluminium rods are dipped in a plasticizer, e.g. Monoplex S-70, and then in a fluidized bed of plasticized cellulose acetatebutyrate. In Example 4, a fibreglass-polyester moulded panel is similarly treated, and in Example 5, aluminium rods wetted with 2-ethylhexanediol-1:3 are similarly treated. In Example 6, a panel as in Example 4 is wetted with 2-ethylhexanediol-1:3 and dipped in a fluidized bed of a powdered composition containing an epoxy resin, dicyandiamide, and a synthetic silica flatting agent. The coated panel is heated at 475 DEG F. In Example 7, aluminium rods, wood, and fibreglass are wetted with 2-ethylhexanediol-1:3 and toluene or with toluene or with water and are coated with a mixture of the powders of Examples 1 and 6. In Example 8, a panel as in Example 4 is wetted with a solution of the epoxy resin of Example 6, a liquid phenolic resin, a polyvinyl butyral resin, and phosphoric acid in a mixture of methyl iso-butyl carbinol, methyl iso-butyl ketone, toluene and xylene and is coated in a fluidized bed either with the powder of Example 6 or with the powder of Example 1. Heating is effected at 450 DEG F.