Use of a microwave energy to disassemble, release and hydrate contact lenses

<u style="single">BACKGROUND OF THE INVENTION</u>

0001The present invention relates generally to an arrangement and method for using microwave energy to disassemble, release, and hydrate contact lenses, and more particularly pertains to the use of microwave energy in one or more microwave heating and processing stations designed to disassemble, release, and hydrate contact lenses.

0002The state of the art of manufacturing hydrogel soft contact lenses has progressed to automated molding systems and assembly lines in which each hydrogel soft contact lens is formed by sandwiching a monomer between front and back mold section halves. The monomer is polymerized to form a lens, which is then removed from the mold section halves, further treated and then packaged for consumer use.

0003In a typical prior art soft contact lens manufacturing process, metal inserts are used in an injection molding machine in an injection molding process to produce many thermoplastic injection molded front curve (FC) molds and back or base curve (BC) molds, each of which FC and BC molds is subsequently used only once to mold a single soft hydrogel contact lens. In this process, the FC mold is dosed with contact lens forming monomer, the BC mold is carefully placed upon the FC mold and the two mold halves pressed together, with excess monomer being expelled into the space outside the optical surfaces of the mold halves. The monomer is then polymerized to form a lens, which is then removed from the mold and further processed to yield the final soft hydrogel lens product.

0004Figure 1 is a side elevational sectional view of a typical prior art mold assembly 8 which includes a front curve mold half 10 and a back curve mold half 12 which define a volume therebetween in which a soft contact lens 14 is molded.

0005The front mold half 10 defines a central curved section with an optical quality concave surface which has a circular circumferential well defined sharp edge 16 extending therearound. The sharp edge 16 is desirable to form a well defined and uniform plastic radius parting line (edge) for the subsequently molded soft contact lens. Similarly, the back curve half 12 defines a central curved section with an optical quality convex surface.

0006The FC and BC molds may be manufactured from any thermoplastic material which is capable of being injection molded and which provides the final cast lens with the required optical properties, with currently preferred materials for mold frames being polystyrene and polypropylene. To injection mold the FC and BC molds, injection metal tool inserts of the required configuration are typically machined and mounted in the injection molding machine. The injection molded FC and BC molds are close and reproducible inverse reproductions of the injection metal mold inserts, and the resultant molded contact lenses are close and reproducible reproductions of the metal mold inserts.

0007After the molding of a contact lens between the FC and BC mold halves, the FC and BC mold halves must be separated. Typically, during separation of the FC and BC mold halves, an excess HEMA ring, which is excess mold material surrounding the mold cavity, adheres to the FC mold which is designed to promote this adhesion, while the molded contact lens adheres to the BC mold.

0008For disassembly of the FC mold which retains the adhered HEMA ring from the BC mold which retains the molded contact lens, the prior art has used IR lamps as a heat source, and less than approximately 20% of the energy from the IR lamps is used to disassemble the product. This is disadvantageous because of the waste of energy, and moreover all of this energy must be subsequently removed by an expensive water cooling process and system which must be operated, monitored, and maintained to remove all of the IR added heat. The IR process is not precise, and many lenses are damaged during the disassembly and opening step.

0009For release of the adhered contact lens from the BC mold, the prior art has used a release basin with typically over a 4 minute soak time. This is disadvantageous compared to a process pursuant to the present invention which requires less than a minute because over 300% more Work In Progress (WIP) is involved in the 4 minute soak time.

0010For hydration of the released contact lens, the prior art has used a minimum 20 minute soak time. This is disadvantageous compared to a process pursuant to the present invention which requires approximately 6 minutes because over 200% more WIP is involved in the 20 minute soak time.

0011For release and hydration of the contact lens, the prior art has used a heated feed tank and insulated piping to deliver a heated solvent. This is disadvantageous compared to a process pursuant to the present invention which delivers a room temperature solvent and provides rapid heating thereof at the point of usage.

<u style="single">SUMMARY OF THE INVENTION</u>

0012Accordingly, it is a primary object of the present invention to provide an arrangement and method for using microwave energy to disassemble, release, and hydrate contact lenses, particularly the use of microwave energy to disassemble, release, and hydrate contact lenses in one or more microwave heating and processing stations. The microwave heating advantageously provides the ability to control intensity and duration of the microwave exposure at each process stage.

0013The present invention uses microwave energy to promote disassembly of the FC mold (or BC mold) with an adhered HEMA ring from the BC mold (or FC mold) with an adhered contact lens, and also uses microwave energy to promote release of the contact lens from the BC mold (or FC mold), and further uses microwave energy to facilitate hydration of the contact lens.

