CA1070066A

CA1070066A - Apparatus for and method of forming optical lenses

Info

Publication number: CA1070066A
Application number: CA225,087A
Authority: CA
Inventors: James A. Clark; Donald V. Livesey; Richard J. Wrue
Original assignee: Bausch and Lomb Inc
Current assignee: Bausch and Lomb Inc
Priority date: 1974-05-06
Filing date: 1975-04-21
Publication date: 1980-01-22
Also published as: SE7505165L; DE2518905A1; AU8063175A; JPS50151966A; IT1032811B; FR2270082A1; SE418822B; DE2518905C2; JPS598219B2; FR2270082B1; GB1511901A

Abstract

ABSTRACT OF THE DISCLOSURE
Apparatus for and method of forming ophthalmic lenses and/or semi-finished lens blanks including those of the eye contact type. The apparatus includes molds having co-operating first and second members each of which includes a longitudinal axis and a mold surface which is symmetrical with respect to such axis. In one embodiment these mold members or halves also include cooperating surfaces which, in operation and in cooperation with the selected lens material, both align the respective mold axes and axially position the mold surface of the first member with respect to the mold surface of the second member to thereby form the desired lens mold cavity.
Further, each of the assembled molds also includes an annular reservoir which surrounds the mold cavity, and is defined by surfaces provided on the first and second mold members. This reservoir is connected to the mold cavity via an annular restriction. In one embodiment this restriction is defined by the cooperating aligning surfaces provided on the first and second mold members. In operation, the reservoir holds a volume of lens material which, during the polymer forming reaction, is kept in a flowable state longer than the lens material in the mold cavity. This arrangement permits the transfer of lens material between the reservoir and the mold cavity during curing. Apparatus is also provided for removing selected portions of the cast lens in those instances where removal is either necessary or expedient.

Description

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DESCRIPTION OF T~E PRIOR ART
-Ophthalmic lenses, including those of the eye contact type may be made from a ~ariety of suitable materials. Such materials include selected polymeri~able monomers, polymerlzable oligomers, polymerizable prepolymers andL cross-linkable polymers.
A series of cross-linked hydrophilic polymers formed by the polymerization of selected monomers is disclosed in U.S. Patents Nos. 2,97Ç,576 and 3,220,960. Articles made from such polymers have the appearance of an elastic and ~ -pliable hydrogel and may be transparent. These articles, in their hydrated condition, are elastically deformable under relatively small pressure but virtually immune to plastic deformation. When the aqueous constituent of such hydrogels is of a composition similax or analogous to that of phy~iological saline solution these materials have been found to be compatible with human body tissue for extended periods of time. Accordingly, such hydrogels have been formed-into objects, such as contact lenses.
U.S. Patent No. 3r361,858 discloses a method and apparatus for making contact lenses from a "xerogel"
which is,generally speaking, a hard material that is converted to a hydrogel by the absorption of water. In one method a cylindrical tube and a coaxially received plunger memoer are used to form a lens blank. A~ter :

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~07al~66 polymerizati.on, the cylindrlcal tube is removed leaving a "xerogel" blank firmly adhering to the plunger member. This blank is then machined, ground and polished while it is rot-. ated about the plunger axis. In an alternate method a lens . is formed by injecting polymerizable material into a cavity de~ined by the sphe:rical surface formed on the end of a rod and a membrane of soft rubber.
In U.S. Patent No. 3,408,429 there is disclosed a method of manufacturing contact lenses of cross-linked hy-10 drophilic polymers of the type disclosed in U.S. Patent Nos.2,976,576 and 3,220,960. The method is performed by poly-merization of the selected monomers in a mold rotating about .
its own central axis. Rotation is fast enough to centrifug-ally dri~e the initially liquid material to the periphery of the mold to form a lens of the desired configuration. The optical power of the lens manufactured according to this :
process is determined by such factors as the shape and size of the mold, the speed of rotation of the mold during polymere ization, inclination of the axis of rotation relative to the mold axis and the density of the polymerizable monomer.
A method and apparatus for producing cast optical elements by photopolymerization of monomeric material is disclosed in U.S. Patent No. 2,524,862. The apparatus dis-closed includes first and second mold members which are separated from each. other by a gasket a~d held in assembled relationship by a series o~ clamps. The apparatus also in cludes a source of llght. According to the process, the thi.cker sections of the lens ~o be cast sh.ould receive more light during th.e polymer forming reaction than the thin-ner sections of such. lens so that polymerization ta:kes place more rapidly in th.e center (assuming that the cen^ter is '~ -, . ,:

