Taking physical foaming a step further

Friedrichshafen, Germany — The largest, main exhibit at the booth of KIMW Kunststoff Institut Lüdenscheid molded a demonstration of a new DryFoam physical foaming process based on a carbon dioxide foaming agent. As with many inventions, the process evolved earlier in the year by coincidence when KIMW was looking at using compressed gas to dry thermoplastic granulates.

So when it was discovered that a large amount of the CO2 became absorbed in the plastic, the idea was born to feed the impregnated resin into an injection molding screw to see what would happen, resulting in the gas becoming released to form foamed material. A wide range of different thermoplastics has been trial molded, leading to lightweight parts.

"Quite honestly, we don't know how it works, and that is subject of basic research activities at various research institutes," said Stefan Schmidt, head of KIMW. "We also found that in evaluation of the foaming effect, it is necessary not just to make conclusions on, for example, ABS as a type of material, but to go into detail with investigations with different ABS grades as they all behave differently in the new foam process from one grade to another."

Schmidt added that KIMW takes a very pragmatic approach, taking both the right tooling and specific material into account before making statements on feasibility to its clients. KIMW has many samples to evaluate for customers; the work will go into early 2018.

Each evaluation takes a few months. The first trial is made free of charge for customers to see if the process works in their material. "After that," Schmidt said, "trials cost 1,000 to 1,600 euros each, which is our normal price for such work. But the result for that price is then a final part put into the customer's hand. I find it a very charming solution with short development routes."

Schmidt stressed the attractiveness of the new foam process in that customers can use existing dryers and injection molding machines, needing only to invest 40,000-60,000 euros into the autoclave system between the dryer and molding machines. "Of course, dryers can also be integrated with the autoclave unit," Schmidt added.

KIMW has partnered with Bensheim, Germany-based ProTec Polymer Processing GmbH, a system supplier with a focus on injection molding. The company is offering mobile Somos RDM granulate dryers for the new foam process. Eventually, it will offer a unifed dryer and autoclaving unit with conveying equipment.

"Our part is the hardware," said Peter Theobald, CEO of ProTec. "We started developing the system just two months ago and currently have a number of prototypes available."

Physical foaming, he explained, permits high foaming pressures and avoids deposits caused by residue arising during chemical reactions.

Theobald and Schmidt said that when the process is a closed circuit, the CO2 gas can remain unused in the granulate for four to six hours.

"There's a window during which you can use it in injection molding machines," Theobald said. He talked about launching a ProTec system solution at Fakuma 2018, which would also include both CO2 and nitrogen gas versions.

Another partner in the development is industrial gas supplier Linde AG, which wants to commercialize the foam process in 2018, based on its Plastinum CO2-based foam system solutions.

The live demonstration at the KIMW booth took place on an IntElect 100-340 electric drive injection molding machine from Sumitomo (SHI) Demag. The display showed unfoamed, foamed and counter-pressure foamed bottle openers, the latter's compact outer skin resulting in less weight saving.

Schmidt sees the new foam process as an addition to existing foam molding processes. The MuCell microcellular physical foaming process from Wilmington, Mass.-based Trexel Inc., for example, may be a more economic solution for very large production volumes, Schmidt said, adding that it depends on the individual application.

Looking ahead, he said KIMW has already received inquiries as to whether the CO2 foam process can be used with silicone rubbers and thermosetting plastics.

Plastics News Europe Editor Karen Laird contributed to this report.