Photocurable compositions and their cured products, and optical materials containing the cured products.

Abstract

According to the present invention, it is possible to provide a photocurable composition comprising: sulfur (a) having a cyclic structure represented by formula (1); an episulfide compound (b); and a photopolymerization initiator (c), wherein the content of the sulfur (a) is 1-28 parts by mass with respect to 100 parts by mass of the total of the sulfur (a) and the episulfide compound (b).

Description

Technical Field

[0001] The present invention relates to a photocurable composition useful for producing optical materials such as optical element adhesives, coating agents for optical elements, resist materials, prisms, optical fibers, information recording substrates, filters, and light guide plates.

Background Art

[0002] Plastic materials are lightweight, tough, and easy to dye, and thus have been widely used in various optical materials in recent years. One of the performances required for many optical materials is a high refractive index. For optical materials with a high refractive index, many episulfide compounds that enable optical materials with a refractive index of 1.7 or more have been found (see Patent Documents 1, 2, and 3). As another method for increasing the refractive index of plastic materials, a method of dispersing inorganic particles in an organic resin is well known. However, since light scattering of the particles cannot be completely avoided and cloudiness occurs, it is preferable to use an episulfide compound from the viewpoint of light transmittance. Most of the curing methods for compositions using episulfide compounds are thermosetting, which thus have great limitations in applications. Also, a photocurable composition is strongly desired to improve productivity. For example, in order to impart an optical function onto a transparent substrate having a refractive index exceeding 1.73 such as lanthanum glass or sapphire glass, a photocurable composition having a refractive index exceeding 1.73 and capable of forming a fine structure is desired.

[0003] In Patent Document 4, a high refractive index resin cured product by photocuring of an episulfide composition containing a photo-base generator is reported. A known method for obtaining resin cured products with higher refractive indices involves copolymerizing sulfur with an episulfide compound. Patent document 5 reports that a transparent resin with a refractive index exceeding 1.73 can be obtained by thermocuring an episulfide compound containing sulfur. However, it has generally been difficult to use sulfur in high refractive index photocurable compositions because its strong UV absorption inhibits photocuring. Patent document 6 reports that a high refractive index photocurable composition can be obtained by avoiding the use of sulfur and substituting it with a cyclic polysulfide compound with low UV absorption, but the refractive index is inferior to that of the resin obtained in Patent document 5. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 9-71580 [Patent Document 2] Japanese Patent Application Publication No. 9-110979 [Patent Document 3] Japanese Patent Application Publication No. 9-255781 [Patent Document 4] Japanese Patent Publication No. 2011-38050 [Patent Document 5] Patent No. 3738817 [Patent Document 6] Japanese Patent Publication No. 2015-255 [Overview of the project] [Problems that the invention aims to solve]

[0005] The object of this invention is to provide a photocurable composition with a higher refractive index, a cured product thereof, and an optical material containing the cured product. [Means for solving the problem]

[0006] The inventors conducted research to solve this problem and found that a specific amount of sulfur contributes significantly to improving the refractive index and inhibits photocuring with little effect. They also found that a photocurable composition containing sulfur (a), an episulfide compound (b), and a photopolymerization initiator (c) exhibits photocurability, and the photocured product exhibits a high refractive index. Furthermore, they found that by using long-wavelength light of 360 nm or more, the photocurable composition can be photocured in a shorter time. In other words, the present invention is as follows:

[0007] [1] A photocurable composition comprising sulfur (a) represented by the following formula (1), an episulfide compound (b), and a photopolymerization initiator (c), wherein the content of sulfur (a) is 1 to 28 parts by mass per 100 parts by mass of the total of sulfur (a) and the episulfide compound (b). [ka] [2] The photocurable composition according to [1], comprising 80 parts by mass or less of a cyclic compound (d) represented by the following formula (2) per 100 parts by mass of the total of sulfur (a) and episulfide compound (b). [ka] (In equation (2), C represents carbon, X represents S, Se, or Te. a to f represent integers from 0 to 3, and 8 ≥ (a + c + e) ​​≥ 1, 8 ≥ (b + d + f) ≥ 2, and (b + d + f) ≥ (a + c + e).) [3] The photocurable composition according to [1] or [2], comprising 0.1 to 20 parts by mass of thiol compound (e) with respect to 100 parts by mass of sulfur (a) and episulfide compound (b) in total. [4] The photocurable composition according to [3], wherein the thiol compound (e) is at least one polyfunctional thiol selected from the group of compounds represented by the following formulas (3) to (5). [ka] (In equation (3), X represents either a sulfide or a disulfide.) [ka] (In equation (4), q represents an integer from 0 to 3, R 1 (This represents an alkylene group with 0 to 3 carbon atoms.) [ka] (In formula (5), p represents an integer between 2 and 4. X and Z each independently represent a hydrogen atom, a mercapto group, or a methylthiol group, and these groups may differ for each repeating unit. At least one of the X and Z groups in the molecule is either a mercapto group or a methylthiol group.) [5] A photocurable composition according to any one of [1] to [4], comprising 0.001 to 1 part by mass of an acidic compound (f) with respect to 100 parts by mass of the total of sulfur (a) and episulfide compound (b). [6] A photocurable composition according to any one of [2] to [5], wherein X is S in formula (2). [7] The cyclic compound (d) is 1,2-dithiethane, trithiethane, 1,2-dithiolane, 1,2,3-trithiolane, 1,2,4-trithiolane, tetrathiolane, 1,2-dithiane, 1,2,3-trithiane, 1,2,4-trithiane, 1,3,5-trithiane, 1,2,3,4-tetrathiane, 1,2,4,5-tetrathiane, pentatiane, 1,2,3-trithiepane, 1,2,4-trithiepane, 1 A photocurable composition according to any one of the following [2] to [6], which is one or more selected from the group consisting of ,2,5-trithiepane, 1,2,3,4-tetrathiepane, 1,2,3,5-tetrathiepane, 1,2,4,5-tetrathiepane, 1,2,4,6-tetrathiepane, 1,2,3,4,5-pentathiepane, 1,2,3,4,6-pentathiepane, 1,2,3,5,6-pentathiepane, and hexathiepane. [8] A photocurable composition according to any one of [1] to [7], wherein the photopolymerization initiator (c) is contained in an amount of 0.1 to 10 parts by mass per 100 parts by mass of sulfur (a) and episulfide compound (b) in total. [9] The photocurable composition according to any one of [1] to [8], wherein the photoinitiator (c) is a photo-base generator.

