GB2219243A - Moulding different lenses having the same edge thickness - Google Patents

Abstract

For producing ophthalmic lenses, selections are made from pluralities of front surface molding dies (111) having concave optical forming surfaces (112) and rear surface molding dies (113) having convex optical forming surfaces (114). Selected molding dies (111, 113) are presented in confronting relationship in a lens molding assembly (as shown) with the concave optical forming surface (112) disposed at a first fixed distance (X) from a molding reference curve (122) and the convex optical forming surface (114) disposed at a second fixed distance (Y) from said molding reference curve, so that different lenses are moulded with different optical curvatures, but the same edge thickness. <IMAGE>

Description

METHOD AND APPARATUS FOR MOLDING AND CASTING USING GATED DIES HAVING

PARAMETRIC MOLDING SURFACES 2 Q 3 aMe270289 Z This invention relates to molding/casting methods at least applicablo to making ophthalmic lenses.

III die field of nianufacturhig of oplifliahnic lenses and the like, t1lele is a great aniount of interest in devising fabrication Processes that ale simple mid economical, and which produce quality lenses requiring little or iio finishing subsequent to manufacturing. Following these ciiteiia, developmental efforts have focused on casting and molding of lenses froin thermoplastic, theiniosetting plastic, and polynierizable fliatelials, due to the inheient economies of scale and die potential for reduced handling and 10 labor costs of such processes.

III casting and molding processes in general, fiont suilace and back surface dies aie used to inilmit to the plastic material the optical sullaces appropriate for the desired oplithahnic cutreclion. Ili casting piocesses in gencial, the dies aie secuted together by a gasket or the like at I desiled spacing, and a liquid casting material is intioduced in the casting cavity defined thereby, and allowed to cuie and harden into a lens. A critical factor is the gasket, and that a large plurality of gaskets aie required to accommodate wid seal with the large plurality of diffeiing optical surfaces of the various dies-while also defining the desired die spacing (aild lelis t1fickness). 'llius a large capital investment is requiied in gaskets and gasket tooling, as well as in the optical surface foiniing dies used in die casting process.

Ill niolding processes ill general, nioie rugged dies ale employed to conipiess a nioldable material ill a closed niolding cavity, inipiessing tile optical sutface configurations oil the material as the iiialciial is haidened 1 iMe270289 1 by diennal or chemical means. Generally speaking, an excess of 111olding material must be intioduced into die cavity to allow for coinpiessive, die movement, and ineans must be provided to vent. die excess material from the cavity and accommodate die sprues formed tlieieby. Also, as in the casting process, the dies must be urged together to die appropriate spacing to create the desired lens thickness. The ainount of molding inatefial, the venting of excess material, and the final thickness of the lens are hiteirelated factors that require precise process contiol to produce lenses of high quality for oplidiahnie use.

It is evident that a critical factor in the molding of lenses is the molding members themselves. Geneially, a large plurality of fiont surface and rear surface molds must be provided, each having a uni(lue optical surface-forming characteristic. To fill a particular ophthalmic piesciiptiun, appiolmiate fiont surface and rear surface moldillg inembels are chosexi, an optimal lens thickness is calculated for the two selected molds, and a gasket or die like is eitlier selected or labiicated to secure the molds togedier to deline the molding cavity. 'llie cavity is flien filled widi lens compound, cured or polymerized by heat, radiation, or chemical action, and die finished lens is iemoved from die assembly.

The process outlined above requires a very large number of front and rear surface molds, in order to fill the hundreds of thousands of ophthalmic prescriptions commonly required. Furthennoie, a large number of gaskets are required for this process, due to the fact that [lie gaskets must fOrm a seal widi the variously curved edge conliguiations of the inold members, and that the dfickness of die lenses must be detennined 9 JMe270289 by the spacing of mold members created by the gaskets. In this regard, die niold spacing is generally measured between the confronting optical forining surfaces of the mold members. It is vital that die mold spacing be greater than a predeternihied mininiuni, both to produce a lells of sufficient thickness and strength, and to prevent mold crashing and mutual destruction.

