Polycarbonate
(PC) is a crystal clear and colorless engineering
thermoplastic known for its high impact resistance. PC
was originally
developed for the aerospace industry to be used in windows for airlines,
space shuttles and face shields for astronaut helmets.
Polycarbonate is the most impact resistant lens material available
today.
When compared to glass or CR-39 Plastic, polycarbonate offers
significantly
greater protection and safety for your eyes.
PC is a very soft material and will not crack or break during an
impact.
In
manufacturing PC an enormous amount of pressure is used to compress the
raw
material. It holds up well under impact because it is flexible and gives
slightly under pressure without breaking. PC lenses are constructed out
of
material that is identical to what is called "bulletproof glass."
Unlike regular glass and plastic eyeglass lenses, polycarbonate will not
shatter upon impact or violent contact, thus preventing injury to the
eye
from the broken pieces. That is why polycarbonate lenses are
recommended,
not only for safety glasses, but for sports goggles and children's
glasses
as well.
A word of caution: Although polycarbonate lenses have been tested to
withstand objects thrown at a high rate of speed, they should not be
tested
while someone is wearing them. PC is impact-resistant, but there is no
guarantee of non-breakage.
The disadvantage with PC is that it has a tendency to scratch easily.
Thus,
most lenses are treated with an anti-scratch coating.
Polycarbonate lenses are sometimes referred to as featherweight lenses
because they are thinner and lighter in weight than the other types of
lenses. This is because less of the polycarbonate lens material is
required
to provide the same amount of visual correction that a traditional
plastic
lens needs.
PC is UV stabilized and, therefore, won't dry out and become brittle
after
exposure to sunlight. UV protection shields the eyes from damaging light
rays similar to the way that sunblock prevents the sun's rays from
damaging
the body. Other types of plastic lenses must be treated to block the
same
amount of UV, but PC lenses automatically offer this protection. PC
filters
out 99.9% of all harmful UV radiation. It has the ability to add UV400
absorber to give extra UV protection for use in environments with high
levels of UV radiation. The UV400 lens with the UV absorber built into
the
material will not scratch off, and is therefore, the best protection.
Lenses
made of glass are not good UV filters.
The chemical resistance of PC is good while being used with diluted
acids,
alcohols, greases and oils.
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