This paper is dealing with structural foam moulding of polypropylene (PP) thermoplastics utilising the MuCell approach to introduce the blowing agent as well as advanced moulding technologies. Till today, structural foam moulding is facing several different challenges, which are limiting a full acceptance in industrial applications. Encountering issues of those parts are the critical surface appearance, the limited density reduction and finally the mechanical properties (stiffness, strength and toughness). Here, two surface improving techniques have been evaluated according to their effectiveness and feasibility. Furthermore, in this experimental study, six different typical automotive PP compounds have been processed to structural foams with a density reduction of 50% and evaluated in regard to their morphologies and mechanical performance. The modulus and strength of structural foams can be correlated to their build-up (skin-layers, foam density), as the toughness performance is heavily dependent on molecular weight, filler-type and filler orientation.

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Over the last few years some highly-efficient manufacturing processes in the field of foam injection moulding occurred based on new developments in the machine, the mould and the material technology. The manufacturing of car interior parts with a soft touch surface for example became possible in a one-step injection moulding process, in which an injection moulded carrier made of a fibre reinforced thermoplastics is overmoulded with a foamed thermoplastic elastomer (TPE). The TPEcomponent with compact skin layers and a foamed core generates a soft touch effect, reduces the part weight and observes the quality standards of the automobile manufacturers. Furthermore this technique offers a much higher economic efficiency compared to conventional manufacturing processes. To lower the part weight even further it is aspired to produce the thermoplastic carrier in a physical or chemical foam injection moulding process. With special mould technologies and the right process management it is already possible to foam light plane parts with a high specific flexural stiffness. As the main function of the carrier is the stiffening of the part an interesting aspect is to combine a stiff foamed carrier with a soft TPE-component by an overmoulding injection moulding process. This paper is going to show the possibility to overmould a plane foam injection moulded part with a second thermoplastic component, e.g. a TPE. The aim is to reach ideal dimensional stability and mechanical properties by the right adjustment of the manufacturing process.

Germany -johannes.mueller@nmbgmbh.de; andreas.spoerrer@nmbgmbh.de; volker.altstaedt@nmbgmbh.de Abstract The manufacturing of car interior parts with a soft touch surface is possible in a one-step injection moulding process, in which an injection moulded carrier is overmoulded with a compatible foamed thermoplastic elastomer (TPE). In contrast to the complex conventional process the structural foaming of the TPE component allows a saving of one material component as it combines a compact skin and a foamed core. Furthermore the manufacturing process can be achieved on a two component injection moulding machine which offers a much higher economic efficiency. One approach to reach an adhesion between a reinforced PP carrier and the foamed TPE component including good surface resistance is the use of an olefinic-/polyester-based TPE blend (TPO/TPC-blend). This paper is going to show the possibility to process a TPO/TPC-blend system by foam injection moulding with MuCell ® and how the resulting foam structure can be influenced by various nucleating agents. For this purpose particles which differ in type, form and size were added in various concentrations to the TPE-blend. Before the structure elucidation of the foamed samples the particle dispersion and their effects on the polymers rheological properties were investigated. Finally abrasion tests were performed to investigate the influence of the particles on the performance characteristics of the foamed blend system. The results showed that the foam structure as well as the surface quality of the foamed TPO/TPC-blend can be improved with the use of suitable nucleating agents. Furthermore the abrasion properties can be advanced with appropriate additives in the right dosage.