Retardation layer, multilayer retardation film including same, method for producing same, and copolymer

Abstract

This retardation layer has an Rth / d of (-20.0×10-3) to (-3.5×10-3), wherein Rth represents a retardation in the thickness direction of the retardation layer and d represents the thickness of the retardation layer, the retardation layer including a copolymer (P1) that includes a structural unit represented by formula (1) and a structural unit represented by formula (2). In formula (1), Rp represents an electron donating substituent or the like, Rq represents a hydrogen atom or the like, and Rr represents a hydrogen atom or the like. In formula (2), Rx and Ry each independently represent a hydrogen atom or the like, and R1, R2, R3, R4, R5, R6, and R7 each independently represent a hydrogen atom, a 1-6C alkyl group, or the like.

Description

Phase difference layer, multilayer phase difference film containing the same, method for producing the same, and copolymer

[0001] The present invention relates to a phase difference layer, a multilayer phase difference film containing the same, a method for producing the same, and a copolymer.

[0002] Phase difference films with a high refractive index in the thickness direction are useful as optical compensation films, such as phase difference films that compensate for the viewing angle characteristics in displays such as super twisted nematic liquid crystal displays (STN-LCDs), vertically aligned liquid crystal displays (VA-LCDs), in-plane aligned liquid crystal displays (IPS-LCDs), and reflective liquid crystal displays (reflective LCDs), as well as viewing angle compensation films for polarizing plates.

[0003] Many polymers have positive intrinsic birefringence, meaning their refractive index in the stretching direction is greater than their refractive index in the direction perpendicular to the stretching direction. A method for producing a film with an increased refractive index in the thickness direction is known using polymers with positive intrinsic birefringence. It is known that the refractive index in the thickness direction of a polymer film can be increased by bonding a heat-shrinkable film to one or both sides of a polymer film to obtain a laminate, and then stretching or shrinking the laminate in the thickness direction or in-plane while heating it (see, for example, Patent Documents 1 and 2).

[0004] Furthermore, films are known in which the refractive index in the thickness direction is increased by stretching a film made of a polymer having negative intrinsic birefringence, where the refractive index in the stretching direction is smaller than the refractive index in the direction perpendicular to the stretching direction. Acrylic resins and polystyrene are known polymers having negative intrinsic birefringence.

[0005] Furthermore, polymers exhibiting negative intrinsic birefringence include polymers having units obtained by polymerizing N-substituted maleimides.

[0006] Patent documents 3 to 13 show that a film can be produced from a copolymer of N-phenylmaleimide and an olefin such as isobutene, and that a phase difference film having negative intrinsic birefringence can be obtained by stretching this film.

[0007] Patent documents 14 and 15 show that a phase difference film having a positive retardation Rth in the thickness direction can be obtained by applying a solution containing a copolymer having N-alkylmaleimide units to a substrate, drying it, and then stretching the resulting laminate. Here, the retardation Rth in the thickness direction is expressed as Rth = [{(nx + ny) / 2} - nz] × d. Here, nx represents the refractive index in the direction perpendicular to the thickness direction of the layer (in-plane direction) that gives the maximum refractive index. ny represents the refractive index in the in-plane direction of the layer that is perpendicular to the direction of nx. nz represents the refractive index in the thickness direction of the layer. d represents the thickness of the layer. Unless otherwise specified, the retardation Rth in the thickness direction is defined similarly below.

[0008] Patent documents 16 to 23 show that a coating layer obtained by applying a solution containing a copolymer having N-alkylmaleimide units to a substrate and drying it has a positive retardation Rth in the thickness direction.

[0009] Patent document 24 shows that a coating layer obtained by applying a solution of a copolymer having units having a maleimide structure to a substrate and drying it has a negative retardation Rth in the thickness direction.

[0010] Patent document 25 shows that a coating layer obtained by applying a solution of a copolymer having trans-stilbene units and N-substituted maleimide units to a substrate and drying it has a negative retardation Rth in the thickness direction.

[0011] Patent document 26 shows that a coating layer obtained by applying a solution of a copolymer having stilbene units to a substrate and drying it has a negative retardation Rth in the thickness direction.

[0012] Patent documents 27 and 28 show that a coating layer obtained by applying a solution of a copolymer having alkoxycinnamic acid units to a substrate and drying it has a negative retardation Rth in the thickness direction.

[0013] Patent documents 29 to 31 show that a coating layer obtained by applying a solution of a copolymer having fumarate diester units to a substrate and drying it has a negative retardation Rth in the thickness direction.

[0014] Patent documents 32 to 36 show that a film formed by casting using modified cellulose ester has a negative retardation Rth in the thickness direction.

[0015] Patent document 37 shows that a coating layer obtained by applying a halogenated polystyrene solution to a substrate and drying it has a negative retardation Rth in the thickness direction.

[0016] Japanese Patent Publication No. 05-297223, Japanese Patent Publication No. 05-323120, Japanese Patent Publication No. 2004-090415, Japanese Patent Publication No. 2004-315788 (Corresponding publication: U.S. Patent Application Publication No. 2004 / 190138), Japanese Patent Publication No. 2006-045368, Japanese Patent Publication No. 2006-045369, Japanese Patent Publication No. 2006-053411, Japanese Patent Publication No. 2006-084700, Japanese Patent Publication No. 2006-257339, Japanese Patent Publication No. 2006-328267 Japanese Patent Publication No. 2007-046059, Japanese Patent Publication No. 2009-025711, Japanese Patent Publication No. 2011-090319, Japanese Patent Publication No. 2011-102867, Japanese Patent Publication No. 2011-102868, Japanese Patent Publication No. 2008-268402, Japanese Patent Publication No. 2008-287226, Japanese Patent Publication No. 2009-156908, Japanese Patent Publication No. 2010-096905, Japanese Patent Publication No. 2010-097115, Japanese Patent Publication No. 2010-102023, Japanese Patent Publication No. 2011-128480 Japanese Patent Publication No. 2011-197181, Japanese Patent Publication No. 2018-95672, Japanese Patent Publication No. 2015-78301, Japanese Patent Publication No. 2015-74759, Japanese Patent Publication No. 2016-108544, Japanese Patent Publication No. 2016-145290, Japanese Patent Publication No. 2016-145289, Japanese Patent Publication No. 2016-145291, Japanese Patent Publication No. 2017-105962, Japanese Patent Publication No. 2014-513178 (corresponding publication: International Publication No. 2012 / 141903), Japanese Patent Publication No. 2020-51 JP 2468 (corresponding publication: International Publication No. 2018 / 183466), JP 2020-515682 (corresponding publication: International Publication No. 2018 / 183467), JP 2020-515689 (corresponding publication: International Publication No. 2018 / 183472), JP 2020-518681 (corresponding publication: International Publication No. 2018 / 183463), JP 2013-539076 (corresponding publication: International Publication No. 2012 / 040366)

[0017] However, acrylic resins with negative intrinsic birefringence may have small retardation in the thickness direction, resulting in insufficient properties as a phase difference film. Furthermore, polystyrene requires a stretching process to increase the retardation Rth in the thickness direction, which increases the number of manufacturing steps for phase difference films and makes the process more complicated.

[0018] The manufacturing methods using polymers with positive intrinsic birefringence described in Patent Documents 1 and 2 have low productivity because the manufacturing process is extremely complex.

[0019] Furthermore, phase difference films using copolymers containing N-substituted maleimide units have the following problems.

[0020] In the technologies described in Patent Documents 3 to 13, it is believed that a stretching process is necessary to increase the retardation Rth in the thickness direction, which increases the number of manufacturing steps for the phase difference film and makes the process complicated. Furthermore, even after the stretching process, only layers with a small absolute value of retardation Rth in the thickness direction (for example, around -3 nm / μm) have been obtained.

[0021] The techniques described in Patent Documents 14 to 23 do not allow for obtaining a layer in which the desired retardation Rth in the thickness direction is a negative value.

[0022] Therefore, the object of the present invention is to provide a phase difference layer having a negative Rth / d value and a large absolute value, which can be manufactured with high productivity by a method that does not require a stretching step and includes a step of applying a polymer-containing solution to a substrate and drying it; a multilayer phase difference film containing the phase difference layer; a manufacturing method that can manufacture the multilayer phase difference film containing the phase difference layer with high productivity; and a copolymer that can manufacture a phase difference layer having a negative Rth / d value and a large absolute value with high productivity.

[0023] The inventors, through diligent research to solve the aforementioned problems, discovered that a phase difference layer containing a specific copolymer can solve the aforementioned problems, and thus completed the present invention. That is, the present invention provides the following:

[0024] <1> Rth / d is (-20.0 × 10 －３ ) or more (-3.5 x 10 －３ A phase difference layer having a thickness of Rth and d, wherein Rth represents the thickness of the phase difference layer and d represents the thickness of the phase difference layer, and the phase difference layer comprises a copolymer (P1) containing structural units represented by the following formula (1) and structural units represented by the following formula (2). (In formula (1), R ｐrepresents an electron-donating substituent or a cyano group, and R ｑ represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, and R ｒ represents a hydrogen atom or a substituent.) (In formula (2), R ｘ and R ｙ each independently represent a hydrogen atom or a methyl group, and R １ , R ２ , R ３ , R ４ , R ５ , R ６ , and R ７ each independently represent a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, a phenyl group, a cyano group, a nitro group, -OR １０ , -C(=O)-R １０ , or -O-C(=O)-R １０ , where R １０ represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms.) <2> The retardation layer according to <1>, wherein the copolymer (P1) further contains a structural unit represented by the following formula (3). (In formula (3), R ｓ and R ｔ each independently represent a hydrogen atom or a methyl group, and R ａ , R ｂ , R ｃ , R ｄ , and R ｅ each independently represent a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, a phenyl group, a cyano group, a nitro group, -OR ２０ , -C(=O)-R ２０ , or -O-C(=O)-R ２０ , where R ２０) represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms.) <3> The phase difference layer according to <1> or <2>, wherein the copolymer (P1) contains 20 mol% to 95 mol% of the structural unit represented by formula (2), with the total of the structural units represented by formula (1) and the structural units represented by formula (2) contained in the copolymer (P1) being 100 mol%. <4> The phase difference layer according to any one of <1> to <3>, wherein the copolymer (P1) has a number average molecular weight in polystyrene terms measured by gel permeation chromatography of 30,000 to 500,000. <5> A multilayer phase difference film comprising the phase difference layer according to any one of <1> to <4> and a base layer, wherein the phase difference layer is provided directly on the base layer. <6> The multilayer phase difference film according to <5>, wherein the base layer contains a cyclic olefin polymer. <7> A method for manufacturing a multilayer phase difference film according to <5> or <6>, comprising the steps of: preparing the base layer; and applying a liquid composition containing the copolymer (P1) and a solvent onto the base layer. <8> A copolymer comprising a structural unit represented by the following formula (1-1) or a structural unit represented by the following formula (1-2), or a structural unit represented by the following formula (1-1) and a structural unit represented by the following formula (1-2), and a structural unit represented by the following formula (2). (In formula (1-1), R ｐ (This represents a biphenylyl group which may have substituents.) (In formula (1-2), R ｐ (This represents a phenyl group which may have substituents.) (In formula (2), R ｘ and R ｙ Each of these independently represents a hydrogen atom or a methyl group, and R １ , R ２ , R ３ , R ４ , R ５ , R ６ , and R ７ These are, independently, a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, a phenyl group, a cyano group, a nitro group, and -OR. １０, -C(=O)-R １０ , or -O-C(=O)-R １０ This represents, and here, R １０ (wherein represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms.) <9> The copolymer according to <8>, further comprising a structural unit represented by the following formula (3). (In formula (3), R ｓ and R ｔ Each of these independently represents a hydrogen atom or a methyl group, and R ａ , R ｂ , R ｃ , R ｄ , and R ｅ These are, independently, a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, a phenyl group, a cyano group, a nitro group, and -OR. ２０ , -C(=O)-R ２０ , or -O-C(=O)-R ２０ This represents, and here, R ２０ (wherein represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms.) <10> The copolymer according to <8> or <9>, comprising a structural unit represented by formula (1-1). <11> The copolymer according to any one of <8> to <10>, wherein the total of the structural unit represented by formula (1-1), the structural unit represented by formula (1-2), and the structural unit represented by formula (2) is 100 mol%, and the copolymer contains 20 mol% to 95 mol% of the structural unit represented by formula (2). <12> The copolymer according to any one of <8> to <11>, wherein the number average molecular weight in polystyrene terms, as measured by gel permeation chromatography, is 30,000 to 500,000. <13> When a layer formation test is performed in which a solution containing only the copolymer and a solvent for dissolving the copolymer is applied and dried to form a copolymer layer containing the copolymer, the copolymer layer satisfies nz > nx ≈ ny, where nx represents the refractive index in the in-plane direction of the copolymer layer that gives the maximum refractive index, ny represents the refractive index in the in-plane direction of the copolymer layer that is perpendicular to the direction of nx, and nz represents the refractive index in the thickness direction of the copolymer layer, the copolymer according to any one of <8> to <12>.

