Optics: eye examining – vision testing and correcting – Spectacles and eyeglasses – Ophthalmic lenses or blanks
Reexamination Certificate
2000-05-30
2002-05-21
Sugarman, Scott J. (Department: 2873)
Optics: eye examining, vision testing and correcting
Spectacles and eyeglasses
Ophthalmic lenses or blanks
C351S168000, C351S161000, C351S177000, C264S002500
Reexamination Certificate
active
06390621
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
In casting and molding processes in general, front surface and back surface dies are used to impart to the plastic material the optical surfaces appropriate for the desired ophthalmic correction. In casting processes in general, the dies are secured together by a gasket or the like at a desired spacing, and a liquid casting material is introduced in the casting cavity defined thereby, and allowed to cure and harden into a lens. A critical factor is the gasket, and that a large plurality of gaskets are required to accommodate and seal with the large plurality of differing optical surfaces of the various dies while also defining the desired die spacing (and lens thickness). Thus a large capital investment is required in gaskets and gasket tooling, as well as in the optical surface forming dies used in the casting process.
2. Background of the Art
In molding processes in general, more rugged dies are employed to compress a moldable material in a closed molding cavity, impressing the optical surface configurations on the material as the material is hardened by thermal or chemical means. Generally speaking, an excess of molding material must be introduced into the cavity to allow for compressive die movement, and means must be provided to vent the excess material from the cavity and accommodate the sprues formed thereby. Also, as in the casting process, the dies must be urged together to the appropriate spacing to create the desired lens thickness. The amount of molding material, the venting of excess material, and the final thickness of the lens are interrelated factors that require precise process control to produce lenses of high quality for ophthalmic use.
U.S. Pat. No. 4,839,110 describes a process for molding or casting ophthalmic lenses in which the apparatus includes a plurality of front surface and back surface dies having differing optical forming surfaces and identical peripheral edge configurations. In the compression molding process, any pair of front surface and back surface dies are received in sliding, sealing fashion in the bore of the molding apparatus. At least one of the pair of dies is provided with at least one ,ate channel formed in the peripheral edge thereof parallel to the axis of the bore and extending from the optical forming surface to a point adjacent to the opposite, external die surface. The gate channel comprises a vent through which excess molding compound is discharged from the molding cavity as the dies are urged together. As the gated die is fully inserted in the bore, the gate channel opening to the exterior is sealed by the bore surface, thus terminating the discharge effect and retaining a predetermined amount of molding material in the molding cavity. The molding material is then solidified by thermal or chemical reaction to form the finished lens. Thus the invention provides intrinsic control of the thickness of the molded part, while also providing positive venting of excess molding material. In the casting, process, the dies are partially inserted in the bore of a casting in sliding, sealing fashion, and the gate channel serves as an injection channel to introduce the casting compound into the casting cavity. The dies are urged together in the bore, the gate channel first serving to vent excess casting compound and gas from the casting cavity. Full die insertion in the bore causes the gate channel opening, to the exterior to be sealed by the bore wall, thus terminating the discharge effect and retaining a predetermined amount of casting material in the casting cavity. The material is then cured or hardened by thermal or chemical reaction to form the finished lens. Thus the invention also provides intrinsic control of the thickness of the cast part, while also permitting easy filling of the casting cavity and venting of excess material and gas from the vent cavity.
U.S. Pat. No. 5,288,221 describes an alternative method of preparing an ophthalmic lens comprising a process wherein a premanufactured polymeric lens or lens wafer is employed as one of two molds required to produce the finished lens. A conventional glass, plastic, ceramic, or metal mold is employed as the second mold, a polymerizable lens material is injected between said two molds, and the relative positions of said two molds are adjusted as required by the prescription to produce the finished lens. The polymerizable lens material and the premanufactured lens or lens wafer adhere to one another through a combination of mechanical and chemical bonding. The joined lens material and the lens wafer are then removed from the glass, plastic, ceramic, or metal mold. In this manner, one of the two molds used to make the lens is incorporated into the lens and becomes an integral part thereof. The respective orientation of the two molds is prepared by a pair of indexing means. The indexing means control the position of one of the two molds while the other mold is held in a fixed position. A first indexing means controls the rotational relationship between the molds and a second indexing means controls the spatial relationship between them. An indicator associated with the first indexing means indicates the angular position of the movable mold on a real time basis and an indicator associated with the second indexing means similarly indicates the instantaneous spatial relationship between the two molds so that the shape and thickness of the polymerizable material between the molds is continuously known; this enables the eye care professional to adjust the indexing means as needed.
Although the above-identified semi-finished lens manufacturing processes are of the types of manufacturing processes that have been commercially successful over the years, there are definite limitations to their utility. These manufacturing processes have been used to manufacture monofocal lenses for a number of reasons. One reason is that processes require significant modification to exchange either one of the lens mold surfaces. This is important because any multifocal lens must have a unique combination of both of the corrective functions of the multifocal lens. Both the cylinder and the diopter of the product must be matched to a specific prescription. As there are many combinations of prescriptions in the public, it has been considered too time consuming to manufacture a full range of prescriptions, particularly with the time delays in changing mold elements within the molding process. Additionally, the molding processes, with their mated diameter mold faces have not been able to control edge thicknesses easily and/or tend to place stress in the ends of the manufactured lenses in injection molding processes which lead to potential physical stresses in the final lens that can result in stress to the plastic under extreme ambient conditions. This is in spite of the fact that numerous alternative processes have been developed for injection molding.
Illustrative of these problems in the context of optical disk molding is Bartholdsten et al (U.S. Pat. No. 4,409,169), which teaches the need for a slow (up to 3 seconds), low-pressure injection of an oversized shot into a partially-open (air gap) mold parting line, then providing for deliberate melt cooling and viscosity-thickening, followed by a short pressing stroke (typically ⅕ to {fraction (1/10)} the disk's thickness, or 0.005-0.010 inch) which initially squeezes out of the reduced mold cavity volume the partially-cooled and viscous excess plastic, then as the pressing continues to the fully-closed parting line position (zero clearance), this radially-extruded overflow is pinched off and full clamping force is thereafter maintained for shrinkage compensation and to assure no prerelease.
Another clamp-induced disk coining, process is disclosed in Matsuda et al (U.S. Pat. Nos. 4,442,061 and 4,519,763) wherein, into a slightly opened moldset, a melt is injected and cooled until fully solidified, then reheated till uniformly above the plastic's melt temperature, at which point clamp-actuated c
Maki Alan D.
Olund David C.
VerMurlen Jeffrey L.
Mark A. Litman & Assoc. P.A.
Sugarman Scott J.
Vision--Ease Lens, Inc.
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