JP2023180140A - Retardation film manufacturing method - Google Patents

Abstract

To provide a retardation film manufacturing method that can improve a stretching orientation of a resin film, and can stretch the resin film to manufacture a retardation film with excellent optical characteristics.SOLUTION: A retardation film manufacturing method according to an embodiment of the present invention includes: a step of dissolving a resin indicating positive birefringence and a resin indicating negative birefringence in a solvent to prepare a resin solution; a step of applying the resin solution onto a support base material to form a coating on the support base material; a step of heating the coating to form a resin film; and a step of stretching the resin film. A Hansen solubility parameter distance between the resin indicating positive birefringence and the solvent is adjusted to 11.15 or less.SELECTED DRAWING: Figure 1

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. (For example, Patent Document 3). Such a retardation film described in Patent Document 3 is produced by stretching a resin film containing a cellulose resin and an ester resin, but the orientation of the resin due to stretching may be insufficient. There remains room for improvement in the optical properties (especially in-plane birefringence) of retardation films.

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

The present invention has been made in order to solve the above-mentioned conventional problems, and its main purpose is to improve the stretching orientation of a resin film, and to create a retardation film with excellent optical properties by stretching the resin film. An object of the present invention is to provide a method for producing a retardation film that can produce a film.

（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）。
［７］１つの実施形態は、上記負の複屈折を示す樹脂が下記式（２）に示す構成単位と、下記式（３）に示す構成単位とを有するエステル系樹脂を含んでいる、上記項目［１］または［２］に記載の位相差フィルムの製造方法である。

（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（前記５員環複素環残基および前記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。）
［８］１つの実施形態は、上記エステル系樹脂が下記式（４）に示す構成単位をさらに有している、上記項目［７］に記載の位相差フィルムの製造方法である。

（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）。 [1] A method for producing a retardation film according to an embodiment of the present invention includes a step of preparing a resin solution by dissolving a resin exhibiting positive birefringence and a resin exhibiting negative birefringence in a solvent; A step of coating the resin film on a supporting substrate to form a coating film on the supporting substrate; a step of heating the coating film to form a resin film; and a step of stretching the resin film. I'm here. The Hansen solubility parameter distance between the resin exhibiting positive birefringence and the solvent is 11.15 or less.
[2] One embodiment is the method for producing a retardation film according to item [1] above, wherein the resin solution satisfies the following formula (I).
{HSP distance ^{* Positive birefringence resin} - HSP distance ^{* Negative birefringence resin} } ² <60...(I)
(In formula (I), HSP distance ^{*positive birefringence resin} indicates the Hansen solubility parameter distance between the resin exhibiting positive birefringence and the solvent. HSP distance ^{*negative birefringence resin} indicates the negative birefringence resin. (Indicates the Hansen solubility parameter distance between the resin and solvent shown.)
[3] One embodiment is the method for producing a retardation film according to item [1] or [2] above, wherein the solvent is a mixed solvent containing a first solvent and a second solvent.
[4] One embodiment is the method for producing a retardation film according to item [3] above, wherein the mixed solvent contains dioxolane.
[5] In one embodiment, Re(450)/Re(550) is 0.8 to 1.0, and Re(650)/Re(550) is 1.0 to 1.2. The method for producing a retardation film according to item [1] or [2] above is capable of producing a retardation film.
[6] One embodiment is the position according to item [1] or [2] above, wherein the resin exhibiting positive birefringence contains a cellulose resin having a structural unit represented by the following formula (1). This is a method for producing a retardation film.

(In formula (1), each of R ₁ to R ₃ represents a hydrogen atom or a substituent having 1 to 12 carbon atoms).
[7] In one embodiment, 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). This is a method for producing a retardation film according to item [1] or [2].

(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 5-membered heterocyclic residue and the (The 6-membered heterocyclic residue may form a fused ring structure with other cyclic structures.)
[8] One embodiment is the method for producing a retardation film according to item [7] above, 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).

