Note: Descriptions are shown in the official language in which they were submitted.
3~
This applica~ion is a divisional of Canadian patent
application 270,945, filed February 2, 1977.
BACKt;ROUND_ OF THE INVENTION
The primary problem to overcome in utilizing a
closed mold system for casting of objects such as contact
, ,
- lenses where surface appearance, edge regularity and surface
finish are important is the compensation for the inevitable
.:
shrin~age that occurs on polymerization. With many
monomeric materials the volumetric shrinkage on polymeriza-
tion is in the range of 12 to 22~. This shrinkage has
heretofore prevented satisfactory casting of objects such
as contact lenses from vinyl monomers such as acrylate and
`1
~ ~ methacrylate esters, vinylpyrrolidone, substituted or
i' ' r- unsubstituted acrylamides or methacrylamides and the like.
For example, as taught in U.S. 3,660,545 (col. 1 & 2) a
,~ polymerizing acrylate, or methacrylate ester mixture held in
~ ,
'~- a closed glass mold invariably would pull away from at ~ ~-
least one mold su~face and cause the formation of surface ~
,, ~
~ ~ voids which rendered the cast object unsuitable as a lens. ~ ~
.
In a further prior art method, (see U.S. 3,660,545)
r
the polymerizing mixture was held between concave and convex i~
glass mold members having an annular gap interposed between
'. '1
~-; them which decreased as polymerization occurred, but again
`~ an irregular edge configuration resulted from polymerization
shrinkage. This edge portion could be removed ~y cutting
but this resulted in an edge of appreciable thickness which
tended to catch the eyelid during movement of the latter,
and cause displacement of the lens.
These difficulties with shrinkage compensation
therefore have heretofore precluded lens production by
casting in closed mold systems and other methods of pro-
:
,;~.,' ' - 1 -
. .
x
,,:
. . ~ - . ~ ., ~ . . .
-`- 1092301~
~,
duciny contact lenses of crosslinked polymeric makerials
such as spin casting and machining and polishing have been
employed.
In the spin casting process as taught in U.S.
3,408,429 and U.S. 3,496,254 the polymerizing mixture i8
contained in a rotating open mold having a concave surface.
The anterior, convex sur~ace of the lens is thus formed by
the mold surface, and the posterior, concave surface of khe
lens is formed as a result of centri~ugal forces, surface
tension of the polymerizing mixture and other factors such
as the size and shape of the mold, the volume of the poly-
meri2in~ mixture, the condition of the mold surface, etc.
The concave surface of the lens thus formed is approximately
parabolic in shape and many factors must be carefully con-
trolled to produce reproducible shapes. Lenses produced by
spin casting usually require post-polymerization edge finish-
ing and optical quality is not of the highest since there
is no truly spherical optical zone due to the aspheric nature
. - - ~
of the posterior surface.
~' 20 Most manufacturers o~ contact lenses of crosslinked
~- polymeric materials use a traditional machining or
; mechanically working and polishing of lens blanks as taught
~: .
~- in U.S. 3,361,858. ~his method has the advantage of being
able to "tailor make" lens curvatures and powers to any
desired degree and to furnish ~igh optical ~uality. The
~; method suffers from the disadvantage of requiring highly
i ~ skilled artisans ~or quality production.
.
~:
.
'~f ~'.~ ' ' '
~.'' , .
'
''~''
';~ '
i il ~ '
~ 2
It is an o~ject of an aspect of this invention
to provide a method for producing cast lenses in a closed
mold system, such lenses having the desirable optical an~
fitting characteristiçs of machined and polished lenses.
SUMMARY OF T~E INVENTION
The invention comprises a novel form of casting
mold and the mode o utiliæing same to produce contact
l~nses. The mold comprises a male portion, a femala portion,
and a flexible rim portion. The male portion comprises a
molding surface, and, in the preferred embodiments a
! substantially cylindrical support segment wherein said
- molding surface is attached circumferentially around the
lower circumference of the support segment~ The molding
surface has a pre-determined curvatuxe which will pro~ide
one of the surfaces of the contact lens.
; The female portion similarly comprises a second
molding surface and, in the preferred embodiments O a hollow
ylindrical support p~rtion. The inner diameter o~ said~
cylinder is substantially equivalent to the external
diameter of the support portion of the male segmént, the
- .
female segment, however, having a diameter just slightly
greater than that of the male segment. The diameters are ~ ~
pre-determined 90 that there is sufficient clearance for ~`
the male segment to fit into the ~emale segment and to permit
excass monomex or other material used in the process to flow
out between the two segments. The clearance, however, should
not be so great as to permit the axis of the two seyments to
be non-alignea to a degree wh~ch woula adversely affect the
. . .
optical centering o the lens to be produced.