[0025] The present invention provides a phase difference layer having a negative Rth / d value and a large absolute value, which can be manufactured with high productivity by a method that includes a step of applying a polymer-containing solution to a substrate and drying it, without requiring a stretching step; a multilayer phase difference film containing the phase difference layer; a manufacturing method that can manufacture the multilayer phase difference film containing the phase difference layer with high productivity; and a copolymer that can manufacture a phase difference layer having a negative Rth / d value and a large absolute value with high productivity.

[0026] This is a schematic cross-sectional view showing a multilayer phase difference film according to one embodiment of the present invention.

[0027] The present invention will be described in detail below with reference to embodiments and examples. However, the present invention is not limited to the embodiments and examples shown below, and can be modified and implemented as appropriate without departing from the scope of the claims and equivalents of the present invention. The components of the embodiments shown below can be combined as appropriate. For example, any numerical value selected from the group of numerical values ​​listed as lower limits and any numerical value selected from the group of numerical values ​​listed as upper limits can be combined as appropriate. Also, for example, the copolymer (P1) described later may include a combination of the structural unit exemplified as a structural unit represented by formula (1) and the structural unit exemplified as a structural unit represented by formula (2). In addition, in the figures, the same reference numerals are used for the same components, and their descriptions may be omitted.

[0028] In the following description, unless otherwise specified, in preferred examples of structural units represented by formula (1), formula (1-1), or formula (1-2) that may be included in copolymer (P1), left and right are not distinguished, and for example, "structural unit represented by formula (1)" includes structural units represented by the structure in which the left and right are reversed in formula (1).

[0029] Unless otherwise specified, any structural unit shown by a chemical formula in this specification that may have stereoisomers is included in all of them. A polymer containing such a structural unit may contain only one of the stereoisomers of that structural unit, or it may contain a combination of multiple stereoisomers of that structural unit.

[0030] In the following description, unless otherwise specified, the “may have substituents” embodiments include both the case without substituents (and therefore the unsubstituted case) and the case with substituents (and therefore the substituted case).

[0031] In the following description, "long film" refers to a film having a length of five times or more its width, preferably 10 times or more its width, and specifically a film of a length that can be wound into a roll for storage or transport. There is no particular upper limit to the length of the film; for example, it may be 100,000 times or less its width.

[0032] In the following explanation, unless otherwise specified, the slow axis of a film or layer refers to the slow axis within the plane of the film or layer.

[0033] In the following explanation, unless otherwise specified, the term "board" includes not only rigid members but also flexible members such as resin films.

[0034] In the following explanation, unless otherwise specified, a material with positive intrinsic birefringence means a material whose refractive index in the stretching direction is greater than its refractive index in the direction perpendicular to it. Similarly, unless otherwise specified, a material with negative intrinsic birefringence means a material whose refractive index in the stretching direction is less than its refractive index in the direction perpendicular to it. The value of intrinsic birefringence can be calculated from the dielectric constant distribution.

[0035] In the following explanation, the term "(meth)acrylic" includes "acrylic," "methacrylic," and combinations thereof.

[0036] A structural unit formed by polymerizing a monomer is called a "monomer unit," with "unit" added after the name of the monomer. For example, a structural unit formed by polymerizing styrene is called a styrene unit. However, the term "monomer unit" is not limited to its formation method. Typically, monomer units are repeating units.

[0037] In the following description, the in-plane retardation Re of a layer is given by the value Re = (nx - ny) × d unless otherwise specified. Also, the retardation Rth in the thickness direction of a layer is given by the value Rth = [{(nx + ny) / 2} - nz] × d unless otherwise specified. Here, nx represents the refractive index in the direction perpendicular to the thickness direction of the layer (in-plane direction) that gives the maximum refractive index. ny represents the refractive index in the aforementioned in-plane direction of the layer that is perpendicular to the direction of nx. nz represents the refractive index in the thickness direction of the layer. d represents the thickness of the layer. The measurement wavelength is 550 nm unless otherwise specified.

[0038] In the following description, the directions of the elements are defined as "parallel," "perpendicular," and "orthogonal" unless otherwise specified, and may include errors within a range that does not impair the effects of the present invention, for example, within a range of ±3°, ±2°, or ±1°.

[0039] In this specification, unless otherwise specified, alkyl groups may be branched or linear. Examples of alkyl groups having 1 to 12 carbon atoms include methyl group, ethyl group, isopropyl group, n-propyl group, n-butyl group, isobutyl group, sec-butyl group, tert-butyl group, n-pentyl group, pentan-2-yl group, pentan-3-yl group, 2-methylbutan-2-yl group, 2,2-dimethylpropyl group, 3-methylbutyl group, 3-methylbutan-2-yl group, 2-methylbutyl group, and n-hexyl group (these are examples of alkyl groups having 1 to 6 carbon atoms); n-heptyl group, n-octyl group, octan-3-yl group, n-nonyl group, n-decyl group, n-undecyl group, and n-dodecyl group (these are examples of alkyl groups having 7 to 12 carbon atoms).

[0040] Examples of substituents include C1-C6 alkyl groups; C1-C6 alkyloxy groups; cyano groups; nitro groups; halogeno groups (e.g., fluoro groups, chloro groups, bromo groups, and iodine groups); C1-C6 halogenated alkyl groups; and hydroxyl groups. In one embodiment, substituents are preferably groups that do not contain halogen atoms. Examples of C1-C6 alkyl groups that a C1-C6 alkyloxy group has are as described above. A C1-C6 halogenated alkyl group is a group in which some or all of the hydrogen atoms of a C1-C6 alkyl group are substituted with halogen atoms. Examples of C1-C6 halogenated alkyl groups include groups in which some or all of the hydrogen atoms of the groups exemplified as C1-C6 alkyl groups are substituted with halogen atoms. Examples of halogen atoms include fluorine atoms, chlorine atoms, bromine atoms, and iodine atoms. Among the halogen atoms included in a C1-C6 halogenated alkyl group, fluorine atoms are particularly preferred.

[0041] <1. Copolymer (P1)> The copolymer (P1) according to one embodiment of the present invention includes a structural unit represented by the following formula (1) and a structural unit represented by the following formula (2).

[0042] In one embodiment, copolymers containing 1-naphthylmaleimide units and styrene units in a total of preferably 80% by weight or more, more preferably 90% by weight or more, even more preferably 95% by weight or more, and even more preferably 98% by weight or more are excluded from the copolymer (P1).

[0043] The copolymer (P1) may contain only one type of structural unit represented by formula (1), or it may contain two or more types (for example, two, three, or four types). In one embodiment, the copolymer (P1) preferably contains only one type of structural unit represented by formula (1). In another embodiment, the copolymer (P1) preferably contains two or more types of structural units represented by formula (1), and more preferably contains two types.

[0044] The copolymer (P1) may contain only one type of structural unit represented by formula (2), or it may contain two or more types (for example, two, three, or four types). In one embodiment, the copolymer (P1) preferably contains only one type of structural unit represented by formula (2). In another embodiment, the copolymer (P1) preferably contains two or more types of structural units represented by formula (2), and more preferably contains two types.

[0045] The copolymer (P1) may be a linear copolymer or a graft copolymer, and is preferably a linear copolymer.

[0046]

[0047] In formula (1), R ｐ R represents an electron-donating substituent or a cyano group. ｑ R represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms. ｒ represents a hydrogen atom or substituent.

[0048] An electron-donating substituent refers to a substituent in monosubstituted ethylene that makes the polarity term e in the so-called Alfray-Price formula negative. Here, the value of the polarity term e for styrene is assumed to be -0.8 (see Polymer Handbook fourth edition Volume 1 (Wiley-Interscience)).

[0049] Examples of electron-donating substituents include alkyl groups, alkyloxy groups, allyl groups, optionally substituted aryl groups, amino groups, alkylamino groups, dialkylamino groups, carbazolyl groups, imide groups, and hydroxyl groups.

[0050] R ｐ Examples of alkyl groups represented by include alkyl groups having 1 to 12 carbon atoms, preferably alkyl groups having 1 to 12 carbon atoms, more preferably alkyl groups having 1 to 6 carbon atoms, and even more preferably methyl groups.

[0051] R ｐExamples of alkyloxy groups represented by include alkyloxy groups having 1 to 12 carbon atoms, preferably alkyloxy groups having 1 to 12 carbon atoms, and more preferably alkyloxy groups having 1 to 6 carbon atoms.

[0052] R ｐ Examples of optionally substituted aryl groups represented by include optionally substituted phenyl groups, optionally substituted naphthyl groups (e.g., 1-naphthyl groups, 2-naphthyl groups), optionally substituted biphenylyl groups, and optionally substituted anthryl groups, preferably optionally substituted phenyl groups, optionally substituted naphthyl groups, or optionally substituted biphenylyl groups, and more preferably optionally substituted phenyl groups or optionally substituted biphenylyl groups.

[0053] R ｐ If the aryl group represented by has substituents, R ｐ The aryl group represented by may have only one substituent or may have multiple substituents. ｐ When the aryl group represented by has multiple substituents, these substituents may be different from each other or may be the same.

[0054] R ｐ Examples of substituents that the aryl group represented by may have include C1-C6 alkyl groups; C1-C6 alkyloxy groups; cyano groups; nitro groups; and hydroxyl groups. Preferably, one or more substituents are selected from the group consisting of C1-C6 alkyl groups; C1-C6 alkyloxy groups; and cyano groups, and more preferably, one or more substituents are selected from the group consisting of C1-C6 alkyl groups and cyano groups.

[0055] R ｐ Examples of biphenylyl groups represented by this include the biphenylyl groups and groups in which the hydrogen atoms of these groups are substituted with substituents.

[0056]

[0057] Among these, Rｐ The biphenylyl group represented by is preferably the group represented by formula (Bi-1) and the group in which the hydrogen atoms of the group represented by formula (Bi-1) are substituted with substituents, and the group represented by formula (Bi-1) is more preferred.

[0058] R ｐ Examples of alkyl groups that the alkylamino group represented by can be found in alkyl groups having 1 to 6 carbon atoms, preferably alkyl groups having 1 to 6 carbon atoms. ｐ Examples of alkyl groups that the dialkylamino group represented by can be found in alkyl groups having 1 to 6 carbon atoms, preferably alkyl groups having 1 to 6 carbon atoms. ｐ The two alkyl groups of the dialkylamino group represented by may be the same, may be different from each other, and are preferably the same.

[0059] R ｐ Examples of imide groups represented by this include succinimide and phthalimide.

[0060] R ｐ Preferably, the substituent is an electron-donating substituent, more preferably a substituted phenyl group, a substituted naphthyl group, or a substituted biphenylyl group, even more preferably a substituted phenyl group or a substituted biphenylyl group, and even more preferably an unsubstituted phenyl group or an unsubstituted biphenylyl group.

[0061] R ｑ R represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms. ｑ It is preferably a hydrogen atom or a methyl group, and more preferably a hydrogen atom.

[0062] R ｒ Examples of substituents represented by include C1-C6 alkyl groups, C1-C6 alkyloxy groups, alkyloxycarbonyl groups, cycloalkyloxycarbonyl groups, phthalimide groups, and phenyl groups.

[0063] R ｒExamples of the alkyl group having 1 to 6 carbon atoms represented by are as described above, and preferably a methyl group.

[0064] R ｒ Examples of the alkyloxy group having 1 to 6 carbon atoms represented by are as described above, and preferably a methoxy group or an ethoxy group.

[0065] R ｒ Examples of the alkyloxycarbonyl group represented by include an alkyloxycarbonyl group having 2 to 7 carbon atoms. Examples of the alkyl group having 1 to 6 carbon atoms that the alkyloxycarbonyl group having 2 to 7 carbon atoms has are as described above.

[0066] R ｒ Examples of the cycloalkyloxycarbonyl group represented by include a cycloalkyloxycarbonyl group having 4 to 7 carbon atoms. The cycloalkyl group having 3 to 6 carbon atoms that the cycloalkyloxycarbonyl group having 4 to 7 carbon atoms has may have an alkyl group as a substituent. Here, the number of carbon atoms of the cycloalkyl group does not include the number of carbon atoms of the substituent.

[0067] R ｒ is preferably a hydrogen atom.

