Composition for urethane-based plastic lens

Abstract: Disclosed are a composition for a urethane-base plastic lens, comprising: (a) at least one ester compound selected from isocyanate compounds, isothiocyanate compounds and isocyanato-containing isothiocyanate compounds, (b) at least one active hydrogen compound selected from hydroxyl compounds, mercapto compounds and mercapto-containing hydroxyl compounds, (c) a tertiary amine, and (d) a Lewis acid; a plastic lens obtained by heating and curing the composition, and a process for the production of the plastic lens. This composition has a long pot life and can produce an optically uniform plastic lens in a short time.

Description: This invention relates to a composition for urethane-based plastic lenses useful as various optical lenses such as eyeglass lenses, a lens obtained from the composition, and also a process for the production of the lens. Plastic lenses are moldings which are required to have a high degree of optical homogeneity for their application purpose. Although the mechanism for the occurrence of optical non-uniformity has not been fully elucidated, it is considered to occur during the molding work of a plastic lens. Thermal non-uniformity appears to take place due to a localized progress of polymerization, resulting in convection of monomers. These monomers under the convection then seem to be solidified, that is, polymerized as they are, leading to optical non-uniformity. Upon molding a plastic lens, casting polymerization is generally adopted, in which raw materials, namely, monomers are injected in a mold and then cured under heat. To obtain an optically uniform molding, the monomers are polymerized by gradually heating them from a low temperature to a high temperature, generally in the course of over ten hours or, to obtain a thick molding tending to develop optical non-uniformity, for several days so that occurrence of thermal non-uniformity inside the lens can be avoided. On the other hand, it has also been attempted in various ways to obtain an optically uniform molding in a short time. A representative example of such attempts is polymerization making use of light or another radiation, whose application has been attempted on radical-polymerizable monomers. This is to conduct polymerization by using light or another radiation which features a high polymerization velocity, so that monomers can be cured in one breath prior to occurrence of any thermal non-uniformity inside the resulting lens [Isao Kaetsu, "Kogaku Gijutsu Contact (Optical Technology Contact)", 7(7), 31 (1979)]. In the meantime, the present inventors proposed urethane-based plastic lenses as plastic lenses having a high refractive index. For example, they proposed, in Japanese Patent Laid-Open No. 199016/1985, a urethane-base plastic lens obtained by heating and curing a composition of a polyisocyanate compound and a polythiol compound and, in Japanese Patent Laid-Open No. 217229/1985, a urethane-base plastic lens obtained by heating and curing a composition of a polyisocyanate compound and a polyol compound. Despite the outstanding demand for a reduction in the polymerization time, it is impossible to adopt, for the molding of these urethane-based plastic lenses, the light- or radiation-dependent instantaneous polymerization unlike compositions of the radical-polymerizable type because urethanation is a reaction governed by heat. Furthermore, upon molding plastic lenses, it generally takes at least 2 to 5 hours from the preparation of a monomer composition until its injection into molds. Use of a high-activity catalyst or of a catalyst in a large proportion to provide an increased polymerization velocity is however accompanied by the problem that a polymerization reaction is allowed to proceed during the preparation of the monomer composition, thereby making it impossible to inject the monomer composition into the molds, in other words, no sufficient pot life is available. As a production process for these urethane-based plastic lenses, the present inventors also proposed in Japanese Patent Laid-Open No. 84021/1991 a process making use of a tertiary amine either singly or in combination with dibutyltin dilaurate. The tertiary amine employed in this process is required to contain an electron attractive group in its molecule. If a tertiary amine free of such an electron attractive group, for example, triethylamine is used, the activity of the amine is said to be so high that the polymerization reaction proceeds uncontrollably fast. This makes it impossible even to inject the monomers into a mold. Even with this process, there is the problem that, when polymerization is conducted under heat in a short time, the resulting lens tends to develop optical non-uniformity. Preferred embodiments of the present invention may enable the attainment of the following: to provide a composition for a urethane-based plastic lens, which comprises at least one compound selected from isocyanate compounds, isothiocyanate compounds and isocyanato-containing isothiocyanate compounds and at least one active hydrogen compound selected from hydroxyl compounds, mercapto compounds and mercapto-containing hydroxyl compounds, and which can produce in a short time a lens having optical uniformity; to provide an optically uniform lens obtained using the composition; to provide a process for producing an optically uniform plastic lens from the composition in a short time. To attain the above objects, the present inventors have proceeded with extensive research, resulting in the following findings and hence leading to the completion of the present invention. 1) Upon molding a urethane-based plastic lens from at least one compound selected from the group consisting of isocyanate compounds, isothiocyanate compounds and isocyanato-containing isothiocyanate compounds and at least one active hydrogen compound selected from hydroxyl compounds, mercapto compounds and mercapto-containing hydroxyl compounds, combined use of a Lewis acid and a tertiary amine having no electron attractive group as a catalyst can prevent any uncontrollably abrupt reaction and can furnish a sufficient pot life even when the tertiary amine is such a tertiary amine that has no electron attractive group and has heretofore been considered impossible to provide any sufficient pot life. 2) Depending on the combination of monomers, lower polymerizability can still be available around room temperature compared with the polymerizability available when the above-described catalyst is not used, thereby providing a longer pot life than that available without the catalyst described above. 3) Although details have not been ascertained, the catalyst making the combined use of the Lewis acid and the tertiary amine having no electron attractive group shows high catalytic activity by heating, thereby allowing the reaction to proceed in a breadth. The resulting lens therefore hardly develop optical non-uniformity even when the polymerization time is shortened significantly. The present invention therefore provides a composition for a urethane-based plastic lens, comprising: (a) at least one compound selected from isocyanate compounds, isothiocyanate compounds and isocyanato-containing isothiocyanate compounds, (b) at least one active hydrogen compound selected from hydroxyl compounds, mercapto compounds and mercapto-containing hydroxyl compounds, (c) a tertiary amine having no electron-attractive group, and (d) a Lewis acid; a plastic lens molded from the composition, and a process for the production of the plastic lens from the composition. Owing to these features of the present invention, it is now possible to mold an optically uniform urethane-based plastic lens in a short time, thereby bringing about a considerable advantage from the industrial standpoint. The composition preferably includes, as an internal mold-releasing agent, a phosphoric acid ester, preferably a mixture of mono- and di-butoxyethyl esters. The present invention will hereinafter be described in detail. Among compounds useful as raw materials for a urethane-base plastic lens in the present invention, each monoisocyanate can be selected from monoisocyanate compounds and monoisothiocyanate compounds. Illustrative monoisocyanate compounds include phenyl isocyanate, butyl isocyanate and cyclohexyl isocyanate. Illustrative monoisothiocyanate compounds include phenyl isothiocyanate, butylisothiocyanate and cyclohexyl isothiocyanate. Also usable are their halogen-substituted derivatives such as chlorine-substituted derivatives and bromine-substituted derivatives, alkyl-substituted derivatives, alkoxyl-substituted derivatives, nitro-substituted derivatives. Illustrative polyisocyanate compounds usable as raw materials for the urethane-base plastic lens in this invention include aliphatic polyisocyanates such as ethylene diisocyanate, trimethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, octamethylene diisocyanate, nonamethylene diisocyanate, 2,2-dimethylpentane diisocyanate, 2,2,4-trimethylhexane diisocyanate, decamethylene 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-isocyanato methyloctane, 2,5,7-trimethyl-1,8-diisocyanato-5-isocyanato methyloctane, bis(isocyanatoethyl) carbonate, bis-(isocyanatoethyl) ether, 1,4-butylene glycol dipropyl ether-ω,ω'-diisocyanate, methyl lysinediisocyanate, lysine triisocyanate, 2-isocyanatoethyl-2,6-diisocyanatohexanoate, 2-isocyanatopropyl-2,6-diisocyanatohexanoate, xylylene diisocyanate, bis-(isocyanatoethyl)benzene, bis(isocyanatopropyl)benzene, α,α,α',α'-tetramethylxylylene diisocyanate, bis-(isocyanatobutyl)benzene, bis(isocyanatomethyl)naphthalene, bis(isocyanatomethyl)diphenyl ether, bis(isocyanatoethyl) phthalate, mesitylylene triisocyanate and 2,6-di(isocyanatomethyl)furan; alicyclic polyisocyanates such as isophorone