Note: Descriptions are shown in the official language in which they were submitted.
~3~i3~6
The present invention provides an "orginal solution" (raw
material) suitable for producing in a facile manner a high-quality
soft contact lens by a direct casting method, with little deviation
in quality at a high yield.
Soft contact lenses have hitherto been generally produced
either by the so-called rod method or by the spin-casting method,
neither of which is fully satisfactory. Direct casting methods
have been proposed but have not been adopted in practice owing to
various shortcomings. The present invention is based on the
discovery of an original solution capable of being transformed into
a soft contact lens by a direct casting method, namel~ by filling
the cavity between concave and convex dies, preferably made of
glass, with said solution; polymerizing to a gel; peeling; and
finally extracting with water.
The solution of this invention is particularly suitable
for use in a process for producing a soft contact lens by pouring
an excess amount of the solution into a concave die; placing a
convex die on said concave die and overflowing the excess of said
solution to thereby uniformly fill said solution in the space
between said concave die and said convex die; gelling said solution
between the two dies to form therebetween a lens having a tensile
strength of at least about 0.1 kgf/cm2; immersing said lens and
said two dies in a liquid to peel said lens from said dies; and
extracting the thus-peeled lens via an extraction treatment with
water.
The invention accordingly provides an original solution
for producing a soft contact lens containing: a component A
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selected from the gxoup consisting of monomers and post cross-
linkable hydrophilic polymers wherein the monomers yield hydrophilic
component when polymerized; a component B selected from the group
consisting of monomers and post cross-linkable hydrophobic polymers
wherein the monomers yield hydrophobic component when polymerized;
and a suitable solvent C, the weight ratio of A:B being from about
85:15 to about 55:45, the amount of solvent C being from about
5 to 95% by weight of the original solution, and at least one of the
components A and B being a post cross-linkable polymer.
In accordance with subgeneric aspects of the invention,
the original solution has a coefficient of gellation contraction
at the same temperature and pressure of less than about 5% by
volume. In one embodiment, the original solution contains a polymer
of a lower alkyl ester of methacrylic acid having an ethylenic
double bond in the side chain and N-vinyl lactam. The two dies
are preferably made of glass, and the convex die preferabl-y has a
non-interference surface.
In a preferred emhodiment, the gellation step is caused
by heating. A preferred embodiment of the peeling step utilizes
a dimethyl sulfo~ide - water mixture.
It is to be understood that besides the monomers referred
to above there may be used in place of one component (i.e. either
A or B~ the partially polymerized form which has not reached the
stage of gellation, particularly with respect to the monomer
component B.
According to the present invention it is possible to
obtain a soft contact lens which is optically homogeneous and
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without bubbles, despite the shape of the lens. Another problem
that is avoided is the problem of "hollows", which may be caused
through polymerization contraction. In some prior art methods an
original solution flows slightly inside the dies, so that a memory
of such flow develops after the hyclration. A further problem
avoided by the present invention concerns the problems with
finishing lenses made by polymerization contraction, such finishing
not being required for the present invention.
In addition to the components A, B and C referred to
above, a cross-linking agent may be used and a polymerization
initiator may also be included.
As monomer for the component A there may be mentioned an
N-vinyl lactam such as N-vinyl pyrrolidone, N-vinyl piperidone and
N-vinyl caprolactam; N-vinyl oxazolidone; a hydroxy lower alkyl
ester of acrylic acid or methacrylic acid such as hydxoxyethyl or
hydroxypropyl ester of acrylic acid or methacrylic acid; glycerin
monoacrylate or glycerin monomethacrylate; and an ortho-lactone
having a hydrophilic group. As used above and throughout the
description of the invention, as preferred lower alkyl may be
mentioned alkyl of up to 6 carbon atoms.
The hydrophilic polymer of the component A is a cross-
linkable hydrophilic polymer having functional group (s) adequate
to form a cross-linkage between one hydrophilic polymer and
another (post cross-linking). Illustxative of such hydrophilic
polymer is the product obtained by (co~ polymerizing one or more
components A and, if necessary, a monomer for introducing
functional group(s) to a polymer (functional group-introducing
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monomer). As said functional group~introducing monomers there may
be mentioned n-butoxymethylacrylamide, glycidyl methacrylate,
vinylene carbonate, hydroxyethyl methacrylate, hydroxyethyl
acrylate, vinyl methacrylate, vinyl acrylate, methacrylic acid
and acrylic acid. The copolymerization ratio of the monomer to
the functional group-introducing monomer is preferably within the
range of about 1000:1 to about 10:1. Of those illustrated above
especially preferred is the product obtained by copolymerizing
N-vinyl pyrrolidone as the monomer and vinylene carbonate as the
functional group-introducing monomer.
