DESCRIPTION
PROCESS FOR PRODUCING RESIN FOR OPTICAL MATERIAL
Technical Field
The present invention relates to a process for producing an optical ma-
terial (e.g. a lens) made of a polyurethane resin having good optical proper-
ties by polymerizing a polymerizable composition composed of a polythiol
compound and a polyiso(thio)cyanate compound.
Background Art
Since a resin optical material is lighter and less fragile than an optical
material made of an inorganic material and tintable, it has been recently rap-
idly accepted for various optical materials, such as a spectacle lens and a
camera lens.
While, a resin for the optical material with higher performance has
been demanded. More particularly, there has been a need for improvements
toward a higher refractive index, a higher Abbe's number, a lower density and
a higher heat resistance. Responding to such a need, various resins for the
optical material have been developed and put into use.
Among others, various polyurethane resins have been proposed ac-
tively. The present inventors have also made many proposals concerning
optical materials, such as a plastic lens, made of a polyurethane resin.
As one of the most representative resins of the polyurethane resin, a
resin obtained by reacting a polythiol compound and a polyiso(thio)cyanate
compound may be exemplified. The resin is transparent and colorless, has

a high refractive index and a low dispersion property, and is excellent in prop-
erties, such as an impact strength, tintability and processability. Conse-
quently, it is one of the best resins for the optical material such as a plastic
lens. Among others, the resin transparency is a crucial property for a lens.
Disclosure of the Invention
On some occasions during production of a resin for an optical material,
striation or clouding may be caused in a resin or optical material obtained by
polymerization. Such striation or clouding may deteriorate the performance
of the optical material. Consequently, an object of the present invention is to
provide a method for producing effectively a high performance, namely trans-
parent and colorless without a strain, optical material (e.g. a lens) made of a
polyurethane resin, without causing striation or clouding.
In order to attain the object, the present inventors have intensively
studied to discover that there is a close relationship between the polymeriza-
tion rate of the polymerizable composition, or presence of clouding or striation
in a lens made of a polyurethane resin, and a water content in the polymeriz-
able composition.
It becomes generally possible to produce a highly transparent lens
without striation or clouding at a high yield by selecting a catalyst amount and
a temperature rise pattern suitable for a particular lens form in the production
of the lens. As well known, in the event a polymerization rate drops far be-
low the normal rate, the occurrence rate of striation or clouding increases in
general dramatically, which may cause frequently deterioration of the trans-
parency of the resin. Meanwhile, the present inventors have discovered
that, in case the water content of a polymerizable composition composed of a

polythiol compound and a polyiso(thio)cyanate compound exceeds a certain
value, the polymerization rate decreases slightly resulting in causing striation
or clouding, which may lower the yield of the product. That is, it has been
discovered that by maintaining the water content in the polymerizable compo-
sition within a certain range, the decrease of the polymerization rate was in-
hibited and a high performance polyurethane resin lens, that is transparent
and colorless without clouding or striation, can be obtained, thereby complet-
ing the present invention.
According to a conventional art, it has been known that at a very high
water content an iso(thio)cyanate compound reacts with the water, so that
foaming or clouding of the resin should take place to lose transparency com-
pletely, and that industrial production of an optical material should become
difficult. Absolutely different from such foaming and clouding phenomena
caused by a very high content of water, the present invention is based on the
discovery of a correlation between a water content in such an extremely low
specific range (in the order of ppm) as has been believed to have no adverse
influence on industrial production and a polymerization rate or striation or
clouding caused therefrom. The correlation has been first discovered by the
present inventors, and had not been known conventionally in the art.
Namely, an aspect of the present invention is a process for producing
a resin for an optical material by polymerizing a polymerizable composition
comprising a polythiol compound and a polyiso(thio)cyanate compound,
characterized in that a water content in the composition is 10 to 300 ppm.
Other aspects of the present invention are a resin obtained by the
process for producing, and an optical material such as a lens comprising the
resin.

According to the present invention, a high performance optical material
(e.g. a lens) made of a polyurethane resin, which is transparent and colorless
without a strain, can be effectively produced at a high yield without causing
striation or clouding.
Best Mode for Carrying Out the Invention
According to the present invention, a polyurethane resin for an optical
material is produced by polymerizing a polymerizable composition composed
of a polythiol compound and a polyiso(thio)cyanate compound. The water
content of the polymerizable composition is in a range of 10 to 300 ppm. Al-
though the water content below 10 ppm is permissible, it is difficult to lower
the water content below 10 ppm, because of existence of moisture in raw ma-
terial polythiol and moisture contamination in a production process at a mixing
operation of a polythiol compound and a iso(thio)cyanate compound, and the
like. Furthermore, the water content of the polymerizable composition is
preferably 10 to 200 ppm.
To limit the water content to 10 to 300 ppm, it is necessary to decrease
the water content to the extent possible at a monomer production stage. For
example, if a solvent is used in monomer production, the water content can
be lowered simultaneously with removal of the solvent by utilizing an
azeotropic mixture with water. The water content in the monomer can be
further decreased by removing the residual moisture in the system through
flushing nitrogen under a reduced pressure at a room or elevated tempera-
ture. In case distillation can be applied for purification, the water content in
the monomer can be lowered by adjusting the initial cut-off amount. The low
water content can be maintained by storing the produced monomer under a

nitrogen atmosphere preventing increase of the water content by absorption
of moisture after the production of monomer.
In the present invention, it is important not only to decrease the water
content in the monomer or the polymerizable composition according to the
aforementioned techniques, but also to inspect the water content in the
monomer or the polymerizable composition in order to judge whether the
same can be utilized for polymerization. That is to say, in case the water
content result according to the inspection should be within the range deter-
mined by the present invention, the monomer or the polymerizable composi-
tion is utilized for polymerization, but in case it should be outside the range,
the same is not utilized for polymerization but additionally treated for decreas-
ing the water content followed by reinspection to judge whether the same can
be utilized for polymerization.
In case the water content in the polymerizable composition is within the
determined range, substantial decrease in the polymerization rate does not
take place and an optical material of a transparent polyurethane resin without
striation and clouding can be obtained. Thereby, the water content in a
polythiol compound to be used for the polymerizable composition is preferably
20 to 600 ppm, and more preferably 20 to 400 ppm from the viewpoint of
suppressing striation and clouding. The water content can be measured by
a Karl-Fisher moisture meter.
The polymerizable composition is a composition containing a polythiol
compound and a polyiso(thio)cyanate compound as the main components.
The composition may contain according to need additionally optional compo-
nents, such as a catalyst, an internal release agent, a UV absorber and a blu-
ing agent.

