Technical considerations in using Xantar® Fantasy Colors

Fantasy color grades (e.g. Xantar RX 1045, Xantar RX 1046) are special injection moulding grades with aluminium flakes to obtain a metallic effect. The flakes are added for aesthetic reasons only.

The Xantar grades are materials based on polycarbonate and in the case of Xantar® RX 1046 is flame retardant (V-0 at 2 mm).

When these type of pigments are used, problems can arise regarding flow and weld lines. These lines in Fantasy colors are caused by the orientation of the flakes at a right angle to the surface of the molding. The result is a dark line created by the relatively low reflectivity of the flake edge.

Although it is not always possible to avoid weld and melt lines completely (especially in existing molds) good results can be obtained by paying extra attention to mold design (including the gating system), processing conditions and the formulation of the Fantasy color.

At the mold design stage, weld lines should be positioned at places were they are out of sight or less visible. Unavoidable weld lines should be located as near to the gate as possible. A single gate is to be preferred above multiple gating because of the inevitable head-on weld lines

•  A good balanced flow pattern also helps prevent problems. This is obtained by avoiding disturbances to the flow (for example: holes, ribs and sudden changes of flow direction) and by having an even wall thickness distribution.
•  Good venting in the weld region is absolutely necessary and tool texture will help to mask the flow and weld lines
•  A relatively large gate size should be used to minimize shear forces and to prevent  the flakes packing in front of the gate. High shear forces could bend or mill the flakes resulting in a reduced surface area to reflect light.

•  For processing it is also important to minimize the shear forces especially in the plasticizing unit of the molding machine in order that the flakes are not milled.
•  High injection speed, mold and melt temperatures will help reduce weld line visibility. Jetting (injection speed) and the limits of heat stability (melt temperature) should be avoided.

Formulation
•  To get the optimum metallic effect, the minimum pigment concentration for opacity in the thinnest section of the mould should be used. This approach will lead to the maximum metallic reflection from deep within the polymer.
•  Although not always desirable the following measures will improve flow and weld line visibility: darker colors and colors with a deeper shade mask  flow and melt lines better than pale shades.  Lower concentrations of flakes and a larger flake size both have a positive influence on the metallic effect.

Properties
•  Apart from the visual effects, the presence of aluminium flakes has a significant effect on some of the properties of fantasy color grades. Impact resistance (Izod, falling dart), steam resistance and ESCR are all lower than of a comparable grade with standard coloring. Moreover electrical properties like CTI are negatively influenced.