Plastic CR-39 Lenses

History

Plastic was first introduced to the optical lens industry as a laminate of glass lenses with the Motex lens in the 1930's. The Motex lens mimicked the technology used at that time on car windshield. Glass laminated with thin sheets of plastic helped prevent excessive splintering of glass in the event of an accident. The laminated glass lens was short lived, but paved the way for the Igard lens, the first true plastic lens. This lens was introduced by and English company named COIL (Combined Optical Industries Limited) and was made of PMMA (Polymerized Methyl Methacrylate). Besides the light weight factor, the Ingard lens turned yellow, scratched easily and were expensive. In 1947 Armolite introduced CR-39 lenses. CR-39 is a material that was derived for the military as durable light weight plastic used on military planes in WWII. CR-39 plastic is actually ADC (Allyl Diglycol Carbonate), invented by an Ohio based company named Columbia Southern Chemical Company (CSCC) a subsidiary of Pittsburg Plate Glass Company (PPGC). CSCC initiated a project named Columbia Resins and achieved its goal on the 39th attempt, hence leading to CR-39. Sola, Essilor, Armolite, Univis Lens Co. and 3M (Minnesota Mining and Manufacturing Company) are notable companies that helped to pave the way for the CR-39 lens.

Specifications

The CR-39 lens has an index of 1.498 and has an Abbe Value of 58 with a specific gravity of 1.32 g/cm3.

Advantages

The most available lens considering lens type and premium lenses.
Almost 50% lighter than Glass
One of the best and easiest mediums to tint

Disadvantages

Low index of refraction (not ideal for heavy prescriptions)
Not as scratch resistant as glass