KR20220093109A - Retardation film, manufacturing method thereof, and circularly polarizing plate - Google Patents

Abstract

A method for producing a retardation film having specific optical properties; The production method is a first to prepare a multilayer film comprising a resin layer (A) formed of a thermoplastic resin A having a positive intrinsic birefringence value and a resin layer (B) formed of a thermoplastic resin B having a negative intrinsic birefringence value a second step of obtaining a retardation film by stretching the multilayer film twice or more at different stretching temperatures; The absolute value |TgA - TgB| of the difference of the glass transition temperature TgA of the thermoplastic resin A and the glass transition temperature TgB of the thermoplastic resin B is 5 degreeC or more, The manufacturing method of retardation film.

Description

Retardation film, manufacturing method thereof, and circularly polarizing plate

The present invention relates to a method for manufacturing a retardation film, a retardation film manufactured by the manufacturing method, and a circularly polarizing plate provided with the retardation film.

A retardation film may be provided in image display apparatuses, such as an organic electroluminescent image display apparatus (Hereinafter, it may call "organic EL image display apparatus" arbitrarily.) and a liquid crystal image display apparatus. Some of these retardation films have a multilayer structure including two or more layers. As a manufacturing method of the retardation film which has such a multilayer structure, the method using a co-stretching method may be employ|adopted (refer patent documents 1-5).

Japanese Patent Laid-Open No. 2012-73646 Japanese Patent Laid-Open No. 2009-192844 Japanese Patent Laid-Open No. 2009-192845 Japanese Patent Laid-Open No. 2009-223163 Japanese Patent Laid-Open No. 2002-40258

In order to reduce reflection of the external light in a display surface in an image display apparatus, a circularly polarizing plate may be provided. As such a circularly polarizing plate, a film obtained by combining a linear polarizer and a λ/4 plate is generally used. However, in reality, most of the conventional λ/4 plates can only function as λ/4 plates in a specific narrow wavelength range. Therefore, although many of the conventional circular polarizing plates can reduce the reflection of external light in a specific narrow wavelength range, it was difficult to reduce the reflection of other external light. When the reflection of external light occurs on the display surface, there is a possibility that the display surface is colored with the color of the reflected light.

In order to suppress the coloration of the display surface as described above, a circular polarizing plate capable of reducing the 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 provided by combining a plurality of layers is known, and for example, a retardation film provided by combining a λ/2 plate and a λ/4 plate is exemplified. A circular polarizing plate provided 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 do.

However, in an oblique direction that is neither parallel nor perpendicular to the display surface, the phase difference value shifts from the ideal value, or the optical axis of each layer shifts, thereby reducing the reflection of external light in a wide wavelength range. There may be cases where it cannot be done. Therefore, in order to implement|achieve the circularly polarizing plate which can suppress coloring by reflection of external light in the oblique direction, it is calculated|required of retardation film to have NZ coefficient of the specific range larger than 0.0 and less than 1.0.

The layer contained in the retardation film which satisfies the above-mentioned requirements usually differs in some or all of optical properties, such as the direction of a slow axis, in-plane retardation, and NZ coefficient. Therefore, conventionally, after manufacturing each layer separately, as for said retardation film, it was common to bond these layers together and to be manufactured. However, in this conventional manufacturing method, since manufacture of each layer is performed separately, there exists a tendency for the number of steps to increase, and to increase effort and cost. Moreover, since it was calculated|required to match the bonding angle correctly when bonding each layer together, the effort of angle adjustment was required, and there existed a tendency for labor to increase also by this.

Under these circumstances, development of a method capable of simply manufacturing a retardation film capable of obtaining a circularly polarizing plate capable of suppressing coloration due to reflection of external light in both the front direction and the oblique direction of the display surface is required.

The present invention was devised in view of the above problems, and it is possible to easily manufacture a retardation film capable of obtaining a circularly polarizing plate capable of suppressing coloration due to reflection of external light in both the front direction and the oblique direction of the display surface. manufacturing method; retardation film manufactured by the manufacturing method; And it aims to provide; a circularly polarizing plate provided with this retardation film.

MEANS TO SOLVE THE PROBLEM This inventor earnestly studied in order to solve the said subject. As a result, the present inventors have a multilayer film provided with a resin layer (A) and a resin layer (B) comprising a thermoplastic resin A and a thermoplastic resin B having a glass transition temperature TgA and a glass transition temperature TgB different by 5 ° C. or more, By the manufacturing method including extending|stretching twice or more at different extending|stretching temperature, it discovered that the retardation film which can solve the said subject is obtained, and completed this invention.

That is, the present invention includes the following.

[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 is

A first step of preparing a multilayer film comprising a resin layer (A) formed of a thermoplastic resin A having a positive intrinsic birefringence value and a resin layer (B) formed of a thermoplastic resin B having a negative intrinsic birefringence value;

By stretching the multilayer film twice or more, the retardation film comprising the resin layer (A) having a slow axis and the resin layer (B) having a slow axis substantially perpendicular to the slow axis of the resin layer (A). a second process of obtaining

The second process is

A 1st extending process of extending|stretching the said multilayer film at extending|stretching temperature Ts1;

a second stretching step of stretching the multilayer film at a stretching temperature Ts2 different from the stretching temperature Ts1;

The absolute value |TgA - TgB| of the difference between the glass transition temperature TgA of the said thermoplastic resin A, and the glass transition temperature TgB of the said thermoplastic resin B is 5 degreeC or more, The manufacturing method of the retardation film.

100 nm ≤ Re _T (550) ≤ 180 nm (1)

Re _T (450) < Re _T (550) < Re _T (650) (2)

0.0 < NZ _T < 1.0 (3)

(only,

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 retardation film.)

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

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

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

{Re _Q (450)/Re _Q (550)} - {Re _H (450)/Re _H (550)} > 0.08 (4)

(only,

Re _H (450) represents the in-plane retardation of the high-order retardation layer at a wavelength of 450 nm,

Re _H (550) represents the in-plane retardation of the higher retardation layer at a wavelength of 550 nm,

Re _Q (450) represents the in-plane retardation of the low retardation layer at a wavelength of 450 nm,

Re _Q (550) represents the in-plane retardation of the low retardation layer at a wavelength of 550 nm,

The high retardation layer represents a layer having a larger in-plane retardation at a wavelength of 550 nm among the resin layer (A) and the resin layer (B) included in the retardation film,

The said low retardation layer represents the layer with the smaller in-plane retardation at wavelength 550nm among the said resin layer (A) and the said resin layer (B) with which the said retardation film is equipped.)

[5] at a wavelength of 550 nm, the resin layer (A) included in the retardation film has a larger in-plane retardation than the resin layer (B) included in the retardation film,

The method for producing the retardation film according to any one of [1] to [4], wherein the glass transition temperature TgA of the thermoplastic resin A is lower than the glass transition temperature TgB of the thermoplastic resin B.

[6] at a wavelength of 550 nm, the resin layer (B) included in the retardation film has a larger in-plane retardation than the resin layer (A) included in the retardation film,

The method for producing the retardation film according to any one of [1] to [4], wherein the glass transition temperature TgB of the thermoplastic resin B is lower than the glass transition temperature TgA of the thermoplastic resin A.

[7] The retardation film produced by the manufacturing method according to any one of [1] to [6].

[8] A circularly polarizing plate comprising a linear polarizer and the retardation film according to [7].

ADVANTAGE OF THE INVENTION According to this invention, in both the front direction and the oblique direction of a display surface, the manufacturing method which can manufacture simply the retardation film which can obtain the circular polarizing plate which can suppress coloring by the reflection of external light; retardation film manufactured by the manufacturing method; And, a circular polarizing plate provided with this retardation film; can be provided.

1 is a perspective view schematically showing a state of an evaluation model set when color space coordinates are calculated in simulations in Examples and Comparative Examples.

Hereinafter, the present invention will be described in detail by showing embodiments and examples. However, this invention is not limited to embodiment and illustration shown below, In the range which does not deviate from the range which does not deviate from the claim of this invention and its equivalent range, it can change arbitrarily and implement it.

In the following description, the in-plane retardation Re represents a value represented by Re = (nx - ny) x d, unless otherwise specified. The thickness direction retardation Rth is a value represented by Rth = {(nx + ny)/2 - nz} × d, unless otherwise specified. In addition, unless otherwise indicated, the NZ coefficient NZ represents a value represented by NZ=Rth/Re+0.5, and thus may be represented by NZ=(nx - nz)/(nx - ny). nx represents the refractive index in the direction (slow axis direction) giving the maximum refractive index as the direction perpendicular to the thickness direction (in-plane direction), ny represents the refractive index in the direction orthogonal to the direction of nx as the in-plane direction, nz represents the refractive index of the thickness direction, and d represents thickness. The measurement wavelength is 550 nm, unless otherwise stated. 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, the slow axis of a certain layer indicates the slow axis in the in-plane direction of the layer unless otherwise specified.

In the following description, unless otherwise specified, the angle formed by the optical axes (absorption axis, transmission axis, slow axis, etc.) of each layer in a member including a plurality of layers is defined as the thickness direction of the layer. Shows the viewing angle.

In the following description, the front direction of a certain surface means the normal direction of the said surface unless otherwise stated, and specifically points out the direction of 0 degree of polarization and 0 degree of azimuth of the said surface.

In the following description, the inclination direction of a surface means a direction that is neither parallel nor perpendicular to the surface, unless otherwise specified, and specifically, a direction in which the declination angle of the surface is greater than 0° and smaller than 90°. points to

In the following description, the directions of elements are "parallel", "vertical" and "orthogonal", unless otherwise specified, within a range that does not impair the effects of the present invention, for example, within a range of ±5°. may contain an error of

In the following description, a "long" film refers to a film having a length of 5 times or more with respect to the width, and preferably has a length of 10 times or more, and specifically, the extent to which it is wound in a roll and stored or transported. A film with a length of The upper limit of the length of the long film is not particularly limited, and can be, for example, 100,000 times or less with respect to the width.

In the following description, the longitudinal direction of a long film is parallel to the flow direction of the film in a production line normally. In addition, the width direction of a long film is perpendicular|vertical with respect to the thickness direction normally and perpendicular|vertical to a longitudinal direction.

In the following description, "polarizing plate", "circularly polarizing plate", "plate", and "λ/2 plate" and "λ/4 plate" are, unless otherwise specified, a rigid member as well as, for example, A member having flexibility such as a resin film is also included.

