The colouring of moulded plastic products can be achieved by adding a small percentage of colour masterbach into the main bulk of plastic resin during processing. Indeed, this practice has been accepted widely in the industry. Since the primary objective of this practice is to colour the products, the amount of the colour masterbatch added being normally less than 4 to 5% by weight, emphasis has only been placed on how well the products are coloured. The effects, if any, brought abouth the addition of the colour masterbatch on other physical properties of the products are often either neglected or assumed to be insignificant. The objective of this study is to investigate these effects experimentally. ABS was chosen to be the moulding polymer in an injection moulding machine having a maximum shot capacity of 4-oz. Four different SAN base colour masterbatches, differing from each other only by their melt index, were mixed separately with the ABS, the amount of the colour masterbatches added being varied from 1 to 4%w/w. The injection moulding process was controlled carefully to produce near “perfect” moulded articles as determined by the naked eye, this set of operational conditions being maintained throughtout all of the moulding studies. While both the visual observation and tensile tests further showed that the higher is the melt index of the masterbatch, the more homogeneous is the colouring. In the results from the latter tests further showed that the higher is the melt index of the masterbatch, the more homogeneous is the colouring. In addition, the analysis from SEM and DSC indicated that the ABS might have transferred from having brittle characteristics to having ductile behaviours.
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