Plastics Engineering - May 2014 - (Page 34)

" A "Game Changing" C18 Diacid for the Plastics Industry? ment with better elasticity at low temperatures, better hydrolytic stability (due to the lower ester content), and lower moisture pick-up in high-humidity environments such as automotive. Although a number of different resin chemistries are used for powder coatings, glycidyl methacrylate acrylic (gMA) powder coatings are known for their high gloss, durability, and abrasion resistance. they are, therefore, frequently the resin systems of choice for high-performance applications such as aluminum wheels and automotive clear coats. the c18 diacid recently has been incorporated as a crosslinker in gMA powder coatings.9 gMA resins are typically crosslinked with diacids such as dodecanedioic acid. the c12 diacid is added into the formulation, micronized into particles, sprayed and thermally cured to form a hard, glossy surface. the resulting coatings have excellent solvent resistance to common organic solvents such as MEK, good weather resistance, high gloss and excellent adhesion to metals. As a result, these materials are suitable for many high-performance outdoor applications such as automotive clear coats, coatings for aluminum wheels and outdoor furniture. A disadvantage of gMA resins is that they can be brittle due to the high crosslink density. Inherent c18 diacid has the potential to improve flexibility and impact resistance to powder coatings due to the longer, more elastic c18 methylene chain. c18 diacid has a melting point of 124°c, compared to 128°c for c12 diacid, and therefore can be dropped into existing production lines with virtually no process changes. Figure 4: Impact resistance of GMA powder coatings (courtesy of Szuping Lu9) 34 ________ High-performance polymers, used in durable goods, have had limited options for using renewable feedstocks, with castor oil being the most significant " Figure 4 shows a chart of the impact resistance9 of powder coatings crosslinked with c18 diacid (added in stoichiometric amounts) compared to the same resins crosslinked with c12 diacid. For both types of gMA resin formulations (1 and 2), the systems crosslinked with c18 have twice the impact resistance of systems crosslinked with c12. Furthermore, the formulations with c18 diacid, when coated on metal test panels, show high gloss, durability, solvent resistance and good adhesion to the panels. these attributes make them attractive candidates for applications requiring higher impact and flexibility than can be obtained from c12 diacid. condensation polymers based on c18 diacid are also expected to have much lower moisture pickup than shorter chain diacids. When c18 diacid is incorporated into polar polymers-such as polyamides, polyesters and polyurethanes-the resulting polymers are expected to have high-temperature performance in high-humidity environments and exhibit better hydrolytic stability. this set of features is critical in under-the-hood automotive applications such as air intake manifolds, tanks for power steering fluids, coolant pumps, electronic housings, connectors and fuel lines. Other applications requiring high-humidity performance include sporting goods (e.g., roller wheels, ski boots, bicycle tires, horseshoes, and athletic shoes), power-tool housings, mobile-phone housings, gears, sprockets, automotive panels, bumpers, and airbags. | PlAStIcS EngInEERIng | MAY 2014 | www.4spe.org | www.plasticsengineering.org http://www.4spe.org http://www.plasticsengineering.org

Plastics Engineering - May 2014

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