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Chemical groups gearing up E-mobility revolution
Source:    Author:By Victor Cheng    Date:24.Dec.2018

Undoubtedly, innovative high-performance materials are getting wider applications in electric vehicles (EVs), in which lightweight, flame retardant, hydrolysis and temperature resistance are crucial properties of the materials.

When developing materials especially targeting to facilitate the rapid development of E-mobility, the aforementioned properties must be put into consideration.

Among the latest products introduced by leading chemical groups and material suppliers, polyamides, polycarbonate and polybutylene terephthalate (PBT) have been commonly used for modification, achieving specific enhanced properties. Meanwhile, higher glass fiber reinforced content is frequently used to increase the thermomechanical properties and processability of the new materials.

Developing polyamides of different crucial properties

In order to meet the different requirements in different EV applications, EMS-GRIVORY designs a comprehensive polyamide portfolio especially for the development of E-mobility.

Long fiber reinforced high-performance polyamides from EMS-GRIVORY provide an alternative to heavy die-cast alloys. Thanks to their partially aromatic matrix that enables them to remain stiff and strong, even after water absorption, these polyamides are used for components such as battery brackets and housings in EVs.

As introduced, the special long glass-fiber reinforcement (LFT) leads to a sustainable improvement of thermomechanical properties at high temperatures so that these LFT products still exhibit high mechanical property values even at temperatures in the region of the glass transition point.
Cooling water valve made of Grivory HT1VA-35 HYS.
In addition, the fiber skeleton makes high energy absorption possible under crash loading. For the simulation of highly dynamic processes, EMS-GRIVORY provides elongation rate dependent material data sets, taking into account anisotropy and kind of load, to enable optimal design of structural components in the field of electric car construction.

For components of the high-voltage on-board power systems in EVs, the leading high-performance polymers manufacturer offers a wide assortment of flame-protected polyamides, ranging from non-reinforced polyamide 6 and glass-fiber reinforced PA66 and PA6 grades up to polyphthalamides solderable at temperatures up to 260°C.

To facilitate challenging applications in cooling systems, such as auxiliary water pumps or thermal management modules, EMS-GRIVORY has developed the new product Grivory HT1VA which demonstrates outstanding resistance to hydrolysis and cooling agents and can withstand long-term use at moderate cooling agent temperatures.

According to the company, after around 12,000 hours in water at 95°C, Grivory HT1VA exhibits 30% higher strength values compared to a traditional PPA under the same conditions. A further advantage of this product when used in electric vehicle applications is that it is equipped with electro-compatible stabilization.

Hydrolysis-resistant PBT materials satisfy growing demand

Meanwhile, BASF has further developed its range of hydrolysis-resistant (HR) thermoplastic polyesters to fulfill the growing demand for components for the expansion of E-mobility and autonomous driving.

The expanded range of Ultradur HR includes: Ultradur B4330 G6 HR High Speed, a particularly flowable and laser markable grade with 30% glass-fiber reinforcement; Ultradur B4330 G10 HR, a highly reinforced grade with 50% glass fibers; Ultradur B4331 G6 HR, the next generation with optimized processing characteristics.

The expanded grades of Ultradur HR offer long service life and excellent operational reliability. With its Ultradur HR grades, BASF offers highly resistant PBT materials which are especially suitable for use in challenging environments. They thus enable a long service life and an excellent operational reliability of automotive components.

The HR grades also have a considerably increased resistance to alkaline media which trigger stress corrosion cracking. This is also true for the new Ultradur B4331 G6 HR grade with considerably improved melt stability and flowability.

In tests, Ultradur B4331 G6 HR does not display any increase in viscosity even with long residence times and at high temperatures. The material can also be colored in orange (RAL 2003) in order to produce high-voltage plug-in connectors for EVs.

Thanks to the unusually high tracking resistance for PBT, the plug-in connectors can be designed smaller and still withstand the higher voltages in EV. Thus savings on costs and component weight are possible.

The Ultradur 4330 G6 HR series, which is available with 30% glass-fiber reinforcement, has been expanded to include the particularly flowable and laser-markable Ultradur B4330 G6 HR High Speed bk15045. With this grade, thin-walled parts and components which show a high ratio of flow path to wall thickness can easily be produced.

As filled with 50% glass fibers, the new Ultradur B4330 G10 HR can therefore be processed to components which are simultaneously exposed to moisture and high temperatures (160°C, short term up to 180°C) and keep a high stiffness, e.g. steering modules in the charge air duct.

In addition, BASF has developed Ultradur B4450 G5 HR for selected automotive applications. The PBT is reinforced with 25% glass fibers, RoHS-compliant and flame retardant. It can be colored in light colors and laser-printed.

