Reinforced plastic moldings, finishing

Reinforced plastics may also include fillers (qv), which are inexpensive materials such as calcium carbonate used to displace resin and reduce cost curing agents (catalysts), promoters, inhibitors, and accelerators, which affect thermosetting resin cure colorants release agents (qv) to facilitate removal from the mold and other additives which can impart a wide variety of properties to the finished part, such as fire resistance, electrical conductivity, static dissipation, and ultraviolet resistance. 

This is an extension of the cold forming process. It uses thermoformed B-stage thermoset reinforced plastic (RP) skin to improve surface and other characteristics to a cold molded thermoplastic. The mold is closed and the fast, room temperature curing RP plastic system hardens. The finished product has the smooth TP-formed sheet. 

Earlier attempts—in the 1970s—to make cellulose-filled thermoplastic compositions had identified a serious obstacle. It became recognized that fillers, particularly cellulose fibers, do not disperse easily throughout the plastic formulations during compounding and molding. Accordingly, the finished products typically do not exhibit the desirable physical characteristics ordinarily associated with fiber-reinforced plastic composites. This problem has been dealt with in a number of patents. 

Most resins that are processed require some type of fillers and/or reinforcements in order to function. Typical fillers and reinforcements are listed in Table 6-1, which shows the properties they influence. (See Chapter 7 for details on reinforced plastics.) Basically fillers and pigments are added in molding resins to reduce shrinkage, minimize crazing, lower the material cost, impart color or opacity, improve the surface finish, and so on. The most commonly used fillers are calcium carbonates, diatomaceous earths, and clays. The excessive use of fillers should be avoided, as the fluidity of the resin can be reduced to the point where it is difficult to process. 

Many plastic products are decorated to make them multi-colored, add distinctive logos, or allow them to imitate wood, metal and other materials. Some plastic products are painted since their as-molded appearance is not satisfactory, as may be the case with reinforced, filled or foamed plastics. Painting or coating is also for product protection. The following section will discuss some of the secondary operations frequently used with plastics. Since plastics vary widely in their ability to be machined and to accept finishes,... 

This moldable material primarily consists of TS polyester resin, glass fiber reinforcement, and filler. Additional ingredients, such as low-profile additives, cure initiators, thickeners, and mold-release agents are used to enhance the performance or processing of the material. As with any material, such as metallics and plastics, SMC can be formulated in-house or by compounders to meet performance requirements of a particular application such as tensile properties or Class A surface finish. Varying the type and percentage of the composition will result in variations in mechanical properties and processability. 

---