DUSSELDORF, GERMANY — Thermoforming machinery suppliers are responding to the growing U.S. demand for high-volume production of polypropylene food containers by building machines featuring in-mold trimming.
Falling polypropylene prices and improvements in the material's quality and clarity have prompted producers of thin-walled food and drink packaging to switch to PP from the traditional polystyrene.
But processors have been accustomed to turning out huge volumes of disposable cups, yogurt cups, dairy tubs and deli containers on big thermoforming machines employing separate post-form trimming.
PP presents a problem here, since its heating characteristics mean containers can sag and distort if they are trimmed outside the mold.
``What's held back polypropylene [for thin-walled thermoforming] in America all these years is the non-availability of reliable, large-capacity thermoformers,'' said Frank Nissel, president and chief executive officer of extruder manufacturer Welex Inc. of Blue Bell, Pa. His firm is a major supplier to thermoformers worldwide.
So, U.S. thermoforming machine makers took a leaf out of Europe's book, where molders have been producing containers in PP for some time, avoiding the shrinkage problem with the use of smaller machines with in-mold trimming.
U.S. equipment suppliers had to overcome one other difficulty with trim-in-place — removing many trimmed, thin-walled containers intact from a big mold.
``The entire American cup and packaging market has been built on large-size thermoforming machines with secondary trimming. The finished parts come out very nicely nested because you have a trim press,'' Nissel said.
In an interview at K'98 in Dusseldorf, Nissel recalled how European thermoforming machine makers came up with their own solutions to sorting containers from in-mold trimming, but these did not transfer easily to large U.S. molds.
One U.S. machine manufacturer that has found answers to the North American dilemma, according to Nissel, is International Thermoforming Systems of Yakima, Wash.
ITS offers the in-mold trimming in its FT-series machines. The trimming is accomplished via an additional movement of the platens at the end of each cycle, according to ITS Vice President James Norton.
ITS has introduced a vacuum paddle on its FT 3000 and FT 7500 machines that is capable of picking up high volumes of formed and trimmed PP cups.
The containers are stacked on transfer conveyors, then moved to a laydown mechanism where they can be automatically collated, boxed, bagged or transferred to a secondary process such as printing.
The FT 7500 can accept a web width of 48 inches, processing 2,860 pounds of PP per hour.
ITS worked closely in developing its machines with German mold maker Marbach Werkzeugbau GmbH of Heilbronn, Germany, and with CBW Automation of Fort Collins, Colo., a producer of handling systems for injection molding lines, Norton said.
He said that polypropylene for thin-walled food containers has come into favor because of improvements in the polymer as well as efficiencies in thermoforming vs. injection molding.
In terms of the material, the resins now are less prone to sag and have greater melt strength. Also, PP is microwaveable and offers greater clarity than ever before, Norton said.
``People are seriously looking at polypropylene for drink cups, and it is going to replace paper,'' he said. His company shipped its first FT 7500 machine for PP containers to Solo Cup Co. of Highland Park, Ill., he said.
``Within the next six months they are going to have the most advanced automation for part handling in thermoforming of anybody,'' Welex sales manager Charles Keener said of ITS.
Another supplier of thermoforming equipment getting in on PP is John Brown Machine of Beaverton, Mich. The company, part of John Brown Plastics Machinery Inc. of South Attleboro, Mass., introduced its CT-800 trim-in-place machine at K'98.
John Brown's new design uses an articulating mold to ease product ejection and stacking. In addition, servo motor-driven platens are used for platen movements as well as for operating plug and part ejection from the mold.
``Everyone has their own concept of how to [eject and stack parts], but the total approach is very similar,'' said William Kent, vice president of John Brown Machine.