WO2024004601A1 - Method for producing phase difference film, and method for producing circularly polarizing plate - Google Patents

Abstract

Provided is a method for producing a phase difference film satisfying specific optical properties, the production method comprising: a first step for preparing a first film that has a resin layer (P1) formed from a thermoplastic resin P having a positive intrinsic birefringence value; a second step for stretching the first film at least one time to produce a second film having a resin layer (P2) that is a layer obtained as the result of the stretching of the resin layer (P1); a third step for laminating a resin layer (N1) formed from a thermoplastic resin N having a negative intrinsic birefringence value on the second film to produce a third film; and a fourth step for stretching the third film at least one time to produce the phase difference film having both of a resin layer (P) that is a layer obtained as the result of the stretching of the resin layer (P2) and has a retardation axis (P) and a resin layer (N) that is a layer obtained as the result of the stretching of the resin layer (N1) and has a retardation axis (N) forming an angle of 90°±5° with the retardation axis (P).

Description

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

The present invention relates to a method for manufacturing a retardation film and a method for manufacturing a circularly polarizing plate.

Image display devices such as organic electroluminescent image display devices (hereinafter sometimes referred to as "organic EL image display devices") and liquid crystal image display devices are sometimes provided with a retardation film. Some of such retardation films have a multilayer structure including two or more layers. As a method for producing a retardation film having such a multilayer structure, a method using a co-stretching method is sometimes adopted (see Patent Documents 1 to 4).

Japanese Patent Application Publication No. 2007-199616 (corresponding foreign publication: US Patent Application Publication No. 2009/290103) Japanese Patent Application Publication No. 2009-169086 International Publication No. 2021/085031 JP2022-052074A

Image display devices are sometimes provided with circularly polarizing plates to reduce reflection of external light on the display surface. As such a circularly polarizing plate, a film that is a combination of a linear polarizer and a λ/4 plate is generally used.

In order to suppress coloring of the display surface, a circularly polarizing plate that can reduce reflection of external light in a wide wavelength range is required. Such a circularly polarizing plate can be manufactured using, for example, a broadband λ/4 plate that can function as a λ/4 plate in a wide wavelength range. As this broadband λ/4 plate, a retardation film comprising a combination of a plurality of layers is known, such as a retardation film comprising a combination of a λ/2 plate and a λ/4 plate. A circularly polarizing plate equipped with a retardation film that can function as a broadband λ/4 plate can reduce the reflection of external light in a wide wavelength range in the front direction perpendicular to the display surface, thereby suppressing coloration of the display surface. can.

However, in an inclined direction that is neither parallel nor perpendicular to the display surface, the phase difference value deviates from the ideal value, and the optical axes of each layer become deviated, resulting in the interference of external light over a wide wavelength range. It may not be possible to reduce reflections. Therefore, in order to realize a circularly polarizing plate that can suppress coloring due to reflection of external light in the tilt direction, the retardation film is required to have an NZ coefficient in a specific range of greater than 0.0 and less than 1.0. It will be done.

The layers included in the retardation film that meet the above requirements usually differ in some or all of their optical properties, such as the direction of the slow axis, in-plane retardation, and NZ coefficient. Therefore, conventionally, the above-mentioned retardation film has generally been manufactured by separately manufacturing each layer and then bonding the layers together. However, in such conventional manufacturing methods, each layer is manufactured separately, which tends to increase the number of steps and increase labor and cost. Furthermore, when bonding each layer together, it is required to accurately match the bonding angle, which requires time and effort to adjust the angle, which also tends to increase the effort.
Further, when producing the above-mentioned retardation film by stretching an unstretched multilayer film, it is complicated to adjust stretching conditions such as the temperature of the thermoplastic resin forming each layer and the stretching temperature.

Therefore, a manufacturing method that can easily produce a retardation film that can produce a circularly polarizing plate that can suppress coloring due to reflection of external light both in the front direction and in the tilt direction of the display surface; There is a need for a manufacturing method that can easily manufacture a circularly polarizing plate that can suppress coloring due to reflection of external light in both directions.

The inventors of the present invention have made extensive studies to solve the above problems. As a result, a first film including a resin layer (P1) formed of a thermoplastic resin P having a positive intrinsic birefringence value is prepared, the first film is stretched at least once, and the resin layer (P1) is stretched at least once. obtaining a second film comprising a resin layer (P2) which is a stretched layer of P1); ) was found to be able to be solved by a manufacturing method that includes laminating a third film to obtain a third film and stretching the third film at least once, and completed the present invention.
That is, the present invention provides the following.

[1] A method for producing a retardation film that satisfies the following formula (1), the following formula (2), and the following formula (3),
The manufacturing method includes:
A first step of preparing a first film comprising a resin layer (P1) formed of a thermoplastic resin P having a positive intrinsic birefringence value;
a second step of stretching the first film at least once to obtain a second film comprising a resin layer (P2) that is a stretched layer of the resin layer (P1);
a third step of laminating a resin layer (N1) formed of a thermoplastic resin N having a negative intrinsic birefringence value on the second film to obtain a third film;
The third film was stretched at least once, and the resin layer (P), which is a layer obtained by stretching the resin layer (P2) and has a slow axis (P), and the resin layer (N1) were stretched. and a resin layer (N) having a slow axis (N) forming an angle within a range of 90° ± 5° with respect to the slow axis (P). and,
A method for producing a retardation film, including:
100nm≦Re _T (550)≦180nm (1)
Re _T (450)<Re _T (550)<Re _T (650) (2)
0.0< _NZT <1.0 (3)
(however,
Re _T (450) represents the in-plane retardation of the retardation film at a wavelength of 450 nm,
Re _T (550) represents the in-plane retardation of the retardation film at a wavelength of 550 nm,
Re _T (650) represents the in-plane retardation of the retardation film at a wavelength of 650 nm,
NZ _T represents the NZ coefficient of the retardation film. )
[2] The method for producing a retardation film according to [1], wherein the resin layer (P2) included in the second film has an in-plane retardation of 20 nm or more.
[3] The method for producing a retardation film according to [1] or [2], wherein the thickness direction retardation of the resin layer (N1) in the third step is -30 nm or less.
[4] The stretching of the first film in the second step is stretching in one direction, and the stretching of the third film in the fourth step is in the stretching direction of the first film in the second step. The method for producing a retardation film according to any one of [1] to [3], which includes stretching in a direction within a range of 0° ± 5°.
[5] The method for producing a retardation film according to any one of [1] to [4], wherein the retardation film satisfies the following formula (4).
{Re _N (450)/Re _N (550)}-{Re _P (450)/Re _P (550)}>0.08 (4)
(however,
Re _N (450) represents the in-plane retardation of the resin layer (N) at a wavelength of 450 nm,
Re _N (550) represents the in-plane retardation of the resin layer (N) at a wavelength of 550 nm,
Re _P (450) represents the in-plane retardation of the resin layer (P) at a wavelength of 450 nm,
Re _P (550) represents the in-plane retardation of the resin layer (P) at a wavelength of 550 nm. )
[6] The method for producing a retardation film according to any one of [1] to [5], which satisfies the following formula (5).
Re _P (550)>Re _N (550) (5)
(however,
Re _N (550) represents the in-plane retardation of the resin layer (N) at a wavelength of 550 nm,
Re _P (550) represents the in-plane retardation of the resin layer (P) at a wavelength of 550 nm. )
[7] A method for manufacturing a circularly polarizing plate including a linear polarizer and a retardation film, comprising:
A fifth step of producing the retardation film using the method for producing a retardation film according to any one of [1] to [6];
a sixth step of laminating the retardation film and the linear polarizer;
A method for manufacturing a circularly polarizing plate, including:

This disclosure also provides:
[8] A retardation film produced by the production method according to any one of [1] to [6].

According to the present invention, a manufacturing method that can easily produce a retardation film that can produce a circularly polarizing plate that can suppress coloring due to reflection of external light both in the front direction and in the inclined direction of the display surface; It is possible to provide a manufacturing method that can easily manufacture a circularly polarizing plate that can suppress coloration due to reflection of external light both in the front direction and in the inclined direction.

FIG. 1 is a perspective view schematically showing an evaluation model set when calculating color space coordinates in simulations in Examples and Comparative Examples.

Hereinafter, the present invention will be described in detail by showing embodiments and examples. However, the present invention is not limited to the embodiments and examples shown below, and may be implemented with arbitrary changes within the scope of the claims of the present invention and equivalents thereof. The components of the embodiments shown below can be combined as appropriate. In addition, in the figures, the same components are given the same reference numerals, and their explanations may be omitted.

In the following description, unless otherwise specified, the in-plane phase difference Re indicates a value expressed by Re=(nx-ny)×d. The thickness direction retardation Rth is a value expressed by Rth={(nx+ny)/2−nz}×d, unless otherwise specified. Further, the NZ coefficient NZ represents a value expressed as NZ=Rth/Re+0.5, unless otherwise specified, and can therefore be expressed as NZ=(nx-nz)/(nx-ny). nx represents the refractive index in the direction perpendicular to the thickness direction (in-plane direction) giving the maximum refractive index (slow axis direction), and ny represents the in-plane direction in the nx direction. It represents the refractive index in the orthogonal direction, nz represents the refractive index in the thickness direction, and d represents the thickness. The measurement wavelength is 550 nm unless otherwise specified. The in-plane retardation, the thickness direction retardation, and the NZ coefficient can be measured using a retardation meter (“AxoScan” manufactured by Axometrics).

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

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 is the angle when the layer is viewed from the thickness direction. represents.

In the following description, the front direction of a certain surface means the normal direction of the surface unless otherwise specified, and specifically refers to the direction of the polar angle of 0° and the azimuth angle of 0° of the surface.

In the following explanation, the inclination direction of a certain surface means a direction that is neither parallel nor perpendicular to the surface unless otherwise specified, and specifically, the range in which the polar angle of the surface is greater than 0° and less than 90°. Point in the direction of

In the following description, the terms "parallel", "perpendicular" and "orthogonal" to the elements include errors within a range that does not impair the effects of the present invention, for example within a range of ±5°, unless otherwise specified. It's okay to stay.

