Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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:
.
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,
-2- ~
''
:
~351~
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;
/
Pg/~ - 3 -
~3~
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-
.~
,~
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).
nam/ _5_
~.
3518
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.
nam/ -8-
