Assessment of plastic mixture quality in injection moulding process

This paper aims to review the existing techniques for measurement of polymer mixture quality and examine the performance of a simple digital image processing technique to characterise the mixture quality of flat moulded samples. Three different polymers were used, namely polypropylene (PP), high density polyethylene (HDPE) and linear low density polyethylene (LLDPE), blended with 1% masterbatch coloured pigment. The moulding process conditions, including back pressure and screw speed, were varied to achieve different pigment agglomerates dispersion and distribution in the polymer matrix. In this process the coefficient of variation and the undispersed area of pigment agglomerate in the polymer matrices were measured and related to the mixture quality. The flow pattern in the gate region was also examined and the streaks of pigment agglomerates were found to be related to the stare of mixture quality. The technique used in this study has proved to be an efficient means of assessing the dispersion and distribution of pigment agglomerates in flat moulded samples. (C) 1997 Elsevier Science Ltd.