~7~ 66 thicker) than at the edges. This, it is stated~ allows the polymerizable liquid to be drawn from the edges o~ the mold as the shrinkage which accompanies polymerization proceeds, thereby preventing the formation of voids and internal strains in the casting. To assure that -the thickest section receives more li~ht t an opaque screen having a cut out of the desired shape is interposed between the mold ancl the source of rad-iation. As this cutout is not s~trical, apparat.us ~or pro-viding continuous relative rotation between the screen and the assembled mold is provided. U.S. Patent No. 2,525,664 covers improvements relating to the screen described in U.S.
Patent No. 2,524,862.
Lenses made of polymerizable monomers such as allyl diglycol carbonate, d.iallyl phthalate and allyl chloro-acrylate are disclosed in U.S. Patent No. 3,222,432. Lenses of such material are formed by polymerizing the constituent materials between two mold halves which are made of ~uenched glass having a uniform thickness and which are urged towards each other by a resilient clamping device. Such design permits, during the polymer forming reaction, the mold halves to follow and conform to any shrinkage variations in the lens material without any separation or breakaway between ~ -the mold wall and the lens material and wi-thout the high clamping pressure required by the prior art~
In recent yeaxs silicone rubber has also been suggested as a substitute :Eor such material as methyl-meth-acrylate in the preparation of, for instance, contact lenses.
Lenses of such material are disclosed in U.S~ Patent Nos~ :
3,228,741 and 3,51~,324.
~ith materials such as those discussed above, :
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material shrinka~e during the curing of thelens is p~esent.
Even when this shrinkage is very $mall it p~esents di~ficul-ties in the casting of lenses. Maintaining mold halves in their proper orientation and spacing when using a lens mat-erial which expands would present similar problems.

SI~RY OF l'H~ INVENTION

In one aspect the invention provides a lens mold comprising: first and second cooperating mold members, said first mold member having a first mold surface, said second mold member having a second mold surface, said first and second mold surfaces cooperating to define a mold cavity, said first and second mold members including means for de-fining an annular reservoir, said first and second mold mem-bers also including means for defining an annular restriction interconnecting said reservoir ~ith said mold cavity, said first and second mold members further including means to axially and radially align said mold members to control both the thickness and prism of the lens to be cast, said aligning means being located on said first and second mold member between said reservoir and said mold cavity.
In a further aspect the invention provides a method of forming a lens from a polymerizable material ~i~h a mold formed from first and second mold halves each having a mold surface, the method characterized by the steps of:
(a) orientating the second mold member so, that the secona mold surface will retain the polymerizable material;
; ~b) depositing the polymerizable material on the second mold surface;

(c) moving the first mold member into position relative to the second mold member to :

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~7~6 (i) form a mold cavity having a center sec-tion and an edge por-tion, (ii) fill the mold cavity with a portion of the polymerizable material;
(iii)form an annular restriction surrounding and connected to said mold cavity, (iv) radially and axially align the mold mem-bers with the aid of structure provided on the mold members and (v) load an annular reservoir connected to said mold cavity via said annular restriction with that portion o~ the polymerizable material which is in excess of the volume of the m~ld cavity and the restriction;
(d) polymerizing the polymerizable material in the mold cavity from the center section to the edge port.ion.
In those instances where the casting is a semi-finished lens, or : where otherwise eY.pedient, apparatus for and method of rem~ving selected portions of the lens material is also provided.
BRIEF DESCRIPTION OF T~IE DRAWINGS
FIGURE 1 is an exploded, sectional view of one embod- :
iment of the lens mold of the invention; ~ :
FIGURE 2 is a partial secional view illustrating the . mold halves of FIGURE 1 in their assembled position;
- FIGURE 3 is a~ec~onal view illustrating an alternate embodiment of the lens mold;
FIGURE 4 is a top plan view of the female mold member .~ . , -: , illustrated in FIGU.RE 3;
FIGURE 5 illustrates, in sectional view, a modified male mold member in combination with the female mold member of FIGURES 1 and 2;
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FIGURE 6 is a top plan vie~ o~ a modi~ied female mold hal~ for use in conjunction with, ~or lnstance, the male mold half of FIGURES 1 and 2;
F~GURE 7 is a partial sectional view of the mold of FIGURE 6, taken along line 7-7 thereof, in combination with the male ~.old member o FIGURES l and 2;
FIGURE 8 is a parkial sectional view of the mold of FIGURE 6, taken along line 8-8 thereof, in combination with the male mold member of FIGURES 1 and 2;
FIGURE 9 is a sectional view of an alternate em~
bodiment of the lens mold of the present invention; a:nd FIGURE 10 is a view, partially schematic and partially in section, illustraking machinery for contouring one of the lens surfaces.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Lens mold 11 illustrated in FIGURES 1 and 2 in-cludes a male member 13 and a cooperating female member 15.
Male member 13 includes a convex surface 17 which has an optical finish and is symmetrical with respect to longitud-inal axis 19. Male member 13 also includes a pair of sur-faces 21 and 23. Surface 21 conveniently lie~ in a plane . which is perpendicular to axis 19. Surface 23, is also con-veniently, in the form of a section of a cylindrical surface that is concentric with respect to axis 19. As viewed in cross section, surface 21 is smoothly blended into surface 17 via a short radius surface 25, Male member 13 also in- :
cludes a second pair of surfaces 27 and 29 that are accurate-ly referenced with respect to mold surface 17 and axis 19.
Thus, in this embodiment, surface 27 is in the form o~ either a section of a cylinder which is symmetrical with respect to ' ~;

