Trends in automotive engineering plastics: The K Show and beyond

Every day, scientists at engineering resins firms are holed up in labs around the world, concocting new thermoplastics as part of an ongoing attempt to get one their biggest customers, the automotive industry, to continue replacing metal with plastic.

Germany’s triennial K Show is where these companies strut their stuff, showing off their newest resin grades, additive technology and resin processing technology. But that’s just half the battle. If the market doesn’t accept it, then all the money spent on research & development (R&D) just trickles down the drain.

That’s why developers of engineering resins target very particular market needs. In fact, when the engineering resins firms were asked to discuss the most important products they released at K last October, the majority cited new resin grades for specific applications in the automotive industry.

This past year, high-flow nylons as well as nylons with high percentages of glass or mineral additives, featured prominently.

GOING WITH THE FLOW

With more pressure on economics, and increasing demands in terms of tolerance and appearance, easy flow or reduced viscosity nylons are becoming much more popular. The trick is how to reduce viscosity without sacrificing the physical properties of the material.

Nylons that have been heavily reinforced with glass fibers benefit from higher tensile strength and tensile modulus. As well, finished parts are less likely to shrink and warp. But they tend to flow slowly, which increases costs and production time.

High-flow nylons make it easier for processors to mold large and complex parts. They also enable molders to use lower injection clamping force. This is because high-flow materials fill the tool faster, allowing the processors to reduce wall thickness, saving money on material.

As a result, processors can increase output by speeding up the injection molding machine, or they can move to smaller machines and run it at the same speed.

Aesthetically speaking, high-flowing glass-filled nylons also have better surface features, because the glass fibers spread out more evenly in the mold, reducing the amount of gritty pockets or swirls that can be seen in the finished product. The resulting glossy surface means that painting can be foregone with some applications.

As well as increasing flow, materials suppliers are starting to push the limit on just how much glass fiber can be comfortably crammed into nylon.

“Until recently, there seemed to be an upper limit of 50% of glass reinforcement for nylon because around that percentage composition, the nylon becomes difficult to hammer into a tool,” noted Rob Cunningham, application engineering team leader for Lanxess Deutschland GmbH.

However, at the K Show, Lanxess released a Nylon 6, with 60% glass fiber, called Durethan BKV60 H2.0 EF 901510.

Lanxess developed BKV60 by modifying the viscosity of the material so it could carry more glass fibers, Cunningham said. As a result, Durethan BKV60 is less viscous than other Durethan grades.

BKV60 is ideal for both replacing metal in engine compartment applications, and for structural components, especially with parts manufactured using plastic/metal composite technology, Lanxess said.

At room temperature, the tensile modulus, which measures stiffness, of BKV60 is almost 20,000 megapascals (Mpa), which is more than twice that of a standard Nylon 6 with 30% glass fiber content.

And, at 170C, BKV60 demonstrates a tensile modulus of 6,700Mpa, said Dr. Detlev Joachimi, head of Durethan product development in Lanxess’ Semi-Crystalline Products Business Unit, in a statement.

“In contrast, long fiber-reinforced polypropylene (PP), a rival to nylon in many applications, achieves a tensile modulus of 6,600Mpa at just 80C, which is shortly before it softens,” he explained.

BKV60 doesn’t have any commercial applications as yet, but Cunningham said tests have shown the material holds promise for front-end bolster systems, which are the components that hold the grill, fascia, headlamps, and occasionally the radiator on the front of the car.

STIFF COMPETITION

Meanwhile, DSM Engineering Plastics also released a 60% glass-fiber reinforced Nylon 4/6, dubbed Stanyl TW241F12.

Designed for automotive underhood applications, DSM is primarily marketing Stanyl TW241F12 for automotive gears as an alternative to Nylon 6/6. Stanyl has already achieved some success in that application, said Bruce Ballance, global marketing communications manager for DSM Engineering Plastics.

“Based on some testing over the past five years, we came to the realization that Stanyl has benefits for gear-makers for high temperatures,” he said.

Although gears are commonly made with Nylon 6 or Nylon 6/6, gears made with Stanyl Nylon 4/6 are only one-quarter of the volume, Ballance explained.

“Shrinking the gear train gives designers more space options and it reduces material, molding and housing costs, so that Stanyl gears are then lower cost than PA6/6. Smaller gear trains allow different motors to be used which are more efficient and lower in cost,” he said.

