Method for manufacturing phase difference films

Abstract

To provide a retardation film manufacturing method that can suitably manufacture a retardation film having high in-plane birefringence and having an in-plane phase difference indicating reverse wavelength dispersion characteristics, by using a resin film including a resin indicating positive birefringence and a resin indicating negative birefringence.SOLUTION: There is provided a method for manufacturing a retardation film in which an in-plane birefringence Δn(590) at a measurement wavelength of 590 nm exceeds 0.003, and a ratio of an in-plane phase difference at a measurement wavelength of 450 nm to an in-plane phase difference at a measurement wavelength of 550 nm (Re(450) / Re(550)) is less than 0.90, and the manufacturing method includes: producing a resin film including a resin indicating positive birefringence and a resin indicating negative birefringence, and in which the birefringence in a thickness direction at a measurement wavelength of 590 nm ΔP(590) exceeds 0.0005, and a ratio of a phase difference in the thickness direction at a measurement wavelength of 450 nm to a phase difference in the thickness direction at a measurement wavelength of 550 nm (Rth(450) / Rth(550)) is less than 0.98; and stretching the resin film.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This invention relates to a method for manufacturing a phase difference film. [Background technology]

[0002] In recent years, image display devices, such as liquid crystal displays and electroluminescent (EL) displays (e.g., organic EL displays and inorganic EL displays), have become rapidly widespread. In organic EL displays, it is known that problems such as reflection of ambient light and reflection of the background can be prevented by placing a circular polarizer containing a λ / 4 plate on the viewing side of the organic EL cell (e.g., Patent Documents 1 and 2).

[0003] Regarding the λ / 4 plate used in the above-mentioned circular polarizer, from the viewpoint of achieving excellent anti-reflective properties over a wide wavelength range, there is a need for a phase difference film that exhibits so-called inverse wavelength dispersion characteristics, where the phase difference is larger in the longer wavelength range. In response to this need, a phase difference film has been proposed that contains a cellulose-based resin exhibiting positive birefringence and an ester-based resin exhibiting negative birefringence, and in which the in-plane phase difference exhibits inverse wavelength dispersion characteristics (Patent Document 3). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2002-311239 [Patent Document 2] Japanese Patent Publication No. 2002-372622 [Patent Document 3] Japanese Patent Publication No. 2021-140095 [Overview of the project] [Problems that the invention aims to solve]

[0005] The inventors of this invention have found that, in the production of a phase difference film using a resin film containing a resin exhibiting positive birefringence and a resin exhibiting negative birefringence, the orientation of the resin film to be stretched greatly affects the optical properties of the resulting phase difference film, and that depending on the orientation of the resin film, it may not be possible to obtain a phase difference film with the desired optical properties.

[0006] The present invention was made to solve the above problems, and its main objective is to provide a method for manufacturing a phase difference film that can suitably produce a phase difference film having high in-plane birefringence and in-plane phase difference exhibiting inverse wavelength dispersion characteristics, using a resin film containing a resin exhibiting positive birefringence and a resin exhibiting negative birefringence. [Means for solving the problem]

[0007] According to one aspect of the present invention, a method for manufacturing a phase difference film is provided, wherein the in-plane birefringence Δn(590) at a measurement wavelength of 590 nm exceeds 0.003 and the ratio of the in-plane phase difference at a measurement wavelength of 450 nm to the in-plane phase difference at a measurement wavelength of 550 nm (Re(450) / Re(550)) is less than 0.90, the method comprising: producing a resin film containing a resin exhibiting positive birefringence and a resin exhibiting negative birefringence, wherein the thickness-direction birefringence ΔP(590) at a measurement wavelength of 590 nm exceeds 0.0005 and the ratio of the thickness-direction phase difference at a measurement wavelength of 450 nm to the thickness-direction phase difference at a measurement wavelength of 550 nm (Rth(450) / Rth(550)) is less than 0.98; and stretching the resin film. In one embodiment, the thickness of the resin film before stretching is 50 μm to 200 μm, and the thickness of the resin film after stretching is 12.5% ​​to 40% of the thickness before stretching. In one embodiment, the production of the resin film includes applying a resin solution containing a resin exhibiting positive birefringence, a resin exhibiting negative birefringence, and a solvent onto a support substrate to form a coating layer, and heating the coating layer to evaporate the solvent. In one embodiment, the coated layer is heated in the range of 50°C to 155°C to evaporate the solvent. In one embodiment, the resin film is a long resin film, and stretching the resin film includes stretching the long resin film in a direction perpendicular to the longitudinal direction while conveying the long resin film in the longitudinal direction. In one embodiment, the stretching ratio of the stretching is 8.0 times or less. In one embodiment, the Rth(450) / Rth(550) of the resin film before stretching is greater than 0.60 and less than 0.98, the Δn(590) of the phase difference film is greater than 0.0035, and the Re(450) / Re(550) is less than 0.88. In one embodiment, the resin exhibiting positive birefringence includes a cellulose resin having the structural units shown in formula (1) below, and the resin exhibiting negative birefringence includes an ester resin having the structural units shown in formula (2) below and the structural units shown in formula (3) below: [ka] (In formula (1), each of R1 to R3 represents a hydrogen atom or a substituent having 1 to 12 carbon atoms;) [ka] (In formula (2), R4 represents a hydrogen atom or an alkyl group having 1 to 12 carbon atoms; R 5a R represents one selected from an alkyl group having 1 to 12 carbon atoms, a nitro group, a bromo group, an iodo group, a cyano group, a chloro group, a sulfonic acid group, a carboxylic acid group, a fluoro group, or a thiol group; R 5b R6 represents a hydrogen atom or an alkyl group having 1 to 12 carbon atoms; R6 represents a species selected from a hydrogen atom, a nitro group, a bromo group, an iodo group, a cyano group, a chloro group, a sulfonic acid group, a carboxylic acid group, a fluoro group, a phenyl group, a thiol group, an amide group, an amino group, a hydroxyl group, an alkoxy group having 1 to 12 carbon atoms, or an alkyl group having 1 to 12 carbon atoms;) [ka] (In formula (3), R7 represents a 5-membered heterocyclic residue or a 6-membered heterocyclic residue containing one or more nitrogen atoms or oxygen atoms as heteroatoms (the 5-membered heterocyclic residue and the 6-membered heterocyclic residue may form a condensed ring structure with other cyclic structures)). In one embodiment, the ester resin further has a structural unit represented by the following formula (4): [Chemical formula] (In formula (4), each of R8 and R9 represents one selected from a hydrogen atom, a linear alkyl group having 1 to 12 carbon atoms, a branched alkyl group having 3 to 12 carbon atoms, or a cyclic alkyl group having 3 to 6 carbon atoms). [Advantages of the Invention]

[0008] According to the method for producing a retardation film according to an embodiment of the present invention, by stretching a resin film containing a resin exhibiting positive birefringence and a resin exhibiting negative birefringence, which has birefringence of a certain level or more in the thickness direction and the retardation in the thickness direction exhibits inverse wavelength dispersion characteristics, a retardation film having high in-plane birefringence and the in-plane retardation exhibiting inverse wavelength dispersion characteristics can be suitably obtained. [Brief Description of the Drawings]

[0009] [Figure 1] It is a conceptual diagram for explaining the wavelength dispersion characteristics of the retardation in the thickness direction of the resin film. [Modes for Carrying Out the Invention]

[0010] Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to these embodiments. In this specification, "~" representing a numerical range includes the upper and lower limit numerical values. Also, in this specification, when it says "weight", it is synonymous with "mass" which is the SI unit system representing weight.