In the following description, "a polymer having a positive intrinsic birefringence value" and "resin having a positive intrinsic birefringence value" refer to "a polymer whose refractive index in the stretching direction is greater than the refractive index in a direction orthogonal to the stretching direction" and "stretching" a resin in which the refractive index of the direction becomes larger than the refractive index of the direction orthogonal to the stretching direction” respectively. In addition, "a polymer having a negative intrinsic birefringence value" and "a resin having a negative intrinsic birefringence value" refer to "a polymer whose refractive index in the stretching direction is smaller than the refractive index in a direction orthogonal to the stretching direction" and "Refractive index in the stretching direction" resin which becomes smaller than the refractive index of the direction orthogonal to this extending|stretching direction", respectively. The intrinsic birefringence value can be calculated from the dielectric constant distribution.

In the following description, the adhesive is not only an adhesive (adhesive having a shear storage modulus of 1 MPa to 500 MPa at 23 ° C after energy ray irradiation or heat treatment after energy ray irradiation or heat treatment), but also at 23 ° C. Also includes pressure-sensitive adhesives having a shear storage modulus of less than 1 MPa.

[One. Manufactured retardation film]

The 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 capable of suppressing coloration due to reflection of external light in both the front direction and the oblique direction of the display surface.

100 nm ≤ Re _T (550) ≤ 180 nm (1)

Re _T (450) < Re _T (550) < Re _T (650) (2)

0.0 < NZ _T < 1.0 (3)

(only,

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 retardation film.)

The above formula (1) will be described 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 is usually 180 nm or less, preferably 160 nm or more. or less, particularly preferably 150 nm or less. When it has in-plane retardation Re _T (550) in this range, the retardation film can function as a λ/4 plate. Therefore, by combining the retardation film with a linear polarizer, a circularly polarizing plate capable of suppressing reflection of external light can be obtained.

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 (A) and the resin layer (B) contained in the retardation film, and the This can be obtained by appropriately adjusting the direction of the slow axis.

The above formula (2) will be described in detail. The in-plane retardation Re _T (450), Re _T (550) and Re _T (650) of the retardation film at wavelengths 450 nm, 550 nm and 650 nm is, Re _T (450) < Re _T (550) < Re _T ( 650) is satisfied. The in-plane retardation of the retardation film which satisfy|fills this Formula (2) usually shows reverse wavelength dispersion property. Specifically, the retardation film usually has a larger in-plane retardation as the measurement wavelength is longer. Accordingly, this retardation film can function as a broadband λ/4 plate capable of uniformly converting the polarization state of light passing 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 capable of suppressing coloring due to reflection of external light.

In-plane retardation Re _T (450), Re _T (550) and Re _T (650) satisfying Formula (2) is, for example, the resin layer (A) and the resin layer (B) contained 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 described in detail. NZ coefficient _NZT of retardation film is larger than normally 0.0, Preferably it is larger than 0.2, Especially preferably larger than 0.3, Moreover, it is usually less than 1.0, Preferably it is less than 0.8, Especially preferably, it is less than 0.7. When retardation film has NZ coefficient _NZT of the said range, this retardation film has the birefringence adjusted suitably in both an in-plane direction and thickness direction. Accordingly, the circularly polarizing plate obtained by combining the retardation film with a linear polarizer can suppress coloring due to reflection of external light in both the front direction and the oblique direction of the display surface.

The NZ coefficient NZ _T of the retardation film is, unless otherwise specified, 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, "NZ _T = {Rth _T (550)/Re _T (550)} + 0.5”. NZ coefficient NZ _T which satisfy|fills Formula (3) can be obtained by adjusting suitably the NZ coefficient of each layer, such as a resin layer (A) and a resin layer (B) contained in retardation film, for example.

In the manufacturing method which concerns on this embodiment, the retardation film which satisfy|fills the above-mentioned Formula (1) - Formula (3), the resin layer (A) containing the thermoplastic resin A, and the resin layer containing the thermoplastic resin B ( It manufactures as retardation film provided in combination with B).

The combination of the thermoplastic resin A and the thermoplastic resin B is selected so that the sign of the intrinsic birefringence value of the thermoplastic resin A differs from the sign of the intrinsic birefringence value of the thermoplastic resin B. Specifically, a combination of a thermoplastic resin A having a positive intrinsic birefringence value and a thermoplastic resin B having a negative intrinsic birefringence value is used in combination. When the manufacturing method mentioned later is performed using these thermoplastic resins A and the thermoplastic resin B in combination, the retardation film which satisfy|fills above-mentioned Formula (1) - Formula (3) can be manufactured easily.

The thermoplastic resin A which has a positive intrinsic birefringence value contains the polymer which has a positive intrinsic birefringence value normally. Examples of the polymer include polyolefins such as polyethylene and polypropylene; polyesters such as polyethylene terephthalate and polybutylene terephthalate; polyarylene sulfides such as polyphenylene sulfide; polyvinyl alcohol; polycarbonate; polyarylate; cellulose ester; polyether sulfone; polysulfone; polyarylsulfone; polyvinyl chloride; alicyclic structure-containing polymers; rod-shaped liquid crystal polymer; and the like. These polymers may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios. Especially, an alicyclic structure containing polymer, a cellulose ester, and a polycarbonate are preferable, and an alicyclic structure containing polymer is especially preferable.

The alicyclic structure-containing polymer is a polymer containing an alicyclic structure in the repeating unit, and is usually an amorphous polymer. As the alicyclic structure-containing polymer, either a polymer containing an alicyclic structure in the main chain or a polymer containing an alicyclic structure in the side chain can be used. As an alicyclic structure, although a cycloalkane structure and a cycloalkene structure are mentioned, for example, From a 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, preferably 30 or less, more preferably 20 or more. or less, particularly preferably 15 or less.

In the alicyclic structure-containing polymer, the proportion of the repeating unit containing the 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 ratio of the repeating unit containing an alicyclic structure is in the said range, the retardation film excellent in heat resistance can be obtained.

Examples of the alicyclic structure-containing polymer include (1) norbornene polymers, (2) monocyclic cyclic olefin polymers, (3) cyclic conjugated diene polymers, (4) vinyl alicyclic hydrocarbon polymers, and these of hydrogenated products. Among these, a cyclic olefin polymer and a norbornene-type polymer are preferable, and a norbornene-type polymer is especially preferable. As a norbornene-type polymer, For example, the ring-opening polymer of the monomer containing a norbornene structure, the ring-opening copolymer of the monomer containing a norbornene structure, and other monomers capable of ring-opening copolymerization, and their hydrides; The addition copolymer of the monomer containing a norbornene structure, the addition copolymer of the monomer containing a norbornene structure, and other monomer copolymerizable, etc. are mentioned. Among these, from a viewpoint of transparency, the ring-opened polymer hydride of the monomer containing a norbornene structure is especially preferable. The alicyclic structure-containing polymer may be selected from, for example, polymers disclosed in Japanese Patent Application Laid-Open No. 2002-321302.

Examples of the cellulose ester include lower fatty acid esters of cellulose (eg, cellulose acetate, cellulose acetate butyrate, and cellulose acetate propionate). A lower fatty acid means a C6 or less fatty acid per molecule. Cellulose acetate may include triacetyl cellulose (TAC) and cellulose diacetate (DAC).

The total acyl group substitution degree of a cellulose ester becomes like this. Preferably they are 2.20 or more and 2.70 or less, More preferably, they are 2.40 or more and 2.60 or less. Here, the total acyl group can be measured according to ASTM D817-91. Moreover, the weight average polymerization degree of a cellulose ester becomes like this. Preferably they are 350 or more and 800 or less, More preferably, they are 370 or more and 600 or less.

A polycarbonate has a repeating unit containing a carbonate bond (-O-C(=O)-O-) normally. Examples of the polycarbonate include a polymer having a structural unit derived from a dihydroxy compound and a carbonate structure (structure represented by -O-(C=O)-O-). As a dihydroxy compound, bisphenol A is mentioned, for example. The number of structural units derived from the dihydroxy compound contained in polycarbonate may be one, and 2 or more types may be sufficient as them.

The weight average molecular weight (Mw) of the polymer contained in the thermoplastic resin A is preferably 10,000 or more, more preferably 15,000 or more, particularly preferably 20,000 or more, preferably 100,000 or less, more preferably 80,000 or less, Especially preferably, it is 50,000 or less. When the weight average molecular weight is in this range, the mechanical strength and moldability of the resin layer (A) are highly balanced. Said 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, when a sample does not melt|dissolve in cyclohexane, you may use toluene as a solvent of GPC.

The molecular weight distribution (weight average molecular weight (Mw)/number average molecular weight (Mn)) of the polymer contained in the thermoplastic resin A is preferably 1.2 or more, more preferably 1.5 or more, particularly preferably 1.8 or more, and preferably is 3.5 or less, more preferably 3.0 or less, particularly preferably 2.7 or less. When molecular weight distribution is more than the lower limit of the said range, productivity of a polymer can be improved and manufacturing cost can be suppressed. Moreover, when molecular weight distribution is below an upper limit, since the quantity of a low molecular component becomes small, the relaxation at the time of high temperature exposure can be suppressed and stability of a resin layer (A) can be improved.

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

The thermoplastic resin A may further contain arbitrary components in combination with said polymer. As an arbitrary component, For example, Stabilizers, such as antioxidant, a heat stabilizer, a light stabilizer, a weathering stabilizer, a ultraviolet absorber, a near-infrared absorber; plasticizer; and the like. These components may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

The thermoplastic resin B which has a negative intrinsic birefringence value contains the polymer which has a negative intrinsic birefringence value normally. Examples of the polymer include a homopolymer of styrene or a styrene derivative, and a polystyrene-based polymer including a copolymer of styrene or a styrene derivative and an optional monomer; polyacrylonitrile polymers; polymethylmethacrylate polymers; poly(2-vinylnaphthalene); or a multi-component copolymer thereof; and the like. Moreover, as arbitrary monomers which can be copolymerized with styrene or a styrene derivative, acrylonitrile, maleic anhydride, methyl methacrylate, butadiene, etc. are mentioned, for example. In addition, these polymers may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

Among the polymers having a negative intrinsic birefringence value, a polystyrene-based polymer is preferable from the viewpoint of high phase difference appearance. Especially, the copolymer of styrene or a styrene derivative, and maleic anhydride is especially preferable from a viewpoint that heat resistance is high. In this copolymer, the amount of maleic anhydride unit is preferably 5 parts by weight or more, more preferably 10 parts by weight or more, particularly preferably 15 parts by weight or more, based on 100 parts by weight of the polystyrene-based polymer. Preferably it is 30 parts by weight or less, more preferably 28 parts by weight or less, particularly preferably 26 parts by weight or less. A maleic anhydride unit means the structural unit which has a structure formed by superposing|polymerizing maleic anhydride.

