Mucell process prevents warping in thin-wall parts

Plastics processors making precision and engineered components have long been plagued by warping, roundness, flatness and sink marks on their newly molded parts, caused by uneven stress patterns that occur when gas comes to the interface between the mold and the material during the molding process.

Now, however, plastics development company Trexel Inc., based in Woburn, Mass., promises to help put an end to this problem with its Mucell microcellular foam injection molding process.

The Mucell technology, which is targeted to precision and engineered parts with a maximum wall thickness of less than 3 mm, involves the controlled use of gas in its supercritical state to create a foamed part that can have between a 50 to 75 per cent better compliance with the mold shape and, therefore, with the dimensional specifications of the part itself.

According to David Bernstein, Trexel’s president and CEO, the Mucell process relies on two key principles. “First, if you use gas in a supercritical state — high pressure but not extraordinarily high pressure — you can measure, meter and control it very precisely,” he explained. “Second, if you fully integrate the gas into the polymer during the processing and then subject it to a very fast pressure drop, like from a nozzle into a mold, you achieve almost instantaneous creation of cells that tend to be very small and uniform, and thus more stable inside the mold.”

The Mucell process is applicable to most resins ranging from filled polypropylenes (PP) to nylons, polybutylene terephthalate (PBT) and high temperature engineering resins, and can be applied on parts of all sizes and on machines as small as 50 tons and as large as 3,000 tons, the company said.

“This technology has tremendously broad applications in the business equipment environment because there are so many precision parts that cannot and must not distort when exposed to heat, such as laser printers, inkjet printers, fax machines and copy machines,” Bernstein said.

And the Mucell process has also been adopted by the automotive industry, he added, being used for lock housings on car doors, and such under-the-hood applications as fan shrouds.

Austrian-based injection molding machine manufacturer Engel Inc. is also using the Mucell technology to enable its Dolphin machinery to produce soft-touch interior automotive applications such as dashboards. “The Mucell process is ideal for soft-touch parts because it eliminates sink markings, which are a big issue when you are covering automotive interiors with a skin,” Bernstein said.

A big step forward for the company came in June 2006, when Trexel entered into a partnership with Farmington, Mich.-based Rhodia Polymide, a division of global chemical supplier Rhodia Engineering Plastics Corp., to develop and commercialize new material technology optimized for the Mucell process.

“The response to the Mucell technology has been good and is getting better,” Bernstein said. “Today we have about 300 systems worldwide and the largest number of systems that we have ever sold will be sold this quarter.”

Trexel Inc. (Woburn, Mass.);

www.trexel.com; 781-932-0202