[0011] (Definition of Terms and Symbols) The definitions of terms and symbols used in this specification are as follows: (1) Refractive index (nx, ny, nz) "nx" is the refractive index in the direction where the refractive index is maximum in the plane (i.e., the slow phase axis direction), "ny" is the refractive index in the direction perpendicular to the slow phase axis in the plane (i.e., the fast phase axis direction), and "nz" is the refractive index in the thickness direction. (2) In-plane birefringence (Δn) "Δn(λ)" is the in-plane birefringence measured with light of wavelength λnm at 23℃. The in-plane birefringence (Δn) can be calculated from the formula: Δn = nx - ny. (3) In-plane phase difference (Re) "Re(λ)" is the in-plane phase difference measured with light of wavelength λnm at 23°C. For example, "Re(550)" is the in-plane phase difference measured with light of wavelength 550nm at 23°C. Re(λ) can be calculated using the formula: Re(λ) = (nx - ny) × d, where d (nm) is the thickness of the layer (film). (4) Birefringence in the thickness direction (ΔP) "ΔP(λ)" is the birefringence in the thickness direction measured with light of wavelength λnm at 23℃. The birefringence in the thickness direction (ΔP) can be calculated from the formula: ΔP = nx - nz. (5) Phase difference in the thickness direction (Rth) "Rth(λ)" is the phase difference in the thickness direction measured with light of wavelength λnm at 23°C. For example, "Rth(550)" is the phase difference in the thickness direction measured with light of wavelength 550nm at 23°C. Rth(λ) can be calculated using the formula: Rth(λ) = (nx - nz) × d, where d (nm) is the thickness of the layer (film). (6) Nz coefficient The Nz coefficient is calculated using the formula Nz = Rth / Re. (7)Angle In this specification, when an angle is referred to, it includes both clockwise and counterclockwise directions with respect to the reference direction. Therefore, for example, "45°" means 45° in either a clockwise or counterclockwise direction.

[0012] A. Method for manufacturing phase difference film A method for manufacturing a phase difference film according to an embodiment of the present invention is a method for manufacturing a phase difference film in which the in-plane birefringence Δn(590) at a measurement wavelength of 590 nm is greater than 0.003, and the ratio of the in-plane phase difference at a measurement wavelength of 450 nm to the in-plane phase difference at a measurement wavelength of 550 nm (Re(450) / Re(550)) is less than 0.90, To produce a resin film comprising a resin exhibiting positive birefringence and a resin exhibiting negative birefringence, wherein the birefringence ΔP(590) in the thickness direction at a measurement wavelength of 590 nm exceeds 0.0005, and the ratio of the phase difference in the thickness direction at a measurement wavelength of 450 nm to the phase difference in the thickness direction at a measurement wavelength of 550 nm (Rth(450) / Rth(550)) is less than 0.98 (resin film production process), and Stretching the resin film (stretching process) This includes the following. Here, "exhibiting positive birefringence" means that when a polymer is oriented by stretching or the like, the refractive index in the direction perpendicular to the stretching direction becomes relatively smaller. In other words, it means that the refractive index in the stretching direction becomes larger. "Exhibiting negative birefringence" means that when a polymer is oriented by stretching or the like, the refractive index in the stretching direction becomes relatively smaller. In other words, it means that the refractive index in the direction perpendicular to the stretching direction becomes larger.

[0013] A-1. Resin film manufacturing process In the resin film manufacturing process, a resin film is produced containing a resin exhibiting positive birefringence and a resin exhibiting negative birefringence, wherein ΔP(590) exceeds 0.0005 and Rth(450) / Rth(550) is less than 0.98. By stretching such a resin film, a phase difference film having the desired optical properties can be suitably obtained. The resin film may further contain any other suitable components as needed.

[0014] A-1-1. Resin film As described above, the resin film contains a resin exhibiting positive birefringence and a resin exhibiting negative birefringence, with ΔP(590) exceeding 0.0005 and Rth(450) / Rth(550) being less than 0.98.

[0015] The ΔP(590) of the resin film typically exceeds 0.0005, preferably is 0.0007 or more, and more preferably is 0.001 or more. Also, the upper limit of ΔP(590) is, for example, 0.004 or less, preferably 0.0035 or less. Since the resin film having ΔP(590) within the above range can exhibit high in-plane birefringence by stretching, a retardation film having a desired in-plane retardation and a small thickness can be suitably obtained.

[0016] The in-plane birefringence (Δn(590)) of the resin film at a measurement wavelength of 590 nm is, for example, 0.0003 or less, preferably 0 to 0.00005. The resin film having Δn(590) within the above range can exhibit stable in-plane orientation by stretching. In one embodiment, the resin film exhibits refractive index characteristics of nx = ny > nz.

[0017] The resin film exhibits reverse wavelength dispersion characteristics with respect to the retardation in the thickness direction. The resin film typically satisfies the relationship of Rth(450) / Rth(550) < 0.98, preferably satisfies the relationship of 0.60 < Rth(450) / Rth(550) < 0.98, and more preferably satisfies the relationship of 0.80 < Rth(450) / Rth(550) < 0.98. According to the resin film satisfying the above relationship, a retardation film that exhibits reverse wavelength dispersion characteristics with respect to the in-plane retardation by stretching can be suitably obtained.

[0018] In one embodiment, a nano-phase separation structure is formed in the resin film. The retardation film obtained by stretching such a resin film also has a nano-phase separation structure, whereby rapid shrinkage in a high-temperature and high-humidity environment (for example, 110°C and 85% RH (relative humidity)) can be suppressed.

[0019] In this specification, "nanophase separation structure" refers to a structure in which two components with different electron densities are phase-separated by domain sizes on the nano-order (typically at the level of several tens of nanometers). The resin exhibiting positive birefringence and the resin exhibiting negative birefringence may have a sea-island structure or a co-continuous structure. Examples of means for confirming the nanophase separation structure include transmission electron microscopy (TEM), scanning electron microscopy (SEM), atomic force microscopy (AFM), and small-angle X-ray scattering (SAXS), with TEM observation of a film cross-section being preferred. When a nanophase separation structure is formed in the film under observation, two types of domains with different electron densities can be confirmed by TEM observation of the film cross-section, and it can be confirmed that the size (maximum length) of all domains is less than 100 nm.

[0020] The glass transition temperature (Tg) of the resin film is, for example, 120°C to 220°C, preferably 125°C to 220°C, and more preferably 125°C to 210°C.

[0021] The thickness of the resin film is, for example, 50 μm to 200 μm, preferably 70 μm to 180 μm, and more preferably 100 μm to 180 μm.

[0022] The resin film may be in the form of a single sheet or in the form of a long strip. The resin film is preferably in the form of a long strip. In this specification, "long strip" means an elongated shape in which the length is sufficiently longer than the width, and for example, includes an elongated shape in which the length is 10 times or more, preferably 20 times or more, than the width. The long strip of resin film can be wound into a roll.

[0023] (A resin that exhibits positive birefringence) The resin exhibiting positive birefringence is not limited as long as the effects of the present invention are obtained, and for example, cellulosic resins such as cellulose and cellulose derivatives can be used. Examples of cellulose derivatives include cellulose ethers in which at least some of the hydroxyl groups of cellulose are etherified, and cellulose ether esters in which at least some of the hydroxyl groups are esterified. Among these, cellulose ethers can be preferably used. The resin exhibiting positive birefringence may be used alone or in combination of two or more types.

[0024] Cellulose resins are typically polymers in which β-glucose units are polymerized in a linear chain, and have the constituent units shown in formula (1) below. Such cellulose resins have flat wavelength dispersion characteristics with respect to the phase difference in the thickness direction and exhibit refractive index characteristics of nx > nz. [ka] (In formula (1), each of R1 to R3 represents a hydrogen atom or a substituent having 1 to 12 carbon atoms).

[0025] Examples of substituents having 1 to 12 carbon atoms represented by R1 to R3 in formula (1) above include alkyl groups such as methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, decanyl, dodecanyl, isobutyl, and t-butyl groups; cycloalkyl groups such as cyclohexyl groups; aryl groups such as phenyl and naphthyl groups; aralkyl groups such as benzyl groups; acyl groups such as acetyl and propionyl groups; cyanoalkyl groups such as cyanoethyl groups; aminoalkyl groups such as aminoethyl groups; and hydroxyalkyl groups such as 2-hydroxyethyl and 3-hydroxypropyl groups. In equation (1) above, R1 to R3 may be the same or different from each other. Preferably, R1 to R3 in formula (1) above are a hydrogen atom and an alkyl group having 1 to 12 carbon atoms, more preferably a hydrogen atom and an alkyl group having 1 to 4 carbon atoms, and even more preferably a hydrogen atom and an ethyl group.

