Polymer, curable composition, and optical film

Abstract

Provided are a novel polymer capable of suppressing the occurrence of pinholes in formation of an optical film, and a curable composition and an optical film containing the same. A polymer (P) having a degree of polymerization of 2 or more has a structural unit (a) corresponding to a polyfunctional polymerizable liquid crystal compound (A1) and a structural unit (b) corresponding to an aliphatic polyfunctional thiol compound (B). A curable composition contains the polymer (P), a polyfunctional polymerizable liquid crystal compound (A2), and a polymerization initiator (C), and an optical film is obtained by curing the curable composition.

Description

Polymer, curable composition and optical film

[0001] The present invention relates to a novel polymer, a curable composition containing the polymer, and an optical film obtained by curing the curable composition.

[0002] In recent years, retardation films (optically anisotropic films) have been used in various forms in the field of displays (liquid crystal displays, organic EL displays, etc.). Such retardation films are produced by applying a liquid crystalline compound, a dye, a conductive compound, etc. to a supporting substrate, such as an alignment film having liquid crystal alignment ability, or a substrate, and then orienting the compound. As optical films such as such retardation films, for example, an optical film obtained by dissolving a polymerizable liquid crystal compound, such as LC242 manufactured by BASF, in a solvent, applying the solution to a supporting substrate, and then polymerizing the solution, is known.

[0003]

[0004] Patent Document 1 discloses an invention that uses a composition containing a compound containing a thiol group and a photopolymerization initiator in addition to the polymerizable liquid crystal compound, in order to improve the degree of polymerization of an optical film obtained from the above-mentioned polymerizable liquid crystal compound LC242.

[0005] JP 2010-126651 A

[0006] However, optical films using the above-mentioned polymerizable liquid crystal compounds such as LC242 have the problem that pinholes are generated during film formation, which affects the optical properties of the resulting optical film.

[0007] Therefore, an object of the present invention is to provide a novel polymer capable of suppressing the occurrence of pinholes during the formation of an optical film, as well as a curable composition and an optical film containing the same.

[0008] That is, the present invention provides: [1] a polymer (P) having a structural unit (a) corresponding to a polyfunctional polymerizable liquid crystal compound (A1) and a structural unit (b) corresponding to an aliphatic polyfunctional thiol compound (B), and having a degree of polymerization of 2 or more; [2] the polymer (P) according to the above [1], in which the structural unit (a) and the structural unit (b) have a molar ratio of 10:5 to 5:10; [3] the polyfunctional polymerizable liquid crystal compound (A1) is a compound represented by formula (I): (In formula (I), R 1 each independently represents a hydrogen atom or a methyl group; p each independently represents a spacer group which is a divalent organic group; y represents a divalent organic group containing a structure in which two or more rings selected from the group consisting of aromatic rings and aliphatic rings, which may have a substituent, are bonded via a single bond or a linking group. [4] A curable composition comprising: a polymer (P) having a degree of polymerization of 2 or more, which has a structural unit (a) corresponding to a polyfunctional polymerizable liquid crystal compound (A1) and a structural unit (b) corresponding to an aliphatic polyfunctional thiol compound (B); a polyfunctional polymerizable liquid crystal compound (A2); and a polymerization initiator (C); [5] A curable composition comprising: a polymer (P) having a structural unit (a) corresponding to a polyfunctional polymerizable liquid crystal compound (A1) and a structural unit (b) corresponding to an aliphatic polyfunctional thiol compound (B), which has a degree of polymerization of 2 or more, a polyfunctional polymerizable liquid crystal compound (A2), and a polymerization initiator (C); (In formula (I), R 1 each independently represents a hydrogen atom or a methyl group; p each independently represents a spacer group which is a divalent organic group; yrepresents a divalent organic group containing a structure in which two or more rings selected from the group consisting of aromatic rings and aliphatic rings, each of which may have a substituent, are bonded via a single bond or a linking group. [6] the curable composition according to the above [4] or [5], wherein the polyfunctional polymerizable liquid crystal compound (A1) and the polyfunctional polymerizable liquid crystal compound (A2) comprise polyfunctional polymerizable liquid crystal compounds having the same structure; [7] the curable composition according to any one of the above [4] to [6], wherein the aliphatic polyfunctional thiol compound (B) is a bifunctional thiol compound having a molecular weight of 200 to 1000; [8] the curable composition according to any one of the above [4] to [7], wherein the weight average molecular weight (Mw) of the polymer (P) is 5,000 to 30,000; [9] the curable composition according to any one of the above [4] to [8], wherein the mass ratio of the polymer (P) to the polyfunctional polymerizable liquid crystal compound (A2) is 50:50 to 3:97; and

[10] an optical film obtained by curing the curable composition according to any one of the above [4] to [9].

[0009] When the polymer (P) according to the present invention is added to a curable composition for forming an optical film, it can suppress the generation of pinholes during the formation of the optical film, and by using the curable composition, an optical film with fewer pinholes can be obtained.

[0010] In this specification, the terms "(meth)acrylic", "(meth)acryloyl", "(meth)acrylate", etc. are general terms for "methacrylic" and "acrylic", "methacrylate" and "acrylate", respectively.

