Ocular lens material and process for producing the same

An ocular lens material comprising a copolymer obtained by copolymerizing a copolymerizable composition of which the main components are a diene polymer and a monomer capable of copolymerizing with the diene polymer, having high oxygen permeability, high refractive index and high mechanical strength, and being excellent in flexibility and shape recoverability, and its production process are disclosed.

TECHNICAL FIELD 
The present invention relates to an ocular lens material and a process for 
producing the same, and more particularly to an ocular lens material 
having high oxygen permeability, high refractive index and high mechanical 
strength, and excellent in flexibility and shape recoverability, which can 
be used in, for instance, ocular lenses such as soft contact lenses and 
intraocular lenses, and a process capable of producing the ocular lens 
material in a short period of time from cheap raw materials. 
BACKGROUND ART 
Conventionally, there have been known a hydrogel material whose main 
component is 2-hydroxyethyl methacrylate and a hydrogel material whose 
main component is N-vinylpyrrolidone as a material for soft contact 
lenses. 
However, since the former is not sufficient for oxygen permeability, it is 
feared that the former exerts bad influences upon the metabolism of the 
cornea. Also, since the latter has a high water content, there is a defect 
in the latter that mechanical strength is insufficient. Also, since any of 
these are hydrogel materials, bacterias and the like easily proliferate in 
the lenses during their use. Therefore, there is a necessity to frequently 
carry out the sterilization by boiling, which also causes a defect that 
the burden on the care of a contact lens is increased. 
On the other hand, as a non-hydrogel soft contact lens material, there have 
been known a non-hydrogel material whose main component is silicone rubber 
and a non-hydrogel material whose main component is acrylic acid ester. 
The former has high oxygen permeability. However, since the silicone rubber 
itself shows hydrophobic property, there occurs a sensation of foreign 
matters when a contact lens made thereof is worn on the surface of cornea, 
and also there arises a defect that stains such as lipid contained in 
lacrimal fluid easily adhere to the contact lens. Also, in order to solve 
the defect of the non-hydrogel material whose main component is silicone 
rubber, there has been studied a material made of a combination of a 
silicone polymer with other monomer or other polymer. However, there is a 
defect that the silicon raw materials are generally expensive. Also, as 
the latter, i.e. the non-hydrogel material whose main component is acrylic 
acid ester, there has been proposed a non-hydrogel soft contact lens 
described in Japanese Unexamined Patent Publication No. 229113/1987. 
However, the material has a disadvantage of factory expenses such that 
esterification or transesterification must be carried out for a 
considerable long period of time after polymerization. 
On the other hand, as an intraocular lens, a hard lens made of polymethyl 
methacrylate is mainly used. When the hard lens is inserted into an eye of 
a patient who is ill with cataract, there is a necessity to carry out the 
incision of his cornea widely. 
However, when the incised portion for inserting the above-mentioned hard 
lens into an eye is wide, there occurs a problem that the patient is apt 
to suffer from troublesome astigmatism. Accordingly, since it is desired 
that the operation for inserting an intraocular lens into the eye of a 
patient who is ill with cataract is an operation for incising a small 
portion of the eye, it has been expected that an intraocular lens material 
which is excellent in flexibility and shape recoverability, and foldable 
and applicable to the operation for incising a small portion of the eye is 
developed. 
The present invention has been accomplished in consideration of the 
above-mentioned prior art, and aims at providing an ocular lens material 
having high oxygen permeability and high mechanical strength and excellent 
in flexibility and shape recoverability, which can be suitably used in 
ocular lenses, particularly soft contact lenses, intraocular lenses and 
the like, and a process capable of producing the ocular lens material in a 
short period of time from cheap raw materials. 
DISCLOSURE OF INVENTION 
The present invention relates to 1 an ocular lens material comprising a 
copolymer obtained by copolymerizing a copolymerizable composition whose 
main components are a diene polymer and a monomer capable of 
copolymerizing with the diene polymer, and 2 a process for producing an 
ocular lens material characterized by mixing a diene polymer with a 
monomer capable of copolymerizing with the diene polymer and then 
copolymerizing the resulting copolymerizable composition when 
copolymerizing the copolymerizable composition whose main components are 
the diene polymer and the monomer capable of copolymerizing with the diene 
polymer.

BEST MODE FOR CARRYING OUT THE INVENTION 
The ocular lens material of the present invention is composed of a 
copolymer obtained by copolymerizing a copolymerizable composition whose 
main components are a diene polymer and a monomer capable of 
copolymerizing with the diene polymer as aforementioned. 
The diene polymer used in the present invention has been generally 
mass-produced, therefore, the diene polymer is very cheap and easily 
available. 
As representative examples of the above-mentioned diene polymer, there can 
be cited, for instance, polybutadiene, polyisoprene, polychloroprene, 
styrene-butadiene copolymer, acrylonitrile-butadiene copolymer, 
isobutylene-isoprene copolymer, and the like. Among these diene polymers, 
polybutadiene, styrene-butadiene copolymer and isobutylene-isoprene 
copolymer can be particularly preferably used in the present invention 
from the viewpoint of the lowering of surface tackiness and the 
improvement of transparency of the ocular lens material. 
It is desired that the number average molecular weight of the 
above-mentioned polybutadiene is at most 1000000, preferably at most 
600000 in order to improve the compatibility with monomers to be 
polymerized, avoid hardening itself and improve its handling. Also, it is 
desired that the number average molecular weight of the polybutadiene is 
at least 500, preferably at least 1000, more preferably at least 3000 in 
order to avoid that the molecular weight of a molecular chain between 
crosslinked points of a resulting copolymer is lowered, improve mechanical 
strength and avoid that the copolymer becomes brittle after crosslinking. 
In either case that the content of the cis-configuration in the 
above-mentioned polybutadiene is high or low, there is little differences 
in the properties of the ocular lens material. Therefore, there is no 
limitation of the content of the cis-configuration in the polybutadiene. 