As well, Stanyl is more durable than Nylon 6 or 6/6 because it responds uniquely to annealing. “Annealing improves Stanyl’s durability by a factor of two or more when it comes to gears,” he said.

For example, Stanyl is being used for electronic throttle control (ETC) gears, electric power steering, and cruise control gears. “Just about all the major manufacturers in Japan are using Stanyl for a particular gear,” Ballance noted. “It’s already in the Hondas, the Toyotas, the Nissans.” American manufacturers aren’t using Stanyl yet.

The new grade can withstand continuous temperatures reaching 200C with transient peaks up to 250C, but has the highest stiffness at temperatures above 120C. In fact, it is 30% stiffer than the next Stanyl grade, the company said.

ROCKING THE BOAT

Meanwhile, Rhodia keeps tweaking its Technyl A family of nylon resins, especially for engine rocker covers, as it tries to position itself as the number one supplier of nylon rocker covers in the world.

At the K Show, Rhodia released a Nylon 6/6 grade loaded with 40% glass or mineral fiber, dubbed Technyl A218 MZ15 V25.

Compared to its predecessor, Technyl A218 MT15 V25, MZ15 has a 20% improvement in flow and a 30% improvement in melt flow, said Chad Waldschmidt, North American director for Rhodia Engineering Plastics.

The way Rhodia combined the glass and mineral fillers in the MZ15 means the finished parts warp less and have greater creep resistance, which translates into an enhanced ability to prevent oil leakage, Rhodia explained. M215’s high resistance to chemicals also makes it easy to paint.

Waldschmidt was tight-lipped about when rocker covers made with the Technyl A218 MZ15 V25 would be released, but he confirmed that some are in the works and at least one is in North America. Recently, MAN Nutzfahzeuge AG in Germany announced it will be making a rigid, one-metre long rocker cover with MT15, reinforced with 15% mineral and 25% glass.

Rocker covers isn’t a new market for Rhodia — it has been supplying them to European auto parts manufacturers for over a decade to replace aluminum and magnesium, Waldschmidt said, but the North American market has been slow to catch on.

FILLING IN THE GAPS

However, thermoplastics are still losing out to metals in some automotive applications, such as body panels for automobiles, said Derek Buckmaster, global automotive market director, body panels and glazing in Bergen op Zoom, The Netherlands.

On average, plastic accounts for only between 5 and 6% of a car’s skin, and the reason is because plastics have higher co-efficients of thermal expansion (CTEs), which measures how much materials expands when heated, he explained.

“Steel panels expand only 10 to 15% as much as a thermoplastic panel when heated,” Buckmaster noted. So
far, it hasn’t been much of a problem for applications such as fenders because auto-makers fix the fender at one end and leave a gap at the other to allow for expansion. But for applications like doors, expansion means the door wouldn’t be able to open or close properly, he said.

However, adding nanocomposite fillers to GE’s Cycoloy PC/ABS, Xenoy PC/polyester and Noryl nylon/PPE families has decreased the materials’ CTEs, he said. While these resins with “high modulus ductility (HMD)” are still in development, GE expects to release commercial versions of Cycoloy HMD and Xenoy HMD within the next two years.

So far, tests with Cycoloy HMD and Xenoy HMD have shown a 20% improvement in CTE, to around 5×10-5mm/mm/C.

Typical plastics that are used for plastic body panels have a CTE of between 8 and 9×10-5mm/mm/C, while steel has a CTE of between 1 and 2×10-5mm/mm/C, Buckmaster said.

The reduction in CTE was first discovered as a side benefit when GE first experimented with nanocomposites to increase the resins’ modulus. “In the past, if we wanted to make a plastic stiffer, or develop a plastic that had high modulus, we would typically add glass or carbon fillers, but we would have trade off in ductility,” Buckmaster said. “So it would be stiffer but not so impact resistant.”

The initial objective with using nano-fillers is to make shorter strand polymers just as tough, but keep them easy to process, he added. Experiments have shown that GE’s HMD materials are achieving a modulus of 4,000 to 5,000 mPa.

Plastic body panels have been accepted in the industry, but only for certain applications, such as small-sized cars and for some fenders, he added.