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

The thermoplastic resin B may further contain arbitrary components in combination with said polymer. As an arbitrary component, the example similar to the arbitrary component which the thermoplastic resin A may contain is mentioned, for example. Arbitrary components may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

The combination of the thermoplastic resin A contained in the resin layer (A) and the thermoplastic resin B contained in the resin layer (B) is the absolute value of the difference between the glass transition temperature TgA of the thermoplastic resin A and the glass transition temperature TgB of the thermoplastic resin B |TgA - TgB| is selected so that it may become a predetermined range. Specifically, the absolute value |TgA - TgB| of the said difference is 5 degreeC or more normally, More preferably, it is 10 degreeC or more, Especially preferably, it is 13 degreeC or more. When a thermoplastic resin having a different glass transition temperature is used as a thermoplastic resin A and a thermoplastic resin B in combination to the above degree, and the manufacturing method described later is performed, a retardation film satisfying the above formulas (1) to (3) It can be manufactured simply. The upper limit of the absolute value of the difference |TgA - TgB| is not particularly limited, and from the viewpoint of smoothly stretching the multilayer film, preferably 40° C. or less, more preferably 30° C. or less, particularly preferably 25°C or less.

Specific values of the glass transition temperature TgA of the thermoplastic resin A and the glass transition temperature TgB of the thermoplastic resin B are arbitrary within the range in which the absolute value |TgA - TgB| of their difference satisfies the above requirements. For example, among the glass transition temperature TgA and the glass transition temperature TgB, the lower temperature Tg(low) is preferably 100°C or higher, more preferably 105°C or higher, particularly preferably 110°C or higher, and preferably Preferably, it may be 140°C or less, more preferably 135°C or less, and particularly preferably 130°C or less. The higher temperature Tg(high) among the glass transition temperature TgA and the glass transition temperature TgB is preferably 120°C or higher, more preferably 125°C or higher, particularly preferably 130°C or higher, and preferably It may be 160 °C or less, more preferably 155 °C or less, and particularly preferably 150 °C or less. When the thermoplastic resin A and the thermoplastic resin B which have these glass transition temperatures TgA and TgB are used, manufacture of retardation film can be performed especially simply.

In particular, at a wavelength of 550 nm, when the resin layer (A) included in the retardation film has a larger in-plane retardation than the resin layer (B) included in the retardation film, the glass transition temperature TgA of the thermoplastic resin A is the thermoplastic resin B It is preferably lower than the glass transition temperature of TgB. According to the combination of the thermoplastic resin A and the thermoplastic resin B, it is particularly easy to manufacture a retardation film comprising a resin layer (A) having a relatively large in-plane retardation and a resin layer (B) having a relatively small in-plane retardation. can

In addition, at a wavelength of 550 nm, when the resin layer (B) included in the retardation film has a larger in-plane retardation than the resin layer (A) included in the retardation film, the glass transition temperature TgB of the thermoplastic resin B is the thermoplastic resin A It is preferably lower than the glass transition temperature of TgA. According to the combination of the thermoplastic resin A and the thermoplastic resin B, it is particularly easy to manufacture a retardation film comprising a resin layer (A) having a relatively small in-plane retardation and a resin layer (B) having a relatively large in-plane retardation. can

The glass transition temperature Tg can be measured using a differential scanning calorimeter ("DSC6220SII" manufactured by Nanotechnology Co., Ltd.) on condition of a temperature increase rate of 10°C/min based on JIS K6911.

The resin layer (A) with which retardation film is equipped has a slow axis. Moreover, the resin layer (B) with which retardation film is equipped has a slow axis substantially perpendicular|vertical with respect to the said slow axis of a resin layer (A). When the slow axis of the resin layer (B) is "approximately perpendicular" to the slow axis of the resin layer (A), the angle between the slow axis of the resin layer (A) and the slow axis of the resin layer (B) is close to 90° indicates that it is within a specific range. Specifically, the angle between the slow axis of the resin layer (A) and the slow axis of the resin layer (B) is usually 85° or more, preferably 87° or more, more preferably 88° or more, particularly preferably It is 89 degrees or more, Usually 95 degrees or less, Preferably it is 93 degrees or less, More preferably, it is 92 degrees or less, Especially preferably, it is 91 degrees or less. In the manufacturing method mentioned later, it is a film of a multilayer structure provided by combining the resin layer (A) and the resin layer (B) which have the slow axis of the said relationship, Comprising: The retardation which satisfy|fills Formula (1) - Formula (3) mentioned above. film can be obtained.

In particular, in a long retardation film, it is preferable that one of the slow axis of the resin layer (A) and the slow axis of the resin layer (B) form an angle in a specific range close to 45° with respect to the width direction of the retardation film. Specifically, the above angle is preferably 40° or more, more preferably 42° or more, still more preferably 43° or more, particularly preferably 44° or more, preferably 50° or less, more preferably preferably 48° or less, more preferably 47° or less, particularly preferably 46° or less. In this case, it is preferable that the other of the slow axis of the resin layer (A) and the slow axis of the resin layer (B) form an angle in a specific range close to 135° with respect to the width direction of the retardation film. Specifically, said angle becomes like this. Preferably it is 130 degrees or more, More preferably, it is 132 degrees or more, More preferably, it is 133 degrees or more, Especially preferably, it is 134 degrees or more, Preferably it is 140 degrees or less, More preferably preferably 138° or less, more preferably 137° or less, particularly preferably 136° or less. A general long linear polarizer has an absorption axis parallel or perpendicular to the width direction of the linear polarizer. A long retardation film having a resin layer (A) and a resin layer (B) having a slow axis in a direction forming an angle of the above range with respect to the width direction is simply a straight line with the width direction of the retardation film in the above general linear polarizer. A circularly polarizing plate can be obtained by making the width direction of a polarizer parallel and bonding together. Therefore, since bonding of retardation film and linear polarizer can be performed by roll-to-roll, a circularly polarizing plate can be manufactured especially simply.

It is preferable to set suitably NZ coefficient _NZA of a resin layer ( _A ), and NZ coefficient NZB of a resin layer ( _B ) so that NZ coefficient NZT of retardation film can be made into Formula (3). NZ coefficient NZ _A of the resin layer (A) is a value represented by "NZ _A = (nx _A - nz _A )/(nx _A - ny _A )", therefore "NZ _A = (Rth _A /Re _A )" + 0.5”. nx _A represents the refractive index of the direction which provides the largest refractive index as an in-plane direction of a resin layer (A). ny _A represents the refractive index of the direction orthogonal to the direction which provides nx _A as an in-plane direction of a resin layer (A). nz _A represents the refractive index of the thickness direction of a resin layer (A). Re _A represents the in-plane retardation of the resin layer (A), and therefore it is represented by "Re _A = (nx _A - ny _A ) x d _A ". Rth _A represents the thickness direction retardation of the resin layer (A), therefore, it is represented by "Rth _A = {(nx _A + ny _A )/2 - nz _A } x d _A ". d _A represents the thickness of the resin layer (A). In addition, the NZ coefficient NZ _B of the resin layer (B) is a value represented by "NZ _B = (nx _B - nz _B )/(nx _B - ny _B )", and therefore "NZ _B = (Rth _B /Re)" _B ) + 0.5”. nx _B represents the refractive index of the direction which provides the largest refractive index as an in-plane direction of a resin layer (B). ny _B represents the refractive index of the direction orthogonal to the direction which provides nx _B as an in-plane direction of a resin layer (B). nz _B represents the refractive index of the thickness direction of a resin layer (B). Re _B represents the in-plane retardation of the resin layer (B), and therefore is represented by "Re _B = (nx _B - ny _B ) x d _B ". Rth _B represents the thickness direction retardation of the resin layer (B), therefore, it is represented by "Rth _B = {(nx _B + ny _B )/2 - nz _B } x d _B ." d _B represents the thickness of the resin layer (B).

As for NZ coefficient NZA of a resin layer ( _A ), 1.00 or more are preferable. Accordingly, the refractive indices ny _A and nz _A of the resin layer (A) preferably satisfy the relationship of ny _A ≥ nz _A. Moreover, as for NZ coefficient NZB of a resin layer ( _B ), less than 0.0 is preferable. Accordingly, the refractive indices nx _B and nz _B of the resin layer (B) preferably satisfy the relationship of nz _B > nx _B. According to the resin layer (A) and the resin layer (B) of such a combination, NZ coefficient _NZT of the whole retardation film can be adjusted easily within the range of Formula (3).

More specifically, NZ coefficient NZA of a resin layer ( _A ) becomes like this. Preferably it is 1.00 or more, More preferably, it is 1.05 or more, Preferably it is 1.30 or less, More preferably, it is 1.20 or less. As described above, the refractive indices nx _A , ny _A and nz _A of the resin layer (A) having an NZ coefficient NZ _A of 1.00 or more may have a relationship of nx _A > ny _A ≥ nz _A . Therefore, the resin layer (A) can function as a positive A plate or a negative B plate.

Moreover, NZ coefficient NZB of a resin layer ( _B ) becomes like this. Preferably it is -2.0 or more, More preferably, it is -1.5 or more, Preferably it is less than 0.0, More preferably, it is -0.2 or less, Especially preferably, -0.4. is below. As described above, the refractive indices nx _B , ny _B and nz _B of the resin layer (B) having an NZ coefficient of less than 0.0 may have a relationship of nz _B > nx _B > ny _B . Accordingly, the resin layer (B) may be a layer (that is, a layer having biaxiality) having different refractive indices nx _B , ny _B and nz _B in three directions. In addition, the resin layer (B) can function as a positive B plate.

It is preferable that sum _NZA +NZB of NZ coefficient _NZA of a resin layer ( _A ) and NZ coefficient NZB of a resin layer ( _B ) falls within a specific range. Specifically, the sum "NZ _A + NZ _B " is preferably -0.3 or more, more preferably 0.0 or more, particularly preferably 0.15 or more, preferably 0.8 or less, more preferably 0.75 or less, particularly Preferably it is 0.65 or less. When the sum "NZ _A + NZ _B " is within the above range, it is possible to realize a retardation film capable of obtaining a circularly polarizing plate capable of effectively suppressing coloration due to reflection of external light in both the front direction and the oblique direction of the display surface. .

It is preferable that retardation film satisfy|fills following formula (4).

