Extrusion and co-extrusion give shape to thermoplastics as they are pressed through a shaping die. Careful planning and machinery care are essential for the effective use of effect pigments in these plastics.

What is extrusion?

In extrusion, thermoplastics are melted to a viscous mass in a screw and then pressed into shape through a nozzle. The variety of possible shapes is huge. Films, foils, and plates are extruded through flat nozzles. Nozzles with larger openings are used for solid rods, tubes, or flat profiles. Irregular shapes such as angled profiles, for example L or T shapes, and complex shapes like window profiles can also be manufactured using an extrusion process.

Tips for using effects pigments in extrusion

Masterbatches or compounds are usually used to color the molten mass with effect pigments. For a satisfactory result in plastic extrusion with effect pigments, a balanced ratio must be maintained between the mixture energy and pigments that are as undamaged as possible. Excessive shear from mixing sections or inappropriate screws or filters destroy effect pigments and dramatically decrease the pearl luster effect.The orientation of the pigments is critical for an even effect. This has to be ensured in the process through corresponding engineering and design of the machinery.

Tips for using effect pigments in co-extrusion

Co-extrusion is used to combine different materials or the same materials with different colors or effects. The two materials are combined into one flow in the co-extrusion die. 

If effect pigments are used in the surface layer, it is possible both to increase the effect strength and to save costs due to the thin layer and the perfect orientation of the effect pigments on the visible surface. However, it must be taken into account that, due to the much thinner co-extrusion layer, a higher concentration of effect pigments must be used than in solid layers in regular extrusion. A lower concentration of pigments is needed when the entire layer mass is colored.

The inner layer in co-extrusion usually uses high coverage. It is also called the substrate layer because of its much higher layer thickness. Functional materials can be used in this layer, such as to improve the barrier or other properties. Or internal recycling materials can be used to save raw materials and further reduce waste and boost economy. Effect pigments are seldom used in this layer.

This technique can be used in all extrusion processes, including extrusion blow molding.

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