Phase difference mode and method for manufacturing the same, and circular polarizing plate

Abstract

The present invention relates to a method for producing a phase difference film having specific optical properties, the method comprising: a first step of preparing a multilayer film having a resin layer (A) and a resin layer (B), wherein the resin layer (A) is formed of a thermoplastic resin A having a positive intrinsic birefringence value, and the resin layer (B) is formed of a thermoplastic resin B having a negative intrinsic birefringence value; and a second step of stretching the multilayer film two or more times at different stretching temperatures to obtain a phase difference film, wherein the absolute value of the difference between the glass transition temperature TgA of the thermoplastic resin A and the glass transition temperature TgB of the thermoplastic resin B |TgA-TgB| is 5°C or more.

Description

Technical Field

[0001] The present invention relates to a method for producing a retardation film, a retardation film produced by the production method, and a circular polarizing plate having the retardation film. Background Art

[0002] In image display devices such as organic electroluminescent image display devices (hereinafter, appropriately referred to as "organic EL image display devices") and liquid crystal image display devices, a phase difference film is sometimes provided. In such a phase difference film, there is a structure having a multilayer structure including two or more layers. As a method for manufacturing a phase difference film having such a multilayer structure, a co-stretching method is sometimes used (refer to Patent Documents 1 to 5).

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Publication No. 2012-73646;

[0006] Patent document 2: Japanese Patent Application Publication No. 2009-192844;

[0007] Patent Document 3: Japanese Patent Application Publication No. 2009-192845;

[0008] Patent Document 4: Japanese Patent Application Publication No. 2009-223163;

[0009] Patent document 5: Japanese Patent Application Publication No. 2002-40258. Summary of the invention

[0010] Problem that the invention aims to solve

[0011] In an image display device, a circular polarizer is provided to reduce the reflection of external light on the display surface. As such a circular polarizer, a film combining a linear polarizer and a λ / 4 wave plate is generally used. However, most existing λ / 4 wave plates can actually only function as λ / 4 wave plates within a specific narrow wavelength range. Therefore, although many existing circular polarizers can reduce the reflection of external light within a specific narrow wavelength range, it is difficult to reduce the reflection of external light beyond this range. When external light is reflected on the display surface, the color of the reflected light may color the display surface.

[0012] In order to suppress the coloration of the above-mentioned display surface, a circular polarizer capable of reducing the reflection of external light in a wide wavelength range is required. Such a circular polarizer can be manufactured, for example, using a broadband λ / 4 wave plate capable of performing the function of a λ / 4 wave plate in a wide wavelength range. As such a broadband λ / 4 wave plate, a phase difference film having a combination of multiple layers is known, and for example, a phase difference film having a combination of a λ / 2 wave plate and a λ / 4 wave plate can be cited. The circular polarizer having a phase difference film capable of functioning as a broadband λ / 4 wave plate can suppress the coloration 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.

[0013] However, in an inclined direction that is neither parallel nor perpendicular to the display surface, the phase difference value deviates from the ideal value, or the optical axis of each layer deviates, and thus it may not be possible to reduce the reflection of external light in a wide wavelength range. Therefore, in order to realize a circular polarizing plate that can suppress 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 of greater than 0.0 and less than 1.0.

[0014] Usually, the slow axis direction, in-plane phase difference, and NZ coefficient of the layers included in the phase difference film that meets the above conditions are partly or completely different. Therefore, it has always been common to manufacture the above-mentioned phase difference film by bonding these layers after manufacturing each layer separately. However, since this existing manufacturing method manufactures each layer separately, the number of processes tends to increase, and the labor, time and cost also tend to increase. In addition, when bonding each layer, it is necessary to accurately match the bonding angle, so it is necessary to adjust the labor and time of the angle, which leads to an increase in labor and time.

[0015] Under such circumstances, it is necessary to develop a method for simply manufacturing a retardation film that can obtain a circularly polarizing plate capable of suppressing coloration caused by reflection of external light in both the front direction and the oblique direction of the display surface.

[0016] The present invention is proposed in view of the above-mentioned problems, and its purpose is to provide a method for simply manufacturing a phase difference film, wherein the phase difference film can obtain a circular polarizer that can suppress the coloring caused by the reflection of external light in both the front direction and the oblique direction of the display surface. It can also provide a phase difference film manufactured by the above-mentioned manufacturing method, and a circular polarizer having the phase difference film.

[0017] Solutions for solving problems

[0018] The present inventors have conducted in-depth research to solve the above problems. As a result, the present inventors have found that a phase difference film that solves the above problems can be obtained by the following manufacturing method, thereby completing the present invention, the manufacturing method comprising a step of stretching a multilayer film having a resin layer (A) and a resin layer (B) at different stretching temperatures for two or more times, wherein the resin layer (A) and the resin layer (B) contain a thermoplastic resin A and a thermoplastic resin B having a glass transition temperature TgA and a glass transition temperature TgB with a difference of 5°C or more.

[0019] That is, the present invention includes the following contents.

[0020] [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),

[0021] The manufacturing method comprises:

[0022] In a first step, a multilayer film having a resin layer (A) and a resin layer (B) is prepared, wherein the resin layer (A) is formed of a thermoplastic resin A having a positive intrinsic birefringence value, and the resin layer (B) is formed of a thermoplastic resin B having a negative intrinsic birefringence value; and

[0023] In the second step, the multilayer film is stretched twice or more to obtain the phase difference film having the resin layer (A) and the resin layer (B), wherein the resin layer (A) has a slow axis, and the resin layer (B) has a slow axis substantially perpendicular to the slow axis of the resin layer (A).

[0024] The second step comprises:

[0025] A first stretching step of stretching the multilayer film at a stretching temperature Ts1; and

[0026] In a second stretching step, the multilayer film is stretched at a stretching temperature Ts2 different from the stretching temperature Ts1.

[0027] The absolute value of the difference between the glass transition temperature TgA of the thermoplastic resin A and the glass transition temperature TgB of the thermoplastic resin B |TgA-TgB| is 5°C or more;

[0028] 100nm≤Re T (550)≤180nm (1)

[0029] Re T (450)<Re T (550)<Re T (650) (2)

[0030] 0.0<NZ T <1.0 (3)

[0031] Among them, Re T (450) represents the in-plane phase difference of the phase difference film at a wavelength of 450 nm.

[0032] Re T (550) represents the in-plane phase difference of the phase difference film at a wavelength of 550 nm,

[0033] Re T (650) represents the in-plane phase difference of the phase difference film at a wavelength of 650 nm,

[0034] NZ T It represents the NZ coefficient of the retardation film.

[0035] [2] The method for producing a retardation film according to [1], wherein an absolute value of a difference between the stretching temperature Ts1 and the stretching temperature Ts2 |Ts1-Ts2| is 5°C or more.

[0036] [3] The method for producing a retardation film according to [1] or [2], wherein the stretching direction in the first stretching step is substantially perpendicular to the stretching direction in the second stretching step.

[0037] [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):

[0038] {Re Q (450) / Re Q (550)}-{Re H (450) / Re H (550)}>0.08(4)

[0039] Among them, Re H (450) represents the in-plane phase difference of the high phase difference layer at a wavelength of 450 nm.

[0040] Re H (550) represents the in-plane phase difference of the high phase difference layer at a wavelength of 550 nm,

[0041] Re Q (450) represents the in-plane phase difference of the low phase difference layer at a wavelength of 450 nm.

[0042] Re Q (550) represents the in-plane phase difference of the low phase difference layer at a wavelength of 550 nm,

[0043] The high retardation layer means a layer having a large in-plane retardation at a wavelength of 550 nm, among the resin layer (A) and the resin layer (B) included in the retardation film.

[0044] The low retardation layer means a layer having a small in-plane retardation at a wavelength of 550 nm, among the resin layer (A) and the resin layer (B) included in the retardation film. ).

[0045] [5] The method for producing a retardation film according to any one of [1] to [4], wherein the resin layer (A) of the retardation film has a larger in-plane retardation than the resin layer (B) of the retardation film at a wavelength of 550 nm,

[0046] The glass transition temperature TgA of the thermoplastic resin A is lower than the glass transition temperature TgB of the thermoplastic resin B.

[0047] [6] The method for producing a retardation film according to any one of [1] to [4], wherein the resin layer (B) of the retardation film has a larger in-plane retardation than the resin layer (A) of the retardation film at a wavelength of 550 nm,

[0048] The glass transition temperature TgB of the thermoplastic resin B is lower than the glass transition temperature TgA of the thermoplastic resin A.

[0049] [7] A retardation film produced by the production method described in any one of [1] to [6].

[0050] [8] A circular polarizing plate comprising a linear polarizer and the phase difference film according to [7].

[0051] Effects of the Invention

[0052] According to the present invention, a manufacturing method can be provided that can simply manufacture a phase difference film, and the phase difference film can obtain a circular polarizer that can suppress the coloring caused by the reflection of external light in both the front direction and the oblique direction of the display surface. It is also possible to provide a phase difference film manufactured by the above-mentioned manufacturing method, and a circular polarizer having the phase difference film. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] 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

[0054] The present invention will be described in detail below by showing embodiments and examples. However, the present invention is not limited to the embodiments and examples described below, and can be implemented with any changes without departing from the scope of the claims of the present invention and the scope of equivalents thereof.

[0055] 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 represents 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, it can also 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 direction of nx in the above-mentioned in-plane direction, nz represents the refractive index in the thickness direction, and 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 Axometrics Co., Ltd.).

[0056] In the following description, unless otherwise specified, the slow axis of a certain layer means the slow axis in the in-plane direction of the layer.

[0057] 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 member having multiple layers means the angle when the layer is observed in the thickness direction.

[0058] 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 of the polar angle 0° and the azimuth angle 0° of the above surface.

[0059] 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°.

[0060] In the following description, unless otherwise specified, the directions of elements being "parallel", "perpendicular" and "orthogonal" mean that they may include an error within a range of, for example, ±5° within a range that does not affect the effects of the present invention.