{Re _Q (450)/Re _Q (550)} - {Re _H (450)/Re _H (550)} > 0.08 (4)

(only,

Re _H (450) represents the in-plane retardation of the high-order retardation layer at a wavelength of 450 nm,

Re _H (550) represents the in-plane retardation of the higher retardation layer at a wavelength of 550 nm,

Re _Q (450) represents the in-plane retardation of the low retardation layer at a wavelength of 450 nm,

Re _Q (550) represents the in-plane retardation of the low retardation layer at a wavelength of 550 nm,

The high retardation layer represents a layer with a larger in-plane retardation at a wavelength of 550 nm among the resin layer (A) and the resin layer (B) included in the retardation film,

The low retardation layer represents a layer with a smaller in-plane retardation at a wavelength of 550 nm among the resin layer (A) and the resin layer (B) included in the retardation film.)

In Formula (4), "Re _Q (450)/Re _Q (550)" represents the wavelength dispersion property of the low retardation layer. In addition, in Formula (4), "Re _H (450)/Re _H (550)" represents the wavelength dispersibility of the higher phase difference layer. Therefore, Formula (4) shows that there exists a difference in the wavelength dispersion property of in-plane retardation between the low retardation layer and high retardation layer with which retardation film is equipped. More specifically, it shows that the in-plane retardation of the low retardation layer has larger wavelength dispersion than the in-plane retardation of the high retardation layer. The parameter "{Re _Q (450)/Re _Q (550)} - {Re _H (450)/Re _H (550)}" indicating the difference in wavelength dispersion is, in detail, preferably larger than 0.08, More preferably, it is larger than 0.09, particularly preferably larger than 0.10, and the upper limit is not particularly limited, and is preferably less than 2.0, more preferably less than 1.5, particularly preferably less than 1.2. Thus, the retardation film provided with the resin layer (A) and the resin layer (B) which differ in the wavelength dispersion property of in-plane retardation can acquire reverse dispersion characteristic easily in a laminated|stacked state.

"Re _Q (450) / Re _Q (550)" is preferably 1.05 or more, more preferably 1.08 or more, particularly preferably 1.1 or more, and the upper limit is not particularly limited, and is preferably 2.0 or less. , More preferably, it is 1.7 or less, Especially preferably, it is 1.5 or less. When "Re _Q (450)/Re _Q (550)" exists in the said range, the circularly polarizing plate which can suppress effectively coloring by reflection of external light can be obtained.

"Re _H (450) / Re _H (550)" is preferably 0.92 or more, more preferably 0.95 or more, particularly preferably 0.98 or more, preferably 1.2 or less, more preferably 1.1 or less, particularly Preferably it is 1.05 or less. When " _ReH (450)/ _ReH (550)" exists in the said range, the circularly polarizing plate which can suppress effectively coloring by reflection of external light can be obtained.

The in-plane retardation Re _Q (550) of the low retardation layer at a wavelength of 550 nm is preferably 80 nm or more, more preferably 100 nm or more, particularly preferably 110 nm or more, preferably 170 nm or less, more preferably preferably 150 nm or less, particularly preferably 140 nm or less. When the in-plane retardation Re _Q (550) is within the above range, the low retardation layer can function as a λ/4 plate. And according to the retardation film provided with this low retardation layer, the circularly polarizing plate which can suppress effectively coloring by reflection of external light can be obtained.

The in-plane retardation Re _H (550) of the high-order retardation layer at a wavelength of 550 nm is preferably 220 nm or more, more preferably 240 nm or more, particularly preferably 250 nm or more, preferably 310 nm or less, more preferably preferably 290 nm or less, particularly preferably 280 nm or less. When the in-plane retardation Re _H (550) is within the above range, the higher retardation layer can function as a λ/2 plate. And according to the retardation film provided with the high retardation layer, the circularly polarizing plate which can suppress effectively coloring by reflection of external light can be obtained.

The difference "Re _H (550) - Re _Q (550)" between the in-plane retardation Re _H (550) and the in-plane retardation Re _Q (550) is preferably 100 nm or more, more preferably 110 nm or more, preferably is 180 nm or less, more preferably 160 nm or less. When "Re _H (550) - Re _Q (550)" exists in the said range, the circular polarizing plate which can suppress effectively coloring by reflection of external light can be obtained.

The retardation film may be provided with arbitrary layers other than a resin layer (A) and a resin layer (B) as needed. Examples of the optional layer include any layer having optical isotropy. The optional layer having this optical isotropy has an in-plane retardation of usually 10 nm or less at a wavelength of 550 nm, for example, a protective film layer for protecting the resin layer (A) and the resin layer (B); Adhesive layer which adhere|attaches each layer, such as a resin layer (A) and a resin layer (B); and the like. Further, other examples of the optional layer include any layer having optical anisotropy. There is no restriction|limiting as for the optical characteristic of the arbitrary layer which has this optical anisotropy in the range which the whole retardation film satisfy|fills Formula (1) - Formula (3). For example, any layer having optical anisotropy and a combination of one or both of the resin layer (A) and the resin layer (B) can function as a λ/4 plate or a λ/2 plate, so that the optional The optical properties of the layer of may be set.

The total light transmittance of the retardation film is preferably 80% or more, more preferably 85% or more, and particularly preferably 90% or more. The total light transmittance can be measured in a 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%. A haze can be measured using a haze meter based on JISK7361-1997.

A single-leaf film may be sufficient as retardation film, and a long film may be sufficient as it.

There is no restriction|limiting in particular in the thickness of retardation film. The specific thickness of the retardation film is, from the viewpoint of thinning, preferably 5 µm or more, more preferably 10 µm or more, particularly preferably 15 µm or more, preferably 200 µm or less, more preferably 150 µm or less , particularly preferably 100 μm or less.

There is no restriction|limiting in particular in the thickness of each layer, such as a resin layer (A) and a resin layer (B) with which retardation film is equipped. The thickness of the resin layer (A) and the resin layer (B) is each independently, preferably 0.5 µm or more, more preferably 1 µm or more, preferably 150 µm or less, more preferably 100 µm or less. .

[2. Outline of the manufacturing method of retardation film]

In the manufacturing method according to an embodiment of the present invention, the retardation film described above,

A first step of preparing a multilayer film comprising a resin layer (A) formed of a thermoplastic resin A and a resin layer (B) formed of a thermoplastic resin B;

2nd process of extending|stretching a multilayer film twice or more

Manufactured by a manufacturing method comprising

The resin layer (A) and the resin layer (B) with which the multilayer film prepared in the 1st process is equipped has optical properties different from the optical properties of the resin layer (A) and the resin layer (B) with which the retardation film is equipped . Specifically, the resin layer (A) and the resin layer (B) which a multilayer film is equipped with normally do not have large optical anisotropy. Therefore, the resin layer (A) and resin layer (B) with which a multilayer film is equipped does not have retardation normally, or even if it has, those values are small. In addition, the resin layer (A) and resin layer (B) with which a multilayer film is equipped does not have a slow axis normally, or even if it has, those slow axes are not substantially perpendicular|vertical.

Therefore, in the manufacturing method which concerns on this embodiment, the 2nd process including extending|stretching twice or more is implemented with respect to this multilayer film. By extending|stretching in this 2nd process, the optical characteristic of a resin layer (A) and a resin layer (B) is adjusted, and the retardation film which has the above-mentioned desired optical characteristic is obtained. For example, by extending|stretching in a 2nd process, large optical anisotropy expresses in resin layer (A) and resin layer (B), and the phase difference which satisfy|fills Formula (1), Formula (2), and Formula (3) A film is obtained. Moreover, mutually perpendicular slow axes express in the resin layer (A) and the resin layer (B) by extending|stretching in a 2nd process. When the resin layer (A) and resin layer (B) with which a multilayer film is equipped had a slow axis, the direction of these slow axes is adjusted by extending|stretching in a 2nd process, and those slow axes become substantially perpendicular|vertical.

[3. 1st process: preparation of multilayer film]

At a 1st process, the multilayer film provided with the resin layer (A) formed from the thermoplastic resin A and the resin layer (B) formed from the thermoplastic resin B is prepared. Thermoplastic resin A and thermoplastic resin B are as having demonstrated in the term of retardation film.

Usually, the resin layer (A) and resin layer (B) with which the multilayer film prepared at a 1st process is equipped does not have large optical anisotropy. Therefore, the phase difference between a resin layer (A) and a resin layer (B) is small normally. If a specific range is given, the in-plane retardation of the resin layer (A) and the resin layer (B) at 550 nm is each independently, preferably 0 nm to 20 nm, more preferably 0 nm to 10 nm, particularly preferably It is usually 0 nm to 5 nm.

Although a single-leaf film may be sufficient as a multilayer film, it is preferable that it is a long film. By preparing a multilayer film as a long film, when manufacturing retardation film, since it is possible to perform a part or all of each process inline, manufacture can be performed simply and efficiently.

There is no restriction|limiting in the manufacturing method of a multilayer film. Examples of the multilayer film include a co-extrusion method, a co-spreading method, and a coating method in which a liquid composition containing a material for a layer other than that on a certain layer is coated. Especially, the method of coating the liquid composition containing the thermoplastic resin B on the resin layer (A), and drying the coated liquid composition as needed is preferable. Hereinafter, the manufacturing method of this multilayer film is demonstrated.

There is no restriction|limiting in the manufacturing method of a resin layer (A). The resin layer (A) can be manufactured by, for example, a melt molding method or a solution casting method. Among them, the melt molding method is preferable. Among the melt molding methods, an extrusion molding method, an inflation molding method, or a press molding method is preferable, and an extrusion molding method is particularly preferable. According to these methods, the resin layer (A) can be manufactured as a long film.

After preparing said resin layer (A), the liquid composition containing the thermoplastic resin B is coated on the resin layer (A). The liquid composition may contain the thermoplastic resin B and a solvent. As the solvent, those capable of dissolving or dispersing the thermoplastic resin B are preferable, and those capable of dissolving the thermoplastic resin B are particularly preferable. In addition, a solvent may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios. The concentration of the thermoplastic resin B in the liquid composition is preferably adjusted so that the viscosity of the liquid composition falls within a range suitable for coating, and may be, for example, 1 wt% to 50 wt%.

There is no restriction|limiting in the coating method of a liquid composition. As the coating method, for example, curtain coating method, extrusion coating method, roll coating method, spin coating method, dip coating method, bar coating method, spray coating method, slide coating method, printing coating method, gravure coating method, die A coating method, a gap coating method, a dipping method, etc. are mentioned.

By coating the liquid composition containing the thermoplastic resin B, a layer of the liquid composition is formed on the resin layer (A). Therefore, by drying the layer of a liquid composition as needed and removing a solvent, a resin layer (B) is formed on a resin layer (A), and a multilayer film can be obtained. There is no restriction|limiting in the drying method, For example, drying methods, such as heat drying and reduced-pressure drying, can be used.

