JP2023180135A - Retardation film manufacturing method - Google Patents

Abstract

To provide a retardation film manufacturing method that can suitably manufacture a retardation film having high in-plane birefringence and having an in-plane phase difference indicating reverse wavelength dispersion characteristics, by using a resin film including a resin indicating positive birefringence and a resin indicating negative birefringence.SOLUTION: There is provided a method for manufacturing a retardation film in which an in-plane birefringence Δn(590) at a measurement wavelength of 590 nm exceeds 0.003, and a ratio of an in-plane phase difference at a measurement wavelength of 450 nm to an in-plane phase difference at a measurement wavelength of 550 nm (Re(450)/Re(550)) is less than 0.90, and the manufacturing method includes: producing a resin film including a resin indicating positive birefringence and a resin indicating negative birefringence, and in which the birefringence in a thickness direction at a measurement wavelength of 590 nm ΔP(590) exceeds 0.0005, and a ratio of a phase difference in the thickness direction at a measurement wavelength of 450 nm to a phase difference in the thickness direction at a measurement wavelength of 550 nm (Rth(450)/Rth(550)) is less than 0.98; and stretching the resin film.SELECTED DRAWING: None

Description

The present invention relates to a method for manufacturing a retardation film.

In recent years, image display devices typified by liquid crystal display devices and electroluminescent (EL) display devices (eg, organic EL display devices and inorganic EL display devices) have rapidly become popular. In organic EL display devices, it is known that problems such as external light reflection and background reflection can be prevented by arranging a circularly polarizing plate including a λ/4 plate on the viewing side of the organic EL cell (for example, Patent Documents 1 and 2).

Regarding the λ/4 plate used in the above-mentioned circularly polarizing plate, from the viewpoint of achieving excellent antireflection properties over a wide wavelength range, a retardation film is required that exhibits so-called reverse wavelength dispersion characteristics, in which the retardation is larger in the longer wavelength range. ing. In response to these demands, a retardation film has been proposed that contains a cellulose resin that exhibits positive birefringence and an ester resin that exhibits negative birefringence, and whose in-plane retardation exhibits reverse wavelength dispersion characteristics. (Patent Document 3).

Japanese Patent Application Publication No. 2002-311239 Japanese Patent Application Publication No. 2002-372622 JP 2021-140095 Publication

The inventor of the present invention has investigated that in producing a retardation film using a resin film containing a resin exhibiting positive birefringence and a resin exhibiting negative birefringence, the orientation of the resin film to be stretched is It has been found that, depending on the orientation of the resin film, it may not be possible to obtain a retardation film having the desired optical properties.

The present invention has been made to solve the above problems, and its main purpose is to achieve high in-plane birefringence by using a resin film containing a resin exhibiting positive birefringence and a resin exhibiting negative birefringence. An object of the present invention is to provide a method for producing a retardation film that can suitably produce a retardation film having the following properties and exhibiting in-plane retardation characteristics of reverse wavelength dispersion.

（式（１）中、Ｒ_１～Ｒ_３のそれぞれは、水素原子または炭素数１～１２の置換基を示す；）

（式（２）中、Ｒ_４は、水素原子または炭素数１～１２のアルキル基を示し；Ｒ_５ａは、炭素数１～１２のアルキル基、ニトロ基、ブロモ基、ヨード基、シアノ基、クロロ基、スルホン酸基、カルボン酸基、フルオロ基、または、チオール基から選択される１種を示し；Ｒ_５ｂは、水素原子または炭素数１～１２のアルキル基を示し；Ｒ_６は、水素原子、ニトロ基、ブロモ基、ヨード基、シアノ基、クロロ基、スルホン酸基、カルボン酸基、フルオロ基、フェニル基、チオール基、アミド基、アミノ基、ヒドロキシ基、炭素数１～１２のアルコキシ基、または、炭素数１～１２のアルキル基から選択される種を示す；）

（式（３）中、Ｒ_７は、ヘテロ原子として窒素原子もしくは酸素原子を１つ以上含む５員環複素環残基または６員環複素環残基（上記５員環複素環残基および上記６員環複素環残基は他の環状構造と縮合環構造を形成してもよい）を示す）。
１つの実施形態において、上記エステル系樹脂は、下記式（４）に示す構成単位をさらに有する：

（式（４）中、Ｒ_８およびＲ_９のそれぞれは、水素原子、炭素数１～１２の直鎖状アルキル基、炭素数３～１２の分岐状アルキル基、または、炭素数３～６の環状アルキル基から選択される１種を示す）。 According to one aspect of the present invention, the in-plane birefringence Δn(590) at a measurement wavelength of 590 nm exceeds 0.003, and the ratio (Re (450)/Re(550)) is less than 0.90, the method includes a resin exhibiting positive birefringence and a resin exhibiting negative birefringence, and the thickness at a measurement wavelength of 590 nm. Birefringence ΔP(590) in the direction exceeds 0.0005, and the ratio (Rth(450)/Rth(550)) of the retardation in the thickness direction at a measurement wavelength of 450 nm to the retardation in the thickness direction at a measurement wavelength of 550 nm is 0. A manufacturing method is provided that includes making a resin film that has a molecular weight of less than 98, and stretching the resin film.
In one embodiment, the thickness of the resin film before stretching is 50 μm to 200 μm, and the thickness of the resin film after stretching is 12.5% to 40% of the thickness before stretching.
In one embodiment, producing the resin film includes applying a resin solution containing the resin exhibiting positive birefringence, the resin exhibiting negative birefringence, and a solvent onto a supporting base material to form a coating layer. and heating the coated layer to evaporate the solvent.
In one embodiment, the coated layer is heated within the range of 50°C to 155°C to evaporate the solvent.
In one embodiment, the resin film is a long resin film, and stretching the resin film includes transporting the long resin film in a longitudinal direction while transporting the long resin film in a direction perpendicular to the longitudinal direction. Including stretching.
In one embodiment, the stretching ratio of the stretching is 8.0 times or less.
In one embodiment, Rth(450)/Rth(550) of the resin film before stretching is more than 0.60 and less than 0.98, and Δn(590) of the retardation film is less than 0.0035. and Re(450)/Re(550) is less than 0.88.
In one embodiment, the resin exhibiting positive birefringence includes a cellulose resin having a structural unit represented by the following formula (1), and the resin exhibiting negative birefringence includes a structure represented by the following formula (2). Contains an ester resin having a unit and a structural unit represented by the following formula (3):

(In formula (1), each of R ₁ to R ₃ represents a hydrogen atom or a substituent having 1 to 12 carbon atoms;)

(In formula (2), R ₄ represents a hydrogen atom or an alkyl group having 1 to 12 carbon atoms; R _5a represents an alkyl group having 1 to 12 carbon atoms, a nitro group, a bromo group, an iodo group, a cyano group, Represents one selected from a chloro group, a sulfonic acid group, a carboxylic acid group, a fluoro group, or a thiol group; R _5b represents a hydrogen atom or an alkyl group having 1 to 12 carbon atoms; R ₆ represents hydrogen Atom, nitro group, bromo group, iodo group, cyano group, chloro group, sulfonic acid group, carboxylic acid group, fluoro group, phenyl group, thiol group, amide group, amino group, hydroxy group, alkoxy having 1 to 12 carbon atoms represents a species selected from a group or an alkyl group having 1 to 12 carbon atoms;)

(In formula (3), R ₇ is a 5-membered heterocyclic residue or a 6-membered heterocyclic residue containing one or more nitrogen atoms or oxygen atoms as a heteroatom (the above 5-membered heterocyclic residue and the above The 6-membered heterocyclic residue may form a fused ring structure with another cyclic structure).
In one embodiment, the ester resin further has a structural unit represented by the following formula (4):

(In formula (4), each of R ₈ and R ₉ is a hydrogen atom, a linear alkyl group having 1 to 12 carbon atoms, a branched alkyl group having 3 to 12 carbon atoms, or a branched alkyl group having 3 to 6 carbon atoms. (represents one type selected from cyclic alkyl groups).

According to the method for producing a retardation film according to an embodiment of the present invention, the resin film includes a resin exhibiting positive birefringence and a resin exhibiting negative birefringence, and has birefringence of a certain level or more in the thickness direction. By stretching a resin film whose retardation in the thickness direction exhibits reverse wavelength dispersion characteristics, a retardation film having high in-plane birefringence and whose in-plane retardation exhibits reverse wavelength dispersion characteristics can be obtained. It can be obtained suitably.