[0061] In the following description, a "long film" refers to a film having a length of 5 times or more relative to the width, preferably 10 times or more, and specifically refers to a film having a length that can be rolled into a roll for storage or transportation. The upper limit of the length of the long film is not particularly limited, for example, it can be less than 100,000 times relative to the width.

[0062] In the following description, the length direction of the long film is generally parallel to the flow direction of the film in the production line. In addition, the width direction of the long film is generally perpendicular to the thickness direction and perpendicular to the length direction.

[0063] 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.

[0064] In the following description, "a polymer having a positive intrinsic birefringence value" and "a resin having a positive intrinsic birefringence value" respectively mean "a polymer having a refractive index in a stretching direction greater than a refractive index in a direction perpendicular to the stretching direction" and "a resin having a refractive index in a stretching direction greater than a refractive index in a direction perpendicular to the stretching direction". In addition, "a polymer having a negative intrinsic birefringence value" and "a resin having a negative intrinsic birefringence value" respectively mean "a polymer having a refractive index in a stretching direction less than a refractive index in a direction perpendicular to the stretching direction" and "a resin having a refractive index in a stretching direction less than a refractive index in a direction perpendicular to the stretching direction". The intrinsic birefringence value can be calculated based on the dielectric constant distribution.

[0065] In the following description, unless otherwise specified, adhesives include not only adhesives in a narrow sense (adhesives having a shear storage elastic modulus of 1 MPa to 500 MPa at 23°C after energy ray irradiation or heat treatment) but also pressure-sensitive adhesives having a shear storage elastic modulus of less than 1 MPa at 23°C.

[0066] [1. Manufactured phase difference film]

[0067] The retardation 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 retardation film can be combined with a linear polarizer to obtain a circular polarizer that can suppress coloration caused by external light reflection in both the front direction and the oblique direction of the display surface.

[0068] 100nm≤Re T (550)≤180nm (1)

[0069] Re T (450)<Re T (550)<Re T (650) (2)

[0070] 0.0<NZ T <1.0 (3)

[0071] (Among them, Re T (450) represents the in-plane phase difference of the phase difference film at a wavelength of 450 nm.

[0072] Re T(550) represents the in-plane phase difference of the phase difference film at a wavelength of 550 nm,

[0073] Re T (650) represents the in-plane phase difference of the phase difference film at a wavelength of 650 nm,

[0074] NZ T Represents the NZ coefficient of the retardation film. ).

[0075] 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 (550), the phase difference film can function as a λ / 4 wave plate. Therefore, by combining the phase difference film with a linear polarizer, a circular polarizing plate capable of suppressing reflection of external light can be obtained.

[0076] The in-plane phase difference Re that satisfies equation (1) T (550) can be obtained by, for example, appropriately adjusting the in-plane phase difference of each layer such as the resin layer (A) and the resin layer (B) included in the phase difference film and the slow axis direction of each layer.

[0077] 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, generally, the longer the measurement wavelength, the greater the in-plane phase difference of the phase difference film. Therefore, the phase difference film can function as a broadband λ / 4 wave plate, which can uniformly convert the polarization state of light transmitting the phase difference film within a wide wavelength range. Therefore, by combining the phase difference film with a linear polarizer, a circular polarizer capable of suppressing coloration caused by reflection of external light can be obtained.

[0078] The in-plane phase difference Re that satisfies equation (2) T (450), Re T (550) and Re T(650) can be obtained by, for example, appropriately adjusting the in-plane phase difference of each layer such as the resin layer (A) and the resin layer (B) included in the phase difference film and the slow axis direction of each layer.

[0079] The above formula (3) is described in detail. NZ coefficient NZ of retardation film T It is usually greater than 0.0, preferably greater than 0.2, and particularly preferably greater than 0.3, and is usually less than 1.0, preferably less than 0.8, and particularly preferably less than 0.7. When the retardation film has an NZ coefficient NZ within the above range T When the phase difference film is used, the phase difference film has a properly adjusted birefringence 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 the coloring caused by the reflection of external light in both the front direction and the oblique direction of the display surface.

[0080] Unless otherwise specified, the NZ coefficient NZ of the retardation film T The in-plane retardation Re of the retardation film used at a wavelength of 550 nm T (550) and thickness direction phase difference Rth T (550) T = {Rth T (550) / Re T (550)}+0.5”. The NZ coefficient NZ that satisfies formula (3) T For example, it can be obtained by appropriately adjusting the NZ coefficient of each layer such as the resin layer (A) and the resin layer (B) included in the retardation film.

[0081] In the production method of this embodiment, a retardation film satisfying the above formulas (1) to (3) is produced as a retardation film having a resin layer (A) containing a thermoplastic resin A and a resin layer (B) containing a thermoplastic resin B in combination.

[0082] The combination of thermoplastic resin A and thermoplastic resin B is selected so that the sign of the intrinsic birefringence value of thermoplastic resin A is different from the sign of the intrinsic birefringence value of thermoplastic resin B. Specifically, a thermoplastic resin A having a positive intrinsic birefringence value and a thermoplastic resin B having a negative intrinsic birefringence value are used in combination. When such a thermoplastic resin A and a thermoplastic resin B are used in combination to perform the production method described later, a retardation film satisfying the above formulas (1) to (3) can be easily produced.

[0083] The thermoplastic resin A 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, polyacrylate, cellulose ester, polyether sulfone, polysulfone, polyallyl sulfone, polyvinyl chloride, alicyclic structure-containing polymers, rod-shaped liquid crystal polymers, and the like. These polymers may be used alone or in combination of two or more in any proportion. In particular, alicyclic structure-containing polymers, cellulose esters, and polycarbonates are preferred, and alicyclic structure-containing polymers are particularly preferred.

[0084] The polymer containing alicyclic structure is a polymer containing alicyclic structure in the repeating unit, and is usually an amorphous polymer. As the polymer containing alicyclic structure, any one of the polymer containing alicyclic structure in the main chain and the 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 one 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.

[0085] 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.

[0086] 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 hydrogenates thereof. Of 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 ring-opening copolymerization, and hydrogenates thereof; addition polymers of monomers containing a norbornene structure, addition copolymers of monomers containing a norbornene structure and other monomers capable of copolymerization, and the like. Of these, hydrogenates of 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, for example, polymers disclosed in Japanese Patent Application Laid-Open No. 2002-321302.

[0087] 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 are fatty acids having 6 or less carbon atoms per molecule. Cellulose acetate may include triacetyl cellulose (TAC) and diacetyl cellulose (DAC).

[0088] 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.

[0089] 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 dihydroxy compounds include bisphenol A. The structural unit derived from the dihydroxy compound contained in the polycarbonate may be one type or two or more types.

[0090] The weight average molecular weight (Mw) of the polymer included in the thermoplastic resin A is preferably more than 10,000, more preferably more than 15,000, particularly preferably more than 20,000, preferably less than 100,000, more preferably less than 80,000, and particularly preferably less than 50,000. When the weight average molecular weight is within the above range, the mechanical strength and molding processability of the resin layer (A) are highly balanced. The above-mentioned weight average molecular weight is the weight average molecular weight converted from polyisoprene or polystyrene measured by gel permeation chromatography (GPC) using cyclohexane as a solvent. However, when the sample is not dissolved in cyclohexane, toluene can also be used as a solvent for GPC.

[0091] The molecular weight distribution (weight average molecular weight (Mw) / number average molecular weight (Mn)) of the polymer contained in the thermoplastic resin A is preferably 1.2 or more, more preferably 1.5 or more, particularly preferably 1.8 or more, preferably 3.5 or less, more preferably 3.0 or less, particularly preferably 2.7 or less. When the molecular weight distribution is above the lower limit of the above range, the productivity of the polymer can be improved and the manufacturing cost can be suppressed. In addition, when the molecular weight distribution is below the upper limit, since the amount of low molecular weight components becomes small, relaxation during high temperature exposure can be suppressed, and the stability of the resin layer (A) can be improved.

[0092] The ratio of the polymer of the thermoplastic resin A is preferably 50 to 100% by weight, more preferably 70 to 100% by weight, and particularly preferably 90 to 100% by weight. When the ratio of the polymer is within the above range, the resin layer (A) can obtain sufficient heat resistance and transparency.

[0093] The thermoplastic resin A may further include any component in combination with the above polymer. As the optional component, for example, stabilizers such as antioxidants, heat stabilizers, light stabilizers, weathering 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 proportion.

[0094] The thermoplastic resin B having a negative intrinsic birefringence value generally includes a polymer having a negative intrinsic birefringence value. Examples of the polymer include: a homopolymer of styrene or a styrene derivative, and a polystyrene polymer including a copolymer of styrene or a styrene derivative and an arbitrary monomer; a polyacrylonitrile polymer; a polymethyl methacrylate polymer; poly(2-vinylnaphthalene); or a multi-polymer thereof. In addition, examples of arbitrary monomers that can be copolymerized with styrene or a styrene derivative include: acrylonitrile, maleic anhydride, methyl methacrylate, butadiene, etc. In addition, these polymers may be used alone or in combination of two or more in any ratio.

[0095] Among the polymers with negative intrinsic birefringence values, polystyrene polymers are preferred from the viewpoint of high manifestation of phase difference. Among them, copolymers of styrene or styrene derivatives and maleic anhydride are particularly preferred from the viewpoint of high heat resistance. In the copolymer, the amount of maleic anhydride unit is preferably 5 parts by weight or more, more preferably 10 parts by weight or more, particularly preferably 15 parts by weight or more, preferably 30 parts by weight or less, more preferably 28 parts by weight or less, and particularly preferably 26 parts by weight or less, relative to 100 parts by weight of the polystyrene polymer. The maleic anhydride unit refers to a structural unit having a structure formed by polymerizing maleic anhydride.

[0096] The ratio of the polymer in the thermoplastic resin B is preferably 50 to 100 wt%, more preferably 70 to 100 wt%, particularly preferably 90 to 100 wt%. When the ratio of the polymer is within the above range, the resin layer (B) can exhibit suitable optical properties.

