With the introduction of coatings that let sunlight and the dispersion of water droplets assist the cleaning process, the glass industry is pledging to make the cleaning of its product easier. Industry observers characterize this new category of product as the most exciting development since the advent of low-emissivity glass 18 years ago.
Toledo, Ohio-based Pilkington North America announced its self-cleaning glass, Activ, last summer. It has a coating that allows the sun's rays to gradually and continuously break down organic dirt through a photocatalytic process. The sun's ultraviolet (UV) rays cause the integrated coating to chemically react with dirt to dislodge it from the glass surface. The glass requires a few days' initial exposure to the sun's UV rays to activate the coating.
The coating simultaneously activates a hydrophilic process that reduces the surface tension of water on the glass surface. This promotes the "sheeting" of water on the glass, preventing the formation of individual droplets and allowing loose dirt to be washed away during rainy weather.
"It's not that you'll never have to clean your windows again, but the frequency and amount of time needed for cleaning windows will decrease significantly," declares Rick Karcher, president of Pilkington Building Products North America.
"We believe we can make a strong financial case for a self-cleaning glass in the commercial market," says Paul Gore, business segment leader - building products with Pilkington. "Building owners know what they spend annually for window cleaning. Savings could be substantial if the frequency of cleaning could be reduced by 50 percent or more." Gore says a major target market is retailers interested in maintaining clean display windows. The coating also will be promoted for use on skylights.
Activ, produced by Pilkington's Ottawa, Ill., plant, is available in thicknesses ranging from 3/32 inch to 1/4 inch, and in sizes as large as 130 inches-by-204 inches.
One of the initial projects on which Pilkington's self-cleaning product is expected to be used is the Museum of the Earth in Albany, N.Y., designed by Weiss/Manfredi Architects of New York City. Self-cleaning glass is consistent with the building's emphasis on sustainability, according to project manager Chris Ballentine.
Kingsport, Tenn.-based AFG Industries is currently introducing a similar self-cleaning coating, called Radiance-TI. It will provide both self-cleaning and low-e coatings on the same light of glass - on the outside (No. 1) and inside (No. 2) surfaces, respectively, of an insulating glass unit that has an inner lite consisting of clear glass.
AFG's product, with both self-cleaning and low-e coatings, will cost four to five times per square foot more than clear glass, according to Marc Massa, AFG's director of marketing. Explaining the rationale for placing both coatings on the same piece of glass, he adds, "We don't foresee customers giving up energy efficiency for self-cleaning. They will want a self-cleaning capability in addition to low-e."
AFG has yet to develop projections for cost savings that could be realized from less frequent window cleaning of nonresidential building windows. But Massa says there is no question that a reduced amount of cleaning would be a major reason for using Radiance-TI. Noting that the windows of some commercial buildings are cleaned almost continuously, he says, "The question is how much is necessary?"
Clearer rainy-day vision
In addition to the coating's self-cleaning capabilities, Massa notes that the absence of water droplets on the glass will provide a less obstructed view to the outside when it rains. During rain-free periods, simply spraying the glass with water will promote a cleaning process.
Pittsburgh-based PPG Industries introduced a self-cleaning glass, SunClean, to the residential market last fall. It hopes to begin marketing the product to the commercial market late this year, says Scott Smith, the company's flat glass architectural market manager. Similar in concept to the Pilkington and AFG offerings, PPG's coating will promote cleaning by both photocatalytic and hyrophilic processes.
Citing dissimilarities between the residential and nonresidential glass markets, Smith says PPG is currently engaged in product testing and market research . The company, for example, wants to evaluate the implications of the field application of glass, which often occurs on nonresidential projects but is not typical for residential projects. PPG also is formulating its strategy for explaining the product's value to the nonresidential market.
For a residential customer, self-cleaning glass is a life-style change that probably will be reflected in fewer window cleanings, Smith says. But a commercial application is likely to be subject to an economic analysis, with the basic question being whether it is less expensive to pay for the coating than to pay someone to wash the windows.
As part of its evaluation of the value of SunClean for the commercial market, PPG is assembling data on projected cost savings, the amount of rainfall and sunlight that create optimal conditions for the product, and the effectiveness of the coating under various moisture conditions (e.g., wind-driven rain, straight falling rain and mist). Smith says the product works effectively in Pittsburgh, which has some of the cloudiest weather in the United States. Initial indications are that the amount of rainfall is a more significant factor than the amount of sunlight in determining the effectiveness of a self-cleaning coating.
French glass manufacturer Saint-Gobain also introduced a self-cleaning glass product last year.
The self-cleaning coatings cannot be installed on the same surface as a low-e coating, and can be applied only to a lite of clear glass. If a tinted appearance is desired, it can be achieved by laminating a tinted lite to a clear lite.
AFG's Massa observes that low-e coatings have evolved through several generations and two different manufacturing processes in their 18 years on the market. "My expectation for self-cleaning coatings is that we'll see similar types of technological improvements. We're in the early stages now."
"It's a new product category," Smith says. "I think that's why everybody in the glass business is excited. It's a new way to grow the technology and to provide benefits to people who want to use glass."
Confusion with "easy cleaning"?
The advent of coatings with both photocatalytic and hydrophilic properties may introduce confusion into a market in which coatings designed for "easy cleaning" were already available. Massa says the definitions of "self-cleaning" and "easy cleaning" are now murky. The two types may subsequently be regarded as part of a single category of products, or as separate categories. "That's part of introducing a new product for which there are no set standards," Smith adds.
London-based Ritec International Limited, for example, produces ClearShield, a non-stick coating that prevents contaminants such as dirt and lime scale from bonding to glass. "Self-cleaning is a bit of a stretch," says Tom Vinopal of Melrose Park, Ill.-based Clearshield Technologies, Ritec's U.S. marketing organization. "We call ours `easy clean.'"
Vinopal notes that the new "self-cleaning" coatings need to be activated by ultraviolet light to initiate a chemical reaction that will eradicate dirt particles, but ClearShield does not. It can be applied in a factory or following installation of the glass. Its U.S. applications include the control tower windows at Los Angeles International Airport. BDC