JP7305949B2 - retardation film - Google Patents

Description

The present invention relates to a retardation film.

2. Description of the Related Art In display devices such as liquid crystal display devices, various types of retardation films are sometimes provided in order to improve display quality. As a retardation film, a film having a multilayer structure (Patent Documents 1 and 2) and a film using a block copolymer having a lamellar structure (Patent Document 3) have been developed.

JP 2011-013378 A WO2008/146924 JP-A-05-164920

Since the film of Patent Document 2 expresses desired optical properties by combining a large number of layers, the structure is complicated, the manufacturing cost of the retardation film is high, and the productivity is low.

Moreover, it is desirable that the optical properties of the retardation film do not change significantly depending on the wavelength of the light to be transmitted, and for this reason, the retardation film preferably has reverse wavelength dispersion. Here, the reverse wavelength dispersion is a property of a film such that Re(450)/Re(550)<1. Here, Re(450) means the in-plane retardation of the film measured at a wavelength of 450 nm, and Re(550) means the in-plane retardation of the film measured at a wavelength of 550 nm. .

Therefore, there is a demand for a retardation film that has reverse wavelength dispersion and can be easily produced at low cost.

The present inventors have conducted extensive studies to solve the above problems. As a result, a resin containing a specific copolymer P is used to form a cylindrical phase-separated structure that exhibits structural birefringence, and the orientation direction of the cylinders in the phase-separated structure is set in a predetermined direction, thereby achieving the above-described The inventors have found that the problem can be solved, and completed the present invention.
That is, the present invention provides the following.

[1] Consists of a resin C containing a copolymer P containing polymerized units A and polymerized units B,
including a cylindrical phase-separated structure that exhibits structural birefringence,
The phase separation structure includes a phase (A) mainly composed of the polymerized unit A and a phase (B) mainly composed of the polymerized unit B, and satisfies the following condition (1) or (2): retardation film.
Condition (1): D(A)>D(B) and f(B)>0.5, and the direction giving the maximum refractive index in the in-plane direction is parallel to the orientation direction of the cylinders in the phase separation structure. is.
Condition (2): D(A)>D(B) and f(A)>0.5, and the direction giving the maximum refractive index in the in-plane direction is orthogonal to the orientation direction of the cylinders in the phase separation structure. are doing.
here,
f (A) represents the total weight ratio of the polymerized units A in the copolymer P,
f (B) represents the total weight ratio of the polymerized units B in the copolymer P,
D(A)=ReA(450)/ReA(550),
D(B)=ReB(450)/ReB(550),
ReA(450) represents the in-plane direction retardation (nm) of the film (A) formed from the polymer (A) consisting of the polymer unit A, measured at a wavelength of 450 nm,
ReA (550) represents the in-plane retardation (nm) of the film (A) measured at a wavelength of 550 nm,
ReB(450) represents the in-plane direction retardation (nm) of the film (B) formed from the polymer (B) consisting of the polymerized units B, measured at a wavelength of 450 nm,
ReB(550) represents the in-plane retardation (nm) of the film (B) measured at a wavelength of 550 nm.
[2] The retardation film of [1], which has an in-plane retardation Re(550) of 100 nm or more and 300 nm or less measured at a wavelength of 550 nm.
[3] The ratio of the in-plane retardation Re(450) measured at a wavelength of 450 nm to the in-plane retardation Re(550) measured at a wavelength of 550 nm (Re(450)/Re(550)) is The retardation film according to [1] or [2], which is 0 or more and less than 1.
[4] The retardation film of any one of [1] to [3], wherein the diameter of the cylinder in the phase separation structure is 50 nm or less.
[5] The absolute value of the difference between the refractive index n(a) of the polymer (A) and the refractive index n(b) of the polymer (B) (|n(a)−n(b)|) is , 0.05 or more, the retardation film according to any one of [1] to [4].
[6] The retardation film of any one of [1] to [5], wherein the interphase distance in the phase separation structure is 200 nm or less.
[7] The copolymer P is a block polymer having a block (A) containing the polymerized unit A as a main component and a block (B) containing the polymerized unit B as a main component, [1] to [ 6], the retardation film according to any one of items.
[8] The copolymer P contains a triblock copolymer P′, and the triblock copolymer P′ is mainly composed of a block (A) mainly composed of the polymerized unit A and the polymerized unit B The retardation film according to any one of [1] to [7], which is a (A)-(B)-(A) triblock copolymer having block (B) as a component.
[9] The copolymer P includes a pentablock copolymer P″, and the pentablock copolymer P″ comprises a block (A) mainly composed of the polymerized unit A and the polymerized unit B as a main component. Any one of [1] to [8], which is a (A)-(B)-(A)-(B)-(A) pentablock copolymer having block (B) as a component The described retardation film.
[10] The retardation film of any one of [1] to [9], wherein the copolymer P has a negative intrinsic birefringence value.
[11] The retardation film of any one of [1] to [10], wherein 0.9>f(A)>0.5 or 0.9>f(B)>0.5.

ADVANTAGE OF THE INVENTION According to this invention, the retardation film which has reverse wavelength dispersion and can be manufactured easily at low cost can be provided.

Hereinafter, the present invention will be described in detail by showing embodiments and examples. However, the present invention is not limited to the embodiments and examples shown below, and can be arbitrarily modified without departing from the scope of the claims of the present invention and their equivalents.

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

In the following description, the term "plate" includes not only rigid members but also flexible members such as resin films.

In the following description, the in-plane direction retardation Re of the film is a value represented by Re=(nx−ny)×d unless otherwise specified. Further, the retardation Rth in the thickness direction of the film is a value represented by Rth=[{(nx+ny)/2}-nz]×d unless otherwise specified. Here, nx represents the refractive index in the direction (in-plane direction) perpendicular to the thickness direction of the film, which gives the maximum refractive index. ny represents the refractive index in the in-plane direction of the film and in the direction orthogonal to the nx direction. nz represents the refractive index in the thickness direction of the film. d represents the thickness of the film. The measurement wavelength is 550 nm unless otherwise stated.

Whether the intrinsic birefringence value of a polymer is positive or negative is defined by the behavior of the refractive index of a molded article of the polymer when the molded article is stretched. That is, a polymer having a positive intrinsic birefringence value is a polymer in which the refractive index of the molded product in the stretching direction is higher than that before stretching. Moreover, a polymer having a negative intrinsic birefringence value is a polymer in which the refractive index of the molded product in the stretching direction is smaller than that before stretching. Intrinsic birefringence values can be calculated from the dielectric constant distribution.

Furthermore, a specific polymer unit has a positive intrinsic birefringence value means that a polymer consisting only of the polymer unit has a positive intrinsic birefringence value, and a specific polymer unit has a negative intrinsic birefringence value. Having a birefringence value means that a polymer composed only of the polymer units has a negative intrinsic birefringence value. Therefore, the positive or negative of the intrinsic birefringence value of the polymerized unit can be determined by preparing a homopolymer consisting only of the polymerized unit, forming the polymer into a molded product of an arbitrary shape, stretching the molded product, and measuring the optical properties. can be easily determined by In general, it is known that many of the polymerized units of hydrocarbons such as alkenes and dienes have positive intrinsic birefringence values. Many are known to have negative intrinsic birefringence values.