[0011] In this specification, the term "polymer" refers to a compound having a degree of polymerization of at least 2. Here, the term "degree of polymerization" refers to the value obtained by dividing the weight-average molecular weight (Mw) of the polymer, measured by gel permeation chromatography (GPC) and converted into polystyrene, by the sum of the molecular weights of the corresponding monomers, that is, the polyfunctional polymerizable liquid crystal compound and the aliphatic polyfunctional thiol compound.

[0012] In this specification, when a numerical range is indicated using "to," it is intended to include both ends of the range.

[0013] [Polymer (P)] In one embodiment of the present invention, a polymer (P) is provided which has a structural unit (a) corresponding to the polyfunctional polymerizable liquid crystal compound (A1) and a structural unit (b) corresponding to the aliphatic polyfunctional thiol compound (B), and has a degree of polymerization of 2 or more. Hereinafter, the polyfunctional polymerizable liquid crystal compound (A1), the corresponding structural unit (a), the aliphatic polyfunctional thiol compound (B), and the corresponding structural unit (b) may be referred to as compound (A1), structural unit (a), compound (B), and structural unit (b), respectively. The polyfunctional polymerizable liquid crystal compound (A2) described below may also be referred to as compound (A2).

[0014] When the polymer (P) according to the present invention is added to a curable composition for film formation and a film is formed, the occurrence of pinholes can be suppressed. It is believed that pinholes in the formed film occur when elements with low surface tension, such as crystals, are present on the substrate, inhibiting the wettability of the curable composition on the substrate, resulting in the absence of the curable composition only in the areas where the elements are present, a phenomenon known as "repellency." Without being bound by theory, it can be assumed that when the polymer (P) according to the present invention is incorporated into a curable composition for film formation, the viscosity of the curable composition after drying increases, reducing its fluidity, and suppressing the occurrence of "repellency."

[0015] The lower limit of the degree of polymerization of the polymer (P) is 2 or more, preferably 4 or more, more preferably 5 or more, and even more preferably 7 or more. The degree of polymerization of the polymer (P) may be 10 or more, or even 20 or more. In other words, even if the structural units (a) and (b) constituting the polymer (P) are incorporated into a curable composition for film formation as their corresponding monomers, compound (A1), and compound (B), respectively, the effect of suppressing the occurrence of pinholes in the formed film cannot be obtained. Furthermore, the upper limit of the degree of polymerization of the polymer (P) is preferably 40 or less, more preferably 35 or less, even more preferably 30 or less, and even more preferably 25 or less. The degree of polymerization of the polymer (P) may be 10 or less, or even 8 or more. When the degree of polymerization of the polymer (P) is 40 or less, the viscosity of the curable composition to which the polymer (P) is added does not become excessively high, and the orientation of the compound (A2) can be maintained well.

[0016] The lower limit of the molecular weight of the polymer (P) is related to the degree of polymerization described above, and is preferably 5,000 or more, more preferably 6,000 or more, in terms of weight average molecular weight (Mw). The molecular weight of the polymer (P) may be 10,000 or more, 12,000 or more, or 15,000 or more. Similarly, the upper limit of the molecular weight of the polymer (P) is preferably 30,000 or less, more preferably 25,000 or less, even more preferably 23,000 or less, and even more preferably 20,000 or less. The molecular weight of the polymer (P) may be 10,000 or less, or even 7,000 or less.

[0017] In the polymer (P), the molar ratio of the structural unit (a) to the structural unit (b) is not particularly limited, but is preferably 10:5 to 5:10, more preferably 10:8 to 8:10. This molar ratio may be 10:9 to 8:10, or even 10:9 to 9:10. When the molar ratio of the structural unit (a) to the structural unit (b) in the polymer (P) is within the above range, it tends to be easier to adjust the weight average molecular weight (Mw) of the polymer (P) to be within the above range.

[0018] The polymer (P) can be produced by reacting the compound (A1) and the compound (B) in a suitable solvent in the presence of a base catalyst using a method known in the art. Specific examples of the solvent include propylene glycol monomethyl ether acetate, cyclopentanone, cyclohexanone, methyl ethyl ketone, and toluene. Typically, the polymer (P) is produced by a Michael addition reaction of the compound (A1) and the compound (B), which are raw materials for the polymer (P), in the presence of a suitable base catalyst such as a tertiary amine. The degree of polymerization of the polymer (P) can be adjusted mainly by the amounts of the compound (A1) and the compound (B) used in the production.

[0019] (Polyfunctional Polymerizable Liquid Crystal Compound (A1)) The structural unit (a) constituting the polymer (P) according to the present invention is derived from the polyfunctional polymerizable liquid crystal compound (A1) which is a monomer. Here, the compound (A1) is not particularly limited as long as it is a liquid crystal compound having two or more polymerizable functional groups. Examples of the polymerizable functional group include a (meth)acryloyl group, a (meth)acryloxy group, a vinyl group, a (meth)acrylamide group, a maleimide group, an epoxy group, and an oxetanyl group. The number of polymerizable functional groups is two or more, and specific examples include 2, 4, and 6. Furthermore, from the viewpoints of manufacturability and ease of incorporation into a curable composition, the number of polymerizable functional groups is more preferably two.

