CA2113257C

CA2113257C - Method and apparatus for molding lenses

Info

Publication number: CA2113257C
Application number: CA002113257A
Authority: CA
Inventors: William J. Appleton; Dennis Hahn; William E. Moucha; Dominic V. Ruscio; John H. Shannon; Steven D. Silbermann; Edwin W. Weaver, Jr.
Original assignee: Bausch and Lomb Inc
Current assignee: Bausch and Lomb Inc
Priority date: 1991-09-12
Filing date: 1992-08-27
Publication date: 1996-01-16
Anticipated expiration: 2012-08-27
Also published as: BR9206432A; ATE137441T1; EP0603284B1; CN1040081C; ES2089562T3; CN1071877A; US5466147A; DE69210407D1; WO1993004848A1; EP0603284A1; MX9205182A; US5271875A; HK1001679A1; JP3370327B2; JPH06510496A; AU666497B2; SG44659A1; AU2565992A; DE69210407T2; JP2003094447A

Abstract

A mold assembly includes first and second mold sections having respective first and second mold cavity defining surfaces, the first mold cavity defining surface terminating in an encircling peripheral rim (52) and the second mold cavity defining surface terminating in a deformable peripheral annulus (47) disposed at a diameter corresponding to the rim, and cooperating tapers (44, 24) depending from each of the first and second molds for relatively centering the molds.

Description

W093/04~8 ~ ~ PCT/US92/07~3 q'TTT.~

THOD AND APPA~ATUS FOR MO~nING T-F~S~

R~CKGROUND OF THE Nv~ ON

Field of the Tnvention ~he present $nvention pertains to a method and ~pp~ratus for molding lenses, and part~cularly to a method and apparatus for molding len~es ~uch as contact lenses which have a f~ h~ edge and which are ~uitable for wear$ng directly on the eye.

n~scr~ption o~ the Related Art ~t has become desir~ble to form lenses, p~rticularly cont~ct lense~ but also other Ly ?S of lenses, by molding ~uch lenses rather th~n by lathing or by other proce5ses. Molded lenses are des$r~ble for ~everal ..~onF. For example, it i~ possible to produce ~uch lenses with great repeatability-- to y G~ce m~ny lenses wh~ch haYe the ~ame ~h~pe and optical characteristics. Moreover, a molded len~
can be formed to ~ny desired ~hape, ~ubject only to producibility constra~nts of the mold.

Wos3/04~8 2 ~ 1 3 2 5 7 In general, ~olded lenQes are formed by depositing curable liguid ~uch ~ a polymeriz~ble ~onomer into a mold cav~ty, curing the liguid into ~ ~oli~ ~tate, ~pe~ the mold cav~ty ~nd removing the l-ns.
Other ~ e-sing ~teps, for example, hydration, ~ay ~l~o be performed. In any event, ~ the lens ~aterial transitions from its liguid or ~emi-liquid ~tate to a sol$d or a~mi-~olid ~tatQ, the mater~al ~hr~nk~. For example, when the lens material is a polymeriz~ble monomer ~uch as hyd~6xy~Lhyl ~et~acrylate t~HEMAn), a~out 15% to 25% volume reduction can be expected ~s the material cur-s.

~aterial ~hrinkage i8 of considerable ~oncern and must be ~cco~modated during molding. If hrinkage i~ not properly accommodated, ~t i~ po~$ble for the curing len~ material to pull ~way from it~
~ c~ted mold ~urface. Any such separation pr~Al~c~ cceptable optical ~urfaces ~nd re~ults in an ~ hle len~. And even if ~eparat$on does not occur, internal st~ e~ often produce rc~ptable distortion of the len~.

~ecause of the problem of len~ material shrinkage during curing, it has heretofore been difficult to provide accept~ble ~olded lenses that do not regu$re ~dditional fin~h~g ~teps. Conventional mol~$ng t~ ues, ~uch ~s describe~ in Lar~en U.~. P~tent 4,~65,348, acco~modate hrinkage with ~old halves which flex during curing. Such ~c~n~ques ~ay have ce~table repeatability due to ~-~lL-lictable ~eformation in ~old shape during curing. In particular, because the lens shape is defined by ~
mold h~lf th~t flexes ~uring curing, the radii that define the optical power of the lens can change 2l 1 3257 unpredictably making it difficult to produce lenses repeatably.

The geometry of contact lenses makes the problems associated with shrinkage even more acute. As des-cribed below, because of lens geometry, the lens material shrinks nonuniformly.

Conventional molding techniques, such as described in the above-mentioned Larsen U.S. Patent 4,565,348, do not compensate satisfactorily for this nonuniform shrinkage. The flexible molds provide their great-est compensation in the middle of the mold cavity and provide no compensation at the periphery of the mold where the greatest shrinkage, as described above, occurs.

It has also been considered to accommodate shrinkage by providing a reservoir of suitable polymerizable monomer at the peripheral region o~ the mold cavity.
See U.S. Patents Nos. 4,113,224 and 4,197,266. In principle, during polymerization, the shrinking mon-omer will draw additional monomer in from the reser-voir. In practice, this configuration has not been found satisfactory inasmuch as it is difficult to mold a finished edge into the lens, and such a lens therefore inevitable requires subsequent machin;ng and lathing processes. Moreover, because the most shrinkage occurs after the lens material gels, res-ervoir techniques are of limited effectiveness. Afurther problem with reservoirs that supply monomer is that there is the potential for polymerizable material to be wicked from within the mold cavity.

