These are used to mold parts with smooth surfaces that can be painted without the need for prior sanding. BMC is supplied in bulk form or as extruded rope for ease of handling. They are supplied in rolls, sandwiched between polyethylene carrier films. Uniformity of SMC materials is closely controlled, making these materials especially suited for automated production. For more details, see the chapter on thermoset composites.
Polyester resins are also available for use as coatings for curing by ultraviolet radiation.
Although some styrene may be lost upon exposure to UV radiation, the amount is small. Properties of thermoset polyesters are so dependent on type, compounding, and processing method that a complete listing covering all combinations would be almost impossible. Outdoor weatherability of polyester resins specifically compounded for such service is good. Thermal, electrical, and environmental properties are generally good and can be individually improved by formulation. They have an excellent balance of properties and processing characteristics and, because they crystallize rapidly and flow readily, mold cycles are short.