Polycarbonate is a thermoplastic polymer invented in 1953 simultaneously by Bayer AG and General Electric. GE was searching for a better wire coating but soon recognized it as a candidate for a large assortment of products where a clear, high impact resistant and stable product was needed. As with the development of CR39 plastic resins destined for military bombers, the need for a better plastic polymer for aircraft canopies and helmet visors was one of the reasons polycarbonate thermoplastic polymers were advanced and perfected through the 1950’s and into the 1960’s. Because polycarbonate material was optically clear, thermally stable and highly impact resistant, NASA used polycarbonate for the bubble helmets worn by astronauts in the early space programs. Further developments made it possible for polycarbonate to be used as shields and sun visors used in later helmets. Due in large part to the success of polycarbonate as a helmet visor, (non-ophthalmic) safety glasses and defense shields used by policing agencies, manufacturers extended the uses of polycarbonate to include ophthalmic lenses used in eyeglasses.
Advancement in the polycarbonate technology eventually resulted in the use of poly as wind screens used in fighter jets, attack helicopters, and even the space shuttles. During the 1980’s polycarbonate materials made their way into consumer goods and today the advancements in the polycarbonate formulations make it the material of choice in the manufacture of CD, DVD’s and Blue Ray disk media that archive and store photos, movies, and documents. The advancements of polycarbonate formulations during the last ten years have been especially good for polycarbonate as an eyeglass lens material because manufacturers of optical storage media like CD’s, DVD’s and Blue Ray disks demanded clearer and more scratch resistant materials for their products. These advancements have helped polycarbonate be the material of choice for some of the best ophthalmic lenses made because of their optical clarity, superior impact resistance and thermal stability.
Poly, or PC, as it is often referred to, has an index refraction value of 1.58 and features natural UV protection from harmful UV-A and UB-B radiation. Poly is considered to be superior to plastic lenses for eyewear due largely to its impact resistance and in that it is similar to Trivex materials in strength. Where Trivex has better overall optical qualities, Poly has the advantage of providing lower cost with only a small compromise in optical clarity for most patients. Poly is the lens of choice for children’s eyewear because it is light and impact resistant and these same features make it a great choice for sports/recreation spectacles and for safety applications too, at more than half the cost less than the Trivex lens materials. Because poly is a softer plastic and is softer than CR39 plastic, it should be coated with an anti-scratch coating to minimize the influence of abrasion and it is usually suggested to also include an anti-reflective coating to minimize the presence of any chromic aberrations and reflected light back to the wearer’s eye.
Polycarbonate lens materials have been constantly improved since they were introduced as a lens material in the 1980’s. Poly lenses from five years ago are inferior to the poly lens materials of today largely because improvements demanded by the music and movie industries resulted in a better material for CD/DVD’s that are used in producing music and movie CD’s, DVD’s and Blue Ray disks. As these improvements are incorporated into eyeglass lenses materials poly stands to grow as a material of choice for its overall capabilities as an eyeglass lens. These days, poly is an excellent lens material free of the many negatives attributes added to the finished product by the manufacturing process of yesteryear and today the polycarbonate lens is a great overall choice for its light weight, clear optics, UV resistance, impact resistance, and relatively low cost compared to Trivex and other high index plastic lens materials.
Poly is perfect for childrens lens products, safety applications, and even drill mount lenses. Cutting poly during the lens shaping process generates a noticeable stink but its blend of low cost, good refractive index and other optical attributes makes it a great choice for many eyeglass prescriptions and especially those for children, workplace uses, sport or other avocation or anywhere impact resistance is required for eye safety of the wearer.
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