CR-39 Information & CR-39 Links at HealthHaven.com

CR-39, or allyl diglycol carbonate (ADC), is a plastic polymer commonly used in the manufacture of eyeglass lenses. It should not be confused with polycarbonate, a homopolymer made from bis-phenol A, a tough polymer widely used for glazing. CR-39 is a trade marked product of PPG Industries, originally developed by Columbia Chemical Co Inc which evolved through acquisition into the Chemical Division of PPG Industries. An alternative use includes a purified version that is used to measure neutron radiation, a type of ionizing radiation, in neutron dosimetry. The CR stands for Columbia Resin. During WWII uncured CR-39 Resin was used to coat aircraft fuel tanks. The CR-39 would "self heal" the tanks when struck by flak.

The trade name for the original and most popular plastic material used for eyeglass lenses. The abbreviation stands for “Columbia Resin #39,” because it was the 39th formula of a thermosetting plastic developed by the Columbia Resins project of PPG Industries back in 1940. The first commercial use of CR-39 monomer was to help create lighter, more durable fuel tanks for the B-17 bomber aircraft in World War II. After the War, the Armorlite Lens Company in California is credited with manufacturing the first CR-39 eyeglass lenses in 1947. CR-39 plastic has an index of refraction of 1.498 and an Abbe number of 58.

[edit] Synthesis

CR-39 is made by polymerization of diethyleneglycol bis allylcarbonate (ADC) in presence of diisopropyl peroxydicarbonate (IPP) initiator. The presence of the allyl groups allows the polymer to form cross-links; thus, it is a thermoset resin. The monomer structure is

CH₂=CH-CH₂-O-CO-O-CH₂CH₂-O-CH₂CH₂-O-CO-O-CH₂-CH=CH₂

The polymerization schedule of ADC monomers using IPP is generally 20 hours long with a maximum temperature of 95°C. The elevated temperatures can be supplied using a water bath or a forced air oven.

Benzoyl peroxide (BPO) is an alternative organic peroxide that may be used to polymerize ADC. Pure benzoyl peroxide is crystalline and less volatile than diisopropyl peroxydicarbonate. Using BPO results in a polymer that has a higher yellowness index, and the peroxide takes longer to dissolve into ADC at room temperature than IPP.

[edit] Applications

CR-39 is transparent in visible spectrum and is almost completely opaque in the ultraviolet range. It has high abrasion resistance, in fact the highest abrasion/scratch resistance of any uncoated optical plastic. CR-39 is about half the weight of glass with an index of refraction only slightly lower than that of crown glass, and its high Abbe number yields low chromatic aberration, altogether making it an advantageous material for eyeglasses and sunglasses. A wide range of colors can be achieved by dyeing of the surface or the bulk of the material. CR-39 is also resistant to most of solvents and other chemicals, to gamma radiation, to aging, and to material fatigue. It can withstand the small hot sparks from welding, something glass cannot do. It can be used continuously in temperatures up to 100 °C and up to one hour in 130 °C.

In the radiation detection application, raw CR-39 material is exposed to proton recoils caused by incident neutrons. The proton recoils cause ion tracks, which are enlarged by an etching process in a caustic solution of sodium hydroxide. The enlarged ion tracks are counted under a microscope (commonly 200x), and the number of ion tracks is proportional to the amount of incident neutron radiation.

It is used in some photographic filters, such as the Cokin filter system.

A direct equivalent is produced by Acomon AG with the brand names RAV

Another direct equivalent is produced by Danyang Yueda FineChemichal Co.Ltd in China.

[edit] See also

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Characteristics of CR-39

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Contents

[edit] Synthesis

[edit] Applications

[edit] See also

[edit] References

[edit] External links