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AOC has launched new products to improve the performance and take-up of SMC, including Atryl TCA resin that reduces paint pops, ChromaTek conductive additive for electrostatically painted parts, and UV-resistant material systems for pickup boxes.
“SMC is specified for its lower weight, lower investment costs, rust-free performance, dent-resistance and freedom to design for aesthetics, function and modularity,” says Mike Dettre, Business Manager – Closed Mold. “By fine-tuning SMC technology to make it more competitive, we are helping molders extend these benefits to more car and truck applications.” Substantially Improved Painting
New Atryl TCA (“Tough Class A”) resin addresses the issue of paint pops that may occur when SMC parts are assembled and finished on-line with metal body panels. During part demold, microcracks that can occur on the edges of the parts provide sites for paint solvents to collect. When the part is exposed to OEM paint and e-coat oven temperatures, the solvents vaporize causing occasional pops on the painted edges of the part.
To address this issue, the new Atryl TCA resin combines the Atryl finish with a toughness that significantly resists microcracking. Atryl TCA resists microcracking during demold and retains its crack resistant characteristics after molding. “Laboratory test results with Atryl TCA resin show at least a 90 percent reduction in the formation of paint pops,” says Dettre. “Similar – and in some cases, even greater – reductions are being recorded on the OEM ‘C/1000’ charts that measure the number of defects per thousand production parts.” The resin is debuting in the SMC Explorer Sport Trac fenders, Ranger hood and various Thunderbird and Navigator body panels that The Budd Company – Plastics Division supplies to Ford Motor Company.
New ChromaTek conductive additive technology saves time and money in the production of SMC parts that are sent through OEM electrostatic painting operations. Electrostatic painting significantly reduces the material cost and solvent emissions associated with overspray. During the technique, finely atomized paint particles are given a negative charge. In an electrostatic field, the negatively charged particles are attracted to a grounded conductive part.
Because SMC is an electrical insulator, most molders apply an in-mold or post-mold conductive coating to get SMC parts to attract the negatively charged particles. Conductive grades of a recently introduced UV-cure sealer for reducing SMC paint pops are especially expensive. New technology from AOC reduces finished costs by providing conductivity in the SMC itself – enabling the use of less costly, non-conductive UV-cure sealer.
AOC optimizes the conductive carbon black dispersion for its inclusion into the overall SMC system. The viscosity of the engineered formulation is low enough to meet processing requirements, and the finished part’s conductivity is high enough for effective electrostatic painting. End-use mechanical properties and Class A surface appearance are unaffected.
The Chroma-Tek conductive additive can be added as a separate dispersion package or as part of an SMC B-side that includes thickener and other ingredients. The new conductive technology is currently being evaluated on the SMC rear fenders that Meridian Automotive Systems molds for the Ford F-150 Super Crew pickup truck.
Also new from AOC is a developmental material system that gives SMC exterior parts excellent resistance to ultraviolet degradation. In accelerated weathering and road tests, untreated, out-of-the-mold SMC demonstrates the same resistance to surface degradation and fiber blooming as SMC that is treated with a protective coating in a post-mold step.
By eliminating the need for an add-on coating, the UV-resistant SMC reduces the installed cost of exterior applications that are not painted in the vehicle’s primary body color. While UV-resistant SMC is more expensive than standard SMC, the new technology eliminates the need for a paint line at new molding facilities that are commonly being located in proximity to OEM assembly plants. The initial application for the new SMC is expected to be a pickup box, set to go into production around the mid-2000 time frame. Reinventing Composites
“Our new pop-resistant, conductive and UV-resistant technologies have automotive engineers looking at SMC in an entirely different way,” Dettre comments.
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