Lineal-surface Systems Offer Anti-dirt Protection

January 30, 2003

Several vinyl window profiles set to come onto the market late this year and in 2004 will feature self-cleaning technologies. A number of German profile processors are deep in their development of the PVC lineals.

Late last year, Gealan Window Systems, Oberkotzau, Germany, introduced its Clean After Rain vinyl profiles, whose surface has a hydrophobic microstructure that is said to reduce particle adhesion and eliminate the need for periodic cleaning. Albrect Spranger, system development director, says all PVC profiles contain surface irregularities that collect soot and thus require regular washing to prevent graying. Geanlan’s aim was to create a profile that could clean itself with rain or dew.

Working with the Institute for Surface Modifications, Leipzig, Germany, the company developed a surface with a fine-structured coating that provides the so-called Lotus Effect. Spranger says through the addition of a proprietary water-repelling “attribute,” rain droplets retain their spherical form when they fall onto the profile’s surface, instead of flattening and clinging to the surface.

The waterdrops roll off the lineal’s surface, carrying dirt with them. The effect is heightened by a cushion of air between the droplets and the surface created by the microstructure as it reduces the contact area for the droplets. Ewald Nisle, Gealan spokesman, says the layers are applied with a proprietary post-extrusion process.

Because the coating cannot be repaired if damaged, a challenge lies in providing a durable surface to avoid scratching of the lineal during installation, says Nisle. The company won’t say how it has overcome this problem, but claims its profiles are both scratch- and weather-resistant. Still in the development stage, Nisle says the profiles could be on the market within one year. A price has not been finalized.

Competing processor HT Troplast, Troisdorf, Germany, which experimented with nanostructures for more than one year before dropping the method, is working on a photocatalyst-based system. Expected to be on the market in 2004, it now consists of a proprietary post-extrusion coating of titanium dioxide (TiO2) nanoparticles that function with UV light and moisture to provide cleaning. HT Troplast has worked with an undisclosed partner to develop a formula and size for the TiO2 nanoparticles.

UV light affects the surface of the nanoparticles so that an electron is activated to form a peroxide and oxidizes it. This prevents soot from attaching to the vinyl profile and slides it away. Wolfgang Frings, HT Troplast’s project development manager, says tests show that normal daylight, even on cloudy days, provides sufficient reaction to activate the cleaning effect. Says Frings: “All that is needed is moisture in the form of humidity or dew. Systems using the Lotus Effect require rain. Parts of profiles under eaves may not get enough [rain] to clean themselves.”

HT Troplast says the photocatalyst-based system works for the life of the profile (20 to 50 years). The company has not priced the profile.

Window profile and sheet extruder Veka, Sendenhorst, Germany, reveals it too is working on a self-cleaning technology, but says it is too early to provide details and a date when it could be commercially available.

While polymer producer BASF, Ludwigshafen, Germany, has developed a spray-on water-repellent film that mimics the Lotus Effect, it sees its development to be suited for graffiti protection. The spray, based on polypropylene, polyethylene, and wax nanoparticles, is designed for rough surfaces, such as walls, and might have problems adhering to PVC profiles, says developer Harald Keller.

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