Method for producing birefringent film, and birefringent film

Abstract

A method for producing a birefringent film, the method comprising: a step (II) for bringing a resin film containing a crystalline polymer having positive intrinsic birefringence into contact with a mixed solvent containing a first solvent compound and a second solvent compound; and a step (III) for drying the resin film brought into contact with the mixed solvent, wherein the first solvent compound is a cyclic hydrocarbon optionally having a substituent, the second solvent compound is an aliphatic alcohol having an alkyl group having at least four carbon atoms, an aliphatic ketone having an alkyl group having at least four carbon atoms, an alkyl ester that has at least four carbon atoms and that is derived from an aliphatic carboxylic acid, or an alicyclic ketone.

Description

Method for manufacturing birefringent film and birefringent film

[0001] The present invention relates to a method for producing a birefringent film and a birefringent film.

[0002] A birefringent film having an NZ coefficient of less than 1.0 can be combined with a display device such as a liquid crystal display device to improve the display quality of the display device, such as the viewing angle, contrast, and image quality. It is known that such a birefringent film having an NZ coefficient of less than 1.0 can be produced by a production method including a step of contacting a predetermined resin film with an organic solvent (see, for example, Patent Documents 1 and 2). Also, a film production method is known that includes a step of contacting a resin film with a mixed solvent containing two solvents in a specific relationship (see, for example, Patent Document 3).

[0003] International Publication No. 2021 / 020023 Japanese Patent Application Laid-Open No. 2022-103573 International Publication No. 2022 / 145238

[0004] A birefringent film having an NZ coefficient of less than 1.0 and a thickness direction retardation Rth of greater than -400 nm can be made into a three-dimensional retardation film either directly or after a simple operation such as uniaxial stretching. Furthermore, a birefringent film is required to have a good appearance as an optical film. However, the techniques of Patent Documents 1 to 3 sometimes fail to produce a birefringent film having all of these optical properties.

[0005] Therefore, there is a need for a method for producing a birefringent film having an NZ coefficient of less than 1.0 and a thickness direction retardation Rth of greater than −400 nm, and having a good appearance; and a novel birefringent film having an NZ coefficient of less than 1.0 and a thickness direction retardation Rth of greater than −400 nm, and having a good appearance.

[0006] The present inventors have conducted extensive research to solve the above-mentioned problems, and as a result have found that the above-mentioned problems can be solved by a production method including a step of contacting a resin film containing a polymer having specific crystallinity with a mixed solvent containing a combination of specific solvent compounds, and have thus completed the present invention.

[0007] <1> A method for producing a birefringent film, comprising: a step (II) of contacting a resin film containing a polymer having positive intrinsic birefringence and crystallinity with a mixed solvent containing a first solvent compound and a second solvent compound; and a step (III) of drying the resin film that has been contacted with the mixed solvent, wherein the first solvent compound is a cyclic hydrocarbon that may have a substituent, and the second solvent compound is an aliphatic alcohol having an alkyl group with 4 or more carbon atoms, an aliphatic ketone having an alkyl group with 4 or more carbon atoms, an alkyl ester of an aliphatic carboxylic acid having 4 or more carbon atoms, or an alicyclic ketone. <2> The method for producing a birefringent film according to <1>, wherein the first solvent compound is a monocyclic or bicyclic aromatic hydrocarbon which may have a substituent; or a monocyclic or bicyclic alicyclic hydrocarbon which may have a substituent, and the second solvent compound is an aliphatic primary alcohol having an alkyl group having 4 to 10 carbon atoms; an aliphatic ketone having an alkyl group having 4 to 10 carbon atoms and a methyl group; an alkyl ester of an aliphatic carboxylic acid having 2 to 5 carbon atoms having 4 to 10 carbon atoms; or an alicyclic ketone having a 5- or 6-membered carbon ring. <3> The method for producing a birefringent film according to <1> or <2>, wherein in the step (II), the resin film is brought into contact with the mixed solvent for 10 seconds or less. <4> The method for producing a birefringent film according to any one of <1> to <3>, comprising, before the step (II), a step (I) of melt-extruding a resin containing the polymer having positive intrinsic birefringence and crystallinity to obtain the resin film. <5> The method for producing a birefringent film according to any one of <1> to <4>, comprising, after the step (III), a step (IV) of stretching the dried resin film, and a step (V) of heating the stretched resin film to crystallize the crystalline polymer, in this order. <6> The method for producing a birefringent film according to any one of <1> to <5>, wherein the crystalline polymer is a polymer containing an alicyclic structure.<7> A birefringent film comprising a polymer having positive intrinsic birefringence and crystallinity, having an NZ coefficient NZ of less than 1.0, and a thickness direction retardation Rth of greater than −150 nm, wherein the total content of a first solvent compound and a second solvent compound is 0.01% by weight or more and 10.00% by weight or less, the first solvent compound is a cyclic hydrocarbon which may have a substituent, and the second solvent compound is an aliphatic alcohol having an alkyl group with 4 or more carbon atoms, an aliphatic ketone having an alkyl group with 4 or more carbon atoms, an alkyl ester of an aliphatic carboxylic acid having 4 or more carbon atoms, or an alicyclic ketone. <8> The birefringent film according to <7>, wherein the first solvent compound is an unsaturated alicyclic hydrocarbon which may have a substituent. <9> The birefringent film according to <7> or <8>, wherein the NZ coefficient NZ is greater than 0.0. <10> The birefringent film according to <7> or <8>, wherein the NZ coefficient NZ is 0.0 or less. <11> The birefringent film according to any one of <7> to <10>, wherein the thickness direction retardation Rth is 0 nm or less. <12> The birefringent film according to any one of <7> to <11>, wherein the birefringent film is an unstretched film. <13> The birefringent film according to any one of <7> to <12>, wherein the crystalline polymer is a polymer containing an alicyclic structure.

[0008] According to the present invention, there can be provided a method for producing a birefringent film having an NZ coefficient of less than 1.0 and a thickness direction retardation Rth of greater than −400 nm, and having a good appearance; and a novel birefringent film having an NZ coefficient of less than 1.0 and a thickness direction retardation Rth of greater than −400 nm, and having a good appearance.

[0009] 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 implemented with any modifications within the scope of the claims of the present invention and their equivalents. The components of the embodiments shown below can be combined as appropriate.

[0010] <1. Explanation of Terms> In the following explanation, a "long" film refers to a film having a length that is 5 times or more its width, preferably 10 times or more its width, and specifically refers to a film having a length that can be wound into a roll for storage or transportation. There is no particular upper limit to the length of the film, and it can be, for example, 100,000 times or less its width.

[0011] In the following description, unless otherwise specified, the slow axis of a film or layer refers to the slow axis in the plane of the film or layer.

[0012] In the following description, unless otherwise specified, the terms "plate" and "board" are not limited to rigid members, but also include flexible members such as resin films.

[0013] In the following description, unless otherwise specified, the tilt direction of a film means a direction that is neither parallel nor perpendicular to the main surface of the film, and specifically refers to a direction in which the polar angle of the main surface is in the range of greater than 0° and less than 90°.

[0014] In the following description, unless otherwise specified, a material with positive intrinsic birefringence (e.g., polymer, resin) means a material whose refractive index in the stretching direction is greater than that in the direction perpendicular to the stretching direction. Furthermore, a material with negative intrinsic birefringence means a material whose refractive index in the stretching direction is smaller than that in the direction perpendicular to the stretching direction. The value of intrinsic birefringence can be calculated from the dielectric constant distribution.

[0015] In the following description, the in-plane retardation Re of a layer is a value expressed by Re = (nx - ny) x d unless otherwise specified. Furthermore, the retardation Rth in the thickness direction of a layer is a value expressed by Rth = [{(nx + ny) / 2} - nz] x d unless otherwise specified. Furthermore, the NZ coefficient NZ of a layer is a value expressed by NZ = (nx - nz) / (nx - ny) unless otherwise specified, and is calculated by NZ = Rth / Re + 0.5. Here, nx represents the refractive index in the direction perpendicular to the thickness direction of the layer (in-plane direction) and giving the maximum refractive index. ny represents the refractive index in the in-plane direction of the layer and perpendicular to the nx direction. nz represents the refractive index in the thickness direction of the layer. d represents the thickness of the layer. The measurement wavelength is 590 nm unless otherwise specified.

[0016] In the following description, unless otherwise specified, the directions of elements as "parallel," "vertical," and "orthogonal" may include an error within a range that does not impair the effects of the present invention, for example, within a range of ±3°, ±2°, or ±1°.