There are tendencies that the oxygen permeability of the ocular lens 
material increases and that its elongation percentage also increases in 
accordance with the increase of the content of the cis-configuration in 
the above-mentioned polybutadiene. Also, there is a tendency that the 
stability of the ocular lens material in water is improved in accordance 
with the lowering of the content of the cis-configuration. 
Also, it is desired that the content of 1,2-configuration (the content of 
vinyl group) in the above-mentioned polybutadiene is at most 70% by 
weight, preferably at most 50% by weight in order to improve the 
flexibility of the ocular lens material. In particular, the 
1,2-configuration may not be contained therein. Also, when at least two 
kinds of the above-mentioned polybutadiene are used by blending, if the 
blending ratio of the polybutadiene having the above-mentioned content of 
1,2-configuration is at most 40% by weight of the total amount of the 
polybutadienes, there is no risk that oxygen permeability, mechanical 
strength, flexibility and the like of the ocular lens material are lowered 
even though the content of 1,2-configuration of other polybutadienes 
exceeds 70% by weight. 
It is desired that the number-average molecular weight of the 
above-mentioned polyisoprene is at most 1000000, preferably at most 700000 
in order to increase the compatibility with monomers to be polymerized, 
avoid hardening itself and improve its handling. Also, it is desired that 
the number average molecular weight of the polyisoprene is at least 1000, 
preferably at least 3000 in order to avoid that the molecular weight of a 
molecular chain between the crosslinked points of a resulting copolymer is 
lowered, improve mechanical strength and avoid that the copolymer becomes 
brittle after crosslinking. 
There is no limitation of the content of the cis-configuration in the 
above-mentioned polyisoprene, but polyisoprene of which content of 
cis-configuration is 91 to 99% by weight, which is obtained by a usual 
polymerization method such as a solution polymerization method using, for 
instance, Ziegler catalyst, lithium catalyst or the like, is preferable 
because an ocular lens material having little differences in properties is 
obtained. 
It is desired that the number average molecular weight of the 
above-mentioned polychloroprene is at most 1000000, preferably at most 
600000 in order to improve the compatibility with monomers to be 
polymerized, avoid hardening itself and improve its handling. Also, it is 
desired that the number-average molecular weight of the polychloroprene is 
at least 1000, preferably at least 3000 in order to avoid that the 
molecular weight of a molecular chain between crosslinked points of a 
resulting copolymer is lowered, improve mechanical strength and avoid that 
the copolymer becomes brittle after crosslinking. 
As the above-mentioned styrene-butadiene copolymer, there can be cited 
emulsion-polymerized styrene-butadiene copolymers and solution-polymerized 
styrene-butadiene copolymers. In the present invention, the 
emulsion-polymerized styrene-butadiene copolymer and the 
solution-polymerized styrene-butadiene copolymer may be used alone or in 
an admixture thereof. In any cases, there are little differences in the 
properties of an ocular lens material. Since a surface active agent and 
the like which are used during emulsion polymerization remain in the 
emulsion-polymerized styrene-butadiene copolymer as impurities by reason 
-of its manufacturing process, the solution-polymerized styrene-butadiene 
copolymer is preferably used from the nature of the ocular lens material. 
It is desired that the styrene content in the above-mentioned 
styrene-butadiene copolymer is at most 50% by weight, preferably at most 
25% by weight in order to avoid that the oxygen permeability of the ocular 
lens material is lowered and that elongation and flexibility are lowered 
based upon the fact that rubber resiliency is lowered with the increase of 
the glass transition temperature of the styrene-butadiene copolymer 
itself. 
It is desired that the number-average molecular weight of the 
above-mentioned styrene-butadiene copolymer is at most 1000000, preferably 
at most 600000 in order to improve the compatibility with monomers to be 
polymerized and also improve its handling without the lowering of the 
fluidity itself. Also, in order to avoid that the molecular weight of the 
molecular chain between crosslinked points of a resulting copolymer is 
lowered, increase mechanical strength and avoid that the copolymer becomes 
brittle after crosslinking, it is desired that the number-average 
molecular weight of the styrene-butadiene copolymer is at least 1000, 
preferably at least 3000. 
It is desired that the number-average molecular weight of the 
above-mentioned acrylonitrile-butadiene copolymer is at most 1000000, 
preferably at most 600000 in order to improve the compatibility with 
monomers to be polymerized, avoid that the copolymer itself becomes hard 
and improve its handling. Also, it is desired that the number average 
molecular weight of the acrylonitrile-butadiene copolymer is at least 
1000, preferably at least 3000 in order to avoid that the molecular weight 
of a molecular chain between crosslinked points of a resulting copolymer 
is lowered, improve mechanical strength and avoid that the copolymer 
becomes brittle after crosslinking. 
Also, a hydrogel ocular lens material can be obtained by copolymerizing the 
above-mentioned acrylonitrile-butadiene copolymer with a hydrophilic 
monomer. In accordance with the increase of the acrylonitrile content in 
the acrylonitrile-butadiene copolymer, the compatibility of the 
acrylonitrile-butadiene copolymer with the hydrophilic monomer is 
improved, and the water-content of the ocular lens material also 
increases. Also, in accordance with the lowering of the acrylonitrile 
content, the compatibility of the acrylonitrile-butadiene copolymer with 
the hydrophilic monomer is lowered and the water-content of the ocular 
lens material is lowered. However, a material excellent in mechanical 
strength is obtained. Accordingly, in order to obtain an ocular lens 
material having a higher water content, it is preferable to use an 
acrylonitrile-butadiene copolymer having an acrylonitrile content of at 
least 43% by weight. Also, in order to obtain an ocular lens material 
having a higher mechanical strength, it is preferable to use an 
acrylonitrile-butadiene copolymer having an acrylonitrile content of at 
most 25% by weight. However, in order to obtain an ocular lens material 
having a good water-content based upon the good compatibility with a 
hydrophilic monomer, good oxygen permeability and suitable mechanical 
stength, it is preferable that the acrylonitrile content in the used 
acrylonitrile-butadiene copolymer is 15 to 50% by weight. 