[0026] The degree of substitution (hereinafter referred to as DS) of cellulose resins is typically between 1.5 and 2.95, preferably between 1.8 and 2.8. DS represents the percentage of hydroxyl groups substituted in the cellulose resin, with DS being 3 when 100% substitution occurs. DS can be calculated from the peak area of ​​gas chromatography, as described in the 17th edition of the Japanese Pharmacopoeia.

[0027] The number-average molecular weight (Mn) of cellulose resins, in terms of standard polystyrene equivalent, is, for example, 1 × 10⁻⁶. 3 The above 1 x 10 6 The following is preferably 5 × 10 3 The above 2 x 10 5 The following applies: The manganese content (Mn) of cellulose-based resins can be calculated from the elution curve measured by gel permeation chromatography (GPC). If the Mn content of the cellulose-based resin is within the above range, the mechanical properties and / or moldability of the resin film can be improved.

[0028] The glass transition temperature (Tg) of cellulose-based resins is, for example, 140°C or lower, preferably 135°C or lower, and for example, 120°C or higher, preferably 125°C or higher. The glass transition temperature (Tg) of cellulose-based resins can be measured by a thermal analyzer such as a DSC (Differential Scanning Calorimetry).

[0029] Specific examples of the cellulose-based resin include alkyl celluloses such as methyl cellulose, ethyl cellulose, and propyl cellulose; hydroxyalkyl celluloses such as hydroxyethyl cellulose and hydroxypropyl cellulose; aralkyl celluloses such as benzyl cellulose; cyanoalkyl celluloses such as cyanoethyl cellulose; carboxyalkyl celluloses such as carboxymethyl cellulose and carboxyethyl cellulose; carboxyalkylalkyl celluloses such as carboxymethylmethyl cellulose and carboxymethylethyl cellulose; and aminoalkyl celluloses such as aminoethyl cellulose. The cellulose-based resin can be used alone or in combination. Among the cellulose-based resins, alkyl cellulose is preferably used, and ethyl cellulose is more preferably used.

[0030] (Resin showing negative birefringence) The resin showing negative birefringence is not limited as long as the effects of the present invention can be obtained. For example, an ester-based resin having a structural unit represented by the following formula (2) and a structural unit represented by the following formula (3) can be used. Such an ester-based resin has positive wavelength dispersion characteristics with respect to the retardation in the thickness direction and shows a refractive index characteristic of nx < nz. The resin showing negative birefringence may be used alone or in combination of two or more. [Chemical formula] (In formula (2), R4 represents a hydrogen atom or an alkyl group having 1 to 12 carbon atoms; R 5a represents one selected from an alkyl group having 1 to 12 carbon atoms, a nitro group, a bromo group, an iodo group, a cyano group, a chloro group, a sulfonic acid group, a carboxylic acid group, a fluoro group, or a thiol group; R 5brepresents a hydrogen atom or an alkyl group having 1 to 12 carbon atoms; R6 represents a species selected from a hydrogen atom, a nitro group, a bromo group, an iodo group, a cyano group, a chloro group, a sulfonic acid group, a carboxylic acid group, a fluoro group, a phenyl group, a thiol group, an amide group, an amino group, a hydroxy group, an alkoxy group having 1 to 12 carbon atoms, or an alkyl group having 1 to 12 carbon atoms.) [Chemical formula] (In formula (3), R7 represents a 5-membered heterocyclic residue or a 6-membered heterocyclic residue containing at least one nitrogen atom or oxygen atom as a heteroatom (the 5-membered heterocyclic residue and the 6-membered heterocyclic residue may form a condensed ring structure with another cyclic structure).)

[0031] The structural unit shown in the above formula (2) is a cinnamic acid ester residue unit. Examples of the alkyl group having 1 to 12 carbon atoms represented by R4 in the above formula (2) include a methyl group, an ethyl group, an isopropyl group, an n-propyl group, an n-butyl group, an s-butyl group, a t-butyl group, an isobutyl group, and an ethylhexyl group. Among R4 in the above formula (2), preferably, an alkyl group having 1 to 4 carbon atoms is included, and more preferably, an ethyl group and an isobutyl group are included.) Among R 5a in the above formula (2), preferably, an alkyl group having 1 to 12 carbon atoms and a cyano group are included, more preferably, an alkyl group having 1 to 4 carbon atoms and a cyano group are included, and even more preferably, a cyano group is included.) Among R 5b in the above formula (2), preferably, a hydrogen atom and an alkyl group having 1 to 4 carbon atoms are included.) R6 in the above formula (2) may be bonded to the benzene ring only once or may be bonded to the benzene ring two or more times. Among R6 in the above formula (2), preferably, a carboxylic acid group and a hydroxy group are included.)

[0032] Specific examples of the constituent units (cinnamic acid ester residue units) shown in formula (2) above include α-cyano-4-hydroxycinnamate methyl residue unit, α-cyano-2-hydroxycinnamate ethyl residue unit, α-cyano-3-hydroxycinnamate ethyl residue unit, α-cyano-4-hydroxycinnamate ethyl residue unit, α-cyano-4-hydroxycinnamate n-propyl residue unit, α-cyano-4-hydroxycinnamate isopropyl residue unit, α-cyano-4-hydroxycinnamate n-butyl residue unit, and α-cyano-4-hydroxycinnamate α-cyano-hydroxycinnamic acid ester residue units such as isobutyl hydroxycinnamate residue units, α-cyano-4-hydroxycinnamate s-butyl residue units, and α-cyano-2,4-dihydroxycinnamate methyl residue units; α-cyano-carboxycinnamic acid ester residue units such as α-cyano-4-carboxycinnamate methyl residue units, α-cyano-4-carboxycinnamate ethyl residue units, α-cyano-2,3-dicarboxycinnamate methyl residue units, and α-cyano-2,3-dicarboxycinnamate ethyl residue units; α-Cyano-2-carboxy-3-hydroxycinnamate methyl residue unit, α-Cyano-2-carboxy-3-hydroxycinnamate ethyl residue unit, and other α-Cyano-2-carboxy-3-hydroxycinnamate ethyl residue unit; 3-alkyl-3-(hydroxyphenyl)-propa-2-enoate methyl residue unit, 3-ethyl-3-(hydroxyphenyl)-propa-2-enoate ethyl residue unit, and other 3-alkyl-3-(hydroxyphenyl)-propa-2-enoate ethyl residue unit; 3-methyl-3-(carboxyphenyl 3-alkyl-3-(carboxyphenyl)-propa-2-enoic acid ester residue units such as methyl methyl residue units and ethyl ethyl ethyl 3-ethyl-3-(carboxyphenyl)-propa-2-enoic acid residue units; 2-cyano-3-alkyl-3-(hydroxyphenyl)-propa-2-enoic acid ester residue units such as methyl methyl 2-cyano-3-methyl-3-(hydroxyphenyl)-propa-2-enoic acid residue units and ethyl ethyl 2-cyano-3-ethyl-3-(hydroxyphenyl)-propa-2-enoic acid residue units;Examples include 2-cyano-3-alkyl-3-(carboxyphenyl)-propa-2-enoic acid ester residue units such as 2-cyano-3-methyl-3-(carboxyphenyl)-propa-2-enoic acid methyl residue units and 2-cyano-3-ethyl-3-(carboxyphenyl)-propa-2-enoic acid ethyl residue units.

[0033] The ester resin may contain only one of the constituent units shown in formula (2) above, or it may contain two or more. Among the constituent units shown in formula (2) above, preferred examples include α-cyano-hydroxycinnamic acid ester residue units, α-cyano-carboxycinnamic acid ester residue units, 3-alkyl-3-(hydroxyphenyl)-propa-2-enoic acid ester residue units, and 3-alkyl-3-(carboxyphenyl)-propa-2-enoic acid ester residue units.