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

In the following description, unless otherwise specified, the tilt direction of a certain film means a direction neither parallel nor perpendicular to the main surface of the film. Refers to a direction with a range less than °.

In the following description, the terms “parallel”, “perpendicular” and “perpendicular” in the directions of the elements are within a range that does not impair the effects of the present invention, such as ±3°, ±2° or ±1°, unless otherwise specified. may contain an error within the range of

[1. retardation film]
The retardation film of this embodiment is made of resin C. As shown in FIG.

[1.1. Resin C]
Resin C contains a specific copolymer P. The copolymer P contains polymerized units A and polymerized units B. The copolymer P is preferably a block copolymer having a block (A) containing polymerized units A as a main component and a block (B) containing polymerized units B as a main component. Generally, a block copolymer is a polymer having a molecular structure in which a plurality of types of blocks are linked, and each block is a chain formed by linking polymer units. A specific block copolymer in one embodiment of the present invention has a specific block (A) and block (B). In the following description, such a specific block copolymer may be simply referred to as "block copolymer". Here, the polymerized units that are the main component in a certain block refer to polymerized units that account for 50% by weight or more of the total weight of the polymerized units that constitute the block.

Polymerized unit A may have a negative intrinsic birefringence value. On the other hand, polymerized unit B may have a positive intrinsic birefringence value.

Examples of polymerized units A include units represented by the following general formula (A).

R ^C is a phenyl group, biphenylyl group (eg, 4-biphenylyl group, 2-biphenylyl group, 3-biphenylyl group), naphthyl group (eg, 1-naphthyl group, 2-naphthyl group), anthracenyl group (e.g., anthracen-1-yl group, anthracen-2-yl group, anthracen-9-yl group), phenanthrenyl group (e.g., phenanthren-1-yl group, phenanthren-2-yl group, phenanthren-3-yl group) , phenanthrene-4-yl group, phenanthrene-9-yl group), naphthacenyl group (e.g., naphthacen-1-yl group, naphthacen-2-yl group, naphthacene-5-yl group), pentacenyl group (e.g., pentacene- 1-yl group, pentacen-2-yl group, pentacen-5-yl group, pentacen-6-yl group), and terphenylyl group.

Each of R ¹ to R ³ is independently a group selected from the group consisting of a hydrogen atom and an alkyl group having 1 to 12 carbon atoms. Examples of such alkyl groups include methyl, ethyl, propyl, and hexyl groups.
In formula (A),
Preferably R ¹ is a hydrogen atom.
Preferably, ^R2 and ^R3 are hydrogen atoms.
Preferably, R ^C is a naphthyl group.
More preferably, R ² and R ³ are hydrogen atoms and R ^{3 C} is a naphthyl group, or R ² and R ³ are hydrogen atoms and R ¹ is a hydrogen atom. More preferably, R ² and R ³ are hydrogen atoms, R ^C is a naphthyl group, and R ¹ is a hydrogen atom.

The polymerized unit A can be obtained by polymerizing the monomer (a) that gives the polymerized unit A. Examples of monomer (a) include vinylnaphthalene and its derivatives. Examples of vinylnaphthalenes include 1-vinylnaphthalene and 2-vinylnaphthalene. Examples of derivatives of vinylnaphthalene are α-methyl-1-vinylnaphthalene, α-ethyl-1-vinylnaphthalene, α-propyl-1-vinylnaphthalene, α-hexyl-1-vinylnaphthalene, α-methyl-2 -vinylnaphthalene, α-ethyl-2-vinylnaphthalene, α-propyl-2-vinylnaphthalene, and α-hexyl-2-vinylnaphthalene. As vinylnaphthalene and derivatives thereof, 2-vinylnaphthalene is preferable from the viewpoint of industrial availability.
The copolymer P may have only one polymer unit A alone, or may have two or more polymer units A in any combination. Therefore, as the monomer (a) for forming the polymerized unit A, only one type may be used alone, or two or more types may be used in combination at any ratio.

Examples of polymerized units B include units represented by the following general formulas (B-1) and (B-2).

Each of R ⁴ to R ⁹ is independently a group selected from the group consisting of a hydrogen atom and an alkyl group having 1 to 6 carbon atoms. Examples of such alkyl groups include methyl, ethyl, propyl, and hexyl groups. Each of R ⁴ to R ⁹ is preferably independently a hydrogen atom or a methyl group.

The polymerized unit B can be obtained by polymerizing the monomer (b) capable of giving the polymerized unit B to obtain a polymerized unit, and further hydrogenating the double bond if present in the polymerized unit. Examples of the monomer (b) include compounds represented by the following general formula (bm).

Preferred examples of the monomer (b) include butadiene (all of R ⁴ to R ⁹ in formula (bm) are hydrogen atoms), isoprene (R 6 or ^{R 7} in R ⁴ to R ⁹ in formula (bm) is a methyl group and the others are hydrogen atoms), 1,3-pentadiene, 2,3-dimethyl-1,3-butadiene, 1,3-hexadiene, 2-methyl-1,3-pentadiene, 3-methyl-1, 3-pentadiene, and 2,4-dimethyl-1,3-pentadiene. Among them, butadiene and isoprene are more preferable from the viewpoint of obtaining Resin C excellent in transparency, heat resistance, and workability. Preferred examples of polymerized units B include those having R ⁴ to R ⁹ the same as R ⁴ to R ⁹ in preferred examples of the monomer (b).
The copolymer P may have only one polymerized unit B alone, or may have two or more polymerized units B in any combination. Therefore, as the monomer (b) for forming the polymerized unit B, only one type may be used alone, or two or more types may be used in combination at any ratio.

When the copolymer P has a block (A), the block (A) may have any polymerized unit other than the polymerized unit A. Examples of such optional polymerized units include units formed by polymerization of any monomer copolymerizable with monomer (a), and units formed by hydrogenation of such units.
When the copolymer P has a block (B), the block (B) may have any polymerized unit other than the polymerized unit B. Examples of such arbitrary polymerized units include those polymerized units obtained by polymerizing the monomer (b) in which a non-hydrogenated double bond remains, and those copolymerizable with the monomer (b). and units formed by hydrogenation of such units and units formed by polymerization of any monomers.
However, from the viewpoint of developing the optical properties and mechanical properties of the resin C, it is preferable that both the proportion of the polymerized units A in the block (A) and the proportion of the polymerized units B in the block (B) are high. The proportion of the polymerized units A in the block (A) is preferably 50% by weight or more, more preferably 75% by weight or more, and still more preferably 95% by weight or more, and particularly preferably the block (A) contains only the polymerized units A. consists of The proportion of the polymerized unit B in the block (B) is preferably 50% by weight or more, more preferably 75% by weight or more, and still more preferably 95% by weight or more, and particularly preferably the block (B) contains only the polymerized unit B. consists of

Block (A) and block (B) are preferably incompatible. Since these are incompatible, a phase separation structure can be obtained more easily in the retardation film. Whether or not the block (A) and the block (B) are incompatible is determined by a homopolymer composed of the polymer unit A and a polymer unit B having a molecular weight similar to the size of these blocks in the block copolymer. It can be determined based on the presence or absence of compatibility of a homopolymer consisting of. The compatibility of such homopolymers can be determined by mixing these homopolymers to form a mixture and determining whether or not phase separation occurs when the mixture is placed at a melting temperature.

