The compression molding process is the oldest and infinitely dynamic molding method in the production of composite materials. It is a method in which a certain amount of premix or prepreg is added to a metal pair mold and then heated and pressurized to solidify and form. The raw materials it needs include resin, reinforcing materials, and auxiliary materials.
(1) Synthetic resin
The molding compound used for composite molding products requires the synthetic resin to have:
① It has good wettability to the reinforced material, so as to form a good bond at the interface between the synthetic resin and the reinforced material;
②With proper viscosity and good fluidity, it can evenly fill the entire cavity with the reinforcing material under the pressing conditions;
③Appropriate curing speed under pressing conditions, no by-products or few by-products during the curing process, and small volume shrinkage;
④It can meet the specific performance requirements of molded products. According to the above material selection requirements, the commonly used synthetic resins are: unsaturated polyester resin, epoxy resin, phenolic resin, vinyl resin, furan resin, silicone resin, polybutadiene resin, allyl ester, melamine resin, Polyimide resin, etc. In order to achieve specific performance indicators for molded products, after selecting resin varieties and grades, corresponding auxiliary materials, fillers and pigments should also be selected.
(2) Reinforced materials
The commonly used reinforcement materials in molded materials mainly include glass fiber open yarn, untwisted roving, twisted roving, continuous glass fiber bundle, glass fiber cloth, glass fiber mat, etc. There are also a few special products that use asbestos felt, asbestos fabric (cloth) and Asbestos paper, high silica fiber, carbon fiber, organic fiber (such as aramid fiber, nylon fiber, etc.) and natural fiber (such as linen, cotton, scouring cloth, non-cooking cloth, etc.) and other varieties. Sometimes two or more fiber blends are used as reinforcing materials.
(3) Supplementary materials
It generally includes auxiliary materials such as curing agent (initiator), accelerator, diluent, surface treatment agent, low shrinkage additive, mold release agent, colorant (pigment) and filler.