WO2000066348A1

WO2000066348A1 - Method of manufacturing contact lenses by curing within a sealed package and package obtained

Info

Publication number: WO2000066348A1
Application number: PCT/US2000/008531
Authority: WO
Inventors: Richard J. Wrue; Joan L. Pierce
Original assignee: Bausch & Lomb Incorporated
Priority date: 1999-04-30
Filing date: 2000-03-31
Publication date: 2000-11-09
Also published as: AU4054100A

Abstract

A system for manufacturing contact lenses using a gas-impermeable, evacuated, resin package (10) is disclosed. Forming a vacuum (28) within the package removes oxygen and humidity and allows external atmospheric pressure to force the upper (8) and lower (5) surfaces of the package inward against the lens molds (6), holding them together and further facilitating lens formation. More specifically, this package facilitates lens curing.

Description

METHOD OF MANUFACTURING CONTACT LENSES BY CURING WITHIN A SEALED PACKAGE AND PACKAGE OBTAINED

TECHNICAL FIELD

This invention is related to the manufacture of contact lenses and an article used during the course of lens production.

BACKGROUND

Many contact lenses are molded and cured using a variety of curing techniques, including thermal, ultraviolet, Infrared, microwave, and other forms of energy. Thermal curing may be performed, for example, in a convection oven as a heat source. Typically in such a case, lens manufacturers place monomer-filled lens molds in an oven, and then heat the molds under pressure in the presence of an inert gas. The applied pressure holds the lens molds together to ensure proper lens formation. The inert gas acts as a heat transfer medium and prevents the presence of oxygen which might otherwise inhibit the curing.

Convection-oven curing may suffer from several disadvantages. First, convection ovens may lack complete thermal uniformity and, therefore, cause incomplete or inconsistent curing. Moreover, holding the lens molds together under pressure may cause monomer overflow that can soil the interior of the oven, which must then be cleaned. The downtime spent cleaning the oven can delay production and add to the overall cost of the manufacturing process. Furthermore, as mentioned above, many curing processes require the use of nitrogen or an alternative inert gas to eliminate oxygen. While nitrogen acts as an effective curing medium, it is costly.

We have developed an improved method of manufacture using a sealed package ancillary to curing in order to eliminate many of the problems encountered during curing. Another potential advantage of the invention is that optionally the cured lenses within their molds may be stored for transport to remote locations for final processing, facilitating the centralization of initial manufacturing steps and allowing the inventory of unhydrated lenses which have a longer shelf life. Furthermore, when used ancillary to thermal curing, our sealed package will allow manufacturers to cure lenses using a more uniform heat medium, eliminate time-consuming monomer overflow clean-up in the oven, and eliminate the need for an inert gas, and even allow the curing of lenses using a continuous process, thereby reducing the expense of lens manufacture.

SUMMARY OF THE INVENTION

We have developed a system for manufacturing contact lenses using a gas- impermeable, evacuated, resin package.

According to the invention, a manufacturer places one or more monomer- filled lens molds between upper and lower resin webs or sheets. The manufacturer then evacuates the space between the webs or sheets and, while applying pressure to the molds to maintain the monomer within the mold cavity, seals the webs or sheets to form a gas-impermeable package around the lens molds. Forming a vacuum within the package removes oxygen and humidity and allows external atmospheric pressure to force the upper and lower surfaces of the package inward against the lens molds, holding them together and further facilitating lens formation. By using atmospheric pressure to hold the lens molds together, manufacturers no longer need to apply additional external pressure during curing to mold the lens. Optionally, the inside of the package may be flushed with an inert gas prior to evacuation and sealing.

To achieve optimum performance, manufacturers should form the storage package from a resin exhibiting several characteristics. First, since the package is to be discarded after curing, the resin used should be relatively economic. In addition, depending on the curing technique, the resin material may need to be selected to permit the transmission of certain wavelengths of light energy or, in the case of thermal curing, the resin material may need to withstand high temperatures (100° C or higher). The package must also be able to flex inward under the force of atmospheric pressure to hold the lens molds together. Therefore, the resin used must have sufficient flexibility. Finally, since the package must be evacuated so that oxygen and water vapor can be removed, the appropriate resin must also be gas impermeable.

The resulting manufacture, using this packaging system, eliminates many of the problems encountered while curing and processing contact lenses during production. By using this system, contact lens manufacturers can reduce process downtime; increase process throughput; provide more cost-effective, more complete, and more consistent curing, and produce contact lenses that more consistently meet rigorous product specifications or industry standards.

These and other objects of the invention will be better understood by referring to the following figures in conjunction with the detailed description.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view of one embodiment of the invention showing filled contact lens molds between an upper and lower resin web, prior to evacuation and sealing of the molds within the web material during manufacture.