The molecular structure of the copolymer P is not particularly limited as long as it has polymerized units A and polymerized units B, and may have any molecular structure. For example, when the copolymer P is a block copolymer, the block copolymer may be a linear block copolymer or a graft block copolymer.
Examples of linear block copolymers include diblock copolymers having a block configuration of (A)-(B) in which block (A) and block (B) are linked; block (A) and block (B). and a triblock copolymer having a block configuration of (A)-(B)-(A) in which another block (A) is linked in this order (in the present application, sometimes referred to as "triblock copolymer P'" A pentablock co-multiplication having a block configuration in which three blocks (A) and two blocks (B) are connected in the order of (A)-(B)-(A)-(B)-(A) coalescing (in this application, sometimes referred to as “pentablock copolymer P″”); and linear block copolymers having a block configuration in which a greater number of blocks are connected. Examples of block configurations in which a large number of blocks are connected include (A)-((B)-(A))n-(B)-(A) and (B)-((A)-(B)) A block configuration of n-(A)-(B) (n is an integer of 1 or more) can be mentioned.
Examples of graft-type block copolymers include block copolymers having a block configuration of (A)-g-(B) in which block (B) is linked to block (A) as a side chain.

From the viewpoint of expressing desired optical properties in the resin C, the copolymer P is preferably a molecule having two or more polymer blocks (A) and one or more polymer blocks (B) per molecule. It can be a block copolymer having a structure. More preferably, the block copolymer can be a triblock copolymer having a block configuration of (A)-(B)-(A).

In yet another embodiment, the block copolymer can preferably be a pentablock copolymer having a block configuration of (A)-(B)-(A)-(B)-(A).

The resin C may contain only one type as the copolymer P alone, or may contain two or more types in combination at an arbitrary ratio.

The copolymer P preferably has a negative intrinsic birefringence value. Such a negative intrinsic birefringence value can be imparted by adjusting the proportion of polymerized units in the copolymer P. Specifically, by adjusting the weight fraction of polymerized units having a negative intrinsic birefringence value among the polymerized units constituting the copolymer P, a copolymer having a negative intrinsic birefringence value can be obtained. . When the copolymer P has a negative intrinsic birefringence value, desired optical properties can be imparted to the retardation film.

The resin C may consist of the copolymer P alone, or may contain an optional component in addition to the copolymer P. Examples of optional ingredients include additives such as dyes, pigments, antioxidants, and the like. The ratio of such optional components can be within a range that does not impair the effects of the present invention. Specifically, the proportion of the copolymer P in the resin C is preferably 98% by weight or more, more preferably 99% or more, and still more preferably the resin C consists of the copolymer P only.

[1.2. Structure Included in Retardation Film]
Retardation films contain cylindrical phase-separated structures that exhibit structural birefringence. A phase-separated structure is formed in the layer of the resin C that constitutes the retardation film. The phase-separated structure of resin C means that a portion (for example, block (A)) composed of polymerized units A of copolymer P in resin C and a portion composed of polymerized units B (for example, block (B)) self Due to the organization, a phase containing polymerized units A as a main component (also referred to as phase (A)) and a phase containing polymerized units B as a main component (also referred to as phase (B)) are distinguished in the layer. Separation into possible separate phases. In the following description, these phases may be simply referred to as "phase of polymerized unit A" and "phase of polymerized unit B". A cylindrical phase-separated structure means a structure in which one phase serves as a matrix and the other phase exhibits a cylindrical structure. An alignment layer exhibiting such a phase separation structure can exhibit structural birefringence when the structure is sufficiently smaller than the wavelength of light.
Here, in a certain phase, the polymerized units that are the main component refer to polymerized units that are contained in an amount of 50% by weight or more with respect to the total weight of the polymerized units that constitute the phase.

The polymerized unit A is preferably 80% by weight or more, more preferably 95% by weight or more, still more preferably 99% by weight or more, and 100% by weight or less, based on the total weight of the polymerized units constituting the phase (A). can be The polymerized units B are preferably 80% by weight or more, more preferably 95% by weight or more, still more preferably 99% by weight or more, and 100% by weight or less, based on the total weight of the polymerized units constituting the phase (B). can be

When the copolymer P is a block copolymer having a block (A) mainly composed of the polymerized units A and a block (B) mainly composed of the polymerized units B, the phase (A) is usually a block (A), and phase (B) is usually composed of block (B).

Structural birefringence is birefringence that occurs in a structure containing multiple types of phases with different refractive indices, such as the phase separation structure. For example, in a structure, when a phase with a refractive index n1 and a phase with a refractive index n2 different from n1 are present, the structure can exhibit structural birefringence. Structural birefringence is clearly different from orientational birefringence caused by molecular orientation by stretching in that birefringence occurs even if each phase is formed of an isotropic medium.

The actual occurrence of structural birefringence can be confirmed by measuring the optical properties of the film. An unstretched film formed by a conventional method such as extrusion molding, press working, solvent casting, etc. usually has random molecular orientation, so Re and Rth are almost zero. On the other hand, in an unstretched film exhibiting structural birefringence, Re and Rth are observed to be larger than the values observed in an ordinary unstretched film produced by a conventional method. Therefore, the expression of structural birefringence can be confirmed by measuring such a value. However, structural observation by an electron microscope or X-ray small-angle scattering can be performed to more reliably confirm the occurrence of structural birefringence.

The interphase distance in the phase separation structure is preferably 200 nm or less, more preferably 150 nm or less, still more preferably 100 nm or less, and can be greater than 0 nm, for example 10 nm or more. The interphase distance refers to the distance between cylinders. As the interphase distance, a value obtained by fitting a scattering pattern obtained by small-angle X-ray scattering measurement with a theoretical curve can be used.
The interphase distance can be adjusted by adjusting the molecular structure of the copolymer P. For example, a block copolymer may be used as the copolymer P, and factors such as the lengths of the blocks (A) and (B) may be appropriately adjusted.

The diameter of the cylinders in the phase-separated structure is preferably 50 nm or less, more preferably 40 nm or less, still more preferably 30 nm or less, and can be greater than 0 nm, for example 10 nm or more.

Structural birefringence can occur because the interphase distance and the size of the cylinder in the phase separation structure are sufficiently smaller than those of visible light. In addition, it is possible to suppress the coloring of the film and to suppress the decrease in light transmittance due to the increase in haze.

[1.3. Conditions met by the retardation film]
[1.3.1. Condition (1)]
The retardation film according to one embodiment of the present invention, D (A) > D (B) and f (B) > 0.5, and a direction giving the maximum refractive index in the in-plane direction and the phase separation structure is parallel to the orientation direction of the cylinders in

Here, f(B) represents the total weight ratio of the polymerized units B in the copolymer P. The total weight ratio of the polymerized units B in the copolymerized units P means the ratio of the total weight of the polymerized units B contained in the copolymer P to the weight of the copolymer P.

f(B) can be determined by measuring the NMR of copolymer P.

