CN116324538A

CN116324538A - Retardation film and method for producing same

Info

Publication number: CN116324538A
Application number: CN202180064565.4A
Authority: CN
Inventors: 熊泽一辉; 大田善也; 须田康裕
Original assignee: Zeon Corp; Osaka Gas Chemicals Co Ltd
Current assignee: Zeon Corp; Osaka Gas Chemicals Co Ltd
Priority date: 2020-09-30
Filing date: 2021-08-31
Publication date: 2023-06-23
Also published as: JPWO2022070729A1; TW202214444A; WO2022070729A1; KR20230077724A

Abstract

The present invention relates to a retardation film comprising: a layer A having a slow axis and a layer B having a slow axis at an angle of 85 DEG to 90 DEG to the slow axis of the layer A; the a layer is formed of a resin a having positive intrinsic birefringence; the B layer is formed of a resin B having negative intrinsic birefringence; the resin B comprises a polyester, a polycarbonate or a polyester carbonate, which contains a fluorene skeleton; the in-plane retardation of the whole layer A and the in-plane retardation of the whole layer B meet a specific relation; the in-plane retardation Re (450) and Re (550) of the retardation film at the wavelength of 450nm and at the wavelength of 550nm satisfy a specific relationship; thickness T of layer A as a whole _A Thickness T of the whole of layer B _B Ratio T of (2) _A /T _B 30/70-65/35.

Description

Retardation film and method for producing same

Technical Field

The present invention relates to a retardation film and a method for producing the same.

Background

A phase difference film may be provided in an image display device (patent document 1). Among such retardation films, there are retardation films having a multilayer structure including two or more layers (patent documents 2 to 3).

Prior art literature

Patent literature

Patent document 1: japanese patent laid-open No. 2002-40258;

patent document 2: japanese patent application laid-open No. 2017-177342;

Patent document 3: japanese patent application laid-open No. 2018-128568.

Disclosure of Invention

Problems to be solved by the invention

In an image display device, a circularly polarizing plate is sometimes provided to reduce reflection of external light on a display surface. As such a circularly polarizing plate, a film combining a linear polarizer and a retardation film is generally used. However, most of the conventional retardation films have positive wavelength dispersion. Therefore, although the conventional circular polarizer can reduce reflection of external light in a specific narrow wavelength range, it is difficult to reduce reflection of external light other than the specific narrow wavelength range, and thus a sufficiently high reflection suppressing ability may not be obtained.

In order to improve the reflection suppressing ability, it is conceivable to provide a retardation film having inverse wavelength dispersion on the circularly polarizing plate. As such a retardation film having inverse wavelength dispersion, there is a film in which a resin having positive intrinsic birefringence and a resin having negative intrinsic birefringence are combined. The retardation film can generally exhibit inverse wavelength dispersion by utilizing the difference between the in-plane retardation exhibited by the resin having positive intrinsic birefringence and the in-plane retardation exhibited by the resin having negative intrinsic birefringence. Specifically, the longer the measurement wavelength is, the larger the difference in-plane retardation is, and thus the inverse wavelength dispersion can be achieved.

However, a retardation film obtained by using a resin having positive intrinsic birefringence and a resin having negative intrinsic birefringence in combination tends to have poor reworkability as shown below.

It is sometimes required that after the phase difference film is first bonded to a certain member, the phase difference film is peeled off and bonded again to the member. The property that the operation of peeling from the member and bonding again can be easily performed is called "reworkability". For example, when a phase difference film is attached to an image display device and then the phase difference film is peeled off from the image display device and reattached again, excellent reworkability is required.

However, the reworkability of a conventional retardation film in which a resin having positive intrinsic birefringence and a resin having negative intrinsic birefringence are combined is poor. Among them, a retardation film having high reflection suppressing ability tends to be significantly deteriorated in reworkability, and it is particularly difficult to achieve both the reflection suppressing ability and reworkability in a thin retardation film.

The present invention has been made in view of the above problems, and an object thereof is to provide: a retardation film having high reflection suppressing ability and excellent reworkability, and a method for producing the same; and a polarizing plate and an image display device having the retardation film.

Solution for solving the problem

The present inventors have conducted intensive studies in order to solve the above-mentioned problems. As a result, the present inventors have found that the above-described problems can be solved in the case where a phase difference film formed by combining an a layer formed of a resin a having positive intrinsic birefringence and a B layer formed of a resin B having negative intrinsic birefringence satisfies specific requirements, and completed the present invention.

Namely, the present invention includes the following.

[1] A retardation film, comprising: one or more than two layers A with slow axis and one or more than two layers B with slow axis at an angle of 85 DEG to 90 DEG with the slow axis of the layers A,

the above-mentioned layer a is formed of a resin a having positive intrinsic birefringence,

the above-mentioned layer B is formed of a resin B having negative intrinsic birefringence,

the resin B contains at least one polymer selected from the group consisting of polyesters, polycarbonates and polyestercarbonates,

the above-mentioned polymer contains a fluorene skeleton,

the in-plane retardation Re (A450) of the entire A layer at a wavelength of 450nm, the in-plane retardation Re (A550) of the entire A layer at a wavelength of 550nm, the in-plane retardation Re (B450) of the entire B layer at a wavelength of 450nm, and the in-plane retardation Re (B550) of the entire B layer at a wavelength of 550nm satisfy the following formula (i):

|Re(A450)/Re(A550)-Re(B450)/Re(B550)|≥0.10 (i)，

The in-plane retardation Re (450) of the retardation film at a wavelength of 450nm and the in-plane retardation Re (550) of the retardation film at a wavelength of 550nm satisfy the following formula (ii):

0.60≤Re(450)/Re(550)≤0.96 (ii)，

thickness T of the whole A layer _A Thickness T of the whole of the B layer _B Ratio T of (2) _A /T _B 30/70-65/35.

[2] The retardation film according to [1], wherein the in-plane retardation Re (B450) and Re (B550) of the entire B layer satisfy the following formula (iii):

1.14≤Re(B450)/Re(B550) (iii)。

[3] the retardation film according to [1] or [2], wherein the polymer comprises a structural unit having a fluorene-9, 9-diyl group.

[4] The retardation film according to any one of [1] to [3], wherein the structural unit having a fluorene-9, 9-diyl group comprises a fluorene dicarboxylic acid unit represented by the following formula (1) and/or a fluorene diol unit represented by the following formula (2), wherein the formula (1) is:

[ chemical formula 1]

(wherein R is ¹ Represents a substituent, k represents an integer of 0 to 8, X ^1a And X ^1b Each independently represents a divalent hydrocarbon group which may have a substituent

The formula (2) is:

[ chemical formula 2]

(wherein R is ² Represents a substituent, m represents an integer of 0 to 8, X ^2a And X ^2b Each independently represents a divalent hydrocarbon group which may have a substituent, A ^1a And A ^1b Each independently represents a linear or branched alkylene group, and n1 and n2 represent an integer of 0 or more)).

[5] The retardation film according to [4], wherein the fluorene diol unit comprises a diol unit represented by the following formula (2A), and the formula (2A) is:

[ chemical formula 3]

(wherein Z is ^1a And Z ^1b Each independently represents an aromatic hydrocarbon ring, R ^3a And R is ^3b Each independently represents a substituent, p1 and p2 each independently represents an integer of 0 or more, R ² 、m、A ^1a And A ^1b N1 and n2 are the same as the above formula (2), respectively.

[6]According to [5]]The retardation film comprises a glycol unit represented by the formula (2A), Z ^1a And Z ^1b Is C _6-12 Aromatic hydrocarbon ring, R ^3a And R is ^3b Is C _1-4 Alkyl or C _6-10 Aryl, p1 and p2 are integers from 0 to 2, A ^1a And A ^1b Is straight or branched C _2-4 Alkylene groups, n1 and n2 are integers from 0 to 2.

[7]According to [4]]～[6]The retardation film according to any one of the above, wherein X is a fluorene dicarboxylic acid unit represented by the above formula (1) ^1a And X ^1b Is straight or branched C _2-4 An alkylene group.

[8] The retardation film according to any one of [1] to [7], wherein the resin B further comprises an alkylene glycol unit represented by the following formula (3), and the formula (3) is:

[ chemical formula 4]

(wherein A ² And q represents an integer of 1 or more).

[9]According to [8]]The retardation film comprises, in the alkylene glycol unit represented by the formula (3), A ² Is straight or branched C _2-4 Alkylene, q is an integer from 1 to 4.

[10] The retardation film according to any one of [1] to [9], wherein the resin A contains a polymer containing no aromatic ring.

[11] The retardation film according to any one of [1] to [10], wherein the resin A comprises a polymer having an isosorbide skeleton.

[12] The retardation film according to any one of [1] to [11], wherein in-plane retardation Re (450) and Re (550) of the retardation film satisfy the following formula (iv):

Re(450)/Re(550)≤0.91 (iv)。

[13] the retardation film according to any one of [1] to [12], wherein the glass transition temperature TgA of the resin A is 100 ℃ or more and 160 ℃ or less,

the glass transition temperature TgB of the resin B is 100 ℃ to 160 ℃.

[14] The retardation film according to any one of [1] to [13], wherein a difference |tga-tgb| between the glass transition temperature TgA of the resin a and the glass transition temperature TgB of the resin B is 15 ℃ or less.

[15] The retardation film according to any one of [1] to [14], wherein the thickness of the retardation film is 90 μm or less.

[16] The retardation film according to any one of [1] to [15], wherein the thickness of the retardation film is 70 μm or less.

[17] A method for producing a retardation film according to any one of [1] to [16], comprising:

a step of preparing a multilayer film having a layer formed of a resin A and a layer formed of a resin B; the resin a has positive intrinsic birefringence, and the resin B has negative intrinsic birefringence; and

and stretching the multilayer film.

[18] The method of producing a retardation film according to [17], wherein the step of preparing the multilayer film comprises the step of melt-extruding the resin A and the resin B.

[19] The method for producing a retardation film according to [17] or [18], wherein the step of stretching the multilayer film comprises a step of stretching at a stretching temperature of "Tg (h) -10 ℃ or higher and" Tg (h) +20 ℃ or lower (wherein Tg (h) represents a higher temperature of the glass transition temperature TgA of the resin A and the glass transition temperature TgB of the resin B).

[20] The method for producing a retardation film according to any one of [17] to [19], wherein the step of stretching the multilayer film comprises a step of stretching at a stretching ratio of 1.5 to 5.0 times.

[21] The method for producing a retardation film according to any one of [17] to [20], wherein the step of stretching the multilayer film comprises a step of stretching the multilayer film in an oblique direction.

[22] A polarizing plate comprising the retardation film of any one of [1] to [16] and a linear polarizer.

[23] An image display device having the retardation film of any one of [1] to [16 ].

Effects of the invention

According to the present invention, there can be provided: a retardation film having high reflection suppressing ability and excellent reworkability, and a method for producing the same; and a polarizing plate and an image display device having the retardation film.

Drawings

Fig. 1 is a graph schematically showing the relative relationship between the in-plane retardation of the entire a layer and the in-plane retardation of the entire B layer in one example.

Detailed Description

Hereinafter, the present invention will be described in detail with reference to embodiments and examples. However, the present invention is not limited to the embodiments and examples described below, and can be arbitrarily modified and implemented within a range not departing from the scope of the present invention and the scope equivalent thereto.

In the following description, unless otherwise specified, the in-plane retardation Re of the layers and films having three-dimensional refractive indices nx, ny and nz is a value represented by re= (nx-ny) ×d. nx represents a refractive index in a direction providing the maximum refractive index among directions perpendicular to the thickness direction (in-plane directions). ny represents the refractive index in the direction orthogonal to the direction of nx in the above-mentioned in-plane direction. nz represents the refractive index in the thickness direction. d represents the thickness.

The in-plane retardation of a film having a plurality of layers having different three-dimensional refractive indices nx, ny, and nz can be generally synthesized from the in-plane retardation of each layer. For example, the in-plane retardation of a film formed of a first layer having a slow axis and a second layer having a slow axis perpendicular to the slow axis of the first layer may be expressed as a difference between the in-plane retardation of the first layer and the in-plane retardation of the second layer. Further, for example, the in-plane retardation of a film formed of a third layer having a slow axis and a fourth layer having a slow axis parallel to the slow axis of the third layer may be expressed as a sum of the in-plane retardation of the third layer and the in-plane retardation of the fourth layer.

The specific value of the in-plane retardation can be measured by using a phase difference meter (KOBRA-WIST, manufactured by prince measuring instruments Co., ltd.). Unless otherwise indicated, the measurement wavelength was 590nm.