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axis 19, or a section of a cone which is symmetrical with respect to axis 19. If a cone~ the an~le of inclination with respect to axis 19, when viewed in cross section, is very small. Surface 29 lies, most conveniently, in a plane which is perpendicular to axis 19. It should be noted that sur~aces 23 and 27 are interconnected by an additional surface 31 which, although ~llustrated as lying in a plane perpendicular to axis 19, may take any one o~ a wide variety o~ contours, such as being the section of a cone. Finally male memher 13 also includes a cavity, designated 33, that extends from surface 35 and is defined by a concave surface 37 and a cylindrical surface 39 both of which are, at least, approxi-mately symmetrical with respect to axis 19.
Female member 15 is provided with a concave mold surface 41 which, when lens mold 11 is used in the production of finished cast lenses, will be optically finished. As ill-ustrated, mold surface 41 terminates at edge 43; is symmet-rical with respect to longitudinal axis 45; and is connected with top sur~ace 47 by a plurality of surfaces ~9, 51, 53 and 55. Surfaces 47 and 49 lie in planes which are perpendicular to a~is 45. ~urther, both have the outline of an uninter-rupted annulus. Surface 51 is the section of a cylindrical taper or cone having its smallest diameter at its juncture with surface 49. Surface 55, though illustrated as a sec- ;
tion of a cylinder, may have any suitable configuration~
Surface 53, of arcuate cross-sectional configuration, inter-connects sur~aces 51 and 55. Female member 15 is also pro-vided with a cylindrical e~tension 57. Ex-tension 57 includes a lower surface 59, that, preferably, lies in a plane which is perpendicular to axis 45 and which, as viewed in FIGURES
1 and 2, lies slightly below exterior surface 61 so as to ' ~ g _ .L.~ .

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form a suitable base.
In operation/ female member 15 is placed in an up-right position as illustrated in FIGVRE 1 and a quantity of lens material 71 is deposited on surface 41. Male member 13 is then moved relative to female member 15 to form lens mold cavity 73. The fact that surface 51 has the configura-tion of a section of a cone facilitates the assembly of the two mold halves. Specifically, as male member 13 and female member 15 are brought into their assembled position surface 17 contacts lens material 71 and forces it outward to fill mold cavity 73. That portion of lens material 71 which is in excess of the ~olume of cavity 73 is collected in the con-tinuous annular reservoir 75 that is formed by surface 53 and by portions of surfaces 23, 51 and 55. Although the filling of mold cavity 73 and the loading of annular reser-voir 75 are not accomplished simultaneously, it should be appreciated that both are accomplished by -the single step of moving male member 13 into its assembled position rela-ti~e to female member 15.
~s is shown in exag~erated form in FIGURE 2, surface 21 is not in direct contact with surface 49 but is separated therefrom by a thin film of lens material 71.
Similarly, though the diameter of the cylinder de~ined by ; surface 23 and the lower diameter of surface 51 are dimen-sioned so that they substantially align axes 19 and 45, they are also separated from each other by a thin film of lens material 71 which, by fillin~ the gap between surfaces 23 and 51l acts to hydrostatically ali~n axes 19 and 45 to minimize prism between mold surfaces 17 and ~1 and, consequ-ently~ between the surfaces of the finished cast lens.

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The net result of the foregoing assembly operation is that reservoir 75 is open to the fluid environment which surrounds mold 11 and to mold cavity 73 via a circum-ferentially extending restriction 77. Additionally, it should be noted that reservoir 75 and circumferentially ex-tending restriction 77 serve to seal mold cavity 73 from the fluid en~ironment in which assembled mold ll is located.
~ n the case where lens mold 11 is dimensioned for use in manufacturing contact Ienses (either corneal or schleral) from, for instance, cross-linked hydrophilic poly-lOmers, a spacing of 0.0002 to 0.0005 inches between surface -~
23 and the lower diameter of surface 51 is utilized. The spacing or gap between surfaces 21 and 49 is also in the same range.
The dimensions set forth in the above example are merely illustrati~e. It has been found that the width of restriction 77 must be sufficiently large so that lens mat-erial in reservoir 75 may be drawn therethrough and into mold ca~ity 73 to fill the void created therein as the orig-inal volume of lens material in mold cavity 73 shrinks during the polymer forming reaction. The spaciny between, for instance, surfaces 21 and 49 and~ hence, the size of restriction 77 will depend upon such factors as the size and shape of the lens being cast, the weight of male member 13, the viscosity of the lens material used and the rate of -polymerization desired. The faster t~e polymerization rate, the greater the spacing between surfaces 21 and 49 and the -larger the size of restriction 77 The fact that, during the polymer ~orming reaction, the polymer tends to pull the mold halves together must also be taken into consideration.

