'WELD LINES? WHAT WELD LINES? GETTING BETTER APPEARANCE FROM METALLIC PIGMENTED MOULDINGS'

摘要

Metal flake pigments are an increasingly common constituent of moulded plastics.Unfortunately,due to their asymmetric shape,their use can make weld lines significantly more visible in the moulded article.The objective of this paper is to describe recent work to establish the degree to which the severity of weld lines may be reduced by judicious choice of pigment type,loading and injection moulding machine parameters.A brief introduction will show why metal flake pigments make weld lines more prominent than other pigment classes.This will be followed by illustrations of the nature of the problem and a description of an injection-moulding tool specially built for this study.The main part of the presentation will cover systematic changes to pigment particle size,shape and concentration,plus moulding machine parameters,chiefly temperatures,injection speed and injection and holding pressures.Finally,the effect of polymer transparency and polymer melt flow index will be considered.In the final part of the presentation,observations made during the study will be brought together to demonstrate synergy capable of virtually eliminating visible weld lines in many formulations.