Change in apparent color; especially when inorganic decorative effect pigments are used the weld line appears as a dark line;conspicuous in dark, brilliant or transparent moldings having smooth surfaces polished to a high gloss.
As far as possible, position weld lines where they have no visual or mechanical impact (flow promoters, flow inhibitors);
check mold engineering: if necessary enlarge sprue channel, gate and machine nozzle;
avoidance of aprupt changes in wall thickness and nonuniform mold filling;
provide effective mold venting.
Processing: Optimization of melt temperature, mold surface,temperature and injection speed; new color formulation (organic or inorganic pigment)