It is a conceptual diagram explaining the wavelength dispersion characteristic regarding the thickness direction retardation of a resin film.

Embodiments of the present invention will be described below, but the present invention is not limited to these embodiments. In this specification, "~" representing a numerical range includes the upper and lower numerical limits thereof. In addition, in this specification, "weight" has the same meaning as "mass" in the SI unit system, which means weight.

(Definition of terms and symbols)
Definitions of terms and symbols used herein are as follows.
(1) Refractive index (nx, ny, nz)
"nx" is the refractive index in the direction in which the in-plane refractive index is maximum (i.e., slow axis direction), and "ny" is the direction perpendicular to the slow axis in the plane (i.e., fast axis direction) "nz" is the refractive index in the thickness direction.
(2) In-plane birefringence (Δn)
"Δn(λ)" is in-plane birefringence measured with light having a wavelength of λnm at 23°C. In-plane birefringence (Δn) is determined from the formula: Δn=nx−ny.
(3) In-plane phase difference (Re)
"Re(λ)" is an in-plane retardation measured with light having a wavelength of λnm at 23°C. For example, "Re(550)" is an in-plane retardation measured with light having a wavelength of 550 nm at 23°C. Re(λ) is determined by the formula: Re(λ)=(nx−ny)×d, where d (nm) is the thickness of the layer (film).
(4) Birefringence in the thickness direction (ΔP)
"ΔP(λ)" is birefringence in the thickness direction measured with light having a wavelength of λ nm at 23°C. Birefringence (ΔP) in the thickness direction is determined from the formula: ΔP=nx−nz.
(5) Phase difference in thickness direction (Rth)
"Rth (λ)" is a retardation in the thickness direction measured with light having a wavelength of λ nm at 23°C. For example, "Rth (550)" is the retardation in the thickness direction measured with light having a wavelength of 550 nm at 23°C. Rth(λ) is determined by the formula: Rth(λ)=(nx−nz)×d, where d (nm) is the thickness of the layer (film).
(6) Nz coefficient The Nz coefficient is determined by Nz=Rth/Re.
(7) Angle When an angle is referred to in this specification, the angle includes both clockwise and counterclockwise directions with respect to the reference direction. Thus, for example, "45°" means 45° clockwise or counterclockwise.

A. Method for manufacturing a retardation film The method for manufacturing a retardation film according to an embodiment of the present invention is such that the in-plane birefringence Δn (590) at a measurement wavelength of 590 nm exceeds 0.003, and the measurement wavelength of the in-plane retardation at a measurement wavelength of 450 nm A method for producing a retardation film having a ratio (Re(450)/Re(550)) to in-plane retardation at 550 nm of less than 0.90,
Contains a resin that exhibits positive birefringence and a resin that exhibits negative birefringence, the birefringence ΔP (590) in the thickness direction at a measurement wavelength of 590 nm exceeds 0.0005, and the retardation in the thickness direction at a measurement wavelength of 450 nm is measured. Producing a resin film whose ratio to the retardation in the thickness direction at a wavelength of 550 nm (Rth(450)/Rth(550)) is less than 0.98 (resin film production process), and stretching the resin film. (Stretching process)
including. Here, "exhibiting positive birefringence" means that when a polymer is oriented by stretching or the like, the refractive index in the direction orthogonal to the stretching direction becomes relatively small. In other words, the refractive index in the stretching direction increases. "Exhibiting negative birefringence" means that when a polymer is oriented by stretching or the like, the refractive index in the stretching direction becomes relatively small. In other words, the refractive index in the direction perpendicular to the stretching direction is increased.

A-1. Resin film manufacturing process The resin film manufacturing process includes a resin exhibiting positive birefringence and a resin exhibiting negative birefringence, ΔP(590) exceeds 0.0005, and Rth(450)/Rth( 550) is less than 0.98. By stretching such a resin film, a retardation film having desired optical properties can be suitably obtained. The resin film may further contain any other appropriate components as necessary.

A-1-1. Resin Film As mentioned above, the resin film includes a resin exhibiting positive birefringence and a resin exhibiting negative birefringence, ΔP(590) exceeds 0.0005, and Rth(450)/Rth(550) It is less than 0.98.

The ΔP(590) of the resin film typically exceeds 0.0005, preferably 0.0007 or more, and more preferably 0.001 or more. Further, the upper limit of ΔP(590) is, for example, 0.004 or less, preferably 0.0035 or less. Since a resin film having ΔP (590) in the above range can exhibit high in-plane birefringence by stretching, a retardation film having a desired in-plane retardation and a small thickness can be suitably obtained. obtain.

The in-plane birefringence (Δn(590)) of the resin film at a measurement wavelength of 590 nm is, for example, 0.0003 or less, preferably 0 to 0.00005. A resin film having Δn (590) within the above range can exhibit stable in-plane orientation upon stretching. In one embodiment, the resin film exhibits a refractive index characteristic of nx=ny>nz.

The resin film exhibits reverse wavelength dispersion characteristics regarding the retardation in the thickness direction. The resin film typically satisfies the relationship Rth(450)/Rth(550)<0.98, preferably 0.60<Rth(450)/Rth(550)<0.98, more preferably satisfies the relationship 0.80<Rth(450)/Rth(550)<0.98. According to a resin film that satisfies the above relationship, a retardation film exhibiting reverse wavelength dispersion characteristics with respect to in-plane retardation can be suitably obtained by stretching.

In one embodiment, a nanophase-separated structure is formed in the resin film. The retardation film obtained by stretching such a resin film also has a nano-phase separation structure, which allows rapid shrinkage in a high-temperature, high-humidity environment (for example, 110°C and 85% RH (relative humidity)). can be suppressed.

As used herein, the term "nanophase-separated structure" refers to a structure in which two components with different electron densities are phase-separated in a domain size on the nano-order (typically on the order of tens of nanometers). The resin exhibiting positive birefringence and the resin exhibiting negative birefringence may have a sea-island structure or a co-continuous structure. Examples of means for confirming the nanophase separation structure include transmission electron microscopy (TEM), scanning electron microscopy (SEM), atomic force microscopy (AFM), and small-angle X-ray scattering (SAXS). One example is TEM observation of a cross section. When a nanophase-separated structure is formed in the film to be observed, two types of domains with different electron densities can be confirmed in TEM observation of a cross section of the film, and the size (maximum length) of all domains is less than 100 nm. You can confirm that.

The glass transition temperature (Tg) of the resin film is, for example, 120°C to 220°C, preferably 125°C to 220°C, more preferably 125°C to 210°C.

The thickness of the resin film is, for example, 50 μm to 200 μm, preferably 70 μm to 180 μm, more preferably 100 μm to 180 μm.

The resin film may be sheet-shaped or elongated. The resin film is preferably elongated. In this specification, "elongated shape" means an elongated shape whose length is sufficiently longer than its width; for example, an elongated shape whose length is at least 10 times, preferably at least 20 times its width. include. The long resin film can be wound into a roll.

(Resin showing positive birefringence)
The resin exhibiting positive birefringence is not limited as long as the effects of the present invention can be obtained, and for example, cellulose resins such as cellulose and cellulose derivatives can be used. Examples of cellulose derivatives include cellulose ether, in which at least a portion of the hydroxyl groups in cellulose are etherified, and cellulose ether ester, in which at least a portion of the hydroxyl groups in cellulose are similarly esterified. Among them, cellulose ether can be preferably used. One type of resin exhibiting positive birefringence may be used alone, or two or more types may be used in combination.

（式（１）中、Ｒ_１～Ｒ_３のそれぞれは、水素原子または炭素数１～１２の置換基を示す）。 Cellulose resin is typically a polymer in which β-glucose units are linearly polymerized, and has a structural unit shown in the following formula (1). Such a cellulose resin has flat wavelength dispersion characteristics with respect to the retardation in the thickness direction, and exhibits a refractive index characteristic of nx>nz.

(In formula (1), each of R ₁ to R ₃ represents a hydrogen atom or a substituent having 1 to 12 carbon atoms).

