Study on Anti-tracking Properties of Unsaturated Polyester Resin 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 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 423K, 453K, 473K, 523K respectively. The anti-tracking properties of UP-SMC were developed when Al(OH)3  and diisocyanate compounds were filled in UP-SMC. The microstructure of UP-SMC struck by electric arc was observed by means of SEM (Scanning Electron Microscopy). The results show that UP-SMC samples with no anti-tracking modification have some part of ablation and charring while the modified sample are with the low electric rot. 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 will be widely used on electrical parts and arc-deflecting cover of AC switch etc
Thickening behaviour and shrinkage control of low profile unsaturated polyester resins
The rheological and morphological changes of a low shrink unsaturated polyester resin during thickening and curing were investigated. The behaviour of low profile additive (LPA) could be modified by adding a thermo-breakable functional group to its molecule. The thickening reaction of the modified LPA with MDI was much faster than that of LPA with MgO, and the viscosity was stable for 3 months. Because of the thermo-decomposition of the thermo-breakable functional group, the thickened mixture of LPA-M with MDI lost its viscosity greatly at elevated temperatures. The unthickened LPA and thickened LPA-M/MDI samples showed clear phase separation, large internal surface areas and good shrinkage control. The thickened LPA/MDI samples showed little phase separation, very small internal surface area, and poor shrinkage control. The thickened LPA/MgO samples showed some phase separation and good shrinkage control at high moulding temperature. At low moulding temperatures, both phase separation and shrinkage control were poor.
Mechanism of low profile behavior in unsaturated polyester systems
The mechanism by which low profile character is achieved in unsaturated polyester systems has been investigated. Using techniques of microscopy, data are developed that support a model in which micro stress cracking is induced to relieve stress promoted by polymerization shrinkage. Thus the strain is accommodated internally in a molded part, rather than through macroscopic shrinkage of the article.