The large number of mold members and gaskets that must be inventoried to carry out the process described above represents a considerable capital investment which is difficult to recoup through commercial sales. Therefore it has been necessary in the prior art to simplify the process by reducing the number of components inventoried. The most straightforward siniplification is to niold lenses having the desired front surface and a stock rear surface (or vice-versa) that can be ground to die desired finislied lens by a dispensing optical laboratory or die like. This tactic introduces a post-nianufacturing labor expense, and requires trained personnel for high quality lenses. Furtheiniore, it is not all improvement in the prior art molding technology, but rather all expedient shortcut to make the technology commercially viable. There is an obvious need in-the prior art for a molding niediodology that reduces the number of molding components while providing the capability of filling the large number of common oplidialinic prescriptions.

1 JMe270289 Suininary of die Present Invention j I'lle present invention generally concerns: a niethod and apparatus for molding or casting oplithalinic lerises or die like. Salient features of its aspects are the provision of simplified process and apparatus that autoniatically determines the proper aniount of casting or molding compound remaining in the finislied lens, and further determines the spacing of the molding or casting dies and thus the thickness of the finished lens.

In one embodiment, a plurality of front surface and back surface dies have differing optical forming surfaces and identical peripheral edge configurations. in a compression molding process, any pair of front surface and back surface dies are received iii sliding, sealing fashion in die bore of die molding apparatus. At least one of the pair of dies is piovided with at least one gate channel formed in a peripheral edge, usually parallel to the axis of the bore, and extending from the optical forming surface to a point adjacent to die opposite, external die surface. The gate channel comprises a vent through which excess molding compound is discharged from die molding cavity as die dies are urged together. As tile gated die is fully inserted iii the bore, the gate channel opening to the exterior is sealed by the bore surface, thus tenninating the discharge effect and retaining a predeten-nined aniourit of inolding material in die molding cavity. The niolding material is then solidified by thermal or chemical reaclion to forin the finished lens. Ilius there is provided intrinsic t iMe270289 1 control of the thickness of the molded part, while also providing positive venting of excess niolding material.

hi one casting process, the dies are partially inserted in the bore f or casting, in sliding, sealing fashion, and die gate chamiel serves as an hijection channel to introduce the casting compound into die casthig cavity. 'llic dies are urged together in the bore, the gate channel first serving to vent excess casting compound and gas froin the casting cavity. Full die insertion in die bore causes the gate cliamiel opening to the exterior to be scaled by the bore wall, thus terminating die discharge effect and retaining -10 a predetermined amount of casting material in the casting cavity. Mie material is then cured or hardened by fliernial or chemical reaction to forin the finished lens. I'lius there is then provided intrinsic control of the thickness of die cast part, while also pennitting easy filling of die casting cavity and venting of excess material and gas from die vent cavity.

Another aspect concerns or includes a method for designing the molding components, and particularly lens molding components. A salient feature Of this aspect is that it reduces the number of molding dies, compared to prior art niolding technology, required to produce tile saine variety of oplitlialinic lenses. Furdiennore, in niolding processes requiring gaskets or the like to secure two niolding members together to form a molding cavity, die number and variety of gaskets required is reduced to a very great extent.

one method for designing a niolding apparatus, especially for molding lenses and die like, comprises defining a nominal inold reference curve disposed between a pair of niold members having smooth, curved iMe270289 j surfaces in confronting relationship to define a inold cavity therebetween.

It is possible to define a single value of reference curvature such that all lenses widiiii a typical design family are bisected by this iniaginary surface widiout interference; that is so that for all plus lerises, front curve ':2t reference curve;-> back curve, and for all minus lenses, back curve! reference curve k front curve.

This phenomenon is a result of the optical and physical uniformity of hunian eye and facial features, and lias been discussed in the prior art.