It is desired that the number-average molecular weight of the 
above-mentioned isobutylene-isoprene copolymer is at most 1000000, 
preferably at most 600000 in order to improve the compatibility with 
monomers to be polymerized, avoid the lowering its fluidity and improve 
its handling. Also, it is desired that the number average molecular weight 
of the isobutylene-isoprene copolymer is at least 1000, preferably at 
least 3000 in order to prevent the lowering of the molecular weight of a 
molecular chain between crosslinked points of a resulting polymer, improve 
mechanical strength and avoid that the copolymer becomes brittle after 
crosslinking. 
Also, in the present invention, the above-mentioned various diene polymers 
may be used alone or in an admixture thereof. 
It is desired that the content of the above-mentioned diene polymer in the 
copolymerizable composition is at least 10% by weight, preferably at least 
30% by weight in order to lower the glass transition temperature of the 
copolymer constituting the ocular lens material, increase oxygen 
permeability and improve flexibility. Also, it is desired that the content 
of the diene polymer in the copolymerizable composition is at most 95% by 
weight, preferably at most 70% by weight in order to impart proper 
hydrophilic property to the ocular lens material. 
As the monomer capable of copolymerizing with the above-mentioned diene 
polymer, there are cited, for instance, hydrophilic monomers, hydrophobic 
monomers, and the like. 
The above-mentioned hydrophilic monomer is a component for imparting 
hydrophilic property to the ocular lens material. 
Representative examples of the above-mentioned hydrophilic monomer are, for 
instance, (meth)acrylic acid; hydroxyalkyl (meth)acrylates such as 
2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate and 
2-hydroxybutyl (meth)acrylate; (meth)acrylamide; 
N,N-dialkyl(meth)acrylamides such as N,N-dimethyl(meth)acrylamide; 
N-vinyllactams such as N-vinylpyrrolidone; alkyleneglycol 
mono(meth)acrylates such as ethyleneglycol mono(meth)acrylate, 
diethyleneglycol mono(meth)acrylate, triethyleneglycol mono(meth)acrylate 
and polyethyleneglycol mono(meth)acrylate; and the like, and these can be 
used alone or in an admixture thereof. 
In the present specification, "(meth)acry" is intended to mean acry or 
methacry, and represents both of them as a general term. 
When the above-mentioned hydrophilic monomer is used as the monomer capable 
of copolymerizing with the diene polymer, it is desired that the 
hydrophilic monomer is contained in the copolymerizable composition in a 
content of at least 5% by weight in order to impart desired hydrophilic 
property to the ocular lens material. Furthermore, in order to improve the 
fluidity of a mixture itself obtained by mixing the hydrophilic monomer 
with the diene polymer, lower tackiness and improve handling, it is more 
preferable that the hydrophilic monomer is contained in the 
copolymerizable composition in the content of at least 10% by weight. 
Also, it is preferable that the hydrophilic monomer is contained in the 
copolymerizable composition in a content of at most 90% by weight in order 
to impart proper flexibility to the ocular lens material. Furthermore, it 
is more preferable that the hydrophilic monomer is contained in the 
copolymerizable composition in a content of at most 70% by weight in order 
to improve oxygen permeability of the ocular lens material. 
When a hydrogel ocular lens material is obtained by using the 
above-mentioned acrylonitrile-butadiene copolymer, it is desired that the 
hydrophilic monomer is contained in the copolymerizable composition in a 
content of at least 10% by weight in order to improve fluidity of a 
mixture itself obtained by mixing the hydrophilic monomer with the 
acrylonitrile-butadiene copolymer and improve moldability. Furthermore, it 
is more preferable that the hydrophilic monomer is contained in the 
copolymerizable composition in a content of at least 30% by weight in 
order to obtain a water content necessary for imparting a proper oxygen 
permeability to the ocular lens material. Also, when a hydrogel ocular 
lens material is obtained, it is desired that the hydrophilic monomer is 
contained in the copolymerizable composition in a content of at most 95% 
by weight in order to impart a proper mechanical strength to the ocular 
lens material. Moreover, it is more preferable that the hydrophilic 
monomer is contained in the copolymerizable composition in a content of at 
most 85% by weight in order to impart proper lens-shape stability 
(stiffness) to the ocular lens material. 
Among the above-mentioned hydrophilic monomers, (meth)acrylic acid is 
excellent in compatibility with the diene polymer. Therefore, the 
(meth)acrylic acid can be solely used by adding to the diene polymer 
without the addition of a hydrophobic monomer showing a function as an 
agent which is dissolved together with the diene polymer to the diene 
polymer, and excellent hydrophilic property can be imparted to the ocular 
lens material. 
Among the above-mentioned hydrophilic monomers, hydroxyalkyl 
(meth)acrylate, (meth)acrylamide, N,N-dialkyl(meth)acrylamide and 
alkyleneglycol mono(meth)acrylate are difficult to be uniformly mixed with 
the diene polymer. Therefore, when these hydrophilic monomers are used, it 
is desired that a hydrophobic monomer showing a function as an agent which 
is dissolved together with the diene polymer is added to the diene 
polymer. Also, since these hydrophilic monomers show high water-absorptive 
property, it is desired that the hydrophilic monomer is contained in the 
copolymerizable composition in a content of at most 30% by weight in order 
to avoid the risk that the ocular lens material becomes cloudy in water. 
Also, in order to impart better hydrophilic property to the ocular lens 
material, it is desired that these hydrophilic monomers are used together 
with (meth)acrylic acid. 
The above-mentioned hydrophobic monomer is a component showing a function 
as an agent which is dissolved together with a hydrophilic monomer for 
imparting hydrophilic property to the ocular lens material and the diene 
polymer. 
Representative examples of the above-mentioned hydrophobic monomer are, for 
instance, alkyl (meth)acrylates such as methyl (meth)acrylate, ethyl 
(meth)acrylate, propyl (meth)acrylate, i-propyl (meth)acrylate, n-butyl 
(meth)acrylate, t-butyl (meth)acrylate, n-hexyl (meth)acrylate, cyclohexyl 
(meth)acrylate, octyl (meth)acrylate, decyl (meth)acrylate, undecyl 
(meth)acrylate and lauryl (meth)acrylate; styrene compounds such as 
styrene and .alpha.-methylstyrene; vinyl esters such as vinyl acetate; and 
the like. These can be used alone or in an admixture thereof. 