As another example of such a hydrophylic polymer,
polyvinyl alcohol may be cited. In this case, hydroxyl groups
in the polymer enable a post cross-linking reaction to take place;
therefore, a new functional group need not be introduced. The
post cross-linking reaction may be carried out by using a
polyvalent isocyanate, a polyvalent aldehyde or methylol melamine
as a post cross-linking agent.
A monomer of component B gives a hydrophobic component
when polymerised, which neither swells nor dissolves in water even
though it is not cross-linked. As such monomer, there may be
cited a lower alkyl ester of acrylic acid or methacrylic acid
(for example, methyl methacrylate); an unsaturated nitrile such
as acrylonitrile or methacrylonitrile; an aromatic olefin such as
styrene and a hydrophobic ortholactone.
The hydrophobic polymer of the component B calls for a
cross-linkable polymer having functional group(s) adequate for
forming a cross-linkage between one hydrophobic polymer and
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another (post cross-linking) and which neither swells nor dissolves
in water. Representative of such cross-linkable hydrophobic polymer
is the product obtained by (co)polymerizing one or more components
B and, if necessary, a functional group-introducing ~onomer. It is
preferable that the copolymerization composition ratio of the
monomer to the aforesaid functional group-introducing monomer
generally ranges from about 1000:1 to about 10:1. As a hydrophobic
polymer, a non-cross-linking polymer, for example, polyvinyl
butyral may be mixed.
In both cases of polymers of the component A and the
component B, when a hydroxyl group is contained as a functional
group, it is possible to convert said polymer into a post-cross-
linkable polymer by esterifying said hydroxyl group with, for
example, methacrylic acid to thereby introduce an ethylenic double
bond to the side chain.
As to combination of the component A with the component
B, there is preferred such combination as will give an "original
solution" whose coefficient of polymerization contraction at the
same temperature and the same pressure (hereinafter referred to as
~ O) is less than about 5~ by volume. More specifically, there are
the following preferable combinations:
(1) The combination of a monomer used as the component A
with a polymer used as the component B: N-vinyl lactam, especially
N-vinyl pyrrolidone as the component A. A polymer having an
ethylenic double bond in the side chain obtained by reacting
(esterifying) methacrylic acid with a lower alkyl ester of
methacrylic acid (especially, methyl methacrylate) - glycidyl
D -5-
. ~
~3~306
methacrylate copolymer, or a non-gelled copolymer of methyl
methacrylate and vinyl methacrylate as the component B.
(2) The combination of polymers used both as the component A
and the component B: A polymer obtained by reacting (esteriEying)
methacrylic acid with a hydrolyzed N-vinyl pyrrolidone-vinylene
carbonate copolymer as the component A. A non-gelled copolymer of
methyl methacrylate and vinyl methacrylate as the component B.
(3) The combination of a post cross-linkable polymer and a
monomer used as the component A and a monomer used as the component
B. This combination is effective because it imparts a proper
viscosity to the original solution for polymerization.
Of the -foregoing, especially preferable are combination
containing, inter alia, N-vinyl pyrrolidone and a methyl
methacrylate polymer.
It is necessary that the mixing ratio of the component A
to the component B should range from about 85:15 to about 55:45.
In case the amount of the component A exceeds the upper limit of
said range, viz. about 85%, a high-tenacity lens cannot be
obtained, and in case the amount of the component A becomes less
than about 55%, a lens having a high water content cannot be
obtained. If said ratio is within the aforesaid range, a lens
having a high tenacity and a high water content in good balance
is obtainable.
The solvent component C must be one that does not
obstruct the polymerization reaction and the post cross-linking
reaction, and must furthermore give a transparent original
solution. When a solvent giving an opaque original solution is
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used, the lens is unsatisfactory in optical properties, and also
in many cases in dynamic properties.
It is possible to select a solvent from a wide range
depending upon the combination of the component A with the
component B. Where N-vinyl pyrrolidone and a methyl methacrylate
polymer are employed, which is an especially preferable mode of
practice of the present invention, there is preferably used
dimethyl sulfoxide and/or ethylene carbonate with or without the
admixture of a small amount of dioxane. In case a polymer of
N-vinyl pyrrolidone is used as -the component A and a polymer of
methyl methacrylate is used as the component B, dimethyl formamide,
N-methyl pyrrolidone and dimethyl acetamide they may be used as a
solvent, as they simultaneously dissolve the two polymers.
It is necessary that the amount of the solvent used be
within the range of about 5-95% by weight based on the total
amount of the original solution; of said range, the range of
about 30-90% by weight is preferable, and the range of about
50-90% by weight is most preferable. Where the amount of the
solvent exceeds about 95% by weight, the tensile strength of a
solvent-containing gel obtained by polymerizing and/or cross-
linking the original solution becomes low, and thus handling of the
solvent-containing lens becomes somewhat difficult.
