Improvement of bonding properties of laser transmibion welded, dibimilar thermoplastics by plasma surface treatment

Abstract

Compared to different welding methods such as ultrasonic welding, laser transmibion welding is a relatively new technology to join thermoplastic parts. The most significant advantages over other methods are the contactleb energy input which can be controlled very precisely and the low mechanical loads on the welded parts. Therefore, laser transmibion welding is used in various areas of application, for example in medical technology or for abembling headlights in the automotive sector. However, there are several challenges in welding dibimilar thermoplastics. This may be due to different melting points on the one hand and different polarities on the other hand. So far these problems are faced with the intermediate layer technique. In this proceb a layer bonding together the two components is placed between the components. This means that an additional step in the production is needed to apply the extra layer. To avoid this additional step, different ways of joining dibimilar thermoplastics are investigated. In this regard, the improvement in the weldability of the dibimilar thermoplastics polyamide 6 (PA 6) and polypropylene (PP) by means of plasma surface modification and contour welding is examined. To evaluate the influence of the plasma surface modification proceb on the subsequent welding proceb of the two dibimilar materials, the treatment time as well as the storage time between treatment and welding are varied. The treatment time in pulsed micro wave excited oxygen plasmas with an electron density of about 1x1017 m-3 is varied from 0.5 s to 120 s and the time between treatment and welding is varied from a few minutes up to a week. As reference, parts being made of the same polymer (PP and PA 6) are welded and tested. For the evaluation of the results of the welding experiments, short-Time tensile tests are used to determine the bond strength. Without plasma treatment the described combination of PA 6/PP cannot be welded with sufficient bond strength to withstand handling of the samples. In contrast, the tear-out force of previously plasma treated samples can be determined to up to 1400 N. The achieved bond strengths are higher than of untreated PP/PP welded parts (about 1000 N).