Investigation of the control and applicability of surface energy by plasma surface activation on automobile bumper paint lines

Higher utilisation of low-density materials such as polymers is a pre-requisite for the lightweight vehicle of the future to achieve the forthcoming strict legislation on emissions and recyclability. Of the commodity polymers polypropylene (PP) is by far the most attractive for the automotive bumpers, since not only does it fulfil these requirements but it is inexpensive. A major problem is that PP has a non-polar surface chemistry which means the wetting characteristics of components made from this material are poor. Ultimately, this will result in poor adhesion of paints, coatings or adhesive bonding products. This problem has been overcome in the majority of instances by treating the surface of the substrate in order to alter the surface chemistry. Plasma treatment is an alternativ technique to flaming surface treatment that can be used to modify the surface properties of polymers without also altering bulk properties that affect their function, since the depth of modification is typically limited to the first few nanometers of the surface. Environment friendly and economical plasma treatments are known to improve wettability, induce cross-linking and chemical functionalization of the surface and cause surface etching and ablation. The type of surface modification generated by a plasma treatment is strongly dependent on the choice of reactive gas and treatment conditions (plasma power, plasma gas flow rates, application angle, distance between plasma torch and surface, holding time). This thesis has investigated the effect of an air plasma pre-treatment technique on the surface chemistry and bond integrity of a bumper paints and primers. Optimisation of the pre-treatment was achieved by coupon testing and then transferred to full scale automotive bumper testing. Plasma treated bumpers were then subjected to standard automotive weatherability testing. In this thesis we investigated the plasma surface activation in order to improve the surface energy and appliciability on the bumper paint production lines. At the end of the work, high quality, environmetally friendly plasma openair surface activation method will be adapted on the real production line. .