Mold clamping and precure of a polymerizable hydrogel

Abstract: The present invention provides a method and apparatus for partially curing a polymerizable monomer or monomer mixture to form a soft contact lens. The apparatus includes a clamping member and a radiant energy source.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention. The present invention relates generally to an apparatus and method for molding soft contact lenses, and particularly an apparatus and method for precuring a polymerizable monomer or monomer mixture under pressure to form a soft contact lens. 2. Discussion of the Prior Art. U.S. Patent 4,495,313 to Larsen, now assigned to the assignee of the present application, discloses the polymerization of a monomer to form a soft contact lens by means of ultraviolet light. In addition, this reference also teaches that an ultraviolet light catalyst can be added to the polymerization system to effect an essentially complete polymerization. U.S. Patent 5,039,459 to Kindt-Larsen et al. entitled "Method of Forming Shaped Hydrogel Articles Including Contact Lenses" teaches the polymerization of soft contact lenses wherein the monomer/diluent mixture in a transparent polystyrene mold is exposed on one side to 1.7 joules/centimeter squared of ultraviolet radiation for ten minutes at 55°C (TL 09 lamps with peak radiation at 350 nm). International patent application WO 93/04848 discloses a method and apparatus for molding contact lenses. The method comprises clamping two mold halves together while the lens material is polymerized under clamping pressure. This polymerization under clamping pressure typically lasts for approximately five minutes. European patent application EP-A-0 484 015 discloses a method for curing contact lenses. The claimed method comprises sequential polymerization of the lens material by first photopolymerization followed thermal polymerization. In addition to these references, U.S. Patents 4,565,348; 4,680,36; 4,640,489 and 5,080,839 all disclose the polymerization of a monomer with ultraviolet light to form a soft contact lens. SUMMARY OF THE INVENTION The present invention is an apparatus and a method for precuring a polymerizable monomer mixture to form a soft contact lens in a mold which enables a more uniform cure for the lens during the cure step, and which reduces "puddling" or cavitation of the lens in the mold during cure. In accordance with the present invention there is provided a method of pre-curing a polymerizable monomer or monomer mixture as part of a process for forming a soft contact lens as set forth hereinafter in claim 15. A polymerizable monomer or monomer mixture is deposited in a lens mold having first concave and second convex mold halves. The mold halves are formed of polystyrene or other material transparent to actinic or visible radiation. An active light source is moved from a first transport position to a second exposure position by means of a frame. The mold halves are clamped together under predetermined pressure for a predetermined period of time which may be done in a low oxygen environment. The second or convex mold half may be slightly thinner than the first or concave mold half to enable mold compliance during cure as the monomer is polymerized. The clamping pressure aligns flanges formed on the first and second mold halves to ensure that the flanges are parallel and that the respective curves of the molds are aligned. The clamping pressure also seats the second convex mold half against an annular edge formed on the first mold half to essentially sever any excess monomer from the monomer contained within the mold. Clamping pressure is provided by a clamping member mounted on the frame. After a predetermined clamping period, the hydrogel is exposed to actinic or visible radiation, such as a UV light source, to partially cure the hydrogel to a gel state. After a second predetermined period of exposure under clamping pressure, the clamping action and the UV radiation may be removed, and the partially precured hydrogel lens is transported in the mold to a curing station for complete polymerization and cure. Alternately, a complete cure may be effected in the apparatus. It is an object of the present invention to provide a novel apparatus for precuring a polymerizable monomer or monomer mixture to form a soft contact lens. The present invention provides an apparatus as set forth hereinafter in claim 1. Clamping pressure may be applied by an annular air cylinder, spring driven annular cylinder, or physical weights which allows actinic radiation to pass through the annulus of the cylinder and through one or more of the mold halves and into the monomer or monomer mixture. The apparatus may include a means for controlling the duration and intensity of the clamping pressure, and the duration and intensity of the actinic radiation. A method of precuring a polymerizable monomer or monomer mixture to form a soft contact lens is described. The method includes a step of depositing a polymerizable monomer or monomer mixture in a contact lens mold having first concave and second convex mold halves with the monomer therebetween. The mold halves are then clamped together with a predetermined pressure and then exposed to radiation to partially polymerize the monomer to a precured gel-like state. The clamping pressure is then relieved and the lens is then cured with additional radiation or a combination of heat and radiation. In the preferred embodiment the radiation source may be actinic, electron beam or radioactive source, but preferably is an ultraviolet lamp which irradiates the monomer at 2-4 mW/cm 2 for 5-60 seconds, but preferably 20-40 seconds. Radiation may also be from a high intensity UV source that is pulsed or cycled. The clamping step aligns the mold halves, causes excess monomer to be removed from the mold cavity, and seats a compliant