Composites, foams, and coatings—innovative plastics at the international K Trade Fair

Oct 01, 2013
This shows foam injection molding techniques prevent striations. Credit: © Engel Austria GmbH

Airbags are standard equipment in automobiles today. They can save lives in emergencies, yet when no danger is present, they lie dormant beneath a cover made of plastic. These kinds of plastic components are usually injection molded. Plastic is melted, then injected into a mold for the corresponding piece and cooled until it is rigid again. Meanwhile, a new process has frequently been employed for producing the airbag covers. The process is called thermoplastic foam injection, or FIM.

The techniques offer several advantages over conventional . For one, they save up to 30 percent in material. For another, the components are less distorted, i.e. have fewer dents. In addition, designing is easier for engineers. While they have to be sure to inject the liquedfied plastic from the thicker parts of the workpiece into the thinner parts, it can also go the other way around with thermoplastic foam injection molding – i.e. from the thinner part to the thicker part of the workpiece. However, the new also conceals a disadvantage: striations are formed on the surfaces of the plastic parts. We don't see these on most airbag covers thanks to the textured appearance that hides the irregularities. Researchers at the Fraunhofer Institute for Chemical Technology ICT in Pfinztal, Germany, now want to eliminate these striations – and so promote the use of the process for highly visible components that should be employed without a textured surface.

Injected foam without striations

Exactly what is thermoplastic foam injection molding, however? Basically, it involves common injection molding technology, in which the plastic is melted and injected into a mold before it becomes rigid. However, an FIM machine has an additional feature: it introduces a propellant into the melt. When this mixture is sprayed into the mold, the air pressure drops drastically – similar to a bottle of carbonated liquid which is shaken, then opened. The result: the plastic – researchers speak of polymers – turns to foam. The finished part is therefore not isopycnic, i.e. equally dense inside and out, but instead has a structure more like a sandwich. The interior consists of the foamed plastic, while the outer surfaces are solid and hard.

Striations appear because the hot polymer melt forms foam bubbles as it flows through the cooled tooling. These are compressed by pressure of the melted polymer against the tooling – with the irregularities becoming rigid along with the melt and remain visible at the surface of the finished piece. "We avoid formation of striations by differentially heating the tooling," says Andreas Menrath, a scientist at ICT. "The polymer remains malleable longer due to the higher tooling temperatures it comes into contact with during injection. The bubbles do not become rigid immediately, but instead the surface is pressed smooth." The researchers have already tested the equipment necessary for this and are employing it. At the moment, they are working on an additional means to prevent striations: the tooling is coated with insulation material that retains the heat within the polymer longer. The engineers are presently testing various materials and coating thicknesses. The scientists will be displaying an FIM machine at K Trade Fair and producing foam-injected frisbees right on site.

24 frisbees highlight new technologies

This is not all that visitors will get to see at the joint Fraunhofer booth. The participating Institutes will be presenting 24 different frisbees, each of which has been produced with new materials or new technologies. For example, researchers of the Fraunhofer Institute for Wood Research, Wilhelm-Klauditz-Institut WKI will be displaying a frisbee consisting of a wood and plastic composite material. This material consists of up to 60 or 70 percent wood flour, up to 20 or 35 percent plastic, and up to 5 or 10 percent additives. An additional frisbee displays laser ablation. Researchers have produced concavities by removing material at particular spots from polypropylene and polyamid substrates using a CO2 laser.

Conjoining plastic and glass

Plastic is light-weight and malleable – that is what makes it so popular. However, this malleability also results in disadvantages: the surface scratches easily. Coatings promise remedies by making the harder and scratch-resistant. However, since the paints and varnishes used for this are likewise polymer-based, there are limits to their hardness. Researchers of the Institute of Interfacial Process Engineering and Plasma Technology (IGVP) of the University of Stuttgart together with the Fraunhofer Institute for Interfacial Engineering and Biotechnology IGB have now developed a new type of coating: instead of plastic, it consists of glass. The scientists have thereby combined light weight and hardness for the first time. In addition, the high-rate deposition of a glass layer by plasma technology requires no more time than applying paint or varnish. The researchers will be displaying this new coating on a sample frisbee as well at K Trade Fair.

