Foam injection-moulding of low density polymer components

摘要

Foam injection-moulded parts with a density reduction of more than 50 % can be obtained using the breathing mould technique and nitrogen as a physical blowing agent. After injection of the gas-laden polymer melt the clamping force is reduced to 1 % and the specimen can reach a maximum thickness or minimum density during the expansion process. Foam injection-moulding experiments were performed on a polypropylene (PP) homopolymer and a glass fibre-reinforced grade, as well as a PP with a higher melt strength (HMS) as a result of polymer branching. The influence of processing parameters, such as melt temperature and mould temperature on the resulting foam density and foam morphology was investigated. It is shown that the general foam morphology as well as the maximum density reduction depend on the melt elongational properties of the polypropylene.