[10] The photocurable composition according to any one of [1] to [9], wherein the episulfide compound (b) has a structure represented by the following formula (6). [Chemical formula] (In the formula, m represents an integer of 0 to 4, and n represents an integer of 0 to 2.)

[11] The photocurable composition according to any one of [1] to

[10] , which is obtained by reacting part or all of sulfur with an amine compound.

[12] A cured product obtained by photocuring the photocurable composition according to any one of [1] to

[11] using light having a wavelength of 360 nm or more.

[13] The cured product according to

[12] , having a refractive index of 1.72 or more measured at the sodium D line.

[14] An optical material containing the cured product according to

[13] .

[15] A method for producing a cured product, which includes a step of obtaining a cured product by photocuring the photocurable composition according to any one of [1] to

[11] using light having a wavelength of 360 nm or more. [Advantages of the Invention]

[0008] The photocurable composition of the present invention has sufficient photocurability, and the cured product has a high refractive index with a refractive index (nD) of 1.72 or more, so that it is possible to provide a high-performance optical material. [Embodiments for Carrying Out the Invention]

[0009] The curable composition of the present invention contains sulfur (a), an episulfide compound (b), and a photoinitiator (c). Hereinafter, sulfur (a), episulfide compound (b), photoinitiator (c), which are raw materials used in the present invention, and compounds that can be added as a photocurable composition will be described in detail.

[0010] The sulfur (a) used in this invention is sulfur having a cyclic structure represented by the following formula (1). The method of obtaining sulfur (a) is not particularly limited. Commercial products may be used, or it may be synthesized by known methods. [ka]

[0011] The proportion of sulfur(a) in the photocurable composition is 1 to 28 parts by mass, preferably 3 to 20 parts by mass, and particularly preferably 5 to 18 parts by mass, per 100 parts by mass of the total of sulfur(a) and episulfide compound(b). If the sulfur(a) content exceeds 28 parts by mass, the resulting photocured product may be yellow in color.

[0012] The episulfide compound (b) used in this invention encompasses all episulfide compounds. The following lists specific examples of episulfide compounds (b), categorized into compounds having a linear aliphatic skeleton, an aliphatic cyclic skeleton, and an aromatic skeleton, but the list is not limited to these.

[0013] Examples of compounds having a chain-like aliphatic skeleton include those represented by the following formula (6). [ka] (In equation (6), m represents an integer between 0 and 4, and n represents an integer between 0 and 2.)

[0014] Specific examples include bis(β-epithiopropyl) sulfide (n=0 in formula (6) above), bis(β-epithiopropyl) disulfide (m=0, n=1 in formula (6) above), bis(β-epithiopropylthio) methane (m=1, n=1 in formula (6) above), 1,2-bis(β-epithiopropylthio)ethane (m=2, n=1 in formula (6) above), 1,3-bis(β-epithiopropylthio) propane (m=3, n=1 in formula (6) above), 1,4-bis(β-epithiopropylthio) butane (m=4, n=1 in formula (6) above), and bis(β-epithiopropylthioethyl) sulfide (m=2, n=2 in formula (6) above).

[0015] Examples of compounds having an aliphatic cyclic skeleton include those represented by the following formulas (7) or (8). [ka] (In equation (7), p and q each represent an integer between 0 and 4 independently.)

[0016] Specific examples include 1,3 and 1,4-bis(β-epithiopropylthio)cyclohexane (p=0, q=0 in formula (7) above) and 1,3 and 1,4-bis(β-epithiopropylthiomethyl)cyclohexane (p=1, q=1 in formula (7) above). [ka] (In equation (8), p and q each represent an integer between 0 and 4 independently.)

[0017] Specific examples include 2,5-bis(β-epithiopropylthio)-1,4-dithiane (p=0, q=0 in formula (8) above) and 2,5-bis(β-epithiopropylthioethylthiomethyl)-1,4-dithiane (p=1, q=1 in formula (8) above).

[0018] Examples of compounds having an aromatic skeleton include those represented by the following formulas (9), (10), or (11). [ka] (In equation (9), p and q each represent an integer between 0 and 4 independently.)

[0019] Specific examples include 1,3 and 1,4-bis(β-epithiopropylthio)benzene (p=0, q=0 in formula (9) above) and 1,3 and 1,4-bis(β-epithiopropylthiomethyl)benzene (p=1, q=1 in formula (9) above). [ka] (In formula (10), R1 and R2 each independently represent a hydrogen atom, a methyl group, an ethyl group, or a phenyl group.)