[0020] A preferred embodiment of the compound (A1) is a liquid crystal compound having two (meth)acrylic groups as polymerizable functional groups, and is, for example, a compound represented by the formula (I): (In formula (I), R 1 each independently represents a hydrogen atom or a methyl group; p each independently represents a spacer group which is a divalent organic group; y represents a divalent organic group containing a structure in which two or more rings selected from the group consisting of aromatic rings and aliphatic rings which may have a substituent are bonded via a single bond or a linking group.

[0021] R in formula (I) 1are each independently a hydrogen atom or a methyl group, but are preferably a hydrogen atom in terms of good reactivity with compound (B). 1 are preferably the same substituents in terms of good reactivity with compound (B).

[0022] S in formula (I) p each independently represents a spacer group which is a divalent organic group. p In this specification, the spacer group which is a divalent organic group refers to a spacer group which is adjacent to the —O— group and —C y - represents an organic group having two bonds bonded to a - group, and the number of atoms in the main chain is preferably 1 or more, more preferably 2 or more, even more preferably 3 or more, and even more preferably 4 or more. From the viewpoint of manufacturability and ease of availability, the number of atoms in the main chain of the spacer group is preferably 20 or less, more preferably 15 or less, even more preferably 12 or less, even more preferably 10 or less, particularly preferably 8 or less, and especially preferably 6 or less. As the spacer group which is a divalent organic group, a preferred example is an alkylene group. Here, one -CH2- group or two or more non-adjacent -CH2- groups contained in the alkylene group are -O-, -O-C(=O)-, -O-C(=O)-O-, and -N(R a )-C(=O)-O-. a represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms.

[0023] The spacer group, which is a divalent organic group, is, for example, an alkylene group having preferably 1 to 20 carbon atoms, more preferably 2 to 20, even more preferably 2 to 15, still more preferably 2 to 12, particularly preferably 3 to 10, and particularly preferably 4 to 8 carbon atoms, in which one -CH2- group or two or more non-adjacent -CH2- groups contained in the alkylene group are -O-, -O-C(=O)-, -O-C(=O)-O-, and -N(R a)-C(=O)-O-, wherein R a represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms.

[0024] The alkylene group includes linear or branched alkylene groups, such as an ethylene group, a propylene group, a butylene group, a pentylene group, a hexylene group, a heptylene group, an octylene group, a dodecylene group, etc. From the viewpoints of manufacturability and availability, the alkylene group is preferably a linear alkylene group.

[0025] One or two or more non-adjacent —CH— groups contained in the alkylene group are selected from the group consisting of —O—, —O—C(═O)—, —O—C(═O)—O— and —N(R a The alkylene group substituted with at least one group selected from the group consisting of -O-, -O-C(=O)-, -O-C(=O)-O-, and -N(R a )—C(═O)—O—. Examples of such groups include —(CH) p A group represented by -Z-, -(CH2) q -Z-(CH2) r a group represented by -, -Z-(CH) s A group represented by -Z-, -(CH2) t -Z-(CH2) uIn the formula, p is preferably 1 to 19, more preferably 2 to 19, even more preferably 1 to 14, still more preferably 1 to 11, especially preferably 2 to 9, and even more preferably 3 to 7, q and r are each independently an integer of 1 or more, the sum of q and r is preferably 1 to 19, more preferably 2 to 19, even more preferably 1 to 14, even more preferably 1 to 11, especially preferably 2 to 9, and even more preferably 3 to 7, s is preferably 1 to 18, more preferably 1 to 13, even more preferably 1 to 10, even more preferably 1 to 8, and especially preferably 2 to 6, and t and u are each independently an integer of 1 or more, the sum of t and u is preferably 1 to 18, more preferably 1 to 13, even more preferably 1 to 10, even more preferably 1 to 8, and especially preferably 2 to 6. In addition, Z in the above formula is each independently —O—, —O—C(═O)—, —O—C(═O)—O—, or —N(R a )-C(═O)-O-.

[0026] C in formula (I) y represents a divalent organic group containing a structure in which two or more rings selected from the group consisting of aromatic rings and aliphatic rings, each of which may have a substituent, are bonded via a single bond or a linking group.

[0027] The aromatic ring and the aliphatic ring may be monocyclic or may be a fused ring in which two or more rings are bonded by sharing some of the elements constituting each ring. The aromatic ring may be an aromatic hydrocarbon ring or an aromatic heterocycle. In the case of an aromatic heterocycle, atoms that may be contained other than carbon atoms include, for example, a nitrogen atom, a sulfur atom, and an oxygen atom. The total number of carbon atoms and atoms other than carbon atoms forming the aromatic ring or the aliphatic ring is not particularly limited, but is preferably 3 to 20, more preferably 4 to 16, and even more preferably 6 to 12.

[0028] Examples of the monocyclic aromatic ring include a benzene ring, a pyridine ring, and a pyrrole ring.

[0029] Examples of the fused aromatic ring include a naphthalene ring, an anthracene ring, and a phenanthrene ring.

[0030] Examples of the monocyclic aliphatic ring include cycloheptane and cyclohexane.