It is preferable to so adjust the original solution as
to make the tensil.e strength of the solvent-containing gel, not
less than about 0.1 kg f/cm2; and for that end, it is necessary
not only to use an amount of solvent within the aforesaid range,
but also to carefully select the kind of solvent. When the amount
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of the solvent is less than about 5~ by weight, the hydrated lens
obtained upon swelling is hard, the water content of the lens is
low or the lens undergoes permanent deformation to such an extent
that parts of the molecules are destroyed due to the swelling force.
It is most preferable that the dimensional chanye brought about
when a solvent contained in a gel i9 replaced by water, is within
the range of from about +20% through about -30%.
The cross-linking agent will now be considered. A
polymer is used either as component A or component B, and there is
employed a post cross~linking agent reacting wi-th the functional
group(s) of the polymer to form cross-linkages between one polymer
molecule and another. As a post cross-linking agent, any suitable
substance may be employed unless it changes the essential
properties of the polymer. For a polymer containing hydroxyl
group(s) as a functional group, a polyvalent isocyanate, a
polyvalent aldehyde or a polyvalent carboxylic acid ester is
usable as a post cross-linking agent. When a polymerizable monomer
is used as the component A or B, a cross-linking agent selected
from compounds each having at least two polymerizable unsaturated
bonds in the same molecule is added to advance the cross-linking
polymerization. As such cross-linking agents, there may be
mentioned di- or tri-allyl compounds such as diallyl succinate,
diallyl phthalate, diallyl maleate, diethylene glycol bis-allyl
carbonate, triallyl cyanurate, triallyl isocyanurate, triallyl
phosphate and triallyl trimellitate; di- or tri-vinyl compounds
such as divinyl benzene, N,N'-methylene bis acrylamide, (poly)ethyl-
lene glycol dimethacrylate, hexamethylene bis maleimide, divinyl
,
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~363~
urea, bisphenol ~ bis-methacrylate, divinyl adipate, glycerin
trimethacrylate, trimethylol propane triacrylate, trivinyl
trimellitate and 1,5-pentadiene; allylvinyl compounds such as
allyl acrylate and allyl methacrylate; and vinyl (meth) acrylate.
The amount of such cross-linking agent to be added is within the
range of about 0.005 - 20 mol % based on the total amount of the
polymeri~able monomers of the component A and the component B.
The cross-linking polymerization is carried out by such
means as heat, radiation or electron ray in the presence of a
polymerization initiator if necessary. As preferred examples of
such a polymerization initiator, there may be mentioned an organic
peroxide such as di-tert-butyl peroxide, benzoyl peroxide, 2,4-
dichlorobenzoyl peroxide, tert-butyl hydroperoxide, tert-butyl
perpivalate, peracid and ammonium persulfate, an azo compound such
as azobisisobutyronitrile, azobiscyclohexane carbonitrile, phenyl-
azoisobutyronitrile and azobis-dime-thylvaleronitrile; and a redox
catalyst. The amount of such polymerization initiator to be
added is within the range of about 0.001 - 3% by weight based on
the polymerizable monomer.
20 ` It will be seen by a worker skilled in the art that in
addition to ~he criteria previously set forth, additives such as
a cross-linking promotor and coloring agents may be added to the
original solution of the present invention as needed. It is also
possible to add a polymer to the original solution which can be
extracted with water from the solvent-containing gel, for
example, poly N-vinyl pyrrolidone. Not only such an extractable
polymer, but other extractable substances may be formally regarded
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as a part of the solvent, so far as in order to calculate the
relative amount of the solvent in the solution.
The smaller is the r O of the original solution, the
more preferable it is. When a casting method is adopked in which
the volume of the lens-defining space gradually decreases as
contraction due to polymerization proceeds, even though the value
of rO is as high as 15-20~, there is no possibility of hollows
occurring. However, where the diopter of the lens is a large
positive or negative value, the thickness of the lens-defining
space varies from place to place, and so the original solution
flows slightly and the memory of such flow develops after the
hydration treatment, which is not desirable. Thus, it is prefer-
able that rO is less than about 10~ by volume, and still more
preferably less than about 5~ by volume.
As preferred embodiments of original solutions for
producing a soft contact lens of the present invention, there may
be mentioned:
(1) The combination, wherein N-vinyl pyrrolidone is
used as a monomer, a non-gelled copolymer of methyl methacrylate
and vinyl methacrylate is used as a post cross-linkable polymer,
triallyl isocyanurate is used as a cross-linking agent,
azobisdimethyl valeronitrile is used as a catalyst and dimethyl
sulfoxide is used as a solvent.