[0020] Specific examples include bisphenol F-type episulfide compounds where both R1 and R2 are hydrogen atoms, and bisphenol A-type episulfide compounds where both are methyl groups. [ka] (In equation (11), p and q each represent an integer of either 0 or 1 independently.)

[0021] Specific examples include compounds where p=0 and q=0 in equation (11) above, and compounds where p=1 and q=1 in equation (11) above.

[0022] These can be used individually or in combination of two or more. From the standpoint of availability, preferred compounds are those represented by formula (6) above, which have a chain-like aliphatic skeleton, and particularly preferred compounds are bis(β-epithiopropyl) sulfide (n=0 in formula (6) above) and bis(β-epithiopropyl) disulfide (m=0, n=1 in formula (6) above).

[0023] The method of obtaining the episulfide compound (b) is not particularly limited. Commercial products may be used, or it may be synthesized by known methods. For example, bis(β-epithiopropyl) sulfide (n=0 in formula (6) above) can be synthesized according to known techniques (Japanese Patent Publication No. 3491660).

[0024] The proportion of episulfide compound (b) in the photocurable composition is preferably 72 parts by mass or more, more preferably 80 to 97 parts by mass, and particularly preferably 82 to 95 parts by mass, based on 100 parts by mass of the total of sulfur (a) and episulfide compound (b). If the amount of episulfide compound (b) is less than 72 parts by mass, the reaction with sulfur (a) may be insufficient.

[0025] The photopolymerization initiator (c) used in the present invention is not particularly limited as long as it can photocurate the episulfide compound (b). For example, radical generators, acid generators, base generators, etc., can be used. Since base catalysts are the most active for polymerization of the episulfide compound (b), the use of a base generator is most desirable. Preferred specific examples of the photopolymerization initiator (c) include tetrabutylammonium butyltriphenyl borate, tetrabutylammonium butyltri(4-t-butylphenyl) borate, tetrabutylammonium butyltri(1-naphthyl) borate, and tetrabutylammonium butyltri(4-methyl-1-naphthyl) borate. Tetrabutylammonium butyltri(1-naphthyl) borate is most preferred because it has a good balance of solubility in the episulfide compound (b), polymerizability of the episulfide compound (b), and pot life of the composition. Other preferred photopolymerization initiators (c) include compounds that generate bases such as amidines (photobase generators) like DBN (diazabicyclononene) and DBU (diazabicycloundecene). Furthermore, a sensitizer can be added to the episulfide compound (b) in this invention. The addition of a sensitizer enables curing with low-energy ultraviolet irradiation. The proportion of the photopolymerization initiator (c) in the photocurable composition is preferably 0.1 to 10 parts by mass, more preferably 0.1 to 3.0 parts by mass, and particularly preferably 0.2 to 1.0 parts by mass, based on 100 parts by mass of the total of sulfur (a) and episulfide compound (b). If the amount of photopolymerization initiator (c) is less than 0.1 parts by mass, the photocurability will be low, and if it exceeds 10 parts by mass, the refractive index of the cured product may decrease significantly.

[0026] The cyclic compound (d) preferably used in the present invention has a structure represented by the following formula (2). [ka] (In equation (2), C represents carbon, and X represents S, Se, or Te. a~f= represents integers from 0 to 3, and 8≧(a+c+e)≧1, 8≧(b+d+f)≧2, and (b+d+f)≧(a+c+e).)

[0027] In formula (2) above, X is preferably S or Se, and more preferably S, from the viewpoint of availability and toxicity. From the viewpoint of availability, refractive index, and low inhibition of photoactivity, a to f are preferably 8≧(a+c+e)≧1 and 7≧(b+d+f)≧2, and more preferably 5≧(a+c+e)≧1 and 7≧(b+d+f)≧2. Even more preferably, the relationship (b+d+f)≧(a+c+e) is also satisfied. Furthermore, in order to obtain a high refractive index, it is preferable that the total amount of S, Se, and Te in the cyclic compound (d) be 50% by mass or more.

[0028] Specific examples of cyclic compounds (d) include, but are not limited to, the following. Dithyran, 1,2-Dithiethane, 1,3-Dithiethane, Trithiethane, 1,2-Dithiolane, 1,3-Dithiolane, 1,2,3-Trithiolane, 1,2,4-Trithiolane, Tetrathiolane, 1,2-Dithiane, 1,3-Dithiane, 1,4-Dithiane, 1,2,3-Trithiane, 1,2,4-Trithiane, 1,3,5-Trithiane, 1,2,3,4-Tetrathiane, 1,2,4,5-Tetrathiane, Bis(1,2,3,5,6-Pentathiopano)methane, Tris(1 ,2,3,5,6-pentathiopano)methane, 1,2-dithiopane, 1,3-dithiopane, 1,4-dithiopane, 1,2,3-trithiopane, 1,2,4-trithiopane, 1,2,5-trithiopane, 1,3,5-trithiopane, 1,2,3,4-tetrathiopane, 1,2,3,5-tetrathiopane, 1,2,4,5-tetrathiopane, 1,2,4,6-tetrathiopane, 1,2,3,4,5-pentathiopane, 1,2,3,5 Examples include 6-pentatiepane, hexatiepane, diselecyclobutane, tricelecyclobutane, diselecyclopentane, tricelecyclopentane, tetracelecyclopentane, diselecyclohexane, tricelecyclohexane, tetracelecyclohexane, pentacelecyclohexane, diselecycloheptane, tricelecycloheptane, tetracelecycloheptane, pentacelecycloheptane, hexacelecycloheptane, ditellocyclobutane, tritellocyclobutane, ditellocyclopentane, tritellocyclopentane, tetratellocyclopentane, ditellocyclohexane, tritellocyclohexane, tetratellocyclohexane, pentatellocyclohexane, ditellocycloheptane, tritellocycloheptane, tetratellocycloheptane, pentatellocycloheptane, hexacelelocycloheptane, and derivatives having these cyclic skeleton structures (compounds in which hydrogen atoms are replaced with various substituents).