A plurality of concave and convex niolding iiieiiibes are provided, all haviiig differing niolding surface curvatures but identical spacing froin the respective curved surface to the nonihial reference curve, measured from the point of closest approach of the curved surface to the reference curve. (That is, between the cemer of a negative lens and the reference curve, or between die edge of a positive lens and the refere.pce curve.) Any paired concave and convex nioldhig surfaces have the saine spacing from the reference curve and thus from each other, so Lliat, for example, a universal gasket can be employed to hold any two paired convex and concavp niolding members in precise spachig, without regard to the curvature of the niolditig surfaces. llius any lens formed by the inetliod under consideration comprises two indivisable portions: a front portion extending from the reference curve to the front surface, and a rear portion extending from the reference surface to the rear surface.

i JMe270289 - 7 Specific implementation of aspects of this invention will now be described, by way of example with reference to the accompanying drawings, in which:

Figure 1 is an exploded view of one lens inolding embodiment of the 5 present invention; Figure 2 is a plan view of a lens molding die of that embodiment of the present hivention; 1 Figure 3 is an enlarged, fragmentary side elevation of the lelis inolding die of Figure 2, showing the gate cliamiel fornied in the peripheral edge thereof; Figures 4-6 are sequential cross -sectional elevation views showing a lens niolding process of die present hivention; Figures 7-9 are sequential cross-sectional elevation views showing a lens casting process of die present invention; Figure 10 is a perspective view of a lens formed in such a manner, showing die sprue created by the gate channel prior to removal thereof.

Figure 11 is a cross -sectional elevation of a lens niolding assembly arranged according to a parametric inold design nietliod of the present JMe270289 - 8 invention and employing a gasket sleeve to join the molding members ill a casting assembly; and Figure 12 is a cross -sectional elevation of a lens molding assembly arranged according to a parametric mold design inethod of present invention and employing compression molding components to forin a lens.

m j JMe270289 Description of the Preferred Einbodinients

1 This description generally concerns methods and apparatus for the fabrication of oplitliahnic lenses and [lie like using niolding and casting techniques. With regard to Figures 1-3, the apparatus for implementing one nioldhig process embodiment of the invention includes a cylindrical niernber 11 having a cylindrical bore 12 extending axially therethrougli. A front surface die 13 and a rear surface die 14 are also provided, each having respective optical forniing surfaces configured to forni a complementary optical surface and thus define the optical properties of the lens to be produced. As is known in die prior art, a large plurality of dies 13 and 14 are provided, each having unique optical forming surfaces, so as to be able to manufacture a variety of ophthalmic lenses covering the range of coninion corrective prescriptions.

A coninion feature of all the front and rear surface dies is that tile peripheral edges 16 and 17 thereof are diniensioned and configured to be slidably received in the bore 12 and to fonn a close tolerance, sealing engagement dierewith.

A salient feature of systems hereof is the provision of at least 20 one gate channel 18 in a peripheral edge portion of at least one of die dies 13 or 14. In die embodiment of Figures 1-3, a pair of gate channels 18 ate forined in the edge portion 16 of the front surface die 13. (Either die lilay be provided with gate channels, and the nuniber of gate channels is not a critical factor.) The gate channels are oriented parallel to the axis of the cylindrical peripheral edge 16, and are disposed in diametrically opposed 1% iMe270289 fashion. 'I'lie gate chamiels 18 are narrow, each subtending an angle of a few degrees about the cylindrical axis of the die. Each channel intersects the optical fonning surface at one end, and extends to a point adjacent to the opposed, outer die surface 21, as shown best in Figure 3. The end of the channel and die adjacent outer die surface 21 define therebetween an interniediate lip 19.

Ilie apparatus of Figures 1-3 is employed in a lens niolditig method depicted graphically in sequential Figures 4-6. As shown in Figure 4, a front surface die 13 and a back surface die 14 are placed in confronting -10 opposition in the bore 12 of the cylindrical member 11, to define a closed lens molding cavity. A charge of lens molding inaterial 22 is disposed in the molding cavity between the dies. The lens nioldhig matclial may be injected into the nioldhig cavity, as disclosed in copendh)g United States Patent Application Serial No.-, filed on by David Spector and Jeff Kingsbury. Alternatively, the niolditig material may be loaded into the cavity after one of the dies is in place in die boic and before the odier die is secured in the bore. In eidier case, it is generally the case to use an amount of molding material in excess of die niatefial that forms die finislied lens, so that subsequent compression of the dies is effective to impress die optical forming surfaces into the material aild form die desired molded optical surfaces.

