Method for producing retardation film and method for producing circularly polarizing plate

Abstract

Provided is a method for producing a retardation film having specific optical characteristics, the method comprising: a first step of preparing a first film having a resin layer (N1) formed from a thermoplastic resin (N) having a negative intrinsic birefringence value; a second step of stretching the first film at least once to obtain a second film having a resin layer (N2), the resin layer (N2) being a layer obtained by stretching the resin layer (N1); a third step for obtaining a third film by laminating a resin layer (P1) on the second film, the resin layer (P1) being formed from a thermoplastic resin (P) having a positive intrinsic birefringence value; and a fourth step of stretching the third film at least once to obtain the phase difference film having a resin layer (N) having a slow axis (N) after the resin layer (N2) has been stretched and a resin layer (P) having a slow axis (P) having an angle in the range of 90 DEG + / -5 DEG with respect to the slow axis (N) after the resin layer (P1) has been stretched.

Description

Technical Field

[0001] The present invention relates to a method for producing a phase difference film and a method for producing a circular polarizing plate. Background Art

[0002] In image display devices such as organic electroluminescent image display devices (hereinafter, sometimes appropriately referred to as "organic EL image display devices") and liquid crystal image display devices, a phase difference film is sometimes provided. Among such phase difference films, there are phase difference films having a multilayer structure having two or more layers. As a method for manufacturing a phase difference film having such a multilayer structure, a method using a co-stretching method is sometimes adopted (refer to Patent Documents 1 to 4).

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Publication No. 2007-199616 (corresponding foreign publication: U.S. Patent Application Publication No. 2009 / 290103);

[0006] Patent Document 2: Japanese Patent Application Publication No. 2009-169086;

[0007] Patent document 3: International Publication No. 2021 / 085031;

[0008] Patent document 4: Japanese Patent Application Publication No. 2022-052074. Summary of the invention

[0009] Problem that the invention aims to solve

[0010] In order to reduce the reflection of external light on the display surface, a circular polarizing plate may be provided in an image display device. As such a circular polarizing plate, a film combining a linear polarizer and a λ / 4 wave plate can be generally used.

[0011] In order to suppress the coloring of the display surface, a circular polarizer that can reduce the reflection of external light in a wide wavelength range is required. Such a circular polarizer can be manufactured using, for example, a broadband λ / 4 wave plate that can function as a λ / 4 wave plate in a wide wavelength range. As the broadband λ / 4 wave plate, it is known that there is a phase difference film with a plurality of layers in combination, and for example, a phase difference film with a λ / 2 wave plate and a λ / 4 wave plate in combination can be cited. The circular polarizer with a phase difference film that can function as a broadband λ / 4 wave plate can suppress the coloring of the display surface because it can reduce the reflection of external light in a wide wavelength range in the front direction perpendicular to the display surface.

[0012] However, in an inclined direction that is neither parallel nor perpendicular to the display surface, the reflection of external light may not be reduced in a wide wavelength range due to the phase difference value deviating from the ideal value or the optical axis of each layer deviating. Therefore, in order to realize a circular polarizer that can suppress the coloration caused by the reflection of external light in an inclined direction, the phase difference film needs to have an NZ coefficient in a specific range greater than 0.0 and less than 1.0.

[0013] The layers included in the phase difference film satisfying the above conditions are usually different in part or all of the optical properties such as the direction of the slow axis, the in-plane phase difference, and the NZ coefficient. Therefore, in the past, it was usually necessary to manufacture the above-mentioned phase difference film by bonding these layers after each layer was manufactured separately. However, this previous manufacturing method has a tendency that the number of processes increases, the labor and time increase, and the cost increases because the manufacture of each layer is carried out separately. In addition, since it is necessary to accurately align the bonding angle when bonding each layer, it is necessary to adjust the labor and time of the angle, thereby having a tendency that the labor and time increase.

[0014] Furthermore, when the retardation film is produced by stretching an unstretched multilayer film, adjustment of stretching conditions such as the temperature of the thermoplastic resin forming each layer and the stretching temperature is also complicated.

[0015] Therefore, there is a need for: a method for simply manufacturing a phase difference film, wherein the phase difference film can obtain a circular polarizer capable of suppressing coloration caused by reflection of external light in both the front direction and the oblique direction of a display surface; and a method for simply manufacturing a circular polarizer, wherein the circular polarizer can suppress coloration caused by reflection of external light in both the front direction and the oblique direction of a display surface.

[0016] Solutions for solving problems

[0017] The present inventors have conducted intensive research to solve the above-mentioned problems. As a result, it was found that the above-mentioned problems can be solved by the following manufacturing method, which includes the following steps: preparing a first film having a resin layer (N1), wherein the resin layer (N1) is formed of a thermoplastic resin N having a negative intrinsic birefringence value; stretching the first film at least once to obtain a second film having a resin layer (N2), wherein the resin layer (N2) is a layer after the resin layer (N1) is stretched; laminating a resin layer (P1) on the second film to obtain a third film, wherein the resin layer (P1) is formed of a thermoplastic resin P having a positive intrinsic birefringence value; and stretching the third film at least once; thereby completing the present invention.

[0018] That is, the present invention provides the following solutions.

[0019] [1] A method for producing a retardation film, wherein the retardation film satisfies the following formula (1), the following formula (2) and the following formula (3),

[0020] The manufacturing method comprises:

[0021] In a first step, a first film having a resin layer (N1) is prepared, wherein the resin layer (N1) is formed of a thermoplastic resin N having a negative intrinsic birefringence value;

[0022] A second step of stretching the first film at least once to obtain a second film having a resin layer (N2), wherein the resin layer (N2) is a layer obtained by stretching the resin layer (N1);

[0023] A third step is to laminate a resin layer (P1) on the second film to obtain a third film, wherein the resin layer (P1) is formed of a thermoplastic resin P having a positive intrinsic birefringence value;

[0024] In a fourth step, the third film is stretched at least once to obtain the phase difference film having a resin layer (N) and a resin layer (P), wherein the resin layer (N) is a layer obtained by stretching the resin layer (N2) and has a slow axis (N), and the resin layer (P) is a layer obtained by stretching the resin layer (P1) and has a slow axis (P) that forms an angle of 90°±5° with the slow axis (N).

[0025]

[0026] (in,

[0027] Re T (450) represents the in-plane phase difference of the above phase difference film at a wavelength of 450 nm,

[0028] Re T (550) represents the in-plane phase difference of the above phase difference film at a wavelength of 550 nm,

[0029] Re T (650) represents the in-plane phase difference of the above phase difference film at a wavelength of 650 nm,

[0030] NZ T represents the NZ coefficient of the above-mentioned retardation film).

[0031] [2] The method for producing a retardation film according to [1], wherein the in-plane retardation of the resin layer (N2) of the second film is 20 nm or more.

[0032] [3] A method for manufacturing a phase difference film according to [1] or [2], wherein the stretching of the first film in the second step is stretching in one direction, and the stretching of the third film in the fourth step includes stretching in a direction within a range of 90°±5° relative to the stretching direction of the first film in the second step.

[0033] [4] The method for producing a retardation film according to any one of [1] to [3], wherein the retardation film satisfies the following formula (4):

[0034]

[0035] (in,

[0036] Re N (450) represents the in-plane phase difference of the resin layer (N) at a wavelength of 450 nm,

[0037] Re N (550) represents the in-plane phase difference of the resin layer (N) at a wavelength of 550 nm,

[0038] Re P (450) represents the in-plane phase difference of the resin layer (P) at a wavelength of 450 nm,

[0039] Re P (550) represents the in-plane phase difference of the above-mentioned resin layer (P) at a wavelength of 550 nm).

[0040] [5] The method for producing a retardation film according to any one of [1] to [4], wherein the retardation film satisfies the following formula (5):

[0041]

[0042] (in,

[0043] Re N (550) represents the in-plane phase difference of the resin layer (N) at a wavelength of 550 nm,

[0044] Re P (550) represents the in-plane phase difference of the above-mentioned resin layer (P) at a wavelength of 550 nm).

[0045] [6] A method for manufacturing a circular polarizer, the circular polarizer comprising a linear polarizer and a phase difference film, the method comprising:

[0046] A fifth step is to manufacture the retardation film using the method for manufacturing a retardation film described in any one of [1] to [5]; and

[0047] In the sixth step, the phase difference film and the linear polarizer are laminated.

[0048] The present invention also provides the following technical solutions.

[0049] [7] A retardation film produced by the production method described in any one of [1] to [5].

[0050] Effects of the Invention

[0051] According to the present invention, there can be provided: a manufacturing method capable of simply manufacturing a phase difference film, wherein the phase difference film can obtain a circular polarizer capable of suppressing coloration caused by reflection of external light in two directions, namely, the front direction and the oblique direction of the display surface; and a manufacturing method capable of simply manufacturing a circular polarizer capable of suppressing coloration caused by reflection of external light in two directions, namely, the front direction and the oblique direction of the display surface. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 It is a perspective view schematically showing the state of the evaluation model set when calculating the color space coordinates in the simulation of the embodiment and the comparative example. DETAILED DESCRIPTION

[0053] Hereinafter, the present invention will be described in detail by showing the embodiments and examples. However, the present invention is not limited to the embodiments and examples shown below, and can be implemented by any changes without departing from the scope of the claims of the present invention and the scope of their equivalents. The constituent elements of the embodiments shown below can be appropriately combined. In addition, in the accompanying drawings, the same reference numerals are marked on the same constituent elements, and their descriptions are sometimes omitted.

[0054] In the following description, unless otherwise stated, the in-plane phase difference Re represents a value represented by Re=(nx-ny)×d. Unless otherwise stated, the thickness direction phase difference Rth is a value represented by Rth={(nx+ny) / 2-nz}×d. Furthermore, unless otherwise stated, the NZ coefficient NZ represents a value represented by NZ=Rth / Re+0.5, and therefore can be represented by NZ=(nx-nz) / (nx-ny). nx represents the refractive index in the direction (slow axis direction) that provides the maximum refractive index in the direction perpendicular to the thickness direction (in-plane direction); ny represents the refractive index in the direction orthogonal to the nx direction in the above-mentioned in-plane direction; nz represents the refractive index in the thickness direction; d represents the thickness. Unless otherwise stated, the measurement wavelength is 550nm. The in-plane phase difference, the thickness direction phase difference and the NZ coefficient can be measured using a phase difference meter ("AxoScan" manufactured by Axon Corporation).