[0029] Specific examples of preferred compositions are those that are easily available and synthesized and have a high refractive index, such as 1,2-dithioethane, trithiumethane, 1,2-dithiolane, 1,2,3-trithiolane, 1,2,4-trithiolane, tetrathiolane, 1,2-dithiane, 1,2,3-trithiane, 1,2,4-trithiane, 1,3,5-trithiane, 1,2,3,4-tetrathiane, 1,2,4,5-tetrathiane, pentatiane, 1,2,3-trithiepane, 1,2,4-trithiepane, 1,2,3,4 -Tetrathiepane, 1,2,3,5-Tetrathiepane, 1,2,4,5-Tetrathiepane, 1,2,4,6-Tetrathiepane, 1,2,3,4,5-Pentathiepane, 1,2,3,4,6-Pentathiepane, 1,2,3,5,6-Pentathiepane, Hexathiepane, and derivatives having these cyclic skeleton structures (compounds with various substituents instead of hydrogen atoms), with 1,2,4,5-Tetrathiane and 1,2,3,5,6-Pentathiepane being particularly preferred from the viewpoint of solubility in episulfide compound (b).

[0030] There are no particular restrictions on how the cyclic compound (d) can be obtained. It may be a commercially available product, extracted from natural products such as crude oil or plants and animals, or synthesized by known methods. Examples of synthesis methods include those described in N. Takeda et al., Bull. Chem. Soc. Jpn., 68, 2757 (1995), F. Feher et al., Angew. Chem. Int. Ed., 7, 301 (1968), and GW Kutney et al., Can. J. Chem, 58, 1233 (1980).

[0031] The proportion of the cyclic compound (d) in the photocurable composition is preferably 80 parts by mass or less, more preferably 12 to 75 parts by mass, and particularly preferably 20 to 70 parts by mass, based on 100 parts by mass of the total of sulfur (a) and episulfide compound (b). If the proportion of the cyclic compound (d) exceeds 80 parts by mass, the resulting photocured product may be yellow in color.

[0032] The structure of the thiol compound (e) that is preferably used in the present invention is not particularly limited, but from the viewpoint of availability and increasing the refractive index of the photocurable composition, polyfunctional thiol compounds represented by the following formulas (3) to (5) are preferred. [ka] (In equation (3), X represents either a sulfide or a disulfide.) [ka] (In equation (4), q represents an integer from 0 to 3, R 1 (This represents an alkylene group with 0 to 3 carbon atoms.) [ka] (In formula (5), p represents an integer between 2 and 4, and X and Z independently represent a hydrogen atom, a mercapto group, or a methylthiol group, and these groups may differ for each repeating unit. At least one of X and Z in the molecule is either a mercapto group or a methylthiol group.)

[0033] Examples of compounds represented by formula (3) include 1,2,6,7-tetramercapto-4-thiaheptane and bis(2,3-dimercaptopropanil) disulfide. Examples of compounds represented by formula (4) include 2,5-dimercapto-1,4-dithiane, 2,5-dimercaptomethyl-1,4-dithiane, and 2,5-dimercaptoethyl-1,4-dithiane. Examples of compounds represented by formula (5) include 1,5-dimercapto-3-thiapentane, 2-mercaptomethyl-1,5-dimercapto-3-thiapentane, 2,4-bis(mercaptomethyl)-1,5-dimercapto-3-thiapentane, 4-mercaptomethyl-1,8-dimercapto-3,6-dithiaoctane, 4,8-bis(mercaptomethyl)-1,11-dimercapto-3,6,9-trithiaundecane, 4,7-bis(mercaptomethyl)-1,11-dimercapto-3,6,9-trithiaundecane, and 5,7-bis(mercaptomethyl)-1,11-dimercapto-3,6,9-trithiaundecane.

[0034] In the present invention, the color tone of the photocured product can be improved by adding thiol compound (e) (Patent Document 6). The amount of thiol compound (e) added is preferably 0.1 to 20 parts by mass, and more preferably 1 to 10 parts by mass, per 100 parts by mass of the total of sulfur (a) and episulfide compound (b). If the amount is less than 0.1 parts by mass, the color tone will not be sufficiently improved, and if it exceeds 20 parts by mass, the resulting cured product may become soft.

[0035] Furthermore, in the present invention, an acidic compound (f) can be added to the photocurable composition. The addition of the acidic compound (f) extends the usable time of the photocurable composition. The acidic compound (f) used in the present invention is not particularly limited as long as it is soluble in the photocurable composition.

