Einfluß der Schneckengeometrie auf die Folienqualität

The extrusion of polymers to semi-finished products as films, pipes or profiles is beside injection moulding of parts the most important polymer processing technology. The solid polymer material is melted in a screw plasticating system. The design of the screw geometry requires the knowledge of the processing relevant material data and takes place with the aid of physical models. Beside the demand of a high mass throughput the achievement of an optimum product quality must be guaranteed. Former scientific work primarily investigated the influence of the post extrusion devices, e.g. the cooling and take off systems, whereas the influence of the extrusion process itself has not been studied systematically yet. In a plasticating screw the material has to be fed, compressed and melted and homogenized in a way that a suitabable melt quality is achieved. In this research project the influence of different screw geometries was analyzed in more detail. The design of the screw channel influences the flow conditions as well as the residence time and the deformation of the melt. Because of the visco-elastic material behaviour applied deformations can relax. A constant influence of the post extrusion devices was ensured in the investigations by mounting a by-pass-system between the extruder and the film die. This allowed the adjustment of the same mass throughput through the extrusion die and therefore the same cooling and orientation conditions during the film forming process when experiments with different screws and screw speeds were performed. The research results show no significant influence of the absolute deformation measure on the product in thermal and mechanical well homogenized melts. This is because of the short relaxation times in comparison to the residence time, which allow a relaxation of the melt deformation applied in the screw before leaving the extrusion die. Property changes using different plasticating screws found in earlier research works are attributed to partly enormous melt temperature deviations because the screw speed had to be varied to get the same throughput. That resulted in different cooling and crystallization conditions yielding different levels of morphology and molecular orientations. The polymer industry is one of to the strongest economy branches with growing rates above average (appr. 10% p.a.). Austria has a great number of small and medium sized companies in the fields of polymer processing as well as plastics machinery and tooling. Many of them can be counted to the market leaders in their special working areas. To ensure respectively to extend the technological advance more and more enterprises realize the necessity of a systematical investigation of physical and mathematical relations in the course of processes in the framework of pre-competitive basic research. Apart from the now finished project the department of plastics processing developed new models and methods in various other FWF- and ÖNB-projekts in the research field extrusion technology and can posses a wide expert knowledge which resulted already in the past in close industry cooperations. Currently two greater research projects with notable enterprises are prepared, which rely on the collected results of the research work of the department of plastics processing and underline the significance of the investigated research subjects.