[0068] In one embodiment, in formula (1), R ｐ the group represented by, R ｑ the group represented by and R ｒ the group represented by are preferably any of the following combinations. R ｐ is a phenyl group which may have a substituent, R ｑ is a hydrogen atom, R ｒ is a hydrogen atom. R ｐ is a biphenylyl group which may have a substituent, R ｑ is a hydrogen atom, R ｑ is a hydrogen atom. R ｐ is a naphthyl group which may have a substituent, R ｑ is a hydrogen atom, R ｒ is a hydrogen atom.

[0069] In one embodiment, the copolymer (P1) preferably contains, as a structural unit represented by the formula (1), a structural unit represented by the following formula (1-1) or a structural unit represented by the following formula (1-2) and a structural unit represented by the following formula (2), or contains both a structural unit represented by the following formula (1-1) and a structural unit represented by the following formula (1-2) and a structural unit represented by the following formula (2).

[0070]

[0071] In the formula (1-1), R ｐ represents a biphenylyl group which may have a substituent.

[0072] The biphenylyl group represented by R ｐ may have a substituent or may not have a substituent. When the biphenylyl group represented by R ｐ has a substituent, the biphenylyl group represented by R ｐ may have only one substituent or may have a plurality of substituents. When the biphenylyl group represented by R ｐ has a plurality of substituents, these plurality of substituents may be different from each other or may be the same.

[0073] In one embodiment, preferably, the substituent that the biphenylyl group represented by R ｐ may have does not contain a halogen atom.

[0074] Examples of the substituent that the biphenylyl group represented by R ｐ may have include an alkyl group having 1 to 6 carbon atoms; an alkyloxy group having 1 to 6 carbon atoms; a cyano group; a nitro group; and a hydroxyl group. Preferably, it is one or more selected from the group consisting of an alkyl group having 1 to 6 carbon atoms; an alkyloxy group having 1 to 6 carbon atoms; and a cyano group; More preferably, it is one or more selected from the group consisting of an alkyl group having 1 to 6 carbon atoms and a cyano group.

[0075]

[0076] In the formula (1-2), R ｐR represents a phenyl group which may have substituents. ｐ The phenyl group represented by may or may not have substituents. ｐ If the phenyl group represented by has substituents, R ｐ The phenyl group represented by may have only one substituent or may have multiple substituents. ｐ If the phenyl group represented by has multiple substituents, these substituents may be different from each other or may be the same.

[0077] In one embodiment, preferably, R ｐ The substituents that the phenyl group may have, as represented by , do not include halogen atoms.

[0078] R ｐ Examples of substituents that the phenyl group represented by may have include C1-C6 alkyl groups; C1-C6 alkyloxy groups; cyano groups; nitro groups; and hydroxyl groups. Preferably, one or more substituents are selected from the group consisting of C1-C6 alkyl groups; C1-C6 alkyloxy groups; and cyano groups, and more preferably, one or more substituents are selected from the group consisting of C1-C6 alkyl groups and cyano groups.

[0079] In one embodiment, the structural unit represented by formula (1) is preferably one or more selected from the group consisting of styrene units; 4-vinylbiphenyl units; and 4-vinyl-4'-cyanobiphenyl units.

[0080] When the copolymer (P1) includes both the structural unit represented by formula (1-1) and the structural unit represented by formula (1-2) as structural units represented by formula (1), the molar ratio of the structural unit represented by formula (1-2) to the structural unit represented by formula (1-1) (formula (1-2) / formula (1-1)) is preferably 1 / 20 or more, more preferably 1 / 15 or more, even more preferably 1 / 10 or more, preferably 20 or less, more preferably 15 or less, and even more preferably 10 or less.

[0081]

[0082] In formula (2), R ｘ and R ｙ Each of these independently represents either a hydrogen atom or a methyl group, preferably both being hydrogen atoms.

[0083] In formula (2), R １ , R ２ , R ３ , R ４ , R ５ , R ６ , and R ７ These are, independently, a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, a phenyl group, a cyano group, a nitro group, and -OR. １０ , -C(=O)-R １０ , or -O-C(=O)-R １０ This represents, and here, R １０ R represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms. In formula (2), R １ , R ２ , R ３ , R ４ , R ５ , R ６ , and R ７ Preferably, each is independently a hydrogen atom or an alkyl group having 1 to 6 carbon atoms.

[0084] R １ , R ２ , R ３ , R ４ , R ５ , R ６ , and R ７ The alkyl group having 1 to 6 carbon atoms represented by may be branched or linear. １ , R ２ , R ３ , R ４ , R ５ , R ６ , and R ７ The C1-C6 alkyl group represented by is preferably a C1-C4 alkyl group, more preferably a C1-C3 alkyl group, and even more preferably a methyl group or an ethyl group.

[0085] R １０ The alkyl group having 1 to 6 carbon atoms represented by may be branched or linear. １０The C1-C6 alkyl group represented by is preferably a C1-C5 alkyl group, more preferably a C1-C4 alkyl group, even more preferably a C1-C3 alkyl group, even more preferably a methyl group or an ethyl group, and even more preferably a methyl group.

[0086] In one embodiment, in formula (2), preferably R １ , R ２ , R ３ , R ４ , R ５ , R ６ , and R ７ All of them are hydrogen atoms. In another embodiment, in formula (2), preferably R １ However, alkyl groups having 1 to 6 carbon atoms, phenyl groups, or -OR １０ is; more preferably R １ However, these are alkyl groups with 1 to 6 carbon atoms.

[0087] The structural unit represented by formula (2) is preferably one or more selected from the group consisting of structural units represented by the following formulas.

[0088]

[0089] Examples of combinations of structural units represented by formula (1) and formula (2) that may be included in the copolymer (P1) are given below.

[0090] Styrene units and structural units represented by formula (201). Styrene units and structural units represented by formula (202). 4-vinylbiphenyl units and structural units represented by formula (201). 4-vinylbiphenyl units and structural units represented by formula (202). Styrene units, 4-vinylbiphenyl units and structural units represented by formula (201). Styrene units, 4-vinylbiphenyl units and structural units represented by formula (202).

[0091] In one embodiment, the copolymer (P1) preferably further comprises a structural unit represented by the following formula (3).

[0092]

[0093] In formula (3), R ｓ and Rｔ Each of these independently represents either a hydrogen atom or a methyl group, preferably both being hydrogen atoms.

[0094] In formula (3), R ａ , R ｂ , R ｃ , R ｄ , and R ｅ These are, independently, a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, a phenyl group, a cyano group, a nitro group, and -OR. ２０ , -C(=O)-R ２０ , or -O-C(=O)-R ２０ This represents, and here, R ２０ R represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms. ａ , R ｂ , R ｃ , R ｄ , and R ｅ Each of these is independently; preferably a hydrogen atom, a C1-C6 alkyl group, or a phenyl group; more preferably a hydrogen atom or a C1-C6 alkyl group.

[0095] R ａ , R ｂ , R ｃ , R ｄ , or R ｅ The alkyl group having 1 to 6 carbon atoms represented by may be branched or linear. ａ , R ｂ , R ｃ , R ｄ , or R ｅ The C1-C6 alkyl group represented by is preferably a C1-C4 alkyl group, more preferably a C1-C3 alkyl group, and even more preferably a methyl group or an ethyl group.

[0096] R ２０ The alkyl group having 1 to 6 carbon atoms represented by may be branched or linear. ２０ The C1-C6 alkyl group represented by is preferably a C1-C5 alkyl group, more preferably a C1-C4 alkyl group, more preferably a C1-C3 alkyl group, even more preferably a methyl group or an ethyl group, and even more preferably a methyl group.

[0097] In one embodiment, in formula (3), preferably R ａ , R ｂ , R ｃ , R ｄ , and R ｅ All of them are hydrogen atoms. In another embodiment, in formula (3), preferably R ａ , R ｃ , and R ｅ At least one selected from each is independently an alkyl group having 1 to 6 carbon atoms, a phenyl group, or -OR ２０ , or a cyano group; more preferably R ａ , R ｃ , and R ｅ At least one selected from is independently a C1-C6 alkyl group, a cyano group, or a phenyl group; more preferably R ａ , R ｃ , and R ｅ At least one of the selected elements is independently an alkyl group or phenyl group having 1 to 6 carbon atoms.

[0098] The structural unit represented by formula (3) is preferably one or more selected from the group consisting of structural units represented by the following formulas.

[0099]

[0100] Of the structural units represented by formula (3), the structural unit represented by formula (304) is more preferable.

[0101] <Content Ratio of Structural Units> From the viewpoint of significantly exhibiting the effects of the present invention, the total content ratio of the structural units represented by formula (1), formula (2), and formula (3) in the copolymer (P1) is preferably 80% by weight or more, more preferably 85% by weight or more, even more preferably 90% by weight or more, even more preferably 95% by weight or more, and even more preferably 98% by weight or more, and is usually 100% by weight or less, and may be 100% by weight. Here, the total of all structural units contained in the copolymer (P1) is defined as 100% by weight. If the copolymer (P1) does not contain the structural units represented by formula (3), then "the total content ratio of the structural units represented by formula (1), formula (2), and formula (3)" is "the total content ratio of the structural units represented by formula (1) and formula (2)".

[0102] If copolymer (P1) contains multiple types of structural units represented by formula (1), the total content ratio of those multiple types of structural units shall be considered the content ratio of the structural unit represented by formula (1). If copolymer (P1) contains multiple types of structural units represented by formula (2), the total content ratio of those multiple types of structural units shall be considered the content ratio of the structural unit represented by formula (2). If copolymer (P1) contains multiple types of structural units represented by formula (3), the total content ratio of those multiple types of structural units shall be considered the content ratio of the structural unit represented by formula (3).

[0103] From the viewpoint of significantly exhibiting the effects of the present invention, the structural units represented by formula (2) contained in the copolymer (P1) are preferably 5 mol% or more, more preferably 10 mol% or more, even more preferably 20 mol% or more, even more preferably 30 mol% or more, particularly preferably 40 mol% or more, preferably 95 mol% or less, more preferably 90 mol% or less, even more preferably 80 mol% or less, and even more preferably 70 mol% or less, with the total of the structural units represented by formula (1) and the structural units represented by formula (2) contained in the copolymer (P1) being 100 mol%, respectively.

[0104] If copolymer (P1) contains multiple types of structural units represented by formula (1), the total mole percentage of these multiple types of structural units shall be considered as the mole percentage of the structural unit represented by formula (1). If copolymer (P1) contains multiple types of structural units represented by formula (2), the total mole percentage of these multiple types of structural units shall be considered as the mole percentage of the structural unit represented by formula (2).

[0105] The copolymer (P1) may contain any structural units other than the structural units represented by formula (1), formula (2), and formula (3). For example, it may contain (meth)acrylic acid ester units. A (meth)acrylic acid ester unit refers to a structural unit having a structure formed by polymerizing (meth)acrylic acid esters, and (meth)acrylic acid esters include acrylic acid esters, methacrylic acid esters, and combinations thereof. However, the amount of (meth)acrylic acid ester units in the copolymer (P1) may be small, or it may not contain any (meth)acrylic acid ester units at all. In one example, the content of (meth)acrylic acid ester units in the copolymer (P1) is preferably 10% by weight or less, more preferably 5% by weight or less, even more preferably 1% by weight or less, and may be 0% by weight. Conventionally, in the production of films with a large negative Rth / d value, materials with negative intrinsic birefringence were sometimes used, but materials with negative intrinsic birefringence generally tended to have low mechanical strength. Therefore, conventionally, it was possible to increase the mechanical strength of the material by using tough (meth)acrylic acid ester units. In contrast, copolymer (P1) can have high mechanical strength even without (meth)acrylic acid ester units. Therefore, from the viewpoint of utilizing this advantage, it is preferable that the content of (meth)acrylic acid ester units be small.

[0106] From the viewpoint of increasing the mechanical strength of the layer formed from the copolymer (P1), the number-average molecular weight of the copolymer (P1) is preferably 30,000 or more, more preferably 40,000 or more, and even more preferably 50,000 or more. From the viewpoint of increasing the solubility of the copolymer (P1) in solvents, it is preferably 500,000 or less, more preferably 400,000 or less, and even more preferably 300,000 or less. Here, the number-average molecular weight of the copolymer (P1) may be a polystyrene-equivalent value measured by gel permeation chromatography (GPC).

[0107] <Refractive Index> When a layer formation test is performed in which a copolymer layer containing copolymer (P1) is formed by coating and drying a solution containing only copolymer (P1) and a solvent that dissolves copolymer (P1) (hereinafter also referred to as the test solution), the copolymer layer preferably satisfies nz > nx ≈ ny. Here, nx ≈ ny means that nx and ny of the copolymer layer are substantially the same value, that is, the value of nx - ny is usually 0.0010 or less, preferably 0.0005 or less, and more preferably 0.0002 or less. The value of nx - ny is usually 0.0000 or more, and preferably 0.0000.