At this time, there are no body panel applications with any grades of Cycoloy or Xenoy, Buckmaster said. Noryl GTX, however, is currently used in some plastic body panels, notably the BMW 6 Series Coupe.

However, because Noryl is a higher temperature material, and adding nanocomposite fillers has not produced such a radical reduction in the material’s CTE, Noryl HMD will be a longer term development cycle, Buckmaster said.

Noryl HMD will be targeted for on-line painted components because its ability to withstand high temperatures allows it to be painted on the production line.

Because Cycoloy and Xenoy don’t share Noryl’s high temperature tolerance levels, Cycoloy HMD and Xenoy HMD will be targeted for PC/ABS offline painted components.

TURNING RUBBER INTO PLASTIC

Rubber has some characteristics that make it ideal for some automotive applications over thermoplastics. DuPont, however, has cooked up a line of engineering thermoplastic vulcanizates (ETOVs), with rubber like properties, which it showcased at the K Show.

Used in body plugs, fuel vent tubes, air brake hoses, and ignition coils, DuPont’s ETPVs compounds are based on copolyster, explained Engineering Polymers Canadian business manager, Chul Lee, in Mississauga Ont., while the majority of TPVs are based on polypropylene (PP).

TPVs typically have two phases: A plastic phase and a rubber phase. The plastic phase allows TPVs and ETPVs to be processed using traditional thermoplastic equipment, Lee explained.

“What differentiates our product, is that unlike traditional TPVs, our products can withstand high temperatures in the 135 to 170C range,” he said. Most TPVs can only withstand maximum temperatures of 120 to 135C.

Additionally, DuPont ETPV has excellent oil resistance, making it ideal for automotive underhood applications.

“Traditionally, automotive underhood temperatures require components to withstand a temperature of 150C for 3,000 hours,” he said.

For example, DuPont EPTV body plugs is one area where rubber has been replaced.

When a car body is manufactured, there are drain holes in it to allow the excess E-coat to drain out. These holes need to be filled with body plugs, but the plugs have to be able to withstand temperatures as high as 170C or up to 30 minutes when a car body is baked during successive painting process.

Right now, body plugs made from a broad range of materials including rubber, metal and other thermoplastics. However, body plugs made with DuPont ETPV provide an excellent combination of flexibility, heat resistance and cost compared to plugs made from other materials.

Unlike thermoset rubber, thermoplastics like DuPont ETPV also enable processors to re-use any scrap generated during processing.

GETTING THE CLEAR PICTURE WTH POLYSULFONE

Solvay’s P-1700 HC polysulfone is nearly colorless, making it ideal for applications such as face shields, sight glasses and lighting.

In the past, design engineers turned up their noses at polysulfone (PSU) for applications requiring clarity, such as face shields, protective eye wear, sight glasses and lighting components.

The resin’s yellow tinge, made them opt for polycarbonates (PC), acrylics or glass, explained Ziad Haddad, Solvay Advanced Polymers LLC’s, product manager, sulfone polymers.

But with a new PSU grade from Solvay, the choice is no longer as clear. At the K Show, Solvay released a nearly colourless UDEL polysulfone grade dubbed UDEL P-1700 HC.

“It’s not as clear as polycarbonate,” Haddad said. “But it’s close.”

The benefits to UDEL P-1700 HC over PC and acrylics is its high heat resistance, withstanding temperatures from -101C up to 149C, and its heat deflection temperature, which is 174C at 1.82Mpa.

Additionally, UDEL P-1700 HC is resistant to acids and bases, hydrolysis by hot water and a range of cleaners and disinfectants, according to Solvay. The material’s resistance to alcohols and aliphatic hydrocarbons is good, but it’s generally not able to withstand polar organic, or chlorinated solvents.

So far, UDEL P-1700 HC has stirred up quite a bit of interest; a lot has been sold and is being sampled at various companies for different applications. However, Haddad said Solvay has non-disclosure agreements and cannot divulge the details.

When using UDEL P-1700 HC with standard screw injection equipment, Solvay noted that the shot size should be between 50 and 75% of barrel capacity because the longer the resin stays in the barrel, the more likely it is to become discoloured. Mold temperatures of at least 121C are recommended, except with complex parts having long flow lengths or thin cross sections when mold temperatures should be 149 to 163C, Solvay said.

Solvay also has a high-flow version UDEL P-1700 HC but its chemical resistance properties are inferior, Haddad said.