After die components and molding material are assembled as shown in Figure 4, the dies 13 and 14 are urged together in compressive actimi, applying substantial pressure to the niolding material 22. The nioldhig material flows under this pressure and assunies the conformation of the JMe270289 optical forming surfaces, and also flows out of the gate channels 18, as shown fil Figure 5. 'I'lie gate channels 18 act as vents to discharge excess molding material 22, the displacement of the molding material from the cavity also pernfitting die dies to move further into the bore and closer together and approximate the spacing of the desired thickness of the finished lens. As die die 13 in particular is driven into the bore a sufficient distance so that die outer surface 21 diereof approaches die end of the bore, the lip 19 of each channel 18 enters the bore 12. At this point of die insertion the external openings of die channels 18 are sealed by the wall of -10 the bore 12, and no further discharge from the gate channels can occur.

Further conipressive force applied to die dies cannot move [lie dies closer togedier, and serves only to apply greater pressure to the niolding material.

After the niolding material solidifies (e.g., by cooling below the glass transition temperature, by catalysis, or the like) the dies aie removed froill die bore, and die finished lens is,4ripped from the dies.

It should be noted that the depth of insertion of the die 13 is controlled by die length of the gate channels 18, and that the depth of die insertion determines the thickness of the finished lens. Furthermore, tile depth of die insertion can be independent of the initial amount of molding material placed in the molding cavity, since excess illatelial is displaced from the cavity. Thus die apparatus provides a process that is self-regulating, producing finished lenses of uniform thickness without requiring precise control of the initial amount of niolding material.

The process described above is suitable for niolding thermoplastic materials such as polycarbonate, or thermosetting plastic, or oilier k JMe270289 12 - materials that can be cured or hardened by pressure, temperature, or chemical reaction while in the molding cavity.

With slight modification a system hereof may be employed to cast oplitlial-inic lenses using casting compounds kliown in the prior art, such as CR39 and its equivalents. Widi rgard to Figures 7-9, front surface die 13 and rear surface die 14 are provided and fashioned as before, including the gate channels 18 fornied in the periplieral edge portion of at least one of the dies. I'lie dies are received in the cylindrical bore 34 of a cylindrical, tubular sleeve 33, and forin a slidable, sealing engagement with die bore wall. The sleeve 33 is shown with a thinner sidewall than the cylindrical member 11, due to the fact that very little pressure is employed in die casting process.

Initially, the dies 13 and 14 are inserted partially into the bore 34, the gate cliannels 18 extending outwardly of the boic 34. - The gate cliainiels may be used as all input port to load a charge of viscous, liquid casting inaterial 32 into die casting cavity defined by die dies and the bore wall, as shown in Figure 7. After a sufficient aniount of casting material is placed in the cavity, the dies are urged further into the bore 34 and hito closer spacing, using a low level of force applied to die dies. 11iis action shrinks the casting cavity, first forcing unwanted air or other gases out of the cavity, and then forcing excess casting material to discharge through die gate channels 18, as shown in Figure 8.

As the dies are moved into full insertion in the bore 34, tile gate channels 18 are sealed by the wall of the bore 34, as explained in tile previous embodiment. Thereafter no more casting material call be 1 JN1e270289 discharged froin die casting cavity, as shown in Figure 9, and die thickness of the lens to be formed is detennined by die amount of casting material remaining in the casting cavity. Low force (from a spring device or the like, as is known in the prior art) is dien applied to die dies to maintain die dies converging on die casting material as the material undergoes curing and solidi f Ication, due to dierinal andjor chemical reaction. After die lens is completely formed, the dies are removed from the sleeve 33 and die finished letis is stripped from die dies.

As noted with regard to the previous embodiment, the depth of insertion of the die 13 is controlled by the length of the gate charuiels 18, and die deptli of die insertion detennines die tlfickness of die finished lells. Furthermore, the depth of die insertion can be independent of the initial amount of casting material placed in the casting cavity, since excess material is displaced from the cavity. Thus the appaiatus provides a process that is self-regulating, producing finished lenses of uniform thickness widiout requiring precise control of die initial amount of casting material.