When the above-mentioned hydrophobic monomer is used, there are the 
following three standards of selection of the hydrophobic monomer. 
The first standard of selection of the hydrophobic monomer is to improve 
the compatibility of the hydrophilic monomer for imparting hydrophilic 
property to the ocular lens material of the present invention with the 
diene polymer. From this viewpoint, as a desirable hydrophobic monomer, 
for instance, a monomer having polar groups in its molecule in a high 
content, such as methyl (meth)acrylate, ethyl (meth)acrylate or vinyl 
acetate can be cited. When these hydrophobic monomers are used, the 
hydrophilic property of the ocular lens material can be enhanced since the 
content of the hydrophilic monomer can be increased, and also productivity 
can be enhanced since the period of time for mixing the diene polymer with 
the hydrophilic monomer can be greatly shortened. 
The second standard of selection of the hydrophobic monomer is that the 
glass transition temperature of a homopolymer obtained by homopolymerizing 
a hydrophobic monomer is low. As the hydrophobic monomer whose homopolymer 
shows a low glass transition temperature, for instance, linear alkyl 
(meth)acrylates and the like can be cited as preferably exemplified ones. 
When the hydrophobic monomer is used, the oxygen permeability of the 
ocular lens material can be more improved. 
The third standard of selection of the hydrophobic monomer is to improve 
the mechanical strength such as tensile strength of the ocular lens 
material of the present invention. From this viewpoint, as desirable 
hydrophobic monomers, for instance, there are cited monomers having a hard 
segment in its molecule such as t-butyl (meth)acrylate, cyclohexyl 
(meth)acrylate, styrene and .alpha.-methylstyrene, and the like. 
In the present invention, desirable physical properties can be imparted to 
an ocular lens material by selecting the hydrophobic monomer according to 
the above-mentioned first to third standards of selection of the 
hydrophobic monomer. 
In consideration of the above-mentioned first to third standards of 
selection of the hydrophobic monomer, alkyl (meth)acrylates having a 
linear alkyl groups having 1 to 12 carbon atoms such as methyl 
(meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl 
(meth)acrylate and n-hexyl (meth)acrylate, octyl (meth)acrylate are 
preferable among the above-mentioned hydrophobic monomers. Also, when the 
number of carbon atoms of the alkyl group is at least 13, there is a 
tendency that the tensile strength of the ocular lens material becomes 
small. 
As aforementioned, when (meth)acrylic acid is used as a hydrophilic 
monomer, the diene polymer and (meth)acrylic acid can be uniformly mixed 
together. When a hydrophilic monomer other than (meth)acrylic acid is 
used, it is preferable that the hydrophobic monomer is added to the diene 
polymer. 
The content of the above-mentioned hydrophobic monomer cannot be absolutely 
determined since the content differs depending upon kinds or content of 
the used hydrophilic monomer and the like. It is desired that the content 
of the hydrophobic monomer in the copolymerizable composition is at least 
5% by weight, preferably at least 10% by weight in consideration of the 
compatibility of the diene polymer with the hydrophilic monomer. Also, it 
is desired that the content of the hydrophobic monomer in the 
copolymerizable composition is usually at most 85% by weight, preferably 
70% by weight in order to impart hydrophilic property to the ocular lens 
material. 
Moreover, a polyfunctional monomer and the like may be used together with 
the above-mentioned hydrophilic monomer and hydrophobic monomer in order 
to more improve optical properties and dynamic properties. 
As representative examples of the above-mentioned polyfunctional monomer, 
there can be cited, for instance, polyfunctional (meth)acrylates such as 
di(meth)acrylates such as ethyleneglycol di(meth)acrylate, 
diethyleneglycol di(meth)acrylate, polyethyleneglycol di(meth)acrylate, 
propyleneglycol di(meth)acrylate, tripropyleneglycol di(meth)acrylate and 
polypropyleneglycol di(meth)acrylate, difunctional (meth)acrylates such as 
allyl (meth)acrylate, tri(meth)acrylates such as trimethylolpropane 
tri(meth)acrylate and tetramethylolmethane tri(meth)acrylate; monomers 
having at least 2 polymerizable double bonds in its molecule such as 
divinylbenzene, and the like. These can be used alone or in an admixture 
thereof. 
Also, when the content of the diene polymer in the copolymerizable 
composition is small, the mechanical strength of the ocular lens material 
is sometimes lowered, which depends upon the nature of the used 
hydrophilic monomer and hydrophobic monomer. In such a case, it is desired 
that the content of the above-mentioned polyfunctional monomer in the 
copolymerizable composition is at least 0.01% by weight, preferably at 
least 0.05% by weight in order to improve the mechanical strength of the 
ocular lens material. Also, it is desired that the content of these 
polyfunctional monomers in the copolymerizable composition is at most 30% 
by weight, preferably at most 20% by weight, more preferably at most 15% 
by weight in order to avoid that the flexibility of the ocular lens 
material is imparted. 
When a copolymer used in the ocular lens material of the present invention 
is prepared, first of all, the diene polymer is dissolved in or swollen by 
a monomer capable of copolymerizing with the diene polymer, and the 
polymer and the monomer are mixed together to give a uniform composition. 
When only (meth)acrylic acid is used as a hydrophilic monomer among the 
monomers capable of copolymerizing with the diene polymer, there is no 
necessity to dissolve or swell the diene polymer using the hydrophobic 
monomer, and the diene polymer can be merely mixed with (meth)acrylic 
acid. On the other hand, when hydrophilic monomers other than this 
(meth)acrylic acid are used, it is desired that the diene polymer be 
previously dissolved in or swollen by the hydrophobic monomer. 
Next, when a hydrophilic monomer other than (meth)acrylic acid is used, the 
hydrophilic monomer is added to the thus dissolved or swollen diene 
polymer. 
