Self-tinting eyeglasses with plastic lenses may soon be significantly improved thanks to a new material developed by Institute scientists. The material, a polymer that darkens when exposed to sun, can be used to create an ultrathin coating on plastic lenses.
Self-tinting spectacles have been around for a while (with up to 10 million pairs being sold annually in the U.S. alone). However, until recently, they could only be made of glass, while about 80 percent of people in industrial countries who wear prescription eyeglasses prefer lightweight plastic lenses.
Even though self-tinting plastic lenses have also become available of late, they are slow to change color and their effectiveness steadily weakens with time. In addition, once their tinting ability is lost, it cannot be restored.
These drawbacks stem from the fact that the photochromic material ? the active substance that changes color when exposed to light ? is dissolved into the plastic. The amount of the photochrome that can be incorporated into the lens in this manner is limited, and its tinting capacity is affected by the properties of the plastic.
Prof. Valeri Krongauz, who pioneered photochromic polymers 20 years ago, developed the new material together with Organic Chemistry Department colleagues Alexander Zelichenok, Frida Buchholtz, Dr. Shlomo Yitzchaik, Professor Emeritus Ernst Fischer and Dr. Judith Ratner. It has been shown to overcome these problems in laboratory tests.
This polymer contains high concentrations of a chemically bound photochromic substance. As a result, a layer only several microns thick has powerful tinting ability. The polymer darkens quickly when exposed to sunlight and immediately clears indoors.
A thin film of the photochromic polymer can be applied to the surface of any plastic lens, according to Prof. Krongauz. He said such film may eventually be easily removed or reapplied in an optometrist's office, such like certain scratch resistant layers are now restored.
A patent application for its production has been filed by the Yeda Research & Development Co., which is responsible for the commercial application of Weizmann research.