When f(B) is greater than 0.5, the phase (B) forms a matrix and the phase (A) exhibits a cylindrical structure in the normally cylindrical phase separation structure.

Also, D(A)=ReA(450)/ReA(550),
D(B)=ReB(450)/ReB(550),
ReA(450) represents the in-plane direction retardation (nm) of the film (A) formed from the polymer (A) consisting of the polymer unit A, measured at a wavelength of 450 nm,
ReA (550) represents the in-plane retardation (nm) of the film (A) measured at a wavelength of 550 nm,
ReB(450) represents the in-plane direction retardation (nm) of the film (B) formed from the polymer (B) consisting of the polymerized units B, measured at a wavelength of 450 nm,
ReB(550) represents the in-plane retardation (nm) of the film (B) measured at a wavelength of 550 nm.

A polymer (A) composed of polymerized units A can be obtained by polymerizing a monomer corresponding to polymerized units A and, if necessary, carrying out a reaction such as hydrogenation. A polymer (B) composed of polymerized units B can be obtained by polymerizing a monomer corresponding to polymerized units B and, if necessary, performing a reaction such as hydrogenation. When the copolymer P has a block (A) and a block (B), the polymer (A) and the polymer (B) are obtained in the same manner as the block (A) and the block (B), respectively. sell.

Film (A) may be produced as follows. First, the polymer (A) is pulverized into powder, the powder is sandwiched between two polyimide films to form a laminate, the laminate is pressed, and then the polyimide film is removed to form a press film having a thickness of 100 μm. (A) is produced. Pressurization conditions can be a temperature of 280° C., a pressure of 40 MPa, and a time of 2 minutes. Then, the film (A) is obtained by uniaxially stretching the press film (A) by 1.5 times.

Film (B) may be produced as follows. First, the polymer (B) was pulverized into powder, the powder was sandwiched between two polyimide films to form a laminate, the laminate was pressurized, the polyimide film was removed, and a press film (100 μm thick) was formed. B) is manufactured. Pressurization conditions can be a temperature of 25° C., a pressure of 20 MPa, and a time of 2 minutes. Then, the film (B) is obtained by uniaxially stretching the press film (B) 3 times.

The orientation direction of the cylinder, that is, the orientation direction of the long axis of the cylinder can be determined by fitting the scattering pattern obtained by small-angle X-ray scattering measurement with a theoretical curve.

The direction that gives the maximum refractive index in the in-plane direction of the retardation film, that is, the direction that gives nx can be measured by a retardation measuring device.

When the retardation film of the present embodiment satisfies the condition (1), the retardation film can have reverse wavelength dispersion.

When the retardation film satisfies the condition (1), f(B) is usually 0.5 or more, preferably 0.55 or more, more preferably 0.6 or more, and preferably less than 0.9. , more preferably 0.85 or less, and still more preferably 0.8 or less. f(B) can be adjusted by appropriately adjusting the materials for production of the copolymer P and the production operation.

A retardation film that satisfies the condition (1) is obtained by, for example, forming a resin C containing a copolymer P that satisfies D(A)>D(B) and f(B)>0.5 into a film by a melt extrusion method. It can be obtained by molding into
From the viewpoint of making the direction of giving nx of the retardation film parallel to the orientation direction of the cylinder, the draft ratio (gap of die lip/film thickness) in the melt extrusion method is preferably 5 or more, more preferably 10 or more. preferably 20 or less, preferably 5 or more and 20 or less, more preferably 10 or more and 20 or less.
The resin temperature in the melt extrusion method is preferably 220° C. or higher, more preferably 230° C. or higher, still more preferably 240° C. or higher, preferably 290° C. or lower, more preferably 280° C. or lower, and still more preferably 270° C. or lower. be.

[1.3.2. Condition (2)]
Further, the retardation film according to another embodiment of the present invention, D (A) > D (B), and f (A) > 0.5, and the direction giving the maximum refractive index in the in-plane direction and the The orientation direction of the cylinders in the phase-separated structure is orthogonal.
Here, f(A) represents the total weight ratio of the polymerized units A in the copolymer P. The total weight ratio of the polymerized units A in the copolymerized units P refers to the ratio of the total weight of the polymerized units A contained in the copolymer P to the weight of the copolymer P.

f(A) can be determined by measuring the NMR of copolymer P.

When f(A) is greater than 0.5, the phase (A) forms a matrix and the phase (B) exhibits a cylindrical structure in a normally cylindrical phase separation structure.

Also, D(A) and D(B) have the same definitions as in the description of condition (1).

The orientation direction of the cylinder is generally parallel to the in-plane direction.
The orientation direction of the cylinder and the direction giving the maximum refractive index in the in-plane direction of the retardation film can be determined by a method similar to the method described in the condition (1).

When the retardation film of the present embodiment satisfies the condition (2), the retardation film can have reverse wavelength dispersion.

When the retardation film satisfies the condition (2), f(A) is usually 0.5 or more, preferably 0.55 or more, more preferably 0.60 or more, and preferably less than 0.9. , more preferably 0.85 or less, and still more preferably 0.80 or less. f(A) can be adjusted by appropriately adjusting the materials for production of the copolymer P and the production operation.

A retardation film that satisfies the condition (2) is obtained by, for example, forming a resin C containing a copolymer P that satisfies D(A)>D(B) and f(A)>0.5 into a film by a melt extrusion method. may be obtained by molding into a polyimide and then stretching the resulting extruded film.

As a method for stretching the extruded film, a known method can be used, but it is preferable to stretch at least in the conveying direction of the extruded film. The draw ratio in the transport direction is preferably 1.3 times or more, more preferably 1.5 times or more, still more preferably 1.7 times or more, and can be 3.0 times or less.

The temperature during stretching is preferably (Tg(C)-5)° C. or higher, more preferably Tg(C)° C. or higher, preferably (Tg(C)+30)° C. or lower, and more preferably ( It is Tg(C)+25)° C. or less, more preferably (Tg(C)+20)° C. or less.
Here, Tg(C) means the glass transition temperature of Resin C (°C).

[1.4. Refractive index difference between phase (A) and phase (B)]
The larger the refractive index difference between the phase (A) and the phase (B), the more efficiently the structural birefringence can be expressed. Therefore, the absolute value of the difference (|n(a) −n(b)|) is preferably large, and can be preferably 0.05 or more, more preferably 0.10 or more, and even more preferably 0.15 or more.

The refractive index n(a) can be obtained by producing a press film (A) from the polymer (A) as described above and measuring the refractive index of the press film (A). The refractive index n(b) can be obtained by producing a press film (B) from the polymer (B) as described above and measuring the refractive index of the press film (B).

[1.5. Other characteristics of retardation film]
The retardation film has an in-plane retardation Re (550) measured at a wavelength of 550 nm, which is preferably 100 nm or more, more preferably 110 nm or more, and still more preferably 120 nm or more. preferably 100 nm or more and 300 nm or less.

