GB1485368A - Coating metal surfaces with siloxane-polyester resins - Google Patents

Abstract

1485368 Coating metal surfaces with siloxanepolyester resins DOW CORNING Ltd 20 Nov 1974 [24 Nov 1973] 54639/73 Headings C3T and C3R A process for coating a metal surface, e.g. of Al or steel, comprises applying thereto a composition comprising a siloxane-polyester resin which has been prepared by reacting (A) from 20-80% wt. of an organosiloxane having the general formula wherein R represents a methyl or ethyl radical, R<SP>1</SP> represents a phenyl or C 2 -C 12 alkyl radical, R<SP>11</SP> represents a methyl or phenyl radical, x is 2-6, y is 1-6 and x+y is 4-8, and (B) from 80-20% wt. of a polyester having on average at least one free hydroxyl group per molecule and prepared from (i) at least one aromatic dicarboxylic acid selected from phthalic, isophthalic and terephthalic acids or an anhydride thereof, and (ii) at least one di- or poly-hydric alcohol having from 2-6 carbon atoms, the percentages being based on the total weight of (A) and (B), and thereafter curing the composition. The polyester may also include less than 20% wt. of a saturated aliphatic dicarboxylic acid, e.g. adipic acid, based on the weight of the polyester. The reaction of (A) and (B) may be carried out in the presence of an organic solvent and a catalyst, e.g. a titanium or zirconium alkoxide. The resulting resins can be used either alone or with various additives, e.g. driers, solvents or pigments. In the example a polyester-polysiloxane resin is prepared by reacting a polysiloxane prepared by the hydrolysis/alcoholysis reaction of a mixture of dimethyldichlorosilane and methylphenyldichlorisilane with water and methyl alcohol followed by condensation of the hydrolysate, with a trimethylolpropane/isophthalic acid polyester in the presence of tetraisopropyl titanate as catalyst and "Cellosolve acetate" (Registered Trade Mark). The resulting resin solution is cured to a thin flexible film on an aluminium panel by heating.