Study on thickening behavior and dielectric properties of unsaturated polyester SMC

A method of thickening hydroxyl-terminated unsaturated polyester with polyurethane (PU) that comes from the reaction between diisocyanate compounds and polyglycol is introduced, and the thickening mechanism and blending miscibility between unsaturated polyester resin (UPR) and PU are discussed. The effect of PU prepolymer on the anti-arc properties of the sheet molding compounds (SMC) is studied according to the standard of ASTM, the electric strength is tested in the transformer oil under 423 K, 453 K, 473 K, 523 K respectively. The results show that the thickening mechanism is an amino group is formed during the reaction. The compatibility of UPR and PU varies with the amount of PU, mechanical properties of UPR/PU-SMC are excellent when the PU is 36%. The arc breakdown time would increase with the usage of PU. The SMC thickened by PU shows good aging resistance as well as anti-arc properties, it is widely used on electrical parts and arc-deflecting covers of AC switch etc.