[0031] Examples of the fused aliphatic ring include bicycloundecane and decahydronaphthalene rings.

[0032] The aromatic ring and the aliphatic ring may have a substituent. Examples of the substituent include at least one group selected from the group consisting of an alkyl group having 1 to 3 carbon atoms, a halogen group (e.g., a fluoro group), and a -CN group. When the aromatic ring and the aliphatic ring have a substituent, the number of the substituents is not particularly limited, but is preferably 1 to 3, and more preferably 1 or 2.

[0033] From the viewpoints of manufacturability and availability, the aromatic ring and the aliphatic ring are preferably aromatic rings, more preferably monocyclic aromatic rings, and even more preferably monocyclic aromatic hydrocarbon rings.

[0034] C in formula (I) y includes a structure in which two or more rings selected from the group consisting of the above aromatic rings and aliphatic rings are bonded via a single bond or a linking group. Examples of the structure in which two or more rings selected from the group consisting of aromatic rings and aliphatic rings are bonded via a single bond include biphenyl, cyclohexylbenzene, and biphenylcyclohexane. Examples of the linking group include -O-, -O-C(=O)-, -O-C(=O)-O-, and -N(R a )-C(=O)-O-. y From the viewpoint of manufacturability and ease of availability, preferably represents a structure in which two or more rings selected from the group consisting of aromatic rings and aliphatic rings are bonded via a single bond or a group selected from the group consisting of -O-, -O-C(=O)-, and -O-C(=O)-O-, and more preferably represents a structure in which two or more rings selected from the group consisting of aromatic rings and aliphatic rings are bonded via a single bond or -O-C(=O)-.

[0035] C in formula (I)y From the viewpoint of manufacturability and ease of availability, *-A-(YA) m -* (wherein, A's each independently represent an aromatic ring or an aliphatic ring which may have a substituent, Y's each independently represent a single bond or a linking group, m represents an integer of 1 to 3, * represents S p With respect to the aromatic ring or aliphatic ring in A, it is preferable that C y The same applies to the aromatic ring or aliphatic ring which may have a substituent as described above for Y. y The above-mentioned descriptions of the linking groups apply analogously.

[0036] In the compound (A1), even when the compound (A1) has a functional group other than a (meth)acrylic group as a polymerizable functional group or when the compound (A1) has more than two polymerizable functional groups, the same as S described above in relation to formula (I) can be used. p and C y In the case where the polymerizable functional group is more than two, for example, in the formula (I), p and the polymerizable functional groups bonded thereto are C y The compound may be further bound to

[0037] Specific examples of compound (A1) include, but are not limited to, the following compounds: In the following formula, m and r represent integers of 1 to 12, and n and l represent integers of 0 to 12. When n and l are 0, oxygen atoms bonded to the adjacent aromatic rings are also absent.

[0038]

[0039] For example, among the above compounds, compounds in which the number of substituents having polymerizable functional groups bonded to an aromatic ring is increased or decreased while the other structures are maintained are also considered to be explicitly specified as specific examples of compound (A1) as long as the number of polymerizable functional groups is two or more.

[0040] The method for producing the compound (A1) is not particularly limited, and the compound (A1) can be appropriately synthesized according to a conventionally known synthesis method. Also, the above-mentioned LC242 available from BASF, RM257 available from Merck, and other commercially available compounds (A1) may be used. The above-mentioned compounds (A1) may be used alone or in combination of two or more.

[0041] (Aliphatic Polyfunctional Thiol Compound (B)) The structural unit (b) constituting the polymer (P) according to the present invention is derived from the aliphatic polyfunctional thiol compound (B) which is a monomer. Here, the compound (B) is not particularly limited as long as it is a compound having two or more thiol groups in an aliphatic group. Specific examples of the compound (B) include hexanedithiol, decanedithiol, 1,4-dimethylmercaptobenzene, butanediol bisthiopropionate, butanediol bisthioglycolate, ethylene glycol bisthioglycolate, trimethylolpropane tristhiopropionate, trimethylolpropane tristhioglycolate, pentaerythritol tetrakisthiopropionate, pentaerythritol tetrathioglycolate, trishydroxyethyl tristhiopropionate, and polyvalent hydroxy compounds thereof such as thioglycolates and thiopropionates. Among these, a bifunctional compound having two thiol groups is preferred because it is less likely to cause gelation of the polymer (P) and is easy to handle. As the compound (B), both primary and secondary thiols can be used.

[0042] Compound (B) is preferably a bifunctional thiol compound having a molecular weight of 200 to 1000. Specifically, the molecular weight of compound (B) is preferably 200 or more, more preferably 220 or more, even more preferably 250 or more, and even more preferably 300 or more. Furthermore, the molecular weight of compound (B) is preferably 1000 or less, more preferably 900 or less, even more preferably 800 or less, and even more preferably 500 or less. This also applies to the above-mentioned embodiment of polymer (P). By setting the molecular weight of compound (B) within the above-mentioned range, it tends to be easier to adjust the weight-average molecular weight (Mw) of polymer (P) within the above-mentioned range.