second mold half against a first mold half for the precure step. It is an object of the present invention to precure a polymerizable monomer or monomer mixture to a gel-like state wherein polymerization has been initiated throughout the monomer, and utilize the shrinkage of the monomer and the compliance of the mold halves to seal and hold the mold halves together for the remainder of the cure period. It is another object of the present invention to precure the hydrogel in a low oxygen environment to prevent undesired absorption of oxygen by the monomer. It is another object of the present invention to provide an adjustable means for varying the clamping pressure during the precure step. It is another object of the present invention to provide a reciprocating means for positioning the actinic light source at an exposure position, and then retracting the light source to a second position for transport of the lens molds. It is further an object of the present invention to provide an alternate reciprocating means for positioning the lens molds against the light source for exposure, and retracting the molds to a second position for transport. BRIEF DESCRIPTION OF THE DRAWINGS The foregoing objects and advantages of the present invention for precuring a polymerizable monomer or monomer mixture may be more readily understood by one skilled in the art with reference to the following detailed description of the two preferred embodiments, taken in conjunction with the accompanying figures wherein like elements are designated by identical reference numerals throughout the several views. Figure 1 is a partially cut away elevation view of one of the embodiments for precuring a polymerizable monomer or monomer mixture to form a soft contact lens. Figure 2 is an end elevational view of the apparatus illustrated in Figure 1. Figure 3 is a diagrammatic and schematic illustration of one embodiment of the invention. Figure 4 is a plan view of a carrier used to transport a plurality of contact lens molds having a polymerizable monomer or monomer mixture therebetween to and from the precure station. Figure 4(a) is a diagrammatic and cross-sectional view of a pair of mold halves in the pallet carrier of Figure 4. Figure 5a is a diagrammatic illustration of one embodiment of the present invention which uses an air driven clamp for clamping the mold halves together. Figure 5b is a diagrammatic illustration of a second embodiment of the present invention which uses a spring driven clamp for clamping the mold halves together. Figure 6 is a plan view of a reciprocating portion of the apparatus for precuring a polymerizable monomer or monomer mixture to form a contact lens. Figure 7 is an elevational view of the apparatus illustrated in Figure 6. Figure 8 is an end elevational view of the apparatus illustrated in Figure 6. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The present invention is useful in a process for forming soft contact lenses from a polymerizable monomer or monomer mixture. The soft contact lenses are formed in a mold assembly having a first concave and a second convex mold half. As illustrated in Figure 4a, the mold halves are formed of polystyrene transparent to visible and ultraviolet light, with a central curved section defining a concave surface 31, a convex surface 33 and circular circumferential edge 31(c), and integral with said edge an annular essentially uniplanar flange 31(a). At least a part of the concave surface 31 and the convex surface 33 have the dimensions of the front or back curves, respectively of a contact lens to be produced in the mold assembly, and are smooth so that the surface of the contact lens formed by polymerization of said polymerizable composition in contact with the surface is optically acceptable. The mold is thin enough to transmit heat therethrough rapidly and has rigidity sufficient to withstand prying forces applied to separate the mold halves during demolding step which occurs after the cure step in the manufacturing process. The present invention may be used with an additional precure step introduced between the assembly of the mold with a polymerizable monomer or monomer mixture, and the cure step. The precure step partially cures the polymerizable monomer or monomer mixture to a viscous gel and initiates polymerization throughout the mixture. During this precure step the parallel alignment of the mold halves are "frozen" by the viscous gel like nature of the partially polymerized monomer gel which prevents decentration and enables unattended and unweighted cure during the remainder of the cure period. The addition of this precure step has substantially reduced the number of defective lenses resulting from traditional methods of manufacture. The complimentary pair of first 31 and second 33 mold halves which define the shape of the final desired lens are used to direct mold the monomer mixture wherein the mixture is dissolved in a nonaqueous water displacable solvent. After the filling or dosing step, in which the front concave mold half 31 is substantially filled with a polymerization mixture 32, the concave front mold half 31 is covered with a base mold half 33 under a vacuum to ensure that no air bubbles are trapped between the mold halves. The base mold half is then brought to rest on the circumferential edge 31(c) of the concave front mold half to ensure that the resultant lenses are properly aligned and without distortion. The first and second mold halves are then clamped together. This clamping step may be done following assembly of the mold halves, during precure, or both. The clamping step displaces any surplus monomer from the mold area and properly aligns the mold halves by alignment of the mold flanges. when the clamping step occurs in the precure process, the mold halves are clamped under pressure, the monomer or monomer mixture is then exposed to