[0034] The content of the constituent units of formula (2) in the ester resin is, for example, 21 mol% or more, for example, 70 mol% or less, preferably 60 mol% or less, and more preferably 49 mol% or less. The content of each constituent unit in the ester resin is, for example, 1 It can be measured by 1H-NMR.

[0035] Specific examples of the ring structure represented by R7 in formula (3) above include 1-vinylpyrrole residue units, 2-vinylpyrrole residue units, 1-vinylindole residue units, 9-vinylcarbazole residue units, 2-vinylquinoline residue units, 4-vinylquinoline residue units, N-vinylphthalimide residue units, N-vinylsuccinimide residue units, 2-vinylfuran residue units, and 2-vinylbenzofuran residue units, with 9-vinylcarbazole residue units and N-vinylphthalimide residue units being preferred.

[0036] The ester resin may contain only one of the constituent units shown in formula (3) above, or it may contain two or more. The content of the constituent unit of formula (3) in the ester resin is, for example, 21 mol% or more, preferably 35 mol% or more, and for example, 70 mol% or less, preferably 60 mol% or less.

[0037] The ester resin preferably has, in addition to the constituent units shown in (2) and (3) above, the constituent unit shown in the following formula (4). [ka] (In formula (4), R8 and R9 each represent one selected from a hydrogen atom, a linear alkyl group having 1 to 12 carbon atoms, a branched alkyl group having 3 to 12 carbon atoms, or a cyclic alkyl group having 3 to 6 carbon atoms.) In formula (4) above, examples of linear alkyl groups having 1 to 12 carbon atoms represented by R8 and R9 include methyl group, ethyl group, n-propyl group, n-butyl group, n-pentyl group, n-hexyl group, and the like. In formula (4) above, examples of branched alkyl groups having 3 to 12 carbon atoms represented by R8 and R9 include isopropyl group, isobutyl group, sec-butyl group, tert-butyl group, etc. In formula (4) above, examples of cyclic alkyl groups having 3 to 6 carbon atoms represented by R8 and R9 include cyclopropyl group, cyclobutyl group, and cyclohexyl group. In equation (4) above, R8 and R9 may be the same or different from each other. In formula (4) above, R8 is preferably a hydrogen atom and a linear alkyl group having 1 to 12 carbon atoms, and more preferably a hydrogen atom and a methyl group. In formula (4) above, R9 is preferably a branched alkyl group having 3 to 12 carbon atoms, and more preferably a branched alkyl group having 3 to 8 carbon atoms.

[0038] The constituent units shown in formula (4) above are typically acrylic resin residue units. Specific examples of the constituent units shown in formula (4) above include acrylic acid residue units, methacrylic acid residue units, 2-ethyl acrylic acid residue units, 2-propyl acrylic acid residue units, 2-isopropyl acrylic acid residue units, 2-pentyl acrylic acid residue units, 2-hexyl acrylic acid residue units, methyl acrylate residue units, ethyl acrylate residue units, n-propyl acrylate residue units, isopropyl acrylate residue units, n-butyl acrylate residue units, isobutyl acrylate residue units, sec-butyl acrylate residue units, n-pentyl acrylate residue units, isopentyl acrylate residue units, sec-pentyl acrylate residue units, 3-pentyl acrylate residue units, neopentyl acrylate residue units, n-hexyl acrylate residue units, isohexyl acrylate residue units, neohexyl acrylate residue units, methyl methacrylate residue units, ethyl methacrylate residue units, and methacrylate residue units. Examples include n-propyl methacrylate residue units, isopropyl methacrylate residue units, n-butyl methacrylate residue units, isobutyl methacrylate residue units, sec-butyl methacrylate residue units, n-pentyl methacrylate residue units, isopentyl methacrylate residue units, sec-pentyl methacrylate residue units, 3-pentyl methacrylate residue units, neopentyl methacrylate residue units, n-hexyl methacrylate residue units, isohexyl methacrylate residue units, neohexyl methacrylate residue units, methyl 2-ethylacrylate residue units, ethyl 2-ethylacrylate residue units, n-propyl 2-ethylacrylate residue units, isopropyl 2-ethylacrylate residue units, n-butyl 2-ethylacrylate residue units, isobutyl 2-ethylacrylate residue units, sec-butyl 2-ethylacrylate residue units, and the like, with isobutyl acrylate residue units being preferred.

[0039] The ester resin may contain only one of the constituent units shown in formula (4) above, or it may contain two or more. The content of the constituent unit of formula (4) in the ester resin is, for example, 0 mol% or more, preferably 1 mol% or more, and for example, 30 mol% or less.

[0040] Ester resins may contain monomer residue units other than those of formulas (2) to (4) above. Examples of such monomer residue units include styrene residues such as styrene residues and α-methylstyrene residues; vinylnaphthalene residues; vinyl ester residues such as vinyl acetate residues and vinyl propionate residues; vinyl ether residues such as methyl vinyl ether residues, ethyl vinyl ether residues and butyl vinyl ether residues; N-substituted maleimide residues such as N-methylmaleimide residues, N-cyclohexylmaleimide residues and N-phenylmaleimide residues; acrylonitrile residues; methacrylonitrile residues; fumarate ester residues; fumarate residues; and olefin residues such as ethylene residues and propylene residues.

[0041] The number-average molecular weight (Mn) of ester resins on a standard polystyrene basis is, for example, 1 × 10⁻⁶. 3 The above 5 x 10 6 The following is preferably 5 × 10 3 The above 3 x 10 5 The following applies: The manganese (Mn) content of ester resins can be calculated from the elution curve measured by gel permeation chromatography (GPC). If the manganese content of the ester resin is within the above range, the mechanical properties and / or moldability of the resin film can be improved.

[0042] The glass transition temperature (Tg) of ester resins is, for example, 220°C or lower, preferably 210°C or lower, and for example, 180°C or higher, preferably 190°C or higher. The glass transition temperature (Tg) of ester resins can be measured by a thermal analyzer such as a DSC (Differential Scanning Calorimetry).

[0043] Specific examples of such ester resins include α-cyano-2-hydroxycinnamic acid ester-styrene-acrylic acid ester copolymer, α-cyano-2-hydroxycinnamic acid ester-2-vinylnaphthalene-acrylic acid ester copolymer, α-cyano-2-hydroxycinnamic acid ester-1-vinylindole-acrylic acid ester copolymer, α-cyano-2-hydroxycinnamic acid ester-9-vinylcarbazole-acrylic acid ester copolymer, α-cyano-3-hydroxycinnamic acid ester-styrene-acrylic acid ester copolymer, α -Cyano-3-hydroxycinnamic acid ester-2-vinylnaphthalene-acrylic acid ester copolymer, α-cyano-3-hydroxycinnamic acid ester-1-vinylindole-acrylic acid ester copolymer, α-cyano-3-hydroxycinnamic acid ester-9-vinylcarbazole-acrylic acid ester copolymer, α-cyano-4-hydroxycinnamic acid ester-styrene-acrylic acid ester copolymer, α-cyano-4-hydroxycinnamic acid ester-2-vinylnaphthalene-acrylic acid ester copolymer, α-cyano-4-hydroxycinnamic acid ester Stel-1-vinylindole-acrylic acid copolymer, α-cyano-4-hydroxycinnamic acid ester-9-vinylcarbazole-acrylic acid copolymer, α-cyano-2-hydroxycinnamic acid ester-styrene-methacrylic acid copolymer, α-cyano-2-hydroxycinnamic acid ester-2-vinylnaphthalene-methacrylic acid copolymer, α-cyano-2-hydroxycinnamic acid ester-1-vinylindole-methacrylic acid copolymer, α-cyano-2-hydroxycinnamic acid ester-9-vinylcarbazole α-Cyano-3-hydroxycinnamic acid-styrene-methacrylic acid copolymer, α-Cyano-3-hydroxycinnamic acid-2-vinylnaphthalene-methacrylic acid copolymer, α-Cyano-3-hydroxycinnamic acid-1-vinylindole-methacrylic acid copolymer, α-Cyano-3-hydroxycinnamic acid-9-vinylcarbazole-methacrylic acid copolymer, α-Cyano-4-hydroxycinnamic acid-styrene-methacrylic acid copolymer,Examples include α-cyano-4-hydroxycinnamic acid ester-2-vinylnaphthalene-methacrylic acid copolymer, α-cyano-4-hydroxycinnamic acid ester-1-vinylindole-methacrylic acid copolymer, and α-cyano-4-hydroxycinnamic acid ester-9-vinylcarbazole-methacrylic acid copolymer.