In the retardation film, the ratio of the in-plane retardation Re (450) measured at a wavelength of 450 nm to the in-plane retardation Re (550) measured at a wavelength of 550 nm (Re (450)/Re (550)) is preferably 0 or more, preferably less than 1, more preferably 0.95 or less, still more preferably 0.90 or less, and preferably 0 or more and less than 1. When the ratio (Re(450)/Re(550)) is within the above range, it is possible to suppress large changes in the optical properties of the retardation film due to the wavelength of light to be transmitted.

[2. Application]
The retardation film of this embodiment can be used as a component of a display device such as a liquid crystal display device or an organic electroluminescence display device.

EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples. However, the present invention is not limited to the examples shown below, and can be arbitrarily modified without departing from the scope of the claims of the present invention and their equivalents.

In the following description, "%" and "parts" representing amounts are by weight unless otherwise specified. In addition, unless otherwise specified, the operations described below were performed under normal temperature and pressure conditions.

[Evaluation method]
(film retardation)
The retardation of the film was measured using a retardation measuring device (“KOBRA-21-ADH” manufactured by Oji Scientific Instruments Co., Ltd.).

(Phase separation structure)
The film was cut to a size of 2 mm × 4 mm, 30 of them were stacked in the thickness direction and fixed in a folder. A scattering pattern was obtained under the conditions of 8.2 KeV, measurement q range: about 0.06 to 3 nm ⁻¹ , and exposure time of 60 seconds per sample. The obtained scattering pattern was fitted with a theoretical curve to determine the phase separation structure, and the radius of the cylinder and the interphase distance were calculated.

The X-ray irradiation surface was the cross section of the film, and the integration range was 20° in each of the thickness direction and the direction perpendicular to the thickness direction. The interphase distance was calculated from the data obtained from each integration, and the average value of the interphase distance in the thickness direction and the direction perpendicular to the thickness direction and the average value of the radius of the cylinder were used as the measured values.

(Measurement of Re(450)/Re(550))
(Measurement of D (A))
(Production of polymer (A))
500 mL of toluene as a solvent and 0.29 mmol of n-butyllithium as a polymerization catalyst are added to a pressure-resistant reactor that has been dried and purged with nitrogen gas, and then 7.0 g of 2-vinylnaphthalene is added as the monomer (a). and reacted at 25° C. for 1 hour to carry out a polymerization reaction. The reaction mixture was poured into a large amount of 2-propanol to precipitate and separate the polymer. The weight average molecular weight (Mw) of the obtained polymer was 100,000 when measured by GPC. The glass transition temperature of the polymer was 145°C as measured by a thermomechanical analyzer (TMA).

(Production of press film (A))
The obtained polymer was pulverized by a pulverizer to obtain a powder. The obtained powder was sandwiched between a pair of polyimide films (thickness: 100 μm each) to form a laminate, and the laminate was pressurized. Pressurization was performed using an electrothermal pressurizer. The pressurization conditions were a temperature of 280° C., a pressure of 40 MPa, and a pressurization time of 2 minutes. After the pressurization was completed, the pressure was released and the substrate was cooled to room temperature in the air to remove the polyimide film. By this operation, an unstretched press film (A) having a thickness of 100 μm was produced.

(Production of film (A))
The produced press film (A) is uniaxially stretched 1.5 times using a heating type tensile tester under the conditions of 80 mm between chucks, a stretching rate of 100%/min, and a temperature of 155 ° C. to obtain a stretched film (film (A )). The in-plane retardation Re(550) of the film (A) measured at a wavelength of 550 nm was 140 nm. Moreover, the Re(450)/Re(550) value (D(A)) of the film (A) was 1.08.

(Measurement of D (B))
(Production of polymer (B))
500 mL of toluene as a solvent and 0.29 mmol of n-butyllithium as a polymerization catalyst were placed in a pressure-resistant reactor that was dried and purged with nitrogen gas. Thereafter, 21 g of isoprene as the monomer (b) was added, and the mixture was further reacted at 25° C. for 1 hour to carry out polymerization. The reaction mixture was poured into a large amount of 2-propanol to precipitate and separate the polymer.

The obtained polymer was dissolved in 700 mL of p-xylene to obtain a solution. 7.6 g of p-toluenesulfonyl hydrazide was added to this solution and reacted at a temperature of 130° C. for 8 hours. This reaction hydrogenated the double bond derived from isoprene. After completion of the hydrogenation, the reaction solution was poured into a large amount of 2-propanol to obtain 20 g of hydrogenated polymer block. The weight average molecular weight of the obtained hydrogenated polymer was 100,000 when measured by gel permeation chromatography (GPC).

(Production of press film (B))
2 g of the hydrogenated polymer mass obtained as the polymer (B) was sandwiched between a pair of polyimide films (thickness: 100 μm each) to form a laminate, and the laminate was pressurized. Pressurization was performed using an electrothermal pressurizer. The pressurization conditions were a temperature of 25° C., a pressure of 20 MPa, and a pressurization time of 2 minutes. After the pressurization was completed, the pressure was released and the polyimide film was removed. By this operation, an unstretched press film (B) having a thickness of 100 μm was produced.

(Production of film (B))
The produced press film (B) is uniaxially stretched to 3 times using a heating type tensile tester under the conditions of 80 mm between chucks, a stretching rate of 100%/min, and a temperature of 25 ° C. to obtain a stretched film (film (B)). got The in-plane retardation Re(550) of the film (B) measured at a wavelength of 550 nm was 140 nm. In addition, the Re(450)/Re(550) value (D(B)) of the film (B) was 1.03.

(refractive index)
Using JA-Woollam's ellipsometer "M-2000U", the press film (A) and press film (B) were measured for refractive index at a wavelength of 550 nm. The refractive index of the press film (A) (n (a )) was 1.67 The refractive index (n(b)) of the press film (B) was 1.52.

(Display performance of liquid crystal display device)
A long polarizer (manufactured by Sanritz Co., Ltd., product name “HLC2-5618S”, thickness 180 μm) having a transmission axis in the width direction was prepared. The protective film on one side of the polarizer was removed, and a film to be evaluated was attached to the side. The lamination was performed so that the slow axis direction of the film to be evaluated and the transmission axis direction of the polarizer formed an angle of 45°. By this operation, a circularly polarizing plate having the film to be evaluated as one of the protective films on both sides was obtained.
The resulting circularly polarizing plate was replaced with the circularly polarizing plate originally provided on the viewing side of a commercially available organic EL display (“OLED55B6P” manufactured by LG Electronics) to obtain an organic EL display having the film to be evaluated. . In the replacement, the circularly polarizing plate was arranged such that the side provided with the film to be evaluated was the organic EL element side. Further, the transmission axis of the polarizer was set in the same direction as that of the polarizer in the circularly polarizing plate originally provided in the organic EL display device.

The display state of the obtained organic EL display device was observed at various azimuth angles from an inclined direction (45° with respect to the normal direction) with respect to the display surface. When the reflectance was suppressed in all directions compared to before replacement, it was evaluated as "good", and when the reflectance was equal to or lower than that in one or more directions compared to before replacement, it was evaluated as "poor".

