Flexible polymer makes thinner cables

A breakthrough in plastic insulation is of exceptional potential interest to automotive electrical engineers. Tom Shelley reports



By giving elastomeric properties to PPO - polyphenylene oxide - it is possible to take 25% of the weight out of standard automotive wiring and greatly reduce the space it occupies.

This should be of interest to all electrical engineers - but particularly those working in the automotive and aerospace industries.

PPO resin is not ordinarily flexible. In order to make it so, something else has to be blended in which is. This apparently just what GE Advanced Materials has done with its new 'Flexible Noryl' resin.

When we asked Kristie Dolan, the company's Product Marketing Director, how this had been achieved, she declined to answer, pointing out that the technology used is highly proprietary.
However, she did mention a "Strong compatibilisation technology" so we gather that the new product is an alloy of two or more normally immiscible phases, rather than a single phase solution or block copolymer. We also gathered that the new product comes in a range of formulations for different applications. Current grades include WCV, which stands for Wire Coating Vehicle and WCD, which stands for Wire Coating DC, and WCP, which stands for Wire Coating Plug, where it is used to give strain relief.

PPO has a number of advantages over PVC - polyvinyl chloride, the most commonly used covering for electric wiring, and also over XLPE, cross linked polyethylene. It has twice the electrical insulating performance of PVC. It has a lower specific gravity, 1.03 versus 1.5 for PVC. It is said to be easier to process on a high speed line, and it is rated at 110 deg C versus PVC's 85 deg C, with further developments expected to boost the rating to 125 deg C. It has better abrasion resistance than XLPE and excellent chemical resistance. The absence of halogens, particularly the chlorine in PVC, means that there is no problem with potential generation of hydrochloric acid gas at end of life when cable insulation is burned off to recover the copper. Flexible Noryl therefore helps meet both Restriction of Hazardous Substances (RoHS) and End of Life Vehicle (ELV) directives.

There is said to be about 1.6km of wire in the average modern car, with perhaps four times this amount in some luxury models. Any saving in weight or volume or wire is therefore likely to have a significant effect. GE Advanced Materials has been working with Delphi Packard Electric. Lynn Long, business line manager for Delphi Packard Electric Specialty Wiring is quoted as saying, "GE worked closely with our team to help us understand the range of options and find the right formulation, and provided at least 20 different options to ensure all our requirements were met."

Flexible Noryl allows a halving of wall thickness. For example, it allows the replacement of 0.4mm thick thin walled cable insulation of XLPE with 0.2mm thick insulation, resulting in an overall size reduction of approximately 25 per cent. Delphi is validating the use of Flexible Noryl on insulation on cable as small as 26 gauge (0.13mm2). Another benefit of smaller cable bundle size and mass is the opportunity to use less tape and secondary covering.

Pointers

* Flexible PPO has better electrical properties allowing it to be used at half the wall thickness of XLPE and PVC. It also has a lower specific gravity

* The net effect is that it allows overall cable weight and space savings of about 25 per cent

* Containing no halogens, it helps meet RoHS and ELV directives. It is also easier to process and has higher temperature ratings

Author
Tom Shelley

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