[4. 2nd process: Stretching of a multilayer film]

After preparing a multilayer film in a 1st process, the 2nd process including extending|stretching the multilayer film twice or more is performed. This second process is

1st extending process of extending|stretching a multilayer film at extending|stretching temperature Ts1;

The 2nd extending process of extending|stretching a multilayer film at extending|stretching temperature Ts2 different from extending|stretching temperature Ts1 is included in this order. The above-mentioned retardation film can be obtained by performing extending|stretching twice or more at these different temperatures.

It is preferable that the absolute value |Ts1 - Ts2| of the difference of the extending|stretching temperature Ts1 in a 1st extending process and the extending|stretching temperature Ts2 in a 2nd extending process exists in a specific range. Specifically, the absolute value of the difference |Ts1 - Ts2| is preferably 5°C or higher, more preferably 8°C or higher, particularly preferably 10°C or higher, preferably 25°C or lower, more preferably Preferably it is 22 degrees C or less, Especially preferably, it is 20 degrees C or less. When the absolute value |Ts1 - Ts2| of the difference of the extending|stretching temperature Ts1 and extending|stretching temperature Ts2 exists in the said range, manufacture of retardation film can be performed especially simply.

Among the stretching temperature Ts1 and the stretching temperature Ts2, the lower temperature is preferably in a specific temperature range close to Tg (low). Specifically, this specific temperature range is preferably Tg(low)-5°C or higher, more preferably Tg(low)-3°C or higher, particularly preferably Tg(low)-1°C or higher, and preferably Preferably Tg(low)+20°C or lower, more preferably Tg(low)+15°C or lower, particularly preferably Tg(low)+12°C or lower. Tg(low) shows the lower temperature among the glass transition temperature TgA and the glass transition temperature TgB. Among the stretching temperature Ts1 and the stretching temperature Ts2, when the lower temperature is in the above range, the orientation of the polymer molecules contained in both the resin layer (A) and the resin layer (B) is effectively promoted, and their refractive index is greatly changed It can be made, and therefore, manufacture of retardation film can be performed especially easily.

Among the stretching temperature Ts1 and the stretching temperature Ts2, the higher temperature is preferably in a specific temperature range close to Tg (high). Specifically, this specific temperature range is preferably Tg(high)-5°C or higher, more preferably Tg(high)-3°C or higher, particularly preferably Tg(high)-1°C or higher, and preferably Preferably, it is Tg(high)+20°C or less, more preferably Tg(high)+15°C or less, particularly preferably Tg(high)+12°C or less. Tg(high) represents the higher temperature among the glass transition temperature TgA and the glass transition temperature TgB. Among the stretching temperature Ts1 and the stretching temperature Ts2, when the higher temperature is within the above range, in the resin layer (A) and the resin layer (B) formed of a thermoplastic resin having a higher glass transition temperature, the polymer molecules Orientation proceeds greatly. Accordingly, the refractive index can be greatly changed. On the other hand, in a resin layer formed of a thermoplastic resin having a lower glass transition temperature, since the stretching temperature is sufficiently higher than the glass transition temperature, the orientation of the polymer molecules proceeds relatively small or does not proceed. Therefore, the refractive index does not change, or even if it does, the amount of change is small. Thereby, since adjustment of the optical characteristic of a resin layer (A) and a resin layer (B) can be made simple, manufacture of retardation film can be performed especially easily.

The extending|stretching in a 2nd process may perform extending|stretching at high temperature first, and may perform extending|stretching at low temperature first. Therefore, the extending|stretching temperature Ts1 in the 1st extending|stretching process performed earlier may be lower than the extending|stretching temperature Ts2 in the 2nd extending|stretching process performed later. Moreover, the extending|stretching temperature Ts1 in the 1st extending process performed earlier may be higher than the extending|stretching temperature Ts2 in the 2nd extending process performed later. Especially, it is preferable that extending|stretching temperature Ts1 in the 1st extending|stretching process performed earlier is higher than extending|stretching temperature Ts2 in the 2nd extending process performed later from a viewpoint of making manufacture of retardation film especially simple.

At a 2nd process, the extending|stretching in a 1st extending process and extending|stretching in a 2nd extending process are normally performed in the other extending|stretching direction. At this time, the extending|stretching in a 1st extending process and extending|stretching in a 2nd extending process can all be performed as unidirectional extending|stretching. Especially, it is preferable to perform extending|stretching in a 2nd process so that the extending|stretching direction in a 1st extending process and the extending|stretching direction in a 2nd extending process may become substantially perpendicular|vertical. When two extending directions are "substantially perpendicular", it shows that the angle which these extending directions make exists in the specific range close|similar to 90 degrees. Specifically, the angle formed by these stretching directions is preferably 85° or more, more preferably 87° or more, still more preferably 88° or more, particularly preferably 89° or more, and preferably 95° or less. , more preferably 93° or less, still more preferably 92° or less, particularly preferably 91° or less. When the extending|stretching direction in a 1st extending|stretching process and the extending|stretching direction in a 2nd extending process are substantially perpendicular|vertical, manufacture of retardation film can be performed especially easily.

In particular, when stretching a long multilayer film in the second step, one of the stretching direction in the first stretching step and the stretching direction in the second stretching step is close to 45° with respect to the width direction of the multilayer film It is desirable to achieve an angle within a certain range. Specifically, the above angle is preferably 40° or more, more preferably 42° or more, still more preferably 43° or more, particularly preferably 44° or more, preferably 50° or less, more preferably preferably 48° or less, more preferably 47° or less, particularly preferably 46° or less. Moreover, in this case, it is preferable that the other of the extending|stretching direction in the extending|stretching direction in a 1st extending|stretching process and a 2nd extending|stretching process forms an angle in the specific range close|similar to 135 degrees with respect to the width direction of retardation film. Specifically, said angle becomes like this. Preferably it is 130 degrees or more, More preferably, it is 132 degrees or more, More preferably, it is 133 degrees or more, Especially preferably, it is 134 degrees or more, Preferably it is 140 degrees or less, More preferably preferably 138° or less, more preferably 137° or less, particularly preferably 136° or less. When extending|stretching at said extending|stretching angle, since a circularly polarizing plate can be manufactured by bonding the retardation film obtained normally by roll-to-roll and a long linear polarizer, it can manufacture a circularly polarizing plate especially easily.

It is preferable to set the draw ratio of extending|stretching performed at a 2nd process suitably so that a desired retardation film may be obtained. In addition, the draw ratio of each extending|stretching may be same or different. Therefore, the draw ratio in a 1st extending process and the draw ratio in a 2nd extending process may be same or different.

Among the first stretching step and the second stretching step, the draw ratio in the stretching step of performing stretching at a relatively low stretching temperature is preferably 1.2 times or more, more preferably 1.3 times or more, particularly preferably 1.35 times or more. and preferably 3.0 times or less, more preferably 2.5 times or less, particularly preferably 2.0 times or less. When the draw ratio in the stretching step of performing stretching at a relatively low stretching temperature is within the above range, the retardation film can be manufactured particularly simply.

Among the first stretching step and the second stretching step, the stretching ratio in the stretching step of performing stretching at a relatively high stretching temperature is preferably 1.05 times or more, more preferably 1.1 times or more, particularly preferably 1.12 times or more. and preferably 2.0 times or less, more preferably 1.5 times or less, particularly preferably 1.3 times or less. When the draw ratio in the extending process of performing extending|stretching at a relatively high extending|stretching temperature exists in the said range, manufacture of retardation film can be performed especially simply.

A 2nd process may include the arbitrary extending process of further extending|stretching a multilayer film in combination with a 1st extending process and a 2nd extending process. The extending|stretching conditions in arbitrary extending|stretching processes can be set suitably in the range which can obtain a desired retardation film.

According to the second step described above, the resin layer (A) and the resin layer (B) with the multilayer film, the resin layer (A) and the resin layer (B) with the retardation film to express the optical properties required can Therefore, by extending|stretching in a 2nd process, retardation film can be obtained as a stretched multilayer film. The present inventor guesses that the structure from which retardation film is obtained by extending|stretching in a 2nd process is as follows. However, the technical scope of the present invention is not limited by the following structure.

A 2nd process includes extending|stretching at extending|stretching temperature Ts1, and extending|stretching at the extending|stretching temperature Ts2 different from the extending|stretching temperature Ts1.

According to extending|stretching at the lower temperature among extending|stretching temperature Ts1 and Ts2, the polymer molecule contained in the resin layer (A) with which a multilayer film is equipped, and a resin layer (B) is orientated in an extending|stretching direction. By this orientation, in the resin layer (A) containing the thermoplastic resin A having a positive intrinsic birefringence value, the refractive index in the direction parallel to the stretching direction becomes large, and the refractive index in the direction perpendicular to the stretching direction becomes small. In addition, in the resin layer (B) containing the thermoplastic resin B having a negative intrinsic birefringence value, the refractive index in the direction perpendicular to the stretching direction becomes large by the above orientation, and the refractive index in the direction parallel to the stretching direction becomes small. .

On the other hand, the polymer molecules contained in the resin layer (A) and the resin layer (B) can be oriented in the stretching direction even by stretching at the higher temperature among the stretching temperatures Ts1 and Ts2. By this orientation, in the resin layer (A), the refractive index in the direction parallel to the stretching direction can be increased, and the refractive index in the direction perpendicular to the stretching direction can be decreased. In addition, in the resin layer (B), the refractive index in the direction perpendicular to the stretching direction may be increased, and the refractive index in the direction parallel to the stretching direction may be decreased. However, the degree of orientation may be different from stretching at a lower temperature. Specifically, among the resin layer (A) and the resin layer (B), in a resin layer formed of a thermoplastic resin having a higher glass transition temperature, the orientation of the polymer molecules advances relatively large, but the glass transition temperature is low. In the resin layer formed of the thermoplastic resin on the side, the orientation of the polymer molecules progresses relatively small, or the orientation does not advance.

Therefore, by performing the stretching at the stretching temperature Ts1 and stretching at the stretching temperature Ts2 in combination, the degree of change in the refractive index and the direction in which the change in the refractive index occurs are determined for each of the resin layer (A) and the resin layer (B). can be adjusted in Usually, it adjusts so that one uniaxial property of a resin layer (A) and a resin layer (B) may become high, and the other biaxial property of a resin layer (A) and a resin layer (B) may become high. And as a result of this adjustment, since the resin layer (A) and the resin layer (B) which have optical characteristics, such as in-plane retardation, thickness direction retardation, and the direction of a slow axis, in appropriate ranges are obtained, the retardation film mentioned above is obtained.

