3~8 D ~ D P 2~RZ~TUS F(~ Y~I~G ~L,P I C LE~SE S
3.~C ~ ?OU~T~ ~F T ~ V:~TO`Y-th Invention:
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Tnis inven~ion relates to the manu~acture of P1GS tic lenses wi~n particular reference to method and apparatus for ac-comp7 ishing volume produc~ion o cast and cured resin lenses.
Discu~ssion of the Prior Art: -.
Plastic ophthalmic lenses are traditionally individually cast be~wsen circumferentially gaslceted mold halves, at least one of which is painstakingly ground and polished to the final shape and rinish required of a side Or a lens tO be cast.
Ln addition to the inherent high cost o~ producing such mold halves, their inventorying and maintenance, the tediousness o~ asse~bly with ~asketing and separat:e filling and curing for lens casting renders end product cost far from optimum.
U.S. Patonts l~os. 2,964,501; 3,321,333; 3,902,693; and 1~ 3,9~S,9i32 are exemplary of single lens gas:~e'Led casting systems and U.S. I~atents ~ios. 3,~06,079; 3,371,610; and 3,871,803 exe;nplify prior art schemes for higher volume rnultiple casting.
The latter, however, have similar disadvantages of hich ecuip-ment cost, mai~te:lGnce and ex~ensive invenlorying wit~ minim 1,
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if any, applicableness to au-tomation~
It is, accordingly, a princ:ipl.e object of -this in-vention to overcome -the aforesai.d and corollary drawbac~s Gf prior art plastic lens manufacturin~ techniques, i.e. to pro-vide for high quality volume production with low investment in capital equipment.
Other objects and advantages of the invention will become apparent from the following description.
SUM~lARY OF T~IE INVENTION
~bjectives of this invention are accomplished by the provision of d.isposable molding strips debossed to form lens casting cups of required diametral size, depth and surface shape. The cups are filled with a casting resin precursor, covered and subjected to resin curing temperatures, e.g. in heated water, air or other heat transfer fluids. Final lens surface shapes are machine generated through the molding strip into the cupped and cured (polymerized) resin which is there-after conventionally optically polished. Material of the molding strip man be retained and used to avoid lens blocking in polishing or final surfacing operations and thereafter dissolved, peeled or otherwise removed from the cured lens.
In summary of the above, therefore, the present inven-tion is seen as providing a method of making plastic lenses comprising the steps of: debossing a multipl.icity of cast cups into a main body strip of mold material, the cups being of diametral sizes, depths and contours subs-tantially corres-ponding to those required of lenses to be cas-t; debossing a second strip of mold material for partial entrance into each of the casting cups as sealing means therefore; placing a casting resin precursor in each of the cups;
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covering the CUpS wi.th debossings of the secorlcl strip -to form with corresponding main body and second strip debossi.ngs a series of closed casting cells; exposing -the closed cast-ing cells to a heat transEer fluid of temperature and fo:r a period of time selected to cure the casting resin in each thereby producing a rigid lens; and m~chining each lens through at least one side of each of the cells to a predetermined sur-face curvature and thereafter polishing sets surface curvature.
The above method may be carried out by utilizing a lens casting mold comprising: a mulitply debossed main body strip of mold material, the debossings being of diametral sizes, depths and contours substantially corresponding to those ~equired of lenses to be cast; a second strip of mold material comprising a cover for the debossings of the main body strip, the cover having multiple debossings geometrically arranged and peripherally shaped to each fit.snugly partially into and seal a one of the debossings of the main body strip when positioned thereover; the main body strip and cover being adaptable to continuous process lens casting technology and both economically disposable after single use.
The foregoing procedure is readily adaptable to con-tinuous process technology, it eliminates mold inventories and pg/~ - 3A -L35~L~
affords the opportunity to machine precise ]ens surface curv-atures thereby relieving the cast lens procluct o~ mold sur~ace i~npurities, dye streaking and/or other such blemishing.
Details of the invention will become more readily ap-parent from the followlng description when ta~en in conjunction with the accompanying drawings.
_ THE DRAWIN~S
Fig. 1 is an illustration, in perspective, of a pre-ferred form of lens casting mold having it~ main body section and cover separated for clarity of illustration;
Fig.2 illustrates use of the lens casting mold ac-cording to the invention;
Figs. 3 and 4 are diagramic illustrations of lens surfacing operations which may be performed subsequent to lens casting and curing with the mold of Figs. 1 and 2; and Figs. 5 and 6 diagramitically illustrate additional lens surfacing operations which may be performed upon the cast lenses.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to the drawings, lens casting mold 10 com-prises main body section 12 and cover 14 each in the form of a debossed strip of sheet plastic or metal. Section 12 is provided nam/ -4-.~
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3~8 with casting cups 16 eacll llaving a diametral size, depth and curvature of bottom 18 ~hich corresponds to the shape and size desired of lenses to be cast according to the invention. Debos-sed portions 20 of cover 14 are so contoured as to enter snuggly into corresponding casting cups 16 when mold 10 is closed as illustrated in Fig. 2 thus sealing out air which would be a det-riment to the curing of casting material placed in cups 16.
