Process for preparing a photochromic lens

Details Process for preparing a photochromic lens Process for preparing a photochromic lens

1999-12-30

2002-04-09

Sugarman, Scott J. (Department: 2873)

Optics: eye examining, vision testing and correcting

Spectacles and eyeglasses

Ophthalmic lenses or blanks

C351S163000, C351S166000

Reexamination Certificate

active

06367930

ABSTRACT:

The invention concerns a photochromic lens and more particularly a process for making optical lenses containing thermoplastic polycarbonate and thermoplastic polyurethane resins.
SUMMARY OF THE INVENTION
A process for making a photochromic optical lens is disclosed. In a first embodiment of the process a multi-plied laminate, containing a ply of photochromic thermoplastic polyurethane (herein “TPU”) and a ply containing thermoplastic polycarbonate, is first placed in the cavity of a suitable mold. The ply that contains polycarbonate resin is placed facing the cavity. Thermoplastic polycarbonate resin is then injected into the cavity. In a second embodiment, referred to as an over-mold method, polycarbonate is first injection molded into a molding cavity to form a substrate. Photochromic TPU is, in a subsequent step, injected into the cavity to form a superstrate overlay. In both embodiments, the articles thus molded are suitable for the preparation of optical lenses.
BACKGROUND OF THE INVENTION
Processes for co-injection and multi-shot injection molding are also well known. Essentially, these refer to processes where a plurality of resins, through a continuous controlled injection, are molded to form a part. Examples include forming a core material, which is then encapsulated by a higher quality skin. These multi-layered “sandwich moldings” allow the use of less expensive or specialized resin for the core, with only a thin skin of material meeting more rigid requirements for aesthetics and durability. Also included is the “two-color” or “multi-shot” process where the material components are “over-molded” selectively onto other segments of a single molding in discrete steps. These processes have been used in the preparation of blow-molded packaging, using multi-cavity tooling and multi-layered structures to achieve barrier-properties in the part.
A process variation known as “mono-sandwich” molding is one where the core material is transported along the barrel of a standard injection system, while the skin material feeds into the end of the main barrel from a side extruder. With the two screws properly sequenced, the skin and core materials are “layered” within the barrel, and then injected with a single stroke.
The processes have been used in applications such as ones requiring placing a soft, tactile material on a stiff base, and in applications where molding of different colors as one component, as with red, clear, and amber segments in automotive tail lamp lenses. Chemically compatible plastics bond to each other best, and over-molding may also connect segments of incompatible plastics using undercuts and mechanical interlocks.
The in-mold decoration method is yet another well known variation of the co-injection molding technique. In this process, decorative artwork may be molded into the part. In the process, a decorated film is placed into a mold, and the injection molding process encapsulates the ink between the film and the later-injected molding resin.
Relevant information respecting mold design, injection molding machine and a method for forming a multi-layer plastic article by over molding has been disclosed in European Patent Application 894604. Further relevant information respecting insert-molding may be found in U.S. Pat. Nos. 5,264,172, 5,512,226, 5,514,317 and 4,917,927, the disclosures of all is incorporated herein by reference.
Articles which have organic photochromic dye(s) applied to or incorporated therein are characterized in that upon exposure to electromagnetic radiation or to solar light they exhibit a reversible change in color and in light transmission. Once the exposure to the original radiation has been discontinued, the composition returns to its original color, or colorless state. Recently, photochromic plastic materials, most notably, such compositions which may be suitable for the preparation of ophthalmic lenses, films and automotive head lamp lenses have been the focus of attention in the relevant arts. It is known that photochromic behavior may be imparted to glass and to certain plastic materials by using inorganic and organic dyes respectively. Photochromic articles prepared from synthetic organic resins such as homopolymers of a poly(allyl carbonate) monomer are known (U.S. Pat. Nos. 4,994,208, 5,246,630, 5,221,721 and 5,200,483.)
