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 -100°C to +135°C
a melting point around 250°C
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
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.