The lens 36 formed by either the casting process or [lie niolding process described above appears as shown in Figure 10. A plurality of sprues 37 extend from the peripheral edge portion of the lens, olle sprue for each of the gate channels provided in the dies. The sprues 37 are narrow and weak, and may easily be removed from the lens by cutting, or manually by snapping diern off at die base thereof. Vie sprues may also form a convenient Iiandle" to facilitate manual or machine transfer and handling of die finished lens. Due to the fact that all oplidialinic lenses are JMe270289 edged to fit into spectacle franies, the sprues 37 are cut away froill die finished spectacle lens, and hi no way interfere widi the fiiial lens product.

The present teaching further includes a niethod for designim, molding components, and particularly lens molding components. The niediod is directed toward a lens molding system that is capable of filling a large portion of the most coninion oplitliahnic prescriptions, using a plurality of molding dies far less numerous than any prior art lens nioldhig tecluiique.

With regard to Figure 11, the shown system provides a plurality of front surface nioldhig dies, represented by the inulding die I I I havilig a concave optical niolding surface 112, and a plurality of rear surface molding dies, represented by the nioldhig die 113 liavii)g a convex optical niolding surface 114. I'lie molding surfaces 112 and 114 may be fornied by giindhig wid polishh)g a glass or nietal material, or by electiodeposition oil previously fornied optical surfaces, both techniques behig well known in the prior art. In the embodiment of Figure 11, both dies ate generally cylindrical, with the axes of the cylinders generally passhig through the central portions of the respective molding surfaces. The die I I I is provided with a flalige 116 extending radially outwardly fioni the die arid spaced axially from the surface 112, and the die 113 is piovided with a flange 117, also exteiiding radially outwardly from [lie die and spaced axially from the surface 114. The flaiiges 116 aiid 117 are provided with annular surfaces 118 and 119, respectively, [flat are disposed in confrontitig, spaced apart relationship.

iMe270289 llic invention also includes a gasket or sleeve 121 adapted to join together the two dies in a casting assembly. The sleeve is generally. cylindrical in configuration, widi a diameter sufficient to forin a sealing engagement about die peripheral surfaces of both dies, with the ends of die sleeve 121 in abutting relationship with the flanges 116 and 117. ne length of the sleeve between the two flanges 116 and 117 is generally constant and die sarne for any combination of dies 111 and 113.

An advantageous provision hereof is the establishment of a reference curve 122 disposed between die niolding surfaces 112 and 114.

The reference curve represents the nominal plano curve of the lelises produced by this niediod; i.e., a plano lens has both front and rear surfaces extending parallel to the reference curve. The reference curve 122 is also used to establish die proper spacing of the dies and of die niolding surfaces 112 and 114. Throughout the plurality of dies 111 and 113, the spacing of (lie surface 112 and the reference curve 122 is fixed and identical, and the spacing of the surface 114 and the reference curve 122 is likewise fixed and identical. The spacing between the surfaces 112 or 114 and the ieference curve is measured froni the point of closest approach of die niolding surface to _the reference curve. 11fis factor detennines that eidier the center of a negative lens, or the edge of a positive lens niolded according to die present invention will have a fixed thickness, throughout the range of ophthalmic prescriptions. - It is significant to note that the flange 116 is disposed -at a predetermined axial distance froin the surface 112, and the flange 117 is likewise disposed at a predetermined axial distance froni the surface 114.

JMe270289 Thus the distance X between the flange surface 118 and the reference curve, and the distance Y froin the flange surface 119 and the reference curve is fixed in die casting assembly by die sleeve, regardless of die dies selected to forin a particular lens.

To employ the system as described in Figure 11, dies 111 and 113 are selected in accordance with die ophtliahnic prescription to be filled, and a sleeve 121 is selected with a length that assures that the optical forniing surfaces 112 and 114 are spaced apart froin the reference curve by the predeteniiined, fixed distance. Lens casting compound is then introduced into the cavity defined between die niolding surfaces and die sleeve interior surface, by injection or the like, and the compound is cured or polynierized to forin the finished lens. The sleeve is then removed, and the lens is stripped froin die dies. Ilie dies inay then be cleined and stoied for reuse.