It is to be understood that mold 10 may be of any length deemed appropriate for a "continuous" lens casting opera-tion or used in relatively short sections each having two, four,six or other numbers of casting cups 16. Mold section 12 and cover 14 may be formed of a polyamide such as nylon or a polyes-ter or other synthetic resin having similar characteristics, e.g. a commercially available synthetic resin sold under the trademard Trogamid. Sheet metals such as aluminum and alloys thereof or other metallic compositions having similar character-istics may be used. It will become apparent hereinafter that, according to at least one aspect of the invention where lens surfaces are machine finished, superficial contamination of the cast lens pleces by mold materials is not of concern.
The term "lens" as it is used herein is intended to include any one or all forms of the article whether unfinished, semi-finished (one side only) or finished (both convex and con-cave sides).
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Following debossing of the plastic or metal stxips of body section 12 and cover 14, cups 16 are fllled with a cat-alyzed liquid monomer 22, e.g. allyl diglycol carbonate which is sold under the trade name CR-39. A peroxide may be used as the catalyst.
Once filled with the casting precursor, debossings 20 of cover 14 are entered into cups 16 forcing a marginal out-ward flow of excess of the casting monomer and tight sealing of each cup 16 of mold 10. The filling and covering of cups 16 may take place successionally along the length of mold 10 for continuous process technology or sections of main body 12 and cover 14 may be individually respectively filled and covered.
Mold 10 may comprise multiple parallel rows of cups 16 and debossings 20 either in staggered or aligned juxtaposition.
The single row embodiment of Fig. 1 is presented merely for ease and simplification of illustration.
In addition to the tight sealing of cups 16 with de-bossings 20 of cover 14, the cover may be cemented, crimped, heat sealed or otherwise prevented from accidental displacement.
The filled and covered mold 10 is subjected to resin curing temperatures, e.g. by immersion in a liquid heat trans-fer fluid such as water 24 (Fig. 2). This may be accomplished on a continuous run basis or by separately immersing relatively nam/ -6-~43518 short sections of the covered mold into the heat trallsfer fluid.
~arious time-temperature cycles may be employed ror curing (polymerizing) the lens casting resin as is apparent from disclosures of the earlier mentioned U.S. Patents. Those desirous of such details may refler to these patents, e.g. lines 26-35, column 3 of U.S. Patent No. 3,902,693.
Following the curing of precursor 22, lenses 22a (Figs. 3-6) may be surface finished as follows:
With mold 10 inverted (Figs. 3 and 4), and the convex bottom 18 of a pocket 16 presented to a preformed plunge cut-ting tool 26, or vice versa, bottom 18 is removed with tool 26O
Corltinued cutting into lens 22a forms a surface shape corres-ponding to that of the tool cutting face 28. This removes surface blemishes resulting from mold material contamination, roughness or other irregularities and further removes occur-rences of less than completely polymerized lens surface material, i.e. the bulk material of a lens 22a is inherently more com-; pletely polymerized than its surface material.
; Having so machined the convex side of lens 22a (Fig. 3) its surface 30 may be optically polished in conventional fashion, e.g. with a polishing tool 32 (Fig. 4).
Second side finishing, i.e. complete surface finishing, ' nam/ 7 :, 35~8 of lenses 22a may be accomplished with plunge cutting tool 3~l (Fig. S) or sweep generatLng tool 36 (Fig.6). The former pro~
duces spherical surface curvatures only while the latter pro-vides for the production of compound (toric) surface curvatures.
Mold 10 may, in either case~ be retained as support for the lens 22a thereby avoiding a need to blok for second side finishing.
The lens surface grinding and polishing procedures and tools illustrated in Figs. 3-6 will be recognized by the art-isan as conventional and not requiring further discussion herein.
The use of mold 10 as a lens holder (i.e. lens block) is, however, unique.
Those skilled in the art will readily appreciate that there are various modifications and adaptations of the precise form of the invention here shown which may sult particular require-ments. For example, cups 16 of mold 10 may be compression molded to the precise surface 18 curvatures and finish required of convex sides of lenses 22a. By such means, volume production lenses may be accomplished without need for the first side finish-ing operations of Figs. 3 and 4.
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