Methods for manufacturing phase retardation thin films and circular polarizers

Abstract

A method for manufacturing a phase retardation film, which is a method for manufacturing a phase retardation film with specific optical properties, the method comprising: a first step of preparing a first film having a resin layer (N1) formed of a thermoplastic resin N having a negative intrinsic birefringence value; a second step of extending the first film at least once to obtain a second film having a resin layer (N2), the resin layer (N2) being an extended layer of the resin layer (N1); a third step of stacking a resin layer (P1) formed of a thermoplastic resin P having a positive intrinsic birefringence value on the second film to obtain a third film; and a fourth step of extending the third film at least once to obtain the aforementioned phase retardation film having a resin layer (N) and a resin layer (P), the resin layer (N) being an extended layer of the resin layer (N2) and having a slow axis (N), the resin layer (P) being an extended layer of the resin layer (P1) and having a slow axis (P) at an angle within the range of 90°±5° relative to the slow axis (N).

Description

Technical Field

[0001] This invention relates to a method for manufacturing a phase retardation thin film and a method for manufacturing a circular polarizer. Prior Technology

[0002] Phase retardation films are sometimes provided in image display devices such as organic electroluminescent image display devices (hereinafter referred to as "organic EL image display devices") and liquid crystal image display devices. These phase retardation films may have a multilayer structure having two or more layers. Sometimes, a co-stretching method is used as a manufacturing method for phase retardation films having this multilayer structure (see Patent Documents 1-4).

[0003] Patent Documents Patent Document 1: Japanese Patent Publication No. 2007-199616 (corresponding foreign publication: U.S. Patent Application Publication No. 2009 / 290103) Patent Document 2, Japanese Patent Publication No. 2009-169086 Patent Document 3, International Patent Publication No. 2021 / 085031 Patent Document 4, Japanese Patent Publication No. 2022-052074 Summary of the Invention

[0004] In image display devices, circular polarizers are sometimes used to reduce the reflection of external light onto the display surface. Such circular polarizers are typically thin films that combine linear polarizers and a λ / 4 plate.

[0005] To suppress color distortion of the display surface, a circular polarizer capable of reducing the reflection of ambient light across a wide wavelength range is required. For example, such a circular polarizer can be manufactured using a broadband λ / 4 polarizer that functions as a λ / 4 polarizer across a wide wavelength range. A retardation film comprising multiple layers is known as such a broadband λ / 4 polarizer; for example, a retardation film combining λ / 2 and λ / 4 polarizers. A circular polarizer equipped with a retardation film that functions as a broadband λ / 4 polarizer can reduce the reflection of ambient light across a wide wavelength range in the front direction perpendicular to the display surface, thus suppressing color distortion of the display surface.

[0006] However, in a tilted direction that is neither parallel nor perpendicular to the display surface, the phase difference value may shift from its ideal value, or the optical axes of each layer may shift, potentially failing to reduce the reflection of external light over a wide wavelength range. Therefore, in order to achieve a circular polarizer that can suppress color distortion caused by reflection of external light in the tilted direction, the phase difference film is required to have an NZ coefficient within a specific range greater than 0.0 and less than 1.0.

[0007] The layers comprising a phase retardation film that meet the aforementioned requirements typically have some or all of the following optical properties: slow axis direction, in-plane phase difference, and NZ coefficient. Therefore, conventionally, phase retardation films are generally manufactured by individually fabricating each layer and then bonding them together. However, this conventional manufacturing method, due to the individual fabrication of each layer, tends to increase the number of steps, the required time, and the cost. Furthermore, since accurate alignment of the bonding angles is required when bonding the layers, angle adjustment is necessary, which also tends to increase the required time.

[0008] Furthermore, when stretching an unstretched multilayer film to produce the aforementioned phase difference film, the adjustment of stretching conditions such as the temperature of the thermoplastic resin forming each layer and the stretching temperature is complicated.

[0009] Therefore, there is a need for a method for manufacturing a phase difference film of a circular polarizer that can be easily manufactured to suppress color changes caused by reflection of external light in both the front and tilted directions of the display surface, and a method for manufacturing a circular polarizer that can be easily manufactured to suppress color changes caused by reflection of external light in both the front and tilted directions of the display surface.

[0010] The inventors have devoted themselves to research in order to solve the aforementioned problems. As a result, they discovered that the aforementioned problems can be solved by a manufacturing method comprising: "preparing a first film having a resin layer (N1) formed of a thermoplastic resin N having a negative intrinsic birefringence value", "extending the first film at least once to obtain a second film having a resin layer (N2), wherein the resin layer (N2) is an extended layer of the resin layer (N1)", "stacking a resin layer (P1) formed of a thermoplastic resin P having a positive intrinsic birefringence value onto the second film to obtain a third film", and "extending the third film at least once", thereby completing the present invention.

[0011] That is, the present invention provides the following content.

[0012] [1] A method for manufacturing a retardation film, which is a method for manufacturing a retardation film that satisfies the following formula (1), the following formula (2), and the following formula (3). The aforementioned manufacturing method includes: a first step of preparing a first film having a resin layer (N1) formed of a thermoplastic resin N having a negative intrinsic birefringence value; a second step of stretching the aforementioned first film at least once to obtain a second film having a resin layer (N2), where the resin layer (N2) is a layer obtained by stretching the aforementioned resin layer (N1); a third step of stacking a resin layer (P1) formed of a thermoplastic resin P having a positive intrinsic birefringence value on the aforementioned second film to obtain a third film; and a fourth step of stretching the aforementioned third film at least once to obtain the aforementioned retardation film having a resin layer (N) and a resin layer (P), where the resin layer (N) is a layer obtained by stretching the aforementioned resin layer (N2) and has a slow axis (N), and the resin layer (P) is a layer obtained by stretching the aforementioned resin layer (P1) and has a slow axis (P) within an angle range of 90° ± 5° with respect to the aforementioned slow axis (N). 100 nm ≦ Re T(550) ≦ 180 nm (1) Re T(450) < Re T(550) < Re T(650) (2) 0.0 < NZ T < 1.0 (3) (where Re T(450) represents the in-plane retardation of the aforementioned retardation film at a wavelength of 450 nm, Re T(550) represents the in-plane retardation of the aforementioned retardation film at a wavelength of 550 nm, Re T(650) represents the in-plane retardation of the aforementioned retardation film at a wavelength of 650 nm, and NZ T represents the NZ coefficient of the aforementioned retardation film.)

[0013] [2] The method for manufacturing a retardation film according to [1], wherein the in-plane retardation of the aforementioned resin layer (N2) of the aforementioned second film is 20 nm or more.

[0014] [3] The method for manufacturing a retardation film according to [1] or [2], wherein the stretching of the aforementioned first film in the aforementioned second step is a one-way stretching, and the stretching of the aforementioned third film in the aforementioned fourth step includes stretching in a direction within an angle range of 90° ± 5° with respect to the stretching direction of the aforementioned first film in the aforementioned second step.

[0015] [4] The method for manufacturing a retardation film according to any one of [1] to [3], wherein the aforementioned retardation film satisfies the following formula (4). [Re N(450) / Re N(550)]-[Re P(450) / Re P(550)]>0.08 (4) (where Re N(450) represents the in-plane phase difference of the resin layer (N) before wavelength 450 nm, Re N(550) represents the in-plane phase difference of the resin layer (N) before wavelength 550 nm, Re P(450) represents the in-plane phase difference of the resin layer (P) before wavelength 450 nm, and Re P(550) represents the in-plane phase difference of the resin layer (P) before wavelength 550 nm.)

[0016] [5] A method for manufacturing a phase difference film as described in any of [1] to [4], wherein the aforementioned phase difference film satisfies the following formula (5). Re P(550)>Re N(550) (5) (where Re N(550) represents the in-plane phase difference of the resin layer (N) before wavelength 550 nm, and Re P(550) represents the in-plane phase difference of the resin layer (P) before wavelength 550 nm.)

[0017] [6] A method for manufacturing a circular polarizer, comprising a linear polarizer and a phase difference film, comprising: The fifth step is to manufacture the aforementioned phase difference film using the manufacturing method of any one of [1] to [5]; and the sixth step is to stack the aforementioned phase difference film with the aforementioned linear polarizer.

[0018] This disclosure also provides the following information.

[0019] [7] A phase difference film, which is manufactured by the manufacturing method described in any one of [1] to [5].

[0020] According to the present invention, a method for manufacturing a phase difference film of a circular polarizer that can be easily manufactured to suppress color changes caused by reflection of external light in both the front and tilt directions of the display surface is provided, as well as a method for manufacturing a circular polarizer that can be easily manufactured to suppress color changes caused by reflection of external light in both the front and tilt directions of the display surface is provided. Simple diagram description

[0021] <Figure 1> Figure 1 is a perspective view illustrating the state of the evaluation model set when calculating color space coordinates in the simulations of the embodiments and comparative examples. Implementation Method

[0022] The following describes embodiments and examples to illustrate the present invention in detail. However, the present invention is not limited to the embodiments and examples disclosed below, and may be implemented in any way without departing from the scope of the claims and their equivalents. The constituent elements of the embodiments disclosed below can be appropriately combined. Furthermore, in the figures, the same constituent elements are sometimes labeled with the same symbols, and their descriptions are omitted.

[0023] In the following description, the in-plane phase difference Re, unless otherwise noted, is represented by Re = (nx - ny) × d. The thickness-direction phase difference Rth, unless otherwise noted, is represented by Rth = [(nx + ny) / 2 - nz] × d. Furthermore, the NZ coefficient NZ, unless otherwise noted, is represented by NZ = Rth / Re + 0.5, which is derived from NZ = (nx - nz) / (nx - ny). nx represents the refractive index in the direction perpendicular to the thickness direction (in-plane direction) and imparting the maximum refractive index (slow axis direction), ny represents the refractive index in the aforementioned in-plane direction and orthogonal to the direction of nx, nz represents the refractive index in the thickness direction, and d represents the thickness. The measurement wavelength, unless otherwise noted, is 550 nm. The in-plane phase difference, thickness direction phase difference, and NZ coefficient must be measured using a phase difference meter (AxoScan, manufactured by Axometrics).

[0024] In the following description, the slow axis of a layer, unless otherwise noted, refers to the slow axis in the in-plane direction of that layer.

[0025] In the following description, the angles between the optical axes (absorption axis, penetration axis, slow axis, etc.) of each layer in a component having multiple layers, unless otherwise noted, represent the angles when viewing the aforementioned layers from the thickness direction.

[0026] In the following description, the term "frontal direction" of a face, unless otherwise noted, means the direction of the normal of that face, specifically the direction where the polar angle of the aforementioned face is 0° and the azimuth angle is 0°.

[0027] In the following description, the inclination direction of a surface, unless otherwise noted, means a direction that is neither parallel nor perpendicular to the surface, specifically a direction within the range where the polar angle of the surface is greater than 0° and less than 90°.

[0028] In the following description, the direction of the requirement is referred to as "parallel", "perpendicular" and "orthogonal", and unless otherwise noted, it may also be included in the range of error within, for example, ±5°, without impairing the effect of the invention.