[0097] Thermoplastic resin B may further contain an optional component in combination with the above-mentioned polymer. Examples of the optional component include the same optional components that may be contained in thermoplastic resin A. The optional component may be used alone or in combination of two or more in any ratio.

[0098] The combination of thermoplastic resin A contained in the resin layer (A) and thermoplastic resin B contained in the resin layer (B) is selected in such a way that the absolute value of the difference between the glass transition temperature TgA of thermoplastic resin A and the glass transition temperature TgB of thermoplastic resin B |TgA-TgB| is within a prescribed range. Specifically, the absolute value of the difference |TgA-TgB| is usually 5°C or more, more preferably 10°C or more, and particularly preferably 13°C or more. In the case where thermoplastic resins having a difference in glass transition temperature of the above degree are combined as thermoplastic resin A and thermoplastic resin B for the manufacturing method described later, a retardation film satisfying the above formulas (1) to (3) can be simply manufactured. The upper limit of the absolute value of the difference |TgA-TgB| is not particularly limited, but is preferably 40°C or less, more preferably 30°C or less, and particularly preferably 25°C or less from the viewpoint of smoothly stretching the multilayer film.

[0099] The specific values ​​of the glass transition temperature TgA of thermoplastic resin A and the glass transition temperature TgB of thermoplastic resin B are arbitrary within the range where the absolute value of their difference |TgA-TgB| satisfies the above conditions. For example, the temperature Tg(low) of the lower one of the glass transition temperature TgA and the glass transition temperature TgB may be preferably 100°C or more, more preferably 105°C or more, particularly preferably 110°C or more, preferably 140°C or less, more preferably 135°C or less, and particularly preferably 130°C or less. In addition, the temperature Tg(high) of the higher one of the glass transition temperature TgA and the glass transition temperature TgB may be preferably 120°C or more, more preferably 125°C or more, particularly preferably 130°C or more, preferably 160°C or less, more preferably 155°C or less, and particularly preferably 150°C or less. When using thermoplastic resin A and thermoplastic resin B having the above-mentioned glass transition temperatures TgA and TgB, the phase difference film can be manufactured particularly simply.

[0100] In particular, when the wavelength is 550 nm, when the resin layer (A) included in the phase difference film has a larger in-plane phase difference than the resin layer (B) included in the phase difference film, it is preferred that the glass transition temperature TgA of the thermoplastic resin A is lower than the glass transition temperature TgB of the thermoplastic resin B. According to such a combination of the thermoplastic resin A and the thermoplastic resin B, a phase difference film having a resin layer (A) having a relatively large in-plane phase difference and a resin layer (B) having a relatively small in-plane phase difference can be manufactured particularly simply.

[0101] In addition, when the resin layer (B) of the retardation film has a larger in-plane phase difference than the resin layer (A) of the retardation film at a wavelength of 550 nm, the glass transition temperature TgB of the thermoplastic resin B is preferably lower than the glass transition temperature TgA of the thermoplastic resin A. According to such a combination of the thermoplastic resin A and the thermoplastic resin B, a retardation film having a resin layer (A) with a relatively small in-plane phase difference and a resin layer (B) with a relatively large in-plane phase difference can be manufactured particularly simply.

[0102] The glass transition temperature Tg can be measured using a differential scanning calorimeter ("DSC6220SII" manufactured by Nanotechnology Co., Ltd.) based on JIS K 6911 under the condition of a temperature increase rate of 10° C. / min.

[0103] The resin layer (A) of the phase difference film has a slow axis. In addition, the resin layer (B) of the phase difference film has a slow axis that is substantially perpendicular to the above-mentioned slow axis of the resin layer (A). The slow axis of the resin layer (B) is "substantially perpendicular" to the slow axis of the resin layer (A) and the slow axis of the resin layer (B) means that the angle formed by the slow axis of the resin layer (A) and the slow axis of the resin layer (B) is in a specific range close to 90°. Specifically, the angle formed by the slow axis of the resin layer (A) and the slow axis of the resin layer (B) is 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 combination of a resin layer (A) and a resin layer (B), and the above-mentioned resin layer (A) and the resin layer (B) have a slow axis of the above-mentioned relationship.

[0104] In particular, in the long strip phase difference film, it is preferred that one of the slow axis of the resin layer (A) and the slow axis of the resin layer (B) 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 slow axis of the resin layer (A) and the slow axis of the resin layer (B) form 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. A conventional long strip linear polarizer has an absorption axis parallel or perpendicular to the width direction of the linear polarizer. The long phase difference film having the resin layer (A) and the resin layer (B) can be simply bonded to the above-mentioned common linear polarizer in 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, wherein the above-mentioned resin layer (A) and the resin layer (B) have a slow axis in a direction that forms an angle within the above-mentioned range with the width direction. Therefore, since the phase difference film and the linear polarizer can be bonded by roll to roll, the circular polarizer can be manufactured particularly simply.

[0105] NZ coefficient NZ of resin layer (A) A and the NZ coefficient NZ of the resin layer (B) B It is preferable to appropriately set the NZ coefficient NZ of the retardation film so that T The NZ coefficient NZ of the resin layer (A) satisfies the formula (3). A It is "NZ A =(nx A -nz A ) / (nx A -ny A )”, so “NZ A =(Rth A / Re A )+0.5” means.nx A It represents the refractive index of the direction which provides the maximum refractive index in the in-plane direction of the resin layer (A). A Indicates the direction in the plane of the resin layer (A) and the direction in which nx is provided A The refractive index in the direction orthogonal to the direction of nz. A Re represents the refractive index in the thickness direction of the resin layer (A). A Indicates the in-plane phase difference of the resin layer (A), so “Re A=(nx A -ny A )×d A " A Indicates the phase difference in the thickness direction of the resin layer (A), so “Rth A ={(nx A +ny A ) / 2-nz A}×d A " means. A represents the thickness of the resin layer (A). In addition, the NZ coefficient NZ of the resin layer (B) B It is "NZ B =(nxB-nz B ) / (nx B -ny B )”, so “NZ B =(Rth B / Re B )+0.5” means.nx B It represents the refractive index in the direction providing the maximum refractive index in the in-plane direction of the resin layer (B). B Indicates the direction in the plane of the resin layer (B) and the direction in which nx is provided B The refractive index in the direction orthogonal to the direction of nz. B Re represents the refractive index in the thickness direction of the resin layer (B). B Indicates the in-plane phase difference of the resin layer (B), so “Re B =(nx B -ny B )×d B " B Indicates the phase difference in the thickness direction of the resin layer (B), so “Rth B ={(nx B +ny B ) / 2-nz B}×d B " means. B It shows the thickness of the resin layer (B).

[0106] NZ coefficient NZ of resin layer (A) A It is preferably 1.00 or more. Therefore, the refractive index ny of the resin layer (A) A and nz A Preferred to meet ny A ≥nz A In addition, the NZ coefficient NZ of the resin layer (B) B It is preferably less than 0.0. Therefore, the refractive index nx of the resin layer (B) B and nz BPreferred to meet nz B >nx B According to the combination of the resin layer (A) and the resin layer (B), the NZ coefficient NZ of the entire phase difference film can be easily T The adjustment is within the range of formula (3).

[0107] More specifically, the NZ coefficient NZ of the resin layer (A) A 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. A The refractive index of the resin layer (A) is nx A ,ny A and nz A Can have nx A >ny A ≥nz A Therefore, the resin layer (A) can function as a positive A plate or a negative B plate.

[0108] In addition, the NZ coefficient NZ of the resin layer (B) B 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. B ,ny B and nz B Can have nz B >nx B >ny B Therefore, the resin layer (B) can have a refractive index nx in three directions. B ,ny B and nz B Different layers (ie, layers having biaxiality). In addition, the resin layer (B) can function as a positive B plate.

[0109] NZ coefficient NZ of resin layer (A) A NZ coefficient NZ of the resin layer (B) B NZ A +NZ B It is preferably in a specific range. Specifically, and "NZ A +NZ B " is preferably -0.3 or more, more preferably 0.0 or more, particularly preferably 0.15 or more, preferably 0.8 or less, more preferably 0.75 or less, particularly preferably 0.65 or less. A +NZ B"Within the above range, it is possible to obtain a retardation film of a circular polarizing plate that can effectively suppress coloration caused by external light reflection in both the front direction and the oblique direction of the display surface.

[0110] The retardation film preferably satisfies the following formula (4).

[0111] {Re Q (450) / Re Q (550)}-{Re H (450) / Re H (550)}>0.08 (4)

[0112] (Among them, Re H (450) represents the in-plane phase difference of the high phase difference layer at a wavelength of 450 nm.

[0113] Re H (550) represents the in-plane phase difference of the high phase difference layer at a wavelength of 550 nm,

[0114] Re Q (450) represents the in-plane phase difference of the low phase difference layer at a wavelength of 450 nm.

[0115] Re Q (550) represents the in-plane phase difference of the low phase difference layer at a wavelength of 550 nm,

[0116] The high retardation layer refers to a layer having a large in-plane retardation at a wavelength of 550 nm, among the resin layer (A) and the resin layer (B) included in the retardation film.

[0117] The low phase difference layer refers to a layer having a small in-plane phase difference at a wavelength of 550 nm among the resin layer (A) and the resin layer (B) of the phase difference film.

[0118] In formula (4), “Re Q (450) / Re Q (550)” represents the wavelength dispersion of the low phase difference layer. In addition, in formula (4), “Re H (450) / Re H (550)" represents the wavelength dispersion of the high phase difference layer. Therefore, formula (4) indicates that there is a difference in the wavelength dispersion of the in-plane phase difference between the low phase difference layer and the high phase difference layer of the phase difference film. More specifically, the wavelength dispersion of the in-plane phase difference of the low phase difference layer is greater than the wavelength dispersion of the in-plane phase difference of the high phase difference layer. The parameter "{Re Q (450) / Re Q (550)}-{Re H (450) / Re H(550)}" In detail, it is preferably greater than 0.08, more preferably greater than 0.09, and particularly preferably greater than 0.10. In addition, there is no particular restriction on the upper limit, but it 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 (A) and a resin layer (B) having a difference in wavelength dispersion of the in-plane phase difference can easily obtain anti-dispersion characteristics in a stacked state.