The slow axis of a layer or film refers to the slow axis of the in-plane direction of the layer or film unless otherwise specified.

The positive wavelength dispersion means a property that the in-plane retardation Re450 and Re550 at the measured wavelengths of 450nm and 550nm satisfies Re450 > Re 550. In general, the longer the measurement wavelength, the smaller the in-plane retardation of a member having positive wavelength dispersion.

Inverse wavelength dispersion refers to the property of determining that the in-plane retardation Re450 and Re550 at wavelengths of 450nm and 550nm satisfies Re450 < Re 550. In general, the longer the measurement wavelength, the greater the in-plane retardation of the member having inverse wavelength dispersion.

Unless otherwise stated, the angle formed by the optical axes (absorption axis, transmission axis, slow axis, etc.) of the respective layers in the member having the plurality of layers indicates the angle when the layers are viewed from the thickness direction.

Directions of the elements are "parallel", "perpendicular", and "orthogonal" may include errors within a range (for example, within a range of ±5°, ±4°, ±3°, ±2°, or ±1°) which does not impair the effects of the present invention, unless otherwise stated.

Unless otherwise specified, "resin having positive intrinsic birefringence" means a resin having a refractive index in the stretching direction that is greater than the refractive index in the direction orthogonal to the stretching direction. Further, unless otherwise specified, "polymer having positive intrinsic birefringence" means a polymer having a refractive index in the stretching direction that is greater than the refractive index in the direction orthogonal to the stretching direction.

Unless otherwise specified, "resin having negative intrinsic birefringence" means a resin having a refractive index in the stretching direction smaller than that in the direction orthogonal to the stretching direction. Unless otherwise specified, "polymer having negative intrinsic birefringence" means a polymer having a refractive index in the stretching direction that is smaller than the refractive index in the direction orthogonal to the stretching direction.

Unless otherwise specified, a "long film" refers to a film having a length of 5 times or more, preferably 10 times or more, relative to the width, and specifically refers to a film having a length of such a degree that it can be rolled into a roll for storage or transportation. The upper limit of the length of the long film is not particularly limited, and may be, for example, 10 ten thousand times or less with respect to the width.

Unless otherwise specified, "polarizer", "circularly polarizer" and "wave plate" include not only rigid members but also flexible members such as films made of resin.

Unless otherwise specified, the adhesive includes not only a narrow adhesive but also an adhesive having a shear storage elastic modulus at 23 ℃ of less than 1 MPa. The narrow adhesive means an adhesive having a shear storage elastic modulus at 23℃of 1MPa to 500MPa after irradiation with energy rays or after heat treatment.

[1. Outline of retardation film ]

The retardation film according to one embodiment of the present invention comprises: one or more a layers formed of a resin a having positive intrinsic birefringence; and one or more B layers formed of a resin B having negative intrinsic birefringence. The a layer and the B layer are optically anisotropic layers and thus have a slow axis. When the retardation film is viewed from the thickness direction, the slow axis of the a layer is perpendicular to the slow axis of the B layer. Further, the resin B contains at least one polymer selected from the group consisting of polyesters, polycarbonates, and polyestercarbonates. The polymer contains a fluorene backbone.

In the present embodiment, the difference between the wavelength dispersion of the a layer and the wavelength dispersion of the B layer falls within a specific range. Specifically, the wavelength dispersion of the a layer is represented by Re (a 450)/Re (a 550). The wavelength dispersion of the B layer is represented by Re (B450)/Re (B550). In this case, the magnitude of the difference between the wavelength dispersion of the a layer and the wavelength dispersion of the B layer is represented by |re (a 450)/Re (a 550) -Re (B450)/Re (B550) |. In this embodiment, the magnitude of the difference in wavelength dispersion satisfies the following formula (i):

|Re(A450)/Re(A550)-Re(B450)/Re(B550)|≥0.10 (i)。

here, re (a 450) represents the in-plane retardation of the entire a layer at a wavelength of 450 nm. Further, re (A550) represents the in-plane retardation of the entire A layer at a wavelength of 550 nm. In the case where the retardation film has one a layer, the "in-plane retardation of the entire a layer" means the in-plane retardation of the a layer. In the case where the retardation film has two or more a layers, the "in-plane retardation of the entire a layer" means the sum of the in-plane retardation of the a layers.

Further, re (B450) represents the in-plane retardation of the entire B layer at a wavelength of 450 nm. In addition, re (B550) represents the in-plane retardation of the entire B layer at a wavelength of 550 nm. In the case where the retardation film has one B layer, the "in-plane retardation of the B layer as a whole" means the in-plane retardation of the B layer. In the case where the retardation film has two or more B layers, the "in-plane retardation of the entire B layer" means the sum of the in-plane retardation of the B layers.

Formula (i) is described in further detail. The magnitude of the difference between the wavelength dispersion of the a layer and the wavelength dispersion of the B layer |re (a 450)/Re (a 550) -Re (B450)/Re (B550) | is usually 0.10 or more, preferably 0.12 or more, more preferably 0.14 or more. The upper limit is not particularly limited, and may be generally 0.8 or less, preferably 0.5 or less, and particularly preferably 0.3 or less. In many cases, the wavelength dispersion Re (B450)/Re (B550) of the B layer is larger than the wavelength dispersion Re (a 450)/Re (a 550) of the a layer, and thus the difference "Re (a 450)/Re (a 550) -Re (B450)/Re (B550)" of the wavelength dispersion of the a layer and the wavelength dispersion of the B layer may be negative.

In the present embodiment, the thickness T of the entire a layer _A Thickness T of the whole of layer B _B Ratio T of (2) _A /T _B Is in a specific range. Specifically, the thickness ratio T _A /T _B It is usually 30/70 or more, preferably 35/65 or more, more preferably 40/60 or more, usually 65/35 or less, preferably 60/40 or less, more preferably 55/45 or less. Here, in the case where the retardation film has one a layer, the thickness T _A The thickness of the a layer is shown. In addition, in the case where the retardation film has two or more a layers, the thickness T _A The sum of the thicknesses of these a layers is indicated. Further, in the case where the retardation film has one B layer, the thickness T _B The thickness of this B layer is shown. In addition, in the case where the retardation film has two or more B layers, the thickness T _B The sum of the thicknesses of these B layers is indicated.

The retardation film of the present embodiment has wavelength dispersion properties in a specific range. Specifically, the wavelength dispersion of the retardation film is represented by Re (450)/Re (550). Further, the wavelength dispersion Re (450)/Re (550) of the retardation film satisfies the following formula (ii):

0.60≤Re(450)/Re(550)≤0.96 (ii)。

here, re (450) represents the in-plane retardation of the retardation film at a wavelength of 450 nm. Further, re (550) represents the in-plane retardation of the retardation film at a wavelength of 550 nm.

Formula (ii) is described in further detail. The wavelength dispersion Re (450)/Re (550) of the retardation film is usually 0.60 or more, preferably 0.70 or more, more preferably 0.80 or more, usually 0.96 or less, preferably 0.93 or less, more preferably 0.92 or less, and further preferably 0.91 or less.

The retardation film of the present embodiment satisfying the above requirements has high reflection suppressing ability and excellent reworkability. Specifically, when a polarizing plate (typically, a circular polarizing plate) is obtained by combining a phase difference film and a linear polarizer, the polarizing plate can effectively suppress reflection on the screen of the image display device. In addition, after the retardation film is first attached to a certain member, the condensation damage of the retardation film can be effectively suppressed when the retardation film is peeled off. This can prevent a part of the retardation film from remaining on the member after the retardation film is peeled off. Therefore, even when the peeled retardation film is bonded again to the above member, deterioration in quality can be suppressed.

[ layer 2.A ]

The retardation film has one or more A layers. Layer a has a slow axis. In the case where the retardation film has two or more a layers, the slow axes of these a layers are generally parallel. Therefore, the angle formed between the slow axes of these a layers is usually 0 ° to 5 °, preferably 0 ° to 4 °, more preferably 0 ° to 3 °, further preferably 0 ° to 2 °, particularly preferably 0 ° to 1 °, and ideally 0 °, when viewed from the thickness direction.

The a layer is formed of a resin a having positive intrinsic birefringence. Thus, the layer a contains the resin a, preferably contains only the resin a. The resin a is typically a thermoplastic resin. The resin a may contain a polymer and any components as needed. In general, part or all of the above-mentioned polymers have positive intrinsic birefringence, and thus the resin a may have positive intrinsic birefringence.

Examples of the polymer contained in the layer a include polymers containing an alicyclic structure. The alicyclic structure-containing polymer preferably has positive intrinsic birefringence. The alicyclic structure-containing polymer is a polymer having an alicyclic structure in a repeating unit, and examples thereof include (1) a norbornene-based polymer, (2) a monocyclic olefin polymer, (3) a cyclic conjugated diene polymer, (4) a vinyl alicyclic hydrocarbon polymer, and a hydride thereof. The alicyclic structure-containing polymer may be selected from those disclosed in JP-A2002-321302, for example. Examples of the alicyclic structure-containing polymer include "ZEONOR" manufactured by japanese patent No. Weng Zhushi, and "ARTON" manufactured by JSR corporation. From the viewpoints of reworkability and adhesion to the B layer, the polymer contained in the a layer preferably contains a heteroatom in the molecule.

The polymer contained in the resin a preferably contains an isosorbide skeleton, and particularly preferably is a polycarbonate containing an isosorbide skeleton. Here, the isosorbide skeleton represents a skeleton represented by the following formula (X1). In formula (X1), the binding site is represented. The polymer containing an isosorbide skeleton preferably has positive intrinsic birefringence. When the isosorbide skeleton-containing polymer, particularly the isosorbide skeleton-containing polycarbonate is used, the adhesion to the layer of the resin B, the reflection suppressing ability of the retardation film, reworkability, and the retardation change suppressing ability upon application of stress can be effectively improved.

[ chemical formula 5]

The polymer contained in the resin a preferably contains no aromatic ring. In the case of using a polymer having no aromatic ring in the molecule, the reflection suppressing ability of the retardation film can be effectively improved. In particular, since the resin a containing a polymer containing no aromatic ring tends to have a small wavelength dispersion Re (a 450)/Re (a 550), the improvement of the reflection suppressing ability is remarkable when it is combined with the resin B containing a polymer having a large wavelength dispersion Re (B450)/Re (B550) such as a polyester containing a fluorene ring, which will be described later.

Examples of the isosorbide skeleton-containing polymer include "DuRABIO" manufactured by Mitsubishi chemical corporation. Furthermore, "DURABIO" manufactured by mitsubishi chemical corporation does not contain an aromatic ring in the molecule of the polymer.

The polymer may be used alone or in combination of two or more kinds in any ratio.

The weight average molecular weight (Mw) of the polymer contained in the resin a is preferably 10000 or more, more preferably 15000 or more, particularly preferably 20000 or more, preferably 100000 or less, more preferably 80000 or less, particularly preferably 50000 or less. When the weight average molecular weight is in such a range, the mechanical strength and molding processability of the a layer are highly balanced.

The 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, in GPC, toluene may be used as a solvent in the case where the sample is insoluble in cyclohexane.

The molecular weight distribution (weight average molecular weight (Mw)/number average molecular weight (Mn)) of the polymer contained in the resin a is preferably 1.2 or more, more preferably 1.5 or more, particularly preferably 1.8 or more, preferably 3.5 or less, more preferably 3.0 or less, particularly preferably 2.7 or less. When the molecular weight distribution is equal to or more than the lower limit of the above range, the productivity of the polymer can be improved, and the production cost can be suppressed. In addition, when the molecular weight distribution is equal to or less than the upper limit, the amount of the low-molecular component becomes small, so that relaxation (relaxation) at the time of high-temperature exposure can be suppressed, and the stability of the a layer can be improved.

The proportion of the polymer in the resin a is preferably 50 to 100% by weight, more preferably 70 to 100% by weight, and particularly preferably 90 to 100% by weight. When the ratio of the polymer is in the above range, the layer a attains sufficient heat resistance and transparency.

Resin a may further comprise any component to be combined with the polymer. Examples of the optional component include: stabilizers such as antioxidants, heat stabilizers, light stabilizers, weather stabilizers, ultraviolet light absorbers, and near infrared light absorbers; plasticizers, and the like. These components may be used singly or in combination of two or more kinds in any ratio.

