Metallic pigments injection molding

To optimize the metallic effect when using an injection-molding machine, a higher screw speed, a longer plasticising period, sufficient backpressure, and a suitable screw design are prerequisites. The pigments are added as ready-to-use compounds, masterbatches, or powders. 

Both injection blow molding and pinch tube processes are especially suitable for metallic pigments, because the expansion of the plastic during the blowing process causes further orientation of the metallic pigment parallel to the surface. 

To optimize the metallic effect, the conditions outlined in Section 14.4.4 under Injection Molding should be maintained. The pigments are added as compound, masterbatch, or powder. The use of static mixers or special mixing screws can improve the homogeneity of the blend. For the pinch tube process the high melt viscosity should be considered when preparing the masterbatch. 

The SCORIM Process. It is possible to attach the SCORIM unit to the injection molder to manipulate the filling process of the mold so that in the area of the weld lines the resin is mixed [16]. This will improve the structural strength substantially and at the same time the unwanted orientation of metallic pigments is prevented. This process typically requires a 10-15°C higher temperature of the resin and the mold. The process is based on a prolonged flow ability of the polymer. 

By offering silver and colored metallic pigments, which avoid flow lines of injection molded plastic parts due to their large particle size, totally new possibilities have been opened for achieving brilliant, metallic like appearance and new, unique color effects of plastic products. 

Polyethylene Terephthalate. Crystallization is difficult and slow. Particularly for injection molding, 0.5 percent of 3- im metal oxide, metal salt, pigment, or other minerals, and ionomer are mentioned. For thermo formed food trays, 1 to 3 percent of low-MW polyolefin. 

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