GB-2 235 408-A also teaches a method of molding con-tact lenses which utilizes a mold assembly formed of - 4 - ~l l 3257 a pair of plastic mold parts having a reservoir for excess polymerizable monomer. Shrinkage is accommo-dated primarily during curing by plastic flow of an annular, rigid projection on one of the first or se-cond mold parts. This plastic flow of the projec-tion, related to the material from which the mold part is formed, the curing temperature and the cur-ing time, allows the two mold parts to approach one another.
In the GB-2 235 408-A method, initially the mold parts are urged axially, or bonded, together, and then heated in an oven to cure the polymerizable ma-terial. During the early part of the curing proc-ess, liquid polymerizable material may be drawn fromthe reservoir and past the projection to replenish shrinking material in the molding cavity. After the material thickens, further shrinkage draws the two mold parts together so as to deform the projection.
It will be appreciated that since sealing of the mold cavity may not be complete until curing has progressed, and shrinkage accommodation relies only on plastic deformation of one of the mold parts, this method does not suf~iciently address the a~ore-mentioned problems.

SUMMARY 9F THE I~VENTION

In one aspect of the invention, the drawbacks assoc-iated with the prior art are addressed through the provision of a mold assembly and a method of using the same, the assembly comprising first and second mold sections having respective first and second mold cavity defining surfaces, the first mold cavity defining surface terminating in an encircling peri-pheral rim, the second mold cavity defining surface terminating in a deformable peripheral mating sur-face disposed at a diameter corresponding to that of the peripheral rim, and centering means for the re-spective first and second mold sections. The mold cavity may be formed such that it includes a central optical zone and a peripheral carrier zone that has a substantially greater volume than the optical zone. The mating surface is an annulus which is re-versely angled with respect to the second mold cav-ity defining surface. By the term ~reversely an-gled~ it is meant that the mating surface angles outwardly, away from the second mold cavity defining surface and toward the first mold cavity defining surface. The annulus may be flat or it may be rad-iused such that it resembles a section of a torus.

The first and second mold sections may be formed ofdifferent materials which have different affinity to cured lens material. This is advantageous in that the molded lens will preferentially remain on one o~
the mold sections after separation of the mold as-sembly. Selection of differing materials for the mold sections may also desirably affect the surface properties of the cured lens.
In another aspect, the invention provides for a pos-terior mold and a method of using the same, the mold preferably having a generally spherical mold cavity defining surface provided at the periphery thereof a reversely angled deformable mating surface adapted to mate with a lens edge-defining rim of an anterior mold. The posterior mold's mating surface may be formed in the shape of an annulus, the annulus being reversely angled with respect to the mold cavity de-fining surface. The annulus may be radiused suchthat it resembles a section of a torus, and the pos-~ 21 ~ 3~

terior mold may be provided with centering means de-pending from the mating surface for providing accu-rate alignment for the anterior mold, and a pressure receiving surface for receiving clamping pressure during the curing of lens material.

In another aspect of the invention, the invention provides for an anterior mold and a method of using the same, the mold having a generally spherical mold cavity defining surface provided at the periphery thereof with a rim. A collar preferably surrounds the rim so as to form a receptacle for confining ex-cess lens material and centering means for centering a posterior mold may depend from the collar. The rim may be defined as the corner of a right cylind-rical wall in the mold cavity defining surface and a radially extending flange between the collar and the mold cavity defining surface.

Further features of the invention are defined in the dependent claims.

This brief summary of the invention has been provi-ded so that the nature of the invention may be un-25 derstood quickly. Embodiments of the invention are - -described below in significant detail in connection with the attached drawings which together form a complete part os this specification.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a cross-sectional view of a contact lens;

Figure 2 is a perspective exploded view of a mold as-sembly including a contact lens;

~;

Figure 3 is a magnified view of a contact lens edge;

Figure ~ is a cross-sectional view of a posterior mold section;

Figure 5 is a cross-sectional view of an anterior mold section;

Figure 6 is a cross-sectional view of a posterior mold section assembled with an anterior mold sec-tion;

Figure 7 is a flow diagram useful for explaining a lens molding method according to the invention;
Figure 8 is a graph for explaining ~-mPnsional sta-bility of mold materials;

Figure 9 is an expanded cross-sectional view of mold sections being assembled to show the position o~
lens material;

Figure 10 is a cross-sectional view of assembled mold sections for showing the formation of a recep-tacle for excess lens material;

Figure 11 is a diagrammatic cross-sectional view of a clamping apparatus for the assem.bled mold sec-tions;
Figure 12 is a magnified view showing edge details of assembled mold sections under clamping pressure.

Figure 13 is an expanded cross-sectional view of assembled mold sections after curing;

..

Figure 14 is a magnified view showing edge details of assembled mold sections after curing;

Figures 15 through 17 are views for explaining mold disassembly and len~ extraction;

Figures 18 and 19 are views for explaining an alter-native embodiment of a posterior mold section which retains excess polymerized monomer;
Figure 20 is a first alternative embodiment of the invention; and Figures 21 through 24 are views for explaining a second alternative embodiment of the invention in which it is not necessary to clamp the mold sections during curing.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIME~TS
Figure 1 is a cross-sectional view of a contact lens 11 which, as shown there, includes a central optical zone 12 and a peripheral carrier zone 14. Typical-ly, the optical zone 12 i~ 7mm - llmm in diameter and the overall diameter of the lens 11 is 13mm -15mm. As seen in Figure 1, the lens is formed in distinct radius zones on both the posterior side 15 and the anterior side 16. Thus, from the central optical zone 12 outward, anterior side 16 is formed first with radius R1, which is selected in accord-ance with desired optical power of the lens, merges into radius R2 in the carrier zone 14 of the lens, and then merges into radius R3 selected to provide a suitable transition to the edge taper. One the pos-terior side 15, the optical zone 12 is formed withradius R4 which is also selected in accordance with - 8a -the desired optical power of the lens, and which merges with radius R5 in the carrier zone 14 of the lens.

In consequence of this configuration, lens 11 is formed with substantially greater volume of material in the peripheral carrier zone 14 than in the cent-ral optical zone 12. This is, whether the optical zone 12 provides positive or negative optical power, because carrier zone 14 surrounds optical zone 12 at a greater diameter, there is more material in the carrier zone. Consequently, there is significantly more shrinkage that must be accommodated in the per-ipheral portion of the lens than there is in the central portion thereof, and the lens material ther-efore shrinks nonuniformly.