[0036] Various protic acids and Lewis acids can be used as the acidic compound (f). As for protic acids, organic acids having a sulfonic acid group, a carboxylic acid group, or a phosphoric acid group are particularly preferred from the viewpoint of solubility in the composition solution. Specific examples of particularly preferred compounds include methanesulfonic acid, trifluoromethanesulfonic acid, benzenesulfonic acid, toluenesulfonic acid, dodecylbenzenesulfonic acid, camphorsulfonic acid, formic acid, acetic acid, propionic acid, butyric acid, benzoic acid, phthalic acid, oxalic acid, ethyl phosphate, diethyl phosphate, butyl phosphate, dibutyl phosphate, ethyl phosphate, diethyl phosphate, butoxyethyl phosphate, and dibutoxyethyl phosphate. Specific examples of preferred Lewis acids include dibutyltin dichloride, butyltin trichloride, dioctyltin dichloride, octyltin trichloride, dibutyldichlorogermanium, butyltrichlorogermanium, diphenyldichlorogermanium, phenyltrichlorogermanium, and triphenylantimony dichloride, with dibutyltin dichloride being a particularly preferred compound. Acidic compound (f) may be used alone or as a mixture of two or more types.

[0037] The amount of acidic compound (f) used is preferably 0.001 to 1 part by mass, and more preferably 0.001 to 0.2 parts by mass, per 100 parts by mass of the total of sulfur (a) and episulfide compound (b). If the amount added is less than 0.001 parts by mass, the stabilizing effect will be small, and if it is more than 1 part by mass, the photocurability may decrease.

[0038] Furthermore, in this invention, a sensitizer (g) can be added to the photocurable composition. By incorporating a sensitizer (g) into the photocurable composition, it becomes possible to more efficiently release the base from the photopolymerization initiator (c). As a result, exposure time can be shortened and polymerization of the photocurable composition can be accelerated. Preferred sensitizers (g) are aromatic ketones such as substituted or unsubstituted benzophenone, thioxanthone, and anthraquinone, or dyes such as oxazine, acridine, phenazine, and rhodamine, and compounds having conjugated heterocycles such as fluorene, fluorenone, and naphthalene. Particularly preferred are substituted or unsubstituted benzophenone, thioxanthone, and fluorene. Specifically, benzophenone, 4,4'-bis(dimethylamino)benzophenone, 4,4'-bis-(diethylamino)benzophenone, 4,4'-bis(ethylmethylamino)benzophenone, 4,4'-diphenylbenzophenone, 4,4'-diphenoxybenzophenone, 4,4'-bis(p-isopropylphenoxy)benzophenone, 4-methylbenzophenone, 2,4,6-trimethylbenzophenone, 4-phenylbenzophenone, 2-methoxycarbonylbenzophenone, 4-benzoyl-4'-methyldiphenyl sulfide, 4-methoxy-3,3'-methylbenzophenone, isopropylthioxanthone, chlorothioxanthone, 1-chloro-4-propoxythioxanthone, 2-(trifluoromethyl) Examples include thioxanthone, 2,4-dimethylthioxanthone, 2,4-diethylthioxanthone, 1,3-dimethyl-2-(2-ethylhexyloxy)thioxanthone, fluorene, 9,9-dimethylfluorene, and 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene, which may be used individually or in combination of two or more. The amount of sensitizer (g) used is preferably 0.05 to 10 parts by mass, more preferably 0.05 to 3 parts by mass, and most preferably 0.1 to 1 part by mass, per 100 parts by mass of the total of sulfur (a) and episulfide compound (b).

[0039] Furthermore, epoxy compounds, isocyanates, phenols, amines, etc., may be added to the photocurable composition of the present invention for the purpose of improving various properties such as weather resistance, oxidation resistance, strength, surface hardness, adhesion to the substrate, refractive index, and dyeability. In this case, a known polymerization curing catalyst may be added separately as needed. In addition, thermosetting catalysts, antioxidants, bluing agents, ultraviolet absorbers, various performance-improving additives, etc., may be added as needed to produce the optical material of the present invention. The amount of these additives added is usually 0.0001 to 5 parts by mass relative to the total amount of the photocurable composition.

[0040] When sulfur (a) is present in an amount of 7% by mass or more per 100 parts by mass of the total of sulfur (a) and episulfide compound (b), it is preferable to add an amine compound to the photocurable composition to pre-react the sulfur and improve its solubility. Preferred amine compounds to be added are hindered amine compounds and imidazole compounds, with specific examples including 1-methyl-2,2,6,6-tetramethyl-4-piperidyl methacrylate and 2-mercapto-1-methyl-4,5-dihydroimidazole.

[0041] The photocurable composition of the present invention is cured by irradiation with ultraviolet light or visible light. The light source used is not particularly limited as long as it is a device that generates ultraviolet light or visible light. Specifically, examples include high-pressure mercury lamps, ultra-high-pressure mercury lamps, metal halide lamps, high-power metal halide lamps, xenon lamps, light-emitting diodes (ultraviolet LEDs), etc. Using a light source with high emission intensity in the 360-410 nm range is preferable as it results in a faster curing speed of the photocurable composition, and a light source of 380 nm or higher is more preferable. Furthermore, it is possible to improve the color tone of the photocured product by cutting out light below 360 nm with a long-pass filter or the like.

[0042] The photocurable composition of the present invention may be subjected to polymerization inhibition due to the influence of oxygen in the air during photocuring. Therefore, it is preferable to expose the photocurable composition in a low-oxygen atmosphere in order to shorten the exposure time and to ensure sufficient polymerization. Specifically, this can be done by exposing the composition by replacing the atmosphere with an inert gas such as nitrogen gas, argon gas, or helium gas, or by exposing it under reduced pressure. The oxygen concentration in this case is preferably 10% or less, and more preferably 5% or less. Other methods include covering the surface of the photocurable composition with a transparent film such as a polypropylene film and then exposing it to light, or sealing and injecting the photocurable composition into a transparent mold made of glass or the like and then exposing it to light.

