Sunrooms By Brady Sunrooms By Brady

September 7, 2009

Four Seasons of Sun: Glass vs. Lexan

As summer enters its last throes, the days are getting shorter and the nights a bit more chilly. Here at Brady-Built Sunrooms, we continue our work to bring the best and highest quality sunrooms to you. We have a series of articles written by our Registered Architect, Robert Wironen, whose knowledge and experience will help guide you through some of the complexities faced when choosing a sunroom. We hope you enjoy these articles and gain helpful information.

Below is the first article addressing the choice of Lexan and Glass in your sunroom. While both have their advantages and disadvantages, Bob breaks down why some manufacturers do not measure up to Brady-Built quality.

Polycarbonate which is commonly known by GE’s brand name, Lexan is an extremely tough plastic that has been used in many applications from helmets to car headlights to bullet proof glazing to eyeglass lenses. The characteristics that make it so well suited for the applications I mentioned are also one of its weaknesses.

Lexan is a polymer that is extremely flexible with very strong molecular bonds. These qualities make it virtually impossible to break, but also make it very soft. The soft surface is very susceptible to scratching. In applications like helmets, minor surface scratching don’t matter.

For headlights, the surface scratching is more of an issue and in glazing and eyeglass applications it is a serious concern. Other issues with Lexan as a glazing material are yellowing due to UV exposure and sag.

The industry responded to the concerns raised by scratching and yellowing by developing special coatings. The most commonly used hardcoat and UV absorber for polycarbonate today is a combination of Alkoxysilane and Colloidal Silica. They form an extremely thin film on the polycarbonate that is chemically similar to glass.

The problem with this coating is that it is only a few microns thick and is bonded to a material (Lexan) that has a vastly different coefficient of expansion. The combination of thermal cycling and the thinness of the hardcoat cause it to delaminate over time. The delamination is at a microscopic level, so it won’t be obvious (big sheets peeling off), but will manifest itself in visual crazing and poor optical quality.

The thinness of the coating also makes it highly susceptible to damage by abrasion. Small particles that are deposited on the surface by rain and wind will damage the surface over time, but the damage is exacerbated by attempts to clean it. Rubbing of the grit covered hardcoat surface with a cleaning cloth will wear the surface coating off.

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