diisocyanate, bis(isocyanatomethyl)cyclohexane, dicyclohexylmethane diisocyanate, cyclohexane diisocyanate, methylcyclohexane diisocyanate, dicyclohexyldimethylmethane diisocyanate, 2,2'-dimethyldicyclohexylmethane diisocyanate, bis(4-isocyanato-n-butylidene)pentaerythritol, dimeric acid diisocyanate, 2-isocyanatomethyl-3-(3-isocyanatopropyl)-5-isocyanatomethylbicyclo[2.2.1]-heptane, 2-isocyanatomethyl-3-(3-isocyanatopropyl)-6-isocyanatomethyl-bicyclo[2.2.1]-heptane, 2-isocyanatomethyl-2-(3-isocyanatopropyl)-5-isocyanatomethyl-bicyclo[2.2.1]-heptane, 2-isocyanatomethyl-2-(3-isocyanatopropyl)-6-isocyanatomethylbicyclo[2,2.1]-heptane, 2-isocyanatomethyl-3-(3-isocyanatopropyl)-6-(2-isocyanatoethyl)-bicyclo[2.2.1]-heptane, 2-isocyanatomethyl-3-(3-isocyanatopropyl)-6-(2-isocyanatoethyl)-bicyclo[2.1.1]-heptane, 2-isocyanatomethyl-2-(3-isocyanatopropyl)-5-(2-isocyanatoethyl) -bicyclo[2.2.1]-heptane, 2-isocyanatomethyl-2-(3-isocyanatopropyl)-6-(2-isocyanatoethyl)-bicyclo[2.2.1]-heptane and 1,3,5-tris(isocyanatomethyl)-cyclohexane; aromatic polyisocyanates such as phenylene diisocyanate, tolylene diisocyanate, ethylphenylene diisocyanate, isopropylenephenylene diisocyanate, dimethylphenylene diisocyanate, diethylphenylene diisocyanate, diisopropylphenylene diisocyanate, trimethylbenzene triisocyanate, benzene triisocyanate, naphthalene diisocyanate, methylnaphthalene diisocyanate, biphenyl diisocyanate, tolidine diisocyanate, 4,4'-diphenylmethane diisocyanate, 3,3'-dimethyldiphenylmethane-4,4'-diisocyanate, bibenzyl-4,4'-diisocyanate, bis(isocyanatophenyl)ethylene, 3,3'-dimethoxybiphenyl-4,4'-diisocyanate, triphenylmethane triisocyanate, polymeric MDI, naphthalene triisocyanate, diphenylmethane-2,4,4'-triisocyanate, 3-methyldiphenylmethane-4,6,4'-triisocyanate, 4-methyldiphenylmethane-3,5,2',4',6'-pentaisocyanate, phenylisocyanatomethylisocyanate, phenylisocyanatoethylisocyanate, tetrahydronaphthylene diisocyanate, hexahydrobenzene diisocyanate, hexahydrodiphenylmethane-4,4'-diisocyanate, diphenyl ether diisocyanate, ethylene glycol diphenyl ether diisocyanate, 1,3-propylene glycol diphenyl ether diisocyanate, benzophenone diisocyanate, diethylene glycol diphenyl ether diisocyanate, dibenzofuran diisocyanate, carbazole diisocyanate, ethylcarbazole diisocyanate and dichlorocarbazole diisocyanate; sulfur-containing aliphatic polyisocyanates such as thiodiethyl diisocyanate, thiodipropyl diisocyanate, thiodihexyl diisocyanate, dimethylsulfone diisocyanate, dithiodimethyl diisocyanate, dithiodiethyl diisocyanate, dithiodipropyl diisocyanate, dicyclohexylsulfide-4,4'-diisocyanate and 1-isocyanatomethylthia-2,3-bis(2-isocyanatoethylthia)propane; aromatic sulfide polyisocyanates such as diphenyl sulfide-2,4'-diisocyanate, diphenyl sulfide-4,4'-diisocyanate, 3,3'-dimethoxy-4,4'-diisocyanatodibenzyl thioether, bis(4-isocyanatomethylbenzene) sulfide and 4,4'-methoxybenzenethioethyleneglycol-3,3'-diisocyanate; aromatic disulfide polyisocyanates such as diphenyldisulfide-4,4'-diisocyanate, 2,2'-dimethyldiphenyldisulfide-5,5'-diisocyanate, 3,3'-dimethyldiphenyldisulfide-5,5'-diisocyanate, 3,3'-dimethyldiphenyldisulfide-6,6'-diisocyanate, 4,4'-dimethyldiphenyldisulfide-5,5'-diisocyanate, 3,3'-dimethoxydiphenyldisulfide-4,4'-diisocyanate and 4,4'-dimethoxydiphenyldisulfide-3,3'-diisocyanate; aromatic sulfone polyisocyanates such as diphenylsulfone-4,4'-diisocyanate, diphenylsulfone-3,3'-diisocyanate, benzidinesulfone-4,4'-diisocyanate, diphenylmethanesulfone-4,4'-diisocyanate, 4-methyldiphenylmethane sulfone-2,4'-diisocyanate, 4,4'-dimethoxydiphenylsulfone-3,3'-diisocyanate, 3,3'-dimethoxy-4,4'-diisocyanatodibenzylsulfone, 4,4'-dimethyldiphenylsulfone-3,3'-diisocyanate, 4,4'-di-tert-butyldiphenylsulfone-3,3'-diisocyanate, 4,4'-methoxybenzeneethylenedisulfone-3,3'-diisocyanate and 4,4'-dichlorodiphenylsulfone-3,3'-diisocyanate; sulfonic acid ester polyisocyanates such as 4-methyl-3-isocyanatobenzenesulfonyl-4'-isocyanatophenol ester and 4-methoxy-3-isocyanatobenzenesulfonyl-4'-isocyanatophenol ester; aromatic sulfonamides such as 4-methyl-3-isocyanatobenzenesulfonylanilido-3'-methyl-4'-isocyanate, dibenzenesulfonyl-ethylenediamine-4,4'-diisocyanate, 4,4'-methoxybenzenesulfonyl-ethylenediamine-3,3'-diisocyanate and 4-methyl-3-isocyanatobenzenesulfonylanilido-4-methyl-3'-isocyanate; sulfur-containing heterocyclic compounds such as thiophene-2,5-diisocyanate, methyl thiophene-2,5-diisocyanate, 1,4-dithiane-2,5-diisocyanate, methyl 1,4-dithiane-2,5-diisocyanate, 1,3-dithiolane-4,5-diisocyanate, methyl 1,3-dithiolane-4,5-diisocyanate, methyl 1,3-dithiolane-2-methyl-4,5-diisocyanate, ethyl 1,3-dithiolane-2,2-diisocyanate, tetrahydrothiophene-2,5-diisocyanate, methyl tetrahydrothiophene-2,5-diisocyanate, ethyl tetrahydrothiophene-2,5-diisocyanate and methyl tetrahydrothiophene-3,4-diisocyanate. Also usable are their halogen-substituted derivatives such as chlorine-substituted derivatives and bromine-substituted derivatives, alkyl-substituted derivatives, alkoxyl-substituted derivatives, nitro-substituted derivatives, prepolymer-type derivatives modified with polyhydric alcohols, carbodiimide-modified derivatives, urea-modified derivatives, biuret-modified derivatives, dimerized reaction products, trimerized reaction products. The polyisothiocyanate compound employed as a raw material in this invention is a compound containing two or more -NCS groups in a molecule and, optionally, one or more sulfur atoms in addition to the isothiocyanate groups. Specific examples include aliphatic polyisothiocyanates such as 1,2-diisothiocyanatoethane, 1,3-diisothiocyanatopropane, 1,4-diisothiocyanatobutane, 1,6-diisothiocyanatohexane and p-phenylenediisopropylidene diisothiocyanate; alicyclic polyisothiocyanates such as cyclohexane diisothiocyanate; aromatic polyisothiocyanates such as 1,2-diisothiocyanatobenzene, 1,3-diisothiocyanatobenzene, 1,4-diisothiocyanatobenzene, 2,4-diisothiocyanatotoluene, 2,5-diisothiocyanato-m-xylene, 4,4'-diisothiocyanato-1,1'-biphenyl, 1,1'-methylenebis(4-isothiocyanatobenzene), 1,1'-methylenebis(4-isothiocyanato-2-methylbenzene), 1,1'-methylenebis(4-isothiocyanato-3-methylbenzene), 1,1'-(1,2-ethanediyl)bis(4-isothiocyanatobenzene), 4,4'-diisothiocyanatobenzophenone, 4,4'-diisothiocyanato-3,3'-dimethylbenzophenone, benzanilido-3,4'-diisothiocyanate, diphenyl ether-4,4'-diisothiocyanate and diphenylamine-4,4'-diisothiocyanate; heterocyclic-ring-containing isothiocyanates such as 2,4,6-triisothiocyanato-1,3,5-triazine; carbonyl isothiocyanates such as hexanedioyl diisothiocyanate, nonanedioyl diisothiocyanate, carbonic diisothiocyanate, 1,3-benzenedicarbonyl diisothiocyanate, 1,4-benzenedicarbonyl diisothiocyanate and (2,2'-bipyridine)-4,4'-dicarbonyl diisothiocyanate. Illustrative bifunctional or higher polyisothiocyanates, which contain one or more sulfur atoms in addition to at least one isothiocyanato group and are usable in the present invention, include sulfur-containing aliphatic isothiocyanates such as thiobis(3-isothiocyanatopropane), thiobis(2-isothiocyanatoethane) and dithiobis(2-isothiocyanatoethane); sulfur-containing aromatic isothiocyanates such as 1-isothiocyanato-4-[(2-isothiocyanato)sulfonyl]benzene, thiobis(4-isothiocyanatobenzene), sulfonylbis(4-isothiocyanatobenzene), dithiobis(4-isothiocyanatobenzene), 4-isothiocyanato-1-[(4-isothiocyanatophenyl)sulfonyl]-2-methoxybenzene, phenyl 4-methyl-3-isothiocyanatobenzenesulfonyl-4'-isothiocyanate, and 4-methyl-3-isothiocyanatobenzenesulfonylanilido-3'-methyl-4'-isothiocyanate; and sulfur-containing heterocyclic compounds such as thiophenone-2,5-diisothiocyanate and 1,4-dithiane-2,5-diisothiocyanate. Also usable are their halogen-substituted derivatives such as chlorine-substituted derivatives and bromine-substituted derivatives, alkyl-substituted derivatives, alkoxyl-substituted derivatives, nitro-substituted derivatives, prepolymer-type derivatives modified with polyhydric alcohols, carbodiimide-modified derivatives, urea-modified derivatives, biuret-modified derivatives, dimerized reaction products, and trimerized reaction products. Exemplary isothiocyanate compounds, which contain an isocyanato group and are usable as raw materials in this invention, include aliphatic or alicyclic compounds such as 1-isocyanato-3-isothiocyanatopropane, 1-isocyanato-5-isothiocyanatopentane, 1-isocyanato-6-isothiocyanatohexane, isocyanatocarbonyl isothiocyanate and 1-isocyanato-4-isothiocyanatocyclohexane; aromatic compounds such as 1-isocyanato-4-isothiocyanatobenzene and 4-methyl-3-isocyanato-1-isothiocyanatobenzene; heterocyclic compounds such as 2-isocyanato-4,5-diisothiocyanato-1,3,5-triazine; and compounds containing one or more sulfur atoms in addition to an isothiocyanato group, such as 4-isocyanato-4'-isothiocyanatodiphenyl sulfide and 2-isocyanato-2'-isothiocyanatodiethyl disulfide. Also usable are their halogen-substituted derivatives such as chlorine-substituted derivatives and bromine-substituted derivatives, alkyl-substituted derivatives, alkoxyl-substituted derivatives, nitro-substituted derivatives, prepolymer-type derivatives modified with polyhydric alcohols, carbodiimide-modified derivatives, urea-modified derivatives, biuret-modified derivatives, dimerized reaction products, and trimerized reaction products. These ester compounds can be used either singly or in combination. The active hydrogen compound employed for the urethane-base plastic lens according to the present invention is selected from hydroxyl compounds, mercapto compounds and mercapto-containing hydroxyl compounds. Illustrative hydroxyl compounds include monoalcohols such as methanol, benzyl alcohol, phenol, ethoxyethanol; aliphatic polyols such as ethylene glycol, diethylene glycol, propylene glycol, dipropyleneglycol, butylene glycol, neopentyl glycol, glycerin, trimethylolethane, trimethylolpropane, butanetriol, 