A polyurethane lens, for example, may be produced by casting a
polythiol compound and a polyiso(thio)cyanate compound as well as an op-
tional component as necessary into a lens mold followed by polymerization.
There is no particular restriction on a polyiso(thio)cyanate compound to
be used for the polymerizable composition, insofar as it is a compound having
2 or more iso(thio)cyanate groups in the molecule. Herein the term
"iso(thio)cyanate" means "isocyanate or isothiocyanate".
Specific examples of a polyiso(thio)cyanate compound include: ali-
phatic polyisocyanate compounds, such as hexamethylene diisocyanate, 2,2-
dimethylpentane diisocyanate, 2,2,4-trimethylhexane diisocyanate, butene
diisocyanate, 1,3-butadiene-1,4-diisocyanate, 2,4,4-trimethylhexamethylene
diisocyanate, 1,6,11-undecane triisocyanate, 1,3,6-hexamethylene
triisocyanate, 1,8-diisocyanato-4-isocyanatomethyloctane, bis(isocyanato-
ethyl)carbonate, bis(isocyanatoethyl) ether, lysine diisocyanatomethyl ester,
and lysine triisocyanate;
alicyclic polyisocyanate compounds, such as 2,5-bis(isocyanato-
methyl)bicyclo[2.2.1]heptane, 2,6-bis(isocyanatomethyl)bicyclo[2.2.1]heptane,
bis(isocyanatomethyl)cyclohexane, dicyclohexylmethane diisocyanate, and
isophorone diisocyanate;
polyisocyanate compounds having an aromatic ring, such as 1,2-
diisocyanatobenzene, 1,3-diisocyanatobenzene, 1,4-diisocyanatobenzene,
2,4-diisocyanatotoluene, ethylphenylene diisocyanate, isopropylphenylene
diisocyanate, dimethylphenylene diisocyanate, diethylphenylene diisocyanate,
diisopropylphenylene diisocyanate, trimethylbenzene triisocyanate, benzene
triisocyanate, biphenyl diisocyanate, toluidine diisocyanate, 4,4'-methylene
bis(phenylisocyanate), 4,4'-methylene bis(2-methylphenylisocyanate),

bibenzyl-4,4'-diisocyanate, bis(isocyanatophenyl)ethylene, bis(isocyanato-
methyl)benzene, bis(isocyanatoethyl)benzene, bis(isocyanatopropyl)benzene,
a,a,a',a'-tetramethylxylylene diisocyanate, bis(isocyanatobutyl)benzene, bis-
(isocyanatomethyl)naphthalene, bis(isocyanatomethyl phenyl)ether, bis(iso-
cyanatoethyl)phthalate, and 2,6-di(isocyanatomethyl)furan;
sulfur-containing aliphatic polyisocyanate compounds, such as bis(iso-
cyanatomethyl)sulfide, bis(isocyanatoethyl)sulfide, bis(isocyanatopropyl)-
sulfide, bis(isocyanatohexyl)sulfide, bis(isocyanatomethyl)sulfone,
bis(isocyanatomethyl)disulfide, bis(isocyanatoethyl)disulfide, bis(isocyanato-
propyl)disulfide, bis(isocyanatomethylthio)methane, bis(isocyanatoethylthio)-
methane, bis(isocyanatomethylthio)ethane, bis(isocyanatoethylthio)ethane,
1,5-diisocyanato-2-isocyanatomethyl-3-thiapentane, 1,2,3-tris(isocyanato-
methylthio)propane, 1,2,3-tris(isocyanatoethylthio)propane, 3,5-dithia-1,2,6,7-
heptane tetraisocyanate, 2,6-diisocyanatomethyl-3,5-dithia-1,7-heptane
diisocyanate, 2,5-diisocyanatomethylthiophene, and isocyanatoethylthio-2,6-
dithia-1,8-octane diisocyanate;
aromatic sulfide polyisocyanate compounds, such as 2-isocyanato-
phenyl-4-isocyanatophenyl sulfide, bis(4-isocyanatophenyl)sulfide and bis(4-
isocyanatomethyl phenyl)sulfide;
aromatic disulfide polyisocyanate compounds, such as bis(4-iso-
cyanatophenyl)disulfide, bis(2-methyl-5-isocyanatophenyl)disulfide, bis(3-
methyl-5-isocyanatophenyl)disulfide, bis(3-methyl-6-isocyanatophenyl)-
disulfide, bis(4-methyl-5-isocyanatophenyl)disulfide, and bis(4-methoxy-3-
isocyanatophenyl)disulftde;
sulfur-containing alicyclic polyisocyanate compounds, such as 2,5-
diisocyanatotetrahydrothiophene, 2,5-diisocyanatomethyltetrahydrothiophene,

3,4-diisocyanatomethyltetrahydrothiophene, 2,5-diisocyanato-1,4-dithiane,
2,5-diisocyanatomethyl-1,4-dithiane, 4,5-diisocyanato-1,3-dithiolane, 4,5-
bis(isocyanatomethyl)-1,3-dithiolane and 4,5-diisocyanatomethyl-2-methyl-
1,3-dithiolane;
aliphatic polyisothiocyanate compounds, such as 1,2-diisothiocyanato-
ethane and 1,6-diisothiocyanatohexane; alicyclic polyisothiocyanate
compounds such as cyclohexanediisothiocyanate; aromatic polyisothio-
cyanate compounds, such as 1,2-diisothiocyanatobenzene, 1,3-diisothio-
cyanatobenzene, 1,4-diisothiocyanatobenzene, 2,4-diisothiocyanatotoluene,
2,5-diisothiocyanato-m-xylene, 4,4'-methylene bis(phenylisothiocyanate), 4,4'-
methylene bis(2-methylphenylisothiocyanate), 4,4'-methylene bis(3-methyl-
phenylisothiocyanate), 4,4'-diisothiocyanatobenzophenone, 4,4'-diisothio-
cyanato-3,3'-dimethylbenzophenone and bis(4-isothiocyanatophenyl) ether;
Furthermore, carbonylpolyisothiocyanate compounds, such as 1,3-
benzenedicarbonyl diisothiocyanate, 1,4-benzenedicarbonyl diisothiocyanate
and (2,2-pyridine)-4,4-dicarbonyl diisothiocyanate; sulfur-containing aliphatic
polyisothiocyanate compounds, such as thiobis(3-isothiocyanatopropane),
thiobis(2-isothiocyanatoethane) and dithiobis(2-isothiocyanatoethane);
sulfur-containing aromatic polyisothiocyanate compounds, such as 1-
isothiocyanato-4-[(2-isothiocyanato)sulfonyl]benzene, thiobis(4-isothio-
cyanatobenzene), sulfonyl(4-isothiocyanatobenzene) and dithiobis(4-
isothiocyanatobenzene); sulfur-containing alicyclic polyisothiocyanate
compounds, such as 2,5-diisothiocyanatothiophene and 2,5-diisothiocyanato-
1,4-dithiane; and
polyiso(thio)cyanate compounds having an isocyanate group and an
isothiocyanate group, such as 1-isocyanato-6-isothiocyanatohexane, 1-

