| Epoxy sheet molding compound(ESMC) is a kind of new compressed material,which is developed from unsaturated polyester sheet molding compound(SMC).It can be used to produce high-strength,high-corrosion-resistance and high-insulation parts.Inefficient thickening system and high-temperature and slow curing velocity of epoxy resin are key factors to restrict the development of ESMC.The molding process of ESMC needs epoxy resin have low viscosity to immerse fiber and have special group to be chemically thickened and have short curing time.So,it is critical to study the thickening system,curing system and fluid rheology system of ESMC.The molded ESMC can widen the application area of compression molding parts.A kind of epoxy resin(EP-LM) with low-viscosity and low molecular weight was synthesized by means of "two-step synthesis process" in this article.And it could be chemically thickened.Gaussian03 software based on quantum chemistry theory was applied to analyze the synthesis mechanism of EP-LM by the method of DFT on the basis of valence bond theory and molecular orbital theory.The reaction nature of EP-LM on the microscopic level was carefully revealed,which provided an evidence for synthesizing epoxy resin.By controlling the reaction temperature and the weight content of reactors,epoxy resin could be thickened by MgO andα-methyl acrylic acid compound and diisocyanate prepolymers.The thickening mechanism was studied by fourier transform infrared spectroscopy and differential scanning calorimetry.In the system of MgO andα-methyl acrylic acid compound,MgO reacted with the terminated carboxyl ofα-methyl acrylic acid to yied a kind of salt and released a great amout of heat.Then the terminated carboxyl ofα-methyl acrylic acid reacted with epoxy resin to yield a kind of ester under the condition of existing heat and MgO catalyst.In the system of diisocyanate prepolymers,when the temperature was below 50℃,the hydroxyl group of EP-LM reacted with isocyanate groups to yield carbamate;when the temperature was beyond 90℃,diisocyanate prepolymers would self-polymerize;and when the temperature was beyond 210℃,the epoxy group of epoxy resin would react with isocyanate groups to yield oxazolidine- menthanone.As the reaction continued,the network structure formed and the viscosity of the system increased.In this study,a kind of microcapsule curing agent(5-500u) was prepared by spraying hot curing agent and PEG-6000 into 0℃methyl methacrylate solution.Epoxy resin with this kind of microcapsule curing agent would not be cured at room temperature and would be quickly cured at high temperature.The isothermal kinetic model and the temperature-rising kinetic model were established by testing DSC curves of the curing system,and then the curing process including gel temperature(Tgel),curing temperature(Tcure) and post-treating temperature(Ttreat) was obtained.The relationship between the initial curing temperature and the conversion rate was calculated on the basis of temperature-rising kinetic model,and the special temperature spots including the initial curing temperature(T0),the peak temperature (Tp) and the finishing temperature(Tf) of the whole curing process were predicted.On the base of thickening system and curing system,the process of manufacturing ESMC sheets and molding ESMC parts were determined.The process of producing ESMC sheets was divided into the following four steps:①preparing and spraying of resin paste;②cutting and dropping of glass fiber;③impregnating of chopped glass fiber and ESMC sheets rolling-up;④thickening and storing of ESMC sheets.And the optimum molding parameters were list as follows:molding temperature 150℃,dwell time 15s,clamping time 15s and pressure holding time 30min.The rheology property,fiber distribution and fiber orientation of ESMC in hot die were systematically researched.The critical factors affecting the theology properties of ESMC included the weight content and length of chopped fiber,the weight content and diameter of filler,molding temperature,pressure keeping time,the feeding area and the velocity of closing mold and so on.At the same time,on the basis of Hele-shaw flowing model and Slip-extrusion flowing model,a new mathematic flowing model for ESMC in hot die was established.It provided an evidence for studying the rheology properties of ESMC.At last,the structure and properties of ESMC were studied in this article.Results showed that the flexural strength of ESMC parts was different at different direction of fiber orientation.When the weight content of glass fiber was 30%,the length of chopped fiber was 24 mm,the weight content of filler was 150%,the diameter of filler was 500eyes,the molding temperature was 150℃,the dwell time was 15s,the clamping time was 15s and the pressure holding time was 30min,the mechanical properties of ESMC parts was optimum.And the weight content and length of chopped fiber,the weight content and diameter of filler had great effect on volume resistance,dielectric properties,voltaic arc property and leakage tracking resistance of ESMC.
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