(2) The combination, wherein a post cross-linkable
polymer obtained by hydrolizing a vinyl pyrrolidone - vinylene
carbonate polymer and thereafter esterifying the resul-tan-t
hydrolyzed copolymer with methacrylic acid, and a non-gelled
copolymer of methyl methacrylate and vinyl methacrylate, are used
.~ -10 -
~L~363~i
as polymers and N-methyl pyrrolidone is used as a solvent.
A pair of dies are preferably used for producing a soft
contact lens in the present invention, that is a pair of a concave
die and a convex die. At least one of these two dies is one whose
lens~defining surface is an interference spherical surface or an
interference paraboloidal surface (hereinafter an interference
spherical surface and an interference paraboloidal surface shall
be generally referred to as an interference surface). The
interference spherical surface or the interference paraboloidal
surface referred to herein refers to a lens defining die surface
whose primary portion corresponding to the optical zone of the lens
is a smooth spherical or paraboloidal surface having a degree of
surface roughness of not more than about 50 ~m and the spherical or
paraboloidal properties are lost at the portion corresponding to
the peripheral portion of the lens. It is preferred that the
concave die and the convex die are so designed as to briny them
into a linear, not surface contact, because it is sometimes
difficult to make the central axes of the two dies exactly
coincident in the latter case.
Examples of the combination of a concave die and a convex
die used in the present invention will be explained by reference to
the accompanying drawings, in which:
Figure 1 represents a pair of convex and concave dies;
Figure 2 represents an alternative pair of convex and
concave dies; ancl
; Figure 3 represents a third possible pattern or a pair of
convex and concave dies.
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Figure 1 is a combination of a concave die 1 having an
interference surface with a convex die 2 having a non-interference
surface (a lens defining die surface having a spherical or
paraboloidal surface only is genera:Lly referred to as a non-
interference surface). This combination is especially preferred
for practising the present invention, because the concave die
having an interference surface is used and a lens having good
permeability to tear flow can be produced, and no inner bevel is
produced. An inner bevel is an inclined surface produced on the
circumferential portion on the concave surface of a lens, which
has been almost indispensable for wearing a conventional contact
lens. On wearing a soft contact lens obtained by the process of
the present invention, no problem is brought abouteven though
there is no inner bevel.
Figure 2 is an example of combination of a concave die
having an interference surface 1 with a convex die also having an
interference surface 4; by the use of such dies, the present
invention can be easily practised also. As a concave die, one
having a non-interference surface may also be used. However,
except for special dies, an outer bevel (an inclined surface
produced on the circumferential portion on the side of the convex
surface of a lens) is generally necessary; therefore, a concave
die having an interference surface is preferred. On the
circumferential portion of the die surface of a convex die, a
thin groove or small hole may be engraved, which results in
producing a projection on the circumferential portion on the
concave surface of the lens and promoting flow of tear. When a
-12-
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hole is marked, such marked hole is also utilizable for identifica-
tion of the kind. The material of the die may be plastic, metal or
glass, preferably glass.
Figure 3 is an example of a combination of a concave die
1 having an interference surface with a convex die 4 also having
an interference surface. This combination is e~cellent in that
any lens flash produced in the overlapping surfaces of the dies
does not contact the cornea. This combination is especially
suitable for manufacturing dies from thermoplastics or metal by
the transcription method.
In the filling step, an original solution in an excess
amount is poured into a concave die. Use of such an excess is
not only necessary for uniformly filling the original solution
into the space between the concave die and a convex die, but also
important for the following reason. In the dies shown in Figure 1
which are preferred for preparing lenses from the original solution
of the present invention, there is a wedge-shaped space 3 adjacent
the seal, the overflow of the original solution is held in that
space 3 to perfect the seal. On the other hand, when contraction
occurs during polymerization, the overflow of the original solution
is supplied through a slight opening of the seal into the sealed
portion to make up for the polymerization contraction. Where such
dies are used, the total amount of overflow is preferabl~ about 5
times or more of the amount of the original solution held in said
wedge-shaped space~ Determination of the amount of the original
solution may also be carried out as follows. A plurality of dies
each charged with the original solution are placed, for the
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purpose of carryiny out the gel producing step, in a sealed vessel
in which the air is replaced by an :inert gas such as nitrogen.
The lowest boiling point component of the original solution is so
chosen that its vapor pressure is at least about 20~ of the
saturated partial pressure exhibited by the original solution inside
said vessel. By charging an excess of such an original solution,
it becomes possible to prevent the :Lens from enfolding bubbles
while at the same time inhibiting slight changes of composition o
the original solution during the gelling step, thus enabling very
high-quality lenses to be obtained in good yield.
