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Abstract

Novel powder coating compositions containing reactive hyperbranched polymers are disclosed and claimed. Preferred embodiments include powder coating compositions formed from hyperbranched polyesters having terminal hydroxy, carboxy, epoxy, and isocyanate groups. Preferred hyperbranched polyesters are formed from .alpha.,.alpha.-bis-(hydroxymethyl)-propionic acid, which act either as crosslinkers, adhesion promotors, or flow and leveling agents. A process for the synthesis of powder coating compositions is also disclosed which involves (a) self condensation of one or more of the multifunctional monomers to form the hyperbranched polymer, optionally, in the presence of suitable reactive end-capping moieties which are described herein; (b) melt blending of the hyperbranched polymer with suitable amounts of one or more of polyesters, epoxy resins, blocked urethane resins, or acrylic resins, a crosslinker, and one or more of suitable additional ingredients including degassers or flow and leveling agents, to form a flake; and (c) grinding and sieving of the flake to form the powder coating composition. These compositions exhibit improved flow and curing properties. These compositions can therefore be formed into thin films and can be cured at low temperatures to form smooth surfaces. Additionally, these films are hard and exhibit enhanced impact resistance properties than the conventional polyester resins. Thus, these powder coating compositions find utilities in automotive, packaging, and appliances.

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First Claim