;', '
:~. .. .
;, . .
. ;;- . . , . ~ , , :
J :10~23()
In a preferred form, one end of the said
female portion is clo~ed with said second molding surface of
predetermined curvature, said molding surface providing the
second surface of the contact lens to be produced.
~; The flexible rim portion is integrally attached to
the molding sur~ace of either the male portion or the female
7 portion in such a manner that it is a coaxial therewith.
The mold surPaces are so arranged that one is a
concave and the other is a convex. As will be seen hereinbelow
all combinations which are concave and convex curvature together
with the rim portion being attached to either, are within the
; ( scope of the present invention.
Accordingly, ~his 1nvention provides a process
~or preparing thermoplastic complementing mold pairs ~or
molding contact lenses comprising:
injection molding a fluid thermoplastic resin into
a first metal master mold of confined space comprising a
convex or concave first metal mold s~rface portion having a
principal longitudinal axis, a predetermined diameter, and
.
- 20 a predetermined radius of curvature defining a first optical
1 .
'` -` surface thereby producing a first thermoplastic article com-
~- prising a first th~rmoplastic mold urface portion which is opposite to and complementary with said first metal mold
surface portion for forming one of the optical surfaces of
the desired contact lens;
. ~- . . .
~- injection molding a fluid thermoplastic r~sin into
a second metal master mold of confined space comprising a
second metal mold surface por ion having a principal long-
- ~ itudinal axis, a predetermined diameter, and a predetermined
. ..................................................................... .
radius of curvature defining a second optical surface thereb~
. :- .
~` producing a second thermoplastic article comprising a second
thermoplastic mold surface portion which is opposite to and
;` ~ complementary with said second metal mold surface for forming
the other optical sur~ace of the desired contact lens;
- - . . . . . . ....
230~ ~
said first optical surface of the first master mold
or said second optical surface of the second master mold
having a circumferential recess therein providing in one of
said thermoplastic articles a thin circumferential, flexible,
rim portion integral with one of said mold surface portions.,
said rim portion having an axis common with the principal
longitudinal axis of its thermoplastic mold surface portion;
said rim portion being capable of seating circumferentially
against the other of the thermoplastic mold surface portions
: 1~ when the axes o the two thermoplastic mold surface portions
are in alignment, the two thermoplastic mold surface portions
defining a totally enclosed space for retaining a lens-forming
. material,
-~ said first master mold and said second master mold
constituting complementary mold pairs whose optical surfaces
: are opposite to and complementary with each other; and ..
said first article and said second article constitut-
ing the thermoplastic complementary mold pairs for molding
contact lenses.
' ~:
BRIEF DESCRIPTION OF THE DRAWINGS
-
. FIGURES 1 through 6 are exploded sectional elevations
of the embodiments of the present invention.
FIGURE 1 shows a convex male molding surface with
the flexible rim attached thereto and a concave female molding
: surace.
`, FIGURE 2 shows a concave male molding surface and
a convex female molding surface with the flexible rim attached
.:~ to the female surface.
FIGURE 3 is similar to FIGURE 2 except that the
: 30 flexible rim is attached to the male ~ortion.
- FIGURE 4 is an alternate embodiment of FIGURB 3.
FIGURE 5 is similar to FIGURE 1 except that the
flexible rim portion is attaahed to the female molding surface.
~ B 4a
: , .
~ ~ .
: ~ :: . .. .. .
FIGU~E 6 shows a simplified version of the
. ~mbodiment of FIGURE 1.
. FIGURE 7 shows a compressed view o~ FIGURE 1
wherein the rim is shown in flexed form.
~: Xn all of the figures the la5t two digit numbers
represent equivalent items numk,ered with three digits
where the last two digits are the same. Thus, Item 110,
I~em ~10, Item 310, and Item 410 all represent the male
molding portion.
ln In the more detailed discussion of the most
pxeferred embodiment below only FIGURE 1 will be discussed,
: ~ and *he discussion relating thereto is egually applicable to
the embodiments of all of the other ~igures.
~ .: ' . , ' :
~ I~ESCRIPTION OF THE PREFERRED _MBODIMENT
- . ' : .
The mold comprises two portions, namely a male
: portion 110 and a female portion 130. The maIe portion, in
~: the preferred embodiments, comprises a substantially
cylindrical support segment 114 having, optionally, attached
. to the upper end thereof a rim 112. In the preferred
:- 2Q embodiment, hecause o~ savings in mold materials, said
~: ~ylindrical portion 114 is, as shown, hollow; however, the
~ . invention should not be considered as being limited
.. thereto. Support member 114 is closed by molding surface i20
. . circumferentially attached to the bottom of cylinder 114.