Another mode of practice of the filling step is to fill
the original solution in a sealed container. In this procedure,
a concave die is fastened in place in a sealable container, and
the original solution is poured into the concave die. Thereafter,
the whole container is inclined and a spherical convex die placed
on the concave die in said container. The air inside the container
is removed or replaced by an inert gas as occasion demands, and
thereafter the container is sealed and lightly shaken to seat the
convex die on the concave die.
In the gellation step, a polymerization and/or cross-
linking reaction is caused to proceed by the action of heat,
radiation or electron ray. When such reaction is caused by heat~
the reaction is carried out normally at a temperature within the
range from room temperature through about 120C.
There are the following five practical methods for
avoiding the production of holes and hollows due to polymeri7ation
contraction of the original solution:
14-
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363~6
(a) Liquid is supplied through the slight opening
between the concave and convex dies.
(b) Pressure acting on the original solution and/or
gel in a space between the concave and convex dies is reduced to
develop elastic expansion.
(c) The original solution and/or gel in the space
between the concave and convex dies is heated to develop thermal
expanslon .
(d) A hole and/or hollow is produced at a position
other than the optical area (an area within a circle having a
radius about 4 mm centering around the optical axis) in a space
between the concave and convex dies.
(e) The volume V of the space between the concave and
convex dies is somewhat decreased during the process from
initiation through termination of the polymerization reaction.
Method (a)
If, as mentioned above, the overflow of the original
solution is held in the wedge-shaped space of the dies, the
overflow of the original solution is naturally absorbed through
the slight opening of the seal between the two dies, because the
pressure inside the dies becomes negative owing to polymerization
contraction. This method is preferred in a metal die rather than
; in a plastic die and most preferable in a glass die. In the case
of glass die, the opening between the two dies is sometimes
excessive. In such case the concave and convex dies are squeezed
together with a force of 10 - 200 kg f, preferably about 50 kg f.
While the liquid used in the just described embodiment
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~L~3~i3a36
is normally the overflow of the original solution, it is not limited
to the original solution since either a monomer of a solvent will
suffice.
Method (b)
The original solution is sealed in a pressurized,
compressed state within the die and as the polymerization proceeds,
the internal pressure is reduced automatically.
The original solution is pressurized by heating or by
pumping it into the sealed space.
When squeezing of the concave and convex dies together
results in incomplete sealing, the seal may be perfected if the
concave and convex dies are placed in an au-toclave and the original
solution is added in the autoclave to both fill the molds and
the autoclave.
Method (c)
This method is achieved by gradually elevating the
temperature of the original solution as polymerization progresses.
The coefficient of thermal expansion of a monomer is not
large, but the following two procedures are effective. One is to
mix the monomer with a solvent having a high coefficient of thermal
expansion and carry out a solution polymerization. The other is to
carry out the polymerization at temperatures ranging from a low
temperature immediately above the freezing point of the solution
to a high temperature just short of the decomposition temperature.
In this case, because a proper thermal polymerization catalyst is
not available, an electron radiation polymerization is desirable.
Method td)
This method seeks to eliminate overall contraction of
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3~6
the entirety by allowing hollows to form in harmless positions.
Such positions are an outer or inner bevel of the lens. In order
to make certain that hollows form in such a position, foaming
nuclei are preferably provided on the outer bevel portion of the
concave die. As such oaming nuclei, a rough sur~ace of the dies,
contamination caused by foreign matters such as a very small amount
of oil or grease or plastic fiber are preferable.
Method (e)
This method is achieved by gradually decreasing the
volume of the lens-defining space V as polymerization proceeds.
If the volume decrease during the polymerization is
termed ~V, up to about ~V/V=3% can be employed in the process
of the present invention. In the case of glass die, when an
assembly of concave and convex dies is squeezed together by a
force of about 100 kg f, a volume decrease of about 2% is achieved.
Of the foregoing methods, those which are preferable
for obtaining satisfactory lens performance, are (a), ~b), and (c),
with (d) and (e~ preferably being used as auxiliary means. These
methods are used in appropriate combination.
Peeling of a solvent-containing gel from die is preferably
carried out in a liquid, especially in an aqueous solution. The
assembly of the concave and convex dies may be immersed as such in
the liquid. However, since contact of the overlapping surface of
the die assembly with the liquid will suffice, the entire die need
not be immersed. By conducting the peeling in the liquid, it is
possible to drastically reduce the ratio of damaged lenses.
This effect is especially remarkable when glass die is used.
-17-
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L3~;306
When peeling operations are carried out in water, exchange
of the solvent contained in the gel for water can be carried out
without any further treatment.
The li~uid used for peeling is not particularly limited
insofar as it does not adversely affect the lens. However, in
generall the same solvent,as used in the original solution with the
addition of water is preferably used. These may be called solvents
weaker in action for swelling the gel than the solvent contained
in the original solution.