Figure 2 shows the overall configuration of an anterior mold section 20 relative to a posterior mold section 21.

W093/04~8 _ g _ PCT/US92/07~3 As ~hown there, anterior mold 20 ~ncludes a cylindrical ba~e 22 which blends into ~ tapered head 24. The tapered head ~erves as centering ~eans to center the anterior ~old 20 within a compl~mentarily ~haped taper ~n po~terior ~old 21. The anterior mold ~l-o $nclude~ an anterior mold cavity defining ~urfaoe 25 formed to provide the desired radii Rl t~ yh R3 ~hown in Figure 1. Advant~g~o~ y, with thi~ ~o..~Ll~ction the tapered hcad wh~ch erves as centering means and the mold cavity def~ning ~urface ~re clo~e to each other, there~y providing the greatest centering effect without the lntervention of ~uperfluous structure.

Posterior mold 21 includes a cylindrical shell 26 dimensioned to allow posterior mold 20 to f~t complementary ~haped centering ~eans within the ~hell. Top flat 27 is provided to receive clamping pressure and to distribute it uniformly to the a~sembled mold. Posterior mold 21 includes a posterior mold cavity defining ~urface, the .e~e~e ~ide of which is indicated at 29, which defines radi~ R4 and R5 in ~igure 1. As ~efore, the centering means for posterior mold 20 are close to the mold cavity defining surface to provide the greatest centering effect.

m e posterior and anterior mold cavity defining ~urfaces are formed ~o a~ to provide the desired eage ~tructure for contact lens 11. The edge ~tructure for lens 11, as shown in Figure 3, include~ a tapered edge 30 which ensures that there are not ~harp or irritating edges that cont~ct ither the eye or the interior ~urface of the eyelid. In particular, tapered edge 30 includes a W093/04&~ - lo - 2 1 1 3 2 5 ~ PCT/US92/07~3 .
rever~ely ~ngled iip 32 wh~ch is contoured awAy from the eye, the ~urface of which is ~n~cated ~chemat~a~ly at 31 Lip 32 may be r~diu~ed, for example, as ~hown by aotted line R7 in Figure 3, or lip 32 may be flat In ~ny event, the ~unction between lip 32 and the po~terior ~ide 15 of lQns 11 ~s ro~ e~ for comfort as ~hown at 34 The ~nterior portion of tap~cl edge 30 include~
corner 35 that ag~in is ro~nAA~ for comfort relative to the interior ~urface of the eyelid The ~
merge~ into vertic~l wall 36 which meet~ lip 32 at tip 37 By virtue of this ~tructure, tip 37 ~s not in contact with either the eye or the interior ~urface of the eyelid, thereby m~ximizing wearer comfort Figures 4 and 5 ~how an -Yp~n~e~ view of the anterior and posterior molds which provide for thi~
edge ~tructure A~ ~hown $n Figure 4, ~nd a~
previously mentioned, posterior mold 21 include~
cylindric~l shell 26, top flat 27 and rev¢r~e side 29 of the posterior mold c~vity defining surface The th~nqr6 of the posterior mold is selected to be ~ufficient so that the mold c~vity def$ning ~urface i~ rigid and does not deform under curing or polymerizing ~tres~ The cylindrical ~hell 26 i~
~oined to top flat 27 at -ho~ r 40 Posterior mold 21 further ~ncludes a ba~e 41 which ~
relatively th~nnqr than the remainder of the mola to provide an interior diameter that is larger than th~t defined by the remainder of the mold, thereby facilit~ting access for anterior mold 20 ~ase 41 includes a ~tepped diameter 42 which leads into taper 44 Taper 44 provides centering me~ns for W093/04~8 - 11 - PCT/US92/07~3 21 1 3~57 ~lig-~ent and centering of ~nterior mold 20 with re~pect to posterior mold 21.

Taper ~4 ~ve~se~ at ~5 and leads to posterior mold cavity defining ~urface ~6 having a generally ~pherical ~urface. ~Generally ~pherical" ~
under~tood to include -~po~ which are not ~tr~ctly ~pherlc~l such as aspheric or toric -hA~
~hown in Figure 4, ~urface 46 i~ ~haped with rcquired radii R4 and R5 (Figure 1) for the ~e optical zone and the peripheral c~rrier zone, re~pectively. At the periphery of mold cavity defining ~urface 46 i5 a mating surface formed from an annulus 47 which corresponds to lip 32 ~hown in Figure 3. This surface may be flat or radiu~ed as previously described. The annulus 47 is rever~ely angled relative to the mold c~vity defining ~urface 46 and thereby permits formation of lip 32 ~o that it i~ away from the eye and smooth at it~ ~unction with mold cavity defining surface 46.

Figure 5 shows anterior mold 20 which, as previou~ly described, includes cylindrical ba~e 22, tapered head 24, and "generally spherical" t~5 defined above) anterior mold cavity defining ~urface 25.
Surface 25 is ~h~pe~ with radii Rl, R2 and R3 (Figure 1) for the ~e~ al optical zone and peripheral carrier zone, respectively. m e diameter of taper 24 is ~elected ~o th~t it i~ slightly ~maller th~n the corresron~ng diameter of taper 44 ~n posterior mold 21. Thi~ ~n~ures that the mold sections ~e~t without interference while al~o ensuring that they are properly centered.
Preferably, the molds ~eat with a 0 to 20 micron W093/0~8 PCT~US92/07~3 ~- 12 ~ 2 ~ t ~2~ ~

