Pyrolytic glass coating debuts

A reflective, low-e coating that its manufacturer says provides significantly higher daylight transmission and lower reflectivity over its former product has been introduced by glass producer Pilkington. The company says its new Eclipse Advantage coating offers 60% more daylight transmission and 40% lower reflectivity than the company's Eclipse product, which it replaces.

The coating will normally be applied to the inside surface of an exterior clear glass lite of an insulating unit. Pilkington says it will also offer the option of applying it to five colors of tinted glass.

Pilkington claims to be the only manufacturer to combine reflective and low-e properties in a single coating. The coating is applied with a pyrolytic (hard coat) process that is said to have greater durability than coatings applied by a sputter (soft coat) process. This will allow a greater number of fabricators to perform secondary operations, such as cutting, chamfering, and laminating, to the glass, according to Pilkington.

Sputter coatings are subject to degradation from contact with oxygen and moisture, which is why glass manufacturers recommend that sputter-coated glass be incorporated into sealed insulating units, their most typical application, within a specified time period.

Glass with a pyrolytic coating, however, can be used in monolithic glazing applications. Pilkington expects to export a significant amount of Eclipse Advantage for both monolithic and insulating glass applications.

Thomas Schwartz, president of the Waltham, Mass., engineering firm of Simpson, Gumpertz & Heger, made a preliminary comparison of published data for Pilkington Eclipse Advantage's low-e coating on clear glass in a one-inch insulating glass unit with PPG's Sungate low-e sputtered and pyrolytic coatings on clear glass. This comparison indicated that Eclipse Advantage's pyrolytic coating is similar to PPG's sputtered coatings with respect to total solar energy transmittance and reflection, solar heat gain coefficient, and shading coefficient. With respect to U-value performance, Schwartz found Eclipse Advantage's coating to be similar to that of PPG's pyrolytic glass.

"The differences are not great, so the processing advantages of the Pilkington pyrolytic glass argue for it to be an attractive addition to the glass repertoire," says Schwartz, an independent consultant with no financial ties to any glassmaker.

Donald Vild, a glazing consultant based in Oregon, Ohio, says a pyrolytic low-e coating generally can't achieve results equal to sputtered coated products. But, he adds, "the results are close enough that I question whether it makes any difference. I think for all practical purposes, you can consider them equivalent."

Charles Kilper, VP of engineering with St. Louis-based enclosure consultant Heitman Associates, says that limited shelf life and vulnerability of coatings to damage during fabrication are recognized limitations of sputter-coated products. "The use of pyrolytic coatings is an obvious way to exploit the advantages of a tougher product," he says. "It remains to be seen whether the marketplace will accept newer pyrolytic low-e products as equivalent to sputter-coated products."

Scott Smith, market manager for PPG's Commercial Construction Group, says his company's sputter-coated product provides superior performance compared to a pyrolytic product because sputtering provides greater flexibility and quality control than the pyrolytic process in the application of coatings.

PPG has a program under which it has certified 28 fabricators to heat treat or laminate sputter-coated product. Certification by PPG involves training of fabricator employees and the use of specialized equipment.