[0043] The curing of a photocurable composition can be further accelerated by irradiating it with ultraviolet or visible light and then performing a heat treatment. After ultraviolet irradiation, the heating temperature and time can be appropriately selected according to the degree of curing required for the optical material, but the heating temperature is preferably from room temperature to 150°C, and the heating time is preferably from 1 minute to 3 days.

[0044] The cured product of the present invention preferably has a refractive index (nD) of 1.72 or higher, more preferably 1.73 or higher, even more preferably 1.74 or higher, and particularly preferably 1.75 or higher, as measured with a sodium D line. The method for measuring the refractive index in the present invention can be the method described in the examples described later. [Examples]

[0045] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these. In the examples, 1,2,3,5,6-pentathiopane was prepared according to the method described in the literature (HCHansen et al., Tetrahedron, 41, 5145 (1985)), bis(β-epithiopropyl) sulfide was prepared according to the method described in Japanese Patent Publication No. 3491660, 1,2,6,7-tetramercapto-4-thiaheptane was prepared according to Japanese Patent Publication No. 4645979, and 2,5-bis(mercaptomethyl)-1,4-di Anne synthesized the polythiols mainly composed of 4,8-dimercaptomethyl-1,11-dimercapto-3,6,9-trithiaundecane, 4,7-dimercaptomethyl-1,11-dimercapto-3,6,9-trithiaundecane, and 5,7-dimercaptomethyl-1,11-dimercapto-3,6,9-trithiaundecane in accordance with Japanese Patent Publication No. 2895987, and WO2007 / 129450. Tetrabutylammonium butyltri(1-naphthyl) borate was obtained from Showa Denko K.K. and used as is. 4-Benzoyl-4'-methyldiphenyl sulfide was obtained from DKSH Japan under the product name Lunacure BMS and used as is. Sulfur was obtained from Hosoi Chemical Industry Co., Ltd. and used as is.

[0046] [Evaluation Method] The light source used when exposing the photocurable composition is a UV-LED light irradiation device 365 (manufactured by Foseon Technology Japan Co., Ltd., peak wavelength 365 nm, light intensity 600 mW / cm²). 2 ), UV-LED light irradiation device 385 (manufactured by Foseon Technology Japan Co., Ltd., peak wavelength 385nm, light intensity 600mW / cm²) 2 ), UV-LED light irradiation device 395 (manufactured by CCS Corporation, peak wavelength 395nm, light intensity 720mW / cm²) 2 ), and UV-LED light irradiation device 405 (manufactured by CCS Corporation, peak wavelength 405nm, light intensity 720mW / cm²). 2 ) was used. For the UV-LED light irradiation device 315, purchased LEDs with a peak wavelength of 315nm (THORLABS, LED315W) were arranged on a substrate, a DC current was passed through them, and it was used as a UV irradiator. The curing rate of the photocurable composition was evaluated by the irradiation time required to reduce the unreacted monomer to less than 5% when the photocurable composition was sandwiched between two glass slides (S9213, manufactured by Matsunami Glass Industry Co., Ltd.) to a thickness of 400-500 μm and irradiated with a UV-LED light irradiation device. The amount of unreacted monomer was measured using the spectrum obtained with an FT / IR measuring device (FT / IR-4200, manufactured by JASCO Corporation) at a wavenumber of 610 cm⁻¹. -1 The calculation was based on the peak area. Curing speed was evaluated as "A" for irradiation time less than 1 minute, "B" for 1 minute to less than 3 minutes, and "C" for 3 minutes or more. The refractive index (nD) of the cured material was measured using an Abbe refractometer (NAR-4T, manufactured by Atago Corporation) at the sodium D line. The cured material for measurement was prepared by sandwiching a photocurable composition with a spacer between two glass slides to a thickness of 400-500 μm, and irradiating it with UV-LED light for 5 minutes. The measurement temperature was 20°C.

[0047] [Example 1] 5 parts by mass of sulfur (a) (hereinafter referred to as compound a-1), 95 parts by mass of bis(β-epithiopropyl) sulfide (hereinafter referred to as compound b-1) as episulfide compound (b), totaling 100 parts by mass of these, were mixed with 0.5 parts by mass of tetrabutylammonium butyltri(1-naphthyl) borate (hereinafter referred to as compound c-1) as a photopolymerization initiator and 0.5 parts by mass of 4-benzoyl-4'-methyldiphenyl sulfide (hereinafter referred to as compound g-1) as a sensitizer. The mixture was stirred at 30°C to obtain a homogeneous solution. This was filtered through a PTFE filter with a pore size of 0.45 μm to obtain a photocurable composition. This was sandwiched between two glass plates facing each other with a spacer of 0.50 mm thickness, and cured by light irradiation with a UV-LED light irradiation device 365. The glass plates were removed to obtain a cured resin product. The evaluation results are shown in Table 1.

[0048] [Example 2] To a total of 100 parts by mass, 5.3 parts by mass of compound a-1 as sulfur and 94.7 parts by mass of compound b-1 as an episulfide compound were added. To this mixture, 5.3 parts by mass of a mixture of 4,8-bis(mercaptomethyl)-1,11-dimercapto-3,6,9-trithiaoundecane, 4,7-bis(mercaptomethyl)-1,11-dimercapto-3,6,9-trithiaoundecane and 5,7-bis(mercaptomethyl)-1,11-dimercapto-3,6,9-trithiaoundecane (hereinafter referred to as compound e-1) was added as thiol compound (e), 0.5 parts by mass of tetrabutylammonium butyltri(1-naphthyl)borate (hereinafter referred to as compound c-1) as a photopolymerization initiator and 0.5 parts by mass of 4-benzoyl-4'-methyldiphenyl sulfide (hereinafter referred to as compound g-1) as a sensitizer were added and the mixture was stirred at 30°C to obtain a homogeneous solution. This was filtered through a PTFE filter with a pore size of 0.45 μm to obtain a photocurable composition. This was sandwiched between two opposing glass plates separated by a 0.50 mm thick spacer, and cured by light irradiation with a UV-LED light irradiation device 365. The glass plates were then removed to obtain a cured resin product. The evaluation results are shown in Table 1.