The glass transition temperature TgA of the resin a is preferably 100 ℃ or higher, more preferably 110 ℃ or higher, particularly preferably 120 ℃ or higher, preferably 160 ℃ or lower, more preferably 150 ℃ or lower, particularly preferably 140 ℃ or lower. When the glass transition temperature TgA of the resin a is equal to or higher than the lower limit value of the above range, the heat resistance of the retardation film can be improved. When the glass transition temperature TgA is equal to or lower than the upper limit of the above range, the film formation and stretching in the method for producing a retardation film can be smoothly performed. The glass transition temperature can be measured using a Differential Scanning Calorimeter (DSC) with a temperature rise of 10℃per minute. The glass transition temperature of the resin a can be adjusted, for example, according to the composition of the resin a.

The difference |tga-tgb| between the glass transition temperature TgA of the resin a and the glass transition temperature TgB of the resin B is preferably 15 ℃ or less, more preferably 10 ℃ or less, particularly preferably 8 ℃ or less. The difference in glass transition temperatures |tga to tgb| falling within the above range means that the glass transition temperature TgA of the resin a is close to the glass transition temperature TgB of the resin B. In this case, when the resin a and the resin B are co-stretched to produce a retardation film, the range of stretching conditions is widened, and the retardation and thickness of the retardation film as the target can be easily obtained. The glass transition temperature TgA of the resin a may be higher or lower than the glass transition temperature TgB of the resin B.

The in-plane retardation Re (A550) of the entire A layer at a wavelength of 550nm is preferably 180nm or more, more preferably 200nm or more, particularly preferably 220nm or more, preferably 320nm or less, more preferably 300nm or less, particularly preferably 280nm or less. When the in-plane retardation Re (a 550) of the entire a layer is within the above range, both the reflection suppressing ability and reworkability can be made particularly good.

The magnitude of the difference between the in-plane retardation Re (a 550) of the entire a layer at wavelength 550nm and the in-plane retardation Re (B550) of the entire B layer at wavelength 550nm, re (a 550) -Re (B550) |, is preferably within a specific range. The specific range is preferably 90nm or more, more preferably 100nm or more, particularly preferably 110nm or more, preferably 200nm or less, more preferably 180nm or less, particularly preferably 160nm or less. When the magnitude of the difference in-plane retardation |re (a 550) -Re (B550) | is within the above range, both the reflection suppressing ability and the reworkability can be made particularly good. The in-plane retardation Re (a 550) of the entire a layer may be larger or smaller than the in-plane retardation Re (B550) of the entire B layer.

The wavelength dispersion Re (a 450)/Re (a 550) of the a layer is preferably 0.98 or more, more preferably 0.99 or more, particularly preferably 1.00 or more, preferably 1.10 or less, more preferably 1.06 or less, particularly preferably 1.04 or less. When the wavelength dispersion Re (a 450)/Re (a 550) of the a layer is within the above range, both the reflection suppressing ability and the reworkability can be made particularly good. The wavelength dispersion Re (a 450)/Re (a 550) of the a layer can be adjusted, for example, according to the composition of the resin a.

The thickness of one A layer is preferably 5 μm or more, more preferably 10 μm or more, particularly preferably 15 μm or more, preferably 100 μm or less, more preferably 80 μm or less, particularly preferably 60 μm or less. When the thickness of the a layer is equal to or greater than the lower limit of the above range, the film formation and stretching for producing the a layer retardation film having such a thickness can be smoothly performed. When the thickness of the a layer is equal to or less than the upper limit of the above range, the thickness of the retardation film can be reduced.

[ layer B ]

The retardation film has one or more B layers. Layer B has a slow axis. In the case where the retardation film has two or more B layers, the slow axes of these B layers are generally parallel. Therefore, the angle formed between the slow axes of these B layers is usually 0 ° to 5 °, preferably 0 ° to 4 °, more preferably 0 ° to 3 °, further preferably 0 ° to 2 °, particularly preferably 0 ° to 1 °, and ideally 0 °, when viewed from the thickness direction.

When the retardation film is viewed from the thickness direction, the slow axis of the B layer is perpendicular to the slow axis of the a layer. Thus, the slow axis of the B layer and the slow axis of the a layer form an angle in a specific range as viewed in the thickness direction. Specifically, the angle between the slow axis of the B layer and the slow axis of the a layer is usually 85 ° to 90 °, preferably 86 ° to 90 °, more preferably 87 ° to 90 °, even more preferably 88 ° to 90 °, particularly preferably 89 ° to 90 °, and most preferably 90 °. In the case where the groups of the slow axis of the a layer and the slow axis of the B layer are two or more, the angles between the slow axes of the a layer and the slow axis of the B layer of all the groups are in the above-described range. For example, in the case where the retardation film has two or more a layers and one B layer, since the slow axis of each a layer may be combined with the slow axis of the B layer, the group of the slow axis of the a layer and the slow axis of the B layer may be two or more. In this case, the angles between the slow axes of the a layers and the B layers of all groups are in the above-described range, and therefore, the angles of the slow axes of the B layers and the slow axes of the a layers are all in the above-described range.

Since the slow axis of the a layer is perpendicular to the slow axis of the B layer, the in-plane retardation of the retardation film including the a layer and the B layer may generally reflect the difference between the in-plane retardation of the a layer and the in-plane retardation of the B layer. Therefore, in general, since the retardation film can have an in-plane retardation reflecting the relationship between the wavelength dispersion of the a layer and the wavelength dispersion of the B layer represented by the formula (i), the retardation film can have an inverse wavelength dispersion.

The B layer is formed of a resin B having negative intrinsic birefringence. Thus, the layer B contains the resin B, preferably contains only the resin B. The resin B is typically a thermoplastic resin. The resin B may contain a polymer and any components as needed. In general, a part or all of the above-mentioned polymers have negative intrinsic birefringence, and thus the resin B may have negative intrinsic birefringence.

The polymer contained in the resin B may be one kind or two or more kinds. The resin B contains at least one polymer selected from the group consisting of polyesters, polycarbonates, and polyestercarbonates. These polyesters, polycarbonates and polyester carbonates preferably have negative intrinsic birefringence. In the case where the resin B contains at least one polymer selected from the group consisting of polyesters, polycarbonates, and polyestercarbonates, the reflection suppressing ability and reworkability of the retardation film can be effectively improved.

The above polymer selected from the group consisting of polyesters, polycarbonates and polyester carbonates contains a fluorene skeleton, for example, a fluorene skeleton in a side chain. The above polymer preferably has negative intrinsic birefringence. In the case where the resin B contains a polymer containing a fluorene skeleton, the reflection suppressing ability and reworkability of the retardation film can be effectively improved. Here, the polymer having a fluorene skeleton in a side chain means a polymer having a structural unit represented by the following formula (X2).

[ chemical formula 6]

The polymer contained in the resin B preferably contains a structural unit having a fluorene-9, 9-diyl group. In the polymer contained in the resin B, the kind of the structural unit having a fluorene-9, 9-diyl group is not limited. For example, the polymer contained in the resin B may contain a dicarboxylic acid unit (a) having a fluorene-9, 9-diyl group. The dicarboxylic acid unit (a) represents a structural unit having a structure formed by polymerizing the dicarboxylic acid component (a). Among the dicarboxylic acid units (a), the dicarboxylic acid unit (a) having a fluorene-9, 9-diyl group is sometimes referred to as "fluorene dicarboxylic acid unit (A1)". Further, for example, the polymer contained in the resin B may contain a diol unit (B) having a fluorene-9, 9-diyl group. The diol unit (B) represents a structural unit having a structure formed by polymerizing the diol component (B). Among the diol units (B), the diol unit (B) having a fluorene-9, 9-diyl group is sometimes referred to as "fluorene diol unit (B1)".

As described above, the resin B may contain at least one polyester-based polymer selected from the group consisting of polyesters, polycarbonates, and polyester carbonates. Among these polyester polymers, polyesters are preferable from the viewpoints of moldability and retardation appearance. Polyesters containing fluorene skeletons are particularly preferred. Polyesters containing fluorene skeletons are suitably referred to as "polyesters containing fluorene rings".

The polyester is generally obtained by polymerizing a polymerization component comprising a dicarboxylic acid component (a) and a diol component (B). Thus, the polyesters generally comprise dicarboxylic acid units (A) and diol units (B). In the polyester containing a fluorene ring, the fluorene skeleton may be contained in a structural unit derived from any polymeric component. Therefore, the fluorene skeleton may be contained only in the dicarboxylic acid unit (a), the fluorene skeleton may be contained only in the diol unit (B), or both the dicarboxylic acid unit (a) and the diol unit (B) may contain the fluorene skeleton. In particular, since the reflection suppressing ability and reworkability of the retardation film can be improved particularly effectively, it is preferable that both the dicarboxylic acid unit (a) and the diol unit (B) contain a fluorene skeleton.

(dicarboxylic acid unit (A))

The polymer contained in the resin B may contain a dicarboxylic acid unit (a). Among them, the polymer contained in the resin B preferably contains fluorene dicarboxylic acid units (A1). For example, in the case where the resin B contains a polyester, the polyester preferably contains a fluorene dicarboxylic acid unit (A1).

Fluorene dicarboxylic acid unit (A1)

Examples of the fluorene dicarboxylic acid unit (A1) include a dicarboxylic acid unit represented by the following formula (1).

[ chemical formula 7]

(in the formula (1), R ¹ Represents a substituent, k represents an integer of 0 to 8, X ^1a And X ^1b Each independently represents a divalent hydrocarbon group which may have a substituent).

In the above formula (1), X is ^1a And X ^1b The divalent hydrocarbon group in (b) is preferably a divalent alicyclic hydrocarbon group such as cyclohexyl or a divalent aliphatic hydrocarbon group, and particularly preferably a divalent aliphatic hydrocarbon group. In X forming the main chain ^1a And X ^1b In the case of a divalent alicyclic or aliphatic hydrocarbon group, the combination with the fluorene ring structure (fluorene-9, 9-diyl) of the side chain reduces the refractive index and wavelength dispersion in the main chain direction, and increases the refractive index and wavelength dispersion in the direction perpendicular to the main chain direction. Thus, it is easy to prepare an oriented birefringent display negative and positive wavePolymers such as polyesters having long-term dispersion and large wavelength dispersion. In particular, when X ^1a And X ^1b In the case of a divalent aliphatic hydrocarbon group, the retardation appearance is high, and stretching can be performed under more gentle stretching conditions. Further, the toughness (flexibility) of the polymer can be improved, and a retardation film which is less likely to break and is excellent in moldability and handleability can be formed. Further, since thermal shrinkage due to residual stress is reduced, a thinner retardation film can be formed.

As a group X ^1a And X ^1b Examples of the divalent aliphatic hydrocarbon group include a linear or branched alkylene group, a linear or branched alkenylene group, and a linear or branched alkynylene group, and a linear or branched alkylene group is preferable. Among them, preferred are linear or branched C such as ethylene and propylene _2-4 An alkylene group; more preferably straight or branched C _2-3 An alkylene group; ethylene is particularly preferred. Appended "C" before the name of the group, unless otherwise specified _x-y The "(x and y represent positive integers) marks indicate that the number of carbon atoms of the group to which the marks are attached is x or more and y or less. In addition, X ^1a And X ^1b May be different from each other but is usually the same group.

In the above formula (1), R is a group ¹ Examples thereof include a non-polymerizable group or a non-reactive substituent which is inactive in polymerization reaction. As a group R ¹ Specific examples of (a) include: cyano group; halogen atoms such as fluorine atom, chlorine atom and bromine atom; alkyl, aryl, and the like. Examples of the aryl group include C such as phenyl _6-10 Aryl, and the like. Examples of the alkyl group include C such as methyl, ethyl, n-propyl, isopropyl, n-butyl and tert-butyl _1-12 Alkyl, preferably C _1-8 Alkyl, particularly preferably C such as methyl _1-4 Alkyl groups, and the like.

Typical dicarboxylic acid units represented by the above formula (1) include X ^1a And X ^1b Is straight or branched C _2-6 Structural units of alkylene groups, for example, 9-bis (2-carboxyethyl) fluorene, 9-bis (2-carboxypropyl) fluorene and the like are derived from 9, 9-bis (carboxyC) _2-6 Alkyl) fluorene junction Building blocks, and the like. These dicarboxylic acid units represented by the above formula (1) may be used singly or in combination of two or more. Of these dicarboxylic acid units represented by the above formula (1), those derived from 9, 9-bis (carboxyl group C) are preferable _2-6 Alkyl) fluorene structural units, more preferably from 9, 9-bis (carboxyl C) _2-4 The structural unit of alkyl) fluorene is particularly preferably a unit containing 9, 9-bis (carboxyl C) derived from 9, 9-bis (2-carboxyethyl) fluorene, 9-bis (2-carboxypropyl) fluorene and the like _2-3 Alkyl) fluorene structural units.