[0119] “Re Q (450) / Re Q (550)" is preferably 1.05 or more, more preferably 1.08 or more, and particularly preferably 1.1 or more. In addition, there is no particular upper limit, but it is preferably 2.0 or less, more preferably 1.7 or less, and particularly preferably 1.5 or less. In "Re Q (450) / Re Q (550)" In the case where the content is within the above range, a circular polarizing plate capable of effectively suppressing coloration caused by reflection of external light can be obtained.

[0120] “Re H (450) / Re H (550)" is preferably 0.92 or more, more preferably 0.95 or more, particularly preferably 0.98 or more, preferably 1.2 or less, more preferably 1.1 or less, particularly preferably 1.05 or less. H (450) / Re H (550)" In the case where the content is within the above range, a circular polarizing plate capable of effectively suppressing coloration caused by reflection of external light can be obtained.

[0121] The in-plane retardation Re of the low retardation layer at a wavelength of 550 nm Q (550) is preferably 80 nm or more, more preferably 100 nm or more, particularly preferably 110 nm or more, and preferably 170 nm or less, more preferably 150 nm or less, particularly preferably 140 nm or less. Q (550) In the case of the above range, the low phase difference layer can function as a λ / 4 wave plate. In addition, according to the phase difference film having the low phase difference layer, a circular polarizing plate that can effectively suppress coloration caused by external light reflection can be obtained.

[0122] The in-plane retardation Re of the high retardation layer at a wavelength of 550 nm H (550) is preferably 220 nm or more, more preferably 240 nm or more, particularly preferably 250 nm or more, and is preferably 310 nm or less, more preferably 290 nm or less, particularly preferably 280 nm or less. H(550) In the case of the above range, the high retardation layer can function as a λ / 2 wave plate. In addition, according to the retardation film having the high retardation layer, a circular polarizing plate that can effectively suppress coloration caused by external light reflection can be obtained.

[0123] In-plane phase difference Re H (550) and in-plane phase difference Re Q (550) difference "Re H (550)-Re Q (550)" is preferably 100 nm or more, more preferably 110 nm or more, and preferably 180 nm or less, more preferably 160 nm or less. H (550)-Re Q (550)" In the case where the content is within the above range, a circular polarizing plate capable of effectively suppressing coloration caused by reflection of external light can be obtained.

[0124] The phase difference film may also have any layer other than the resin layer (A) and the resin layer (B) as required. As an example of any layer, any layer with optical isotropy can be cited. The in-plane phase difference of the arbitrary layer with optical isotropy at a wavelength of 550nm is usually less than 10nm, such as a protective film layer for protecting the resin layer (A) and the resin layer (B), an adhesive layer for bonding the resin layer (A) and the resin layer (B), etc. In addition, as other examples of any layer, any layer with optical anisotropy can also be cited. The optical properties of the arbitrary layer with optical anisotropy are not limited within the range that the phase difference film as a whole satisfies formula (1) to formula (3). Specifically, for example, the optical properties of the arbitrary layer can be set so that the combination of the arbitrary layer with optical anisotropy and one or both of the resin layer (A) and the resin layer (B) can function as a λ / 4 wave plate or a λ / 2 wave plate.

[0125] The total light transmittance of the retardation film is preferably 80% or more, more preferably 85% or more, and particularly preferably 90% or more. The total light transmittance can be measured using an ultraviolet-visible spectrophotometer in a wavelength range of 400 nm to 700 nm.

[0126] 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.

[0127] The phase difference film can be a single film or a long strip film.

[0128] 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.

[0129] The thickness of each layer of the phase difference film, such as the resin layer (A) and the resin layer (B), is not particularly limited. The thickness of the resin layer (A) and the resin layer (B) 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.

[0130] [2. Overview of the method for producing a phase difference film]

[0131] In a manufacturing method according to one embodiment of the present invention, the retardation film is manufactured by the following manufacturing method, which comprises:

[0132] In a first step, a multilayer film having a resin layer (A) and a resin layer (B) is prepared, wherein the resin layer (A) is formed of a thermoplastic resin A and the resin layer (B) is formed of a thermoplastic resin B; and

[0133] In the second step, the multilayer film is stretched two or more times.

[0134] The resin layer (A) and the resin layer (B) of the multilayer film prepared in the first step have optical properties different from the optical properties of the resin layer (A) and the resin layer (B) of the phase difference film. Specifically, the resin layer (A) and the resin layer (B) of the multilayer film generally do not have a large optical anisotropy. Therefore, the resin layer (A) and the resin layer (B) of the multilayer film generally do not have a phase difference, or even if there is a phase difference, its value is very small. In addition, the resin layer (A) and the resin layer (B) of the multilayer film generally do not have a slow axis, or even if there is a slow axis, these slow axes are not approximately vertical.

[0135] Therefore, in the manufacturing method of the present embodiment, the multilayer film is subjected to a second step including more than two stretching steps. By stretching in the second step, the optical properties of the resin layer (A) and the resin layer (B) are adjusted to obtain a phase difference film having the above-mentioned desired optical properties. For example, by stretching in the second step, a large optical anisotropy is exhibited in the resin layer (A) and the resin layer (B), and a phase difference film satisfying formula (1), formula (2) and formula (3) is obtained. In addition, by stretching in the second step, slow axes perpendicular to each other are exhibited in the resin layer (A) and the resin layer (B). In the case where the resin layer (A) and the resin layer (B) of the multilayer film have slow axes, the directions of these slow axes are adjusted by stretching in the second step so that these slow axes are approximately perpendicular.

[0136] [3. First step: preparing multilayer film]

[0137] In the first step, a multilayer film is prepared which has a resin layer (A) formed of a thermoplastic resin A and a resin layer (B) formed of a thermoplastic resin B. The thermoplastic resin A and the thermoplastic resin B are the resins described in the section of the retardation film.

[0138] Usually, the resin layer (A) and the resin layer (B) of the multilayer film prepared in the first step do not have large optical anisotropy. Therefore, the phase difference between the resin layer (A) and the resin layer (B) is usually small. As an example of a specific range, the in-plane phase difference of the resin layer (A) and the resin layer (B) at a wavelength of 550nm is preferably 0nm to 20nm, more preferably 0nm to 10nm, and particularly preferably 0nm to 5nm.

[0139] The multilayer film may be a single film, preferably a long film. By preparing the multilayer film in the form of a long film, when manufacturing a retardation film, part or all of the steps can be performed on a production line, and the production can be simple and efficient.

[0140] There is no limitation on the method for producing the multilayer film. For the multilayer film, for example, a coextrusion method, a cocasting method, a coating method of applying a liquid composition containing layer materials other than the layer on a certain layer, etc. are mentioned. In particular, a method of applying a liquid composition containing a thermoplastic resin B on the resin layer (A) and drying the applied liquid composition as needed is preferred. The method for producing the multilayer film is described below.

[0141] The method for producing the resin layer (A) is not limited. The resin layer (A) can be produced by, for example, a melt forming method or a solution casting method. The melt forming method is particularly preferred. Among the melt forming methods, extrusion forming method, inflation forming method or compression forming method are preferred, and extrusion forming method is particularly preferred. According to these methods, the resin layer (A) can be made into a long film.

[0142] After the resin layer (A) is prepared, a liquid composition containing a thermoplastic resin B is applied to the resin layer (A). The liquid composition may contain a thermoplastic resin B and a solvent. As the solvent, a solvent that can dissolve or disperse the thermoplastic resin B is preferred, and a solvent that can dissolve the thermoplastic resin B is particularly preferred. In addition, the solvent may be used alone or in combination of two or more in any proportion. The concentration of the thermoplastic resin B in the liquid composition is preferably adjusted to a range in which the viscosity of the liquid composition is suitable for coating, for example, it may be 1% by weight to 50% by weight.

[0143] 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, slit coating, and dipping.

[0144] By applying a liquid composition containing a thermoplastic resin B, a layer of the liquid composition is formed on the resin layer (A). Therefore, by drying the layer of the liquid composition to remove the solvent as needed, a resin layer (B) can be formed on the resin layer (A) to obtain a multilayer film. The drying method is not limited, and drying methods such as heating drying and reduced pressure drying can be used.

[0145] [4. Second step: stretching of multilayer film]

[0146] After the multilayer film is prepared in the first step, a second step is performed, which includes stretching the multilayer film twice or more. The second step includes:

[0147] A first stretching step of stretching the multilayer film at a stretching temperature Ts1; and

[0148] In the second stretching step, the multilayer film is stretched at a stretching temperature Ts2 different from the stretching temperature Ts1. By performing the stretching twice or more at such different temperatures, the above-mentioned retardation film can be obtained.

[0149] The absolute value of the difference between the stretching temperature Ts1 in the first stretching process and the stretching temperature Ts2 in the second stretching process |Ts1-Ts2| is preferably within a specific range. Specifically, the absolute value of the difference |Ts1-Ts2| is preferably above 5°C, more preferably above 8°C, particularly preferably above 10°C, preferably below 25°C, more preferably below 22°C, and particularly preferably below 20°C. When the absolute value of the difference between the stretching temperature Ts1 and the stretching temperature Ts2 |Ts1-Ts2| is within the above range, the phase difference film can be manufactured particularly simply.