isocyanato-4-isothiocyanatocyclohexane, 1-isocyanato-4-isothiocyanato-
benzene, 4-methyl-3-isocyanato-1 -isothiocyanatobenzene, 2-isocyanato-4,6-
diisothiocyanato-1,3,5-triazine, 4-isocyanatophenyl-4-isothiocyanatophenyl
sulfide and 2-isocyanatoethyl-2-isothiocyanatoethyl disulfide.
Furthermore, a halogenated substitution product, such as a chlorinated
substitution product and a brominated substitution product, an alkylated
substitution product, an alkoxylated substitution product, a nitrated
substitution product, a prepolymer-type modified product with a polyhydric
alcohol, a carbodiimide-modified product, a urea-modified product, a biuret-
modified product, and a dimerized or trimerized product thereof may be used.
Notwithstanding the above, the polyiso(thio)cyanate compound is not
limited to the exemplified compounds. The exemplified compounds may be
used singly or in a combination of two or more thereof.
Among the exemplified compounds, especially at least one alicyclic
isocyanate compound should be used preferably. As such an alicyclic iso-
cyanate compound, at least one compound selected from the group consist-
ing of 2,5-bis(isocyanatomethyl)bicyclo[2.2.1]heptane, 2,6-bis(isocyanato-
methyl)bicyclo[2.2.1 ]heptane, bis(isocyanatomethyl)cyclohexane, dicyclo-
hexylmethane diisocyanate and isophorone diisocyanate should be used
preferably.
There is no particular restriction on a polythiol compound to be used
for the polymerizable composition, insofar as it is a compound having 2 or
more thiol groups in the molecule.
Specific examples of a polythiol compound include: aliphatic polythiol
compounds, such as methanedithiol, 1,2-ethanedithiol, 1,1-propanedithiol,
1,2-propanedithiol, 1,3-propanedithiol, 2,2-propanedithiol, 1,6-hexanedithiol,

1,2,3-propanetrithiol, 1,1-cyclohexanedithiol, 1,2-cyclohexanedithiol, 2,2-
dimethylpropane-1,3-dithiol, 3,4-dimethoxybutane-1,2-dithiol, 2-methylcyclo-
hexane-2,3-dithiol, 1,1-bis(mercaptomethyl)cyclohexane, bis(2-mercapto-
ethyl) thiomalate, 2,3-dimercapto-1-propanol (2-mercaptoacetate), 2,3-
dimercapto-1-propanol (3-mercaptopropionate), diethyleneglycol bis(2-
mercaptoacetate), diethyleneglycol bis(3-mercaptopropionate), 1,2-di-
mercaptopropyl methyl ether, 2,3-dimercaptopropyl methyl ether, 2,2-
bis(mercaptomethyl)-1,3-propanedithiol, bis(2-mercaptoethyl) ether,
ethyleneglycol bis(2-mercaptoacetate), ethyleneglycol bis(3-mercapto-
propionate), trimethylolpropane bis(2-mercaptoacetate), trimethylolpropane
bis(3-mercaptopropionate), pentaerythritol tetrakis(2-mercaptoacetate),
pentaerythritol tetrakis(3-mercaptopropionate) and tetrakis(mercaptomethyl)-
methane;
aromatic polythiol compounds, such as 1,2-dimercaptobenzene, 1,3-
dimercaptobenzene, 1,4-dimercaptobenzene, 1,2-bis(mercaptomethyl)-
benzene, 1,3-bis(mercaptomethyl)benzene, 1,4-bis(mercaptomethyl)benzene,
1,2-bis (mercaptoethyl)benzene, 1,3-bis(mercaptoethyl)benzene, 1,4-bis-
(mercaptoethyl)benzene, 1,2,3-trimercaptobenzene, 1,2,4-trimercapto-
benzene, 1,3,5-trimercaptobenzene, 1,2,3-tris(mercaptomethyl)benzene,
1,2,4-tris(mercaptomethyl)benzene, 1,3,5-tris(mercaptomethyl)benzene,
1,2,3-tris(mercaptoethyl)benzene, 1,2,4-tris (mercaptoethyl)benzene, 1,3,5-
tris(mercaptoethyl)benzene, 2,5-toluenedithiol, 3,4-toluenedithiol, 1,3-di(p-
methoxyphenyl)propane-2,2-dithiol, 1,3-diphenylpropane-2,2-dithiol, phenyl-
methane-1,1-dithiol and 2,4-di(p-mercaptophenyl)pentane;
aromatic polythiol compounds containing a sulfur atom in addition to a
mercapto group, such as 1,2-bis(mercaptoethylthio)benzene, 1,3-

bis(mercaptoethylthio)benzene, 1,4-bis(mercaptoethylthio)benzene, 1,2,3-
tris(mercaptomethylthio)benzene, 1,2,4-tris(mercaptomethylthio)benzene,
1,3,5-tris(mercaptomethylthio)benzene, 1,2,3-tris(mercaptoethylthio)benzene,
1,2,4-tris(mercaptoethylthio)benzene and 1,3,5-tris(mercaptoethylthio)-
benzene, as well as nuclear alkylated derivatives thereof;
aliphatic polythiol compounds containing a sulfur atom in addition to a
mercapto group, such as bis(mercaptomethyl) sulfide, bis(mercaptomethyl)
disulfide, bis(mercaptoethyl) sulfide, bis(mercaptoethyl) disulfide, bis-
(mercaptopropyl) sulfide, bis(mercaptomethylthio)methane, bis(2-mercapto-
ethylthio)methane, bis(3-mercapto propylthio)methane, 1,2-bis(mercapto-
methylthio)ethane, 1,2-bis(2-mercaptoethylthio)ethane, 1,2-bis(3-mercapto-
propyl)ethane, 1,3-bis(mercaptomethylthio)propane, 1,3-bis(2-mercapto-
ethylthio)propane, 1,3-bis(3-mercaptopropylthio)propane, 1,2,3-tris(mercapto-
methylthio)propane, 1,2,3-tris(2-mercaptoethylthio)propane, 1,2,3-tris(3-
mercaptopropylthio)propane, 1,2-bis[(2-mercaptoethyl)thio]-3-mercapto-
propane, 4,8-dimercaptomethyl-1,11-dimercapto-3,6,9-trithiaundecane, 4,7-
dimercaptomethyl-1,11-dimercapto-3,6,9-trithiaundecane, 5,7-dimercapto-
methyl 1,11-dimercapto-3,6,9-trithiaundecane, bis(mercaptomethyl)-3,6,9-
trithia-1,11-undecanedithiol, tetrakis(mercaptomethylthiomethyl)methane,
tetrakis(2-mercaptoethylthiomethyl)methane, tetrakis(3-mercaptopropyl-
thiomethyl)methane, bis(2,3-dimercaptopropyl) sulfide, bis(1,3-dimercapto-
propyl) sulfide, 2,5-dimercapto-1,4-dithiane, 2,5-dimercaptomethyl-1,4-
dithiane, 2,5-dimercapto methyl-2,5-dimethyl-1,4-dithiane, bis(mercapto-
methyl) disulfide, bis(mercaptoethyl) disulfide and bis(mercaptopropyl)
disulfide, as well as thioglycolates and mercaptopropionates ester thereof;
other aliphatic polythiol compounds containing an ester bond and a