0014The present invention provides: <ul id="ul0001" list-style="none" compact="compact"><li>three advantages for disassembly 1) superior energy containment and direction, resulting in a reduced energy requirement, 2) simplification of the disassembly equipment, and 3) improved product yield;</li><li>two advantages for release 1) reduced time required for release of the lens from the back curve mold and 2) dosing with a room temperature release solvent;</li><li>three advantages for hydration 1) reduced extraction time, especially for the Darocur 1173 product line, 2) simplification of the hydration equipment, and 3) a microwave system allows hydration in the primary package for the contact lens.</li></ul>

0015The present invention results in a substantial simplification of the disassembly, release and hydration equipment which is a significant factor. The microwave equipment consists of a power supply, a microwave generator, a microwave waveguide, and possibly a wave valve. Waveguides can be produced from sheet metal so they are low cost (the expense is in the design) and waveguides are virtually 100% efficient at containing and directing microwaves and are not subject to accelerated corrosion.

0016The transfer of microwave energy depends on coupling of the electromagnetic field with a polar group within the material to be heated. Hydroxyl groups are among those subject to this type of heating. Heating of the solvent and solutes significantly increases diffusion of materials from the lenses. The transfer of microwave energy to hydroxyl groups (with standard microwaves) is very efficient, and also is advantageously delivered at the point of usage. Thus, hydroxyl-containing molecules like Darocur 1173 should be extracted faster by microwave application.

0017Release has been accomplished in approximately 1 minute (compared to 3 to 5 minutes in 70°C 150ppm tween 80/DI (distilled water) using a NIC cured assembly in a conventional microwave oven, which reduces the release time requirement by at least 75%.

0018Hydration time has been reduced by approximately 67%.

0019The use of microwave heating during the release and hydration processes eliminates the need for storing and transporting a heated solvent as the microwaves deliver heat at the point of usage. 1 ml of room temperature packing solution has been boiled in approximately 3 seconds.

<u style="single">BRIEF DESCRIPTION OF THE DRAWINGS</u>

0020The foregoing objects and advantages of the present invention for the use of microwave energy to disassemble, release, and hydrate contact lenses may be more readily understood by one skilled in the art with reference being had to the following detailed description of several embodiments thereof, taken in conjunction with the accompanying drawings wherein like elements are designated by identical reference numerals throughout the several views, and in which: <ul id="ul0002" list-style="none" compact="compact"><li>Figure 1 is a side elevational sectional view of a typical prior art mold assembly which includes a front curve mold half and a back curve mold half which define a volume therebetween in which a soft contact lens is molded.</li><li>Figure 2 illustrates a contact lens/mold assembly of a front curve mold and a base curve mold after a hydrogel soft contact lens has been molded therein supported by a vacuum operated conveyance device which has positioned the lens/mold assembly in a microwave heating and processing demolding station.</li><li>Figure 3 shows a process step and position in which the cured lens/back curve mold are demolded or disassembled from the front curve mold, with the excess HEMA ring being secured to the front curve mold.</li><li>Figure 4 shows a process step wherein a primary contact lens package has been dosed with a room temperature release solvent and is positioned over a microwave waveguide so that the release solvent is being heated by microwaves.</li><li>Figure 5 shows a process step and position wherein a conveyance device has lowered a lens/back curve mold assembly such that the lens is in intimate contact with and immersed in release solvent within the primary package which is being heated by microwaves.</li><li>Figure 6 shows a process step and position wherein sufficient microwave energy has been transferred so that release of the lens from the back curve mold is achieved, and the conveyance device has lifted the back curve mold from the primary package, leaving the lens in the primary package immersed in release solvent which is being heated by microwaves.</li><li>Figure 7 shows a continuation of the microwave heating process whereby continued lens hydration is facilitated by continued microwave heating of the lens and release solvent within the primary package.</li><li>Figure 8 shows a process step wherein dirty release and extraction solvent is being expelled from the lens/primary package, and clean extraction solvent is being added to the lens/primary package.</li><li>Figure 9 shows a process step wherein the lens hydration process is being facilitated by continued microwave heating.</li><li>Figure 10 illustrates a further processing step wherein a DI removal nozzle is positioned over the primary package/contact lens, and compressed air enters through a central passage and displaces the extraction solvent through evacuation passages in the DI removal nozzle.</li><li>Figure 11 illustrates a further processing step wherein a dosing tube transfers a metered quantity of DI rinse solvent into the primary package/contact lens.</li><li>Figure 12 illustrates a further processing step, similar to the processing step of Figure 10, wherein the final rinse solvent is being displaced and evacuated by compressed air.</li><li>Figure 13 illustrates a further processing step, similar to the processing step of Figure 11, wherein a metered quantity of DI rinse solvent is dosed into the primary package/contact lens, which is now ready for the application a package cover/seal thereover.</li></ul>

<u style="single">DETAILED DESCRIPTION OF THE INVENTION</u>

0021Figure 2 illustrates a contact lens/mold assembly 8 of a front curve mold and a base curve mold after a hydrogel soft contact lens has been molded therein, in a manner as has been explained with reference to Figure 1. The contact lens/mold assembly 8 is supported by a vacuum 20 operated conveyor device 22 which secures the back curve mold 12 thereto by a vacuum.

