Plastic and nonmetallic article shaping or treating: processes – Optical article shaping or treating – Composite or multiple layer
Reexamination Certificate
2000-02-16
2002-07-09
Vargot, Mathieu D. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Optical article shaping or treating
Composite or multiple layer
C264S001360, C264S001380
Reexamination Certificate
active
06416690
ABSTRACT:
FIELD OF THE INVENTION
This invention is related to the fields of polymerization and molding. More particularly, it is related to a process for quickly and inexpensively producing an optical quality lens. It is also related to optimal materials of construction and to the resulting composite structure.
BACKGROUND OF THE INVENTION
Ophthalmic lenses are used to correct vision by changing the focal length of the light rays entering the pupil of an eyeglass-wearer. When the patient is near-sighted or far-sighted, the correction is rather simply made using a single vision lens in which the outer and inner surfaces of the lens are both spherical, but have different radii of curvature. An added level of complication occurs when a patient exhibits astigmatism in one or both eyes. In this case the back surface of the lens is made toroidal by imposing two different radii of curvature on the same surface. In order to properly correct for astigmatism, the rotational position of the toroidal surface must be fixed with respect to the pupil of the eyeglass-wearer (typically accomplished with the eyeglass frames). Yet another level of complication is introduced in patients who require multi-vision lenses, such as bifocals and progressives. In this case, a bifocal pocket is molded into the front surface of the lens, providing a region that corrects to one focal length while the remainder of the lens corrects to a second focal length. The most common example of this is someone who is both near-sighted (needs eyeglasses to see objects at a distance) and far-sighted (needs a bifocal pocket to read text for example).
When a patient needs both multi-vision lenses and astigmatic correction, the toroidal back surface must be fixed rotationally with respect to the location and orientation of the bifocal pocket. This presents an obstacle to high-throughput manufacturing of plastic ophthalmic lenses, for reasons which will be discussed below.
Polycarbonate is widely used as an optical material for the production of ophthalmic lenses. It has a refractive index of 1.586, reasonably good light transmission, and extremely good impact resistance. Imparting scratch resistance to polycarbonate lenses must typically be accomplished with a secondary coating.
Polycarbonate ophthalmic lenses are formed by injection molding. Injection molding is a process that requires high injection and clamping pressures. As a result, molds are quite expensive for industrial-scale equipment. In addition, changing molds from one to another is time-consuming and involves a significant amount of down-time for the injection molding system.
Typical ophthalmic lenses have a prescription range of +2 to −6 diopters in ¼ diopter increments, a bifocal pocket of 0 to +3 diopters in ½ increments, and an astigmatic correction from 0 to 2 in ¼ increments and a specified rotational angle of 0 to 90 degrees in 1-degree increments. Thus, taking into account all of the possible variations, there are roughly 10
5
different prescriptions possible. In terms of injection molding, there would have to be approximately 150 different front molds and 720 different back molds in order to accommodate the prescription ranges covering multi-vision lenses with astigmatic correction. These numbers increase even more when other design features such as aspherical lenses or progressives are considered. The high-volume production of polycarbonate lenses with only a few variations can be quite economical. However, since molds are expensive and change-out time is excessive, injection molding of multi-vision lenses incorporating astigmatic corrections is not practical due to the large number of variations. Even if such a manufacturing process could be economically carried out, long tooling change-out times would require stocking the entire range of prescriptions, adding substantially to the cost of the lens.
Thus, polycarbonate lenses have only captured a relatively small market share compared to conventional lens manufacturing materials and processes, namely the mechanical grinding and polishing of CR-39 lens blanks. Multi-focal lenses with astigmatic corrections are produced today primarily by mechanical grinding of one or more of the surfaces, another labor-intensive, time-consuming, and expensive process.
SUMMARY OF THE INVENTION
The present invention is directed to a fabrication method whereby the beneficial properties of polycarbonate (especially the impact resistance) or other optical quality materials may be realized in multi-focal lenses, without the drawbacks of injection-molding or mechanically grinding a wide variety of lens prescriptions. The method makes use of a polycarbonate or other desirable core that is sandwiched with one or more semi-solid polymerizable materials to give a composite lens having a desired geometry and configuration. Core materials may be chosen to give good impact resistance, elasticity, photochromic behavior, etc.
More particularly, the process of the invention includes the steps of obtaining a core; placing a semi-solid-like polymerizable composition in contact with at least one of the front or back surfaces of the core; compressing and/or heating the resulting semi-solid/core sandwich between two mold halves, where the mold contacting the semi-solid polymerizable material has a desired surface geometry; and exposing the semi-solid/core sandwich to a source of polymerizing energy, to yield the finished lens, which is a composite sandwich of one or more previously semi-solid layers combined with a core. The resulting composite lens may have exceptional impact resistance when incorporating a polycarbonate core, but is also easily fabricated with both toroidal curves and multi-focal pockets as a result of the semi-solid molding process. Other beneficial properties may be included by appropriate choice of the core or semi-solid material(s).
Also included within the present invention is a composite optical lens comprising a core portion and at least one layer of a cured resin bonded to the core portion, the cured resin comprising a semi-interpenetrating crosslinked polymer network of reactive plasticizer within an entangled dead polymer. In one embodiment, the reactive plasticizer polymer network is further crosslinked to the dead polymer. The composite lens exhibits dimensional stability, high-fidelity replication of an internal mold cavity, and high impact resistance. In a presently preferred embodiment, the final lens is a multi-vision lens and further may incorporate astigmatic corrections.
DETAILED DESCRIPTION OF THE INVENTION
The terms “a” and “an” as used herein and in the appended claims mean “one or more”.
The optical lens core composition of the present invention is selected to provide high impact-resistance or any other desirable property to the resulting lens. In accordance with an embodiment of the present invention, preferred polymers for use as optical lens cores are aromatic halogenated or non-halogenated polycarbonate polymers. More preferred polymers are bisphenol A polycarbonate, ortho-methoxy bisphenol A polycarbonate, &agr;,&agr;′-dichloro bisphenol A polycarbonate, and poly(diphenyl methane bis(4-phenyl)carbonate), with the most preferred material for use in connection with the present invention being bisphenol A polycarbonate. Bisphenol A polycarbonate is commercially available in the form of finished or semi-finished single vision lens preforms from Essilor. Bisphenol A polycarbonate has a high impact resistance, a refractive index of about 1.58 and an Abbe number of about 28-30.
Other core materials may be useful for the present invention as well. For example, optical quality or photochromic glasses, bisallyl carbonates, polyethylene terephthalates, polybutylene terephthalates, polystyrenes, polymethyl methacrylates, acrylonitrile-butadiene-styrene copolymers, polystyrene-co-butadiene copolymers, polystyrene-co-isoprene copolymers, polycyclohexylethylene-co-butadiene copolymers, amorphous polyolefins, polyurethanes, or variations thereof, and others, may be advantageo
Houston Michael R.
Soane David S.
Larson Jacqueline S.
Vargot Mathieu D.
ZMS LLC
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