[5. arbitrary process]

The manufacturing method of retardation film may further include arbitrary processes in combination with the 1st process and 2nd process mentioned above. For example, when a long retardation film is obtained using a long multilayer film, the manufacturing method of the retardation film may include the trimming process of cutting out the obtained retardation film into a desired shape. According to the trimming process, the retardation film of the sheet|leaf which has a desired shape is obtained. Moreover, the manufacturing method of retardation film may include the process of forming a protective layer in retardation film, for example.

[6. Preferred first example]

Hereinafter, a first preferred example of the manufacturing method according to the above-described embodiment will be described. In this 1st example, the retardation film is manufactured using the thermoplastic resin A and the thermoplastic resin B which have glass transition temperature TgA and glass transition temperature TgB which satisfy|fill TgA<TgB.

In the manufacturing method which concerns on a 1st example, the 1st process of preparing the multilayer film provided with the resin layer (A) formed from the said thermoplastic resin A, and the resin layer (B) formed from the thermoplastic resin B is performed. Then, the 2nd process containing the 1st extending process of extending|stretching a multilayer film in one direction at extending|stretching temperature Ts1, and the 2nd extending process of extending|stretching in the other one direction at extending|stretching temperature Ts2 is performed. In the second step of the manufacturing method according to the first example, the stretching direction in the first stretching step and the stretching direction in the second stretching step are substantially perpendicular.

In this first example, according to the stretching at the lower temperature among the stretching temperatures Ts1 and Ts2, in both the resin layer (A) and the resin layer (B) of the multilayer film, in the stretching direction of the polymer molecules Orientation proceeds greatly. Accordingly, in the resin layer (A), the refractive index in the stretching direction becomes large, and the refractive index in the direction perpendicular to the stretching direction becomes small. On the other hand, in the resin layer (B), the refractive index of an extending|stretching direction becomes small and the refractive index of the direction perpendicular|vertical to an extending|stretching direction becomes large.

Moreover, according to the stretching at the higher temperature among the stretching temperatures Ts1 and Ts2, the orientation of the polymer molecules in the stretching direction greatly advances in the resin layer (B), but in the resin layer (A), the polymer molecules The orientation in the stretching direction progresses small, or the orientation does not advance. Therefore, in the resin layer (A), the refractive index does not change, or even if it changes, the change is small. On the other hand, in the resin layer (B), the refractive index of an extending|stretching direction becomes small and the refractive index of the direction perpendicular|vertical to an extending|stretching direction becomes large.

In a 1st example, the extending|stretching direction in a 1st extending process and the extending|stretching direction in a 2nd extending process are substantially perpendicular|vertical. Therefore, according to the combination of said 1st extending process and 2nd extending process, uniaxial property becomes large in resin layer (A), and biaxial property becomes large in resin layer (B). And as a film provided with the resin layer (A) with large uniaxial property and the resin layer (B) with high biaxial property in this way, a desired retardation film can be obtained. The manufacturing method which concerns on such a 1st example can be used suitably for manufacture of the retardation film provided with the resin layer (A) as a high retardation layer, and the resin layer (B) as a low retardation layer.

[7. Preferred second example]

Hereinafter, a second preferred example of the manufacturing method according to the above-described embodiment will be described. In this 2nd example, the retardation film is manufactured using the thermoplastic resin A and the thermoplastic resin B which have glass transition temperature TgA and glass transition temperature TgB which satisfy|fill TgA>TgB.

In the manufacturing method according to the second example, the first step and the second step are performed similarly to the manufacturing method according to the first example. Therefore, in the 2nd process of the manufacturing method which concerns on a 2nd example, the extending|stretching direction in a 1st extending process and the extending|stretching direction in a 2nd extending process are substantially perpendicular|vertical.

In such a second example, according to the stretching at the lower temperature among the stretching temperatures Ts1 and Ts2, in both the resin layer (A) and the resin layer (B) of the multilayer film, the polymer is similar to the first example. The orientation in the stretching direction of the molecules proceeds greatly. Accordingly, in the resin layer (A), the refractive index in the stretching direction becomes large, and the refractive index in the direction perpendicular to the stretching direction becomes small. On the other hand, in the resin layer (B), the refractive index of an extending|stretching direction becomes small and the refractive index of the direction perpendicular|vertical to an extending|stretching direction becomes large.

On the other hand, according to the stretching at the higher temperature among the stretching temperatures Ts1 and Ts2, the orientation of the polymer molecules in the stretching direction greatly advances in the resin layer (A), but in the resin layer (B), the polymer molecules Orientation in the stretching direction proceeds small, or the orientation does not proceed. Accordingly, in the resin layer (A), the refractive index in the stretching direction becomes large, and the refractive index in the direction perpendicular to the stretching direction becomes small. On the other hand, in the resin layer (B), the refractive index does not change, or even if it changes, the change is small.

In a 2nd example, the extending|stretching direction in a 1st extending process and the extending|stretching direction in a 2nd extending process are substantially perpendicular|vertical. Therefore, according to the combination of said 1st extending process and 2nd extending process, biaxial property becomes large in a resin layer (A), and uniaxial property becomes large in a resin layer (B). And as a film provided with the resin layer (A) with large biaxial property and the resin layer (B) with high uniaxial property in this way, a desired retardation film can be obtained. The manufacturing method which concerns on this 2nd example can be used suitably for manufacture of the retardation film provided with the resin layer (A) as a low retardation layer, and the resin layer (B) as a high retardation layer.

[8. Main Advantages of Manufacturing Method of Retardation Film]

According to the above-described manufacturing method, by simultaneously stretching the resin layer (A) and the resin layer (B) provided in the multilayer film, to produce a desired retardation film having the stretched resin layer (A) and the resin layer (B) can Therefore, since there is no need to separately prepare the resin layer (A) and the resin layer (B), the number of steps can be reduced, and effort and cost can be suppressed. Moreover, since bonding of the resin layer (A) and the resin layer (B) by which adjustment of a precise bonding angle is calculated|required is unnecessary, trouble can be suppressed also by this.

By using the retardation film obtained in this way, in both the front direction and the oblique direction of a display surface, the circularly polarizing plate which can suppress coloring by reflection of external light can be manufactured.

[9. circular polarizer]

A circularly polarizing plate according to an embodiment of the present invention includes a linear polarizer and a retardation film. By providing this circularly polarizing plate on the display surface of an image display apparatus, reflection of external light can be suppressed. According to the circularly polarizing plate provided with the retardation film mentioned above, in any case when the display surface is seen from the front direction and when the display surface is seen from the oblique direction, reflection of external light can be suppressed and coloring can be suppressed effectively.

The circularly polarizing plate may be equipped with a linear polarizer, a resin layer (A), and a resin layer (B) in this order. The circularly polarizing plate may be equipped with a linear polarizer, a resin layer (B), and a resin layer (A) in this order. A specific order can be set according to the in-plane retardation of a resin layer (A) and a resin layer (B).

Circularly polarizing plate WHEREIN: It is preferable that the angle which the width direction of a linear polarizer and one of the slow axis of the resin layer (A) and the slow axis of the resin layer (B) make exists in the specific range close|similar to 45 degrees. Specifically, the above angle is preferably 40° or more, more preferably 42° or more, still more preferably 43° or more, particularly preferably 44° or more, preferably 50° or less, more preferably preferably 48° or less, more preferably 47° or less, particularly preferably 46° or less. Moreover, in this case, it is preferable that the width direction of a linear polarizer and the angle which the other of the slow axis of a resin layer (A) and the slow axis of a resin layer (B) make exist in the specific range close|similar to 135 degrees. Specifically, said angle becomes like this. Preferably it is 130 degrees or more, More preferably, it is 132 degrees or more, More preferably, it is 133 degrees or more, Especially preferably, it is 134 degrees or more, Preferably it is 140 degrees or less, More preferably preferably 138° or less, more preferably 137° or less, particularly preferably 136° or less.

As the linear polarizer, any linear polarizer can be used. As an example of a linear polarizer, after making an iodine or a dichroic dye adsorb|suck to a polyvinyl alcohol film, the film obtained by uniaxial stretching in a boric acid bath; A film obtained by adsorbing an iodine or a dichroic dye to a polyvinyl alcohol film, extending|stretching, and also modifying a part of polyvinyl alcohol unit in a molecular chain with a polyvinylene unit; is mentioned. Among these, as a linear polarizer, the polarizer containing polyvinyl alcohol is preferable.

When natural light is made incident on a linear polarizer, only one polarized light is transmitted. Although the polarization degree of this linear polarizer is not specifically limited, Preferably it is 98 % or more, More preferably, it is 99 % or more.

Moreover, the thickness of a linear polarizer becomes like this. Preferably they are 5 micrometers - 80 micrometers.

The above-described circularly polarizing plate may further include an optional layer. As an arbitrary layer, For example, a polarizer protective film layer; Adhesive layer for bonding a linear polarizer and retardation film together; hard-coat layers, such as an impact-resistant polymethacrylate resin layer; a mat layer for improving the film's slipperiness; reflection suppression layer; antifouling layer; antistatic layer; and the like. These arbitrary layers may form only one layer, and may form two or more layers.

[10. image display device]

The above-mentioned circularly polarizing plate can be installed in an image display apparatus. In particular, it is preferable to provide a circularly polarizing plate to an organic electroluminescent image display apparatus. This organic electroluminescent image display apparatus is equipped with a circularly polarizing plate and an organic electroluminescent element (Hereinafter, it may call "organic electroluminescent element" arbitrarily.). This organic electroluminescent image display apparatus is normally equipped with a linear polarizer, retardation film, and organic electroluminescent element in this order.

The organic EL device includes a transparent electrode layer, a light emitting layer, and an electrode layer in this order, and when a voltage is applied from the transparent electrode layer and the electrode layer, the light emitting layer can generate light. Examples of the material constituting the organic light emitting layer include polyparaphenylenevinylene-based, polyfluorene-based, and polyvinylcarbazole-based materials. Moreover, the light emitting layer may have a laminated body of a plurality of layers having different emission colors, or a mixed layer in which a layer of a certain dye is doped with another dye. 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.

Said image display apparatus can suppress the reflection of the external light in a display surface. Specifically, as for the light incident from the outside of the device, only a part of the linearly polarized light passes through the linear polarizer, and then it becomes circularly polarized light by passing the retardation film. Circularly polarized light is reflected by a light-reflecting component (reflecting electrode in an organic EL element, etc.) in the image display device, passes through the retardation film again, and is a straight line having a vibration direction orthogonal to the vibration direction of the incident linearly polarized light. It becomes polarized light and does not pass through a linear polarizer. Here, the oscillation direction of linearly polarized light means the oscillation direction of the electric field of linearly polarized light. Thereby, the function of reflection suppression is achieved.

