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2005-11-21 News Headlines

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High-Performance Rubbers for Injection Molding Articles

Proven EVM elastomer from LANXESS is cost-effective, versatile and suitable for a whole range of rubbers for injection molded products.

Sealing elements made from elastomers need to withstand a great deal of stress including high surface pressure and operating temperatures, mostly in the presence of aggressive media. This makes the seal sector an ideal area of application for high-performance rubbers – provided they can be processed using injection molding techniques. As a result of complex trials, rubber experts at LANXESS Deutschland GmbH, Leverkusen, were able to show how the proven ethylene vinylacetate copolymer (EVM) elastomer Levapren® can also be used for this effective manufacturing technique with excellent results. Thanks to LANXESS, seal manufacturers can now augment their portfolio of materials with a further high-quality elastomer with state-of-the-art properties and an excellent price/performance ratio.

"As well as natural rubber, the seal sector is also a prime consumer of a whole range of high-performance synthetic rubbers such as NBR and HNBR," says Dr. Hans Magg, rubber expert at LANXESS. Oddly, however, these have not as yet included ethylene vinyl acetate copolymers (EVM): "Despite their good price/performance ratio, these elastomers have not yet found the niche in sealing technology they deserve on the basis of their feature profile," says Dr. Magg. "This is because they have up till now been regarded as unsuitable for injection molding."

This claim has now been put to the test by LANXESS experts in the light of the company's longstanding experience with this material. And the result? "The old problems that certainly existed have now been solved," says Dr. Magg. "Levapren® is fully compatible with injection molding provided a few precautions are taken." The trials at LANXESS have demonstrated, for example, that the mold soiling frequently observed in the past can be largely prevented if metallic soaps are not used as a processing aid. The formation of bubbles can be effectively eradicated if the injection molding process is performed in such a way that the rubber parts are vulcanized under high internal pressure. "The ease of removal of the articles from the mold can, where necessary and useful, be further improved by shortening the vulcanization time and subsequent straightforward post-curing. This also improves product quality," explains Dr. Magg.

This means the seal sector can now add to its portfolio a material that is not only cost-effective, but also enormously versatile. "A correctly composed, peroxide-crosslinked Levapren® vulcanizate has a lifespan of 1,000 hours at 170 °C. If the Arrhenius approach is used, this figure increases to 20,000 hours’ continuous exposure at over 110 °C – in other words, over two years! Levapren vulcanizates therefore bridge the gap between hydrogenated nitrile rubber and fluororubber," says Dr. Magg.

Levapren® also boasts good compression set (for O-rings measuring 76 x 4 mm at 150 °C/1000 h, a very good 35 percent in accordance with ASTM D 1914), good oil resistance, and polarity and low-temperature flexibility that can be regulated by the vinyl acetate content. Dr. Magg adds: "The elastomer is also weather- and ozone-resistant, easily dyed and – provided certain rules are observed – also suitable for use in food-contacting articles."

Levapren® a heat-resistant rubber with a high filler tolerance is effective as a sheathing material for fuel lines, particularly in high-performance cars . Click on photo for larger image.

The EVM rubber Levapren® can also be formulated as an outer layer for hose so that it can resist long-term service temperatures of up to 175 °C. It is resistant to oxidative aging and thus represents a compromise between low-temperature flexibility and oil resistance. It thus complies with important demands of the automotive industry.

Possible uses in the automotive sector include seals for engine hoods, valve shafts and oil pans with hardnesses ranging from 50 to 70 Shore A. Hans Magg: "The key factors here are the resistance of Levapren® to engine oils with high additive levels and its excellent heat resistance." Added to this is a combination of vulcanizate hardness and low mixing viscosity that is particularly effective for the manufacture of large parts. "For hydraulic seals, the high modulus of the vulcanized product ensures excellent resilience when subjected to compressive forces. The rubber delivers leak-free seals even under extreme pressure and temperature fluctuations. For mobile hydraulics in the construction and forestry industries and in stationary plant, Levapren® seals are the answer to many problems that can currently only be solved with expensive fluoropolymers. In terms of its applications in the seal industry, this is without doubt just the start for Levapren®," says Dr. Magg.

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