Solutions to Common Obscuration Band Problems
By Kris Vockler, Jeff Nicholson, Abram Scurlock – ICD High Performance Coatings
Today’s automobiles are changing and driving technology at a staggering rate. From heads-up displays to greater comfort amenities, what was once science fiction has turned out to be last year’s model. Everything from the bumper to the windshield in modern cars is evolving, yet it’s not always an easy process. Laminated glass windshields and glass sidelites are often left struggling to keep up with new technology embedded into their laminate interlayers. ICD High Performance Coating’s newest coating technology, CeramiGlass™, saves money, time, and helps solve many of today’s auto glass laminate problems. [i]
Automobiles on the design floor today (soon to appear on the showroom floor) are calling for high tech windshields. As Brandon Griggs noted in aCNN.com article on January 13, 2012, “Imagine a future in which icons flash on your car windshield, hologram style, as your car approaches restaurants, stores, historic landmarks or the homes of friends.” Key research and development is going into decreasing our carbon footprint in autos. Reflective (sputter low-e) coatings are deposited in the laminated configuration to repel the infrared light (IR) spectrum, which will ultimately keep heat gain out of the overall automobile and lower energy costs to cool in the summer. Offering the same technology (in reverse) for winter, our near future cars will leave a less negative impact on the environment.[ii]
More electronic technology is winding up in our auto glass as well. Heads-up displays are soon to become as normal as a navigation system. Defoggers and antennae are becoming more efficient and must be embedded into the interlayers of front and back windshields.
All front windshields and many side and back lites of glass in an auto will have a black obscuration band that is very visible. The reason for this black band is to protect the polyurethane glue that is specially designed to hold the glass lites in the auto. These adhesives are notorious for breaking down in direct sunlight. The obscuration band keeps the harmful UV light from degrading the glue, which would result in failure over time. This black band has historically been printed on the “S4,” or inside, surface of the glass (S1 is the surface you can touch on the outside; S2 and S3 are on either side of the laminate interlayer).
In the last ten years, the desire to print the black band on the inside of the layers has been increasing for several reasons. First, the reflective coatings applied to keep more IR out of the auto aren’t durable and they require mechanical protection as well as protection from oxidation. Printing the black band on the S4 surface and placing the reflective coatings on either S2 or S3 will produce an aesthetic that is unacceptable to the automakers, and will potentially create heat gain that can lead to interlayer degradation. With defogging and antennae strength technology, these components are usually embedded in the obscuration band with conductive metals, which is another reason why they need to be sandwiched between the lites of glass. The third big reason why printing the obscuration band on the S2 or S3 surface is needed is because, by this method, one can eliminate, or significantly reduce, the “burn-line” visible just above the printed surface and into the laminate—a defect that appears almost invariably with S4 printing. It is theorized that this optical distortion is due to the possible heat differential that occurs between the heat-absorbing black band and the open clear area of a lite of laminated auto glass.[iii]
Clearly, the industry is moving toward more reflective coatings, technology, and obscuration bands on the inside of laminated glass. This can present many problems to overcome during the fabrication process, some of which can be costly. There are two ways to print the obscuration band so that both lites of glass can be bent and laminated into a windshield. The first is a “pre-cure” method, by which ceramic frit is printed and cured before bending and laminating. This creates a separate step that must be conducted as well as added energy cost (as the frit and glass must be brought up to 450-500°C for a full cure of the enamel). The second is a “direct-firing” process, which provides a direct solution for printing on the S2 side of the glass. In this method, the black coating would be printed and still retain enough properties or “green strength,” which is just cured enough to attain full cure during the laminating process.
The pre-cure method is difficult, time-consuming, and it adds cost to a process that won’t accept much greater costs. It should be said that both methods require a pre-cure, but in the first the cure of the enamel is complete, and in the second just enough cure is attained to have a solid “green strength.” The direct-fire method is the best process, but it still offers challenges for ceramic enamel (the industry workhorse). Although great strides have been made which enable ceramic enamel to be cured enough and still retain sufficient green strength, the process remains flawed. Ceramic enamels contain some organic polymers that bind the coating together; if these organics are not adequately burned off in pre-cure, they will burn off in the bending process (600° C) and leave a haze on the glass as they try to escape. Often the enamel cannot develop enough “green strength” to remain defect-free throughout the bending and laminating process. Mechanically, the process can leave clip or press marks on the enamel and defects may also appear as enamel transfer to the second lite during bending. Additionally, the bending process creates shear stresses that can crack and damage the enamel if it is not cured enough prior to bending.
CeramiGlass™ was created to solve many of the current problems with the direct-fire method which, as described, requires narrow curing and printing parameters to deliver a final product that is defect-free. CeramiGlass™ is an inorganic, water-based coating. It is as durable as ceramic enamel but far from it. It is also a “zero VOC” coating that is free of heavy metals. CeramiGlass™ can be printed with the same fine detail as ceramic enamel, but uses a much lower (345°C) pre-cure temperature and cures in less time than ceramic enamel—meaning less energy cost and less time overall. Unlike ceramic enamel, there are no organic polymers or solvents used; so the fear of a “haze” left behind from improperly pre-cured enamel isn’t there. Finally, the green strength of CeramiGlass™ is much greater when compared to ceramic enamel, which means no defects will develop during the bending process and no ink transfer will appear on the second lite.
CeramiGlass™ is a revolution in glass coating technology. Not only can it solve some of the big issues with auto glass, the coating and its dual-cure nature also has some interesting possibilities for the architectural glass world. Large stock sheets of glass can be coated with dots, lines, (any pattern) or even solid flood coats, then cured and placed in storage. While cured at the lower temperature range, the coating is considered cured and will pass any architectural test the coating could be subjected to for interior architectural glass use. That stock sheet can then be cut, notched, drilled, and worked prior to being placed into a tempering oven. The result is a printed glass product very similar to ceramic enamel and with equal performance. This includes a line of “frost” and “sandblast” products that one would be hard-pressed to determine whether or not they were actually sandblasted or acid-etched. The opportunities are massive.
Today’s auto glass and architectural glass markets are working hard to change with the technological advancements of the end products they go into. The opportunity to satisfy the great desire for direct-fire enamel in auto windshields is now here with CeramiGlass™—except it is not ceramic enamel. It solves the big S2 laminated auto glass problems and it creates a new world of coated architectural glass products—all with zero VOCs, heavy metals, or organic matter.
[ii] “IRIS© coating for automotive glass,” AGC Glass Europe, accessed March 21, 2013, http://www.agc-glass.eu/English/Homepage/Our-Values/Environment/Environmental-Report-2011/Environment-friendly-products/Energy-saving-products/page.aspx/1665#part_2.
[iii] “Decoration of S2 & S3 on Automotive Glass,” Nick Westra, Johnson Matthey B.V. from Glass Processing Days 2003
©2013 ICD High Performance Coatings – All Right Reserved
For more information: www.icdcoatings.com