FIG. 2 is a schematic view of a second embodiment of the invention showing filled contact lens molds being folded within a single resin web prior to evacuation and sealing of the molds within the web material during manufacture.

FIG. 3 is a schematic top plan view of one embodiment of a supply of contact lens molds stored within an evacuated, sealed resin package during continuous production.

FIG. 4 is a schematic cross-sectional view of one embodiment of the invention showing the formation of a sealed package, around the lens molds, from two rolls of webs, and subsequent curing the lenses in a liquid heating medium.

FIG. 5 is a schematic view of one embodiment of the invention showing a in cross section monomer-filled contact lens molds inside an evacuated, sealed resin package after curing within the package.

DETAILED DESCRIPTION OF THE INVENTION

Our invention arises from recognition of the advantages of using a gas- impermeable, evacuated, resin package for the curing of contact lenses during lens production.

Contact lenses according to the present invention can be manufactured, employing various conventional techniques, to yield a shaped article having the desired posterior and anterior lens surfaces. Static casting methods are disclosed in U.S. Patent Nos. 4,113,224 and 4,197,266. Further machining operations may follow the lathe cutting of the lens surface, for example, edge-finishing operations.

In one embodiment, a mold assembly includes a posterior mold having a posterior mold cavity defining surface which forms the posterior surface of the molded lens, and ab anterior mold having an anterior mold cavity defining surface which forms the anterior surface of the molded lens. When the mold sections are assembled, a mold cavity is formed between the two defining surfaces that corresponds to the desired shape of the contact lens molded therein. Each of the mold sections is injection molded from a plastic resin in an injection molding apparatus.

Typically, the manufacturing process for static casting of lenses comprises, as a first step, tooling, whereby based on a given lens design, metal tools are fabricated by traditional machining and polishing operations. These metal tools are then used in injection or compression molding to produce a plurality of thermoplastic molds, which in turn are used to cast the desired lenses from polymerizable compositions. Thus, a set of metal tools can yield a large number of thermoplastic molds. The thermoplastic molds may be disposed after forming a single lens. The metal molds fabricated during tooling are then used for anterior molding and posterior molding in order to produce, respectively, the anterior mold section for forming the desired anterior lens surface and the posterior mold section for forming the desired posterior lens surface. Subsequently, during the operation of casting, a monomer mixture or other precured mixture is injected into the anterior mold section and the posterior mold section is pressed together at a given pressure to form the desired lens shape, either by clamping or by external pressue. As mentioned above, the pressed molds may be cured thermally or by photopolymerization, for example, by exposure to UV light or other photo-energy source for a certain period of time, preferably by conveying the molds through a curing chamber, after which the molds are separated and cured. Alternately, a plastic mold assembly containing a plurality of male sections having convex molding sections and corresponding female sections having concave mold sections may be used to mold lenses. See, for example, US Patent No. 4,640,489 to Larsen.

Subsequent to assembling the mold sections and curing the lenses, the mold assembly is disassembled and the molded lens removed therefrom. Other processing steps which may be included, depending on the specific process, include lens inspection, hydration in the case of hydrogel contact lenses, and lens packaging.

In accordance to the present invention, the contact-lens molds are placed in an evacuated sealed package prior to curing, preferably without the uss of clamps, wherein a clamping pressure of up to one atmosphere provided by the external environment to the package, preferably a pressure of about one atmosphere, is employed to press the mold sections together during curing.

Package formation can occur in a variety of ways. For example, referring to FIGS. 1, manufacturers can use two resin webs to form the package 10. When using two resin webs, an upper web 8 and lower 5 form the package 10. The monomer- filled lens molds 6, are placed upon the lower resin web 5 and a second web 8 is positioned above the first web 5 (see Figure 1). The webs are then sealed, as explained below, leaving an opening of sufficient size to permit evacuation. The space between the upper and lower webs is evacuated while pressing the molds together with an applied force, and the webs are then finally sealed forming a package 10 enclosing the lens molds 6 or 7. Alternatively, the lens molds may contain uncured polymer material in addition to or instead of monomers. The lens molds may each form individual contact lenses as, for example, described in US Patent No. 5,466,147, hereby incorporated by reference in its entirety or may consist of an assembly having a plurality male and female molding sections, as described in US Patent No. 4,640,489, hereby incorporated by reference in its entirety.