The peeled lens is next subjected to an extraction
treatment with water (including physiological saline and other
aqueous solutions). At this time, the monomer(s~, polymer(s),
cross-linking agent, catalyst and solvent elute, while water or
an artificial tear solution flow in.
When ~his step is completed J a hydrated gel whose percent
transmission of visible light is more than about 90~ per thickness
of 0.1 mm, may be obtained.
Example 1 (Reference)
The concave die used in this example is made of a low-
pressure polyethylene, having a shape like 1 of Figure 2, theradius of curvature and the diameter of which are 7.5 mm and 13 mm,
respectively. The convex die used in this example is a glass ball
having a radius of curvature of 8 mm. A gap in the central portion
is 0.9 mm.
The original solution for polymerization is a mixture of
hydrophilic monomers and solvents as shown below.
-18-
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1~3t~3~)6
hydroxyethyl methacrylate ~HE~A) 70 g
N-vinyl pyrrolidone (~VP) 30 g
acrylic acid 2 g
ethyleneglycol dimethacrylate (EGDM~) 1.5 g
triallyl isocyanurate (TAIC) 0.5 g
ammonium persulfate 2 g
ethylene glycol 150 g
water 150 g
The original solution in an amount in excess of 20~ 1
was poured into the concave die and the convex die was carefully
centered thereon. Because the excess amount of said solution was
considerable, the probability of enfolding bubbles was low.
The two dies were clamped by a force of 0.5 kgf and the
polymerization conducted in a hot air oven, said solution being
heated at 60C. for 16 hours and then at 90C. for 4 hours. The rO
of the original solution was 3.5%, a greater part of which, however,
was made up for by reduction of the volume of the diies.
After immersing the assembly of the two dies in water,
the clamps were loosened, and the assembly allowed to stand over-
night as such in water and the two dies were separated in thewater. By so doing the ratio of the number of lenses with a broken
circumference decreased by about 10~ tas compared with the case of
loosening the clamps in air and separating the two dies in air).
If a lens initially adhered to the concave die, allowing
the die to stand in water for 5 hours promoted natural peeling
die.
The water content of the lens obtained in this manner
using water at pH 8 was about 75% and a lens having an intact edge
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113~3~36
was obtained. The percent transmission of light was 85~.
In order to determine the approximate value of the
tensile strength of the solvent~containing lens, after being
heated at 90C. for 4 hours, the lens was taken out into air, the
convex die was separated from the concave die and the lens was
peeled by a pair of tweezers. From the finger touch at that time,
the tensile strength of the lens was inferred to be about 0.5-2
kgf/cm .
Example 2 (Reference)
Using the same die and the same original solution as
used in Example 1, the original solution was charged by the same
method. Thereafter, the two dies were clamped together by a
force of 0.5 kgf and the original solution was polymerized in a
water bath. After heating the die under the same conditions as
in Example 1, the clamps were loosened in water, the two dies were
allowed to stand in water for overnight and thereafter the two dies
were separated.- A lens whose edge was little destroyed was
obtained.
Example 3 (Reference)
The concave die used in this example was a non
interference sphere made of glass having a radius of curvature
of 7 mm and a diameter of 13 mm. The convex die used was the
same as that used in Example 1. The gap in the central portion
was 1 mm. At the contact portion of the two dies, a wedge-shaped
space like 3 in Figure 1 was provided. As both of the two dies
had a non-interference spherical surface, the lens became a thick
concave lens having a crescent-like sectional configuration.
-20-
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306
Composition of the original solution for polymerization
was as follows, a mixture containing a hydrophilic monomer, a
hydrophobic monomer and a solvent.
NVP
methyl methacrylate (MMA) 30 g
TAIC 1 g
triethyleneglycol dimethacrylate
~TEGDMA) 3 g
vinyl methacrylate (VMe) 0.5 g
azobisdimethyl valeronitrile (ADVN) 0.1 g
dimethyl sulfoxide (DMSO) 400 g
The y of this original solution was about 3.5%.
The concave die was placed inside a high-rigidity,
pressure~resistant 5000 kgf/cm2 autoclave, the original solution
was overflowingly poured inside the autoclave, the convex die was
placed on the concave die and the autoclave was covered. Heating
was effected at 40C for the first 9.5 hours, at 50C. for the
succeeding 1.7 hours, at 60C. for the next 2.5 hours, at 70C.
for the next 0.4 hour (24 minutes), and at 80C. for the next 0.8
hour (48 minutes). The temperature was still raised at 90C.
in 0.9 hour, where the autoclave was allowed to stand for the next
2.2 hours. Thus, the total heating -time was 18 hours~ While care
was taken so as not to cool the autoclave, the assembly of the
concave die and convex die was quickly taken out and immediately
immersed in a treating liquid. The treating liquid was a 70%
aqueous solution of DMSO (at 95C.), after 5 hours, the convex die
was separated from the concave die, said concave die was immersed
in a 10% aqueous solution of DMSO ~at 95 C.) for 5 hours. During
the period, the
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lens naturally peeled from the concave die. Although the
circumference of the lens was very thin, the lens free from damage
was obtained. When the lens was boiled in water for o~ernight, it
became a transparent soft contact lens.