actinic light, preferably from a UV lamp, while the mold halves are clamped. Typically the mold halves are clamped for approximately 40 seconds with 30 seconds of actinic radiation. At the completion of the precure step, the monomer or monomer mixture has formed a partially polymerized gel, with polymerization initiated throughout the mixture. Following the precure step, the monomer/diluent mixture is then cured in a UV oven whereby polymerization of the monomer(s) is completed. This irradiation with actinic, visible or ultraviolet radiation produces a polymer/diluent mixture in the shape of the final desired hydrogel lens. After the polymerization process is completed, the two halves of the mold are separated in a demolding step typically leaving the contact lens in the first or front curve mold half, from which it is subsequently removed. The front and base curve mold halves are used for a single molding and then discarded or disposed of. After the demolding step, the solvent is displaced with water to produce a hydrated lens, which when fully hydrated and buffered, will be of the final shape and size which, in most cases, is nominally 10% larger than the original molded polymer/diluent article. The precure step is inserted in the process immediately after the polymerizable composition is placed in the front curve mold half, and the mold halves assembled. The compositions to which this precure step may be directed include copolymers based on 2-hydroxyethyl methacrylate ("HEMA") and one or more comonomers such as 2-hydroxyethyl acrylate, methyl acrylate, methyl methacrylate, vinyl pyrrolidone, N-vinyl acrylamide, hydroxypropyl methacrylate, isobutyl methacrylate, styrene, ethoxyethyl methacrylate, methoxy triethyleneglycol methacrylate, glycidyl methacrylate, diacetone acrylamide, vinyl acetate, acrylamide, hydroxytrimethylene acrylate, methoxyethyl methacrylate, acrylic acid, methacryl acid, glyceryl methacrylate, and dimethylamino ethyl acrylate. Preferred polymerizable compositions are disclosed in U.S. Patent No. 4,495,313 to Larsen, U.S. Patent No. 5,039,459 to Larsen et al. and U.S. Patent No. 4,680,336 to Larsen et al.,. Such compositions comprise anhydrous mixtures of a polymerizable hydrophilic hydroxy ester of acrylic acid or methacrylic acid and a polyhydric alcohol, and a water displaceable ester of boric acid and a polyhydroxyl compound having preferably at least 3 hydroxyl groups. Polymerization of such compositions, followed by displacement of the boric acid ester with water, yields a hydrophilic contact lens. The mold assembly of the present invention described herein may be used to make hydrophobic or rigid contact lenses, but the manufacture of hydrophilic lenses is preferred. The polymerizable compositions preferably contain a small amount of a cross-linking agent, usually from 0.05 to 2% and most frequently from 0.05 to 1.0%, of a diester or triester. Examples of representative cross linking agents include: ethylene glycol diacrylate, ethylene glycol dimethacrylate, 1,2-butylene dimethacrylate, 1,3-butylene dimethacrylate, 1,4-butylene dimethacrylate, propylene glycol diacrylate, propylene glycol dimethacrylate, diethylglycol dimethacrylate, dipropylene glycol dimethacrylate, diethylene glycol diacrylate, dipropylene glycol diacrylate, glycerine trimethacrylate, trimethylol propane triacrylate, trimethylol propane trimethacrylate, and the like. Typical cross-linking agents usually, but not necessarily, have at least two ethylenically unsaturated double bonds. The polymerizable compositions generally also include a catalyst, usually from about 0.05 to 1% of a free radical catalyst. Typical examples of such catalysts include lauroyl peroxide, benzoyl peroxide, isopropyl percarbonate, azobisisobutyronitrile and known redox systems such as the ammonium persulfate-sodium metabisulfite combination and the like. Irradiation by ultraviolet light, electron beam or a radioactive source may also be employed to catalyze the polymerization reaction, optionally with the addition of a polymerization initiator. Representative initiators include camphorquinone, ethyl-4-(N,N-dimethyl-amino)benzoate, and 4-(2-hydroxyethoxy)phenyl-2-hydroxyl-2-propyl ketone. Polymerization of the polymerizable composition in the mold assembly is preferably carried out by exposing the composition to polymerization initiating conditions. The preferred technique is to include in the composition initiators which work upon expose to ultraviolet or visible radiation; and exposing the composition to ultraviolet or visible radiation of an intensity and duration effective to initiate polymerization and to allow it to proceed. For this reason, the mold halves are preferably transparent to ultraviolet or visible radiation. After the precure step, the monomer is again exposed to ultraviolet or visible radiation in a cure step in which the polymerization is permitted to proceed to completion. The required duration of the remainder of the reaction can readily be ascertained experimentally for any polymerizable composition. After the polymerizable composition has polymerized, the mold assembly is disassembled to permit further processing of the polymerized hydrogel into a contact lens (such processing including e.g. washing and hydrating, and packaging of the lens). Preferably, the flanges of the front and back curve mold halves are gripped and pulled away from each other, either in directly opposite directions or through an angle in a prying sort of motion. Advantageously, the back curve is first heated moderately to facilitate separation of the polymerized article from the back curve mold half surfaces. The Precure Apparatus Figure 1 and Figure 2 represent a side elevation view and an end elevation view, respectively, of an apparatus for practicing the present invention. As illustrated in Figures 1 and 2, a support frame 11 having