[Example 1]
(Production of triblock copolymer P1)
500 mL of toluene as a solvent and 0.29 mmol of n-butyllithium as a polymerization catalyst were placed in a pressure-resistant reactor that had been dried and purged with nitrogen gas. Thereafter, 3.5 g of 2-vinylnaphthalene as the monomer (a) was added and reacted at 25° C. for 1 hour to carry out the first stage polymerization reaction.

After completion of the first-stage polymerization reaction, 28 g of isoprene as the monomer (b) was added, and the mixture was further reacted at 25° C. for 1 hour to carry out the second-stage polymerization reaction. As a result, a diblock copolymer having a (2-vinylnaphthalene block)-(isoprene block) block configuration was obtained in the reaction mixture.

Thereafter, 3.5 g of 2-vinylnaphthalene as the monomer (a) was further added to the reaction mixture and reacted at 25° C. for 1 hour to carry out the third stage polymerization reaction. As a result, a reaction mixture containing a triblock copolymer having a block structure of (2-vinylnaphthalene block)-(isoprene block)-(2-vinylnaphthalene block) was obtained. The reaction mixture was poured into a large amount of 2-propanol to precipitate and separate the triblock copolymer.

The resulting triblock copolymer was dissolved in 700 mL of p-xylene to form a solution. 7.6 g of p-toluenesulfonyl hydrazide was added to this solution and reacted at a temperature of 130° C. for 8 hours. This reaction added hydrogen to the double bond of the isoprene unit. After completion of the hydrogenation, the reaction solution was poured into a large amount of 2-propanol to obtain 32 g of a triblock copolymer P1 as a blocky product. The obtained triblock copolymer P1 is composed of "polymer block (A) containing a 2-vinylnaphthalene unit as a polymer unit A" - "polymer block (B) containing a hydrogenated isoprene unit as a polymer unit B ”-“Polymer block (A) containing 2-vinylnaphthalene unit as polymerized unit A”.

The obtained triblock copolymer P1 was analyzed by ¹ H-NMR. As a result, the weight ratio (wA:wB) of the 2-vinylnaphthalene units and the hydrogenated isoprene units in the triblock copolymer P1 was 20:80. The modulus wA was 0.20. Also, the hydrogenation rate for isoprene units in the triblock copolymer P1 was 99%. The weight average molecular weight of triblock copolymer P1 measured by GPC was 200,000. The glass transition temperature of the triblock copolymer P1 measured by TMA was 100°C. Also, the triblock copolymer P1 exhibited positive birefringence properties.

(Production of retardation film)
The triblock copolymer P1 obtained in the above item (Production of the triblock copolymer P1) was used as the resin C. The resin C was pulverized by a pulverizer into a powder. The obtained powder is put into an extruder with a screw diameter of 40 mmφ, and is discharged from a die having a resin temperature of 260 ° C., a width of 400 mm, and a lip gap of 0.5 mm at a discharge rate of 20 kg / min on a casting drum with a surface temperature of 80 ° C. extruded to Film 1 was thus obtained as a retardation film having a width of 300 mm and a thickness of 100 μm. The thickness of film 1 was adjusted by the number of rotations of the casting drum.

When X-rays were incident on the obtained film 1 from the cross section by the above method and observed by the small-angle scattering method, it was found that the interphase distance was 40 nm, the radius was 10 nm (diameter: 20 nm), and the cylindrical structure was oriented in the flow direction. was observed.

The in-plane direction retardation Re(550) and the thickness direction retardation Rth(550) of the resulting film 1 were measured at a wavelength of 550 nm, and were found to be Re(550)=140 nm and Rth(550)=50 nm. Therefore, it is considered that structural birefringence due to the cylindrical phase separation structure is developed. Also, the direction (in-plane slow axis) that gives the maximum refractive index nx in the in-plane direction coincides with the flow direction of the film 1 . Therefore, the orientation direction of the cylinders in the phase-separated structure was parallel to the direction giving nx.

Film 1 had Re(450)/Re(550)=0.80<1 and exhibited reverse wavelength dispersion.

The thus-obtained film (retardation film) 1 functioning as a λ/4 plate was incorporated into an organic EL display device as a circularly polarizing plate by the method described above, and the display performance of the organic EL display device was evaluated. As a result, the display characteristics of the organic EL display device were good.

[Example 2]
(Production of triblock copolymer P2)
500 mL of toluene as a solvent and 0.29 mmol of n-butyllithium as a polymerization catalyst were placed in a pressure-resistant reactor that was dried and purged with nitrogen. Thereafter, 14 g of 2-vinylnaphthalene as the monomer (a) was added and reacted at 25° C. for 1 hour to carry out the first stage polymerization reaction.

After completion of the first-stage polymerization reaction, 7 g of isoprene as a monomer (b) was added, and the mixture was further reacted at 25° C. for 1 hour to carry out the second-stage polymerization reaction. As a result, a diblock copolymer having a (2-vinylnaphthalene block)-(isoprene block) block configuration was obtained in the reaction mixture.

Thereafter, 14 g of 2-vinylnaphthalene as the monomer (a) was further added to the reaction mixture and reacted at 25° C. for 1 hour to carry out the third-stage polymerization reaction. As a result, a reaction mixture containing a triblock copolymer having a block structure of (2-vinylnaphthalene block)-(isoprene block)-(2-vinylnaphthalene block) was obtained. The reaction mixture was poured into a large amount of 2-propanol to precipitate and separate the triblock copolymer.

The resulting triblock copolymer was dissolved in 700 mL of p-xylene to form a solution. 7.6 g of p-toluenesulfonyl hydrazide was added to the solution and reacted at a temperature of 130° C. for 8 hours. This reaction added hydrogen to the double bond of the isoprene unit. After completion of the hydrogenation, the reaction solution was poured into a large amount of 2-propanol to obtain 32 g of a triblock copolymer P2 as a blocky product. The triblock copolymer P2 is "a polymer block (A) containing a 2-vinylnaphthalene unit as a polymer unit A" - "a polymer block (B) containing a hydrogenated isoprene unit as a polymer unit B" - " It has a block configuration of "a polymer block (A) containing a 2-vinylnaphthalene unit as a polymer unit A".

The obtained triblock copolymer P2 was analyzed by ¹ H-NMR. As a result, the weight ratio (wA:wB) between the 2-vinylnaphthalene units and the hydrogenated isoprene units in the triblock copolymer P2 was 80:20. The modulus wA was 0.80. Also, the hydrogenation rate for the isoprene units in the triblock copolymer P2 was 99%. The weight average molecular weight of triblock copolymer P2 measured by GPC was 250,000. The glass transition temperature of the triblock copolymer P2 measured by TMA was 135°C. Also, the triblock copolymer P2 exhibited negative birefringence properties.