According to the embodiments of the present invention, it is possible to realize a method for producing a retardation film that can improve the stretching orientation of a resin film and produce a retardation film with excellent optical properties by stretching the resin film.

It is a graph showing the correlation between the Hansen solubility parameter distance (HSP ^{*positive birefringence resin} ) between a positive birefringent resin and a solvent and Δn/stretching ratio. It is a graph showing the correlation between the Hansen solubility parameter distance (HSP ^{*negative birefringence resin} ) between a negative birefringent resin and a solvent and Δn/stretching ratio. It is a graph showing the correlation between {HSP ^{*Positive birefringence resin} -HSP ^{*Negative birefringence resin} } ² and Δ dispersion.

Hereinafter, typical embodiments of the present invention will be described, but the present invention is not limited to these embodiments.

(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 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).
(3) In-plane birefringence (Δn)
"Δn(λ)" is in-plane birefringence measured with light having a wavelength of λnm at 23°C. For example, "Δn(550)" is the in-plane birefringence measured with light having a wavelength of 550 nm at 23°C. In-plane birefringence (Δn) is determined from the formula: Δn=nx−ny.
(4) 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).
(5) Nz coefficient The Nz coefficient is determined by Nz=Rth/Re.

A. Method for manufacturing a retardation film A method for manufacturing a retardation film according to an embodiment of the present invention includes a resin exhibiting positive birefringence (hereinafter referred to as positive birefringence resin) and a resin exhibiting negative birefringence (hereinafter referred to as positive birefringence resin). negative birefringence resin) in a solvent to prepare a resin solution (solution preparation step); applying the resin solution onto a supporting substrate to form a coating film on the supporting substrate The method includes a step (coating step); a step of heating the coating film to form a resin film (heating step); and a step of stretching the resin film (stretching step). The Hansen solubility parameter distance (hereinafter referred to as HSP distance ^{* positive birefringence resin) between the positive birefringent} resin and the solvent is 11.15 or less, preferably 11.10 or less, more preferably 11.00 or less, It is particularly preferably 10.00 or less, particularly preferably 9.00 or less.
The present inventors discovered that in the production of a retardation film containing a positive birefringent resin and a negative birefringent resin, the HSP distance ^{*positive birefringent resin} greatly affects the stretching orientation of the resin film, The present invention has been completed. According to one embodiment of the present invention, since the HSP ^{*positive birefringence resin} is below the above upper limit, the stretching orientation of the resin film (specifically, in-plane birefringence Δn/stretching ratio) is significantly improved. It is possible to improve the optical properties of a retardation film produced by stretching a resin film. Note that the lower limit of HSP distance ^{* positive birefringence resin} is typically 6.0 or more.

In one embodiment, the resin solution satisfies the following formula (I).
{HSP distance ^{* Positive birefringence resin} - HSP distance ^{* Negative birefringence resin} } ² <60...(I)
(In formula (I), HSP distance ^{*positive birefringence resin} indicates the Hansen solubility parameter distance between the resin exhibiting positive birefringence and the solvent. HSP distance ^{*negative birefringence resin} indicates the negative birefringence resin. (Indicates the Hansen solubility parameter distance between the resin and solvent shown.)
{HSP distance ^{*positive birefringence resin} −HSP distance ^{*negative birefringence resin} } ² is preferably 55 or less, more preferably 50 or less, still more preferably 45 or less, particularly preferably 30 or less.
According to such a configuration, by stretching a resin film containing a positive birefringent resin and a negative birefringent resin, the retardation film has an inverse dispersion property (the retardation value increases depending on the wavelength of the measurement light). wavelength dependence of inverse dispersion) can be fully expressed. {HSP distance ^{*positive birefringence resin} −HSP distance ^{*negative birefringence resin} } The lower limit of ² is typically 10 or more.