Second dicarboxylic acid unit (A2)

The polymer contained in the resin B may not contain a dicarboxylic acid unit (second dicarboxylic acid unit (A2)) other than the fluorene dicarboxylic acid unit (or first dicarboxylic acid unit) (A1) as the dicarboxylic acid unit (a), but may be contained as needed as long as the effect of the present invention is not impaired. For example, in the case where the resin B contains a polyester, the polyester may contain the second dicarboxylic acid unit (A2).

Examples of the second dicarboxylic acid unit (A2) include structural units derived from an aromatic dicarboxylic acid component [ among them, excluding the fluorene dicarboxylic acid component (A1) ], an alicyclic dicarboxylic acid component, an aliphatic dicarboxylic acid component, and the like.

Examples of the aromatic dicarboxylic acid component include phthalic acid, isophthalic acid, terephthalic acid, 4-methyl isophthalic acid, 5-methyl isophthalic acid, 1, 2-naphthalene dicarboxylic acid, 1, 4-naphthalene dicarboxylic acid, 1, 5-naphthalene dicarboxylic acid, 1, 8-naphthalene dicarboxylic acid, 2, 3-naphthalene dicarboxylic acid, 2, 6-naphthalene dicarboxylic acid, anthracene dicarboxylic acid, phenanthrene dicarboxylic acid, 2 '-biphenyl dicarboxylic acid, 3' -biphenyl dicarboxylic acid, 4 '-biphenyl dicarboxylic acid, and 4,4' -diphenylmethane dicarboxylic acid.

Examples of the alicyclic dicarboxylic acid component include di-or tricycloolefin dicarboxylic acids such as 1, 4-cyclohexane dicarboxylic acid, decalin dicarboxylic acid, norbornane dicarboxylic acid, adamantane dicarboxylic acid, tricyclodecane dicarboxylic acid, cyclohexene dicarboxylic acid, and norbornene dicarboxylic acid.

Examples of the aliphatic dicarboxylic acid component include succinic acid, adipic acid, sebacic acid, decanedicarboxylic acid, maleic acid, fumaric acid, itaconic acid, and the like.

These second dicarboxylic acid units (A2) may be used singly or in combination.

The ratio of the fluorene dicarboxylic acid unit (A1) to the entire dicarboxylic acid unit (a) can be selected from, for example, a range of about 1 mol% or more, specifically about 10 mol% to 100 mol%, and the following ranges are preferably 30 mol% or more, 50 mol% or more, 60 mol% or more, 70 mol% or more, 80 mol% or more, 90 mol% or more, 95 mol% or more, particularly preferably 100 mol% and substantially no second dicarboxylic acid unit (A2) in stages. When the ratio of the fluorene dicarboxylic acid unit (A1) is equal to or greater than the lower limit of the above range, a polymer such as a polyester exhibiting negative-orientation birefringence and positive-wavelength dispersion can be easily obtained.

(diol unit (B))

The polymer contained in the resin B may contain a diol unit (B). Among them, the polymer contained in the resin B preferably contains a fluorene diol unit (B1). For example, in the case where the resin B contains a polyester, the polyester preferably contains a fluorene diol unit (B1).

Fluorene diol unit (B1)

The fluorene diol unit (B1) may be, for example, a diol unit represented by the following formula (2).

[ chemical formula 8]

(in the formula (2), R ² Represents a substituent, m represents an integer of 0 to 8, X ^2a And X ^2b Each independently represents a divalent hydrocarbon group which may have a substituent, A ^1a And A ^1b Each independently represents a linear or branched alkylene group, and n1 and n2 represent an integer of 0 or more).

In the above formula (2), R ² The substituent represented and the substitution number m thereof include a specific group, a range of substitution numbers, substitution positions, and the like, and are respectively the same as R in the above formula (1) ¹ The substituents represented and the substitution numbers k are the same.

At X ^2a And X ^2b Wherein X in the above formula (1) is a divalent hydrocarbon group ^1a And X ^1b Examples of the same include divalent aliphatic hydrocarbon groups such as linear or branched alkylene groups, divalent alicyclic hydrocarbon groups such as cyclohexylene groups, and divalent aromatic hydrocarbon groups such as phenylene groups. The divalent hydrocarbon group is preferably a divalent aliphatic hydrocarbon group or a divalent aromatic hydrocarbon group. X is X ^2a And X ^2b The kinds of (c) can be different from each other but are usually the same.

As R as above ² Examples of the hydrocarbyl group include: straight-chain or branched C such as methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl and the like _1-10 An alkyl group; c such as cyclopentyl and cyclohexyl _5-10 Cycloalkyl; phenyl, methylphenyl (or tolyl), dimethylphenyl (or xylyl), and the like _1-4 Alkyl-phenyl; c such as biphenyl, naphthyl, etc _6-12 An aryl group; benzyl, phenethyl and the like C _6-10 aryl-C _1-4 An alkyl group.

As alkylene A ^1a And A ^1b Examples thereof include linear or branched C such as ethylene, propylene (1, 2-propanediyl), trimethylene, 1, 2-butanediyl and tetramethylene _2-6 Alkylene group, etc., preferably straight chain or branched C _2-4 Alkylene groups, more preferably straight-chain or branched C such as ethylene and propylene _2-3 Alkylene groups, particularly ethylene groups, are preferred.

Oxyalkylene (-OA) ^1a -) and (-OA ^1b The repetition numbers (addition mole numbers) n1 and n2 of (-) may be 0 or more, and may be selected from the range of integers of about 0 to 15, for example, and the following ranges are stepwise 0 to 10, 0 to 8, 0 to 6, 0 to 4, 0 to 2, and 0 to 1 as preferable ranges.

Typical diol units represented by the above formula (2) include, for example, X ^2a And X ^2b A diol unit (hereinafter, also simply referred to as a dialkylfluorene diol unit) which is a linear or branched alkylene group, a diol unit (hereinafter, also simply referred to as a diarylfluorene diol unit) represented by the following formula (2A), or the like. These fluorene diol units (B1) may be used singly or in combination of two or more.

Typical examples of the dialkylfluorenediol units include 9, 9-bis (hydroxy straight-chain or branched-chain C derived from 9, 9-bis (hydroxymethyl) fluorene, 9-bis (2-hydroxyethyl) fluorene, 9-bis (3-hydroxypropyl) fluorene, 9-bis (4-hydroxybutyl) fluorene and the like _1-6 Alkyl) fluorene structural units. These dialkylfluorendiol units may be used singly or in combination of two or more. Structural units derived from 9, 9-bis (hydroxymethyl) fluorene are particularly preferred.

The bisaryl fluorene diol unit represented by the following formula (2A) is easy to raise the glass transition temperature of the polymer, and thus can reduce thermal shrinkage due to residual stress, and effectively improve environmental resistance (heat resistance and water resistance (moisture resistance), dimensional stability against heat and moisture, and phase difference stability). That is, the bisaryl fluorene diol unit is effective for adjusting the balance of the phase difference manifestation property and the wavelength dispersion property with the environmental resistance reliability.

[ chemical formula 9]

(in the formula (2A), Z ^1a And Z ^1b Each independently represents an aromatic hydrocarbon ring, R ^3a And R is ^3b Each independently represents a substituent, p1 and p2 each independently represents an integer of 0 or more, R ² 、m、A ^1a And A ^1b Each of n1 and n2 includes a preferable embodiment, and is the same as the above formula (2).

In the above formula (2A), Z is ^1a And Z ^1b Examples of the aromatic hydrocarbon ring (aromatic hydrocarbon ring) include benzene ring, naphthalene ring, indene ring, anthracene ring, phenanthrene ring, biphenyl ring, phenyl naphthalene ring, binaphthyl ring, and terphenyl ring, and C such as benzene ring, naphthalene ring, and biphenyl ring is preferable _6-12 Aromatic hydrocarbon ring, more preferably C such as benzene ring and naphthalene ring _6-10 Aromatic hydrocarbon rings, particularly preferably benzene rings.

As R ^3a And R is ^3b Examples of the substituent include: a halogen atom; alkyl, cycloalkyl, aryl, aralkyl, and the like; an alkoxy group; an acyl group; a nitro group; cyano group; substituted amino groups, and the like. Wherein R is ^3a And R is ^3b Alkyl and aryl are each independently preferred, with C being particularly preferred _1-4 Alkyl and C _6-10 Aryl groups.

p1 and p2 are each independently preferably 0 or more, preferably 8 or less, more preferably 4 or less, further preferably 3 or less, and still further preferably 2 or less.

Representative examples of the bisaryl fluorene diol unit include a diol unit of 9, 9-bis (hydroxyaryl) fluorene type corresponding to n1 and n2 of 0 in the above formula (2A); corresponding to a diol unit of 9, 9-bis [ hydroxy (poly) alkoxyaryl ] fluorene type in which n1 and n2 are 1 or more, for example, about 1 to 10.

Examples of 9, 9-bis (hydroxyaryl) fluorenes include: 9, 9-bis [ (mono or di) C such as 9, 9-bis (4-hydroxyphenyl) fluorene, 9-bis (4-hydroxy-3-methylphenyl) fluorene, 9-bis (4-hydroxy-3-isopropylphenyl) fluorene, 9-bis (4-hydroxy-3, 5-dimethylphenyl) fluorene and the like _1-4 Alkyl-hydroxyphenyl groups]Fluorene; 9, 9-bis (C) such as 9, 9-bis (4-hydroxy-3-phenylphenyl) fluorene _6-10 Aryl-hydroxyphenyl) fluorene; 9, 9-bis (6-hydroxy-2-naphthyl) fluorene, 9-bis (5-hydroxy-1-naphthyl) fluorene, and the like.

As 9, 9-bis [ hydroxy (poly) alkoxyaryl ]]Fluorene compounds include, for example: 9, 9-bis [4- (2-hydroxyethoxy) phenyl ]]Fluorene, 9-bis [4- (2- (2-hydroxyethoxy) ethoxy) phenyl]Fluorene, 9-bis [4- (2-hydroxypropoxy) phenyl ]]Fluorene or the like 9, 9-bis [ hydroxy (one to ten) C _2-4 Alkoxy-phenyl]Fluorene; 9, 9-bis [4- (2-hydroxyethoxy) -3-methylphenyl ]]Fluorene, 9-bis [4- (2- (2-hydroxyethoxy) ethoxy) -3-methylphenyl]Fluorene, 9-bis [4- (2-hydroxyethoxy) -3, 5-dimethylphenyl ]]Fluorene, 9-bis [4- (2-hydroxypropoxy) -3-methylphenyl]Fluorene or the like 9, 9-bis [ (one or two) C _1-4 Alkyl-hydroxy (one to ten) C _2-4 Alkoxy-phenyl]Fluorene, and the like.

As 9, 9-bis [ aryl-hydroxy (poly) alkoxyphenyl ]]Fluorene compounds include, for example: 9, 9-bis (4- (2-hydroxyethoxy) -3-phenylphenyl) fluorene and 9, 9-bis [4- (2- (2-hydroxyethoxy) ethoxy) -3-phenylphenyl ]9, 9-bis [ C ] fluorene such as fluorene and 9, 9-bis (4- (2-hydroxypropoxy) -3-phenylphenyl) fluorene _6-10 Aryl-hydroxy (one to ten) C _2-4 Alkoxy-phenyl]Fluorene; 9, 9-bis[6- (2-hydroxyethoxy) -2-naphthyl ]]Fluorene, 9-bis [5- (2-hydroxyethoxy) -1-naphthyl]Fluorene, 9-bis [6- (2- (2-hydroxyethoxy) ethoxy) -2-naphthyl]Fluorene, 9-bis [6- (2-hydroxypropoxy) -2-naphthyl]Fluorene or the like 9, 9-bis [ hydroxy (one to ten) C _2-4 Alkoxy-naphthyl]Fluorene, and the like.

In the fluorene diol unit (B1), the dialkylfluorene diol unit and the diarylfluorene diol unit may be used singly or in combination of two or more.

The proportion of the fluorene diol unit (B1) relative to the entire diol unit (B) can be selected from, for example, a range of about 1 mol% or more, specifically about 10 mol% to 100 mol%, and as a preferable range, the following ranges are stepwise 30 mol% to 100 mol%, 50 mol% to 99 mol%, 60 mol% to 98 mol%, 70 mol% to 97 mol%, 80 mol% to 96 mol%, and particularly preferably 85 mol% to 95 mol%. When the ratio of the fluorene diol unit (B1) is equal to or greater than the lower limit of the above range, a polymer such as a polyester exhibiting negative-orientation birefringence and positive-wavelength dispersion can be easily obtained. In addition, when the ratio of the fluorene diol unit (B1) is equal to or less than the upper limit value of the above range, moldability and handleability can be improved.