In the following description, a "long" film refers to a film having a length of 5 times or more, preferably 10 times or more, of the width, and specifically a roll A film that is long enough to be rolled up into a shape for storage or transportation. The upper limit of the length of the long film is not particularly limited, and may be, for example, 100,000 times or less the width.

In the following description, the longitudinal direction of a long film is usually parallel to the flow direction of the film on the production line. Further, the width direction of a long film is usually perpendicular to the thickness direction and perpendicular to the longitudinal direction.

In the following explanation, "polarizing plate", "circularly polarizing plate", "plate", "λ/2 plate", and "λ/4 plate" refer not only to rigid members, but also to e.g. It also includes flexible members such as resin films.

In the following explanation, "polymer having a positive intrinsic birefringence value" and "resin having a positive intrinsic birefringence value" mean that the refractive index in the stretching direction is lower than the refractive index in the direction perpendicular to the stretching direction. and "a resin whose refractive index in the stretching direction is larger than the refractive index in the direction perpendicular to the stretching direction" respectively. In addition, "polymer having a negative intrinsic birefringence value" and "resin having a negative intrinsic birefringence value" refer to "a polymer whose refractive index in the stretching direction is smaller than the refractive index in the direction orthogonal to the stretching direction". "coalescence" and "resin whose refractive index in the stretching direction is smaller than the refractive index in the direction orthogonal to the stretching direction" respectively. The intrinsic birefringence value can be calculated from the dielectric constant distribution.

In the following description, unless otherwise specified, adhesives are not only adhesives in the narrow sense (adhesives with a shear storage modulus of 1 MPa to 500 MPa at 23°C after energy ray irradiation or heat treatment); Also included are adhesives having a shear storage modulus of less than 1 MPa at 23°C.

[1. Manufactured retardation film]
A retardation film manufactured by the manufacturing method according to an embodiment of the present invention satisfies the following formula (1), the following formula (2), and the following formula (3). By combining this retardation film with a linear polarizer, it is possible to obtain a circularly polarizing plate that can suppress coloring due to reflection of external light both in the front direction and in the tilt direction of the display surface.

100nm≦Re _T (550)≦180nm (1)
Re _T (450)<Re _T (550)<Re _T (650) (2)
0.0< _NZT <1.0 (3)
(however,
Re _T (450) represents the in-plane retardation of the retardation film at a wavelength of 450 nm,
Re _T (550) represents the in-plane retardation of the retardation film at a wavelength of 550 nm,
Re _T (650) represents the in-plane retardation of the retardation film at a wavelength of 650 nm,
NZ _T represents the NZ coefficient of the retardation film. )

The above formula (1) will be explained in detail. The in-plane retardation Re _T (550) of the retardation film at a wavelength of 550 nm is usually 100 nm or more, preferably 115 nm or more, particularly preferably 125 nm or more, and usually 180 nm or less, preferably 160 nm or less, particularly preferably 150 nm. It is as follows. When having an in-plane retardation Re _T (550) in such a range, the retardation film can function as a λ/4 plate. Therefore, by combining the retardation film with a linear polarizer, it is possible to obtain a circularly polarizing plate that can suppress reflection of external light.

The in-plane retardation Re _T (550) that satisfies formula (1) is, for example, the in-plane retardation of each layer such as the resin layer (P) and the resin layer (N) included in the retardation film, and the in-plane retardation of each layer. This can be obtained by appropriately adjusting the direction of the slow axis.

The above formula (2) will be explained in detail. The in-plane retardations Re _T (450), Re _T (550), and Re _T (650) of the retardation film at wavelengths of 450 nm, 550 nm, and 650 nm are as follows: Re _T (450)<Re _T (550)<Re _T (650) ) is satisfied. The in-plane retardation of a retardation film that satisfies this formula (2) usually exhibits reverse wavelength dispersion. Specifically, the retardation film generally has a larger in-plane retardation as the measurement wavelength is longer. Therefore, this retardation film can function as a broadband λ/4 plate that can uniformly convert the polarization state of light that passes through the retardation film in a wide wavelength range. Therefore, by combining the retardation film with a linear polarizer, it is possible to obtain a circularly polarizing plate that can suppress coloring due to reflection of external light.

The in-plane retardations Re _T (450), Re _T (550), and Re _T (650) that satisfy formula (2) are, for example, the resin layer (P) and resin layer (N) included in the retardation film. This can be obtained by appropriately adjusting the in-plane retardation of each layer and the direction of the slow axis of each layer.

The above formula (3) will be explained in detail. The NZ coefficient NZ _T of the retardation film is usually larger than 0.0, preferably larger than 0.2, particularly preferably larger than 0.3, and usually smaller than 1.0, preferably smaller than 0.8, especially Preferably it is less than 0.7. When the retardation film has the NZ coefficient NZ _T in the above range, the retardation film has appropriately adjusted birefringence in both the in-plane direction and the thickness direction. Therefore, a circularly polarizing plate obtained by combining the retardation film with a linear polarizer can suppress coloring due to reflection of external light both in the front direction and in the inclined direction of the display surface.

The NZ coefficient NZ _T of the retardation film is calculated using the in-plane retardation Re _T (550) and the thickness direction retardation Rth _T (550) of the retardation film at a wavelength of 550 nm, unless otherwise specified _. Rth _T (550)/Re _T (550)}+0.5''. The NZ coefficient NZ _T that satisfies formula (3) can be obtained, for example, by appropriately adjusting the NZ coefficient of each layer such as the resin layer (P) and the resin layer (N) included in the retardation film.

In the manufacturing method according to the present embodiment, a retardation film satisfying the above-mentioned formulas (1) to (3) is formed into a resin layer (P) containing a thermoplastic resin P and a resin layer (P) containing a thermoplastic resin N. N) is manufactured as a retardation film comprising the following in combination.

Here, the thermoplastic resin P has a positive intrinsic birefringence value, and the thermoplastic resin N has a negative intrinsic birefringence value. When the manufacturing method described below is performed using a combination of these thermoplastic resins P and thermoplastic resin N, a retardation film that satisfies the above-mentioned formulas (1) to (3) can be easily manufactured.

The thermoplastic resin P having a positive intrinsic birefringence value usually contains a polymer having a positive intrinsic birefringence value. Examples of this polymer include polyolefins such as polyethylene and polypropylene; polyesters such as polyethylene terephthalate and polybutylene terephthalate; polyarylene sulfides such as polyphenylene sulfide; polyvinyl alcohol; polycarbonate; polyarylate; cellulose ester; polyether sulfone; polysulfone; Polyarylsulfone; polyvinyl chloride; alicyclic structure-containing polymer; rod-shaped liquid crystal polymer; and the like. One type of these polymers may be used alone, or two or more types may be used in combination in any ratio. Among these, alicyclic structure-containing polymers, cellulose esters, and polycarbonates are preferred, and alicyclic structure-containing polymers are particularly preferred.

The alicyclic structure-containing polymer is a polymer containing an alicyclic structure in its repeating units, such as a cyclic olefin polymer and its hydrogenated product, and is usually an amorphous polymer. As the alicyclic structure-containing polymer, both a polymer containing an alicyclic structure in the main chain and a polymer containing an alicyclic structure in the side chain can be used. Examples of the alicyclic structure include a cycloalkane structure and a cycloalkene structure, and from the viewpoint of thermal stability, a cycloalkane structure is preferable. 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, and preferably 30 or less, more preferably 20 or less, Particularly preferably, the number is 15 or less.

In the alicyclic structure-containing polymer, the proportion of repeating units containing an alicyclic structure is preferably 50% by weight or more, more preferably 70% by weight or more, particularly preferably 90% by weight or more. When the proportion of repeating units containing an alicyclic structure is within the above range, a retardation film with excellent heat resistance can be obtained.

Examples of alicyclic structure-containing polymers include (1) norbornene polymers, (2) monocyclic olefin polymers, (3) cyclic conjugated diene polymers, and (4) vinyl alicyclic hydrocarbon polymers. Examples include coalescence, hydrogenated products thereof, and the like. Among these, cyclic olefin polymers and norbornene polymers are preferred, and norbornene 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 therewith, and hydrides; addition polymers of monomers containing a norbornene structure, addition copolymers of monomers containing a norbornene structure and other monomers copolymerizable therewith, and the like. Among these, from the viewpoint of transparency, hydrogenated ring-opening polymers of monomers containing a norbornene structure are particularly preferred. The alicyclic structure-containing polymer may be selected from, for example, the polymers disclosed in JP-A No. 2002-321302.

Examples of cellulose esters include lower fatty acid esters of cellulose (eg, cellulose acetate, cellulose acetate butyrate, and cellulose acetate propionate). Lower fatty acid means a fatty acid having 6 or less carbon atoms per molecule. Cellulose acetate may include triacetylcellulose (TAC) and cellulose diacetate (DAC).

The total degree of acyl group substitution of the 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 groups can be measured according to ASTM D817-91. Further, the weight average degree of polymerization of the cellulose ester is preferably 350 or more and 800 or less, more preferably 370 or more and 600 or less.

Polycarbonate usually has repeating units containing carbonate bonds (-OC(=O)-O-). Examples of the polycarbonate include a polymer 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 number of structural units derived from dihydroxy compounds contained in the polycarbonate may be one, or two or more.

The weight average molecular weight (Mw) of the polymer contained in the thermoplastic resin P is preferably 10,000 or more, more preferably 15,000 or more, particularly preferably 20,000 or more, and preferably 100,000 or less, It is more preferably 80,000 or less, particularly preferably 50,000 or less. When the weight average molecular weight is within such a range, the mechanical strength and moldability of the resin layer (P) are highly balanced. The above weight average molecular weight is a weight average molecular weight in terms of polyisoprene or polystyrene measured by gel permeation chromatography (GPC) using cyclohexane as a solvent. However, if the sample does not dissolve in cyclohexane, toluene may be used as the GPC solvent.