1,2-methylglycoside, pentaerythritol, dipentaerythritol, tripentaerythritol, sorbitol, erythritol, threitol, ribitol, arabinitol, xylitol, allitol, mannitol, durcitol, iditol, glycol, inositol, hexanetriol, triglycerose, diglyperol, triethylene glycol, polyethylene glycol, tris(2-hydroxyethyl) cyanurate, cyclobutanediol, cyclopentanediol, cyclohexanediol, cycloheptanediol, cyclooctanediol, cyclohexanedimethanol, hydroxypropylcyclohexanol, tricyclo-[5.2.1.0.2.6]decane-dimethanol, bicyclo[4.3.0]nonanediol, dicyclohexanediol, tricyclo[5.3.1.1]dodecanediol, bicyclo[4.3.0]nonanedimethnaol, tricyclo[5.3.1.1]dodecane-diethanol, hydroxypropyltricyclo[5.3.1.1]dodecanol, spiro[3.4]octanediol, butylcyclohexanediol, 1,1'-bicyclohexylidenediol, cyclohexanetriol, maltitol and lactitol; aromatic polyols such as dihydroxynaphthalene, trihydroxynaphthalene, tetrahydroxynaphthalene, dihydroxybenzene, benzenetriol, biphenyltetraol, pyrrogallol, (hydroxynaphthyl)pyrogallol, trihydroxyphenanthrene, bisphenol A, bisphenol F, xylylene glycol, di(2-hydroxyethoxy)benzene, bisphenol A-bis(2-hydroxyethyl ether), tetrabromobisphenol A, tetrabromobisphenol A-bis(2-hydroxyethyl ether); halogenated polyols such as dibromoneopentyl glycol; high molecular polyols such as epoxy resins; condensation reaction products between organic acids such as oxalic acid, glutamic acid, adipic acid, acetic acid, propionic acid, cyclohexanecarboxylic acid, β-oxocyclohexanepropionic acid, dimer acid, phthalic acid, isophthalic acid, salicylic acid, 3-bromopropionic acid, 2-bromoglycol dicarboxycyclohexane, pyromellitic acid, butanetetracarboxylic acid and bromophthalic acid and the above-described polyols; addition reaction products between the above-described polyols and alkylene oxides such as ethylene oxide and propylene oxide; addition reaction products between alkylene polyamines and alkylene oxides such as ethylene oxide and propylene oxide; and sulfur-containing polyols such as bis[4-(hydroxyethoxy)phenyl] sulfide, bis[4-(2-hydroxypropoxy)phenyl] sulfide, bis[4-(2,3-dihydroxypropoxy)phenyl] sulfide, bis[4-(4-hydroxycyclohexyloxy)phenyl] sulfide, bis[2-methyl-4-(hydroxyethoxy)-6-butylphenyl] sulfide, compounds obtained by adding ethylene oxide and/or propylene oxide at a rate of 3 molecules on average per hydroxyl group to these sulfides, di-(2-hydroxyethyl) sulfide, 1,2-bis(2-hydroxyethylmercapto)ethane, bis(2-hydroxyethyl) disulfide, 1,4-dithiane-2,5-diol, bis(2,3-dihydroxypropyl) sulfide, tetrakis(4-hydroxy-2-thiabutyl)methane, bis(4-hydroxyphenyl)sulfone ("Bisphenol S", trade name), tetrabromobisphenol S, tetramethylbisphenol S, 4,4'-thiobis(6-tert-butyl-3-methylphenol) and 1,3-bis(2-hydroxyethylthioethyl)cyclohexane. Illustrative mercapto compounds include monothiols such as methyl mercaptan, benzenethiol, benzylthiol; aliphatic polythiols 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, tetrakis(mercaptomethyl)methane, 1,1-cyclohexanedithiol, 1,2-cyclohexanedithiol, 2,2-dimethylpropane-1,3-dithiol, 3,4-dimethoxybutane-1,2-dithiol, 2-methylcyclohexane-2,3-dithiol, bicyclo[2.2.1]hepta-exo-cis-2,3-dithiol, 1,1-bis(mercaptomethyl) cyclohexane, bis(2-mercaptoethyl) thiomalate, 2-mercaptoethyl-2,3-dimercaptosuccinate, 2,3-dimercapto-l-propanol-2-mercaptoacetate, 2,3-dimercapto-1-propanol-3-mercaptoacetate, diethylene glycol bis(2-mercaptoacetate), diethylene glycol bis(3-mercaptopropionate), 1,2-dimercaptopropyl methyl ether, 2,3-dimercaptopropyl methyl ether, 2,2-bis(mercaptomethyl)-1,3-propanedithiol, bis(2-mercaptoethyl) ether, ethylene glycol bis(2-mercaptoacetate), ethylene glycol bis(3-mercaptopropionate), trimethylolpropane tris(2-mercaptoacetate), trimethylolpropane tris(3-mercaptopropionate), pentaerythritol tetrakis(2-mercaptoacetate), pentaerythritol tetrakis(3-mercaptopropionate) and 1,2-bis(2-mercaptoethylthio)-3-mercaptopropane; aromatic polyols 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-bis(mercaptomethyleneoxy) benzene, 1,3-bis(mercaptomethyleneoxy)benzene, 1,4-bis(mercaptomethyleneoxy)benzene 1,2-bis(mercaptoethyleneoxy)benzene, 1,3-bis(mercaptoethyleneoxy)benzene; 1,4-bis(mercaptoethyleneoxy)benzene, 1,2,3-trimercaptobenzene, 1,2,4-trimercaptobenzene, 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, 1,2,3-tris(mercaptomethyleneoxy)benzene, 1,2,4-tris(mercaptomethyleneoxy)benzene, 1,3,5-tris(mercaptomethyleneoxy)benzene, 1,2,3-tris(mercaptoethyleneoxy)benzene, 1,2,4-tris(mercaptoethyleneoxy)benzene, 1,3,5-tris(mercaptoethyleneoxy)benzene, 1,2,3,4-tetramercaptobenzene, 1,2,3,5-tetramercaptobenzene, 1,2,4,5-tetramercaptobenzene, 1,2,3,4-tetrakis(mercaptomethyl)benzene, 1,2,3,5-tetrakis(mercaptomethyl)benzene, 1,2,4,5-tetrakis(mercaptomethyl)benzene, 1,2,3,4-tetrakis(mercaptoethyl)benzene, 1,2,3,5-tetrakis(mercaptoethyl)benzene, 1,2,4,5-tetrakis(mercaptoethyl)benzene, 1,2,3,4-tetrakis(mercaptoethyl)benzene, 1,2,3,5-tetrakis(mercaptomethyleneoxy)benzene, 1,2,4,5-tetrakis(mercaptomethyleneoxy)benzene, 1,2,3,4-tetrakis(mercaptoethyleneoxy)benzene, 1,2,3,5-tetrakis(mercaptoethyleneoxy)benzene, 1,2,4,5-tetrakis(mercaptoethyleneoxy)benzene, 2,2'-dimercaptobiphenyl, 4,4'-dimercaptobiphenyl, 4,4'-dimercaptobibenzyl, 2,5-toluenedithiol, 3,4-toluenedithiol, 1,4-naphthalenedithiol, 1,5-naphthalenedithiol, 2,6-naphthalenedithiol, 2,7-naphthalenedithiol, 2,4-dimethylbenzene-1,3-dithiol, 4,5-dimethylbenzene-1,3-dithiol, 9,10-anthracenedimethanethiol, 1,3-di(p-methoxyphenyl)propane-2,2-dithiol, 1,3-diphenylpropane-2,2-dithiol, phenylmethane-1,1-dithiol and 2,4-di(p-mercaptophenyl)pentane; halogen-substituted aromatic polythiols, e.g., chlorine-substituted aromatic polythiols and bromine-substituted aromatic polythiols such as 2,5-dichlorobenzene-1,3-dithiol, 1,3-di(p-chlorophenyl)propane-2,2-dithiol, 3,4,5-tribromo-1,2-dimercaptobenzene and 2,3,4,6-tetrachloro-1,5-bis(mercaptomethyl)benzene; polythiols containing one or more heterocyclic rings, such as 2-methylamino-4,6-dithiol-sym-triazine, 2-ethylamino-4,6-dithiol-sym-triazine, 2-amino-4,6-dithiol-sym-triazine, 2-morpholino-4,6-dithiol-symtriazine, 2-cyclohexylamino-4,6-dithiol-sym-triazine, 2-methoxy-4,6-dithiol-sym-triazine, 2-phenoxy-4,6-dithiol-sym-triazine, 2-thiobenzeneoxy-4,6-dithiol-symtriazine and 2-thiobutyloxy-4,6-dithiol-sym-triazine; aromatic polythiols containing one or more sulfur atoms other than a mercapto group, such as 1,2-bis(mercaptomethylthio)benzene, 1,3-bis(mercaptomethylthio)benzene, 1,4-bis(mercaptomethylthio)benzene, 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, 1,3,5-tris(mercaptoethylthio)benzene, 1,2,3,4-tetrakis(mercaptomethylthio)benzene, 1,2,3,5-tetrakis(mercaptomethylthio)benzene, 1,2,4,5-tetrakis(mercaptomethylthio)benzene, 1,2,3,4-tetrakis(mercaptoethylthio)benzene, 1,2,3,5-tetrakis(mercaptoethylthio)benzene and 1,2,4,5-tetrakis(mercaptoethylthio)benzene, and nucleus-alkylated derivatives of these aromatic polythiols; aliphatic polythiols containing one or more sulfur atoms other than a mercapto group, such as bis(mercaptomethyl) sulfide, bis(mercaptoethyl) sulfide, bis(mercaptopropyl) sulfide, bis(mercaptomethylthio)methane, bis(2-mercaptoethylthio)methane, bis(3-mercaptopropylthio)methane, 1,2-bis(mercaptomethylthio) ethane, 1,2-bis(2-mercaptoethylthio)ethane, 1,2-bis(3-mercaptopropylthio) ethane, 1,3-bis(mercaptomethylthio)propane, 1,3-bis(2-mercaptoethylthio)propane, 1,3-bis(3-mercaptopropylthio)propane, 1,2-bis(2-mercaptoethylthio)-3-mercaptopropane, 2-mercaptoethylthio-1,3-propanedithiol, 1,2,3-tris(mercaptomethylthio)propane, 1,2,3-tris(2-mercaptoethylthio)propane, 1,2,3-tris(3-mercaptopropylthio)propane, tetrakis(mercaptomethylthiomethyl)methane, tetrakis(2-mercaptoethylthiomethyl)methane, tetrakis(3-mercaptopropylthiomethyl)methane, bis(2,3-dimercaptopropyl) sulfide, 2,5-dimercapto-1,4-dithiane, bis(mercaptomethyl) disulfide, bis(merpcatoethyl) disulfide and bis(mercaptopropyl) disulfide, as well as thioglycolic acid and mercaptopropionic acid esters of these polythiols, for example, hydroxymethyl sulfide bis(2-mercaptoacetate), hydroxymethyl sulfide bis(3-mercaptopropionate), hydroxyethyl sulfide bis(2-mercaptoacetate), hydroxyethyl sulfide bis(3-mercaptopropionate), hydroxypropyl sulfide bis(2-mercaptoacetate), hydroxypropylsulfide bis(3-mercaptopropionate), hydroxymethyl disulfide bis(2-mercaptoacetate), hydroxymethyl disulfide bis(3-mercaptopropionate), hydroxyethyl disulfide bis(2-mercaptoacetate), hydroxyethyl disulfide bis(3-mercaptopropionate), hydroxypropyl disulfide bis(2-mercaptoacetate), hydroxypropyl disulfide bis(3-mercaptopropionate), 2-mercaptoethyl ether bis(2-mercaptoacetate), 2-mercpatoethyl ether bis(3-mercaptopropionate), 1,4-dithiane-2,5-diol bis(2-mercaptoacetate), 1,4-dithiane-2,5-diol bis(3-mercaptopropionate), bis(2-mercaptoethyl) thioglycolate, bis(2mercaptoethyl) thiodipropionate, bis(2-mercaptoethyl) 4,4-thiodibutyrate, bis(2-mercaptoethyl)dithioglycolate, bis(2-mercaptoethyl) dithiodipropionate, bis(2-mercaptoethyl) 4,4-dithiodibutyrate, bis(2,3-dimercaptopropyl) thiodiglycolate, bis(2,3-dimercaptopropyl) thiodipropionate, bis(2,3-dimercaptopropyl) dithioglycolate and (2,3-dimercaptopropyl) dithiodipropionate; and heterocyclic compounds containing one or more sulfur atoms other than a mercapto group, such as 3,4-thiophenedithiol, tetrahydrothiophene-2,5-dimercaptomethyl, 2,5-dimercapto-1,3,4-thiadiazole, 2,5-dimercapto-1,4-dithiane and 2,5-dimercaptomethyl-1,4-dithiane. Illustrative mercapto-containing hydroxyl compounds include 2-mercaptoethanol, 3-mercapto-1,2-propanediol, glycerin di(mercaptoacetate), 1-hydroxy-4-mercaptocyclohexane, 2,4-dimercaptophenol, 2-mercaptohydroquinone, 4-mercaptophenol, 1,3-dimercapto-2-propanol, 2,3-dimercapto-1-propanol, 1,2-dimercapto-1,3-butanediol, pentaerythritol tris(3-mercaptopropionate), pentaerythritol