[0017] Unless otherwise specified, a "substituent" refers to an atom or atomic group that replaces a hydrogen atom in a compound or group, and includes a halogen atom. Unless otherwise specified, a "substituent" is typically monovalent. Examples of monovalent substituents include a halogen atom, an alkyl group, an alkenyl group, and an alkyloxy group. The term "optionally substituted" encompasses both cases where the compound or group has no substituent and cases where the compound or group has a substituent, unless otherwise specified. The term "substituted" encompasses cases where one or more hydrogen atoms in the compound or group are substituted with a substituent, and includes both cases where some (e.g., one, two, or three) of the hydrogen atoms in the compound or group are substituted with a substituent, and cases where all of the hydrogen atoms are substituted with a substituent. Examples of "halogen atoms" include fluorine atoms, chlorine atoms, bromine atoms, and iodine atoms, with fluorine atoms and chlorine atoms being preferred, and chlorine atoms being more preferred. An "alkyl group" may be either branched or linear, unless otherwise specified. The number of carbon atoms in the alkyl group is preferably 1 to 20, more preferably 1 to 15, and even more preferably 1 to 10. Specific examples of the "alkyl group" include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, a 1,1-dimethylethyl group (tert-butyl group), a 1-methylpropyl group (sec-butyl group), a 2-methylpropyl group (isobutyl group), an n-pentyl group, a 1-methylbutyl group, a 2-methylbutyl group, a 3-methylbutyl group, a 1,1-dimethylpropyl group, a 2,2-dimethylpropyl group, an n-hexyl group, a 1-methylpentyl group, a 2-methylpentyl group, a 3-methylpentyl group, a 4-methylpentyl group, a 2-ethylbutyl group, an n-heptyl group, an n-octyl group, an n-nonyl group, an n-decyl group, a 3,7-dimethyloctyl group, an n-dodecyl group, and an n-icosyl group.

[0018] Unless otherwise specified, the "alkenyl group" may be either branched or linear. The number of carbon atoms in the alkenyl group is preferably 2 to 20, more preferably 2 to 15, even more preferably 2 to 10, and still more preferably 2 to 5. Specific examples of the "alkenyl group" include a vinyl group, an allyl group, a 1-propenyl group, and a 1-methyl-1-ethenyl group.

[0019] Unless otherwise specified, the alkyl group of the "alkyloxy group" may be either branched or linear. The number of carbon atoms in the alkyl group of the alkyloxy group is preferably 1 to 20, more preferably 1 to 15, even more preferably 1 to 10, and still more preferably 1 to 5. Specific examples of the "alkyloxy group" include a methoxy group, an ethoxy group, a propyloxy group, an isopropyloxy group, a butoxy group, a 1,1-dimethylethyloxy group, a 1-methylpropyloxy group, a 2-methylpropyloxy group, a pentyloxy group, a 1-methylbutyloxy group, a 2-methylbutyloxy group, a 3-methylbutyloxy group, a 1,1-dimethylpropyloxy group, a 2,2-dimethylpropyloxy group, a hexyloxy group, a 1-methylpentyloxy group, a 2-methylpentyloxy group, a 3-methylpentyloxy group, a 4-methylpentyloxy group, a 2-ethylbutyloxy group, a heptyloxy group, an octyloxy group, a nonyloxy group, a decyloxy group, a 3,7-dimethyloctyloxy group, a dodecyloxy group, and an icosyloxy group.

[0020] Unless otherwise specified, a "monovalent aliphatic hydrocarbon group" may be either branched or linear. Monovalent aliphatic hydrocarbon groups include methyl groups. The number of carbon atoms in the monovalent aliphatic hydrocarbon group is preferably 1 to 20, more preferably 1 to 15, even more preferably 1 to 10, and even more preferably 1 to 5. Unless otherwise specified, the monovalent aliphatic hydrocarbon group may be an alkyl group, an alkenyl group, or an alkynyl group, preferably an alkyl group or an alkenyl group, and more preferably an alkyl group. Specific examples of the alkyl group and alkenyl group, which are monovalent aliphatic hydrocarbon groups, include the examples described above.

[0021] When stereoisomerism exists in a solvate, the term "solvate" encompasses both single stereoisomers and mixtures of stereoisomers unless otherwise specified. For example, "decalin" encompasses "cis-decalin," "trans-decalin," and "a mixture of cis-decalin and trans-decalin." Furthermore, when a solvate is a cyclic hydrocarbon having a substituent, unless otherwise specified, a solvate without restrictions on the substitution position of the substituent encompasses cyclic hydrocarbons substituted at any substitution position and mixtures thereof. For example, "xylene" encompasses "o-xylene," "m-xylene," "p-xylene," and mixtures of two or more of these.

[0022] 2. Method for Producing Birefringent Film 2.1. Overview of Method for Producing Birefringent Film A method for producing a birefringent film according to one embodiment of the present invention comprises: a step (II) of contacting a resin film containing a polymer having positive intrinsic birefringence and crystallinity with a mixed solvent containing a first solvent compound and a second solvent compound; and a step (III) of drying the resin film that has been contacted with the mixed solvent. Steps (II) and (III) are typically performed in this order. Here, the first solvent compound is a cyclic hydrocarbon that may have a substituent, and the second solvent compound is an aliphatic alcohol having an alkyl group with 4 or more carbon atoms, an aliphatic ketone having an alkyl group with 4 or more carbon atoms, an alkyl ester of an aliphatic carboxylic acid having 4 or more carbon atoms, or an alicyclic ketone.

[0023] According to the manufacturing method of this embodiment, it is possible to manufacture a birefringent film that has a good appearance, Rth greater than −400 nm, and an NZ coefficient NZ less than 1. The birefringent film will be described in detail later.

[0024] The method for producing a birefringent film may include optional steps in addition to the steps (II) and (III). Examples of the optional steps include the following steps (I), (IV), and (V). Step (I): A step of forming a film of the resin containing the polymer having positive intrinsic birefringence and crystallinity by melt extrusion to obtain the resin film. Step (IV): A step of stretching the dried resin film. Step (V): A step of heating the stretched resin film to crystallize the crystalline polymer. Step (I) is usually performed before step (II). Steps (IV) and (V) are usually performed after step (III), and are usually performed in the order of steps (IV) and (V).

[0025] 2.2. Step (II) In step (II), a resin film containing a polymer having positive intrinsic birefringence and crystallinity is brought into contact with a mixed solvent containing a first solvent compound and a second solvent compound.

[0026] <Polymers that can be contained in the resin film> The resin film contains a polymer that has positive intrinsic birefringence and crystallinity, and any optional components that can be contained as needed. A "polymer that has crystallinity" refers to a polymer that has a melting point Tm. That is, a "polymer that has crystallinity" refers to a polymer whose melting point can be observed with a differential scanning calorimeter (DSC). In the following description, a polymer that has crystallinity may be referred to as a "crystalline polymer." A resin that contains a crystalline polymer as a main component may exhibit properties based on the crystalline polymer. Such a resin may be referred to as a crystalline resin. The crystalline resin is preferably a thermoplastic resin.

[0027] The crystalline polymer contained in the resin film has positive intrinsic birefringence. By using a polymer that is crystalline and has positive intrinsic birefringence, a birefringent film having an NZ coefficient NZ of less than 1.0 can be easily produced.

[0028] The crystalline polymer may be, for example, polyesters such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN); polyolefins such as polyethylene (PE) and polypropylene (PP); etc., and is not particularly limited, but preferably contains an alicyclic structure. By using a crystalline polymer containing an alicyclic structure, the mechanical properties, heat resistance, transparency, low moisture absorption, dimensional stability, and light weight of the film can be improved. A polymer containing an alicyclic structure refers to a polymer having an alicyclic structure in the molecule. Such a polymer containing an alicyclic structure may be, for example, a polymer obtainable by polymerization using a cyclic olefin as a monomer, or a hydrogenated product thereof.

[0029] Examples of alicyclic structures include cycloalkane structures and cycloalkene structures. Among these, cycloalkane structures are preferred because they are more likely to produce birefringent films with excellent properties such as thermal stability. The number of carbon atoms contained in one alicyclic structure is preferably 4 or more, more preferably 5 or more, and preferably 30 or less, more preferably 20 or less, and particularly preferably 15 or less. When the number of carbon atoms contained in one alicyclic structure is within the above range, mechanical strength, heat resistance, and moldability are highly balanced.

[0030] In a crystalline polymer containing an alicyclic structure, the ratio of structural units having an alicyclic structure to all structural units is preferably 30% by weight or more, more preferably 50% by weight or more, and particularly preferably 70% by weight or more. By increasing the ratio of structural units having an alicyclic structure as described above, heat resistance can be improved. The ratio of structural units having an alicyclic structure to all structural units can be 100% by weight or less. Furthermore, in a crystalline polymer containing an alicyclic structure, the remainder other than the structural units having an alicyclic structure is not particularly limited and can be appropriately selected depending on the purpose of use.

