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Project leader: Prof. Dr. W. Maus-Friedrichs, Dr. F. Voigts
Funding period: 01/2012 - 12/2013
Funding agency: BMWi via AiF
Funding code: IGF 403ZN/2
Researcher: M.Sc. René Gustus
Spotting in plastic molded parts due to the formation of deposits on steel surfaces in plastics processing machines and on the surfaces of extrusion tools, for example, is a widespread cause of production disruptions and interruptions as well as quality impairments. Particularly critical areas are the preparation and production processes for high-quality molded parts with high demands on optical properties or with high-quality surfaces.
In the past, speck problems were often exacerbated by inadequate fluidic design of the melt-carrying channels in machines (e.g. non-return valves) and molds. Through optimization measures, many years of experience and the possibility of numerical flow simulation, these causes have been largely eliminated or minimized by machine and tool manufacturers. Despite these measures, however, problems with speck formation are still acute in certain applications.
Although the formation of deposits and the resulting speck problems have been known for many years, the underlying causes and in particular the early mechanisms of formation and growth of the deposits are still largely unknown. Improvement measures have been found for individual specific problems, e.g. through the selection of coatings and suitable additives in the molding compound formulations, such as certain lubricants or surfactants. However, neither raw material manufacturers nor plastics processing companies have a clear idea of the mechanisms and interrelationships and therefore have no systematic solution strategy to prevent the formation of deposits in production. For example, it is not at all clear today why the coatings or additives used have any effect at all or what the mechanisms of action are.
The aim of the project is to gain an in-depth understanding of the mechanisms of the early phases of coating formation, coating growth and coating detachment. The aim is to overcome the current trial-and-error approach to steel selection, coating selection and molding compound formulation for the first time and subsequently develop targeted remedial measures. In this project, the formation of coatings is to be investigated with the highest possible resolution, both with regard to the changes in the metallic surface and the organic components of the boundary layer, in order to record interactions and reactions taking place between the polymer and the metal material or its passive layer. The basic mechanisms of the formation, growth and detachment of coatings in plastics processing, such as those occurring in tools, extruders, injection molding machines and hot runner systems, will be used to develop recommendations for action for compounders, processors and machine manufacturers.