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Clamping pressure, such as se-t forth in U.S.
Patent 3,222,432 or the prior art de$cri~ed therein, is not only not required but would effectively seal reservoir 75 from mold ca~ity 73 and thus defeat the ;purpose of having such a reservoir.
The illustrated configuration of the cooperating surface pairs 21, 23and 49, 51 is one of the preferred arrangements for positioning mold surface 17 in its proper orientation with respect to mold surface 41 and for defining restriction 77. However, it will be evident to those skilled ;:.
in the art that other cooperating surface configurations provided on each of the mold members would be acceptable for the same purpose as long as the required spacing, align-ment and restriction size are achieved Thus, for instance, : each of the surface pairs 21, 23 and 49, 51 could be replaced .
: by a single surPace having the configuration of a section of .~
a cone. A surface having, in cross section, an arcuate con~ `
figuration would also be possible. Regardless of the config-uration it should be realized that the width of, in the ill-ustrated example, restriction 77 must be taken into account in the design of members 13 and 15 so as to achieve the desired spacing between mold surfaces 17 and 41 and, hence, the thickness of the lens. It should also be noted that in those instances where the mold members are provided with non-symmetrical aspherical surfaces such mold members will have to be keyed to each other to insure that the mold surfaces are properly oriented.
The arrangement illustrated in FIGURE 2, wherein the width of restriction 77 is determined by the weight of male member 13 and the viscosity of the lens material util-~1 6~

ized, etc., is not the only wa~ of maintainin~ the mold halves in the desired pos~tion and obtaining the desired restriction. ~n alternate system is illustrated in FIGURES
3 and ~. ~n this second embodiment lens mold 111 comprises male member 13 and female member 115. Female member 115 includes a cylindrical extension 117, a lower surface 119 and an exterior mold surface 121 which are substantially the same as, respectively, extension 57 and sur~aces 59 and 61 o~ female member 15. Female mold member 115 also includes a mold surface 123 that is symmetrical with xespect lQ to axis 125 and a top surface 127 which, in conjunction with mold surface 123, forms edge 129. Mold surface 123 may be optically finished. Further, surface 127 is provided with a plurality of upstanding projections 131 that are symmetrical about axis 125 and, preferably, are outwardly spaced from edge 129. While the illustrated embodiment includes only three projections 131 it will be appreciated that additional projections may be provided.
In operation, as with the previous embodiment, a quantity of lens material is deposited upon mold surface 123. Male member 13 is then moved relative to female member 115 until mold surface 17 engages projections 131 and forms, as illustrated in FIGURE 3, mold cavity 133. Although, in FIGURE 3, axes 19 and 125 are illustrated as being coincident, it will be appreciated that so long as a mold surface 17 is spherical and is in engagement with all of projections 131, axis 19 need not be aligned with axis 125 in order for mold cavity 133 to be symmetrical about axis 125.
In a manner similar to the previous embodiment, as male member 13 and female member 115 are brought into ~Sj~f.~
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:~ . ~ . . :, their assembled postion, surface 17 contacts the lens material and forces it outwaxd to fill mold ca~ity 133. That portion of the lens material which is in excess of the volume of mold cavity 133 is collected in annular reservoir 135 which is sepatated fromand connected to mold cavity 133 by an annu-lar restriction 137. Reservoir 135 is defined by surface 127 of ~emale member 115 and by surfaces 21 and 25 and a portion of surface 17 o~ male member 13. Surf-ace tension holcls the lens material in reservoir 135 in approximately the postion illustrated in FIGURE 3.
With the embodiment illustrated in FIGURES 3 and-4 the height of projections 131 above surface 127 and hence the size of restriction 137 will depend upon the same factors that determine the size of restriction 77. That is, -the size of restriction 137 must be sufficiently large so that the lens material in reservoir 135 may be drawn therethrough and into mold cavity 133 to fill any voids created therein as the original volume of monomer shrink~ during the polymer forming reaction.