[0043] Examples of commercially available products of compound (B) include Karenz (registered trademark) MT BD1, Karenz (registered trademark) MT PE1, Karenz (registered trademark) MT TPMB (manufactured by Resonac Corporation), TMMP, PEMP, EGMP-4, and DPMP (manufactured by Sakai Chemical Industry Co., Ltd.).

[0044] Furthermore, the compound (B) is preferably a compound containing an —O—C(═O)—R—SH group (wherein R represents a linear or branched alkylene group having 1 to 5 carbon atoms). Specific examples are shown below.

[0045]

[0046] The method for producing the compound (B) described above is not particularly limited, and the compound (B) can be appropriately synthesized according to a conventionally known synthesis method. Also, as described above, a commercially available compound (B) may be used. Furthermore, the compound (B) described above may be used alone or in combination of two or more kinds.

[0047] (Base Catalyst) The base catalyst is not particularly limited, but typically, a base catalyst that does not have active hydrogen, such as a tertiary amine, can be used without any particular restriction, and specific examples include dimethylbenzylamine, triethylamine, and triphenylphosphine.

[0048] In producing the polymer (P), the following elements can be further used.

[0049] (Organic Solvent) Suitable organic solvents include, but are not limited to, tetrahydrofuran, alcohol-based solvents such as ethanol, propanol, and butanol, ketone-based solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, and cyclopentanone, ester-based solvents such as ethyl acetate, butyl acetate, and propylene glycol monomethyl ether acetate, ether-based solvents such as diethyl ether and diglyme, hydrocarbon-based solvents such as hexane, cyclohexane, methylcyclohexane, toluene, and xylene, nitrile-based solvents such as acetonitrile, and amide-based solvents such as N-methylpyrrolidone and dimethylacetamide. Any of these organic solvents may be used alone, or two or more may be used in combination.

[0050] As will be described later, the polymer (P) according to the present invention can be added in an appropriate amount to a curable composition and used to suppress the occurrence of pinholes during film formation.

[0051] [Curable Composition] In one aspect of the present invention, a curable composition is provided, which comprises a polymer (P) having a degree of polymerization of 2 or more, a structural unit (a) corresponding to a multifunctional polymerizable liquid crystal compound (A1), a structural unit (b) corresponding to an aliphatic multifunctional thiol compound (B), a multifunctional polymerizable liquid crystal compound (A2), and a polymerization initiator (C). The curable composition may further contain, as appropriate, components typically contained in polymerizable compositions that undergo polymerization by light or heat, such as organic solvents, surface modifiers, and adhesion promoters. The content of these optional components is not particularly limited.

[0052] (Polymer (P)) The polymer (P) used in the curable composition is as described above. In addition, in the curable composition, the above-mentioned polymer (P) may be used alone or in combination of two or more kinds.

[0053] (Polyfunctional polymerizable liquid crystal compound (A2)) The explanation of the polyfunctional polymerizable liquid crystal compound (A2) used in the curable composition is the same as that of the polyfunctional polymerizable liquid crystal compound (A1) described above. The compounds (A2) used in the curable composition may be used alone or in combination of two or more. In the curable composition, at least one of the compounds (A1) and (A2) used in the production of the polymer (P) is a compound represented by formula (I): (In formula (I), R 1 each independently represents a hydrogen atom or a methyl group; p each independently represents a spacer group which is a divalent organic group; y represents a divalent organic group containing a structure in which two or more rings selected from the group consisting of aromatic rings and aliphatic rings, each of which may have a substituent, are bonded via a single bond or a linking group. ) Here, the explanation given above regarding compound (A1) also applies to formula (I).

[0054] The compound (A2) used in the curable composition may have the same structure as or a different structure from the compound (A1) used in producing the polymer (P). From the viewpoints of manufacturability and ease of availability, it is preferable that the compound (A1) and the compound (A2) contain polyfunctional polymerizable liquid crystal compounds having the same structure.

[0055] The lower limit of the content of the polymer (P) is usually preferably 3 parts by mass or more, more preferably 5 parts by mass or more, and may be 8 parts by mass or more, 10 parts by mass or more, or 15 parts by mass or more, relative to 100 parts by mass of the total of the polymer (P) and the compound (A2). The upper limit of the content of the polymer (P) is usually preferably 50 parts by mass or less, more preferably 40 parts by mass or less, even more preferably 30 parts by mass or less, and even more preferably 25 parts by mass or less, relative to 100 parts by mass of the total of the polymer (P) and the compound (A2). By making the content of the polymer (P) 3 parts by mass or more relative to 100 parts by mass of the total of the polymer (P) and the compound (A2), the occurrence of pinholes in the formation of an optical film tends to be sufficiently suppressed, and by making it 50 parts by mass or less, the reactivity of the curable composition tends to be improved.

[0056] On the other hand, the lower limit of the content of compound (A2) is usually preferably 50 parts by mass or more, more preferably 60 parts by mass or more, even more preferably 70 parts by mass or more, and even more preferably 80 parts by mass or more, relative to 100 parts by mass of the total of polymer (P) and compound (A2). The upper limit of the content of compound (A2) is usually preferably 97 parts by mass or less, more preferably 95 parts by mass or less, and may be 92 parts by mass or less, or 90 parts by mass or less, relative to 100 parts by mass of the total of polymer (P) and compound (A2). By setting the content of compound (A2) to 50 parts by mass or more, relative to 100 parts by mass of the total of polymer (P) and compound (A2), the reactivity of the curable composition tends to be improved, and by setting it to 97 parts by mass or less, the occurrence of pinholes in the formation of an optical film tends to be suppressed.