[0031] Examples of crystalline polymers containing an alicyclic structure include polymers (α) to (δ) below. Among these, polymer (β) is preferred because it is easy to obtain a birefringent film with excellent heat resistance. Polymer (α): A ring-opening polymer of a cyclic olefin monomer, which has crystallinity. Polymer (β): A hydrogenated product of polymer (α), which has crystallinity. Polymer (γ): An addition polymer of a cyclic olefin monomer, which has crystallinity. Polymer (δ): A hydrogenated product of polymer (γ), which has crystallinity.

[0032] Specifically, as the crystalline polymer containing an alicyclic structure, a crystalline ring-opening polymer of dicyclopentadiene and a crystalline hydrogenated ring-opening polymer of dicyclopentadiene are more preferred. Among them, a crystalline hydrogenated ring-opening polymer of dicyclopentadiene is particularly preferred. Here, the ring-opening polymer of dicyclopentadiene refers to a polymer in which the ratio of dicyclopentadiene-derived structural units to all structural units is usually 50% by weight or more, preferably 70% by weight or more, more preferably 90% by weight or more, and even more preferably 100% by weight.

[0033] The hydrogenated product of the ring-opening polymer of dicyclopentadiene preferably has a high ratio of racemo dyads. Specifically, the ratio of racemo dyads in the repeating units of the hydrogenated product of the ring-opening polymer of dicyclopentadiene is preferably 51% or more, more preferably 70% or more, and particularly preferably 85% or more. A high ratio of racemo dyads indicates high syndiotactic stereoregularity. Therefore, the higher the ratio of racemo dyads, the higher the melting point of the hydrogenated product of the ring-opening polymer of dicyclopentadiene tends to be. The ratio of racemo dyads can be determined by the method described in the Examples below. １３ It can be determined based on C-NMR spectrum analysis.

[0034] As the polymers (α) to (δ), polymers obtained by the production method disclosed in WO 2018 / 062067 can be used.

[0035] The melting point Tm of the crystalline polymer is preferably 200° C. or higher, more preferably 230° C. or higher, and preferably 290° C. or lower. By using a crystalline polymer having such a melting point Tm, a birefringent film having an even better balance between formability and heat resistance can be obtained.

[0036] Generally, a crystalline polymer has a glass transition temperature TgP, which is generally 85°C or higher and generally 170°C or lower.

[0037] The glass transition temperature (TgP) and melting point (Tm) of a polymer can be measured by the following method: First, the polymer is melted by heating, and the melted polymer is rapidly cooled with dry ice. Then, using this polymer as a test sample, the glass transition temperature (TgP) and melting point (Tm) of the polymer can be measured using a differential scanning calorimeter (DSC) at a heating rate of 10°C / min (heating mode).

[0038] The weight-average molecular weight (Mw) of the crystalline polymer is preferably 1,000 or more, more preferably 2,000 or more, and preferably 1,000,000 or less, more preferably 500,000 or less. A crystalline polymer having such a weight-average molecular weight has an excellent balance between moldability and heat resistance.

[0039] The molecular weight distribution (Mw / Mn) of the crystalline polymer is preferably 1.0 or more, more preferably 1.5 or more, and preferably 4.0 or less, more preferably 3.5 or less. Here, Mn represents the number average molecular weight. A crystalline polymer having such a molecular weight distribution has excellent moldability.

[0040] The weight average molecular weight (Mw) and molecular weight distribution (Mw / Mn) of the polymer can be measured as polystyrene equivalent values ​​by gel permeation chromatography (GPC) using tetrahydrofuran as a developing solvent.

[0041] The crystalline polymer may be used alone or in combination of two or more kinds in any ratio.

[0042] The proportion of the crystalline polymer contained in the resin film is preferably 50% by weight or more, more preferably 70% by weight or more, and particularly preferably 90% by weight or more. When the proportion of the crystalline polymer is equal to or greater than the lower limit, the birefringence development and heat resistance of the film can be improved. The upper limit of the proportion of the crystalline polymer is usually 100.0% by weight or less, and can be 99.99% by weight or less.

[0043] The crystalline polymer contained in the resin film preferably has a low degree of crystallinity. The crystallinity of the crystalline polymer contained in the resin film used in step (II) is preferably less than 10%, more preferably less than 5%, and particularly preferably less than 3%. If the crystallinity of the resin film before contacting with the mixed solvent in step (II) is low, many crystalline polymer molecules can be oriented in the thickness direction by contact with the mixed solvent, making it possible to adjust the NZ coefficient of the birefringent film over a wide range. The degree of crystallinity can be measured by X-ray diffraction.

[0044] <Optional Components> The resin film in the production method of this embodiment may contain optional components in addition to the crystalline polymer. Examples of the optional components include antioxidants such as phenol-based antioxidants, phosphorus-based antioxidants, and sulfur-based antioxidants; light stabilizers such as hindered amine-based light stabilizers; waxes such as petroleum waxes, Fischer-Tropsch waxes, and polyalkylene waxes; nucleating agents such as sorbitol-based compounds, metal salts of organic phosphoric acids, metal salts of organic carboxylic acids, kaolin, and talc; diaminostilbene derivatives, coumarin derivatives, and azole-based derivatives (e.g., benzoxazole derivatives, benzotriazole derivatives, and benzimidazoline derivatives); Examples of the optional component include fluorescent brighteners such as benzothiazole derivatives and benzothiazole derivatives), carbazole derivatives, pyridine derivatives, naphthalic acid derivatives, and imidazolone derivatives; ultraviolet absorbers such as benzophenone-based ultraviolet absorbers, salicylic acid-based ultraviolet absorbers, and benzotriazole-based ultraviolet absorbers; inorganic fillers such as talc, silica, calcium carbonate, and glass fiber; colorants; flame retardants; flame retardant assistants; antistatic agents; plasticizers; near-infrared absorbers; lubricants; fillers; and any polymer other than crystalline polymers, such as soft polymers. One type of optional component may be used alone, or two or more types may be used in combination in any ratio.

[0045] The resin film used in step (II) before contacting with the mixed solvent preferably has a small content of organic solvent, and more preferably does not contain any organic solvent. The weight ratio (solvent content) of the organic solvent contained in the resin film relative to 100% by weight of the resin film is preferably 1% by weight or less, more preferably 0.5% by weight or less, particularly preferably 0.1% by weight or less, and ideally 0.0% by weight. Since the amount of organic solvent contained in the resin film before contacting with the organic solvent is small, many crystalline polymer molecules can be oriented in the thickness direction upon contact with the mixed solvent, making it possible to adjust the NZ coefficient over a wide range. The solvent content of the resin film can be measured by density.

[0046] The thickness of the resin film used in step (II) is preferably set according to the thickness of the birefringent film to be produced. Usually, the thickness increases by contacting with the mixed solvent in step (II). On the other hand, when stretching is performed in step (IV), the thickness decreases due to the stretching. Therefore, the thickness of the resin film may be set taking into consideration the change in thickness in the steps after step (II) as described above.

[0047] The resin film may be a sheet film, but is preferably a long film. By using a long resin film, the birefringent film can be continuously produced by a roll-to-roll method, and therefore the productivity of the birefringent film can be effectively improved.

[0048] As a method for producing a resin film, resin molding methods such as injection molding, melt extrusion molding, press molding, inflation molding, blow molding, calendar molding, cast molding, and compression molding are preferred because they can produce a resin film that does not contain an organic solvent. Among these, melt extrusion molding is preferred because it is easy to control the thickness.

[0049] <Solvent Compound> In step (II), the resin film is brought into contact with a mixed solvent containing the first solvent compound and the second solvent compound.

[0050] <First Solvent Compound> The first solvent compound is a cyclic hydrocarbon which may have a substituent. The first solvent compound may be contained in the mixed solvent alone or in a combination of two or more types.