0022The lens/mold assembly 8 is positioned in a microwave heating and processing demolding station which includes a microwave generator 24, a microwave waveguide 26, and possibly a microwave valve. The microwave waveguide 26 can be produced from low cost sheet metal, with the expense being in its design. A waveguide can be virtually 100% efficient at containing and directing microwaves, and further is not subject to accelerated corrosion by the various release, rinse and DI solutions used during the practice of the present invention. The lens/mold assembly is positioned in relation to the microwave waveguide and heating apparatus such that the contact lens and its interface with the surface of the front curve mold of the lens/mold assembly can be preferentially heated by microwaves.

0023The demold process can be promoted and achieved by a differential thermal expansion between the contact lens material and the demold material. This may occur by differences in thermal conductivity and conduction, or by differences in absorption of microwave energy between the contact lens and the mold. As an example of the latter, one demold half could be nylon with a high dipolar moment which will heat quickly when exposed to microwaves. The contact lens material or diluents contained therein could also be adjusted to a desired polarity.

0024The process of demolding a contact lens from a mold assembly 8, which includes a front curve mold 10 and a base curve mold 12 with a contact lens 14 molded therebetween, can be facilitated by producing a thermal gradient between the contact lens and the front or base curve mold which is to be demolded or separated from the contact lens. The mold assembly can be designed to first separate or demold the front curve mold from the base curve mold and the contact lens which remain adhered together, which is the process illustrated herein, or to first separate the base curve mold from the front curve mold and the contact lens which remain adhered together.

0025In this patent application, the curve mold which retains the contact lens adhered thereto after the demolding/separating process is referred to as the adhere curve mold, and the other curve mold which is demolded and separated from the adhere curve mold and contact lens is referred to as the demold curve mold. The microwave heating can generate a thermal expansion differential between the contact lens and the demold curve mold with the thermal expansion differential resulting in reduced adhesion between the contact lens and the demold curve mold.

0026Typically, the separated demold curve mold is designed to adhere and retain an excess HEMA ring which is removed therewith, leaving the contact lens adhered to the other adhere curve mold.

0027A thermal gradient between the contact lens and the demolded or separated curve mold can be produced by microwaves by designing one of the contact lens or the demolded curve mold to absorb more microwaves than the other. The ability of a material to absorb microwaves depends, among other factors, on the material having dipolar molecules, such as water, which are vibrated and heated by microwaves. The curve molds can typically fabricated from polystyrene, which is not a dipolar material, and so is virtually invisible to and not heated by microwaves. Accordingly, the molded contact lens can be molded of a material having dipolar molecules, such that the contact lens is heated by microwaves, while the polystyrene curve molds are not heated by microwaves, to create the desired thermal gradient between the contact lens and the demolded curve mold. In alternative embodiments, the curve molds can be fabricated from materials having dipolar molecules, such as nylon, acrylic, or polyester materials which are heated by microwaves.

0028Figure 2 illustrates a view wherein a conveyor device 22 has positioned a cured lens/mold assembly over the microwave waveguide 24 in a position in which the front curve mold is held and secured in place by a front curve mold and HEMA ring hold-down device 28 so that the contact lens, and more particularly the interface between the contact lens and the front curve lens surface can be preferentially heated by microwaves 30 to loosen the adhesion of the front curve mold to the molded contact lens. The assembly conveyor device 22 and back curve mold 12 are then retracted and lifted vertically while the front curve mold 10 is restrained by the hold-down device 28. This causes the back curve mold and adhered contact lens to separate from the front curve mold, with the excess HEMA ring remaining adhered to the front curve mold, which is designed to promote such adherence.

0029Figure 3 shows a process step and position in which the cured lens/back curve mold are demolded and disassembled from the front curve mold, with the excess HEMA ring remaining secured to the front curve mold. The front curve mold is then removed from the demold or disassembly processing station, as by a front curve vacuum conveyance device.

0030The process steps of the present invention can be carried out and performed at different processing stations, such that the demolding process is performed at a demolding station, the release process of releasing or separating the contact lens from the remaining curve mold to which it is adhered is performed at a separate release station, and the hydration process of hydrating the released contact lens is performed at a separate hydration station, or alternatively one or more of the above processes can be performed at a common station. It appears preferable to perform the different processing steps at different processing stations since the different processing steps will generally require different amounts of microwave heating time, and may also utilize different wavelengths of microwave energy. Moreover, different processing stations provide an ability to control the intensity and duration of the microwave exposure at each process stage.