[0029] In the following description, "strip-shaped" film refers to a film having a length of 5 times or more relative to its width, preferably 10 times or more. Specifically, it refers to a film of a length that can be rolled up for storage or transport. There is no particular upper limit to the length of the strip-shaped film, which may be defined as, for example, less than 100,000 times its width.

[0030] In the following description, the long side of the elongated film is generally parallel to the flow direction of the film in the production line. Furthermore, the width direction of the elongated film is generally perpendicular to the thickness direction and also perpendicular to the long side direction.

[0031] In the following description, the terms "polarizing plate", "circular polarizing plate", "plate", "λ / 2 plate" and "λ / 4 plate" unless otherwise noted, include not only rigid components but also flexible components such as resin films.

[0032] In the following description, "polymer with positive intrinsic birefringence" and "resin with positive intrinsic birefringence" respectively mean "polymer whose refractive index in the extension direction is greater than that in the direction orthogonal to the extension direction" and "resin whose refractive index in the extension direction is greater than that in the direction orthogonal to the extension direction." Similarly, "polymer with negative intrinsic birefringence" and "resin with negative intrinsic birefringence" respectively mean "polymer whose refractive index in the extension direction is smaller than that in the direction orthogonal to the extension direction" and "resin whose refractive index in the extension direction is smaller than that in the direction orthogonal to the extension direction." The intrinsic birefringence value is calculated from the dielectric constant distribution.

[0033] In the following description, the term "bonding agent" unless otherwise noted includes not only bonding agents in the narrow sense (bonding agents with a shear storage modulus of 1 MPa to 500 MPa at 23°C after energy beam irradiation or heat treatment), but also adhesives with a shear storage modulus of less than 1 MPa at 23°C.

[0034] [1. The manufactured phase retardation film]

[0035] The phase retardation film manufactured by the manufacturing method of one embodiment of the present invention satisfies the following formulas (1), (2), and (3). By combining this phase retardation film with a linear polarizer, a circular polarizer that can suppress color distortion caused by reflection of external light in both the front and tilt directions of the display surface can be obtained. 100 nm≦Re T(550)≦180 nm (1) Re T(450) <Re T(550)<Re T(650) (2) 0.0 <NZ T<1.0 (3) (in, ReT(450) represents the in-plane phase difference of the aforementioned phase difference film at a wavelength of 450 nm. ReT(550) represents the in-plane phase difference of the aforementioned phase difference film at a wavelength of 550 nm. ReT(650) represents the in-plane phase difference of the aforementioned phase difference film at a wavelength of 650 nm. NZT represents the NZ coefficient of the aforementioned phase descent film.

[0036] The aforementioned equation (1) will now be explained in detail. The in-plane phase difference ReT(550) of the 550 nm wavelength retardation film is typically 100 nm or more, preferably 115 nm or more, and even more preferably 125 nm or more; and is typically 180 nm or less, preferably 160 nm or less, and even more preferably 150 nm or less. With an in-plane phase difference ReT(550) within this range, the retardation film can function as a λ / 4 plate. Accordingly, by combining this retardation film with a linear polarizer, a circular polarizer capable of suppressing the reflection of external light can be obtained.

[0037] The in-plane phase difference Re T(550) that satisfies Equation (1) can be obtained, for example, by appropriately adjusting the in-plane phase difference of each layer, such as resin layer (P) and resin layer (N), contained in the phase difference film, as well as the direction of the slow axis of each layer.

[0038] The above formula (2) will now be described in detail. The in-plane phase differences Re T(450), Re T(550), and Re T(650) of the retardation film at wavelengths of 450 nm, 550 nm, and 650 nm satisfy Re T(450) < Re T(550) < Re T(650). The in-plane phase difference of the retardation film that satisfies this formula (2) generally exhibits inverse wavelength dispersion. Specifically, the longer the wavelength at which the retardation film is generally measured, the greater the in-plane phase difference. Accordingly, this retardation film can function as a broadband λ / 4 plate that can uniformly convert the polarization state of light passing through the retardation film in a wide wavelength range. Accordingly, by combining this retardation film with a linear polarizer, a circular polarizer capable of suppressing color change caused by reflection of external light can be obtained.

[0039] The in-plane phase differences Re T(450), Re T(550), and Re T(650) that satisfy formula (2) can be obtained, for example, by appropriately adjusting the in-plane phase differences of each layer such as the resin layer (P) and the resin layer (N) included in the retardation film and the directions of the slow axes of these layers.

[0040] The above formula (3) will now be described in detail. The NZ coefficient NZ T of the retardation film is generally greater than 0.0, preferably greater than 0.2, more preferably greater than 0.3, and generally less than 1.0, preferably less than 0.8, more preferably less than 0.7. When the retardation film has the NZ coefficient NZ T within the above range, this retardation film has birefringence appropriately adjusted in both the in-plane direction and the thickness direction. Accordingly, the circular polarizer obtained by combining this retardation film with a linear polarizer can suppress color change caused by reflection of external light in both the front direction and the tilt direction of the display surface.

[0041] Unless otherwise noted, the NZ coefficient NZ T of the retardation film is represented by "NZ T = [Rth T(550) / Re T(550)] + 0.5" using the in-plane phase difference Re T(550) and the thickness direction phase difference Rth T(550) of the retardation film at a wavelength of 550 nm. The NZ coefficient NZ T that satisfies formula (3) can be obtained, for example, by appropriately adjusting the NZ coefficients of each layer such as the resin layer (P) and the resin layer (N) included in the retardation film.

[0042] In the manufacturing method related to this embodiment, a retardation film that satisfies the above formulas (1) to (3) is manufactured in the form of a retardation film having a resin layer (P) containing a thermoplastic resin P and a resin layer (N) containing a thermoplastic resin N combined.

[0043] Here, thermoplastic resin P has a positive intrinsic birefringence value, and thermoplastic resin N has a negative intrinsic birefringence value. When these thermoplastic resins P and N are combined and used in the manufacturing method described below, phase difference films satisfying the above-described formulas (1) to (3) can be easily manufactured.

[0044] Thermoplastic resin P with a positive intrinsic birefringence value typically contains polymers with a positive intrinsic birefringence value. Examples of such polymers include: polyolefins such as polyethylene and polypropylene; polyesters such as polyethylene terephthalate and polybutylene terephthalate; polyaryl sulfides such as polyphenylene sulfide; polyvinyl alcohol; polycarbonate; polyaryl esters; cellulose esters; polyether ether; polyether ether; polyaryl ether ether; polyaryl ether ether; polyvinyl ether ether; polyvinyl ether ether; polyvinyl chloride; alicyclic polymers; rod-shaped liquid crystal polymers; etc. These polymers can be used alone or in any combination of two or more. Among these, alicyclic polymers, cellulose esters, and polycarbonates are preferred, with alicyclic polymers being particularly preferred.

[0045] Polymers containing alicyclic structures are cyclic olefin polymers and their hydrides, which are polymers containing alicyclic structures in repeating units, and are usually amorphous polymers. As alicyclic polymers, either polymers containing alicyclic structures in the main chain or polymers containing alicyclic structures in the side chains can be used. Examples of alicyclic structures include cycloalkanes and cycloenes, but from the viewpoint of thermal stability, cycloalkanes are preferred. The number of carbon atoms contained in one alicyclic structure is preferably 4 or more, more preferably 5 or more, especially 6 or more, and preferably 30 or less, more preferably 20 or less, and especially preferably 15 or less.

[0046] In alicyclic polymers, the proportion of repeating alicyclic units is preferably 50% by weight or more, more preferably 70% by weight or more, and even more preferably 90% by weight or more. When the proportion of repeating alicyclic units is within the aforementioned range, a phase retardation film with excellent heat resistance can be obtained.

[0047] Examples of alicyclic polymers include: (1) norethene polymers, (2) monocyclic cyclic olefin polymers, (3) cyclic conjugated diene polymers, (4) ethylene alicyclic hydrocarbon polymers, and their hydrides. Among these, cyclic olefin polymers and norethene polymers are preferred, with norethene polymers being particularly preferred. Examples of norethene polymers include: ring-opening polymers containing monomers with a norethene structure, ring-opening copolymers containing monomers with a norethene structure and other monomers capable of ring-opening copolymerization therewith, and their hydrides; addition polymers containing monomers with a norethene structure, addition copolymers containing monomers with a norethene structure and other monomers capable of copolymerization therewith. Among these, from the viewpoint of transparency, ring-opening polymer hydrides containing monomers with a norethene structure are particularly preferred. The aforementioned polymers containing alicyclic structures may be selected from, for example, polymers disclosed in Japanese Patent Publication No. 2002-321302.

[0048] Examples of cellulose esters include, for example, lower fatty acid esters of cellulose (e.g., cellulose acetate, cellulose butyrate acetate, and cellulose propionate acetate). Lower fatty acids are fatty acids with 6 or fewer carbon atoms per molecule. Cellulose acetate may also include triacetylcellulose (TAC) and cellulose diacetate (DAC).

[0049] The total acetylation degree of cellulose esters is preferably 2.20 to 2.70, and more preferably 2.40 to 2.60. The total acetylation degree must be measured according to ASTM D817-91. Furthermore, the weight-average degree of polymerization of cellulose esters is preferably 350 to 800, and more preferably 370 to 600.

[0050] Polycarbonate typically contains repeating units comprising carbonate bonds (-OC(=O)-O-). Examples of polycarbonate include polymers having structural units derived from dihydroxy compounds and a carbonate structure (the structure shown by -O-(C=O)-O-). Examples of dihydroxy compounds include bisphenol A. The dihydroxy compound-derived structural units contained in polycarbonate may be one type or two or more types.

[0051] The weight-average molecular weight (Mw) of the polymer contained in the thermoplastic resin P is preferably 10,000 or higher, more preferably 15,000 or higher, especially 20,000 or higher, and preferably 100,000 or lower, more preferably 80,000 or lower, and especially preferably 50,000 or lower. When the weight-average molecular weight is within this range, a high balance can be achieved between the mechanical strength and processability of the resin layer (P). The aforementioned weight-average molecular weight is the weight-average molecular weight converted from polyisoprene or polystyrene measured by gel permeation chromatography (GPC) using cyclohexane as a solvent. However, if the sample is insoluble in cyclohexane, toluene may also be used as the solvent for GPC.

[0052] The proportion of polymer in the thermoplastic resin P is preferably 50% to 100% by weight, more preferably 70% to 100% by weight, and even more preferably 90% to 100% by weight. When the proportion of polymer is within the aforementioned range, the resin layer (P) can obtain sufficient heat resistance and transparency.

[0053] The thermoplastic resin P may further include any combination of components in the aforementioned polymer. Examples of such components include: antioxidants, heat stabilizers, light stabilizers, weather stabilizers, ultraviolet absorbers, near-infrared absorbers, and other stabilizers; plasticizers; etc. These components may be used individually or in any combination of two or more in any ratio.

