Q: We are a manufacturer of polyester resins for powder coatings. Our customer (a powder coating formulator/producer) is having difficulty in achieving consistent high gloss and impact resistance in their powder coatings. Can you help us determine the root cause of this problem?
A: One basic question for you: How is the solvent resistance of these coatings? Chemical resistance is a good indication of cure, and it will be poor if the stoichiometry of the binder is incorrect. Poor cure as evidenced by poor solvent resistance will produce poor impact resistance.
If the stoichiometry is theoretically correct and the impact resistance remains poor, I would investigate the molecular weight distribution of the polyester resin. If it is too broad, the fact that there are too many polymeric species could account for poor cure due to variable functionality. Broad molecular weight distribution can also account for poor gloss.