mono(3-mercaptopropionate), pentaerythritol bis(3-mercaptopropionate), pentaerythritol tris(thioglycolate), pentaerythritol pentakis(3-mercaptopropionate), hydroxymethyl-tris(mercaptoethylthiomethyl)methane, l-hydroxyethylthio-3-mercaptoethylthiobenzene, 4-hydroxy-4'-mercaptodiphenylsulfone, 2-(2-mercaptoethylthio)ethanol, dihydroxyethyl sulfide mono(3-mercaptopropionate), dimercaptoethane mono(salicylate) and hydroxyethylthiomethyl-tris(mercaptoethylthio)methane. Further, these active hydrogen compounds may also be used in the forms of their halogen-substituted derivatives such as chlorine-substituted derivatives and bromine-substituted derivatives. They can be used either singly or in combination. Illustrative tertiary amines having no electron attractive group usable in the present invention include compounds to be set out below. Illustrative aliphatic tertiary amines include triethylamine, tripropylamine, dipropylethylamine, tributylamine, trihexylamine, dimethylcylohexylamine, dicyclohexylmethylamine, tricyclohexylamine, diethylcyclohexylamine, dicyclohexylethylamine, dipropylcyclohexylamine, dicyclohexylpropylamine, dibutylcyclohexylamine, dicyclohexylbutylamine, N,N-dimethylbenzylamine, N,N-diethylbenzylamine, N,N-dipropylbenzylamine, N,N-dibutylbenzylamine, N-methylbenzylamine, 2-dimethylaminomethylphenol, 2,4,6-tris(N,N-dimethylaminomethyl)phenol, triethylenediamine, tetramethylethylenediamine, tetraethylethylenediamine, tetrapropylethylenediamine, tetrabutylethylenediamine, pentamethyldiethylenetriamine, pentaethyldiethylenetriamine, pentapropyldiethylenetriamine, pentabutyldiethylenetriamine, N-methylpiperidine, N-ethylpiperidine, N-propylpiperidine, N-butylpiperidine, N,N-dimethylpiperazine, N,N-diethylpiperazine, N,N-dipropylpiperazine, N,N-dibutylpiperazine, hexamethylenetetramine, N-methylmorpholine, N-ethylmorpholine, N-propylmorpholine, N-butylmorpholine, N-cyclohexylmorpholine, N-methylpiperidone, N-ethylpiperidone, N-propylpiperidone, N-butylpiperidone, N-methylpyrrolidine, N-ethylpyrrolidine, N-propylpyrrolidine, N-butylpyrrolidine, N-methylpyrrolidone, N-ethylpyrrolidone, N-propylpyrrolidone and N-butylpyrrolidone. Illustrative aromatic tertiary amines include N,N-dimethylaniline, N,N-diethylaniline, N,N-dipropylaniline, N,N-dibutylaniline, N,N-cyclohexylmethylaniline, N,N-dicyclohexylaniline, diphenylmethylamine, diphenylethylamine, triphenylamine, N,N-dimethyltoluidine, N,N-diethyltoluidine, N-cyclohexyl-N-methyltoluidine, N,N-dicyclohexyltoluidine, N,N-dimethylnaphthylamine, N,N-diethynaphthylamine, N,N-dimethylanisidine, N,N-diethylanisidine and N,N,N',N'-tetramethylphenylenediamine. Other illustrative tertiary amines include pyridine, picoline, dimethylpyridine, 2,2'-bipyridyl, 4,4'-bipyridyl, pyrazine, N-methylpyrazole, N-ethylpyrazole, N-propylpyrazole, N-butylpyrazole, N-cyclohexylpyrazole, pyridazine, pyrimidine, pyrinoline, oxazole, thiazole, 1-methylimidazole, 1-benzylimidazole, 1-methyl-2-methylimidazole, 1-benzyl-2-methylimidazole, 1-ethyl-4-methylimidazole, 1-ethyl-2-ethyl-4-methylimidazole, N-methylpyrrole, N-ethylpyrrole, N-butylpyrrole, N-methylpyrroline, N-ethylpyrroline, N-butylpyrroline, pyrimidine, purine, quinoline, isoquinoline, N-methylcarbazole, N-ethylcarbazole and N-butylcarbazole. Lewis acids usable in the present invention are those capable of forming strong complexes or salts with the above-mentioned tertiary amines. Dibutyltin dilaurate, dibutyltin diacetate and stannous octoate are not preferred. Such Lewis acids include the following compounds: Zinc compounds such as zinc chloride, zinc acetylacetone and zinc dibutyldithiocarbamate; iron compounds such as iron (II) or (III) chloride and iron (II) or (III) acetylacetone; aluminum compounds such as alumina, aluminum fluoride, aluminum chloride and triphenylaluminum; tin compounds such as tetrafluorotin, tetrachlorotin, tetrabromotin, tetraiodotin, methyltin trichloride, butyltin trichloride, dimethyltin dichloride, dibutyltin dichloride, trimethyltin chloride, tributyltin chloride, triphenyltin chloride, dibutyltin sulfide and di(2-ethylhexyl)tin oxide; titanium compounds such as tetrachlorotitanium; antimony compounds such as trichloroantimony, pentachloroantimony and dichlorotriphenylantimony; uranium compounds such as uranium nitrate; cadmium compounds such as cadmium nitrate; cobalt compounds such as cobalt (II) chloride and cobalt (III) bromide; thorium compounds such as thorium nitrate; mercury compounds such as diphenylmercury; nickel compounds such as nickelocene; calcium compounds such as calcium nitrate and calcium acetate; vanadium compounds such as trichlorovanadium; copper compounds such as copper (II) chloride and copper (II) iodide; manganese compounds such as manganese (II) chloride; zirconium compounds such as zirconium chloride; arsenic compounds such as triphenylarsenic and trichloroarsenic; and boron compounds such as boron trifluoride. Of these Lewis acids, metal halides or organometal halides are preferably used in general. Usually preferred are tin compounds, with organotin halides being particularly preferred. These preferred Lewis acids are however not always preferred because preferred Lewis acids vary depending on the tertiary amine and the monomer combination employed together. It is important for the present invention to use such a tertiary amine having no electron attractive group and Lewis acid in combination as a catalyst. The combined use of both the tertiary amine having no electron attractive group and the Lewis acid has made it possible to impart a sufficient pot life even around room temperature and also to give a certain degree of freedom to the kind and amount of the tertiary amine to be employed. These tertiary amine and Lewis acid can each be used generally in an amount of 5 ppm to 5%, preferably in an amount of 10 ppm to 2%. Their amounts however vary depending on the monomer combination, the tertiary amine-Lewis acid combination, the kinds and amounts of additives such as the internal mold releasing agent, the configurations of the molding, etc. and can be determined as needed. The ester compound and the active hydrogen compound, which are both employed as raw materials in the present invention, can be used at an (NCO + NCS)/(OH + SH) molar ratio generally in a range of 0.5-3.0, preferably in a range of 0.5-1.5. Depending on the application purpose as in conventional forming processes, it is also possible to add various materials such as internal mold releasing agents, chain extenders, crosslinking agents, light stabilizers, ultraviolet absorbers, antioxidants, oil-soluble dyes and fillers. In general, the lens of this invention can be obtained by casting polymerization. Described specifically, one or more ester compounds and one or more active hydrogen compounds are mixed with a tertiary amine and a Lewis acid. After degasifying the resultant liquid mixture by a suitable method as needed, the liquid mixture is cast in a mold. While gradually raising the temperature of the liquid mixture from a low temperature to a high temperature, the above compounds are polymerized. Although the polymerization temperature and time vary depending on the kinds of the monomers, the lens shape and the additives such as a catalyst, the polymerization temperature and time are generally - 20°C to 200°C and 0.5 to 10 hours, respectively. Further, the polymerization can be conducted in the surrounding atmosphere, in an inert gas such as nitrogen, or in a liquid medium such as water. Especially when a molding has a greater thickness and tends to develop optical non-uniformity, good results can often be obtained if the polymerization is carried out in part or entirely in a medium having good thermal conductivity such as water. In addition, the lens so polymerized can then be subjected to annealing as needed. Physical or chemical treatment, processing or working - such as surface polishing, anti-electrostatic treatment, hard coating treatment, non-reflective coating treatment, dyeing treatment or photochromic treatment - can be applied, as needed, to each lens according to the present invention to impart anti-reflective properties, high hardness, anti-mist properties or fashionability or to improve abrasion resistance or chemical resistance. The present invention will hereinafter be described more specifically by the following examples and comparative examples. Among the performance tests of the lens obtained in each example, its refractive index, Abbe's number, specific gravity and optical strain were determined by the following testing methods, respectively. Refractive index and Abbe's number: Measured at 20°C by a Pulfrich refractometer. Specific gravity: Measured by the Archimedes' method. Optical Strain: Each lens was observed using a polarizing plate and a high pressure mercury vapor lamp. The following ranking standard was employed: A: Substantially free of strain. B: Slight strain. C: Marked strain. Further, the viscosity of each monomer composition before injection into a mold was measured at 20°C by a Brookfield rotational viscometer. Example 1 Mixed into a homogeneous solution were 68.8 parts (0.262 mole) of dicyclohexylmethane-4,4'-diisocyanate (hereinafter abbreviated as "HMDi"), 10.4 parts (0.096 mole) of 1-thioglycerin, 20.8 parts (0.114 mole) of 3,6-dioxaoctane-1,8-dimercaptan, 0.8 wt.% of tributylamine (based on the total weight of the ester compounds and the active hydrogen compounds; this applies equally to all subsequent designations of "wt.%"), 0.4 wt.% of dibutyltin dichloride (hereinafter abbreviated as "DBC") and, as an internal mold releasing agent, 1.2 wt.