(Poly) alkylene glycol unit (B2)

The polymer contained in the resin B may contain, as the diol unit (B), a (poly) alkylene glycol unit (B2) represented by the following formula (3), if necessary. For example, in the case where the resin B contains a polyester, the polyester may contain a (poly) alkylene glycol unit (B2). In the case of containing the (poly) alkylene glycol unit (B2), it is effective for producing a retardation film excellent in moldability and handleability because the polymerization reactivity of the polymer can be improved to increase the molecular weight, or the toughness can be improved by a soft chemical structure.

[ chemical formula 10]

(in the formula (3), A ² Representing straight or branched chainsAlkylene group, q represents an integer of 1 or more).

In the above formula (3), A is ² Examples of the alkylene group include linear or branched C such as ethylene, propylene, trimethylene, 1, 2-butylene, 1, 3-butylene, tetramethylene, 1, 5-pentanediyl, 1, 6-hexanediyl, 1, 8-octanediyl, and 1, 10-decanediyl _2-12 Alkylene groups, and the like. Preferably a straight or branched C such as ethylene or propylene _2-4 An alkylene group; more preferably straight or branched C _2-3 An alkylene group; ethylene is particularly preferred.

The repetition number q can be selected from a range of about 1 to 10, for example, and is preferably 1 to 8, 1 to 6, 1 to 4, 1 to 3, 1 to 2, particularly preferably 1 in the following stages.

Examples of the diol component corresponding to the (poly) alkylene glycol unit (B2) include: linear or branched C such as ethylene glycol, propylene glycol, trimethylene glycol, 1, 2-butanediol, 1, 3-butanediol, tetramethylene glycol (or 1, 4-butanediol), 1, 5-pentanediol, neopentyl glycol, 1, 6-hexanediol, 1, 8-octanediol, and 1, 10-decanediol _2-12 An alkylene glycol; di-to decalinear or branched C such as diethylene glycol, dipropylene glycol, triethylene glycol, etc _2-12 Alkylene glycol, and the like. These (poly) alkylene glycol units (B2) may be contained singly or in combination. Structural units derived from ethylene glycol are particularly preferred.

The proportion of the (poly) alkylene glycol unit (B2) relative to the whole glycol unit (B) can be selected from the range of about 0 to 100 mol%, for example, about 1 to 50 mol%, and the following ranges are preferably 3 to 30 mol%, 5 to 20 mol%, 7 to 15 mol%, and particularly preferably 8 to 12 mol% in stages. When the ratio of the (poly) alkylene glycol unit (B2) is equal to or less than the upper limit of the above range, a polymer such as a polyester exhibiting negative-orientation birefringence and positive-wavelength dispersion can be easily obtained. In addition, when the ratio of the (poly) alkylene glycol unit (B2) is equal to or more than the lower limit value of the above range, moldability and handleability can be improved.

The method for producing the polymer is not particularly limited. For example, in the case of producing polyesters as polymers, conventional methods can be used for the production method. For example, the polymer may be produced by reacting a dicarboxylic acid component (a) corresponding to each dicarboxylic acid unit or the like with a diol component (B) corresponding to the diol unit or the like, and may be produced by a conventional method such as a melt polymerization method such as a transesterification method or a direct polymerization method, a solution polymerization method or an interfacial polymerization method, and a melt polymerization method is preferable. In addition, the reaction may be carried out in the presence or absence of a solvent according to the polymerization method. As a specific production method, for example, a method described in Japanese patent application laid-open No. 2017-198956 can be used.

The weight average molecular weight (Mw) of the polymer contained in the resin B is preferably 20000 or more, more preferably 25000 or more, more preferably 30000 or more, more preferably 35000 or more, more preferably 40000 or more, particularly preferably 50000 or more, preferably 100000 or less, more preferably 80000 or less, more preferably 70000 or less. When the weight average molecular weight is within such a range, the production of the B layer by stretching can be smoothly performed.

The proportion of the polymer in the resin B is preferably 50 to 100% by weight, more preferably 70 to 100% by weight, and particularly preferably 90 to 100% by weight. When the ratio of the polymer is in the above range, the heat resistance and transparency of the B layer are sufficient.

Resin B may further comprise any component to be combined with the polymer. Examples of the optional component include the same ones as those that the resin a may contain. These components may be used singly or in combination of two or more kinds in any ratio.

The glass transition temperature TgB of the resin B is preferably 100 ℃ or higher, more preferably 110 ℃ or higher, particularly preferably 120 ℃ or higher, preferably 160 ℃ or lower, more preferably 150 ℃ or lower, particularly preferably 140 ℃ or lower. When the glass transition temperature TgB of the resin B is equal to or higher than the lower limit value of the above range, the heat resistance of the retardation film can be improved. When the glass transition temperature TgB is equal to or lower than the upper limit of the above range, the film formation and stretching in the method for producing a retardation film can be smoothly performed. The glass transition temperature TgB of the resin B may be adjusted, for example, according to the composition of the resin B.

The in-plane retardation Re (B550) of the entire B layer at a wavelength of 550nm is preferably 60nm or more, more preferably 80nm or more, particularly preferably 100nm or more, preferably 180nm or less, more preferably 160nm or less, particularly preferably 140nm or less. When the in-plane retardation Re (B550) of the entire B layer is within the above range, both the reflection suppressing ability and reworkability can be made particularly good.

The in-plane retardation Re (B450) and Re (B550) of the B layer as a whole preferably satisfies the following formula (iii):

1.14≤Re(450)/Re(550) (iii)

specifically, the wavelength dispersion Re (B450)/Re (B550) of the B layer is preferably 1.14 or more, more preferably 1.15 or more, particularly preferably 1.16 or more, preferably 1.30 or less, more preferably 1.24 or less, particularly preferably 1.20 or less. When the wavelength dispersion Re (B450)/Re (B550) of the B layer is within the above range, both the reflection suppressing ability and reworkability can be made particularly good. The wavelength dispersion Re (B450)/Re (B550) of the B layer can be adjusted, for example, according to the composition of the resin B.

The thickness of one B layer is preferably 5 μm or more, more preferably 10 μm or more, particularly preferably 15 μm or more, preferably 100 μm or less, more preferably 80 μm or less, particularly preferably 60 μm or less. When the thickness of the B layer is equal to or greater than the lower limit of the above range, film formation and stretching for producing a retardation film having the B layer with such a thickness can be smoothly performed. When the thickness of the B layer is equal to or less than the upper limit of the above range, the thickness of the retardation film can be reduced.

[4. Optional layer ]

The retardation film may have any layer other than the a layer and the B layer as required. Examples of the optional layer include a layer having optical isotropy. A layer having optical isotropy means a layer having small in-plane retardation. The in-plane retardation at a wavelength of 550nm of the layer having optical isotropy is usually 10nm or less, preferably 7nm or less, and more preferably 5nm or less. Specific examples of any layer include: a protective film layer; and an adhesive layer for bonding the layers of the layer A and the layer B.

[5 ] Properties of retardation film ]

When the retardation film is used in combination with a linear polarizer, it can exhibit high reflection suppressing ability. The applicant speculates that a structure capable of exhibiting such high reflection suppressing ability is as follows. However, the technical scope of the present invention is not limited to the following configuration.

Fig. 1 is a graph schematically showing the relative relationship between the in-plane retardation of the entire a layer and the in-plane retardation of the entire B layer in one example. In fig. 1, the horizontal axis represents wavelength, and the vertical axis represents the magnitude of in-plane retardation. In fig. 1, an example in which the in-plane retardation of the entire a layer is larger than the in-plane retardation of the entire B layer is described.

The combined in-plane retardation of the a-layer and the B-layer is expressed as a combination of the in-plane retardation of the a-layer and the in-plane retardation of the B-layer. In the case where the slow axis of the a layer is perpendicular to the slow axis of the B layer, as shown in fig. 1, the in-plane retardation of the combination of the a layer and the B layer is expressed as a difference of the in-plane retardation of the a layer as a whole and the in-plane retardation of the B layer as B whole, a difference of the in-plane retardation of the B layer as a whole. As in the above embodiment, when the formula (i) is satisfied by the method of selecting the resin a, selecting the resin B, or the like, the gradient of the in-plane retardation ReA of the entire a layer is different from the gradient of the in-plane retardation ReB of the entire B layer, and thus the longer the wavelength, the larger the difference in-plane retardation ReA-ReB. Thus, the combination of the a layer and the B layer exhibits inverse wavelength dispersion, and the longer the inverse wavelength dispersion wavelength, the greater the in-plane retardation. Therefore, the retardation film including the combination of the a layer and the B layer can have inverse wavelength dispersion satisfying the formula (ii). The retardation film having inverse wavelength dispersion can exhibit a uniform optical function in a wide range of the visible wavelength range (400 nm to 700 nm), and therefore the polarization state of light transmitted through the retardation film can be uniformly changed. Therefore, a polarizing plate (typically, a circular polarizing plate) having a combination of the retardation film and the linear polarizer can effectively suppress reflection of light in a wide range of the visible wavelength region. Thus, a high reflection suppressing ability can be achieved.

The retardation film is excellent in reworkability. The applicant speculates that a structure with such excellent reworkability can be obtained as follows. However, the technical scope of the present invention is not limited to the following configuration.

Consider the case where the difference in inverse wavelength dispersion between resin a and resin B is small and equation (i) is not satisfied. In this case, in order for the retardation film to exhibit inverse wavelength dispersion, the in-plane retardation of each of the a layer and the B layer is required to be large. As a method for increasing the in-plane retardation, for example, the degree of orientation of polymer molecules contained in the resin a and the resin B is increased. The degree of orientation can be increased by stretching at a large stretch ratio or stretching at a low temperature. However, when the degree of orientation of the polymer molecules is large, cohesive failure due to Delamination (Delamination) is liable to occur. When the retardation film is peeled off after the first lamination of the retardation film to a certain member, if delamination occurs on the a layer or the B layer, a part of the damaged a layer or B layer may remain on the surface of the member. Therefore, even if the phase difference film is bonded to the member again, the desired optical characteristics cannot be obtained at the portion where a part of the damaged a layer or B layer remains. Therefore, reworkability of the film which is easily delaminated is poor.

In contrast, the retardation film according to the present embodiment can obtain in-plane retardation satisfying the formulas (i) and (ii) without excessively increasing the degree of orientation of polymer molecules by appropriately combining the resin a having positive intrinsic birefringence with the resin B having negative intrinsic birefringence, controlling the thickness ratio of the a layer to the B layer within a specific range, and the like. Therefore, delamination accompanying cohesive failure of the a layer and the B layer is suppressed, and therefore excellent reworkability can be obtained.

The retardation film preferably has an in-plane retardation in an appropriate range according to its use. Among these, from the viewpoint of obtaining a polarizing plate having particularly excellent reflection suppressing ability in combination with a linear polarizer, the in-plane retardation Re (590) of the retardation film at a measurement wavelength of 590nm may be preferably 100nm or more, more preferably 110nm or more, particularly preferably 120nm or more, and may be preferably 180nm or less, more preferably 170nm or less, particularly preferably 160nm or less. Since the retardation film having the in-plane retardation Re (590) in such a range can function as a 1/4 wave plate, a circularly polarizing plate can be obtained by combining the retardation film with a linear polarizer.

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 400nm to 700nm 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 preferably 0%. Haze can be measured according to JIS K7361-1997 using a haze meter.

The retardation film preferably has a small photoelastic coefficient from the viewpoint of improving the retardation change suppressing ability upon application of stress. Specifically, the photoelastic coefficient of the retardation film is preferably 30 Brewster or less. The photoelastic coefficient is a value indicating the stress dependence of birefringence generated when subjected to stress. In general, birefringence (refractive index difference nx-ny) Δn has a relationship obtained by the product of stress σ and photoelastic coefficient C (Δn=c·σ). The smaller the absolute value of the photoelastic coefficient is, the better the optical performance can be exhibited even when an impact is applied or when the display device is deformed so as to be suitable for a display surface having a curved surface.

The photoelastic coefficient can be measured by preparing a load- Δn curve and obtaining the slope thereof. The load- Δn curve can be prepared by performing an operation of obtaining the birefringence value Δn while applying a load in the range of 50g to 150g to the film while changing the load. The birefringence value Δn can be measured by measuring retardation in the film surface using a retardation measuring apparatus (KOBRA-21 ADH, manufactured by prince measuring instruments Co., ltd.), and dividing the retardation by the thickness of the film.

