Optics: eye examining – vision testing and correcting – Spectacles and eyeglasses – Ophthalmic lenses or blanks
Reexamination Certificate
2001-03-21
2004-08-10
Epps, Georgia (Department: 2873)
Optics: eye examining, vision testing and correcting
Spectacles and eyeglasses
Ophthalmic lenses or blanks
C351S162000, C351S163000
Reexamination Certificate
active
06773108
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a novel process for coating one or both surfaces of a non-prescription, prescription, multifocal or progressive optical lens with an elastomeric film that contains a photochromic dye. The invention further provides photochromic lenses and eyeglasses produced by the method. The lens produced by this process has a high level of activation, and rapid activation and deactivation time. The present invention is applicable to all lens materials and is simple, quick and cost-effective.
BACKGROUND OF THE INVENTION
Photochromism is a phenomenon in which a compound, upon exposure to light containing ultraviolet rays, changes color, and, upon removal from light irradiation, returns to its original color. The color changes that occur in photochromic compounds are generally reversible. Photochromic dyes can be utilized in lenses and eyeglasses in order to protect the eyes from the harmful effects of the sun's ultraviolet radiation.
Photochromic dyes reversibly alter their color upon exposure to ultraviolet (“UV”) sources. These dyes respond to UV irradiation, such as sunlight, by changing in color. When the UV stimulus is removed, the dye returns to a partially or completely colorless state. Photochromic dyes are not reactive in the crystalline state, and need to be dissolved in a polymer or solvent to function.
The production of mineral glass lenses that are photochromic is well known in the art. These lenses, however, possess certain drawbacks. In addition to being too heavy in weight, photochromic mineral glass lenses possess a slow photochromic deactivation time. The photochromic deactivation time is the time it takes for the lens to change back to its normal color upon moving from exposure to an ultraviolet source to a darker indoors environment.
Lenses and eyeglasses are now frequently made of plastic and glass-plastic composites. Such plastics include acrylic, PPMA (a product of PPG-Pittsburgh Plate Glass) also known as CR-39®, and Lexan® (a polycarbonate made by General Electric). Methods have been developed to render plastic lenses photochromic, although this has not been easy because of the chemistry involved in making plastic lenses.
Ethylene glycol diallyl dicarbonate is the most commonly used monomer for producing plastic optical or contact lenses. Generally, the lens is made by casting the monomer in a lens mold and polymerizing with a catalyst such as isopropyl percarbonate. This process, however, results in an inhibition of the photochromic dyes following polymerization of the organic material. This inhibition of the photochromic dyes is apparently caused by the catalyst used for polymerization. Thus, successful incorporation of photochromic dyes into the commonly used monomer ethylene glycol diallyl dicarbonate for the production of contact lenses from an organic material has not been achieved.
In addition, previously disclosed methods do not permit an optician or lens crafter to utilize simple stock lenses and provide an array of beneficial features such as photochromic properties, tinting, UV protection and scratch resistance. Furthermore, none of the previously disclosed methods result in producing a photochromic lens having rapid photochromic activation and deactivation times.
In addition to a plastic polymer, another type of polymer that can be utilized in the manufacturing of lenses is an elastomer. Elastomers have been utilized as film coatings on lenses to render them abrasion resistant and, to a certain extent, impact resistant. An elastomer is a polymer that is characterized by a high degree of resiliency and elasticity. Elastomers may be natural (rubber) or synthetic. Examples of synthetic elastomers include polyurethanes and polysiloxanes. An elastomer is capable of recovering its original shape after being stretched to a great extent. When stretched, the molecules of an elastomer are aligned and often take on aspects of a crystalline arrangement. Upon release, however, elastomers return to their natural disordered and entangled state. This return to their natural disordered state distinguishes elastomers from plastic polymers, which are normally glassy or crystalline and retain much of the shape to which they are deformed.
Elastomers have low glass transition temperatures. The glass transition temperature, T
g
, is the temperature above which a polymer becomes soft and pliable, and below which it becomes hard and glassy. If an amorphous polymer has a T
g
below room temperature, it is an elastomer. If an amorphous polymer has a T
g
above room temperature, it will be a thermoplastic polymer and hard and glassy at room temperature.
U.S. Pat. No. 5,462,698 (Kobayakawa, et al.) is directed to forming a lens having photochromic compounds dispersed throughout. Kobayakawa discloses use of a resin compound having at least one epoxy group in the molecule as the resin for forming the photochromic lens. Koboayakawa requires the presence of multiple types of photochromic compounds in combination and polymerization in a heat furnace for between 2 to 40 hours. Also, as seen in Table 1, the resins disclosed in Kobayakawa as useful for producing photochromic lenses possess an average fading time to ½ density of 3 minutes as measured after exposure to light for 60 seconds. Thus, the photochromic resin disclosed in Kobayakawa is produced by a time-consuming process and possesses a rather slow photochromic response time.
U.S. Pat. No. 5,531,940 (Gupta et al.) discloses methods for making optical plastic lenses with photochromic additives. According to an embodiment of this invention, a casting resin having a low cross link density comprising polymerizable components (preferably including up to 50 wt % bisallyl carbonate) and photochromic additives, wherein all polymerizable components have a functionality not greater than two, is arranged between a mold and a lens preform, and then cured. Upon polymerization, the resin has a low crosslink density and forms a soft matrix that is unsuitable as the outer layer for photochromic lenses. Gupta et al. do not discuss photochromic reversal rates. The practical utility of the process disclosed by Gupta et al. is limited in that it is complex and time consuming. Furthermore, the photochromic material disclosed by Gupta et al. is described as being too soft for exposure to the environment.
U.S. Pat. No. 5,975,696 (Kohan), which is incorporated herein by reference, describes a photochromic lens and a method for making it. The process disclosed in Kohan involves dipping a lens into a solution comprising a non-polar solvent containing a photochromic dye and a polar solvent. The lens is then removed, dried and exposed to very high temperatures to melt and spread the photochromic dye crystals on the lens surface. The solutions described in this patent do not include components that form elastomeric films.
U.S. Pat. No. 4,267,208 teaches coating of the convex side of an optical lens for blocking purposes by immersing the downwardly facing convex side in a liquid coating material in a can, upwardly withdrawing the lens above the level of the coating material but below the lip of the can, and spinning the lens about its vertically disposed axis to spread the coating material by centrifugal force as a uniformly thin film over the convex side, to create an edge buildup of coating material to form a thickened bead-like peripheral or rim portion at the periphery of the convex side, and to spin-off excess coating material against the inside of the can for reuse. This method requires complex apparatus and is not simple to carry out.
U.S. Pat. No. 5,164,228 also teaches the coating of a plastic ophthalmic lens with a scratch-resistant coating using a spin coating process.
None of the foregoing prior art patents, which are incorporated herein by reference, discloses a method for producing a photochromic lens having an elastomeric film coating, i.e., a lens coated with an elastomeric film dye or mixture of dyes dispersed therein.
The benefit of previously disclosed photochromic lenses is limited b
deRojas Agustin Alberto
Thangamathesvaran Pallapalayam Muthusamy
Epps Georgia
Hasan M.
Invicta Corporation
Proskauer Rose LLP
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