HSP distance ^{*positive birefringence resin} can be calculated, for example, using the following formula (II).
Formula (II):
HSP distance ^{* Positive birefringence resin} = [4 (δ _d2 - δ _d1 ) ² + (δ _p2 - δ _p1 ) ² + (δ _h2 - δ _h1 ) ² ] ^0.5
(In formula (II), δ _d1 represents the dispersion force energy between the molecules of the solvent; δ _d2 represents the dispersion force energy between the molecules of the positive birefringent resin; δ _p1 represents the dipole interaction between the molecules of the solvent. δ _p2 represents the intermolecular dipole interaction energy of the positive birefringent resin; δ _h1 represents the hydrogen bond energy between the solvent molecules; δ _h2 represents the intermolecular dipole interaction energy of the positive birefringent resin )

HSP distance ^{*negative birefringence resin} can be calculated, for example, using the following formula (III).
Formula (III):
HSP distance ^{* negative birefringence resin} = [4 (δ _d3 - δ _d1 ) ² + (δ _p3 - δ _p1 ) ² + (δ _h3 - δ _h1 ) ² ] ^0.5
(In formula (III), δ _d3 represents the intermolecular dispersion force energy of the negative birefringent resin; δ _p3 represents the dipole interaction energy between the molecules of the negative birefringent resin; δ _h3 represents the negative It shows the intermolecular hydrogen bond energy of the birefringent resin; δ _d1 , δ _p1 and δ _h1 each show the intermolecular energy of the solvent as in the above formula (II).)
The HSP distance ^{*negative birefringence resin} is, for example, 6.0 or less, preferably 5.5 or less, and, for example, 2.0 or more.

B. Solution Preparation Step In the solution preparation step, a resin exhibiting positive birefringence (positive birefringence resin) and a resin exhibiting negative birefringence (negative birefringence resin) are dissolved in a solvent.
"Exhibiting positive birefringence" means that when a polymer is oriented by stretching or the like, the refractive index in the direction perpendicular 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.

B-1. Resin that exhibits positive birefringence (positive birefringence resin)
The positive birefringent resin 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 some of the hydroxyl groups in cellulose are etherified, and cellulose ether ester, in which at least some of the hydroxyl groups in cellulose are similarly esterified. The positive birefringent resin may be used alone or in combination of two or more.

（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).

(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). When the Mn of the cellulose resin is within the above range, it is possible to improve the mechanical properties and/or moldability of the retardation layer.

Cellulose resins have a relatively low glass transition temperature (Tg), and ester resins have a relatively high Tg. 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.

The proportion of the positive birefringent resin used is typically more than 50% by mass, preferably 60% by mass or more, when the sum of the positive birefringence resin and the negative birefringence resin is 100% by mass. More preferably, it is 70% by mass or more. If the proportion of the positive birefringent resin used is equal to or higher than the above lower limit, a nanophase-separated structure, which will be described later, can be formed from the positive birefringent resin and the negative birefringent resin. Note that the upper limit of the proportion of the positive birefringent resin used is typically 90% by mass or less.

（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（前記５員環複素環残基および前記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。） B-2. Resin that exhibits negative birefringence (negative birefringence resin)
The negative birefringent resin is not limited as long as the effect of the present invention can be obtained, and for example, an ester resin having a structural unit shown in the following formula (2) and a structural unit shown in the following formula (3) can be used. Can be used. The negative birefringence resin may be used alone or in combination of two or more.

(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 5-membered heterocyclic residue and the (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; methyl α-cyano-2-carboxy-3-hydroxycinnamate residue units, α-cyano-2 -α-cyano-carboxy-hydroxycinnamate ester residue units such as ethyl carboxy-3-hydroxycinnamate residue units; methyl 3-methyl-3-(hydroxyphenyl)-prop-2-enoate 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－ヘキシル基などが挙げられる。
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－ブチル基などが挙げられる。
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、シクロヘキシル基などが挙げられる。
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, and a cyclohexyl group.
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, and butyl vinyl ether residues; N-substituted maleimide residues such as N-methyl maleimide residues, N-cyclohexyl maleimide residues, and N-phenyl maleimide residues; 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, the mechanical properties and/or moldability of the retardation layer can be improved.

