Film history: Thin interlayers and coatings co-star with glazing

The roots of thin interlayers used in and on windows and glazing date to the 1930s, the first Golden Age of the American automobile. A consortium, including DuPont of Wilmington, Del., developed glass fashioned from tough, clear polyvinyl butyral. Sandwiched between glass, it created a safety windshield, and lamination was born. Since then, the processes, applications, thicknesses, colors and performance characteristics of diverse interlayers, films and coatings for fenestration have continued to proliferate. 

While there are no published industry figures on these markets, Nick Limb at Ducker Research of Troy, Mich., in a recent phone interview, estimated the film market alone to be a $150 million to $250 million business, based on proprietary information.

Laminated glass for buildings
Moving beyond windshields, the use of laminated glass quickly spread to buildings. Unlike ordinary or tempered glass that falls apart when fractured, laminated glass stays in place. It helps hold together the building envelopes, contains shards, and helps prevent people from falling through sudden openings. Hurricane and blast-mitigation fenestration includes laminated glass with various interlayer thicknesses.

Users of laminated glass eventually discovered that it also helped reduce noise, block harmful ultraviolet rays, cut energy bills and protect against break-ins.

The strength and properties of laminated glass can be tailored to meet specific needs: Softer interlayers reduce noise; stiffer interlayers help glass perform more like a structural composite material. The latest interlayers provide color, clarity and decorative design control, and offer clean, open-edged and silicone butt-joined glazing.

Glazing contractors want laminated glass to be problem-free, easy to install and reliable. Meanwhile, innovative framing systems and structural attachment advances give installers high-efficiency options in lightweight, high-performance fenestration. Glaziers find laminated glass simple to install: Standard-sized, two-ply glass panels can be cut to size on site, and also can be drilled or notched.

Applied film for retrofits
The 1960s saw the debut of applied film technology, or film applied to glazed surfaces. It brought some of the same benefits of laminated and suspended film products to the retrofit market, as well as to new construction. This class of film products offers limited storm, blast and security protection.

Today’s applied film products are durable and sophisticated, thanks to innovations such as Houston-based Huper Optics’ ceramic-coated thin-film technology by Southwall Technologies Inc. of Palo Alto, Calif. It combines alternating layers of microscopic precious gold and silver metals and dielectric substances onto ultra-clear films to create a combination heat, glare and ultraviolet shield. The nano-ceramic coated film rejects more heat and, being ceramic, provides scratch-resistance, easy cleaning and durability, company officials say.

Other recent advances have come from Diamon-Fusion International Inc. of San Clemente, Calif.  DFI’s flagship product is a patented “nano-film” or coating for creating extremely low-maintenance surfaces on materials that contain silica, most notably glass, tile, porcelain and granite. Technically, it is cross-linked and branched, capped silicone film nanotechnology. The finished coating averages 16-to-35 nanometers. Another recent innovation is Invisible Art Glass, DFI’s process of imbedding art or graphics into clear glass that remain invisible to the eye until fogged, misted or steamed.

Madico Inc. of Woburn, Mass., a leading manufacturer of safety and security films, claims to have developed the first roll-to-roll metalizer, the first laminated film, and the first waterproof film adhesive, among other innovations. Its engineers designed the FrameGard anchoring system to prevent filmed glass from vacating from its frame under blast loads.

Film Technologies International of St. Petersburg, Fla., claims to have introduced innovations such as the first dry adhesive system, optically clearer adhesives, dye-in laminating adhesives and their Spandrel Gard original-equipment manufacturers’ product line.

CPFilms of Martinsville, Va., a division of Solutia of St. Louis, developed the original technology for ultraviolet absorbing polyester, and provides integrated performance film enhancement, including vacuum metallizing, sputter coating, deep dyeing, coating and laminating—available in combination—to meet specific needs. CPFilms’ LLumar Magnum Graffiti Film numbers among the popular surface-protection systems for windows and surfaces vulnerable to vandalism.

In 1983, Southwall Technologies claimed to have developed the first low-emissivity sputter-coated insulating film for glazing systems. The film was suspended between two or three panels of glass. Heat Mirror suspended film systems offered control over light transmission and kept infrared heat from escaping, and the additional air space added insulation value beyond laminated glass. Later, spectrally-selective clear film in multiple formulas added various degrees of sun control to Heat Mirror glazing.