[0150] The temperature of the lower one of the stretching temperature Ts1 and the stretching temperature Ts2 is preferably in a specific temperature range close to Tg(low). Specifically, the specific temperature range is preferably above Tg(low)-5°C, more preferably above Tg(low)-3°C, particularly preferably above Tg(low)-1°C, preferably below Tg(low)+20°C, more preferably below Tg(low)+15°C, and particularly preferably below Tg(low)+12°C. Tg(low) represents the temperature of the lower one of the glass transition temperature TgA and the glass transition temperature TgB. When the temperature of the lower one of the stretching temperature Ts1 and the stretching temperature Ts2 is within the above range, the orientation of the polymer molecules contained in both the resin layer (A) and the resin layer (B) can be effectively carried out, and their refractive indices can be greatly changed, so that the phase difference film can be manufactured particularly simply.

[0151] The temperature of the higher one of the stretching temperature Ts1 and the stretching temperature Ts2 is preferably in a specific temperature range close to Tg(high). Specifically, the specific temperature range is preferably above Tg(high)-5°C, more preferably above Tg(high)-3°C, particularly preferably above Tg(high)-1°C, preferably below Tg(high)+20°C, more preferably below Tg(high)+15°C, and particularly preferably below Tg(high)+12°C. Tg(high) represents the temperature of the higher one of the glass transition temperature TgA and the glass transition temperature TgB. When the temperature of the higher one of the stretching temperature Ts1 and the stretching temperature Ts2 is in the above range, in the resin layer formed by the thermoplastic resin having the higher glass transition temperature in the resin layer (A) and the resin layer (B), the polymer molecules are oriented to a large extent. Therefore, the refractive index can be greatly changed. On the other hand, in the resin layer formed of a thermoplastic resin having a low glass transition temperature, since the stretching temperature is sufficiently higher than the glass transition temperature, the polymer molecules are oriented relatively slightly or not oriented. Therefore, the refractive index does not change, or even if it changes, the amount of change is very small. Thus, the optical properties of the resin layer (A) and the resin layer (B) can be easily adjusted, so the phase difference film can be manufactured particularly easily.

[0152] In the stretching in the second step, stretching can be performed at a high temperature first or at a low temperature first. Therefore, the stretching temperature Ts1 in the first stretching step performed first can be lower than the stretching temperature Ts2 in the second stretching step performed later. In addition, the stretching temperature Ts1 in the first stretching step performed first can also be higher than the stretching temperature Ts2 in the second stretching step performed later. In particular, from the perspective of making the manufacture of the phase difference film particularly simple, it is preferred that the stretching temperature Ts1 in the first stretching step performed first is higher than the stretching temperature Ts2 in the second stretching step performed later.

[0153] In the second process, the stretching in the first stretching process and the stretching in the second stretching process are usually carried out in different stretching directions. At this time, the stretching in the first stretching process and the stretching in the second stretching process can be carried out as unidirectional stretching. The stretching in the second process is particularly preferably carried out in a manner that the stretching direction in the first stretching process is approximately perpendicular to the stretching direction in the second stretching process. The two stretching directions are "approximately perpendicular" to each other, indicating that the angle formed by their stretching directions is in a specific range close to 90°. Specifically, the angle formed by their stretching directions is 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. When the stretching direction in the first stretching process and the stretching direction in the second stretching process are approximately perpendicular, the phase difference film can be manufactured particularly simply.

[0154] In the case of stretching a long multilayer film in the second process, it is preferred that one of the stretching directions in the first stretching process and the stretching direction in the second stretching process forms an angle close to a specific range of 45° with the width direction of the multilayer film. Specifically, the above angle is preferably more than 40°, more preferably more than 42°, more preferably more than 43°, particularly preferably more than 44°, preferably less than 50°, more preferably less than 48°, more preferably less than 47°, and particularly preferably less than 46°. Furthermore, in this case, it is preferred that the stretching direction in the first stretching process and the stretching direction in the second stretching process form an angle close to a specific range of 135° with the width direction of the phase difference film. Specifically, the above angle is preferably more than 130°, more preferably more than 132°, more preferably more than 133°, particularly preferably more than 134°, preferably less than 140°, more preferably less than 138°, more preferably less than 137°, and particularly preferably less than 136°. When the film is stretched at the above stretching angle, a circular polarizing plate can be produced generally by roll-to-roll bonding the obtained retardation film and a long linear polarizer. Therefore, the circular polarizing plate can be produced particularly easily.

[0155] The stretching ratio for stretching in the second step is preferably appropriately set to obtain the desired phase difference film. In addition, the stretching ratios for each stretching may be the same or different. Therefore, the stretching ratio in the first stretching step may be the same or different from the stretching ratio in the second stretching step.

[0156] In the first stretching process and the second stretching process, the stretching ratio in the stretching process at a relatively low stretching temperature is preferably 1.2 times or more, more preferably 1.3 times or more, particularly preferably 1.35 times or more, preferably 3.0 times or less, more preferably 2.5 times or less, particularly preferably 2.0 times or less. When the stretching ratio in the stretching process at a relatively low stretching temperature is within the above range, the phase difference film can be manufactured particularly simply.

[0157] In the first stretching process and the second stretching process, the stretching ratio in the stretching process at a relatively high stretching temperature is preferably 1.05 times or more, 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. When the stretching ratio in the stretching process at a relatively high stretching temperature is within the above range, the phase difference film can be manufactured particularly simply.

[0158] The second step may include an arbitrary stretching step of further stretching the multilayer film in combination with the first stretching step and the second stretching step. The stretching conditions in the arbitrary stretching step can be appropriately set within the range in which a desired retardation film is obtained.

[0159] According to the above-mentioned second process, the resin layer (A) and the resin layer (B) of the multilayer film can show the optical properties required by the resin layer (A) and the resin layer (B) of the phase difference film. Therefore, by stretching in the second process, the phase difference film can be obtained in the form of a stretched multilayer film. The inventors speculate that the mechanism of the phase difference film obtained by stretching in the second process is as follows. However, the technical scope of the present invention is not limited to the following mechanism.

[0160] The second step includes stretching at a stretching temperature Ts1 and stretching at a stretching temperature Ts2 different from the stretching temperature Ts1.

[0161] According to the stretching at the lower temperature of the stretching temperature Ts1 and Ts2, the polymer molecules contained in the resin layer (A) and the resin layer (B) of the multilayer film are oriented along the stretching direction. Through this orientation, in the resin layer (A) containing the thermoplastic resin A having a positive intrinsic birefringence value, the refractive index in the direction parallel to the stretching direction becomes larger, and the refractive index in the direction perpendicular to the stretching direction becomes smaller. In addition, through the above orientation, in the resin layer (B) containing the thermoplastic resin B having a negative intrinsic birefringence value, the refractive index in the direction perpendicular to the stretching direction becomes larger, and the refractive index in the direction parallel to the stretching direction becomes smaller.

[0162] On the other hand, according to the stretching at the temperature of the higher one of the stretching temperatures Ts1 and Ts2, the polymer molecules contained in the resin layer (A) and the resin layer (B) can also be oriented along the stretching direction. Through this orientation, in the resin layer (A), the refractive index in the direction parallel to the stretching direction becomes larger, and the refractive index in the direction perpendicular to the stretching direction becomes smaller. In addition, in the resin layer (B), the refractive index in the direction perpendicular to the stretching direction becomes larger, and the refractive index in the direction parallel to the stretching direction becomes smaller. However, the degree of this orientation is different from the stretching at the temperature of the lower one of the stretching temperatures Ts1 and Ts2. Specifically, in the resin layer formed by the thermoplastic resin of the higher glass transition temperature of the resin layer (A) and the resin layer (B), the polymer molecules are oriented relatively largely, but in the resin layer formed by the thermoplastic resin of the lower glass transition temperature, the polymer molecules are oriented relatively slightly, or not oriented.

[0163] Therefore, by combining stretching at a stretching temperature Ts1 and stretching at a stretching temperature Ts2, the degree of change in the refractive index and the direction of the refractive index change can be adjusted in the resin layer (A) and the resin layer (B), respectively. Usually, it is adjusted so that the uniaxiality of one of the resin layer (A) and the resin layer (B) is high, and the biaxiality of the other of the resin layer (A) and the resin layer (B) is high. Moreover, as a result of such adjustment, the optical properties such as the in-plane phase difference, the thickness direction phase difference, and the slow axis direction of the resin layer (A) and the resin layer (B) can be obtained in an appropriate range, so that the above-mentioned phase difference film can be obtained.

[0164] [5. Any process]

[0165] The method for manufacturing a phase difference film may further include any process combined with the first process and the second process. For example, in the case of using a long multilayer film to obtain a long phase difference film, the method for manufacturing a phase difference film may include a trimming process, which cuts the obtained phase difference film into a desired shape. According to the trimming process, a monolithic 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.

[0166] [6. Preferred first example]

[0167] Hereinafter, a preferred first example of the production method according to the above embodiment will be described. In this first example, a retardation film is produced using a thermoplastic resin A and a thermoplastic resin B having a glass transition temperature TgA and a glass transition temperature TgB satisfying TgA<TgB.

[0168] In the manufacturing method of the first example, a first step of preparing the multilayer film having a resin layer (A) formed of a thermoplastic resin A and a resin layer (B) formed of a thermoplastic resin B is performed. Then, a second step is performed, the second step including a first stretching step of stretching the multilayer film in one direction at a stretching temperature Ts1 and a second stretching step of stretching the multilayer film in another direction at a stretching temperature Ts2. In the second step of the manufacturing method of the first example, the stretching direction in the first stretching step is substantially perpendicular to the stretching direction in the second stretching step.

[0169] In the first example, according to the stretching at the lower temperature of the stretching temperatures Ts1 and Ts2, in both the resin layer (A) and the resin layer (B) of the multilayer film, the polymer molecules are largely oriented in the stretching direction. Therefore, in the resin layer (A), the refractive index in the stretching direction becomes larger, and the refractive index in the direction perpendicular to the stretching direction becomes smaller. On the other hand, in the resin layer (B), the refractive index in the stretching direction becomes smaller, and the refractive index in the direction perpendicular to the stretching direction becomes larger.

