The use of mica flakes for reducing internal stress in cured epoxy resin

Abstract

AbstractMica, in the form of flakes of different sizes and size distributions, was mixed with a difunctional epoxy resin to the extent of 10 to 50 parts by weight of the resin. To this resin–filler mixture, a stoichiometric amount of a tetrafunctional curing agent was added. First, a thin a aluminium strip was coated with the mica–resin–amine mixture and was subjected to two curing cycles. Second, sheets were cast from the mixture by subjecting them to the same two cure cycles. The internal stresses that developed in the coated samples, and their relaxation with time, were studied. The dynamic torsional spectra of rectangular bars cut from the sheet were also mapped. The debonding and microcracking, resulting from internal stress, have been shown to result in a significant reduction in internal stress in the mica‐filled samples, particularly in samples containing large mica flakes in which delamination of the mica layers in the flake has also been shown to occur. However, despite this phenomenon, the filled samples were found to have adequate mechanical and electrical properties. © 1994 John Wiley & Sons, Inc.