[0044] (Content ratio of resin showing positive birefringence and resin showing negative birefringence) When the total of the resin showing positive birefringence and the resin showing negative birefringence is 100% by mass, the content ratio of the resin showing positive birefringence in the resin film typically exceeds 50% by mass, preferably 70% by mass or more, more preferably 80% by mass or more. Also, the upper limit of the content ratio of the resin showing positive birefringence is typically 90% by mass or less. If the content ratio of the resin showing positive birefringence is at least the above lower limit, the resin showing positive birefringence and the resin showing negative birefringence can stably form a nano-phase separation structure. Further, as shown in FIG. 1, the wavelength dispersion characteristic of the retardation in the thickness direction of the resin film can be understood as being synthesized from the wavelength dispersion characteristics of the retardation in the thickness direction of each of the resin showing positive birefringence and the resin showing negative birefringence. Therefore, by including the above cellulose-based resin having a flat wavelength dispersion characteristic with respect to the retardation in the thickness direction and showing a refractive index characteristic of nx>nz, and the above ester-based resin having a positive wavelength dispersion characteristic and showing a refractive index characteristic of nx<nz in the above ratio, a resin film having an inverse wavelength dispersion characteristic with respect to the retardation in the thickness direction and showing a refractive index characteristic of nx>nz can be suitably obtained.

[0045] (Other components) Other components may be appropriately selected depending on the purpose. Examples of other components include antioxidants such as hindered phenol antioxidants, phosphorus antioxidants, sulfur antioxidants, lactone antioxidants, amine antioxidants, hydroxylamine antioxidants, vitamin E antioxidants, and other antioxidants; hindered amine light stabilizers; UV absorbers such as benzotriazole, benzophenone, triazine, and benzoate; surfactants; polymer electrolytes; conductive complexes; pigments; dyes; antistatic agents; antiblocking agents; and lubricants. The content of other components is, for example, 0.01 to 0.3 parts by weight per 100 parts by weight of the resin component.

[0046] A-1-2. Method for manufacturing resin film The resin film is manufactured by mixing the components that make up the resin film described in Section A-1-1 to prepare a resin composition, and then molding it into a film.

[0047] Mixing methods include melt mixing and solution mixing. Melt mixing involves melting resins and other materials by heating and then kneading them. Solution mixing involves dissolving resins and other materials in a solvent and then mixing them.

[0048] As for the solvent used in the solution mixing method, from the viewpoint of minimizing solvent residue in the film formation process, a solvent with a boiling point of 200°C or lower is preferred, and a solvent with a boiling point of 170°C or lower is more preferred. Specific examples of solvents include halogenated hydrocarbons such as chloroform, dichloromethane, carbon tetrachloride, dichloroethane, tetrachloroethane, trichloroethylene, tetrachloroethylene, chlorobenzene, and dichlorobenzene; phenols such as phenol and chlorophenol; aromatic hydrocarbons such as benzene, toluene, xylene, methoxybenzene, mesitylene, and dimethoxybenzene; ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone (MIBK), cyclohexanone, cyclopentanone (CPN), 2-pyrrolidone, and N-methyl-2-pyrrolidone; ester solvents such as ethyl acetate and butyl acetate; and butanol, t-butyl alcohol, glycerin, and ethyl acetate. Examples of solvents include alcohol-based solvents such as ethylene glycol, triethylene glycol, ethylene glycol monomethyl ether, diethylene glycol dimethyl ether, propylene glycol, dipropylene glycol, and 2-methyl-2,4-pentanediol; amide-based solvents such as dimethylformamide and dimethylacetamide; nitrile-based solvents such as acetonitrile and butyronitrile; ether-based solvents such as 1,3-dioxolane, cyclopentyl methyl ether (CPME), propylene glycol methyl ether acetate (PGMEA), diethyl ether, dibutyl ether, and tetrahydrofuran; carbon disulfide, ethyl cellosolve, butyl cellosolve, and mixtures thereof.

[0049] Among the solvents, mixed solvents are preferred. Examples of mixed solvent combinations include ester solvent / aromatic hydrocarbons, ether solvent / aromatic hydrocarbons, ester solvent / ether solvent, ester solvent / alcohol solvent, ester solvent / ketone solvent, two types of ether solvents, and two types of ester solvents.

[0050] More preferably, the mixed solvent is an ester solvent / aromatic hydrocarbon, even more preferably ethyl acetate / toluene, and particularly preferably a mixed solvent of ethyl acetate / toluene = 40% by mass / 60% by mass to 60% by mass / 40% by mass. When the solvent is such a mixed solvent, a resin film with the desired orientation can be suitably obtained. Furthermore, in the phase difference film, the cellulose resin and the ester resin can form a nanophase separation structure more stably.

[0051] Any suitable method can be used to mold the resin composition. Specific examples include compression molding, transfer molding, injection molding, extrusion molding, blow molding, powder molding, FRP molding, cast coating (e.g., casting), calendering, and hot pressing. Among these, cast coating is preferred. Cast coating is a method of obtaining a film by applying (e.g., casting) a resin solution containing the above-mentioned resin and solvent onto a support substrate to form a coating layer, and then heating the coating layer to evaporate the solvent.

[0052] The coating method is not particularly limited, and conventional methods can be used. Examples include the T-die method, doctor blade method, bar coater method, slot die method, lip coater method, reverse gravure coating method, microgravure method, spin coating method, brush coating method, roll coating method, and flexographic printing method. The molding conditions can be appropriately set according to the composition and type of resin used, the desired properties of the phase difference film, etc.

[0053] Examples of supporting substrates include polymer substrates made of polyester, polycarbonate, polystyrene, polyethylene, polypropylene, polyvinyl chloride, polyvinylidene chloride, triacetylcellulose, polyvinyl alcohol, polyimide, polyarylate, polysulfone, polyethersulfone, epoxy resins, etc.; glass substrates such as glass plates and quartz substrates; metal substrates such as aluminum, stainless steel, and ferrotype; and inorganic substrates such as ceramic substrates. The above substrates are preferably polymer substrates or metal substrates.

[0054] From the perspectives of productivity, formability, etc., the viscosity of the resin composition (melt or solution) during molding is preferably 100 cps to 30,000 cps, more preferably 300 cps to 20,000 cps, and even more preferably 500 cps to 15,000 cps. The viscosity of the resin composition can be adjusted by the molecular weight, concentration of each component, type of solvent, etc.

[0055] The solid content concentration of the resin solution is, for example, 1 wt% to 30 wt%, preferably 5 wt% to 30 wt%, and more preferably 10 wt% to 24 wt%.

[0056] The coating thickness (thickness of the coating layer) of the resin solution is, for example, 50 μm to 1000 μm, preferably 50 μm to 900 μm, more preferably 70 μm to 800 μm, and even more preferably 100 μm to 700 μm (for example, 300 μm to 700 μm). If the coating thickness is within this range, the in-plane orientation per unit thickness can be ensured without significantly reducing it, and the film thickness after stretching can be guaranteed. For example, the in-plane retardation characteristics required for a λ / 4 plate can be ensured.

[0057] The drying method in the drying of the coating layer is not particularly limited, and ordinary heating means can be adopted. For example, a hot air blower, a heating roll, an infrared heater, etc. can be mentioned.