In the case of contact lenses manufactured of, for example, cross-linked hydrophilic polymers, the weight of the male member 13 is sufficient to hold mold sur~ace 17 in engagement with projections 131.
After the mold ~ cavity and the reservoir have been ~illed, the lens material in the mold cavity is poly-merized while the lens material in the reservoir is inhibited -from polymerizing. As used in this specification the term "polymerize" (and its~arious tenses) means a polymer forming reacti~n in which the polymer is prepared by: (1) the poly-~ merization o~ suitable monomers, obligomers and~or prepoly-; mers; or (2) a cross-linking reac-tion.
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The specific details o~ poly~erizin~ in the mold cavity; of keeping the lens material in the reser~oir in a flowa~le st~te longer than the lens material in the mold cavity; and the material from which the mold is made will vary depending on the particular lens material selected and the manner of initiating the polymer forming reaction. Heat or other ~orms o~ radiation such as ultraviolet light may be utilized. The fluid environment to which the lens material in the reser~oir is exposed may be an inert one/ such as nitrogen, or may be one which inhibits polymerization with r ~' out contaminating such lens material. Additionally, -depen-ding upon the nature and intensity of the radiat:ion, it may be necessary to shield the reservoir from the particular radiation used to polymerize the lens ma~erial in the mold cavity. Finally, the material from which the mold hal~es are formed must be one which is inert to the particular lens material selected and which permits the desired form of poly-mer forming reaction.
As has been previously stated~ the embodiments illustrated in, respectively, FIGURES 1 and 2 and FIGURES
3 and ~ may be used to form ~ontac~ lenses of hydrophilic mateial such as disclosed in U.S. Patent Nos. 2,976,576 and 3,220,960. ~ith regard to such materials it is noted that oxygen in the air acts as an inhibitor without contaminating the material. Thus, by exposing that portion of the lens material that is in ~he reservoir to air, i~
will, at least for low levels of radiation, be inhibited from polymerizing and thus remain in its fluid condition.
It s~ould be appreciated that the polymexization of the lens material should proceed from the center of the 15~ :

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mold outw~rds in order to avoid pol~merizin~ that portion o~
the lens material in the mold which is adjacent the edge of the mold cavity and, consequently, blocking off the reservoir from the center section of the mold cavity. One expeditious ~ay of avoiding the foregoin~ problem is to polymerize the lens material with, for instance, ultra violet radiation while using a diaphragm such as schematically illustrated at 141 in FIGURE 3. In the case of a symmetrical lens, it has been determined that diaphragm 141 may, most simply, be an opaque screen having a circular opening 143 therein. The diameter of opening 143 should be smaller that the diameter of the lens being cast in order to insure that the lens mat-erial adjacent to the edge of the mold is shi lded from the radiation. In operation, once the lens material in the center of the mold cavity has been polymerized, diaphragm 141 is removed to permit polymerization of the lens ~aterial ad-jacent to the edge of the mold. Alternately, a diaphragm with an adjustable opening may be utilized. When using a diaphxagm is it preferred that the direction of radiation should be approximately parallel to, in the embodiment illustrated in FIGURE 3, axis 125~ As is evident from U.S.
Patent No. 3,40~,429 the mold halves in this instance may be made from glass or suitable plastics which are inert to the polymerizable material and which permit the transmission of the ultra violet radiation.
The position of diaphragm 141 is FIGU~E 3 is merely illustrati~e. This diaphragm and, of course, the source of radiation may just as easily be positionecl above ; male member 13 during the polymer forming reaction. Further, although the use of diaphragm 141 is preferred it has been ~ound that, with the lens material in either the reservoir .. ' .. .~. . .