When the diene polymer is dissolved in or swollen by monomers capable of 
copolymerizing with the diene polymer, in case that the hydrophilic 
monomer is used together with the hydrophobic monomer at the same time, it 
takes a long period of time for dissolving or swelling the diene polymer 
with these monomers. Therefore, it is desired in the present invention 
that the diene polymer is previously dissolved in or swollen by the 
hydrophobic monomer. 
When the above-mentioned copolymerizable composition is subjected to 
copolymerization, it is desired that a polymerization initiator from which 
a radical is generated by its thermal decomposition or a redox auxiliary 
is used. As the polymerization initiator, there can be cited, for 
instance, a radical polymerization initiator and the like. 
As the above-mentioned radical polymerization initiator, there can be 
cited, for instance, organic peroxides such as benzoyl peroxide, 
t-butylcumyl peroxide, dicumyl peroxide and 
1,3-bis(t-butylperoxyisopropyl)benzene; azo compounds such as 
azobisisobutyronitrile and azobisdimethylvaleronitrile, and the like. 
These can be used alone or in an admixture thereof. 
The amount of the above-mentioned polymerization initiator is not 
particularly limited. It is desired that the amount of the polymerization 
initiator is usually 0.001 to 10 parts by weight based upon 100 parts by 
weight of the copolymerizable composition. 
After the above-mentioned polymerization initiator is added to the 
copolymerizable composition, the resulting mixture is heated to a 
temperature in the vicinity of the decomposition temperature of the 
polymerization initiator or at least the decomposition temperature, and 
the copolymerization is completed to give an ocular lens material made of 
a resulting copolymer. 
As a method for producing a contact lens from the ocular lens material of 
the present invention, there is cited, for instance, a method comprising 
pressing a mixture which is prepared by adding a polymerization initiator 
to the above-mentioned copolymerizale composition, into a mold for 
injection molding having a shape corresponding to a contact lens or 
injecting the mixture into a mold for a casting mold, and then heating the 
mixture to a prescribed temperature, a method comprising interposing the 
above-mentioned mixture between a convex mold and a concave mold, 
compressing and heating the mixture, and the like. The present invenion is 
not limited to those methods. As a method for producing an intraocular 
lens from the ocular lens material of the present invention, there are 
cited, for instance, the methods similar to the above-mentioned methods 
for producing a contact lens, and the like. When producing an intraocular 
lens, an optic portion and haptics can be molded at a time, or the optic 
portion and the haptics are separately molded and thereafter they can be 
united with each other in a body. 
The characteristic of the method for producing the ocular lens material of 
the present invention also resides in that the ocular lens material can be 
produced in an extremely short period of time. 
It is thought that the reason why the ocular lens material can be produced 
in the thus extremely short period of time according to the process of the 
present invenion is based upon that numerous unsaturated double bonds 
present in the diene polymer which is used as a main component in the 
present invention act as reaction points, and that the diene polymer is 
rapidly reacted with the monomer capable of polymerizing with the diene 
polymer at the unsaturated double bonds in the form of graft 
polymerization. 
Accordingly, although it has hitherto taken a long period of time such as 
several tens of hours for polymerization to give an ocular lens material, 
according to the present invention, the copolymerization can be carried 
out in an extremely short period of time such as 5 seconds to 24 hours or 
so, which differs depending upon the kinds and amounts of the used 
polymerization initiator. 
When benzoyl peroxide is for instance used as the above-mentioned 
polymerization initiator, the period of time needed for copolymerization 
becomes as extremely short as 30 seconds to 20 minutes or so. As an 
example, for instance, when 1 part by weight of benzoyl peroxide is added 
to 100 parts by weight of the copolymerizable composition, they are mixed 
together, thereafter the resulting mixture is poured into a mold, and the 
temperature of the mold is increased to 130.degree. C. or so, an ocular 
lens material is obtained after about 2 to 3 minutes passed. Also, when 
the mold is previously preheated to, for instance, 70.degree. to 
80.degree. C. or so, since the period of time for increasing the 
temperature of the mold to a predetermined temperature can be shortened, 
the period of time necessary for molding can be more shortened. 
Also, for instance, when 1,3-bis(t-butylperoxyisopropyl)benzene is used as 
the polymerization initiator, an ocular lens material is obtained after 
about 2 to 4 minutes passed by adding 0.02 part by weight of 
1,3-bis(t-butylperoxyisopropyl)benzene to 100 parts by weight of the 
copolymerizable composition, mixing them, pouring the resulting mixture 
into a mold and increasing the temperature of the mold to 180.degree. C. 
or so. Also, when the mold is previously preheated to, for instance, 
100.degree. to 120.degree. C. or so, since the period of time for 
increasing the temperature of the mold to a predetermined temperature can 
be shortend, the period of time necessary for molding can be more 
shortened. 
Also, after the ocular lens material is formed into a prescribed shape of 
an ocular lens, a treatment using an alkaline solution may be applied to 
the ocular lens material in order to improve hydrophilic property of its 
lens surface. 
The thus obtained ocular lens material of the present invention is 
excellent in flexibility and shape recoverability, and moreover has high 
mechanical strength, high oxygen permeability and high refractive index. 
Accordingly, since the thinning of an ocular lens at the central portion, 
which cannot have been carried out for conventional soft contact lenses 
from the viewpoint of mechanical strength, can be carried out, a soft 
contact lens having a more increased oxygen permeability can be obtained, 
and also there can be obtained, for instance, an intraocular lens which is 
foldable and applicable to an operation for a small incision. 
Also, according to the process of the present invenion, since the 
aforementioned ocular lens material can be produced from cheap raw 
materials in a short period of time, its cost can be brought down and 
productivity can be improved. 
Next, the ocular lens material and the process for producing the same of 
the present invention are more specifically explained on the basis of 
examples. However, the present invention is not limited to only the 
examples. 