[0049] [Example 3] A photocurable composition was prepared and evaluated using the same method as in Example 2. A cured resin product was obtained using the same method as in Example 2, except for the curing conditions shown in Table 1. The evaluation results are shown in Table 1.

[0050] [Example 4] To a total of 100 parts by mass of a-1 compound (12.6 parts by mass as sulfur) and b-1 compound (87.4 parts by mass as episulfide), 10 ppm of 1,2,2,6,6-pentamethyl-4-piperidyl methacrylate (hereinafter referred to as LA-82) was added as a preliminary reaction catalyst, and the mixture was stirred at 60°C for 5 hours to dissolve a-1 and b-1 compounds and obtain a homogeneous solution. Subsequently, this composition was cooled to 30°C, and to a total of 100 parts by mass of a-1 and b-1 compounds, 0.5 parts by mass of c-1 compound as a photopolymerization initiator, 0.5 parts by mass of g-1 compound as a sensitizer, and 5.3 parts by mass of e-1 compound as a thiol compound were added, and the mixture was stirred at 30°C to obtain a homogeneous solution. This was filtered through a PTFE filter with a pore size of 0.45 μm to obtain a photocurable composition. This was sandwiched between two opposing glass plates separated by a 0.50 mm thick spacer, cured by light irradiation with a UV-LED light irradiation device 365, and then the glass plates were removed to obtain the cured resin product. The evaluation results are shown in Table 1.

[0051] [Examples 5 and 6] A photocurable composition was prepared and evaluated using the same method as in Example 4. The cured resin product was obtained using the same method as in Example 4, except for the curing conditions shown in Table 1. The evaluation results are shown in Table 1.

[0052] [Example 7] To a total of 100 parts by mass, consisting of 10.8 parts by mass of compound a-1 as sulfur and 89.2 parts by mass of compound b-1 as an episulfide compound, 24.8 parts by mass of a polythiol (hereinafter referred to as compound d-1) mainly composed of the cyclic compound 1,2,3,5,6-pentatiepane compound was added, 0.5 parts by mass of compound c-1 as a photopolymerization initiator, 0.5 parts by mass of compound g-1 as a sensitizer, and 10.0 parts by mass of compound e-1 as a thiol compound were added and stirred at 30°C to obtain a homogeneous solution. This was filtered through a PTFE filter with a pore size of 0.45 μm to obtain a photocurable composition. This was sandwiched between two opposing glass plates separated by a 0.50 mm thick spacer and cured by light irradiation with a UV-LED light irradiation device 385, and the glass plates were removed to obtain a cured resin product. The evaluation results are shown in Table 1.

[0053] [Example 8] To a total of 100 parts by mass of the following compounds, 10.8 parts by mass of compound a-1 as sulfur and 89.2 parts by mass of compound b-1 as an episulfide compound, 24.8 parts by mass of a polythiol (hereinafter referred to as compound d-1) mainly composed of the cyclic compound 1,2,3,5,6-pentatiepane compound was added, and 1.0 ppm of LA-82 as a preliminary reaction catalyst was added. The mixture was stirred at 60°C for 5 hours to dissolve compounds a-1, b-1, and d-1 into a homogeneous solution. Subsequently, this composition was cooled to 30°C, and to a total of 100 parts by mass of compounds a-1 and b-1, 0.5 parts by mass of compound c-1 as a photopolymerization initiator, 0.5 parts by mass of compound g-1 as a sensitizer, and 10.0 parts by mass of compound e-1 as a thiol compound were added, and the mixture was stirred at 30°C to obtain a homogeneous solution. This was filtered through a PTFE filter with a pore size of 0.45 μm to obtain a photocurable composition. This was sandwiched between two opposing glass plates separated by a 0.50 mm thick spacer, cured by light irradiation with a UV-LED light irradiation device 385, and then the glass plates were removed to obtain the cured resin product. The evaluation results are shown in Table 1.

[0054] [Example 9] A photocurable composition was prepared and evaluated in the same manner as in Example 8, except for the composition ratio shown in Table 1. The evaluation results are shown in Table 1.

[0055] [Examples 10, 11] A photocurable composition was prepared and evaluated using the same method as in Example 9. A cured resin product was obtained using the same method as in Example 8, except for the curing conditions shown in Table 1. The evaluation results are shown in Table 1.

[0056] [Examples 12, 13] A photocurable composition was prepared and evaluated in the same manner as in Example 8, except for the compounds and composition ratios shown in Table 1. A cured resin product was obtained in the same manner as in Example 8, except for the curing conditions shown in Table 1. The evaluation results are shown in Table 1.

[0057] [Example 14] A photocurable composition was prepared and evaluated in the same manner as in Example 8, except for the composition ratio shown in Table 1. A cured resin product was obtained in the same manner as in Example 8, except for the curing conditions shown in Table 1. The evaluation results are shown in Table 1.