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

The thickness of the retardation film is preferably 90 μm or less, more preferably 70 μm or less, further preferably 60 μm or less, particularly preferably 50 μm or less. In the past, it has been particularly difficult to achieve both high reflection suppressing ability and excellent reworkability in such a thin retardation film. Therefore, the retardation film of the above embodiment is useful in that it has high reflection suppressing ability and excellent reworkability and can be thinned. The lower limit of the thickness of the retardation film is not particularly limited, and may be, for example, 10 μm or more, 20 μm or more, 30 μm or more, or the like.

[6. Method for producing retardation film ]

The method for producing the retardation film is not limited as long as the desired retardation film can be obtained. For example, the retardation film can be produced by a production method including the steps of:

a first step of preparing a multilayer film having a layer formed of a resin A and a layer formed of a resin B; and

and a second step of stretching the multilayer film.

The method can simply manufacture the phase difference film by a small number of steps and simple manufacturing condition control.

[6.1. First step ]

The multilayer film prepared in the first step has a layer formed of a resin a and a layer formed of a resin B. In order to distinguish the "layer formed of the resin a" and the "layer formed of the resin B" before stretching from the a layer and the B layer of the retardation film, they are sometimes referred to as "layer (a)" and "layer (B)".

The layers (a) and (B) of the multilayer film prepared in the first step may have optical characteristics different from those of the a layer and the B layer of the retardation film. Specifically, the layers (a) and (b) of the multilayer film generally do not have large optical anisotropy. Thus, the in-plane retardation of layers (a) and (b) is typically small. The in-plane retardation of the layer (a) and the layer (b) at 550nm is, for example, preferably 0nm to 20nm, more preferably 0nm to 10nm, particularly preferably 0nm to 5nm, independently of each other.

The multilayer film may be a monolithic film, preferably a long strip of film. By preparing the multilayer film as a long film, a part or all of the steps can be performed on the production line in the case of producing the retardation film, and thus the production can be performed simply and efficiently.

There is no limitation on the method of producing the multilayer film. The multilayer film can be produced by, for example, the following production method: coextrusion molding methods such as a coextrusion T-die method, a coextrusion blow molding method, and a coextrusion lamination method; co-casting; a coating forming method; film lamination molding such as dry lamination. Among these, the coextrusion molding method is preferable from the viewpoint of production efficiency and the viewpoint of no volatile components such as solvents remaining in the film. Among the coextrusion molding methods, the coextrusion T-die method is preferable. Among the coextrusion T-die methods, a feed block method and a multi-manifold method are exemplified, and the multi-manifold method is particularly preferable in view of reducing the variation in thickness of each layer.

In the case of producing a multilayer film using a coextrusion molding method, the first step generally includes a step of melt-extruding a resin a and a resin B to form a layer (a) and a layer (B). In this case, the melting temperature of the extruded resin is preferably tg+80 ℃ or higher, more preferably tg+100 ℃ or higher, preferably tg+180 ℃ or lower, more preferably tg+150 ℃ or lower. Here, "Tg" means the glass transition temperatures of the resin a and the resin B. The above-mentioned melting temperature means, for example, the melting temperature of the resin in the extruder having the T die in the coextrusion T die method. When the melting temperature of the extruded resin is equal to or higher than the lower limit of the above range, the fluidity of the resin can be sufficiently improved to improve the moldability, and when the melting temperature of the extruded resin is equal to or lower than the upper limit, the deterioration of the resin can be suppressed.

In the coextrusion molding method, a molten resin in a film form extruded from a die lip is cooled by being brought into close contact with a cooling roll, and is solidified. In this case, examples of a method for adhering the molten resin to the cooling roll include an air knife method, a vacuum box method, and an electrostatic adhesion method.

In the case of producing a multilayer film using a coating molding method, the first process generally includes: preparing a layer of one of the resins a and B; and applying a coating liquid containing the other of the resin a and the resin B on the prepared layer. The method for preparing the layer of one of the resin a and the resin B is not limited, and may be prepared by a method described in a bonding method described later, for example.

After the layer of one of the resin a and the resin B is prepared, the coating liquid is applied on the layer. The coating liquid generally includes the other of the resin a and the resin B and a solvent. As the solvent, a solvent capable of dissolving or dispersing the other of the resin a and the resin B is preferable, and a solvent capable of dissolving it is particularly preferable. The solvent may be used alone, or two or more solvents may be used in combination in any ratio. Examples of the solvent include: aromatic solvents such as benzene, toluene, and xylene; ketone solvents such as diacetone alcohol, acetone, cyclopentanone, cyclohexanone, methyl ethyl ketone, and methyl isopropyl ketone; ester solvents such as methyl lactate and ethyl lactate; cycloolefin solvents such as cyclohexane, ethylcyclohexane and 1, 2-dimethylcyclohexane; halogen-containing solvents such as methylene chloride and chloroform; ether solvents such as tetrahydrofuran and dioxane; alcohol solvents such as 1-pentanol and 1-butanol. The concentration of the resin in the coating liquid may be 1 to 50% by weight from the viewpoint of obtaining a viscosity suitable for coating.

There is no limitation on the coating method of the coating liquid. Examples of the coating method include curtain coating, extrusion coating, roll coating, spin coating, dip coating, bar coating, spray coating, slide coating, printing coating, gravure coating, die coating, gap coating, and dip coating.

By applying the coating liquid, a film of the coating liquid is formed on the layer of one of the resin a and the resin B. Therefore, if necessary, the coating liquid is dried to remove the solvent, whereby a multilayer film having the layer (a) and the layer (b) can be obtained. The drying method is not limited, and for example, a drying method such as heat drying or reduced pressure drying may be used.

The multilayer film may also be produced using a lamination method. In the case of producing a multilayer film by using a lamination method, the first step includes: preparing a layer (a); preparing a layer (b); and bonding layer (a) and layer (b).

The method of preparing the layers (a) and (b) is not limited. The layer (a) and the layer (b) can be produced by, for example, a melt molding method, a solution casting method, among which the melt molding method is preferable. Among the melt molding methods, extrusion molding, blow molding or compression molding is preferable, and extrusion molding is particularly preferable.

The bonding of the layers (a) and (b) may be performed using an adhesive as needed. The adhesive is preferably selected according to the kind of the resin a and the resin B. Examples of the adhesive include an acrylic adhesive, a urethane adhesive, a polyester adhesive, a polyvinyl alcohol adhesive, a polyolefin adhesive, a modified polyolefin adhesive, a polyvinyl alkyl ether adhesive, a rubber adhesive, an ethylene-vinyl acetate adhesive, a vinyl chloride-vinyl acetate adhesive, an SEBS (styrene-ethylene-butylene-styrene copolymer) adhesive, an SIS (styrene-isoprene-styrene block copolymer) adhesive, and an ethylene adhesive such as an ethylene-styrene copolymer, an ethylene- (meth) methyl acrylate copolymer, and an ethylene- (meth) ethyl acrylate copolymer.

In the case of using an adhesive, an adhesive layer may be formed from the adhesive generally between the layer (a) and the layer (b). The average thickness of the adhesive layer is preferably 0.1 μm to 10. Mu.m, more preferably 0.5 μm to 5. Mu.m.

[6.2. Second step ]

The second process step includes stretching the multilayer film. By this stretching, birefringence can be developed in the layer (a), and a slow axis parallel to the stretching direction appears. In addition, birefringence may be developed in layer (b), with slow axes perpendicular to the direction of stretching. Therefore, according to the stretching, a retardation film having an in-plane retardation satisfying the above-described requirements and having a layer a and a layer B with a slow axis can be obtained.

The stretching temperature of the multilayer film is preferably "Tg (h) -10 ℃ or higher", more preferably "Tg (h) -5 ℃ or higher", particularly preferably "Tg (h) °c) or higher, preferably" Tg (h) +20 ℃ or lower, more preferably "Tg (h) +15 ℃ or lower, particularly preferably" Tg (h) +10 ℃ or lower. Here, tg (h) represents the higher temperature of the glass transition temperature TgA of the resin a and the glass transition temperature TgB of the resin B. When stretching is performed at a stretching temperature in the above range, a retardation film particularly excellent in reworkability can be obtained.

The stretching ratio of the multilayer film is preferably 1.5 times or more, more preferably 1.6 times or more, particularly preferably 1.8 times or more, preferably 5.0 times or less, more preferably 4.0 times or less, particularly preferably 3.0 times or less. When stretching is performed at a stretching ratio in the above range, a retardation film particularly excellent in reworkability can be obtained.

The stretching of the multilayer film may be performed by a uniaxial stretching method in which stretching is performed in one direction, or may be performed by a biaxial stretching method in which stretching is performed in two directions.

Examples of the uniaxial stretching method include: a method of uniaxial stretching in the longitudinal direction using a difference in peripheral speed between rolls; a method of stretching uniaxially in the transverse direction using a tenter frame, and the like.

Examples of the biaxial stretching method include: a simultaneous biaxial stretching method of stretching in the transverse direction by the spread angle of the rail while stretching in the longitudinal direction by pulling the interval of the fixed jigs apart; and a sequential biaxial stretching method in which the difference in peripheral speed between rolls is used to stretch the rolls in the longitudinal direction, and then both ends are held by a jig and stretched in the transverse direction by a tenter.

As another stretching method, a tenter stretching machine capable of applying a push force, a pull force, or a pull force at different speeds in the lateral direction or the longitudinal direction is used, and stretching is continuously performed in an oblique direction at an arbitrary angle θ to the width direction of the multilayer film. The oblique direction means a direction that is neither parallel nor perpendicular to the width direction of the film.

These stretching methods can be performed using, for example, a stretching machine such as a longitudinal uniaxial stretching machine, a tenter stretching machine, a bubble stretching machine, or a roll stretching machine.

The second process preferably includes a step of stretching the multilayer film in an oblique direction. The retardation film manufactured through the second process including stretching in the oblique direction may have a slow axis in the oblique direction. Therefore, the retardation film can be bonded to a normal linear polarizer having a transmission axis parallel or perpendicular to the longitudinal direction by a roll-to-roll method to obtain a polarizing plate. Therefore, a polarizing plate can be efficiently manufactured using a long retardation film and a long linear polarizer.

[6.3. Optional procedure ]

The method for producing a retardation film may further include any step in combination with the first step and the second step. For example, in the case of obtaining a long retardation film using a long multilayer film, the method for producing a retardation film may include a trimming step of cutting the obtained retardation film into a desired shape. According to the trimming step, a monolithic retardation film having a desired shape can be obtained. The method for producing the retardation film may further include a step of providing an optional layer on the retardation film, for example.

[6.4. Other methods of manufacture ]

The retardation film can be produced by a method different from the above production method. For example, the retardation film can be produced by a method including the steps of: a step of preparing a layer, a step of preparing a layer B, and a step of bonding the layer a and the layer B.

The layer a can be produced, for example, by a method including the steps of: manufacturing the layer (a) by a melt molding method, a solution casting method, or the like; and stretching the layer (a). The stretching of the layer (a) may be performed under the same conditions as described in the description of the second step.

The B layer can be produced, for example, by a method including the steps of: manufacturing the layer (b) by a melt molding method, a solution casting method, or the like; and stretching the layer (b). The stretching of the layer (b) may be performed under the same conditions as described in the description of the second step.

Bonding of the layers a and B may be performed using an adhesive. The type of adhesive and the thickness of the adhesive layer may be the same as the bonding of the layers (a) and (b).

[7. Polarizer ]

The polarizing plate according to one embodiment of the present invention has a linear polarizer and a phase difference film. The polarizing plate can generally function as a circular polarizing plate, and is provided on a display surface of an image display device, thereby suppressing reflection of external light.

The polarizer may have a linear polarizer, an a layer, and a B layer in that order. In addition, the polarizer may have a linear polarizer, a B layer, and an a layer in this order.

In the polarizing plate, the angle formed by the transmission axis of the linear polarizer and the slow axis of the a layer is preferably in a specific range of approximately 45 °. Specifically, the angle is preferably 40 ° or more, more preferably 42 ° or more, further preferably 43 ° or more, particularly preferably 44 ° or more, preferably 50 ° or less, more preferably 48 ° or less, further preferably 47 ° or less, particularly preferably 46 ° or less.

As the linear polarizer, any linear polarizer may be used. As an example of the linear polarizer, there may be mentioned: a film obtained by uniaxially stretching a polyvinyl alcohol film after adsorbing iodine or a dichroic dye in a boric acid bath; a film obtained by stretching a polyvinyl alcohol film by adsorbing iodine or a dichroic dye, and further modifying a part of polyvinyl alcohol units in a molecular chain into polyethylene units. Among these, a polarizer containing polyvinyl alcohol is preferable as the linear polarizer.