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

The thermoplastic resin P may further contain arbitrary components in combination with the above polymer. Examples of optional components include stabilizers such as antioxidants, heat stabilizers, light stabilizers, weathering stabilizers, ultraviolet absorbers, and near-infrared absorbers; plasticizers; and the like. One type of these components may be used alone, or two or more types may be used in combination in any ratio.

The thermoplastic resin N having a negative intrinsic birefringence value usually includes a polymer having a negative intrinsic birefringence value. Examples of this polymer include aromatic vinyl compound-based polymers, including homopolymers of aromatic vinyl compound monomers and/or copolymers of aromatic vinyl compound monomers and arbitrary monomers; polyacrylonitrile polymers; Polymers; polymethyl methacrylate polymers; or multi-component copolymers thereof; and the like. Furthermore, examples of arbitrary monomers that can be copolymerized with the aromatic vinyl compound monomer include acrylonitrile, maleic anhydride, methyl methacrylate, and butadiene. Further, these polymers may be used alone or in combination of two or more in any ratio.

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

Among polymers having a negative intrinsic birefringence value, from the group consisting of styrene polymers, polymers of styrene derivatives, vinylnaphthalene polymers (preferably poly(2-vinylnaphthalene)), and polymers of vinylnaphthalene derivatives. One or more selected polymers are preferred, vinylnaphthalene polymers are more preferred, and poly(2-vinylnaphthalene) is particularly preferred.

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

The thermoplastic resin N may further contain arbitrary components in combination with the above polymer. Examples of the optional component include the same examples as the optional components that the thermoplastic resin P may contain. One type of arbitrary components may be used alone, or two or more types may be used in combination in any ratio.

As the thermoplastic resin N and the thermoplastic resin P, resins each having an arbitrary glass transition temperature can be used.
In the fourth step described below, from the viewpoint of smoothly stretching the third film comprising a layer of thermoplastic resin N and a layer of thermoplastic resin P, the glass transition temperature TgN of thermoplastic resin N and the thermoplastic resin P The absolute value of the difference from the glass transition temperature TgP |TgN-TgP| is preferably 40°C or less, more preferably 30°C or less, even more preferably 25°C or less, even more preferably less than 10°C, particularly preferably less than 5°C. The lower limit is usually 0°C or higher.

The resin layer (N) included in the retardation film has a slow axis (N). Further, the resin layer (P) included in the retardation film has a slow axis (P) substantially perpendicular to the slow axis (N) of the resin layer (N). The slow axis (P) is "substantially perpendicular" to the slow axis (N) when the angle between the slow axis (N) and the slow axis (P) is in a specific range close to 90°. represents something. Specifically, the angle formed by the slow axis (N) with respect to the slow axis (P) is usually within the range of 90° ± 5°, usually 85° or more, preferably 87° or more, and more preferably is 88° or more, particularly preferably 89° or more, and usually 95° or less, preferably 93° or less, more preferably 92° or less, particularly preferably 91° or less. In the manufacturing method described below, a film having a multilayer structure comprising a combination of a resin layer (P) and a resin layer (N) having slow axes in the above relationship satisfies the above formulas (1) to (3). A retardation film can be obtained.

In particular, in a long retardation film, one of the slow axis (P) of the resin layer (P) and the slow axis (N) of the resin layer (N) is 45° with respect to the width direction of the retardation film. Preferably, the angle is within a certain range close to . Specifically, the angle is preferably 40° or more, more preferably 42° or more, even more preferably 43° or more, particularly preferably 44° or more, and preferably 50° or less, more preferably 48°. The angle is more preferably 47° or less, particularly preferably 46° or less. Furthermore, in this case, the other of the slow axis (P) and the slow axis (N) preferably forms an angle in a specific range close to 135° with respect to the width direction of the retardation film. Specifically, the angle is preferably 130° or more, more preferably 132° or more, even more preferably 133° or more, particularly preferably 134° or more, and preferably 140° or less, more preferably 138°. The angle is more preferably 137° or less, particularly preferably 136° or less. A typical long linear polarizer has an absorption axis that is parallel or perpendicular to the width direction of the linear polarizer. A long retardation film comprising a resin layer (P) and a resin layer (N) having slow axes in a direction forming an angle in the above range with respect to the width direction is a simple method that is similar to the general linear polarizer described above. A circularly polarizing plate can be obtained by laminating the retardation film and the linear polarizer in parallel with each other in the width direction. Therefore, since the retardation film and the linear polarizer can be bonded together in a roll-to-roll manner, the circularly polarizing plate can be manufactured particularly easily.

The NZ coefficient NZ _P of the resin layer (P) and the NZ coefficient NZ _N of the resin layer (N) should be appropriately set so that the NZ coefficient NZ _T of the retardation film is within the range of formula (3). is preferred. The NZ coefficient NZ _P of the resin layer (P) is a value expressed by "NZ _P = (nx _P - nz _P )/(nx _P - ny _P )", and therefore "NZ _P = (Rth _P /Re _P )+0.5". _nxP represents the refractive index in the in-plane direction of the resin layer (P) and the direction that provides the maximum refractive index. ny _P represents the refractive index in the in-plane direction of the resin layer (P) and perpendicular to the direction giving nx _P. nz _P represents the refractive index in the thickness direction of the resin layer (P). Re _P represents the in-plane retardation of the resin layer (P), and is therefore expressed as “Re _P =(nx _P −ny _P )×d _P ”. Rth _P represents the retardation in the thickness direction of the resin layer (P), and is therefore expressed as "Rth _P = {(nx _P +ny _P )/2-nz _P }×d _P ". _dP represents the thickness of the resin layer (P). Further, the NZ coefficient NZ _N of the resin layer (N) is a value expressed by "NZ _N = (nx _N - nz _N )/(nx _N - ny _N )", and therefore, "NZ _N = (Rth _N /Re _N )+0.5". _nxN represents the refractive index in the in-plane direction of the resin layer (N) in the direction that provides the maximum refractive index. ny _N represents the refractive index in the in-plane direction of the resin layer (N) and perpendicular to the direction giving nx _N. nz _N represents the refractive index in the thickness direction of the resin layer (N). Re _N represents the in-plane retardation of the resin layer (N), and is therefore expressed as “Re _N =(nx _N −ny _N )×d _N ”. Rth _N represents the retardation in the thickness direction of the resin layer (N), and is therefore expressed as “Rth _N = {(nx _N +ny _N )/2−nz _N }×d _N ”. _dN represents the thickness of the resin layer (N).

The NZ coefficient NZ _P of the resin layer (P) is preferably 1.00 or more. Therefore, it is preferable that the refractive indices ny _P and nz _P of the resin layer (P) satisfy the relationship ny _P ≧nz _P. Further, the NZ coefficient NZ _N of the resin layer (N) is preferably less than 0.0. Therefore, it is preferable that the refractive indices nx _N and nz _N of the resin layer (N) satisfy the relationship nz _N >nx _N. According to such a combination of resin layer (P) and resin layer (N), the NZ coefficient NZ _T of the entire retardation film can be easily adjusted within the range of formula (3).

More specifically, the NZ coefficient NZ _P of the resin layer (P) is preferably 1.00 or more, more preferably 1.05 or more, and preferably 1.30 or less, more preferably 1.20 or less. . As described above, the refractive indices nx _P , ny _P and nz _P of the resin layer (P) having the NZ coefficient NZ _P of 1.00 or more may have the relationship of nx _P >ny _P ≧nz _P. Therefore, the resin layer (P) can function as a positive A plate or a negative B plate.

Further, the NZ coefficient NZ _N of the resin layer (N) is preferably -2.0 or more, more preferably -1.5 or more, preferably less than 0.0, more preferably -0.2 or less, especially It is preferably -0.4 or less. As described above, the refractive indices nx _N , ny _N and nz _N of the resin layer (N) having an NZ coefficient of less than 0.0 may have a relationship of nz _N > nx _N > ny _N. Therefore, the resin layer (N) may be a layer having different refractive indexes nx _N , ny _N and nz _N in three directions (ie, a biaxial layer). Further, the resin layer (N) can function as a positive B plate.

The sum NZ P +NZ _{N of the NZ coefficient NZ P of the resin layer (P) and the NZ coefficient NZ N of the resin} layer (N) preferably falls within a specific range. Specifically, the sum "NZ _P + NZ _N " is preferably -0.3 or more, more preferably 0.0 or more, particularly preferably 0.10 or more, and preferably 0.8 or less, more preferably It is 0.75 or less, particularly preferably 0.65 or less. When the sum "NZ _P + NZ _N " is within the above range, a retardation film capable of obtaining a circularly polarizing plate that can effectively suppress coloration due to reflection of external light both in the front direction and in the inclined direction of the display surface. can be realized.

It is preferable that the retardation film satisfies the following formula (4).
{Re _N (450)/Re _N (550)}-{Re _P (450)/Re _P (550)}>0.08 (4)
(however,
Re _N (450) represents the in-plane retardation of the resin layer (N) at a wavelength of 450 nm,
Re _N (550) represents the in-plane retardation of the resin layer (N) at a wavelength of 550 nm,
Re _P (450) represents the in-plane retardation of the resin layer (P) at a wavelength of 450 nm,
Re _P (550) represents the in-plane retardation of the resin layer (P) at a wavelength of 550 nm. )

In formula (4), "Re _N (450)/Re _N (550)" represents the wavelength dispersion of the resin layer (N). Moreover, in Formula (4), "Re _P (450)/Re _P (550)" represents the wavelength dispersion of the resin layer (P). Therefore, formula (4) represents that there is a difference in wavelength dispersion of in-plane retardation between the resin layer (N) and the resin layer (P) included in the retardation film. More specifically, it means that the in-plane retardation of the resin layer (N) has greater wavelength dispersion than the in-plane retardation of the resin layer (P). In detail, the parameter “{Re _N (450)/Re _N (550)}−{Re _P (450)/Re _P (550)}” representing the difference in wavelength dispersion is preferably larger than 0.08. , more preferably greater than 0.09, particularly preferably greater than 0.10, and the upper limit is not particularly limited, preferably less than 2.0, more preferably less than 1.5, particularly preferably 1.2 less than As described above, a retardation film including a resin layer (P) and a resin layer (N) having different in-plane retardation wavelength dispersion properties can easily obtain reverse wavelength dispersion properties in a laminated state.