Since retardation film has the above-mentioned optical characteristic, said organic electroluminescent image display apparatus can exhibit the function of reflection suppression not only in the front direction of a display surface, but also in an oblique direction. Thereby, in both the front direction and the oblique direction of a display surface, reflection of external light can be suppressed effectively, and it is possible to suppress coloring.

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

[Equation 1]

Also, in general, the coloring of the display surface by the reflected light may vary depending on the azimuth in the observation direction. Therefore, when observed from the oblique direction of the display surface, the measured chromaticity may be different depending on the azimuth in the observation direction, and thus the color difference ΔE ^* ab may also be different. Therefore, in order to evaluate the degree of coloration when observed from the oblique direction of the display surface as described above, it is preferable to evaluate the coloration by the average value of the color difference ΔE ^* ab obtained by observation in a plurality of azimuth directions. Specifically, the color difference ΔE ^{* ab is measured in the range where the azimuth φ (see Fig. 1) is 0° or more and less than 360° in units of 5° in the azimuth direction, and the average value of the measured color difference ΔE * ab} ( average color difference) to evaluate the degree of coloration. The smaller the average color difference, the smaller the coloration of the display surface when observed from the oblique direction of the display surface.

Example

Hereinafter, the present invention will be specifically described with reference to Examples. However, this invention is not limited to the Example shown below, In the range which does not deviate from the range which does not deviate from the claim of this invention and its equivalent, it can change arbitrarily and implement it.

In the following description, "%" and "part" indicating a quantity are based on weight, unless otherwise specified. In addition, the operation demonstrated below was performed under conditions of normal temperature and normal pressure, unless otherwise indicated.

[Assessment Methods]

(Measurement method of phase difference and NZ coefficient)

In-plane retardation Re at wavelengths 450 nm, 550 nm and 650 nm of the evaluation target (retardation film, resin layer (A) and resin layer (B)) using a retardation meter ("AxoScan" manufactured by Axometrics); Then, the thickness direction retardation Rth at a wavelength of 550 nm was measured. When calculating|requiring the physical property of each layer of a resin layer (A) and a resin layer (B), it computed by measuring a sample from multiple directions, and fitting analysis with the attached multi-layer analysis software. Moreover, the NZ coefficient was computed using the in-plane retardation Re and thickness direction retardation Rth in wavelength 550nm.

(Measuring method of orientation angle)

The direction of the slow axis of the resin layer (A) and the resin layer (B) contained in retardation film was measured using the retardation meter ("AxoScan" by Axometrics). An angle formed by this slow axis with respect to the width direction of the retardation film was calculated as an orientation angle θ (0°≤θ<180°).

(Method of calculating color difference by simulation)

Using "LCD Master" manufactured by Syntech Corporation as software for simulation, the circularly polarizing plates manufactured in each Example and Comparative Example were modeled, and the following calculations were performed.

In the model for simulation, a configuration in which a circular polarizing plate is provided on the reflective surface of a mirror having a planar reflective surface was set. In Examples 1-4 and Comparative Example 1, a circular polarizing plate having a low retardation layer, a high retardation layer, and a linear polarizer in this order from the side of the reflective surface was set. In Comparative Example 2, it was set to have a layer of norbornene-based resin, a layer of styrene maleic anhydride copolymer resin, a layer of norbornene-based resin, and a linear polarizer in this order from the reflective surface side. As the low retardation layer, the high retardation layer, the norbornene-based resin layer, and the styrene maleic anhydride copolymer resin layer, those obtained in Examples and Comparative Examples were set. In addition, as a linear polarizer, the polarizing plate with a polarization degree of 99.99% which is generally used was set. In addition, as a mirror, an ideal mirror capable of mirror-reflecting incident light with a reflectance of 100% was set.

1 is a perspective view schematically showing a state of an evaluation model set when color space coordinates are calculated in simulations in Examples and Comparative Examples.

As shown in Fig. 1, when illuminated by a D65 light source (not shown), the color space coordinates observed on the reflective surface 10 of a mirror provided with a circularly polarizing plate were calculated. In addition, color space coordinates when not illuminated by a light source were set to a0 ^* =0, b0 ^* =0, and L0 ^* =0. Then, the color difference ΔE ^* ab was calculated from (i) the color space coordinates when illuminated by the light source and (ii) the color space coordinates when not illuminated by the light source.

The above color difference ΔE ^* ab was calculated in the observation direction 20 in which the declination angle ρ with respect to the reflective surface 10 was 0°, and the color difference ΔE ^* ab in the front direction was obtained. The declination angle ρ represents an angle formed with respect to the normal direction 11 of the reflective surface 10 .

In addition, the above-mentioned color difference ΔE ^* ab was calculated in the observation direction 20 in which the declination angle ρ with respect to the reflective surface 10 was 60°. The calculation at the declination angle ρ = 60° was performed by moving the observation direction 20 in the azimuth direction and moving the azimuth angle φ in the range of 0° or more and less than 360° in units of 5°. The azimuth angle phi represents an angle formed by a direction parallel to the reflective surface 10 with respect to 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 observation directions 20 was calculated to obtain a color difference ΔE ^* ab in the inclination direction of the declination angle ρ = 60°.

(Evaluation method of circularly polarizing plate by visual observation in the front direction)

An image display device (“AppleWatch” (registered trademark) by Apple Corporation) including an organic EL image display device was prepared. This image display apparatus was decomposed|disassembled, the polarizing plate pasted on the surface of the organic electroluminescent image display apparatus was peeled, and the reflective electrode was exposed. The surface of this reflective electrode and the surface on the opposite side to the linear polarizer of the circular polarizing plate obtained by each Example and the comparative example were bonded together through the adhesive ("CS9621" by Nitto Denko). Thereby, the sample provided with a reflective electrode, an adhesive, and a circularly polarizing plate in this order was obtained.

The circular polarizer on the reflective electrode was visually observed while the circular polarizer of the sample was illuminated with sunlight on a clear day. Observation was performed in the front direction of 0 degree of polarization angle of polarization, and 0 degree of azimuth of a circularly polarizing plate. As a result of observation, when a chromatic color was visually recognized, it determined with "bad", and when a chromatic color was not visually recognized, it determined with "good|favorableness".

(Evaluation method of circularly polarizing plate by visual observation in an oblique direction)

The circularly polarizing plate on the reflective electrode was visually observed while the circularly polarizing plate of the sample prepared in the above (evaluation method of the circularly polarizing plate by viewing in the front direction) was irradiated with sunlight on a clear day. Observation was performed in the oblique direction of 60 degrees of polarization angle of a circular polarizing plate, and 0 degrees - 360 degrees of azimuth. As a result of observation, superiority and inferiority in reflection luminance and coloration were comprehensively judged, and Examples and Comparative Examples were ranked. Then, to the ranked Examples and Comparative Examples, scores corresponding to the rankings (1st place 6 points, 2nd place 5 points, ... lowest 1 point) were given.

The above observation was performed by a large number of people, and the sum total of the scores given for each Example and the comparative example was calculated|required. Examples and Comparative Examples were arranged in the order of the above sum points, and evaluated in the order of A, B, C, D and E from the upper group within the range of the total points.

[Example 1]

(1-1. Formation of resin layer (A))

The pellet-form norbornene-type resin (made by Nippon Zeon Corporation; glass transition temperature of 126 degreeC) was dried at 100 degreeC for 5 hours, and the thermoplastic resin A was obtained. This thermoplastic resin A was supplied to an extruder, and it extruded in the form of a sheet from a T-die on a casting drum through a polymer pipe and a polymer filter. The extruded thermoplastic resin A was cooled to obtain a long resin film with a thickness of 100 μm as a resin layer (A). The obtained resin layer (A) was wound up in roll shape and collect|recovered.

(1-2. Formation of resin layer (B))

500 ml of toluene as a solvent and 0.29 mmol of n-butyllithium as a polymerization catalyst were put in a dry, nitrogen-substituted internal pressure reactor, followed by adding 35 g of 2-vinylnaphthalene and reacting at 25° C. for 1 hour. As a result, a reaction product containing poly(2-vinylnaphthalene) as a homopolymer of 2-vinylnaphthalene was obtained. The reaction product was poured into a large amount of 2-propanol to precipitate poly(2-vinylnaphthalene) and aliquoted. The obtained poly(2-vinylnaphthalene) was dried at 200 degreeC for 24 hours using a vacuum dryer, and the thermoplastic resin B was obtained. The weight average molecular weight of poly(2-vinylnaphthalene) measured by GPC was 250000. In addition, the glass transition temperature of poly(2-vinylnaphthalene) measured by differential scanning calorimetry was 142 degreeC.

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

The resin layer (A) was taken out from the roll, and said liquid composition was coated on the withdrawn resin layer (A). Thereafter, the coated liquid composition was dried to form a poly(2-vinylnaphthalene) layer (thickness: 12 µm) as the resin layer (B) on the resin layer (A). Thereby, the multilayer film provided with the resin layer (A) formed from norbornene-type resin, and the resin layer (B) formed from poly(2-vinylnaphthalene) was obtained. The obtained multilayer film was wound up in roll shape and collect|recovered.

[1-3. 1st drawing process]

The multilayer film was taken out from the roll, and the pulled out multilayer film was supplied to the vertical tenter stretching machine. Using this tenter stretching machine, the multilayer film was stretched at a stretching temperature of 140°C and a draw ratio of 1.10 in the stretching direction forming an angle of 135° with respect to the width direction of the multilayer film. After cooling to room temperature, the stretched multilayer film wound up and collect|recovered in roll shape.

[1-4. 2nd drawing process]

The multilayer film extended|stretched by the 1st extending process was taken out from a roll, and the pulled multilayer film was supplied to the tenter stretching machine. Using this tenter stretching machine, the multilayer film was stretched in a stretching direction forming an angle of 45° with respect to the width direction of the multilayer film at a stretching temperature of 128° C. and a stretching ratio of 1.50 times to obtain a long retardation film. This retardation film was equipped with the resin layer (A) as a high retardation layer, and the resin layer (B) as a low retardation layer. The obtained retardation film and the optical properties (in-plane retardation, thickness direction retardation, direction of slow axis, NZ coefficient) of each layer contained in the said retardation film were measured by the method mentioned above.

[1-5. Preparation of circular polarizer]

A long polyvinyl alcohol resin film dyed with iodine was prepared. This film was extended|stretched in the longitudinal direction which makes an angle of 90 degrees with respect to the width direction of the said film, and the linear polarizer as a long polarizing film was obtained. 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.