[0170] In addition, according to the stretching at the higher temperature of the stretching temperature Ts1 and Ts2, the polymer molecules in the resin layer (B) are largely oriented in the stretching direction, but the polymer molecules in the resin layer (A) are slightly oriented in the stretching direction, or are not oriented. Therefore, in the resin layer (A), the refractive index does not change, or even if it changes, the change is very small. On the other hand, in the resin layer (B), the refractive index in the stretching direction becomes smaller, and the refractive index in the direction perpendicular to the stretching direction becomes larger.

[0171] In the first example, the stretching direction in the first stretching process is approximately perpendicular to the stretching direction in the second stretching process. Therefore, according to the combination of the first stretching process and the second stretching process, the uniaxiality in the resin layer (A) becomes larger, and the biaxiality in the resin layer (B) becomes larger. And the desired phase difference film can be obtained as a film having a resin layer (A) with large uniaxiality and a resin layer (B) with large biaxiality like this. Such a first example of the manufacturing method can be preferably used to manufacture a phase difference film having a resin layer (A) as a high phase difference layer and a resin layer (B) as a low phase difference layer.

[0172] [7. Preferred second example]

[0173] A preferred second example of the production method according to the above embodiment is described below. In the second example, a retardation film is produced using a thermoplastic resin A and a thermoplastic resin B having glass transition temperatures TgA and TgB satisfying TgA>TgB.

[0174] In the manufacturing method of the second example, the first step and the second step are performed in the same manner as in the manufacturing method of the first example. Therefore, in the second step of the manufacturing method of the second example, the stretching direction in the first stretching step is substantially perpendicular to the stretching direction in the second stretching step.

[0175] In the second example, according to the stretching at the lower temperature of the stretching temperatures Ts1 and Ts2, the polymer molecules in both the resin layer (A) and the resin layer (B) of the multilayer film are largely oriented in the stretching direction as in the first example. Therefore, in the resin layer (A), the refractive index in the stretching direction becomes larger, and the refractive index in the direction perpendicular to the stretching direction becomes smaller. On the other hand, in the resin layer (B), the refractive index in the stretching direction becomes smaller, and the refractive index in the direction perpendicular to the stretching direction becomes larger.

[0176] In contrast, according to the stretching at the higher temperature of the stretching temperatures Ts1 and Ts2, the polymer molecules in the resin layer (A) are largely oriented in the stretching direction, but the polymer molecules in the resin layer (B) are slightly oriented in the stretching direction, or are not oriented. Therefore, in the resin layer (A), the refractive index in the stretching direction becomes larger, and the refractive index in the direction perpendicular to the stretching direction becomes smaller. On the other hand, in the resin layer (B), the refractive index does not change, or even if it changes, the change is very small.

[0177] In the second example, the stretching direction in the first stretching process is approximately perpendicular to the stretching direction in the second stretching process. Therefore, according to the combination of the first stretching process and the second stretching process, the biaxiality in the resin layer (A) becomes larger, and the uniaxiality in the resin layer (B) becomes larger. And the desired phase difference film can be obtained as a film having a resin layer (A) with large biaxiality and a resin layer (B) with large uniaxiality like this. Such a manufacturing method of the second example can be preferably used to manufacture a phase difference film having a resin layer (A) as a low phase difference layer and a resin layer (B) as a high phase difference layer.

[0178] [8. Main advantages of the method for manufacturing phase difference film]

[0179] According to the above-mentioned manufacturing method, the resin layer (A) and the resin layer (B) of the multilayer film can be stretched at the same time to manufacture the desired phase difference film having the stretched resin layer (A) and the resin layer (B). Therefore, it is not necessary to prepare the resin layer (A) and the resin layer (B) separately, so the number of processes can be reduced, and labor, time and cost can be suppressed. In addition, it is not necessary to require precise adjustment of the bonding angle of the resin layer (A) and the resin layer (B), so labor and time can also be suppressed.

[0180] By using the retardation film obtained in this way, a circularly polarizing plate capable of suppressing coloration due to reflection of external light in both the front direction and the oblique direction of the display surface can be produced.

[0181] [9. Circular polarizer]

[0182] A circular polarizer according to an embodiment of the present invention has a linear polarizer and a phase difference film. By arranging the circular polarizer on the display surface of an image display device, the reflection of external light can be suppressed. According to the circular polarizer having the phase difference film, the reflection of external light can be suppressed regardless of whether the display surface is observed from the front direction or from the oblique direction, and coloring can be effectively suppressed.

[0183] The circular polarizer may have a linear polarizer, a resin layer (A) and a resin layer (B) in sequence. The circular polarizer may also have a linear polarizer, a resin layer (B) and a resin layer (A) in sequence. The specific order may be set according to the in-plane phase difference of the resin layer (A) and the resin layer (B).

[0184] In the circular polarizing plate, the angle formed by the width direction of the linear polarizer and one of the slow axis of the resin layer (A) and the slow axis of the resin layer (B) is preferably in a specific range close to 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. Furthermore, in this case, the angle formed by the width direction of the linear polarizer and the other of the slow axis of the resin layer (A) and the slow axis of the resin layer (B) is in a specific range close to 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] Any linear polarizer can be used as the linear polarizer. Examples of linear polarizers include: a film obtained by uniaxially stretching a polyvinyl alcohol film after adsorbing iodine or a dichroic dye in a boric acid bath; and a film obtained by stretching a polyvinyl alcohol film after adsorbing iodine or a dichroic dye and then modifying a part of the polyvinyl alcohol units in the molecular chain into polyvinylidene units. Among them, a polarizer containing polyvinyl alcohol is preferably used as the linear polarizer.

[0186] When natural light is incident on the linear polarizer, only one polarized light is transmitted. The polarization degree of the linear polarizer 130 is not particularly limited, but is preferably 98% or more, and more preferably 99% or more.

[0187] In addition, the thickness of the linear polarizer is preferably 5 μm to 80 μm.

[0188] The circular polarizer may further include any layer. As the arbitrary layer, for example, a polarizer protective film layer, an adhesive layer for laminating a linear polarizer and a phase difference film, a hard coating layer such as an impact-resistant polymethacrylate resin layer, a mat for improving the smoothness of the film, an antireflection layer, an antifouling layer, an antistatic layer, etc. can be cited. These arbitrary layers may be provided with only one layer, or may be provided with two or more layers.

[0189] [10. Image display device]

[0190] The circular polarizer may be provided in an image display device. It is particularly preferred to provide the circular polarizer in an organic EL image display device. The organic EL image display device comprises a circular polarizer and an organic electroluminescent element (hereinafter, appropriately referred to as an "organic EL element"). The organic EL image display device generally comprises a linear polarizer, a phase difference film, and an organic EL element in this order.

[0191] 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 through the transparent electrode layer and the electrode layer. Examples of materials constituting the organic light-emitting layer include poly(p-phenylene vinylene)-based materials, polyfluorene-based materials and polyvinyl carbazole-based materials. 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 also 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.

[0192] 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 cannot pass 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. Thus, the function of suppressing reflection is achieved.

[0193] Since the phase difference film has the above optical properties, the organic EL image display device can not only suppress reflection in the front direction of the display surface, but also suppress reflection in the oblique direction. Therefore, it is possible to effectively suppress reflection of external light in both the front direction and the oblique direction of the display surface, thereby suppressing coloration.

[0194] The degree of coloring can be evaluated by observing the color difference ΔE*ab between the chromaticity measured on the display surface with reflection and the chromaticity of the black display surface without reflection. The chromaticity can be obtained by the following method: measure the spectrum of light reflected on the display surface, and multiply the spectrum by the spectral sensitivity (isochromatic function) corresponding to the human eye to obtain the tristimulus values ​​X, Y, and Z, and calculate the chromaticity (a*, b*, and L*). In addition, the color difference ΔE*ab can be obtained by the following formula (X) based on the chromaticity (a0*, b0*, and L0*) when the display surface is not irradiated by external light and the chromaticity (a1*, b1*, and L1*) when it is irradiated by external light.

[0195] [Number 1]

[0196]

[0197] In addition, the coloring of the display surface caused by the reflected light usually varies depending on the azimuth of the viewing direction. Therefore, when observing from an inclined direction of the display surface, the measured chromaticity varies depending on the azimuth of the viewing direction, and therefore the color difference ΔE*ab also varies. Therefore, in order to evaluate the degree of coloring when observing from an inclined direction of the display surface as described above, it is preferred to perform coloring evaluation by taking the average value of the color difference ΔE*ab obtained from observing from multiple azimuth directions. Specifically, at an azimuth of (refer to Figure 1 ) In the range of 0° to less than 360°, the color difference ΔE*ab is measured every 5° along the azimuth direction, and the degree of coloration is evaluated by the average value (average color difference) of the measured color difference ΔE*ab. The smaller the above average color difference, the smaller the coloration of the display surface when viewed from the oblique direction of the display surface.

[0198] Example

[0199] 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 equivalents thereof.

[0200] In the following description, "%" and "parts" indicating amounts are by weight unless otherwise specified. In addition, unless otherwise specified, the operations described below are performed under normal temperature and pressure.

[0201] [Evaluation method]

[0202] (Method for measuring phase difference and NZ coefficient)

[0203] The in-plane phase difference Re of the evaluation object (phase difference film, resin layer (A) and resin layer (B)) at wavelengths of 450nm, 550nm and 650nm, and the phase difference Rth in the thickness direction at a wavelength of 550nm were measured using a phase difference meter ("AxoScan" manufactured by Axometrics Co., Ltd.). When calculating the physical properties of each layer of the resin layer (A) and the resin layer (B), the sample was measured from multiple directions, and the fitting analysis was performed using the attached multi-layer analysis software to calculate the result. In addition, the NZ coefficient was calculated using the in-plane phase difference Re and the phase difference Rth in the thickness direction at a wavelength of 550nm.

[0204] (Method for measuring orientation angle)

[0205] The directions of the slow axes of the resin layers (A) and (B) included in the retardation film were measured using a phase difference meter ("AxoScan" manufactured by Axometrics Co., Ltd.) The angle between the slow axis and the width direction of the retardation film was calculated as the orientation angle θ (0°≤θ<180°).