Since the market launch, BASF has developed around a dozen HR-modified Ultradur grades, with 15%, 30% and 50% glass-fiber reinforcement. Typical applications can be found primarily in automotive electronics, e.g. housings of control units, connectors, sensors, but also charging plugs, housings of battery stacks or connectors in the high-voltage circuit of electric cars.

Expanding flame-retardant PBT product range

In order to capture opportunities in unattended EV applications, specialty chemical company LANXESS is expanding its range of halogen-free flame-retardant compounds based on PBT to include variants with outstanding fire resistance in glow wire tests.

The first in the product range is a compound reinforced with a glass fiber content of 25%. There are plans to introduce the trial product onto the market shortly.
 LANXESS conducts flame retardancy tests in compliance with standards on test specimens and components, for example, glow wire tests.
Due to their high glow wire resistance, such PBT materials have great potential in components used in unattended household appliances. In addition, we see very good opportunities for electrical and electronic components of electrified vehicles, e.g. in the area of battery charging,” said Alexander Radeck, application developer in the High Performance Materials (HPM) business unit at LANXESS.

The new PBT material has already been certified by VDE Prüf- und Zertifizierungsinstitut GmbH with a GWIT value of 775°C for wall thicknesses of 0.4 to 3.0 millimeters (Glow Wire Ignition Temperature, IEC 60695-2-13). It also achieves excellent results in glow wire tests on finished parts according to IEC 60695-2-11.

The other properties of the new glow wire-resistant material are similar to those of other halogen-free flame-retardant PBT compounds already on the market from LANXESS. These include product variants reinforced with a glass fiber content of 13 to 30 percent and an unreinforced compound.

They all achieve the best classification of V-0 in flammability testing pursuant to the United States’ UL 94 (Underwriter Laboratories Inc.) standard. They are also highly resistant to UV light and rarely corrode when in contact with live components. Another advantage is their high thermal stability.

Among these products, the unreinforced Pocan BFN2502 particularly stands out. Its properties make it a rarity on the market. Despite the halogen-free flame-retardant package, it has a high elongation at break of more than 7%. It is particularly suitable for components that must be both dimensionally stable and permanently electrically insulating.

Some of our customers use the material to replace unreinforced polyamide 66 compounds with halogen-containing flame-retardant packages if the water absorption of polyamide in the component leads to problems with dimensional stability,” added Radeck.

The new PBT is also an alternative for corresponding unreinforced PBT compounds because it provides a better tracking resistance of 600 volts (CTI A, Comparative Tracking Index, IEC 60112) for DC applications, for example.

Tailor-made polycarbonate blends protect the heart of E-mobility

One of Covestro's current focal points is the use of polycarbonate plastics in EVs. The heart of future electric cars and hybrid vehicles is a lithium-ion battery. In order to position a large number of battery cells precisely and in a small space, cell holders and frames as well as housing components must be very dimensionally stable and mechanically robust.

Depending on the design principle of the battery pack, the material must also be flame-retardant and meet category V-0 of Underwriters Laboratories' UL94 flammability classification even at low wall thicknesses down to 0.75 millimeters.

To achieve this, Covestro has developed various polycarbonate blends that meet these requirements and are also extremely impact-resistant over a wide temperature range, especially at sub-zero temperatures.

The flame-retardant polycarbonate ABS (acrylonitrile-butadiene-styrene) blend of the Bayblend FR type was developed for cell holders and battery modules. It is temperature resistant and dimensionally stable, and the parts can be produced efficiently with injection molding.

The crash absorber exhibited at Fakuma 2018 is made of the PC-PBT Makroblend KU-2 7912/4. The material has very high impact strength and particularly high ductility at low temperatures. The honeycomb structure contributes to the extreme impact resistance of the crash absorber.

Another special material is the highly filled polycarbonates of the Makrolon TC product family, which are already used for heat sinks in LED lamps. These products are thermally conductive but also available as electrically insulating versions so they can contribute to the efficient thermal management of batteries.

Innovative hybrid materials ready for opportunities

Kraiburg TPE has recently launched the ground breaking thermoplastic elastomer hybrids (TEH) which can withstand permanent operating temperatures up to 150°C and remain chemically stable when exposed to oils, lubricants, fuels and coolants. They are available in hardnesses from 55 to 80 Shore A.

Drive-train and battery heat-management systems in EVs represent immediate opportunities for TEH materials. Other key applications include automotive components, seals and gaskets, lubrication and cooling systems.

Our TEH manufacturing technology enables us to combine different mixtures of various elastomers and thermoplastics with respective crosslinked systems to form materials with unprecedented properties,” explained Dr. Frieder Vielsack, Head of Advance Development at Kraiburg TPE. “Their properties include high media and temperature resistances, which are adjusted to the requirements of each application.”



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