sulfur atom in addition to a mercapto group, such as hydroxymethylsulfide
bis(2-mercaptoacetate), hydroxymethylsulfide bis(3-mercaptopropionate),
hydroxyethylsulfide bis(2-mercaptoacetate), hydroxyethylsulfide bis(3-
mercaptopropionate), hydroxypropylsulfide bis(2-mercaptoacetate), hydroxy-
propylsulfide bis(3-mercaptopropionate), hydroxymethyldisulfide bis(2-
mercaptoacetate), hydroxymethyldisulfide bis(3-mercaptopropionate),
hydroxyethyldisulfide bis(2-mercaptoacetate), hydroxyethyldisulfide bis(3-
mercaptopropionate), hydroxypropyldisulfide bis(2-mercaptoacetate),
hydroxypropyldisulfide bis(3-mercaptopropionate), 2-mercaptoethylether
bis(2-mercaptoacetate), 2-mercaptoethylether bis(3-mercaptopropionate),
1,4-dithiane-2,5-diol bis(2-mercaptoacetate), 1,4-dithiane-2,5-diol bis(3-
mercaptopropionate), bis(2-mercaptoethyl)thiodiglycolate, bis(2-mercapto-
ethyl)thiodipropionate, bis(2-mercaptoethyl)-4,4-thiodibutyrate, bis(2-
mercaptoethyl)dithiodiglycolate, bis(2-mercaptoethyl)dithiodipropionate, bis-
(2-mercaptoethyl)-4,4-dithiodibutyrate, bis(2,3-dimercaptopropyl)thiodi-
glycolate, bis(2,3-dimercaptopropyl)thiodipropionate, bis(2,3-dimercapto-
propyl)dithiodiglycolate, and bis(2,3-dimercaptopropyl)dithiodipropionate;
heterocyclic compounds containing a sulfur atom in addition to a
mercapto group, such as 3,4-thiophenedithiol, and 2,5-dimercapto-1,3,4-
thiadiazole;
compounds containing a hydroxy group in addition to a mercapto
group, such as 2-mercaptoethanol, 3-mercapto-1,2-propanediol, glycerin
di(mercaptoacetate), 1 -hydroxy-4-mercaptocyclohexane, 2,4-dimercapto-
phenol, 2-mercaptohydroquinone, 4-mercaptophenol, 3,4-dimercapto-2-
propanol, 1,3-dimercapto-2-propanol, 2,3-dimercapto-1-propanol, 1,2-
dimercapto-1,3-butanediol, pentaerythritol tris(3-mercaptopropionate),

pentaerythritol mono(3-mercaptopriopionate), pentaerythritol bis(3-
mercaptopropionate), pentaerythritol tris(thioglycolate), dipentaerythritol
pentakis(3-mercaptopropionate), hydroxymethyltris(mercaptoethylthio-
methyl)methane and 1 -hydroxyethylthio-3-mercaptoethylthiobenzene;
compounds having a dithioacetal or dithioketal skeleton, such as
1,1,3,3-tetrakis(mercaptomethylthio)propane, 1,1,2,2-tetrakis(mercapto-
methylthio) ethane, 4,6-bis(mercaptomethylthio)-1,3-dithiacyclohexane,
1,1,5,5-tetrakis(mercaptomethylthio)-3-thiapentane, 1,1,6,6-tetrakis(mercapto-
methylthio)-3,4-dithiahexane, 2,2-bis(mercaptomethylthio)ethanethiol, 2-(4,5-
dimercapto-2-thiapentyl)-1,3-dithiacyclopentane, 2,2-bis(mercaptomethyl)-
1,3-dithiacyclopentane, 2,5-bis(4,4-bis(mercaptomethylthio)-2-thiabutyl)-1,4-
dithiane, 2,2-bis(mercaptomethylthio)-1,3-propanedithiol, 3-mercapto-
methylthio-1,7-dimercapto-2,6-dithiaheptane, 3,6-bis(mercaptomethylthio)-
1,9-dimercapto-2,5,8-trithianonane, 4,6-bis(mercaptomethylthio)-1,9-
dimercapto-2,5,8-trithianonane, 3-mercaptomethylthio-1,6-dimercapto-2,5-
dithiahexane, 2-(2,2-bis(mercaptodimethylthio)ethyl)-1,3-dithiethane, 1,1,9,9-
tetrakis(mercaptomethylthio)-5-(3,3-bis(mercaptomethylthio)-1-thiapropyl)-
3,7-dithianonane, tris(2,2-bis(mercaptomethylthio)-ethyl)methane, tris(4,4-
bis(mercaptomethylthio)-2-thiabutyl)methane, tetrakis(2,2-bis(mercapto-
methylthio)ethyl)methane, tetrakis(4,4-bis(mercaptomethylthio)-2-
thiabutyl)methane, 3,5,9,11-tetrakis(mercaptomethylthio)-1,13-dimercapto-
2,6,8,12-tetrathiatridecane, 3,5,9,11,15,17-hexakis(mercaptomethylthio)-1,19-
dimercapto-2,6,8,12,14,18-hexathianonadecane, 9-(2,2-bis(mercaptomethyl-
thio)ethyl)-3,5,13,15-tetrakis(mercaptomethylthio)-1,17-dimercapto-
2,6,8,10,12,16-hexathiaheptadecane, 3,4,8,9-tetrakis(mercaptomethylthio)-
1,11 -dimercapto-2,5,7,10-tetrathiaundecane, 3,4,8,9,13,14-hexakis(mercapto-

