Viscosity Change of an Epoxy Compound for Low Pressure Transfer Molding by Means of Rheological Data Analyzing System

For quick and accurate evaluation of rheological properties of thermosets, an automatic data measuring and analyzing apparatus consisting of a transfer molding press, test molds, transducers and data processing and computing units has been developed. Values such as pressure drop, flow rate, flow length and apparent mean viscosity (ηa) during mold filling process can be calculated at pre-set time intervals up to the period at which the flow stops due to gelation. Characteristics of an epoxy compound for low pressure transfer molding in three kinds of circular channels having equivalent cross-sectional areas to those used for manufacturing were examined under three mold temperatures. For every molding condition, the minimum values of ηa, (ηaM) were observed about halfway through the flowing time. Apparent gel time (ta), definded as the time of flow stopping, was obtained precisely by utilizing pressure profiles. Values of both ηaM and ta were found to decrease with decreasing of channel diameter and with increasing of mold temperature. The developed apparatus can provide more useful data for predicting moldability of thermosets in manufacturing processes as compared with that from conventional methods such as EMMI spiral flow test.