legs 12 provides support for the device at an elevation of an infeed conveyor 13. As shown in Figure 3, the precure apparatus receives a plurality of pallets, one of which is illustrated in Figure 4, having a plurality of contact lens molds therein, from the infeed conveyor 13. As seen in Figure 3, the infeed conveyor 13 delivers the pallets 30 and molds 31, 33 to a low oxygen environment, which environment is accomplished by pressurizing an enclosure 14 with nitrogen gas. Prior to polymerization, the monomer is susceptible to absorption of oxygen which results in degradation of the resultant lens. The enclosure 14 may be pivoted about pivot point 15 by lifting on handle member 16. A gas strut assist device 17 will hold the enclosure 14 in an open position for servicing of the apparatus. As illustrated in Figure 3, the conveyor 13 delivers pallets 30 containing a plurality of molds 31,33 to an accumulating section generally indicated 18 which gathers a plurality of pallets for the precure step. In the embodiment illustrated in Figures 1-2 and 6-8, twelve pallets of the type illustrated in Figure 4 are accumulated for a total of 96 molds in each batch operation. In the embodiment illustrated in Figures 9 and 10 a total of 12 pallets having 96 contact lens molds thereon are batched for each precure operation. Accumulator 18 thus enables the precure apparatus of the present invention to batch process a plurality of molds for an extended period of time of 30 to 60 seconds while continuously receiving new pallets from the production line at the rate of 1 every 6 to 12 seconds. The precure assembly 19 is partially visible in the breakaway portion of Figure 1, and is further described with respect to Figures 6-8. It is raised and lowered into engagement with pallets containing contact lens molds by virtue of a pneumatic cylinder 20 which raises and lowers an intermediate support beam 21 and reciprocating shaft members 22 which are journaled for reciprocating support in member 23 as will be hereinafter subsequently described in greater detail. After the precure operation, the pallets with contact lens molds therein are discharged through a nitrogen ventilation airlock mechanism 24 (illustrated in Figure 1) for subsequent cure by heat and cycled actinic radiation. The present invention is particularly adapted to cooperate with a plurality of pallets as illustrated in Figure 4 and 4a which have a plurality of cavities for receiving a plurality of contact lens molds. As illustrated in Figure 4a, the contact lenses of the present invention are formed by placing an amount of polymerizable composition, generally on the order of about 60 µl, in the first or concave mold half 31. The desired amount depends on the dimensions (i.e., the diameter and thickness) of the desired lens, taking into account the generation of by-products upon polymerization and exchange water for those by-products and diluent, if any, following polymerization. Then a second or convex mold half 33 is placed onto the polymerizable composition 32 with the first and second mold halves aligned so that their axes of rotation are collinear and the respective flanges 31(a), 33(a) are parallel. The mold halves 31 are carried in an annular recess 30(a) which receives and supports the annular flange 31(a) of the first or concave mold half. The pallet 30 also has a plurality of recesses 30(b) for receiving the concave portion of the mold. The pallet also carries a plurality of oriented recesses 30(c) which receive a triangular tab portion 31(c) of the base mold half to provide a predefined angular position. The second or convex mold half 33 also includes a triangular tab 33(c) which overlies tab 31(c) to provide a collinear axis of rotation with respect to the two mold halves. The pallet 30 illustrated in Figure 4 also contains a unique bar code number 35 for use in pallet tracking and quality control procedures. Figure 3 is a diagrammatic representation of a portion of the apparatus more fully illustrated in Figures 6-9 and Figures 9-10 which is particularly suited to an overview of the present invention. As illustrated in Figure 3, the apparatus includes a conveyor system 13 for transporting a plurality of pallets 30 into and away from the precure station. Batch mode forks 36(a), 36(b) are used to gather and move a plurality of pallets into the precure apparatus. The apparatus 19 includes multiple vertical reciprocal movements, a first one of which is in response to movement from air cylinder 20(a) and reciprocating beam 21(a). As the precure apparatus 19 is lowered in the direction illustrated by arrow A, a plurality of annular clamping means 40 will engage the upper annular flange 33(a) of each of the mold halves contained within pallets 30. A plurality of annular clamping means 40 are mounted on and travel with a reciprocating platform 41 of the apparatus, and are resiliently mounted therein for a second reciprocal movement along the directions of arrow B illustrated in Figure 3. As illustrated in Figure 3, the clamping means 40 are biased within frame 41 by springs 42 (illustrated diagrammatically) which may be the air spring 42(a) illustrated in Figure 5a or a helical spring 42 as illustrated in Figure 5b. As the apparatus is lowered, the clamping means will engage and clamp the first and second mold halves together with the force determined by the spring means 42. When air springs are used, the force will be determined by the amount of pressure provided to the air cylinder 42(a). While clamping means 40 have been illustrated as four members in Figure 3 for illustrative purposes, it is understood that in the embodiments illustrated in Figure 6-8 and the embodiment illustrated in Figures 9-10 that there are 96 individual clamping means, with an individual clamping means for each of the mold halves. Positioned above the clamping apparatus are a