Further, it is preferable that the retardation film satisfies the following formula (5).
Re _P (550)>Re _N (550) (5)
(however,
Re _N (550) represents the in-plane retardation of the resin layer (N) at a wavelength of 550 nm,
Re _P (550) represents the in-plane retardation of the resin layer (P) at a wavelength of 550 nm. )
When the retardation film satisfies formula (5), the retardation film can easily function in a wide band.

The value of {Re _P (550) - Re _N (550)} is preferably 120 nm or more, more preferably 125 nm or more, particularly preferably 130 nm or more, and preferably 160 nm or less, more preferably 155 nm or less, particularly preferably It is 150 nm or less. Thereby, the retardation film can be made into a λ/4 plate that functions in a wide band.

The retardation film may include any layer other than the resin layer (P) and the resin layer (N), if necessary. Examples of the arbitrary layer include any layer having optical isotropy. This arbitrary layer having optical isotropy usually has an in-plane retardation of 10 nm or less at a wavelength of 550 nm, and includes, for example, a protective film layer for protecting the resin layer (P) and the resin layer (N); (P) and an adhesive layer that adheres each layer such as the resin layer (N); and the like. Further, another example of the arbitrary layer is an arbitrary layer having optical anisotropy. The optical properties of this arbitrary layer having optical anisotropy are not limited as long as the entire retardation film satisfies formulas (1) to (3). To give a specific example, a combination of an arbitrary layer having optical anisotropy and one or both of the resin layer (P) and the resin layer (N) can function as a λ/4 plate or a λ/2 plate. The optical properties of any layer thereof may be set.

The ultraviolet/visible light transmittance of the retardation film is preferably 80% or more, more preferably 85% or more, particularly preferably 90% or more. The ultraviolet/visible light transmittance can be measured in the wavelength range of 400 nm to 700 nm using an ultraviolet/visible spectrometer.

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

The retardation film may be a sheet film or a long film.

There is no particular limit to the thickness of the retardation film. 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, and preferably 200 μm or less, more preferably 150 μm or less, particularly preferably 100 μm. It is as follows.

There is no particular restriction on the thickness of each layer such as the resin layer (P) and the resin layer (N) included in the retardation film. The thicknesses of the resin layer (P) and the resin layer (N) are each independently preferably 0.5 μm or more, more preferably 1 μm or more, and preferably 150 μm or less, more preferably 100 μm or less.

[2. Overview of manufacturing method of retardation film]
In the manufacturing method according to one embodiment of the present invention, the above-mentioned retardation film is
A first step of preparing a first film comprising a resin layer (P1) formed of a thermoplastic resin P having a positive intrinsic birefringence value;
a second step of stretching the first film at least once to obtain a second film comprising a resin layer (P2) that is a stretched layer of the resin layer (P1);
a third step of laminating a resin layer (N1) formed of a thermoplastic resin N having a negative intrinsic birefringence value on the second film to obtain a third film;
The third film was stretched at least once, and the resin layer (P), which is a layer obtained by stretching the resin layer (P2) and has a slow axis (P), and the resin layer (N1) were stretched. and a resin layer (N) having a slow axis (N) forming an angle within a range of 90° ± 5° with respect to the slow axis (P). and,
Manufactured by a manufacturing method including.

In the method for manufacturing a retardation film of this embodiment, a third film having a multilayer structure is manufactured and stretched. Therefore, compared to the case where each layer of the retardation film is manufactured separately and laminated by laminating them together, the method for manufacturing the retardation film of this embodiment requires less effort. Further, there is no need to adjust the angle when bonding each layer.
Furthermore, in the method for manufacturing a retardation film of this embodiment, the first film is stretched in the second step. As a result, compared to the case where a retardation film is obtained by stretching a multilayer film without performing the second step, stretching conditions such as the temperature of the thermoplastic resin forming each layer of the retardation film and the stretching temperature can be adjusted. , you can set fewer limits.

[3. First step: Preparation of first film]
In the first step, a first film including a resin layer (P1) made of a thermoplastic resin P having a positive intrinsic birefringence value is prepared. The thermoplastic resin P is as described in the section of the retardation film.

The resin layer (P1) included in the first film preferably does not have large optical anisotropy. Therefore, the retardation of the resin layer (P1) is preferably small. To give a specific range, the in-plane retardation of the resin layer (P1) at 550 nm is preferably 0 nm to 20 nm, more preferably 0 nm to 10 nm, particularly preferably 0 nm to 5 nm. Further, the absolute value of the retardation in the thickness direction of the resin layer (P1) at 550 nm is preferably 0 nm to 20 nm, more preferably 0 nm to 10 nm, particularly preferably 0 nm to 5 nm.

The first film may be a sheet film, but is preferably a long film. By preparing the first film as a long film, it is possible to perform part or all of each process in-line when manufacturing a retardation film, so that manufacturing can be performed simply and efficiently. .

There are no restrictions on the method of manufacturing the first film. The first film can be manufactured by, for example, a melt molding method or a solution casting method. Among these, melt molding is preferred. Among the melt molding methods, extrusion molding, inflation molding, or press molding are preferred, and extrusion molding is particularly preferred. According to these methods, the first film including the resin layer (P1) can be manufactured as a long film.

[4. Second step: Production of second film]
In the second step, the first film is stretched at least once to obtain a second film including a resin layer (P2) that is a layer obtained by stretching the resin layer (P1).

The first film may be stretched once, or twice or more. When the first film is stretched twice or more, it is preferable that the stretching direction is the same in each of the two or more times. In each of these two or more times of stretching, the stretching ratio may be the same or different. In one embodiment, preferably the stretching of the first film is a single stretching.
The stretching ratio of the first film in the second step is preferably 1.05 times or more, more preferably 1.1 times or more, particularly preferably 1.12 times or more, and preferably 2.0 times or more in the stretching direction. It is at most 1.5 times, more preferably at most 1.5 times, particularly preferably at most 1.3 times. Here, when the first film is stretched twice or more in the second step, the stretching ratio of the first film in the second step is a ratio obtained by multiplying the stretching ratios of each stretch.

When the first film is long, the stretching direction in the second step is preferably an oblique direction with respect to the width direction of the first film. Thereby, a long retardation film whose slow axis is in an oblique direction can be obtained.

The stretching direction in the second step preferably forms an angle within a specific range, preferably close to 45°, with respect to the width direction of the long first film. Specifically, the angle is preferably 40° or more, more preferably 42° or more, even more preferably 43° or more, particularly preferably 44° or more, and preferably 50° or less, more preferably 48°. The angle is more preferably 47° or less, particularly preferably 46° or less. Thereby, a retardation film having a slow axis forming an angle in a specific range of approximately 45° with respect to the width direction of the long retardation film can be manufactured.

The stretching temperature in the second step can be selected within an appropriate range depending on the glass transition temperature TgP of the thermoplastic resin P forming the resin layer (P1). For example, the stretching temperature in the second step is preferably TgP-5°C or higher, more preferably TgP-3°C or higher, particularly preferably TgP-1°C or higher, and preferably TgP+20°C or lower, more preferably TgP+15°C. Hereinafter, the temperature is particularly preferably TgP+12°C or lower. Thereby, breakage of the resin layer (P2) obtained by stretching the resin layer (P1) and increase in haze can be effectively suppressed.

By stretching the first film, the resin layer (P1) included in the first film is stretched, and a slow axis in a direction substantially parallel to the stretching direction is developed in the resin layer (P2). Specifically, the angle between the stretching direction in the second step and the slow axis of the resin layer (P2) is usually within the range of 0° ± 5°, usually -5° or more, preferably -3 The angle is at least 1°, more preferably at least -2°, particularly preferably at least -1°, and usually at most 5°, preferably at most 3°, more preferably at most 2°, particularly preferably at most 1°.

The in-plane retardation of the second film at a wavelength of 550 nm is preferably 20 nm or more, more preferably 50 nm or more, particularly preferably 70 nm or more, and preferably 300 nm or less, more preferably 270 nm or less, particularly preferably 250 nm or less. .
The in-plane retardation at a wavelength of 550 nm of the resin layer (P2) included in the second film is preferably 20 nm or more, more preferably 50 nm or more, particularly preferably 70 nm or more, and preferably 300 nm or less, more preferably 270 nm or less, Particularly preferred is 250 nm or less.
Further, the thickness direction retardation of the resin layer (P2) at a wavelength of 550 nm is preferably 10 nm or more, more preferably 30 nm or more, particularly preferably 40 nm or more, and preferably 200 nm or less, more preferably 180 nm or less, particularly preferably It is 170 nm or less.
The retardation between the second film and the resin layer (P2) can be adjusted by adjusting the stretching ratio in the second step.

[5. Third step: Production of third film]
In the third step, a resin layer (N1) formed of a thermoplastic resin N having a negative intrinsic birefringence value is laminated on the second film to obtain a third film. The resin layer (N1) may be formed by any method, including a melt molding method, a solution casting method, and a coating method in which a liquid composition containing materials for other layers is applied onto a certain layer. It will be done.

Among these, preferred is a method in which a liquid composition containing the thermoplastic resin N is applied onto the resin layer (P2) of the second film, and the applied liquid composition is dried as necessary. This method will be explained below.

