Barrier coatings for flexible packaging based on hyperbranched resins

Hyperbranched resins have been evaluated for use as barrier coatings. Diffe rent types of modified hydroxy-functional hyperbranched polyester resins we re prepared and partially end-capped with acrylate or methacrylate units. C rystalline end-groups (poly(epsilon -caprolactone) were grafted onto some r esins. The coatings were applied on poly(ethylene terephthalate) and polypr opylene substrates and crosslinked by UV light and their barrier against ox ygen and water vapour determined. The results show that hyperbranched coati ngs give a pronounced improvement in oxygen barrier on both substrates. Exp ressed in terms of oxygen permeability coefficient, the improvement was a f actor of up to 60 times compared to polypropylene and up to 2.2 times compa red to poly(ethylene terephthalate). As for other hydroxy-functional barrie r polymers, the amount of hydroxyl groups in the hyperbranched resins was f ound to play a major role concerning the oxygen barrier, controlling both p erformance and water sensitivity. It was seen that humidity led to a decrea se in barrier at the highest hydroxyl group concentration, whereas the barr ier performance of coatings with lower concentration of hydroxyl groups ins tead improved under humid conditions. It was also found that crystalline en d-groups did not improve the oxygen barrier and that none of the synthesise d resins gave any improvement in water vapour barrier. (C) 2001 Elsevier Sc ience Ltd. All rights reserved.