plurality of actinic light sources 44 which may be UV lamps. The lamps are separated from the clamping area by Pyrex glass 100 which separates the precure apparatus into two separate heat zones. This enables cooling of the actinic lamps 44, while maintaining the clamping zone at an optimal cure temperature. The glass 100 also protects the lamps from monomer emissions which collect on the glass 100 rather than the lamps 44. After the clamping means has engaged the mold halves to clamp them together, a shutter mechanism 45 is opened by air cylinder 46 to enable the actinic light source 44 to initiate polymerization of the polymerizable composition in each of the mold halves 33. Shutter 45 has a plurality of openings 43 defined therein and is reciprocal along the x axis as indicated by arrow C in Figure 3 in order to open and close the exposure passage ways 47. The operation of the precure apparatus 19 is set by control circuit 10 which controls the duration of the clamping period by the length of time air cylinder 20(a) is activated to its reciprocal down position. Control circuit 10 also controls the amount of radiation received by the molds controlling the duration of the exposure period through operation of shutter 45 and air cylinder 46. The intensity may also be manually adjusted by raising or lowering the lamps 44 with respect to molds 31,33. Optionally, the polymerization radiation may be generated remotely and routed to the clamped mold halves and polymerizable material via a fiber optic system, with control system 10 providing control of exposure time and energy level. The amount of force applied by clamping means 40 may be varied from approximately 4.903 to 19.613 N/per lens (0.5 Kgf to 2.0 Kgf/per lens) and is applied to keep the flange 33(a) of the second convex mold half parallel to the flange 31(a) of the first concave mold half for the duration of the exposure. The clamping weight is applied for 10 to 60 seconds, but typically for a period of 40 seconds by control means 10. After approximately 0-20 seconds of weight, preferably 10 seconds, actinic radiation from UV lamps 44 is applied to the assembled mold and the polymerizable monomer. Typically, the intensity of the UV light source is 2-4 mW/cm 2 , and this intensity of light is applied for 10 to 50 seconds, but in the preferred embodiment, is applied for 30 seconds. In the preferred embodiment, the UV lamp source are tubular low pressure mercury vapor fluorescent lamps which emit a long wave ultraviolet radiation having a highly concentrated radiation between 320 and 390 nm. In one embodiment, by way of example, the lamps are manufactured by Philips as model TL' 29 D 16/09 N having a nominal wattage of 14 watts and an average radiation of 1.8 watts in the desired spectrum. The mold halves are first clamped together for a predetermined period of time, prior to exposure, in order to allow equilibrium to develop between the monomer and the mold cavity, and to allow any excess monomer to be extruded out of the mold cavity into the space between flanges 31(a) and 32(a) where it forms a ring of excess monomer 32(a), which is generally referred to as a "HEMA" ring when hydroxyethylmethacrylate monomer is used. The first or concave mold cavity includes a sharp annular edge 31(c) to cleanly contact the convex portion of mold half 33 and thereby separate the contact lens 32 from the HEMA ring 32(a). The pre-exposure clamping period allows for any excess monomer to migrate from the mold cavity to the HEMA ring, enables the second mold cavity to seat cleanly on parting edge 31(c), and allows an equilibrium to develop between the mold halves and the monomer. Although the mold halves may be held together until the monomer(s) are completely cured, in the preferred embodiment actinic radiation on the order of 2-4 mW/cm 2 is applied for approximately 30 seconds. Different intensities and exposure times could be used, including pulsed and cycled high intensity UV on the order of 10 to 150 mW/cm 2 with exposure times running from 5 to 60 seconds. In a pulsed or cycled exposure, the actinic-radiation may be cycled on for 3 to 10 seconds and then off for 3 to 10 seconds with a total of 1 to 10 cycles of radiation. At the end of the radiation period, the shutter 45 is closed by reciprocating it to the right as illustrated in Figure 3 and the weight is removed by energizing cylinder 20(a) to lift the precure assembly 19 upwardly by means of push rods 22(a). As the assembly 19 is lifted, the clamping means 40 will be lifted clear of the molds and pallets to enable them to be transported out of the precure means by means of conveyor 13(a). During the precure time, the temperature in the system may be varied from ambient to 50°C. At the conclusion of the precure process, the monomer has gone through initiation and some degree of polymerization. The resultant product is in a gel state with some areas of the product that have the least thickness, i.e., the edge, having a higher degree of polymerization than the body. As the monomer polymerizes it forms a seal along the parting edge 31(c), which together with the inherent shrinkage of the monomer from polymerization, forms a secure mold package that may be cured in atmospheric conditions. The clamping pressure aligns the mold flanges to provide substantially parallel alignment of the flanges, and the seal maintains them in a parallel position which results in improved optical characteristics near the theoretical maximum of the plastic mold halves. Further, the clamping, and resultant seal from the partial cure results in an improved "clean" edge at the circumference of the lens. Figures 5a and 5b are schematic illustrations of two alternate means for clamping the mold halves together. In Figure 5a an air spring is used to displace the clamping means 40 downwardly with respect to the movement of reciprocating platform 