A liquid composition containing thermoplastic resin N is applied onto the resin layer (P2) of the second film. The liquid composition may include thermoplastic resin N and a solvent. A liquid composition containing a thermoplastic resin and a solvent is also referred to as a resin solution. As the solvent, a solvent capable of dissolving or dispersing the thermoplastic resin N is preferable, and a solvent capable of dissolving the thermoplastic resin N is particularly preferable. Moreover, one type of solvent may be used alone, or two or more types may be used in combination in any ratio. The concentration of the thermoplastic resin N in the liquid composition is preferably adjusted so that the viscosity of the liquid composition is within a range suitable for coating, and may be, for example, 1% by weight to 50% by weight.

There are no restrictions on the method of applying the liquid composition. Examples of coating methods include curtain coating, extrusion coating, roll coating, spin coating, dip coating, bar coating, spray coating, slide coating, print coating, gravure coating, and die coating. , and gap coating method.

By applying the liquid composition containing the thermoplastic resin N, a layer of the liquid composition is formed on the resin layer (P2). Therefore, by drying the liquid composition layer and removing the solvent as necessary, the resin layer (N1) can be laminated on the resin layer (P2) to obtain a third film. There are no restrictions on the drying method, and for example, drying methods such as natural drying, heat drying, and reduced pressure drying can be used.

From the viewpoint of developing a larger negative thickness direction retardation in the resin layer (N1), a method that can rapidly dry the layer of the liquid composition is preferable, and the drying can be carried out by heating drying, reduced pressure drying, or a combination thereof. It is preferable to do so.

The reason why the negative thickness direction retardation appears in the resin layer (N1) is that when drying the layer of the liquid composition containing the thermoplastic resin N, the layer of the liquid composition contracts in-plane, and the thermoplastic This is thought to be because the polymer contained in resin N is oriented in the thickness direction. Generally, it is thought that by increasing the drying rate of the liquid composition layer, relaxation of the orientation of the thermoplastic resin N in the resin layer (N1) is suppressed, and a larger negative thickness direction retardation is developed.

The thickness direction retardation of the resin layer (N1) at 550 nm is preferably -30 nm or less, more preferably -40 nm or less, particularly preferably -50 nm or less, and the lower limit is not particularly limited, but for example, -300 nm or more, - It is 250 nm or more, or -200 nm or more.

Since the absolute value of the thickness direction retardation at 550 nm of the resin layer (N1) is thus large, the resin layer (N1) is a stretched layer after stretching the third film in the fourth step described below. Biaxiality can be easily imparted to the resin layer (N).

The thickness direction retardation at 550 nm of the resin layer (N1) can be determined by adjusting the thickness of the resin layer (N1), and when forming the resin layer (N1) by a coating method, it includes the coated thermoplastic resin N. It can be adjusted by appropriately adjusting the drying rate of the layer of the liquid composition.

The in-plane retardation of the resin layer (N1) at 550 nm is preferably 0 nm to 20 nm, more preferably 0 nm to 10 nm, particularly preferably 0 nm to 5 nm.

The thickness of the resin layer (N1) may be set to any thickness depending on the desired retardation of the resin layer (N1), and is, for example, 3 μm or more, 5 μm or more, 50 μm or less, or 40 μm or less.

[6. Fourth step: Stretching of third film]
In the fourth step, the third film is stretched at least once to form a resin layer (P), which is a layer obtained by stretching the resin layer (P2) and has a slow axis (P), and a resin layer (N1). ) is a stretched layer and has a slow axis (N) forming an angle within a range of 90°±5° with respect to the slow axis (P); get.

The third film may be stretched once, or twice or more. When the third film is stretched twice or more, it is preferable that the stretching direction of each of the two or more times is the same. In each of these two or more times of stretching, the stretching ratio may be the same or different. In one embodiment, preferably the stretching of the third film is a single stretching.

The stretching ratio E4 of the third film in the fourth step is preferably 1.05 times or more, more preferably 1.1 times or more, particularly preferably 1.13 times or more, and preferably 2 times in the stretching direction. Below, it is more preferably 1.7 times or less, particularly preferably 1.5 times or less. Here, when the third film is stretched twice or more in the fourth step, the stretching ratio of the third film in the fourth step is a ratio obtained by multiplying the stretching ratio of each time.

The ratio (E4/E2) of the stretch ratio E4 of the third film in the fourth step to the stretch ratio E2 of the first film in the second step is preferably 0.5 or more, more preferably 0.6 or more, especially It is preferably 0.7 or more, preferably 2.0 or less, more preferably 1.7 or less, particularly preferably 1.5 or less. As a result, the resin layer (N) included in the retardation film is effectively made to exhibit biaxiality, while the resin layer (P) is made to exhibit the desired in-plane retardation. A retardation film that satisfies (3) can be particularly easily produced.

The stretching of the first film in the second step is stretching in one direction, and the stretching of the third film in the fourth step is in a direction substantially parallel to the stretching direction of the first film in the second step. Specifically, it is preferable to include stretching in a direction within a range of 0°±5°. The stretching direction of the third film is preferably within the range of 0°±5°, preferably −5° or more, more preferably −3° or more, and further Preferably it is -2° or more, particularly preferably -1° or more, preferably 5° or less, more preferably 3° or less, still more preferably 2° or less, particularly preferably 1° or less.

In the fourth step, the third film is stretched in a direction substantially parallel to the stretching direction in the second step, specifically, in a direction within the range of 0°±5°. ) to formula (3) can be produced.

The resin layer (P2) included in the third film is made of thermoplastic resin P having a positive intrinsic birefringence value, so when the third film is stretched in a certain stretching direction in the fourth step, the resin layer (P2) ) is a stretched layer, and the resin layer (P) exhibits a slow axis (P) in a direction substantially parallel to the stretching direction. On the other hand, since the resin layer (N1) included in the third film is formed of thermoplastic resin N having a negative intrinsic birefringence value, the resin layer (N1) which is a layer obtained by stretching the resin layer (N1) In this case, the refractive index in the in-plane direction of the resin layer (N) increases, which is substantially perpendicular to the stretching direction.
Therefore, when the stretching of the third film in the fourth step includes stretching in a direction substantially parallel to the stretching direction of the first film in the second step, the slow phase of the resin layer (P2) developed in the second step Since the axial direction and the stretching direction in the fourth step are approximately parallel, the slow axis (P) of the resin layer (P) included in the retardation film is adjusted to be approximately parallel to the stretching direction in the fourth step. It is especially easy to do so. As a result, the direction of the slow axis (N) of the resin layer (N) and the direction of the slow axis (P) of the resin layer (P) can be particularly easily made substantially perpendicular.

Here, in the resin layer (N1), the polymer contained in the thermoplastic resin N is considered to be oriented in the thickness direction of the resin layer (N1), but after stretching the third film in the fourth step, Also, the orientation direction of the polymer does not coincide with the in-plane direction of the resin layer (N), and the resin layer (N) is considered to exhibit biaxiality.
In both the second step and the fourth step, a film provided with a layer of thermoplastic resin P (resin layer (P1) or resin layer (P2)) is stretched to give the resin layer (P) a desired in-plane position. By developing the phase difference, the stretching ratio of the third film in the fourth step can be set lower than that in the case where no stretching is performed in the second step. As a result, even by stretching the third film in the fourth step, the biaxiality of the resin layer (N) is maintained, and a retardation film that satisfies formulas (1) to (3) can be easily manufactured. Can be done.

The angle formed by the direction of stretching of the third film in the fourth step with respect to the slow axis of the resin layer (P2) included in the second film is preferably within the range of 0°±5°, and preferably - 5° or more, more preferably -3° or more, even more preferably -2° or more, particularly preferably -1° or more, preferably 5° or less, more preferably 3° or less, even more preferably 2° or less, Particularly preferably, the angle is 1° or less.

The stretching temperature in the fourth step can be appropriately set depending on the glass transition temperature TgP of the thermoplastic resin P and the glass transition temperature TgN of the thermoplastic resin N. From the viewpoint of suppressing film breakage during stretching and performing stretching smoothly, preferably Tg (high) -5°C or higher, more preferably Tg (high) -3°C or higher, particularly preferably Tg (high) -1. ℃ or more, preferably Tg (high) + 20 ℃ or less, more preferably Tg (high) + 15 ℃ or less, still more preferably Tg (high) + 12 ℃ or less, still more preferably Tg (high) + 10 ℃ or less, particularly preferably is below Tg(high)+9°C. Tg (high) represents the higher temperature of the glass transition temperature TgP and the glass transition temperature TgN. When the glass transition temperature TgP and the glass transition temperature TgN are the same temperature, they represent the same temperature.

[7. [Optional steps that the retardation film may include]
The method for producing a retardation film may include any steps in addition to the first to fourth steps described above. For example, when a long first film is used to obtain a long retardation film, the method for manufacturing the retardation film may include a trimming step of cutting out the obtained retardation film into a desired shape. . According to the trimming process, a sheet of retardation film having a desired shape is obtained. Further, the method for producing a retardation film may include, for example, a step of providing a protective layer on the retardation film.

[8. Overview of manufacturing method of circularly polarizing plate]
A method for manufacturing a circularly polarizing plate according to an embodiment of the present invention includes:
A method for manufacturing a circularly polarizing plate including a linear polarizer and a retardation film,
a fifth step of manufacturing the retardation film in the retardation film manufacturing method;
a sixth step of laminating the retardation film and the linear polarizer;
including.

[9. Fifth step]
The method for manufacturing a circularly polarizing plate according to this embodiment includes a fifth step. The fifth step is a step of manufacturing a retardation film using the method for manufacturing a retardation film described above.
Specifically, the fifth step is a step of manufacturing a retardation film by a manufacturing method including the first step, second step, third step, and fourth step described above. The retardation film obtained by the fifth step is the same as described in [1. This is the same as the retardation film explained in the section ``Produced Retardation Film''.

[10. Sixth step]
In the sixth step, the retardation film produced in the fifth step and a linear polarizer are laminated.