[0058] When the resin film contains a plurality of types of resins in a single layer, each resin can be independently oriented within the resin film. Also, the orientation of each resin can vary depending on the drying temperature, coating thickness, solution concentration of the resin, etc. For example, the higher the drying temperature (as a result, the higher the evaporation rate of the solvent), the more likely the orientation of the resin in the resin film is to be disrupted. Therefore, for example, when forming a resin film using the above cellulose-based resin and the above ester-based resin as a resin showing positive birefringence and a resin showing negative birefringence, respectively, since the cellulose-based resin exhibits a refractive index characteristic of nx = ny > nz and the ester-based resin exhibits a refractive index characteristic of nx = ny < nz, a relationship as shown in Table 1 below can be established between the retardation in the thickness direction of the obtained resin film and the drying temperature.

[0059] [Table 1]

[0060] Therefore, when using the above-mentioned cellulose resin and ester resin in combination, from the viewpoint of exhibiting a certain level or higher of ΔP in each resin, the drying temperature of the coated layer may be, for example, in the range of 35°C to 160°C, preferably 50°C to 155°C. The drying time is, for example, 60 seconds to 1200 seconds, preferably 60 seconds to 900 seconds, more preferably 90 seconds to 900 seconds.

[0061] Drying may be carried out at a constant temperature or while the temperature is varied. For example, drying may be carried out by gradually or stepwise increasing the temperature. When drying is carried out while the temperature is varied, the weighted average temperature, weighted by the processing time at each temperature, is, for example, 50°C to 140°C, preferably 70°C to 140°C, and more preferably 70°C to 130°C.

[0062] When drying is carried out with a stepwise increase in temperature, the drying temperature for the first stage is set to, for example, 35°C to 65°C, preferably 45°C to 65°C, and the drying time for the first stage is set to, for example, 1 minute to 30 minutes, preferably 1 minute to 8 minutes. Thereafter, the drying temperature is increased in each stage, for example, 10°C to 60°C, preferably 10°C to 40°C. The drying time for each stage from the second stage onward is typically shorter than the drying time for the first stage, preferably 20 seconds to 20 minutes, more preferably 30 seconds to 5 minutes. The number of drying stages is preferably 2 to 4, more preferably 3 or fewer. By performing drying in multiple stages in this way, the orientation in the thickness direction of each resin can be ensured, and a nanophase separation structure can be suitably formed in the resulting resin film (ultimately, a phase difference film).

[0063] In one embodiment, the maximum temperature in the multi-stage drying process (the final drying temperature) is, for example, greater than 130°C and less than or equal to 160°C, preferably greater than 130°C and less than or equal to 155°C, and more preferably between 135°C and 155°C. When the maximum temperature is within this range, the resulting resin film exhibits a relatively low ΔP (e.g., ΔP < 0.0015) while being able to be stretched at a relatively high stretching ratio (e.g., 3.0 times or more, or 3.5 times or more). Therefore, by applying a high stretching ratio, a wide phase difference film with desired optical properties (in-plane phase difference, inverse wavelength dispersion properties, etc.) can be obtained, which can be applied to the production of large-area optical laminates (e.g., circular polarizers) by a roll-to-roll process. Specifically, for example, by stretching at a stretching ratio of 3.0 times or more, preferably 3.5 times or more, a phase difference film with Re(550) of 130 nm to 160 nm can be obtained. In another embodiment, the maximum temperature in multi-stage drying (the drying temperature in the final stage) is, for example, 100°C to 140°C, preferably 100°C to 130°C, more preferably 100°C to 120°C, and even more preferably 110°C to 120°C. When the maximum temperature is within this range, the resulting resin film exhibits a relatively high ΔP (e.g., ΔP ≥ 0.0015), making it possible to obtain a phase difference film with desired optical properties even at a relatively low stretching ratio. Specifically, for example, by stretching at a stretching ratio of less than 3.5 times, preferably less than 3.0 times, a phase difference film with Re(550) of 130 nm to 160 nm can be obtained. As described above, the drying temperature of the coated layer is one of the factors that affect the ΔP of the resin film, and by performing stretching with characteristic stretching conditions such as stretching ratio and stretching temperature according to the ΔP of the resin film, a desired phase difference film such as an inverse wavelength dispersion λ / 4 plate can be obtained.

[0064] The method for producing the resin film may include a secondary drying step (annealing step) in which the coated layer is heated to 110°C or higher after drying. The drying temperature of the secondary drying step (annealing step) is, for example, 110°C or higher, preferably 130°C or higher, and for example, 180°C or lower, preferably 165°C or lower. The drying time of the secondary drying step (annealing step) is, for example, 1 minute or more, preferably 5 minutes or more, and for example, 60 minutes or lower, preferably 45 minutes or lower. Preferably, the coated layer after drying is cooled to, for example, 50°C or lower, preferably 30°C or lower, more preferably room temperature (23°C) before the secondary drying step is performed. Once the coated layer after drying is cooled, the orientation and nanophase separation structure formed during the drying process can be fixed and retained in the subsequent secondary drying step.

[0065] The solvent content (residual rate) in the resin film after drying (or after the secondary drying step, if a secondary drying step is included) is, for example, 0% to 10% by weight, preferably 0% to 5% by weight.

[0066] A-2.Stretching process In the stretching process, the resin film described above is stretched. The stretching method is not limited as long as the phase difference film described in Section B is obtained, and any appropriate stretching method can be adopted. Specifically, various stretching methods such as free-end stretching, fixed-end stretching, free-end shrinking, and fixed-end shrinking can be used individually, simultaneously, or sequentially. The stretching direction can also be in various directions and dimensions, such as the length direction, width direction, thickness direction, and diagonal direction.

[0067] Specific examples of stretching methods include fixed-end uniaxial stretching, free-end uniaxial stretching, and oblique stretching. Fixed-end uniaxial stretching can be performed, for example, by using a tenter-type stretching device to transport a long resin film in the longitudinal direction while stretching it in a direction perpendicular to the longitudinal direction (width direction). Free-end uniaxial stretching can be performed, for example, by passing a long resin film between rolls with different peripheral speeds and stretching it in the longitudinal direction. Oblique stretching can be performed, for example, by continuously stretching a long resin film obliquely in a direction at an angle θ with respect to the longitudinal direction. By employing oblique stretching, a long phase difference film having an orientation angle of angle θ with respect to the longitudinal direction of the film (the slow phase axis in the direction of angle θ) can be obtained, which allows for roll-to-roll lamination with a polarizer, for example, and simplifies the manufacturing process. The angle θ may be the angle between the absorption axis of the polarizer and the slow phase axis of the phase difference film in a polarizing plate with a phase difference layer. The angle θ is preferably 40° to 50°, more preferably 42° to 48°, and even more preferably about 45°.

[0068] The stretching ratio can be appropriately selected based on the desired in-plane phase difference, etc. The stretching ratio is, for example, 2.0 times or more, preferably 2.5 times or more, more preferably 3.0 times or more, and also, for example, 8.0 times or less, preferably 7.5 times or less, and more preferably 5.0 times or less.

[0069] The thickness of the stretched resin film is, for example, 10 μm to 80 μm, preferably 10 μm to 70 μm, and more preferably 10 μm to 50 μm. Furthermore, the thickness of the stretched resin film is, for example, 50% or less of the thickness of the unstretched resin film, preferably 12.5% ​​to 50%, and more preferably 12.5% ​​to 40%. When the film thickness before and after stretching satisfies this relationship, a phase difference film with high in-plane birefringence can be obtained.

[0070] The stretching temperature can vary depending on the in-plane retardation and thickness desired for the retardation film, the type of resin used, the thickness of the resin film, the stretching ratio, etc. The stretching temperature varies in relation to the Tg of the materials contained in the resin film, and is, for example, Tg1 - 20°C to Tg1 + 50°C, preferably Tg1 - 20°C to Tg1 + 40°C, more preferably Tg1 - 10°C to Tg1 + 40°C with respect to the glass transition temperature (Tg1) of the resin having the lowest Tg among the resins having orientation properties. If the stretching temperature is within this range, stable stretching can be achieved.