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.

B-3. Solvent The solvent is not particularly limited as long as the Hansen solubility parameter (HSP) distance with the positive birefringent resin is within the above range. 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, xylene, Aromatic hydrocarbons such as methoxybenzene, mesitylene, and dimethoxybenzene; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone (MIBK), cyclohexanone, cyclopentanone (CPN), 2-pyrrolidone, and N-methyl-2-pyrrolidone Solvent: 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, Alcohol solvents such as 4-pentanediol; Amide solvents such as dimethylformamide and dimethylacetamide; Nitrile solvents such as acetonitrile and butyronitrile; 1,3-dioxolane, cyclopentyl methyl ether (CPME), propylene glycol methyl ether acetate (PGMEA) ), diethyl ether, dibutyl ether, tetrahydrofuran, and other ether solvents; carbon disulfide, ethyl cellosolve, butyl cellosolve, and mixed solvents thereof.

The solubility parameter (SP value) of the solvent is, for example, 6.0 or more, preferably 7.0 or more, and is, for example, 13.0 or less, preferably 12.0 or less. The SP value is, for example, a dissolution test in which the resin is dissolved in an indicator solvent with greatly different polarity (e.g., hexane, methanol, trichlorobenzene, gamma butyrlactone, toluene, etc.) (how much it dissolves in the solvent after 24 hours of standing) Based on the results (confirm visually), the Hansen solubility parameter can be calculated using simulation software such as HSP-iP (manufactured by Pirika.com) that can calculate the Hansen solubility parameter.

Among the solvents, mixed solvents are preferred. The mixed solvent contains a first solvent and a second solvent. The first solvent typically has a lower boiling point than the second solvent. When the solvent is such a mixed solvent, a nanophase-separated structure can be stably formed from the positive birefringent resin and the negative birefringent resin in the heating step.

The boiling point of the first solvent is, for example, 60°C or higher, preferably 70°C or higher, and, for example, 95°C or lower, preferably 85°C or lower. The boiling point of the second solvent is, for example, 70°C or higher, preferably 75°C or higher, more preferably over 95°C, still more preferably 100°C or higher, and, for example, 160°C or lower, preferably 150°C or lower. The boiling point of the mixed solvent is, for example, 60°C or higher, preferably 70°C or higher, and, for example, 130°C or lower, preferably 110°C or lower. When the boiling point of the solvent is within the above range, volatilization of the solvent from the coating film can be suitably controlled in the heating step, and a nanophase-separated structure can be smoothly formed.

The content of the first solvent in the mixed solvent is, for example, 30% by mass or more, preferably 40% by mass or more, more preferably more than 50% by mass, particularly preferably 60% by mass or more, and, for example, 90% by mass or less, Preferably it is 80% by mass or less.
The content of the second solvent in the mixed solvent is, for example, 10% by mass or more, preferably 20% by mass or more, and, for example, 70% by mass or less, preferably 60% by mass or less, more preferably 50% by mass or less, particularly preferably It is 40% by mass or less.

The combination of the first solvent and the second solvent (first solvent/second solvent) is preferably ether solvent/aromatic hydrocarbons, ether solvent/ester solvent, ester solvent/alcohol solvent, or ester. Examples include solvents/ketone solvents, ester solvents/ether solvents, and two types of ester solvents, more preferably ether solvents/aromatic hydrocarbons, and ether solvents/ester solvents.

Among the solvents (ether solvents and ester solvents) suitable as the first solvent, dioxolane and ethyl acetate are preferred.
Among the solvents suitable as the second solvent (aromatic hydrocarbon solvents, ester solvents, alcohol solvents, ketone solvents, ether solvents), toluene, ethyl acetate, butyl acetate, CPME, butanol are preferred. , PGMEA, and MIBK, more preferably toluene, butanol, and PGMEA.

