This invention relates to coating compositions comprising a crosslinking agent containing N-methylol and/or N-methylol ether groups and linear polyesters having free hydroxyl groups and free carboxylic groups made from a cyclo- aliphatic dicarboxylic acid and a mixture of cycloaliphatic and acyclic polyols in which the latter predominate. It relates more particularly to coatings which because of their superior flexibility, hardness, and weatherability are especially useful on architectural siding and on automobiles.
Coatings said to have the somewhat mutually antagonistic properties of a high degree of elasticity and a high degree of hardness, as well as high gloss and resistance to weathering are taught in U.S. Pat. No. 3,668,275. These coatings are made from linear polyesters wherein at least 70 and preferably 80 mole percent of the dihydric alcohol moiety is derived from 1,4-bis-(hydroxymethyl)-cyclohexane and as much as 91 mole percent, preferably at least 50 mole percent, of the dicarboxylic acid moiety is derived from an aromatic or cycloaliphatic dicarboxylic acid. A preference for aromatic acids is shown in the working examples of the polyester and coatings therefrom.
In U.S. Pat. No. 2,901,466, Eastman Kodak Company discloses highly polymeric linear polyesters which because of their surprisingly high melting points are especially advantageous in the formation of fibers and films. Such polyesters are prepared by condensing 1,4-bis-(hydroxymethyl) cyclohexane, also known as 1,4-cyclohexane dimethanol or CHDM, with a hexacarbocyclic dicarboxylic acid. The highest melting polyesters are preferably prepared from a diol composition containing at least 50 mole percent of the CHDM and up to 50 mole percent of another diol and an acid composition containing at least 50 mole percent of a hexacarbocyclic dicarboxylic compound and up to about 50 mole percent of another bifunctional dicarboxylic compound.
State of the art architectural coatings, however, still rely on silicone protected polyester backbones to boost their exterior durability to acceptable levels. Such state of the art coatings, however, are characterized by high cost, poor hardness and poor flexibility.