Alternatively, now referring to FIG. 2, a single resin web 5 can be used to form the package 10. In this case, a single web 5 is laid flat so that a portion of the web 5 can receive the lens molds 6. The remaining portion of the web 5 can then be folded over to envelop the lens molds 6 within the web 5. Seal the open ends of the web 5 again, as explained below, leaving a small opening (not shown) to allow for evacuation. Finally, evacuate the space within the sealed folded web 5 while pressing the molds together, and completely seal the web 5, to form the package 10. Still another embodiment, for example, would be the use of preformed bags having an opening for inserting lens molds. Still another embodiment would be the use of a web or sheet folded lengthwise, so that one longitudinal edge of the package does not require sealing. For example, a Fuji Impulse® V-300 Vacuum Sealer can be employed to seal the open edge of a package.

Regardless of how the package is formed, it is important to select an appropriate resin to form the package. An appropriate resin should be relatively inexpensive, flexible, gas impermeable, and capable of permitting the transmission of the particular curing energy being used. Fortunately, many resins offer these characteristics. Polyethylene, for instance, is a preferred resin for this system. Other resins are, for example, polyvinyl chloride, polyester, and polypropylene.

Our packaged curing system is particularly effective in simplifying lens manufacture. Referring to FIG. 3, after filling the molds with monomer or other lens- forming material and placing them between an upper and lower package surfaces, the webs can be sealed along longitudinal edge 21 and cross-sealed along borders 22 and 23, leaving one longitudinal edge open for evacuation purposes. Next, manufacturing personnel should evacuate the package 10, to minimize internal pressure and allow atmospheric pressure to force the upper 5 and lower 8 surfaces of the package 10 inward, which holds the lens molds 6 together, ensuring proper lens formation. By thusly using atmospheric pressure to hold the lens molds 6 together, manufacturers can avoid having to apply additional external pressure during curing. While evacuating the package, pressure is preferably applied to the molds to prevent leakage of monomer solution contained in the mold cavities. Pressure may be manually or mechanically applied by a press, plate or other device, preferably automated along a manufacturing line. Alternate ways to seal the package include sealing around individual molds in a matrix fashion. Still another embodiment would involve sealing both longitudinal edges and one border edge, leaving the other cross border for evacuation and sealing. Still another embodiment would involve forming a package that is entirely sealed prior to evacuation and puncturing the package to form an inlet for evacuation. FIG. 4 shows in cross- section the packaging system 20 of the embodiment of FIG. 3 in which the monomer- filled molds 6 with package 10 after evacuation and sealing. Within the cross-sealed borders 22 and 23, the spaces between the molds are flattened due to the top and bottom package surfaces coming together during evacuation. By curing lenses in the package 10 shown in FIG. 3, manufacturers can contain monomer overflow typically produced during lens manufacture. When curing is complete, the overflow can be easily cleaned up by simply discarding the soiled package. As a result, time-consuming clean up of overflow becomes unnecessary, making lens production more efficient and economical.

Furthermore, by reducing process downtime due to cleanup, manufacturers can make lens production more continuous. For example, referring to the embodiment of FIG. 5, a manufacturer can place lens molds between a continuous length of upper and lower resin webs 8 and 5 continuously generated by reel means 25 and 26. The sandwiched lens molds may be supported by a table, conveyor belt, or other support means. Shown diagrammatically by unit operation 27, the package is partially sealed along certain edges or borders, for example, as described above in FIGs 3 and 4, including cross sealing. In unit operation 28, the package is evacuated and completely sealed, to form a succession of packages 10. In the embodiment of FIG. 5, the lenses are thermally cured in the molds, while packaged, in a liquid heating bath, for example, a water bath. In doing so, manufacturers can then cure a packaged supply of lens molds 6 while simultaneously packaging the next supply of lens molds 6 for curing. Therefore, by forming a partial package, evacuating, sealing, curing, removing the molds from the package, and then discarding soiled storage packages 10 in a cyclic, automated manner, manufacturers can sustain continuous lens production and significantly increase product throughput. Of course, IR or UV light curing would be an another suitable means of continuously curing the lenses, for example, along a conveyor belt. Microwave curing by means of continuos batch processing is still another alternative.

An advantage of the present system is that it eliminates the need for nitrogen or a comparable inert gas-curing medium for eliminating the presence of oxygen and water vapor, which can deleteriously affect curing. By curing lenses in a sealed, evacuated package, manufacturers can eliminate the risk of improper, incomplete or inconsistent curing of lenses, ensuring that the lens quality is maintained within strict standards. Furthermore, because the resin package material can be selected to permit the transmission of a desired curing energy, a variety of curing techniques can be used. Another advantage of the present package system is that, since the lens molds are sealed in the gas-impermeable resin package that may also be liquid impermeable, the package can be used to allows lens makers to cure lenses in a liquid heating bath, which may offer advantages over convection heating, as discussed above. Unlike convection ovens, liquid heating baths offer improved thermal uniformity and more complete and consistent curing, since it is less dependent on convection though a gas. Although the present invention has obvious advantages for curing in a liquid heating bath, other curing methods including UV, ultrasonic, microwave, etc. can also benefit from the use of our storage package system. Regardless of the curing technique used, our package system successfully eliminates the adverse affects of oxygen and humidity in curing processes, without the need for an inert gas such as nitrogen. As a result, manufacturers can achieve more consistent and more complete curing at a reduced cost.

