A warmer plastic

On icy days, it would be nice if vehicle windscreen washer systems did not freeze up. In the future, heatable nozzles may ensure that they do not

On cold icy days, car drivers are faced with many problems. Even if the car starts, the windscreen cannot be cleared because frozen water refuses to come out of the washer nozzles. Although developers at BASF do not claim to have solved the former problem, they may well have an answer to the latter, in the form of a new electroconductive plastic that could be used to design heatable washer nozzles for both windscreens and headlamps.

In addition to windscreen washers, it is expected that another particularly promising application will be in fuel tanks, where electrostatic charges must be avoided at all costs.

The secret to the new plastic lies in the company’s Ultraform range. Researchers started off with Ultraform N2520L, developed by the company some time ago, and enhanced it so that it would be electrically conductive. The result was Ultraform N2520XL2.

Plastics, usually thought of as having excellent electrical insulation properties, are used extensively in electrical engineering applications. But they can be forced to be electroconductive by the addition of conductive particles.

The usual method is to mix the plastic with conductive black, giving the material antistatic properties. Unfortunately, this method comes up against limits, since an increase in the proportion of carbon black in the polymer matrix is accompanied by dramatic changes in the properties of the product, leading to a resulting decrease in flow of the product in a mould.

To solve this problem, it is possible to increase the temperature of the melt and the tool that is used to manufacture the part, but only to a certain extent. Otherwise thermal damage occurs and the strength and rigidity of the part will not meet its application requirements.

Although the new plastic also uses high carbon black, the developers have managed to retain good flow in the mould, good thermal stability and high rigidity, as well as a good low volume resistance and very low surface resistance. The low surface resistance of the product means that it can also be painted electrostatically without application of a conductive primer, which was previously unavoidable for plastics.

The electrical properties are not affected by the processing conditions like the temperature of the mould surface. And the low resistance of the product enables production of parts that can be heated electrically.

To prove the point, a voltage of 12V at a current of 250mA was applied to a 6cm x 6cm sheet of the material with a thickness of 0.2cm. Within about 7min, the sheet warmed from room temperature to a constant value of 55 degreesC. The process can be repeated many times, and work is continuing on accelerating the warm up time still further.