[0054] Thermoplastic resin N with a negative intrinsic birefringence value typically comprises a polymer with a negative intrinsic birefringence value. Examples of such polymers include: homopolymers comprising aromatic vinyl monomers and / or copolymers of aromatic vinyl monomers with any monomer; polyacrylonitrile polymers; polymethyl methacrylate polymers; or multi-component copolymers thereof; etc. Furthermore, examples of monomers copolymerized to aromatic vinyl monomers include: acrylonitrile, maleic anhydride, methyl methacrylate, and butadiene. Moreover, such polymers can be used alone or in any combination of two or more in any ratio.

[0055] Examples of monomers of aromatic ethylene compounds include: styrene, styrene derivatives, vinylnaphthalene, and vinylnaphthalene derivatives. Examples of styrene or vinylnaphthalene derivatives include: compounds in which the aromatic ring of styrene or vinylnaphthalene is substituted with a substituent, and compounds in which the α- or β-position of styrene or vinylnaphthalene is substituted with a substituent.

[0056] Among polymers with negative intrinsic birefringence, polymers selected from one or more of the group consisting of styrene polymers, styrene derivative polymers, vinylnaphthalene polymers (preferably poly(2-vinylnaphthalene)) and vinylnaphthalene derivative polymers are preferred, with vinylnaphthalene polymers being more preferred, and poly(2-vinylnaphthalene) being even more preferred.

[0057] The proportion of polymer in thermoplastic resin N is preferably 50% to 100% by weight, more preferably 70% to 100% by weight, and even more preferably 90% to 100% by weight. When the proportion of polymer is within the aforementioned range, the resin layer (N) can exhibit appropriate optical properties.

[0058] Thermoplastic resin N may further comprise any combination of components in the aforementioned polymer. Examples of such components include those found in thermoplastic resin P. Any component may be used alone or in combination of two or more components in any ratio.

[0059] Thermoplastic resin N and thermoplastic resin P can each be a resin having an arbitrary glass transition temperature.

[0060] In the fourth step described later, from the viewpoint of smoothly extending the third film having a layer of thermoplastic resin N and a layer of thermoplastic resin P, the absolute value of the difference between the glass transition temperature TgN of thermoplastic resin N and the glass transition temperature TgP of thermoplastic resin P, |TgN-TgP|, is preferably below 40°C, more preferably below 30°C, even more preferably below 25°C, even more preferably below 10°C, and especially preferably below 5°C, and the lower limit is usually above 0°C.

[0061] The retardation film has a resin layer (N) with a slow axis (N). Furthermore, the retardation film also has a resin layer (P) with a slow axis (P) that is slightly perpendicular to the aforementioned slow axis (N) of the resin layer (N). The phrase "slightly perpendicular" to the slow axis (N) means that the angle between the slow axis (N) and the slow axis (P) is within a specific range close to 90°. Specifically, the angle between the slow axis (P) and the slow axis (N) is typically within the range of 90° ± 5°, typically 85° or higher, preferably 87° or higher, more preferably 88° or higher, and especially preferably 89° or higher, and typically 95° or lower, preferably 93° or lower, more preferably 92° or lower, and especially preferably 91° or lower. In the manufacturing method described below, a multilayer structure of a thin film having a slow axis having the aforementioned relationship can be obtained, which satisfies the above-described formulas (1) to (3).

[0062] In particular, in the elongated retardation film, it is preferable that one of the slow axis (P) of the resin layer (P) and the slow axis (N) of the resin layer (N) forms an angle of approximately 45° with respect to the width direction of the retardation film. Specifically, the aforementioned angle is preferably 40° or more, more preferably 42° or more, more preferably 43° or more, especially 44° or more, and preferably 50° or less, more preferably 48° or less, more preferably 47° or less, and especially preferably 46° or less. Furthermore, in this case, the other slow axis (P) and slow axis (N) are preferably an angle of approximately 135° with respect to the width direction of the retardation film. Specifically, the aforementioned angle is preferably 130° or higher, more preferably 132° or higher, even better 133° or higher, especially 134° or higher, and preferably 140° or lower, more preferably 138° or lower, even better 137° or lower, and especially preferably 136° or lower. A typical elongated linear polarizer has an absorption axis parallel or perpendicular to its width direction. An elongated retardation film, comprising resin layers (P) and (N) having a slow axis in a direction relative to the aforementioned range of angles within the width direction, can be simply bonded to the aforementioned typical linear polarizer to obtain a circular polarizer by aligning the width direction of the retardation film parallel to the width direction of the linear polarizer. Therefore, the retardation film and the linear polarizer can be bonded roll-to-roll, making the manufacture of circular polarizers particularly simple.

[0063] The NZ coefficients NZ P and NZ N of the resin layer (P) are preferably set appropriately so that the NZ coefficient NZ T of the phase difference film falls within the range of Equation (3). The NZ coefficient NZ P of the resin layer (P) is represented by "NZ P = (nx P - nz P) / (nx P - ny P)", which is represented by "NZ P = (Rth P / Re P) + 0.5". nx P represents the refractive index of the resin layer (P) in the in-plane direction and the direction that imparts the maximum refractive index. ny P represents the refractive index of the resin layer (P) in the in-plane direction and the direction orthogonal to the direction that imparts nx P. nz P represents the refractive index in the thickness direction of the resin layer (P). Re P represents the in-plane phase difference of the resin layer (P), which is represented by "Re P = (nx P - ny P) × d P". Rth P represents the phase difference in the thickness direction of the resin layer (P), and is therefore represented by "Rth P = [(nx P + ny P) / 2 - nz P] × d P". d P represents the thickness of the resin layer (P). Furthermore, the NZ coefficient NZ N of the resin layer (N) is represented by "NZ N = (nx N - nz N) / (nx N - ny N)", and is therefore represented by "NZ N = (Rth N / Re N) + 0.5". nx N represents the refractive index of the resin layer (N) in the in-plane direction, which imparts the maximum refractive index. ny N represents the refractive index of the resin layer (N) in the in-plane direction, which is orthogonal to the direction imparting nx N. nz N represents the refractive index in the thickness direction of the resin layer (N). Re N represents the in-plane phase difference of the resin layer (N), and is therefore represented by "Re N = (nx N - ny N) × d N". Rth N represents the phase difference in the thickness direction of the resin layer (N), which is represented by "Rth N = [(nx N + ny N) / 2 - nz N] × d N". d N represents the thickness of the resin layer (N).

[0064] The NZ coefficient NZP of the resin layer (P) is preferably 1.00 or higher. Accordingly, the refractive indices nyP and nzP of the resin layer (P) preferably satisfy the relationship nyP ≥ nzP. Furthermore, the NZ coefficient NZN of the resin layer (N) is preferably not 0.0. Accordingly, the refractive indices nxN and nzN of the resin layer (N) preferably satisfy the relationship nzN > nxN. With this combination of resin layer (P) and resin layer (N), the overall NZ coefficient NZT of the phase retardation film can be easily adjusted to the range of Equation (3).

[0065] More specifically, the NZ coefficient NZ P of the resin layer (P) is preferably 1.00 or higher, more preferably 1.05 or higher, and preferably 1.30 or lower, and more preferably 1.20 or lower. Thus, the refractive indices nx P, ny P, and nz P of the resin layer (P) with an NZ coefficient NZ P of 1.00 or higher must have the relationship nx P > ny P ≥ nz P. Accordingly, the resin layer (P) can function as either a positive A-plate or a negative B-plate.

[0066] Furthermore, the NZ coefficient (NZ N) of the resin layer (N) is preferably -2.0 or higher, more preferably -1.5 or higher, preferably not reaching 0.0, more preferably -0.2 or lower, and especially preferably -0.4 or lower. Thus, the refractive indices nx N, ny N, and nz N of the resin layer (N) with an NZ coefficient not reaching 0.0 should have a relationship of nz N > nx N > ny N. Accordingly, the resin layer (N) is a layer with different refractive indices nx N, ny N, and nz N in the three directions (i.e., a layer with biaxiality). Furthermore, the resin layer (N) can function as a positive B-plate.

[0067] The sum of the NZ coefficients NZ P of the resin layer (P) and NZ N of the resin layer (N), NZ P + NZ N, is preferably within a specific range. Specifically, NZ P + NZ N is preferably -0.3 or higher, more preferably 0.0 or higher, especially preferably 0.10 or higher, and preferably 0.8 or lower, more preferably 0.75 or lower, and especially preferably 0.65 or lower. When NZ P + NZ N is within the aforementioned range, a phase retardation film of a circular polarizer that can effectively suppress color changes caused by reflection of external light in both the front and tilt directions of the display surface can be obtained.

[0068] The phase difference film is preferably satisfied by the following formula (4). [Re N(450) / Re N(550)]-[Re P(450) / Re P(550)]>0.08 (4) (in, Re N(450) represents the in-plane phase difference of the aforementioned resin layer (N) at a wavelength of 450 nm. Re N(550) represents the in-plane phase difference of the aforementioned resin layer (N) at a wavelength of 550 nm. Re P(450) represents the in-plane phase difference of the aforementioned resin layer (P) at a wavelength of 450 nm. Re P(550) represents the in-plane phase difference of the aforementioned resin layer (P) at a wavelength of 550 nm.

[0069] In equation (4), "Re N(450) / Re N(550)" represents the wavelength dispersion of the resin layer (N). Furthermore, in equation (4), "Re P(450) / Re P(550)" represents the wavelength dispersion of the resin layer (P). Therefore, equation (4) represents the difference in wavelength dispersion of the in-plane phase difference between the resin layer (N) and the resin layer (P) in the phase difference film. More specifically, it indicates that the wavelength dispersion of the in-plane phase difference of the resin layer (N) is greater than the wavelength dispersion of the in-plane phase difference of the resin layer (P). The parameter representing the difference in wavelength dispersion is "[Re N(450) / Re N(550)]-[Re P(450) / Re P(550)]". Specifically, it is preferable to be greater than 0.08, better than 0.09, and even better than 0.10. There is no particular upper limit, but it is preferable to be less than 2.0, better than 1.5, and even better than 1.2. In this way, a phase difference film with a difference in wavelength dispersion of resin layer (P) and resin layer (N) with an in-plane phase difference can easily obtain inverse wavelength dispersion characteristics in a stacked state.

[0070] Furthermore, the phase difference film is preferably satisfied by the following equation (5). Re P(550)>Re N(550) (5) (in, Re N(550) represents the in-plane phase difference of the aforementioned resin layer (N) at a wavelength of 550 nm. Re P(550) represents the in-plane phase difference of the aforementioned resin layer (P) at a wavelength of 550 nm.

[0071] By satisfying equation (5) with a phase difference film, a phase difference film that can function in a wide bandwidth can be easily made.

[0072] The value of [Re P(550)-Re N(550)] is preferably above 120 nm, more preferably above 125 nm, especially above 130 nm, and preferably below 160 nm, more preferably below 155 nm, and especially preferably below 150 nm. This allows the phase retardation film to be fabricated into a λ / 4 plate that functions over a wide bandwidth.