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~.137(~66 75 or 135 exposed to air and with low levels o~ r~diation, the configuration of e~terior surfaces 61 and 121 of female mold members 15 and 115 is such that the center section of mold cavities 73 and 133 receive more radiation than the edge portions thereof. The configuration of male member 13 produces a slmilar result.
In the foregoing example the surface of the lens material in the reservoir is inhibited from polymerizing be-cause of the fact that such material is exposed to air. How-ever, for convenience in later handling, it is preferred that after the lens material within the mold cavity has been polymerized, any uncured lens material remaining in the reservoir also be polymerized. This may be accomplished by placing the mold in a nitrogen or other inert gas environ-ment and subjecting the remaining reservoir material to ultra violet radiation.
. . The quantity of lens material necsssary will depend upon the size of the lens to be cast and the volume change which such lens material undergoes as it is cured, Thus, for e~ample, the amount of lens material 71 deposited upon sur~
face 41 will equal the volume o~ the lens to be cast plus a volume slightly in excess of the amount required to compen-sate for shrinkage as this material cures. For any given mold cavity, this amount may readily be determined by routine experimentation. I~ a test run indicates that the reservoir . is d~ained during the polymer forming reaction the inject v~lume .~s simply increased. It should be appreciated, how-~ ever, that there is no critical inject volume such as is re-quired for the manufacture of contact!.lenses by the process .disclosed in U.S. Patent No. 3,408,429.
:~ 30 It should be also noted that the process is not restricted : to those situations where lens material.flows only . -, : ' ..
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. ,:, . , ~7~0~6 from the reservoir into the mold cav:it~, ~ith re~ard to allyl diglycol carbonate, for instance( it should be noted that as this material is heated during the polymerizing or curing process it undergoes a temporary expansion. In this situation the reservoir serves as a catch basin to collect and hold the initially expelled material. Molds 11 and 111 may thus be used in molding lenses from suitable lens mater-ials that undergo permanent expansion upon curing. The exis-tence of a monomer which expands on polymerization is dis-closed in the article "Polymerization of a Spiro Ortho Car-bonate with Expansion in Volume" by W.J. Bailey and H. Katsuki,Polymer Preprints, ~merican Chemical Society, Volume 14 (2), pages 1169-1174, August, 1973. In this last situation the mold halves 13 and 15 must be held together by force suffic-ient to prevent them from separating but insufficient to seal the mold ca~ity from the reservoir. The presence of projections 131 on female member 115, insures that the ~orce necessary to prevent members 13 and 115 from separating will not seal reservoir 135 from mold cavity 133. In view of the foregoing it will also be evident that, as withthe case where the lens material shrinks upon cuxing, the amount of lens material deposited on surface 41 or 123 does not have to be exactly determined.
AFter the polymer forming reaction has been com-pleted male and female members (either 13 and 15 or 13 and 115) are separated from each other leaving a finished lens of the desired thickness and having convex and concave sur:~aces of the prescribed contour. As those skilled in the art will appreciate, the mold member to which the cured lens will adhere will depend upon the materials from which the mold s~ 18-''' - ' ~

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members are made. Thus, by fabricatin~ the ma}e and female mold members o~ materials which~ while both ~ettable, have different degrees of wettability, one can insure that the cured lens materlal will adhere to the desired mold half upon separation. ~urther, if both mold members are of the same material~ adherence to one mold member or the other can be assured hy mechanical means such as the configuration of mold members and~or by knurling selected surface areas of - one or the other mold members.
In the case where the lens as cast has the desired curvatures and finish and where such lens adheres to the female mold member, the flash which is formed by the polymer-izing of the lens makerial in the reservoir and/or restriction, may conveniently be removed by apparatus such as illustrated in U.S. Pak. No. 3,835,596. Since such apparatus is adapted to edge a lens while it is secured to a female mold member it is preferable that the flash also remain with, for instance, female member 115 rather than stick to male member 13. This may be further assured by, for example, knurling or roughen-ing surface 127 of female member 115.
~t will be evident to those skilled in the art that numerous changes may be made in the details of either lens mold 11 or lens mold 111. One such modification is illustrated in FIGURE 5. In this embodiment lens mold 211 includes female member 15 and male member 213. Male member 213 includes a~longi~udinal axis 215, surfaces 219, 221 and cavity 223 all of which are identical to, respectively, long-itudinal axis 19, surfaces 27, 29 and cavity 33 of male mem-ber 13. Male member 213 also includes surfaces 225 and 227 which are, respectively, of the same con~iguration as sur-;

faces 23 and 31. However, male member 213 differs from the --19-- :
,~., ~i~ il , ,, ,~, . : . : ' ~7~i6 previous embodiment in that lens mold suxface 231 includes a recessed portion 233 which form$ with tapered sur:Eace 235 and ed~e 237. With male half 213 assembled with ~emale half 15, surface 225 is received within surface 51, so in conjunction with an appropriately select:ed lens material, as to align axes 215 and 45 and form mold ca~ity 239 and reservoir 241. With cavity 239 filled and reservoir 241 loaded with the selected lens material, edge 237 is in op-posing relation to but separated fromedge 43 by a thin layer of lens material which is exaggerated for purposes of illustration. Operationally, mold 211 functions in the same manner as molds 11 and 111-. Edges 43 and 237 thus cooperate to define annular restriction 243.
FIGURES 6, 7 and 8 illustrate lens mold 311 formed of alternate female member 315 and male member 13. Alter-nately, female member 315 may be combined with male member 213. Female member 315 includes mold surface 317 which is illustrated as bein~ symmetrical with respect to the long-itudinal axis 319. Female member 315 also includes a sur-face 321 that is similar to surface 49 of female men~er 15.