: The curvature o~ 120 is pre-determined to comply with the
;~ optical requiremen~s of the lens to be producedO The
: . - curvature m~y be entirely`spherical or aspherical or combina-
. ~ions of both. Further, the su~ace may be toxic i~ the
central or optical zone; however, the peripheral portion must `
.
.` 5 , : .
:.
~.. ~ ' ' .
230~
be symmetrical in respect to the central axis of the lens in
order to achieve proper seating or mating with the rim to be
discussed herein ~elow. In the modification o ~IGU~ 1 a
flexi~le circumferential ring 116 is located around the
m~lding surface integral therewith. Said ring 116 comprises
an outer surface 117, an inner surface ll9, and a contact
edge 118.
~ The female portion 130 comprises, in the preferred
i ~ embodiments, a cylindrical support member 134 sat, optionally,
in a base 132 set circumferentially thereto and a molding
surface 140 set internally in cylinder 134. As with respect
to male molding surface 120 the curvature of ~emale moldinq
~ur~ace 140 is pre-determined and may vary in the same manner
as the cur~ature of mold surface 120. The only limitation
placed upon the mutual relationship of curvature of surfaces
t ~ 120 and 140, which will be aiscussed in greater detail herein
. ! ,
below, is that the article to be molded therebetween~shall
, have the general characteristics suitable for a contact
lens, namely that the article produced thereby shall have.
a ~oncave surface which will contact, when in use, the
eyeball of the wearer and a second, convex surface, which
shall contact the internal portion o the eyelid of the
wearer.
During the operation o~ the process which will be
discussed in greater detail herein below, the material which
will constitute the contact lens is placed in the female
portion o~ the mold. The male portion placed into the
; female portion in such a manner that tip 118 of the rim in
this case attached circumferentially ar~und the male molding
surface 120 just touches the sur~ace 140 of the female molding
:~,'
~, . - '. ' -'
~' . - ' ~; .
.' ~
. . .. ~ . .
~ .. . .
~ 32;3~
surface. At this point excess molding mat~ial is squeezed
out between the outer edge of cylindrical support means 114
and the inner edge of cylindrical support means 133. In the
embodiment shown in the figures no runoff channels in said
cylindrical portions are shown or provided. Nevertheless,
r the provision of molds having such channels i5 to be
considered in the scope o~ thel present invention. They are
' no~ utilized in the preferred embodiments since the provision
of ~uch molds requires an additional, and more expensive,
step in manufacturing the molds and provision thereof has not
been found to be needful.
The drawings herein are not to scale, in particular,
with regard to the rim segments -- say 116, and the
~learance between, say 114 and 133.
~- The two parts of the mold containing ~he molding
material are then subjected to the molding processes which
are discussed in detail herein below. During the molding
~ s~age, the molding material will contract, this contraction
; may be as much as 20% of the volume of the molding materialoriginally present between sur~aces 119, 120, and 140.
~ Since such a contraction takes place in a totally enclosed
-~ space~ a potential vacuum is formed which will be counter-
- acted by external atmospheric pressure causing the two
~ - molds llO and 130 to move towards each other. The flexibil-
~.
ity of rim 116 permits the molds to thus approach each other
.
~ more clo5ely due to the flexing of rim 116 in a uniform
- manner. If desired, external pressure can be ap~lied to
ensure that the molding sur~aces do approach each other as
closely as possible. However 9 the application o~ such
ex~ernal pressure is optional and, while in certain cases~
may give rise to improved results the operation of the
processes will pro~eed without said external pressure.
'''` . " ' ' ' .
:;
'.' '. . ' ,' ~ ; ' ' " ' .: . ' . ' `
:~9~ 8
Upon completion of the molding step, the molds are
separ~ted and the lens produced stripped out from the
~: mold in a condition read~.. to use except for cleaning and
polishing of the ed~es. The optical surfaces -- that is
tc say,-the contact surfaces -- are in their desired state.
: AS stated herein before, the set of molds shown
. in FIGURE 1 is the most preferred embodiment, in that it
: is the simplest of the preferred embodiments in the present
invention to manufacture. Nevextheless, as stated herein-
~: 10 above, the invention is in no way limited to this embodi-
.. mentO FIGURE 5 shows a variation of FIGURE 1 wherein the
rim herein 536 is int~gral with female molding surface 540.