In order to know the approximate value of the tensile
strength of the solvent-containing lens, the concave and con~ex
dies taken out from the autoclave were separated in air and the
solvent-containing lens was peeled by a pair of tweezers. From
the finger touch at that time, the tensile strength of the lens
was inferred to be about 0.1 - 1 kgf/cm2.
The hydrated lens had a water content of 75%, a
percent transmission of light of 85% and a tensile strength of
4 kgf/cm .
Example 4 (Reference)
An experiment showing toughness of a pressure
polymerization was carried out. The temperature elevation
program of Example 3 was modified by reducing the speed of
temperature elevation, which was made an optimum value in an
atmospheric pressure polymerization shown in Example 5.
Increase of a hollow occurring ratio due to polymerization
contraction was hardly recognized. Number of flashes formed on the
overlapping surface of the two dies was rather small. This was
recognized to be the slowest speed temperature elevation. The
pressure inside the space between the dies at this time was
inferred to be always close to atmospheric pressure. Accordingly,
the internal pressure in Example 3 is believed to be considerable.
As such, in a pressure polymerization, the possible
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range of the temperature elevation programme iB broad, which is
contrastive to delicacy of an atmospheric pressure polymerization
indicated in Example 5.
Example 5 (Reference~
The same mold as used in Example 3 was used. A concave
die was placed horizontally on the bottom o-f an autoclave in
advance, on which was placed a convex die, through the overlapping
surface of the t~o dies, a needle was inserted to inject about
1 ml of the same original solution as used in Example 3 and -the
needle was pulled out. Bubbles were hardly enfolded. The
overflowed original solution wetted the circumference o the
concave die to say nothing of a wedge-sha~ed space, accumulated
on the bottom of the autoclave. The autoclave was filled with
nitrogen gas and covered. The inside of the autoclave must be
filled with the vapor of the original solution.
A polymerization was carried out according to the
following temperature elevation programme, connecting smoothly
the following temperature elevation curve.
Unit 8 1/4 hours 39C.
At 9 1/4 hours 46 C.
~ At 10 1/4 hours 50.5 C.
- At 11 1/2 hours 54 C.
At 12 hours 56 C.
At 12 1/2 hours 60 C.
At 13 hours 74 C.
At 14 hours 84.5 C.
From 14 1/2 hours through
16 hours 90C.
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-23-
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The steps thereafter were the same as those in Example 3.
The obtained lens was, the same as in Example 3, low in
damaging ratio with few hollows, having about the same values of
physical properties. This temperature elevation programme was
the values in atmospheric pressure polymerization and when the
temperature changed by ~3C. (for over 10 minutes) from the values
mentioned above, a lens with many hc)llows and (flange-like)
projections tended to be produced.
Example 6 (Refarence)
A part of Example 5 was changed. Namely, after
squeezing the assembly of the concave die and the convex die with
the pressure of 50 kgf, the autoclave was covered.
A temperature elevation programme the same as in
Example 5 was optimum; however, it was seen that a more severe
precision was required in this example as compared with that of
Example 5.
The number of flashes at the circumference of the
obtained lens was small. There were no large differences in:
damage ratio as a result o-f peeling, ratio of hollows obtained
and values of physical properties, between the lens of this
example and the lens oE Example 5.
Example 7
A concave die used in this example was made of glass,
having an interference spherical surface li~e that of 1 in
Figure 1, having a radius of curvature of about 9 mm and a diameter
of 13 mm. Because this die was manufactured manually by fire
.
forging, the precision of the optical surface was very poor.
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As a convex die, that used in Example 1 was employed.
The gap in the central portion(s) was about 0.4 mm.
~ omposition of the original solution for polymerization
was, as shown below, a mixture of a hydrophilic monomer, a post
cross-linkable hydrophobic polymer and a solvent.
post cross-linkable polymethyl methacrylate
28 g
NVP
TAIC 1 g
ADVN 0.1 g
DMSO 416 g
Using this original solution for polymerization, by the
method of Example 5, a polymerization was effected. The solvent
contained in the obtained lens was exchanged for water (allowed
to stand in boiling water for 16 hours)O The resultant product,
at 37C., was a soft contact lens of good transparency having a
!. water content of about 80% and a tensile strength of about 10
kgf/cm .
