Thin-Disk Test for Adhesion-Bond Strength in Solvent Environments

Abstract

ABSTRACT A number of the popular tests for adhesive strength are difficult to apply to the study of adhesion under solvent environments. Complex applications, in which two different substrate materials need to be bonded and for which the substrates are thin sections, can be particularly difficult to study. The thin-disk test described here uses a thin annular disk of adhesive to bond two dissimilar materials while exposing the bond line to a circulating solvent. The new test was evaluated for a typical inkjet print-head application using surrogates for inkjet water-based inks. The joint is an epoxy adhesive joining a silicon wafer to a thermoplastic part (Rynite®), in which the silicon substrate, the thermoplastic, or the various adhesive interfaces might fail. A conventional lap-shear test was compared with the thin-disk test for samples exposed to four different solvent systems plus water at two different temperatures. Lap-shear test failures occurred mostly in the thermoplastic part, with the exception of two samples exposed to the most aggressive solvents at high temperature. By contrast, thin-disk test failures occurred either in the silicon substrate or in the thermoplastic–adhesive interface. The thin-disk failure strengths at the thermoplastic–adhesive interface correlated with the equilibrium solvent swelling that could occur in the adhesive under the test conditions. This method could be adapted to other mixed-substrate bonding systems and would be particularly appropriate for thin section solids and thin adhesive layers.