methylthio)-1,16-dimercapto-2,5,7,10,12,15-hexathiahexadecane, 8-{bis-
(mercaptomethylthio)methyl}-3,4,12,13-tetrakis(mercaptomethylthio)-1,15-
dimercapto-2,5,7,9,11,14-hexathiapentadecane, 4,6-bis{3,5-bis(mercapto-
methylthio)-7-mercapto-2,6-dithiaheptylthio}-1,3-dithiane, 4-{3,5-bis-
(mercaptomethylthio)-7-mercapto-2,6-dithiaheptylthio}-6-mercaptomethylthio-
1,3-dithiane, 1,1-bis{4-(6-mercaptomethylthio)-1,3-dithianylthio}-3,3-bis-
(mercaptomethylthio)propane, 1,3-bis{4-(6-mercaptomethylthio)-1,3-dithianyl-
thio}-1,3-bis(mercaptomethylthio)propane, 1-{4-(6-mercaptomethylthio)-1,3-
dithianylthio}-3-{2,2-bis(mercaptomethylthio)ethyl}-7,9-bis(mercaptomethyl-
thio)-2,4,6,10-tetrathiaundecane, 1-{4-(6-mercaptomethylthio)-1,3-dithianyl-
thio}-3-{2-(1,3-dithietanyl)}methyl-7,9-bis(mercaptomethylthio)-2,4,6,10-
tetrathiaundecane, 1,5-bis{4-(6-mercaptomethylthio)-1,3-dithianylthio}-3-{2-
(1,3-dithietanyl)}methyl-2,4-dithiapentane, 4,6-bis[3-{2-(1,3-dithietanyl)}-
methyl-5-mercapto-2,4-dithiapentylthio]-1,3-dithiane, 4,6-bis{4-(6-mercapto-
methylthio)-1,3-dithianylthio}-1,3-dithiane, 4-{4-(6-mercaptomethylthio)-1,3-
dithianylthio}-6-{4-(6-mercaptomethylthio)-1,3-dithianylthio}-1,3-dithiane, 3-{2-
(1,3-dithietanyl)}methyl-7,9-bis(mercaptomethylthio)-1,11-dimercapto-
2,4,6,10-tetrathiaundecane, 9-{2-(1,3-dithietanyl)}methyl-3,5,13,15-tetrakis-
(mercaptomethylthio)-1,17-dimercapto-2,6,8,10,12,16-hexathiaheptadecane,
3-{2-(1,3-dithietanyl)}methyl-7,9,13,15-tetrakis(mercaptomethylthio)-1,17-
dimercapto-2,4,6,10,12,16-hexathiaheptadecane, 3,7-bis{2-(1,3-dithietanyl)}-
methyl-1,9-dimercapto2,4,6,8-tetrathianonane, 4-{3,4,8,9-tetrakis(mercapto-
methylthio)-11 -mercapto-2,5,7,10-tetrathiaundecyl}-5-mercaptomethylthio-
1,3-dithiolane, 4,5-bis{3,4-bis(mercaptomethylthio)-6-mercapto-2,5-dithia-
hexylthio}-1,3-dithiolane, 4-{3,4-bis(mercaptomethylthio)-6-mercapto-2,5-
dithiahexylthio}-5-mercaptomethylthio-1,3-dithiolane, 4-{3-bis(mercapto-

methylthio)methyl-5,6-bis(mercaptomethylthio)-8-mercapto-2,4,7-trithiaoctyl}-
5-mercaptomethylthio-1,3-dithiolane, 2-[bis{3,4-bis(mercaptomethylthio)-6-
mercapto-2,5-dithiahexylthio}methyl]-1,3-dithiethane, 2-{3,4-bis(mercapto-
methylthio)-6-mercapto-2,5-dithiahexylthio}mercaptomethylthiomethyl-1,3-
dithiethane, 2-{3,4,8,9-tetrakis(mercaptomethylthio)-11-mercapto-2,5,7,10-
tetrathiaundecylthio}mercaptomethylthiomethyl-1,3-dithiethane, 2-{3-bis-
(mercaptomethylthio)methyl-5,6-bis(mercaptomethylthio)-8-mercapto-2,4,7-
trithiaoctyl}mercaptomethylthiomethyl-1,3-dithiethane, 4,5-bis[1-{2-(1,3-
dithietanyl)}-3-mercapto-2-thiapropylthio]-1,3-dithiolane, 4-[1-{2-(1,3-
dithietanyl)}-3-mercapto-2-thiapropylthio]-5-{1,2-bis(mercaptomethylthio)-4-
mercapto-3-thiabutylthio}-1,3-dithiolane, 2-[bis{4-(5-mercaptomethylthio-1,3-
dithiolanyl)thio}]methyl-1,3-dithiethane, and 4-{4-(5-mercaptomethylthio-1,3-
dithiolanyl)thio}-5-[1 -{2-(1,3-dithietanyl)}-3-mercapto-2-thiapropylthio]-1,3-
dithiolane, as well as oligomers thereof;
compounds having a skeleton of an orthotrithioformate ester, such as
tris(mercaptomethylthio)methane, tris(mercaptoethylthio)methane, 1,1,5,5-
tetrakis(mercaptomethylthio)-2,4-dithiapentane, bis(4,4-bis(mercapto-
methylthio)-1,3-dithiabutyl)(mercaptomethylthio)methane, tris(4,4-bis-
(mercaptomethylthio)-1,3-dithiabutyl)methane, 2,4,6-tris(mercaptomethylthio)-
1,3,5-trithiacyclohexane, 2,4-bis(mercaptomethylthio)-1,3,5-trithiacyclo-
hexane, 1,1,3,3-tetrakis(mercaptomethylthio)-2-thiapropane, bis(mercapto-
methyl)methylthio-1,3,5-trithiacyclohexane, tris((4-mercaptomethyl-2,5-
dithiacyclohexyl-1 -yl)methylthio)methane, 2,4-bis(mercaptomethylthio)-1,3-
dithiacyclopentane, 2-mercaptoethylthio-4-mercaptomethyl-1,3-dithia-
cyclopentane, 2-(2,3-dimercaptopropylthio)-1,3-dithiacyclopentane, 4-
mercaptomethyl-2-(2,3-dimercaptopropylthio)-1,3-dithiacyclopentane, 4-

mercaptomethyl-2-( 1,3-d imercapto-2-propylth io)-1,3-d ith iacyclopentane,
tris(2,2-bis(mercaptomethylthio)-1-thiaethyl)methane, tris(3,3-bis(mercapto-
methylthio)-2-thiapropyl)methane, tris(4,4-bis(mercaptomethylthio)-3-thia-
butyl)methane, 2,4,6-tris(3,3-bis(mercaptomethylthio)-2-thiapropyl)-1,3,5-
trithiacyclohexane, and tetrakis(3,3-bis(mercaptomethylthio)-2-thiapropyl]-
methane, as well as oligomers thereof; and
compounds having an orthotetrathiocarbonic ester skeleton, such as
3,3'-di(mercaptomethylthio)-1,5-dimercapto-2,4-dithiapentane, 2,2'-di-
(mercaptomethylthio)-l ,3-dithiacyclopentane, 2,7-di(mercaptomethyl)-1,4,5,9-
tetrathiaspiro[4,4] nonane, and 3,9-dimercapto-1,5,7,11-tetrathiaspiro[5,5]-
undecane, as well as oligomers thereof.
Notwithstanding the above, the polythiol compound is not limited to the
exemplified compounds. The exemplified compounds may be used singly or
in a combination of two or more thereof.
Among the exemplified compounds, at least one polythiol compound
selected from the group consisting of 1,2-bis[(2-mercaptoethyl)thio]-3-
mercaptopropane, bis(mercaptomethyl)-3,6,9-trithia-1,11-undecanedithiol,
pentaerythritol tetrakis(3-mercaptopropionate), 1,1,3,3-tetrakis(mercapto-
methylthio)propane and 2-mercaptoethanol should preferably be used.
The usage ratio of a polythiol compound to a polyiso(thio)cyanate
compound is normally in a range of SH group / NCO group = 0.5 to 3.0, and
preferably 0.6 to 2.0, further preferably 0.8 to 1.3.
In order to improve physical properties, handling properties and po-
lymerization reactivity of the polyurethane resin, in addition to a polythiol
compound and an iso(thio)cyanate compound that build the urethane resin,
one or more compounds other than the raw materials forming urethane, such