Examples of substituents having 1 to 12 carbon atoms represented by R ₁ to R ₃ in the above formula (1) include methyl group, ethyl group, propyl group, butyl group, pentyl group, hexyl group, heptyl group, octyl group, Alkyl groups such as decanyl, dodecanyl, isobutyl, and t-butyl; cycloalkyl groups such as cyclohexyl; aryl groups such as phenyl and naphthyl; aralkyl groups such as benzyl; acetyl, propionyl, etc. Acyl groups; cyanoalkyl groups such as cyanoethyl groups; aminoalkyl groups such as aminoethyl groups; hydroxyalkyl groups such as 2-hydroxyethyl groups and 3-hydroxypropyl groups;
In the above formula (1), R ₁ to R ₃ may be the same or different.
Each of R ₁ to R ₃ in the above formula (1) preferably includes a hydrogen atom and an alkyl group having 1 to 12 carbon atoms, more preferably a hydrogen atom and an alkyl group having 1 to 4 carbon atoms. Examples include alkyl groups, more preferably hydrogen atoms and ethyl groups.

The degree of substitution (hereinafter referred to as DS) of the cellulose resin is typically 1.5 or more and 2.95 or less, preferably 1.8 or more and 2.8 or less. DS is the proportion of hydroxyl groups substituted in the cellulose resin, and when 100% substitution is made, DS is 3. DS can be calculated from the peak area of gas chromatography as described in the 17th edition of the Japanese Pharmacopoeia.

The number average molecular weight (Mn) of the cellulose resin in terms of standard polystyrene is, for example, 1×10 ³ or more and 1×10 ⁶ or less, preferably 5×10 ³ or more and 2×10 ⁵ or less. Mn of a cellulose resin can be calculated from an elution curve measured by gel permeation chromatography (GPC). If the Mn of the cellulose resin is within the above range, it is possible to improve the mechanical properties and/or moldability of the resin film.

The glass transition temperature (Tg) of the cellulose resin is, for example, 140°C or lower, preferably 135°C or lower, and, for example, 120°C or higher, preferably 125°C or higher. The glass transition temperature (Tg) of cellulose resin can be measured by a thermal analysis device such as DSC (Differential Scanning Calorimetry).

Specific examples of cellulose resins include alkylcelluloses such as methylcellulose, ethylcellulose, and propylcellulose; hydroxyalkylcelluloses such as hydroxyethylcellulose and hydroxypropylcellulose; aralkylcelluloses such as benzylcellulose; cyanoalkylcelluloses such as cyanoethylcellulose; carboxymethylcellulose, Examples include carboxyalkylcelluloses such as carboxyethylcellulose; carboxyalkylalkylcelluloses such as carboxymethylmethylcellulose and carboxymethylethylcellulose; and aminoalkylcelluloses such as aminoethylcellulose. Cellulosic resins can be used alone or in combination.
Among cellulose resins, alkyl cellulose is preferred, and ethyl cellulose is more preferred.

（式（２）中、Ｒ_４は、水素原子または炭素数１～１２のアルキル基を示し；Ｒ_５ａは、炭素数１～１２のアルキル基、ニトロ基、ブロモ基、ヨード基、シアノ基、クロロ基、スルホン酸基、カルボン酸基、フルオロ基、または、チオール基から選択される１種を示し；Ｒ_５ｂは、水素原子または炭素数１～１２のアルキル基を示し；Ｒ_６は、水素原子、ニトロ基、ブロモ基、ヨード基、シアノ基、クロロ基、スルホン酸基、カルボン酸基、フルオロ基、フェニル基、チオール基、アミド基、アミノ基、ヒドロキシ基、炭素数１～１２のアルコキシ基、または、炭素数１～１２のアルキル基から選択される種を示す。）

（式（３）中、Ｒ_７は、ヘテロ原子として窒素原子もしくは酸素原子を１つ以上含む５員環複素環残基または６員環複素環残基（上記５員環複素環残基および上記６員環複素環残基は他の環状構造と縮合環構造を形成してもよい）を示す。） (Resin showing negative birefringence)
The resin exhibiting negative birefringence is not limited as long as the effect of the present invention can be obtained, and for example, an ester-based resin having a structural unit shown in the following formula (2) and a structural unit shown in the following formula (3) Resin can be used. Such an ester-based resin has a positive wavelength dispersion characteristic regarding the retardation in the thickness direction, and exhibits a refractive index characteristic of nx<nz. One type of resin exhibiting negative birefringence may be used alone, or two or more types may be used in combination.

(In formula (2), R ₄ represents a hydrogen atom or an alkyl group having 1 to 12 carbon atoms; R _5a represents an alkyl group having 1 to 12 carbon atoms, a nitro group, a bromo group, an iodo group, a cyano group, Represents one selected from a chloro group, a sulfonic acid group, a carboxylic acid group, a fluoro group, or a thiol group; R _5b represents a hydrogen atom or an alkyl group having 1 to 12 carbon atoms; R ₆ represents hydrogen Atom, nitro group, bromo group, iodo group, cyano group, chloro group, sulfonic acid group, carboxylic acid group, fluoro group, phenyl group, thiol group, amide group, amino group, hydroxy group, alkoxy having 1 to 12 carbon atoms (Indicates a species selected from a group or an alkyl group having 1 to 12 carbon atoms.)

(In formula (3), R ₇ is a 5-membered heterocyclic residue or a 6-membered heterocyclic residue containing one or more nitrogen atoms or oxygen atoms as a heteroatom (the above 5-membered heterocyclic residue and the above (The 6-membered heterocyclic residue may form a fused ring structure with other cyclic structures.)

The structural unit shown in the above formula (2) is a cinnamate residue unit. Examples of the alkyl group having 1 to 12 carbon atoms represented by R ₄ in the above formula (2) include methyl group, ethyl group, isopropyl group, n-propyl group, n-butyl group, s-butyl group, t- Examples include butyl group, isobutyl group, and ethylhexyl group. Among R ₄ in the above formula (2), an alkyl group having 1 to 4 carbon atoms is preferred, and an ethyl group and an isobutyl group are more preferred.
Among R _5a in the above formula (2), preferred are alkyl groups having 1 to 12 carbon atoms and cyano groups, more preferred are alkyl groups having 1 to 4 carbon atoms and cyano groups, and further Preferred is a cyano group.
Among R _5b in the above formula (2), preferred are a hydrogen atom and an alkyl group having 1 to 4 carbon atoms.
In the above formula (2), only one R ₆ may be bonded to the benzene ring, or two or more R 6 may be bonded to the benzene ring. Among R ₆ in the above formula (2), preferred are a carboxylic acid group and a hydroxy group.

Specific examples of the structural unit (cinnamate ester residue unit) shown in the above formula (2) include α-cyano-4-hydroxycinnamate methyl residue unit, α-cyano-2-hydroxycinnamate ethyl residue unit, α-cyano-3-hydroxycinnamate ethyl residue unit, α-cyano-4-hydroxycinnamate ethyl residue unit, α-cyano-4-hydroxycinnamate n-propyl residue unit , α-cyano-4-hydroxycinnamate isopropyl residue unit, α-cyano-4-hydroxycinnamate n-butyl residue unit, α-cyano-4-hydroxycinnamate isobutyl residue unit, α- α-cyano-hydroxycinnamate ester residue units such as s-butyl cyano-4-hydroxycinnamate residue units and methyl α-cyano-2,4-dihydroxycinnamate residue units; α-cyano- 4-carboxycinnamate methyl residue unit, α-cyano-4-carboxycinnamate ethyl residue unit, α-cyano-2,3-dicarboxycinnamate methyl residue unit, α-cyano-2, α-cyano-carboxycinnamate ester residue units such as ethyl 3-dicarboxycinnamate residue units; α-cyano-2-carboxy-3-hydroxycinnamate methyl residue units, α-cyano-2 -α-cyano-carboxy-hydroxycinnamate ester residue units such as carboxy-3-hydroxycinnamate ethyl residue units; 3-methyl-3-(hydroxyphenyl)-prop-2-enoic acid methyl residues unit, 3-alkyl-3-(hydroxyphenyl)-prop-2-enoic acid ester residue unit such as 3-ethyl-3-(hydroxyphenyl)-prop-2-enoic acid ethyl residue unit; 3-methyl -3-(carboxyphenyl)-prop-2-enoic acid methyl residue unit, 3-ethyl-3-(carboxyphenyl)-prop-2-enoic acid ethyl residue unit, etc. phenyl)-prop-2-enoic acid ester residue unit; 2-cyano-3-methyl-3-(hydroxyphenyl)-prop-2-enoic acid methyl residue unit, 2-cyano-3-ethyl-3- 2-cyano-3-alkyl-3-(hydroxyphenyl)-prop-2-enoic acid ester residue units such as (hydroxyphenyl)-prop-2-enoic acid ethyl residue units; 2-cyano-3-methyl 2-cyano- such as -3-(carboxyphenyl)-prop-2-enoic acid methyl residue unit, 2-cyano-3-ethyl-3-(carboxyphenyl)-prop-2-enoic acid ethyl residue unit, etc. Examples include 3-alkyl-3-(carboxyphenyl)-prop-2-enoic acid ester residue units.