[0071] The stretching speed is, for example, 1 mm / second or more, preferably 2 mm / second or more, and is, for example, 200 mm / second or less, preferably 100 mm / second or less.

[0072] The resin film is preferably preheated before stretching. The preheating temperature is also set with respect to Tg1 in the same manner as the stretching temperature. The preheating temperature is, for example, Tg1 - 20°C or higher, preferably Tg1 - 10°C or higher, and is, for example, Tg1 + 50°C or lower, preferably Tg1 + 40°C or lower. The preheating temperature is typically higher than the stretching temperature, preferably 5°C or more higher than the stretching temperature.

[0073] If necessary, the process may include heat - shrinking the stretched resin film in the stretching direction. The heat - shrinking temperature is also set with respect to Tg1 in the same manner as the preheating and stretching temperatures, and is, for example, Tg1 - 20°C or higher, preferably Tg1 - 15°C or higher, and is, for example, Tg1 + 45°C or lower, preferably Tg1 + 35°C or lower. The heat - shrinking temperature is more preferably below the stretching temperature. The shrinkage ratio is typically 1% or more and 5% or less.

[0074] B. Retardation Film The retardation film produced by the method for producing a retardation film described in section A typically exhibits a refractive index characteristic showing the relationship of nx > ny ≧ nz. Here, "ny = nz" includes not only the case where ny and nz are completely equal but also the case where they are substantially equal. Therefore, within the range that does not impair the effects of the present invention, ny < nz may occur.

[0075] The in-plane birefringence (Δn(590)) of the retardation film (in other words, the resin film after stretching) at a measurement wavelength of 590 nm typically exceeds 0.003, preferably exceeds 0.0035, more preferably is 0.0037 or more, and still more preferably is 0.0040 or more. The Δn(590) of the retardation film can be, for example, 0.007 or less.

[0076] The in-plane retardation of the retardation film can be any appropriate value depending on the application and the like. In one embodiment, the retardation film can function as a λ / 4 plate. In this case, Re(550) of the retardation film is preferably 100 nm to 190 nm, more preferably 110 nm to 170 nm, and still more preferably 130 nm to 160 nm.

[0077] The Nz coefficient of the retardation film is preferably 0.9 to 3, more preferably 0.9 to 2.5, still more preferably 0.9 to 1.5, and particularly preferably 0.9 to 1.3. By satisfying such a relationship, when used in an image display device as a circular polarizing plate in combination with a polarizer, an extremely excellent reflected hue can be achieved.

[0078] The retardation film typically exhibits an inverse dispersion wavelength characteristic in which the in-plane retardation increases as the wavelength of the measurement light increases. The retardation film typically satisfies the relationship of Re(450) / Re(550) < 0.90, preferably satisfies the relationship of Re(450) / Re(550) < 0.88, and more preferably satisfies the relationship of 0.70 < Re(450) / Re(550) < 0.88. When a retardation film satisfying such a relationship is used in an image display device as a circular polarizing plate in combination with a polarizer, extremely excellent antireflection characteristics can be realized.

[0079] The thickness of the retardation film is, for example, 10 μm to 80 μm, preferably 10 μm to 50 μm, and more preferably 10 μm to 30 μm. Since the retardation film obtained by the manufacturing method of the embodiment of the present invention has high in-plane birefringence, it can have a practically sufficient in-plane retardation with a small thickness.

Examples

[0080] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. The measurement methods for each characteristic are as follows. Unless otherwise specified, "parts" and "%" in the examples and comparative examples are based on weight. (1) Thickness The measurement was performed using a dial gauge (PEACOCK Corporation, product name "DG-205 type pds-2"). (2) In-plane phase difference (Re(λ)) and phase difference in the thickness direction (Rth(λ)) The film to be measured was cut into sections 4 cm long and 4 cm wide to form the measurement samples. The in-plane phase difference or the phase difference in the thickness direction at a measurement wavelength of λ nm was measured for these samples using an Axometrics Axoscan device. The measurement temperature was 23°C. (3) In-plane birefringence (Δn(λ)) and birefringence in the thickness direction (ΔP(λ)) The in-plane phase difference at the measurement wavelength λnm of the sample measured in (2) above was divided by the thickness of the sample to calculate the in-plane birefringence at the measurement wavelength λnm. Similarly, the thickness-direction birefringence at the measurement wavelength λnm of the sample measured in (2) above was divided by the thickness of the sample to calculate the thickness-direction birefringence at the measurement wavelength λnm. (4) Glass transition temperature (Tg) Measurements were taken in accordance with JIS K 7121.

[0081] [Synthesis Example 1] Synthesis of cinnamic acid ester copolymer (9-vinylcarbazole / α-cyano-4-hydroxycinnamate isobutyl / acrylate isobutyl) 12.20 g of 9-vinylcarbazole, 7.74 g of isobutyl α-cyano-4-hydroxycinnamate, 4.05 g of isobutyl acrylate, and 0.453 g of 2,5-dimethyl-2,5-di(2-ethylhexanoylperoxy)hexane and 36.00 g of methyl ethyl ketone, which are polymerization initiators, were placed in a 50 mL glass ampoule. After repeated nitrogen purging and pressure release, the ampoule was sealed under reduced pressure. Radical polymerization was carried out by placing this ampoule in a 54°C constant temperature bath and maintaining it for 24 hours. After the polymerization reaction was complete, the polymer was removed from the ampoule, 100 g of tetrahydrofuran was added, and this polymer solution was added dropwise to 800 g of methanol / water mixed solvent (weight ratio 80 / 20) to precipitate. After filtration, the filtrate was washed five times with 110 g of methanol / water mixed solvent (weight ratio 90 / 10) and filtered again. The obtained resin was vacuum-dried at 80°C for 10 hours to yield 22.3 g of a cinnamic acid ester copolymer exhibiting negative birefringence. The number-average molecular weight of the obtained cinnamic acid ester copolymer was 50,000, and the ratio of residue units was 50 mol% 9-vinylcarbazole residue units, 25 mol% α-cyano-4-hydroxycinnamate isobutyl residue units, and 25 mol% isobutyl acrylate residue units.

[0082] [Example 1] 80g of ethylcellulose (Dow Chemical's "ETHOCEL standard 100", number average molecular weight Mn=58,000, weight average molecular weight Mw=180,000, Mw / Mn=3.2, degree of total substitution DS=2.51) as a cellulosic resin, 20g of cinnamic acid ester resin obtained in Synthesis Example 1 as an ester resin, and 0.1g of hindered phenol antioxidant (BASF Japan, product name "Irganox 245") were dissolved in a toluene / ethyl acetate = 4 / 6 (weight ratio) solution to obtain a resin solution with a resin concentration of 16% by weight. This solution was poured onto a polyethylene terephthalate film using a coater to obtain a coating layer with a target thickness of 560 μm. The coating layer was dried at 65°C for 360 seconds, 85°C for 60 seconds, and 110°C for 120 seconds in that order, and then peeled off from the polyethylene terephthalate film to obtain a resin film with a thickness of 109 μm. The obtained resin film was preheated at a temperature 10°C higher than the stretching temperature, then uniaxially stretched to 3.0 times its original size at 155°C using a tenter stretcher, and then thermally shrunk by 2.4% in the stretching direction at 155°C to obtain a phase difference film.

[0083] A sample was taken from the vicinity of the center in the thickness direction of the stretched resin film (phase difference film) (specifically, a region within ±20% of the center in the thickness direction of the phase difference film when the thickness of the phase difference film is set to 100%). The cross-section of the phase difference film was observed using a TEM (HT7820, Hitachi Corporation) with an ultrathin sectioning method including heavy metal staining (cross-sectional TEM observation), and it was confirmed that a nanophase separation structure was formed in which the size (maximum length) of all domains was less than 100 nm.

[0084] [Example 2] A phase difference film was obtained in the same manner as in Example 1, except that the thickness of the coating layer was changed and thermal shrinkage was not performed.