~n this modification as in that of FIGURE 1 the male surface
is convex and the female surface is concave. The upper
~:~ edge 538 of ring 536 contacts male molding surface 520 and
the surfaces enclosing the lens creating molded material
. - are defined by the surfaces between the point on surface
A' s2n conta~ted by edge 538, and by internal sur~ace 539
~.~; o~ edge 536 together.with the internal portion of molding
t , ~ 20 surface 540. The operation of th~ process is similar to that
, ..
. described generally with respect to FIGURE 1 and in more
~: de*ail herein below.
. FIGURE 2 shows yet another embodiment of the
: invention wherein the edge ring 236 is attached to female.
.
m~lding surface 240. In this modification, howevex, the
female molding surface 240 is convex and therefore, the male
. molding sur~ace 220 is concave. In other respe~ts the
~ opexation of the process and the mutual relationship of its
: .
~ component paxts are as be~ore
:','' . ' '' ,''
. .
.,
:.
~: ' -,
~ 308
.,.
FIGURE 3 shows a modific~tion o~ the embodiment of
A FIGURE 2 wherein the flexible ring portion 316 is attached to
the male, concave portion 320 rather than ~he female, convex
molding surface 340.
In the modification of FIGURE 4 a variation of
the embodiment of FIGURE 3 is presented wherein the
flexible edge ring 16 (herein 416) is actually loCated on
the eage of molding surface 420 rather than internally as
: shown in the modification of FIGU~E 3.
t 10 In the simplified embodiment of FIGURE 1 above~
, ~
: ~ ln FIGURE 6 the cylindrical support member 14 of the
: ~ ~ male portion and the cylindrical support member 34 of the
female.portion-are eliminated so that the mold surfaces
. 620 and 640 are set directly into each other. While this
.- modification is operative and illustratés basic features! ~ .
; of the invention, the modifications additionally including
.~ the cylindrical support means are preferred in view of ~.
their additional handling stability. :-
,
:-. ~he advance in the art represented by the present
: i ~ invention depends upon the interaction of several ~actors,
~;1 one of which is the form of the mold set forth herein and
... .
: above. The other factors are the nature of the materials
utilized to construct the mold. The material utilized for the . ;~
.. ; ~ .
onstxuction of the mold must, under the conditions utilized
. - in the molding procedure be ~ufficiently .rigid to preserve
.
. the pre-determ.ined curvatures of the molding surfaces. Yet,
. .
:~ when formed in a thin ring such as ring 116, be 1exible :
. . enough to perm:it the contraction of the molding volume
: . : .
.~ mentioned herein above.
,
. .
:' '' . . .
': ~ ' ' .
. ,
.
. :: . . , , , . . ~ : . .
I~ has been foun~Ç~ uitable mate~ials
for constructîon of the molds are thermoplastic resins
whi~ll are i~ert to the polymerizing media, which have the
; requisite flexibility under polymerization conditions,
w~ich do not strongly adhere to the polymerized species and -
which can be molded to an optical quality sur~ce. Especial
ly suitable materials include polyolefins such as low,
medium, and high density polyethylene, polypropylene,
propylene copolymers known as polyallomers, polybutene-l,
poly-4-methylpentene-1, ethylene vinyl acetate and
ethylene vinyl alcohol copolymers, and ethylene copol~mers
such as polyionomers. Other suitable materials are
polyacetal resins and acetal copolymer resins, polyaxyl-
ethers, polyphenylene sulfides, polyaryl sulfones,
polyarylether sulfones~ Nylon 6, Nylon 66 and Nylon 11,
- thermoplastic polyester, polyurethanes and varlous
. fluorinated materials such as fluorinated ethylene-propylene copolymers a~d ethylenefl~oroethylene copolymers.
The choice of a particular thermoplastic material
for use ~n fabrication of molds is governed to an extent by
.,'.
the polymerization conditions to be used in the novel
process for manufacturing the contact lenses. In general,
a guide is the heat distortioh temperature at 66 psi ~iber
stress (ASTM D648) of the thermoplastic materialO
-:
- Thermoplastlc molds are generally suitable in this lnvention
-- at polymerization temperatures ranging from 20 to 40C,
: . .
and more, below the heat distortion temperature o~ the
thermoplastic materlal up to a few degrees, suitably
10, and more, above said heat distortion temperature.
. 30 - ~or example, low density polyethylene shows a heat
- distortion temperature of 40-50C, and acceptable results
unde~r light loading are obtained with this material at
p~lymerization temperatures of from 30 to above 70C.
~hove 70C, some distox~ion of opti~al surfaces may occurO
.
~,: 10
: ., .
. , . . - . . .
' :;;, , - ' ' .: . :
..: : . .