A further enibudinient of the present invention, depicted in Figure 12, is adapted to forni lenses by compression niolding, using principles as elucidated in the embodiment of Figure 11. A pair of inolding dies 111' and 113' are provided with optical forming surfaces 112' and 114', as described previously. In this embodiment, the dies are provided with smooth peripheral -walls, and are dimensioned to be slidably received within the bore 132 of a cylindrical sleeve 131. As before, the inolding surfaces 112' and 114' are positioned at a fixed, constant distance froin a reference curve 12F.]lie die 111' is secured to a piston 133 aligned coaxially with the sleeve 131, and die die 113' is secured to a coaxial piston - 134. A pair of piston stops 136 and 137 are also provided to limit die travel of the respective pistons 133 and 134 toward the reference curve 1 JMe270289 121' to dismices X wid Y'. lbe distaiices X' and Y' are calculated so that the molding surfaces 112' mid 114' can be moved curve by their respective pistons toward the reference curve only as close as die spachig limit from the reference curve.

hi the embodiment of Figure 12, a pair of dies 114' and 113' are selected in accordance widi the oplidiahnic prescription to be filled, and the dies are assembled to their respective pistons. A charge of lens-formirig inaterial is introduced into the bore 132 between the dies, and the dies are moved together by the pistons to compress the lens forming material and 10niold it into the shape detennined by the surfaces 112' and 114'. Ilie material is then solidified by curhig, polymerization, cooling, or the like, depending oil the coinposition and properties of the material. The pistolis are flien retracted, and die finislie-d lens is stripped from die dies. 'I'lie dies may dien be removed, cleaned, and stored for future use.

In. the method depicted in Figure 12, the lens forinhig material may be injected into the cavity widiin the cylinder, witli the dies inserted to die limit detennitied by the stops 136 and 137, as in prior art injection molding tecluiiques. Likewise, a hybrid lens foriiihig tecluiique eniployhig injection of die material followed by compression of die dies may also be practiced widiin die scope of die teaching hereof.

It may be appreciated that die gated die concept is well suited for controlling the depth of insertion of a die in a bore, as explained previously, and gated dies are a favored nicans of establislihig tile predetermined distances from die molditig surfaces to the reference curve.

one system includes conibinhig die concepts of providing a plurality of iMe270289 gated dies having a family of parametric molding surfaces in a lens fabricating apparatus.

Ilie mediod described with regard to Figures 11 and 12, termed the parametric niold design, not only produces lenses of uniform diickness, it also minimizes the number of dies required to produce a full range of multifocal lenses, either stock lenses (without cylinder power) or finished lenses with cylinder power. For example, die following table illustrates a comparison of the parametric design method with a typical prior art lens molding system for producing 75 nini CR39 stock lenses in a range of base powers froin -4.0013 to +4.OOD. Add powers are in 0.25 diopter increments to +3.OOD, and cylinder powers are in 0.25 diopter increments to -2.OOD.

NuNiBL:i 01; PARTS REQUIRED Single Vision Multifocal Mullifucal widiout cylinder widi cylinder Parametric fronts 5 65 65 Parametric backs 153 17 153 TOTAL 158 82 218 CR39 fronts 33 429 429 CR39 backs 63 7 63 TOTAL 96 436 492 1 JMe270289 1 The parametric mold design method thus requires 458 mold dies to produce the full range of lenses, while the prior art method requires 1024 dies. Thus it is apparent that the present teaching obtains substantial savings, not only in the high capital costs associated withprocuring molding dies, but also in maintaining a large inventory of dies. Furthermore,the present teaching prevents clashing of the dies in the molding process, an event that occurs occasionally in prior art molding systems and results in destruction of the dies.