[0108] A layer where nz > nx ≈ ny is useful as a viewing angle compensation film for liquid crystal displays, polarizing plates, etc., and copolymer (P1) is suitable for forming such a layer.

[0109] As a solvent for dissolving the copolymer (P1) in the layer formation test, for example, a solvent can be used that can prepare a 15% by weight solution in which all of the copolymer (P1) is dissolved, with the total weight ratio of copolymer (P1) and solvent being 100% by weight. Examples of solvents include ketone solvents such as cyclopentanone.

[0110] The concentration of the copolymer (P1) in the test solution during the layer formation test can be, for example, 10% to 20% by weight, or for example, 15 ± 1% by weight.

[0111] The coating thickness of the test solution in the layer formation test can be, for example, 5 μm to 15 μm, or 10 μm ± 1 μm, as the thickness of the solid content after drying (after solvent evaporation). The drying temperature in the layer formation test can be set appropriately according to the volatility of the solvent used, for example, 100°C to 120°C, or 120°C ± 1°C if the solvent is cyclopentanone. The drying time in the layer formation test can be set appropriately according to the volatility of the solvent used and the drying temperature, for example, 1 minute to 5 minutes, or 3 minutes.

[0112] When the above layer formation test is performed, the Rth / d of the copolymer layer is preferably (-3.5 × 10 －３ ) More preferably (-4.5 × 10 －３ ) More preferably (-5.0 × 10 －３ ) is less than or equal to (-20.0 × 10) －３ ) More preferably (-17.5 × 10 －３ ) More preferably (-15.0 × 10 －３ That's all.

[0113] <2. Method for Producing Copolymer (P1)> Copolymer (P1) can be produced using conventionally known methods. For example, copolymer (P1) can be produced by polymerizing a monomer composition containing monomer 1, which can obtain a structural unit represented by formula (1) by polymerization, and monomer 2, which can obtain a structural unit represented by formula (2) by polymerization, using a known method.

[0114] Examples of monomer 1 include styrene monomers such as styrene, cyanostyrene, and nitrostyrene; vinyl biphenyl monomers such as vinyl biphenyl; and vinyl naphthalene monomers such as vinyl naphthalene. Monomer 1 may be used alone or in combination of two or more types.

[0115] Examples of monomer 2 include N-(1-naphthyl)maleimide and N-(2-naphthyl)maleimide. Furthermore, monomer 2 may be used alone or in combination of two or more types.

[0116] Monomer 1 and monomer 2 can each be produced by known methods and are also commercially available. For example, monomer 1 and monomer 2 can each be synthesized by combining known synthetic reactions without particular limitations. Examples of literature describing known synthetic reactions include Sandler-Calo's Methods for the Synthesis of Organic Compounds by Functional Group [I] and [II] (Hirokawa Shoten), and MARCH'S ADVANCED ORGANIC CHEMISTRY SIXTH EDITION (by Michael B. Smith and Jerry March; WILEY). For example, monomer 2 can be synthesized by combining, for example, maleic anhydride, citraconic anhydride, or 2,3-dimethylmaleic anhydride with R in formula (2) above. １ , R ２ , R ３ , R ４ , R ５ , R ６ , or R ７ It can be obtained by reacting a substituted naphthylamine, which is substituted with a group represented by , under acidic conditions.

[0117] Copolymer (P1) can be synthesized by combining known polymerization reactions. Examples of literature describing known polymerization reactions include the Revised Radical Polymerization Handbook (published by NTS Corporation) and Basic Polymer Chemistry (published by Tokyo Kagaku Dojin Co., Ltd.), edited by the Society of Polymer Science, Japan. Radical polymerization is preferred as the polymerization method for obtaining copolymer (P1). The radical polymerization method is not particularly limited and includes methods such as bulk polymerization, solution polymerization, suspension polymerization, precipitation polymerization, and emulsion polymerization. From the viewpoint of improving the transparency of copolymer (P1), solution polymerization or suspension polymerization is preferred.

[0118] Examples of polymerization initiators used in polymerization reactions include azo-based polymerization initiators such as 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(2-butyronitrile), 2,2'-azobisisobutyronitrile, dimethyl-2,2'-azobisisobutyrate, and 1,1'-azobis(cyclohexane-1-carbonitride); and organic peroxides such as benzoyl peroxide, lauryl peroxide, octanoyl peroxide, acetyl peroxide, di-t-butyl peroxide, t-butylcumyl peroxide, dicumyl peroxide, t-butyl peroxyacetate, t-butyl peroxybenzoate, perbutyl neodecanoate, and t-butyl peroxypivalate.

[0119] Examples of solvents used in polymerization reactions include alicyclic hydrocarbon solvents such as cyclohexane; aromatic hydrocarbon solvents such as toluene and xylene; alcohol solvents such as methanol, ethanol, propanol, and butanol; ether solvents such as dioxane, tetrahydropyran, tetrahydrofuran, and dibutyl ether; ketone solvents such as acetone and methyl ethyl ketone; ester solvents such as ethyl acetate and isopropyl acetate; aprotic polar solvents such as dimethyl sulfoxide, N,N-dimethylformamide, and N-methylpyrrolidone; water; and mixtures thereof.

[0120] The polymerization reaction temperature can be any temperature within the range in which the polymerization reaction proceeds, for example, 30°C to 200°C, or 30°C to 160°C. The polymerization reaction time can be any temperature within the range in which the polymerization reaction proceeds, for example, 1 hour or more, 2 hours or more, 3 hours or more, or 10 hours or less, or 8 hours or less.

[0121] The copolymer (P1) contains structural units represented by formula (1) and structural units represented by formula (2), and the polymerization reaction proceeds in good yield under mild conditions such as 30°C to 140°C, with a short reaction time of 10 hours or less.

[0122] <3. Applications of Copolymer (P1)> Layers formed by solution casting from a liquid composition containing copolymer (P1) and optional components and solvents as needed typically have a negative Rth / d and a large absolute value of Rth / d. Therefore, copolymer (P1) can be suitably used to easily manufacture phase difference layers, which can be used as optical compensation layers for optical elements such as liquid crystal displays and polarizing plates, with a small number of steps using solution casting.

[0123] <4. Phase Difference Layer> The phase difference layer according to one embodiment of the present invention has a normal Rth / d of (-20.0 × 10 －３ ) or more (-3.5 x 10 －３ The copolymer (P1) is the same as described above. The copolymer (P1) contained in the phase difference layer is the copolymer (P1) described above. Examples and preferred examples of the copolymer (P1) contained in the phase difference layer are the same as described above.

[0124] The phase difference layer may contain only one type of copolymer (P1), or it may contain two or more types in any proportion.

[0125] The phase difference layer may contain any components in addition to the copolymer (P1), as long as they do not hinder the effects of the present invention. Examples of optional components include polymers other than copolymer (P1); antioxidants; ultraviolet absorbers; antistatic agents; surfactants; colorants such as pigments and dyes; lubricants; plasticizers; and fillers.

[0126] The content of copolymer (P1) in the phase difference layer is preferably 60% by weight or more, more preferably 70% by weight or more, even more preferably 80% by weight or more, and even more preferably 90% by weight or more, with the total content of all components constituting the phase difference layer being 100% by weight, and is usually 100% by weight or less, and may be 100% by weight. Here, if the phase difference layer contains two or more types of copolymer (P1), it is preferable that the sum of the content of the two or more types of copolymer (P1) contained in the phase difference layer falls within the above content range.

[0127] The Rth / d of the phase difference layer is typically (-20.0 × 10⁻⁶). －３ ) or more, and usually (-3.5 × 10 －３ ) Preferably (-4.5 × 10－３ ) More preferably (-5.0 × 10 －３ The following is the result. This allows the phase difference layer to function well as an optical compensation layer for optical elements such as liquid crystal displays and polarizing plates.

[0128] The phase difference layer contains a copolymer (P1), which allows the Rth / d of the phase difference layer to be within the aforementioned range.

[0129] The thickness of the phase difference layer is preferably 25 μm or less, more preferably 20 μm or less, and even more preferably 15 μm or less, and is usually greater than 0 μm, for example, 1 μm or more. Since the phase difference layer contains a copolymer (P1), even when the thickness of the phase difference layer is small, it can be a layer with a negative retardation Rth in the thickness direction and a large absolute value.

[0130] The Rth of the phase difference layer can be measured using a phase difference meter (for example, AxoScan from Axometrics).

[0131] The thickness d of the phase difference layer can be measured using an optical film thickness measurement system (for example, the F20 from Filmetrix).

[0132] <Method for Manufacturing the Phase Difference Layer> The phase difference layer can be manufactured using a copolymer (P1) by any method. The phase difference layer may be manufactured by methods such as solution casting or melt extrusion. It is preferable to manufacture the phase difference layer by solution casting because it is possible to easily manufacture a phase difference layer with a small thickness. Solution casting is a method of obtaining a layer of raw materials by applying a liquid composition (preferably a solution of the raw materials) obtained by dissolving raw materials in a solvent to a support and removing the solvent by drying.

[0133] When a phase difference layer is manufactured by a solution casting method, examples of supports to which a liquid composition containing a copolymer (P1) and a solvent is applied include glass plates, metal plates, and resin films. A long phase difference layer may be obtained by applying the liquid composition to a continuously conveyed support. The support may be a stretched resin film or an unstretched resin film. The support may also be a multilayer body comprising multiple layers.

[0134] Any method can be used to apply the liquid composition containing the copolymer (P1) and solvent to a support, including curtain coating, extrusion coating, roll coating, spin coating, dip coating, bar coating, spray coating, slide coating, print coating, gravure coating, die coating, and gap coating.

[0135] The phase difference layer formed on the support by the solution casting method may be peeled off from the support and used as a phase difference film, or it may be used as a multilayer body including the phase difference layer and the support.

[0136] Any solvent capable of dissolving all or part of the copolymer (P1) can be used as the solvent in the liquid composition used in the solution casting method. Examples of such solvents are not limited to cyclohexane or other alicyclic hydrocarbon solvents; toluene or xylene or other aromatic hydrocarbon solvents; methanol or ethanol or propanol or butanol or other alcohol solvents; dioxane or tetrahydrofuran or other ether solvents; ketone solvents or acetone or methyl ethyl ketone or cyclohexanone or other ester solvents such as isopropyl acetate or other ester solvents.

[0137] The concentration of the copolymer (P1) in the liquid composition can be arbitrarily set according to the coating conditions such as the thickness of the phase difference layer to be formed and the coating speed. For example, with the weight of the liquid composition being 100% by weight, the concentration can be, for example, 5% or more by weight, for example, 10% or more by weight, for example, 40% or less by weight, for example, 30% or less by weight.

[0138] Any drying method can be used in the solution casting method, including, for example, heat drying, vacuum drying, hot air drying, or a combination thereof.

[0139] The method for manufacturing the phase difference layer may include any additional steps in combination with the above-mentioned steps. For example, the method for manufacturing the phase difference layer may include a step of stretching or shrinking the layer formed by the solution casting method. However, from the viewpoint of taking advantage of the benefit that a large absolute value of Rth / d can be obtained without stretching or shrinking, it is preferable that the method for manufacturing the phase difference layer does not include stretching or shrinking the layer formed by the solution casting method.

[0140] <5. Multilayer phase difference film> A multilayer phase difference film according to one embodiment of the present invention includes the phase difference layer and a substrate layer, wherein the phase difference layer is provided directly on the substrate layer.

[0141] The multilayer phase difference film according to this embodiment will be described below with reference to the figures. Figure 1 is a schematic cross-sectional view showing a multilayer phase difference film according to one embodiment of the present invention. The multilayer phase difference film 100 comprises a phase difference layer 110 and a base layer 120. The phase difference layer 110 is provided directly on the base layer 120. That is, there is no arbitrary layer between the phase difference layer 110 and the base layer 120. In this embodiment, the base layer 120 has a single-layer structure, but in another embodiment, the base layer may have a multilayer structure. In another embodiment, the base layer includes an anchor layer that has the function of improving the adhesion between the base layer and the phase difference layer, and the anchor layer provided on the base layer may be directly connected to the phase difference layer.

[0142] The base layer is preferably a resin layer. The resin usually contains a polymer. The base layer preferably contains a cyclic olefin polymer. A cyclic olefin polymer means a polymer or its hydride having structural units obtained by polymerizing a cyclic olefin. The cyclic olefin may or may not have substituents. A cyclic olefin polymer contains a cyclic structure within its molecule. Typically, a cyclic olefin polymer has an alicyclic structure in the repeating units of the polymer. A cyclic olefin polymer can be a polymer having an alicyclic structure in the main chain, a polymer having an alicyclic structure in the side chains, a polymer having an alicyclic structure in both the main chain and side chains, or a mixture of two or more of these in any ratio. From the viewpoint of mechanical strength and heat resistance, a cyclic olefin polymer containing an alicyclic structure in the main chain is preferred.