In 1997, V-Kool of Houston, North American distributor of Southwall Technologies’ applied films, introduced a spectrally selective film that blocks 94 percent of infrared heat while simultaneously transmitting 70 percent of visible light.

Meanwhile, a polyester film tape developed by 3M Co. of St. Paul, Minn., has become an economical answer for edge-and-hole reinforcement, including application over nailing fin insertion points on window frames to protect against moisture intrusion.

Innovative decorative film employs translucent geometric and custom patterns to heighten privacy and provide the appearance of etched glass. Decolite, distributed by Glassfilm Enterprises Inc. of Acton, Mass., for instance, enhances the décor of rooms shown below. Custom applications include logos, graphics and designs offering the same appearance as etched glass.

Diverse benefits from retrofit film
Applied or retrofit window film provides specific personal and property protection from the effects of the sun as well as added safety and security in events that result in broken glass. The concept of window film for use in solar-control flat-glass applications dates to the early 1960s. The original film design objective was to control heating and cooling imbalances that result from solar loading. Such early films were found to reflect solar radiation back from a window, preventing the warming of inside surfaces hit by direct sunlight while still allowing vision through the glass. As the window film concept was developed and improved, demand developed for colored sun-control films that complement architectural design. Coloration was achieved through various means to produce bronze, gray, gold and amber films.

The energy crisis of the early 1970s prompted an interest in another aspect of window film use: reduction of heat loss to outside. It was discovered that polyester film tended to absorb and re-radiate long-wave infrared heat rather than act as a transparent medium. Through experimentation, new film materials and constructions were developed that enhanced this characteristic. These films greatly improved heat retention.

The efficiencies of solar-control window films relate to weather, building orientation, window size, and factors such as exterior shading. However, with escalating energy costs, products such as window film become valuable investments for commercial and residential owners and commercial facility managers. Peak-load demand can make a substantial difference in a building’s electrical costs. Many utility companies base their rate structures for a building on the maximum peak-load measurement. Solar-control window film helps reduce that peak and thereby the total electrical bill.

There are many types and constructions of solar-control and safety window films. These “retrofit” products go on existing buildings as opposed to new construction. In their simplest forms, window films contain polyester substrates and scratch-resistant coating on one side; a mounting adhesive layer and a protective release liner on the other side. After removal of the release liner, that side goes on the interior surface of the glass.

Glaziers can rely on film for “quick fixes for solving problems of graffiti and the need for precise, inexpensive color matching without the inventory requirements of colored glass,” says Ginny Kubler, CPFilms marketing director.

Caveats on selection of applied film
Safety and security window films help hold glass fragments in place after glass breaks. Solar-energy-saving films and decorative films are manufactured to be energy efficient or provide certain design and styling benefits, but any glass-breakage protection becomes only a side benefit and should not be a reason for buying such a product. Although there might be some incidental added safety to any window covered by any type of film, there is no intended safety or security benefit unless the product has been tested and listed as such by its manufacturer.

The International Window Film Association of Martinsville, Va., features a 38-page paper, first published in 1999, Safety-Security Window Film, containing general caveats for film selection, at www.iwfa.org. The site also contains specific film-to-glass recommendations from manufacturer members.

Association members take a strong position when it comes to responding to window manufacturers who have elected to void their warranties on insulating glass units covered with retrofit films. “We strongly suggest that anyone considering using applied film on windows, first check the film manufacturer’s written recommendations. Film manufacturers typically offer up to ‘lifetime’ warranties on residential applications, and five-year to 15-year product warranties on commercial projects,” says Daryl Smith, executive director of IWFA. “In addition to the primary product warranties, the manufacturers offer a ‘secondary’ warranty on broken glass and seal failures, thus protecting home owners whose window warranties have been declared void. Our members want to do the right thing by our customers.”

Film on low-e windows
According to IWFA, three factors determine whether window film should be used on low-e windows and how much users will benefit:

•  Type of low-e coating on glass
•  Location of low-e coating in the window system
•  The desired amount of heat-gain reduction, heat-loss reduction, or other film benefits. See www.iwfa.org for details.

Can applied film cause glass to break?
Glass breaks when stressed. Thermal stress from absorption of solar radiation can cause glass breakage under certain circumstances. Window film manufacturers recommend film-to-glass tables for use by factory-trained dealer installers. If a consumer is in doubt, he or she should request a copy of such guidelines. Below, some glass types or conditions where the use of solar-control—not clear safety—type of window film is not recommended without extreme caution. 