[0051] "Cyclic hydrocarbons" are hydrocarbons having a cyclic structure, and unless otherwise specified, include alicyclic hydrocarbons, aromatic hydrocarbons, and hydrocarbons in which aromatic hydrocarbons and alicyclic hydrocarbons are fused. "Cyclic hydrocarbons" may be monocyclic containing only one ring, or polycyclic containing two or more rings. When a cyclic hydrocarbon contains two or more rings, they may be fused rings, spiro rings, bridged rings, or may form a ring assembly, and are preferably fused rings. The number of carbon atoms in a "cyclic hydrocarbon," not including the number of carbon atoms in substituents, is preferably 3 or more, more preferably 4 or more, even more preferably 5 or more, and preferably 20 or less, more preferably 12 or less, and even more preferably 10 or less. "Alicyclic hydrocarbons" include both saturated alicyclic hydrocarbons and unsaturated alicyclic hydrocarbons, unless otherwise specified. The unsaturated bond in an unsaturated alicyclic hydrocarbon may be a double bond or a triple bond, and is preferably a double bond. The unsaturated alicyclic hydrocarbon may have only one unsaturated bond, or may have two or more (e.g., two or three) unsaturated bonds. Specific examples of "alicyclic hydrocarbons" include cyclopentane, cyclohexane, cycloheptane, decalin, and cyclohexene, preferably cyclohexane, decalin, and cyclohexene, more preferably cyclohexene. Specific examples of "aromatic hydrocarbons" include benzene and naphthalene, preferably benzene, more preferably benzene having a substituent. Specific examples of hydrocarbons in which an alicyclic hydrocarbon and an aromatic hydrocarbon are condensed include tetralin.

[0052] The cyclic hydrocarbon may or may not have a substituent. When the cyclic hydrocarbon has multiple substituents, the multiple substituents may be the same or different from each other.

[0053] Examples of the substituent that the cyclic hydrocarbon may have include a halogen atom, an alkyl group, an alkenyl group, and an alkyloxy group, and preferred are a halogen atom, an alkyl group, and an alkenyl group.

[0054] Examples of cyclic hydrocarbons which may have a substituent include cyclohexane which may have a substituent, cyclohexene which may have a substituent, decalin which may have a substituent, benzene, and benzene which has a substituent (substituted benzene).

[0055] Examples of the substituent that cyclohexane may have include alkyl groups, preferably alkyl groups having 1 to 5 carbon atoms, more preferably ethyl groups or methyl groups.

[0056] Examples of substituents that cyclohexene may have include one or more selected from the group consisting of alkyl groups and alkenyl groups, preferably one or more selected from the group consisting of alkyl groups having 1 to 5 carbon atoms and alkenyl groups having 1 to 5 carbon atoms, more preferably one or more selected from the group consisting of alkyl groups having 1 to 3 carbon atoms and alkenyl groups having 1 to 3 carbon atoms, and even more preferably a methyl group and a 1-methylethenyl group.

[0057] Examples of substituents that benzene may have include one or more selected from the group consisting of a halogen atom, an alkyl group, and an alkyloxy group, preferably one or more selected from the group consisting of a halogen atom and an alkyl group, more preferably one or more selected from the group consisting of a chlorine atom and an alkyl group having 1 to 5 carbon atoms, even more preferably an alkyl group having 1 to 3 carbon atoms, and even more preferably a methyl group.

[0058] Preferably, the first solvent compound is an optionally substituted monocyclic aromatic hydrocarbon, an optionally substituted bicyclic aromatic hydrocarbon, an optionally substituted monocyclic alicyclic hydrocarbon, or an optionally substituted bicyclic alicyclic hydrocarbon.

[0059] Further specific examples of the cyclic hydrocarbon which may have a substituent include cyclohexane, methylcyclohexane, ethylcyclohexane, pinene, limonene (preferably d-limonene), decalin, toluene, and chlorobenzene, of which cyclohexane and limonene (preferably d-limonene) are preferred, limonene is more preferred, and d-limonene is even more preferred.

[0060] In one embodiment, from the viewpoints of being able to shorten the contact time of the resin film with the mixed solvent, efficiently reducing the retardation Rth in the thickness direction of the resin film, and improving the appearance of the birefringent film, the first solvent compound is preferably an unsaturated alicyclic hydrocarbon which may have a substituent; more preferably an unsaturated monocyclic alicyclic hydrocarbon which may have a substituent; even more preferably cyclohexene which may have a substituent; and particularly preferably limonene (preferably d-limonene). Limonene is particularly preferred because of its excellent workability and low environmental impact.

[0061] <Second Solvent Compound> The second solvent compound is an aliphatic alcohol having an alkyl group of 4 or more carbon atoms, an aliphatic ketone having an alkyl group of 4 or more carbon atoms, an alkyl ester of an aliphatic carboxylic acid having 4 or more carbon atoms, or an alicyclic ketone. Hereinafter, an aliphatic alcohol having an alkyl group of 4 or more carbon atoms as the second solvent compound will also be referred to as a specific aliphatic alcohol, an aliphatic ketone having an alkyl group of 4 or more carbon atoms as the second solvent compound will also be referred to as a specific aliphatic ketone, and an alkyl ester of an aliphatic carboxylic acid having 4 or more carbon atoms as the second solvent compound will also be referred to as a specific alkyl ester. The second solvent compound may be contained in the mixed solvent alone or in a combination of two or more types.

[0062] (Specific aliphatic alcohol) The specific aliphatic alcohol is a compound in which one or more hydrogen atoms of an aliphatic hydrocarbon are substituted with an alcoholic hydroxy group, and is preferably an aliphatic monool in which one hydrogen atom of an aliphatic hydrocarbon is substituted with a hydroxy group, and more preferably an aliphatic primary monool.

[0063] As described above, the specific aliphatic alcohol has an alkyl group having 4 or more carbon atoms. That is, the specific aliphatic alcohol has an alkyl group having 4 or more carbon atoms bonded to an alcoholic hydroxy group. Hereinafter, an alkyl group having 4 or more carbon atoms will be referred to as C （４－） Also called an alkyl group.

[0064] C of specific aliphatic alcohol （４－）The number of carbon atoms in the alkyl group is preferably 10 or less, more preferably 8 or less, even more preferably 6 or less, still more preferably 5 or less, preferably 4 to 10, more preferably 4 to 8, even more preferably 4 to 6, and still more preferably 4 or 5.

[0065] When the specific aliphatic alcohol is a secondary or tertiary alcohol, preferably the specific aliphatic alcohol is C （４－） In addition to the alkyl group, it preferably has a monovalent aliphatic hydrocarbon group, which is bonded to the carbon atom to which the alcoholic hydroxy group is bonded.

[0066] When the specific aliphatic alcohol is a secondary or tertiary alcohol, the number of carbon atoms in the monovalent aliphatic hydrocarbon group that is preferably contained therein is preferably 1 to 10, more preferably 1 to 5, and even more preferably 1 to 4. Examples of the monovalent aliphatic hydrocarbon group include an alkyl group or an alkenyl group, and an alkyl group is preferred.

[0067] Specific examples of the specific aliphatic alcohol include 1-butanol, isobutyl alcohol, tert-butyl alcohol, 1-pentanol, 3-methyl-1-butanol, 1-hexanol, 1-heptanol, 1-octanol, and 2,6-dimethyl-4-heptanol, and isobutyl alcohol is preferred.

[0068] (Specific aliphatic ketone) The specific aliphatic ketone has a carbonyl group having C （４－） It is a compound in which an alkyl group and a monovalent aliphatic hydrocarbon group are directly bonded. （４－）The number of carbon atoms in the alkyl group is preferably 10 or less, more preferably 8 or less, even more preferably 5 or less, preferably 4 to 10, more preferably 4 to 8, even more preferably 4 to 6, and even more preferably 4 or 5. The number of carbon atoms in the monovalent aliphatic hydrocarbon group contained in the specific aliphatic ketone is preferably 1 to 10, more preferably 1 to 5, and even more preferably 1 to 4. The monovalent aliphatic hydrocarbon group is preferably an alkyl group or an alkenyl group, and more preferably an alkyl group. The C （４－） The alkyl group is preferably an n-butyl group or an isobutyl group, and more preferably an isobutyl group. The monovalent aliphatic hydrocarbon group contained in the specific aliphatic ketone is preferably a methyl group. A specific example of the specific aliphatic ketone is methyl isobutyl ketone, and preferably methyl isobutyl ketone.

[0069] (Specific alkyl ester) The specific alkyl ester is a C alkyl ester of an aliphatic carboxylic acid. （４－） alkyl ester, R １ -(C=O)-OR ２ where R １ represents a monovalent aliphatic hydrocarbon group, preferably an alkyl group or an alkenyl group, more preferably an alkyl group. ２ is C （４－） represents an alkyl group. １ The number of carbon atoms in the aliphatic carboxylic acid residue represented by "-(C=O)-O-" is usually 2 or more, preferably 5 or less, more preferably 4 or less, even more preferably 3 or less, preferably 2 to 5, more preferably 2 to 4, and even more preferably 2 or 3. （４－） The number of carbon atoms in the alkyl group is preferably 10 or less, more preferably 8 or less, even more preferably 5 or less, preferably 4 to 10, more preferably 4 to 8, even more preferably 4 to 6, and even more preferably 4 or 5. １ The aliphatic carboxylic acid residue represented by "-(C=O)-O-" is preferably an acetic acid residue (i.e., R １is a methyl group), or a propanoic acid residue (i.e., R １ is an ethyl group), and more preferably an acetic acid residue. ２ C represented by （４－） The alkyl group is preferably an n-butyl group, a 1-methylpropyl group, or an isobutyl group, and more preferably an n-butyl group.

