SMC Raw materials
1. The raw materials of SMC are composed of three categories: synthetic resins, reinforcing materials and auxiliary materials.
(1) Synthetic resin Synthetic resin is unsaturated polyester resin. Different unsaturated resins have a direct impact 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:
①Low viscosity, good wettability to glass fiber;
② It has sufficient reactivity with the thickener to meet the thickening requirements;
③ Rapid curing, short production cycle and high efficiency;
④The cured product has sufficient thermal strength to facilitate the thermal demoulding of the product;
⑤ The cured product has sufficient toughness, and the product does not crack when some deformation occurs;
⑥ lower shrinkage rate.
(2) Reinforcing material The reinforcing 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%.
(3) Auxiliary materials Auxiliary materials include curing agents (initiators), surface treatment agents, thickeners, low shrinkage additives, mold release agents, colorants, fillers and crosslinking agents.
2. Preparation process of SMC
The process flow of SMC production mainly includes resin paste preparation, paste operation, fiber cutting and sedimentation and impregnation, resin thickening and other processes. The process flow chart is as follows:
(1) Preparation of resin paste and paste operation There are two methods for the preparation of resin paste – batch method and continuous method. The intermittent procedure is as follows:
①Pour the unsaturated polyester resin and styrene into the batching kettle and stir evenly;
②Pour the initiator into the batching kettle and mix it with the resin and styrene;
③ Add thickener and release agent under stirring;
④Add fillers and low shrinkage additives under low-speed stirring;
⑤ Stop stirring until the components listed in the formula are dispersed, and let it stand for use. The continuous method is to divide the resin paste in the SMC formula into two parts, that is, the thickener, release agent, part of the filler and styrene as one part, and the other components into another part, which are respectively measured and mixed, and then sent to the SMC unit. In the corresponding storage container set on the top, it is metered by the pipeline metering pump and then enters the static mixer when needed. After mixing evenly, it is transported to the pasting area of the SMC unit, and then coated on the polyethylene film.
(2) Impregnation and compaction The lower bearing film coated with resin paste enters the chopped glass fiber sedimentation chamber under the traction of the unit, and the cut chopped glass fibers are evenly settled on the resin paste. After reaching the required sedimentation amount, With the transmission device, it leaves the sedimentation chamber, and overlaps with the upper carrier film coated with resin paste, and then enters a series of staggered arrays. It is tightly pressed together with the chopped glass fiber, and after many repetitions, the chopped glass fiber is impregnated with resin and the air bubbles in it are driven away to form a dense and uniform continuous SMC sheet.
Post time: Sep-14-2022