•  Single-pane glass larger than 100 square feet
•  Double-pane glass larger than 40 square feet
•  Clear glass thicker than 3⁄8 inch
•  Tinted glass thicker than 1⁄4 inch
•  Window framing systems of concrete, solid aluminum or solid steel
•  Glass where sealant or glazing compound has hardened
•  Visibly chipped, cracked or otherwise damaged glass
•  Reflective, wired, textured or patterned glass
•  Triple-pane glass
•  Laminated glass windows.

Safety-security film limitations
Safety or security window films applied to glass get tested to the same standards required of tempered glass, heat-strengthened glass and laminated glass. Window-film manufacturers have copies of the test reports validating whether their products do or don’t meet specific impact testing.

Upon repeated impacts to the same area, films can begin to tear due to the edges of the broken glass fragments penetrating the film. This means, although films can help greatly by reducing glass hazards upon initial impact, with repeated impacts they might not continue to perform as well. Thicker films and films made from multiple layers—laminated films—perform better in situations where there will be repeated impact to the glass, even after breakage has occurred.

A product may pass the Dade County small-missile impact requirements, but that does not mean it can get Dade County product approval, as it might not withstand the repeated impact-cycling part of the approval process. As of summer 2005, window-film industry trade association officials said they were not aware of any window-film product that had met Dade County’s large-missile impact test. Any claim by the seller of a product should alert the consumer to ask for a copy of the written approval.

Federal agencies and owners of buildings rented by federal agencies have begun to have safety or security films installed for increased protection from the hazards of flying glass fragments during bomb blasts or other weaponry attacks. There are published standards of performance at different levels of protection established by the U.S. General Services Administration, and most film manufacturers have many products tested and approved for these uses.

Films can be installed:
•  On only the daylight area of the glass
•  If the frame is removed and replaced, on the entire glass surface, called an edge-to-edge installation
•  As part of a film-attachment system.

Films installed on the daylight portion only hold the glass together and in the frame as long as some of the glass edge remains unbroken along the line where the daylight part of the glass meets the frame.  Once the total edge of the glass breaks, then the film and broken glass held by it vacate the frame.

Films installed edge-to-edge hold glass in the frame better since a part of the film installed on the glass sits under the frame, holding broken glass in place even with total breakage of the daylight area of the glass. Films installed as a part of attached film systems are anchored to the window frames using either structural silicone adhesive or mechanical devices or both.

Cleaning film applied to glass
Some common-sense guidelines include: Use a soft clean cloth, soft paper towel or clean synthetic sponge. Use a soft cloth or squeegee for drying the window. Use any normal glass-cleaning solution that contains no abrasive materials. Today’s scratch-resistant coatings—standard with high-quality films—have virtually eliminated the need for special precautions when cleaning. 

A multipurpose future
Check carefully for products’ compatibility when combining glass and film products. Yet as demonstrated above, film and glass, in endless complementary combinations—and sharing some of the same technologies—form multipurpose platforms to serve the needs of new and retrofit construction.

Next up: Energy rating for film products
The retrofit window industry’s product performance claims will soon receive a boost.
Officials at the National Fenestration Rating Council of Silver Spring, Md., announced that “procedures for rating and certifying window film energy performance and labels” will be in place by the end of 2006, according to spokesperson Kristine Martin. The online directory of NFRC-certified products, called the Certified Products Directory, will ultimately list specific window-film products and certified energy ratings for each, when applied to different types of glass, as expressed in the products’ “solar heat-gain coefficient” and “visible transmittance.”

Under the program, film manufacturers will submit samples and data to an NFRC-licensed inspection agency that can authorize certification of the film and conduct annual in-plant inspections of the facility. The IA might require lab testing or computer simulation. The simulator then obtains a spectral data file for established default glazings and for the film via the International Glazing Database and Window 5.2, a software program for calculating total window thermal performance indices such as U-values, solar heat-gain coefficients, shading coefficients and visible transmittance. Product-rating data will be uploaded to the NFRC Certified Products Database. After the IA has conducted an in-plant inspection and determines that all certification requirements have been met, it will generate a certification authorization report to the film manufacturer and product labels authorized for four years.

“The advantage of NFRC-rated and certified window film is increased credibility for the manufacturer and increased value to the consumer,” Martin said in a recent telephone interview. “Consumers can compare products in ’apples to apples’ fashion and make informed choices.”