[0058] [Reference example 1] 5.0 parts by mass of compound a-1 as sulfur, 95 parts by mass of compound b-1 as an episulfide compound, and a total of 100 parts by mass of these were added. To this mixture, 5.0 parts by mass of compound e-1 as thiol compound (e), 0.5 parts by mass of compound c-1 as a photopolymerization initiator, and 0.5 parts by mass of compound g-1 as a sensitizer were added and the mixture was stirred at 30°C to obtain a homogeneous solution. This was filtered through a PTFE filter with a pore size of 0.45 μm to obtain a photocurable composition. This was sandwiched between two opposing glass plates separated by a 0.50 mm thick spacer and cured by light irradiation with a UV-LED light irradiation device 315. The glass plates were removed to obtain a cured resin product. The evaluation results are shown in Table 1.

[0059] [Table 1] a-1: Sulfur b-1: Bis(β-epithiopropyl) sulfide c-1: Tetrabutylammonium = butyltri(1-naphthyl)borate d-1: Polythiol with 1,2,3,5,6-pentatiepane as the main component e-1: A mixture of 4,8-bis(mercaptomethyl)-1,11-dimercapto-3,6,9-trithiaundecane, 4,7-bis(mercaptomethyl)-1,11-dimercapto-3,6,9-trithiaundecane, and 5,7-bis(mercaptomethyl)-1,11-dimercapto-3,6,9-trithiaundecane. e-2:2,5-bis(mercaptomethyl)-1,4-thidian e-3:1,2,6,7-Tetramercapto-4-thiaheptane g-1: 4-benzoyl-4'-methyldiphenyl sulfide

Claims

1. A photocurable composition containing sulfur (a) having a cyclic structure represented by the following formula (1), an episulfide compound (b), and a photopolymerization initiator (c), wherein the content of sulfur (a) is 5 to 20 parts by mass per 100 parts by mass of the total of sulfur (a) and episulfide compound (b), The total of 100 parts by mass of the sulfur (a) and the episulfide compound (b) contains 12 to 75 parts by mass or less of the cyclic compound (d) represented by the following formula (2): The photocurable composition contains 1 to 10 parts by mass of a thiol compound (e) with respect to a total of 100 parts by mass of sulfur (a) and episulfide compound (b). 【Chemistry 1】 【Chemistry 2】 (In the formula, C represents a carbon atom, and X represents S, Se, or Te.) a through f represent integers from 0 to 3, and 8 ≥ (a + c + e) ​​≥ 1, 8 ≥ (b + d + f) ≥ 2, and (b + d + f) ≥ (a + c + e).

2. The photocurable composition according to claim 1, wherein the thiol compound (e) is at least one polyfunctional thiol selected from the group of compounds represented by the following formulas (3) to (5). 【Transformation 3】 (In equation (3), X represents either a sulfide or a disulfide.) 【Chemistry 4】 (In equation (4), q represents an integer from 0 to 3, R １ (This represents an alkylene group with 0 to 3 carbon atoms.) 【Transformation 5】 (In formula (5), p represents an integer between 2 and 4. X and Z each independently represent a hydrogen atom, a mercapto group, or a methylthiol group, and these groups may differ for each repeating unit. At least one of X and Z in the molecule is either a mercapto group or a methylthiol group.)

3. The photocurable composition according to claim 1 or 2, comprising 0.001 to 1 part by mass of an acidic compound (f) per 100 parts by mass of the total of the sulfur (a) and the episulfide compound (b).

4. The photocurable composition according to any one of claims 1 to 3, wherein X is S in formula (2).

5. The cyclic compound (d) is 1,2-dithiethane, trithiethane, 1,2-dithiolane, 1,2,3-trithiolane, 1,2,4-trithiolane, tetrathiolane, 1,2-dithiane, 1,2,3-trithiane, 1,2,4-trithiane, 1,3,5-trithiane, 1,2,3,4-tetrathiane, 1,2,4,5-tetrathiane, pentatiane, 1,2,3-trithiepane, 1,2,4-trithiepane, 1 A photocurable composition according to any one of claims 1 to 4, wherein the composition is one or more selected from the group consisting of 2,5-trithiepane, 1,2,3,4-tetrathiepane, 1,2,3,5-tetrathiepane, 1,2,4,5-tetrathiepane, 1,2,4,6-tetrathiepane, 1,2,3,4,5-pentathiepane, 1,2,3,4,6-pentathiepane, 1,2,3,5,6-pentathiepane, and hexathiepane.

6. The photocurable composition according to any one of claims 1 to 5, wherein the photopolymerization initiator (c) is contained in an amount of 0.1 to 10 parts by mass per 100 parts by mass of the total of sulfur (a) and episulfide compound (b).

7. The photocurable composition according to any one of claims 1 to 6, wherein the photopolymerization initiator (c) is a photobase generator.

8. The photocurable composition according to any one of claims 1 to 7, wherein the episulfide compound (b) has a structure represented by the following formula (6). 【Transformation 6】 (In the formula, m represents an integer between 0 and 4, and n represents an integer between 0 and 2.)

9. A photocurable composition according to any one of claims 1 to 8, obtained by reacting some or all of the sulfur with an amine compound.

10. A cured product obtained by photocuring a photocurable composition according to any one of claims 1 to 9 using light with a wavelength of 360 nm or more.

11. The cured product according to claim 10, wherein the refractive index measured with sodium D line is 1.72 or higher.

12. An optical material comprising the cured product according to claim 11.

13. A method for producing a cured product, comprising the step of photocuring a photocurable composition according to any one of claims 1 to 9 using light with a wavelength of 360 nm or more to obtain a cured product.

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