Any linear polarizer can be used as the linear polarizer. Examples of linear polarizers include films obtained by adsorbing iodine or dichroic dyes on polyvinyl alcohol films and then uniaxially stretching them in a boric acid bath; adsorbing iodine or dichroic dyes on polyvinyl alcohol films. Examples include a film obtained by stretching, stretching, and further modifying a part of the polyvinyl alcohol units in the molecular chain into polyvinylene units. Among these, as the linear polarizer, a polarizer containing polyvinyl alcohol is preferable.

When natural light is incident on a linear polarizer, only one polarized light is transmitted. The degree of polarization of this linear polarizer is not particularly limited, but is preferably 98% or more, more preferably 99% or more.
Further, the thickness of the linear polarizer is preferably 5 μm to 80 μm.

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

Further, the lamination in the sixth step is preferably performed such that the angle between the width direction of the linear polarizer and the slow axis (P) of the resin layer (P) is within a specific range close to 45°. . Specifically, the angle is preferably 40° or more, more preferably 42° or more, even more preferably 43° or more, particularly preferably 44° or more, and preferably 50° or less, more preferably 48°. The angle is more preferably 47° or less, particularly preferably 46° or less.
Furthermore, in this case, it is preferable that the angle between the width direction of the linear polarizer and the slow axis (N) of the resin layer (N) falls within a specific range close to 135°. Specifically, the angle is preferably 130° or more, more preferably 132° or more, even more preferably 133° or more, particularly preferably 134° or more, and preferably 140° or less, more preferably 138°. The angle is more preferably 137° or less, particularly preferably 136° or less.

An appropriate adhesive can be used for laminating the retardation film and the linear polarizer.

The method for manufacturing a circularly polarizing plate may include any steps in addition to the fifth and sixth steps described above. Examples of the arbitrary steps include a step of laminating a functional layer on a retardation film, a linear polarizer, and/or a circularly polarizing plate. Examples of the functional layer include a polarizer protective film layer; a hard coat layer such as an impact-resistant polymethacrylate resin layer; a matte layer that improves the slipperiness of the film; a reflection suppression layer; an antifouling layer; an antistatic layer; etc. Can be mentioned.

[11. Application example of circularly polarizing plate]
The above-described circularly polarizing plate can be provided in an image display device. In particular, it is preferable to provide the circularly polarizing plate in an organic EL image display device. This organic EL image display device includes a circularly polarizing plate and an organic electroluminescent element (hereinafter, sometimes referred to as an "organic EL element"). This organic EL image display device usually includes a linear polarizer, a retardation film, and an organic EL element in this order.

An organic EL element includes a transparent electrode layer, a light-emitting layer, and an electrode layer in this order, and the light-emitting layer can generate light when a voltage is applied from the transparent electrode layer and the electrode layer. Examples of materials constituting the organic light-emitting layer include polyparaphenylenevinylene-based, polyfluorene-based, and polyvinylcarbazole-based materials. Further, the light-emitting layer may have a laminate of a plurality of layers emitting light of different colors, or a mixed layer in which a certain dye layer is doped with different dyes. Further, the organic EL device may include 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 generation layer.

The image display device described above can suppress reflection of external light on the display surface. Specifically, only a portion of the linearly polarized light incident from outside the device passes through a linear polarizer, and then passes through a retardation film, thereby becoming circularly polarized light. The circularly polarized light is reflected by components that reflect light in the image display device (such as reflective electrodes in organic EL elements) and passes through the retardation film again, causing vibrations perpendicular to the vibration direction of the incident linearly polarized light. It becomes linearly polarized light with a direction and does not pass through the linear polarizer. Here, the vibration direction of linearly polarized light means the vibration direction of the electric field of linearly polarized light. This achieves the function of reflex suppression.

Since the retardation film has the above-mentioned optical properties, the organic EL image display device can exhibit the function of suppressing reflection not only in the front direction of the display surface but also in the inclined direction. Thereby, it is possible to effectively suppress reflection of external light and suppress coloring in both the front direction and the inclined direction of the display surface.

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

Furthermore, in general, the coloring of the display surface due to reflected light may vary depending on the azimuth angle of the viewing direction. Therefore, when observed from the direction of inclination of the display surface, the measured chromaticity may vary depending on the azimuth of the viewing direction, and therefore the color difference ΔE ^* ab may also vary. Therefore, in order to evaluate the degree of coloring when observed from the tilt direction of the display surface as described above, the coloring is evaluated using the average value of the color difference ΔE ^* ab obtained by observing from multiple azimuthal directions. It is preferable to do so. Specifically, the color difference ΔE*ab is measured in 5° increments in the azimuth direction in a range where the azimuth angle φ (see FIG ^{. 1) is 0° or more and less than 360°, and the measured color difference ΔE* ab} The degree of coloring is evaluated based on the average value (average color difference). The smaller the average color difference, the smaller the coloring of the display surface when observed from the direction of inclination of the display surface.

Hereinafter, the present invention will be specifically described with reference to Examples. However, the present invention is not limited to the embodiments shown below, and may be implemented with arbitrary changes within the scope of the claims of the present invention and equivalents thereof.

In the following description, "%" and "part" expressing amounts are based on weight, unless otherwise specified. Further, the operations described below were performed at room temperature (20° C.±15° C.) and normal pressure (1 atm) unless otherwise specified.

[Evaluation method]
(Glass-transition temperature)
The glass transition temperature Tg of the resin was measured using a differential scanning calorimeter ("DSC6220SII" manufactured by Nano Technology Co., Ltd.) under conditions of a heating rate of 10° C./min based on JIS K 6911.

(thickness of film or layer)
The thickness of the film or layer was measured using a reflection spectroscopic film thickness measurement system "F20" manufactured by Filmetrics.

(Method of measuring phase difference and NZ coefficient)
In-plane retardation Re at wavelengths 450 nm, 550 nm, and 650 nm of the evaluation target; and thickness direction retardation Rth at wavelength 550 nm were measured using a retardation meter ("AxoScan" manufactured by Axometrics). The physical properties of each layer of the inseparable laminate were calculated by measuring the sample from multiple directions and performing a fitting analysis using the included multilayer analysis software. Further, the NZ coefficient was calculated using the in-plane retardation Re and the thickness direction retardation Rth at a wavelength of 550 nm.

(Method of measuring orientation angle)
The direction of the slow axis (P) of the resin layer (P) included in the retardation film and the direction of the slow axis (N) of the resin layer (N) are determined using a retardation meter (“AxoScan” manufactured by Axometrics). It was measured using The angle that this slow axis makes with respect to the width direction of the retardation film was calculated as the orientation angle θ (0°≦θ<180°).

(Haze)
The haze of the retardation film was measured using a haze meter in accordance with JIS K7361-1997.

(How to calculate color difference by simulation)
Using "LCD Master" manufactured by Shintech as simulation software, the circularly polarizing plates manufactured in each example and comparative example were modeled, and the following calculations were performed.

In the simulation model, a configuration was set in which a circularly polarizing plate was provided on the reflective surface of a mirror having a planar reflective surface. Moreover, a circularly polarizing plate was set that had a resin layer (N) of a retardation film, a resin layer (P) of a retardation film, and a linear polarizer in this order from the reflective surface side. As the retardation film, those obtained in each Example and Comparative Example were set. Further, as the linear polarizer, a commonly used polarizing plate with a degree of polarization of 99.99% was set. Furthermore, an ideal mirror that can specularly reflect the incident light with a reflectance of 100% was set as the mirror.

FIG. 1 is a perspective view schematically showing an evaluation model set when calculating color space coordinates in simulations in Examples and Comparative Examples.
As shown in FIG. 1, 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) were calculated. Further, the color space coordinates when not illuminated by a light source were set as a0 ^* =0, b0 ^* =0, and L0 ^* =0. Then, the color difference ΔE ^* ab was determined from (i) the color space coordinates when illuminated by a light source and (ii) the color space coordinates when not illuminated by a light source.

The above calculation of the color difference ΔE ^* ab was performed in the observation direction 20 where the polar angle ρ with respect to the reflective surface 10 was 0°, and the color difference ΔE ^* ab in the front direction was determined. The polar angle ρ represents the angle formed with respect to the normal direction 11 of the reflective surface 10.

Further, the above-mentioned calculation of the color difference ΔE ^* ab was performed in the observation direction 20 where the polar angle ρ with respect to the reflective surface 10 was 60°. This calculation at the polar angle ρ=60° was performed multiple times by moving the observation direction 20 in the azimuth direction and the azimuth angle φ in the range of 0° or more and less than 360° in 5° increments. The azimuth angle φ represents the angle that a direction parallel to the reflective surface 10 makes with a certain reference direction 12 parallel to the reflective surface 10. Then, the average of the calculated color differences ΔE ^* ab in the plurality of viewing directions 20 was calculated to obtain the color difference ΔE ^* ab in the tilt direction with the polar angle ρ=60°.

(Evaluation method of circularly polarizing plate by visual inspection in front direction)
An image display device (“Apple Watch” (registered trademark) by Apple Inc.) including an organic EL image display device was prepared. This image display device was disassembled, and the polarizing plate bonded to the surface of the organic EL image display device was peeled off to expose the reflective electrode. The surface of this reflective electrode and the surface of the circularly polarizing plate obtained in each Example and Comparative Example on the opposite side from the linear polarizer were bonded together via an adhesive ("CS9621" manufactured by Nitto Denko Corporation). Thereby, a sample was obtained which included a reflective electrode, an adhesive, and a circularly polarizing plate in this order.

The circularly polarizing plate on the reflective electrode was visually observed on a sunny day with the circularly polarizing plate of the sample illuminated by sunlight. The observation was performed in the front direction of the circularly polarizing plate at a polar angle of 0° and an azimuth angle of 0°. As a result of the observation, if a chromatic color was visually recognized, it was determined to be "bad", and if a chromatic color was not visually recognized, it was determined to be "good".

