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Kuraray Explores Real Potential of its GENESTAR™ PA9T Resins for High CTI (>600V)

Published on 2019-09-05. Author : SpecialChem

Kuraray-Genestar-CTI-Tests TAGS:  Automotive      Electrical & Electronics      High Heat Materials     Thermoplastic Composites    

Today, focus of the automotive industry towards electrical vehicles (EV) is tremendously catalyzed. One of the major challenges consists in increasing the driving range, which makes that optimizing the car’s efficiency is one of the key points. While earlier developed EV’s made use of battery voltage levels of 300-400 VDC, latest developments such as the Porsche Taycan takes advantage of an 800 V battery.

Next to higher voltages, also mass reduction and thus part miniaturization are a piece of the puzzle towards a higher efficiency. When these two trends are combined, the demands on the insulating materials rise because failure caused by electric breakdown becomes a risk.

Nowadays, more and more plastic materials are rated as PLC 0, either by native properties such as polyphtalamides (PPA) or by additives to increase the tracking resistance. With higher voltages and continuous size-reduction in mind, thinking beyond the PLC table could be a next opportunity for further improvements.

Therefore, recently Kuraray’s R&D dove deeper into the topic. The company started to evaluate the limits of its GENESTER™ PA9T resins, a long chain PPA. The range is characterized by its low water absorption that exhibits a CTI > 600 V or PLC-class 0 for most of its grades, from unreinforced to halogen-free V0 grades with 30% glass-fiber reinforcement.

CTI Measurements According to IEC 60112

In a first attempt to find the limits of GENESTAR™ PA9T resins, CTI measurements according to IEC 60112 were initiated and the voltage was ramped up to 625 V. Yet, it became clear that the 600 V upper limit of current PLC-classes is most likely caused by the experiment setup as a partial breakdown over the air occurred.

  • It was anticipated that this breakdown is caused by the edge of the electrode knowing that such an edge causes a higher field strength compared to a flat surface.
  • To circumvent this issue, electrodes were turned 180°C, which results in a higher clearance between the electrodes and the electrode’s edge turned away while keeping the clearance the same.

With this minor adaptation, the voltage could be ramped up to 750V without influencing the tracking on the material, which was confirmed by a control measurement of a material with a CTI of 550V. Using this setup, five GENESTAR™ grades were evaluated with a voltage up to 750V.

  • For only two grades, a standard unreinforced (N1000A-M41) and standard 30%GF grade (G1300A-M41) tracking was observed at respectively 675 V and 725 V.
  • For the three other grades, which were developed for parts in the electrical environment, no tracking was observed even at 750 V.

Influence of Glass-fibers and Electro-friendly Heat Stabilizers

It can be observed that inorganic fillers such as glass-fiber have a positive effect as all GF-reinforced grades exhibit a higher tracking resistance or even did not caused discharge at 750 V. For the unreinforced grade, tracking that occurred at 675 V is still well beyond the current maximum rating. Considering its higher ductility, excellent resistance against heat shock cracking can be foreseen, which makes such an unreinforced grade a perfect candidate for overmolding of metal parts.

GENESTAR™ grade Grade description Breakdown voltage (V)

    Standard, unreinforced

    Standard, 30% GF

    E-friendly, 30% GF

    Halogen-free, V0, 30% GF

    Halogen-free, V0, 45% GF

Although it was not achieved to find the real limits as the test setup did not enable going beyond 750 V, these experiments teach us that there is still a big margin above 600 V as no tracking was observed for three common GENESTAR™ grades even 150 V above the current limit.

Select the suitable GENESTAR™ PA9T resin for your application:

Source: Kuraray
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