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

Further, the thickness of the linear polarizer is preferably 5 μm to 80 μm.

The polarizing plate may further include any layer. Examples of the optional layer include: a polarizer protective film layer; an adhesive layer for adhering the linear polarizer and the phase difference film; a hard coat layer such as an impact-resistant polymethacrylate resin layer; a mat layer that improves the smoothness of the film; a reflection suppressing layer; an anti-fouling layer; a charge suppressing layer, and the like. These arbitrary layers may be provided in only one layer, or may be provided in two or more layers.

[8. Image display device ]

An image display device according to an embodiment of the present invention includes the above-described retardation film. In general, an image display device includes the polarizing plate including a retardation film. The polarizing plate is preferably provided in an organic electroluminescent display device (hereinafter sometimes referred to as an "organic EL display device"). The organic EL display device includes a polarizing plate and an organic electroluminescent element (hereinafter, sometimes referred to as an "organic EL element"). The organic EL display device generally has a linear polarizer, a phase difference film, and an organic EL element in this order.

The organic EL element has a transparent electrode layer, a light-emitting layer, and an electrode layer in this order, and the light-emitting layer can emit light by applying a voltage from the transparent electrode layer and the electrode layer. Examples of the material constituting the organic light-emitting layer include a Poly (p-phenylene vinylene)) type material, a polyfluorene type material, and a polyvinylcarbazole type material. The light-emitting layer may be a laminate of a plurality of layers having different emission colors, or a mixed layer in which a layer of a certain dye is doped with different dyes. The organic EL element may further include a functional layer such as a hole injection layer, a hole transport layer, an electron injection layer, an electron transport layer, an equipotential surface forming layer, and a charge generation layer.

The image display device can restrain reflection of external light on a display surface. The structure of the reflection suppression will be described by taking a case where the polarizing plate is a circular polarizing plate as an example. Only a part of the light incident from the outside of the device passes through the linear polarizer, and then it passes through the phase difference film, thereby becoming circularly polarized light. The circularly polarized light is reflected by a structural element (a reflective electrode or the like in an organic EL element) of the reflected light in the image display device, and passes through the phase difference film again, thereby becoming linearly polarized light having a vibration direction orthogonal to the vibration direction of the incident linearly polarized light, and cannot pass through the linear polarizer. Here, the vibration direction of the linearly polarized light refers to the vibration direction of the electric field of the linearly polarized light. Thereby, a function of suppressing reflection is realized.

Examples

The present invention will be specifically described with reference to the following examples. However, the present invention is not limited to the embodiments described below, and may be arbitrarily modified and implemented within the scope not departing from the scope of the claims and the equivalents thereof.

In the following description, unless otherwise indicated, "%" and "parts" representing amounts are weight basis. The operations described below are performed in the atmosphere at normal temperature and normal pressure unless otherwise described.

[ evaluation method ]

(method for measuring thickness of layers)

The thickness of each layer was measured using a reflection spectrometer (FE-3000, manufactured by Katsukamu electronics Co., ltd.).

(method for measuring the direction of the slow axis of each layer)

The direction of the slow axis of each layer was measured using a phase difference meter (KOBA-WIST, manufactured by prince measuring instruments Co., ltd.).

(method for measuring in-plane delay)

The in-plane retardation was measured using a retardation meter (KOBRA-WIST, manufactured by prince measuring instruments Co., ltd.).

(method for measuring photoelastic coefficient)

The in-plane retardation of the retardation film was measured while applying a load to the retardation film in the range of 50g to 150 g. The measured in-plane retardation was divided by the thickness of the retardation film to determine the birefringence Δn of the retardation film when the load was applied. The birefringence value Δn is obtained by performing the above-described operations a plurality of times while changing the load, and a load- Δn curve is produced. As the slope of the load- Δn curve, the photoelastic coefficient of the retardation film was obtained.

(method for evaluating reflection suppressing Properties)

A long polarizing plate (HLC 2-5618S, manufactured by SANRITZ Co., ltd., thickness 180 μm) having a protective film, a linear polarizer and a protective film in this order was prepared. The linear polarizer has a transmission axis in the width direction. The protective film on one surface side of the polarizing plate was removed, and the retardation film obtained in the example or comparative example was bonded to the surface. The lamination was performed such that the slow axis of the retardation film was at an angle of 45 ° to the transmission axis of the linear polarizer. In particular, the retardation films of example 5 and comparative example 3 were laminated such that the a layer and the B layer were arranged in order from the linear polarizer side. By the above-described operations, a polarizing plate sample was obtained as a circularly polarizing plate having a phase difference film, a linear polarizer, and a protective film in this order.

A commercially available organic EL display device (OLED 55EG9600 manufactured by LG electronic system) having an organic EL element and a circularly polarizing plate provided on the visual inspection side of the organic EL element was prepared. The circularly polarizing plate of the organic EL display device was replaced with the above-described polarizing plate sample. In the replacement, the polarizing plate sample was arranged such that the retardation film and the linear polarizer were arranged in order from the organic EL element side. The transmission axis of the linear polarizer included in the polarizer sample provided in the organic EL display device was in the same direction as the transmission axis of the linear polarizer of the circular polarizer originally included in the organic EL display device.

The display surface of the obtained organic EL display device was observed from the front direction (normal direction) with respect to the display surface while being irradiated with a light source. When the reflectance of the display surface is significantly suppressed compared to that before the substitution, it is determined as "excellent". When the reflectance of the display surface is suppressed as compared with that before the replacement, it is determined as "ok". When the reflectance of the display surface was equal to or increased as compared with that before the replacement, the display surface was evaluated as "defective".

(method for evaluating adhesion)

An unstretched film (glass transition temperature 160 ℃ C., thickness 100 μm, manufactured by Japanese patent application No. Weng Zhushi Co., ltd.) formed of a resin containing a norbornene polymer was prepared. Corona treatment is applied to one side of the unstretched film.

One side of the retardation film obtained in the example or comparative example was subjected to corona treatment. In particular, the retardation films of example 5 and comparative example 3 were subjected to corona treatment on the a-layer side surface. The adhesive is adhered to the corona-treated surface of the retardation film and the corona-treated surface of the unstretched film, and the adhesive-adhered surfaces are bonded to each other to cure the adhesive. As the adhesive, an ultraviolet curable adhesive is used. Thus, a sample film having a retardation film and an unstretched film was obtained.

The sample film was cut to a width of 15mm to obtain a sample sheet. The retardation film side of the sample sheet was bonded to the surface of the slide glass with an adhesive (double-sided adhesive tape "CS9621" manufactured by niton corporation).

The 90-degree peel test was performed by sandwiching the unstretched film at the front end of the load cell and stretching it in the direction normal to the surface of the slide. In this case, the force measured at the time of peeling the unstretched film is the force required for peeling the retardation film and the unstretched film, and therefore the magnitude of the force is measured as the peeling strength.

In general, the greater the peel strength, the more the breakage of the phase change film is suppressed when the film is reattached, and therefore the reworkability is excellent. Therefore, when the peel strength is 2.0N or more, the reworkability is judged as "excellent". Further, when the peel strength is 1.0N or more and less than 2.0N, reworkability is judged as "possible". Further, when the peel strength is less than 1.0N, the reworkability is judged as "poor".

Synthesis example 1

After 1.00 moles of FDPM (9, 9-bis (2-methoxycarbonylethyl) fluorene), 0.90 moles of BPEF (9, 9-bis [4- (2-hydroxyethoxy) phenyl)]Fluorene, manufactured by osaka gas chemical Co., ltd.), 2.10 mol of EG (ethylene glycol), 2X 10 as a transesterification catalyst was added ^-4 Molar manganese acetate tetrahydrate and 8X 10 ^-4 The molar calcium acetate monohydrate was melted by heating slowly with stirring. After heating to 230 ℃, 14×10 is added ^-4 Molar trimethyl phosphate, 20X 10 ^-4 The molar germanium oxide was gradually heated and depressurized to 270 ℃ and 0.13kPa or less to remove EG. After a predetermined stirring torque was reached, the content was taken out of the reactor to prepare pellets of a polyester containing a fluorene ring.

The FDPM is a dimethyl ester of 9, 9-bis (2-carboxyethyl) fluorene (or fluorene-9, 9-dipropionic acid). The FDPM was synthesized in the same manner as described in JP-A2005-89422, except that t-butyl acrylate in example 1 was changed to methyl acrylate [37.9g (0.44 mol) ].

By passing through ¹ As a result of H-NMR analysis of the obtained pellets, 100 mol% of dicarboxylic acid units introduced into the fluorene ring-containing polyester were derived from FDPM, 90 mol% of diol units introduced were derived from BPEF, and 10 mol% were derived from EG.

The glass transition temperature Tg of the obtained fluorene ring-containing polyester was 125℃and the weight average molecular weight Mw was 60000.

Example 1

(1-1. Production of multilayer film)

A film forming machine is prepared having a T-die, a feedblock connected to the T-die, and a plurality of single-screw extruders connected to the feedblock via a polymer tube and a polymer filter.

As the resin A, "DURABIO" (resin containing a polymer having an isosorbide skeleton and containing no aromatic ring. Glass transition temperature 127 ℃) manufactured by Mitsubishi chemical Co., ltd was prepared. The resin a was fed to a single-screw extruder.

As the resin B, the fluorene ring-containing polyester produced in Synthesis example 1 was prepared. The resin B was fed to a single-screw extruder different from that to which the resin a was fed.

The melt coextrusion of the resin a and the resin B was performed using a film forming machine. Specifically, the resin a and the resin B were melted in a single-screw extruder, respectively, and supplied to a feed block via a polymer pipe and a polymer filter. Resin a and resin B merge in a feedblock and are extruded through a T die onto a casting drum into a sheet. The extruded sheet-like resin was cooled on a cooling drum to obtain a long multilayer film having a three-layer structure of "layer of resin a/layer of resin B/layer of resin a".

(1-2. Stretching of multilayer film)

The multilayer film was subjected to free-end uniaxial stretching in the longitudinal direction under stretching conditions of a stretching temperature of 135 ℃ and a stretching ratio of 2.0 times using a stretching machine with a constant temperature bath, to obtain a retardation film as a stretched film. The "free-end uniaxial stretching" refers to stretching in a certain direction, and does not apply a constraint force in a direction other than the direction in which the stretching is performed. The obtained retardation film had a three-layer structure of "a layer/B layer/a layer", and the ratio of the thicknesses of these layers was a layer to B layer to a layer=22.5:55:22.5.

The obtained retardation film was evaluated by the above method.

(measurement of in-plane retardation of A layer and B layer)

Etching was performed from the surface of the retardation film using a dry etching apparatus (RIE-10 NE, manufactured by Sesamck Co., ltd.). Various samples were collected with the etching time varying every 10 minutes, and the retardation and thickness of the samples were measured, respectively. The retardation of each layer was calculated from the retardation and the amount of thickness change.

Example 2

The ratio of the thickness of the retardation film to the thickness of the three layers (i.e., a layer and B layer) included in the retardation film is changed by changing the extrusion amounts of the resin a and the resin B. The thickness ratio is layer a to layer B to layer a=30:40:30. Except for the above, the retardation film was produced and evaluated in the same manner as in example 1.

Example 3

The ratio of the thickness of the retardation film to the thickness of the three layers (i.e., a layer and B layer) included in the retardation film is changed by changing the extrusion amounts of the resin a and the resin B. The thickness ratio is layer a to layer B to layer a=17.5:65:17.5. The stretching method of the multilayer film was changed from free-end uniaxial stretching to oblique stretching using a tenter. In the above-described oblique stretching, the multilayer film is stretched in a stretching direction at an angle of 45 ° to the width direction thereof by adjusting an angle (draw-out angle) between the moving direction of the multilayer film supplied to the tenter and the moving direction of the retardation film sent from the tenter. Except for the above, the retardation film was produced and evaluated in the same manner as in example 1.

Example 4

(4-1. Production of multilayer film)

As the resin B, a long unstretched film made of a polyester containing a fluorene ring produced in synthesis example 1 was prepared.

As the resin A, "ARTON" (resin containing alicyclic structure-containing polymer having polar groups. Glass transition temperature 130 ℃ C.) manufactured by JSR Co., ltd. Was prepared. Resin A was dissolved in cyclohexane to give a 20% strength by weight solution. The solution of the resin a was applied to one side of an unstretched film made of the resin B using a doctor blade, and dried to form a layer of the resin a. Drying was performed at a drying temperature of 120℃for 2 minutes using a dryer. Then, the other surface of the unstretched film formed of the resin B was coated with the solution of the resin a and dried in the same manner to form a layer of the resin a. By the above operation, a long multilayer film having a three-layer structure of "layer of resin a/layer of resin B/layer of resin a" was obtained.