cl-arance between tapers 24 ~nd 44, more prefer~bly with ~ 10 micron cle~rance TaPQr 24 1QadS tO a ~011Ar SO which forms an inwardly ~loping area ~9 ~nd ~ e_~Lacle in ~rea 51 Ihe $nw~rdly ~lop~ng area 49 ~nteracts with the stepped diameters of posterior mold 21 to f~cilitate as~Omhly A sharp rim 52 encircl~s the p~riphery of ~old cavity defining surface 25, the rlm 52 ~eing formed by the corner ~unction of right cylindrical wall 54 that CO~ G--~S to vertical wall 36 in Figure 3 and r~d~ally ext~n~ing flange 53 that leads from collar S0 ~everse surface 56 of the anterior mold generally follows the contour~ of the above described surfaces The thickne~s of anterior mold 20 is selected so that it i~ sufficient to ~levenL flexing of the ~old ca~ity defining ~urface under polymerizing or curing stress Figure 6 diagrammatically illustrates posterior mold 21 and ~nterior mold 20 ln their ~s ~l~led form As shown in ~igure 6, posterior mold 21 ~eat~ snugly against anterior mold 20 such that rim 52 ~eats against ~nnulus 47 Taper~ ~4 ~nd 24 ~eet with the ~LOVL GLed clearance ~o as to center the anter~or and posterior mold~ thereby to prevent pri~m or other undesired defects caused ~y ~ ntering A~
~o ~s-embled, the mold ~ections form mold cavity 57 in which cura~le lens material such as polymerizable ~EMA is held during curing As assembled, the ~olds al~o form recept cle 59 in ~rea ~1 h~h ~ n~ coll~r 50 Receptacle 59 is provided to receive excess lens material that is ejected rom mold cavity 57 when the molds are seated. Any such excess material is retained in receptacle 59 where it is prevented from reaching the junction between tapers 24 and 44. If excess lens material reaches that junction, it has been found that capillary action undesirably causes the excess material to be wicked from receptacle 59. Until mold cavity 57 is sealed as described below. there is the potential for lens material also to be wicked from within mold cavity 57. Collar 50 prevents this.

The materials for posterior mold 21 and anterior mold 20 should be selected in consideration of their relative deformability and their affinity for cured lens material. In particular, during curing, it is desired for annulus 47 and rim 52 to deform each other, and the relative deformability of these two surfaces should be selected accordingly. It has been found that a combination o polypropylene (e.g., MARLEX* ~rom Phillips 66) ~or posterior mold 21 and rigid (unplasticized) polyvinyl chloride (e.g., GEON* from B.F. Goodrich) for anterior mold 20 provides a suitable combination of materials such that annulus 47 and rim 52 may be relatively deformed during curing. Other materials may be used, for example ionomer, polyarylsulfone, polyetherimide, polyester, polystyrene, rubber modified copolymer or rigid polyurethane, and the same material may be used for both the anterior and posterior mold although it is preferable to use different materials. In terms of hardness, the posterior mold material should range from approximately Shore D 50 to Rockwell M 110, preferably from ~hore D 65 to Rockwell M 65.

* Trade-mark f .-=~ ~

W093/04~8 ~ 2 1 1 3 2 5 7 PCT/US92/07~3 (Pol~ lene is approximately Shore D 75.) The anterior mold material ~hould range from a~.o~imately Shore D ~0 to Rockwell M 120, preferably-from Shore D 80 to Ror~cll M 110. (PVC
i~ approximately Shore D 87).

m e ~election of poly~v~lene and PVC for the posterior and anterior mold, respectively, ~ al~o ~dvantageous in that the~e material~ prov$de r~gid mold cavity defining ~urface~ which elimlnate the adver~e effect~ of optic~l zone deformation during curing. This ensures that lenses produced by the moldæ have predictable characteri~tic~ and are repeatable from mold-to-mold.

It haæ al~o been found that when HEMA ~ u~ed for lens m~terial, cured len~ material h~s greater affin~ty for the PYC of anterior mold 20 than for the poly~o~ylene of posterior mold 21. Thus, the com~ination of PVC and polypropylene $8 advantageous in that $t ~n_~ e that the cured lens remains $n the anterior mold where ~e~vval, for exa~ple, by hydration, i5 more re~dily achieved.

~inally, it is noted that polypropylene transmit~
ultraviolet light which $~ a commonly u~ed medium for ~nitiating cur$ny or polymerization.

Becau~e the molds are de~igned ~uch that rim 52 and per$pheral ~nnulus 47 rel~t$~ely deform eac~ other, the molds ~re prefera~ly u~ed one t$me and one time only. T~e molds may ~e fabricated through ~t~n~d in~ection molding technjques ~uch as are conventionzl to those ~killed in the art.

_ W093/0~8 ~CT/US92/07~3 Figure 7 ~s flow diagram for lxrl~n~ng ~ method for molding len~es ~ccording to the ~-ent invention.

In step Sl, the ~nterior ~nd po~terior molds ~re formed, G..~e,.$ently through in~ection molding ~8 described ~bove. Mold~ ~o forme~, especi~lly of the poly~G~ylene ~aterial mentioned ~bove, ~re ~sp~c~ally prone to ~imen~ion~l instabilitie~ that ~r~ ~ignificant to the optical tolerances th~t mu~t ~e ~int~nf~ in the practice of the invention. For exa~ple, ~ ~hown in Figure 8, during an initi~l period ~fter injection molding until a time tl, the molds ~re ~ub~ect to thermal and other dimensional distortions which cau~e their dimensions to ch~nge dramatically. The molds ~re not usable during ~i5 period. During the period ~fter tl, the molds continue dimensional change, but ~t ~ much ~l~wer rate. It has been found desirable to u~e the molds within ~ range of time determined by dimensional operating tolerances. This i~ represented in Figure 8 by the period between tl ~nd t2.
Typically, for polypropylene, tl is about one hour and t2 i5 ~bout four hours.

Thus, ~L~l..ing to ~igure 7, ~tep S2 inaicate~ ~
delay period during which the mold~ ~re not u~ed until ~ window between tl ~nd t2. Then, in step S3 predetermined or metered ~mount of lens materi~l, in this case, HEMA, i~ deposited in the ~nterior ~old. The ~mount of len~ material deposited in the ~old $6 c~lculated to accommodate ~ny dimensional tolerance~ in~olved in the fabrication of the mold~, any variation in the metering capabilitie~ of the metering pump, and other effect~. In addition, a sliqhtly greater amount of lens material than that -W093/0~8 - 16 ~ 2 1 1 3 2 5 7 PCT/US92/07~3 .. ..
calculated ~bove $~ deposited. The ~Y~es~ ~mount of lens material ~8 provided to ensure that a ~mall amount of~-Yc-~c $~ ~o~med along the periphery of the a~embled mold cavity. The ~ F~ len~ ~aterial el.~uL~ that no bubbles or other edge defect~ ~re formed in the ~dge region of the l-ns when the len~
caYity S7 ~eal~.

