The Dream of Polycarbonate Car Windows is Still Just a Dream (updated)

The Fiat 500L polycarbonate rear quarter window

Originally posted on 4/25/2016.

In 1997, GE Plastics and Bayer AG announced that they were forming a joint venture with an initial investment of 40 million dollars to develop and market polycarbonate materials that could be used to replace glass for automotive side windows. 15 years later in 2012 the Fiat 500L became the first car to use polycarbonate side window glazing. Sounds like the beginning of a great new market for polycarbonate. Unfortunately the only windows on the Fiat 500L that are made from polycarbonate are the tiny rear corner windows at the back of the vehicle. To make matters worse, the Fiat 500L remains the only car that has used polycarbonate side window glazing. What happened?

It seemed like a great idea. Polycarbonate is 40% lighter than glass and the weight savings is at the top of the car which has the added benefit of lowering the center of gravity. Polycarbonate is more expensive than glass and the tooling cost for plastic is probably higher as well but molding the side glass out of polycarbonate might enable trim pieces and other decorative elements to be molded in a two shot operation. This could reduce costs. The automakers should have jumped at this, but they never have. There are some problems.

The first problem is UV stability. While UV stability of plastics has improved dramatically over the last few decades, polycarbonate does not have the UV stability of glass which seems to be all but impervious to the damaging effects of the sun. Polycarbonate is going to get yellow and foggy long before the life expectancy of the vehicle and customers are not going to be comfortable with this. Customers have an expectation that they will not have to replace the glazing on a car as a wear item.

Polycarbonate has a big advantage over glass in that it is much more impact resistant. The problem is that when it comes to car side windows, this is not an advantage. Modern tempered glass is very impact resistant but if need be it can be broken to get a passenger out of a vehicle in a severe accident. I was sitting at a light last year behind a minivan. When the light turned, the van started into the intersection only to be T-boned by a vehicle so hard that the van ended up on it’s roof. I pulled over to see if I could help. A security guard working near by at a bank ran out and tried to break the side window to pull the shocked passenger out. It took about 10 hard hits with a metal object to break the window but it did eventually shatter into a lot of tiny pieces. That security would not have been able to break a polycarbonate window. The only way to get through it would be to cut through it with a saw.

Glass is also a lot harder than polycarbonate and resists scratches and abrasions. Polycarbonate can be coated with various chemicals to improve the scratch resistance. Most eye-glasses are coated polycarbonate and I find that they are pretty difficult to scratch. I have dropped mine many times and I am surprised how durable they are.

GE and Bayer estimated in 1997 that replacing side window glass with polycarbonate had the potential to become a 5 to 6 billion dollar market. That potential has only grown with increased worldwide car sales and current light-weighting efforts that are widespread in the industry. Unfortunately, the thing that makes polycarbonate so great in everything from eye glass lenses to motorcycle helmets is the biggest problem for automotive glazing applications.

The best application for polycarbonate glazing might be as a replacement for glass in removable roof panels and sun roofs. There have already been a few small applications where it has been used. With so many newer vehicles having large glass sunroof panels, the weight savings potential is fairly large. Also, most of the panels are tinted which will help with UV stability. The impact strength of polycarbonate would certainly not be a liability for roof panels as they are not typically needed for vehicle egress.  There have been some reports of large sun roof panels unexpectedly shattering while the vehicle is being driven and that torsional stresses in the roof might be the cause. The flexibility of polycarbonate compared to glass might help solve this problem and actually increase safety. All that being said, I suspect that old fashioned glass side windows are going to be the norm in automotive for the foreseeable future.

Update: It has just been announced that the next generation Buick GL8 minivan that is sold in China and manufactured by the SAIC/GM joint venture there will feature a polycarbonate rear quarter window. You can read about it here at The Molding Blog. I still stand by opinion in my post. I still do not believe that PC automotive glazing will ever be widely used.

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