Sheet Molding Compound (SMC) is a type of sheet molding compound made of resin paste impregnated fiber or chopped fiber mat, covered with polyethylene film on both sides, belonging to the scope of prepreg material. It is one of the most widely used molding materials in the world. SMC raw materials
The raw materials of SMC are composed of synthetic resins, reinforcing materials and auxiliary materials.
(1) Synthetic resin: The synthetic resin is an unsaturated polyester resin. Different unsaturated resins have a direct influence on the thickening effect, process characteristics, product performance, shrinkage rate and surface state of the resin paste.
SMC has the following requirements for unsaturated polyester resin: ① low viscosity, good wetting performance for glass fiber; ② sufficient reactivity with thickeners to meet the thickening requirements; ③ fast curing, short production cycle and high efficiency; ④ The cured product has sufficient thermal strength to facilitate the thermal release of the product; ⑤The cured product has sufficient toughness, and the product will not crack when some deformation occurs; ⑥Low shrinkage.
(2) Reinforcement material The reinforcement material is chopped glass fiber roving or raw silk. Among the unsaturated polyester resin molding compounds, the reinforcing material used for SMC is currently only chopped glass fiber mat, while there are many reinforcing materials used for premix, including chopped glass fiber, asbestos fiber, hemp and other various Organic fiber. In SMC, the glass fiber content can be adjusted between 5% and 50%.
Chopped glass fiber roving
(3) Auxiliary materials Auxiliary materials include curing agents (initiators), surface treatment agents, thickeners, low-shrinkage additives, mold release agents, colorants, fillers and crosslinking agents.