[0073] The phase retardation film may also include any layer other than the resin layer (P) and resin layer (N) as required. Examples of arbitrary layers include: optically isotropic arbitrary layers. These optically isotropic arbitrary layers typically have an in-plane phase difference of less than 10 nm at a wavelength of 550 nm. Examples include: protective film layers for protecting the resin layers (P) and (N); bonding layers for joining the resin layers (P) and (N); etc. Furthermore, another example of an arbitrary layer is: optically anisotropic arbitrary layers. The optical properties of these optically anisotropic arbitrary layers are not limited to satisfying equations (1) to (3) for the entire phase retardation film. Specifically, the optical properties of this arbitrary layer can be configured such that one or a combination of optically anisotropic arbitrary layers and resin layers (P) and (N) function as a λ / 4 or λ / 2 plate.

[0074] The UV / Vis transmittance of the phase retardation film is preferably above 80%, better above 85%, and even better above 90%. UV / Vis transmittance can be measured using a UV / Vis spectrometer in the wavelength range of 400 nm to 700 nm.

[0075] The haze of the phase retardation film is preferably below 5%, better below 3%, and especially better below 1%, with 0% being ideal. Haze can be measured using a haze meter in accordance with JIS K7361-1997.

[0076] Phase difference films can be cut into sheets or made into strips.

[0077] There are no particular limitations on the thickness of the retardation film. From the perspective of thinning, the specific thickness of the retardation film is preferably 5 μm or more, preferably 10 μm or more, especially 15 μm or more, preferably less than 200 μm, preferably less than 150 μm, and especially preferably less than 100 μm.

[0078] There are no particular limitations on the thickness of the resin layer (P) and resin layer (N) in the phase retardation film. The thickness of the resin layer (P) and resin layer (N) is preferably 0.5 μm or more, preferably 1 μm or more, preferably 150 μm or less, and preferably 100 μm or less.

[0079] [2. Overview of the manufacturing method of phase retardation thin film]

[0080] In one embodiment of the present invention, a type-dependent manufacturing method is used to manufacture the aforementioned phase difference film by a manufacturing method comprising the following steps: The first step involves preparing a first thin film having a resin layer (N1) formed from a thermoplastic resin N having a negative intrinsic birefringence value; The second step involves extending the first film at least once to obtain a second film having a resin layer (N2), wherein the resin layer (N2) is an extended layer of the aforementioned resin layer (N1); The third step involves stacking a resin layer (P1) formed of a thermoplastic resin P with a positive intrinsic birefringence value onto the aforementioned second film to obtain a third film; and In the fourth step, the aforementioned third film is extended at least once to obtain the aforementioned phase difference film having a resin layer (N) and a resin layer (P), wherein the resin layer (N) is an extended layer of the aforementioned resin layer (N2) and has a slow axis (N), and the resin layer (P) is an extended layer of the aforementioned resin layer (P1) and has a slow axis (P) with an angle within the range of 90°±5° relative to the aforementioned slow axis (N).

[0081] In the manufacturing method of the phase retardation film of this embodiment, a third film having a multilayer structure is manufactured and extended. Therefore, compared to the case where each layer of the phase retardation film is manufactured individually and then stacked by bonding, the manufacturing method of the phase retardation film of this embodiment requires less time. Furthermore, there is no need to adjust the angle when bonding the layers.

[0082] Furthermore, in the manufacturing method of the phase retardation film of this embodiment, the first film is stretched in the second step. Therefore, compared to obtaining the phase retardation film by stretching multiple layers of film without performing the second step, the stretching conditions, such as the temperature of the thermoplastic resin used to form each layer of the phase retardation film and the stretching temperature, can be set with fewer restrictions.

[0083] [3. First step: Preparation of the first film]

[0084] In the first step, a first thin film is prepared having a resin layer (N1) formed of a thermoplastic resin N having a negative intrinsic birefringence value. The thermoplastic resin N is as described in the section on phase difference films.

[0085] The resin layer (N1) of the first thin film preferably does not have large optical anisotropy. Accordingly, the phase difference of the resin layer (N1) is preferably small. To give a specific range, the in-plane phase difference of the resin layer (N1) at 550 nm is preferably 0 nm to 20 nm, more preferably 0 nm to 10 nm, and even more preferably 0 nm to 5 nm. Furthermore, the absolute value of the phase difference in the thickness direction of the resin layer (N1) at 550 nm is preferably 0 nm to 20 nm, more preferably 0 nm to 10 nm, and even more preferably 0 nm to 5 nm.

[0086] The first film can also be a film cut into sheets, but a long strip film is preferred. By preparing the first film in the form of a long strip film, some or all of the processes in the manufacture of phase difference films can be carried out in the production line, thus making the manufacturing process simple and efficient.

[0087] There are no limitations on the manufacturing method of the first film. For example, the first film can be manufactured by melt molding or solution casting. Melt molding is preferred. Among melt molding methods, extrusion molding, blow molding, or pressure molding are preferred, with extrusion molding being particularly preferred. By these methods, a first film having a resin layer (N1) can be manufactured in the form of a strip-shaped film.

[0088] [4. Second process: Manufacturing of the second thin film]

[0089] In the second process, the first film is stretched at least once to obtain a second film having a resin layer (N2), wherein the resin layer (N2) is a stretched layer of the aforementioned resin layer (N1).

[0090] The first film may be stretched once or twice or more. When the first film is stretched twice or more, it is preferable that the stretching directions of these stretches are the same. The stretching ratios of these stretches may be the same or different. In one embodiment, it is preferable that the first film is stretched once.

[0091] In the second process, the elongation ratio of the first film in the elongation direction is preferably 1.05 times or more, more preferably 1.1 times or more, especially preferably 1.12 times or more, and preferably 2.0 times or less, more preferably 1.5 times or less, and especially preferably 1.3 times or less. Where the first film is elongated two or more times in the second process, the elongation ratio of the first film in the second process is obtained by multiplying the elongation ratios of each elongation.

[0092] When the first film system is elongated, it is preferable that the extension direction in the second process is oblique relative to the width direction of the first film. In this way, an elongated phase retardation film with an oblique slow axis can be obtained.

[0093] In the second process, the extension direction is preferably at an angle within a specific range of approximately 135° relative to the width direction of the elongated first film. Specifically, the aforementioned angle is preferably 130° or higher, more preferably 132° or higher, even better 133° or higher, especially 134° or higher, and preferably 140° or lower, more preferably 138° or lower, even better 137° or lower, and especially lower than 136°. This allows the fabrication of a phase retardation film with a slow axis having an angle within a specific range of approximately 45° relative to the width direction of the elongated phase retardation film.

[0094] The stretching temperature in the second process should be selected within an appropriate range according to the glass transition temperature (TgN) of the thermoplastic resin N that forms the resin layer (N1). For example, the stretching temperature in the second process is preferably above TgN-5°C, more preferably above TgN-3°C, especially above TgN-1°C, and preferably below TgN+20°C, more preferably below TgN+15°C, and especially preferably below TgN+12°C. This effectively suppresses the breakage of the resin layer (N2) obtained by stretching the resin layer (N1) and the increase in haze.

[0095] By extending the first film, the resin layer (N1) of the first film is extended, and a slow axis appears in the resin layer (N2) in a direction slightly perpendicular to the extension direction. Specifically, the angle between the extension direction in the second process and the slow axis of the resin layer (N2) is generally within the range of 90°±5°, generally 85° or more, preferably 87° or more, more preferably 88° or more, and especially preferably 89° or more, and generally 95° or less, preferably 93° or less, more preferably 92° or less, and especially preferably 91° or less.

[0096] The second thin film preferably has an in-plane phase difference of more than 20 nm at a wavelength of 550 nm, more preferably more than 25 nm, more preferably more than 27 nm, and preferably less than 150 nm, more preferably less than 130 nm, and more preferably less than 110 nm.

[0097] The resin layer (N2) of the second thin film preferably has an in-plane phase difference of 20 nm or more at a wavelength of 550 nm, more preferably 25 nm or more, especially 27 nm or more, and preferably 150 nm or less, more preferably 130 nm or less, especially 110 nm or less.

[0098] Furthermore, the phase difference of the resin layer (N2) in the thickness direction at a wavelength of 550 nm is preferably below -5 nm, more preferably below -10 nm, especially below -13 nm, and preferably above -90 nm, more preferably above -80 nm, and especially preferably above -70 nm.

[0099] The phase difference between the second film and the resin layer (N2) can be adjusted by adjusting the stretching ratio in the second process.

[0100] By extending the first thin film in the second process in such a way that the phase difference of the resin layer (N2) falls within the aforementioned range, it is possible to make the resin layer (N) exhibit biaxiality particularly easily after the extension in the fourth process described later. Specifically, it is possible to make the resin layer (N) exhibit the desired in-plane phase difference and negative thickness direction phase difference particularly easily. Therefore, it is possible to make the phase difference thin film having the resin layer (N) and the resin layer (P) particularly easily into a thin film that satisfies equations (1) to (3).

[0101] [5. Third process: Manufacturing of the third thin film]

[0102] In the third step, a resin layer (P1) formed of a thermoplastic resin P having a positive intrinsic birefringence value is stacked on the aforementioned second film to obtain a third film. The resin layer (P1) can be stacked on the second film by any method. The resin layer (P1) can be formed by any method, such as melt molding, solution casting, or coating a liquid composition containing materials other than the layers on a layer.

[0103] The preferred method is to coat a liquid composition comprising thermoplastic resin P onto the resin layer (N2) of the second film and, if necessary, dry the coated liquid composition. This method is described below.

[0104] A liquid composition comprising thermoplastic resin P is coated onto the resin layer (N2) of the aforementioned second film. The liquid composition comprises thermoplastic resin P and a solvent. The liquid composition comprising thermoplastic resin and solvent is also referred to as a resin solution. As a solvent, it is preferable to have a solvent that can dissolve or disperse thermoplastic resin P, and even more preferably a solvent that can dissolve thermoplastic resin P. Furthermore, a single solvent can be used alone, or two or more solvents can be used in any ratio. The concentration of thermoplastic resin P in the liquid composition is preferably adjusted in a way that makes the viscosity of the liquid composition fall within a suitable range for coating, and is, for example, 1% to 50% by weight.

[0105] There are no limitations on the coating method for liquid components. Examples of coating methods include: curtain coating, extrusion coating, roller coating, spin coating, dip coating, bar coating, spray coating, slant coating, printing coating, rotary gravure coating, die coating, and gap coating.

[0106] A liquid composition comprising thermoplastic resin P is coated onto a resin layer (N2), forming a layer of this liquid composition. Accordingly, by drying the liquid composition layer as needed to remove the solvent, a third film can be obtained by stacking a resin layer (P1) on the resin layer (N2). The drying method is not limited and can include, for example, natural drying, heat drying, or reduced pressure drying.