as an active hydrogen compound as represented by an amine, an epoxy
compound, an olefin compound, a carbonate compound, an ester compound,
a metal, a metal oxide, an organometallic compound and a mineral, may be
added.
Furthermore according to a purpose, various substances, such as a
chain extending agent, a cross-linking agent, a light stabilizer, a UV absorber,
an antioxidant, an oil-soluble dye, a filler, a release agent, and a bluing agent,
may be optionally added as in a publicly known molding process. To regu-
late the reaction rate at a desired level, S-alkyl thiocarbamate ester or a pub-
licly known reaction catalyst used for producing polyurethane may be appro-
priately added.
An optical material composed of a polyurethane resin is in general
produced by cast polymerization. More specifically, a polythiol compound
and a polyiso(thio)cyanate compound are mixed, and optionally, as needed,
degassed by an appropriate method. The mixture (a polymerizable compo-
sition) is then cast in a mold for an optical material, which is usually heated up
gradually from a low temperature to a high temperature for polymerization,
followed by demolding to obtain the optical material.
A polyurethane resin produced according to the process of the present
invention has a high refractive index and a low dispersion property, is superior
in heat resistance and durability, and enjoys favorable properties of light-
weight and high impact-resistance as well as a good hue. Consequently the
resin is suitable for optical materials, such as a lens and a prism, and espe-
cially good for use in a lens, such as a spectacle lens and a camera lens.
Furthermore, the optical material may be optionally subjected to a
physical or chemical treatment, such as surface polishing, an antistatic treat-

ment, hard coating, an anti-reflection coating, a tinting treatment and a photo-
chromic treatment for a purpose of improvements by inhibiting reflection, im-
parting high hardness, improving abrasion resistance, improving chemical re-
sistance, imparting an antifogging property or imparting fashionability.
The optical material made of the polyurethane resin according to the
present invention is characterized by extremely rare striation or clouding. In
other words, the optical material of the present invention is characterized in
that it has excellent properties and can be produced at a high yield. As for
specific measuring method of the occurrence rates of striation and clouding,
100 pieces of an optical material are visually inspected under a high-pressure
mercury lamp. If a stria is observed the sample is judged to have striation,
and if turbidity is observed the sample is judged to have clouding.
Examples
The present invention will be described in more detail by means of Ex-
amples. The water content in a polymerizable composition, the polymeriza-
tion rate and the occurrence rates of striation and clouding of a resin are
measured according to the following methods. Hereinafter "part(s)" means
"part(s) by weight".
Water Content: It was measured by a Karl-Fisher moisture meter.
More specifically an automatic moisture meter KF-100 (by Mitsubishi Chemi-
cal Corp.) and a water vaporizer VA-100 with a board (by Mitsubishi Chemical
Corp.) were used.
Polymerization Rate: It was evaluated by defining the time of prepa-
ration of a polymerizable composition as time zero (0), and using as an index
the viscosity at hour 7.

Occurrence Rate of Striation: The "striation" means a phenomenon
of existence of localized difference from a normal refractive index of the sur-
roundings due to nonuniformity of the composition, etc. The occurrence rate
was determined in the Example using 100 lenses by judging a lens as having
striation, in which a stria was identified by means of visual observation under
a high-pressure mercury lamp.
Occurrence Rate of Clouding: It was determined using 100 lenses by
judging a lens as having clouding, in which turbidity was identified by means
of visual observation under a high-pressure mercury lamp.
[Example 1]
(Measurement of viscosity of polymerizable composition)
At 10 to 15°C, 60 parts of dicyclohexylmethane diisocyanate, 0.05
parts of dimethyltin dichloride as a curing catalyst, 0.10 parts of acidic
phosphate ester (Trade name: Zelec UN by Stepan Company), 0.05 parts of
a UV absorber (Trade name: Viosorb 583 by Kyodo Chemical Co., Ltd.) were
mixed and dissolved. Additionally, 40 parts of a polythiol composed of 1,2-
bis[(2-mercaptoethyl)thio]-3-mercaptopropane as a main component was
charged and mixed together to obtain a homogeneous liquid mixture (a poly-
merizable composition). The water content of the used polythiol was 50
ppm, and the water content of the polymerizable composition was 20 ppm.
Defining the time of preparation of the homogeneous liquid mixture as time
zero (0), the viscosity at hour 7 was measured. The result is shown in Table
1.
(Production of plastic lens)
At 10 to 15°C, 60 parts of dicyclohexylmethane diisocyanate, 0.05
parts of dimethyltin dichloride as a curing catalyst, 0.10 parts of acidic

phosphate ester (Zelec UN), 0.05 parts of a UV absorber (Viosorb 583) were
mixed and dissolved. Additionally, 40 parts of a polythiol composed of 1,2-
bis[(2-mercaptoethyl)thio]-3-mercaptopropane as a main component was
charged and mixed together to obtain a homogeneous liquid mixture (a poly-
merizable composition). The water content of the used polythiol was 50
ppm, and the water content of the polymerizable composition was 20 ppm.
The homogeneous liquid mixture was degassed at 600 Pa for 1 hour and fil-
trated by a 1 |wm PTFE (polytetrafluoroethylene) filter. The liquid was then
cast into a lens mold constituted of a glass mold of diameter 75 mm for-4D
and a tape. The mold was then placed in an oven, whose temperature was
kept at 40°C for 2 hours, raised to 50°C over 4 hours, kept there for 2 hours,
raised to 60°C over 3 hours, and kept there for 2 hours. The temperature
was further raised to 70°C over 3 hours, kept there for 2 hours, raised to
100°C over 3 hours, then further raised to 130°C over 1 hour, and kept there
for 2 hours. As described above, the polymerization was carried out in the
temperature range of 40°C to 130°C for totally 24 hours. After the comple-
tion of the polymerization, the mold was removed from the oven and the lens
was demolded. Then the obtained lens was further annealed at 120°C for 3
hours. One hundred (100) lenses were produced as above and the striation
occurrence rate and the clouding occurrence rate were determined. The re-
sults are shown in Table 1.
[Example 2]
Except that a polymerizable composition with the water content of 100
ppm was used instead of the polymerizable composition used in Example 1,
the measurement of the viscosity of the polymerizable composition and the
production of the plastic lens were carried out identically to Example 1. The