(Method for evaluating circularly polarizing plate by visual inspection in tilt direction)
The circularly polarizing plate of the sample prepared in the above (method for evaluating circularly polarizing plate by visual inspection in the front direction) was illuminated with sunlight on a clear day, and the circularly polarizing plate on the reflective electrode was visually observed. The observation was performed with a circularly polarizing plate tilted at a polar angle of 60° and an azimuth angle of 0° to 360°. As a result of the observation, the quality of reflection brightness and coloring were comprehensively judged, and the Examples and Comparative Examples were ranked. Then, the ranked Examples and Comparative Examples were given points corresponding to their rankings (7 points for 1st place, 6 points for 2nd place, 1 point for last place).

The above observations were made by a large number of people, and the total points given for each example and comparative example were determined. The Examples and Comparative Examples were arranged in the order of the above-mentioned 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.

[Example 1]
(1-1. First step: Preparation of first film)
As a thermoplastic resin P having a positive intrinsic birefringence value, a resin containing a norbornene polymer (hereinafter also referred to as norbornene resin) (manufactured by Zeon Corporation; glass transition temperature 126 ° C.) was dried at 100 ° C. for 5 hours. . The dried thermoplastic resin P was supplied to an extruder, passed through a polymer pipe and a polymer filter, and extruded into a sheet form from a T-die onto a casting drum. The extruded thermoplastic resin P was cooled to obtain a long unstretched film made of the thermoplastic resin P and having a thickness of 60 μm as a first film. The obtained unstretched film was wound up into a roll and collected. The first film included only a resin layer (P1) formed from thermoplastic resin P. The optical properties of the resin layer (P1) included in the first film were evaluated by the method described above.

(1-2. Second step: stretching of first film)
The first film was pulled out from the roll, and the pulled out first film was supplied to a tenter stretching machine. Using this tenter stretching machine, the first film is stretched in a stretching direction forming an angle of 45° with respect to the width direction of the first film at a stretching temperature of 128°C and a stretching ratio of 1.15 times in the stretching direction. In this way, a second film was obtained, which included a resin layer (P2) that was a stretched resin layer (P1). The second film included only the resin layer (P2). The obtained second film was cooled to room temperature, then wound up into a roll and collected. The optical properties of the resin layer (P2) included in the second film were evaluated by the method described above.

(1-3. Third step: Lamination of resin layer (N1))
(Preparation of resin solution for forming resin layer (N1))
500 mL of toluene as a solvent and 0.29 mmol of n-butyllithium as a polymerization catalyst were placed in a pressure-resistant reactor that had been dried and purged with nitrogen, 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) as a homopolymer of 2-vinylnaphthalene was obtained. After adding triphenyl phosphate as a plasticizer to the reaction mixture, the reaction mixture was poured into a large amount of 2-propanol to precipitate a resin containing poly(2-vinylnaphthalene), which was then fractionated. The obtained resin containing poly(2-vinylnaphthalene) was dried at 200° C. for 24 hours using a vacuum dryer to obtain a thermoplastic resin N. This thermoplastic resin N contains about 5% by weight of a plasticizer. The weight average molecular weight of poly(2-vinylnaphthalene) measured by GPC was 250,000. Further, the glass transition temperature of the thermoplastic resin N was 127° C. as measured by a differential scanning calorimeter. This thermoplastic resin N has a negative intrinsic birefringence value.

The produced thermoplastic resin N and 1,3-dioxolane as a solvent were mixed to obtain a resin solution containing the thermoplastic resin N as a liquid composition. The concentration of thermoplastic resin N in this liquid composition was 15% by weight.

The second film was pulled out from the roll, and the resin solution was applied onto the surface of the pulled out second film, that is, the surface of the resin layer (P2) to form a resin solution layer. Thereafter, the coated resin solution layer was rapidly dried at 120° C. to form a 15 μm thick resin layer (N1) on the second film. Through the above operations, a third film including a resin layer (P2) and a resin layer (N1) laminated on this resin layer (P2) was obtained. The optical properties of the resin layer (P2) and resin layer (N1) included in the third film were evaluated by the method described above.

(1-4. Fourth step: stretching of third film)
The obtained third film was supplied to a tenter stretching machine. Using this tenter stretching machine, the third film is stretched in a stretching direction that makes an angle of 45 degrees with respect to the width direction of the third film, that is, a stretching direction that makes an angle of 0 degrees with respect to the stretching direction of the first film. The film was stretched at a stretching temperature of 128° C. and a stretching ratio of 1.30 times in the stretching direction to obtain a long retardation film. This retardation film included a resin layer (P) that was a stretched resin layer (P2) and a resin layer (N) that was a stretched resin layer (N1). The optical properties of the retardation film and each layer included in the retardation film were evaluated by the method described above.

(1-5. Manufacturing of circularly polarizing plate)
A long polyvinyl alcohol resin film dyed with iodine was prepared. This film was stretched in the longitudinal direction making an angle of 90° with respect to the width direction of the film to obtain a linear polarizer as a long polarizing film. This linear polarizer had an absorption axis in the longitudinal direction of the linear polarizer, and a transmission axis in the width direction of the linear polarizer.

The linear polarizer and the retardation film were bonded together via an optically isotropic adhesive ("CS9621" manufactured by Nitto Denko Corporation) to obtain a long circularly polarizing plate. The above bonding was performed with the width direction of the linear polarizer and the width direction of the retardation film being parallel to each other. The obtained circularly polarizing plate was equipped with a linear polarizer, a resin layer (P), and a resin layer (N) in this order.
The obtained circularly polarizing plate was evaluated by the method described above.

[Examples 2 to 4]
In step (1-2), the stretching ratio of the first film was changed as shown in Table 1.
In step (1-3), the coating thickness of the resin solution was changed so that the resin layer (N1) had the thickness shown in Table 1.
In step (1-4), the stretching ratio was changed as shown in Table 1.
Except for the above matters, a retardation film and a circularly polarizing plate were manufactured and evaluated in the same manner as in Example 1.

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

(C1-1. Preparation of film of thermoplastic resin P)
As a thermoplastic resin P having a positive intrinsic birefringence value, a resin containing a norbornene polymer (hereinafter also referred to as norbornene resin) (manufactured by Zeon Corporation; glass transition temperature 126 ° C.) was dried at 100 ° C. for 5 hours. . The dried thermoplastic resin P was supplied to an extruder, passed through a polymer pipe and a polymer filter, and extruded into a sheet form from a T-die onto a casting drum. The extruded thermoplastic resin P was cooled to obtain a long unstretched film made of the thermoplastic resin P and having a thickness of 60 μm. The obtained unstretched film was wound up into a roll and collected.

(C1-2. Lamination of layers of thermoplastic resin N)
500 mL of toluene as a solvent and 0.29 mmol of n-butyllithium as a polymerization catalyst were placed in a pressure-resistant reactor that had been dried and purged with nitrogen, 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) as a homopolymer of 2-vinylnaphthalene was obtained. The reaction mixture was poured into a large amount of 2-propanol to precipitate poly(2-vinylnaphthalene), which was separated. The obtained poly(2-vinylnaphthalene) was dried at 200° C. for 24 hours using a vacuum dryer to obtain a thermoplastic resin N. The weight average molecular weight of poly(2-vinylnaphthalene) measured by GPC was 250,000. Further, the glass transition temperature of poly(2-vinylnaphthalene) measured by a differential scanning calorimeter was 142°C. This thermoplastic resin N has a negative intrinsic birefringence value.

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

The unstretched film (resin layer CP1) was pulled out from the roll, and the resin solution was applied onto the surface of the unstretched film to form a resin solution layer. Thereafter, the resin solution layer was rapidly dried at 120° C. to form a 12 μm thick poly(2-vinylnaphthalene) layer on the unstretched film. Through the above operations, a laminated film comprising an unstretched film formed of thermoplastic resin P (resin layer CP1) and a layer of poly(2-vinylnaphthalene) as thermoplastic resin N (resin layer CN1) was obtained. . The obtained laminated film was wound up into a roll and collected.

(C1-3. Stretching of laminated film)
The laminated film was pulled out from the roll and continuously supplied to a tenter stretching machine. Then, using this tenter stretching machine, the laminated film is stretched in a stretching direction forming an angle of 45° with respect to the longitudinal direction of the laminated film at a stretching temperature of 140° C. and a stretching ratio of 1.5 times in the stretching direction. , a long retardation film was obtained. This retardation film is obtained by stretching a resin layer (P) obtained by stretching a norbornene resin layer (resin layer CP1) and a poly(2-vinylnaphthalene) layer (resin layer CN1). It was equipped with a resin layer (N).

(C1-4. Manufacturing of circularly polarizing plate)
Using the obtained retardation film, a circularly polarizing plate was manufactured in the same manner as in step (1-5) of Example 1. The obtained circularly polarizing plate was equipped with a linear polarizer, a resin layer (P), and a resin layer (N) in this order. The obtained retardation film and circularly polarizing plate were evaluated by the method described above.

[Comparative example 2]
A retardation film was produced in the same manner as in Example 1 of JP-A-2007-199616. Specifically, a retardation film was obtained by the following operation.

(C2-1. Preparation of film of thermoplastic resin P)
As the thermoplastic resin P having a positive intrinsic birefringence value, a film (thickness: 70 μm) of a resin containing a norbornene polymer (“Arton FLZU” manufactured by JSR Corporation; glass transition temperature: 128° C.) was prepared.

(C2-2. Lamination of layers of thermoplastic resin N)
As a thermoplastic resin N having a negative intrinsic birefringence value, a copolymer of styrene and maleic anhydride (glass transition temperature 148 ° C.) was prepared in the same manner as in Example 1 of JP 2007-199616 A. did.
The obtained copolymer was mixed with methyl ethyl ketone as a solvent to obtain a resin solution of styrene-maleic anhydride copolymer at a concentration of 33% by weight as a liquid composition.
The resin solution was applied onto the film of the thermoplastic resin P containing the norbornene polymer to form a layer of the resin solution. Thereafter, the resin solution layer was dried at 80° C. for 10 minutes to form a 40 μm thick layer of thermoplastic resin N on the film formed of thermoplastic resin P. Through the above operations, a laminated film including a film formed of thermoplastic resin P (resin layer CP1) and a layer of thermoplastic resin N (resin layer CN1) was obtained.

