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Additives are proving the key to thermoplastic olefin (TPO) formulations that can more aggressively pursue the interior real estate of cars, especially instrument panels (IPs). These new additives help boost scratch and mar resistance, without sacrificing ductility or impact.

Tony Deligio

January 7, 2009

3 Min Read
Additives help drive TPO instrument panels forward

At the SPE Automotive TPO conference this fall in Sterling Heights, MI, Evonik Goldschmidt (part of Evonik Industries) and talc supplier IMI FABI SpA released details on the pairing of Evonik’s new Tegomer antiscratch additive and IMI Fabi’s NS (no scratch) 140 micronized talc for TPOs that have dual strengths of scratch/mar resistance and no loss in stiffness. A delamination process is used to reduce the talc to the micron level, resulting in augmented scratch resistance, no variation of stiffness, and better impact, for a TPO system that was 20% talc filled with the Tegomer Antiscratch 100 additive. In addition to boosting scratch resistance, Evonik’s Kathrin Lehmann said Tegomer has been shown to boost mold release, augment impact with little effect on rigidity, and, in some cases, improve melt flow for the TPO system. Tegomer, which is a siloxane polyolefin compound, comes as a granule and can be mixed in at loadings of 2-3%.

Lehmann told MPW that Tegomer launched at the end of 2007, and some 50,000 dashboards pairing Tegomer and the IMI FABI NS 140 micronized talc have already been produced for OEMs including Mercedes, in Europe, Asia, and Russia.

In related talc news at the conference, Rio Tinto Minerals plans to bring a proprietary milling technology, which extends talc delamination to preserve the lamellarity of the structural plates to about 1 µm median particle size, to North America.

The milling technology creates the Jetfine line of talc products, which were especially developed to provide the highest balance of stiffness/toughness. Jetfine 3CA is the most commonly used for plastic applications, and in the last year, Rio Tinto Minerals began offering the talc to North America.

Rio Tinto Minerals’ Saied Kochesfahani said the Jetfine 3CA uses highly lamellar talc, mined in Ontario. Talc traditionally boosts impact resistance and lessens stiffness, but Kochesfahani says to maximize stiffness in application that are ductile at -30° to -40°C, the company used two microcrystalline and three macrocrystalline talcs.

Axel Plastics Research Laboratories and Rutgers University presented results for three new additive formulations designed to boost scratch/mar resistance for TPOs. 35 CPD, which is an existing product, as well as 701S, which is new, and 702S, which is still under development, were subjected to the Ford five-finger and ASTM scratch tests. According to Axel’s Ashutosh Sharma, the products use a proprietary formulation that doesn’t bloom or move to the surface during molding, and has dissimilar phases that stay separate.

Axel found that the 701S improved resistance with no scratch whitening up to 13N. It also improved talc and rubber dispersion in the TPO, and had strong fog-test performance, augmented percent strain at fracture, and improved impact and flow. Testing continues on 702S, but initial results showed that it had also improved scratch performance, with 1-3% loadings allowing up to 5N with the Ford five-finger test. Under the ASTM test, no scratches were visible at up to 9N. Here too, the additive increased percent strain at fracture and flow properties, while reducing resin viscosity. Ashutosh said the 35CPD yielded the best value in higher rubber and filler content TPO, while 701S offered the greatest value at lower rubber, lower filler content TPOs. For 702S, testing continues.

Also on the developmental front, Dow Elastomers is working on an impact modifier to join its family of Engage butene- and octene-based based products. To be commercially available by mid-2009, the product was described at the conference by Dow Elastomers’ Kim Walton as a higher efficiency impact modifier for rigid TPOs. In surveys, Dow found that when it comes to automotive TPO systems, its customers worry about, in order, flexural modulus, ductility, heat deflection, “tiger striping,” and knit lines. Addressing these concerns, Walton said Dow’s prototype impact modifier “looks very promising,” with higher dart and Izod impact, similar modulus, and improved stiffness.—[email protected]

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