news | Technology P&R serves up thin wall PET
UK-based injection moulder Patterson & Rothwell (P&R) claims to be taking thin wall PET moulding to new limits with a newly developed range of premium dessert pots. With wall thicknesses between 0.8mm and 1.0mm and flow lengths up to 80mm, the company says the new pots are at least 0.4mm thinner than previously available PET alternatives and result from a two-year £0.5m R&D and tooling project. “We developed the new PET packaging in response to the food industry wanting a move from GPPS, which can crack easily, to more hard-wearing and widely recyclable dessert packaging,” said P&R Sales and Marketing Manager Dave Bowden. “Major retailers have already expressed interest in the product and we’re anticipating that many more will follow suit. The pots are ideal for premium brands wanting an eco-friendly, yet aesthetically pleasing design.” The Oldham-based moulder
is achieving flow ratios significantly beyond the 50:1 limit normally recommended for processing PET. Technical
P&R claims walls at least 0.4mm thinner than current PET alternatives
Manager Steve Pollitt said it had to look to all aspects of the process to be able to produce the parts on its 8-cavity tooling. “Basically it is a combination of part design, tooling, material and injection moulding machine,” he said. The company is using a
standard high flow PET grade from Artenius, which it is running on a 280 tonne all-electric IntElect Smart series machine from Sumi- tomo SHI Demag equipped
with its Active Flow Balance technology. This exploits the rapid dynamics and precise injection control of the all-electric design, stopping the screw before the cavity is full and using the pressure in the melt to complete the fill. “When you use high
pressures and high velocities you have a problem with the parts sticking in the fixed half of the mould. Using AFM and a special hand finish on the cavities helps overcome this,” said Pollitt. The part design also uses a large 3mm valve gate and a progressive base that thins from the injection point to the wall to ease filling. Tooling is by UK-based Rye
Rye Tools produced this 8-cavity mould for P&R 10 INJECTION WORLD | July/August 2015
Tools. It uses a cavity break feature to release the pot base from the fixed half together with high thermal conductivity beryllium copper cores that help draw heat away from the gate. “With PET you need to cool fast to get the thermal
shock required to give high clarity,” said Pollitt. P&R currently moulds similar parts in GPPS. Pollitt said clarity of the PET versions cannot quite match GPPS due to inherent resin characteris- tics but he said cycle times are competitive. “We make these pots in GPPS on an 8-impres- sion tool at around 12s and we are not that dissimilar in PET,” he said. The new PET containers are
now undergoing final moulding and filling trials that it is hoped will lead to first market introductions later this year. Customer response to date is said to have been very positive. Dessert suppliers like the premium feel of PET, Pollitt said, while fillers appreciate that, unlike GPPS, the resin does not shatter so lengthy filling line shutdowns to eliminate risk of shard contamination are avoided. ❙
www.patterson-rothwell.co.uk
www.injectionworld.com
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