[0107] The resin layer (P1) of the third thin film preferably does not have large optical anisotropy. Accordingly, the phase difference of the resin layer (P1) is preferably small. To give a specific range, the in-plane phase difference of the resin layer (P1) at 550 nm is preferably 0 nm to 20 nm, more preferably 0 nm to 10 nm, and even more preferably 0 nm to 5 nm. Furthermore, the absolute value of the phase difference in the thickness direction of the resin layer (P1) at 550 nm is preferably 0 nm to 20 nm, more preferably 0 nm to 10 nm, and even more preferably 0 nm to 5 nm.

[0108] By ensuring that the phase difference of the resin layer (P1) falls within the aforementioned range, it is particularly easy to make the resin layer (P) exhibit the desired in-plane phase difference in the fourth step described later. Therefore, it is particularly easy to fabricate a thin film with a phase difference of resin layer (N) and resin layer (P) that satisfies formulas (1) to (3).

[0109] [6. Fourth process: Extension of the third film]

[0110] In the fourth step, the aforementioned third film is extended at least once to obtain the aforementioned phase difference film having a resin layer (N) and a resin layer (P), wherein the resin layer (N) is an extended layer of the aforementioned resin layer (N2) and has a slow axis (N), and the resin layer (P) is an extended layer of the aforementioned resin layer (P1) and has a slow axis (P) with an angle within the range of 90°±5° relative to the aforementioned slow axis (N).

[0111] The third film may be stretched once or twice or more. When the third film is stretched twice or more, it is preferable that the stretching directions of these stretches are the same. The stretching ratios of these stretches may be the same or different. In one embodiment, it is preferable that the third film is stretched once.

[0112] In the fourth process, the elongation ratio E4 of the third film is preferably 1.1 times or more, more preferably 1.2 times or more, especially more preferably 1.3 times or more, and preferably 3.0 times or less, more preferably 2.5 times or less, and especially preferably 2.0 times or less. Here, when the third film is elongated two or more times in the fourth process, the elongation ratio of the third film in the fourth process is obtained by multiplying the elongation ratios of each elongation.

[0113] In the fourth process, the elongation ratio E4 of the third film is preferably greater than the elongation ratio E2 of the first film in the second process in the elongation direction. The ratio of elongation ratio E4 to elongation ratio E2 (E4 / E2) is preferably greater than 1, preferably 1.05 or more, especially 1.1 or more, preferably 3.0 or less, preferably 2.5 or less, and especially 2.0 or less. In this way, the resin layer (N) of the phase retardation film effectively exhibits biaxiality, and the resin layer (P) exhibits the desired in-plane phase retardation, making it particularly easy to manufacture phase retardation films that satisfy equations (1) to (3).

[0114] Preferably, the extension of the first film in the second process is an extension in one direction, and the extension of the third film in the fourth process includes an extension in a direction slightly perpendicular to the extension direction of the first film in the second process—specifically, within a range of 90° ± 5°. The extension direction of the third film relative to the extension direction of the first film in the second process is preferably within a range of 90° ± 5°, preferably 85° or higher, more preferably 87° or higher, even better 88° or higher, particularly preferably 89° or higher, and preferably 95° or lower, more preferably 93° or lower, even better 92° or lower, and particularly preferably 91° or lower.

[0115] By extending the third film in the fourth process in a direction that is slightly perpendicular to the extension direction in the second process—specifically within the range of 90°±5°—it is particularly easy to manufacture phase difference films that satisfy equations (1) to (3).

[0116] Since the resin layer (P1) of the third film is formed of thermoplastic resin P with a positive intrinsic birefringence value, if the third film is extended along a certain extension direction in the fourth process, the resin layer (P) of the extended layer (P1) will exhibit a slow axis (P) in a direction slightly parallel to this extension direction. On the other hand, since the resin layer (N2) of the third film is formed of thermoplastic resin N with a negative intrinsic birefringence value, the refractive index in the resin layer (N) of the extended layer (N2) will increase in a direction slightly perpendicular to this extension direction. When the extension of the third film in the fourth process includes an extension in a direction slightly perpendicular to the extension direction of the first film described above in the second process, the slow axis direction of the resin layer (N2) appearing in the second process is slightly parallel to the extension direction in the fourth process. Therefore, it becomes particularly easy to adjust the slow axis (N) of the resin layer (N) of the phase retardation film to be slightly perpendicular to the extension direction in the fourth process. As a result, it becomes particularly easy to make the direction of the slow axis (N) of the resin layer (N) slightly perpendicular to the direction of the slow axis (P) of the resin layer (P).

[0117] Therefore, the angle between the extension direction of the third film in the fourth process and the slow axis of the resin layer (N2) of the second film is preferably within the range of 0°±5°, preferably above -5°, more preferably above -3°, even better above -2°, especially better above -1°, and preferably below 5°, more preferably below 3°, even better below 2°, and especially better below 1°.

[0118] The stretching temperature in the fourth process should be appropriately set according to the glass transition temperature TgP of thermoplastic resin P and the glass transition temperature TgN of thermoplastic resin N. From the viewpoint of suppressing film breakage during stretching and ensuring smooth stretching, a Tg(high) of -5°C or higher is preferred, a Tg(high) of -3°C or higher is better, a Tg(high) of -1°C or higher is especially preferred, a Tg(high) of +20°C or lower is preferred, a Tg(high) of +15°C or lower is better, a Tg(high) of +12°C or lower is even better, a Tg(high) of +10°C or lower is even better, and a Tg(high) of +9°C or lower is especially preferred. Tg(high) represents the higher of the glass transition temperature TgP and the glass transition temperature TgN. When the glass transition temperatures TgP and TgN are the same, this same temperature is indicated.

[0119] [7. Any process including phase retardation thin film]

[0120] In addition to the first to fourth steps described above, the method for manufacturing the retardation film may also include any other steps. For example, when obtaining a strip-shaped retardation film using a strip-shaped first film, the method for manufacturing the retardation film may also include a trimming step of cutting the obtained retardation film into a desired shape. Through the trimming step, a retardation film cut into sheets with the desired shape can be obtained. Furthermore, the method for manufacturing the retardation film may also include a step, for example, of applying a protective layer to the retardation film.

[0121] [8. Overview of the manufacturing method of circular polarizing plates]

[0122] One embodiment of the present invention is a method for manufacturing a circular polarizing plate with a specific form. A method for manufacturing a circular polarizing plate comprising a linear polarizer and a phase difference film, comprising: The fifth step involves manufacturing the aforementioned phase retardation film using the method described above; and The sixth step involves stacking the aforementioned phase difference film with the aforementioned linear polarizer.

[0123] [9. Fifth Process]

[0124] The manufacturing method of the circular polarizer related to this embodiment includes a fifth step. The fifth step is the step of manufacturing a phase retardation film using the aforementioned method for manufacturing a phase retardation film.

[0125] The fifth step is specifically the process of manufacturing a phase retardation film using the aforementioned manufacturing method that includes the first, second, third, and fourth steps. The phase retardation film obtained by the fifth step is the same as the phase retardation film described in the aforementioned [1. Manufactured Phase Retardation Film] section.

[0126] [10. Sixth Process]

[0127] In the sixth process, the phase difference film manufactured in the fifth process will be stacked with the linear polarizer.

[0128] As a linear polarizer, any linear polarizer can be used. Examples of linear polarizers include: films obtained by uniaxially extending a polyvinyl alcohol film after adsorbing iodine or dichroic dye onto it in a boric acid bath; and films obtained by adsorbing iodine or dichroic dye onto a polyvinyl alcohol film, extending it, and further modifying a portion of the polyvinyl alcohol units in the molecular chain into polyethylene units. Among these, a polarizer containing polyvinyl alcohol is preferred as a linear polarizer.

[0129] If natural light is incident on a linear polarizer, only one polarized beam will pass through. The polarization degree of this linear polarizer is not particularly limited, but 98% or higher is preferred, and 99% or higher is even better.

[0130] Furthermore, the thickness of the linear polarizer is preferably 5 μm to 80 μm.

[0131] The sixth process, stacking, is carried out by sequentially adding a resin layer (N), a resin layer (P), and a linear polarizer to a circular polarizing plate.

[0132] Furthermore, the stacking in the sixth process is preferably performed in a manner where the angle between the width direction of the linear polarizer and the slow axis (P) of the resin layer (P) is approximately 45°. Specifically, the aforementioned angle is preferably 40° or higher, more preferably 42° or higher, even better 43° or higher, especially 44° or higher, and preferably 50° or lower, more preferably 48° or lower, even better 47° or lower, and especially lower than 46°.

[0133] Furthermore, in this case, it is preferable to use an angle between the width direction of the linear polarizer and the slow axis (N) of the resin layer (N) that is close to 135°. Specifically, the aforementioned angle is preferably 130° or higher, more preferably 132° or higher, even better 133° or higher, especially 134° or higher, and preferably 140° or lower, more preferably 138° or lower, even better 137° or lower, and especially preferably 136° or lower.

[0134] A suitable bonding agent should be used for the stacking of the phase difference film and the linear polarizer.

[0135] In addition to the fifth and sixth steps mentioned above, the manufacturing method of a circular polarizer may also include any other steps. Examples of such arbitrary steps include: the step of stacking functional layers on the phase décor film, the linear polarizer, and / or the circular polarizer. Examples of functional layers include: a protective film layer for the polarizer; a hard coating such as an impact-resistant polymethyl methacrylate resin layer; a base layer that optimizes the smoothness of the film; an anti-reflective layer; an anti-fouling layer; an antistatic layer; etc.

[0136] [11. Examples of applications of circular polarizers]

[0137] The circular polarizer described above can be disposed in an image display device. In particular, the circular polarizer is preferably disposed in an organic EL image display device. This organic EL image display device includes a circular polarizer and an organic electroluminescent element (hereinafter referred to as "organic EL element"). This organic EL image display device typically includes a linear polarizer, a phase retardation film and an organic EL element in sequence.

[0138] Organic EL devices sequentially comprise a transparent electrode layer, a light-emitting layer, and an electrode layer. Light is generated in the light-emitting layer by applying a voltage to the transparent electrode layer and the electrode layer. Examples of materials constituting the organic light-emitting layer include poly(p-phenylenevinyl)-based, polyvinyl chloride-based, and polyvinylcarbazole-based materials. Furthermore, the light-emitting layer can also be a stack of multiple layers with different emission colors, or a mixed layer in which different pigments are doped into a single pigment layer. Moreover, organic EL devices can also include functional layers such as a hole injection layer, a hole transport layer, an electron injection layer, an electron transport layer, an equipotential surface formation layer, and a charge generation layer.

[0139] The aforementioned image display device can suppress the reflection of external light onto the display surface. Specifically, light incident from outside the device is first linearly polarized (only a portion of it) by passing through a linear polarizer, and then through a phase retardation film to become circularly polarized. This circularly polarized light is then reflected by light-reflecting elements within the image display device (such as reflective electrodes in organic EL elements), and passes through the phase retardation film again, thus becoming linearly polarized light with a vibration direction orthogonal to the vibration direction of the incident linearly polarized light, and thus no longer passes through the linear polarizer. Here, the vibration direction of the linearly polarized light refers to the vibration direction of the electric field of the linearly polarized light. This achieves the function of reflection suppression.