[0143] Examples of alicyclic structures include saturated alicyclic hydrocarbon (cycloalkane) structures and unsaturated alicyclic hydrocarbon (cycloalkene, cycloalkyne) structures. Among these, cycloalkane and cycloalkene structures are preferred from the viewpoint of mechanical strength and heat resistance, and cycloalkane structures are particularly preferred.

[0144] The range of the number of carbon atoms constituting the alicyclic structure is preferably 4 or more, more preferably 5 or more, preferably 30 or less, more preferably 20 or less, and particularly preferably 15 or less per alicyclic structure. When the number of carbon atoms constituting the alicyclic structure is within the above range, mechanical strength, heat resistance, and moldability are highly balanced.

[0145] In cyclic olefin polymers, the proportion of repeating units having an alicyclic structure to the total number of repeating units is preferably 55% by weight or more, more preferably 70% by weight or more, and even more preferably 90% by weight or more. When the proportion of repeating units having an alicyclic structure to the total number of repeating units is within this range, transparency and heat resistance are good.

[0146] Among cyclic olefin polymers, norbornene polymers are preferred. Examples of norbornene polymers include ring-opening polymers of monomers having a norbornene structure and their hydrides; addition polymers of monomers having a norbornene structure and their hydrides. Examples of ring-opening polymers of monomers having a norbornene structure include ring-opening homopolymers of one type of monomer having a norbornene structure, ring-opening copolymers of two or more types of monomers having a norbornene structure, and ring-opening copolymers of a monomer having a norbornene structure and any monomer copolymerizable therewith. Examples of addition polymers of monomers having a norbornene structure include addition homopolymers of one type of monomer having a norbornene structure, addition copolymers of two or more types of monomers having a norbornene structure, and addition copolymers of a monomer having a norbornene structure and any monomer copolymerizable therewith. Among these, hydrides of ring-opening polymers of monomers having a norbornene structure, addition copolymers of monomers having a norbornene structure and α-olefins, and hydrides of addition copolymers of monomers having a norbornene structure and α-olefins are preferred.

[0147] Examples of monomers having a norbornene structure include bicyclo[2.2.1]hept-2-ene (common name: norbornene), tricyclo[4.3.0.1 ２，５ Deca-3,7-diene (common name: dicyclopentadiene), 7,8-benzotricyclo[4.3.0.1 ２，５ Deca-3-ene (common name: metanotetrahydrofluorene), tetracyclo[4.4.0.1 ２，５ 1. ７，１０ Examples include dodeca-3-ene (common name: tetracyclododecene) and derivatives of these compounds (for example, those having substituents on the ring). Here, examples of substituents include alkyl groups, alkylene groups, polar groups, etc. Multiple substituents may be bonded to the ring, either identical or different in nature. Monomers having a norbornene structure may be used individually or in combination of two or more types.

[0148] Examples of polar groups include heteroatoms or groups of atoms containing heteroatoms. Examples of heteroatoms include oxygen atoms, nitrogen atoms, sulfur atoms, silicon atoms, and halogen atoms. Specific examples of polar groups include carboxyl groups, carbonyloxycarbonyl groups, epoxy groups, hydroxyl groups, oxy groups, ester groups, silanol groups, silyl groups, amino groups, nitrile groups, and sulfonic acid groups.

[0149] Examples of monomers capable of ring-opening copolymerization with monomers having a norbornene structure include monocyclic olefins such as cyclohexene, cycloheptene, and cyclooctene, and their derivatives; and cyclic conjugated dienes such as cyclohexadiene and cycloheptadiene, and their derivatives. Monomers capable of ring-opening copolymerization with monomers having a norbornene structure may be used individually or in combination of two or more types.

[0150] Ring-opening polymers of monomers having a norbornene structure can be produced, for example, by polymerizing or copolymerizing monomers in the presence of a ring-opening polymerization catalyst.

[0151] In addition copolymers of monomers having a norbornene structure and α-olefins, examples of α-olefins include α-olefins having 2 to 20 carbon atoms, such as ethylene, propylene, and 1-butene, and their derivatives. Among these, ethylene is preferred. One type of α-olefin may be used alone, or two or more types may be used in combination.

[0152] Addition polymers of monomers having a norbornene structure can be produced, for example, by polymerizing or copolymerizing monomers in the presence of an addition polymerization catalyst.

[0153] The hydrides of the ring-opening polymers and addition polymers described above can be produced, for example, by hydrogenating the carbon-carbon unsaturated bonds by preferably 90% or more in a solution of the ring-opening polymer or addition polymer in the presence of a hydrogenation catalyst containing a transition metal such as nickel or palladium.

[0154] Examples of norbornene polymer trade names include "ZEONOR" and "ZEONEX" from Nippon Zeon Corporation; "ARTON" from JSR Corporation; and "APPEL" from Mitsui Chemicals, Inc.

[0155] Norbornene polymers may be used individually or in combination of two or more types.

[0156] The weight-average molecular weight Mw of the cyclic olefin polymer is preferably 10,000 or more, more preferably 15,000 or more, particularly preferably 20,000 or more, preferably 100,000 or less, more preferably 80,000 or less, and particularly preferably 50,000 or less. When the weight-average molecular weight is within this range, the mechanical strength and moldability of the resin containing the cyclic olefin polymer are highly balanced.

[0157] The thickness of the substrate layer can be arbitrarily set from the standpoint of the mechanical strength of the substrate layer and the required retardation, and can be, for example, 5 μm or more, for example, 10 μm or more, for example, 200 μm or less, for example, 100 μm or less.

[0158] As described above, the base layer may have a multilayer structure. For example, the base layer may comprise a layer of resin containing a cyclic olefin polymer and the anchor layer. Examples of anchor layers include layers containing cured products of various resins including polymers. Examples of materials for forming the anchor layer include resins containing a (meth)acrylic polymer and a crosslinking agent such as an oxazoline compound. Examples of (meth)acrylic polymers include polymers having (meth)acrylic acid ester units. The thickness of the anchor layer can be, for example, 80 nm or more, for example 90 nm or more, and for example 1.0 μm or less.

[0159] The retardation of the substrate layer can be any value that can achieve the retardation required for the multilayer phase difference film. In one embodiment, the in-plane retardation Re of the substrate layer is preferably 110 nm or more, more preferably 120 nm or more, even more preferably 130 nm or more, preferably 160 nm or less, more preferably 155 nm or less, and even more preferably 150 nm or less. In one embodiment, the thickness-direction retardation Rth of the substrate layer is preferably 40 nm or more, more preferably 45 nm or more, even more preferably 50 nm or more, preferably 150 nm or less, more preferably 140 nm or less, and even more preferably 130 nm or less.

[0160] <6. Method for Manufacturing a Multilayer Phase Difference Film> The above-mentioned multilayer phase difference film can be manufactured by any method. From the viewpoint of easily manufacturing the phase difference layer contained in the multilayer phase difference film with a small number of steps, it is preferable to manufacture the multilayer phase difference film by a method that includes the following steps (1) and (2) in this order. Step (1): A step of preparing a base layer. Step (2): A step of applying a liquid composition containing the copolymer (P1) and a solvent onto the base layer. In addition to steps (1) and (2), the multilayer phase difference film may include any other steps. A preferred method for manufacturing a multilayer phase difference film will be described below.

[0161] <6.1. Process (1)> The base layer may be manufactured by any method, for example, the method described below, or a commercially available product may be used.

[0162] The base layer can be manufactured by any method, and can be produced from a resin containing a polymer (e.g., a cyclic olefin polymer) by melt molding or solution casting. More specific examples of melt molding methods include extrusion molding, press molding, inflation molding, injection molding, blow molding, and stretch molding. Among these methods, extrusion molding, inflation molding, and press molding are preferred for obtaining a base layer with excellent mechanical strength and surface accuracy, and extrusion molding is particularly preferred from the viewpoint of efficiently and easily manufacturing the base layer. It is preferable to manufacture long base layers due to their excellent manufacturing efficiency.

[0163] The base layer may be manufactured by a method that includes stretching a resin film formed by the method described above before stretching. The direction of stretching is arbitrary; for example, a long resin film before stretching may be stretched substantially in the longitudinal direction, or it may be stretched in a direction that forms an angle with respect to the longitudinal direction, for example, in the range of 0°±10°, for example, in the range of 0°±8°, for example, in the range of 0°±5°, or for example, in the range of 0°±3°. Since resins containing cyclic olefin polymers usually have a positive intrinsic birefringence, a film of a resin containing a cyclic olefin polymer usually exhibits a slow axis in the stretching direction when stretched. A multilayer phase difference film containing a substrate layer having an in-plane slow phase axis in approximately the longitudinal direction can be efficiently manufactured by laminating it with a linear polarizer having an absorption axis or transmission axis in the longitudinal direction, so that their respective longitudinal directions coincide, resulting in a laminate in which the slow phase axis of the multilayer phase difference film and the absorption axis of the linear polarizer are in a predetermined angular relationship (approximately 0° or 90°).

[0164] The base layer may be manufactured, for example, by a method that includes performing a modification treatment such as corona treatment or plasma treatment on the surface of a resin film formed by the above method before or after stretching.

[0165] If the base layer includes an anchor layer, the base layer may be manufactured by a method that includes forming the anchor layer on a layer of resin containing a polymer such as a cyclic olefin polymer.

[0166] <6.2. Process (2)> The liquid composition applied to the substrate layer includes the copolymer (P1) and a solvent. Examples of solvents included in the liquid composition are not particularly limited and include solvents that can be used when manufacturing the phase difference layer by the solution casting method. The concentration of copolymer (P1) in the liquid composition can be arbitrarily set according to the thickness of the phase difference layer to be formed, the coating speed, and other coating conditions, and can be, for example, within the same range as the concentration of copolymer (P1) in the liquid composition that can be used when manufacturing the phase difference layer by the solution casting method.

[0167] <6.3. Optional Steps> Examples of optional steps include, for example, a step of drying the liquid composition applied to the substrate layer, and a step of laminating the multilayer phase difference film to an optical element such as a liquid crystal display. An optional step may include a step of stretching the multilayer phase difference film, but since the phase difference layer obtained by drying the liquid composition has a negative Rth / d and a large absolute value even without a stretching step, it is preferable not to include a step of stretching the multilayer phase difference film from the viewpoint of obtaining a multilayer phase difference film with the desired retardation in a small number of steps.

[0168] The present invention will be specifically described below with reference to examples. However, the present invention is not limited to the examples shown below, and can be modified and implemented as appropriate without departing from the scope of the claims and equivalents of the present invention.

[0169] In the following explanation, "%" and "parts" used to express quantities refer to weight unless otherwise specified. Furthermore, the operations described below were performed under normal temperature (20°C ± 15°C) and atmospheric pressure (1 atm) conditions unless otherwise specified.

[0170] <Measurement and Evaluation Method> (Thickness) The thickness of the film or layer was measured using a film thickness measuring system (Filmetrics "F20").

[0171] (Method for measuring phase difference) The phase differences Re and Rth were measured using a phase difference meter (AxoScan, manufactured by Axometrics) at a temperature of 23°C. When determining the physical properties of each layer of an inseparable multilayer material, the measurement target was measured from multiple directions and the properties were calculated by fitting analysis using the accompanying multilayer analysis software. The measurement wavelength was 550 nm.

[0172] (Measurement of Number-Average Molecular Weight) The number-average molecular weight of the polymer was measured using an HLC-8420 GPC (manufactured by Tosoh Corporation). The GPC conditions were as follows: Temperature: 40°C Column: TSKgel guardcolumn SuperH-H 4.6 mm x 3.5 cm, TSKgel SuperH5000 6.0 mm x 15 cm, TSKgel SuperH4000 6.0 mm x 15 cm, and TSKgel SuperH2000 6.0 mm x 15 cm were used in series. Injection volume: 50 microliters Solvent: Tetrahydrofuran Flow rate: 0.5 mL / min Reference: Polystyrene Sample concentration: 0.5 wt%

[0173] (Method for measuring film strength) The strength of the phase difference layer (film strength) was evaluated according to JIS K5600-5-6 (adhesion (cross-cut method)) using the multilayer phase difference films obtained in the examples and comparative examples. A grid pattern of 5 vertical x 5 horizontal cuts was made in the coated film, which is the phase difference layer, and the coated film was divided into 16 sections. The interval between the cuts was 1 mm. A tape peel test was performed by attaching tape to the cuts and peeling it off, and the film strength was evaluated on a scale of 0 to 5. The smaller the evaluation number, the less peeling there was and the greater the film strength. 0: The edges of the sections of the coated film are perfectly smooth, and there is no damage to the sections at all. 1: There is slight peeling at the intersections of the cuts in the coated film. Peeling is less than 5%. 2: Peeling occurs along the edges of the sections of the coated film and / or at the intersections of the cuts. Peeling is 5% or more and less than 15%. 3: Large areas of peeling, either partially or entirely, along the edges of the coated film sections; and / or several sections are partially or entirely peeled. The peeling is between 15% and 35%. 4: Large areas of peeling, either partially or entirely, along the edges of the coated film sections; and / or several sections are partially or entirely peeled. The peeling is less than 35%. 5: The entire coated film section is peeled and destroyed.