The resulting packaging system according to the present invention provides a cost-effective way to improve lens production. Our system reduces process downtime, increases process throughput, and achieves more complete and more consistent curing at a reduced cost. Alternatively to cutting open the package in-line following the curing, to remove the lens from the mold for hydration and packaging for customer use, the present package system may also find use as a way to transport to, and store unhydrated contact lenses at, a remote location, where final processing, including hydration and packaging for final consumer use can occur. This is particularly advantageous when the lenses are distributed for use in countries where high temperatures are common that may have an adverse affect over time on hydrated lenses.

While the invention has been described in conjunction with specific examples thereof, this is illustrative only. Accordingly, many alternatives, modifications and variations will be apparent to those skilled in the art in light of the foregoing description and it is, therefore, intended to embrace all such alternatives, modifications and variations as to fall within the spirit and scope of the appended claims.

Claims

We Claim:

1. A contact lens curing method comprising curing the lens material in at least one contact-lens mold while the contact-lens mold is contained in a sealed gas- impermeable evacuated package and, thereafter removing the contact-lens mold holding the cured lens from the sealed package prior to hydration of the lens for customer use.

2. The method of claim 1, wherein the contact-lens mold comprises an anterior mold section and a posterior mold section and wherein the mold sections are pressed together by atmospheric pressure external to the package to form lenses during curing.

3. The method of claim 1 , including collecting lens material overflow produced during curing in the sealed package.

4. The method of claim 1, including selecting a resin for the package that is gas impermeable and can survive temperatures encountered during curing of over 100°C.

5. The method of claim 4, including selecting a flexible resin for the package, allowing the upper and lower surfaces of the sealed package to flex under external atmospheric pressure, thereby holding the lens molds together when the package is evacuated.

6. The method of claim 4, including selecting a resin that transmits curing energy so that lenses are cured while within the sealed package.

7. The method of claim 6, including selecting a clear resin that transmits UV energy so that lenses are cured while within the sealed package.

8. The method of claim 1, including after the curing is complete, cutting open the package, removing the at least one lens mold and cured contact lens from the package, and discarding the package.

9. The method of claim 1, wherein the package is formed from two sheets or webs of resin.

10. The method of claim 1, wherein the package is formed from a sheet or web that is folded.

11. The method of claim 1 , wherein the lens molds are placed in a preformed bag open at one end.

12. The method of claim 1, wherein the webs are continously taken from a reel.

13. The method of claim 1, wherein hydration of the lenses occurs in the same production plant where the lenses are cured.

14. The method of claim 1, wherein the hydration of the lenses occurs at a remote location after being transported from the production plant curing the lenses.

15. The method of claim 1, including selecting a resin that is sufficiently flexible so that when the package is evacuated, it flexes inward under the force of external atmospheric pressure, forcing upper and lower surfaces of the package to press the lens mold parts together, facilitating formation of contact lenses, and wherin the separate mold assemblies are isolated from each other within the package.

16. The method of claim 1, including evacuating and sealing the package so that no inert gas is required to effectuate curing.

17. The method of claim 1, wherein the package is cured within a liquid medium.

18. An article of manufacture used in the production of contact lenses, comprising a sealed evacuated gas-impermeable resin package containing one or more contact-lens molds containing either a cured lens or uncured lens-material for molding the lens.

19. The article of claim 18, wherein the package is formed from a resin through which curing energy can be transmitted.

20. The article of claim 18, wherein the resin can transmit UN radiation for curing of the lens material.

21. The article of claim 18, wherein the resin can survive temperatures encountered during curing.

22. The article of claim 18, containing a plurality of lens molds contained cured lenses.

23. The article of claim 2, wherein the vacuum within the package holds the lens molds together.

24. The article of claim 23 wherein the force holding the lens molds together is at about atmospheric pressure.

25. The article of claim 18, wherein the package contains lens material monomer overflow produced during curing.

26. The article of claim 18, wherein the package is capable of isolating the contact lens material from water vapor and oxygen.

27. The article of claim 18, wherin the package contains nitrogen due to flushing the package prior to evacuation and sealing.