Story of CR-39!

The abbreviation stands for “Columbia Resin #39,” because it was the 39th formula of a thermosetting plastic developed by the Columbia Resins project in 1940.

CR-39, or Allyl Diglycol Carbonate (ADC), is a plastic polymer commonly used in the manufacture of eyeglass lenses.

The first commercial use of CR-39 monomer was to help create glass-reinforced plastic fuel tanks for the B-17 bomber aircraft in World War II, reducing weight and increasing range of the bomber. 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. CR-39 is now a trademarked product 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.
CR-39 should not be confused with polycarbonate, a tough homopolymer usually made from bis-phenol A.

Applications

CR-39 is transparent in the 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 name RAV, and another one by Danyang Yueda FineChemichal Co. Ltd in China

PROPERTIES	GLASS	PC	PMMA	CR39
Superior optical quality	YES	NO	NO	YES
Lightness and strength	NO	YES	YES	YES
Scratch resistant	YES	NO	NO	YES
Stress cracking resistant	NO	NO	NO	YES
Solvents and chemical resistant	YES	NO	NO	YES
Welding sparks resistant	NO	YES	NO	YES
Plasticizer migration resistant	YES	NO	NO	YES
Ageing resistant	YES	NO	NO	YES
Gamma radiation resistant	YES	NO	NO	YES
Wide range of color	NO	YES	YES	YES
Wide range of U. V. absorption	NO	YES	NO	YES

PC: Aromatic Polycarbonate

PMMA: Polymethyl methacrylate

The CR39 plastic :

·         are colorless and completely transparent to the visible light and almost completely opaque in infrared and ultraviolet region of the spectrum. For these reasons, it is largely used for the production of sun glass lenses. They can be colored by surface dyeing or bulk tinting;

·         have high abrasion resistance and high-quality optical properties;

·         weigh about half as much as glass;

·         keep their excellent optical properties despite long-term exposure to chemicals like solvents, highly oxidizing acids, and strong basis;

·         resist to heat distortion up to 100 ° C and are resistant to small hot flying particles such as welding sparks.

Optical Property	Value
Refractive Index	1.498
Abbe value	59.3
Density	1.31 g/cm³

|| stand up to scratches, heat and household chemicals || have less chromatic aberration than polycarbonate lenses || are lightweight and less prone to shattering than glass ||

credit: Wikipedia, other reliable sources in internet