The ester resin may contain only one type of structural unit shown in the above formula (2), or may contain two or more types. Among the structural units represented by the above formula (2), α-cyano-hydroxycinnamate ester residue units, α-cyano-carboxycinnamate ester residue units, 3-alkyl-3-(hydroxy Examples thereof include a phenyl)-prop-2-enoic acid ester residue unit and a 3-alkyl-3-(carboxyphenyl)-prop-2-enoic acid ester residue unit.

The content of the structural unit of formula (2) in the ester resin is, for example, 21 mol% or more, and is, for example, 70 mol% or less, preferably 60 mol% or less, and more preferably 49 mol% or less. The content ratio of each structural unit in the ester resin can be measured by, for example, ¹ H-NMR.

Specific examples of the ring structure represented by R ₇ in the above formula (3) include 1-vinylpyrrole residue unit, 2-vinylpyrrole residue unit, 1-vinylindole residue unit, and 9-vinylcarbazole residue unit. , 2-vinylquinoline residue unit, 4-vinylquinoline residue unit, N-vinylphthalimide residue unit, N-vinylsuccinimide residue unit, 2-vinylfuran residue unit, and 2-vinylbenzofuran residue unit. Preferable examples include a 9-vinylcarbazole residue unit and an N-vinylphthalimide residue unit.

The ester resin may contain only one type of structural unit shown in the above formula (3), or may contain two or more types.
The content of the structural unit of formula (3) in the ester resin is, for example, 21 mol% or more, preferably 35 mol% or more, and, for example, 70 mol% or less, preferably 60 mol% or less.

（式（４）中、Ｒ_８およびＲ_９のそれぞれは、水素原子、炭素数１～１２の直鎖状アルキル基、炭素数３～１２の分岐状アルキル基、または、炭素数３～６の環状アルキル基から選択される１種を示す）。
上記式（４）において、Ｒ_８およびＲ_９で示される炭素数１～１２の直鎖状アルキル基として、例えば、メチル基、エチル基、ｎ－プロピル基、ｎ－ブチル基、ｎ－ペンチル基、ｎ－ヘキシル基等が挙げられる。
上記式（４）において、Ｒ_８およびＲ_９で示される炭素数３～１２の分岐状アルキル基として、例えば、イソプロピル基、イソブチル基、ｓｅｃ－ブチル基、ｔｅｒｔ－ブチル基等が挙げられる。
上記式（４）において、Ｒ_８およびＲ_９で示される炭素数３～６の環状アルキル基として、例えば、シクロプロピル基、シクロブチル基、シクロヘキシル基等が挙げられる。
上記式（４）においてＲ_８およびＲ_９は、互いに同じであってもよく、互いに異なっていてもよい。
上記式（４）におけるＲ_８のなかでは、好ましくは、水素原子、炭素数１～１２の直鎖状アルキル基が挙げられ、より好ましくは、水素原子、メチル基が挙げられる。
上記式（４）におけるＲ_９のなかでは、好ましくは、炭素数３～１２の分岐状アルキル基が挙げられ、より好ましくは、炭素数３～８の分岐状アルキル基が挙げられる。 The ester resin preferably further includes a structural unit shown in the following formula (4) in addition to the structural units shown in (2) and (3) above.

(In formula (4), each of R ₈ and R ₉ is a hydrogen atom, a linear alkyl group having 1 to 12 carbon atoms, a branched alkyl group having 3 to 12 carbon atoms, or a branched alkyl group having 3 to 6 carbon atoms. (represents one type selected from cyclic alkyl groups).
In the above formula (4), the linear alkyl group having 1 to 12 carbon atoms represented by R ₈ and R ₉ includes, for example, a methyl group, an ethyl group, an n-propyl group, an n-butyl group, an n-pentyl group. , n-hexyl group, etc.
In the above formula (4), examples of the branched alkyl group having 3 to 12 carbon atoms represented by R ₈ and R ₉ include isopropyl group, isobutyl group, sec-butyl group, and tert-butyl group.
In the above formula (4), examples of the cyclic alkyl group having 3 to 6 carbon atoms represented by R ₈ and R ₉ include a cyclopropyl group, a cyclobutyl group, a cyclohexyl group, and the like.
In the above formula (4), R ₈ and R ₉ may be the same or different.
Among R ₈ in the above formula (4), preferred are a hydrogen atom and a linear alkyl group having 1 to 12 carbon atoms, and more preferred are a hydrogen atom and a methyl group.
Among R ₉ in the above formula (4), a branched alkyl group having 3 to 12 carbon atoms is preferred, and a branched alkyl group having 3 to 8 carbon atoms is more preferred.

The structural unit represented by the above formula (4) is typically an acrylic resin residue unit. Specific examples of the structural units shown in the above formula (4) include acrylic acid residue units, methacrylic acid residue units, 2-ethyl acrylic acid residue units, 2-propylacrylic acid residue units, and 2-isopropylacrylic acid residue units. group unit, 2-pentyl acrylic acid residue unit, 2-hexyl acrylic acid residue unit, methyl acrylate residue unit, ethyl acrylate residue unit, n-propyl acrylate residue unit, isopropyl acrylate residue unit , n-butyl acrylate residue unit, isobutyl acrylate residue unit, sec-butyl acrylate residue unit, n-pentyl acrylate residue unit, isopentyl acrylate residue unit, sec-pentyl acrylate residue unit , 3-pentyl acrylate residue unit, neopentyl acrylate residue unit, n-hexyl acrylate residue unit, isohexyl acrylate residue unit, neohexyl acrylate residue unit, methyl methacrylate residue unit, ethyl methacrylate residue unit, n-propyl methacrylate residue unit, isopropyl methacrylate residue unit, n-butyl methacrylate residue unit, isobutyl methacrylate residue unit, sec-butyl methacrylate residue unit, n-pentyl methacrylate residue unit, isopentyl methacrylate residue unit, sec-pentyl methacrylate residue unit, 3-pentyl methacrylate residue unit, neopentyl methacrylate residue unit, n-hexyl methacrylate residue unit , isohexyl methacrylate residue unit, neohexyl methacrylate residue unit, methyl 2-ethyl acrylate residue unit, ethyl 2-ethyl acrylate residue unit, n-propyl 2-ethyl acrylate residue unit , 2-ethylacrylate isopropyl residue unit, 2-ethylacrylate n-butyl residue unit, 2-ethylacrylate isobutyl residue unit, 2-ethylacrylate sec-butyl residue unit, etc., preferably. is an isobutyl acrylate residue unit.

The ester resin may contain only one type of structural unit shown in the above formula (4), or may contain two or more types.
The content of the structural unit of the formula (4) in the ester resin is, for example, 0 mol% or more, preferably 1 mol% or more, and, for example, 30 mol% or less.

The ester resin may contain monomer residue units other than those of formulas (2) to (4) above. Such monomer residue units include, for example, styrene residues such as styrene residues and α-methylstyrene residues; vinylnaphthalene residues; vinyl esters such as vinyl acetate residues and vinyl propionate residues; Vinyl ether residues such as methyl vinyl ether residues, ethyl vinyl ether residues, butyl vinyl ether residues; N-substituted maleimides such as N-methylmaleimide residues, N-cyclohexylmaleimide residues, N-phenylmaleimide residues, etc. Residues; acrylonitrile residues; methacrylonitrile residues; fumaric acid ester residues; fumaric acid residues; olefin residues such as ethylene residues and propylene residues.

The number average molecular weight (Mn) of the ester resin in terms of standard polystyrene is, for example, 1×10 ³ or more and 5×10 ⁶ or less, preferably 5×10 ³ or more and 3×10 ⁵ or less. The Mn of the ester resin can be calculated from the elution curve measured by gel permeation chromatography (GPC). If the Mn of the ester resin is within the above range, it is possible to improve the mechanical properties and/or moldability of the resin film.

The glass transition temperature (Tg) of the ester resin is, for example, 220°C or lower, preferably 210°C or lower, and, for example, 180°C or higher, preferably 190°C or higher. The glass transition temperature (Tg) of the ester resin can be measured by a thermal analysis device such as DSC (Differential Scanning Calorimetry).