[0070] Specific examples of the specific alkyl ester include butyl acetate, 1-methylpropyl acetate, and isobutyl acetate, with butyl acetate being preferred.

[0071] (Alicyclic Ketones) Alicyclic ketones are compounds in which a methylene group of an alicyclic hydrocarbon is substituted with a carbonyl group. The alicyclic hydrocarbon substituted with a carbonyl group is preferably a saturated alicyclic hydrocarbon. The alicyclic hydrocarbon substituted with a carbonyl group may be a monocyclic hydrocarbon containing only one ring, or a polycyclic hydrocarbon containing two or more rings, and is preferably a monocyclic hydrocarbon. Alicyclic ketones have a carbon ring. The number of ring members in the carbon ring of an alicyclic ketone is usually 3 or more, preferably 4 or more, more preferably 5 or more, and preferably 10 or less, more preferably 8 or less, even more preferably 6 or less, preferably 3 to 10, more preferably 5 to 8, even more preferably 5 or 6. Specific examples of alicyclic ketones include cyclohexanone and cyclopentanone, and preferably cyclohexanone and cyclopentanone.

[0072] The weight ratio of the first solvent compound to the second solvent compound in the mixed solvent (first solvent compound / second solvent compound) is preferably 20 / 80 or more, more preferably 30 / 70 or more, even more preferably 40 / 60 or more, and preferably 80 / 20 or less, more preferably 70 / 30 or less, even more preferably 60 / 40 or less.By adjusting the weight ratio of the first solvent compound to the second solvent compound in the mixed solvent, the thickness direction retardation Rth of the birefringent film can be adjusted within a desired range.When this weight ratio is increased, the thickness direction retardation Rth of the obtained birefringent film tends to be smaller.

[0073] The mixed solvent may contain any solvate in addition to the first solvate and the second solvate, or may not contain any solvate. Preferably, the mixed solvent does not contain any solvate, or if it contains any solvate, it is in a smaller amount than each of the first solvate and the second solvate. The total weight ratio of the first solvate and the second solvate in the mixed solvent is preferably 90% by weight or more, more preferably 95% by weight or more, and even more preferably 98% by weight or more, based on 100% by weight of the mixed solvent, and is usually 100% by weight or less, and may be 100% by weight.

[0074] <Examples of Combinations of First Solvents and Second Solvents> The following table shows examples of combinations of first solvates and second solvates. In one embodiment, the mixed solvent may contain only the first solvates and second solvates of the following example combinations. In another embodiment, the mixed solvent may contain, in addition to the first solvates and second solvates of the following example combinations, a different type of first solvate, a different type of second solvate, or any solvate other than the first solvate and the second solvate.

[0075]

[0076] The resin film may be brought into contact with the mixed solvent by any method. Examples of the contact method include a spraying method in which an organic solvent is sprayed onto the resin film, a coating method in which an organic solvent is applied to the resin film, and an immersion method in which the resin film is immersed in an organic solvent. Among these, the immersion method is preferred because it allows for easy continuous contact.

[0077] The temperature of the mixed solvent brought into contact with the resin film may be any temperature within a range in which the mixed solvent can remain in a liquid state, and therefore can usually be set within a range from the melting point to the boiling point of the solvent compound contained in the mixed solvent.

[0078] The time for contacting the resin film with the mixed solvent is not particularly specified, but is preferably 0.5 seconds or more, more preferably 1.0 second or more, particularly preferably 5.0 seconds or more, and preferably 60 seconds or less, more preferably 10 seconds or less. When the contact time is equal to or greater than the lower limit of the above range, the NZ coefficient of the birefringent film and the thickness direction retardation Rth can be effectively adjusted by contact with the mixed solvent. Since the resin film is contacted with a specific mixed solvent, the contact time with the solvent can be shortened while adjusting the NZ coefficient and thickness direction Rth to the desired range. Therefore, birefringent films can be produced with high productivity.

[0079] <2.3. Step (III)> The resin film that has been brought into contact with the mixed solvent in step (II) is dried in step (III). The method for drying the resin film is not particularly limited, and any method can be used. Examples of drying methods include natural drying, heat drying, reduced-pressure drying, heated and reduced-pressure drying, and combinations thereof. Step (III) may include a step of wiping the mixed solvent from the resin film.

[0080] The drying temperature can be set appropriately depending on the boiling point, vapor pressure, and other properties of the mixed solvent and the solvent compounds contained therein, and the glass transition temperature Tg of the crystalline polymer contained in the resin film. Although not particularly limited, the drying temperature may be, for example, 20°C or higher, for example, 35°C or higher, for example, 40°C or higher, or for example, 50°C or higher, and may be, for example, Tg or lower, for example, "Tg-5°C" or lower, or for example, "Tg-10°C" or lower. Here, "Tg" represents the glass transition temperature of the crystalline polymer contained in the resin film.

[0081] The drying time can be set appropriately depending on conditions such as the drying temperature, the degree of reduced pressure, etc. Although not particularly limited, the drying time is, for example, 1 minute or more, for example, 5 minutes or more, and for example, 30 minutes or less, for example, 20 minutes or less.

[0082] 2.4. Step (I) The method for producing a birefringent film may include the step (I) described above. In the step (I), the resin film used in the step (II) is formed by melt extrusion.

[0083] The manufacturing conditions for melt extrusion are preferably as follows. The cylinder temperature (molten resin temperature) is preferably Tm or higher, more preferably "Tm + 10°C" or higher, and preferably "Tm + 100°C" or lower, more preferably "Tm + 50°C" or lower. The cooling body that the extruded molten resin first comes into contact with is not particularly limited, but a cast roll is typically used. The cast roll temperature is preferably "Tg - 50°C" or higher, preferably "Tg + 70°C" or lower, more preferably "Tg + 40°C" or lower. Furthermore, the chill roll temperature is preferably "Tg - 70°C" or higher, more preferably "Tg - 50°C" or higher, and preferably "Tg + 60°C" or lower, more preferably "Tg + 30°C" or lower. When a resin film is manufactured under these conditions, a resin film having a thickness of 1 μm to 1 mm can be easily manufactured. Here, "Tm" represents the melting point of the crystalline polymer, and "Tg" represents the glass transition temperature of the crystalline polymer.

[0084] <2.5. Step (IV)> The method for producing a birefringent film may include step (IV) as described above. Stretching can orient the molecules of the crystalline polymer contained in the resin film in a direction corresponding to the stretching direction. Therefore, stretching can adjust the NZ coefficient and thickness direction retardation Rth of the resin film.

[0085] The stretching direction is not limited, and examples thereof include the longitudinal direction, the width direction, and an oblique direction. Here, the oblique direction refers to a direction perpendicular to the thickness direction, and is neither parallel nor perpendicular to the width direction. The stretching direction may be one direction or two or more directions. Therefore, examples of the stretching method include uniaxial stretching methods such as a method of uniaxially stretching a resin film in the longitudinal direction (longitudinal uniaxial stretching method) and a method of uniaxially stretching a resin film in the width direction (transverse uniaxial stretching method); biaxial stretching methods such as a simultaneous biaxial stretching method in which a resin film is stretched in the longitudinal direction and simultaneously stretched in the width direction, and a sequential biaxial stretching method in which a resin film is stretched in one of the longitudinal direction and the width direction and then stretched in the other direction; and a method of stretching a resin film in an oblique direction (oblique stretching method).

[0086] The stretching ratio is preferably 1.1 times or more, more preferably 1.2 times or more, and preferably 20.0 times or less, more preferably 10.0 times or less, even more preferably 5.0 times or less, and particularly preferably 2.0 times or less. It is desirable to appropriately set the specific stretching ratio depending on factors such as the optical properties, thickness, and strength of the birefringent film to be produced. When the stretching ratio is equal to or greater than the lower limit of the above range, the birefringence can be significantly changed by stretching. Furthermore, when the stretching ratio is equal to or less than the upper limit of the above range, the direction of the slow axis can be easily controlled and breakage of the resin film can be effectively suppressed.

[0087] The stretching temperature is preferably "Tg + 5°C" or higher, more preferably "Tg + 10°C" or higher, and preferably "Tg + 100°C" or lower, more preferably "Tg + 90°C" or lower. Here, "Tg" represents the glass transition temperature of the crystalline polymer. When the stretching temperature is equal to or higher than the lower limit of the above range, the resin film can be sufficiently softened and stretched uniformly. When the stretching temperature is equal to or lower than the upper limit of the above range, hardening of the resin film due to the progress of crystallization of the crystalline polymer can be suppressed, so stretching can be carried out smoothly and large birefringence can be developed by stretching.

