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 product category as the most exciting development in glass technology since the advent of low-emissivity (low-e) glass 18 years ago.
Toledo, Ohio-based Pilkington North America unveiled its self-cleaning glass, Activ, last summer. It has a coating that allows the sun's rays gradually and continuously to 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 coating simultaneously activates a hydrophilic process that reduces the surface tension of water on the glass surface. This promotes "sheeting," 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," predicts Rick Karcher, president of Pilkington Building Products.
"We believe we can make a strong financial case for a self-cleaning glass in the commercial market," says Paul Gore, Pilkington business segment leader, building products. "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.
Produced by Pilkington's Ottawa, Ill., plant, Activ is available in thicknesses ranging from 3/32 inch to 1/4 inch, and in sizes as large as 130 inches by 204 inches.
Kingsport, Tenn.-based AFG Industries is currently introducing a similar self-cleaning coating, called Radiance-Ti, which will provide both self-cleaning and low-e coatings on the same lite of glass.
A side-by-side comparison of water-soaked windows illustrates absence of water droplets on glass with a self-cleaning coating (left), in contrast to glass without.
AFG's product will cost four to five times more per square foot 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 buildings. 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.
Last fall, Pittsburgh-based PPG Industries introduced a self-cleaning glass, SunClean, to the residential market. 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 promotes cleaning by both photocatalytic and hyrophilic processes.
Citing dissimilarities between the residential and nonresidential glass markets, Smith says PPG is currently engaged in market research. 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 a window washer.
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, mist, etc.). 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. Smith says the product works effectively in Pittsburgh, which has some of the cloudiest weather in the United States.
French manufacturer Saint-Gobain also introduced a self-cleaning glass last year.
The self-cleaning coatings cannot be placed 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.
"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 even be regarded as a single category in the future.
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 [for Ritec] is a bit of a stretch," says Tom Vinopal, director of business development for Melrose Park, Ill.-based ClearShield Technologies, Ritec's U.S. marketing organization. "We call ours 'easy clean.'"