(C2-3. Stretching of laminated film)
Next, the laminated film was uniaxially stretched at a stretching temperature of 110°C and a stretching ratio of 2.0 times to obtain a retardation film. This retardation film is obtained by stretching a resin layer (P) obtained by stretching a layer of norbornene resin (resin layer CP1) and a layer of styrene-maleic anhydride copolymer (resin layer CN1). It was equipped with a resin layer (N).

(C2-4. Manufacturing of circularly polarizing plate)
Using the obtained retardation film, a circularly polarizing plate was manufactured in the same manner as in step (1-5) of Example 1. The obtained circularly polarizing plate was equipped with a linear polarizer, a resin layer (P), and a resin layer (N) in this order. The obtained retardation plate and circularly polarizing plate were evaluated by the method described above.

[Comparative example 3]
(C3-1. Preparation of film of thermoplastic resin P)
A pelletized norbornene resin (manufactured by Nippon Zeon Co., Ltd.; glass transition temperature: 126°C) was dried at 100°C for 5 hours to obtain a thermoplastic resin P. This thermoplastic resin P was supplied to an extruder, passed through a polymer pipe and a polymer filter, and was extruded into a sheet form from a T-die onto a casting drum. The extruded thermoplastic resin P was cooled to obtain a long unstretched film with a thickness of 110 μm. The obtained unstretched film was wound up into a roll and collected.

(C3-2. Lamination of layers of thermoplastic resin N)
500 mL of toluene as a solvent and 0.29 mmol of n-butyllithium as a polymerization catalyst were placed in a pressure-resistant reactor that had been dried and purged with nitrogen, 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) as a homopolymer of 2-vinylnaphthalene was obtained. The reaction mixture was poured into a large amount of 2-propanol to precipitate poly(2-vinylnaphthalene), which was separated. The obtained poly(2-vinylnaphthalene) was dried at 200° C. for 24 hours using a vacuum dryer to obtain a thermoplastic resin N. The weight average molecular weight of poly(2-vinylnaphthalene) measured by GPC was 250,000. Further, the glass transition temperature of poly(2-vinylnaphthalene) measured by a differential scanning calorimeter was 142°C. This thermoplastic resin N has a negative intrinsic birefringence value.

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

The unstretched film was pulled out from the roll, and the resin solution was applied onto the unstretched film to form a resin solution layer. Thereafter, the resin solution layer was dried to form a 13 μm thick poly(2-vinylnaphthalene) layer on the unstretched film. Through the above operations, a laminate comprising an unstretched film (resin layer CP1) formed of norbornene resin which is thermoplastic resin P and a layer (resin layer CN1) of poly(2-vinylnaphthalene) which is thermoplastic resin N A film was obtained.The obtained laminated film was wound up into a roll and collected.

(C3-3. Stretching of laminated film; first stretching step)
The laminated film was pulled out from the roll, and the pulled out laminated film was supplied to a tenter stretching machine. Using this tenter stretching machine, the laminated film was stretched in a stretching direction forming an angle of 135° with respect to the width direction of the laminated film at a stretching temperature of 140° C. and a stretching ratio of 1.15 times in the stretching direction. The stretched laminated film was cooled to room temperature, then wound up into a roll and collected.

(C3-4. Stretching of laminated film; second stretching step)
The laminated film stretched in the first stretching step was drawn out from the roll, and the drawn laminated film was supplied to a tenter stretching machine. Using this tenter stretching machine, the laminated film was stretched in a stretching direction forming an angle of 45° with respect to the width direction of the laminated film at a stretching temperature of 128°C and a stretching ratio of 1.50 times in the stretching direction. , a long retardation film was obtained. This retardation film is obtained by stretching a resin layer (P) obtained by stretching a norbornene resin layer (resin layer CP1) and a poly(2-vinylnaphthalene) layer (resin layer CN1). It was equipped with a resin layer (N).

(C3-5. Manufacturing of circularly polarizing plate)
Using the obtained retardation film, a circularly polarizing plate was manufactured in the same manner as in step (1-5) of Example 1. The obtained circularly polarizing plate was equipped with a linear polarizer, a resin layer (P), and a resin layer (N) in this order. The obtained retardation film and circularly polarizing plate were evaluated by the method described above.

In the above-mentioned examples and comparative examples, the visual evaluation in the front direction is judged in two stages of "good" and "poor", while the visual evaluation in the inclined direction is judged in 5 grades from "A" to "E". It is judged in stages. The reason why the criteria are different in this way is as follows.
That is, the brightness of reflected light is sufficiently lower in the front direction than in the inclined direction. Therefore, if strong coloration does not occur, the viewer cannot recognize the coloration. Therefore, we adopted a two-stage determination of whether or not the coloring can be visually recognized.
On the other hand, in the inclined direction, the brightness of the reflected light is high. Therefore, even if the coloration is weak, the viewer can easily recognize the coloration. Therefore, we adopted a five-level detailed evaluation of merits and demerits.

[result]
Manufacturing conditions in Examples and Comparative Examples are shown in Tables 1 and 2, and Table 3 shows the results.
In the table below, the abbreviations have the following meanings.
"VN": Resin containing poly(2-vinylnaphthalene) "COP1": Norbornene resin manufactured by Zeon Corporation (glass transition temperature 126°C)
"COP2": Norbornene resin "Arton FLZU" manufactured by JSR (glass transition temperature 128°C)
"ST-MA": Styrene-maleic anhydride copolymer "N1/P2": Laminate comprising a resin layer (N1) and a resin layer (P2) "CN1/CP1": A resin layer (CN1) and a resin layer (CP1) Laminated body "P/N": Retardation film "wavelength dispersion difference" comprising a resin layer (P) and a resin layer (N): {Re _N (450)/Re _{N (} 550)} - Value of {Re _P (450)/Re _P (550)} "θ": Angle formed by the slow axis of the film or layer with respect to the width direction of the film or layer Item in Table 2 ""1st": Item in the first stretching process table 2 "2nd" in the fourth step: Second stretching process

From the above results, it can be seen that by the method of the example, a retardation film that satisfies formulas (1) to (3) and has a small haze can be obtained. Further, the circularly polarizing plate provided with the retardation film satisfying formulas (1) to (3) obtained by the method of the example may be used in the front direction and the inclined direction of the display surface of the image display device equipped with the circularly polarizing plate. It can be seen that in both cases, coloration due to reflection of external light can be suppressed.

10 Reflection surface 11 Normal direction 12 Reference direction 20 Observation direction φ Azimuth angle ρ Polar angle

Claims (7)

1. A method for producing a retardation film satisfying the following formula (1), the following formula (2), and the following formula (3),
   The manufacturing method includes:
   A first step of preparing a first film comprising a resin layer (P1) formed of a thermoplastic resin P having a positive intrinsic birefringence value;
   a second step of stretching the first film at least once to obtain a second film comprising a resin layer (P2) that is a stretched layer of the resin layer (P1);
   a third step of laminating a resin layer (N1) formed of a thermoplastic resin N having a negative intrinsic birefringence value on the second film to obtain a third film;
   The third film was stretched at least once, and the resin layer (P), which is a layer obtained by stretching the resin layer (P2) and has a slow axis (P), and the resin layer (N1) were stretched. and a resin layer (N) having a slow axis (N) forming an angle within a range of 90° ± 5° with respect to the slow axis (P). and,
   A method for producing a retardation film, including:
   100nm≦Re _T (550)≦180nm (1)
   Re _T (450)<Re _T (550)<Re _T (650) (2)
   0.0< _NZT <1.0 (3)
   (however,
   Re _T (450) represents the in-plane retardation of the retardation film at a wavelength of 450 nm,
   Re _T (550) represents the in-plane retardation of the retardation film at a wavelength of 550 nm,
   Re _T (650) represents the in-plane retardation of the retardation film at a wavelength of 650 nm,
   NZ _T represents the NZ coefficient of the retardation film. )
2. The method for producing a retardation film according to claim 1, wherein the resin layer (P2) included in the second film has an in-plane retardation of 20 nm or more.
3. The method for producing a retardation film according to claim 1, wherein the thickness direction retardation of the resin layer (N1) in the third step is -30 nm or less.
4. The stretching of the first film in the second step is stretching in one direction, and the stretching of the third film in the fourth step is 0 with respect to the stretching direction of the first film in the second step. The method for producing a retardation film according to claim 1, comprising stretching in a direction within a range of ±5°.
5. The method for producing a retardation film according to claim 1, wherein the retardation film satisfies the following formula (4).
   {Re _N (450)/Re _N (550)}-{Re _P (450)/Re _P (550)}>0.08 (4)
   (however,
   Re _N (450) represents the in-plane retardation of the resin layer (N) at a wavelength of 450 nm,
   Re _N (550) represents the in-plane retardation of the resin layer (N) at a wavelength of 550 nm,
   Re _P (450) represents the in-plane retardation of the resin layer (P) at a wavelength of 450 nm,
   Re _P (550) represents the in-plane retardation of the resin layer (P) at a wavelength of 550 nm. )
6. The method for producing a retardation film according to claim 1, which satisfies the following formula (5).
   Re _P (550)>Re _N (550) (5)
   (however,
   Re _N (550) represents the in-plane retardation of the resin layer (N) at a wavelength of 550 nm,
   Re _P (550) represents the in-plane retardation of the resin layer (P) at a wavelength of 550 nm. )
7. A method for manufacturing a circularly polarizing plate including a linear polarizer and a retardation film,
   A fifth step of manufacturing the retardation film in the method for manufacturing a retardation film according to any one of claims 1 to 6;
   a sixth step of laminating the retardation film and the linear polarizer;
   A method for manufacturing a circularly polarizing plate, including:

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