Experimental elucidation on the mechanism of ultrasonic joining of thin polyethylene films using torsional vibrations

Abstract

To clarify the mechanism of ultrasonic plastic joining, we have conducted the joining experiments using torsional vibrations for thin (0.1 mm) film specimens of three types of polyethylene viz. linear low-density polyethylene (L-LDPE), low-density polyethylene (LDPE) and high-density polyethylene (HDPE). From the experimental results, the following important facts have been found: first, the preprocessing of L-LDPE film by electron beam irradiation significantly increases the joint strength of the film specimens. Secondly, the joint strength of less tractable HDPE film specimens is approximately four times higher than that of LDPE film specimens if they have been joined under the common joining condition. Consequently, we have reached the conclusion that the mechanism of ultrasonic joining of polyethylene films should be attributed to the entanglement of the amorphous molecules or molecular chains in the vicinity of the joining interface with other ones such as the tie molecules connecting the lamella structures in the crystalline region.