EXAMPLE 1 
Fifty parts by weight of polybutadiene (number average molecular weight: 
180000, content of 1,2-configuration: 1% by weight, made by Nippon Zeon 
Co., Ltd., BR 1220) and 35 parts by weight of n-hexyl methacrylate were 
mixed together with a stirring mixer (made by Custom Scientific 
Instruments, Inc., CS-183 MMX) at room temperature for 1 hour, and then 15 
parts by weight of methacrylic acid and 1 part by weight of 
benzoylperoxide as a polymerization initiator were added thereto, followed 
by mixing them with a mixing stirrer at room temperature for 1 hour. 
The resulting mixture was heated and compressed for polymerization at 
130.degree. C. for 3 minutes in a hot-press machine (made by TESTER SANGYO 
CO., LTD., SA3 03-II-S) to give a colorless and transparent film having a 
thickness of 0.2 mm. 
In the present Example, a film having a thickness of 0.2 mm was molded. The 
reason why the film was molded is to measure the following physical 
properties. The fact that a film can be molded is intended to mean, in 
other words, that the ocular lens material can be molded into a contact 
lens and an intraocular lens. The same may be said of the following 
Examples. 
Next, as physical properties of the obtained film, oxygen permeability, 
tensile strength, elongation percentage, refractive index, flexibility and 
shape recoverability were examined in accordance with the following 
methods. The results are shown in Table 1. 
(A) Oxygen permeability 
The oxygen permeability of a film having a thickness of 0.2 mm was measured 
in 0.9% saline with a Seikaken-type film oxygen-gas permeater. 
(B) Tensile strength and elongation percentage 
A test piece was produced by stamping out from a film having a thickness of 
0.2 mm by means of a tensile and compression tester (mady by IMADA 
SEISAKUSHO CO., LTD., SV-201). The load when the test piece was broken and 
the length when the test piece was broken were measured at room 
temperature (23.degree. C.) at a tensile speed of 10 mm/minute, and 
tensile strength and elongation percentage thereof were calculated in 
accordance with the following equations, respectively. The tensile 
strength prescribed herein is intended to mean tensile strength at 
breaking, and the elongation percentage is intended to mean elongation 
percentage at breaking by tension. 
##EQU1## 
(C) Refractive index 
The refractive index of a film having a thickness of 0.2 mm was measured at 
20C by means of an Abbe's refractometer (made by ATAGO CO., LTD.). 
(D) Flexibility 
A circular test piece having a diameter of 6 mm was produced by stamping 
out from a film having a thickness of 0.2 mm, and the test piece was 
placed on a flat stand. One end of the test piece was held with a tweezer 
and folded in two at the central portion. At that time, the state of the 
test piece was observed with naked eyes, and evaluated in accordance with 
the following criteria for evaluation. 
(Criteria for evaluation) 
A: It is possible to fold the test piece until both ends of the test piece 
are touched with each other, and no crease remains in the test piece after 
folding. 
B: It is impossible to fold the test piece until both ends of the test 
piece are touched with each other. However, the bending angle is at least 
90.degree. and no crease remains in the test piece after folding. 
C: It is possible to fold the test piece until both ends of the test piece 
are touched with each other. However, crease remains in the test piece 
after folding, or the bending angle is less than 90.degree., or a crack is 
generated on the crease when the test piece is folded. 
When the evaluation for flexibility is A, it is recognized that the test 
piece has flexibility needed for, in particular, intraocular lenses. 
(E) Shape recoverability 
After one end of the test piece was held with a tweezer and folded in two 
at the central position in the same manner as in the above-mentioned (D) 
Flexibility, the tweezer which has held the test piece was released from 
the test piece. There was measured a period of time from the release of 
the tweezer from the test piece, to the recovery of the test piece which 
has been folded in two to the original even state, and shape 
recoverability was evaluated in accordance with the following criteria for 
evaluation. 
(Criteria for evaluation) 
A: The period of time is less than 1 minute. 
B: The period of time is at least 1 minute and less than 2 minutes. 
C: The period of time is at least 2 minutes and less than 5 minutes. 
D: The period of time is at least 5 minutes. 
EXAMPLES 2 TO 17 
A colorless and transparent film having a thickness of 0.2 mm was obtained 
in the same manner as in Example 1 except that the components for the 
copolymerizable composition used in Example 1 were changed to those shown 
in Table 1. 
The physical properties of an obtained film were examined in the same 
manner as in Example 1. The results are shown in Table 1. 
EXAMPLES 18 TO 22 
A colorless and transparent film having a thickness of 0.2 mm was obtained 
in the same manner as in Example 1 except that the components for the 
copolymerizable composition were changed to those shown in Table 1, that 
0.2 part by weight of 1,3-bis(t-butylperoxyisopropyl)benzene was used 
instead of 1 part by weight of benzoylperoxide as a polymerization 
initiator and that a resulting mixture was heated and compressed for 
polymerization at 170.degree. C. for 4 minutes in Example 1. 
The physical properties of an obtained film were examined in the same 
manner as in Example 1. The results are shown in Table 1. 
Each code shown in Table 1 is intended to mean the following. 
(Diene polymer) 
BR 1: Polybutadiene (number average molecular weight: 
180000, content of 1,2-configuration: 1% by weight, made by Nippon Zeon 
Co., Ltd., BR1220) 
BR 2: Polybutadiene (number average molecular weight: 
170000, content of 1,2-configuration: 10% by weight, made by Nippon Zeon 
Co., Ltd., BR1241N) 
BR 3: Polybutadiene (number average molecular weight: 
2000, content of 1,2-configuration: 64% by weight, made by NIPPON OIL 
COMPANY, LTD., B-2000) 
IR: Polyisoprene (number average molecular weight: 
530000, cis configuration content: 98% by weight, made by Nippon Zeon Co., 
Ltd., IR2205) 
SBR: Styrene-butadiene copolymer (number average molecular weight: 140000, 
styrene content: 19.5% by weight, made by Nippon Zeon Co., Ltd., NS218) 
(Monomer capable of copolymerizing with diene polymer) 
MAc: Methacrylic acid 
HEMA: 2-Hydroxyethyl methacrylate 
DMAA: N, N-Dimethylacrylamide 
NVP: N-Vinylpyrrolidone 
MMA: Methyl methacrylate 
nBuMA: n-Butyl methacrylate 
nHMA: n-Hexyl methacrylate 
CyHMA: Cyclohexyl methacrylate 
LMA: Lauryl methacrylate 
AMA: Allyl methacrylate 
EDMA: Ehtyleneglycol dimethacrylate 
TABLE 1 
__________________________________________________________________________ 
Physical properties of film 
Oxygen 
permeability 
Components of copolymerizable 
(cm.sup.3 .multidot. cm/ 
Tensile 
Elongation 
Refractive 
Ex. 
composition (sec .multidot. cm.sup.2 .multidot. 
strength 
percentage 
index Shape 
No. 