[0088] By carrying out the stretching treatment, a stretched film can be obtained as a stretched resin film.As mentioned above, since the birefringence can be changed by the stretching in step (IV), the NZ coefficient and the retardation Rth in the thickness direction of the film can be adjusted.Therefore, when a resin film as a stretched film having desired optical properties can be obtained by stretching, the resin film can be obtained as a birefringent film.

[0089] 2.6. Step (V) As described above, the method for producing a birefringent film may include step (V). By including step (V) after step (III), the crystalline polymer contained in the resin film can be crystallized. When the method for producing a birefringent film includes step (IV), step (V) is usually performed after step (IV). By crystallizing the crystalline polymer, the orientation of the crystalline polymer can be improved. Here, crystallizing the crystalline polymer in step (V) means increasing the crystallinity of the crystalline polymer contained in the resin film. Therefore, the crystallinity of the crystalline polymer does not need to be 100% in step (V). Usually, in step (V), the resin film is heated to a temperature near the crystallization temperature Tc of the crystalline polymer or higher and below the melting point Tm of the crystalline polymer, thereby promoting the crystallization of the crystalline polymer and increasing the crystallinity. More specifically, the heating temperature is preferably Tc-10°C or higher, more preferably Tc°C or higher, even more preferably Tc+10°C or higher, and is preferably Tm-20°C or lower, more preferably Tm-40°C or lower.

[0090] The heating time is preferably 1 second or more, more preferably 5 seconds or more, and is preferably 30 minutes or less, more preferably 15 minutes or less.

[0091] 2.7. Other Optional Steps The method for producing a birefringent film may further include optional steps in combination with the above steps. An example of such an optional step is a step of preheating the resin film to a stretching temperature before step (III). Usually, the preheating temperature and the stretching temperature are the same, but they may be different. The preheating temperature is preferably T1-10°C or higher, more preferably T1-5°C or higher, and preferably T1+5°C or lower, more preferably T1+2°C or lower, relative to the stretching temperature T1. The preheating time is optional and may be preferably 1 second or longer, more preferably 5 seconds or longer, and may also be preferably 60 seconds or shorter, more preferably 30 seconds or shorter.

[0092] According to the above-described manufacturing method, a long birefringent film can be manufactured using a long resin film. The manufacturing method of a birefringent film may include a step of winding the long birefringent film manufactured in this manner into a roll. Furthermore, the manufacturing method of a birefringent film may include a step of cutting the long birefringent film into a desired shape.

[0093] <3. Birefringent Film> A birefringent film according to one embodiment of the present invention can be produced by the above-described method for producing a birefringent film. The birefringent film contains a polymer having positive intrinsic birefringence and crystallinity, which is typically contained in a resin film. Examples and preferred examples of the polymer having positive intrinsic birefringence and crystallinity that can be contained in the birefringent film are the same as the examples and preferred examples of the crystalline polymer that can be contained in the resin film. The proportion of the crystalline polymer contained in the birefringent film is preferably 50% by weight or more, more preferably 70% by weight or more, and particularly preferably 90% by weight or more, and is typically 100.0% by weight or less, and may be 99.99% by weight or less.

[0094] (Crystallization degree) The crystallinity of the crystalline polymer contained in the birefringent film is not particularly limited, but is usually high to a certain extent. When measuring the crystallinity of a resin containing a crystalline polymer, the specific range of the crystallinity is preferably 10% or more, more preferably 15% or more, and particularly preferably 30% or more. The upper limit of the crystallinity can be 100% or less. The crystallinity can be measured by X-ray diffraction.

[0095] (Containing Solvent) The birefringent film may contain at least one solvent selected from the group consisting of the first solvent compound and the second solvent compound. The birefringent film may contain the first solvent compound but not the second solvent compound, may contain the second solvent compound but not the second solvent compound, or may contain a combination of the first solvent compound and the second solvent compound. These solvent compounds are usually incorporated into the film in step (II) of the production method.

[0096] Since all or part of the solvent compound incorporated into the film in step (II) may penetrate into the crystalline polymer, it may be difficult to completely remove the solvent compound. Therefore, the birefringent film subjected to step (II) may contain at least one solvent compound selected from the group consisting of a first solvent compound and a second solvent compound. The first solvent compound has the same meaning as above and is preferably an unsaturated alicyclic hydrocarbon which may have a substituent; more preferably an unsaturated monocyclic alicyclic hydrocarbon which may have a substituent, and even more preferably cyclohexene which may have a substituent; and from the viewpoint of improving the appearance of the birefringent film, limonene (preferably d-limonene) is particularly preferred. The second solvent compound has the same meaning as above and may be any of the preferred compounds listed above as the second solvent compound.

[0097] The total content of the first solvent compound and the second solvent compound in the birefringent film is preferably 0.01 wt% or more, preferably 10.00 wt% or less, preferably 8.00 wt% or less, more preferably 3.00 wt% or less, and even more preferably 2.00 wt% or less. When the total content of the first solvent compound and the second solvent compound in the birefringent film is not more than the above-mentioned upper limit, undesirable phenomena such as deterioration of the birefringent film over time during use and adverse effects on other components of a device in which the birefringent film is incorporated can be effectively suppressed.

[0098] The birefringent film may contain any solvent compound other than the first solvent compound and the second solvent compound, or may not contain any solvent compound. When the total content of solvents in the birefringent film is taken as 100% by weight, the total content of the first solvent compound and the second solvent compound is preferably higher than the total content of any solvent other than the first solvent compound and the second solvent compound. Therefore, when the total content of solvents in the birefringent film is taken as 100% by weight, the total content of the first solvent compound and the second solvent compound is preferably more than 50% by weight, more preferably 90% by weight or more, even more preferably 95% by weight or more, and even more preferably 98% by weight or more. It is usually 100% by weight or less, and may be 100% by weight.

[0099] The type, composition, and content ratio of the solvent compound in the birefringent film can be analyzed by an appropriate analytical method. The total content of the solvent in the birefringent film can be measured by mass spectrometry such as gas chromatography mass spectrometry or thermogravimetric analysis. A gas chromatography mass spectrometry device equipped with a headspace device can be used as the gas chromatography mass spectrometry device. When a resin film is produced by melt extrusion at a high temperature (e.g., 280°C or higher), the solvent content of the resin film may be set to 0.0%.

[0100] (NZ Coefficient NZ) The birefringent film of this embodiment usually has an NZ coefficient NZ of less than 1.0.

[0101] In one embodiment, the NZ coefficient NZ of the birefringent film is preferably 0.0 or less, with the lower limit being, for example, -400 or more. By performing an operation such as stretching on a birefringent film having an NZ coefficient in this range, it can be easily made into a birefringent film that can function as a three-dimensional retardation film. In this embodiment, the Rth in the thickness direction of the birefringent film is preferably greater than -400 nm, preferably greater than -150 nm, more preferably greater than -100 nm, and preferably 0 nm or less. In this embodiment, the in-plane retardation Re of the birefringent film is preferably 20 nm or less, more preferably 10 nm or less, and is usually 0 nm or more.

[0102] In one embodiment, the birefringent film is an unstretched film.

[0103] In another embodiment, the NZ coefficient NZ of the birefringent film is preferably greater than 0.0 and, as described above, is usually less than 1.0. A birefringent film having an NZ coefficient within this range can function as a three-dimensional retardation film. A three-dimensional retardation film is a film whose NZ coefficient NZ satisfies 0.0 < NZ < 1.0. A three-dimensional retardation film can be provided in a display device such as a liquid crystal display device to reduce coloring of the display surface when viewed from an oblique direction. In this embodiment, the thickness direction retardation Rth of the birefringent film is preferably greater than -100 nm, more preferably -50 nm or more, and preferably 100 nm or less, more preferably 50 nm or less. In this embodiment, the in-plane retardation Re of the birefringent film is preferably 100 nm or more, more preferably 150 nm or more, and preferably 300 nm or less, more preferably 250 nm or less.

[0104] In one embodiment, the birefringent film is a stretched film.

[0105] (Thickness direction retardation Rth of birefringent film) The birefringent film can have a thickness direction retardation Rth of at least a certain level. The thickness direction retardation Rth of the birefringent film is usually greater than −400 nm, preferably greater than −150 nm, and more preferably greater than −100 nm. A birefringent film having a thickness direction retardation Rth equal to or greater than the above lower limit can be stretched as necessary to form a three-dimensional retardation film. The thickness direction retardation Rth of the birefringent film can be adjusted by adjusting the weight ratio of the first solvent compound to the second solvent compound in the mixed solvent.