[0057] (Polymerization initiator (C)) Examples of the polymerization initiator used in the curable composition include a photopolymerization initiator and a thermal polymerization initiator. Any initiator known to a person skilled in the art in this technical field can be used without any particular limitation. However, a photopolymerization initiator is preferred from the viewpoint of not leaving a thermal history in the polymerized product.

[0058] Examples of the photopolymerization initiator include 2,4,6-trimethylbenzoyldiphenylphosphine oxide, 2,2'-bis(o-chlorophenyl)-4,4',5,5'-tetraphenyl-1,1'-biimidazole, 2,4,6-tris(trichloromethyl)-1,3,5-triazine, 2,4-bis(trichloromethyl)-6-(p-methoxyphenylvinyl)-1,3,5-triazine, diphenyliodonium tetrafluoroborate, diphenyliodonium hexafluorophosphate, 4,4'-di-tert-butyl ... t-butyldiphenyliodonium tetrafluoroborate, 4-diethylaminophenylbenzenediazonium hexafluorophosphate, benzoin, 2-hydroxy-2-methyl-1-phenylpropan-2-one, benzophenone, thioxanthone, 2,4,6-trimethylbenzoyldiphenylacylphosphine oxide (TPO), triphenylbutylborate tetraethylammonium, diphenyl-4-phenylthiophenylsulfonium hexafluorophosphate, 2,2-dimethoxy-1,2-diphenyl photoradical polymerization initiators such as phenylethan-1-one, phenylglyoxylic acid methyl ester, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one, bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, 1,2-octanedione, 1-[4-(phenylthio)-2-(o-benzoyloxime)], and bis(η5-2,4-cyclopentadien-1-yl)bis[2,6-difluoro-3-(1H-pyrrol-1-yl)phenyltitanium]; Examples of the photopolymerization initiator include cationic ring-opening photopolymerization initiators such as 2,4,6-tris(trichloromethyl)-1,3,5-triazine, 2,4-bis(trichloromethyl)-6-(p-methoxyphenylvinyl)-1,3,5-triazine, diphenyliodonium tetrafluoroborate, 4,4'-di-tert-butyldiphenyliodonium tetrafluoroborate, 4-diethylaminophenylbenzenediazonium hexafluorophosphate, and diphenyl-4-phenylthiophenylsulfonium hexafluorophosphate. These photopolymerization initiators may be used alone or in combination of two or more.

[0059] From the viewpoint of good reactivity, the lower limit of the content of the polymerization initiator in the curable composition is usually, relative to 100 parts by mass of the total of the polymer (P) and the compound (A2), preferably 1 part by mass or more, more preferably 2 parts by mass or more, even more preferably 3 parts by mass or more, and still more preferably 5 parts by mass or more. From the viewpoint of suppressing coloration of the obtained cured product (optical film), the upper limit of the content when a polymerization initiator is used is usually, relative to 100 parts by mass of the total of the polymer (P) and the compound (A2), preferably 20 parts by mass or less, more preferably 15 parts by mass or less, even more preferably 10 parts by mass or less, and still more preferably 8 parts by mass or less.

[0060] A surface conditioner can also be added to the curable composition. Surface conditioners that can be incorporated into the curable composition include any of the surface conditioners (surfactants) commonly used to form a smooth film. Specific examples include anionic surfactants such as sodium lauryl sulfate, ammonium lauryl sulfate, triethanolamine lauryl sulfate, polyoxyethylene alkyl ether sulfate, alkyl ether phosphate, sodium oleyl succinate, potassium myristate, potassium coconut oil fatty acid, and sodium lauroyl sarcosinate; nonionic surfactants such as polyethylene glycol monolaurate, sorbitan stearate, glyceryl myristate, glyceryl dioleate, sorbitan stearate, and sorbitan oleate; stearyl trimethylammonium chloride, behenyl trimethylammonium chloride, and the like. cationic surfactants such as ammonium chloride, stearyldimethylbenzylammonium chloride, and cetyltrimethylammonium chloride; alkyl betaines such as lauryl betaine, alkyl sulfobetaine, cocamidopropyl betaine, and alkyl dimethylaminoacetic acid betaine, amphoteric surfactants such as alkyl imidazolines, sodium lauroyl sarcosinate, and sodium cocoamphoacetate; and surface conditioners such as BYK-361, BYK-306, and BYK-307 (manufactured by BYK Japan Co., Ltd.), Fluorad FC430 (manufactured by 3M Japan Co., Ltd.), and Megafac F171 and R08 (manufactured by DIC Corporation). These surface conditioners may be used alone or in combination of two or more.

