Fenestration Forum – Coatings have come a long way
By Brian Burton
Coatings have come a long way
By Brian Burton
Glass and glazing elements like most primary construction materials including concrete, masonry, metals and plastics have benefited a great deal from improvements in advanced coating technologies. The use of advanced coating techniques and materials to improve appearance and performance of glass in particular has proven to be a constant source of successful innovation over time.
Their widespread use has been a driver in the industry since the 1970’s with the realization that we were about to experience an energy crisis. The markets for the coated architectural glass sector are very large and continue to grow. Industry statistics show that millions of square feet of glass are coated each year.
Low-E glass for example, has evolved a great deal since its inception, enabling new variations of high-performance and reflective glass. Coatings often supplement glazing to help control solar heat gain or loss and/or to minimize conductive heat loss.
Coating technologies have also produced several “easy-clean” glass products and what some refer to as “intelligent glass.” Research in Europe indicates that newer coating materials have the potential to further reduce reflection and improve solar control at reasonable cost.
Glass coatings can improve performance by filtering natural light, solar heat, ultraviolet radiation, sound transmission and glare. They can be divided into roughly two types: low-E coatings, which improve the energy efficiency and/or safety of architectural and automotive glass; and specialty coatings, which enhance or improve performance in some of the other useful characteristics of glass.
Coatings are also applied in two different methods. In hard coating (or pyrolytic coating) coatings are applied during the manufacturing process, also called an on-line coating process. In this process the coatings are fused into the glass at 650-700 C. When cooled, the coating becomes a durable part of the glass and can be heat strengthened, toughened or laminated.
The second method, soft coating, otherwise known as vacuum coating or off-line coating, utilizes a process called cathodic vapour deposition or magnetron sputtering vapour deposition.
Using silver and/or titanium in high voltage processes, these soft coatings can produce a lower solar heat gain factor compared to hard-coat glass and are often used in double glazed units. The process, which is also called sputter coating or more accurately sputter disposition, is also used to manufacture computer disks. Remember CDs and DVDs?
Glass is typically sputter coated after it has been cut and tempered and is in its final shape in a special chamber designed for the purpose. However, because coating is accomplished in batches it can add cost to manufacturing and production process.
Anti-reflective coatings are applied to auto mirrors to aid vision. Coatings with photocatalytic and hydrophilic properties make self-cleaning windows. Conductive coatings can produce frost-free windscreens and a range of electro-optical applications. One method of producing a conductive coating is by depositing tin salts on the glass. Baked-on ceramic coatings, or frit, can also be applied to the surface of glass in many different patterns, colours, and densities.
One type of specialized glass coating can also contribute, in part at least, to the relatively new concept of switchable glazing, which can enable commercial specifiers to add options for security or privacy glazing by utilizing liquid crystal glazing. Predicated on the successful installation of a transparent electrically conductive film and wired to a power supply, the coating scatters light when switched off and one layer of glass appears translucent, thereby obscuring direct view to provide a security screen or privacy. When the power is turned back on, the liquid crystals and the glazing regain transparency, permitting view in both directions.
Brian is involved with an innovative multi-disciplinary firm specializing in website design and development; Award Bid Management Services http://award-bid-management-services.com. The firm also assists companies interested in selling goods and services to governments and institutions. He can be reached at; firstname.lastname@example.org