Said linear polarizer and retardation film were bonded through the optically isotropic adhesive ("CS9621" by Nitto Denko Corporation), and the elongate circularly polarizing plate was obtained. Said bonding was performed in parallel with the width direction of a linear polarizer, and the width direction of retardation film. The obtained circularly polarizing plate was equipped with the resin layer (A) as a linear polarizer, the high retardation layer, and the resin layer (B) as a low retardation layer in this order.

The obtained circularly polarizing plate was evaluated by the method mentioned above.

[Examples 2 to 4]

In the process (1-1), the extrusion conditions by the extruder were adjusted, and the thickness of the elongate resin layer (A) was changed as Table 1 showed.

In addition, in the process (1-2), the thickness of the resin layer (B) was changed as Table 1 shows by adjusting the coating amount of the liquid composition.

In addition, in the process (1-3), the draw ratio was changed as shown in Table 1.

Except for the above, the retardation film and the circularly polarizing plate were manufactured and evaluated by the method similar to Example 1.

[Comparative Example 1]

In the process (1-1), the extrusion conditions by the extruder were adjusted, and the thickness of the elongate resin layer (A) was changed as Table 1 showed.

In addition, in the process (1-2), the thickness of the resin layer (B) was changed as Table 1 shows by adjusting the coating amount of the liquid composition.

In addition, in the process (1-3), as shown in Table 1, the extending|stretching temperature and a draw ratio were changed.

Except for the above, the retardation film and the circularly polarizing plate were manufactured and evaluated by the method similar to Example 1.

[Comparative Example 2]

A retardation film was manufactured in the same manner as in Example 5 of Japanese Patent Application Laid-Open No. 2002-40258.

Specifically, as the thermoplastic resin A having a positive intrinsic birefringence value, a norbornene-based resin (manufactured by Nippon Zeon, glass transition temperature of 136°C) was prepared. Further, as the thermoplastic resin B having a negative intrinsic birefringence value, a styrenic maleic anhydride copolymer resin (“Diraq D332” manufactured by Nova Chemicals, a glass transition temperature of 130° C.) was prepared. These resins were previously dried under a nitrogen purge to reduce the moisture content.

A film forming apparatus capable of co-extruding the thermoplastic resin A and the thermoplastic resin B to produce a multilayer film having a layer structure of “layer of thermoplastic resin A/layer of thermoplastic resin B/layer of thermoplastic resin A” (manufactured by Toyo Seiki) 「LABO PLASTOMILI」) was prepared. The above norbornene-based resin and styrenic maleic anhydride copolymer resin are supplied to this film forming apparatus, and co-extrusion is performed to provide "norbornene-based resin layer/styrene maleic anhydride copolymer resin layer/norbornene-based resin layer". A multilayer film (thickness 186 µm) having a three-layer structure of “layer” was obtained.

This multilayer film was stretched using a tenter stretching machine in a stretching direction forming an angle of 45° with respect to the width direction of the multilayer film at a stretching temperature of 120° C. and a stretching ratio of 1.65 times to obtain a long retardation film. The obtained retardation film has a three-layer structure of "a layer of norbornene-based resin (thickness 36 µm)/layer of styrene maleic anhydride copolymer resin (thickness 39 µm)/layer of norbornene-based resin (thickness 38 µm)” there was. The obtained retardation film and the optical properties (in-plane retardation, thickness direction retardation, direction of slow axis, NZ coefficient) of each layer contained in the said retardation film were measured by the method mentioned above. Since the retardation film obtained in Comparative Example 2 had two layers of norbornene-based resin as the thermoplastic resin A, in the columns of the in-plane retardation, thickness direction retardation, and NZ coefficient of the resin layer (A) of Table 2 to be described later. , the value of the sum of these two layers was described.

This retardation film and the same elongate linear polarizer as that used in Example 1 were bonded through the optically isotropic adhesive ("CS9621" by Nitto Denko Corporation), and the elongate circularly polarizing plate was obtained. Said bonding was performed in parallel with the width direction of a linear polarizer, and the width direction of retardation film. The obtained circularly polarizing plate was equipped with the linear polarizer, the layer of norbornene-type resin, the layer of styrene maleic anhydride copolymer resin, and the layer of norbornene-type resin in this order.

The obtained circularly polarizing plate was evaluated by the method mentioned above.

[result]

Table 1 shows the manufacturing conditions of the retardation film in the Example and the comparative example mentioned above, and Table 2 shows an evaluation result. In Table 1 and Table 2 below, the meaning of the abbreviation is as follows.

"COP": Norbornene-type resin.

"VN": poly(2-vinylnaphthalene).

"PSt": Styrenic maleic anhydride copolymer resin.

"Plus" in the column of intrinsic birefringence value: intrinsic birefringence value is plus.

"Minus" in the column of intrinsic birefringence value: The intrinsic birefringence value is negative.

"Stretching angle": The angle which an extending|stretching direction makes with respect to the width direction of a multilayer film.

"Orientation angle θ": The angle formed by the slow axis with respect to the width direction of the retardation film.

In the above-described Examples and Comparative Examples, the visual evaluation in the front direction was judged in two stages of “good” and “poor”, whereas the visual evaluation in the oblique direction was judged in five stages, from “A” to “E”. are doing The reason why the judgment criteria are different in this way is as follows.

That is, in the front direction, compared with the oblique direction, the luminance of the reflected light is sufficiently low. Therefore, when strong coloration is not occurring, the observer cannot recognize the coloration. For this reason, the determination in two steps of whether or not coloring can be visually recognized was employ|adopted.

On the other hand, in the oblique direction, the luminance of the reflected light is high. Therefore, even if the coloration is weak, the observer is easy to recognize the coloration. Accordingly, a detailed superiority and inferiority evaluation of five stages was employed.

[examine]

In Examples 1-4, in a 1st extending process, extending|stretching is performed at the temperature sufficiently higher than the glass transition temperature TgA of the thermoplastic resin A. Therefore, the orientation of the polymer molecule contained in the resin layer (A) is advancing small in a 1st extending process, and advancing large in a 2nd extending process. Therefore, the resin layer (A) with which retardation film is equipped has high uniaxial property, and has a slow axis parallel to the extending|stretching direction in a 2nd extending process.

On the other hand, the orientation of the polymer molecules contained in the resin layer (B) containing the thermoplastic resin B having a glass transition temperature TgB higher than the glass transition temperature TgA of the thermoplastic resin A is determined in both the first stretching step and the second stretching step. , is progressing significantly. Therefore, the resin layer (B) with which retardation film is equipped has high biaxiality. Moreover, in Examples 1-4, since the direction of a 2nd extending process is extending|stretching by a larger draw ratio than a 1st extending process, the resin layer (B) with which retardation film is equipped is the extending|stretching direction in a 2nd extending process. has a slow axis in the direction perpendicular to

And the retardation film provided with these resin layer (A) and a resin layer (B) satisfy|fills Formula (1) - Formula (3) as a whole, as Table 2 shows. Therefore, the circularly polarizing plate provided with this retardation film can suppress coloring by reflection of external light in both the front direction and the diagonal direction of the display surface of the image display apparatus provided with the said circularly polarizing plate.

10 reflective surface
11 Normal direction of the reflective surface
12 reference direction
20 observation direction
φ azimuth
ρ declination

Claims (8)

As a method for producing a retardation film satisfying the following formula (1), the following formula (2) and the following formula (3),
The manufacturing method is
A first step of preparing a multilayer film comprising a resin layer (A) formed of a thermoplastic resin A having a positive intrinsic birefringence value and a resin layer (B) formed of a thermoplastic resin B having a negative intrinsic birefringence value;
By stretching the multilayer film twice or more, the retardation film comprising the resin layer (A) having a slow axis and the resin layer (B) having a slow axis substantially perpendicular to the slow axis of the resin layer (A). a second process of obtaining
The second process is
A 1st extending process of extending|stretching the said multilayer film at extending|stretching temperature Ts1;
a second stretching step of stretching the multilayer film at a stretching temperature Ts2 different from the stretching temperature Ts1;
The absolute value |TgA - TgB| of the difference of the glass transition temperature TgA of the said thermoplastic resin A, and the glass transition temperature TgB of the said thermoplastic resin B is 5 degreeC or more, The manufacturing method of the retardation film.
100 nm ≤ Re _T (550) ≤ 180 nm (1)
Re _T (450) < Re _T (550) < Re _T (650) (2)
0.0 < NZ _T < 1.0 (3)
(only,
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.) According to claim 1,
The absolute value |Ts1 - Ts2| of the difference of the said extending|stretching temperature Ts1 and the said extending|stretching temperature Ts2 is 5 degreeC or more, The manufacturing method of retardation film. 3. The method of claim 1 or 2,
The manufacturing method of retardation film whose extending|stretching direction in a said 1st extending process and the extending|stretching direction in a said 2nd extending process are substantially perpendicular|vertical. 4. The method according to any one of claims 1 to 3,
The method for producing a retardation film, wherein the retardation film satisfies the following formula (4).
{Re _Q (450)/Re _Q (550)} - {Re _H (450)/Re _H (550)} > 0.08 (4)
(only,
Re _H (450) represents the in-plane retardation of the high retardation layer at a wavelength of 450 nm,
Re _H (550) represents the in-plane retardation of the higher retardation layer at a wavelength of 550 nm,
Re _Q (450) represents the in-plane retardation of the low retardation layer at a wavelength of 450 nm,
Re _Q (550) represents the in-plane retardation of the low retardation layer at a wavelength of 550 nm,
The higher retardation layer represents a layer having a larger in-plane retardation at a wavelength of 550 nm among the resin layer (A) and the resin layer (B) included in the retardation film,
The low retardation layer represents a layer having a smaller in-plane retardation at a wavelength of 550 nm among the resin layer (A) and the resin layer (B) included in the retardation film.) 5. The method according to any one of claims 1 to 4,
At a wavelength of 550 nm, the resin layer (A) included in the retardation film has a larger in-plane retardation than the resin layer (B) included in the retardation film,
The glass transition temperature TgA of the said thermoplastic resin A is lower than the glass transition temperature TgB of the said thermoplastic resin B, The manufacturing method of retardation film. 5. The method according to any one of claims 1 to 4,
At a wavelength of 550 nm, the resin layer (B) included in the retardation film has a larger in-plane retardation than the resin layer (A) included in the retardation film,
The glass transition temperature TgB of the said thermoplastic resin B is lower than the glass transition temperature TgA of the said thermoplastic resin A, The manufacturing method of retardation film. The retardation film manufactured by the manufacturing method in any one of Claims 1-6. a linear polarizer,
A circularly polarizing plate provided with the retardation film of Claim 7.

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