[0206] (Method of calculating color difference by simulation)

[0207] Using "LCD Master" manufactured by Shintech Co., Ltd. as simulation software, the circular polarizing plates manufactured in the respective Examples and Comparative Examples were modeled and the following calculations were performed.

[0208] In the simulation model, a structure in which a circular polarizer is provided on the above-mentioned reflection surface of a mirror having a flat reflection surface is set. In Examples 1 to 4 and Comparative Example 1, as a circular polarizer, it is set to have a low phase difference layer, a high phase difference layer and a linear polarizer in order from the above-mentioned reflection surface side. In addition, in Comparative Example 2, as a circular polarizer, it is set to have a norbornene resin layer, a styrene maleic anhydride copolymer resin layer, a norbornene resin layer and a linear polarizer in order from the above-mentioned reflection surface side. As the low phase difference layer, the high phase difference layer, the norbornene resin layer and the styrene maleic anhydride copolymer resin layer, it is set to be the layer obtained in each embodiment and comparative example. In addition, as a linear polarizer, it is set to be a commonly used polarizer with a polarization degree of 99.99%. In addition, as a mirror, it is set to be an ideal mirror that can reflect incident light with a reflectivity of 100%.

[0209] 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.

[0210] like Figure 1 As shown, the color space coordinates observed on the reflective surface 10 of the mirror provided with a circular polarizer when illuminated by a D65 light source (not shown) are calculated. In addition, the color space coordinates when not illuminated by the light source are set to a0*=0, b0*=0, and L0*=0. Then, the color difference ΔE*ab 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.

[0211] The above calculation of the chromatic aberration ΔE*ab is performed in the observation direction 20 at a polar angle ρ of 0° with respect to the reflection surface 10 , and the chromatic aberration ΔE*ab in the front direction is obtained. The polar angle ρ represents the angle with the normal direction 11 of the reflection surface 10 .

[0212] The above-mentioned calculation of the chromatic aberration ΔE*ab is performed in the observation direction 20 at a polar angle ρ of 60° with respect to the reflection surface 10. In the calculation of the polar angle ρ=60°, the observation direction 20 is set at an azimuth angle The calculation is performed multiple times within the range of 0° to less than 360°, moving every 5° in the azimuth direction. represents the angle formed by the direction parallel to the reflection surface 10 with respect to a certain reference direction 12 parallel to the reflection surface 10. Then, the color difference ΔE*ab obtained in the observation direction 20 is averaged to obtain the color difference ΔE*ab in the oblique direction with a polar angle ρ=60°.

[0213] (Method for evaluating circular polarizing plate based on visual observation in the front direction)

[0214] An image display device having an organic EL image display device (Apple Watch (registered trademark) of Apple Inc.) was prepared. The image display device was disassembled, and the polarizer 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 was attached to the surface of the circular polarizer obtained in each embodiment and comparative example on the opposite side to the linear polarizer via a pressure-sensitive adhesive ("CS9621" manufactured by Nitto Denko). Thus, a sample having a reflective electrode, a pressure-sensitive adhesive, and a circular polarizer in this order was obtained.

[0215] 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. The circular polarizer was observed in the front direction with a polar angle of 0° and an azimuth angle of 0°. According to the results of the observation, the case where color was visually confirmed was judged as "bad", and the case where no color was visually confirmed was judged as "good".

[0216] (Method for evaluating circular polarizing plate based on visual observation in an oblique direction)

[0217] On a sunny day, the circular polarizer of the sample prepared above (based on the method of visually observing the circular polarizer in the front direction) is illuminated with sunlight, and the circular polarizer on the reflective electrode is visually observed. The circular polarizer is observed in an inclined direction with a polar angle of 60° and an azimuth angle of 0° to 360°. According to the results of the observation, the advantages and disadvantages of the reflection 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 ranks (6 points for the first place, 5 points for the second place, ... 1 point for the last place).

[0218] The above observations were performed by multiple persons, and the total score given to each Example and Comparative Example was calculated. The Examples and Comparative Examples were arranged in the order of the above total score, and evaluated in the order of A, B, C, D and E from the top group within the range of the total score.

[0219] [Example 1]

[0220] (1-1. Formation of Resin Layer (A))

[0221] A granular norbornene-based resin (manufactured by Japan Zeon Co., Ltd.; glass transition temperature of 126° C.) was dried at 100° C. for 5 hours to obtain a thermoplastic resin A. The thermoplastic resin A was supplied to an extruder, passed through a polymer tube and a polymer filter, and extruded from a T-die head in a sheet form onto a casting drum. The extruded thermoplastic resin A was cooled to obtain a long resin film with a thickness of 100 μm as a resin layer (A). The obtained resin layer (A) was wound into a roll and recovered.

[0222] (1-2. Formation of resin layer (B))

[0223] In a pressure-resistant reactor replaced with dry nitrogen, 500 ml of toluene as a solvent and 0.29 mmol of n-butyl lithium as a polymerization catalyst were added, and then 35 g of 2-vinylnaphthalene was added and reacted at 25°C for 1 hour. As a result, a reactant containing poly(2-vinylnaphthalene) which is a homopolymer of 2-vinylnaphthalene was obtained. The reactant was poured into a large amount of 2-propanol to precipitate and separate the poly(2-vinylnaphthalene). The obtained poly(2-vinylnaphthalene) was dried at 200°C for 24 hours in a vacuum dryer to obtain a thermoplastic resin B. 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.

[0224] Poly(2-vinylnaphthalene) and 1,3-dioxolane were mixed to obtain a liquid composition containing a thermoplastic resin B. The concentration of poly(2-vinylnaphthalene) in the liquid composition was 15% by weight.

[0225] The resin layer (A) was drawn out from the roll, and the above-mentioned liquid composition was applied on the drawn-out resin layer (A). Then, the applied liquid composition was dried to form a layer (thickness of 12 μm) of poly(2-vinylnaphthalene) as the resin layer (B) on the resin layer (A). Thus, a multilayer film having a resin layer (A) formed of a norbornene-based resin and a resin layer (B) formed of poly(2-vinylnaphthalene) was obtained. The obtained multilayer film was wound into a roll and recovered.

[0226] [1-3. First stretching step]

[0227] The multilayer film was drawn out from the roll and supplied to a vertical tenter stretching machine. The multilayer film was stretched at a stretching temperature of 140°C and a stretching ratio of 1.10 times in a stretching direction at an angle of 135° to the width direction of the multilayer film using the tenter stretching machine. The stretched multilayer film was cooled to room temperature, wound into a roll and recovered.

[0228] [1-4. Second stretching step]

[0229] The multilayer film stretched in the first stretching process is extracted from the roller, and the extracted multilayer film is supplied to the widening stretching machine. Using the widening stretching machine, the multilayer film is stretched at a stretching temperature of 128°C and a stretching ratio of 1.50 times along the stretching direction at an angle of 45° to the width direction of the multilayer film to obtain a long strip phase difference film. The phase difference film has a resin layer (A) as a high phase difference layer and a resin layer (B) as a low phase difference layer. By the above method, the optical properties (in-plane phase difference, thickness direction phase difference, direction of the slow axis, NZ coefficient) of the obtained phase difference film and each layer contained in the phase difference film are measured.

[0230] [1-5. Production of circular polarizing plate]

[0231] A long polyvinyl alcohol resin film dyed with iodine was prepared. The film was stretched along a length direction at an angle of 90° to the width direction of the film to obtain a linear polarizer as a long polarizing film. The linear polarizer had an absorption axis in the length direction of the linear polarizer and a transmission axis in the width direction of the linear polarizer.

[0232] The linear polarizer and the phase difference film were bonded together via an optically isotropic pressure-sensitive adhesive ("CS9621" manufactured by Nitto Denko Corporation) to obtain a long circular polarizer. The bonding was performed in a manner that the width direction of the linear polarizer was parallel to the width direction of the phase difference film. The obtained circular polarizer sequentially comprises a linear polarizer, a resin layer (A) as a high phase difference layer, and a resin layer (B) as a low phase difference layer.

[0233] The obtained circularly polarizing plate was evaluated by the above-mentioned method.

[0234] [Examples 2 to 4]

[0235] In the step (1-1), the extrusion conditions of the extruder were adjusted so that the thickness of the long resin layer (A) was changed as shown in Table 1.

[0236] In addition, in the step (1-2), the thickness of the resin layer (B) was changed as shown in Table 1 by adjusting the amount of the liquid composition applied.

[0237] Furthermore, in the step (1-3), the stretching ratio was changed as shown in Table 1.

[0238] A retardation film and a circular polarizing plate were produced and evaluated by the same method as in Example 1 except for the above items.

[0239] [Comparative Example 1]

[0240] In the step (1-1), the extrusion conditions of the extruder were adjusted so that the thickness of the long resin layer (A) was changed as shown in Table 1.

[0241] In addition, in the step (1-2), the thickness of the resin layer (B) was changed as shown in Table 1 by adjusting the amount of the liquid composition applied.

[0242] Furthermore, in the step (1-3), the stretching temperature and the stretching ratio were changed as shown in Table 1.

[0243] A retardation film and a circular polarizing plate were produced and evaluated by the same method as in Example 1 except for the above items.

[0244] [Comparative Example 2]

[0245] A retardation film was produced by the same method as in Example 5 of Japanese Patent Application Laid-Open No. 2002-40258.

[0246] Specifically, a norbornene-based resin (manufactured by Zeon Co., Ltd., with a glass transition temperature of 136° C.) was prepared as a thermoplastic resin A having a positive intrinsic birefringence value. In addition, a styrene-based maleic anhydride copolymer resin ("Dylark D332" manufactured by NOVAChemicals, with a glass transition temperature of 130° C.) was prepared as a thermoplastic resin B having a negative intrinsic birefringence value. These resins were dried in advance under nitrogen purge to reduce the water content.