It will be appreciated that achieving a prescribed final mold volume in the Figures 4 to 6 and 7 to 9 embodiments requires full movement of the dies 14. before the gate channels of the dies 13 seal in the bores of members 11,33. That may be achieved by abutments between the dies 14 and the members 11 or 33, or by other movement limitation, such as stroke limit of mechanical pressure applying means for those dies, or sealing of gate channels in the die parts 14 before those of the die parts 13. For prescribed final volumes, relative to particular ones of a choice of available members 11 or 33 and/or the dies 13 and/or 14 themselves and/or lengths of gate channels 18 thereof,, a reference curve effect will arise automatically whether -----or not relative to mechanical abutment and thus of 1 JMe270289 --20 necessarily fixed physical location.

It will also be appreciated that discharge of excess molding material can be provided in the Figure 11 embodiment by gate channel formations in the dies 111 and/or 113 extending to or adjacent to the flanges 116,118 and/or 117,119, and that sealing of the gate channels would then arise at or adjacent to the flanges. For the Figure 12 embodiment, discharge gate channels that stopped short of the outer edge of the die 111' or 113' could cooperate with channels in and ending a: prescribed positions on the parts 121 to seal where ends of the former met ends of the latter.

c JMe05O689 - 21

Claims (18)

1 - A mediod for producing oplithalinic lenses, comprishig the steps of providing a first plurality of front surface molding dies having concave optical forming surfaces, providing a second plurality of rear surface molding dies having convex optical forming surfaces, selecting a front surface molding die and a rear surface molding die from said pluralities of dies, defining a molding reference curve, joining said selected molding dies in confronting relationship in a molding assembly widi said concave optical forming surface disposed at a first fixed distance from said molding reference curve and said convex optical fonning surface disposed at a second fixed distance from said molding reference curve, and thereafter niolding a lens between said dies.

jr.l(' (1 ',0 0 8 0 22 -

2. The inetliod of clahn 1, wherein said first fixed distance froin said refejence curve and said second fixed distance froin said iel'eieiice curve are both constants for any of said first and second plurality of dies.

3. The inetliod of claiin 1 or claim 2, wherein said reference curve is disposed between said confronting dies.

4. The inediod of clairn 1, 2 or 3, further including providing a sleeve for joining said selected dies together in a lens casting assembly, said sleeve maintaining said first and second fixed distances of said dies from said reference curve.

5. The inediod of claiiii I, 2 or 3, further including providing a bore for receiving said selected dies in slidably translating fashion therein in a compression molding assembly

6. A inetliod for produchig oplithahnic lenses, comprising the steps of providing a first plurality of front surface inolding dies having concave optical forming susfaces, providing a second plurality of rear surface inolding dies having convex optical forming suifaces, selecting a front surface inolding die and a rear surface inolding die from said plulalitics of dies, defining a inolding reference curve, joining said selected niolding dies in confionting relationship in a niolding assembly widi said concave optical forining surface disposed at a first fixed distance from said niolding 0 JMe050689 23 telbience curve and said convex optical fonning surface disposed at a second fixed distance floin said moldhig rel'erence curve, at least one of said selected molding dies having a peripheral edge surface and an opposed, outer die surface, providing at least one gate charutel ki said peripheral edge surface, said gate channel extending from an intersection widi the respective optical foinfing surface to a point adjacent to said outer die surface, pioviding a boie to receive said selected molding dies in said molding assembly, inseiting said dies paitially into said bore in confronting iclationship with a charge of flowable molding material disposed thetebetween, said article forming surface impinging on said molding material, urging said dies together to compress said charge of molding material and to cause said molding material to flow and assume the configuration of said article forming surface, the compression of said molding material also causing excess molding material to flow dirough and discharge from said gate channel, inserting said one of said dies fully into said bore to seal said gate channel and tenninate discharge from said gate channel, and solidifying said molding material to fonn a finished article.

iMeO5O689

7 - A method for producing molded articles, comprising the steps of:

providing a bore in a molding apparatus, providing a pair of molding dies, said molding dies being received in said bore in sliding, sealing engagement, at least one of said dies having an article forming surface, an opposed, outer die surface, and a peripheral edge surface disposed to inipinge on said bore in slidable, sealing fashion, providhig at least one gate channel in said peripheral edge surface, said gate channel extending froin an intersection with said article forniffig surface to a point adjacent to said outer die surface, inserthig said dies partially into said bore in confronting relationship with a charge of flowable inolditig material disposed therebetween, said article fonning surface iniphiging on said molding material, urging said dies together to compress said charge of molding material and to cause said nioldfilg material to flow and assume the configuration of said article forming surface, the compression of said moldhig material also causing excess molding material to flow dirough and discharge from said gate channel, inserting said one of said dies fully into said bore to seal said gate charuiel. and terminate discharge from said gate channel, and solidifying said molding material to form a finished article.

