In extrusion, thermoplastics are melted to a viscous mass in a screw and then pressed into shape through a shaping die.
Machine parameters for the success with Effect pigments
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 which 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 a requirement for an even effect. This has to be ensured in the process through an corresponding engineering and design of the machinery.
Special possibilities in Co-extrusion
Co-extrusion is used to combine different materials or the same materials in different colors or effects. The two materials are combined into one flow in the coextrusion die. If an effect pigments is used in the surface layer, it is possible to increase the effect strength and by the same time saving cost due to a thin layer and the perfect orientation of the effect pigment 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 pigment must be used than in solid layers in regular extrusion – this could mean up to ten percent in the plastic, depending on the layer thickness and desired effect. Less pigment 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, such as to improve the barrier or other properties, or internal recycling materials can be used to save raw materials and boost waste reduction and economy. Effect pigments are seldom used in this layer.
This technique can be used in all extrusion processes, including extrusion blow molding.