Specific examples of such ester resins include α-cyano-2-hydroxycinnamic acid ester-styrene-acrylic acid ester copolymer, α-cyano-2-hydroxycinnamic acid ester-2-vinylnaphthalene- Acrylic ester copolymer, α-cyano-2-hydroxycinnamic ester-1-vinylindole-acrylic ester copolymer, α-cyano-2-hydroxycinnamic ester-9-vinylcarbazole-acrylic acid Ester copolymer, α-cyano-3-hydroxycinnamate-styrene-acrylate copolymer, α-cyano-3-hydroxycinnamate-2-vinylnaphthalene-acrylate copolymer, α-cyano-3-hydroxycinnamate ester-1-vinylindole-acrylic ester copolymer, α-cyano-3-hydroxycinnamate ester-9-vinylcarbazole-acrylic ester copolymer, α- Cyano-4-hydroxycinnamate-styrene-acrylate copolymer, α-cyano-4-hydroxycinnamate-2-vinylnaphthalene-acrylate copolymer, α-cyano-4-hydroxy Cinnamate ester-1-vinylindole-acrylic ester copolymer, α-cyano-4-hydroxycinnamate ester-9-vinylcarbazole-acrylic ester copolymer, α-cyano-2-hydroxycinnamate Acid ester-styrene-methacrylic acid ester copolymer, α-cyano-2-hydroxycinnamic acid ester-2-vinylnaphthalene-methacrylic acid ester copolymer, α-cyano-2-hydroxycinnamic acid ester-1- Vinyl indole-methacrylic acid ester copolymer, α-cyano-2-hydroxycinnamic acid ester-9-vinylcarbazole-methacrylic acid ester copolymer, α-cyano-3-hydroxycinnamic acid ester-styrene-methacrylic acid Ester copolymer, α-cyano-3-hydroxycinnamate ester-2-vinylnaphthalene-methacrylate ester copolymer, α-cyano-3-hydroxycinnamate ester-1-vinylindole-methacrylate ester copolymer Polymer, α-cyano-3-hydroxycinnamic acid ester-9-vinylcarbazole-methacrylic acid ester copolymer, α-cyano-4-hydroxycinnamic acid ester-styrene-methacrylic acid ester copolymer, α- Cyano-4-hydroxycinnamate-2-vinylnaphthalene-methacrylate copolymer, α-cyano-4-hydroxycinnamate-1-vinylindole-methacrylate copolymer, α-cyano- Examples include 4-hydroxycinnamate ester-9-vinylcarbazole-methacrylate ester copolymer.

(Content ratio of resin showing positive birefringence and resin showing negative birefringence)
The content ratio of the resin exhibiting positive birefringence in the resin film typically exceeds 50% by mass when the sum of the resin exhibiting positive birefringence and the resin exhibiting negative birefringence is 100% by mass. However, it is preferably 70% by mass or more, more preferably 80% by mass or more. Furthermore, the upper limit of the content of the resin exhibiting positive birefringence is typically 90% by mass or less. If the content ratio of the resin exhibiting positive birefringence is equal to or higher than the above lower limit, the resin exhibiting positive birefringence and the resin exhibiting negative birefringence can stably form a nanophase-separated structure. In addition, as shown in Figure 1, the wavelength dispersion characteristics of the retardation in the thickness direction of the resin film are the wavelength dispersion characteristics of the retardation in the thickness direction of each of the resin exhibiting positive birefringence and the resin exhibiting negative birefringence. It can be understood as a composite of the following. Therefore, the cellulose-based resin has flat wavelength dispersion characteristics with respect to the retardation in the thickness direction and exhibits refractive index characteristics of nx>nz, and the cellulose resin has positive wavelength dispersion characteristics and exhibits refractive index characteristics of nx<nz. By containing the above-mentioned ester-based resin exhibiting a refractive index characteristic in the above ratio, a resin film having a reverse wavelength dispersion characteristic with respect to a retardation in the thickness direction and exhibiting a refractive index characteristic of nx>nz can be suitably obtained. .

(other ingredients)
Other components may be appropriately selected depending on the purpose. Other ingredients include, for example, hindered phenol antioxidants, phosphorus antioxidants, sulfur antioxidants, lactone antioxidants, amine antioxidants, hydroxylamine antioxidants, and vitamin E. Antioxidants such as antioxidants and other antioxidants; hindered amine light stabilizers; ultraviolet absorbers such as benzotriazole, benzophenone, triazine, and benzoate; surfactants; polymer electrolytes; conductive complexes; pigments; dyes ; antistatic agents; antiblocking agents; lubricants. The content of other components is, for example, 0.01 part by weight to 0.3 part by weight based on 100 parts by weight of the resin component.

A-1-2. Method for Producing a Resin Film The resin film is produced by preparing a resin composition by mixing the components constituting the resin film described in Section A-1-1, and molding the resin composition into a film.

Examples of the mixing method include a melt mixing method and a solution mixing method. The melt mixing method is a method of mixing by melting resin etc. by heating and kneading. The solution mixing method is a method in which a resin or the like is dissolved in a solvent and mixed.

The solvent used in the solution mixing method is preferably a solvent with a boiling point of 200° C. or lower, more preferably 170° C. or lower, from the viewpoint of reducing residual solvent in the film forming process. Specific examples of solvents include halogenated hydrocarbons such as chloroform, dichloromethane, carbon tetrachloride, dichloroethane, tetrachloroethane, trichloroethylene, tetrachloroethylene, chlorobenzene, and dichlorobenzene; phenols such as phenol and chlorophenol; benzene, toluene, and xylene. , methoxybenzene, mesitylene, dimethoxybenzene, and other aromatic hydrocarbons; acetone, methyl ethyl ketone, methyl isobutyl ketone (MIBK), cyclohexanone, cyclopentanone (CPN), 2-pyrrolidone, N-methyl-2-pyrrolidone, and other ketones. Ester solvents such as ethyl acetate and butyl acetate; butanol, t-butyl alcohol, glycerin, ethylene glycol, triethylene glycol, ethylene glycol monomethyl ether, diethylene glycol dimethyl ether, propylene glycol, dipropylene glycol, 2-methyl-2 , 4-pentanediol, and other alcoholic solvents; dimethylformamide, dimethylacetamide, and other amide solvents; acetonitrile, butyronitrile, and other nitrile solvents; 1,3-dioxolane, cyclopentyl methyl ether (CPME), propylene glycol methyl ether acetate ( Examples include ether solvents such as PGMEA), diethyl ether, dibutyl ether, and tetrahydrofuran; carbon disulfide, ethyl cellosolve, butyl cellosolve, and mixed solvents thereof.

Among the solvents, mixed solvents are preferred. Examples of mixed solvent combinations include ester solvents/aromatic hydrocarbons, ether solvents/aromatic hydrocarbons, ester solvents/ether solvents, ester solvents/alcohol solvents, and ester solvents/ketone solvents. , two types of ether solvents, and two types of ester solvents.

More preferred mixed solvents include ester solvents/aromatic hydrocarbons, still more preferred include ethyl acetate/toluene, particularly preferred ethyl acetate/toluene = 40% by mass/60% by mass to 60% by mass. A mixed solvent of mass %/40 mass % may be mentioned. When the solvent is such a mixed solvent, a resin film having desired orientation can be suitably obtained. Furthermore, in the retardation film, the cellulose resin and the ester resin can more stably form a nanophase-separated structure.

Any suitable method can be used to mold the resin composition. Specific examples include compression molding method, transfer molding method, injection molding method, extrusion molding method, blow molding method, powder molding method, FRP molding method, cast coating method (e.g. casting method), calendar molding method, hot press method. Laws, etc. can be cited. Among these, the cast coating method is preferred. In the cast coating method, a resin solution containing the above-mentioned resin and a solvent is applied (e.g., cast) onto a supporting substrate to form a coating layer, and the coating layer is heated to evaporate the solvent to form a film. This is the way to get it.

The coating method is not particularly limited, and any conventional method can be used. For example, T-die method, doctor blade method, bar coater method, slot die method, lip coater method, reverse gravure coating method, microgravure method, spin coating method, brush coating method, roll coating. method, flexographic printing method, etc. The molding conditions can be appropriately set depending on the composition and type of the resin used, the desired characteristics of the retardation film, and the like.