% of "JP-506" (trade name; product of Johoku Kagaku K.K.; acidic butoxyethyl phosphate, monoester-diester mixture), followed by degasification at 20°C. One hour later, the solution was injected into a mold for a concave lens having a central thickness of 1.5 mm. The mold was composed of two glass molds and a gasket. The viscosity of the solution immediately before the injection was below 0.1 Pa.s, namely 0.035 Pa.s so that the injection was extremely easy. A similar test was also conducted separately at 20°C. As a result, its viscosity upon elapsed time of 5 hours was found to be 0.072 Pa.s, i.e. still lower than 0.1 Pa.s and hence to be extremely low. The mold was then gradually heated from 40°C to 140°C, at which the solution was heated and cured for 5 hours. After cooling, the resulting lens was taken out of the mold and was heated again at 120°C for 1 hour. The lens so obtained was inspected using a polarizing plate and a high pressure mercury vapor lamp. Optical strain was not observed practically. This result is also shown in Table 1. The lens so obtained was colorless and transparent, and had a refractive index of 1.548 and an Abbe number of 47 as optical properties and a specific gravity of 1.18 as a physical property. Example 2 A test similar to that in Example 1 was conducted by changing the Lewis acid to 0.3 wt.% of dimethyltin dichloride (hereinafter abbreviated as "DMC") and 0.5 wt.% of TBA. The result was good as in Example 1, as also shown in Table 1. Similarly to Example 1, the lens so obtained was colorless and transparent and free of optical strain, and had a refractive index of 1.548 and an Abbe number of 47 as optical properties and a specific gravity of 1.18 as a physical property. Examples 3-11 & Comparative Examples 1-3 To confirm advantageous effects of a catalyst making combined use of a tertiary amine and a Lewis acid, plastic lenses were produced in the same manner as in Example 1. The results are shown in Table 1. Those examples were repeated with the internal mold releasing agent changed to "Zelec UN" (trade name; product of E.I. Du Pont de Nemours & Co., Inc.; acidic alkyl phosphate), dibutyl phosphate and "JP-506", respectively. The results were similar, namely, good. Example or Comp. Ex. Tertiary amine (wt.%) Lewis acid (wt.%) Viscosity after 5 hrs (Pa.s x 10 3 ) Optical strain Comp. Ex. 1 - - 120 C Comp. Ex. 2 TBA 0.8 - Resinified C Comp. Ex. 3 - DBC 0.4 250 C Example 1 TBA 0.8 DBC 0.4 <100 A Example 2 TBA 0.5 DMC 0.2 <100 A Example 3 Triethylamine 0.4 DBC 0.4 <100 A Example 4 N,N-Dibuthylaminoethanol 0.6 DBC 0.4 <100 A Example 5 Dimethylcyclohexylamine 0.6 DBC 0.4 <100 A Example 6 Dimethylaniline 0.5 DBC 0.4 <100 A Example 7 2,2'-Dipyridyl 0.4 DBC 0.4 <100 A Example 8 N-Methylpyrrole 0.3 DBC 0.4 <100 A Example 9 Triethylenediamine 0.2 DBC 0.4 <100 A Example 10 Tris(2,4,6-dimethylamino methyl)phenol 0.2 DBC 0.4 <100 A Example 11 Diethylcyclohexylamine 0.6 DBC 0.4 <100 A Example 12 A test similar to that in Example 1 was conducted using 43.5 parts (0.23 mole) of m-xylylene diisocyanate (hereinafter abbreviated as "XDi"), 56.5 parts (0.115 mole) of pentaerythritol tetrakis(3-mercaptopropionate) (hereinafter abbreviated as "PEMP"), 0.005 wt.% of N,N-diethylcyclohexylamine (hereinafter abbreviated as "DEC"), 0.01 wt.% of DBC and, as an internal mold releasing agent, 0.1 wt.% of "Zelec UN". The result is shown in Table 2. The lens so obtained was colorless and transparent, and had a refractive index of 1.594 and an Abbe number of 36 as optical properties and a specific gravity of 1.34 as a physical property. Examples 13-47 & Comparative Examples 4-5 To confirm advantageous effects of a catalyst making combined use of a tertiary amine and a Lewis acid, plastic lenses were produced in the same manner as in Example 12. The results are shown in Table 2. Those examples were repeated with the internal mold releasing agent changed to "Zelec UN", dibutyl phosphate and "JP-506", respectively. The results were similar, namely, good without any problem. Example or Comp. Ex. Tertiary amine (wt.%) Lewis acid (wt.%) Viscosity after 5 hrs (Pa.s x 10 3 ) Optical strain Comp. Ex. 4 DEC 0.005 - <100 C Comp. Ex. 5 - DBC 0.01 150 C Example 12 DEC 0.005 DBC 0.01 <100 A Example 13 DEC 0.003 Alumina 0.003 <100 A Example 14 DEC 0.003 Zinc chloride 0.005 <100 A Example 15 DEC 0.001 Iron (III) chloride 0.002 <100 A Example 16 DEC 0.05 Tetrachlorotitanium 0.1 <100 B Example 17 DEC 0.005 DMC 0.07 <100 A Example 18 TBA 0.005 DMC 0.07 <100 A Example 19 TBA 0.005 DBC 0.01 <100 A Example 20 Dimethylcyclohexylamine 0.005 DBC 0.01 <100 A Example 21 Pyridine 0.02 DBC 0.01 <100 A Example 22 2,2'-Bipyridyl DBC 0.01 <100 A Example 23 Dimethylaniline 0.01 DBC 0.01 <100 A Example 24 N-Ethylcarbazole 0.005 DBC 0.01 <100 A Example 25 Triethylamine 0.005 DBC 0.01 <100 A Example 26 1-Methylimidazole 0.005 DBC 0.01 <100 A Example 27 N-Ethylpyrroline 0.005 DBC 0.01 <100 A Example 28 N-Methylpyrroline 0.005 OBC 0.01 <100 A Example 29 N-Hethylpyrazole 0.005 DBC 0.01 <100 A Example 30 Pyridazine 0.005 DBC 0.01 <100 A Example 31 Pyrimidine 0.005 DBC 0.01 <100 A Example 32 Pyrinoline 0.005 DBC 0.01 <100 A Example 33 Oxazole 0.005 DBC 0.01 <100 A Example 34 Thiazole 0.005 DBC 0.01 <100 A Example 35 Purine 0.005 DBC 0.01 <100 A Example 36 Quinoline 0.005 DBC 0.01 <100 A Example 37 Isoquinoline 0.005 DBC 0.01 <100 A Example 38 N,N-dimethylbenzylamine 0.008 DBC 0.01 <100 A Example 39 N-Ethylpiperidine 0.005 DBC 0.01 <100 A Example 40 N-methylpiperazine 0.005 DBC 0.01 <100 A Example 41 Dimethylaminoethylacetate 0.005 DBC 0.01 <100 A Example 42 N-Methylmorpholine 0.005 DBC 0.01 <100 A Example 43 N-Methylpiperidone 0.005 DBC 0.01 <100 A Example 44 N-Methylpyrrolidine 0.005 DBC 0.01 <100 A Example 45 Triethylenediamine 0.002 DBC 0.01 <100 A Example 46 Pentamethyldiethylenetriamine 0.003 DBC 0.01 <100 A Example 47 2,4,6-Tris(dimethylaminomethylphenol) 0.002 DBC 0.01 <100 A Example 48 A test similar to that in Example 1 was conducted using 52.0 parts (0.276 mole) of XDi, 48.0 parts (0.184 mole) of 1,2-bis(2-mercaptoethylthio)-3-mercaptopropane (hereinafter abbreviated as "GST"), 0.015 wt.% of DEC, 0.015 wt.% of DBC and 0.1 wt.% of "Zelec UN". As a result, the viscosity of the solution immediately before injection was lower than 100 cps so that the solution permitted extremely easy injection. The lens so obtained was colorless and transparent, and had a refractive index of 1.660, an Abbe number of 32 and a specific gravity of 1.35. Optical strain was not observed practically. The example was also repeated with the internal mold releasing agent changed from "Zelec UN" to dibutyl phosphate, dioctyl phosphate and "JP-506", respectively. The results were similar, namely, good without any problem. Comparative Example 6 A test similar to that in Example 1 was conducted using 52.0 parts (0.276 mole) of XDi, 48.0 parts (0.184 mole) of GST, 0.014 wt.% of dimethylaminoethyl acetate, 0.14 wt.% of dibutyltin dilaurate and 0.1 wt.% of "Zelec UN". This composition is equivalent to the composition of Example 2 in Japanese Patent Laid-Open No. 84021/1991. As a result, the viscosity of the solution immediately before injection was lower than 0.1 Pa.s so that the solution permitted extremely easy injection. The lens so obtained was colorless and transparent, and had a refractive index of 1.660, an Abbe number of 32 and a specific gravity of 1.35. The lens however contained substantial optical strain. Comparative Example 7 A test similar to that in Example 1 was conducted using 52.0 parts (0.276 mole) of XDi, 48.0 parts (0.184 mole) of GST, 0.069 wt.% of diethylaminoacrylonitrile and 0.1 wt.% of "Zelec UN". This composition is equivalent to the composition of Example 4 in Japanese Patent Laid-Open No. 84021/1991. As a result, the viscosity of the solution immediately before injection was lower than 100 cps so that the solution permitted extremely easy injection. The lens so obtained was colorless and transparent, and had a refractive index of 1.660, an Abbe number of 32 and a specific gravity of 1.35. The lens however contained substantial optical strain. Example 49 A test similar to that in Example 1 was conducted using 60.2 parts (0.229 mole) of HMDi, 39.8 parts (0.153 mole) of GST, 0.05 wt.% of dimethyltin dichloride (hereinafter abbreviated as "DMC"), 0.05 wt.% of dimethylcyclohexylamine (hereinafter abbreviated as "DCA") and 0.015 wt.% of "Zelec UN". As a result, the viscosity of the solution immediately before injection was lower than 0.1 Pa.s so that the solution permitted extremely easy injection. The lens so obtained was colorless and transparent, and had a refractive index of 1.594, an Abbe number of 42 and a specific gravity of 1.22. Optical strain was not observed practically. The example was also repeated with the internal mold releasing agent changed from "Zelec UN" to dibutyl phosphate, dioctyl phosphate and "JP-506", respectively. The results were similar, namely, good without any problem. Example 50 A test similar to that in Example 1 was conducted using 30.0 parts (0.114 mole) of HMDi, 30.0 parts (0.135 mole) of isophorone diisocyanate (hereinafter abbreviated as "IPDi"), 43.3 parts (0.166 mole) of GST, 0.05 wt.% of DMC, 0.05 wt.% of DCA and 0.015 wt.% of "Zelec UN". As a result, the viscosity of the solution immediately before injection was lower than 0.1 Pa.s so that the solution permitted extremely easy injection. The lens so obtained was colorless and transparent, and had a refractive index of 1.594, an Abbe number of 40 and a specific gravity of 1.23. Optical strain was not observed practically. The example was also repeated with the internal mold releasing agent changed from "Zelec UN" to dibutyl phosphate, dioctyl phosphate and "JP-506", respectively. The results were similar, namely, good without any problem. Example 51 A test similar to that in Example 1 was conducted using 50.0 parts (0.225 mole) of IPDi, 10.0 parts (0.059 mole) of hexamethylene diisocyanate (hereinafter abbreviated as "HDi"), 49.4 parts (0.190 mole) of GST, 0.08 wt.