[0106] (Thickness of birefringent film) The thickness of the birefringent film can be adjusted appropriately to a thickness that achieves desired optical properties. The thickness of the birefringent film is preferably 10 μm or more, more preferably 15 μm or more, and is preferably 200 μm or less, more preferably 150 μm or less. When the thickness of the birefringent film is equal to or greater than the lower limit, the birefringent film can effectively exhibit the desired optical properties. When the thickness is equal to or less than the upper limit, the device equipped with the birefringent film can be made thinner.

[0107] <4. Uses of Birefringent Film> The birefringent film according to this embodiment has a thickness direction retardation Rth equal to or greater than the lower limit, an NZ coefficient NZ of less than 1.0, and a good appearance. Such a birefringent film is useful as a positive C plate or a three-dimensional retardation film. A positive C plate refers to a film that satisfies nz > nx ≒ ny. Here, nx ≒ ny means that the value of (nx - ny) is 0 or close to 0, and the value of (nx - ny) is preferably 0.001 or less, more preferably 0.0005 or less, even more preferably 0.0001 or less, and is usually 0.0 or more, and may even be 0.0. A birefringent film that is a positive C plate can be easily made into a three-dimensional retardation film by stretching it.

[0108] The present invention will be described in detail below with reference to examples. However, the present invention is not limited to the examples shown below, and can be practiced with any modifications within the scope of the claims of the present invention and their equivalents.

[0109] In the following description, the "%" and "parts" that represent amounts are by weight unless otherwise specified. Furthermore, the operations described below were carried out at room temperature (20°C ± 15°C) and atmospheric pressure (1 atm) unless otherwise specified.

[0110] <Evaluation Methods> (Method for Measuring Weight-Average Molecular Weight Mw and Number-Average Molecular Weight Mn of Polymer) The weight-average molecular weight Mw and number-average molecular weight Mn of the polymer were measured as polystyrene equivalent values ​​using a gel permeation chromatography (GPC) system ("HLC-8320" manufactured by Tosoh Corporation). During the measurement, an H-type column (manufactured by Tosoh Corporation) was used as the column, and tetrahydrofuran was used as the solvent. The temperature during the measurement was 40°C.

[0111] (Method for measuring the hydrogenation rate of polymer) The hydrogenation rate of polymer was measured by orthodichlorobenzene-d ４ as a solvent at 145°C, １ The measurement was carried out by H-NMR measurement.

[0112] (Method for measuring glass transition temperature Tg, crystallization temperature Tc, and melting point Tm) The glass transition temperature Tg, crystallization temperature Tc, and melting point Tm of a polymer were measured as follows. First, the polymer was melted by heating, and the melted polymer was rapidly cooled with dry ice. Next, using this polymer as a test sample, the glass transition temperature Tg, crystallization temperature Tc, and melting point Tm of the polymer were measured using a differential scanning calorimeter (DSC) at a heating rate of 10°C / min (heating mode). The crystallization temperature Tc was taken as the value at the top of the exothermic peak during the heating process.

[0113] (Method for measuring the ratio of racemo-dyads in a polymer) The ratio of racemo-dyads in a polymer was measured as follows. ４ The polymer was decoupling by the inverse-gated decoupling method at 200°C using １３ C-NMR measurement was carried out. １３ As a result of C-NMR measurement, orthodichlorobenzene-d ４ Using the peak at 127.5 ppm as the reference shift, the signal at 43.35 ppm from the meso dyad and the signal at 43.43 ppm from the racemo dyad were identified. The ratio of the racemo dyads in the polymer was calculated based on the intensity ratio of these signals.

[0114] (Method for measuring in-plane retardation Re, thickness direction retardation Rth, and NZ coefficient of film) The optical properties of the film, such as the in-plane retardation Re and thickness direction retardation Rth, were measured using a retardation meter ("AxoScan OPMF-1" manufactured by AXOMETRICS). The measurement wavelength was 590 nm.

[0115] (Method for Measuring Film Thickness) The film thickness was measured using a contact type thickness meter (manufactured by MITUTOYO Corporation, Code No. 543-390).

[0116] (Method for measuring residual solvent content in film) The unstretched birefringent films obtained in Examples 1 to 3 and Comparative Example 2 were dried in a drying oven and then left at room temperature (25°C) for at least one week. The residual solvent content of the birefringent films was then measured using a headspace gas chromatograph mass spectrometer. The headspace apparatus used was an "HS-20" manufactured by Shimadzu Corporation, and the gas chromatograph mass spectrometer used was a "GCMS-QP2010 Ultra" manufactured by Shimadzu Corporation. The treatment conditions were 230°C for 30 minutes. The detection limit was 0.005 wt%. Since the resin film before immersion in the solvent was produced by hot-melt extrusion at high temperatures (280°C to 300°C), it was considered to contain no solvent, and therefore its solvent content was set to 0.0 wt%.

[0117] (Method for Evaluating Film Appearance) The appearance of the film was evaluated by visually checking the reflected light and transmitted light using a three-wavelength fluorescent lamp. If irregularities were observed on the film surface or the film was whitened, it was rated as poor. If no particular abnormalities were observed, it was rated as good.

[0118] Production Example 1: Production of a crystalline resin containing a hydride of a ring-opening polymer of dicyclopentadiene. A metal pressure-resistant reactor was thoroughly dried and then purged with nitrogen. 154.5 parts of cyclohexane, 42.8 parts of a 70% cyclohexane solution of dicyclopentadiene (endo isomer content of 99% or more) (30 parts as dicyclopentadiene), and 1.9 parts of 1-hexene were added to this metal pressure-resistant reactor and heated to 53°C. 0.014 parts of tetrachlorotungsten phenylimide (tetrahydrofuran) complex was dissolved in 0.70 parts of toluene to prepare a solution. 0.061 parts of a 19% diethylaluminum ethoxide / n-hexane solution was added to this solution and stirred for 10 minutes to prepare a catalyst solution. This catalyst solution was added to the pressure-resistant reactor to initiate the ring-opening polymerization reaction. The reaction was then carried out for 4 hours while maintaining the temperature at 53°C, yielding a solution of a ring-opening polymer of dicyclopentadiene. The number average molecular weight (Mn) and weight average molecular weight (Mw) of the resulting ring-opened polymer of dicyclopentadiene were 8,750 and 28,100, respectively, and the molecular weight distribution (Mw / Mn) calculated from these values ​​was 3.21.

[0119] To 200 parts of the obtained solution of ring-opened dicyclopentadiene polymer, 0.037 parts of 1,2-ethanediol as a terminator was added, heated to 60 ° C., and stirred for 1 hour to terminate the polymerization reaction. One part of a hydrotalcite-like compound (Kyowa Chemical Industry Co., Ltd.'s "Kyoward (registered trademark) 2000") was added, heated to 60 ° C., and stirred for 1 hour. Thereafter, 0.4 parts of a filter aid (Showa Chemical Industry Co., Ltd.'s "Radiolite (registered trademark) #1500") was added, and the adsorbent and solution were filtered off using a PP pleated cartridge filter (ADVANTEC Toyo Co., Ltd.'s "TCP-HX").

[0120] To 200 parts of the filtered solution of the ring-opened polymer of dicyclopentadiene (30 parts polymer), 100 parts of cyclohexane was added, and 0.0043 parts of chlorohydridocarbonyltris(triphenylphosphine)ruthenium was added, followed by hydrogenation reaction at 180°C under a hydrogen pressure of 6 MPa for 4 hours. This yielded a reaction solution containing a hydride of the ring-opened polymer of dicyclopentadiene. The hydride precipitated from this reaction solution, forming a slurry solution.

[0121] The hydrogenated product and the solution contained in the reaction mixture were separated using a centrifuge and dried under reduced pressure at 60°C for 24 hours to obtain 28.5 parts of a hydrogenated crystalline ring-opening polymer of dicyclopentadiene. This hydrogenated product had a hydrogenation rate of 99% or more, a glass transition temperature (Tg) of 93°C, a crystallization temperature (Tc) of 120°C, a melting point (Tm) of 262°C, and a racemo-dyad ratio of 89%. Furthermore, this hydrogenated product was a polymer with positive intrinsic birefringence, i.e., when molded into a resin film and stretched, the refractive index in the stretching direction was greater than the refractive index in the direction perpendicular to the stretching direction.

[0122] 100 parts of the obtained hydrogenated product of the ring-opening polymer of dicyclopentadiene was mixed with 1.1 parts of an antioxidant (tetrakis[methylene-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate]methane; "Irganox (registered trademark) 1010" manufactured by BASF Japan Ltd.), and the mixture was then fed into a twin-screw extruder (product name "TEM-37B" manufactured by Toshiba Machine Co., Ltd.) equipped with four die holes with an inner diameter of 3 mm.