results are shown in Table 1.
[Example 3]
Except that a polymerizable composition with the water content of 200
ppm was used instead of the polymerizable composition used in Example 1,
the measurement of the viscosity of the polymerizable composition and the
production of the plastic lens were carried out identically to Example 1. The
results are shown in Table 1.
[Example 4]
Except that a polymerizable composition with the water content of 300
ppm was used instead of the polymerizable composition used in Example 1,
the measurement of the viscosity of the polymerizable composition and the
production of the plastic lens were carried out identically to Example 1. The
results are shown in Table 1.
[Example 5]
(Measurement of viscosity of polymerizable composition)
At 10 to 15°C, 50.6 parts of a mixture of 2,5-bis(isocyanatomethyl)-
bicyclo[2.2.1]heptaneand 2,6-bis(isocyanatomethyl)bicyclo[2.2.1]heptane,
0.06 parts of dibutyltin dichloride as a curing catalyst, 0.12 parts of acidic
phosphate ester (Zelec UN), 0.05 parts of a UV absorber (Viosorb 583) were
mixed and dissolved. Additionally, 25.5 parts of a polythiol composed of 1,2-
bis[(2-mercaptoethyl)thio]-3-mercaptopropane as a main component and 23.9
parts of pentaerythritol tetrakis(mercaptopropionate) were charged
respectively and mixed together to obtain a homogeneous liquid mixture (a
polymerizable composition). The water content of the used polythiol com-
posed of 1,2-bis[(2-mercaptoethyl)thio]-3-mercaptopropane as a main com-
ponent was 40 ppm, the water content of pentaerythritol tetrakis(mercapto-

propionate) was 20 ppm and the water content of the polymerizable composi-
tion was 15 ppm. Defining the time of preparation of the homogeneous liq-
uid mixture as time zero (0), the viscosity at hour 7 was measured. The re-
sult is shown in Table 1.
(Production of plastic lens)
At 10 to 15°C, 50.6 parts of a mixture of 2,5-
bis(isocyanatomethyl)bicyclo[2.2.1 Jheptane and 2,6-bis(isocyanatomethyl)-
bicyclo[2.2.1]heptane, 0.06 parts of dibutyltin dichloride as a curing catalyst,
0.12 parts of acidic phosphate ester (Zelec UN), 0.05 parts of a UV absorber
(Viosorb 583) were mixed and dissolved. Additionally, 25.5 parts of a
polythiol composed of 1,2-bis[(2-mercaptoethyl)thio]-3-mercaptopropane as a
main component and 23.9 parts of pentaerythritol tetrakis(mercapto-
propionate) were charged respectively and mixed together to obtain a homo-
geneous liquid mixture (a polymerizable composition). The water content of
the used polythiol composed of 1,2-bis[(2-mercaptoethyl)thio]-3-mercapto-
propane as a main component was 40 ppm, the water content of
pentaerythritol tetrakis(mercaptopropionate) was 20 ppm and the water con-
tent of the polymerizable composition was 15 ppm. The homogeneous liquid
mixture was degassed at 600 Pa for 1 hour and filtrated by a 1 |am PTFE fil-
ter. The liquid was then cast into a lens mold constituted of a glass mold of
diameter 75 mm for-4D and a tape. The mold was then placed in an oven,
whose temperature was kept at 40°C for 2 hours, raised to 50°C over 4 hours,
kept there for 2 hours, raised to 60°C over 3 hours, and kept there for 2
hours. The temperature was further raised to 70°C over 3 hours, kept there
for 2 hours, raised to 100°C over 3 hours, then further raised to 130°C over 1
hour, and kept there for 2 hours. As described above, the polymerization

was carried out in the temperature range of 40°C to 130°C for totally 24
hours. After the completion of the polymerization, the mold was removed
from the oven and the lens was demolded. Then the obtained lens was an-
nealed at 120°C for 3 hours. One hundred (100) lenses were produced as
above and the striation occurrence rate and the clouding occurrence rate
were determined. The results are shown in Table 1.
[Example 6]
Except that a polymerizable composition with the water content of 150
ppm was used instead of the polymerizable composition used in Example 5,
the measurement of the viscosity of the polymerizable composition and the
production of the plastic lens were carried out identically to Example 5. The
results are shown in Table 1.
[Example 7]
Except that a polymerizable composition with the water content of 300
ppm was used instead of the polymerizable composition used in Example 5,
the measurement of the viscosity of the polymerizable composition and the
production of the plastic lens were carried out identically to Example 5. The
results are shown in Table 1.
[Example 8]
(Measurement of viscosity of polymerizable composition)
At 10 to 15°C, 49.7 parts of a mixture of 2,5-bis(isocyanatomethyl)-
bicyclo[2.2.1]heptaneand2,6-bis(isocyanatomethyl)bicyclo[2.2.1]heptane,
0.03 parts of dibutyltin dichloride as a curing catalyst, 0.12 parts of acidic
phosphate ester (Zelec UN), 0.05 parts of a UV absorber (Viosorb 583) were
mixed and dissolved. Additionally, 25.9 parts of a polythiol composed of
bis(mercaptomethyl)-3,6,9-trithia-1,11-undecanedithiol as a main component

and 24.4 parts of pentaerythritol tetrakis(mercaptopropionate) were charged
respectively and mixed together to obtain a homogeneous liquid mixture (a
polymerizable composition). The water content of the used polythiol com-
posed of bis(mercaptomethyl)-3,6,9-trithia-1,11-undecanedithiol as a main
component was 70 ppm, the water content of pentaerythritol tetrakis
(mercaptopropionate) was 20 ppm and the water content of the polymerizable
composition was 21 ppm. Defining the time of preparation of the homoge-
neous liquid mixture as time zero (0), the viscosity at hour 7 was measured.
The result is shown in Table 1.
(Production of plastic lens)
At 10 to 15°C, 50.6 parts of a mixture of 2,5-bis(isocyanatomethyl)-
bicyclo[2.2.1]heptaneand 2,6-bis(isocyanatomethyl)bicyclo[2.2.1]heptane,
0.06 parts of dibutyltin dichloride as a curing catalyst, 0.12 parts of acidic
phosphate ester (Zelec UN), 0.05 parts of a UV absorber (Viosorb 583) were
mixed and dissolved. Additionally, 25.5 parts of a polythiol composed of
bis(mercaptomethyl)-3,6,9-trithia-1,11-undecanedithiol as a main component
and 23.9 parts of pentaerythritol tetrakis (mercaptopropionate) were charged
respectively and mixed together to obtain a homogeneous liquid mixture (a
polymerizable composition). The water content of the used polythiol com-
posed of bis(mercaptomethyl)-3,6,9-trithia-1,11-undecanedithiol as a main
component was 70 ppm, the water content of pentaerythritol tetrakis
(mercaptopropionate) was 20 ppm and the water content of the polymerizable
composition was 21 ppm. The homogeneous liquid mixture was degassed
at 600 Pa for 1 hour and filtrated by a 1 |am PTFE filter. The liquid was then
cast into a lens mold constituted of a glass mold of diameter 75 mm for-4D
and a tape. The mold was then placed in an oven, whose temperature was