41. In the embodiment illustrated in Figure 5b, a resilient coil spring 42 is used to drive the clamping means 40 downwardly with respect to the movement of reciprocating platform 41. As illustrated in Figure 5a, reciprocating platform 41 includes a plurality of annular cylinders 40, each of which has an annular flange 51 formed thereon, which reciprocates within a cylinder defined by spacer plate 52 to form an air spring or air cylinder 42(a). The cylinder is vented to atmosphere by vents, one of which is illustrated at 53 in Figure 5a to enable air pressure in the air cylinder 42(a) to drive the flange 51 and clamping means 40 downwardly against a stop plate 55 when the air cylinder 42(a) is pressurized. The carriage 50 also includes an upper stop member 56 which defines the upper limit of travel by annular flange 51, and serves as reciprocal bearing support for the clamping means 40. The upper stop member 56 also defines a plurality of air plenums, one of which is schematically illustrated at 71, which provide air pressure for the air cylinder 42(a). Air pressure is supplied to plenum 71 by solenoid air valve 72 which is activated by control means 10. As indicated previously, the air pressure supplied to air cylinder 42(a) is variable to generate a clamping force of 4.903 to 19.613 N/per lens (0.5 Kgf to 2.0 Kgf) on the annular flange 33(a). As the reciprocating platform 41 is lowered over the pallet 30 and the contact lens molds, the annular clamping means 40 engages the annular flange 33(a) formed on the second or convex mold half to urge it downwardly and clamp it into engagement with mold half 31. The movement of reciprocating platform 41 is defined by the movement of the entire assembly 19 as driven by air cylinder 20. As illustrated in Figure 5b, the annular clamping cylinder 40 also includes an annular flange 51 which is engaged by a resilient coil spring 42 and driven downwardly, as illustrated in Figure 5b, against stop plate 55. The other end of coil spring 42 is mounted within upper stop plate 56(a). Spacer plate 52 and the upper stop plate 56 provide support and guidance for the vertical reciprocation of clamping members 40. The clamping member 40 is formed of stainless steel, and optionally the mass of the clamping members may be increased to enable the clamping members to clamp by weight alone, without air or spring assist. However, the combination of the individual reciprocal clamping means 40 and locally driven resilient biasing means enable precise control of the amount of clamping pressure exerted on the plastic flanges 33(a) of the upper mold regardless of the amount of force needed to move the mass of the entire precure assembly 19. Figures 6-8 are top side and end elevation views of one embodiment of the apparatus for performing the present invention. As illustrated in Figures 6-8, the precure assembly 19 is mounted on reciprocating support shafts 22 which are journaled for reciprocating motion within support members 23 which are fixably mounted to a frame. Each of the support members 23 include upper and lower bearings or journals 23(a), 23(b) to provide for precision guidance of the reciprocating shafts 22. Shafts 22 are driven by intermediate support frame 21 which is in turn driven by air cylinder 20 as previously described. The precure assembly 19 is reciprocated vertically with respect to the upper most surface of the conveyor 13 illustrated schematically in Figures 7 and 8. The precure assembly 19 is supported from an upper support frame 60 from which various operating components are suspended by intermediate support members at each corner generally illustrated at 61, 62 in Figure 7 and 62, 63 in Figure 8. These members suspend the reciprocating platform 41, into which the individual clamping means 40 are fitted for a secondary reciprocation along the same axis. A separate subframe 65 is mounted on platform 41 and provides support for the ultraviolet lamps 44 and the ballast members 66 which provide the high voltage for the UV lamps, and the starters 67 which are used to initiate fluorescence. In one embodiment, by way of example, the ballast members may be BTP 30C05S, as manufactured by Philips and the starters may be model S2, as manufactured by Philips. The intermediate support frame 65 may be lifted free from the reciprocating platform 41 by means of a plurality of handles 67 which are mounted via straps 68 to the intermediate support frame 65. Pyrex glass member 100 separates the lamps 44 from the clamping area to protect the lamps from monomer emissions, and to enable the lamps to be cooled, while keeping the precure zone at a temperature of ambient to 50°C to facilitate polymerization. An oxygen detector 69 is also provided to monitor the low oxygen environment maintained within the protective cabinet 14 and an alarm is initiated if the oxygen content rises to an unacceptable level. Shutter 45 is positioned above the reciprocating platform 41 between the UV lamps 44 and the clamping means 40 and is reciprocated between its open and closed position by virtue of air cylinder 46. The embodiment illustrated in Figures 6-8 utilizes the air cylinder or air springs depicted schematically in Figure 5a with an internal common plenum formed in the reciprocating platform 41 by means of passageways in stop plate 56. Thus, each of the 96 clamping members 40 are reciprocated by their respective air cylinders, which are fed from common plenums, one of which is illustrated in Figure 5a as plenum 71 formed in the upper stop plate 56. While the invention has been particularly shown and described with respect to the preferred embodiments thereof, it will be understood by those skilled in the art that the foregoing and other changes in form and details may be made therein without departing from scope of the invention, which should be limited only by the scope of the appended claims.

