COOLING RATE-INDUCED GLASS-ADHESION VARIATIONS USING CRYSTALLIZING HOT-MELT ADHESIVES

Polychlorotrifluoroethylene (PCTFE) and PCTFE copolymeric films are be i ng used in the electronic packaging industry as insulating dielectri c layers between microwave circuits. Because these films are semicryst alline and, in this application, are being used as hot-melt adhesives, the cooling rate is an important processing variable, affecting the c rystallinity of the PCTFE films which, in turn, affect many properties including dielectric characteristics and mechanical properties. In th is study, the crystallinity of PCTFE and PCTFE copolymeric films as a function of cooling rate was characterized by wide-angle X-ray scatter ing. As expected, the degree of crystallinity decreased as the cooling rate increased. Analysis of mechanical properties as a function of co oling rate by tensile testing showed that the mechanical behaviour of the films became more ductile with faster cooling rates. Because the c ooling rate has also been shown to significantly affect adhesion in pr evious studies, the effect of cooling rate on the bond strength betwee n PCTFE and a glass substrate was analysed. Peel testing was performed on PCTFE/glass laminates revealing that the adhesive bond strength in creased as the cooling rate was increased. Thus, optimum adhesion is a chieved with faster cooling rates. This was attributed to the higher f racture energy and greater ductility of the adhesive.