Examples of the supporting base material include polyester, polycarbonate, polystyrene, polyethylene, polypropylene, polyvinyl chloride, polyvinylidene chloride, triacetylcellulose, polyvinyl alcohol, polyimide, polyarylate, polysulfone, polyethersulfone, epoxy resin, etc. Examples include polymer substrates, glass substrates such as glass plates and quartz substrates, metal substrates such as aluminum, stainless steel, and ferrotype substrates, and inorganic substrates such as ceramic substrates. Preferably, the base material is a polymer base material or a metal base material.

The viscosity of the resin composition (melt or solution) during molding is preferably 100 cps to 30,000 cps, more preferably 300 cps to 20,000 cps, and still more preferably 500 cps to 15,000 cps, from the viewpoint of productivity, moldability, etc. The viscosity of the resin composition can be adjusted by adjusting the molecular weight, concentration, type of solvent, etc. of each component.

The solid content concentration of the resin solution is, for example, 1% to 30% by weight, preferably 5% to 30% by weight, more preferably 10% to 24% by weight.

The coating thickness of the resin solution (thickness of the coating layer) is, for example, 50 μm to 1000 μm, preferably 50 μm to 900 μm, more preferably 70 μm to 800 μm, and still more preferably 100 μm to 700 μm (for example, 300 μm to 700 μm). If the coating thickness is within this range, the film thickness after stretching can be ensured without significantly reducing the in-plane orientation per thickness, and for example, the in-plane retardation characteristics necessary for a λ/4 plate can be ensured. .

The drying method for drying the coating layer is not particularly limited, and ordinary heating means can be used. Examples include hot air blowers, heating rolls, far-infrared heaters, and the like.

When a resin film contains a plurality of types of resin within a single layer, each resin can be independently oriented within the resin film. Further, the orientation of each resin can vary depending on the drying temperature, coating thickness, resin solution concentration, etc. For example, the higher the drying temperature (as a result, the higher the solvent volatilization rate), the more disordered the orientation of the resin in the resin film tends to be. Therefore, for example, when forming a resin film using the cellulose resin and the ester resin as a resin exhibiting positive birefringence and a resin exhibiting negative birefringence, respectively, the cellulose resin is nx=ny>nz Since the ester resin exhibits the refractive index characteristic of nx=ny<nz, the relationship between the retardation in the thickness direction of the resulting resin film and the drying temperature is shown in the table below. A relationship as shown in 1 can be established.

Therefore, when using the cellulose resin and the ester resin in combination, the drying temperature of the coating layer is, for example, 35°C to 160°C, preferably 50°C, from the viewpoint of making each resin develop a ΔP of a certain level or more. It may be within the range of 155°C to 155°C. Further, the drying time is, for example, 60 seconds to 1200 seconds, preferably 60 seconds to 900 seconds, and more preferably 90 seconds to 900 seconds.

Drying may be performed at a constant temperature or while changing the temperature. For example, drying can be carried out while increasing the temperature gradually or stepwise. When the treatment is carried out while changing the temperature, the weighted average temperature based on the processing time at each temperature is, for example, 50°C to 140°C, preferably 70°C to 140°C, more preferably 70°C to 130°C.

When drying is performed while raising the temperature in stages, the first stage drying temperature is set to, for example, 35°C or higher and 65°C or lower, preferably 45°C or higher and 65°C or lower, and the first stage drying time is set to, for example, 45°C or higher and 65°C or lower. It is set to 1 minute or more and 30 minutes or less, preferably 1 minute or more and 8 minutes or less. Thereafter, the drying temperature is increased in each step, for example from 10°C to 60°C, preferably from 10°C to 40°C. The drying time of each stage after the second stage is typically shorter than the drying time of the first stage, preferably 20 seconds or more and 20 minutes or less, more preferably 30 seconds or more and 5 minutes or less. The number of drying stages is preferably 2 or more and 4 or less, more preferably 3 or less. By drying in multiple stages in this way, it is possible to ensure the orientation of each resin in the thickness direction, and the resulting resin film (ultimately, retardation film) has a nano-phase separation structure. can be formed.

In one embodiment, the maximum temperature in multi-stage drying (drying temperature in the final stage) is, for example, higher than 130°C and lower than 160°C, preferably higher than 130°C and lower than 155°C, more preferably 135°C to 155°C. be. When the maximum temperature is within this range, the resulting resin film exhibits a relatively low ΔP (e.g., ΔP<0.0015) while exhibiting a relatively high draw ratio (e.g., 3.0 times or more or 3.5 It is possible to stretch the film by 2 times or more. Therefore, by applying a high stretching ratio, a retardation film with desired optical properties (in-plane retardation, reverse wavelength dispersion characteristics, etc.) and a wide width can be obtained, and a large retardation film can be obtained by the roll-to-roll process. It can be applied to the production of optical laminates (for example, circularly polarizing plates). Specifically, by stretching at a stretching ratio of, for example, 3.0 times or more, preferably 3.5 times or more, a retardation film having Re(550) of 130 nm to 160 nm can be obtained. In another embodiment, the maximum temperature in multi-stage drying (drying temperature in the final stage) is, for example, 100°C or more and 140°C or less, preferably 100°C to 130°C, more preferably 100°C to 120°C, and even more preferably The temperature is 110°C to 120°C. When the maximum temperature is within this range, the resulting resin film exhibits a relatively high ΔP (for example, ΔP≧0.0015), so even at a relatively low stretching ratio, a retardation film with desired optical properties can be obtained. You can get the film. Specifically, a retardation film having Re(550) of 130 nm to 160 nm can be obtained by stretching at a stretching ratio of, for example, less than 3.5 times, preferably less than 3.0 times. As described above, the drying temperature of the coating layer is one of the factors that affects the ΔP of the resin film, and the stretching conditions such as the stretching ratio and stretching temperature have characteristics depending on the ΔP of the resin film. By carrying out the stretching, a desired retardation film such as a reverse wavelength dispersion λ/4 plate can be obtained.

The method for producing a resin film may include a secondary drying step (annealing step) of heating at 110° C. or higher after drying the coating layer. The drying temperature in the secondary drying step (annealing step) is, for example, 110° C. or higher, preferably 130° C. or higher, and, for example, 180° C. or lower, preferably 165° C. or lower. The drying time of the secondary drying step (annealing step) is, for example, 1 minute or more, preferably 5 minutes or more, and is, for example, 60 minutes or less, preferably 45 minutes or less. Preferably, the secondary drying step is performed after the dried coating layer is cooled to, for example, 50° C. or lower, preferably 30° C. or lower, and more preferably room temperature (23° C.). Once the dried coating layer is cooled, the orientation and nanophase separation structure formed during the drying process can be fixed, and these can be maintained even in the subsequent secondary drying process.

The content ratio (residual rate) of the solvent in the resin film after the above drying (after the secondary drying step if a secondary drying step is included) is, for example, 0% to 10% by weight, preferably 0% to 5% by weight. It is.

A-2. Stretching process In the stretching process, the resin film is stretched. The stretching method is not limited as long as the retardation film described in Section B can be obtained, and any appropriate stretching method may be employed. Specifically, various stretching methods such as free end stretching, fixed end stretching, free end contraction, and fixed end contraction can be used alone, simultaneously, or sequentially. Regarding the stretching direction, stretching can be carried out in various directions and dimensions, such as the length direction, width direction, thickness direction, and diagonal direction.

Specific examples of the stretching method include fixed end uniaxial stretching, free end uniaxial stretching, and diagonal stretching. Fixed-end uniaxial stretching may be performed, for example, by using a tenter-type stretching device to convey a long resin film in the longitudinal direction and stretching it in a direction perpendicular to the longitudinal direction (width direction). Free end uniaxial stretching can be performed, for example, by stretching a long resin film in the longitudinal direction between rolls having different circumferential speeds. The diagonal stretching may be performed, for example, by continuously diagonally stretching a long resin film in a direction at an angle θ with respect to the longitudinal direction. By employing diagonal stretching, a long retardation film having an orientation angle of θ (slow axis in the direction of angle θ) with respect to the longitudinal direction of the film can be obtained, and for example, it can be laminated with a polarizer. In this case, roll-to-roll is possible, which simplifies the manufacturing process. Note that the angle θ may be an angle between the absorption axis of the polarizer and the slow axis of the retardation film in the polarizing plate with a retardation layer. The angle θ is preferably 40° to 50°, more preferably 42° to 48°, and even more preferably about 45°.