[0174] <Synthesis Example 1: Synthesis of Compound 1>

[0175]

[0176] In a four-port reactor equipped with a thermometer, 32.3 g (0.22 mol) of 2,6-diethylaniline and 800 ml of acetic acid were added under a nitrogen stream. To this solution, 25.0 g (0.26 mol) of maleic anhydride was slowly added while maintaining the temperature at 20-30°C. After stirring at room temperature for 30 minutes, the temperature was raised in an oil bath and heated under reflux for 10 hours. After the reaction was complete, the mixture was cooled to room temperature, and the reaction solution was added to 2 liters of distilled water and extracted twice with 500 ml of ethyl acetate. The resulting ethyl acetate layer was washed five times with 300 ml of distilled water. The ethyl acetate layer was further washed with 500 ml of saturated brine, and then the ethyl acetate layer was dried over anhydrous sodium sulfate, and the sodium sulfate was filtered off. The resulting ethyl acetate layer was concentrated under reduced pressure using a rotary evaporator to obtain a pale yellow solid. This pale yellow solid was purified by silica gel column chromatography (hexane:ethyl acetate = 80:20 (volume ratio)) to obtain 44.3 g of compound 1 as a pale yellow solid (yield: 89.1 mol%). The structure is １ It was identified by H-NMR. １ The H-NMR spectral data is shown below. １ H-NMR (500MHz, CDCl ３ , TMS, δppm): 7.36 (dd, 1H, J=7.5Hz, 7.5Hz), 7.20 (d, 2H, J=7.5Hz), 6.86 (s, 2H), 2.40 (q, 4H, J=7.5Hz), 1.13 (t, 6H, J=7.5Hz).

[0177] <Synthesis Example 2: Synthesis of Compound 2>

[0178]

[0179] In a four-port reactor equipped with a thermometer, 26.3 g (0.18 mol) of 1-aminonaphthalene and 700 ml of acetic acid were added under a nitrogen stream. To this solution, 20.0 g (0.20 mol) of maleic anhydride was slowly added while maintaining the temperature at 20-30°C. After stirring at room temperature for 30 minutes, the temperature was raised in an oil bath and heated under reflux for 6 hours. After the reaction was complete, the mixture was cooled to room temperature, and the reaction solution was added to 2 liters of distilled water and extracted twice with 500 ml of ethyl acetate. The resulting ethyl acetate layer was washed five times with 500 ml of distilled water. The ethyl acetate layer was further washed with 300 ml of saturated brine, and the ethyl acetate layer was dried over anhydrous sodium sulfate, after which the sodium sulfate was filtered off. The resulting ethyl acetate layer was concentrated under reduced pressure using a rotary evaporator to obtain a yellow solid. This pale yellow solid was purified by silica gel column chromatography (hexane:ethyl acetate = 70:30 (volume ratio)) to obtain compound 2 as a yellow solid. Furthermore, the obtained yellow solid was purified by recrystallization using ethyl acetate as the solvent. As a result, 28.2 g of pale yellow solid was obtained (yield: 68.8 mol%). The structure is １ It was identified by H-NMR. １ The H-NMR spectral data is shown below. １ H-NMR (500MHz, CDCl ３ , TMS, δppm): 7.96 (d, 1H, J = 8.0Hz), 7.94-7.92 (m, 1H), 7.58-7.51 (m, 4H), 7.37 (dd, 1H, J = 1.0Hz, 7.0Hz), 6.97 (s, 2H).

[0180] <Synthesis Example 3: Synthesis of Compound 3>

[0181]

[0182] In a four-port reactor equipped with a thermometer, 28.9 g (0.18 mol) of 1-amino-2-methylnaphthalene and 700 ml of acetic acid were added under a nitrogen stream. To this solution, 20.0 g (0.20 mol) of maleic anhydride was slowly added while maintaining the temperature at 20-30°C. After stirring at room temperature for 30 minutes, the temperature was raised in an oil bath and heated under reflux for 6 hours. After the reaction was complete, the mixture was cooled to room temperature, and the reaction solution was added to 2 liters of distilled water and extracted twice with 500 ml of ethyl acetate. The resulting ethyl acetate layer was washed five times with 500 ml of distilled water. The ethyl acetate layer was further washed with 300 ml of saturated brine, and the ethyl acetate layer was dried over anhydrous sodium sulfate, after which the sodium sulfate was filtered off. The resulting ethyl acetate layer was concentrated under reduced pressure using a rotary evaporator to obtain a yellow solid. This pale yellow solid was purified by silica gel column chromatography (hexane:ethyl acetate = 80:20 (volume ratio)) to obtain compound 3 as a pale yellow solid. Furthermore, the obtained pale yellow solid was purified by recrystallization using ethyl acetate as the solvent. As a result, 33.0 g of the pale yellow solid was obtained (yield: 75.7 mol%). The structure is １ It was identified by H-NMR. １ The H-NMR spectral data is shown below. １ H-NMR (500MHz, CDCl ３ , TMS, δppm): 7.86 (d, 2H, J=8.5Hz), 7.50-7.42 (m, 4H), 6.96 (s, 2H), 2.31 (s, 3H).

[0183] <Polymerization Example 1: Synthesis of Copolymer 1> 5.0 g (48.0 mmol) of styrene from which the polymerization inhibitor had been removed, 11.4 g (48.0 mmol) of compound 3 synthesized in Synthesis Example 3, 20 ml of toluene, and 12.6 mg (0.08 mmol) of 2,2'-azobis(isobutyronitrile), which is the polymerization initiator, were placed in a 100 ml sealed pressure-resistant glass container and sealed. Then, the container was depressurized using a diaphragm pump, and the nitrogen purging operation was repeated five times to completely purge the container with nitrogen. After that, the pressure-resistant glass container was placed in an oil bath at 100°C and held for 5 hours to carry out radical polymerization. After the polymerization reaction was complete, the polymer was diluted with 70 ml of tetrahydrofuran, removed from the container, and added dropwise to 400 ml of methanol to precipitate the polymer, which was then recovered by vacuum filtration. The recovered polymer was vacuum-dried at 100°C for 6 hours to obtain 15.4 g of copolymer 1 (yield: 94.2% by weight). The molecular weight of the obtained copolymer was measured by GPC, and the number-average molecular weight was 93,700. The copolymer composition ratio was as follows: １ H-NMR measurement (DMSO-d ６ Based on this, the ratio of styrene units to compound units (3 units) was 50 / 50 (mol%).

[0184] <Polymerization Example 2: Synthesis of Copolymer 2> 5.0 g (48.0 mmol) of styrene from which the polymerization inhibitor had been removed, 5.5 g (24.0 mmol) of compound 1 synthesized in Synthesis Example 1, 5.7 g (24.0 mmol) of compound 3 synthesized in Synthesis Example 3, 30 ml of tetrahydropyran, and 15.4 mg (0.09 mmol) of 2,2'-azobis(isobutyronitrile), which is the polymerization initiator, were placed in a 100 ml sealed pressure-resistant glass container and sealed. Then, the container was depressurized using a diaphragm pump, and nitrogen purging was performed five times to completely purge the container with nitrogen. After that, the pressure-resistant glass container was placed in an oil bath at 85°C and held for 4 hours to carry out radical polymerization. After the polymerization reaction was complete, the polymer was diluted with 70 ml of tetrahydrofuran, removed from the container, and added dropwise to 300 ml of methanol to precipitate the polymer, which was then recovered by vacuum filtration. The recovered polymer was vacuum-dried at 100°C for 6 hours to obtain 14.8 g of copolymer 2 (yield: 91.3% by weight). The molecular weight of the obtained copolymer was measured by GPC, and the number-average molecular weight was 68,200. The copolymer composition ratio was as follows: １ H-NMR measurement (DMSO-d ６ Based on this, the ratio of styrene units / compound 1 unit / compound 3 units was 53 / 14 / 33 (mol%). If the total of styrene units and compound 3 units is assumed to be 100 mol%, then the ratio of styrene units / compound 3 units was 62 / 38 (mol%).

[0185] <Polymerization Example 3: Synthesis of Copolymer 3> 5.0 g (48.0 mmol) of styrene from which the polymerization inhibitor had been removed, 10.7 g (48.0 mmol) of compound 2 synthesized in Synthesis Example 2, 30 ml of tetrahydropyran, and 18.9 mg (0.12 mmol) of 2,2'-azobis(isobutyronitrile), which is the polymerization initiator, were placed in a 100 ml sealed pressure-resistant glass container and sealed. Then, the container was depressurized using a diaphragm pump, and the nitrogen purging operation was repeated five times to completely purge the container with nitrogen. After that, the pressure-resistant glass container was placed in an oil bath at 85°C and held for 5 hours to carry out radical polymerization. After the polymerization reaction was complete, the polymer was diluted with 70 ml of tetrahydrofuran, removed from the container, and added dropwise to 250 ml of methanol to precipitate the polymer, which was then recovered by vacuum filtration. The recovered polymer was vacuum-dried at 100°C for 6 hours to obtain 14.7 g of copolymer 3 (yield: 93.3% by weight). The molecular weight of the obtained copolymer was measured by GPC, and the number-average molecular weight was 68,200. The copolymer composition ratio was as follows: １ H-NMR measurement (DMSO-d ６ Based on this, the ratio of styrene units to compound units was 50 / 50 (mol%).

[0186] <Polymerization Example 4: Synthesis of Copolymer 4> 6.0 g (33.3 mmol) of 4-vinylbiphenyl from which the polymerization inhibitor had been removed, 7.9 g (33.3 mmol) of compound 3 synthesized in Synthesis Example 3, 30 ml of tetrahydropyran, and 13.1 mg (0.08 mmol) of 2,2'-azobis(isobutyronitrile), which is the polymerization initiator, were placed in a 100 ml sealed pressure-resistant glass container and sealed. Then, the container was depressurized using a diaphragm pump, and the nitrogen purging operation was repeated five times to completely purge the container with nitrogen. After that, the pressure-resistant glass container was placed in an oil bath at 85°C and held for 5 hours to carry out radical polymerization. After the polymerization reaction was complete, the polymer was diluted with 65 ml of tetrahydrofuran, removed from the container, and added dropwise to 300 ml of methanol to precipitate the polymer, which was then recovered by vacuum filtration. The recovered polymer was vacuum-dried at 100°C for 6 hours to obtain 13.1 g of copolymer 4 (yield: 94.2% by weight). The molecular weight of the obtained copolymer was measured by GPC, and the number-average molecular weight was 73,700. The copolymer composition ratio was as follows: １ H-NMR measurement (DMSO-d ６ ) The result was 4-vinylbiphenyl units / 3 units of compound = 50 / 50 (mol%).

[0187] <Polymerization Example 5: Synthesis of Copolymer 5> 5.0 g (27.7 mmol) of 4-vinylbiphenyl from which the polymerization inhibitor had been removed, 9.3 g (41.6 mmol) of compound 2 synthesized in Synthesis Example 2, 25 ml of tetrahydropyran, and 9.1 mg (0.055 mmol) of 2,2'-azobis(isobutyronitrile), which is the polymerization initiator, were placed in a 100 ml sealed pressure-resistant glass container and sealed. Then, the container was depressurized using a diaphragm pump, and the nitrogen purging operation was repeated five times to completely purge the container with nitrogen. After that, the pressure-resistant glass container was placed in an oil bath at 85°C and held for 5 hours to carry out radical polymerization. After the polymerization reaction was complete, the polymer was diluted with 120 ml of tetrahydrofuran, removed from the container, and added dropwise to 1.5 liters of methanol to precipitate the polymer, which was then recovered by vacuum filtration. The recovered polymer was vacuum-dried at 100°C for 6 hours to obtain 13.1 g of copolymer 5 (yield: 91.6% by weight). The obtained copolymer was subjected to molecular weight analysis by GPC, and its number-average molecular weight was found to be 61,000. The copolymer composition ratio was as follows: １ H-NMR measurement (DMSO-d ６ ) The result was 4-vinylbiphenyl units / 2 units of compound = 30 / 70 (mol%).