~ 230~
Whereas, with polypropylene, which has a heat
disto~tion temperature in the range o lOO to 120C, with
little or no applied pressure, acceptable results are
r obtained at polymerization temperatur~s from about",65 to
120C. Below 65C, flexibility of the plastic rim is not
sufficient to compensate for shrinkage, and above 120C,
distortion of optics occurs.
High pol~merization temperatures may be used for
materials such a5 nylons, polyphenylene ~ulfiaes, polysulfone~
and fluorinated polymers showing higher heat distortion
temperatures.
In addition, it is pofisible to operate at lower
polymerization temperatures by increasing the "load" or
mold closing pressure applied. For example, shrink marks or
~ux~ace voids are likely to appear in cast lenses made with
the polypropylene molds of ~his invention at a polymerization
~; temperature of below 65~C at light closing pressure applied to
the mold; however, if the closing pressuxe is increased to,
- ~or example, 10 psi, (calculated on the total mold area) lenses
free from surface blemishes are obtained. Thus the re~uisite
' ~ flexibility of t~e mold rim may be obtained through a combi-
. nation of polyGerization temperature and closing pressure.
It is noted that the male mold member, say, 110
has the rim 116 integrally formed at the periphery o~ the
male molding surface 120. The junction of the base o~ the
rim 116 with the surface 120 forms the posterior portion
of the edge of the lens, while the mating line 118 of the
.
rim with the female mold member 140 forms the anterior
shape of the edge. The overall thickness of the edge
thus formed is the "height" of the rim 116--i.e., outer
edge 118 to inner edge 113--less the distance the rim
~` ' ' 11
' , ':
';
~:
.
-'' ' " :''' ~ ' ' . -. ': ' ' '
, . . .
;
3 0 ~
flexes to compensate for the shrinkag~ tha~ occurs on
polymerization. Depending on the ed~e tllickness desired,
the hei~h~ of the rim 116 may vary from about .05 mm for a
very thin edge, to as much as~ 0.3 m~ or a rather thick,
rounded edge. Xn a typical example! the height of the
xim 116 from the edge 118 to edge 113 of the curve is
O.10 mm~ If a polymerizing mixture which has a volum~tric
shrinkage of 20% is employed~ then the rim must ~lex
sufficiently to allow the thickness of the edge to contract
to 0.08 mm. This flexing takes place generally by an
inwaxd bending as illustrated in FIGURE 7. Similar flexing
occurs in the embodiments of FIGURES 2-6.
.~
' J It is desirable that the apex of the rim be as
thin as possible to minimize the irregularity of the "mating
``` or parting line"~ In practice, the thickness of the apex
of the rim is held below 0.04 mm, and preferably below
O.01 mm. The rim is very delicate and the male mold member
must be ha~dled with care to avoid damage.
The outside diameter of the male mold hal~ ~ust
~ . ~
be-sufficiently smaller than that of the female half to
t ~ permit escape of excess o the material to be polymerized
upon closing the mold. Tapering of the male and female
halves aids in removal of excess material but is not critical.
. .
In general, the male half is preferably from 0.1 to 0.3
-mm smaller in diameter than the emale half. I~ the size
'
difference is too great, for example 0.5 mm, then alignment
of the optical centers of the two mold halves becomes
problematic~ although th~-~nvention is still operable.
. 12
:
''
;" . ' , -.
.
. .'
.,
:~ . -
. . . . .:
,- - : . ~ :.:
~09~
.
In the practice of this invention, me~al molds,
designated ko produce the idesired male and female thermo-
plastic molds are fabricated by traditional machining
and polishing operations. These metal molds are then
used in injection or compression molding machines to
produce a plurality of thermoplastic molds which in turn
are used to cast the desired lenses from polymerizable
or vulcanizable mixtures. ~hus, a set of metal molds
can yield a large number o~ thexmoplastic molds which,
in turn, yield an even larger number of lenses since
the thermoplastic molds may be reused i handled wit~
care~ This constitutes a considerable saving over the
traditional method of machining and polishing individual
lenses, since the machining and polishing operations
. :,
are carried out only on the original metal molds.
The design of the lenses produced by this invention
is not restricte~ to any particular set of parameters.
~ 80th anterior and posterior suraces of ~he lenses may -
; ~ ~ ~ ~ consist of entire~y spherical curves or aspherical curves
~ . . .~ .
or combinations of both. For example, the central portion ~ ;
of the lens may consist of spherical curves on both the
anterior and posterior surface, and the periphery of
-- ~ the anterior surface may consist of a steeper or flatter
spherical curve, and the periphery of the posterior surface
may be aspheric to achieve improved fitting characteristics.
In additlon, one or both of the surfaces may be toric
in the central or optical zone~ however, the peripheral
portion must be symmetrical with xespect to the central
axis of the lens to achieve proper seating or mating
~::
- 30 o~ the integral rim.