8. The inethod for producing molded articles of claim 7, further including the step of providitig a pair of gate chatmels in said oiie die.

iMeO5O689

9. The inethod for producing niolded articles of clailli 7, or claim 8, wherein said article comprises an optical lens, and said article forming surface of said one die includes an optical forming surface.

10. The nietliod for producing niolded articles of any preceding claim, wherein said at least one gate channel extends generally parallel to the axis of said bore.

11. An apparatus for producing niolded articles, hicluding: a bore fornied in a niolding apparatus, a pair of niolding dies insertable in said bore in sliding, sealing engagement, at least one of said dies having aii article forming surface, an opposed, outer die surface, and a peripheral edge surface disposed to inipinge on said bore in slidable, scaling fashion, at least one gate channel in said peripheral edge surface, said gate climulel having an huier end intersecting with said article forming surface and extending to an outer end adjacent to but not intersecting with said outer die surface, means for urging said dies together in said bore to compress a niolding material therebetween and to discharge excess niolding material dirough said at least one gate channel.

12. The apparatus of claini 11, wherein said at least one gate channel extends generally parallel to the axis of said bore.

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13. A method for producing cast articles, comprising the steps of.

providing a bore in a casting apparatus, providing a pair of casting dies, said casting dies being received in said bore in sliding, scaling engagement, at least one of said dies having an article forming surface, an opposed, outer die surface, and a peripheral edge surface disposed to impinge on said bore in slidable, scaling fashion, providing at least one gate chaiinel in said peripheral edge surface, said gate channel extending froin an intersection with said article forming surface to a point adjacent to said outer die surface, inserting said dies partially into said bore in confronting relationship to define a casting cavity therebetween, injecting a charge of flowable casting matefial through said gale channel into said casting cavity, urging said dies togedier to compress said charge of casting material and to cause said casting material to flow and assume die configuration of said article forming surface, the compression of said casting material also causing excess casting material and gas to flow through and discharge from said gate clian.nel, inserting said one of said dies fully into said bore to seal said gate channel and terminate discharge from said gate channel, and solidifying said casting material to forni a finished article:

14. An apparatus for producing cast articles, including:

1.

z JMe050689 a bore fonned in a casting apparatus, a pair of casting dies insertable in said bore in sliding, sealing engagement, at least one of said dies having an article forming surface, an opposed, outer die surface, and a peripheral edge surface disposed to impinge on said bore hi slidable, sealing fashion, at least one gate channel in said peripheral edge surface, said gate channel having an inner end intersecting with said article forming surface and extending to an outer end adjacent to but not intersecting with said outer die surface, means for urging said dies together hi said bore to compress a casting material therebetween and to discharge excess molding casting through said at least one gate channel.

15. A method for producing ophthalmic lenses substantially as herein described with reference to Figures 4 to 6 or Figures 7 to 9 or Figure 11 or Figure 12 of the accompanying drawings.

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16. Apparatus for producing ophthalmic lenses arranged and adapted to operate substantially as herein described with reference to and as shown in Figures 1 to 3 or Figures 4 to 6 or Figures 7 to 9 or Figure 11 or Figure 12 of the accompanying drawings.

17. An ophthalmic lens as made by the method of any one of claims 1 to 4 or 7 or 9 to 15.

18. An ophthalmic lens substantially as herein described with reference to and as shown in Figure 10 of the accompanying drawings.

1 Published 1989 at The Patent Office, State House, 66f7l High Holborn, London WCIR 4TP. Further copies may be obtained from The Patent OfficeSales Branch, St Mary Cray, Orptn4gton, Kent BR5 3RD. Printed by Multiplex techniques ltd, St Mary Cray, Kent, Coil. 1/87 1 n.

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