New Physical Foaming Process Debuts at Fakuma

Pellets are impregnated with CO2 gas in a sealed chamber, which need not be mounted on the injection machine.

Testimony to what numerous industry sources say is growing interest in physical foaming processes for thermoplastic injection molding, a brand-new version emerged at October’s Fakuma 2017 show in Friedrichshafen, Germany. The technique, called Plastinum, was developed in Germany by The Kunststoff-Institute Lüdenscheid (KIMW) and Linde AG, together with equipment partners ProTec Polymer Processing GmbH and Sumitomo (SHI) Demag Plastics Machinery GmbH. The process involves batch impregnating plastic pellets with inert gas inside a pressurized container before feeding them into the injection machine. This distinguishes the process from others in which gas is injected into the melt through a port in the barrel wall.

At first blush, Plastinum seems a close cousin to the ProFoam process commercialized in 2015 by Arburg (U.S. office in Rocky Hill, Conn.) and developed at the Institute for Plastics Processing (IKV) in Aachen, Germany. Both processes can use standard screws and barrels, unlike gas-injection processes, so a machine can be used efficiently for foam or solid parts. What’s different is that in the Plastinum process, pellets are impregnated with CO2 in an autoclave, which takes 1.5 to 2 hr. The pellets are then conveyed to the machine hopper, which is not sealed or under pressure. According to KIMW, the gas will remain in the pellets at ambient conditions for 4 to 6 hr. Thus, Plastinum separates the gas-impregnation step from injection molding—one autoclave could feed two machines, for example, or could be moved on a cart between machines as needed. ProFoam, by contrast, impregnates the pellets (usually with nitrogen) inside a sealed hopper on the injection machine and requires a seal at the back of the screw to hold in the gas, as well as a shutoff nozzle in front. Plastinum requires no extra seals, only a shutoff nozzle. Both KIMW and ProTec sources say there is no patent conflict between the Plastinum process and Profoam or any other known foaming process.

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KIMW has tested Plastinum with PC, ABS, 30% glass-filled nylon, PP, PLA, TPE, and PTT polyester with 15% glass. In principle, any material could be used, KIMW says, though it has been observed that each material—even different grades of the same resin—absorbs the gas differently and thus requires testing.

Plastinum was demonstrated at Fakuma on a 110-ton IntElect all-electric press from Sumitomo Demag (U.S. office in Strongsville, Ohio). A ProTec Somos dryer fed pellets to the autoclave, also built by ProTec (in 100- and 200-liter sizes), as was the conveying system to load the machine hopper. The current system is suited to processing about 110 lb/hr. ProTec expects to commercialize it in 2018. It is working to combine the dryer and autoclave into a single unit.

Linde (U.S. office for plastics in Bridgewater, N.J.) supplies the CO2 gas.

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