[0085] [Example 3] A phase difference film was obtained in the same manner as in Example 1, except that the stretching temperature and the heat shrinkage temperature (isothermal to the stretching temperature) were changed.

[0086] [Example 4] A phase difference film was obtained in the same manner as in Example 1, except that the stretching ratio, stretching temperature, and heat shrinkage temperature (isothermal to the stretching temperature) were changed.

[0087] [Example 5] A phase difference film was obtained in the same manner as in Example 1, except that the thickness of the coating layer was changed and the coating layer was dried in the following order: 360 seconds at 65°C, 60 seconds at 85°C, and 120 seconds at 155°C.

[0088] [Example 6] A phase difference film was obtained in the same manner as in Example 5, except that the stretching ratio, stretching temperature, and heat shrinkage temperature (isothermal to the stretching temperature) were changed.

[0089] [Comparative Example 1] As a cellulosic resin, 100g of ethylcellulose (Dow Chemical's "ETHOCEL standard 100," number average molecular weight Mn=58,000, weight average molecular weight Mw=180,000, Mw / Mn=3.2, degree of total substitution DS=2.51) and 0.1g of a hindered phenol antioxidant (BASF Japan, product name "Irganox 245") were dissolved in a toluene / ethyl acetate = 4 / 6 (weight ratio) solution to obtain a resin solution with a resin concentration of 16% by weight. This solution was poured onto a polyethylene terephthalate film using a coater to obtain a coating layer. The coating layer was dried at 80°C for 150 seconds, 120°C for 150 seconds, and 150°C for 150 seconds in that order, and then peeled off from the polyethylene terephthalate film to obtain a resin film. The obtained resin film was preheated at a temperature 10°C higher than the stretching temperature, and then uniaxially stretched to 3.0 times its original size at 150°C using a tenter stretcher to obtain a phase difference film.

[0090] [Comparative Example 2] 90g of ethylcellulose (Dow Chemical Company's "ETHOCEL standard 100," number average molecular weight Mn=58,000, weight average molecular weight Mw=180,000, Mw / Mn=3.2, degree of total substitution DS=2.51) as a cellulosic resin, 10g of cinnamic acid ester resin obtained in Synthesis Example 1 as an ester resin, and 0.1g of a hindered phenol antioxidant (BASF Japan, product name "Irganox 245") were dissolved in a toluene / ethyl acetate = 4 / 6 (weight ratio) solution to obtain a resin solution with a resin concentration of 16% by weight. This solution was poured onto a polyethylene terephthalate film using a coater to obtain a coating layer. The coating layer was dried at 65°C for 360 seconds, 85°C for 60 seconds, and 110°C for 120 seconds in that order, and then peeled off from the polyethylene terephthalate film to obtain a resin film. The obtained resin film was preheated at a temperature 10°C higher than the stretching temperature, and then uniaxially stretched to 3.0 times its original size at 150°C using a tenter stretcher to obtain a phase difference film.

[0091] [Comparative Example 3] A phase difference film was obtained in the same manner as in Example 1, except that the coating layer was dried in the order of 360 seconds at 65°C, 60 seconds at 85°C, and 120 seconds at 165°C, the stretching conditions were changed, and no thermal shrinkage was performed. [Table 2]

[0092] As shown in Table 2, a phase difference film exhibiting high in-plane birefringence and inverse wavelength dispersion characteristics in the plane can be suitably obtained by stretching a resin film that has high orientation in the thickness direction and exhibits inverse wavelength dispersion characteristics with respect to the phase difference in the thickness direction. Furthermore, such a resin film can be obtained by appropriately adjusting the coating thickness of the resin solution, drying conditions, etc. [Industrial applicability]

[0093] The phase difference film obtained by the method for manufacturing a phase difference film according to an embodiment of the present invention can be suitably used in image display devices such as liquid crystal displays and EL displays, and in particular in organic EL displays.

Claims

1. A method for manufacturing a phase difference film, wherein the in-plane birefringence Δn(590) at a measurement wavelength of 590 nm is greater than 0.003, and the ratio of the in-plane phase difference at a measurement wavelength of 450 nm to the in-plane phase difference at a measurement wavelength of 550 nm (Re(450) / Re(550)) is less than 0.90, To produce a resin film comprising a resin exhibiting positive birefringence and a resin exhibiting negative birefringence, wherein the birefringence ΔP(590) in the thickness direction at a measurement wavelength of 590 nm exceeds 0.0005, the ratio of the phase difference in the thickness direction at a measurement wavelength of 450 nm to the phase difference in the thickness direction at a measurement wavelength of 550 nm (Rth(450) / Rth(550)) is less than 0.98, and the in-plane birefringence Δn(590) at a measurement wavelength of 590 nm is 0.0003 or less, and This includes stretching the resin film, The process of producing the resin film is A resin solution containing a resin exhibiting positive birefringence, a resin exhibiting negative birefringence, and a solvent is applied to a support substrate to form a coating layer with a thickness of 300 μm to 700 μm, and This includes heating the coating layer while gradually increasing its temperature to evaporate the solvent, A manufacturing method in which the first heating stage is at a temperature of 50°C to 65°C, and the final heating stage is at a temperature of 100°C to 160°C.

2. The thickness of the aforementioned resin film before stretching is 50 μm to 200 μm. The method for manufacturing a phase difference film according to claim 1, wherein the thickness of the resin film after stretching is 12.5% ​​to 40% of the thickness before stretching.

3. The aforementioned resin film is a long resin film, The method for manufacturing a phase difference film according to claim 1 or 2, wherein stretching the resin film includes stretching the elongated resin film in a direction perpendicular to the longitudinal direction while conveying it in the longitudinal direction.

4. A method for manufacturing a phase difference film according to claim 1 or 2, wherein the stretching ratio of the stretching is 8.0 times or less.

5. A method for manufacturing a phase difference film according to claim 1 or 2, wherein the Rth(450) / Rth(550) of the resin film before stretching is greater than 0.60 and less than 0.98, the Δn(590) of the phase difference film is greater than 0.0035, and the Re(450) / Re(550) is less than 0.

88.

6. The resin exhibiting positive birefringence includes a cellulose-based resin having the constituent units shown in the following formula (1). A method for producing a phase difference film according to claim 1 or 2, wherein the resin exhibiting negative birefringence includes an ester resin having a structural unit shown in the following formula (2) and a structural unit shown in the following formula (3): 【Chemistry 1】 (In formula (1), R １ ~R ３ Each of these represents a hydrogen atom or a substituent having 1 to 12 carbon atoms;) 【Chemistry 2】 (In formula (2), R ４ R represents a hydrogen atom or an alkyl group having 1 to 12 carbon atoms; ５ａ R represents one selected from an alkyl group having 1 to 12 carbon atoms, a nitro group, a bromo group, an iodo group, a cyano group, a chloro group, a sulfonic acid group, a carboxylic acid group, a fluoro group, or a thiol group; R ５ｂ R represents a hydrogen atom or an alkyl group having 1 to 12 carbon atoms; ６ This indicates a species selected from a hydrogen atom, a nitro group, a bromo group, an iodo group, a cyano group, a chloro group, a sulfonic acid group, a carboxylic acid group, a fluoro group, a phenyl group, a thiol group, an amide group, an amino group, a hydroxyl group, an alkoxy group having 1 to 12 carbon atoms, or an alkyl group having 1 to 12 carbon atoms. 【Transformation 3】 (In formula (3), R ７ This represents a five-membered heterocyclic residue or a six-membered heterocyclic residue containing one or more nitrogen or oxygen atoms as heteroatoms (the five-membered heterocyclic residue and the six-membered heterocyclic residue may form a fused ring structure with other cyclic structures).

7. The ester resin further comprises the constituent units shown in the following formula (4), wherein the method for manufacturing a phase difference film according to claim 6: 【Chemistry 4】 (In formula (4), each of R ８ and R ９ represents one selected from a hydrogen atom, a linear alkyl group having 1 to 12 carbon atoms, a branched alkyl group having 3 to 12 carbon atoms, or a cyclic alkyl group having 3 to 6 carbon atoms).

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