[0188] <Polymerization Example 6: Synthesis of Copolymer 6> 5.0 g (27.7 mmol) of 4-vinylbiphenyl from which the polymerization inhibitor had been removed, 6.8 g (30.5 mmol) of compound 2 synthesized in Synthesis Example 2, 25 ml of toluene, and 11.4 mg (0.047 mmol) of the polymerization initiator V-40 (1,1'-azobis(cyclohexane-1-carbonitride)) were placed in a 100 ml sealed pressure-resistant glass container and sealed. Then, the container was depressurized using a diaphragm pump, and nitrogen purging was performed five times to completely purge the container with nitrogen. After that, the pressure-resistant glass container was placed in an oil bath at 100°C and held for 7 hours to carry out radical polymerization. After the polymerization reaction was complete, the polymer was diluted with 100 ml of N,N-dimethylacetamide, removed from the container, and added dropwise to 1 liter of methanol to precipitate the polymer, which was then recovered by vacuum filtration. The recovered polymer was vacuum-dried at 100°C for 6 hours to obtain 11.1 g of copolymer 6 (yield: 93.8% by weight). The molecular weight of the obtained copolymer was determined by GPC, and the number-average molecular weight was 92,700. The copolymer composition ratio was as follows: １ H-NMR measurement (DMSO-d ６ Based on this, the ratio of 4-vinylbiphenyl units to 2 units of the compound was 42 / 58 (mol%).

[0189] <Polymerization Example 7: Synthesis of Copolymer 7> 5.0 g (27.7 mmol) of 4-vinylbiphenyl from which the polymerization inhibitor had been removed, 7.2 g (30.5 mmol) of compound 3 synthesized in Synthesis Example 3, 15 ml of tetrahydropyran, and 7.7 mg (0.047 mmol) of 2,2'-azobis(isobutyronitrile), which is the polymerization initiator, were placed in a 100 ml sealed pressure-resistant glass container and sealed. Then, the container was depressurized using a diaphragm pump, and the nitrogen purging operation was repeated five times to completely purge the container with nitrogen. After that, the pressure-resistant glass container was placed in an oil bath at 75°C and held for 9.5 hours to carry out radical polymerization. After the polymerization reaction was complete, the polymer was diluted with 150 ml of N,N-dimethylacetamide, removed from the container, and added dropwise to 1.5 liters of methanol to precipitate the polymer, which was then recovered by vacuum filtration. The recovered polymer was vacuum-dried at 100°C for 6 hours to obtain 11.3 g of copolymer 7 (yield: 92.8% by weight). The molecular weight of the obtained copolymer was determined by GPC, and the number-average molecular weight was 97,300. The copolymer composition ratio was as follows: １ H-NMR measurement (DMSO-d ６ Based on this, the ratio of 4-vinylbiphenyl units to 3 units of the compound was 64 / 36 (mol%).

[0190] <Polymerization Example 8: Synthesis of Copolymer 8> 5.0 g (27.7 mmol) of 4-vinylbiphenyl from which the polymerization inhibitor had been removed, 7.2 g (30.5 mmol) of compound 3 synthesized in Synthesis Example 3, 25 ml of toluene, and 7.1 mg (0.029 mmol) of the polymerization initiator V-40 (1,1'-azobis(cyclohexane-1-carbonitride)) were placed in a 100 ml sealed pressure-resistant glass container and sealed. Then, the container was depressurized using a diaphragm pump, and nitrogen purging was performed five times to completely purge the container with nitrogen. After that, the pressure-resistant glass container was placed in an oil bath at 100°C and held for 10 hours to carry out radical polymerization. After the polymerization reaction was complete, the polymer was diluted with 120 ml of N,N-dimethylacetamide, removed from the container, and added dropwise to 1.5 liters of methanol to precipitate the polymer, which was then recovered by vacuum filtration. The recovered polymer was vacuum-dried at 100°C for 6 hours to obtain 11.4 g of copolymer 8 (yield: 93.7% by weight). The molecular weight of the obtained copolymer was determined by GPC, and the number-average molecular weight was 63,600. The copolymer composition ratio was as follows: １ H-NMR measurement (DMSO-d ６ Based on this, the ratio of 4-vinylbiphenyl units to 3 units of the compound was 45 / 55 (mol%).

[0191] <Polymerization Example 9: Synthesis of Copolymer 9> 1.0 g (9.6 mmol) of styrene with polymerization inhibitor removed, 1.7 g (9.6 mmol) of 4-vinyl biphenyl, 4.3 g (19.2 mmol) of compound 2 synthesized in Synthesis Example 2, 12 ml of tetrahydropyran, and 5.0 mg (0.031 mmol) of 2,2'-azobis(isobutyronitrile), which is a polymerization initiator, were placed in a 100 ml sealed pressure-resistant glass container and sealed. Then, the container was depressurized using a diaphragm pump, and nitrogen purging was performed five times to completely purge the container with nitrogen. After that, the pressure-resistant glass container was placed in an oil bath at 75°C and held for 8 hours to carry out radical polymerization. After the polymerization reaction was complete, the polymer was diluted with 120 ml of N,N-dimethylacetamide, removed from the container, and added dropwise to 1.5 liters of methanol to precipitate the polymer, which was then recovered by vacuum filtration. The recovered polymer was vacuum-dried at 100°C for 6 hours to obtain 6.8 g of copolymer 9 (yield: 96.8% by weight). The molecular weight of the obtained copolymer was determined by GPC, and the number-average molecular weight was 59,500. The copolymer composition ratio was as follows: １ H-NMR measurement (DMSO-d ６ Based on this, the ratio of styrene units / 4-vinylbiphenyl units / 2 compound units was 11 / 40 / 49 (mol%).

[0192] <Polymerization Example 10: Synthesis of Copolymer 10> 5.0 g (27.7 mmol) of 4-vinylbiphenyl from which the polymerization inhibitor had been removed, 1.9 g (8.3 mmol) of compound 2 synthesized in Synthesis Example 2, 13 ml of toluene, and 6.2 mg (0.025 mmol) of the polymerization initiator V-40 (1,1'-azobis(cyclohexane-1-carbonitride)) were placed in a 100 ml sealed pressure-resistant glass container and sealed. Then, the container was depressurized using a diaphragm pump, and nitrogen purging was performed five times to completely purge the container with nitrogen. After that, the pressure-resistant glass container was placed in an oil bath at 100°C and held for 8 hours to carry out radical polymerization. After the polymerization reaction was complete, the polymer was diluted with 100 ml of N,N-dimethylacetamide, removed from the container, and added dropwise to 1.5 liters of methanol to precipitate the polymer, which was then recovered by vacuum filtration. The recovered polymer was vacuum-dried at 100°C for 6 hours to obtain 6.6 g of copolymer 10 (yield: 96.4% by weight). The molecular weight of the obtained copolymer was determined by GPC, and the number-average molecular weight was 100,600. The copolymer composition ratio was as follows: １ H-NMR measurement (Dioxane-d ８ Based on this, the ratio of 4-vinylbiphenyl units to 2 units of the compound was 70 / 30 (mol%).

[0193] <Polymerization Example 11: Synthesis of Copolymer 11> 5.0 g (27.7 mmol) of 4-vinylbiphenyl from which the polymerization inhibitor had been removed, 0.62 g (2.77 mmol) of compound 2 synthesized in Synthesis Example 2, 10 ml of toluene, and 5.2 mg (0.021 mmol) of the polymerization initiator V-40 (1,1'-azobis(cyclohexane-1-carbonitride)) were placed in a 100 ml sealed pressure-resistant glass container and sealed. Then, the container was depressurized using a diaphragm pump, and nitrogen purging was performed five times to completely purge the container with nitrogen. After that, the pressure-resistant glass container was placed in an oil bath at 100°C and held for 8 hours to carry out radical polymerization. After the polymerization reaction was complete, the polymer was diluted with 100 ml of N,N-dimethylacetamide, removed from the container, and added dropwise to 1.5 liters of methanol to precipitate the polymer, which was then recovered by vacuum filtration. The recovered polymer was vacuum-dried at 100°C for 6 hours to obtain 5.4 g of copolymer 11 (yield: 96.2% by weight). The molecular weight of the obtained copolymer was determined by GPC, and the number-average molecular weight was 100,300. The copolymer composition ratio was as follows: １ H-NMR measurement (Dioxane-d ８ ) The result was 4-vinylbiphenyl units / 2 units of compound = 85 / 15 (mol%).

[0194] <Polymerization Example 12: Synthesis of Copolymer 12> 5.0 g (27.7 mmol) of 4-vinylbiphenyl from which the polymerization inhibitor had been removed, 1.8 g (8.3 mmol) of compound 3 synthesized in Synthesis Example 3, 10 ml of toluene, and 6.2 mg (0.025 mmol) of the polymerization initiator V-40 (1,1'-azobis(cyclohexane-1-carbonitride)) were placed in a 100 ml sealed pressure-resistant glass container and sealed. Then, the container was depressurized using a diaphragm pump, and nitrogen purging was performed five times to completely purge the container with nitrogen. After that, the pressure-resistant glass container was placed in an oil bath at 100°C and held for 10 hours to carry out radical polymerization. After the polymerization reaction was complete, the polymer was diluted with 100 ml of tetrahydrofuran, removed from the container, and added dropwise to 1.5 liters of methanol to precipitate the polymer, which was then recovered by vacuum filtration. The recovered polymer was vacuum-dried at 100°C for 6 hours to obtain 6.5 g of copolymer 12 (yield: 95.3% by weight). The molecular weight of the obtained copolymer was determined by GPC, and the number-average molecular weight was 114,400. The copolymer composition ratio was as follows: １ H-NMR measurement (Dioxane-d ８ ) The result was 4-vinylbiphenyl units / 3 units of compound = 72 / 28 (mol%).

[0195] <Polymerization Example 13: Synthesis of Copolymer 13> 5.0 g (27.7 mmol) of 4-vinylbiphenyl from which the polymerization inhibitor had been removed, 0.66 g (2.77 mmol) of compound 3 synthesized in Synthesis Example 3, 8 ml of toluene, and 5.2 mg (0.021 mmol) of the polymerization initiator V-40 (1,1'-azobis(cyclohexane-1-carbonitride)) were placed in a 100 ml sealed pressure-resistant glass container and sealed. Then, the container was depressurized using a diaphragm pump, and nitrogen purging was performed five times to completely purge the container with nitrogen. After that, the pressure-resistant glass container was placed in an oil bath at 100°C and held for 10 hours to carry out radical polymerization. After the polymerization reaction was complete, the polymer was diluted with 100 ml of tetrahydrofuran, removed from the container, and added dropwise to 1.5 liters of methanol to precipitate the polymer, which was then recovered by vacuum filtration. The recovered polymer was vacuum-dried at 100°C for 6 hours to obtain 5.2 g of copolymer 13 (yield: 91.6% by weight). The molecular weight of the obtained copolymer was determined by GPC, and the number-average molecular weight was 117,000. The copolymer composition ratio was as follows: １ H-NMR measurement (Dioxane-d ８ Based on this, the ratio of 4-vinylbiphenyl units to 3 units of the compound was 86 / 14 (mol%).

[0196] <Polymerization Example C1: Polymerization of Styrene> 20.0 g (0.19 mol) of styrene from which the polymerization inhibitor had been removed, 20 ml of toluene, and 25.2 mg (0.15 mmol) of 2,2'-azobis(isobutyronitrile), a polymerization initiator, were placed in a 100 ml sealed pressure-resistant glass container and sealed. Then, the container was depressurized using a diaphragm pump, and nitrogen purging was performed five times to completely purge the container with nitrogen. After that, the pressure-resistant glass container was placed in an oil bath at 100°C and held for 5 hours to carry out radical polymerization. After the polymerization reaction was complete, the polymer was diluted with 80 ml of tetrahydrofuran, removed from the container, and precipitated by adding it dropwise to 300 ml of methanol. The polymer was recovered by vacuum filtration. The recovered polymer was vacuum-dried at 100°C for 6 hours to obtain 19.0 g of polystyrene (yield: 95.1% by weight). The molecular weight of the obtained polymer was measured by GPC, and the number average molecular weight was 100,000.

[0197] <Polymerization Example C2: Polymerization of 4-Vinylbiphenyl> 20.0 g (0.11 mol) of 4-vinylbiphenyl, from which the polymerization inhibitor had been removed, 20 ml of toluene, and 21.9 mg (0.13 mmol) of 2,2'-azobis(isobutyronitrile), a polymerization initiator, were placed in a 100 ml sealed pressure-resistant glass container and sealed. Then, the container was depressurized using a diaphragm pump, and nitrogen purging was performed five times to completely purge the container with nitrogen. After that, the pressure-resistant glass container was placed in an oil bath at 100°C and held for 5 hours to carry out radical polymerization. After the polymerization reaction was complete, the polymer was diluted with 80 ml of tetrahydrofuran, removed from the container, and added dropwise to 300 ml of methanol to precipitate the polymer, which was then recovered by vacuum filtration. The recovered polymer was vacuum-dried at 100°C for 6 hours to obtain 18.8 g of poly(4-vinylbiphenyl) (yield: 94.0 wt%). When the molecular weight of the obtained polymer was measured by GPC, the number-average molecular weight was found to be 110,000.