Surface 321 extends from edge 323 outward to a series of surface segments 325 interconnected by projecting elements 327. Each projecting element 327 includes an inwardly facin~ surface 329 and lateral faces 331 all of which extend upward from surface 321 to top surface 333. Surfaces 329 lie in an imaginary cylindrical surface, indicated by broken line 335, that is symmetrical with respect to axis 319. Further, the distance between opposin~ surfaces 329 is dimensioned so as to (when female part 315 is assembled with, for instance, male part 13) snu~ly receive surface 23 and, consequently, ,~
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.' : . ' . ' ~ . : . ' ' ': ' .' align axes 319 and 19 to minimi~e prism in the lens to be cast. Finall~, in order to control the spacing between mold surfaces 17 and 317, the base of each projecting element 327 includes, as illustrated in FIGURES 6 and 7, an inwardly extending foot 337. Each foot 337 inclul~es a sur~ace 339 adapted to, in the case of male portion 13 and as illustrated in FIGURE 7, en~age surface 21 to thereby control lens thic~
ness.
In operation female portion 315 functions in the same manner as female portion 15. However, when assembled with, for instance~ male portion 13 a series of reservoirs (such as illustrated in cross-section in FIGURE 8) in the form of a segmented annulus, as opposed to a continuous reservoir, will surround and be open to the mold cavityu Each of these reservoirs is defined by a surface segment 325, opposing lateral faces 331, portions of surface 321 and portions of surface 23 of male member 13. A continuous annular restriction will interconnect the several r~servoirs with the mold cavity.
FIGURE 9 illustrates alternate mold assembly 411 formed of male member 413 and female member 15. Male mem-ber 413 is the same as the male member 13 insofar as it in-cludes surfaces 415 and 417 which correspond to surfaces 21 and 23 and which, in conjunction with the selected lens mat-erial, function to align axis 419 with axis 45 of female mold member 15 in the manner described in connec-tion wi-th the embodiments of FIGURES 1 and 2~ Male member 413 is also the same as male member 13 insofar as it includes surfaces 421 and 423 which correspond to surfaces 27 and 29. Male member 413 differs from mold half 13 in that it is provicled with k~
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concave mold surface 425 which, most convenientl~, is s~m-metrical ~i-th respect to axis 419. A modi~ed ca~ity 427 is also provided.
In operation r mola 411 functions in the same manner as mold 11. Opposing surfaces 49 and 415 cooperate to define restric~ion 429 which interconnects mold cavity 431 with reservoir 433. Thus, when used with allyl diglycol carbonate, such monomer will be drawn from reservoir 433 into mold ca~ity 431 (as the original volume therein shrinks during the polymer formin~ reaction) due to the vacuum ~ormed within mold cavity 431 and the pressure of the atmosphere exerted on the exposed monomer in reservoir 433. It will be appreci-ated that female member 315 may also be u-tilized w.ith male member 413 in place of member 15.
As those skilled in the art will appreciate, mach-inin~ may be utilized with the lenses cast using mold 11, 111, 211, 311, or 411 if it is desired to minimize the required inventory of, particularly, a series of female mold member~
each having a mold surface of different curvature. For this purpose, surfaces 27 and 29 are accurately referenced to axis 19 and mold surface 17. Similarly, surfaces 219 and 221 are accurately referenced to axis 215 and mold surface 231 and surfaces 421 and 423 are accurately referenced to axis 4I9 an~ surface 425. Thus, in thQse instances where the cured lens material adheres to the male mold member and lens mater-ial is to be mechanically remo~ed, surfaces 21, 29 or sur- -faces 219, 221 or surfaces 421, 423 ser~e as machine refer-ence surfaces to accura~ely position the lens during machin-in~. In the~case of production of symmetrical lenses such a system minimizes prism between the cast and the machi.ned sur~ace of the lens.

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The surfaces generating apparatus illustrated in FIGURE 10 includes a rotatable spindle ~.not illustrated) having a centerin~ ring 501 which snuggly receives surface : 27 within opening 503 so as to align axis 19 with the axis of rotation of the spindle. Further, mold surface 17 and lens 499 secured thereto are properly aligned in the axial direction by the abutting of surface 29 wi-th surface 505 of centerin~ ring 501. The surface generating machine also in- .
cludes a rotating cutter head 507 having a fly cutter 509.
As with standard generatingapparatus, head 507 rotates about axis 511 which intersects the axis of rotation of centering ring 501 (which coincides with axis 19) at the radius, desig-nated R, of the curve to be generated on the convex side of lens 499.
In view of the foregoing, it will he appreciated that, as used in this specification, the term "lens" includes lenses which are cast in the final desired shape (except for edging) as well as semi-finished lens blanks.
Finally, it should be noted that while the fore-; going embodiments illustrate molds designed for the produc-tion of symmetrical lenses those skilled in the art will ` appreciate that the disclosed process is e~ually suited to the production of aspherical surfaces and surfaces other than .. surfaces of revolution. Those skilled in the art will also ~. .
- appreciate that bifocal lenses can be produced by the inser-tion in the mold cavity of a suitable insert having an index of refraction different from that of the selected lens material or by forming the mold surfaces in the manner sug-gested by U~S. Patent No. 3,297,422, ..
Whereas the drawings and accompanying description '~

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have shown and described several preferred embodiments of the present invention, it should be apparent to those skilled in the art that various changes may be made in the form of the invention ~ithout affecting the scope thereof.

