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An OEM-led research collaboration is developing new interrelated technologies to allow SMC parts to be powder-primed whilst maintaining a Class A surface.
Key technology participants include General Motors Research and Development, Tier One supplier Meridian Automotive Systems, resin supplier AOC and coatings supplier Red Spot Paint & Varnish.
When powder-primed, conventional SMC develops a leather-like surface appearance during the powder primer high-temperature cure cycle. Jeff Robbins, Director R&D for SMC supplier Meridian Automotive Systems, says, “GM research concluded that the failure mechanism was a combination of air and moisture that is released when a common low profile additive (LPA) is used. After defining the problem and determining the thresholds, Hamid Kia of General Motors challenged companies in the automotive supplier value chain to work together toward a synergistic solution.”
To evaluate different SMCs, Meridian Automotive provided tooling and moulding equipment that are used in regular production. Full-size parts moulded with different SMCs were sent to GM assembly plants for standard powder primer application and cure. These production-scale trials validated laboratory data and ensured that the solution could be implemented without changing process or equipment parameters. AOC’s role was to develop a special, low-moisture content SMC formulation, which incorporated new LPAs in a synergistic fashion. The new additives are said to continue to provide the traditional LPA function of contributing to reduced shrinkage and improved surface finish.
“All our new low moisture content SMCs are based on high performance Atryl TCA resins,” points out Ed Kleese, Technical Services Manager for AOC. “SMCs made with Atryl TCA are bringing increased toughness, reduced surface waviness and superior Class A finishes to a host of car and truck applications.”
To achieve even greater surface quality in powder primed parts, Hamid Kia encouraged automotive plastics coating leader Red Spot to develop a new SMC primer. The Red Spot primer is applied by Meridian before SMC parts are shipped to the GM facility. The Red Spot primer is conductive so that the electrostatically-charged solid particles of the OEM powder coating process will be attracted to the SMC part surface.
“Red Spot research led by Dr. Keith Cannon resulted in a conductive powder-capable SMC primer with a unique patent-pending technology,” says Marilyn Bara, New Product Marketing Director for Red Spot. “In essence, the new low-permeability coating technology forms a layer that significantly controls the release of moisture from the SMC into the powder primer. Combining our proprietary primer with low moisture composite takes the surface quality of powder-primed SMC to extraordinary levels.”
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