Improvement in Molecular-Level Adhesive Strength of PTFE Film Treated by Atmospheric Plasma Combined Processing

Abstract

Atmospheric pressure plasma graft polymerization-treated fluorocarbon plastics are bonded with a metal, to evaluate adhesiveness. In this research, the atmospheric nonthermal plasma graft polymerization technique is used in treating the surface of polytetrafluoroethylene (PTFE) in a dry process, capable of reducing environmental loading. The treated PTFE is joined with the stainless steel plate to perform a peeling test. We examine the peeling strength and the best condition for practical application using peeling strength as an optimization variable. A concrete numerical target is 2 N/mm, which is the standard adhesive strength applicable for industry uses. To conduct the graft polymerization, we use a monomer such as acrylic acid (CH2 = CHCOOH) and target material such as PTFE. Peeling strength is maximized (averaged value of 1.56 N/mm, largest value of 2.0 N/mm) when the temperature of the acrylic acid is 60 °C and the Ar main flow rate is 40 L/min. Influence of plasma torch cover on peeling strength and entrained flow near the torch are investigated to realize the stronger adhesion, and better shape of the cover is determined. Furthermore, by analyzing X-ray photoelectron spectroscopy and scanning electron microscope images, we evaluate the atmospheric pressure plasma graft polymerization process from a different perspective and search for optimal operating conditions of the processing method.