The extrusion of polyethylene or polypropylene films is often accompanied by various flaws, namely:
- « Orange peel » (or shark skin, or melt fracture), which is an instability in the matter's flow at its exit from the draw-plate
- « Draw-plate deposits », which are made up of small oxidised polymer masses combined with mineral fillers that accumulate on the draw-plate's lip, and can be dragged by the film thus causing holes.
The addition of a processing aid that is dispersed microscopically within the polymer creates a constant lubricating layer on the draw plate's surface during extrusion, which fosters the polymer's flow and protects against the undesirable problems mentioned above (AID PE F5, AID PP F4)
In some cases, the use of these additives allows the machine's flow rate to be increased, without increasing the pressure.