Monomer, prepolymer or vulcanizable mixtures
particularly useful in the practice of this invention
13
:
. ,. ... ..
:~:~ ., , : . - . . .
.. .. . . .
~s` `
~ lnclude hydrophobic~acrylic esters, suitably lower alkyl
's acrylic esters, the alkyl moiety containing 1-5 carbon
;~ atoms, such a~ methyl ac~ylate or methacrylate, ethyl
~; acrylate, or methacrylate, n~propyl acrylate or methacrylate,
isopropyl acrylate, or methacrylate~ lsobutyl acrylate
. or methacrylate, n-butyl acrylate or methacrylate, or
various mixtures of these monomers. For increased dimensional
stability and resistance to warpage the ~bove monomers or
monomer mixtures may be further admixed with a minor
1~ proportlon of di or poly~unctional polymerizable species
. ,
; to cause cross linking of the polymeric matrix as polymerization
proceeds. Examples of such di- or polyfunctional species
lnclude: divinylbenzene, ethylene glycol diacr~late or
methacrylate, propylene glycol diacrylate or methacrylate, and
~; - the acrylate or methacrylate esters of the following polyols,
- triethanol amine, glycerol, pentaerythritol, butylene glycol,5, ', diethylene glycol, triethylene glycol, tetraethylene glycol,s mannltol, sorbitol and the like. Other cross llnking monomers
s ~ may include N,N-methylene-bis-acrylamide or methacrylamide,
20 sulfonated divinylbenzene, and divinyl sul~one.
.-
Further, the above monomers or mixtures thereo~ may
~e ~urther mixed with linear polymeric specles which are
soluble therein as long as the viscosity of the solution or
~casting syrup" formed thereby does not become sufficiently
great that di~ficulty in removing bubbles therefrom is
encountered.
-
Other monoméric materials suitable for producing
s ` lenses via thls invention are hydrophillc monomer mixtures
formlng three dimensional cross linked networks such as
30 those disclosed in U.S. 3,822,089. Illustrative hydrophillc
14
: ,
:~, :
" ~- ' . ' ~,. ' . ,, '
:1~92;t~
monomers lnclude water soluble rnonoesters Or an acryllc acid
or methacrylic aci~ wi~h an alcohol having an esterifiable
hydroxyl group and at least one additional hydroxyl group
such as the mono- and polyalkylene glycol monoesters of
methacrylic ac~d and acrylic aci~, e.g., ethylene glycol
monomethacrylate, ethylene ~lycol monoacrylate, diethylene
glycol monomethacrylate, die~hylene glycol monoacrylate,
propylene glycol monomethylate, dipropylene glycol monoacrylate,
and the like; the N-alkyl and N,N-dialkyl substituted
acrylamides and methacrylamides such as N-methylacrylamide,
N,N-dimethylacrylamide, N-methylmethacrylamide, N~f-
dimethylmethacrylamide, and the like; N-vinylpyrrolidone;
the alkyl substituted N-vinyl pyrrolidones, e.g., methyl-
f . . ', .
substituted N-vinylpyrrolidone, glycidyl methacrylate;
~lycidyl acrylate, and others known to the art. Also
useful are ~he alkyl ether acrylates and methacrylates and
the vulcanizable silicone fluids or elastomers. The alkyl
moieties which are especially suitable in the a~orementioned
~ ,~
~; compounds are those which contain from 1 to 5 carbon atoms
~0 therein.
With the hydrophilic monomer or mixtures thereof,
it is essential that a 3-dimensional cross linked network
.
I be formed since the polymerized materials absorb water
--I and become soft and flexible and would lack shape retention
. . , .
if not cross linked. For this purpose it is desirable to
employ small amounts of crosslinking monomers such as those
; illustrated above. with respect to the discussion on hydrophobic
. I
acryllc esters.
Pre~erred monomeric mixtures contain at least
- 30 one alkylene glycol monoester of methacrylic acid, especlally
, .
'
~ 15
.
~ . ~ ,
:.
''
.
.; - ~ . .
., ~
~923~3~
ethylene glycol monomethacrylate, and at least one crosslinkln~
monomer such as the alkylene glycol diester Or methacrylic
Z acid, especially ethylene glycol dlmethacrylate. Such
, ~ mixtures may contain other polymerizable monomers, desirably
in minor amounts such as N-vlnylpyrrolidone, methyl methacrylate,
acrylamide, N-methacrlyamide, diethylene glycol monomethacrylate,
and others illustrated above.