U.S. Pat. No. 5,244,602 describes a naphthopyran useful for photochromic polymers and also organic hosts such as polyurethanes for such materials. McBain, et al. (U.S. Pat. No. 4,994,208) demonstrated that the photochromic performance of matrices prepared by the free radical polymerization of polyol(allyl carbonates), e.g., diethylene glycol bis(allyl carbonate), could be improved by the incorporation of 10 to 40 weight percent of an aliphatic polyurethane having terminal ethylenic unsaturation. Selvig (U.S. Pat. No. 5,200,483), showed an improvement over McBain. et al.
DETAILED DESCRIPTION OF THE INVENTION
The lens prepared by the inventive process contains a polycarbonate substrate and a photochromic superstrate. Lenses prepared by the insert-molding method contain a superstrate which is formed from a multi-plied laminate containing a ply of photochromic TPU and a polycarbonate ply. The superstrate of the lens prepared by the over-mold method contains photochromic TPU. In terms of relative sizes, the substrate is about 2.0 to 12.5 millimeters (mm), preferably 2 to 8 mm, more preferably 2 to 5 mm in thickness and the superstrate has a thickness of 0.1 to 1.25 mm, preferably 0.2 to 0.5 mm. In the superstrate prepared in accordance with the insert-molding embodiment of the invention, the thickness of the polycarbonate ply is about 0.1 to 0.5 mm, preferably 0.127 to 0.381 mm, and the thickness of the ply containing photochromic TPU is about 0.1 to 1.25 mm, preferably 0.127 to 0.254 mm.
Suitable polycarbonate resins for preparing the substrate of the inventive lens are transparent homopolycarbonates and copolycarbonates and mixtures thereof. Transparency, a requirement of the lens of the present invention, means that the polycarbonate (substrate) has a total light transmission of at least 89% and a haze value of less than 1% as determined on a substrate having a thickness of 0.1 inch (2.54 mm).
The polycarbonates generally have a weight average molecular weight of 10,000 to 200,000, preferably 15,000 to 80,000 and their melt flow rate, per ASTM D-1238 at 300° C., is about 1 to about 85 g/10 min., preferably about 2 to 24 g/10 min. They may be prepared, for example, by the known diphasic interface process from a carbonic acid derivative such as phosgene and dihydroxy compounds by polycondensation (see German Offenlegungsschriften 2,063,050; 2,063,052; 1,570,703; 2,211,956; 2,211,957 and 2,248,817; French Patent 1,561,518; and the monograph by H. Schnell, “Chemistry and Physics of Polycarbonates”, Interscience Publishers, New York, N.Y., 1964, all incorporated herein by reference).
In the present context, dihydroxy compounds suitable for the preparation of the polycarbonates of the invention conform to the structural formulae (1) or (2).
wherein
A denotes an alkylene group with 1 to 8 carbon atoms, an alkylidene group with 2 to 8 carbon atoms, a cycloalkylene group with 5 to 15 carbon atoms, a cycloalkylidene group with 5 to 15 carbon atoms, a carbonyl group, an oxygen atom, a sulfur atom, —SO— or —SO
2
or a radical conforming to
e and g both denote the number 0 to 1;
Z denotes F, Cl, Br or C
1
-C
4
-alkyl and if several Z radicals are substituents in one aryl radical, they may be identical or different from one another;
d denotes an integer from 0 to 4; and
f denotes an integer from 0 to 3.
Among th e dihydroxy compounds useful in the practice of the invention are hydroquinone, resorcinol, bis-(hydroxyphenyl)-alkanes, bis-(hydroxyphenyl)-ethers, bis-(hydroxyphenyl)-ketones, bis-(hydroxyphenyl)-sulfoxides, bis-(hydroxyphenyl)-sulfides, bis-(hydroxyphenyl)-sulfones, dihydroxydiphenyl cycloalkanes, and &agr;,&agr;-bis-(hydroxyphenyl)-diisopropyl-benzenes, as well as their nuclear-alkylated compounds. These and furt

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