[0055] In the following description, unless otherwise specified, the slow axis of a certain layer refers to the slow axis in the in-plane direction of the layer.

[0056] In the following description, unless otherwise specified, the angle formed by the optical axis (absorption axis, transmission axis, slow axis, etc.) of each layer in a multilayer member means the angle when the layer is observed in the thickness direction.

[0057] In the following description, unless otherwise specified, the front direction of a certain surface refers to the normal direction of the surface, specifically, the direction in which the polar angle of the surface is 0° and the azimuth angle is 0°.

[0058] In the following description, unless otherwise specified, the inclination direction of a certain surface refers to a direction that is neither parallel nor perpendicular to the surface, specifically, a direction in the range where the polar angle of the surface is greater than 0° and less than 90°.

[0059] In the following description, unless otherwise specified, the directions of elements being “parallel”, “perpendicular”, and “orthogonal” may include errors within a range of, for example, ±5° within a range that does not impair the effects of the present invention.

[0060] In the following description, a "long film" refers to a film having a length of more than 5 times the width, preferably 10 times or more, and specifically refers to a film having a length that can be rolled up for storage or transportation. The upper limit of the length of the long film is not particularly limited, and can be, for example, less than 100,000 times the width.

[0061] In the following description, the length direction of the long film is usually parallel to the flow direction of the film on the production line. In addition, the width direction of the long film is usually perpendicular to the thickness direction and perpendicular to the length direction.

[0062] In the following description, unless otherwise specified, "polarizer", "circular polarizer", "plate", "λ / 2 wave plate" and "λ / 4 wave plate" include not only rigid components but also flexible components such as resin films.

[0063] In the following description, "a polymer having a positive intrinsic birefringence value" and "a resin having a positive intrinsic birefringence value" refer to "a polymer having a larger refractive index in a stretching direction than in a direction perpendicular to the stretching direction" and "a resin having a larger refractive index in a stretching direction than in a direction perpendicular to the stretching direction", respectively. In addition, "a polymer having a negative intrinsic birefringence value" and "a resin having a negative intrinsic birefringence value" refer to "a polymer having a smaller refractive index in a stretching direction than in a direction perpendicular to the stretching direction" and "a resin having a smaller refractive index in a stretching direction than in a direction perpendicular to the stretching direction", respectively. The intrinsic birefringence value can be calculated from the dielectric constant distribution.

[0064] In the following description, unless otherwise specified, adhesives include not only adhesives in a narrow sense (adhesives having a shear storage modulus of 1 MPa to 500 MPa at 23°C after energy beam irradiation or heat treatment), but also pressure-sensitive adhesives having a shear storage modulus of less than 1 MPa at 23°C.

[0065] [1. Manufactured phase difference film]

[0066] The phase difference film manufactured by the manufacturing method of one embodiment of the present invention satisfies the following formula (1), the following formula (2) and the following formula (3). The phase difference film can be combined with a linear polarizer to obtain a circular polarizer that can suppress coloring caused by reflection of external light in both the front direction and the oblique direction of the display surface.

[0067]

[0068] (in,

[0069] Re T (450) represents the in-plane phase difference of the above phase difference film at a wavelength of 450 nm,

[0070] Re T (550) represents the in-plane phase difference of the above phase difference film at a wavelength of 550 nm,

[0071] Re T (650) represents the in-plane phase difference of the above phase difference film at a wavelength of 650 nm,

[0072] NZ T represents the NZ coefficient of the above-mentioned retardation film).

[0073] The above formula (1) will be described in detail. The in-plane retardation Re of the retardation film at a wavelength of 550 nm T (550) is usually 100 nm or more, preferably 115 nm or more, particularly preferably 125 nm or more, and is usually 180 nm or less, preferably 160 nm or less, particularly preferably 150 nm or less. T In the case of (550), the retardation film can function as a λ / 4 wave plate. Therefore, by combining the retardation film with a linear polarizer, a circular polarizing plate capable of suppressing reflection of external light can be obtained.

[0074] The in-plane phase difference Re that satisfies equation (1) T (550) can be obtained by appropriately adjusting the in-plane phase difference of each layer, such as the resin layer (P) and the resin layer (N) included in the phase difference film, and the direction of the slow axis of each layer.

[0075] The above formula (2) will be described in detail. The in-plane retardation Re of the retardation film at wavelengths of 450 nm, 550 nm, and 650 nm T (450), Re T (550) and Re T (650)SatisfyRe T (450)<Re T (550)<Re T (650). The in-plane phase difference of the phase difference film satisfying the formula (2) generally shows inverse wavelength dispersion. Specifically, the phase difference film generally has a larger in-plane phase difference as the measured wavelength is longer. Therefore, the phase difference film can function as a broadband λ / 4 wave plate in a wide wavelength range, and the broadband λ / 4 wave plate can uniformly convert the polarization state of light passing through the phase difference film. Therefore, by combining the phase difference film with a linear polarizer, a circular polarizer that can suppress coloring caused by reflection of external light can be obtained.

[0076] The in-plane phase difference Re that satisfies equation (2) T (450), Re T (550) and Re T (650) can be obtained by appropriately adjusting the in-plane phase difference of each layer, such as the resin layer (P) and the resin layer (N) included in the phase difference film, and the direction of the slow axis of each layer.

[0077] The above formula (3) will be described in detail. NZ coefficient NZ of retardation film T It is usually greater than 0.0, preferably greater than 0.2, particularly preferably greater than 0.3, and is usually less than 1.0, preferably less than 0.8, particularly preferably less than 0.7. T In the case of, the phase difference film has birefringence that is appropriately adjusted in both the in-plane direction and the thickness direction. Therefore, the circular polarizing plate obtained by combining the phase difference film with the linear polarizer can suppress coloration caused by reflection of external light in both the front direction and the oblique direction of the display surface.

[0078] Unless otherwise specified, the NZ coefficient NZ of the retardation film T The in-plane retardation Re of the retardation film at a wavelength of 550 nm can be used. T (550) and thickness direction phase difference Rth T (550) By "NZ T ={Rth T (550) / Re T (550)}+0.5”. The NZ coefficient NZ that satisfies formula (3) is TFor example, it can be obtained by appropriately adjusting the NZ coefficient of each layer such as the resin layer (P) and the resin layer (N) included in the retardation film.

[0079] In the manufacturing method of this embodiment, a retardation film satisfying the above-mentioned formulas (1) to (3) is manufactured as a retardation film having a combination of a resin layer (P) and a resin layer (N), wherein the above-mentioned resin layer (P) contains a thermoplastic resin P and the above-mentioned resin layer (N) contains a thermoplastic resin N.

[0080] Here, the thermoplastic resin P has a positive intrinsic birefringence value, and the thermoplastic resin N has a negative intrinsic birefringence value. When the thermoplastic resin P and the thermoplastic resin N are used in combination to perform the production method described below, a retardation film satisfying the above formulas (1) to (3) can be easily produced.

[0081] The thermoplastic resin P having a positive intrinsic birefringence value generally includes a polymer having a positive intrinsic birefringence value. Examples of the polymer include: polyolefins such as polyethylene and polypropylene; polyesters such as polyethylene terephthalate and polybutylene terephthalate; polyarylene sulfides such as polyphenylene sulfide; polyvinyl alcohol; polycarbonate; polyarylate; cellulose ester; polyether sulfone; polysulfone; polyallyl sulfone; polyvinyl chloride; alicyclic structure-containing polymers; rod-shaped liquid crystal polymers, etc. These polymers may be used alone or in combination of two or more in any ratio. Among them, alicyclic structure-containing polymers, cellulose esters and polycarbonates are preferred, and alicyclic structure-containing polymers are particularly preferred.

[0082] The polymer containing alicyclic structure is a polymer containing alicyclic structure in a repeating unit such as a cycloolefin polymer and its hydrogenated product, and is generally an amorphous polymer. As the polymer containing alicyclic structure, any one of a polymer containing alicyclic structure in the main chain and a polymer containing alicyclic structure in the side chain can be used. As the alicyclic structure, for example, a cycloalkane structure and a cycloolefin structure can be cited. From the viewpoint of thermal stability, a cycloalkane structure is preferred. The number of carbon atoms contained in an alicyclic structure is preferably 4 or more, more preferably 5 or more, particularly preferably 6 or more, preferably 30 or less, more preferably 20 or less, and particularly preferably 15 or less.

[0083] In the alicyclic structure-containing polymer, the ratio of repeating units containing alicyclic structures is preferably 50 wt % or more, more preferably 70 wt % or more, and particularly preferably 90 wt % or more. When the ratio of repeating units containing alicyclic structures is within the above range, a retardation film having excellent heat resistance can be obtained.

[0084] Examples of polymers containing an alicyclic structure include: (1) norbornene-based polymers, (2) monocyclic cyclic olefin polymers, (3) cyclic conjugated diene polymers, (4) vinyl alicyclic hydrocarbon polymers, and hydrogenated products thereof. Among these, cyclic olefin polymers and norbornene-based polymers are preferred, and norbornene-based polymers are particularly preferred. Examples of norbornene-based polymers include: ring-opening polymers of monomers containing a norbornene structure, ring-opening copolymers of monomers containing a norbornene structure and other monomers capable of being ring-opened copolymerized therewith, and hydrogenated products thereof; addition polymers of monomers containing a norbornene structure, addition copolymers of monomers containing a norbornene structure and other monomers capable of being copolymerized therewith, and the like. Among these, hydrogenated ring-opening polymers of monomers containing a norbornene structure are particularly preferred from the viewpoint of transparency. The above-mentioned polymers containing an alicyclic structure can be selected from polymers disclosed in, for example, Japanese Patent Application Laid-Open No. 2002-321302.

[0085] Examples of cellulose esters include lower fatty acid esters of cellulose (e.g., cellulose acetate, cellulose acetate butyrate, and cellulose acetate propionate). Lower fatty acids refer to fatty acids having 6 or less carbon atoms per molecule. Cellulose acetate esters may include cellulose triacetate (TAC) and cellulose diacetate (DAC).

[0086] The total acyl substitution degree of cellulose ester is preferably 2.20 or more and 2.70 or less, more preferably 2.40 or more and 2.60 or less. Here, the total acyl group can be measured according to ASTM D817-91. In addition, the weight average degree of polymerization of cellulose ester is preferably 350 or more and 800 or less, more preferably 370 or more and 600 or less.

