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Polycarbonate Windows

What is polycarbonate

Polycarbonates are a particular group of thermoplastics. They are easily worked, molded, and thermoformed; as such, these plastics are very widely used in modern manufacturing. They are called polycarbonates because they are polymers having functional groups linked together by carbonate groups (-O-CO-O-) in a long molecular chain.

The most common type of polycarbonate plastic is one made from Bisphenol A, in which groups from Bisphenol A are linked together by carbonate groups in a polymer chain. This polycarbonate is a very durable material, and can be laminated to make bullet-proof "glass", though "bullet-resistant" would be more accurate. The characteristics of polycarbonate are quite like those of polymethyl methacrylate (PMMA; acrylic), but polycarbonate is stronger and more expensive. This polymer is highly transparent to visible light and has better light transmission characteristics than many kinds of glass. CR-39 is a specific polycarbonate material with good optical and mechanical properties, frequently used for eyeglass lenses.

Polycarbonate has :

a density of 1.20 g/cm3
a use range from -100C to +135C
a melting point around 250C
a refractive index equal to 1.585 0.001
a light transmission index equal to 90% 1%
poor weathering in an ultraviolet (UV) light environment
Polycarbonate is becoming more common in housewares as well as laboratories and in industry. It is often used to create protective features, for example in banks as well as vandal-proof windows and lighting lenses for many buildings. Other products made from polycarbonate include sunglass/eyeglass lenses, compact discs, DVDs, and automotive headlamp lenses. It is the major component of one variety of Nalgene bottles. It is also used for animal enclosures and cages used in research.

Why use polycarbonate instead of glass?

Glass offers visual clarity, but has many drawbacks. To comply with building codes, safety glass is required if installed within 12" of a door, 18" of the floor or overhead. In vertical applications tempered glass is OK, but in overhead applications tempered over laminated annealed (windshield type glass) is required. In roof applications this glass cracks very easily and is very expensive.

To have a reasonable insulation value two lites of glass, in an insulated unit, are necessary. On wall two lites of tempered, on roof tempered over laminated annealed. Insulated glass has a service life. The seals will eventually fail and the unit will fog. Seal warranty is 5 to 10 years, but is void in high moisture greenhouse and pool enclosure applications.

Since clear glass does not diffuse the light hot spots occur in greenhouse applications. Glass is also heavy, requiring a strong frame. A sophisticated install system with aluminum and rubber gaskets is required or leaks occur, especially on overhead glazing. Often numerous lites of glass are required in a roof slope, resulting in horizontal mullion bars that dam water and can easily lead to leaks. Insulated glass should not overhang the eave, requiring a horizontal mullion bar at this location and possible leaks.

Polycarbonate is virtually indestructible and is inherently safety glazing! Football helmets and the inner layers of bullet proof glass are made of polycarbonate.

Multi-wall polycarbonate is inexpensive and has an insulation value similar to insulated glass. Polycarbonate diffuses the light and is very easy to install. One sheet of polycarbonate goes from the roof peak all the way to the overhanging eave, effectively shedding water.

Polycarbonate is a resilient material. When the Cap is snugly installed, the pressure of the legs of the Cap cause the polycarbonate to slightly give, creating a watertight seal. One of the great advantages to polycarbonate is that gaskets are not required to achieve a watertight seal. The more parts of a glazing system, the more likelihood for leakage. Gaskets in install system caps will often shrink, creating a gap for water to enter.

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