Novel semi-crystalline polyesters, blends thereof with amorphous polyesters and powder coating compositions based on such blends

摘要

Disclosed are thermosetting, powder coating compositions comprised of blends of certain amorphous polyesters and semi-crystalline polyesters in combination with a blocked polyisocyanate which, when applied to a substrate and heated, provide cross-linked coatings having a combination of desirable properties including good gloss, impact strength and flexibility. The semi-crystalline polyesters have a Tg of less than 50°C, a hydroxyl number of 20 to 100, an inherent viscosity of 0.1 to 0.5, a melting range of 70 to 150°C, a number average molecular weight of 1500 to 10,000 and a heat of fusion (second heating cycle of differential scanning calorimetry) of greater than 5 cal/g-°C and are comprised of:(i) diacid residues comprised of (a) 80 to 98 mole percent terephthalic acid and (b) 2 to 20 mole percent of 1,4-cyclohexanedicarboxylic acid residues, 1,3-cyclohexanedicarboxylic acid residues, adipic acid residues or a mixture thereof; and(ii) glycol residues comprised of at least 50 mole percent of residues having the formula -O-(CH₂)_n-O- wherein n is 4 to 12.