[0087] Polycarbonate generally has a repeating unit containing a carbonate bond (-OC(=O)-O-). Examples of polycarbonate include polymers having a structural unit derived from a dihydroxy compound and a carbonate structure (a structure represented by -O-(C=O)-O-). Examples of the dihydroxy compound include bisphenol A. The structural unit derived from the dihydroxy compound contained in the polycarbonate may be one type or two or more types.

[0088] The weight average molecular weight (Mw) of the polymer contained in the thermoplastic resin P is preferably more than 10000, more preferably more than 15000, particularly preferably more than 20000, preferably less than 100000, more preferably less than 80000, particularly preferably less than 50000. When the weight average molecular weight is in this range, the mechanical strength and molding processability of the resin layer (P) are highly balanced. The above-mentioned weight average molecular weight is the weight average molecular weight converted by polyisoprene or polystyrene measured by gel permeation chromatography (GPC) using cyclohexane as a solvent. However, when the sample is insoluble in cyclohexane, toluene can be used as a solvent for GPC.

[0089] The ratio of the polymer in the thermoplastic resin P is preferably 50 to 100 wt %, more preferably 70 to 100 wt %, and particularly preferably 90 to 100 wt %. When the ratio of the polymer is within the above range, the resin layer (P) can obtain sufficient heat resistance and transparency.

[0090] The thermoplastic resin P may further contain any component in combination with the above polymer. As the optional component, for example, stabilizers such as antioxidants, heat stabilizers, light stabilizers, weather stabilizers, ultraviolet absorbers, near infrared absorbers, and plasticizers may be cited. These components may be used alone or in combination of two or more in any ratio.

[0091] The thermoplastic resin N having a negative intrinsic birefringence value generally includes a polymer having a negative intrinsic birefringence value. Examples of the polymer include: an aromatic vinyl compound-based polymer including a homopolymer of an aromatic vinyl compound monomer and / or a copolymer of an aromatic vinyl compound monomer and an arbitrary monomer; a polyacrylonitrile polymer; a polymethyl methacrylate polymer; or a multi-component copolymer thereof. In addition, examples of arbitrary monomers copolymerizable with the aromatic vinyl compound monomer include acrylonitrile, maleic anhydride, methyl methacrylate, and butadiene. In addition, these polymers may be used alone or in combination of two or more in an arbitrary ratio.

[0092] Examples of aromatic vinyl compound monomers include styrene, styrene derivatives, vinylnaphthalene, and vinylnaphthalene derivatives. Examples of styrene derivatives and vinylnaphthalene derivatives include compounds in which the aromatic ring of styrene or vinylnaphthalene is substituted with a substituent, and compounds in which the α-position or β-position of styrene or vinylnaphthalene is substituted with a substituent.

[0093] Among polymers having negative intrinsic birefringence values, one or more polymers selected from styrene polymers, polymers of styrene derivatives, vinylnaphthalene polymers (preferably poly(2-vinylnaphthalene)) and polymers of vinylnaphthalene derivatives are preferred, vinylnaphthalene polymers are more preferred, and poly(2-vinylnaphthalene) is particularly preferred.

[0094] The proportion of the polymer in the thermoplastic resin N is preferably 50 to 100 wt %, more preferably 70 to 100 wt %, particularly preferably 90 to 100 wt %. When the proportion of the polymer is within the above range, the resin layer (N) can express suitable optical properties.

[0095] The thermoplastic resin N may further contain an arbitrary component in combination with the above-mentioned polymer. Examples of the arbitrary component include the same arbitrary components that may be contained in the thermoplastic resin P. The arbitrary component may be used alone or in combination of two or more at any ratio.

[0096] As the thermoplastic resin N and the thermoplastic resin P, resins having arbitrary glass transition temperatures can be used.

[0097] In the fourth step described later, from the viewpoint of smoothly stretching 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 40°C or less, more preferably 30°C or less, further preferably 25°C or less, further preferably less than 10°C, particularly preferably less than 5°C, and the lower limit is usually 0°C or more.

[0098] The resin layer (N) possessed by the phase difference film has a slow axis (N). In addition, the resin layer (P) possessed by the phase difference film has a slow axis (P) that is substantially perpendicular to the above-mentioned slow axis (N) of the resin layer (N). The slow axis (P) and the slow axis (N) are "substantially perpendicular" to each other, indicating that the angle formed by the slow axis (N) and the slow axis (P) is in a specific range close to 90°. Specifically, the angle formed by the slow axis (P) and the slow axis (N) is usually within the range of 90°±5°, usually 85° or more, preferably 87° or more, more preferably 88° or more, particularly preferably 89° or more, usually 95° or less, preferably 93° or less, more preferably 92° or less, and particularly preferably 91° or less. In the manufacturing method described later, a phase difference film satisfying the above-mentioned formulas (1) to (3) can be obtained, as a film having a multilayer structure of a resin layer (P) and a resin layer (N), wherein the above-mentioned resin layer (P) and the resin layer (N) have a slow axis having the above-mentioned relationship.

[0099] In particular, in the long strip phase difference film, it is preferred 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 close to a specific range of 45° with the width direction of the phase difference film. Specifically, the above angle is preferably 40° or more, more preferably 42° or more, further preferably 43° or more, particularly preferably 44° or more, preferably 50° or less, more preferably 48° or less, further preferably 47° or less, and particularly preferably 46° or less. Furthermore, in this case, it is preferred that the other of the slow axis (P) and the slow axis (N) forms an angle close to a specific range of 135° with the width direction of the phase difference film. Specifically, the above angle is preferably 130° or more, more preferably 132° or more, further preferably 133° or more, particularly preferably 134° or more, preferably 140° or less, more preferably 138° or less, further preferably 137° or less, and particularly preferably 136° or less. Conventional long strip linear polarizers have an absorption axis parallel or perpendicular to the width direction of the linear polarizer. The long phase difference film having the resin layer (P) and the resin layer (N) having a slow axis in the direction forming the above-mentioned angle with the width direction can be simply bonded to the above-mentioned conventional linear polarizer in such a manner that the width direction of the phase difference film is parallel to the width direction of the linear polarizer to obtain a circular polarizer. Therefore, since the phase difference film and the linear polarizer can be bonded in a roll-to-roll manner, the circular polarizer can be manufactured particularly simply.

[0100] NZ coefficient NZ of resin layer (P) P and the NZ coefficient NZ of the resin layer (N) N It is preferable to appropriately set the NZ coefficient NZ of the retardation film so that T falls within the range of formula (3). NZ coefficient NZ of the resin layer (P) P It was created by "NZ P =(nx P -nz P ) / (nx P -ny P )”, so the value represented by “NZ P =(Rth P / Re P )+0.5”.nx P Indicates the refractive index of the direction providing the maximum refractive index in the in-plane direction of the resin layer (P). P Indicates the in-plane direction of the resin layer (P) and provides nx P The refractive index in the direction orthogonal to the direction of nz. P Re represents the refractive index in the thickness direction of the resin layer (P). P Represents the in-plane phase difference of the resin layer (P), so “Re P =(nx P-ny P )×d P " P Indicates the thickness direction phase difference of the resin layer (P), so “Rth P ={(nx P +ny P ) / 2-nz P}×d P " to indicate. P Indicates the thickness of the resin layer (P). In addition, the NZ coefficient NZ of the resin layer (N) N It was created by "NZ N =(nx N -nz N ) / (nx N -ny N )”, so the value represented by “NZ N =(Rth N / Re N )+0.5”.nx N Indicates the refractive index of the direction providing the maximum refractive index in the in-plane direction of the resin layer (N). N Indicates the in-plane direction of the resin layer (N) and provides nx N The refractive index in the direction orthogonal to the direction of nz. N Re represents the refractive index in the thickness direction of the resin layer (N). N Represents the in-plane phase difference of the resin layer (N), so “Re N =(nx N -ny N )×d N " N Indicates the thickness direction phase difference of the resin layer (N), so “Rth N ={(nx N +ny N ) / 2-nz N}×d N " to indicate. N Indicates the thickness of the resin layer (N).

[0101] NZ coefficient NZ of resin layer (P) P It is preferably 1.00 or more. Therefore, the refractive index ny of the resin layer (P) P and nz P Preferred to meet ny P ≥nz P In addition, the NZ coefficient NZ of the resin layer (N) N It is preferably less than 0.0. Therefore, the refractive index nx of the resin layer (N) N and nz N Preferred to meet nzN >nx N According to the combination of the resin layer (P) and the resin layer (N), the NZ coefficient NZ of the entire phase difference film can be T It can be easily adjusted to within the range of formula (3).

[0102] More specifically, the NZ coefficient NZ of the resin layer (P) P It is preferably 1.00 or more, more preferably 1.05 or more, and preferably 1.30 or less, more preferably 1.20 or less. P The refractive index of the resin layer (P) is nx P ,ny P and nz P Can have nx P >ny P ≥nz P Therefore, the resin layer (P) can function as a positive A plate or a negative B plate.

[0103] In addition, the NZ coefficient NZ of the resin layer (N) N It is preferably not less than -2.0, more preferably not less than -1.5, preferably less than 0.0, more preferably not more than -0.2, and particularly preferably not more than -0.4. The refractive index nx of the resin layer (N) having an NZ coefficient of less than 0.0 is N ny N and nz N Can have nz N >nx N >ny N Therefore, the resin layer (N) can have a refractive index nx in three directions. N ny N and nz N Different layers (ie, layers having biaxiality). In addition, the resin layer (N) can function as a positive B plate.

[0104] NZ coefficient NZ of resin layer (P) P NZ coefficient NZ of the resin layer (N) N and NZ P +NZ N It is preferred to fall within a specific range. Specifically, and "NZ P +NZ N " is preferably -0.3 or more, more preferably 0.0 or more, particularly preferably 0.10 or more, preferably 0.8 or less, more preferably 0.75 or less, particularly preferably 0.65 or less. P +NZ NIn the case of the above range, it is possible to realize a retardation film that can obtain a circular polarizing plate that can effectively suppress coloration caused by reflection of external light in both the front direction and the oblique direction of the display surface.

[0105] The retardation film preferably satisfies the following formula (4).

[0106]

[0107] (in,

[0108] Re N (450) represents the in-plane phase difference of the resin layer (N) at a wavelength of 450 nm,

[0109] Re N (550) represents the in-plane phase difference of the resin layer (N) at a wavelength of 550 nm,

[0110] Re P (450) represents the in-plane phase difference of the resin layer (P) at a wavelength of 450 nm,

[0111] Re P (550) represents the in-plane phase difference of the above-mentioned resin layer (P) at a wavelength of 550 nm).