In step 84, the posterior mold $~ embled and ~eated against the anterior ~old, ~ ~h~wn $n Figures 9 and 10. As ~hown in Figure 9, the mold ~ections may at fir~t ~ove tow~rds e~ch other relatively guickly, facilitated by $nteraction between the ~tepped diameters in posterior mold 21 and ~ngled ~urface ~9 in anterior mold ~0. As the posterior mold c~vity defining ~urface ~ppro~h-r the lens 2aterial 60 that has been deposited in the anterior mold, the molds ~hould be moved together at very low ~re~ to ensure that lens material 60 wets the entire ~urfaces of the anterior and posterior mold cavity defining ~urf~ccs without the form~tion or i~ Gd~ction of bubbles or other defect~.
Movement of the two molds cont~ s until rim S2 ~eats ~gainst annulus 47, a~ shown in Figure 10.
Tapers 24 and 44 function to center the two mold ~ections relative to each other. FYc~sF len~
material 61 i~ depo~ited into receptacle 59 where collar 50 prevents tYcQr~ material from flowing between ~urfaces 24 and ~4.

In step S5, the mold ~ssembly i~ clamped. A
~uit~bl~ clamping ~tructure i~ shown ~chematically in Figure 11. As ~een there, the clampinq structure include~ a base 64, ~ piston 65, and ~n upper plate 67. The upper plate includes port 69 through which W093/04~8 PCT/US92/07~3 ~ 17 -ultraviolet radiation may ~e pro~ected to cure lens ~aterial 60. ~ort 69 is of a di~meter ~uit~ble to expose not only lens material in mold cavity 57 but aleo exce~s lens material 61 in receptacle S9.

The ~r-~hled anterior and posterior molds are rlac~ on piston 65, after which ~n unshown air cyl~ d ides the piston up to clamp the fl_t 27 ~gainst the upper plate 67, thereby to ~ub~ect the ~ssembled mold to A predetermined clamping force.
An air cylinder ~c preferably used for this purpose ~o that the clamp force r~ ubstantially the ~ame regardless of the amount of ~ubsequent movement, particularly during curing, between the anterior and posterior mold_.

The force with which the mold _ssembly is clamped i~
sclected so that rim 52 ~eats against annulus 47 in a continuous line around the edge of the mold cavity to form a fluid-tight seal. The clamp force ~h be ~elected so that it is large ono~gh to ~nsure that ~uch a seal is ~chieved without ~ny gaps, ~ut so that it is small ^no~gh th_t ~nnulus 47 ~nd rim 52 ~re not deformed excessively under the force.
FY~e~ive deformation at this ~e ~e stage re~l~r--the ~mount of further deformation avail~le to a level below that n~c---ary to ~eeommodate ~hrinXage during euring. With the ~bove mentioned pol~ yl¢ne/PVC eombination, it h~s been ~ound that 20-40 pounds of elamping foree i~ preferable.

Figure 12 ~hows the eondition of the ~nterior mold, the pofiterior mold, the lens material in mold eavity 57 and the len~ material in reeeptAcle 59 ~8 a result of elamping by the Figure 11 ~tructure. A~

W093/04~8 18 2 1 1 3 2 5 7 PCT/US92/07243 ~en there, rim 52 ~eals ~gainst ~nnulus 47 ~ut neither rim 52 nor annulus 47 has been significantly deformed. Mold cavity 57 is effectively ~ealed from receptacle ~9 and ~Y~-e~fi ~onomer 61 in receptacle 59 i~ conta~ within the receptacle by the ~ction of ~OllAr 50.

nelur.ling to Figure 7, ln ~tep ~6 the lens ~aterial i8 cured from its liquid or ~emi-liquid state to its ~olid or ~emi-solid ~tate. In the part~cular embodiment described here, ~uch curing is achiev~d through polymerization of polymerizabl~ HEMA monomer in a nitrogen atmosphere with the assistance of ultraviolet cxposure through port 69 in the clamping assembly. Other curing tech~igues are al~o possible, for example thermal curing.

As mentioned ~bove, polypropylene plastic used for the posterior mold 21 tr~nsmits ultraviolet irradiation and thus effectively permi~s curing of the lens materi~l contained ~oth $n receptacle S9 ~nd in mold cavity 57. To ensure ~ufficient curing of polymerizable HEMA monomer, ultraviolet irr~diation cont~ s for a~oximately five minutes under clamping pres~ure, the mold is unclamped (~tep S7), and further polymerization to remove residual unreacted constituents is obta~n~ through five further minutes of ultr~violet ~cs~e (step 58).
Cure times will vary ~ep~n~ng on the p~rt~c~ r ~onomer mix e~ployed, as will ~e apparent to one of ordinary ~kill in the art.

Figure 13 ~hows the ~old assembly after curing. As ~een there, rim ~2 and annulus 47 have relatively ~eformed each other. In particular, rlm 52 has W093/0~8 PCT/US92/07~3 deformed the surfAce of annulus 47 a~ shown at 71 and annulus 47 hac ~olln~ the edge of rim 52 ~
also ~hown at 71. As ~hown ~o~ceptu~lly ln Figure 14, ~im 52 has emhe~e~ itself into ~nnulus 47 to the extent th~t ~fter curing the original height of vertical wall 54 has been a~ xim~tely halved. In a rpecific example, the origin~l height of wall S4 is a~oximately 50 micron~, and the undistorted beight after curing is ~ 6~imately 25 microns.
The indent~tion in annulus 47 was ~out 5 microns.
CAlculations ha~e ~hown that this degree of deformation is ~ufficient to accommodate ~ubstantially all shrinkage expected for the lens material entr~ined in mo~d cavity 57.