(Production of retardation film)
The triblock copolymer P2 obtained in the above item (Production of the triblock copolymer P2) was used as the resin C. The resin C was pulverized by a pulverizer into a powder. The obtained powder is put into an extruder with a screw diameter of 40 mm, and is discharged from a die having a resin temperature of 250° C., a width of 400 mm, and a lip gap of 0.5 mm, onto a casting drum having a surface temperature of 120° C. pushed out. The edge portion of the obtained film was trimmed to obtain a film 2 having a width of 300 mm and a thickness of 100 μm. The thickness of film 2 was adjusted by the number of rotations of the casting drum.

The obtained film 2 was observed by the small-angle scattering method by irradiating X-rays from the cross section by the method described above. was observed.

The in-plane direction retardation Re (550) and the thickness direction retardation Rth (550) of the obtained film 2 were measured at a wavelength of 550 nm. The direction that gave the maximum refractive index nx in the inward direction (in-plane slow axis) coincided with the flow direction of the film 2 . Therefore, it is considered that structural birefringence due to the cylindrical phase separation structure is developed.

Film 2 had Re(450)/Re(550)=1.2>1, and Film 2 exhibited positive wavelength dispersion.

Subsequently, film 2 was stretched in the machine direction at a stretching ratio of 1.8 times at a stretching temperature of 135° C. using a float-type longitudinal stretching machine to obtain film 3 .

When X-rays were incident on the obtained film 3 from the cross section by the method described above and the film was observed by the small-angle scattering method, a cylindrical structure oriented in the flow direction was observed as before the stretching. The interphase distance was 30 nm, and the radius of the cylinder structure was 12 nm (24 nm in diameter).

When the in-plane retardation Re (550) and Rth (550) of the obtained film 3 were measured at a wavelength of 550 nm, Re (550) = 140 nm and Rth (550) = 65 nm, indicating cylindrical phase separation. Birefringence appeared in the film 3 due to the effects of both the structural birefringence due to the structure and the negative birefringence of the 2-vinylnaphthalene block. In addition, the direction (in-plane slow axis) giving the maximum refractive index nx in the in-plane direction coincided with the width direction of the film 3 (direction perpendicular to the flow direction). Therefore, the orientation direction of the cylinders in the phase-separated structure was orthogonal to the direction giving nx.

Film 3 had Re(450)/Re(550)=0.81<1 and exhibited reverse wavelength dispersion.

The film (retardation film) 3 functioning as a λ/4 plate thus obtained was incorporated into an organic EL display device as a circularly polarizing plate by the method described above, and the display performance of the organic EL display device was evaluated. As a result, the display characteristics of the organic EL display device were good.

[Comparative Example 1]
(Production of triblock copolymer CP1)
500 mL of toluene as a solvent and 0.29 mmol of n-butyllithium as a polymerization catalyst were placed in a pressure-resistant reactor that was dried and purged with nitrogen gas. Thereafter, 14 g of 2-vinylnaphthalene as the monomer (a) was added and reacted at 25° C. for 1 hour to carry out the first stage polymerization reaction.

After completion of the first-stage polymerization reaction, 3.5 g of isoprene as a monomer (b) was added, and the mixture was further reacted at 25° C. for 1 hour to carry out the second-stage polymerization reaction. As a result, a diblock copolymer having a (2-vinylnaphthalene block)-(isoprene block) block configuration was obtained in the reaction mixture.

Thereafter, 14 g of 2-vinylnaphthalene as the monomer (a) was further added to the reaction mixture and reacted at 25° C. for 1 hour to carry out the third-stage polymerization reaction. As a result, a reaction mixture containing a triblock copolymer having a block structure of (2-vinylnaphthalene block)-(isoprene block)-(2-vinylnaphthalene block) was obtained. The reaction mixture was poured into a large amount of 2-propanol to precipitate and separate the triblock copolymer.

The resulting triblock copolymer was dissolved in 700 mL of p-xylene to form a solution. 7.6 g of p-toluenesulfonyl hydrazide was added to this solution and reacted at a temperature of 130° C. for 8 hours. This reaction added hydrogen to the double bond of the isoprene unit. After completion of the hydrogenation, the reaction solution was poured into a large amount of 2-propanol to obtain 32 g of triblock copolymer CP1 as a blocky product. The obtained triblock copolymer CP1 is composed of "polymer block (A) containing a 2-vinylnaphthalene unit as a polymer unit A" - "polymer block (B) containing a hydrogenated isoprene unit as a polymer unit B ”-“Polymer block (A) containing 2-vinylnaphthalene unit as polymerized unit A”.

The obtained triblock copolymer CP1 was analyzed by NMR. As a result, the weight ratio (wA:wB) of the 2-vinylnaphthalene units and the hydrogenated isoprene units in the triblock copolymer CP1 was 90:10. The modulus wA was 0.90. Also, the hydrogenation rate for the isoprene units in the triblock copolymer CP1 was 99%. The weight average molecular weight of the triblock copolymer CP1 measured by GPC was 250,000. The glass transition temperature of the triblock copolymer CP1 measured by TMA was 140°C.

(Production of retardation film)
A film C1 having a width of 300 mm and a thickness of 100 μm was obtained in the same manner as in Example 1 (preparation of retardation film) except for the following items.
- A triblock copolymer CP1 was used as the resin C instead of the triblock copolymer P1.

When X-rays were incident on the obtained film C1 from the cross section by the above method and observed by the small-angle scattering method, the phase distance was 40 nm and a sphere-like structure with a radius of 10 nm (diameter 20 nm) was observed.

The in-plane direction retardation Re(550) and the thickness direction retardation Rth(550) of the obtained film C1 were measured at a wavelength of 550 nm. No development of sexual birefringence was observed.

Subsequently, the film C1 was stretched in the machine direction using a float-type longitudinal stretching machine at a longitudinal stretching ratio of 1.8 times and a stretching temperature of 145° C. to obtain a film C2.

When X-rays were incident on the obtained film C2 from the cross section by the method described above and the film was observed by the small angle scattering method, a sphere-like structure was observed as before the stretching. Also, the interphase distance was 50 nm, and the radius of the sphere-like structure was 13 nm.

When the in-plane direction retardation Re (550) and Rth (550) were measured at a wavelength of 550 nm for the obtained film C2, Re (550) = 140 nm and Rth (550) = 71 nm. The direction that gives the refractive index nx of (in-plane slow axis) coincides with the width direction of the film C2.

Film C2 had Re(450)/Re(550)=1.1>1, and film C2 exhibited positive wavelength dispersion.

The thus-obtained film (retardation film) C2 functioning as a λ/4 plate was incorporated into an organic EL display device as a circularly polarizing plate by the method described above, and the display performance of the organic EL display device was evaluated. As a result, an increase in reflectance and a change in color were observed depending on the orientation, and the display characteristics of the organic EL display device were poor.

[Comparative Example 2]
(Production of retardation film)
As the resin C, the triblock copolymer P2 produced in Example 2 was used. The resin C was pulverized by a pulverizer into a powder. The obtained powder was sandwiched between a pair of polyimide films (thickness: 100 μm each) to form a laminate, and the laminate was pressurized. Pressurization was performed using an electrothermal pressurizer. The pressurization conditions were a temperature of 280° C., a pressure of 40 MPa, and a pressurization time of 2 minutes. After the pressurization was completed, the pressure was released and the substrate was cooled to room temperature in the air to remove the polyimide film. By this operation, a film C3 having a thickness of 100 μm was produced.