[0140] Because the phase retardation film possesses the optical properties described above, the aforementioned organic EL image display device can suppress reflections not only in the front direction of the display surface but also in the tilt direction. This effectively suppresses the reflection of external light and inhibits color distortion in both the front and tilt directions of the display surface.

[0141] The degree of color change mentioned above can be evaluated by the color difference ΔE*ab between "the chromaticity measured by observing the reflective display surface" and "the chromaticity of the non-reflective black display surface". The aforementioned chromaticity can be obtained by measuring the spectrum of light reflected from the display surface, multiplying this spectrum by the corresponding spectroscopic sensitivity (color matching function) of the human eye to obtain the tristimulus values ​​X, Y, and Z, and calculating the chromaticity (a*, b*, L*). Furthermore, the aforementioned color difference ΔE*ab is obtained from the chromaticity (a0*, b0*, L0*) of the display surface when it is not illuminated by external light and the chromaticity (a1*, b1*, L1*) when it is illuminated by external light, and is obtained by the following formula (X).

[0142] Mathematical Formula 1

[0143] Furthermore, the color change of the display surface caused by reflected light may vary depending on the azimuth angle of the viewing direction. Therefore, when viewed from an angle, the measured chromaticity may vary depending on the azimuth angle of the viewing direction, and thus the color difference ΔE*ab may also vary. Therefore, in order to evaluate the degree of color change when viewed from an angle, as described above, it is preferable to evaluate the color change by using the average value of the color difference ΔE*ab obtained from observations from multiple azimuth angles. Specifically, within an azimuth angle ϕ (see Figure 1.) of 0° or higher but less than 360°, the color difference ΔE*ab is measured every 5° in the azimuth direction, and the degree of color change is evaluated by the average value of the measured color difference ΔE*ab (average color difference). The smaller the aforementioned average color difference, the smaller the color change of the display surface when viewed from an angle.

[0144] Example

[0145] The following embodiments are disclosed to specifically illustrate the present invention. However, the present invention is not limited to the embodiments disclosed below, and may be implemented in any way without departing from the scope of the claims and their equivalents.

[0146] In the following description, the terms "%" and "parts" are by weight unless otherwise noted. Furthermore, the operations described below are performed at room temperature (20℃±15℃) and normal pressure (1 atm) unless otherwise noted.

[0147] [Evaluation Method]

[0148] (Glass transfer temperature)

[0149] The glass transition temperature (Tg) of the resin was measured using a differential scanning calorimeter (DSC6220SII, manufactured by SII NanoTechnology Inc.) according to JIS K 6911 at a heating rate of 10°C / min.

[0150] (Thickness of the film or layer)

[0151] The thickness of thin films or layers was measured using the FILMETRICS F20 reflective spectrophotometric film thickness measurement system.

[0152] (Methods for measuring phase difference and NZ coefficient)

[0153] The in-plane phase difference Re at wavelengths of 450 nm, 550 nm, and 650 nm, and the thickness-direction phase difference Rth at wavelength 550 nm were measured using a phase difference meter (AxoScan, manufactured by Axometrics). When determining the properties of individual layers in an inseparable stack, the properties were calculated by fitting analysis using the accompanying multilayer thin film analysis software, based on samples measured from multiple directions. Furthermore, the NZ coefficient was calculated using the in-plane phase difference Re at wavelength 550 nm and the thickness-direction phase difference Rth.

[0154] (Method for measuring orientation angle)

[0155] The orientation of the slow axis (P) of the resin layer (P) and the slow axis (N) of the resin layer (N) contained in the phase difference film were measured using a phase difference meter (Axometrics "AxoScan"). The angle between this slow axis and the width direction of the phase difference film was calculated as the orientation angle θ (0° ≦ θ < 180°).

[0156] (Haze)

[0157] The haze of phase difference films was measured using a haze meter in accordance with JIS K7361-1997.

[0158] (Calculation method using simulated color difference)

[0159] Using Shintech's "LCD Master" software for simulation, the circular polarizers manufactured in each embodiment and comparative example were modeled, and the following calculations were performed.

[0160] In the simulation model, a structure is set up in which a circular polarizer is provided on the reflective surface of a mirror having a planar reflective surface. Furthermore, a circular polarizer is defined as having a resin layer (N) with a phase retardation film, a resin layer (P) with a phase retardation film, and a linear polarizer in sequence from the reflective surface side. The phase retardation film is the type obtained in each embodiment and comparative example. Furthermore, a polarizer with a polarization of 99.99% commonly used is used as the linear polarizer. Finally, an ideal mirror capable of mirror-reflecting incident light with 100% reflectivity is defined as the mirror.

[0161] Figure 1 is a perspective view schematically illustrating the state of the evaluation model set when calculating color space coordinates in the simulations of the embodiments and comparative examples.

[0162] As shown in Figure 1, calculate the color space coordinates observed on the reflecting surface 10 of a mirror equipped with a circular polarizer when illuminated by a D65 light source (not shown in the figure). Furthermore, define the color space coordinates when not illuminated by the light source as a0*=0, b0*=0, and L0*=0. Then, calculate the color difference ΔE*ab between the color space coordinates (i) when illuminated by the light source and (ii) when not illuminated by the light source.

[0163] The aforementioned color difference ΔE*ab is calculated in the observation direction 20, where the polar angle ρ relative to the reflecting surface 10 is 0°, to obtain the color difference ΔE*ab in the frontal direction. The polar angle ρ represents the angle relative to the normal direction 11 of the reflecting surface 10.

[0164] Furthermore, the aforementioned color difference ΔE*ab is calculated in the observation direction 20 with a polar angle ρ of 60° relative to the reflecting surface 10. This calculation of the polar angle ρ=60° is performed by moving the observation direction 20 multiple times along the azimuth direction at 5° intervals within a range of azimuth angles ϕ greater than 0° but less than 360°. The azimuth angle ϕ represents the angle between a direction parallel to the reflecting surface 10 and a reference direction 12 parallel to the reflecting surface 10. Then, the average of the color differences ΔE*ab calculated in multiple observation directions 20 is calculated to obtain the color difference ΔE*ab in the tilted direction with a polar angle ρ=60°.

[0165] (Evaluation method using a circular polarizer viewed from the front)

[0166] An image display device (Apple Watch, Inc., a registered trademark) equipped with an organic EL image display device is prepared. This image display device is disassembled, and the polarizing plate attached to the surface of the organic EL image display device is peeled off, exposing the reflective electrode. An intermediate adhesive (CS9621, manufactured by Nitto Denko Corporation) is used to bond the surface of this reflective electrode to the side of the circular polarizing plate obtained in the various embodiments and comparative examples that is opposite to the linear polarizer. This yields a sample having a reflective electrode, adhesive, and circular polarizing plate in sequence.

[0167] The circular polarizer of the aforementioned sample was visually observed on the reflective electrode under sunlight on a sunny day. The observation was conducted from the frontal direction with a polar angle of 0° and an azimuth angle of 0°. The results of the observation were judged as "defective" if color was observed and "good" if no color was observed.

[0168] (Evaluation method using a circular polarizing plate viewed in an inclined direction)

[0169] Under sunny conditions, with sunlight illuminating the sample circular polarizer prepared in the aforementioned (evaluation method using a circular polarizer viewed from the front) the circular polarizer was visually observed on the reflective electrode. The observation was conducted at an angle of 60° polarity and 0° to 360° azimuth of the circular polarizer. Based on the observation results, the reflectivity and color distortion were comprehensively assessed, and the examples and comparative examples were ranked. Then, scores corresponding to this ranking were assigned to the ranked examples and comparative examples (1st place: 7 points, 2nd place: 6 points, ..., last place: 1 point).

[0170] Multiple individuals conducted the aforementioned observations, and a total score was calculated for each embodiment and comparative example. The embodiments and comparative examples were arranged in order of the aforementioned total score, and evaluated in the range of this total score, starting from the highest group, in the order of A, B, C, D, and E.

[0171] [Example 1]

[0172] (1-1. First step: Preparation of the first film)

[0173] In a dry, nitrogen-purged pressure reactor, 500 mL of toluene as the solvent and 0.29 mmol of n-butyllithium as the polymerization catalyst were added, followed by 35 g of 2-vinylnaphthalene. The reaction was carried out at 25°C for 1 hour. This yielded a reactant containing poly(2-vinylnaphthalene) as a homopolymer of 2-vinylnaphthalene. Triphenyl phosphate was added to this reactant as a plasticizer, and the reactant was injected into a large amount of 2-propanol, causing the resin containing poly(2-vinylnaphthalene) to precipitate and separate. The obtained resin containing poly(2-vinylnaphthalene) was dried at 200°C for 24 hours using a vacuum dryer to obtain thermoplastic resin N. This thermoplastic resin N contains approximately 5% by weight of plasticizer. The weight-average molecular weight of poly(2-vinylnaphthalene) was measured to be 250,000 by GPC. Furthermore, the glass transition temperature of thermoplastic resin N was measured to be 127°C by differential scanning calorimetry. This thermoplastic resin N has a negative intrinsic birefringence value.

[0174] The obtained thermoplastic resin N is supplied to an extruder, passes through a polymer tube and a polymer filter, and is extruded into a sheet shape onto a casting roller through a T-die. The extruded thermoplastic resin N is cooled to obtain a long strip of resin film with a thickness of 50 μm, which serves as the first film having a resin layer (N1). The first film only has a resin layer (N1). The obtained first film is wound into a roll for recycling. The optical properties of the resin layer (N1) of the first film are evaluated using the aforementioned method.

[0175] (1-2. Second process: stretching of the first film)

[0176] A first film is unwound and supplied to a tenter frame. Using this tenter frame, the first film is stretched along a stretching direction at an angle of 135° relative to its width direction at a stretching temperature of 128°C, with a stretching ratio of 1.15 times in the stretching direction, to obtain a second film having a resin layer (N2), which is a stretched layer of the resin layer (N1). The second film only has the resin layer (N2). After cooling at room temperature, the obtained second film is wound up and recycled. The optical properties of the resin layer (N2) in the second film are evaluated using the aforementioned method.

[0177] (1-3. Third process: Stacking of resin layers (P1))

[0178] (Preparation of resin solution for resin layer (P1) formation)

[0179] A resin comprising a norethene polymer (ZEONOR, manufactured by Zeon Corporation, Japan; glass transition temperature 126°C, hereinafter also referred to as norethene resin) and cyclohexane as a solvent were mixed to form a liquid composition, thereby obtaining a resin solution with a norethene resin concentration of 15% by weight. This thermoplastic resin P has a positive intrinsic birefringence value.

[0180] The second film is unwound, and the aforementioned resin solution is coated onto the surface of the unwound second film—that is, the surface of the resin layer (N2)—to form a resin solution layer. Then, the resin solution layer is dried at 120°C for 2 minutes to form a resin layer (P1) with a thickness of 40 μm on the second film. Through the above operations, a third film is obtained having a resin layer (N2) and a resin layer (P1) stacked on top of this resin layer (N2). The optical properties of the resin layer (N2) and resin layer (P1) of the third film are evaluated using the aforementioned method.