[0198] <Polymerization Example C3: Polymerization of Compound 1> 20.0 g (87.2 mmol) of Compound 1 synthesized in Synthesis Example 1, 20 ml of toluene, and 14.3 mg (0.087 mmol) of 2,2'-azobis(isobutyronitrile), a polymerization initiator, were placed in a 100 ml sealed pressure-resistant glass container and sealed. Then, the container was depressurized using a diaphragm pump, and a nitrogen purging operation was repeated five times to completely purge the container with nitrogen. After that, the pressure-resistant glass container was placed in a 100°C oil bath and held for 5 hours to carry out radical polymerization. After the polymerization reaction was complete, the polymer was removed from the container and added dropwise to 200 ml of methanol to precipitate the polymer, which was then recovered by vacuum filtration. The recovered polymer was vacuum-dried at 100°C for 6 hours to obtain 2.0 g of polymer of Compound 1 (yield: 10.2% by weight). The molecular weight of the obtained polymer was measured by GPC, and the number average molecular weight was 13,400.

[0199] <Polymerization Example C4: Polymerization of Compound 2> 10.0 g (44.8 mmol) of Compound 2 synthesized in Synthesis Example 2, 10 ml of tetrahydropyran, and 11.0 mg (0.07 mmol) of 2,2'-azobis(isobutyronitrile), a polymerization initiator, were placed in a 100 ml sealed pressure-resistant glass container and sealed. Then, the container was depressurized using a diaphragm pump, and nitrogen purging was performed five times to completely purge the container with nitrogen. After that, the pressure-resistant glass container was placed in an oil bath at 85°C and held for 5 hours to carry out radical polymerization. After the polymerization reaction was complete, the polymer was diluted with 65 ml of tetrahydrofuran, removed from the container, and added dropwise to 500 ml of methanol to precipitate the polymer, which was then recovered by vacuum filtration. The recovered polymer was vacuum-dried at 100°C for 6 hours to obtain 0.8 g of polymer of Compound 2 (yield: 8.3 wt%). The molecular weight of the obtained polymer was measured by GPC, and the number average molecular weight was 8,200.

[0200] <Polymerization Example C5: Polymerization of Compound 3> 10.0 g (42.1 mmol) of Compound 3 synthesized in Synthesis Example 3, 10 ml of tetrahydropyran, and 10.4 mg (0.06 mmol) of 2,2'-azobis(isobutyronitrile), a polymerization initiator, were placed in a 100 ml sealed pressure-resistant glass container and sealed. Then, the container was depressurized using a diaphragm pump, and nitrogen purging was performed five times to completely purge the container with nitrogen. After that, the pressure-resistant glass container was placed in an oil bath at 85°C and held for 5 hours to carry out radical polymerization. After the polymerization reaction was complete, the polymer was diluted with 65 ml of tetrahydrofuran, removed from the container, and added dropwise to 500 ml of methanol to precipitate the polymer, which was then recovered by vacuum filtration. The recovered polymer was vacuum-dried at 100°C for 6 hours to obtain 0.9 g (yield: 9.1% by weight) of Compound 3 polymer. The molecular weight of the obtained polymer was measured by GPC, and the number average molecular weight was 7,700.

[0201] <Polymerization Example C6: Polymerization of N-(1-naphthyl)maleimide (compound 2) and isobutene> Polymerization was carried out in the same manner as in Synthesis Example 1 of Japanese Patent Application Publication No. 2006-45368, except that N-phenylmaleimide was replaced with compound 2 synthesized in Synthesis Example 2, to obtain an N-(1-naphthyl)maleimide-isobutene copolymer. The yield was 37.2% by weight. The molecular weight of the obtained copolymer was measured by GPC, and the number average molecular weight was 71,000. The copolymer composition ratio was: １ H-NMR measurement (DMSO-d ６ Based on this, the ratio of N-(1-naphthyl)maleimide units (2 units of compound) to isobutene units was 55 / 45 (mol%).

[0202] <Example 1> (1-1. Preparation of the base layer) (Melting extrusion of resin film) A pelletized resin containing a norbornene polymer (manufactured by Nippon Zeon Co., Ltd.; glass transition temperature 126°C) was dried at 100°C for 5 hours. The dried resin was supplied to an extruder and extruded in a sheet form from a T-die onto a casting drum through a polymer pipe and polymer filter. The extruded resin was cooled to obtain a long, unstretched resin film with a thickness of 100 μm. The obtained resin film was wound onto a roll and recovered.

[0203] (Stretching of resin film) The resin film was pulled from the roll and continuously fed into a longitudinal stretcher. The resin film was then uniaxially stretched in the longitudinal direction at a 90° angle to the width direction at a stretching temperature of 135°C and a stretching ratio of 1.35 times, to obtain a long resin film A. The phase difference of resin film A was Re 142 nm and Rth 73 nm.

[0204] (Formation of the anchor layer) An anchoring solution was prepared by mixing 100 parts by weight of acrylic emulsion (TOCRYL4402 from Toyo Chem Co., Ltd.), 30 parts by weight of oxazoline resin emulsion (Epocross KE2020E from Nippon Shokubai Co., Ltd.), and 700 parts by weight of water. The stretched resin film A was pulled from the roll, and the surface of this resin film A was subjected to a process of 80 W・min / m ２ After corona treatment, an anchoring solution was applied to a thickness of 0.5 μm and dried at 100°C for 2 minutes to form an anchoring layer on resin film A, thereby obtaining a substrate layer comprising resin film A made of a resin containing norbornene polymer and an anchoring layer.

[0205] (1-2. Formation of the Phase Difference Layer) A resin solution (liquid composition) was prepared by dissolving the copolymer 1 produced in polymerization example 1 in cyclopentanone at a concentration of 15% by weight. The resin solution was applied to the anchor layer of the base layer so that its thickness after drying was 10 μm, and dried at 120°C for 3 minutes to form a phase difference layer containing copolymer 1 on the base layer. This resulted in a multilayer phase difference film comprising a base layer and a phase difference layer directly provided on the anchor layer of the base layer. The obtained multilayer phase difference film was wound onto a roll and recovered.

[0206] The thickness d and thickness-direction retardation Rth of the phase difference layer contained in the obtained multilayer phase difference film were measured using the method described above. The film strength of the phase difference layer was also evaluated using the method described above.

[0207] <Examples 2-13, Comparative Examples 1-6> In (1-2), copolymer 1 was replaced with a copolymer or polymer from the polymerization examples listed in Table 1 or Table 2. Except for the operations described above, the procedure was the same as in Example 1 to form a phase difference layer on the substrate layer and obtain a multilayer phase difference film. The thickness d and thickness direction retardation Rth of the phase difference layer contained in the obtained multilayer phase difference film were measured by the method described above. The film strength of the phase difference layer was also evaluated by the method described above.

[0208] <Results> The results are shown in the table below. The abbreviations in the composition (molar ratio) column of the table have the following meanings: St: Styrene unit VB: 4-vinyl biphenyl unit iBu: Isobutene unit U1, U2, and U3: Compound 1 unit, Compound 2 unit, and Compound 3 unit Also, "Molecular weight (MN)" in the table means number average molecular weight. Rth / d = Rth / d (nm / μm) × 10 －３ That is the case.

[0209]

[0210]

[0211] *1 in Table 2: Indicates that the obtained phase difference layer was too brittle to be measured.

[0212] The copolymer according to the example can be produced in good yield under mild, short polymerization conditions and has a number-average molecular weight of 30,000 to 500,000. Furthermore, a phase difference layer with good strength and an Rth / d within the desired range can be formed from the copolymer according to the example by solution casting.

[0213] The copolymers in Comparative Examples 3, 4, and 5 had low molecular weights, and these copolymers could not form phase difference layers with good strength. The copolymers in the Comparative Examples could not form phase difference layers with Rth / d within the desired range by the solution casting method.

[0214] 100 Multilayer phase difference film 110 Phase difference layer 120 Substrate layer

Claims

1. A retardation layer in which Rth / d is not less than (-20.0×10 －３ ) and not more than (-3.5×10 －３ ), where Rth represents the retardation in the thickness direction of the retardation layer and d represents the thickness of the retardation layer, the retardation layer containing a copolymer (P1) containing a structural unit represented by the following formula (1) and a structural unit represented by the following formula (2). (In formula (1), R ｐ represents an electron-donating substituent or a cyano group, R ｑ represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, and R ｒ represents a hydrogen atom or a substituent.) (In formula (2), R ｘ and R ｙ each independently represent a hydrogen atom or a methyl group, and R １ , R ２ , R ３ , R ４ , R ５ , R ６ , and R ７ each independently represent a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, a phenyl group, a cyano group, a nitro group, -OR １０ , -C(=O)-R １０ , or -O-C(=O)-R １０ , where R １０ represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms.) 2. The phase difference layer according to claim 1, wherein the copolymer (P1) further comprises a structural unit represented by the following formula (3). (In formula (3), R ｓ and R ｔ Each of these independently represents a hydrogen atom or a methyl group, and R ａ , R ｂ , R ｃ , R ｄ , and R ｅ These are, independently, a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, a phenyl group, a cyano group, a nitro group, and -OR. ２０ , -C(=O)-R ２０ , or -O-C(=O)-R ２０ This represents, and here, R ２０ (This represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms.) 3. The phase difference layer according to claim 1, wherein the copolymer (P1) contains 20 mol% to 95 mol% of the structural units represented by formula (2), with the total amount of structural units represented by formula (1) and structural units represented by formula (2) contained in the copolymer (P1) being 100 mol%.

4. The phase difference layer according to claim 1, wherein the copolymer (P1) has a number-average molecular weight in terms of polystyrene, measured by gel permeation chromatography, of 30,000 or more and 500,000 or less.

5. A multilayer phase difference film comprising a phase difference layer according to claim 1 and a substrate layer, wherein the phase difference layer is provided directly on the substrate layer.

6. The multilayer phase difference film according to claim 5, wherein the base layer comprises a cyclic olefin polymer.

7. A method for manufacturing a multilayer phase difference film according to claim 5, comprising the steps of: preparing the base layer; and applying a liquid composition containing the copolymer (P1) and a solvent onto the base layer.

8. A copolymer comprising a structural unit represented by the following formula (1-1) or a structural unit represented by the following formula (1-2), or a structural unit represented by the following formula (1-1) and a structural unit represented by the following formula (1-2), and a structural unit represented by the following formula (2). (In formula (1-1), R ｐ (This represents a biphenylyl group which may have substituents.) (In formula (1-2), R ｐ (This represents a phenyl group which may have substituents.) (In formula (2), R ｘ and R ｙ Each of these independently represents a hydrogen atom or a methyl group, and R １ , R ２ , R ３ , R ４ , R ５ , R ６ , and R ７ These are, independently, a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, a phenyl group, a cyano group, a nitro group, and -OR. １０ , -C(=O)-R １０ , or -O-C(=O)-R １０ This represents, and here, R １０ (This represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms.) 9. The copolymer according to claim 8, further comprising a structural unit represented by the following formula (3). (In formula (3), R ｓ and R ｔ Each of these independently represents a hydrogen atom or a methyl group, and R ａ , R ｂ , R ｃ , R ｄ , and R ｅ These are, independently, a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, a phenyl group, a cyano group, a nitro group, and -OR. ２０ , -C(=O)-R ２０ , or -O-C(=O)-R ２０ This represents, and here, R ２０ (This represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms.) 10. The copolymer according to claim 8, comprising a structural unit represented by formula (1-1).

11. The copolymer according to claim 8, wherein the total of the structural units represented by formula (1-1), the structural units represented by formula (1-2), and the structural units represented by formula (2) is 100 mol%, and the copolymer contains 20 mol% to 95 mol% of the structural units represented by formula (2).

12. The copolymer according to claim 8, wherein the number-average molecular weight in terms of polystyrene, as measured by gel permeation chromatography, is 30,000 or more and 500,000 or less.

13. When a layer formation test is performed in which a solution containing only the copolymer and a solvent for dissolving the copolymer is applied and dried to form a copolymer layer containing the copolymer, the copolymer layer satisfies nz > nx ≈ ny, where nx represents the refractive index in the in-plane direction of the copolymer layer that gives the maximum refractive index, ny represents the refractive index in the in-plane direction of the copolymer layer that is perpendicular to the direction of nx, and nz represents the refractive index in the thickness direction of the copolymer layer, the copolymer according to claim 8.

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