Thin PET film, sheet gets the polish

Thin PET film processing requires high line pressure for polishing, often resulting in roller deflection. As the film width increases, the tendency to get higher deflection results in an uneven film thickness cross profile. Often convex rolls are used to compensate, but if they have fixed geometry they can only cope with a single setup while highly flexible lines require adjustable crowning to cover a wide thickness range, different resins, and flat die deckling.

To alleviate these problems, this equipment producer has introduced the JuBo polishing roll (Justierbare = adjustable; Bombage = crowning), the first roll in a 3-roll stack. The technology is suitable for wide roll stack extrusion lines producing film in thickness from 1200-1000 µm. Films down to 100 µm are possible by slight modification of the unit.

An oil-filled cavity is placed under the cooling spirals, its shape calculated by finite element method. During operation, the cavity reaches the temperature level needed for the polishing roll's cooling water. Depending on the temperature, pressure up to 300 bar can be reached within the oil cavity. This is said to create symmetrical deformation of the roll's outer shell, resulting in a crowing up to 300 µm in the centerline. The unit is intended for credit card overlay film, graphic arts sheet, as well as form-fill-seal and thermoforming web. Brückner Formtec GmbH, Siegsdorf, Germany; +49 8662 63268; www.brueckner.com