[0181] (1-4. Fourth step: Extension of the third film)

[0182] The obtained third film is supplied to a tenter frame. Using this tenter frame, the third film is stretched at an angle of 45° relative to the width direction of the third film—that is, at an angle of 90° relative to the stretching direction of the first film—at a stretching temperature of 128°C, with a stretching ratio of 1.50 in the stretching direction, to obtain a strip-shaped retardation film. This retardation film comprises a resin layer (N) which is a stretched layer of resin layer (N2) and a resin layer (P) which is a stretched layer of resin layer (P1). The optical properties of the retardation film and each layer of the retardation film are evaluated using the aforementioned method.

[0183] (1-5. Manufacturing of circular polarizing plates)

[0184] Prepare a strip-shaped polyvinyl alcohol resin film dyed with iodine. Extend this film along its long side at a 90° angle relative to its width direction to obtain a linear polarizer as a strip-shaped polarizing film. This linear polarizer has an absorption axis along its long side and a transmission axis along its width direction.

[0185] The aforementioned linear polarizer is bonded to an optically isotropic adhesive (Nitto Denko Corporation's "CS9621") used as an intervening optical medium for the retardation film to obtain a long strip-shaped circular polarizer. The bonding process is performed with the width direction of the linear polarizer parallel to the width direction of the retardation film. The resulting circular polarizer sequentially comprises a linear polarizer, a resin layer (P), and a resin layer (N).

[0186] The obtained circular polarizer was evaluated using the aforementioned method.

[0187] [Examples 2-4]

[0188] In process (1-2), the elongation ratio of the first film is changed as shown in Table 1.

[0189] Apart from the above, the phase difference film and the circular polarizer were manufactured and evaluated in accordance with Example 1.

[0190] [Comparative Example 1]

[0191] A phase retardation film was manufactured using the same method as in Example 1 of Japanese Patent Publication No. 2022-052074. Specifically, the phase retardation film was obtained by the following operations.

[0192] (C1-1. Preparation of films of thermoplastic resin P)

[0193] A resin containing a northoene polymer (hereinafter also referred to as northoene resin) (manufactured by Zeon Corporation, Japan; glass transfer temperature 126°C) is dried at 100°C for 5 hours to obtain a thermoplastic resin P with a positive intrinsic birefringence. The dried thermoplastic resin P is supplied to an extruder, passed through a polymer tube and a polymer filter, and extruded into a sheet shape onto a casting roller through a T-die. The extruded thermoplastic resin P is cooled to obtain an unstretched film with a thickness of 60 μm formed from the thermoplastic resin P. The obtained unstretched film is wound into rolls for recycling.

[0194] (C1-2. Stacking of layers of thermoplastic resin N)

[0195] In a dry, nitrogen-purged pressure reactor, 500 mL of toluene as the solvent and 0.29 mmol of n-butyllithium as the polymerization catalyst were added, followed by 35 g of 2-vinylnaphthalene. The reaction was carried out at 25°C for 1 hour. The result was a reactant containing poly(2-vinylnaphthalene) as a homopolymer of 2-vinylnaphthalene. This reactant was injected into a large amount of 2-propanol, causing the poly(2-vinylnaphthalene) to precipitate, which was then separated. The obtained poly(2-vinylnaphthalene) was dried at 200°C for 24 hours using a vacuum dryer to obtain thermoplastic resin N. The weight-average molecular weight of the poly(2-vinylnaphthalene) was measured to be 250,000 by GPC. Furthermore, the glass transition temperature of the poly(2-vinylnaphthalene) was measured to be 142°C by differential scanning calorimetry. This thermoplastic resin N has a negative intrinsic birefringence.

[0196] The poly(2-vinylnaphthalene) used as thermoplastic resin N is mixed with 1,3-dioxane used as a solvent to obtain a resin solution containing thermoplastic resin N. The concentration of poly(2-vinylnaphthalene) in this resin solution is 15% by weight.

[0197] The aforementioned unstretched film (resin layer CP1) is pulled out from the roll, and the aforementioned resin solution is coated on the surface of the pulled-out unstretched film to form a resin solution layer. Then, the resin solution layer is rapidly dried at 120°C to form a 12 μm thick poly(2-vinylnaphthalene) layer on the unstretched film. Through the above operations, a stacked film is obtained having an unstretched film (resin layer CP1) formed of thermoplastic resin P and a poly(2-vinylnaphthalene) layer (resin layer CN1) formed of thermoplastic resin N. The obtained stacked film is then wound into a roll for recycling.

[0198] (C1-3. Extension of stacked thin films)

[0199] The stacked film is drawn from the roll and continuously supplied to a tenter frame. Then, using this tenter frame, the stacked film is stretched along a stretching direction at a 45° angle relative to its long side, at a stretching temperature of 140°C, with a stretching ratio of 1.5 times in the stretching direction, to obtain a strip-shaped retardation film. This retardation film comprises a resin layer (P) obtained by stretching a layer of norethene-based resin (resin layer CP1) and a resin layer (N) obtained by stretching a layer of poly(2-vinylnaphthalene) (resin layer CN1).

[0200] (C1-4. Manufacturing of circular polarizing plates)

[0201] Using the obtained retardation film, a circular polarizer was manufactured following the procedures (1-5) of Example 1. The obtained circular polarizer sequentially comprises a linear polarizer, a resin layer (P), and a resin layer (N). The obtained retardation film and circular polarizer were evaluated using the aforementioned method.

[0202] [Comparative Example 2]

[0203] A phase retardation film was manufactured using the same method as in Example 1 of Japanese Patent Publication No. 2007-199616. Specifically, the phase retardation film was obtained by the following operations.

[0204] (C2-1. Preparation of films of thermoplastic resin P)

[0205] A film (70 μm thick) containing a resin (ARTON FLZU, manufactured by JSR Corporation; glass transition temperature 128°C) was prepared as a thermoplastic resin P with a positive intrinsic birefringence value.

[0206] (C2-2. Stacking of layers of thermoplastic resin N)

[0207] Following the procedure described in Example 1 of Japanese Patent Publication No. 2007-199616, a copolymer of styrene and maleic anhydride (glass transition temperature 148°C) was prepared as a thermoplastic resin N with a negative intrinsic birefringence value.

[0208] The obtained copolymer was mixed with methyl ethyl ketone as a solvent to form a liquid composition, resulting in a resin solution with a concentration of 33% by weight of styrene-maleic anhydride copolymer.

[0209] The aforementioned resin solution is coated onto the film containing the thermoplastic resin P, which is a northoene polymer, to form a resin solution layer. Then, the resin solution layer is dried at 80°C for 10 minutes to form a 40 μm thick layer of thermoplastic resin N on the film formed from the thermoplastic resin P. Through the above operations, a stacked film is obtained comprising a film formed from thermoplastic resin P (resin layer CP1) and a layer of thermoplastic resin N (resin layer CN1).

[0210] (C2-3. Extension of stacked thin films)

[0211] Subsequently, the aforementioned stacked films were uniaxially stretched at a stretching temperature of 110°C and a stretching ratio of 2.0 to obtain a phase retardation film. This phase retardation film comprises a resin layer (P) obtained by stretching a layer of norethene-based resin (resin layer CP1) and a resin layer (N) obtained by stretching a layer of styrene-maleic anhydride copolymer (resin layer CN1).

[0212] (C2-4. Manufacturing of circular polarizing plates)

[0213] Using the obtained retardation film, a circular polarizer was manufactured following the procedures (1-5) of Example 1. The obtained circular polarizer sequentially comprises a linear polarizer, a resin layer (P), and a resin layer (N). The obtained retardation plate and circular polarizer were evaluated using the aforementioned method.

[0214] [Comparative Example 3]

[0215] (C3-1. Preparation of films of thermoplastic resin P)

[0216] Particulate norethene-based resin (manufactured by Zeon Corporation, Japan; glass transition temperature 126°C) was dried at 100°C for 5 hours to obtain thermoplastic resin P. This thermoplastic resin P was fed to an extruder, passed through a polymer tube and a polymer filter, and extruded into a sheet shape onto a casting roller via a T-die. The extruded thermoplastic resin P was cooled to obtain an unstretched film with a thickness of 110 μm. The obtained unstretched film was then wound into rolls for recycling.

[0217] (C3-2. Stacking of layers of thermoplastic resin N)

[0218] In a dry, nitrogen-purged pressure reactor, 500 mL of toluene as the solvent and 0.29 mmol of n-butyllithium as the polymerization catalyst were added, followed by the addition of 35 g of 2-vinylnaphthalene. The reaction was carried out at 25°C for 1 hour. The result was a reactant containing poly(2-vinylnaphthalene) as a homopolymer of 2-vinylnaphthalene. This reactant was injected into a large volume of 2-propanol, causing the poly(2-vinylnaphthalene) to precipitate, which was then separated. The obtained poly(2-vinylnaphthalene) was dried at 200°C for 24 hours using a vacuum dryer to obtain thermoplastic resin N. The weight-average molecular weight of the poly(2-vinylnaphthalene) was measured to be 250,000 by GPC. Furthermore, the glass transition temperature of the poly(2-vinylnaphthalene) was measured to be 142°C by differential scanning calorimetry. This thermoplastic resin N has a negative intrinsic birefringence.

[0219] The poly(2-vinylnaphthalene) used as thermoplastic resin N is mixed with 1,3-dioxane used as a solvent to obtain a resin solution containing thermoplastic resin N. The concentration of poly(2-vinylnaphthalene) in this resin solution is 15% by weight.

[0220] The aforementioned unstretched film (resin layer CP1) is pulled out from the roll, and the aforementioned resin solution is coated onto the pulled-out unstretched film to form a resin solution layer. Then, the resin solution layer is dried, forming a 13 μm thick poly(2-vinylnaphthalene) layer on the unstretched film. Through the above operations, a stacked film is obtained comprising an unstretched film (resin layer CP1) formed from a thermoplastic resin P (norphene-based resin) and a poly(2-vinylnaphthalene) layer (resin layer CN1) formed from a thermoplastic resin N. The obtained stacked film is then wound into a roll for recycling.

[0221] (C3-3. Stretching of stacked films; first stretching process)

[0222] The stacked film is drawn from the roll and supplied to a tenter frame. Using this tenter frame, the stacked film is stretched along a stretching direction at an angle of 135° relative to the width direction of the stacked film, at a stretching temperature of 140°C, with a stretch ratio of 1.15 times in the stretching direction. After being cooled at room temperature, the stretched stacked film is wound into a roll for recycling.

[0223] (C3-4. Stretching of stacked films; second stretching process)

[0224] The stacked film stretched in the first stretching process is pulled out from the roll and supplied to a tenter frame. Using this tenter frame, the stacked film is stretched along a stretching direction at an angle of 45° relative to the width direction of the stacked film, at a stretching temperature of 128°C, with a stretching ratio of 1.50 in the stretching direction, to obtain a strip-shaped phase reversal film. This phase reversal film comprises a resin layer (P) obtained by stretching a layer of norethene-based resin (resin layer CP1) and a resin layer (N) obtained by stretching a layer of poly(2-vinylnaphthalene) (resin layer CN1).

