Effects of Introduction of Siloxane Segments on Single Lap Shear Strength of Thermoplastic Polyimides

Abstract

In recent years, several kinds of adhesive films have been developed and applied in aerospace and electronic industries. Processability at moderate conditions, high initial lap shear strength, durability under high humidity and high temperature conditions are major requirement in their applications. Recently, the polyimide adhesives have been also applied in microelectronics and printed wiring boards industries in Japan. However, they ought to be processed at high temperature (>300 °C) and pressure (>20MPa) due to the low fluidity. In this work, the relationship between structure and single lap shear bond strength of various polyimides were studied for developing the polyimides suited as film-adhesives with good processability and adhesive strength. It was found that the polyimides derived from 4, 4'-carbonyldiphthalic anhydride (CDPA) and bis [4- (3-aminophenoxy) phenyl] sulfone (BAPSM) exhibit excellent lap shear strength at room temperature. In addition, various kinds of polysiloxane-block-copolyimides were synthesized and examined as film-adhesives to study the effects of polysiloxane incorporation into aromatic polyimides on the initial lap shear strength. The all of copolyimides containing 10 wt% of polysiloxane were found to have excellent lap shear strength, despite the difference in aromatic components. Their adhesive durability under a highly humid condition (25 °C, 90%RH) was also improved mainly due to their lower moisture sorption and lower moisture permeability. However, further incorporation of polysiloxane into polymer backbone gradually lowered the initial lap shear strength and the durability.