Recycled Styropor

An additional frisbee consists of recycled Styropor®. This is a first, as expanded polystyrene has always been considered unrecyclable. The reason: most Styropor is employed for thermal insulation of buildings and is therefore mixed with additives that are intended to inhibit flammability. Researchers at the Fraunhofer Institute for Process Engineering and Packaging IVV in Freising, Germany, have now developed a technology with which Styropor can indeed be recycled. The CreaSolv process produces recycled plastics whose quality is just as high as virgin .

Explore further: Adding precision to plastics testing

add to favorites email to friend print save as pdf

Related Stories

Adding precision to plastics testing

Sep 02, 2013

Plastics play an important role in many consumer items. But testing precisely how much load these plastic parts can bear has up to now been a very complicated task. Now, a new instrument achieves simpler ...

Composites for large-scale manufacturing

Dec 10, 2012

Continuous fiber-reinforced composites with thermoplastic matrix resins are very well suited for use in automotive manufacturing. However, to manufacture them is complicated. A new approach now makes it possible ...

The smallest puzzle in the world

Jul 15, 2013

Three pieces of less than 1 mm in size each may be put together to the probably smallest puzzle in the world. For production, researchers used LIGA2.X, a new process to manufacture microstructured casting ...

Plastic monitors itself

Oct 18, 2010

A new polymer-metal material that has sensory properties makes it possible to produce plastic component parts that monitor themselves. This material can be combined with various others and used in a variety ...

Sorting plastic waste: A magnetic game

Jun 14, 2013

More than one third of the total plastic production in Europe—about 14 million tonnes per year—are polyolefins, also known as polyalkenes. This is a family of polymers used for the manufacture of a variety ...

Recommended for you

A smart prosthetic knee with in-vivo diagnoses

Apr 22, 2014

The task was to develop intelligent prosthetic joints that, via sensors, are capable of detecting early failure long before a patient suffers. EPFL researchers have taken up the challenge.

Old tires become material for new and improved roads

Apr 22, 2014

( —Americans generate nearly 300 million scrap tires every year, according to the Environmental Protection Agency (EPA). Historically, these worn tires often end up in landfills or, when illegally ...

Students take clot-buster for a spin

Apr 21, 2014

( —In the hands of some Rice University senior engineering students, a fishing rod is more than what it seems. For them, it's a way to help destroy blood clots that threaten lives.

User comments : 0

More news stories

SK Hynix posts Q1 surge in net profit

South Korea's SK Hynix Inc said Thursday its first-quarter net profit surged nearly 350 percent from the previous year on a spike in sales of PC memory chips.

FCC to propose pay-for-priority Internet standards

The Federal Communications Commission is set to propose new open Internet rules that would allow content companies to pay for faster delivery over the so-called "last mile" connection to people's homes.

Brazil enacts Internet 'Bill of Rights'

Brazil's president signed into law on Wednesday a "Bill of Rights" for the digital age that aims to protect online privacy and promote the Internet as a public utility by barring telecommunications companies ...

Is nuclear power the only way to avoid geoengineering?

"I think one can argue that if we were to follow a strong nuclear energy pathway—as well as doing everything else that we can—then we can solve the climate problem without doing geoengineering." So says Tom Wigley, one ...

When things get glassy, molecules go fractal

Colorful church windows, beads on a necklace and many of our favorite plastics share something in common—they all belong to a state of matter known as glasses. School children learn the difference between ...

FDA proposes first regulations for e-cigarettes

The federal government wants to prohibit sales of electronic cigarettes to minors and require approval for new products and health warning labels under regulations being proposed by the Food and Drug Administration.