High solids, high heat resistant polyester resins and coating compositions containing the same

#During recent years there has been substantial impact on industrial finishing brought about by the environmental movement. Legislation and stringent regulations have been enacted limiting the amounts and kinds of volatile organic liquids that can be emitted during industrial finishing operations and curing of coatings. As a means of meeting these new strict standards, there has been considerable investigation into the development of polyester resins which can be formulated into high solids coatings and paints. It is to the production of such high solids polyester resins, coatings and paints that the present invention is directed.

#The present invention relates to high solids, high heat resistant polyester resins and coating compositions and paints produced therefrom displaying excellent application properties. The polyester resins of the present invention can be prepared by combining specific types of multifunctional monomers in specific proportions with low levels of monofunctional carboxylic acids. The multifunctional monomers and monofunctional carboxylic acid are, per se, known in the art. They are described, for example, in U.S. Pat. No. 3,714,090 to Edward A. Lasher, issued Jan. 30, 1973, and the disclosure of that patent is incorporated herein by reference. The polyester resin of this invention are produced by heating a reaction mixture comprising (a) a fatty acid, (b) a polyol moiety consisting of both a triol and a diol and (c) a polycarboxylic acid moiety consisting of both an aliphatic and an aromatic polycarboxylic acid to a temperature and for a sufficient time to esterify the reactants. It has been found that in order to produce a polyester resin which can be formulated into a high solids coating or paint, the reactants as herein described must be employed in the following amounts:

#(a) a saturated fatty acid having from 8 to 18 carbon atoms in an amount between about 3 and about 8 percent;

#The invention is illustrated by the following non-limiting example.

#1. A five-liter round bottom flask was charged with 969.3 g of neopentyl glycol, 457.3 g of trimethylolpropane, 457.3 g of adipic acid and 152.3 g of lauric acid. It was heated to 140.degree. C. under nitrogen at which time 1164.2 g of phthalic anhydride and 3.2 g of dibutyltin oxide were added. The reaction vessel contents were then heated to 160.degree. C., where distillation of water began. Removal of water was continued until a temperature of 225.degree. C. was attained, and this temperature was maintained until an acid number of 10.1 was achieved. The reaction product was the reduced to 74.4% non-volatiles with Butyl Cellosolve to afford a material with a Gardner-Holt viscosity of Z4-, an acid number of 8.2, a hydroxyl number of 120, a weight per gallon of 9.14, and a Gardner color of 1.

#2. Paint was made from the resin solution from Item 1 by combining it with 11% of hexamethoxymethyl melamine crosslinker on resin solids, pigmenting it with Ti-Pure R902 TiO.sub.2 pigment at a 1/1 pigment/resin solids ratio and reducing it to 75.6% non-volatile material with methyl isobutylketone. It was catalyzed with 0.6% of a 20% para toluene sulfonic acid solution in isopropyl alcohol based on the resin solids. This paint was coated on 20 mil cold rolled steel at 0.9 mils dry film thickness and baked at 177.degree. C. for 15 minutes. The baked paint film had a 90 gloss, a B-HB pencil hardness, and showed only slight cracking on a 120 in-lb. reverse impact. When rebaked at 233.degree. C. for 30 minutes, the coating showed only slight color change (.DELTA.E=2.7) and loss of gloss (90 to 81).