[0112] In formula (4), “Re N (450) / Re N (550)” represents the wavelength dispersion of the resin layer (N). In addition, in formula (4), “Re P (450) / Re P (550)" represents the wavelength dispersion of the resin layer (P). Therefore, formula (4) indicates that there is a difference in the wavelength dispersion of the in-plane phase difference between the resin layer (N) and the resin layer (P) possessed by the phase difference film. More specifically, it means 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). In detail, the parameter "{Re N (450) / Re N (550)}-{Re P (450) / Re P (550)}" is preferably greater than 0.08, more preferably greater than 0.09, and particularly preferably greater than 0.10. In addition, the upper limit is not particularly limited, but is preferably less than 2.0, more preferably less than 1.5, and particularly preferably less than 1.2. The phase difference film having a resin layer (P) and a resin layer (N) having a difference in the wavelength dispersion of the in-plane phase difference can easily obtain an inverse wavelength dispersion characteristic in a stacked state.

[0113] Furthermore, the retardation film preferably satisfies the following formula (5).

[0114]

[0115] (in,

[0116] Re N (550) represents the in-plane phase difference of the resin layer (N) at a wavelength of 550 nm,

[0117] Re P (550) represents the in-plane phase difference of the above-mentioned resin layer (P) at a wavelength of 550 nm).

[0118] By making the retardation film satisfy the formula (5), it is possible to easily obtain a retardation film that functions in a wide frequency band.

[0119] {Re P (550)-Re N The value of (550)} is preferably 120 nm or more, more preferably 125 nm or more, particularly preferably 130 nm or more, preferably 160 nm or less, more preferably 155 nm or less, particularly preferably 150 nm or less. Thus, the retardation film can be made into a λ / 4 wave plate that functions in a wide frequency band.

[0120] The phase difference film may have any layer other than the resin layer (P) and the resin layer (N) as required. As an example of an arbitrary layer, an arbitrary layer having optical isotropy may be cited. Such an arbitrary layer having optical isotropy generally has an in-plane phase difference of 10 nm or less at a wavelength of 550 nm, and may include, for example: a protective film layer for protecting the resin layer (P) and the resin layer (N); an adhesive layer for bonding the resin layer (P) and the resin layer (N), etc. In addition, as another example of an arbitrary layer, an arbitrary layer having optical anisotropy may be cited. The optical properties of such an arbitrary layer having optical anisotropy are not limited within the range that the phase difference film as a whole satisfies formula (1) to formula (3). When a specific example is cited, the optical properties of the arbitrary layer may be set so that the arbitrary layer having optical anisotropy and a combination of one or both of the resin layer (P) and the resin layer (N) can function as a λ / 4 wave plate or a λ / 2 wave plate.

[0121] The ultraviolet / visible light transmittance of the retardation film is preferably 80% or more, more preferably 85% or more, and particularly preferably 90% or more. The ultraviolet / visible light transmittance can be measured using an ultraviolet / visible spectrophotometer within a wavelength range of 400 nm to 700 nm.

[0122] The haze of the retardation film is preferably 5% or less, more preferably 3% or less, particularly preferably 1% or less, and ideally 0%. The haze can be measured using a haze meter in accordance with JIS K7361-1997.

[0123] The retardation film may be a single film or a long film.

[0124] The thickness of the retardation film is not particularly limited. From the viewpoint of thinning, the specific thickness of the retardation film is preferably 5 μm or more, more preferably 10 μm or more, particularly preferably 15 μm or more, preferably 200 μm or less, more preferably 150 μm or less, particularly preferably 100 μm or less.

[0125] The thickness of each layer such as the resin layer (P) and the resin layer (N) of the phase difference film is not particularly limited. The thickness of the resin layer (P) and the resin layer (N) is preferably 0.5 μm or more, more preferably 1 μm or more, preferably 150 μm or less, and more preferably 100 μm or less.

[0126] [2. Overview of the method for producing a phase difference film]

[0127] In a manufacturing method according to one embodiment of the present invention, the retardation film is manufactured by a manufacturing method including the following steps:

[0128] In a first step, a first film having a resin layer (N1) is prepared, wherein the resin layer (N1) is formed of a thermoplastic resin N having a negative intrinsic birefringence value;

[0129] A second step of stretching the first film at least once to obtain a second film having a resin layer (N2), wherein the resin layer (N2) is a layer obtained by stretching the resin layer (N1);

[0130] A third step is to laminate a resin layer (P1) on the second film to obtain a third film, wherein the resin layer (P1) is formed of a thermoplastic resin P having a positive intrinsic birefringence value;

[0131] In the fourth step, the third film is stretched at least once to obtain the phase difference film having a resin layer (N) and a resin layer (P), wherein the resin layer (N) is a layer obtained by stretching the resin layer (N2) and has a slow axis (N), and the resin layer (P) is a layer obtained by stretching the resin layer (P1) and has a slow axis (P) which forms an angle of 90°±5° with the slow axis (N).

[0132] In the method for manufacturing a phase difference film of the present embodiment, a third film having a multilayer structure is manufactured and stretched. Therefore, compared with the case where each layer of the phase difference film is manufactured separately and laminated, the method for manufacturing a phase difference film of the present embodiment requires less labor and time. In addition, it is not necessary to adjust the angle when laminating each layer.

[0133] In addition, in the method for producing a retardation film of the present embodiment, the first film is stretched in the second step. Thus, compared with the case where the multilayer film is stretched without the second step to obtain the retardation film, the stretching conditions such as the temperature of the thermoplastic resin forming each layer of the retardation film and the stretching temperature can be set with less restrictions.

[0134] [3. First step: Preparation of the first film]

[0135] In the first step, a first film having a resin layer (N1) is prepared, wherein the resin layer (N1) is formed of a thermoplastic resin N having a negative intrinsic birefringence value. The thermoplastic resin N is as described in the section of the retardation film.

[0136] The resin layer (N1) possessed by the first film preferably does not have a large optical anisotropy. Therefore, the phase difference of the resin layer (N1) is preferably small. When a specific range is cited, the in-plane phase difference of the resin layer (N1) at 550nm is preferably 0nm to 20nm, more preferably 0nm to 10nm, and particularly preferably 0nm to 5nm. In addition, the absolute value of the thickness direction phase difference of the resin layer (N1) at 550nm is preferably 0nm to 20nm, more preferably 0nm to 10nm, and particularly preferably 0nm to 5nm.

[0137] The first film may be a single film, preferably a long film. By preparing the first film as a long film, a part or all of the steps in manufacturing the retardation film can be performed on a production line, so that the retardation film can be manufactured simply and efficiently.

[0138] The manufacturing method of the first film is not limited. The first film can be manufactured by, for example, a melt molding method or a solution casting method. The melt molding method is particularly preferred. Among the melt molding methods, extrusion molding, inflation molding or compression molding are preferred, and extrusion molding is particularly preferred. According to these methods, the first film having a resin layer (N1) can be made into a long film.

[0139] [4. Second step: production of second film]

[0140] In the second step, 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 layer obtained by stretching the resin layer (N1).

[0141] The stretching of the first film can be a single stretching or two or more stretchings. In the case where the stretching of the first film is two or more stretchings, it is preferred that the stretching directions of each of the two or more stretchings are the same. The stretching ratios of each of the two or more stretchings may be the same as or different from each other. In one embodiment, it is preferred that the stretching of the first film is a single stretching.

[0142] The stretching ratio of the first film in the second step is preferably 1.05 times or more in the stretching direction, more preferably 1.1 times or more, particularly preferably 1.12 times or more, preferably 2.0 times or less, more preferably 1.5 times or less, particularly preferably 1.3 times or less. Here, in the case where the first film is stretched twice or more in the second step, the stretching ratio of the first film in the second step is the ratio obtained by multiplying the stretching ratios of each time.

[0143] When the first film is long, the stretching direction in the second step is preferably an oblique direction with respect to the width direction of the first film. Thereby, a long phase difference film having a slow axis in an oblique direction can be obtained.

[0144] The stretching direction in the second step is preferably close to the width direction of the first film of the long strip at an angle of preferably 135° in a specific range. Specifically, the angle is preferably 130° or more, more preferably 132° or more, further preferably 133° or more, particularly preferably 134° or more, preferably 140° or less, more preferably 138° or less, further preferably 137° or less, and particularly preferably 136° or less. Thus, a phase difference film having a slow axis with an angle of a specific range of 45° with the width direction of the long phase difference film can be manufactured.

[0145] The stretching temperature in the second step can be selected from an appropriate range according to the glass transition temperature TgN of the thermoplastic resin N forming the resin layer (N1). For example, the stretching temperature in the second step is preferably TgN-5°C or higher, more preferably TgN-3°C or higher, particularly preferably TgN-1°C or higher, preferably TgN+20°C or lower, more preferably TgN+15°C or lower, particularly preferably TgN+12°C or lower. Thus, the breakage of the resin layer (N2) obtained by stretching the resin layer (N1) and the increase in haze can be effectively suppressed.

[0146] By stretching the first film, the resin layer (N1) possessed by the first film is stretched, so that the resin layer (N2) exhibits a slow axis in a direction substantially perpendicular to the stretching direction. Specifically, the angle formed by the stretching direction in the second step and the slow axis of the resin layer (N2) is usually within the range of 90°±5°, usually 85° or more, preferably 87° or more, more preferably 88° or more, particularly preferably 89° or more, usually 95° or less, preferably 93° or less, more preferably 92° or less, and particularly preferably 91° or less.

[0147] The in-plane retardation of the second film at a wavelength of 550 nm is preferably 20 nm or more, more preferably 25 nm or more, particularly preferably 27 nm or more, and is preferably 150 nm or less, more preferably 130 nm or less, particularly preferably 110 nm or less.

[0148] The in-plane phase difference of the resin layer (N2) possessed by the second film at a wavelength of 550 nm is preferably greater than 20 nm, more preferably greater than 25 nm, particularly preferably greater than 27 nm, and is preferably less than 150 nm, more preferably less than 130 nm, particularly preferably less than 110 nm.

[0149] In addition, the thickness direction phase difference of the resin layer (N2) at a wavelength of 550nm is preferably less than -5nm, more preferably less than -10nm, particularly preferably less than -13nm, preferably greater than -90nm, more preferably greater than -80nm, particularly preferably greater than -70nm.

