Coextrusion

In extrusion technology , coextrusion stands for the merging of identical or foreign plastic melts before they leave the profile nozzle.

One-step process

In the one-step process, also called direct extrusion, z. B. the wood particles and the plastic granulate for wood-plastic composites are fed to the extruder in the same place at the same time. For single-stage processes, conical, counter-rotating twin-screw extruders are usually used, which simultaneously fulfill the task of intensive mixing and the necessary pressure build-up for extrusion.

Two-step process

In the two-stage extrusion process, plastic granulate and wood particles are first mixed and compacted in parallel twin-screw extruders (compounders), heating-cooling mixers or pelletizing presses. The actual extrusion then takes place in another, directly coupled or spatially and temporally separate unit. In addition to extrusion, the WPC intermediate products produced in the two-stage process can also be used in injection molding , rotational molding or in plate press technology.

Composites

The multi-layer composite panels produced in this way are divided as follows:

• Similar compounds: z. B. Acrylic glass with acrylic glass
• External bonds without adhesion promoter: z. B. ABS / acrylic
• External bonds with bonding agent: z. B. ABS / polymer / acrylic

Others

An example of coextrusion can also be found in private households : toothpaste with colorful stripes. Both pastes are extruded together through a nozzle.

Also coextruded films that are special plastic films are produced by the coextrusion.