[0123] A mixture of the hydrogenated ring-opening polymer of dicyclopentadiene and the antioxidant was formed into a strand by hot-melt extrusion, and then chopped with a strand cutter to obtain a crystalline resin in the form of pellets. The operating conditions of the twin-screw extruder were as follows: barrel set temperature = 270 to 280°C, die set temperature = 250°C, screw rotation speed = 145 rpm.

[0124] Examples 1 to 6, Comparative Examples 1 to 3 Production of Unstretched Birefringent Film: Steps (I) to (III) The crystalline resin produced in Production Example 1 was molded using a hot melt extrusion film molding machine equipped with a T-die ("Measuring Extruder Type Me-20 / 2800V3" manufactured by Optical Control Systems) to obtain a long resin film (film (p)) having a thickness of 39 μm. The operating conditions of the film molding machine were as follows: Barrel set temperature = 280°C to 300°C Die temperature = 270°C Screw rotation speed = 30 rpm Cast roll temperature = 80°C The obtained resin film (p) was cut into a piece of 100 mm x 100 mm, immersed in a tray filled with a solvent, and removed after 10 seconds. The solvent used contained a first solvent compound in the ratio shown in the table, and in the examples, a solvent containing a second solvent compound was used. After immersion, the film was air-dried at room temperature for 3 minutes, and then the solvent on the film surface was wiped off with gauze. This was followed by further drying in a drying oven at 80°C for 10 minutes to obtain a birefringent film as an unstretched film. The obtained birefringent film was evaluated by the above-mentioned method.

[0125] Example 7: Production of Stretched Birefringent Film: Steps (I) to (IV) A stretching apparatus ("SDR-562Z" manufactured by Eto Corporation) was prepared. This stretching apparatus was equipped with clips capable of gripping the edges of a rectangular resin film and an oven. A total of 24 clips were provided, five per side of the film and one at each vertex, and the film could be stretched by moving these clips. Two ovens were also provided, each capable of being set to a stretching temperature and a heat treatment temperature. Furthermore, in this stretching apparatus, the resin film could be transferred from one oven to the other while still being gripped by the clips. The birefringent film obtained in Example 4 was preheated for 120 seconds in an oven set to 80°C and then freely uniaxially stretched in the direction corresponding to the longitudinal direction of the long resin film, thereby obtaining a birefringent film as a stretched film. The stretching ratio was as shown in the table, and the stretching speed was 0.2 mm / s. The birefringent film thus obtained was evaluated by the above-mentioned method.

[0126] Example 8 Production of Stretched Birefringent Film: Steps (I) to (IV) A birefringent film was obtained as a stretched film by the same procedure as in Example 7, except that the birefringent film obtained in Example 5 was used instead of the birefringent film obtained in Example 4. The stretching ratio was as shown in the table, and the stretching speed was 0.2 mm / s. The obtained birefringent film was evaluated by the method described above.

[0127] Example 9: Production of heat-crystallized stretched birefringent film: steps (I) to (V) A birefringent film was obtained as a stretched film by the same procedure as in Example 7, except that the birefringent film obtained in Example 3 was used instead of the birefringent film obtained in Example 4. The stretching ratio was as shown in the table, and the stretching speed was 0.2 mm / s. Next, while holding the stretched film with clips, it was transferred to an oven set to a temperature of 160°C, which is higher than the crystallization temperature (Tc) of the polymer contained therein, and heat-treated for 300 seconds, thereby obtaining a birefringent film as a stretched film in which crystallization had been promoted by heating. The obtained birefringent film was evaluated by the method described above.

[0128] <Evaluation Results> The manufacturing conditions and evaluation results of the birefringent film are shown in Tables 2 and 3. The abbreviations in the tables have the following meanings: Limonene: d-limonene AcOBu: n-butyl acetate Me(iBu)K: methyl isobutyl ketone iBuOH: isobutyl alcohol iPrOH: isopropyl alcohol First solvent compound ratio: ratio of the first solvent compound in the mixed solvent (unit: wt%) Total residual solvent amount: total content (wt%) of the first solvent compound and the second solvent compound in the birefringent film

[0129] The compound described as the second solvent compound in the comparative examples does not fall under any of the specific aliphatic alcohols, specific aliphatic ketones, specific alkyl esters, and alicyclic ketones, but is described in the section on second solvent compounds for convenience. In the section on stretching ratio, the stretching ratio is recorded if the stretching step of step (IV) was performed, and "none" is recorded if the stretching step was not performed. In the section on thermal crystallization, whether or not step (V) was performed is recorded, and "none" is recorded if it was not performed. The symbols used to evaluate the film appearance have the following meanings. *1: The film surface is uneven and is poor. *2: The film has turned white and transparency is poor. The symbols used in the section on total residual solvent amount have the following meanings. *3: Not measured

[0130]

[0131]

[0132] From the above results, it can be seen that the birefringent films obtained by the production methods of Examples 1 to 9 using mixed solvents containing a combination of a specific first solvent compound and a specific second solvent compound have an NZ coefficient of less than 1.0, an Rth of greater than -400 nm, and good appearance. On the other hand, the birefringent films obtained by the production methods of Comparative Examples 1 and 3 using solvents that do not contain a specific second solvent compound have poor appearance. Furthermore, the birefringent film of Comparative Example 3 has an NZ coefficient of 1.0 or more. Furthermore, the birefringent film obtained by the production method of Comparative Example 2 using a solvent that does not contain a specific second solvent compound has good appearance but an Rth of -400 nm or less.

Claims

1. A method for producing a birefringent film, comprising: a step (II) of contacting a resin film containing a polymer having positive intrinsic birefringence and crystallinity with a mixed solvent containing a first solvent compound and a second solvent compound; and a step (III) of drying the resin film that has been contacted with the mixed solvent, wherein the first solvent compound is a cyclic hydrocarbon that may have a substituent, and the second solvent compound is an aliphatic alcohol having an alkyl group with 4 or more carbon atoms, an aliphatic ketone having an alkyl group with 4 or more carbon atoms, an alkyl ester of an aliphatic carboxylic acid having 4 or more carbon atoms, or an alicyclic ketone.

2. The method for producing a birefringent film according to claim 1, wherein the first solvent compound is an optionally substituted monocyclic or bicyclic aromatic hydrocarbon; or an optionally substituted monocyclic or bicyclic alicyclic hydrocarbon, and the second solvent compound is an optionally substituted aliphatic primary alcohol having an alkyl group with 4 to 10 carbon atoms; an aliphatic ketone having an alkyl group with 4 to 10 carbon atoms and a methyl group; an alkyl ester having 4 to 10 carbon atoms of an aliphatic carboxylic acid having 2 to 5 carbon atoms; or an alicyclic ketone having a 5- or 6-membered carbon ring.

3. The method for producing a birefringent film according to claim 1, wherein in step (II), the resin film is brought into contact with the mixed solvent for 10 seconds or less.

4. A method for producing a birefringent film according to claim 1, which comprises, before step (II), step (I) of forming a resin containing a polymer having positive intrinsic birefringence and crystallinity into a film by melt extrusion to obtain the resin film.

5. The method for producing a birefringent film according to claim 1, comprising, after step (III), step (IV) of stretching the dried resin film, and step (V) of heating the stretched resin film to crystallize the crystalline polymer, in this order.

6. The method for producing a birefringent film according to any one of claims 1 to 5, wherein the crystalline polymer is a polymer containing an alicyclic structure.

7. A birefringent film comprising a polymer having positive intrinsic birefringence and crystallinity, having an NZ coefficient NZ of less than 1.0 and a thickness direction retardation Rth of greater than -150 nm, wherein the total content of a first solvent compound and a second solvent compound is 0.01% by weight or more and 10.00% by weight or less, the first solvent compound is a cyclic hydrocarbon which may have a substituent, and the second solvent compound is an aliphatic alcohol having an alkyl group with 4 or more carbon atoms, an aliphatic ketone having an alkyl group with 4 or more carbon atoms, an alkyl ester of an aliphatic carboxylic acid with 4 or more carbon atoms, or an alicyclic ketone.

8. The birefringent film according to claim 7, wherein the first solvent compound is an unsaturated alicyclic hydrocarbon which may have a substituent.

9. The birefringent film according to claim 7, wherein the NZ coefficient NZ is greater than 0.

0.

10. The birefringent film according to claim 7, wherein the NZ coefficient NZ is 0.0 or less.

11. The birefringent film according to claim 7, wherein the thickness direction retardation Rth is 0 nm or less.

12. The birefringent film according to claim 7, which is an unstretched film.

13. The birefringent film according to any one of claims 7 to 12, wherein the crystalline polymer is a polymer containing an alicyclic structure.

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