[0150] The phase difference between the second film and the resin layer (N2) can be adjusted by adjusting the stretching ratio in the second step.

[0151] By stretching the first film in the second step so that the phase difference of the resin layer (N2) falls within the above range, the resin layer (N) can be made particularly easy to show biaxiality after stretching in the fourth step described later. Specifically, the resin layer (N) can be made particularly easy to show the desired in-plane phase difference and negative thickness direction phase difference. Therefore, it is particularly easy to make a phase difference film having a resin layer (N) and a resin layer (P) into a film that satisfies formulas (1) to (3).

[0152] [5. Third step: production of third film]

[0153] In the third step, a resin layer (P1) is laminated on the second film to obtain a third film, wherein the resin layer (P1) is formed of a thermoplastic resin P having a positive intrinsic birefringence value. The resin layer (P1) can be laminated on the second film by any method. The resin layer (P1) can be formed by any method, for example, a melt molding method, a solution casting method, and a coating method in which a liquid composition containing a material of a layer other than the layer is coated on a certain layer.

[0154] In particular, a method of applying a liquid composition containing the thermoplastic resin P on the resin layer (N2) of the second film and, if necessary, drying the applied liquid composition is preferred. This method will be described below.

[0155] A liquid composition containing a thermoplastic resin P is applied to the resin layer (N2) possessed by the above-mentioned second film. The liquid composition may contain a thermoplastic resin P and a solvent. The liquid composition containing a thermoplastic resin and a solvent is also referred to as a resin solution. As a solvent, a solvent capable of dissolving or dispersing the thermoplastic resin P is preferred, and a solvent capable of dissolving the thermoplastic resin P is particularly preferred. In addition, the solvent may be used alone or in combination of two or more in any ratio. The concentration of the thermoplastic resin P in the liquid composition is preferably adjusted so that the viscosity of the liquid composition falls within a range suitable for coating, and may be, for example, 1% by weight to 50% by weight.

[0156] There is no limitation on the coating method of the liquid composition. Examples of the coating method include curtain coating, extrusion coating, roll coating, spin coating, dip coating, rod coating, spray coating, slide coating, print coating, gravure coating, die coating, and slit coating.

[0157] By applying the liquid composition containing the thermoplastic resin P, a layer of the liquid composition is formed on the resin layer (N2). Therefore, by drying the layer of the liquid composition as needed to remove the solvent, the resin layer (P1) is laminated on the resin layer (N2) to obtain a third film. The drying method is not limited, and drying methods such as natural drying, heating drying, and reduced pressure drying can be used.

[0158] The resin layer (P1) possessed by the third film preferably does not have a large optical anisotropy. Therefore, the phase difference of the resin layer (P1) is preferably small. When a specific range is cited, the in-plane phase difference of the resin layer (P1) at 550nm is preferably 0nm to 20nm, more preferably 0nm to 10nm, and particularly preferably 0nm to 5nm. In addition, the absolute value of the thickness direction phase difference of the resin layer (P1) at 550nm is preferably 0nm to 20nm, more preferably 0nm to 10nm, and particularly preferably 0nm to 5nm.

[0159] By making the phase difference of the resin layer (P1) fall within the above range, the resin layer (P) can be made particularly easy to show the desired in-plane phase difference in the fourth step described later. Therefore, it is particularly easy to make a phase difference film having the resin layer (N) and the resin layer (P) into a film that satisfies formulas (1) to (3).

[0160] [6. Fourth step: stretching of the third film]

[0161] In the fourth step, the third film is stretched at least once to obtain the phase difference film having a resin layer (N) and a resin layer (P), wherein the resin layer (N) is a layer obtained by stretching the resin layer (N2) and has a slow axis (N), and the resin layer (P) is a layer obtained by stretching the resin layer (P1) and has a slow axis (P) forming an angle of 90°±5° with the slow axis (N).

[0162] The stretching of the third film can be a single stretching or two or more stretchings. In the case where the stretching of the third film is two or more stretchings, it is preferred that the stretching directions of each stretching in the two or more stretchings are the same. The stretching ratios of each stretching in the two or more stretchings may be the same as or different from each other. In one embodiment, it is preferred that the stretching of the third film is a single stretching.

[0163] The stretching ratio E4 of the third film in the fourth step is preferably 1.1 times or more in the stretching direction, more preferably 1.2 times or more, particularly preferably 1.3 times or more, preferably 3.0 times or less, more preferably 2.5 times or less, and particularly preferably 2.0 times or less. Here, when the third film is stretched twice or more in the fourth step, the stretching ratio of the third film in the fourth step is the ratio obtained by multiplying the stretching ratios of each time.

[0164] The stretching ratio E4 of the third film in the fourth step is preferably greater than the stretching ratio E2 of the first film in the second step in the stretching direction. The ratio (E4 / E2) of the stretching ratio E4 to the stretching ratio E2 is preferably greater than 1, more preferably 1.05 or more, particularly preferably 1.1 or more, preferably 3.0 or less, more preferably 2.5 or less, and particularly preferably 2.0 or less. Thus, while the resin layer (N) possessed by the phase difference film effectively exhibits biaxiality, the resin layer (P) exhibits the desired in-plane phase difference, and a phase difference film satisfying formulas (1) to (3) can be manufactured particularly easily.

[0165] The stretching of the first film in the second step is stretching in one direction, and the stretching of the third film in the fourth step preferably includes stretching in a direction substantially perpendicular to the stretching direction of the first film in the second step, specifically in a direction within the range of 90°±5°. The stretching direction of the third film is preferably within the range of 90°±5° relative to the stretching direction of the first film in the second step, preferably 85° or more, more preferably 87° or more, further preferably 88° or more, particularly preferably 89° or more, preferably 95° or less, more preferably 93° or less, further preferably 92° or less, and particularly preferably 91° or less.

[0166] In the fourth step, by stretching the third film in a direction substantially perpendicular to the stretching direction in the second step, specifically in a range of 90°±5°, a retardation film satisfying Formulae (1) to (3) can be produced particularly easily.

[0167] The resin layer (P1) possessed by the third film is formed by a thermoplastic resin P having a positive intrinsic birefringence value, so when the third film is stretched in a certain stretching direction in the fourth step, the resin layer (P) as the layer after the resin layer (P1) is stretched will show a slow axis (P) in a direction roughly parallel to the stretching direction. On the other hand, the resin layer (N2) possessed by the third film is formed by a thermoplastic resin N having a negative intrinsic birefringence value, so in the resin layer (N) as the layer after the resin layer (N2) is stretched, the refractive index in the direction roughly perpendicular to its stretching direction will increase. In the case where the stretching of the third film in the fourth step includes stretching in a direction roughly perpendicular to the stretching direction of the above-mentioned first film in the second step, the slow axis direction of the resin layer (N2) manifested in the second step is roughly parallel to the stretching direction in the fourth step, so it is particularly easy to adjust the slow axis (N) of the resin layer (N) possessed by the phase difference film to a direction roughly perpendicular to the stretching direction in the fourth step. As a result, the direction of the slow axis (N) of the resin layer (N) and the direction of the slow axis (P) of the resin layer (P) can be made substantially perpendicular to each other particularly easily.

[0168] Therefore, the angle formed by the stretching direction of the third film in the fourth step relative to the slow axis of the resin layer (N2) possessed by the second film is preferably in the range of 0°±5°, preferably above -5°, more preferably above -3°, further preferably above -2°, particularly preferably above -1°, preferably below 5°, more preferably below 3°, further preferably below 2°, and particularly preferably below 1°.

[0169] The stretching temperature in the fourth step can be appropriately set according to the glass transition temperature TgP of the thermoplastic resin P and the glass transition temperature TgN of the thermoplastic resin N. From the viewpoint of suppressing film breakage during stretching and smoothly stretching, it is preferably Tg(high)-5°C or higher, more preferably Tg(high)-3°C or higher, particularly preferably Tg(high)-1°C or higher, preferably Tg(high)+20°C or lower, more preferably Tg(high)+15°C or lower, further preferably Tg(high)+12°C or lower, further preferably Tg(high)+10°C or lower, and particularly preferably Tg(high)+9°C or lower. Tg(high) represents the higher temperature of the glass transition temperature TgP and the glass transition temperature TgN. When the glass transition temperature TgP and the glass transition temperature TgN are the same temperature, the same temperature is represented.

[0170] [7. Optional steps that may be included in the phase difference film]

[0171] The method for manufacturing a phase difference film may include any process in addition to the first to fourth processes described above. For example, in the case of using a long first film to obtain a long phase difference film, the method for manufacturing a phase difference film may also include a trimming process of cutting the obtained phase difference film into a desired shape. According to the trimming process, a single phase difference film having a desired shape can be obtained. In addition, the method for manufacturing a phase difference film may also include, for example, a process of providing a protective layer on the phase difference film.

[0172] [8. Overview of the method for producing a circular polarizing plate]

[0173] A method for manufacturing a circular polarizer according to one embodiment of the present invention is a method for manufacturing a circular polarizer including a linear polarizer and a phase difference film, comprising: a fifth step of manufacturing the phase difference film using the phase difference film manufacturing method; and a sixth step of stacking the phase difference film and the linear polarizer.

[0174] [9. Fifth step]

[0175] The method for producing a circular polarizing plate according to the present embodiment includes a fifth step. The fifth step is a step of producing a retardation film by using the method for producing a retardation film described above.

[0176] The fifth step is specifically a step of manufacturing a retardation film by a manufacturing method including the above-mentioned first step, second step, third step and fourth step. The retardation film obtained by the fifth step is the same as the retardation film described in the above-mentioned item [1. manufactured retardation film].

[0177] [10. Sixth step]

[0178] In the sixth step, the phase difference film and the linear polarizer manufactured in the fifth step are laminated.

[0179] Any linear polarizer can be used as the linear polarizer. Examples of linear polarizers include: a film obtained by adsorbing iodine or a dichroic dye on a polyvinyl alcohol film and then uniaxially stretching it in a boric acid bath; and a film obtained by adsorbing iodine or a dichroic dye on a polyvinyl alcohol film and then stretching it to modify part of the polyvinyl alcohol units in the molecular chain into polyvinylidene units. Among these, a linear polarizer containing polyvinyl alcohol is preferred.

[0180] When natural light is incident on the linear polarizer, only polarized light in one direction is transmitted. The polarization degree of the linear polarizer is not particularly limited, but is preferably 98% or more, and more preferably 99% or more.

[0181] Furthermore, the thickness of the linear polarizer is preferably 5 μm to 80 μm.