[0061] When a surface conditioner is used, the lower limit of its content is, from the viewpoint of high leveling property, usually, relative to 100 parts by mass of the total of the polymer (P) and the compound (A2), preferably 0.01 parts by mass or more, more preferably 0.02 parts by mass or more, even more preferably 0.03 parts by mass or more, and still more preferably 0.05 parts by mass or more. When a surface conditioner is used, the upper limit of its content is, from the viewpoint of good orientation of the resulting cured product (optical film), usually, relative to 100 parts by mass of the total of the polymer (P) and the compound (A2), preferably 3 parts by mass or less, more preferably 1 part by mass or less, even more preferably 0.5 parts by mass or less, and still more preferably 0.2 parts by mass or less.

[0062] The curable composition according to the present invention thus obtained can be used, for example, to form an optical film by adjusting the solid content to an appropriate range using an organic solvent to ensure coatability. The solid content is usually 10 to 50 mass%. The organic solvent used in this case is also the same as that described for the polymer (B).

[0063] (Optical Film) According to a third aspect of the present invention, there is provided an optical film obtained by curing the above-mentioned curable composition. The optical film refers to a film having the function of converting linearly polarized light into circularly polarized light or elliptically polarized light. The optical film according to the present invention is suppressed in the occurrence of pinholes and can exhibit excellent conversion characteristics.

[0064] The optical film according to the present invention can be used in applications such as optical films having excellent wavelength dispersion characteristics, and specific examples thereof include retardation films, antireflection films such as antireflection (AR) films, polarizing films, elliptically polarizing films, viewing angle widening films, and optical compensation films for compensating the viewing angle of transmission liquid crystal displays.

[0065] When compounds having the same structure are used alone as compound (A1) and compound (A2), the phase difference value (retardation value, Re (λ)) of the obtained optical film depends on the film thickness as shown in the following formula. Re (λ) = d × Δn (λ) (where Re (λ) is the phase difference value at a wavelength of λ nm, d is the film thickness, and Δn (λ) represents the refractive index anisotropy at a wavelength of λ nm.) When the optical film is used as a phase difference film, the lower limit of the phase difference value is preferably 50 nm or more, more preferably 80 nm or more, even more preferably 100 nm or more, and even more preferably 120 nm or more, from the viewpoint of exhibiting good optical compensation function. From the same viewpoint, the upper limit of the phase difference value is preferably 360 nm or less, more preferably 300 nm or less, even more preferably 260 nm or less, and even more preferably 240 nm or less.

[0066] From the viewpoint of exhibiting good alignment, the lower limit of the film thickness of the optical film is preferably 0.1 μm or more, more preferably 0.5 μm or more, even more preferably 0.8 μm or more, and still more preferably 1.0 μm or more. From the same viewpoint, the upper limit of the film thickness of the optical film is preferably 5.0 μm or less, more preferably 4.0 μm or less, even more preferably 3.0 μm or less, and still more preferably 2.0 μm or less.

[0067] As a method for producing an optical film, a method known in the art can be used. For example, the optical film can be produced by applying the curable composition to a substrate, distilling off the solvent as necessary, and then curing the composition by UV (ultraviolet) irradiation, heating, or the like.

[0068] Examples of the substrate include glass substrates such as quartz glass, alkali glass, and non-alkali glass; resin substrates such as polyimide, polyamide, acrylic resin, polyvinyl alcohol, triacetyl cellulose, polyethylene terephthalate, cycloolefin polymer, polyethylene, polycarbonate, polystyrene, and polytrifluorochloroethylene; and metal substrates such as iron, aluminum, and copper, with glass substrates and triacetyl cellulose being more preferred.

[0069] The curable composition may be applied by any method generally known in the art, such as spin coating, bar code coating, die coating, screen printing, or spray coating.

[0070] Furthermore, a photo-alignment film can be formed on a substrate, and a film can be formed on the photo-alignment film using the curable composition according to the present invention, thereby obtaining various optically anisotropic films such as retardation films, viewing angle improving films, brightness improving films, and polarizing films.

[0071] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples. Note that the names of compounds shown in the following examples and comparative examples do not necessarily all conform to the IUPAC nomenclature.

[0072] The chemicals used are shown below. In the present specification, the following abbreviations and trade names may also be used. <Polyfunctional polymerizable liquid crystal compounds A1 and A2> RM257: (manufactured by Merck) LC242: (manufactured by BASF) <Aliphatic polyfunctional thiol compound> 1,4-butanediol bis(thioglycolate): (manufactured by Tokyo Chemical Industry Co., Ltd.) <Catalyst> Dimethylbenzylamine: (manufactured by Tokyo Chemical Industry Co., Ltd.) <Polymerization initiator> OXE-01: (manufactured by BASF) <Surface conditioner> BYK-361N: (manufactured by BYK Japan, acrylic polymer)

[0073] Example 1 Polymer (P1) 10.0 g (17 mmol) of RM-257 (compound (A1)), 3.64 g (15 mmol) of 1,4-butanediol bis(thioglycolate), and 52 mg (0.4 mmol) of a catalyst (dimethylbenzylamine) were dissolved in 30 mL of cyclopentanone, and the mixture was reacted at 70° C. for 50 hours to synthesize polymer (P1).

[0074] Example 2 Polymer (P2) A polymer (P2) was synthesized in the same manner as in Example 1, except that 10.0 g (14 mmol) of LC242 was used as the compound (A1) instead of RM257, 3.04 g (13 mmol) of 1,4-butanediol bis(thioglycolate), 43 mg (0.3 mmol) of a catalyst (dimethylbenzylamine), and 30 mL of a solvent were used.

