Tetra Pak

Background

The market for Flexible Packaging, including drinks packs, bubble wrap and foil based packaging, has seen the rise of many companies. The essential concept revolves around the extrusion lamination process whereby an extrusion head drops molten polymer onto various substrates – most commonly card and foil – in a nip pressure situation provided by a metallic chill roller which is water cooled and a rubber nip roller which provides the flexible pressure

Problem

At the edge of the product and, in some cases where holes are created for the insertion of drinking straws, the molten extrudant comes in contact with the roller and there is an unacceptable build-up of polymer. Typically the running temperature of the extruder is over 300 °C – which is normally far beyond the capabilities of any fluoropolymer

Solution

Because of the extremely arduous conditions of high temperature and pressure, only PFA has a chance to survive. The PFA surface offers the non-stick surface needed whilst it also insulates the bonding agent. Typically Holscot will shrink and fit a 0.64mm thick or 1.5mm thick PFA etched sleeve to the rubber roll and bond it using a high temperature adhesive. The fitted sleeve can be post treated to get the smoothest possible surface.

Special attention must be made to the rubber which must be over 75 deg shore and preferably EPDM. Silicone cannot be covered.

Although the lifespan will never be extensive because of the arduous nature of the application, it is accepted by all the major flexible packaging manufacturers that a PFA covered nip roller is the only solution to this most common problem.