[0182] The lamination in the sixth step is preferably performed so that the circularly polarizing plate includes the resin layer (N), the resin layer (P), and the linear polarizer in this order.

[0183] In addition, the lamination of the sixth step is preferably carried out in a manner such that the angle formed by the width direction of the linear polarizer and the slow axis (P) of the resin layer (P) is close to a specific range of 45°. Specifically, the above angle is preferably 40° or more, more preferably 42° or more, further preferably 43° or more, particularly preferably 44° or more, preferably 50° or less, more preferably 48° or less, further preferably 47° or less, and particularly preferably 46° or less.

[0184] Furthermore, in this case, it is preferred to carry out the process in a manner such that the angle formed by the width direction of the linear polarizer and the slow axis (N) of the resin layer (N) is close to a specific range of 135°. Specifically, the above angle is preferably 130° or more, more preferably 132° or more, further preferably 133° or more, particularly preferably 134° or more, preferably 140° or less, more preferably 138° or less, further preferably 137° or less, and particularly preferably 136° or less.

[0185] An appropriate adhesive can be used for lamination of the phase difference film and the linear polarizer.

[0186] The method for manufacturing a circular polarizer may include any process in addition to the fifth and sixth processes described above. As an example of any process, a process of laminating a functional layer on a phase difference film, a linear polarizer and / or a circular polarizer may be cited. As examples of functional layers, polarizer protective film layers; hard coating layers such as impact-resistant polymethacrylate resin layers; mat layers for improving the sliding properties of the film; anti-reflection properties; antifouling layers; antistatic layers, etc. may be cited.

[0187] [11. Application examples of circular polarizers]

[0188] The circular polarizer can be provided in an image display device. The circular polarizer is particularly preferably provided in an organic EL image display device. The organic EL image display device comprises a circular polarizer and an organic electroluminescent element (hereinafter, sometimes appropriately referred to as an "organic EL element"). The organic EL image display device usually comprises a linear polarizer, a phase difference film and an organic EL element in this order.

[0189] The organic EL element has a transparent electrode layer, a light-emitting layer and an electrode layer in sequence, and the light-emitting layer can be made to emit light by applying a voltage from the transparent electrode layer and the electrode layer. As examples of materials constituting the organic light-emitting layer, poly(p-phenylenevinylene)-based, polyfluorene-based and polyvinylcarbazole-based materials can be cited. In addition, the light-emitting layer can have a laminate of multiple layers with different luminous colors, or a mixed layer in which different pigments are doped in a layer of a certain pigment. Furthermore, the organic EL element can have functional layers such as a hole injection layer, a hole transport layer, an electron injection layer, an electron transport layer, an equipotential surface forming layer, and a charge generating layer.

[0190] The above-mentioned image display device can suppress the reflection of external light on the display surface. Specifically, only a part of the linearly polarized light of the light incident from the outside of the device passes through the linear polarizer, and then passes through the phase difference film, thereby becoming circularly polarized light. The circularly polarized light is reflected by the structural element of the reflected light in the image display device (the reflective electrode in the organic EL element, etc.), and passes through the phase difference film again, thereby becoming a linearly polarized light having a vibration direction orthogonal to the vibration direction of the incident linearly polarized light, and 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. The function of reflection suppression is thereby achieved.

[0191] Since the phase difference film has the above optical properties, the organic EL image display device can not only play the function of suppressing reflection in the front direction of the display surface, but also in the oblique direction. Therefore, the reflection of external light and coloration can be effectively suppressed in both the front direction and the oblique direction of the display surface.

[0192] The degree of coloration can be measured by observing the chromaticity of a certain display surface with reflection and the color difference ΔE of the chromaticity of the black display surface without reflection. * The above chromaticity can be obtained by measuring the spectrum of light reflected from the display surface, multiplying the spectrum by the spectral sensitivity (isochromatic function) corresponding to the human eye, and obtaining the tristimulus values ​​X, Y, and Z to calculate the chromaticity (a * ,b * ,L * ). In addition, the color difference ΔE * ab can be calculated based on the chromaticity (a0 * ,b0 * ,L0 * ) and the chromaticity when illuminated by external light (a1 * ,b1 * ,L1 * ), is obtained by the following formula (X).

[0193] [Mathematical formula 1]

[0194]

[0195] In addition, the coloring of the display surface caused by reflected light may generally differ depending on the azimuth of the viewing direction. Therefore, when observing from an oblique direction of the display surface, the measured chromaticity may differ depending on the azimuth of the viewing direction, so the color difference ΔE * Therefore, in order to evaluate the degree of coloration when the display surface is observed from an oblique direction as described above, it is preferable to calculate the color difference ΔE obtained by observing from multiple azimuth directions. * Specifically, at the azimuth angle φ (reference Figure 1 ) is within the range of 0° to less than 360°, the color difference ΔE is calculated every 5° along the azimuth direction * Determination of ab by measuring the color difference ΔE * The smaller the average color difference is, the smaller the coloration of the display surface is when the display surface is viewed from an oblique direction.

[0196] Example

[0197] The present invention will be described in detail below with reference to the following examples, but the present invention is not limited to the following examples and can be arbitrarily modified without departing from the scope of the claims of the present invention and the scope of their equivalents.

[0198] In the following description, "%" and "parts" indicating amounts are based on weight unless otherwise specified. In addition, unless otherwise specified, the operations described below are performed at room temperature (20°C ± 15°C) and normal pressure (1 atm).

[0199] [Evaluation method]

[0200] (Glass transition temperature)

[0201] The glass transition temperature Tg of the resin was measured using a differential scanning calorimeter ("DSC6220SII" manufactured by Seiko Nanotech Corporation) in accordance with JIS K6911 at a temperature increase rate of 10°C / min.

[0202] (Thickness of film or layer)

[0203] The thickness of the film or layer was measured using the reflection spectroscopic film thickness measurement system "F20" produced by FILMETRICS.

[0204] (Method for measuring phase difference and NZ coefficient)

[0205] The in-plane phase difference Re of the evaluation object at wavelengths of 450nm, 550nm and 650nm was measured using a phase difference meter (AxoScan, manufactured by Axon Corporation); and the thickness direction phase difference Rth at a wavelength of 550nm. When calculating the physical properties of each layer of the laminate that cannot be separated, the sample is measured from multiple directions, and the fitting analysis is performed using the attached multilayer analysis software to calculate it. In addition, the NZ coefficient is calculated using the in-plane phase difference Re and the thickness direction phase difference Rth at a wavelength of 550nm.

[0206] (Method for measuring orientation angle)

[0207] The directions of the slow axis (P) of the resin layer (P) and the slow axis (N) of the resin layer (N) contained in the retardation film were measured using a retardation meter (AxoScan, Inc.). The angle between the slow axis and the width direction of the retardation film was calculated as the orientation angle θ (0°≤θ<180°).

[0208] (Haze)

[0209] The haze of the retardation film is measured using a haze meter in accordance with JIS K7361-1997.

[0210] (Calculation method of color difference based on simulation)

[0211] The circular polarizing plates produced in the respective Examples and Comparative Examples were modeled using "LCD Master" manufactured by Shintech as simulation software, and the following calculations were performed.

[0212] In the simulation model, a structure in which a circular polarizer is provided on the above-mentioned reflecting surface of a mirror having a planar reflecting surface is set. In addition, as a circular polarizer, a resin layer (N) of a phase difference film, a resin layer (P) of a phase difference film, and a circular polarizer of a linear polarizer are set in order from the above-mentioned reflecting surface side. As the phase difference film, the phase difference film obtained in each embodiment and comparative example is set. In addition, as a linear polarizer, a polarizer with a polarization degree of 99.99% commonly used is set. In addition, as a mirror, an ideal mirror capable of specularly reflecting the incident light with a reflectivity of 100% is set.

[0213] Figure 1 It is a perspective view schematically showing the state of the evaluation model set when calculating the color space coordinates in the simulation of the embodiment and the comparative example.

[0214] like Figure 1 As shown in FIG. 1 , the color space coordinates observed on the reflective surface 10 of the mirror provided with a circular polarizer when irradiated with a D65 light source (not shown) are calculated. In addition, the color space coordinates when not irradiated with the light source are set to a0 *=0,b0 * =0,L0 * = 0. Then, the color difference ΔE is calculated based on (i) the color space coordinates when illuminated by the light source and (ii) the color space coordinates when not illuminated by the light source. * ab.

[0215] The above-mentioned chromatic aberration ΔE is calculated in the observation direction 20 with a polar angle ρ of 0° relative to the reflection surface 10. * Calculation of ab to find the color difference ΔE in the front direction * The polar angle ρ represents the angle formed with the normal direction 11 of the reflecting surface 10 .

[0216] In addition, the above-mentioned chromatic aberration ΔE is calculated in the observation direction 20 at a polar angle ρ of 60° with respect to the reflection surface 10. * The observation direction 20 is moved every 5° in the azimuth direction within the range of azimuth angle φ being greater than 0° and less than 360°, and the calculation is performed multiple times when the polar angle ρ = 60°. The azimuth angle φ represents the angle between the direction parallel to the reflection surface 10 and a certain reference direction 12 parallel to the reflection surface 10. Then, the color difference ΔE calculated in multiple observation directions 20 is calculated. * The average of ab gives the color difference ΔE in the tilt direction with a polar angle ρ = 60°. * ab.

[0217] (Evaluation method of circular polarizing plate based on visual observation in the front direction)

[0218] An image display device (Apple Watch (registered trademark) manufactured by Apple Inc.) having an organic EL image display device was prepared. The image display device was disassembled, and the polarizing plate attached to the surface of the organic EL image display device was peeled off to expose the reflective electrode. The surface of the reflective electrode and the surface on the opposite side of the linear polarizer of the circular polarizing plate obtained in each embodiment and comparative example were attached via a pressure-sensitive adhesive (CS9621 manufactured by Nitto Denko Corporation). Thus, a sample having a reflective electrode, a pressure-sensitive adhesive, and a circular polarizing plate in this order was obtained.

[0219] The circular polarizer of the sample was irradiated with sunlight on a sunny day and the circular polarizer on the reflective electrode was visually observed in this state. The observation was performed in the front direction with the polar angle of the circular polarizer being 0° and the azimuth angle being 0°. According to the results of the observation, it was judged as "bad" when color was visually confirmed, and "good" when no color was visually confirmed.

