Heat Resistance And Thermal Conductivity Behavior Of Modified Unsaturated Polyester Insulating Varnish

The shortcomings of unsaturated polyester in the heat-resistant and thermal conductive properties restrict its further application. In order to obtain unsaturated polyester with higher heat-resistance and themal conductivity, several methods were used to modify it in this dissertation.First of all, the epoxy was used to modify unsaturated polyester. And the effects of functional styrene and vinyl toluene solvents, divinyl benzene (DVB) cross-linking agent on the performance of insulating varnish were investigated. The experimental results showed that the unsaturated polyester possesses better heat-resistance when the vinyl toluene is used as solvent. A small amount of DVB can improve obviously the heat-resistance of the insulating varnish. The mechanical properties of insulating varnish increases firstly with increasing the DVB content. However, as the DVB content arrives at a particular amount, the mechanical properties become lower. The thermal conductivity of the insulating varnish has a trend of monotonic increasing with the DVB content, while its dielectric loss value exhibits the opposite variation regularity. Secondly, the effects of two types of polyhedral oligomeric silsesquioxanes (POSS) derivatives contenting vinyl or amino-group on the mechanical, electrical and heat-resistant properties of insulating varnish were studied. Both the adhesive strength and electrical strength of unsaturated polyester insulating varnish decrease slightly after an increase with increasing POSS content. And the heat-resistance and thermal conductivity of insulating varnish are enhanced by POSS derivatives.At last, the unsaturated polyester insulating varnishes were prepared by adding thermal conductive fillers, such as alumina (Al2O3), aluminum nitride (AlN) and silica (SiO2), in polyester matrix. The effects of the kinds, content, and dispersion technology of fillers on the dispersion structure, thermal conductivity, electrical insulation and heat stability of insulating varnish were researched by means of thermal conductivity tester, high resistance meter,Digital Bridge, TGA, SEM, etc. The results reveal that the best dispersion and anti-sedimentation properties of fillers in unsaturated polyester can be obtained via sand mill dispersing technology. The fillers have little influence on the electrical properties of unsaturated polyester. But, they all improve the thermal conductivity of polyester insulating varnish. Especially, the enhancement is most notable when the nano-sized AlN/Al2O3 mixed fillers are employed.