PPG unveils glass that practically cleans itself
PITTSBURGH (AP) – When PPG Industries’ top technician in 1995 pitched the idea of a window that practically cleans itself, the company’s brass were skeptical. But Charles B. Greenberg, a former corporate fellow at PPG, delayed his retirement by almost a year to see the project through. And in January, the Pittsburgh-based company began selling SunClean, a glass that is coated with a thin layer of titanium dioxide.
“When we say ‘self-cleaning,’ we don’t mean that the window’s going to grow arms and clean itself,” said Caroline Hed as a white pigment in paints and some foods; it can also be used as a sunblock.
But in the 1970s, researchers at the University of Tokyo discovered that when titanium dioxide is activated by ultraviolet light, it destroys any organic molecules it touches, including dirt.
The researchers – Akira Fujishima, Kazuhito Hashimoto and Toshiya Watanabe – also discovered that titania transforms water and oxygen molecules into superoxides and hydroxyl radicals, which also destroy organic molecules.
When a thin coat of titanium dioxide is applied to glass, the titania can’t eliminate dirt and grime, but they loosen it. The dirt sloughs off when it rains or the window is sprayed with a garden hose.
The coated glass also doesn’t get visible watermarks like untreated glass does.
The titanium dioxide coating turns the glass into a water magnet, pulling the liquid so close to the surface that it creates a thin layer that dries quickly and doesn’t attract much grime.
Untreated glass, however, repels water, creating beads and rivulets that attract dirt and leave behind marks.
SunClean isn’t the only titania-coated glass on the market.
Pilkington North America late last year introduced a window, called Activ Self-Cleaning Glass, that uses the sun’s ultraviolet rays to break down dirt and rainwater to wash it away.
Pilkington and PPG’s windows cost about 20 percent more than untreated windows, which cost between $200 and $600.
PPG, which is known for coating glass with thin films, experienced a few obstacles as it developed the glass.
For example, the film must be very thin and very uniform because the human eye can detect variations in film thickness that are equivalent to the diameter of a single water molecule, Harris said.
To overcome that obstacle, PPG applies the titanium dioxide to the glass as a gas.
Greenberg, who retired in January, and Brian Fannelli, a marketing manager for the company, also had to convince PPG officials that customers would buy the product.
“It’s a breakthrough product,” and some customers are skeptical about the technology, Fannelli said.
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