! The polymerization reaction can be carried out in
bulk or with an inert solvent. Suitable solvents include
10 water; organic solvents such as water-soluble lower aliphatic
monohydric alcohols as well as polyhydric alcohols, e.g.,
glycol, glycerol, dioxane, etc.; and mixtures thereo~. In
general, the solvent, if employed, will comprise a minor
amount of th0 reaction medium, i.e., less than about 50
; weight percent.
Polymerization of monomer mixtures is usually~
carried out with free radical catalysts of the type ln
common use in vinyl polymerization. Such catalyst species
include organic peroYides, percarbonates, hydrogen peroxides, ~`
0 and inorganic materials such as ammonium, sodium, or
~ potassium persulfate. Polymerization using such catalysts
-~ may occur at temperatures between ambient temperature --
,.,,
i.e., ca 20C and about 120C -- depending on the speed
of polymerization desired.
Polymerization may also occur between monomer or
` ~ prepolymer mixtures under the influence of ele~ated
temperatures or radiation (U~V., X-ray, or radioactive decay).
With silicone elastomers, vulcanization may
take place via a ~ree radical curing mechanism, or, in
30 the case of two part so called RTV compounds vulcaniæation
may occur throu~h displacement or condensatio~ reactions.
'.'`' . ' ".
16
.
'. " '' '.. ' ' ', ', : ' "'
.. .
tZ3~ ~
:
,.
The following examples serve to further illustrate
the invention.
~ -
EXAMPLE la) ~ormation of Molds
' ~ Female high density polyethylene molds were
~` prepared by injection molding on a convex male steel
mold having an outside diameter of 12.0 mm, a central
radius of curvature of 7.50 mm with a chord diameter of
- 10.0 mm and a peripherical radius of curvature of 7.00
, ` { mm. ~ale high density polyethylene molds were prepared
0 ~y injection molding in a concave steel mold having an
f. ' '' . inside diameter of 11.9 mm, central radius of ? . 00 mm
i , with a chord diameter of 11.0 mm, and a peripheral curve
::
having a radius of 12.5 mm. The periphery of the curved
mold suxface was recessed to provide a peripheral rim
.01 mm wide at the apex extending 0.12 mm from the edge
- of the curve. Radiuscope measurement showed the central
radius of curvature o the ~emale concave mol~s to be
, . . .
7.43~ .04 mm and the inside diameter measured i2.1 mml
The outside diameter of the male molas was 11.8 mm, and
the central radius of curvature was 6.95~ .03 mm.
:............ ' . ' : ''
EXAMP~E lb) Formation of Lens
Ten concave female molds were placed on a flat
surface with ~he cavity projecting upward. A svlution `
consisting of care~ully purified 2-hydroxyethyl methacrylate~
0 parts; d:istilled water, 30 parts; ethylene glycol
dimethyl ethex~ 25 parts; triethylene glycol dimethacrylate,
- 0.4 parts; and di-isopropyl percarbonate, 0.2 parts:
was prepared by thorough mixing. One-half ml. o~ the
.~, .
~` ' .
Z,;~
` --
solution was placed in the female mold, and the male mold
halves were slowly inserted to displace excess solution
and to displace any ~ubbles. Slight pressure was applied
on the male halves to ensure seating of the rim. The
- filled molds were then placed in a circulating air oven
at 45C for 1-1~2 hours. After cooling to room temperature,
the molds were opened, the "ring" o~ polymerized material
~illing the cylindrical void in the annulus between the
mold halves was removed, and the ~lexible lenses which
adhered lightly to the male half of the mold were care~ully
- peeled offO After soaking in physiological saline to ~-
leach the ethylene glycol dimethyl ether from the lenses,
the lenses were examined. ;
The edges were smooth and evenly formed, requiring
no further treatment, and the surfaces were smooth and -
." . .
-- unblemishe~. The lenses had a center thickness of ~
, .
~ o.lg+ .b2 ~, optical powers o~ -2.50 to -2.75 diopters,
... .
and diame'er of 12.0 mm.
, , , .
EXAMPLE lc~ Formation of Lens
~ solution consisting of purified 2-hydroxy-ethyl
~ methacrylate, 55 parts; N,N-dimethyl acrylamide, ¦
-.~ .-
45 parts; water, 30 parts; diethylene glycol dimethyl
- ether, 20 parts; methylene-bis acrylamide, 0.3 part;
and diisopropyl percarbonate, 0.3 part; was cast in the -
. ,
molds of Example la), in a manner identical to that of
Example lb).
Unblemished lenses haviny a center thickness
of 0.21~ .03 mm, edge thickness of 0.10~ .0~ mm, diameter
of 13.0 mm, and optical powers of from -2.25 to -2.50
-, 18
:, . . .