The stretching ratio can be appropriately selected depending on the desired in-plane retardation and the like. The stretching ratio is, for example, 2.0 times or more, preferably 2.5 times or more, more preferably 3.0 times or more, and, for example, 8.0 times or less, preferably 7.5 times or less, more preferably 5. It is 0 times or less.

The thickness of the resin film after stretching is, for example, 10 μm to 80 μm, preferably 10 μm to 70 μm, and more preferably 10 μm to 50 μm. Further, the thickness of the resin film after stretching is, for example, 50% or less, preferably 12.5% to 50%, more preferably 12.5% to 40% of the thickness of the resin film before stretching. When the film thicknesses before and after stretching satisfy the relationship, a retardation film having high in-plane birefringence can be obtained.

The stretching temperature can vary depending on the desired in-plane retardation and thickness of the retardation film, the type of resin used, the thickness of the resin film, the stretching ratio, and the like. The stretching temperature varies in relation to the Tg of the material contained in the resin film, and is, for example, Tg1-20°C to Tg1+50°C with respect to the glass transition temperature (Tg1) of the resin with the lowest Tg among the oriented resins. , preferably Tg1-20°C to Tg1+40°C, more preferably Tg1-10°C to Tg1+40°C. If the stretching temperature is within this range, stable stretching can be achieved.

The stretching speed is, for example, 1 mm/sec or more, preferably 2 mm/sec or more, and, for example, 200 mm/sec or less, preferably 100 mm/sec or less.

The resin film is preferably preheated before stretching. The preheating temperature is also set with respect to Tg1 similarly to the stretching temperature. The preheating temperature is, for example, Tg1-20°C or higher, preferably Tg1-10°C or higher, and, for example, Tg1+50°C or lower, preferably Tg1+40°C or lower. The preheating temperature is typically higher than the stretching temperature, preferably 5° C. or more higher than the stretching temperature.

If necessary, the process may include a step of heat-shrinking the stretched resin film in the stretching direction. The heat shrinkage temperature is also set with respect to Tg1 in the same manner as the preheating and stretching temperatures, and is, for example, Tg1-20°C or higher, preferably Tg1-15°C or higher, and, for example, Tg1+45°C or lower, preferably Tg1+35°C or lower. The heat shrinkage temperature is more preferably equal to or lower than the stretching temperature. The shrinkage rate is typically 1% or more and 5% or less.

B. Retardation Film The retardation film manufactured by the retardation film manufacturing method described in Section A typically has a refractive index characteristic of nx>ny≧nz. Here, "ny=nz" includes not only the case where ny and nz are completely equal but also the case where they are substantially equal. Therefore, there may be a case where ny<nz within a range that does not impair the effects of the present invention.

The in-plane birefringence (Δn(590)) of the retardation film (in other words, the resin film after stretching) at a measurement wavelength of 590 nm typically exceeds 0.003, preferably exceeds 0.0035, and more Preferably it is 0.0037 or more, more preferably 0.0040 or more. Δn(590) of the retardation film may be, for example, 0.007 or less.

The in-plane retardation of the retardation film can be any appropriate value depending on the application and the like. In one embodiment, the retardation film can function as a λ/4 plate. In this case, Re (550) of the retardation film is preferably 100 nm to 190 nm, more preferably 110 nm to 170 nm, and even more preferably 130 nm to 160 nm.

The Nz coefficient of the retardation film is preferably 0.9 to 3, more preferably 0.9 to 2.5, even more preferably 0.9 to 1.5, particularly preferably 0.9 to 1.3. . By satisfying such a relationship, when used in an image display device as a circularly polarizing plate in combination with a polarizer, an extremely excellent reflected hue can be achieved.

A retardation film typically exhibits inverse dispersion wavelength characteristics that increase as the wavelength of measurement light increases with respect to in-plane retardation. The retardation film typically satisfies the relationship Re(450)/Re(550)<0.90, preferably the relationship Re(450)/Re(550)<0.88, more preferably 0.90. The relationship 70<Re(450)/Re(550)<0.88 is satisfied. When a retardation film satisfying such a relationship is combined with a polarizer and used as a circularly polarizing plate in an image display device, extremely excellent antireflection properties can be achieved.

The thickness of the retardation film is, for example, 10 μm to 80 μm, preferably 10 μm to 50 μm, more preferably 10 μm to 30 μm. Since the retardation film obtained by the manufacturing method of the embodiment of the present invention has high in-plane birefringence, it can have a practically sufficient in-plane retardation with a small thickness.

EXAMPLES Hereinafter, the present invention will be specifically explained with reference to Examples, but the present invention is not limited to these Examples. The method for measuring each characteristic is as follows. Note that unless otherwise specified, "parts" and "%" in Examples and Comparative Examples are based on weight.
(1) Thickness Measured using a dial gauge (manufactured by PEACOCK, product name "DG-205 type pds-2").
(2) In-plane retardation (Re(λ)) and thickness direction retardation (Rth(λ))
The film to be measured was cut out to a length of 4 cm and a width of 4 cm, and used as a measurement sample. Regarding the measurement sample, the in-plane retardation or the thickness direction retardation at a measurement wavelength of λ nm was measured using a product name "Axoscan" manufactured by Axometrics. The measurement temperature was 23°C.
(3) In-plane birefringence (Δn(λ)) and thickness direction birefringence (ΔP(λ))
The in-plane birefringence at the measurement wavelength λnm was calculated by dividing the in-plane retardation at the measurement wavelength λnm of the measurement sample measured in (2) above by the thickness of the measurement sample. Similarly, the birefringence in the thickness direction at the measurement wavelength λnm was calculated by dividing the retardation in the thickness direction at the measurement wavelength λnm of the measurement sample measured in (2) above by the thickness of the measurement sample.
(4) Glass transition temperature (Tg)
Measured according to JIS K 7121.

[Synthesis Example 1] Synthesis of cinnamate ester copolymer (9-vinylcarbazole/α-cyano-4-hydroxyisobutyl cinnamate/isobutyl acrylate) 12.20 g of 9-vinylcarbazole in a 50 mL glass ampoule, 7.74 g of isobutyl α-cyano-4-hydroxycinnamate, 4.05 g of isobutyl acrylate, 0.0 g of 2,5-dimethyl-2,5-di(2-ethylhexanoylperoxy)hexane as a polymerization initiator. 453 g and 36.00 g of methyl ethyl ketone were put therein, nitrogen substitution and depressurization were repeated, and then the mixture was sealed under reduced pressure. This ampoule was placed in a constant temperature bath at 54° C. and maintained for 24 hours to carry out radical polymerization. After the polymerization reaction was completed, the polymer was taken out from the ampoule, 100 g of tetrahydrofuran was added, and this polymer solution was dropped into 800 g of methanol/water mixed solvent (weight ratio 80/20) to precipitate. After filtration, the filtrate was It was washed five times with 110 g of methanol/water mixed solvent (weight ratio 90/10) and filtered. By vacuum drying the obtained resin at 80° C. for 10 hours, 22.3 g of a cinnamate ester copolymer exhibiting negative birefringence was obtained. The number average molecular weight of the obtained cinnamate ester copolymer was 50,000, and the ratio of residue units was 50 mol% of 9-vinylcarbazole residue units, isobutyl α-cyano-4-hydroxycinnamate. The residue units were 25 mol% and the isobutyl acrylate residue units were 25 mol%.

[Example 1]
As a cellulose resin, ethyl cellulose ("ETHOCEL standard 100" manufactured by Dow Chemical Company, number average molecular weight Mn = 58,000, weight average molecular weight Mw = 180,000, Mw/Mn = 3.2, total substitution degree DS = 2. 51) 80 g of ester resin, 20 g of cinnamate ester resin obtained in Synthesis Example 1, and 0.1 g of hindered phenol antioxidant (manufactured by BASF Japan, product name "Irganox 245") in toluene/acetic acid. It was dissolved in an ethyl=4/6 (weight ratio) solution to obtain a resin solution with a resin concentration of 16% by weight. The solution was dripped onto a polyethylene terephthalate film using a coater to obtain a coating layer with a target thickness of 560 μm. The coated layer was dried at 65° C. for 360 seconds, 85° C. for 60 seconds, and 110° C. for 120 seconds, and then peeled off from the polyethylene terephthalate film to obtain a resin film with a thickness of 109 μm. The obtained resin film was preheated at a temperature 10°C higher than the stretching temperature, and then uniaxially stretched horizontally by 3.0 times at 155°C using a tenter stretching machine, and then heated at 2.4% in the stretching direction at 155°C. A retardation film was obtained by shrinking.