In ~tep S9, the posterior and anterior molded surf~ces ~re ~ fi--~hled. As ~hown in Figure lS, this ifi preferably performed by a ~trictly ~ertical motion without any angular or a lateral translational motion ~o as to prevent damage to the cured lens 72. As further ~hown in Figure 15, be~a~^ the cured lens material has greater affinity for anterior mold 20, cured lens 72 s well as cured excess lens material 61 remain~ with the anterior mold.

As further chown in Figure 15, ~eca~-c the deformation of annulu5 47 i5 pl~tic deformation it results in a permanent ~coring 73 ~long a middle c$rc~mference o~ the annulus. Similarly, rim 52 remain~ permanently ro~ . It i~ for the~e r~a-on~ that the molds are preferably u~ed once only.

~ - 20 - 2 1 1 3257 In step S10, the lens is subjected to inspection.
During such an inspection, it is possible to deter-mine if foreign materials or bubbles were retained in mold cavity 27 during the molding process, or if any other cont~mln~nts or undesirable features of the lens have been obtained.

In step Sll, the lens is hydrated to facilitate removal from the mold. During hydration, as shown in Figure 17, the cured lens material expands from a somewhat shrunken state as depicted in Figure 16 as it absorbs water. secause of this expansion, edge 74 of the cured lens interacts with edge 75 of the cured excess 61. To ensure that pieces of mat-erial do not chip away from these edges and contam-inate the finished lens, a surfactant is normally added to the hydrating fluid. A suitable surfact-ant is polyoxyethylenesorbitan-20 monoleate (TWEEN-80*) added at a rate of 0.5% by weight to a hydra-ting fluid consisting of distilled or purified wat-er. Hydration preerably occurs at an elevated temperature, for example, between 30C and 100C.

In step S12, the finished lens is packaged. During packaging, additional steps may also be perormed, for example further optical inspection steps, ster-ilization, grading, addition of tint or coloring, etc.

It is, of course, possible to interchange several o the steps described above. For example, the inspection of step S10 can be perormed at a later point or eliminated altogether. In addition, it is possible to demold the lens before hydration in a so-called "dry release" step. In this step, care * Trade-mark W093/0~8 - 21 - CT/US92/07~3 must be exercised to ensure that the cured ~e~6 m~teri~l 61 does not interfere with the demolding ~ , and to ensure that the lens is not damaged during release Figures 18 ~nd 19 ~how an altern~tive configuration for posterior ~old 21 wh~ch is p~rticul~rly cuited for dry release of lens 72 As ~hown in Figure 18, posterior mold 21 include~ reta~n~n~ means for ret~ n~ t~e cured ~YcQPF 61, the re~ n~ me~ns being in the form of groove 75 ~t a point ad~acent annulus 47 and in the area of receptacle S9 As ~hown in Figures 18 and 19, ~,oo~e 75 becomes filled with ~Yre~s lens m~teri~l while the lens material is in the liquid or ~emi-liquid ~tate When the len~
material ~ cured, groove 75 ret~ins the cured ~Yco~F material thereby to ensure that the Y~orr i~
retained with the posterior mold 21 during the ~i~a~embly step (step S9) Advant~geously, thi~
ensures that the cured eY~ese materi~l does not interfere with the lens demolding p C~-~6, whether that proce~s is performed through hydration or through dry rele~e While Figures 18 and 19 depict the ret~ning mean~
as ~ y~o~e, other forms ~re possible Thus, the ret~n~n~ ~e~n~ may t~ke the form of plur~l hole~ in posterior ~old 21, or a foot ext~n~ from posterior mold 21 into r-cept~cle 59, or simply a ro~7h~neA surf~ce texture for the posterior mold Likewise, if it is desired for the cured l-n~ to rem~in with the posterior mold r~ther th~n the anterior mold, then ret~n~n~ me~ns m~y be provided on the ~nterior mold inste~d W093/0~8 22 -i 2 1 t 3 ~ 5 7 PCT/US92/07~3 ! _ Figure 20 illustrates a first a lternative ~mbodiment of the invention in which centering me~ns is provided by vertically ~xt,rn~ng cylindric~l walls 24' and 44~. ~n all other respect~, the ~mbodi~ent of Figure 20 ~s substantially ~imilar to th~t ~escr~bed ~bove ~nd a detailed ~ rion thereof ~s omitted for the ~ake of brevity.

Figure~ 21 to 24 ~llustrate a ~con~ ~ltern~tive ~mbodiment of the present ~nvention which uses a t~per-lock clamping mean~ wherein it is not n~ er-~ry to externally clamp the asse~bled mold during curing. Superficially, the em~odiment of Figures 20 through 23 resembles that of Figures 1 through 19 and ~ccordingly ~imilar reference numbers have been used. Thus, in Figure 21, po~terior mold 121 includes upst~ g cylindrical ~hell 126, top flat 127, the reverse ~ide 129 of posterior mold ca~ity defining ~urface 146, shoulder 140, taper 144, ~ev~se 145, posterior mold defining ~urface 146, and annulus 147. Anterior mold 120 includes cylindric~l b~se 122, tapered head 124, anterior mold cavity defining surface 125, inwar~ly sloping area 149, collar 150, ~e_e~Lacle forming area 151, rim 152, and rig~t cylindrical wall 154.

In this embodiment, flanges 156 and 15? ~re provided for poster~or mold 121 and anterior mold ~20, respectively. Such flanges incre~se the rig~dity of t~e mold sections and facilitate me~n;cal ~anipul~tion ~nd may, accordingly, al~o be u~ed in other of the a~o~e described e~ho~ments.

