Volume 8, Issue 5 - September/October 2006

Off the Line
Glass Manufacturing News

Why More Laminated Glass? 
by Russ Corsi

The automotive industry has begun a movement to offer laminated glass in many sidelite applications, in addition to a very limited number of backlite applications.

Those of us that have been around long enough might remember that most vehicles in the early 1950s were glazed completely with laminated glass. Although tempered glass originally was introduced in 1938, laminated glass continued to be used in most flat glass applications such as sidelites and vent glass.

As automotive designs evolved, the need to provide glass that could be formed to cylindrical and conical shapes surfaced. Tempering furnace technologies improved to the point where they could produce a product that could be shaped quite easily at a cost that was significantly lower than laminated glass. 

Over time, drivers began to expand their expectations for the vehicles they were considering purchasing. For example, they began to assign values to the noise level inside the vehicle, the amount of UV rays that were entering the vehicle, and the ability to maintain a comfortable temperature level in the vehicle. 

New Offerings
Several “high end” car manufacturers in Europe began offering new glass configurations that addressed many of these consumer expectations. Mercedes offered insulated sidelites that were constructed quite similar to the insulating glass units that many of us have in our homes with an air space sealed between two plies of glass. The replacement cost for this design was quite high while the overall thickness of the product presented a rather awkward appearance when the window was down. 

The next product that evolved was a return to a laminated cross-section. Two plies of glass were sandwiched around a ply of PVB, similar to the windshield. However, the glass was heat-strengthened (sort of half way between full tempered and annealed glass) to make it more difficult to break. (It should be noted that windshield glass cannot be heat-strengthened because it is expected to break easily to minimize injury to an individual who is thrown into the windshield during a collision.) The thickness of the two plies of glass was minimized to allow the overall thickness to fit easily into a door window channel. 
Enhancements to this base product included laminating a ply of a metallic film against the PVB (many car companies call this product insulated), or coating one of the internal glass surfaces (against the PVB) with a metallic coating. The base product addressed the consumer’s desires to reduce the noise level and the amount of UV rays that entered the vehicle while the enhanced products both improved the reduction of UV rays while significantly reducing the amount of external heat that entered the vehicle (for passenger comfort and air conditioning efficiency).

Theft Deterrent
Another attribute that was identified for the laminated door glass was the difficulty for an intruder to break into the vehicle. Many car thieves know that the tempered sidelites can be broken easily by hitting them with a sharp object. Access to the inside of a vehicle can be attained in seconds. The laminated product requires a lot more work for an intruder to get into the vehicle. Multiple blows with a rather large tool (i.e., a hammer or tire iron) would be required to gain access to the vehicle. This extra effort not only takes a good deal of time, but it also attracts a lot of attention. 

We shouldn’t overlook the aesthetic capabilities of the laminated sidelites. The PVB (or a substitute interlayer) can be used to either change the color of the laminate or to introduce a decorative pattern in the laminated glass.

The impressive attributes of the laminated sidelites have begun to develop an aftermarket opportunity for this value-added product. In many cases, the tempering tooling can be used to manufacture the two plies of heat-strengthened glass needed for the laminated product. If the manufacturer has a windshield assembly room and PVB processing equipment, it could theoretically make the laminated product. 

Growing Demand
Once the consumer becomes aware of the advantages of the laminated product, many will (and have already) express an interest in replacing their existing tempered sidelites. Currently, the number of vehicles manufactured in the United States that either offer laminated glass as an option or provide it as standard equipment is growing annually. This growing vehicle population will continue to increase the opportunity for an auto glass technician to replace a broken, laminated sidelite.

It should be noted that although some vehicles do offer laminated rear windows, the technology doesn’t currently exist to heat strengthen two plies of thin glass (1.8 to 2.1 mm) to complex shapes or to successfully laminate them together. A limited number of vehicles with less complex backlites do offer a laminated back window that often includes a fine wire mesh aircraft-like defroster grid on the PVB surface. This grid is a very efficient way to defrost the back window under freezing external conditions. 

© Copyright 2006 Key Communications Inc. All rights reserved.
No reproduction of any type without expressed written permission.