Note: Descriptions are shown in the official language in which they were submitted.
0~.~
DESCRIPTION OF T~E PRIOR ART
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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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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
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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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(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
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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-
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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
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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
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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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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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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
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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
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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
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66
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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66
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.
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