High-frequency welding of an industrial thermoplastic polyurethane elastomer-coated fabric

Abstract

The high frequency (27.12 MHz) weldability of a thermoplastic polyurethane elastomer coated fabric was investigated after determination of its dielectric properties. It was shown that at 27.12 MHz, maximum heating occurred at 50°C. Subsequent tests were thus carried out at this temperature. Temperature needs to be measured continuously during the welding operation as the integrity of the weld depends on the core temperature. Since conventional methods using probes or adhesive indicator strips are disrupted by high frequency (HF) radiation, the integrity of the weld obtained by HF was compared to that obtained by impulse welding at a given temperature under the same conditions of pressure with the same peeling performance and with the same temperature variation after welding, measured by the i.r. thermometer. The highest peeling forces were found when the welding temperature exceeded that of the melting point (180°C) of the hard segments in the polymer. The interactions occurring during welding were found to depend on the temperature. At temperatures below 180°C, the peeling resistance only derived from entanglements of flexible segments at the interface between the two TPU-coated fabrics. At temperatures of 180°C and above, melting and mixing of hard segments produced total cohesion of the two coated fabrics resulting in an enhanced peeling force.