.j. ~24-. . .

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A lens mold comprising first and second cooperating mold members, said first mold member having a first mold surface, said second mold member having a second mold surface, said first and second mold surfaces cooperating to define a mold cavity, said first and second mold members including means for defining an annular reservoir/ said first and second mold members also including means for defining an annular restriction interconnecting said reservoir with said mold cavity, said first and second mold members further including means to axially and radially align said mold members to control both the thickness and prism of the lens to be cast, said aligning means being located on said first and second mold member between said reservoir and said mold cavity.

2. The lens mold as claimed in Claim 1, wherein said reservoir is open to the environment in which said mold is located.

3. The lens mold as set forth in Claim 1, wherein said reservoir is a continuous annulus.

4. The lens mold as set forth in Claim 1, wherein said reservoir is a segmented annulus.

5. The lens mold as set forth in Claim 1, wherein one of said first and second mold members includes machine referencing means, said machine referencing means being accurately referenced to the corresponding one of said first and second mold surfaces.

6. The lens mold as claimed in Claim 1, wherein said aligning means includes first axial spacing means on said first mold member, second axial spacing means on said second mold member, first radial alignment means on said first mold member and second radial alignment means on said second mold member, said first and second axial spacing means and said first and second radial alignment means being separated from each other by lens material to thereby define said annular restriction interconnecting said reservoir with said mold cavity.

7. The mold as set forth in Claim 6, wherein said reservoir is open to the environment in which said mold is located.

8. The lens mold as set forth in Claim 6, wherein one of said first and second mold members includes machine referencing means, said machine referencing means being accurately referenced to the corresponding one of said first and second mold surfaces.

9. The lens mold as claimed in Claim 1, wherein said second mold surface is in the form of a section of a sphere and said aligning means include upstanding projections provided on said first mold member and outwardly spaced from said first mold surface and symmetrical with respect to the longitudinal axis of said first mold member, said projections adapted to engage said second mold surface to control lens thickness and eliminate lens prism.

10. The lens mold as set forth in Claim 9, wherein said reservoir is open to the environment in which said mold is located.

11. The lens mold as set forth in Claim 9, wherein one of said first and second mold members includes machine referencing means, said machine referencing means being accurately referenced to the corresponding one of said first and second mold surfaces.

12. A method of forming a lens from a polymerizable material with a mold formed from first and second mold halves each having a mold surface, the method characterized by the steps of:
(a) orientating the second mold member so that the second mold surface will retain the polymerizable material;
(b) depositing the polymerizable material on the second mold surface;
(c) moving the first mold member into position relative to the second mold member to:
(i) form a mold cavity having a center section and an edge portion, (ii) fill the mold cavity with a portion of the polymerizable material;
(iii) form an annular restriction surrounding and connected to said mold cavity, (iv) radially and axially align the mold members with the aid of structure provided on the mold members and (v) load an annular reservoir connected to said mold cavity via said annular restriction with that portion of the polymerizable material which is in excess of the volume of the mold cavity and the restriction;
(d) polymerizing the polymerizable material in the mold cavity from the center section to the edge portion.

13. The method as set forth in Claim 12, characterized in:
(a) spacing first axial alignment means provided on the first mold member from second axial alignment means provided on the second mold member by a layer of the poly-merizable material to thereby axially position the first mold surface relative to the second mold surface, and (b) hydrostatically aligning a first longitudinal axis provided on the first mold member with a second longitudinal axis provided on the second mold member.

14. The method as set forth in either claim 12 or 13, characterized in:
(a) directing polymerization inducing radiation towards the mold cavity;
(b) shielding, via a suitable shield, the radiation from the edge portion of the mold cavity; and (c) removing the shield means to thereby permit the radiation to polymerize the polymerizable material in the edge portion of the mold cavity.

15. The method as set forth in either Claim 12 or 13, characterized in:
(a) disengaging the first and second mold members so as to leave the polymerized material of the desired shape adhering to the mold member on which is provided machine referencing means;
(b) providing a contouring apparatus including a cutting means and a rotating chuck provided with a centering means;
(c) engaging the machine referencing means with the centering means;
(d) rotating the chuck; and (e) engaging the cutting means with the polymerized material of the desired shape to remove selected portions thereof.