Reactive hyperbranched polymers for powder coatings

A powder coating composition comprising an intimate blend in a finely divided form of:

• (a) from about 60 to 90 percent by weight of a polymeric binder selected from the group consisting of an epoxy, a polyester, blocked urethane resin, or an acrylic resin;
• (b) from about 10 to 40 percent by weight of a hyperbranched polyester having reactive groups selected from the group consisting of hydroxy, carboxy, epoxy, blocked isocyanates, acid anhydrides, dicyanadiamide, and mixtures thereof, wherein said reactive groups are capable of reacting with the reactive functionality on said polymeric binder (a);
• and
• (c) from about 0 to 2 percent by weight of a degasser;
• wherein said hyperbranched polyester has a number average molecular weight of at least 1200 and a glass transition temperature (T.sub.g) of from about 35.degree. C. to about 150.degree. C.

A process for the production of powder coating compositions comprising the steps of:

• (a) subjecting one or more of self condensable monomers to polycondensation reaction conditions for a sufficient period of time and under suitable conditions of temperature and pressure, and optionally adding one or more of chain linkers and reactive end-capping moieties to said self condensable monomers at the end of said polycondensation reaction to form the corresponding hyperbranched polymer;
• (b) melt blending suitable amounts of said hyperbranched polymer to act either as a polymeric co-reactant, or as a flow and leveling agent, or as an adhesion promotor in the presence of:
• (i) an epoxy, a polyester, a blocked urethane resin, or an acrylic resin;
• (ii) optionally a co-reactant capable of reacting with said polyester or acrylic resin;
• (iii) optionally one or more of additional ingredients selected from the group consisting of flow and leveling agents, degassers, catalysts, fillers, coloring agents, and biocides;
• for a sufficient period of time and under suitable conditions of temperature and pressure to form the corresponding powder coating composition in the form of flakes;
• and
• (c) grinding and sieving of said flakes to form the powder coating compositions.

A process for the production of powder coating compositions comprising the steps of:

• (a) subjecting .alpha.,.alpha.-bis-(hydroxymethyl)-propionic acid to polycondensation reaction conditions in an aqueous dispersion in the presence of methanesulfonic acid as a catalyst for a period of about 15 minutes to about 8 hours at a temperature of about 120.degree. C. to about 220.degree. C. and at graded pressure conditions of initial 1 atmosphere to subatmospheric pressure of about 1 mbar to about 0.1 mbar at the end of the polycondensation reaction to form the corresponding hyperbranched polyester;
• (b) melt blending said hyperbranched polyester in the presence of:
• (i) a polyester;
• (ii) .epsilon.-caprolactam blocked isophorone isocyanate as the crosslinker;
• and
• (iii) optionally benzoin as the degasser;
• for a period of about 5 minutes to about 10 minutes at a temperature of about 50.degree. C. to about 180.degree. C. and at autogenic pressure to form the corresponding powder coating composition in the form of flakes;
• and
• (c) grinding and sieving of said flakes to form the powder coating compositions having a particle distribution of about 10 to 100 microns;
• wherein said hyperbranched polyester is used either as a flow and leveling agent in the amounts of from about 0.5 to 5 percent by weight or as a crosslinking resin in the amounts of from about 10 to 40 percent by weight based on the total weight of the powder coating composition.