Thermosetting powder compositions based on polyesters and acrylic copolymers

摘要

Powdered thermosetting compositions including (a) a specific polyester containing carboxyl end groups and (b) an acrylic copolymer containing glycidyl groups. The polyester (a) containing carboxyl end groups has an acid value of 15 to 70 mg of KOH/g and is necessarily prepared in two stages. In the first stage a polyester containing hydroxyl end groups is prepared from at least one polycarboxylic acid other than 1,4-cyclohexanedicarboxylic acid and from at least one aliphatic or cycloaliphatic polyol and, in the second stage, the polyester containing hydroxyl end groups thus obtained is esterified with 1,4-cyclohexanedicarboxylic acid alone. Moreover, the composition of the polyester (a) is highly specific: it contains at least 75 mol% of terephthalic acid, at least 10 mol% of 1,4-cyclohexanedicarboxylic acid and not more than 14 mol% of at least one other aromatic and/or aliphatic and/or cycloaliphatic polycarboxylic acid, relative to the total of the carboxylic acids forming part of its composition. The powdered thermosetting compositions obtained from polyester (a) and from the acrylic copolymer (b) are particularly useful for the preparation of powdered paints and varnishes. They yield coatings exhibiting high gloss, excellent mechanical properties and, at the same time, good weathering resistance.