(parts by weight) 
mmHg)) 
(gf/mm.sup.2) 
(%) (-) Flexibility 
recoverability 
__________________________________________________________________________ 
1 BR1(50),nHMA(35),MAc(15) 
35 .times. 10.sup.-11 
1152 380 1.5154 
A A 
2 BR2(40),MAc(60) 
20 .times. 10.sup.-11 
674 210 1.5098 
A B 
3 BR2(50),LMA(35),MAc(15) 
38 .times. 10.sup.-11 
667 258 1.5158 
A A 
4 BR1(40),nHMA(45),MAc(15) 
28 .times. 10.sup.-11 
1296 287 1.5126 
A A 
5 BR1(60),nHMA(25),MAc(15) 
37 .times. 10.sup.-11 
1158 407 1.5192 
A A 
6 IR(50),nHMA(35),MAc(15) 
21 .times. 10.sup.-11 
933 412 1.5146 
A A 
7 IR(60),nHMA(25),MAc(15) 
22 .times. 10.sup.-11 
831 532 1.5196 
A A 
8 BR2(40),nHMA(45),MAc(15) 
27 .times. 10.sup.-11 
1111 217 1.5120 
A A 
9 BR2(50),nHMA(35),MAc(15) 
31 .times. 10.sup.-11 
1126 235 1.5148 
A A 
10 BR2(60),nHMA(25),MAc(15) 
34 .times. 10.sup.-11 
866 274 1.5187 
A A 
11 BR2(50),nHMA(30),CyHMA(15), 
30 .times. 10.sup.-11 
512 372 1.5194 
A A 
HEMA(5) 
12 SBR(60),nHMA(25),MAc(15) 
21 .times. 10.sup.-11 
954 314 1.5238 
A A 
13 BR1(50),MMA(35),MAc(15) 
31 .times. 10.sup.-11 
1237 430 1.5143 
A A 
14 BR1(50),nBuMA(35),MAc(15) 
40 .times. 10.sup.-11 
1255 333 1.5148 
A A 
15 BR1(50),LMA(35),MAc(15) 
34 .times. 10.sup.-11 
526 345 1.5150 
A A 
16 BR2(50),MMA(35),MAc(15) 
25 .times. 10.sup.-11 
979 317 1.5144 
A A 
17 BR2(50),nBuMA(35),MAc(15) 
26 .times. 10.sup.-11 
1242 252 1.5147 
A A 
18 BR2(45),MMA(35),MAc(20) 
27 .times. 10.sup.-11 
1222 311 1.5140 
A A 
19 BR2(45),MMA(22),MAc(15), 
27 .times. 10.sup.-11 
1669 211 1.5145 
A A 
AMA(10),EDMA(6),DMAA(2) 
20 BR2(45),MMA(22),MAc(15), 
29 .times. 10.sup.-11 
1820 228 1.5146 
A A 
AMA(10),EDMA(6),NVP(2) 
21 BR2(40),BR3(10),MMA(27), 
27 .times. 10.sup.-11 
920 262 1.5148 
A A 
MAc(23) 
22 BR2(40),BR3(10),MMA(19), 
26 .times. 10.sup.-11 
1275 232 1.5150 
A A 
MAc(15),AMA(10),EDMA(6) 
__________________________________________________________________________ 
From the results shown in Table 1, it can be seen that all of the films 
obtained in Examples 1 to 22 show high tensile strength and high 
elongation percentage, are excellent in flexibility and shape 
recoverability, and furthermore have a high refractive index of at least 
1.51 or so. 
Moreover, as is clear from the comparison of the films obtained in Examples 
1 to 18 with the films obtained in Examples 19 to 20, and the comparison 
of the films obtained in Example 21 with the film obtained in Example 22, 
it can be seen that a film having a higher tensile strength can be 
obtained when a polyfunctional monomer is employed as Examples 19 to 20 
and Example 22. 
Then, using the films obtained in Examples 18 and 22, an elution test was 
carried out in accordance with "(3) Extract by water, E. Testing method 
for titrating potassium permanganate-reducible substance" prescribed in 
the item of "III. 6 Elution test" described in "the Approval Standards for 
Intraocular lenses" from. Notice No. 489 of the Pharmaceutical Affairs 
Bureau, dated 10 May, 1985. After each film was subjected to a boiling 
treatment for 30 minutes with distilled water, the amount of potassium 
permanganate consumed in the treated water was measured. As a result, as 
to the film obtained in Example 18, the difference between the amount of 
potassium permanganate consumed in the treated water after the boiling 
treatment of the film with distilled water for 30 minutes and the amount 
of potassium permanganate consumed in the distilled water before the 
treatment was 0.27 ml, and as to the film obtained in Example 22, the 
above difference between both was 0.77 ml. When the difference between 
both is at most 1.0 ml, the film satisfy the acceptable standard of the 
above-mentioned elution test. Accordingly, the films obtained in Examples 
18 and 22 satisfy the above-mentioned acceptable standard, and therefore, 
it can be seen that the films are excellent in stability in water. 
EXAMPLE 23 
A colorless and transparent film having a thickness of 0.2 mm was obtained 
in the same manner as in Example 1 except that the components of the 
copolymerizable composition were changed to those shown in Table 2. 
The obtained film was subjected to a hydrating and swelling treatment, and 
oxygen permeability and water content of the film to which the hydrating 
and swelling treatment was subjected were measured. The results are shown 
in Table 2. 