% of DMC, 0.15 wt.% of DEC and 0.015 wt.% of "Zelec UN". As a result, the viscosity of the solution immediately before injection was lower than 0.1 Pa.s so that the solution permitted extremely easy injection. The lens so obtained was colorless and transparent, and had a refractive index of 1.596, an Abbe number of 40 and a specific gravity of 1.24. Optical strain was not observed practically. The example was also repeated with the internal mold releasing agent changed from "Zelec UN" to dibutyl phosphate, dioctyl phosphate and "JP-506", respectively. The results were similar, namely, good without any problem. Example 52 A test similar to that in Example 1 was conducted using 63.0 parts (0.334 mole) of XDi, 15.0 parts (0.139 mole) of thioglycerin (hereinafter abbreviated as "TG"), 30.0 parts (0.061 mole) of PEMP, 0.01 wt.% of DBC, 0.005 wt.% of N,N-dibutylaminoethanol and 0.5 wt.% of dibutyl phosphate. As a result, the viscosity of the solution immediately before injection was lower than 0.1 Pa.s so that the solution permitted extremely easy injection. The lens so obtained was colorless and transparent, and had a refractive index of 1.598, an Abbe number of 35 and a specific gravity of 1.33. Optical strain was not observed practically. The example was also repeated with the internal mold releasing agent changed from dibutyl phosphate to "Zelec UN", dioctyl phosphate and "JP-506", respectively. The results were similar, namely, good without any problem. Example 53 A test similar to that in Example 1 was conducted using 50.0 parts (0.225 mole) of IPDi, 59.8 parts (0.150 mole) of trimethylolpropane tris(3-mercaptopropionate), 0.10 wt.% of DMC, 0.05 wt.% of DEC and 0.015 wt.% of "Zelec UN". As a result, the viscosity of the solution immediately before injection was lower than 0.1 Pa.s so that the solution permitted extremely easy injection. The lens so obtained was colorless and transparent, and had a refractive index of 1.541, an Abbe number of 47 and a specific gravity of 1.21. Optical strain was not observed practically. The example was also repeated with the internal mold releasing agent changed from "Zelec UN" to dibutyl phosphate, dioctyl phosphate and "JP-506", respectively. The results were similar, namely, good without any problem. Example 54 A test similar to that in Example 1 was conducted using 50.0 parts (0.225 mole) of IPDi, 55.0 parts (0.113 mole) of pentaerythritol tetrakis(3-mercaptopropionate), 0.10 wt.% of DMC, 0.05 wt.% of DEC and 0.015 wt.% of "Zelec UN". As a result, the viscosity of the solution immediately before injection was lower than 0.1 Pa.s so that the solution permitted extremely easy injection. The lens so obtained was colorless and transparent, and had a refractive index of 1.550, an Abbe number of 47 and a specific gravity of 1.22. Optical strain was not observed practically. The example was also repeated with the internal mold releasing agent changed from "Zelec UN" to dibutyl phosphate, dioctyl phosphate and "JP-506", respectively. The results were similar, namely, good without any problem. Comparative Example 8 A test similar to that in Example 1 was conducted using 50.0 parts (0.225 mole) of IPDi, 55.0 parts (0.113 mole) of pentaerythritol tetrakis(3-mercaptopropionate), 0.02 wt.% of dimethylaminoethyl acetate, 0.1 wt.% of dibutyltin dilaurate and 0.1 wt.% of "Zelec UN". This composition is equivalent to the composition of Example 1 in Japanese Patent Laid-Open No. 84021/1991 As a result, the viscosity of the solution immediately before injection was lower than 0.1 Pa.s so that the solution permitted extremely easy injection. The lens so obtained was colorless and transparent, and had a refractive index of 1.550, an Abbe number of 47 and a specific gravity of 1.22. The lens however contained substantial optical strain. Example 55 A test similar to that in Example 1 was conducted using 50.0 parts (0.191 mole) of HMDi, 50.6 parts (0.127 mole) of trimethylolpropane tris(3-mercaptopropionate), 0.10 wt.% of DMC, 0.05 wt.% of DEC and 0.015 wt.% of "Zelec UN". As a result, the viscosity of the solution immediately before injection was lower than 0.1 Pa.s so that the solution permitted extremely easy injection. The lens so obtained was colorless and transparent, and had a refractive index of 1.546, an Abbe number of 48 and a specific gravity of 1.21. Optical strain was not observed practically. The example was also repeated with the internal mold releasing agent changed from "Zelec UN" to dibutyl phosphate, dioctyl phosphate and "JP-506", respectively. The results were similar, namely, good without any problem. Example 56 A test similar to that in Example 1 was conducted using 58.3 parts (0.300 mole) of 1,3-bis(isocyanatomethyl)cyclohexane (hereinafter abbreviated as "H6XDi"), 38.2 parts (0.180 mole) of 1,4-dithiane-2,5-bis(mercaptomethyl), 26.0 parts (0.06 mole) of pentaerythritol tetrakis(thioglycolate), 0.10 wt.% of TBA, 0.10 wt.% of DMC and 0.15 wt.% of "JP-506". As a result, the viscosity of the solution immediately before injection was lower than 0.1 Pa.s so that the solution permitted extremely easy injection. The lens so obtained was colorless and transparent, and had a refractive index of 1.529, an Abbe number of 41 and a specific gravity of 1.30. Optical strain was not observed practically. The example was also repeated with the internal mold releasing agent changed from "JP-506" to dibutyl phosphate, dioctyl phosphate and "Zelec UN", respectively. The results were similar, namely, good without any problem. Example 57 A test similar to that in Example 1 was conducted using 50.5 parts (0.260 mole) of H6XDi, 42.5 parts (0.200 mole) of 1,4-dithiane-2,5-bis(mercaptomethyl), 4.3 parts (0.040 mole) of TG, 0.10 wt.% of TBA, 0.10 wt.% of DBC and 0.70 wt.% of "JP-506". As a result, the viscosity of the solution immediately before injection was lower than 0.1 Pa.s so that the solution permitted extremely easy injection. The lens so obtained was colorless and transparent, and had a refractive index of 1.590, an Abbe number of 42 and a specific gravity of 1.29. Optical strain was not observed practically. The example was also repeated with the internal mold releasing agent changed from "JP-506" to dibutyl phosphate, dioctyl phosphate and "Zelec UN", respectively. The results were similar, namely, good without any problem. Example 58 A test similar to that in Example 1 was conducted using 47.1 parts (0.250 mole) of XDi, 21.2 parts (0.100 mole) of 1,4-dithiane-2,5-bis(mercaptomethyl), 26.1 parts (0.100 mole) of GST, 0.01 wt.% of TBA, 0.01 wt.% of DMC and 0.10 wt.% of "JP-506". As a result, the viscosity of the solution immediately before injection was lower than 0.1 Pa.s so that the solution permitted extremely easy injection. The lens so obtained was colorless and transparent, and had a refractive index of 1.660, an Abbe number of 32 and a specific gravity of 1.35. Optical strain was not observed practically. The example was also repeated with the internal mold releasing agent changed from "JP-506" to dibutyl phosphate, dioctyl phosphate and "Zelec UN", respectively. The results were similar, namely, good without any problem. Example 59 A test similar to that in Example 1 was conducted using 68.8 parts (0.262 mole) of HMDi, 8.8 parts (0.096 mole) of glycerin, 20.8 parts (0.114 mole) of 3,6-dioxaoctane-1,8-dimercaptan, 0.8 wt.% of TBA, 0.4 wt.% of DBC and 1.2 wt.% of "JP-506". As a result, the viscosity of the solution immediately before injection was lower than 0.1 Pa.s so that the solution permitted extremely easy injection. The lens so obtained was colorless and transparent, and had a refractive index of 1.535, an Abbe number of 50 and a specific gravity of 1.17. Optical strain was not observed practically. The example was also repeated with the internal mold releasing agent changed from "JP-506" to dibutyl phosphate, dioctyl phosphate and "Zelec UN", respectively. The results were similar, namely, good without any problem. Example 60 Mixed into a homogeneous solution were 18.5 parts (0.110 mole) of hexamethylene diisocyanate, 30.0 parts (1.14 mole) of hydrogenated MDi, 30.0 parts (0.326 mole) of glycerin, 0.02 wt.% of TBA, 0.01 wt.% of DBC and, as an internal mold releasing agent, 1.2 wt.% of "JP-506", followed by degasification at 20°C. One hour later, the solution was injected into a mold for a concave lens having a central thickness of 1.5 mm. The mold was composed of two glass molds and a gasket. The viscosity of the solution immediately before the injection was 0.035 Pa.s, namely, lower than 0.1 Pa.s so that the injection was extremely easy. A similar test was also conducted separately at 20°C. As a result, its viscosity upon elapsed time of 5 hours was found to be 0.096 Pa.s, namely, still lower than 0.1 Pa.s and hence to be extremely low. The mold was then gradually heated from 40°C to 140°C, at which the solution was heated and cured for 5 hours. After cooling, the resulting lens was taken out of the mold and was heated again at 120°C for 1 hour. The lens so obtained was inspected using a polarizing plate and a high pressure mercury vapor lamp. Optical strain was not observed practically. This result is also shown in Table 3. The lens so obtained was colorless and transparent, and had a refractive index of 1.523 and an Abbe number of 51 as optical properties and a specific gravity of 1.20 as a physical property. Example 61 A test similar to that in Example 60 was conducted by changing the Lewis acid to 0.007 wt.% of DMC and 0.02 wt.