Twincure UV - New Concepts for the Surface Treatment of Glass-Fiber-Reinforced Plastics

Glass fiber reinforced, or composite plastics are attractive alternatives to conventional sheet metals in automobile construction. The common Sheet Molding Compound (SMC) is the main example. It is composed of an unsaturated polyesters with additives, mineral extenders and the glass fibers. The use of this material has fluctuated as the automotive market changes at an increasingly rapid rate. During the 1980's the automotive industry utilized SMC or BMC in a multitude of components and body panels. During the early 90's the industry entered a phase of disillusionment. Surface quality problems, due to unreliable material properties and unstable reproducibility, caused many projects to be abandoned. This change in usage set the stage for a drop in the number of unsaturated polyester resins suppliers for composite applications. In 1988 there were nine manufacturers. Today only five manufacturers remain. DSM has taken over the activities of Bayer and Hills, Reichhold has purchased Jotum, and DSM has set up a joint venture with BASF. The number of semifinished and finished product manufacturers has fallen even more drastically. (1] We are now experiencing a renewed period of SMC awareness, reflected in a number of interesting projects. SMC is seen as viable solution to the manufacturing issues surrounding complex design projects by allowing the consolidation of multiple piece assemblies into one molded piece. SMC 59 demonstrates the structural integrity of steel at weight savings of up to 33%. In addition, SMC reduces the processing and molding costs versus the rapid stamping of steel making it a match for low run vehicles of less than 200,000 units/year. These qualities are certainly the reasons for its widespread use in the commercial transportation sector. In addition, SMC provides the potential of online or inline painting. In the past it was sufficient to supply parts raw or with primer. Increasingly, car body parts have to be supplied in body color. In this case, online painting offers the molder the opportunity to provide a value-added option to the assembly plant.