Each code shown in Table 2 is intended to mean the following. 
NBR: Acrylonitrile-butadiene copolymer (number average molecular weight: 
470000, acrylonitrile content: 33.5% by weight, made by Nippon Zeon Co., 
Ltd., DN200) 
HEMA: 2-Hydroxyethyl methacrylate 
DMAA: N, N-dimethylacrylamide 
EDMA: Ethyleneglycol dimethacrylate 
Also, oxygen permeability was measured in the same manner as in Example 1, 
and water content was calculated based on the following equation. 
TABLE 2 
______________________________________ 
Components of 
copolymerizable 
Oxygen permeability 
Ex. composition (cm.sup.3 .multidot. cm/ 
Water content 
No. (parts by weight) 
(sec .multidot. cm.sup.2 .multidot. mmHg)) 
(% by weight) 
______________________________________ 
23 NBR(20),HEMA(38), 
21 .times. 10.sup.-11 
52 
DMAA(40),EDMA(2) 
______________________________________ 
TABLE 2 
______________________________________ 
Components of 
copolymerizable 
Oxygen permeability 
Ex. composition (cm.sup.3 .multidot. cm/ 
Water content 
No. (parts by weight) 
(sec .multidot. cm.sup.2 .multidot. mmHg)) 
(% by weight) 
______________________________________ 
NBR(20), HEMA(38), 
21 .times. 10.sup.-11 
52 
DMAA(40), EDMA(2) 
______________________________________ 
From the results shown in Table 2, it can be seen that the film obtained in 
Example 23 has a high oxygen permeability and a high water content. 
EXAMPLE 24 
As a polymerization initiator, 1 part by weight of benzoylperoxide was 
added to a copolymerizable composition having the same components as in 
Example 17, and these were mixed together in the same manner as in Example 
17 with a stirring mixer. 
After the obtained mixture was poured into a mold for contact lenses made 
of stainless steel, the mold for contact lenses was set up in the same 
hot-press machine as used in Example 1, which was previously preheated to 
130.degree. C. 
After the mold for contact lenses set up in the hot-press machine was 
heated for 4 minutes under a pressure of 50 kg/cm.sup.2, the mold for 
contact lenses was taken out from the hot-press machine and allowed to 
cool. Then, the mold for contact lenses was opened, and a molded contact 
lens was taken out from the mold. 
The obtained contact lens had a thickness of 0.07 mm in center and a base 
curve of 8.40 mm, was transparent, and had elasticity. Also, the contact 
lens had excellent physical properties similar to the film obtained in 
Example 17. 
EXAMPLE 25 
As a polymerization initiator, 0.2 part by weight of 
1,3-bis(t-butylperoxyisopropyl)benzene was added to a copolymerizable 
composition having the same components as in Example 19, and these were 
mixed together in the same manner as in Example 19 with a stirring mixer. 
After the obtained mixture was poured into a mold for intraocular lenses 
(optic portion) made of stainless steel, the mold for intraocular lenses 
was set up in the same hot-press machine as used in Example 1, which was 
previously preheated to 180.degree. C. 
Then, after the mold for intraocular lenses set up in the hot-press machine 
was heated for 4 minutes under a pressure of 60 kg/cm.sup.2, the mold for 
intraocular lenses was taken out from the hot-press machine and allowed to 
cool. Then, the mold for intraocular lenses was opened, and a molded optic 
portion of an intraocular lens was taken out from the mold. 
The obtained optic portion of the intraocular lens had a thickness of 0.7 
mm in center and a diameter of 6.0 mm, was transparent and had 
flexibility. Also, the optic portion had excellent physical properties 
similar to the film obtained in Example 19, and was foldable. 
Next, loops made of polypropylene as haptics were jointed with the obtained 
optic portion with the aid of a cyanoacrylate-type adhesive agent to give 
an intraocular lens. 
EXAMPLE 26 
As a polymerization initiator, 0.2 part by weight of 
1,3-bis(t-butylperoxyisopropyl)benzene was added to a copolymerizable 
composition having the same components as in Example 19, and these were 
mixed together in the same manner as in Example 19 with a stirring mixer. 
After the obtained mixture was poured into a mold for one-piece intraocular 
lenses made of stainless steel, the mold for intraocular lenses was set up 
in the same hot-press machine as used in Example 1, which was previously 
preheated to 180.degree. C. 
Then, after the mold for intraocular lenses set up in the hot-press machine 
was heated for 4 minutes under a pressure of 60 kg/cm.sup.2, the mold for 
intraocular lenses was taken out from the hot-press machine and allowed to 
cool. Then, the mold for intraocular lenses was opened, and a molded 
one-piece intraocular lens was taken out from the mold. 
The obtained one-piece intraocular lens had a thickness of 0.7 mm in center 
and a diameter of 6.0 mm in its optic portion, and a total length 
including haptics of 13.0 mm, was transparent, and had flexibility. Also, 
the intraocular lens had excellent physical properties similar to the film 
obtained in Example 19, and was foldable. 
INDUSTRIAL APPLICABILITY 
The ocular lens material of the present invention is excellent in 
flexibility and shape recoverability and extremely high in mechanical 
strength, and had a high oxygen permeability and a high refractive index. 
Accordingly, for instance, contact lenses such as soft contact lenses 
having a very thin thickness in the center can be obtained, and the 
obtained contact lenses are more excellent in oxygen permeability in 
addition to high oxygen permeability based upon its lens material. Also, 
since the ocular lens material of the present invention is excellent in, 
particularly, flexibility and shape recoverability, for instance, 
intraocular lenses which are foldable and applicable to an operation for 
incising a small portion can be obtained from the ocular lens material. 
Also, in the process for producing an ocular lens material of the present 
invention, much cheaper raw materials are used in comparison with 
conventional ocular lens materials, and the process is very simple for 
producing a needed lens in a short period of time. Accordingly, according 
to the process, an ocular lens material having the aforementioned 
excellent physical properties can be easily produced, and moreover 
lowering of costs and improvement of productivity are achieved.