Anti Fog coatings for Polycarbonate explained

Fogging can often occur on the surface of a Polycarbonate window when moisture from the air condenses onto the cold surface of the sheet or window. The condensed moisture forms droplets that then obscure the view through the window. This fogging effect also occurs on glass and is most often seen on the windshield of a car on a cold morning or on a bathroom mirror if the room is filled with steam.

There are a number of ways to prevent fogging on Polycarbonate and most of them involve some type of coating. Most of these coatings have hydrophilic properties. The term hydrophilic comes from the Greek words “hydros” meaning water and “philia” meaning friendship. A hydrophilic surface attracts the water. This attraction means that the water condensation, instead of forming droplets, forms a thin water layer along the surface of the sheet or window. This thin film of water will then not obstruct vision in the way that water droplets obstruct vision. Hence a hydrophilic material has anti-fog properties. The thin film of water is also able to evaporate quickly if there is air movement near the window.

One problem for some high-tech applications such as lenses and optical sights is that the thin film of water can cause focusing problems. These issues can become severe in environments where the thin film of water is allowed to build up such as telescopes where the users eye is placed against an eyecup. The moisture from the users eye can condense on the lens and because there is an enclosed space with no air movement, the water film can build up with a hydrophilic coating.

One potential solution is a super-hydrophobic coating. A super-hydrophobic coating actually works in the opposite way to a hydrophilic coating and it actually repels water. This effect means that when water condenses on the window or sheet, it will actually bead up into an almost perfect sphere and immediately roll off the surface rather than sit on the surface as a drop, which obscures vision. At the moment super-hydrophobic coatings exist for opaque surfaces, but there are no commercially available options for transparent plastics.

HighLine Polycarbonate has a range of hydrophilic coatings available for Polycarbonate sheet and we have applied these to a number of commercial products. During 2010 we will be looking at the opportunity to develop a super-hydrophobic anti-fog coating for high-tech Polycarbonate applications.