kept at 40°C for 2 hours, raised to 50°C over 4 hours, kept there for 2 hours,
raised to 60°C over 3 hours, and kept there for 2 hours. The temperature
was further raised to 70°C over 3 hours, kept there for 2 hours, raised to
100°C over 3 hours, then further raised to 130°C over 1 hour, and kept there
for 2 hours. As described above, the polymerization was carried out in the
temperature range of 40°C to 130°C for totally 24 hours. After the comple-
tion of the polymerization, the mold was removed from the oven and the lens
was demolded. Then the obtained lens was annealed at 120°C for 3 hours.
One hundred (100) lenses were produced as above and the striation occur-
rence rate and the clouding occurrence rate were determined. The results
are shown in Table 1.
[Example 9]
Except that a polymerizable composition with the water content of 150
ppm was used instead of the polymerizable composition used in Example 8,
the measurement of the viscosity of the polymerizable composition and the
production of the plastic lens were carried out identically to Example 8. The
results are shown in Table 1.
[Example 10]
Except that a polymerizable composition with the water content of 300
ppm was used instead of the polymerizable composition used in Example 8,
the measurement of the viscosity of the polymerizable composition and the
production of the plastic lens were carried out identically to Example 8. The
results are shown in Table 1.
[Comparative Example 1]
Except that a polymerizable composition with the water content of 500
ppm was used instead of the polymerizable composition used in Example 1,

the measurement of the viscosity of the polymerizable composition and the
production of the plastic lens were carried out identically to Example 1. The
results are shown in Table 1.
[Comparative Example 2]
Except that a polymerizable composition with the water content of
1,000 ppm was used instead of the polymerizable composition used in Exam-
ple 1, the measurement of the viscosity of the polymerizable composition and
the production of the plastic lens were carried out identically to Example 1.
The results are shown in Table 1.
[Comparative Example 3]
Except that a polymerizable composition with the water content of 500
ppm was used instead of the polymerizable composition used in Example 5,
the measurement of the viscosity of the polymerizable composition and the
production of the plastic lens were carried out identically to Example 5. The
results are shown in Table 1.
[Comparative Example 4]
Except that a polymerizable composition with the water content of 500
ppm was used instead of the polymerizable composition used in Example 8,
the measurement of the viscosity of the polymerizable composition and the
production of the plastic lens were carried out identically to Example 8. The
results are shown in Table 1.

[Table 1]

The occurrence rates of striation and clouding of a resin obtained from
a polymerizable composition with the low water content using an appropriate
catalyst amount and polymerization profile are 0 to about 15%. From the re-
sults of Examples and Comparative Examples, it was confirmed that with the
increase of the water content in the polymerizable composition the polymeri-
zation rate decreased and the viscosity at hour 7 decreased. As the result,
the striation occurrence rate and the clouding occurrence rate increased,
which increase changed dramatically beyond the threshold water content of
300 ppm. It is so considered that mismatch between a polymerization recipe
and a polymerization rate should arise, if the water content exceeds a certain

level, which results in increase of the striation occurrence rate and the cloud-
ing occurrence rate. In case of this polymerizable composition, if the water
content is higher than 300 ppm, the viscosity at hour 7 is about 60% com-
pared to the viscosity obtained from a lower water content, which indicates
that the decrease of the polymerization rate should be limited to such level in
order to inhibit striation or clouding. In other words, it has been found that by
use of a polymerizable composition with the water content of 10 to 300 ppm,
a highly transparent polyurethane resin can be provided.
Industrial Applicability
A polyurethane resin to be obtained by reacting a polythiol compound
and a polyiso(thio)cyanate compound is transparent and colorless, has a high
refractive index and a low dispersion property, is excellent in an impact
strength, tintability and processability, and therefore constitutes one of the
most suitable resins for a plastic lens. Among others, the resin properties of
transparency and good hue are crucial. The present invention provides a
transparent and high performance optical material securing such crucial
properties for an optical material such as a lens stably at a high yield, contrib-
uting to development of the relevant art.

We claim :
1. A process for producing a resin for an optical material by polymerizing a
polymerizable composition comprising a polythiol compound and a
polyiso(thio)cyanate compound, characterized in that a water content in the
composition is 10 to 300 ppm.
2. The process for producing a resin for an optical material according to claim 1,
wherein a water content in the polythiol compound is 20 to 600 ppm.
3. The process for producing a resin for an optical material according to claim 1,
wherein the polythiol compound comprises at least one compound selected from
the group consisting of 1,2-bis[(2-mercaptoethyl)thio]-3-mercaptopropane, bis
(mercaptomethyl)-3,6,9-trithia-1,11-undecanedithiol, pentaerythritol tetrakis (3-
mercaptopropionate),1,1,3,3-tetrakis (mercaptomethylthio)propane and 2-
mercaptoethanol; and the iso (thio)cyanate compound comprises at least one
alicyclic isocyanate compound.
4. The process for producing a resin for an optical material according to claim 3,
wherein the alicyclic isocyanate compound comprises at least one compound
selected from the group consisting of 2,5-bis(isocyanatomethyl)-
bicyclo[2.2.1]heptane,2,6-bis(isocyanatomethyl)bicycle[2.2.1]-heptance,
bis(isocyanatomethyl)cyclohexane, dicyclohexylmethane diisocyanate and
isophorone diisocynate.

5. The process for producing a resin for an optical material according to claim 1,
wherein the optical material is a lens.
6. A resin for an optical material to be obtained by the process according to claim 1.
7. An optical material comprising the resin according to claim 6.
8. A lens comprising the resin according to claim 6.

Disclosed is a process for producing effectively a high performance optical material (e.g. a lens) made of a polyurethane resin, which is transparent and colorless without a strain. In this process, the optical material is produced
without causing striation or clouding by polymerizing a polymerizable composition comprising a polythiol compound and a polyiso(thio)cyanate compound, and characterized in that a water content in the composition is 10 to 300 ppm.