[0220] (Evaluation method of circular polarizing plate by visual inspection in an oblique direction)

[0221] On a sunny day, irradiate the circular polarizer of the sample prepared in the above (evaluation method of circular polarizer based on visual observation in the front direction) with sunlight and visually observe the circular polarizer on the reflective electrode in this state. The observation is carried out in the oblique direction of the circular polarizer with a polar angle of 60° and an azimuth angle of 0° to 360°. According to the results of the observation, the reflective brightness and coloring are comprehensively judged, and the embodiments and comparative examples are ranked. Then, the ranked embodiments and comparative examples are given scores corresponding to their rankings (the first place is 7 points, the second place is 6 points... the last place is 1 point).

[0222] The above observations were performed by multiple people, and the total score of the scores given to each Example and Comparative Example was calculated. The Examples and Comparative Examples were ranked according to the above total score, and evaluated in order from the highest group to A, B, C, D, and E within the range of the total score.

[0223] [Example 1]

[0224] (1-1. First step: preparation of first film)

[0225] After adding 500 mL of toluene as a solvent and 0.29 mmol of n-butyl lithium as a polymerization catalyst to a pressure-resistant reactor that was dried and replaced with nitrogen, 35 g of 2-vinylnaphthalene was added and reacted at 25° C. for 1 hour. As a result, a reactant containing poly(2-vinylnaphthalene) as a homopolymer of 2-vinylnaphthalene was obtained. After adding triphenyl phosphate as a plasticizer to the reactant, the reactant was injected into a large amount of 2-propanol to precipitate the resin containing poly(2-vinylnaphthalene) and separate and take out. The obtained resin containing poly(2-vinylnaphthalene) was dried at 200° C. for 24 hours in a vacuum dryer to obtain thermoplastic resin N. The thermoplastic resin N contains about 5% by weight of a plasticizer. The weight average molecular weight of poly(2-vinylnaphthalene) measured by GPC is 250,000. In addition, the glass transition temperature of thermoplastic resin N measured by a differential scanning calorimeter is 127° C. The thermoplastic resin N has a negative intrinsic birefringence value.

[0226] The obtained thermoplastic resin N is supplied to an extruder, and extruded into a sheet from a T-die onto a casting drum via a polymer tube and a polymer filter. The extruded thermoplastic resin N is cooled to obtain a long resin film with a thickness of 50 μm as a 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 and recovered. The optical properties of the resin layer (N1) possessed by the first film are evaluated using the above method.

[0227] (1-2. Second step: stretching of first film)

[0228] The first film is pulled out from the roller, and the pulled out first film is supplied to a tentering stretching machine. Using the tentering stretching machine, the first film is stretched in a stretching direction at an angle of 135° to the width direction of the first film, the stretching temperature is 128°C, and the stretching ratio in the stretching direction is 1.15 times, to obtain a second film having a resin layer (N2), wherein the resin layer (N2) is a layer after the resin layer (N1) is stretched. The second film only has a resin layer (N2). After the obtained second film is cooled at room temperature, it is wound into a roll and recovered. The optical properties of the resin layer (N2) possessed by the second film are evaluated by the above method.

[0229] (1-3. Third step: Lamination of resin layer (P1))

[0230] (Preparation of Resin Solution for Forming Resin Layer (P1))

[0231] A resin containing a norbornene polymer (ZEONOR manufactured by Zeon Corporation; glass transition temperature 126° C., hereinafter also referred to as a norbornene resin) as a thermoplastic resin P and cyclohexane as a solvent were mixed to obtain a resin solution having a norbornene resin concentration of 15% by weight as a liquid composition. The thermoplastic resin P has a positive intrinsic birefringence value.

[0232] The second film is pulled out from the roller, and the above-mentioned resin solution is applied on the surface of the pulled-out second film, that is, the surface of the resin layer (N2), to form a layer of the resin solution. Thereafter, the layer of the resin solution is dried at 120°C for two minutes to form a resin layer (P1) with a thickness of 40 μm on the second film. Through the above operation, a third film having a resin layer (N2) and a resin layer (P1) laminated on the resin layer (N2) is obtained. The optical properties of the resin layer (N2) and the resin layer (P1) of the third film are evaluated by the above method.

[0233] (1-4. Fourth step: stretching of the third film)

[0234] The obtained third film is supplied to a tentering stretching machine. Using the tentering stretching machine, the third film is stretched in a stretching direction at an angle of 45° to the width direction of the third film, that is, in a stretching direction at an angle of 90° relative to the stretching direction of the first film, and the stretching temperature is 128°C, and the stretching ratio in the stretching direction is 1.50 times to obtain a long strip of phase difference film. The phase difference film has a resin layer (N) and a resin layer (P), the resin layer (N) is a layer after the resin layer (N2) is stretched, and the resin layer (P) is a layer after the resin layer (P1) is stretched. The above method is used to evaluate the optical properties of the phase difference film and each layer of the phase difference film.

[0235] (1-5. Production of Circular Polarizing Plate)

[0236] A long strip of polyvinyl alcohol resin film dyed with iodine is prepared. The film is stretched in a longitudinal direction at an angle of 90° relative to the width direction of the film to obtain a linear polarizer as a long strip of polarizing film. The linear polarizer has an absorption axis in the longitudinal direction of the linear polarizer and a transmission axis in the width direction of the linear polarizer.

[0237] The linear polarizer and the phase difference film are bonded together via an optically isotropic pressure-sensitive adhesive ("CS9621" manufactured by Nitto Denko Corporation) to obtain a long circular polarizing plate. The bonding is performed so that the width direction of the linear polarizer is parallel to the width direction of the phase difference film. The obtained circular polarizing plate has a linear polarizer, a resin layer (P) and a resin layer (N) in this order.

[0238] The obtained circularly polarizing plate was evaluated by the above method.

[0239] [Examples 2 to 4]

[0240] In the step (1-2), the stretching ratio of the first film was changed as shown in Table 1.

[0241] Except for the above matters, it carried out similarly to Example 1, and produced and evaluated the retardation film and circular polarizing plate.

[0242] [Comparative Example 1]

[0243] A retardation film was produced by the same method as in Example 1 of JP-A-2022-052074. Specifically, a retardation film was obtained by the following operation.

[0244] (C1-1. Preparation of film of thermoplastic resin P)

[0245] A resin containing a norbornene polymer (hereinafter referred to as a norbornene resin) (manufactured by Japan Zeon Co., Ltd.; glass transition temperature 126°C) as a thermoplastic resin P having a positive intrinsic birefringence value was dried at 100°C for 5 hours. The dried thermoplastic resin P was supplied to an extruder and extruded into a sheet from a T-die onto a casting drum via a polymer tube and a polymer filter. The extruded thermoplastic resin P was cooled to obtain a long unstretched film having a thickness of 60 μm formed of the thermoplastic resin P. The obtained unstretched film was wound into a roll and recovered.

[0246] (C1-2. Lamination of Thermoplastic Resin N Layers)

[0247] After adding 500 mL of toluene as a solvent and 0.29 mmol of n-butyl lithium as a polymerization catalyst to a pressure-resistant reactor that had been dried and replaced with nitrogen, 35 g of 2-vinylnaphthalene was added and reacted at 25° C. for 1 hour. As a result, a reaction product containing poly(2-vinylnaphthalene) as a homopolymer of 2-vinylnaphthalene was obtained. The reaction product was injected into a large amount of 2-propanol to precipitate the poly(2-vinylnaphthalene), which was separated and taken out. The obtained poly(2-vinylnaphthalene) was dried at 200° C. for 24 hours in a vacuum dryer to obtain a thermoplastic resin N. The weight average molecular weight of the poly(2-vinylnaphthalene) measured by GPC was 250,000. In addition, the glass transition temperature of the poly(2-vinylnaphthalene) measured by a differential scanning calorimeter was 142° C. The thermoplastic resin N has a negative intrinsic birefringence value.

[0248] The produced poly(2-vinylnaphthalene) as the thermoplastic resin N and 1,3-dioxolane as the solvent were mixed to obtain a resin solution containing the thermoplastic resin N. The concentration of the poly(2-vinylnaphthalene) in the resin solution was 15% by weight.

[0249] The unstretched film (resin layer CP1) is pulled out from a roll, and the resin solution is applied to the surface of the unstretched film to form a layer of the resin solution. Thereafter, the layer of the resin solution is rapidly dried at 120°C to form a layer of poly(2-vinylnaphthalene) with a thickness of 12 μm on the unstretched film. By the above operation, a laminated film having an unstretched film (resin layer CP1) formed of a thermoplastic resin P and a layer of poly(2-vinylnaphthalene) as a thermoplastic resin N (resin layer CN1) is obtained. The obtained laminated film is wound into a roll and recovered.

[0250] (C1-3. Stretching of laminated film)

[0251] The laminated film is pulled out from the roll and continuously supplied to a tenter stretching machine. Then, the laminated film is stretched in a stretching direction at an angle of 45° to the longitudinal direction of the laminated film by the tenter stretching machine, the stretching temperature is 140°C, and the stretching ratio in the stretching direction is 1.5 times, to obtain a long phase difference film. The phase difference film has a resin layer (P) obtained by stretching a layer of norbornene-based resin (resin layer CP1) and a resin layer (N) obtained by stretching a layer of poly(2-vinylnaphthalene) (resin layer CN1).

[0252] (C1-4. Production of Circular Polarizing Plate)

[0253] The obtained retardation film was used to produce a circular polarizing plate in the same manner as step (1-5) of Example 1. The obtained circular polarizing plate had a linear polarizer, a resin layer (P), and a resin layer (N) in this order. The obtained retardation film and circular polarizing plate were evaluated by the above methods.

[0254] [Comparative Example 2]

[0255] A retardation film was produced by the same method as in Example 1 of JP-A-2007-199616. Specifically, a retardation film was obtained by the following operation.

[0256] (C2-1. Preparation of film of thermoplastic resin P)

[0257] As the thermoplastic resin P having a positive intrinsic birefringence value, a film (70 μm in thickness) of a resin containing a norbornene-based polymer (“ARTON FLZU” manufactured by JSR Corporation; glass transition temperature: 128° C.) was prepared.

[0258] (C2-2. Lamination of Thermoplastic Resin N Layers)

[0259] In the same manner as in Example 1 of JP-A-2007-199616, a copolymer of styrene and maleic anhydride (glass transition temperature: 148°C) was prepared as a thermoplastic resin N having a negative intrinsic birefringence value.