In Figure 21, the t~per ~ngle for tapers 144 ~nd 124, and the relative diameters of the molds in the W093/04~8 --- ~ PCT/US92/07~3 region of t~pers 124 ~nd 144, are ~elected ~o that the anterior and posterior ~olds lock together under action of the taper. Thus, for Qx~mple, t~per 144 $s ~elected at ~n ~ngle of 2 1/2 degree~ from vertic~l while t~per 124 $s ~elected at an angle of 3 de~es from vertical. Accordingly, a~ ~hown ~n Figure 22, the lnner xtremity of base 141 initially contacts the surf~ce of t~per 124 at ~ point 158 before r~m 152 contact~ annulu~ 147. ~urther downward tr~vel of posterior mold 121 with respect to anterior mold 120 c~uses the rim 152 to ~eat against annulus 147 and causes taper~ 124 ~nd 144 to lock rel~tive to each other, a~ shown in Figure 23.
In the preferred e~ho~iment~ lock i~ achieved after a downward travel, or ~taper interference," of about 75 micron~. The downward and outw~rd compressive forces caused by the loo~n~ act~on of the taper~
c~u~e cylindrical ~hell 126 to pivot outward around ~houlder 140 there~y generating ~ downward ~ealing force. Straightforward ~nAlysis, for example, fin~te element methods, yields the ~mount of taper lock compressive force ~e~e~ to generate a downward ~ealing force equivalcnt to th~t ~n the case of the first ~ho~ment. In the e~ho~ment ~llustr~ted in Figure 21 through 24, $t h~s been found th~t ~5 to 25 ro~ of clo~ure force yields ~ 35 ~GUl.d ~e~ling or cl~mping force and ensures that the mold ~ection~
are locked.

In l~ke manner to th~t $n the fir~t e~ho~ment, the a~e~bled mold with lens material 160 ~n place i~
~ub~ected to curing. The combination of the ~eal$ng force generated by downward and outward ~G~sive forces from the taper lock with the vacuum force caused by hr~nk~ge $8 adequ~te to n~ure that rim W093/04~8 - 24 ~ 2 1 ~ 3 2 5 7 PCT/USs2/07~ ~

152 and annulus 147 are relatively deformed ~o a~ to accommodate ~hrinkage during curing. Accordingly, clamping assemblie~ may be el~min~ted al~ho~gh they may, of cour~e, ~till ~e used. It ha~ been found that after curing, ~urface 140 and flange 156 tend to pivot upward around ~houlder 140, ~ ~hown by the dot, dash line in Figure 24, in an apparent react~on to the relative deformation of rim 52 and ~nnulus 147.

After curing, steps S9 through S12 of ~igure 7 are performed as before with ~e_t to the ~irst o~iment of the invention whereby a lens ~aving a f~n~e~ edge with any desired ~hape may be formed.

The foregoing h~s been provided ~o that the nature of the invention may be under~tood easily. It ~hould, however, be apparent that modific~tions of the foregoing ~mbodiments may be made without departing from the nature and ~cope of the ~nvention. For exAmple, it is po~sible to provide the first described D~ho~ment of the invention with unequAl t~per angles for tapers 24 and 44 since these tapers ~re intended simply to provide alignment an~ centering and not nec~ rily to provide any taper lock force a~ in the ~eco~
a~ternative embodiment. It is also po~ible to provide the e~on~ alternative embodiment wlth retA~ng means such a~ thAt described above with respect to the first embodiment. Accordingly, the r~e of the inventlon ~hould not be limited to the ~pecifics described above but inste~d ~hould be ~easured with respect to the appended cl~ims.

Claims

WHAT IS CLAIMED IS

1. A lens molding method characterized by:
depositing lens material in a first mold section;
seating a second mold section adjacent the first mold section and sealing the first and second mold sections so as to define a mold cavity sealed at the edge thereof, with excess lens material being received and confined in a space adjacent the sealed edge of the mold cavity; and curing the lens material from a liquid or semi-liquid state to a solid or semi-solid state to form a molded lens;
wherein said first and second mold sections are clamped by applying a clamping force that is sufficient to seal the mold cavity but without excessive deformation, and shrinkage in the lens material is accommodated during curing by relatively deforming a rim of one of said first and second mold sections and a deformable mating surface on the other of said first and second mold sections, and wherein the edge of the lens is formed at a point of deformation of the rim and deformation of the mating surface.

2. The method of claim 1, wherein the amount of lens material deposited in said depositing step is metered such that excess lens material is deposited in the first mold section.

3. The method of claim 1, wherein the excess lens material is confined in the space adjacent to the sealed edge of the mold cavity by a collar surrounding the rim.

4. The method of claim 3, wherein the clamping force is within the range of about 20-40 pounds.

5. The method of claim 1 wherein the first and second mold sections are clamped by applying an external clamping force.

6. The method of claim 5, wherein the clamping force is maintained at a constant level throughout curing of the lens material.

7. The method of claim 1, wherein the first and second mold sections are clamped by taper-lock clamping means.

8. The method of claim 1, further comprising disassembling the first and second mold sections such that the molded lens remains with one of said first and second mold sections.

9. The method of claim 8, wherein the mold sections are formed from different materials such that the molded lens preferentially remains on one of the mold sections after disassembly of the mold sections.

10. The method of claim 9, wherein excess lens material is retained in the other of said first and second mold sections.

11. The method of claim 8, further comprising hydrating the molded lens.

12. The method of claim 1, further comprising centering the first mold section with respect to the second mold section during said seating step.

13. The method of claim 12, wherein said centering comprises inserting a generally cylindrical shell of one of said first and second mold sections into a correspondingly shaped generally cylindrical shell of the other of said first and second mold sections.

14. The method of claim 13, wherein the cylindrical shells are tapered and the tapers are substantially equal.

15. The method of claim 13, wherein the cylindrical shells are tapered and the tapers are different.

16. The method of claim 13, wherein the first mold section comprises a generally cylindrical base and a tapered head.

17. The method of claim 1, wherein the first mold section comprises a mold cavity defining surface including a central optical zone and, at a periphery of the mold cavity defining surface, a right cylindrical wall whose corner defines the deformable rim.

18. The method of claim 17, wherein the first mold section further comprises a collar surrounding the rim for confining the excess lens material in the space adjacent to the edge of the mold cavity.