Said post cross-linkable polymethyl methacrylate was
synthesized by the following method.
MMA
VMe 1 g
ADVN 0.1 g
DMSO 400 g
A composition consisting of the aforementioned components
` was charged in a l-liter 3-neck flask equipped with a stirrer,
air inside said flask was r~placed by argon, and thereafter,
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the composition in the flask was stirred while immersed in a 50C.
water bath for 7 hours and then the polymer was precipitated by
pouring the viscous solution into methanol in the state of a very
fine powder. The precipitate was freed of solvent by centrifugation,
and thereafter washed twice with fresh methanol, and dried to
constant weight in ~acuo at a temperature not more than 40C. for
about 24 hours.
The obtained polymer had an [~] 0.8 and the yield was
about 30 g.
Example 8
In the process of Example 7, there was used a post
cross-linkable polymer synthesized by the following method:
MMA 95 h
glycidyl methacrylate (GMA) 5 g
ADVN 0.6 g
n-dodecylmercap-tan (n-DSH) 0.14 g
DMSO 233 g
The composition consisting of the aforesaid components
was polymerized at 50C. for 9.5 hours in the same manner as the
: 20 synthesis of the polymer in Example 7. ~he obtained polymer was
refined and dried. The resultant polymer was obtained in a
yield of about 33 g and had an [~] 0.5.
In order to add methacrylic acid to this polymer, the
following reaction was carried out.
said polymer 10 g
methacrylic acid (MeAA) 6 g
trimethyl benzylammonium chloride
(TMBAC) 1 g
J -26-
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Topanol A (trade mark) C 3 0.05 g
H3C ~ C(CH3~3
OH
1,2-dichloroethane 80 g
A composition consisting of the aforesaid components was
charged into a 300-ml, 3-neck flask e~uipped with a stirrer. The
addition reaction was effected with the flask immersed in a water
bath at 80C. for 8 hours. After the reaction, the obtained
reaction product was added to methanol and precipitated as a very
fine powder. It was freed of solvent by centrifugation, thereafter
washed twice with methanol and used for the polymerization.
Examination of the product by nuclear magnetic resonance showed
a methacrylic group content of about 3~ by weight.
The resultant polymer exhibited about the same viscosity
as that of the starting polymer. The obtained lens after
replacement of the solvent by water had a somewhat weaker tensile
strenght, but satisfactory transparency.
Example 9
In Example 7, the cross-linking agent in the original
solution for a polymerization only was changed. Namely, the
composition of the original solution was as follows.
PM~A* 28 g
NVP
ethylidene-bis-3-(N-vinyl-2-pyrrolidone)
(ENVP) 1 g
ADVN 0.6 g
DMSO 416 g
The obtained lens after its solvent was exchanged
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for water, was even higher in transparency than that of Example 7.
Example 10
In Example 8, only the cross-linking agent in the
original solution for a polymerization was changed. Namely, the
composition of the original solution was as follows.
* 28 g
NVP
VMe 1 g
ADVN 0.1 g
DMSO 416 g
The obtained lens after its solvent was exchanged for
water was as transparent as that of Example 7.
Example 11 (Reference~
Method of synthesizing post cross-linkable
polyvinyl pyrrolidone
N-vinyl pyrrolidone and vinylene carbonate were
polymerized.
~VP 29.1 g
vinylene carbonate (VCa) 0.9 g
ADVN 0.03 g
benzene 70 g
An original solution for a polymerization consisting
of the aforesaid components was placed in a 300-ml, 3-neck flask
equipped with a stirrer, the air inside the flask was replaced bv
argon, and the solution was polymerized with stirring at 50C.
for 7 hours.
After the polymerization, the polymer was precipitated
by pouring the solution into petroleum benzine.
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The polymer was dried ln vacuo at 70C. and the yield
was 14 g.
Six grams of the obtained polymer was dissolved in 100 g
of a 40% aqueous solution of hydrazine, allowed to stand at room
temperature for 3 days thereafter freed of water by an evaporator,
again dissolved in water, and thereafter the hydrazine was
completely removed therefrom by an ion exchange resin.
After removal of hydrazine, the polymer was dehydraked
in the evaporator and further dried ln vacuo. Four grams of the
dried polymer was dissolved in 50 g of dry methylene chloride,
and to the resultant solution was added dropwise a mixture of
2 g of methacrylic acid chloride and 8 g of dry methylene chloride
at room temperature with stirring. After completion of the
addition, the resultant mixture was allowed to stand with stirring
for 2 hours and the polymer ~hen precipitated by adding to
petroleum benzine.
Nuclear magnetic resonance of the obtained polymer was
measured in deuterium-methanol solvent and it was confirmed that
a methacrylic acid group was introduced.
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