Cost-effective PET sheet processing

THERE are differences in the manufacturing processes of PET sheets compared to others. For any packaging thermoformer looking for a competitive advantage, it is in their best interest to examine these differences.

The main difficulty in the extrusion of APET sheet lies in the traditional manufacturing process that typically requires the use of granulated resin from a third-party supplier. After delivery from this supplier, the resin requires drying in a four-to-six hour energy-intensive operation before being fed into the extruder. From there, the extruder compresses and heats the resin into a melt, which is then transferred to the die and onto the rollers to form the sheet.

The direct-to-sheet process (DPET?) from Octal eliminates five energy-intensive stages of the conventional sheet production process (pelletiser, SSP, compactor, dryer and extruder). Because now the PET melt can arrive at the calendar stack heated to the proper temperature, so it does not have to be dried and re-melted from the granular form.

Product purity maintained
This process eliminates the chances for contamination to enter the system and ensures a finished polymer that is fully devoid of moisture. Thus, thermoformers will see an elimination of all moisture defects. There is absolute traceability as the resin is constrained to one source – providing origin of the resin and quality. Food processors and packers can be assured of product purity.

Moreover, the uniformity of the sheet allowed Octal to design a winder that constructs precision rolls with unnoticeable weave and near perfect formation. Thermoformers benefit from this advantage by being able to minimise side trim, a direct material savings.

Gauge consistency in conventional PET sheeting is in the 3% to 8% range, with 5% as an average. DPET, on the other hand, is manufactured to a typical caliper variation of +/- 1%. Operationally, this outstanding consistency allows thermoformers to specify a thinner sheet and still achieve package performance in finished trays.

DPET’s direct-to-sheet process results in a material with superior clarity and gloss. Any food packager or retailer knows well that these are characteristics that translate into an end user perception of higher quality. The DPET surface also allows for subsequent printing processes to allow for high-impact merchandising.

The new processing technology can be run at a 10% faster cycle time, and at temperatures up to 5 degrees lower than conventional APET, whilst still retaining clarity and gloss. This translates directly into lower electricity and overhead costs per finished unit.

Apart from these, DPET has excellent flow characteristics, resulting in 3% to 8% more material reaching inside corners of mould profiles. Combined with an intrinsic viscosity of 0.78, and the implication is, that finished containers are tougher, more resistant to cracking, and better able to withstand the rigours of shipping to retailers and end users. Its high intrinsic viscosity also means less scrap and skeletal waste.

All in all, the new product cuts costs by as much as 24% compared to conventional PET sheeting, as confirmed in laboratory testing by the company.

The Octal production process brings a major advantage in addition to the unbeatable product quality: a carbon footprint 25% below that of traditionally produced APET films, according to an Intertek study. The direct-to-sheet process eliminates the most energy intensive and defect prone processes, to deliver a spotless sheet with a fraction of the energy.