When X-rays were incident on the obtained film C3 from the cross section by the above method and observed by the small-angle scattering method, a cylindrical structure with an interphase distance of 40 nm and a radius of 15 nm was observed.

The in-plane direction retardation Re(550) and the thickness direction retardation Rth(550) of the obtained film C3 were measured at a wavelength of 550 nm. No development of birefringence was observed.

Film C3 was then stretched using a float-type longitudinal stretching machine at a stretching ratio of 1.8 times in the longitudinal direction at a stretching temperature of 140° C. to obtain film C4.

When X-rays were incident on the obtained film C4 from the cross section by the above method and observed by the small-angle scattering method, a cylindrical structure slightly oriented in the stretching direction, with an interphase distance of 35 nm and a radius of 10 nm was observed. was done.

The in-plane direction retardation Re (550) and the thickness direction retardation Rth (550) of the obtained film C4 were measured at a wavelength of 550 nm. The direction (in-plane slow axis) giving the maximum refractive index nx in the inward direction coincided with the width direction of the film C4. Therefore, the orientation direction of the cylinders in the phase-separated structure was orthogonal to the direction giving nx.

Film C4 had Re(450)/Re(550)=1.12>1 and exhibited positive wavelength dispersion.

The film (retardation film) C4 functioning as a λ/4 plate thus obtained was incorporated into an organic EL display device as a circularly polarizing plate by the method described above, and the display performance of the organic EL display device was evaluated. As a result, an increase in reflectance and a change in color were observed depending on the orientation, and the display characteristics of the organic EL display device were poor.

From the above results, the following matters are known.
Film C2 according to Comparative Example 1, which does not contain a cylindrical phase separation structure that exhibits structural birefringence, does not exhibit reverse wavelength dispersion, and the display characteristics of an organic EL display incorporating film C1 is bad.
Film C4 according to Comparative Example 2, which does not satisfy either condition (1) or condition (2) even if it contains a cylindrical phase separation structure, does not exhibit reverse wavelength dispersion, and film C4 is The display characteristics of the built-in organic EL display device are poor.

On the other hand, f (B) (in Example 1, the weight fraction wB of the polymerized unit B in the triblock copolymer P1)>0.5, and the direction that gives nx and the cylinder in the phase separation structure The film 1 according to Example 1, which satisfies the condition (1) in which the orientation direction of the film is parallel to the orientation direction of , exhibits reverse wavelength dispersion, and the display characteristics of the organic EL display device are good.

In addition, f (A) (in Example 2, the weight fraction wA of the polymerized unit A in the triblock copolymer P2)>0.5, the direction that gives nx and the orientation direction of the cylinder in the phase separation structure The film 3 according to Example 2 that satisfies the condition (2), which is orthogonal to the above, exhibits reverse wavelength dispersion, and the display characteristics of the organic EL display device are good.

The above results show that the retardation film of the present invention has reverse wavelength dispersion and can be easily produced at low cost.

Claims (12)

Consists of a resin C containing a copolymer P containing polymerized units A and polymerized units B,
The polymerized unit A is a unit represented by the following general formula (A),
including a cylindrical phase-separated structure that exhibits structural birefringence,
The phase separation structure includes a phase (A) mainly composed of the polymerized unit A and a phase (B) mainly composed of the polymerized unit B, and satisfies the following condition (1) or (2): retardation film.
Condition (1): D(A)>D(B) and f(B)>0.5, and the direction giving the maximum refractive index in the in-plane direction is parallel to the orientation direction of the cylinders in the phase separation structure. is.
Condition (2): D(A)>D(B) and 0.8≧f(A)>0.5, and the direction giving the maximum refractive index in the in-plane direction and the orientation of the cylinders in the phase separation structure are perpendicular to the direction.
here,
f (A) represents the total weight ratio of the polymerized units A in the copolymer P,
f (B) represents the total weight ratio of the polymerized units B in the copolymer P,
D(A)=ReA(450)/ReA(550),
D(B)=ReB(450)/ReB(550),
ReA(450) represents the in-plane direction retardation (nm) of the film (A) formed from the polymer (A) consisting of the polymer unit A, measured at a wavelength of 450 nm,
ReA (550) represents the in-plane retardation (nm) of the film (A) measured at a wavelength of 550 nm,
ReB(450) represents the in-plane direction retardation (nm) of the film (B) formed from the polymer (B) consisting of the polymerized units B, measured at a wavelength of 450 nm,
ReB(550) represents the in-plane retardation (nm) of the film (B) measured at a wavelength of 550 nm.

(In the general formula (A),
R ^C is a group selected from the group consisting of a phenyl group, a biphenylyl group, a naphthyl group, an anthracenyl group, a phenanthrenyl group, a naphthacenyl group, a pentacenyl group, and a terphenylyl group;
Each of R ¹ to R ³ is independently a group selected from the group consisting of a hydrogen atom and an alkyl group having 1 to 12 carbon atoms. ) 2. The retardation film according to claim 1, which has an in-plane retardation Re (550) of 100 nm or more and 300 nm or less measured at a wavelength of 550 nm. The ratio of the in-plane retardation Re (450) measured at a wavelength of 450 nm to the in-plane retardation Re (550) measured at a wavelength of 550 nm (Re (450)/Re (550)) is 0 or more and 1 The retardation film according to claim 1 or 2, which is less than. The retardation film according to any one of claims 1 to 3, wherein the diameter of the cylinder in the phase separation structure is 50 nm or less. The absolute value of the difference (|n(a)−n(b)|) between the refractive index n(a) of the polymer (A) and the refractive index n(b) of the polymer (B) is 0.5. 05 or more, the retardation film according to any one of claims 1 to 4. The retardation film according to any one of claims 1 to 5, wherein the interphase distance in the phase separation structure is 200 nm or less. 7. Any one of claims 1 to 6, wherein the copolymer P is a block polymer having a block (A) containing the polymerized units A as a main component and a block (B) containing the polymerized units B as a main component. 2. The retardation film according to item 1. The copolymer P contains a triblock copolymer P', and the triblock copolymer P' contains the block (A) containing the polymerized unit A as a main component and the polymerized unit B as a main component. The retardation film according to any one of claims 1 to 7, which is a (A)-(B)-(A) triblock copolymer having a block (B). The copolymer P contains a pentablock copolymer P″, and the pentablock copolymer P″ has a block (A) containing the polymerized unit A as a main component and a polymerized unit B as a main component. The retardation film according to any one of claims 1 to 8, which is a (A)-(B)-(A)-(B)-(A) pentablock copolymer having a block (B). . The retardation film according to any one of claims 1 to 9, wherein the copolymer P has a negative intrinsic birefringence value. 11. The retardation film according to any one of claims 1 to 10, wherein 0.9>f(B)>0.5. A method for producing a retardation film according to any one of claims 1 to 10,
The retardation film satisfies the condition (2),
The manufacturing method is
A production method comprising a step of forming the resin C into a film by a melt extrusion method to obtain an extruded film, and then a step of stretching the obtained extruded film.