(4-2. Stretching of multilayer film)

The multilayer film was subjected to free-end uniaxial stretching in the longitudinal direction under stretching conditions of a stretching temperature of 135 ℃ and a stretching ratio of 2.5 times using a stretching machine with a thermostatic bath, to obtain a retardation film as a stretched film. The obtained retardation film had a three-layer structure of "a layer/B layer/a layer", and the ratio of the thicknesses of these layers was a layer to B layer to a layer=22.5:55:22.5.

The obtained retardation film was evaluated by the above method.

(measurement of in-plane retardation of A layer and B layer)

Etching was performed from the surface of the retardation film using a dry etching apparatus (RIE-10 NE, manufactured by Sesamck Co., ltd.). Samples were collected for varying the etching time every 10 minutes, and the retardation and thickness of the samples were measured, respectively. The retardation of each layer was calculated from the retardation and the amount of thickness change.

Example 5

(production of 5-1.A layer)

Preparing a film forming machine having: a T-die, a single-screw extruder connected to the T-die via a polymer tube and a polymer filter.

As the resin A, "ZEONOR" (resin containing alicyclic structure-containing polymer containing no polar group. Glass transition temperature 126 ℃ C.) manufactured by Japanese Rui Weng Zhushi Co., ltd., was prepared. The resin a was fed to a single-screw extruder and melt-extruded. Specifically, the resin a was melted in a single-screw extruder, supplied to a T die via a polymer tube and a polymer filter, and extruded into a sheet on a casting drum through the T die. The extruded sheet-like resin was cooled on a cooling drum to obtain a single-layer stretched film formed of the resin a.

The free end uniaxial stretching was performed on the film before stretching in the longitudinal direction under a stretching condition of a stretching temperature of 135 ℃ and a stretching ratio of 2.5 times by using a stretching machine with a constant temperature tank, to obtain a layer a as a stretched film. The in-plane retardation of the a layer was measured by the above measurement method.

(production of 5-2.B layer)

Instead of the resin a, the fluorene ring-containing polyester produced in synthesis example 1 was used as the resin B. Further, the thickness of the film before stretching was changed by changing the rotational speed of the casting drum. Except for the above, a B layer as a stretched film was produced by the same method as in the above step (5-1). The in-plane retardation of the B layer was measured by the above measurement method.

(bonding of layer A and layer B)

As the adhesive, a double-sided adhesive tape "CS9621" manufactured by nito electric corporation was prepared. The adhesive is an optically isotropic adhesive, and therefore does not have in-plane retardation. The layer a and the layer B are bonded together with the adhesive to obtain a retardation film. The bonding is performed such that the stretching direction of the layer a is parallel to the stretching direction of the layer B. The obtained retardation film had a three-layer structure of "layer a/layer of adhesive/layer B", and the ratio of the thicknesses of layer a and layer B was a layer: layer b=45:55. Further, the thickness of the adhesive layer was 10. Mu.m.

The obtained retardation film was evaluated by the above method.

Comparative example 1

As the resin B, XIRAN (resin comprising polystyrene. Glass transition temperature 130 ℃) manufactured by POLYSCOPE was used instead of the fluorene ring-containing polyester manufactured in Synthesis example 1. The thickness of the retardation film is changed by changing the extrusion amounts of the resin a and the resin B. Further, the stretching conditions of the multilayer film were changed to a stretching temperature of 130℃and a stretching ratio of 2.5 times. Except for the above, the retardation film was produced and evaluated in the same manner as in example 1.

Comparative example 2

As the resin B, XIRAN manufactured by POLYSCOPE was used instead of the fluorene ring-containing polyester produced in Synthesis example 1. The ratio of the thickness of the retardation film to the thickness of the three layers (i.e., a layer and B layer) including the retardation film is changed by changing the extrusion amounts of the resin a and the resin B. The thickness ratio is layer a to layer B to layer a=20:60:20. Further, the stretching conditions of the multilayer film were changed to a stretching temperature of 130℃and a stretching ratio of 3.5 times. Except for the above, the retardation film was produced and evaluated in the same manner as in example 1.

Comparative example 3

As the resin a, DURABIO manufactured by mitsubishi chemical corporation was used instead of ZEONOR manufactured by japanese patent No. Weng Zhushi. The thickness of the layers a and B is changed by changing the extrusion amounts of the resins a and B. Further, the stretching ratio of the film before stretching was changed to 2.0 times. The bonding of the a layer and the B layer is performed by making the stretching direction of the a layer perpendicular to the stretching direction of the B layer. Except for the above, the retardation film was produced and evaluated in the same manner as in example 5.

Comparative example 4

The ratio of the thickness of the retardation film to the thickness of the three layers (i.e., a layer and B layer) including the retardation film is changed by changing the extrusion amounts of the resin a and the resin B. The thickness ratio is layer a to layer B to layer a=10:80:10. Except for the above, the retardation film was produced and evaluated in the same manner as in example 1.

Comparative example 5

The ratio of the thickness of the retardation film to the thickness of the three layers (i.e., a layer and B layer) including the retardation film is changed by changing the extrusion amounts of the resin a and the resin B. The thickness ratio is layer a to layer B to layer a=35:30:35. Except for the above, the retardation film was produced and evaluated in the same manner as in example 1.

Results (results)

The results of the above examples and comparative examples are shown in the following table. In the following table, the shorthand meanings are as follows.

Relation of slow axis: relation of slow axis of layer a to slow axis of layer B.

Thickness ratio (T) _A /T _B ): thickness T of layer A as a whole _A Thickness T of the whole of layer B _B Ratio T of (2) _A /T _B 。

ΔRe450/Re550：|Re(A450)/Re(A550)-Re(B450)/Re(B550)|

TABLE 1

TABLE 1 results for the examples

TABLE 2

TABLE 2 results of comparative examples

Description of the reference numerals

In-plane retardation of the whole of the ReA a layer

In-plane retardation of the ReB layer as a whole

Claims

1. A retardation film, comprising: one or more than two layers A with a slow axis and one or more than two layers B with a slow axis at an angle of 85 DEG to 90 DEG to the slow axis of the layers A,

The a layer is formed of a resin a having positive intrinsic birefringence,

the B layer is formed of a resin B having negative intrinsic birefringence,

the resin B contains at least one polymer selected from polyester, polycarbonate and polyester carbonate,

the polymer contains a fluorene skeleton,

the in-plane retardation Re (a 450) of the entire a layer at a wavelength of 450nm, the in-plane retardation Re (a 550) of the entire a layer at a wavelength of 550nm, the in-plane retardation Re (B450) of the entire B layer at a wavelength of 450nm, and the in-plane retardation Re (B550) of the entire B layer at a wavelength of 550nm satisfy the following formula (i):

|Re(A450)/Re(A550)-Re(B450)/Re(B550)|≥0.10 (i)，

an in-plane retardation Re (450) of the retardation film at a wavelength of 450nm and an in-plane retardation Re (550) of the retardation film at a wavelength of 550nm satisfy the following formula (ii):

0.60≤Re(450)/Re(550)≤0.96 (ii)，

thickness T of the whole A layer _A Thickness T integral with the B layer _B Ratio T of (2) _A /T _B 30/70-65/35.

2. The retardation film as claimed in claim 1, wherein in-plane retardation Re (B450) and Re (B550) of the B layer as a whole satisfy the following formula (iii):

1.14≤Re(B450)/Re(B550) (iii)。

3. the retardation film as claimed in claim 1 or 2, wherein the polymer comprises a structural unit having fluorene-9, 9-diyl.

4. The retardation film according to any one of claims 1 to 3, wherein the structural unit having a fluorene-9, 9-diyl group comprises a fluorene dicarboxylic acid unit represented by the following formula (1) and/or a fluorene diol unit represented by the following formula (2), wherein the formula (1) is:

[ chemical formula 1]

Wherein R is ¹ Represents a substituent, k represents an integer of 0 to 8, X ^1a And X ^1b Each independently represents a divalent hydrocarbon group which may have a substituent,

the formula (2) is:

[ chemical formula 2]

Wherein R is ² Represents a substituent, m represents an integer of 0 to 8, X ^2a And X ^2b Each independently represents a divalent hydrocarbon group which may have a substituent, A ^1a And A ^1b Each independently represents a linear or branched alkylene group, n1And n2 represents an integer of 0 or more.

5. The retardation film as claimed in claim 4, wherein the fluorene diol unit comprises a diol unit represented by the following formula (2A), the formula (2A) being:

[ chemical formula 3]

Wherein Z is ^1a And Z ^1b Each independently represents an aromatic hydrocarbon ring, R ^3a And R is ^3b Each independently represents a substituent, p1 and p2 each independently represents an integer of 0 or more, R ² 、m、A ^1a And A ^1b N1 and n2 are the same as the above formula (2), respectively.

6. The retardation film as claimed in claim 5, wherein Z is a diol unit represented by the formula (2A) ^1a And Z ^1b Is C _6-12 Aromatic hydrocarbon ring, R ^3a And R is ^3b Is C _1-4 Alkyl or C _6-10 Aryl, p1 and p2 are integers from 0 to 2, A ^1a And A ^1b Is straight or branched C _2-4 Alkylene groups, n1 and n2 are integers from 0 to 2.

7. The retardation film as claimed in any one of claims 4 to 6, wherein in the fluorene dicarboxylic acid unit represented by formula (1), X ^1a And X ^1b Is straight or branched C _2-4 An alkylene group.

8. The retardation film as claimed in any one of claims 1 to 7, wherein the polymer further comprises an alkylene glycol unit represented by the following formula (3), the formula (3) being:

[ chemical formula 4]

Wherein A is ² And q represents an integer of 1 or more.

9. The retardation film as claimed in claim 8, wherein, in the alkylene glycol unit represented by formula (3), A ² Is straight or branched C _2-4 Alkylene, q is an integer from 1 to 4.

10. The retardation film as claimed in any one of claims 1 to 9, wherein the resin a comprises a polymer containing no aromatic ring.

11. The retardation film as claimed in any one of claims 1 to 10, wherein the resin a comprises a polymer containing an isosorbide skeleton.

12. The retardation film according to any one of claims 1 to 11, wherein in-plane retardation Re (450) and Re (550) of the retardation film satisfy the following formula (iv):

Re(450)/Re(550)≤0.91 (iv)。

13. the retardation film as claimed in any one of claims 1 to 12, wherein the glass transition temperature TgA of the resin a is 100 ℃ or more and 160 ℃ or less,

the glass transition temperature TgB of the resin B is 100-160 ℃.

14. The phase difference film according to any one of claims 1 to 13, wherein a difference |tga-tgb| between the glass transition temperature TgA of the resin a and the glass transition temperature TgB of the resin B is 15 ℃ or less.

15. The retardation film as claimed in any one of claims 1 to 14, wherein the thickness of the retardation film is 90 μm or less.

16. The retardation film as claimed in any one of claims 1 to 15, wherein the thickness of the retardation film is 70 μm or less.

17. A method for producing the retardation film according to any one of claims 1 to 16, comprising:

a step of preparing a multilayer film having a layer formed of a resin A and a layer formed of a resin B; the resin a has positive intrinsic birefringence and the resin B has negative intrinsic birefringence; and

and stretching the multilayer film.

18. The method for producing a retardation film as claimed in claim 17, wherein the step of preparing the multilayer film comprises a step of melt-extruding the resin a and the resin B.

19. The method for producing a retardation film according to claim 17 or 18, wherein the step of stretching the multilayer film comprises a step of stretching at a stretching temperature of "Tg (h) -10 ℃ or higher and" Tg (h) +20 ℃ or lower, wherein Tg (h) represents a temperature of the higher one of the glass transition temperature TgA of the resin a and the glass transition temperature TgB of the resin B.

20. The method for producing a retardation film as claimed in any one of claims 17 to 19, wherein the step of stretching the multilayer film comprises a step of stretching at a stretching ratio of 1.5 times or more and 5.0 times or less.

21. The method for producing a retardation film as claimed in any one of claims 17 to 20, wherein the step of stretching the multilayer film comprises a step of stretching the multilayer film in an oblique direction.

22. A polarizing plate having the retardation film of any one of claims 1 to 16 and a linear polarizer.

23. An image display device having the phase difference film according to any one of claims 1 to 16.