0031At each microwave heating station, it is preferable that the microwave generator be maintained on continuously to maximize the life of the microwave generator, such that a microwave valve might be utilized, or alternatively the microwaves can be redirected to perform another heating chore when a microwave processing station does not require microwave heating, such as during periods of transport of mold assemblies or mold components or primary packages, or dosing or fluid change periods.

0032Moreover the processes of the present invention can be performed on a continuous or semi-continuous production line, and can be performed on a single mold assembly or contact lens or a plurality of mold assemblies or contact lenses positioned in a pallet holding an array of those assemblies or contact lenses, or can be performed on small lots, such as several hundred, of mold assemblies or contact lenses.

0033Figure 4 illustrates a process step wherein a primary package base 32 is positioned in a release processing station, as by a primary package vacuum conveyor device. The primary package 32 is dosed through a dosing tube 34 with a metered quantity of release solvent 36, preferably at ambient or room temperature. The primary package and release solvent are positioned over a microwave waveguide 38 so that the release solvent can be heated by microwaves 40. Another advantage to a microwave system is that a microwave system allows hydration to be performed in the primary package.

0034Figure 5 shows a process step and position wherein a conveyor device 42 has lowered and positioned a lens/back curve mold 14, 12 such that the lens 14 is in intimate contact with and entirely immersed and submerged in the heated release solvent 36 within the primary package, release solvent, and the release solvent and also possibly the contact lens are being heated by microwaves. If the contact lens is heated by microwaves and the base curve mold is not, a thermal gradient is created therebetween to promote release of the contact lens from the base curve mold, such that the base curve mold can then be removed from the station, as illustrated in Figure 6.

0035Figure 6 shows a process step and position wherein sufficient microwave energy has been transferred such that release of the contact lens from the back curve mold has been achieved. Figure 6 also shows a position wherein the conveyor device 42 has lifted the back curve mold 12 from the primary package, leaving the lens 14 immersed in release solvent in the primary package 32.

0036Figure 7 shows a continuation of the microwave heating process whereby continued lens hydration is facilitated by continued microwave heating of the lens and release solvent within the primary package, and wherein the lens is now positioned in the primary package immersed in dirty release solvent.

0037Figure 8 shows a process step wherein a specialized distilled water (DI) removal and vaporization nozzle 44 is positioned over the primary package. Liquid rinse extraction solvent 46 flows through a check valve 48 into a vaporization chamber 50, where it is vaporized by applied microwaves 40, generating pressure to force the vaporized solvent out the bottom into the primary package 32. A vacuum 52 is also applied to extraction passageways 54, such that the dirty release and extraction solvent is displaced and expelled from the lens/primary package by the high pressure and high velocity rinse extraction solvent vapor, and clean rinse extraction solvent 46 is added to the lens/primary package, with continued additional heating by microwaves facilitating further hydration.

0038Figure 9 shows the resulting system wherein the lens 14 is entirely immersed in condensed rinse extraction solvent 46, after which a sufficient time is allowed for passive diffusion of undesirable materials and molecules from the lens. This lens hydration process can be facilitated by continued microwave 40 heating. The microwave heating system has the ability to raise the temperature of the rinse extraction solvent to exceed the normal boiling point of the rinse extraction solvent to further enhance lens hydration by continued microwave heating.

0039Figure 10 illustrates a further processing step wherein a DI removal nozzle 56 is positioned over the primary package/contact lens 32, 14, and compressed air 58 enters through a central passage 60 in the DI removal nozzle, and displaces the now dirty rinse extraction solvent 46 through evacuation passages 62 in the DI removal nozzle which have a vacuum 64 applied thereto.

0040Figure 11 illustrates a further processing step wherein a dosing tube 66 transfers a metered quantity of fresh DI rinse extraction solvent 68 into the primary package/contact lens 32, 14.

0041Figure 12 illustrates a further processing step, similar to the processing step of Figure 10, wherein, after a period of hydration time, the now dirty DI rinse extraction solvent 68 is being displaced and evacuated by compressed air 58. A DI removal nozzle 58 is positioned over the primary package/contact lens 32, 14, and compressed air 58 enters through a central passage 60 in the DI removal nozzle, and displaces the now dirty rinse extraction solvent 68 through evacuation passages 62 in the DI removal nozzle which have a vacuum 64 applied thereto.

0042Figure 13 illustrates a further processing step, similar to the processing step of Figure 11, wherein a metered quantity of fresh DI rinse extraction solvent 70 is dosed through tube 66 into the primary package/contact lens 32, 14, which is now ready for the application a package cover/seal thereover. The primary package with the lens and solvent therein can be removed from the microwave heating and processing station to complete further packaging and processing of the product.

0043While several embodiments and variations of the present invention for the use of microwave energy to disassemble, release, and hydrate contact lenses are described in detail herein, it should be apparent that the disclosure and teachings of the present invention will suggest many alternative designs to those skilled in the art.