Innovations | thin wall moulding
Mould innovations StackTeck Systems picked up the Gold Award for ‘Best Thin Wall Package’ at the recent In-Mold Decorating Association’s Parts Competition. Developed for brand owner Kentucky Fried Chicken, the 64oz carry-out pail used StackTeck’s Thin Recess Injection Molding (TRIM) technology, previously described in Injection World here. The pail, moulded by SriThai Superware of Bangkok, Thailand for KFC, was the fi rst commercial application of the TRIM technology. StackTeck says that SriThai Superware challenged StackTeck to fi nd a way to reduce the weight of the pail, used for popcorn at movie theatres, that was already at the limit of conventional thin-wall packaging. “By pushing the TRIM part design to the limit, covering approximately 90% of the part with ultra-thin panels, a weight saving of approximately 40% was achieved,” says Jordan Robertson, StackTeck’s general manager for business development and marketing. “Most of the surface of this part has a wall thickness that corresponds to an L/T ratio of 550.” More innovative mould technology for thin-wall packaging is being developed at UK-based GR8 Engineering, which is headed by Peter Clarke. He is currently at an advanced stage of develop- ment with a process he calls two-stage injection compres- sion moulding (ICM), which is
sion moulding (ICM), which is intended for production of fl at preforms to be used in the company’s proprietary EcoForm process. GR8’s initial target is to produce amorphous PET container preforms with an L/T of
250:1, but the ultimate goal is
500:1. Using polypropylene, Clarke says L/T ratios of 1000:1 are possible (by comparison, he says standard PET preforms for bottles have L/T ratios of around 50). The two-stage ICM technology is the latest from
Clarke’s 16-year involvement in the multi-cavity thin wall ICM sector, which included development of the Im-Pak ICM process. This used external shooting pots to control melt delivery, one of the key challenges in implementing a multi-cavity ICM mould. Two-stage ICM incorporates a pre-dosing step to control the amount of material injected into the cavity. “The process uses internal movement in the mould
to accelerate the material to the end of fl ow. Hydraulics are built into the mould to control the movement. There is nothing special about the machine, this is a mould technology,” he says. “Two-stage ICM accelerates the fl ow way beyond anything achieved to date, by anyone.”
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The two-stage ICM preforms are intended to be used in GR8’s EcoForm hybrid stretch-blow moulding process, which is similar to two-stage stretch-blow moulding for PET bottles but can handle containers and jars that have dimensions beyond the capability of current ISBM technology. “It fi ts between thermoform- ing and stretch blow moulding, overlapping both processes,” Clarke says. EcoForm has already been used to make jars using preforms produced with another thin-wall process moulding devel- oped by Clarke, called Active Flow Moulding
(AFM). This involves moving a 20-mm diameter pin positioned opposite the gate back 3mm during
injection and then re-setting it
at the end of packing. It reduces stress in the preform and therefore warpage, according to Clarke. “AFM is a gentle process that just allows easier fl ow, faster injection rate and less stress,” he says.
Another way of improving fl ow of polymer in thin wall moulds could be to use foam, according to US-based Trexel, which has been supplying its MuCell
Left: The fl at fl anged preform (right) used to produce this Ecoform PET container is produced using Active Flow Moulding (AFM) technology
January/February 2015 | INJECTION WORLD 37
Above: IML container
production on a 200 tonne El-Exis SP
hybrid machine from Sumitomo Demag
Left: Mucell foaming technology cut part weight by more than 10% for this IML tub by Coveris Rigid
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