Plastic and nonmetallic article shaping or treating: processes – Optical article shaping or treating – Utilizing plasma – electric – electromagnetic – particulate – or...
Reexamination Certificate
2001-04-06
2003-12-16
Mackey, James P. (Department: 1722)
Plastic and nonmetallic article shaping or treating: processes
Optical article shaping or treating
Utilizing plasma, electric, electromagnetic, particulate, or...
C264S002700, C425S143000, C425S174400, C425S4360RM, C425S808000
Reexamination Certificate
active
06663801
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the invention
The present invention relates generally to the production of ophthalmic lenses, and, in particular pertains to a method and a device for removing molded soft contact lenses, high-precision intraocular lenses and the like, from the individual molds in which they are produced.
2. Discussion of the Prior Art
In view of the intense growth of the ophthalmic contact lens industry, it has become desirable and even necessary to be able to supply contact lenses which are periodically and frequently replaced in order to minimize the possibility of user induced contamination. This has created an opportunity for manufacturers to strive for automated methods and apparatuses that are able to automatically produce high quality ophthalmic lenses in a cost-effective and highly efficient manner.
It is currently the practice in the manufacturing technology for ophthalmic lenses, such as soft contact lenses of the hydrogel type, to form a monomer or monomer mixture that may be polymerized in a plastic mold. Details of typical direct mold processes for forming soft hydrogel contact lenses are described in U.S. Pat. Nos. 5,080,839, 5,039,459, 4,889,664, and 4,495,313. The process for forming soft contact lenses as generally described in the above-mentioned patents includes the steps of dissolving a monomer mixture in a non-aqueous, water-displaceable solvent and placing the monomer/solvent mixture in a mold having the shape of the final desired hydrogel lens. Thereafter, the monomer/solvent mixture is subjected to conditions whereby the monomer(s) polymerize, to thereby produce a polymer/solvent mixture in the shape of the final desired hydrogel lens. After the polymerization is complete, the solvent is displaced with water to produce a hydrated lens whose final size and shape are similar to the shape of the original molded polymer/solvent article.
Examples of typical plastic molds used for carrying the polymerizable feed material are disclosed in U.S. Pat. Nos. 5,094,609, 4,565,348 and 4,640,489. The mold disclosed in U.S. Pat. No. 4,640,489 is a two-piece mold with a female mold portion having a generally concave lens surface, and a male mold portion having a generally convex lens surface, both mold portions preferably made of a thermoplastic material such as polystyrene. As discussed in U.S. Pat. No. 4,640,489, polystyrene and copolymers thereof are preferred mold materials because they do not crystallize during cooling from the melt, and exhibit little or no shrinkage when subject to the processing conditions required during the direct molding process discussed above. Alternatively, it is also possible to employ molds made of polypropylene or polyethylene, such as described in U.S. Pat. No. 4,121,896.
During the molding process, the monomer and monomer mixture is supplied in excess to the female concave mold portion prior to the mating of the molds. After the mold portions are placed together, defining the lens and forming a lens edge, the excess monomer or monomer mixture is expelled from the mold cavity and rests on or between flanges that surround one or both mold portions. Upon polymerization this excess material forms an annular (HEMA) ring around the formed lens between the flange portions of the molds.
As discussed in the above-mentioned U.S. Pat. Nos. 5,039,459, 4,889,664, and 4,565,348, there is the requirement that the materials, chemistry, and processes be controlled so that the mold portions may be separated without having to apply an undue force, which may be necessary when the lens sticks to one or more of the lens mold or when the lens mold portions are adhered to each other by the excess HEMA ring after polymerization.
The prior art process for separating the mold portions and removing the lens therefrom consists of a heating stage, a mold half separation stage, and a lens removal stage. The heating stage of the prior art lens removal process is to apply heated air to the back mold portion thereby causing a differential expansion between the heated mold polymer and the cooler lens polymer. This differential expansion provides a shearing impetus which weakens the adhesion forces between the mold surface and the lens formed thereon. The mold half separation stage, which follows the heating stage is characterized by removal of the previously heated mold half. With respect to prior art systems for removing the back curve mold halves, inefficient means and damaging forces associated therewith have rendered such devices less desirable for producing high quality lenses, inasmuch as the steps of heating and separation that break the polymerized lens/polymer mold adhesion and provide access to the nearly formed lens occasionally damage the lens, and thereby decreasing the yield rate of the process.
With respect to the temperature gradient between the mold halves and the lens, the larger the thermal gradient, the more reduced will be the residual adhesion forces present between the lens and the mold halves, and correspondingly, the more reduced will be the force required to separate the mold portions. Conversely, the lower the thermal gradients created between the mold halves and the lens, the greater will be the required force to separate the mold portions. The greater the forces which may be required in separating the mold from the lens, the greater becomes the possibility of fracturing a mold portion and/or damaging the lens. Furthermore, it is to be understood that a process in which a thermal gradient must be applied on a repeated basis must be such whereby the environment does not heat appreciably, therein reducing the effectiveness of the process.
With respect to the separation of the mold halves, and thereby, the separation of the top mold half from the lens, it is understood that devices must be employed which do not damage, or apply undue stress on the contact lenses. When front and back curve mold parts, which are designed to form an integral frame such as are illustrated in U.S. Pat. No. 4,640,489, are placed together to form a lens shaped volume therebetween, the resultant combined structure provides limited accessible space for a separating means to engage and displace one mold from the other. Even minimal warpage of either mold half can adversely affect both accessibility to the space as well as the accuracy of the displacing forces.
The same requirements apply to the removal of the lens from the mold section in which it remains after separation.
Presently, as widely employed in the technology and as described in European Patent 0 775 571 A2 “Infra-red Heat Source for Demolding Contact Lenses” which is commonly assigned to the assignee of the present application, in order to assist in the demolding of the lens from the mold section there is employed infra-red heat source providing a thermal gradient wherein the infra-red energy is directed against the back curve of the mold through the intermediary of reflective tubes or buffers. In that instance, the structure as described that publication employs quartz or sapphire windows on the infra-red heater which filters out some of the infra-red radiation. This necessitates a longer period of heating and consequently lengthier demold times are required for demolding the lenses. Furthermore, pursuant to the foregoing construction, the infra-red heater employs one heater for multiple molds, in effect one heater for four molds, which in essence does not take into consideration potential variations in heat distribution among the various molds due to the presence of only a single infra-red heat output across the current sources for a plurality of molds.
Pursuant to another embodiment of the prior art, the thermal gradient which assists in the demolding of the lenses comprises the employment of a plurality of steam injection tubes each of which directs a jet of steam onto the concave surfaces of a back curve section. Pursuant to further variation described in the European patent publication, the thermal gradient is provided by a laser wherein a selected amount of concentrated, cohere
Bingaman Thomas P.
Kimble Allan W.
Pegram Stephen C.
Ricard Joseph W.
Voss Leslie A.
Heckenberg Donald
Johnson & Johnson Vision Care Inc.
Mackey James P.
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