[0247] A film forming apparatus ("LABO PLASTOMILI" manufactured by Toyo Seiki Co., Ltd.) was prepared, which could produce a multilayer film having a layer structure of "thermoplastic resin A layer / thermoplastic resin B layer / thermoplastic resin A layer" by co-extruding thermoplastic resin A and thermoplastic resin B. The above-mentioned norbornene-based resin and styrene-based maleic anhydride copolymer resin were supplied to the film forming apparatus and co-extruded to obtain a multilayer film having a three-layer structure of "norbornene-based resin layer / styrene-maleic anhydride copolymer resin layer / norbornene-based resin layer" (thickness 186 μm).

[0248] Using a wide-open stretching machine, the multilayer film is stretched at a stretching temperature of 120°C and a stretching ratio of 1.65 times along a stretching direction at an angle of 45° to the width direction of the multilayer film to obtain a long strip phase difference film. The obtained phase difference film has a three-layer structure of "norbornene resin layer (thickness is 36μm) / styrene maleic anhydride copolymer resin layer (thickness is 39μm) / norbornene resin layer (thickness is 38μm)". The optical properties (in-plane phase difference, thickness direction phase difference, direction of slow axis, NZ coefficient) of the obtained phase difference film and each layer contained in the phase difference film are measured by the above method. The phase difference film obtained in Comparative Example 2 has two layers of norbornene resin layers as thermoplastic resin A, so the total value of the two layers is recorded in the columns of in-plane phase difference, thickness direction phase difference and NZ coefficient of the resin layer (A) in Table 2 described later.

[0249] The phase difference film and the same long linear polarizer as used in Example 1 were bonded together via an optically isotropic pressure-sensitive adhesive ("CS9621" manufactured by Nitto Denko Corporation) to obtain a long circular polarizer. The bonding was performed in such a way that the width direction of the linear polarizer was parallel to the width direction of the phase difference film. The obtained circular polarizer sequentially comprises a linear polarizer, a norbornene-based resin layer, a styrene maleic anhydride copolymer resin layer, and a norbornene-based resin layer.

[0250] The obtained circularly polarizing plate was evaluated by the above-mentioned method.

[0251] [result]

[0252] The production conditions of the retardation films in the above-mentioned Examples and Comparative Examples are shown in Table 1, and the evaluation results are shown in Table 2. In the following Tables 1 and 2, the meanings of the abbreviations are as follows.

[0253] “COP”: norbornene-based resin.

[0254] "VN": poly(2-vinylnaphthalene).

[0255] “PSt”: styrene-based maleic anhydride copolymer resin.

[0256] "Positive" in the intrinsic birefringence value column: the intrinsic birefringence value is positive.

[0257] "Negative" in the Intrinsic Birefringence Value column: The intrinsic birefringence value is negative.

[0258] “Stretching angle”: the angle between the stretching direction and the width direction of the multilayer film.

[0259] “Orientation angle θ”: An angle formed between the slow axis and the width direction of the retardation film.

[0260] 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 of "A" to "E". The reason for the different judgment standards is as follows.

[0261] That is, the brightness of the reflected light in the front direction is quite low compared to the oblique direction. Therefore, if strong coloration is not produced, the observer cannot recognize the coloration. Therefore, two levels are used to judge whether the coloration can be visually recognized.

[0262] On the other hand, the brightness of reflected light in an oblique direction is high. Therefore, even if the coloring is very weak, the observer can easily recognize the coloring. Therefore, a detailed evaluation of quality is adopted with 5 levels.

[0263] [Table 1]

[0264] [Table 1. Manufacturing conditions of phase difference film]

[0265] Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Resin layer (A) Resin A COP COP COP COP COP COP Intrinsic birefringence just just just just just just TgA[℃] 126℃ 126℃ 126℃ 126℃ 126℃ 136℃ Thickness [μm] 100 110 120 130 125 59 / 63 Resin layer (B) Resin B VN VN VN VN VN Psf Intrinsic birefringence burden burden burden burden burden burden TgB[℃] 142℃ 142℃ 142℃ 142℃ 142℃ 130℃ Thickness [μm] 12 13 14 15 14.5 64 First stretching process Stretching temperature [℃] 140 140 140 140 128 120 Stretching ratio [times] 1.10 1.15 1.20 1.25 1.15 1.65 Stretch angle [°] 135 135 135 135 135 45 Second stretching process Stretching temperature [℃] 128 128 128 128 128 - Stretching ratio [times] 1.5 1.5 1.5 1.5 1.5 - Stretch angle [°] 45 45 45 45 45 -

[0266] [Table 2]

[0267] [Table 2. Results of Examples and Comparative Examples]

[0268]

[0269] [analyze]

[0270] In Examples 1 to 4, in the first stretching step, stretching is performed at a temperature sufficiently higher than the glass transition temperature TgA of the thermoplastic resin A. Therefore, the orientation of the polymer molecules contained in the resin layer (A) is slightly performed in the first stretching step, and is greatly performed in the second stretching step. Therefore, the resin layer (A) of the phase difference film has high uniaxiality and has a slow axis parallel to the stretching direction in the second stretching step.

[0271] On the other hand, in the resin layer (B) containing a thermoplastic resin B having a glass transition temperature TgB higher than the glass transition temperature TgA of the thermoplastic resin A, the orientation of the polymer molecules contained therein is greatly carried out in both the first stretching process and the second stretching process. Therefore, the resin layer (B) possessed by the phase difference film has high biaxiality. In addition, in Examples 1 to 4, since the second stretching process is stretched at a larger stretching ratio than the first stretching process, the resin layer (B) possessed by the phase difference film has a slow axis in a direction perpendicular to the stretching direction in the second stretching process.

[0272] As shown in Table 2, the phase difference film having the resin layer (A) and the resin layer (B) satisfies the formula (1) to (3) as a whole. Therefore, the circular polarizing plate having the phase difference film 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 polarizing plate.

[0273] Description of Reference Numerals

[0274] 10: Reflective surface

[0275] 11: Normal direction of the reflecting surface

[0276] 12: Reference direction

[0277] 20: Observation direction

[0278] Azimuth

[0279] 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 the first step, a multilayer film having a resin layer (A) and a resin layer (B) is prepared, wherein the resin layer (A) is formed of a thermoplastic resin A having a positive intrinsic birefringence value, and the resin layer (B) is formed of a thermoplastic resin B having a negative intrinsic birefringence value; as well as In the second step, the multilayer film is stretched twice or more to obtain the phase difference film having the resin layer (A) and the resin layer (B), wherein the resin layer (A) has a slow axis, and the resin layer (B) has a slow axis substantially perpendicular to the slow axis of the resin layer (A). The NZ coefficient of the resin layer (A) after the second step is taken as NZ A The NZ coefficient of the resin layer (B) after the second step is taken as NZ B When the NZ A and the NZ B and "NZ A +NZ B ” is greater than or equal to 0.15 and less than or equal to 0.8, The second process comprises: A first stretching step of stretching the multilayer film at a stretching temperature Ts1; and In a second stretching step, the multilayer film is stretched at a stretching temperature Ts2 different from the stretching temperature Ts1, The absolute value of the difference between the glass transition temperature TgA of the thermoplastic resin A and the glass transition temperature TgB of the thermoplastic resin B |TgA-TgB| is 5° C. or more; 100nm≤Re T (550)≤180nm (1) Re T (450)<Re T (550)<Re T (650) (2) 0.0<NZ T <1.0 (3) Among them, 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 absolute value of the difference between the stretching temperature Ts1 and the stretching temperature Ts2 |Ts1-Ts2| is 5°C or more.

3. The method for producing a phase difference film according to claim 1 or 2, wherein: The stretching direction in the first stretching step is substantially perpendicular to the stretching direction in the second stretching step.

4. The method for producing a phase difference film according to claim 1 or 2, wherein: The phase difference film satisfies the following formula (4): {Re Q (450) / Re Q (550)}-{Re H (450) / Re H (550)}>0.08 (4) Among them, Re H (450) represents the in-plane phase difference of the high phase difference layer at a wavelength of 450 nm. Re H (550) represents the in-plane phase difference of the high phase difference layer at a wavelength of 550 nm, Re Q (450) represents the in-plane phase difference of the low phase difference layer at a wavelength of 450 nm. Re Q (550) represents the in-plane phase difference of the low phase difference layer at a wavelength of 550 nm, The high retardation layer refers to a layer having a large in-plane retardation at a wavelength of 550 nm, among the resin layer (A) and the resin layer (B) included in the retardation film. The low retardation layer refers to a layer having a small in-plane retardation at a wavelength of 550 nm, among the resin layer (A) and the resin layer (B) included in the retardation film.

5. The method for producing a phase difference film according to claim 1 or 2, wherein: At a wavelength of 550 nm, the resin layer (A) included in the retardation film has a larger in-plane retardation than the resin layer (B) included in the retardation film, The glass transition temperature TgA of the thermoplastic resin A is lower than the glass transition temperature TgB of the thermoplastic resin B.

6. The method for producing a phase difference film according to claim 1 or 2, wherein: At a wavelength of 550 nm, the resin layer (B) included in the retardation film has a larger in-plane retardation than the resin layer (A) included in the retardation film, The glass transition temperature TgB of the thermoplastic resin B is lower than the glass transition temperature TgA of the thermoplastic resin A.

7. The method for producing a phase difference film according to claim 1 or 2, wherein: The NZ A It is 1.00 or more and 1.30 or less.

8. The method for producing a phase difference film according to claim 1 or 2, wherein: The NZ B It is greater than -2.0 and less than 0.

0.

9. The method for producing a phase difference film according to claim 1 or 2, wherein: The NZ A is 1.00 or more and 1.30 or less, the NZ B It is greater than -2.0 and less than 0.

0. 10 . A retardation film produced by the production method according to claim 1 . 11 . A circular polarizing plate comprising a linear polarizer and the phase difference film according to claim 10 .

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