Claims: An apparatus for partially curing a polymerizable monomer or monomer mixture as part of a process for forming a soft contact lens, said apparatus comprising: (a) a clamping member (40) for clamping a first contact lens mold half against a second contact lens mold half at a pre-cure station (19) at a predetermined pressure and for a predetermined period of time, said first and second mold halves (31, 33) having a polymerizable monomer or monomer mixture therebetween, and wherein said clamping member pressure aligns the mold halves to maintain them in parallel position; (b) a radiant energy source (44) for generating a radiant energy and directing said radiant energy to said monomer or monomer mixture while said first and second mold halves (31, 33) are clamped together to initiate polymerization, wherein said radiant energy source (44) is movable from a first transport position to a second exposure position for polymerizing said monomer or monomer mixture; (c) a frame (65) for moving said radiant light source (44) from said transport position to said exposure position, wherein said clamping member (40) is mounted on said frame (65) and resiliently engages said second mold half as said radiant energy source is moved into said exposure position. An apparatus for partially curing a polymerizable monomer or monomer mixture as claimed in Claim 1 wherein said apparatus further includes a transport (13) for intermittently transporting a plurality of contact lens mold halves (31, 33) to and from said precure station (19). An apparatus according to Claim 1, wherein each of the first and second mold halves has a flange and a curved surface, and the clamping member forces alignment of said to ensure that the flanges are parallel and that the respective curved surfaces of the mold halves are aligned. An apparatus according to Claim 1, wherein the first mold half has an annular edge, the curved surface of the second mold half is a convex shaped surface, and the clamping member (40) also forces the second mold half to seat against said annular edge on the first mold half to sever excess monomer from the monomer between the mold halves (31, 33). An apparatus for partially curing a polymerizable monomer or monomer mixture as claimed in Claim 1 wherein said clamping member (40) includes a reciprocating clamping member positioned between said second mold half and said radiant energy source (44). An apparatus for partially curing a polymerizable monomer or monomer mixture as claimed in Claim 5 wherein said clamping member (40) includes an annular cylinder having an in annular diameter greater than the diameter of the contact lens to be polymerized. An apparatus for partially curing a polymerizable monomer or monomer mixture as claimed in Claim 6 herein said annular cylinder is biased into engagement with said mold. An apparatus for partially curing a polymerizable monomer or monomer mixture as claimed in Claim 7 wherein bias pressure is 4.903 to 19.613 N/per lens (0.5 to 2.0 Kgf/lens) of clamping force. An apparatus for partially curing a polymerizable monomer or monomer mixture as claimed in Claim 1 wherein said frame (65) includes a fixed mount for a plurality of lamps which emit actinic radiation, said mount being reciprocal from a transport position to an exposure position. An apparatus for partially curing a polymerizable monomer or monomer mixture as claimed in Claim 9 wherein said actinic radiation is emitted by ultraviolet lamps at 320 to 390 nm. An apparatus for partially curing a polymerizable monomer or monomer mixture as claimed in Claim 2 wherein said transport means (13) includes a mold carrier for transporting a plurality of mold halves (31, 33) to said exposure position. An apparatus for partially curing a polymerizable monomer or monomer mixture as claimed in Claim 11 wherein said transport is intermittently paused when said UV source is moved to said second exposure position. An apparatus for partially curing a polymerizable monomer or monomer mixture as claimed in Claim 9 wherein said UV light source includes a plurality of UV lamps with each lamp (44) having a longitudinal axis, wherein a plurality of mold halves (31, 33) are aligned with said longitudinal axis during said exposure. An apparatus as claimed in any one of the preceding Claims wherein said apparatus further comprises a control circuit for controlling the quantity of energy received by said monomer or monomer mixture during said exposure step. A method of pre-curing a polymerizable monomer or monomer mixture as part of a process for forming a soft contact lens, the method comprising: (a) providing a contact lens mold having first and second mold halves (31, 33); (b) depositing a polymerizable monomer or monomer mixture in the contact lens mold, between said first and second mold halves (31,33); (c) moving an actinic light source from a first transport position to a second exposure position, said light source being moved by means of a frame (65); (d) clamping the first mold half against the second mold half with the polymerizable monomer or monomer mixture therebetween, at a predetermined clamping pressure and for a predetermined period of time, wherein said clamping pressure properly aligns the mold halves and said clamping is provided by a clamping member (40) mounted on said frame (65), said clamping member resiliently engaging said second mold half as said radiant energy source is moved into said exposure position; (e) exposing the monomer or monomer mixture to radiation to initiate polymerization and to partially polymerize said monomer or monomer mixture to a viscous gel throughout the monomer or monomer mixture, A method according to Claim 15, wherein steps (b) - (d) are conducted in a low oxygen environment. A method of partially curing a polymerizable monomer or monomer mixture as claimed in Claim 15 wherein said monomer is exposed to actinic, electron beam or radioactive source of energy. A method of partially curing a polymerizable monomer or monomer mixture as claimed in Claim 17 wherein said source of energy is an ultraviolet lamp (44). A method of partially curing a polymerizable monomer or monomer mixture as claimed in Claim 18 wherein said monomer is exposed to 2 to 150 mW/cm 2 of ultraviolet radiation at a wavelength of 320 to 390 nm. A method of partially curing a polymerizable monomer or monomer mixture as claimed in Claim 18 wherein said monomer is exposed to 2.4 mW/cm 2 of ultraviolet radiation at a wavelength of 350 nm. A method of partially