Near the center in the thickness direction of the stretched resin film (retardation film) (specifically, when the thickness of the retardation film is 100%, an area of ±20% from the center in the thickness direction of the retardation film) The cross-section of the retardation film was sampled and observed using a TEM (HT7820, manufactured by Hitachi) using an ultra-thin section method including heavy metal staining (cross-sectional TEM observation), and the size (maximum length) of all domains was 100 nm. It was confirmed that a nanophase-separated structure was formed.

[Example 2]
A retardation film was obtained in the same manner as in Example 1, except that the thickness of the coating layer was changed and heat shrinkage was not performed.

[Example 3]
A retardation film was obtained in the same manner as in Example 1 except that the stretching temperature and heat shrinkage temperature (isothermal to the stretching temperature) were changed.

[Example 4]
A retardation film was obtained in the same manner as in Example 1 except that the stretching ratio, stretching temperature, and heat shrinkage temperature (same temperature as the stretching temperature) were changed.

[Example 5]
A retardation film was prepared in the same manner as in Example 1, except that the thickness of the coating layer was changed, and the coating layer was dried in the following order: 65°C for 360 seconds, 85°C for 60 seconds, and 155°C for 120 seconds. I got it.

[Example 6]
A retardation film was obtained in the same manner as in Example 5 except that the stretching ratio, stretching temperature, and heat shrinkage temperature (same temperature as the stretching temperature) were changed.

[Comparative example 1]
As a cellulose resin, ethyl cellulose ("ETHOCEL standard 100" manufactured by Dow Chemical Company, number average molecular weight Mn = 58,000, weight average molecular weight Mw = 180,000, Mw/Mn = 3.2, total substitution degree DS = 2. 51) Dissolve 100g and 0.1g of a hindered phenol antioxidant (manufactured by BASF Japan, product name "Irganox 245") in a toluene/ethyl acetate = 4/6 (weight ratio) solution to obtain a resin concentration of 16% by weight. A resin solution was prepared. The solution was dripped onto a polyethylene terephthalate film using a coater to obtain a coating layer. The coating layer was dried at 80° C. for 150 seconds, at 120° C. for 150 seconds, and at 150° C. for 150 seconds, and then peeled off from the polyethylene terephthalate film to obtain a resin film. The obtained resin film was preheated at a temperature 10° C. higher than the stretching temperature, and then horizontally uniaxially stretched 3.0 times at 150° C. using a tenter stretching machine to obtain a retardation film.

[Comparative example 2]
As a cellulose resin, ethyl cellulose ("ETHOCEL standard 100" manufactured by Dow Chemical Company, number average molecular weight Mn = 58,000, weight average molecular weight Mw = 180,000, Mw/Mn = 3.2, total substitution degree DS = 2. 51) 90 g of ester resin, 10 g of cinnamate ester resin obtained in Synthesis Example 1, and 0.1 g of hindered phenol antioxidant (manufactured by BASF Japan, product name "Irganox 245") in toluene/acetic acid. It was dissolved in an ethyl=4/6 (weight ratio) solution to obtain a resin solution with a resin concentration of 16% by weight. The solution was dripped onto a polyethylene terephthalate film using a coater to obtain a coating layer. The coating layer was dried at 65° C. for 360 seconds, at 85° C. for 60 seconds, and at 110° C. for 120 seconds, and then peeled off from the polyethylene terephthalate film to obtain a resin film. The obtained resin film was preheated at a temperature 10° C. higher than the stretching temperature, and then horizontally uniaxially stretched 3.0 times at 150° C. using a tenter stretching machine to obtain a retardation film.

[Comparative example 3]
Same as Example 1 except that the coating layer was dried at 65°C for 360 seconds, 85°C for 60 seconds, and 165°C for 120 seconds, the stretching conditions were changed, and no heat shrinkage was performed. A retardation film was obtained.

As shown in Table 2, by stretching a resin film that has high orientation in the thickness direction and exhibits reverse wavelength dispersion characteristics in terms of retardation in the thickness direction, it has high in-plane birefringence and exhibits reverse wavelength dispersion characteristics in the plane. A retardation film can be suitably obtained. Further, such a resin film can be obtained by appropriately adjusting the coating thickness of the resin solution, drying conditions, etc.

The retardation film obtained by the retardation film manufacturing method according to the embodiment of the present invention can be suitably used in image display devices such as liquid crystal display devices and EL display devices, particularly in organic EL display devices.

Claims (9)

The in-plane birefringence Δn(590) at the measurement wavelength of 590 nm exceeds 0.003, and the ratio of the in-plane retardation at the measurement wavelength of 450 nm to the in-plane retardation at the measurement wavelength of 550 nm (Re(450)/Re(550)) A method for producing a retardation film having a retardation value of less than 0.90,
Contains a resin that exhibits positive birefringence and a resin that exhibits negative birefringence, the birefringence ΔP (590) in the thickness direction at a measurement wavelength of 590 nm exceeds 0.0005, and the retardation in the thickness direction at a measurement wavelength of 450 nm is measured. A manufacturing method comprising: producing a resin film having a ratio of retardation in the thickness direction at a wavelength of 550 nm (Rth(450)/Rth(550)) of less than 0.98; and stretching the resin film. The thickness of the resin film before stretching is 50 μm to 200 μm,
The method for producing a retardation film according to claim 1, wherein the thickness of the resin film after stretching is 12.5% to 40% of the thickness before stretching. Producing the resin film comprises:
Coating a resin solution containing the resin exhibiting positive birefringence, the resin exhibiting negative birefringence, and a solvent onto a supporting base material to form a coating layer;
heating the coating layer to evaporate the solvent;
The method for producing a retardation film according to claim 1 or 2, comprising: The method for producing a retardation film according to claim 3, wherein the coating layer is heated within a range of 50° C. to 155° C. to evaporate the solvent. The resin film is a long resin film,
Manufacturing the retardation film according to claim 1 or 2, wherein stretching the resin film includes stretching the elongated resin film in a direction perpendicular to the longitudinal direction while conveying the long resin film in the longitudinal direction. Method. The method for producing a retardation film according to claim 1 or 2, wherein the stretching ratio of the stretching is 8.0 times or less. Rth (450)/Rth (550) before stretching of the resin film is more than 0.60 and less than 0.98, Δn (590) of the retardation film is more than 0.0035, and Re (450) The method for producing a retardation film according to claim 1 or 2, wherein /Re(550) is less than 0.88. The resin exhibiting positive birefringence includes a cellulose resin having a structural unit represented by the following formula (1),
The retardation according to claim 1 or 2, wherein the resin exhibiting negative birefringence includes an ester resin having a structural unit represented by the following formula (2) and a structural unit represented by the following formula (3). Film manufacturing method:

(In formula (1), each of R ₁ to R ₃ represents a hydrogen atom or a substituent having 1 to 12 carbon atoms;)

(In formula (2), R ₄ represents a hydrogen atom or an alkyl group having 1 to 12 carbon atoms; R _5a represents an alkyl group having 1 to 12 carbon atoms, a nitro group, a bromo group, an iodo group, a cyano group, Represents one selected from a chloro group, a sulfonic acid group, a carboxylic acid group, a fluoro group, or a thiol group; R _5b represents a hydrogen atom or an alkyl group having 1 to 12 carbon atoms; R ₆ represents hydrogen Atom, nitro group, bromo group, iodo group, cyano group, chloro group, sulfonic acid group, carboxylic acid group, fluoro group, phenyl group, thiol group, amide group, amino group, hydroxy group, alkoxy having 1 to 12 carbon atoms represents a species selected from a group or an alkyl group having 1 to 12 carbon atoms;)

(In formula (3), R ₇ is a 5-membered heterocyclic residue or a 6-membered heterocyclic residue containing one or more nitrogen atoms or oxygen atoms as a heteroatom (the 5-membered heterocyclic residue and the The 6-membered heterocyclic residue may form a fused ring structure with another cyclic structure). The method for producing a retardation film according to claim 8, wherein the ester resin further has a structural unit represented by the following formula (4):

(In formula (4), each of R ₈ and R ₉ is a hydrogen atom, a linear alkyl group having 1 to 12 carbon atoms, a branched alkyl group having 3 to 12 carbon atoms, or a branched alkyl group having 3 to 6 carbon atoms. (represents one type selected from cyclic alkyl groups).

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