[0075] Test Example 1: Measurement of weight-average molecular weight (Mw) The weight-average molecular weight (Mw) of the polymers P1 and P2 obtained in Examples 1 and 2 was measured using GPC. The weight-average molecular weight (Mw) calculated in terms of polystyrene is shown in Table 1. The degree of polymerization was calculated using the following formula: degree of polymerization = weight-average molecular weight (Mw) / (molecular weight of polyfunctional polymerizable liquid crystal compound (A1) + molecular weight of aliphatic polyfunctional thiol compound (B)).

[0076]

[0077] Examples 3 to 6 and Comparative Examples 1 and 2: Curable compositions and retardation films (1) Preparation of curable compositions According to the compositions shown in Table 2, the compound (A2), the polymer (P), the polymerization initiator (C), and the surface conditioner were mixed in cyclopentanone as a solvent under light shielding to prepare curable compositions with a solids content of 20%.

[0078] (2) Preparation of Retardation Film The curable composition obtained above was applied to a glass substrate having a size of 10 cm × 10 cm using a spin coater so as to have a thickness of about 1.0 μm. Thereafter, the glass substrate on which the curable composition was applied was placed on a hot plate set to 90 ° C. and heated by leaving it to stand for 5 minutes, and then irradiated with UV at 1,000 mJ / cm. 2 The retardation films according to the examples and comparative examples were prepared by irradiation.

[0079] Test Example 2: Measurement of Pinholes The number of pinholes generated on the obtained retardation films according to each of the Examples and Comparative Examples was visually measured.

[0080] Test Example 3: Measurement of Retardation Value The retardation value (Re) of the retardation films obtained according to each of the Examples and Comparative Examples was measured using a retardation measurement device (OPTIPRO-standard, manufactured by Shintech Co., Ltd.) under conditions of a measurement wavelength (λ) of 550 nm and a film thickness of 1.0 μm. The results are shown in Table 2.

[0081] Test Example 4: Evaluation of Alignment The alignment uniformity of the retardation films obtained in each of the Examples and Comparative Examples was evaluated using a polarizing microscope. The retardation films were observed under crossed Nicols, and those in which no light leakage due to alignment defects of the liquid crystal was observed were recorded as ○, and those in which no light leakage due to alignment defects of the liquid crystal was observed were recorded as ×. The results are shown in Table 2.

[0082]

[0083] From Table 2, it can be seen that in the retardation films of Examples 3 to 6, the occurrence of pinholes can be suppressed compared to the comparative examples without affecting the optical properties.

Claims

1. A polymer (P) having a structural unit (a) corresponding to a polyfunctional polymerizable liquid crystal compound (A1) and a structural unit (b) corresponding to an aliphatic polyfunctional thiol compound (B), and having a degree of polymerization of 2 or more.

2. The polymer (P) according to claim 1, wherein the molar ratio of the structural unit (a) to the structural unit (b) is 10:5 to 5:

10.

3. The polymer (P) according to claim 1, wherein the polyfunctional polymerizable liquid crystal compound (A1) is represented by formula (I). (In formula (I), R 1 each independently represents a hydrogen atom or a methyl group; p each independently represents a spacer group which is a divalent organic group; y represents a divalent organic group containing a structure in which two or more rings selected from the group consisting of aromatic rings and aliphatic rings, each of which may have a substituent, are bonded via a single bond or a linking group.

4. A curable composition comprising: a polymer (P) having a degree of polymerization of 2 or more, which polymer (P) has a structural unit (a) corresponding to a polyfunctional polymerizable liquid crystal compound (A1) and a structural unit (b) corresponding to an aliphatic polyfunctional thiol compound (B); a polyfunctional polymerizable liquid crystal compound (A2); and a polymerization initiator (C).

5. The curable composition according to claim 4, wherein at least one of the polyfunctional polymerizable liquid crystal compound (A1) and the polyfunctional polymerizable liquid crystal compound (A2) is represented by formula (I). (In formula (I), R 1 each independently represents a hydrogen atom or a methyl group; p each independently represents a spacer group which is a divalent organic group; y represents a divalent organic group containing a structure in which two or more rings selected from the group consisting of aromatic rings and aliphatic rings, each of which may have a substituent, are bonded via a single bond or a linking group.

6. The curable composition according to claim 4, wherein the polyfunctional polymerizable liquid crystal compound (A1) and the polyfunctional polymerizable liquid crystal compound (A2) contain polyfunctional polymerizable liquid crystal compounds having the same structure.

7. The curable composition according to claim 4, wherein the aliphatic polyfunctional thiol compound (B) is a bifunctional thiol compound having a molecular weight of 200 to 1,000.

8. The curable composition according to claim 4, wherein the weight average molecular weight (Mw) of the polymer (P) is 5,000 to 30,000.

9. The curable composition according to claim 4, wherein the mass ratio of the polymer (P) to the polyfunctional polymerizable liquid crystal compound (A2) is 50:50 to 3:

97.

10. An optical film obtained by curing the curable composition according to any one of claims 4 to 9.

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