% of TBA. The result was good as in Example 60, as also shown in Table 3. Similarly to Example 60, the lens so obtained was colorless and transparent, and had a refractive index of 1.523 and an Abbe number of 50 as optical properties and a specific gravity of 1.24 as a physical property. Examples 62-70 & Comparative Examples 10-12 To confirm advantageous effects of a catalyst making combined use of a tertiary amine and a Lewis acid, plastic lenses were produced in the same manner as in Example 60. The results are shown in Table 3. Those examples were repeated with the internal mold releasing agent changed to "Zelec UN", dibutyl phosphate and "JP-506", respectively. The results were similar, namely, good. Example or Comp. Ex. Tertiary amine (wt.%) Lewis acid (wt.%) Viscosity after 5 hrs (Pa.s x 10 3 ) Optical strain strain Comp. Ex. 10 - - >1000 C Comp. Ex. 11 TBA 0.02 - Immediately Resinified C Comp. Ex. 12 - DBC 0.01 >1000 C Example 60 TBA 0.02 DBC 0.01 <100 A Example 61 TBA 0.02 DMC 0.007 <100 A Example 62 Triethylamine 0.02 DBC 0.01 <100 A Example 63 Dimethylcyclohexylamine 0.02 DBC 0.01 <100 A Example 64 Diethylcyclohexylamine 0.02 DBC 0.01 <100 A Example 65 Dimethylaniline 0.02 DBC 0.01 <100 A Example 66 2.2'-Dipyridyl 0.02 DBC 0.01 <100 A Example 67 N-Methylpyrrole 0.01 DBC 0.01 <100 A Example 68 Triethyldiamine 0.01 DBC 0.01 <100 A Example 69 Tris(2,4,6-dimethylaminomethyl)phenol 0.01 DBC 0.01 <100 A Example 70 Dibutylaminoethanol 0.01 DBC 0.01 <100 A Example 71 A test similar to that in Example 60 was conducted using 108.0 parts (0.574 mole) of XDi, 30.0 parts (0.326 mole) of glycerin, 40.0 parts (0.154 mole) of 1,2-bis(3-mercaptoethylthio)-3-mercaptopropane, 0.005 wt.% of DEC, 0.01 wt.% of DBC and, as an internal mold releasing agent, 1.0 wt.% of dibutyl phosphate. The result is shown in Table 4. The lens so obtained was colorless and transparent, and had a refractive index of 1.593 and an Abbe number of 36 as optical properties and a specific gravity of 1.33 as a physical property. Examples 72-106 & Comparative Examples 13-14 To confirm advantageous effects of a catalyst making combined use of a tertiary amine and a Lewis acid, plastic lenses were produced in the same manner as in Example 71. The results are shown in Table 4. Those examples were repeated with the internal mold releasing agent changed to "Zelec UN", dibutyl phosphate, dioctyl phosphate and "JP-506", respectively. The results were similar, namely, good without any problem. Example or Comp. Ex. Tertiary amine (wt.%) Lewis acid (wt.%) Viscosity after 5 hrs (Pa.s x 10 3 ) Optical strain strain Comp. Ex. 13 DEC 0.005 - 400 C Comp. Ex. 14 - DBC 0.01 150 C Example 71 DEC 0.005 DBC 0.01 <100 A Example 72 DEC 0.003 Alumina 0.003 <100 A Example 73 DEC 0.003 Zinc chloride 0.005 <100 A Example 74 DEC 0.001 Iron (III) chloride 0.002 <100 A Example 75 DEC 0.05 Zinc chloride 0.05 <100 8 Example 76 DEC 0.005 DMC 0.007 <100 A Example 77 TBA 0.005 DMC 0.007 <100 A Example 78 TBA 0.005 DBC 0.01 <100 A Example 79 Dimethylcyclohexylamine 0.005 DBC 0.01 <100 A Example 80 Pyridine 0.02 DBC 0.01 <100 A Example 81 2,2'-Bipyridyl DBC 0.01 <100 A Example 82 Dimethylaniline 0.01 DBC 0.01 <100 A Example 83 N-Ethylcarbazole 0.005 DBC 0.01 <100 A Example 84 Triethylamine 0.005 DBC 0.01 <100 A Example 85 1-Methylimidazole 0.005 DBC 0.01 <100 A Example 86 N-Ethylpyrroline 0.005 DBC 0.01 <100 A Example 87 N-Methylpyrroline 0.005 DBC 0.01 <100 A Example 88 N-Methylpyrazole 0.005 DBC 0.01 <100 A Example 89 Pyridazine 0.005 DBC 0.01 <100 A Example 90 Pyrimidine 0.005 DBC 0.01 <100 A Example 91 Pyrinoline 0.005 DBC 0.01 <100 A Example 92 Oxazole 0.005 DBC 0.01 <100 A Example 93 Thiazole 0.005 DBC 0.01 <100 A Example 94 Purine 0.005 DBC 0.01 <100 A Example 95 Quinoline 0.005 DBC 0.01 <100 A Example 96 Isoquinoline 0.005 DBC 0.01 <100 A Example 97 N,N-dimethylbenzylamine 0.008 DBC 0.01 <100 A Example 98 N-Ethylpiperidine 0.005 DBC 0.01 <100 A Example 99 N-Methylpiperazine 0.005 DBC 0.01 <100 A Example 100 Dimethylaminoethylacetate 0.005 DBC 0.01 <100 A Example 101 N-Methylmorpholine 0.005 DBC 0.01 <100 A Example 102 N-Methylpiperidone 0.005 DBC 0.01 <100 A Example 103 N-Methylpyrrolidine 0.005 DBC 0.01 <100 A Example 104 Triethylenediamine 0.002 DBC 0.01 <100 A Example 105 Pentamethyldiethylenetriamine 0.003 DBC 0.01 <100 A Example 106 2,4,6-Tris(dimethylaminomethylphenol) 0.002 DBC 0.01 <100 A Example 107 A test similar to that in Example 60 was conducted using 53.0 parts (0.282 mole) of XDi, 48.0 parts (0.184 mole) of 1,3-bis(2-hydroxyethylthio)-2-propanol (hereinafter abbreviated as "GSA"), 0.005 wt.% of DEC, 0.005 wt.% of DBC and 1.0 wt.% of "JP-506". As a result, the viscosity of the solution immediately before injection was lower than 0.1 Pa.s so that the solution permitted extremely easy injection. The lens so obtained was colorless and transparent, and had a refractive index of 1.592, an Abbe number of 36 and a specific gravity of 1.32. Optical strain was not observed practically. The example was also repeated with the internal mold releasing agent changed from "JP-506" to "Zelec UN", dibutyl phosphate and dioctyl phosphate, respectively. The results were similar, namely, good without any problem. Example 108 A test similar to that in Example 60 was conducted using 84.5 parts (0.322 mole) of HMDi, 30.0 parts (0.141 mole) of GSA, 20.0 parts (0.110 mole) of 3,6-dioxaoctane-1,8-dimercaptan, 0.005 wt.% of DEC and 0.005 wt.% of DBC. As a result, the viscosity of the solution immediately before injection was lower than 0.1 Pa.s so that the solution permitted extremely easy injection. The lens so obtained was colorless and transparent, and had a refractive index of 1.560, an Abbe number of 45 and a specific gravity of 1.19. Optical strain was not observed practically. Example 109 Mixed into a homogeneous solution were 13.5 parts (0.070 mole) of 1,4-diisothiocyanatobenzene, 7.7 parts (0.07 mole) of hydroquinone, 0.02 wt.% of TBA, 0.01 wt.% of DBC and, as an internal mold releasing agent, 1.2 wt.% of "JP-506", followed by degasification at 20°C. One hour later, the solution was injected into a mold for a concave lens having a central thickness of 1.5 mm. The mold was composed of two glass molds and a gasket. The viscosity of the solution immediately before the injection was 0.035 Pa.s, namely, lower than 0.01 Pa.s, so that the injection was extremely easy. A similar test was also conducted separately at 20°C. As a result, its viscosity upon elapsed time of 5 hours was found to be 0.075 Pa.s, namely, still lower than 0.1 Pa.s and hence to be extremely low. The mold was then gradually heated from 40°C to 140°C, at which the solution was heated and cured for 5 hours. After cooling, the resulting lens was taken out of the mold and was heated again at 120°C for 1 hour. The lens so obtained was inspected using a polarizing plate and a high pressure mercury vapor lamp. Optical strain was not observed practically. The lens so obtained was colorless and transparent, and had a refractive index of 1.78. Example 110 Mixed into a homogeneous solution were 10 parts (0.05 mole) of hexamethylene diisothiocyanate, 11 parts (0.025 mole) of tetrakis(mercaptoethylthiomethyl)methane, 0.02 wt.% of TBA, 0.01 wt.% of DBC and, as an internal mold releasing agent, 1.2 wt.% of "JP-506", followed by degasification at 20°C. One hour later, the solution was injected into a mold for a concave lens having a central thickness of 1.5 mm. The mold was composed of two glass molds and a gasket. The viscosity of the solution immediately before the injection was 0.035 Pa.s, namely, lower than 0.1 Pa.s so that the injection was extremely easy. A similar test was also conducted separately at 20°C. As a result, its viscosity upon elapsed time of 5 hours was found to be 0.06 Pa.s cps, namely, still lower than 0.1 Pa.s and hence to be extremely low. The mold was then gradually heated from 40°C to 140°C, at which the solution was heated and cured for 5 hours. After cooling, the resulting lens was taken out of the mold and was heated again at 120°C for 1 hour. The lens so obtained was inspected using a polarizing plate and a high pressure mercury vapor lamp. Optical strain was not observed practically. The lens so obtained was colorless and transparent, and had a refractive index of 1.70. Example 111 Mixed into a homogeneous solution were 16.3 parts (0.08 mole) of diisothiocyanatoethyl sulfide, 17.0 parts of hydroxyethylthiomethyl-tris(mercaptoethylthiomethyl)methane, 0.02 wt.% of TBA, 0.01 wt.% of DBC and, as an internal mold releasing agent, 1.2 wt.% of "JP-506", followed by degasification at 20°C. One hour later, the solution was injected into a mold for a concave lens having a central thickness of 1.5 mm. The mold was composed of two glass molds and a gasket. The viscosity of the solution immediately before the injection was 0.035 Pa.s, namely, lower than 0.1 Pa.s so that the injection was extremely easy. A similar test was also conducted separately at 20°C. As a result, its viscosity upon elapsed time of 5 hours was found to be 0.075 Pa.s, namely, still lower than 0.1 Pa.s and hence to be extremely low. The mold was then gradually heated from 40°C to 140°C, at which the solution was heated and cured for 5 hours. After cooling, the resulting lens was taken out of the mold and was heated again at 120°C for 1 hour. The lens so obtained was inspected using a polarizing plate and a high pressure mercury vapor lamp. Optical strain was not observed practically. The lens so obtained was colorless and transparent, and had a refractive index of 1.71. Example 112 Mixed into a homogeneous solution were 10.6 parts (0.06 mole) of 1-isocyanato-4-isothiocyanatobenzene, 6.6 parts (0.06 mole) of hydroquinone, 0.02 wt.% of TBA, 0.01 wt.% of DBC and, as an internal mold releasing agent, 1.2 wt.