,
109Z30~1 1
diopters were obtained after equilibration in 0.9%
~aline solution. The larger size and somewhat lower
optical power of these ~enses ovex those of Example 1
I is caused by the higher swel~ing coefficient of this
j polymer composition in water.
: ~ ,.
EXAMPLE 2a~ Formation of Mo1d~
~emale molds were pxepared using an ethylene-
vinyl acetate copolymer (having a 10~ vinyl acetate content)
b~ injection molding on a convex male steel mold having
{ 10 an outside diameter of 8.3 mm, central radius of curvature
of 8.60 mm at a chord diameter of 6.5 mm and a peripheral
radius of cur~ature of 7.55 mmO Male molds were produced ~-
from the same copolymer by injection molding in a female
! steel cavity having a central concave radius o~ curvature
of 7.50 mm with a chord diameter of 7.8 mm and a peripheral
radius of curvature of 9.50 mm. The periphery of the -
~ concave mold was recessed to pro~ide a rim on the mold~d ;~;
- ~ part protruding 0.1 mm from the edge of the curved surface
with a~ apex thickness of 0.015 mm. The inside diameter
of the concave steel mold was 8.0 mm.
. The inside diameter of the injection molded
female cavities was 8~2 to 8.4 mm and the central radius
~- of curvature was 8.55 ~05 mm~ The outside diameter
of the male convex plastic molds was 7.9 mm and the central
i radius of cur`vature was 7.45~ .03 mm.
. ~., . _
. ., .
:"~
EXAMPLE 2b) Foxmation of LenseS
A solution consisting of methyl methacrylate,
98 parts; ethylene dimethacrylate, 20 paxts: and di-t-
butylcyclohexylperoxy dicarbonate J 0.3 parts; was
.` ' 1~ ' . . .
~ .
~ .! .
. ' , ' :: , -,, .'
i(:)9Z3~)~
pr~pared, and 0.3 ml of the solution was introduced into
each of 10 of the upward facing concave ~emale molds.
The male molds were slow~y lowered into cavities to displace
aix and excess monomer mixture. The male molds were
pxessed lightly to ensure seating of the rim on the concave
female mold surface and the molds were placed in a circulating
air oven at 60C for 1-1/2 hours. The molds were then
cooled and opened. ~`
Lenses free from defects having a diameter
of 7.9 mm; central thickness of 0.10~ .02 mm, central -
poSteriQr radii of curvature of 7.47~ 0.4 mm and optical
power in the range of -7.50 to -8.50 diopters were obtained.
These lenses exhibited superior resistance to
warpage and could be flexed without permanent deformation
as opposed to lenses of the same dimensions fabricated
from non-cross linked polyme~hyl methacrylate.
EXAMPLE 3a) Formation of Molds
~ .
` C Using the metal molds of Example la, female
and male thermoplastic molds were prepared using N'ylon-
11. Female concave nylon molds having an inside diameter
of 12.0 mm and a central radius of curvature of 7.48~
.03 mm were obtained. Male nylon molds having an outside
diameter of 11.8 mm and a central convex radius o~ curvature
of 6.99~ .03 mm were obtainedO The peripheral rim projected
0.14 mm from the edge of the curved surface and was less ~"
than .01 mm thick at its apex.
. :. . . . .
:
1` : ' .
~ EX~MPLE 3b) Formation of Lenses
~ _ _ _ _ _ . _ _ _ _ _ _ .
A two part room temperat~lre vulcanizable transparent
: ~ .-. . .
~ ' 20
.
. .
:
. . . .
109~3~8
methyl silicone liquid was mixed, and 0.4 cc of the mixture
was placed in the upward facing concave female molds.
he male molds were inserted to displace excess fluid
and the molds were lightly pressed to ensure seating of
x~ the rim. Molds were placed in a circulating air oven
at 135~C for two hours. i . .
.
; : A~ter cooling the molds were opened and lenses
.~. ` measured. The center thickness was 0.22~.02 mm, the
edge thickness was 0.11~ .02 mm, and the optical power .
ranged from -2 L 00 to -2.50 diopters.
.~'' '' '
" ' .
~,.',,., . .
.- . - ' .
~:
,. .
,,. ' . ~-
:. . . :
. . -:- .
.' . ' '
... . ' . , .
~ ` . :~
., , , ,
:~ ' ' .
~,," ' , , , , ' , '. .
, . . .
, ~ , , ' ~, .,'.
, ................................................. .
, .
' ' ~ '.
~ , .
.'' ' ' ' , . ,
,...................................................... . .
, 21 . ~
- ~,
,
~`~'' ~ ' ' . , ' ,
