Photochromic Plastic Lenses
Photochromic Plastic Lenses –
In-Mass Photochromic Monomer
(SunSensors® by Corning / SunSensors +)
The first technology to manufacture SunSensors photochromic lenses is to use a photochromic monomer or, more precisely, the mix of a transparent liquid monomer and different types of specific photochromic dyes (including some Corning-patented dye/liquid resin components).
The result is a gray or brown liquid resin, which is delivered in drums to our customers worldwide in order to manufacture high-quality SunSensors photochromic lenses, using a typical casting process.
In the first step of lens casting, the resin is mixed with several types of catalysts, following Corning’s process recommendations. The mix is then degassed before being poured into the mold set. The mold assembly requires special gasket or tape to hold the two separate glass molds together and the in-between space is filled with the mixed liquid. This takes place in a clean room to avoid any dust that could affect the lens cosmetic quality.
Semi-finished blanks or different base curved or powered finished lenses can be made using different glass molds and adjusting the space between them, the most critical area being the inside surface of the back mold, whose quality and cleanliness should be flawless.
Since mold quality is vital to plastic lenses, Corning’s highly regarded progressive and aspherical glass molds can be supplied to our customers in tailor-made or independent designs, always using Free-Form technology. This is a further guarantee of overall excellence throughout the production line for SunSensors lens casters.
After filling, the monomer resin is ready to be polymerized either by a combination of ultraviolet (UV) and thermal curing or by thermal curing alone. Typical durations of over a dozen hours with different heating stages are common thermal curing profiles to transform liquid monomer into solid lenses.
After thermal curing, the SunSensors photochromic lens is removed from the mold and an automatic loading machine carries it through a cleaning / rinsing process in a series of detergents and water tanks.
Finally, the lens edge is polished, and in order to protect its surface while handling, a hard-coat lacquer (HC) is applied either by dip-coat or spin-coat process, providing an anti-scratch protective layer (typical 3 to 5 microns).
Anti-reflect coating can then be applied on the hard-coated lens, an increasingly popular treatment for extra vision comfort and esthetics.
Photochromic Plastic Lenses – Coating Process
(SunSensors HPC)
The technology used by Corning Ophthalmic to develop its newest and most efficient photochromic solution, SunSensors HPC, is a patented, state-of-the-art coating process.
The challenge is to deposit a fully homogeneous photochromic resin layer of the desired thickness on different substrates such as high-index (1.6 and 1.67) and polycarbonate lenses, each one having its specific surface properties.
The Corning manufacturing process is automated and carried out in a clean room environment to avoid any dust contamination.
First of all, the semi-finished blanks go through a typical lens-cleaning line to assure lens cleanliness and specific surface preparation.
Two layers are then applied, for a total thickness of a few dozen microns:
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a thin layer of primer, which acts as an interface to provide perfect adhesion between the photochromic layer and the different types of substrates, and
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the photochromic resin layer, including a mix of specific photochromic dyes for plastic lenses.
Both layers are applied by spin coating, assuring homogeneous distribution.
After curing under proper conditions and undergoing thorough quality control, a certified SunSensors- HPC photochromic lens is obtained.
This lens must then go through hard coating (HC) and anti-reflective (AR) treatments to improve scratch protection and vision comfort. Most commercially available HC and AR processes used for high index and polycarbonate lenses are applicable on SunSensors HPC lenses.