TWI Bulletin, July - August 2008

Case study: Non-stick developments underway...to counter paint, dirt and grease

Graffiti proofing, or more scientifically, making surfaces with a high degree of anti-soiling capability has become a subject of considerable attention at TWI recently.

'The clear objective' says project leader Alan Taylor, 'is to develop a coating that is both abrasion resistant and has a very low surface energy. So effectively we have entered the realm of designing molecules that will undertakespecific roles that we demand.'

The way this has been tackled is to devise a three component system, based on silicates; one is heavily loaded with fluorine atoms which lowers the surface energy of the coating creating a hydrophobic, or water hating, material witha contact angle well above 90°.

Those fluorine atoms are extremely highly polarised electronically, are very stable and repel the oxygen in the water, making it a very difficult material to which to adhere.

'Our aim is to use the chemistry of the fluorine to give us the desired hydrophobicity' explains Taylor, 'and also the chemistry of silicate systems to give us a three dimensional network that has structural integrity allowingcontinuous films to be deposited but also allows adhesion to the substrates.'

The TWI team now has a suitable coating under development which features good abrasion resistance and a contact angle between 105° and 120°.

'We are aiming to improve on that, the technology is still developing' according to Taylor. 'We are still trying to understand the detailed mechanics of how one does that. The first generation of materials was developed to give ourpartner Visteon a coating which has very good anti coking and anti soiling properties when applied to an aluminium heat exchanger.'

Visteon now has a patent for the coating in place in which two of TWI's specialists are named inventors.