[0260] The obtained copolymer was mixed with methyl ethyl ketone as a solvent to obtain a resin solution having a concentration of 33% by weight of a styrene-maleic anhydride copolymer as a liquid composition.

[0261] The resin solution was applied to the film of the thermoplastic resin P containing the norbornene-based polymer to form a layer of the resin solution. Thereafter, the layer of the resin solution was dried at 80° C. for 10 minutes to form a layer of the thermoplastic resin N having a thickness of 40 μm on the film formed of the thermoplastic resin P. Through the above operation, a laminated film having a film formed of the thermoplastic resin P (resin layer CP1) and a layer of the thermoplastic resin N (resin layer CN1) was obtained.

[0262] (C2-3. Stretching of laminated film)

[0263] Next, the laminated film was uniaxially stretched at a stretching temperature of 110° C. and a stretching ratio of 2.0 to obtain a phase difference film having a resin layer (P) obtained by stretching a layer of a norbornene-based resin (resin layer CP1) and a resin layer (N) obtained by stretching a layer of a styrene-maleic anhydride copolymer (resin layer CN1).

[0264] (C2-4. Production of Circular Polarizing Plate)

[0265] The obtained retardation film was used to produce a circular polarizing plate in the same manner as step (1-5) of Example 1. The obtained circular polarizing plate had a linear polarizer, a resin layer (P), and a resin layer (N) in this order. The obtained retardation plate and circular polarizing plate were evaluated by the above method.

[0266] [Comparative Example 3]

[0267] (C3-1. Preparation of film of thermoplastic resin P)

[0268] A granular norbornene resin (manufactured by Japan Zeon Co., Ltd.; glass transition temperature 126°C) was dried at 100°C for 5 hours to obtain a thermoplastic resin P. The thermoplastic resin P was supplied to an extruder and extruded from a T-die onto a casting drum via a polymer tube and a polymer filter into a sheet. The extruded thermoplastic resin P was cooled to obtain a long unstretched film with a thickness of 110 μm. The obtained unstretched film was wound into a roll and recovered.

[0269] (C3-2. Lamination of Thermoplastic Resin N Layers)

[0270] After adding 500 mL of toluene as a solvent and 0.29 mmol of n-butyl lithium as a polymerization catalyst to a pressure-resistant reactor that had been dried and replaced with nitrogen, 35 g of 2-vinylnaphthalene was added and reacted at 25° C. for 1 hour. As a result, a reaction product containing poly(2-vinylnaphthalene) as a homopolymer of 2-vinylnaphthalene was obtained. The reaction product was injected into a large amount of 2-propanol to precipitate the poly(2-vinylnaphthalene), which was separated and taken out. The obtained poly(2-vinylnaphthalene) was dried at 200° C. for 24 hours in a vacuum dryer to obtain a thermoplastic resin N. The weight average molecular weight of the poly(2-vinylnaphthalene) measured by GPC was 250,000. In addition, the glass transition temperature of the poly(2-vinylnaphthalene) measured by a differential scanning calorimeter was 142° C. The thermoplastic resin N had a negative intrinsic birefringence value.

[0271] The produced poly(2-vinylnaphthalene) as the thermoplastic resin N and 1,3-dioxolane as the solvent were mixed to obtain a resin solution containing the thermoplastic resin N. The concentration of the poly(2-vinylnaphthalene) in the resin solution was 15% by weight.

[0272] The unstretched film (resin layer CP1) is pulled out from a roll, and the resin solution is applied to the unstretched film to form a layer of the resin solution. Thereafter, the layer of the resin solution is dried to form a layer of poly(2-vinylnaphthalene) with a thickness of 13 μm on the unstretched film. Through the above operation, a laminated film having an unstretched film (resin layer CP1) formed of a norbornene-based resin as a thermoplastic resin P and a layer of poly(2-vinylnaphthalene) as a thermoplastic resin N (resin layer CN1) is obtained. The obtained laminated film is wound into a roll and recovered.

[0273] (C3-3. Stretching of Laminated Film; First Stretching Step)

[0274] The laminated film was pulled out from the roll and supplied to a tenter stretching machine. The tenter stretching machine was used to stretch the laminated film in a stretching direction at an angle of 135° to the width direction of the laminated film, with the stretching temperature being 140°C and the stretching ratio in the stretching direction being 1.15 times. After the stretched laminated film was cooled to room temperature, it was wound into a roll and recovered.

[0275] (C3-4. Stretching of Laminated Film; Second Stretching Step)

[0276] The laminate film stretched in the first stretching step is pulled out from the roller, and the pulled laminate film is supplied to a tenter stretching machine. The tenter stretching machine is used to stretch the laminate film in a stretching direction at an angle of 45° to the width direction of the laminate film, the stretching temperature is 128°C, and the stretching ratio in the stretching direction is 1.50 times, to obtain a long phase difference film. The phase difference film has a resin layer (P) obtained by stretching a layer of norbornene-based resin (resin layer CP1) and a resin layer (N) obtained by stretching a layer of poly(2-vinylnaphthalene) (resin layer CN1).

[0277] (C3-5. Production of circular polarizing plate)

[0278] The obtained retardation film was used to produce a circular polarizing plate in the same manner as step (1-5) of Example 1. The obtained circular polarizing plate had a linear polarizer, a resin layer (P), and a resin layer (N) in this order. The obtained retardation film and circular polarizing plate were evaluated by the above methods.

[0279] In the above-mentioned Examples and Comparative Examples, the visual evaluation in the front direction was judged in two grades of "good" and "bad", whereas the visual evaluation in the oblique direction was judged in five grades from "A" to "E". The reason for the different judgment criteria is as follows.

[0280] That is, the brightness of the reflected light in the front direction is sufficiently lower than that in the oblique direction. Therefore, if strong coloration is not generated, the observer cannot recognize the coloration. Therefore, a two-level judgment based on whether the coloration can be visually recognized is adopted.

[0281] On the other hand, the brightness of reflected light in an oblique direction is high. Therefore, even if the coloring is weak, it is easy for the observer to see the coloring. Therefore, a detailed evaluation of the quality of the five-level is adopted.

[0282] [result]

[0283] The production conditions in Examples and Comparative Examples are shown in Tables 1 and 2, and the results are shown in Table 3.

[0284] In the following table, the abbreviations have the following meanings.

[0285] "VN": a resin comprising poly(2-vinylnaphthalene);

[0286] “COP1”: norbornene-based resin manufactured by Zeon Corporation (glass transition temperature: 126°C);

[0287] “COP2”: JSR’s norbornene-based resin “ARTON FLZU” (glass transition temperature 128°C);

[0288] “ST-MA”: styrene-maleic anhydride copolymer;

[0289] “P1 / N2”: a laminate having a resin layer (P1) and a resin layer (N2);

[0290] “CN1 / CP1”: a laminate having a resin layer (CN1) and a resin layer (CP1);

[0291] “P / N”: a phase difference film having a resin layer (P) and a resin layer (N);

[0292] “Wavelength dispersion difference”: {Re N (450) / Re N (550)}-{Re P (450) / Re P (550)};

[0293] "θ": the angle between the slow axis of the film or layer and the width direction of the film or layer;

[0294] "First" in the fourth step of item 2: first stretching step;

[0295] "Second" in the fourth step of item 2: second stretching step;

[0296] [Table 1]

[0297]

[0298] [Table 2]

[0299]

[0300] [Table 3]

[0301]

[0302] From the above results, it can be seen that according to the method of the embodiment, a phase difference film that satisfies formulas (1) to (3) and has a small haze can be obtained. In addition, it can be seen that the circular polarizer having a phase difference film that satisfies formulas (1) to (3) obtained by the method of the embodiment can suppress the coloring caused by the reflection of external light in both the front direction and the oblique direction of the display surface of the image display device having the circular polarizer.

[0303] Description of Reference Numerals

[0304] 10: Reflective surface;

[0305] 11: normal direction;

[0306] 12: reference direction;

[0307] 20: Observation direction;

[0308] φ: azimuth;

[0309] ρ: polar angle.

Claims

1. A method for producing a phase difference film, wherein the phase difference film satisfies the following formula (1), the following formula (2) and the following formula (3), The manufacturing method comprises: In a first step, a first film having a resin layer (N1) is prepared, wherein the resin layer (N1) is formed of a thermoplastic resin N having a negative intrinsic birefringence value; A second step of stretching the first film at least once to obtain a second film having a resin layer (N2), wherein the resin layer (N2) is a layer obtained by stretching the resin layer (N1); A third step of laminating a resin layer (P1) on the second film to obtain a third film, wherein the resin layer (P1) is formed of a thermoplastic resin P having a positive intrinsic birefringence value; In a fourth step, the third film is stretched at least once to obtain the phase difference film having a resin layer (N) and a resin layer (P), wherein the resin layer (N) is a layer obtained by stretching the resin layer (N2) and has a slow axis (N), and the resin layer (P) is a layer obtained by stretching the resin layer (P1) and has a slow axis (P) that forms an angle of 90°±5° with the slow axis (N). in, Re T (450) represents the in-plane phase difference of the phase difference film at a wavelength of 450 nm, Re T (550) represents the in-plane phase difference of the phase difference film at a wavelength of 550 nm, Re T (650) represents the in-plane phase difference of the phase difference film at a wavelength of 650 nm, NZ T It represents the NZ coefficient of the retardation film.

2. The method for producing a phase difference film according to claim 1, wherein: The in-plane phase difference of the resin layer (N2) included in the second film is 20 nm or more.

3. The method for producing a phase difference film according to claim 1, wherein: The stretching of the first film in the second step is stretching in one direction, and the stretching of the third film in the fourth step includes stretching in a direction within a range of 90°±5° with respect to the stretching direction of the first film in the second step.

4. The method for producing a phase difference film according to claim 1, wherein: The phase difference film satisfies the following formula (4): in, 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, Re P (550) represents the in-plane phase difference of the resin layer (P) at a wavelength of 550 nm.

5. The method for producing a phase difference film according to claim 1, wherein: The phase difference film satisfies the following formula (5): in, Re N (550) represents the in-plane phase difference of the resin layer (N) at a wavelength of 550 nm, Re P (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 polarizing plate, wherein the circular polarizing plate comprises a linear polarizer and a phase difference film, The method for manufacturing the circular polarizer comprises: A fifth step, manufacturing the retardation film by using the method for manufacturing a retardation film according to any one of claims 1 to 5; as well as In a sixth step, the phase difference film and the linear polarizer are laminated.

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