ABSTRACT
Abstract Flock coating is a widely used process to create a textile-like texture on substrates of various shapes and materials. In the process, flock fibers — short fibers typically 1-3 mm long — are oriented and accelerated towards the substrate by means of an electric field. Impacting fibers are stuck to the substrate surface by an appropriate adhesive. Primary quality criteria are adhesion of the flock fibers to the adhesive, and also the so-called flock density, i.e. number of fibers per unit area, and evenness. The influential physical and chemical factors refer to interfacial adhesion, but also charging effects by the impacting fibers. The system presently under investigation is based on aliphatic polyamides as material for a molded car component, hot-melt adhesive, and flock fibers. Experiments reported here refer to the application of an air plasma pretreatment of the polyamide (PA) substrate, mainly in order to increase the adhesion of the hot-melt layer. It was found that the plasma treatment affects the polar energy of the PA surface with a related increase in wettability due to a reduction of C-C and C-H bonds and an increase of carboxylic groups. Surface carbonization occurred at higher plasma doses. The effect on hot-melt adhesion was rather small, however two types of failures were observed in these experiments, either due to insufficient adhesion of the hot-melt or due to a break of one of the PA plates with the bond still intact. The characterization of flock coatings on these samples showed no effect on flock fiber adhesion in pull-out as well as on abrasion resistance, but an increased flock density was observed. This is assumed to be due to enhanced dissipation of charges by the conductive water layer adsorbed on the substrate surface.