[0225] (C3-5. Manufacturing of circular polarizing plates)

[0226] Using the obtained retardation film, a circular polarizer was manufactured following the procedures (1-5) of Example 1. The obtained circular polarizer sequentially comprises a linear polarizer, a resin layer (P), and a resin layer (N). The obtained retardation film and circular polarizer were evaluated using the aforementioned method.

[0227] In the aforementioned embodiments and comparative examples, the visual evaluation in the frontal direction is determined using a two-stage system of "good" and "poor," while the visual evaluation in the tilted direction is determined using a five-stage system of "A" to "E." The reason for this difference in evaluation criteria is as follows.

[0228] In other words, the reflected light is sufficiently dim in the frontal direction compared to the tilted direction. Therefore, unless a strong color change occurs, the observer cannot perceive the color change. Thus, a two-stage determination is used to determine whether the color change is visible.

[0229] On the other hand, the reflected light is brighter in the tilted direction. Therefore, even a weak color change is easily perceived by the observer. Thus, a detailed evaluation of its merits and demerits is adopted in five stages.

[0230] [result]

[0231] The manufacturing conditions in the examples and comparative examples are disclosed in Tables 1 and 2, and the results are disclosed in Table 3.

[0232] In the table below, the abbreviations have the following meanings. "VN": Resin containing poly(2-vinylnaphthalene). "COP1": Norbenzene-based resin manufactured by Zeon Corporation of Japan (glass transfer temperature 126°C) "COP2": JSR Corporation's norethene-based resin "ARTON FLZU" (glass transfer temperature 128°C) "ST-MA": Styrene-maleic anhydride copolymer "P1 / N2": A stack having a resin layer (P1) and a resin layer (N2). "CN1 / CP1": A stack having a resin layer (CN1) and a resin layer (CP1). "P / N": A phase difference film having a resin layer (P) and a resin layer (N). "Wavelength Dispersion Difference": The value of [Re N(450) / Re N(550)] - [Re P(450) / Re P(550)]. "θ": The angle between the slow axis of the film or layer and its width direction. In Table 2, under the fourth process step, "Step 1": the first extended process. In the fourth process of item 2 in Table 2, "2": Second extended process

[0233] Table 1 Table 1 Example 1 Example 2 Example 3 Example 4 Process 1 First Thin Film Structure N1 N1 N1 N1 Resin layer (N1) Material VN VN VN VN Inherent birefringence value burden burden burden burden Tg 127℃ 127℃ 127℃ 127℃ Re(550)(nm) 0.7 0.7 0.7 0.7 Rth(550)(nm) -0.2 -0.2 -0.2 -0.2 Process 2 Extended temperature 128℃ 128℃ 128℃ 128℃ Extension ratio E2 (times) 1.15 1.2 1.25 1.3 Second thin film structure N2 N2 N2 N2 Resin layer (N2) Re(550)(nm) 30.0 40.0 50.0 60.0 Rth(550)(nm) -18.0 -24.0 -30.0 -36.0 Process 3 Third thin film structure P1 / N2 P1 / N2 P1 / N2 P1 / N2 Resin layer (P1) Material COP1 COP1 COP1 COP1 Inherent birefringence value just just just just Tg 126℃ 126℃ 126℃ 126℃ Re(550)(nm) 1.2 1.2 1.2 1.2 Rth(550)(nm) 4.8 4.8 4.8 4.8 Process 4 Extended temperature 128℃ 128℃ 128℃ 128℃ Extension ratio E4 (times) 1.5 1.5 1.5 1.5 Phase difference thin film construction P / N P / N P / N P / N E4 / E2 1.30 1.25 1.20 1.15

[0234] Table 2 Table 2 Comparative Example 1 Comparative Example 2 Comparative Example 3 Process 1 First Thin Film Structure CP1 CP1 CP1 Resin layer (CP1) Material COP1 COP2 COP1 Inherent birefringence value just just just Tg 126℃ 128℃ 126℃ Re(550)(nm) 0.2 0.2 0.2 Rth(550)(nm) 2.4 2.4 2.4 Process 2 Extended temperature - - - Extension ratio (times) 0 (not extended) 0 (not extended) 0 (not extended) Second thin film structure CP1 CP1 CP1 Process 3 Third thin film structure CN1 / CP1 CN1 / CP1 CN1 / CP1 Resin layer (CN1) Material VN ST―MA VN Inherent birefringence value burden burden burden Tg 142℃ 148℃ 142℃ Re(550)(nm) 1.0 1.2 0.7 Rth(550)(nm) -49.0 -0.1 -0.2 Process 4 Extended temperature 140℃ 110℃ Chapter 1:140℃ Chapter 2:128℃ Extension ratio (times) 1.5 2 Chapter 1:1.15 Chapter 2:1.5 Phase difference thin film construction P / N P / N P / N

[0235] Table 3 Table 3 Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Comparative Example 3 Resin layer (P) Re P(450)(nm) 272.6 272.6 272.6 272.6 292.8 292.8 272.6 Re P(550)(nm) 270.5 270.5 270.5 270.5 290.6 290.6 270.5 Re P(650)(nm) 269.4 269.4 269.4 269.4 289.3 289.3 269.4 Rth P(550)(nm) 162.3 162.3 162.3 162.3 168.5 145.3 162.3 θ(°) 45.0 45.0 45.0 45.0 45.0 45.0 45.0 NZ P 1.10 1.10 1.10 1.10 1.08 1.00 1.10 Resin layer (N) Re N(450)(nm) 151.3 151.3 151.3 151.3 171.7 166.7 151.3 Re N(550)(nm) 135.6 135.6 135.6 135.6 154.0 155.6 135.6 Re N(650)(nm) 128.4 128.4 128.4 128.4 145.8 149.4 128.4 Rth N(550)(nm) -122.1 -149.2 -176.3 -203.4 -92.4 -77.8 -149.2 θ(°) 135.0 135.0 135.0 135.0 135.0 135.0 135.0 NZ N -0.40 -0.60 -0.80 -1.00 -0.10 0.00 -0.60 Phase difference film Re T(450)(nm) 121 121 121 121 121 126 121 Re T(550)(nm) 135 135 135 135 137 135 135 Re T(650)(nm) 141 141 141 141 144 140 141 NZ T 0.80 0.60 0.40 0.20 1.06 1.00 0.60 wavelength dispersion 1.08 1.08 1.08 1.08 1.08 0.06 1.08 Fog level (%) <1.0 <1.0 <1.0 <1.0 <1.0 <1.0 1.8 Reflective properties Front direction ΔE*ab (vs. Black) 12.4 12.4 12.4 12.4 9.5 20.6 12.4 visual inspection good good good good good good good Tilt direction (60°) ΔE*ab (vs. Black) 20.7 15.6 16.2 20.4 26.3 28.3 15.6 visual B A A B D D A

[0236] As can be seen from the above results, a phase difference film that satisfies formulas (1) to (3) and has low haze can be obtained by the method of the embodiment. Furthermore, it can be seen that the circular polarizer with a phase difference film that satisfies formulas (1) to (3) obtained by the method of the embodiment can suppress color change caused by reflection of external light on both the front and tilt directions of the display surface of the image display device equipped with the circular polarizer.

[0237] 10: Reflective surface 11: Normal direction 12: Reference Direction 20: Observation direction ϕ: azimuth angle ρ: Polar angle

Claims

1. A method for manufacturing a phase retardation thin film, which is a method for manufacturing a phase retardation thin film satisfying the following formulas (1), (2), and (3), the aforementioned manufacturing method comprising: a first step of preparing a first thin film having a resin layer (N1) formed of a thermoplastic resin N having a negative intrinsic birefringence value; a second step of stretching the aforementioned first thin film at least once to obtain a second thin film having a resin layer (N2), wherein the resin layer (N2) is a layer of the aforementioned resin layer (N1) after stretching; a third step of stacking the aforementioned second thin film... A third film is obtained by stacking a resin layer (P1) formed of a thermoplastic resin P having a positive intrinsic birefringence value; and a fourth step is to extend the aforementioned third film at least once to obtain the aforementioned phase difference film having a resin layer (N) and a resin layer (P), wherein the resin layer (N) is an extended layer of the aforementioned resin layer (N2) and has a slow axis (N), and the resin layer (P) is an extended layer of the aforementioned resin layer (P1) and has a slow axis (P) with an angle within the range of 90° ± 5° relative to the aforementioned slow axis (N); 100 nm≦Re T(550)≦180 nm (1)Re T(450)<Re T(550)<Re T(650) (2)0.0<NZ T<1.0 (3)(where, Re T(450) represents the in-plane phase difference of the aforementioned phase difference film at a wavelength of 450 nm, Re T(550) represents the in-plane phase difference of the aforementioned phase difference film at a wavelength of 550 nm, Re T(650) represents the in-plane phase difference of the aforementioned phase difference film at a wavelength of 650 nm, and NZ T represents the NZ coefficient of the aforementioned phase difference film).

2. The method for manufacturing a phase difference thin film as described in claim 1, wherein the in-plane phase difference of the aforementioned resin layer (N2) in the second thin film is 20 nm or more.

3. A method for manufacturing a phase difference film as claimed in claim 1 or 2, wherein in the aforementioned second step, the extension of the first film is an extension in one direction, and in the aforementioned fourth step, the extension of the third film includes an extension in a direction within a range of 90° ± 5° relative to the extension direction of the first film in the aforementioned second step.

4. A method for manufacturing a phase retardation thin film as described in claim 1 or 2, wherein the aforementioned phase retardation thin film satisfies the following formula (4); [Re N(450) / Re N(550)] - [Re P(450) / Re P(550)] > 0.08 (4) (wherein, Re N(450) represents the in-plane phase difference of the resin layer (N) at a wavelength of 450 nm, Re N(550) represents the in-plane phase difference of the resin layer (N) at a wavelength of 550 nm, Re P(450) represents the in-plane phase difference of the resin layer (P) at a wavelength of 450 nm, and Re P(550) represents the in-plane phase difference of the resin layer (P) at a wavelength of 550 nm.

5. A method for manufacturing a phase retardation thin film as described in claim 1 or 2, wherein the aforementioned phase retardation thin film satisfies the following equation (5); Re P (550) > Re N (550) (5) (wherein, Re N(550) represents the in-plane phase difference of the resin layer (N) at a wavelength of 550 nm, and ReP(550) represents the in-plane phase difference of the resin layer (P) at a wavelength of 550 nm.

6. A method for manufacturing a circular polarizer, comprising a linear polarizer and a phase difference film, comprising: a fifth step of manufacturing the phase difference film using the method for manufacturing the phase difference film as described in any one of claims 1 to 5; and a sixth step of stacking the phase difference film and the linear polarizer.

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