% of "JP-506", followed by degasification at 20°C. One hour later, the solution was injected into a mold for a concave lens having a,central thickness of 1.5 mm. The mold was composed of two glass molds and a gasket. The viscosity of the solution immediately before the injection was 0.045 Pa.s, namely, lower than 0.1 Pa.s so that the injection was extremely easy. A similar test was also conducted separately at 20°C. As a result, its viscosity upon elapsed time of 5 hours was found to be 0.075 Pa.s, namely, still lower than 0.1 Pa.s, and hence to be extremely low. The mold was then gradually heated from 40°C to 140°C, at which the solution was heated and cured for 5 hours. After cooling, the resulting lens was taken out of the mold and was heated again at 120°C for 1 hour. The lens so obtained was inspected using a polarizing plate and a high pressure mercury vapor lamp. Optical strain was not observed practically. The lens so obtained was colorless and transparent, and had a refractive index of 1.70. Example 113 Mixed into a homogeneous solution were 8.5 parts (0.06 mole) of 1-isocyanato-3-isothiocyanatopropane, 7.0 parts (0.04 mole) of benzenetrithiol, 0.02 wt.% of TBA, 0.01 wt.% of DBC and, as an internal mold releasing agent, 1.2 wt.% of "JP-506", followed by degasification at 20°C. One hour later, the solution was injected into a mold for a concave lens having a central thickness of 1.5 mm. The mold was composed of two glass molds and a gasket. The viscosity of the solution immediately before the injection was 0.045 Pa.s, namely, lower than 0.1 Pa.s so that the injection was extremely easy. A similar test was also conducted separately at 20°C. As a result, its viscosity upon elapsed time of 5 hours was found to be 0.075 Pa.s, namely, still lower than 0.1 Pa.s and hence to be extremely low. The mold was then gradually heated from 40°C to 140°C, at which the solution was heated and cured for 5 hours. After cooling, the resulting lens was taken out of the mold and was heated again at 120°C for 1 hour. The lens so obtained was inspected using a polarizing plate and a high pressure mercury vapor lamp. Optical strain was not observed practically. The lens so obtained was colorless and transparent, and had a refractive index of 1.75. Example 114 Mixed into a homogeneous solution were 17.0 parts (0.06 mole) of 4-isocyanato-4'-isothiocyanatodiphenyl sulfide, 7.6 parts (0.06 mole) of 4-mercaptophenol, 0.02 wt.% of TBA, 0.01 wt.% of DBC and, as an internal mold releasing agent, 1.2 wt.% of "JP-506", followed by degasification at 20°C. One hour later, the solution was injected into a mold for a concave lens haying a central thickness of 1.5 mm. The mold was composed of two glass molds and a gasket. The viscosity of the solution immediately before the injection was 0.045 Pa.s, namely, lower than 0.1 Pa.s so that the injection was extremely easy. A similar test was also conducted separately at 20°C. As a result, its viscosity upon elapsed time of 5 hours was found to be 0.075 Pa.s, (namely, still lower than 0.1 Pa.s and hence to be extremely low. The mold was then gradually heated from 40°C to 140°C, at which the solution was heated and cured for 5 hours. After cooling, the resulting lens was taken out of the mold and was heated again at 120°C for 1 hour. The lens so obtained was inspected using a polarizing plate and a high pressure mercury vapor lamp. Optical strain was not observed practically. The lens so obtained was colorless and transparent, and had a refractive index of 1.74. Example 115 Mixed into a homogeneous solution were 43.5 parts (0.23 mole) of m-xylylene diisocyanate, 56.5 parts (0.115 mole) of pentaerythritol tetrakis(3-mercaptopropionate), 0.005 wt.% of N,N-diethylcyclohexylamine, 0.01 wt.% of DBC and, as an internal mold releasing agent, 0.1 wt.% of "Zelec UN", followed by degasification at 20°C. One hour later, the solution was injected into a mold for a concave lens having a central thickness of 1.5 mm. The mold was composed of two glass molds and a gasket. The mold was then heated for 2 hours in water of 40°C and for additional 1 hour in water of 60°C. The mold was thereafter placed in an oven, where it was heated at 100°C for 30 minutes and then at 140°C for 1 hour so that the solution was cured under heat. After cooling, the resulting lens was taken out of the mold and was heated again at 120°C for 1 hour. The lens so obtained was inspected using a polarizing plate and a high pressure mercury vapor lamp. Optical strain was not observed practically. Example 116 Mixed into a homogeneous solution were 43.5 parts (0.23 mole) of m-xylylene diisocyanate, 56.5 parts (0.115 mole) of pentaerythritol tetrakis(3-mercaptopropionate), 0.005 wt.% of N,N-diethylcyclohexylamine and 0.01 wt.% of DBC, followed by degasification at 20°C. One hour later, the solution was injected into a mold for a concave lens having a central thickness of 1.5 mm. The mold was composed of two glass molds on which a baking internal mold releasing agent ("YSR-6209", trade name; product of Toshiba Silicone Co., Ltd.) had been baked and a gasket. The mold was then heated for 2 hours in water of 40°C and for additional 1 hour in water of 60°C. The mold was thereafter placed in an oven, where it was heated at 100°C for 30 minutes and then at 140°C for 1 hour so that the solution was cured under heat. After cooling, the resulting lens was taken out of the mold and was heated again at 120°C for 1 hour. The lens so obtained was inspected using a polarizing plate and a high pressure mercury vapor lamp. Optical strain was not observed practically.

Claims: A composition for a urethane-based plastic lens, comprising: (a) at least one compound selected from isocyanate compounds, isothiocyanate compounds and isocyanato-containing isothiocyanate compounds; (b) at least one active hydrogen compound selected from hydroxyl compounds, mercapto compounds and mercapto-containing hydroxyl compounds; (c) a tertiary amine having no electron attractive group; and (d) a Lewis acid. A composition for a urethane-based plastic lens, comprising: (a) at least one compound selected from isocyanate compounds, isothiocyanate compounds and isocyanato-containing isothiocyanate compounds; (b) at least one active hydrogen compound selected from hydroxyl compounds, mercapto compounds and mercapto-containing hydroxyl compounds; (c) a tertiary amine having no electron attractive group; and (d) a Lewis acid; wherein the tertiary amine is selected from: triethylamine, tripropylamine, dipropylethylamine, tributylamine, trihexylamine, dimethylcylohexylamine, dicyclohexylmethylamine, tricyclohexylamine, diethylcyclohexylamine, dicyclohexylethylamine, dipropylcyclohexylamine, dicyclohexylpropylamine, dibutylcyclohexylamine, dicyclohexylbutylamine, N,N-dimethylbenzylamine, N,N-diethylbenzylamine, N,N-dipropylbenzylamine, N,N-dibutylbenzylamine, N-methylbenzylamine, 2-dimethylaminomethylphenol, 2,4,6-tris(N,N-dimethylaminomethyl)phenol, triethylenediamine, tetramethylethylenediamine, tetraethylethylenediamine, tetrapropylethylenediamine, tetrabutylethylenediamine, pentamethyldiethylenetriamine, pentaethyldiethylenetriamine, pentapropyldiethylenetriamine, pentabutyldiethylenetriamine, N-methylpiperidine, N-ethylpiperidine, N-propylpiperidine, N-butylpiperidine, N,N-dimethylpiperazine, N,N-diethylpiperazine, N,N-dipropylpiperazine, N,N-dibutylpiperazine, hexamethylenetetramine, N-methylmorpholine, N-ethylmorpholine, N-propylmorpholine, N-butylmorpholine, N-cyclohexylmorpholine, N-methylpiperidone, N-ethylpiperidone, N-propylpiperidone, N-butylpiperidone, N-methylpyrrolidine, N-ethylpyrrolidine, N-propylpyrrolidine, N-butylpyrrolidine, N-methylpyrrolidone, N-ethylpyrrolidone, N-propylpyrrolidone and N-butylpyrrolidone, N,N-dimethylaniline, N,N-diethylaniline, N,N-dipropylaniline, N,N-dibutylaniline, N,N-cyclohexylmethylaniline, N,N-dicyclohexylaniline, diphenylmethylamine, diphenylethylamine, triphenylamine, N,N-dimethyltoluidine, N,N-diethyltoluidine, N-cyclohexyl-N-methyltoluidine, N,N-dicyclohexyltoluidine, N,N-dimethylnaphthylamine, N,N-diethynaphthylamine, N,N-dimethylanisidine, N,N-diethylanisidine and N,N,N',N'-tetramethylphenylenediamine, pyridine, picoline, dimethylpyridine, 2,2'-bipyridyl, 4,4'-bipyridyl, pyrazine, N-methylpyrazole, N-ethylpyrazole, N-propylpyrazole, N-butylpyrazole, N-cyclohexylpyrazole, pyridazine, pyrimidine, pyrinoline, oxazole, thiazole, 1-methylimidazole, 1-benzylimidazole, 1-methyl-2-methylimidazole, 1-benzyl-2-methylimidazole, 1-ethyl-4-methylimidazole, 1-ethyl-2-ethyl-4-methylimidazole, N-methylpyrrole, N-ethylpyrrole, N-butylpyrrole, N-methylpyrroline, N-ethylpyrroline, N-butylpyrroline, pyrimidine, purine, quinoline, isoquinoline, N-methylcarbazole, N-ethylcarbazole and N-butylcarbazole. A composition according to claim 1 or claim 2 wherein the Lewis acid is a metal halide compound. A composition according to claim 1 or claim 2 wherein the Lewis acid is an organometal halide compound. A composition according to claim 4, wherein the organometal halide compound is an organotin halide compound. A composition according to any preceding claim, further comprising a phosphoric acid ester as an internal mold releasing agent. A composition according to claim 6, wherein the phosphoric acid ester is a mixture of mono- and di-butoxyethyl esters of phosphoric acid. A plastic lens obtained by casting polymerisation by heating and curing a composition according to any preceding claim. A process for the production of a urethane-base plastic lens, which comprises effecting casting polymerisation by heating and curing a composition according to any of claims 1-7 in a mold. A process according to claim 9, wherein a part of the heating is conducted in water.

Inventors: KANEMURA YOSHINOBU, KAWAUCHI NOBUYA, KOBAYASHI SEIICHI, NAGATA TERUYUKI, OKAZAKI KOJU, SASAGAWA KATSUYOSHI, SHIMAKAWA CHITOSHI, TAJIRI YOKO, TANAKA MAMORU, KANEMURA, YOSHINOBU, KAWAUCHI, NOBUYA, KOBAYASHI, SEIICHI, NAGATA, TERUYUKI, OKAZAKI, KOJU, SASAGAWA, KATSUYOSHI, SHIMAKAWA, CHITOSHI, TAJIRI, YOKO, TANAKA, MAMORU
Applicants: MITSUI CHEMICALS INC, MITSUI CHEMICALS, INC.
Application year: 1995
Main classification: C08G18
IPC codes: C08G18, G02B1