19. The method of claim 1, wherein the second mold section comprises a mold cavity defining surface including a central optical zone and, at a periphery of the mold cavity defining surface, a reversely angled deformable mating surface.

20. The method of claim 19, wherein the deformable mating surface comprises an annulus.

21. The method of claim 20, wherein said annulus is radiused.

22. The method of claim 1, wherein the first and second mold sections comprise respective anterior and posterior mold cavity defining surfaces, said first mold section including, at a periphery of the anterior mold cavity defining surface, a right cylindrical wall whose corner defines the deformable rim, said second mold section including, at a periphery of the posterior mold cavity defining surface, a reversely angled deformable mating surface disposed at a diameter that corresponds to said deformable rim.

23. The method of claim 22, wherein the anterior and posterior mold cavity defining surfaces define a rigid mold cavity having a central optical zone.

24. The method of claim 22, wherein the deformable rim of the first mold section is a corner formed of the right cylindrical wall and an outwardly extending flange.

25. The method of claim 24, wherein the first mold section includes a collar surrounding the rim and extending from the flange for confining the excess lens material in the space adjacent to the edge of the mold cavity.

26. In a mold assembly for molding lenses comprising first and second mold sections having respective first and second mold cavity defining surfaces forming a mold cavity therebetween, wherein the first mold cavity defining surface of the first mold first section terminates in an encircling peripheral rim, the mold assembly characterized by the second mold cavity defining surface terminating in a reversely angled deformable mating surface disposed at a diameter corresponding to said peripheral rim; and cooperating centering means provided for each of said first and second mold sections.

27. The mold assembly of claim 26, wherein the first mold section has a rigid, generally spherical anterior mold cavity defining surface, and the second mold section has a rigid, generally spherical posterior mold cavity defining surface.

28. The mold assembly of claim 26, wherein the first mold section further comprises confining means for confining excess lens material in a space adjacent to the edge of the mold cavity.

29. The mold assembly of claim 28, wherein the confining means comprises a collar surrounding the rim of the first mold section.

30. The mold assembly of claim 26, wherein the peripheral rim is defined by the corner of a right cylindrical wall of the mold cavity and an outwardly extending flange.

31. The mold assembly of claim 30, wherein said first mold section further comprises a collar surrounding the peripheral rim and extending from the flange.

32. The mold assembly of claim 26, wherein the second mold section further comprises a pressure receiving surface for receiving clamping pressure and distributing the pressure uniformly.

33. The mold assembly of claim 26, wherein said mating surface is an annulus.

34. The mold assembly of claim 33, wherein said annulus is radiused.

35. The mold assembly of claim 26, wherein said centering means includes a first cylindrical shell depending from said rim and a second cylindrical shell engagable with the first cylindrical shell depending from the mating surface.

36. The mold assembly of claim 35, wherein said first cylindrical shell includes a cylindrical base and a tapered head.

37. The mold assembly of claim 35, wherein said first and second cylindrical shells are tapered.

38. The mold assembly of claim 37, wherein said first and second cylindrical shells have the same taper.

39. The mold assembly of claim 37, wherein the tapers lock the first and second mold sections.

40. The mold assembly of claim 35, wherein the cylindrical shell of one of said first and second mold sections has a stepped diameter and the other of said first and second mold sections has an inwardly sloped surface adapted to interact with the stepped diameter.

41. The mold assembly of claim 26, wherein said first and second mold cavity defining surfaces define a rigid mold cavity having a central optical zone.

42. The mold assembly of claim 26, wherein one of said first and second mold sections has greater affinity for cured lens forming material than that of the other.

43. The mold assembly of claim 26, wherein one of said first and second mold sections includes means for retaining excess cured lens material.

44. The mold assembly of claim 26, wherein one of said first and second mold sections is formed from PVC and the other of said first and second mold sections is formed from polypropylene.

45. The mold assembly of claim 26, wherein said first mold section is formed of a material different from said second mold section.

46. The mold assembly of claim 45, wherein the second mold section has a hardness of approximately from Shore D 50 to Rockwell M 110 and the first mold section has a hardness of approximately from Shore D
70 to Rockwell M 120.

47. The mold assembly of claim 46, wherein the second mold section has a hardness of approximately from Shore D 65 to Rockwell M 65 and the first mold section has a hardness of approximately from Shore D
80 to Rockwell M 110.

48. The mold assembly of claim 47, wherein the second mold section has a hardness of approximately from Shore D 75 and the first mold section has a hardness of approximately from Shore D 87.

49. In a mold assembly for molding lenses com-prising first and second mold sections having res-pective first and second mold cavity defining sur-faces forming a mold cavity therebetween, the first mold cavity defining surface of the first mold first section terminating in an encircling peripheral rim, the mold assembly characterized by:
the encircling peripheral rim of the first mold cavity defining surface being defined by the corner of a right cylindrical wall of the mold cavity and an outwardly extending flange, said first mold sec-tion further comprising a collar surrounding the peripheral rim and extending from the flange; and the second mold cavity defining surface termi-nating in a deformable mating surface disposed at a diameter corresponding to said peripheral rim.

50. The mold assembly of claim 26, wherein the peripheral rim is deformable.

51. The mold assembly of claim 49, wherein the first mold section has a rigid, generally spherical anterior mold cavity defining surface, and the sec-ond mold section has a rigid, generally spherical posterior mold cavity defining surface.

52. The mold assembly of claim 49, wherein the second mold section further comprises a pressure re-ceiving surface for receiving clamping pressure and distributing the pressure uniformly.

53. The mold assembly of claim 49, wherein one of said first and second mold sections includes means for retaining excess cured lens material.

54. The mold assembly of claim 49, wherein one of said first and second mold sections is formed from PVC, and the other of said first and second mold sections, is formed from polypropylene.

55. The mold assembly of claim 49, wherein the peripheral rim is deformable.

56. The mold assembly of claim 49, wherein the mating surface is reversely angled from the second mold cavity defining surface.