Charging ahead with polycarbonates for high voltage components in EVs and EE

The automotive industry is transforming before our eyes. Covestro is charging ahead with improved Bayblend® and Makrolon® grades that comply with Comparative Tracking Index (CTI) ratings and flame retardancy (FR) specifications for high-voltage components, including lithium ion batteries and power electronics
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e-mobility material innovation: Bayblend® and Makrolon® grades for high-voltage components

Polycarbonates from Covestro offer excellent electrical properties that have been proven in a wide range of applications in the EE industry. 

Today, due to current trends toward increasing energy density and reducing component size, electric vehicles (EVs) require increasingly more FR materials that provide a CTI of 600V (The CTI assesses the relative resistance of the insulating materials to tracking). It indicates the highest voltage at which no specimen fails when tested on five samples, each after the application of 50 drops of a defined test solution).

Traditionally, polycarbonates have fallen short of this rating. But now, Covestro has once again shifted its innovation into high gear, developing new solutions based on amorphous polycarbonates that combine an UL94 V-0 flame retardancy rating with a maximum CTI of 600V according to IEC60112. These new materials include grades belonging to our flame retardant Bayblend® and Makrolon® product line. Such amorphous materials provide additionally a high dimensional stability with low warpage and a thermally isotropic behavior.

The newly developed grades are designed for applications in Li-ion-battery housings, high-voltage components of the electric powertrain and general E&E applications like EV charging stations and photovoltaics.

And there’s more.

Covestro has developed a tool box of different possibilities to increase the CTI of polycarbonates. For example, Covestro is able to support customers by developing new grades with additional thermally conductive properties for heat management in high-voltage applications which require a CTI of 600V and flame retardancy (Covestro internal tests, preliminary data). More materials are in the product pipeline or can be developed according to customer requirements. 

Bayblend® FR3015 CTI and Makrolon® FR6019 CTI available for Li-Ion batteries, power electronics and other high-voltage applications

Bayblend® FR3015 CTI is a flame retardant and ductile PC blend, developed for Li-ion battery applications, such as cell holders or bus bar carriers. Characterized by a high Vicat temperature of 120°C this unreinforced and low warpage grade can be used for components with increased safety requirements, e.g. a CTI of 600V combined with a UL94V-0 rating at 1.5mm, in addition to the already available Bayblend® FR solutions. The high Vicat temperature results in stable mechanical properties over its entire temperature range, thus making glass-fiber reinforcement unnecessary.

Makrolon® FR6019 CTI is an unreinforced and flame-retardant polycarbonate with UL94V-0 classification at 1.5mm with a high CTI of 600V designed for applications in the power electronics and can also be used in Li-ion batteries. It is impact-resistant and has an even higher Vicat temperature of 130°C. Below  the softening temperature, the mechanical properties remain nearly constant which again makes any glass-fiber reinforcement unnecessary. As a result, Makrolon® FR6019 CTI is distinguished by its thermally isotropic behavior and low warpage. 

Both, Bayblend® FR3015 CTI and Makrolon® FR6019 CTI, are opaque grades and easy to color. Customers should bear in mind that the color, being part of the recipe, might modify the CTI value. Covestro therefore offers its customers technical support.

Materials that measure up: tested according to IEC60112

The CTI is measured and rated according to IEC60112. Its result is a voltage rating of the tested material ranging between 175V and 600V. Depending on the rated voltage, the materials can be allocated to insulating material groups  Based on the CTI rating, the operating voltage and the degree of pollution, a minimum distance between tracks can be derived, which provides orientation to the design engineer. 

The CTI test consists of two electrodes placed in a pre-defined distance on the substrate. Starting between 300 and 350V, at each voltage test level 50 drops of a conductive solution is applied between the electrodes. If a voltage level is successfully tested, it can be gradually increased until it reaches the maximum test voltage of 600V. If a voltage level failed in the test, the CTI is defined as the last voltage level having passed the test.

“Until now, flame-retardant polycarbonates failed to provide an electrical creepage resistance of 600V. Extensive fundamental research and valuable customer input from the target industries set the foundation to develop polycarbonate-based grades that combine the positive properties from amorphous materials, such as dimensional stability and low warpage, in combination with improved electrical properties.”

Dr. Matthias Knaupp

Global Technology Development & Project Lead CTI Materials

Range of materials options for low voltage components

When it comes to thermal conductivity, metals typically outperform their thermally conductive plastic counterparts. But in terms of design or mass production, plastics surpass metals any time. By exploiting the advantages of plastics, an intelligent design of a plastic heat sink can often result in cooling performances similar to that of a metal heat sink.

In addition to Bayblend® FR3015 CTI and Makrolon® FR6019 CTI, both flame-retardant with a CTI of 600V, Covestro offers a wide portfolio of black, electrically conductive, and white, electrically insulating, thermally conductive plastics with a lower CTI. Some of these grades are equipped with an additional flame retardancy (FR) package yielding a UL94 V-0 rating. 

In order to achieve moderate heat dissipation, we recommend Makrolon® TC110 FR.  It also has a low carbon footprint. 

For higher heat dissipation rates, Makrolon® TC629 is the material of choice. Beside of being thermally conductive, Makrolon® TC629 provides electrical conductivity with a surface resistivity of 4∙103 Ω and a volume resistivity of 1∙102 Ωm. Due to these electrical properties, it provides an EMI shielding effectiveness of up to 55dB at 3mm thickness for frequencies ranging between 1 and 18GHz according to internal tests performed by Covestro (preliminary data, depending on part thickness and design). It could, therefore, support EMI shielding efforts at OEMs and tiers.

Beyond supplying materials, Covestro offers a wide range of support to help customers take their ideas from the drawing board to consumer driveways. This includes digital engineering, such as thermal simulations, structural simulations, rheological simulations and mold design support, as well as on-site processing and production support.


Key Benefits

  • Burning behavior and improved electric properties:  UL94 V-0 in combination with a CTI rating of 600V (acc. to IEC60112)
  • Operating temperatures: Vicat temperatures from 105 – 130 °C for various applications
  • Dimensional stability:  Low & predictable shrinkage, low warpage
  • Mechanical behavior:  Almost constant tensile modulus over a wide temperature range in combination with high ductility without reinforcement

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(CTI / FR) Polycarbonates Overview

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