curing a polymerizable monomer or monomer mixture as claimed in Claim 19 wherein said precure radiation is set for a time period of 1 to 60 seconds. A method of partially curing a polymerizable monomer or monomer mixture as claimed in Claim 20 wherein said precure radiation step is 20 to 40 seconds. A method of partially curing a polymerizable monomer or monomer mixture as claimed in Claim 15 wherein the force exerted during the clamping step is variable from 4.903 to 19.613 N/per lens (0.5 to 2.0 Kgf/per lens). A method according to claim 15 for curing a polymerizable monomer or monomer mixture to form a soft contact lens, said method further comprising the steps of: (e) transferring the lens mold to a final cure station; and (f) at the final cure station, polymerizing the monomer or monomer mixture to a cured state. A method as claimed in Claim 15 wherein a plurality of contact lens molds are intermittently transported through a pre-cure station (19), said method further comprising the step of using a control circuit (10) to set said predetermined pressure and time. A method of partially curing a polymerizable monomer or monomer mixture as claimed in Claim 25 wherein said control circuit (10) further comprises a means for varying the quantity of energy received by said monomer during said exposure step. A method of partially curing a polymerizable monomer or monomer mixture as claimed in Claim 25 wherein said control circuit (10) controls the duration of the exposure. A method of partially curing a polymerizable monomer or monomer mixture as claimed in Claim 25 wherein the clamping number (40) is positioned between the molds and the radiant energy source (44). A method of partially curing a polymerizable monomer or monomer mixture as claimed in Claim 25, in which the transporting step includes the step of using a transport (13) to move the contact lens molds, and said transport is movable from a first transport position to a second exposure position for polymerizing said monomer. A method of partially curing a polymerizable monomer or monomer mixture as claimed in Claim 29 wherein the clamping step includes the step of using a clamping member (40) to apply the clamping pressure, and said clamping member is resiliently mounted and said transport (13) moves said molds into resilient engagement with said clamping member (40) as said molds are moved into said exposure position. A method of partially curing a polymerizable monomer or monomer mixture as claimed in Claim 28 wherein said clamping member (40) includes an annular cylinder having an in annular diameter greater than the diameter of the contact lens to be polymerized. A method of partially curing a polymerizable monomer or monomer mixture as claimed in Claim 31 wherein said annular cylinder is resiliently biased into engagement with said mold. A method of partially curing a polymerizable monomer or monomer mixture as claimed in Claim 32 wherein said clamping pressure is 4.903 to 19.613 N/ per lens (0.5 to 2.0 Kgf/per lens). A method of partially curing a polymerizable monomer or monomer mixture as claimed in Claim 25 wherein the exposing step includes the step of using a fixed mount for a plurality of lamps (44) which emit actinic radiation, and the transporting step includes the step of using a transport (13) to move the contact lens molds, with said transport being reciprocal from a transport position to an exposure position. A method of partially curing a polymerizable monomer or monomer mixture as claimed in Claim 34 wherein said actinic radiation is emitted by an ultraviolet lamps at 320 to 390 nm. A method of partially curing a polymerizable monomer or monomer mixture as claimed in Claim 25 wherein the clamping step includes the step of using a plurality of clamping members (40) to apply the clamping pressure, and the transporting step includes the step of using a plurality of mold pallets (30) for transporting a plurality of mold halves (31, 33) to said exposure position. A method of partially curing a polymerizable monomer or monomer mixture as claimed in Claim 36 wherein said pallets (30) means are intermittently reciprocated towards said UV source (44) to said second exposure position. A method of partially curing a polymerizable monomer or monomer mixture as claimed in Claim 367, wherein the transporting step includes the step of using a plurality of lifting standards for raising said pallets (30) into engagement with said plurality of clamping members (40). A method of partially curing a polymerizable monomer or monomer mixture as claimed in Claim 38 wherein said clamping member (40) includes an annular clamping member positioned between said lifting standards and said radiant energy source (44). A method of partially curing a polymerizable monomer or monomer mixture as claimed in Claim 39 wherein said clamping member (40) is resiliently biased and moves from an engagement position to an exposure position when clamping said mold halves (31, 33). A method according to Claim 25, wherein each of the mold halves (31, 33) includes a respective flange (31a, 33a), the first mold halves include concave curved surfaces and the second mold halves include convex curved surfaces, and wherein the clamping pressure forces alignment of the flanges (3 la, 33a) of the first and second mold halves of each mold to ensure that the flanges are parallel and that the respective curved surfaces of the mold halves (31, 33) of the mold are aligned. A method according to Claim 25, wherein the first mold half of each mold has an annular flange (31a, 33a), and the clamping pressure also forces the second mold half of each mold to seat against the annular edge of the first mold half of the lens mold to sever excess monomer from the monomer between the mold halves (31, 33) of the mold. A method of curing a polymerizable monomer or monomer mixture as claimed in Claim 42 wherein said clamping step forms a clean lens edge for said contact lens.

Inventors: ADAMS JONATHAN PATRICK, BJERRE KAJ, CHRISTENSEN SVEND, KINDT-LARSEN TURE, MARTIN WALLACE ANTHONY, WALKER CRAIG WILLIAM, WANG DANIEL TSU-FANG, WIDMAN MICHAEL FRANCIS, ADAMS, JONATHAN PATRICK, BJERRE, KAJ, CHRISTENSEN, SVEND, KINDT-LARSEN, TURE, MARTIN, WALLACE ANTHONY, WALKER, CRAIG WILLIAM, WANG, DANIEL TSU-FANG, WIDMAN, MICHAEL FRANCIS
Applicants: JOHNSON & JOHNSON VISION PROD, JOHNSON & JOHNSON VISION PRODUCTS, INC.
Application year: 1995
Main classification: B29D11
IPC codes: B29C35, B29C33, B29D11, B29L11, G02C7, B29C69, B29K105, B29C43