To dissolve the above-mentioned positive birefringence resin and negative birefringence resin in the above-mentioned solvent, typically, after adding the positive birefringence resin and the negative birefringence resin to the solvent and stirring for a predetermined time, , let stand to defoam.
The stirring time is, for example, 5 minutes or more, preferably 10 minutes or more, and is, for example, 3 hours or less, preferably 1 hour or less.
The defoaming time (standing time) is, for example, 30 minutes or more, preferably 1 hour or more, and is, for example, 5 hours or less, preferably 3 hours or less.

As a result, a resin solution in which the positive birefringent resin and the negative birefringent resin are dissolved is prepared. The solid content concentration in the resin solution is, for example, 1% by mass or more, preferably 5% by mass or more, and, for example, 30% by mass or less, preferably 20% by mass or less.

In addition to the resin components described above, additives may be added to the resin solution in any appropriate proportion. Examples of additives include hindered phenolic antioxidants, phosphorus antioxidants, sulfur-based antioxidants, lactone-based antioxidants, amine-based antioxidants, hydroxylamine-based antioxidants, and vitamin E-based antioxidants. 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.

C. Coating Step Next, the resin solution is coated onto the supporting base material to form a coating film.
The coating method is not particularly limited, and any appropriate method can be employed. Examples of coating methods include doctor blade method, bar coater method, slip coater method, reverse gravure coating method, microgravure method, spin coating method, brush coating method, roll coating method, and flexographic coating method. One example is the printing method. The coating method can be appropriately set depending on the composition and type of the resin solution used, the desired characteristics of the retardation film, and the like.

Examples of the supporting base material include polyethylene terephthalate (PET), polyester, polycarbonate, polystyrene, polyethylene, polypropylene, polyvinyl chloride, polyvinylidene chloride, triacetylcellulose, polyvinyl alcohol, polyimide, polyarylate, polysulfone, polyethersulfone, Examples include polymer base materials such as epoxy resin, glass base materials such as glass plates and quartz substrates, metal base materials such as aluminum, stainless steel, and ferrotype, and inorganic base materials such as ceramic substrates. Examples include metal base materials, and more preferably PET base materials.

A coating film is thereby formed. The coating film can have any suitable wet thickness depending on the desired thickness of the retardation film. The wet thickness of the coating film is, for example, 400 μm or more and 1200 μm or less, preferably 600 μm or more and 1000 μm or less.

D. Heating Step Next, the coating film on the supporting base material is heated to prepare a resin film. The heating temperature is, for example, 35° C. or more and 165° C. or less, and the heating time is 1 minute or more and 30 minutes or less. More specifically, such a heating step includes a primary heating step (drying step) of heating at 165° C. or lower, and a secondary heating step (annealing step) of heating at 110° C. or higher.

The drying process may be performed in one stage or in multiple stages. The drying process is preferably carried out in multiple stages. When the drying process is carried out in multiple stages, the heating temperature in the first drying process 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 heating temperature in the first drying process is The time is set to, for example, 1 minute or more and 30 minutes or less, preferably 1 minute or more and 8 minutes or less. Thereafter, each time the number of stages in the drying process increases, the heating temperature is increased, for example, by 10°C to 130°C, preferably by 10°C to 40°C. The heating time of each stage after the second stage is typically shorter than the heating time of the first stage drying step, preferably 20 seconds or more and 20 minutes or less, more preferably 30 seconds or more and 5 minutes or less. . The number of stages in the drying step is preferably 2 or more and 4 or less, more preferably 3 or less. The maximum temperature in the drying step is, for example, 165°C or lower, preferably lower than 130°C, more preferably lower than 120°C, even more preferably 115°C or lower.

Thereafter, if necessary, the coating film heated in the drying step is cooled, for example, to 30° C. or lower, preferably to room temperature (23° C.). Next, in an annealing step, the coating film is heated. The heating temperature in the annealing step is typically higher than the maximum temperature in the drying step. The heating temperature in the annealing step is, for example, 110°C or higher, preferably 120°C or higher, more preferably 130°C or higher, and, for example, 180°C or lower, preferably 165°C or lower, more preferably 150°C or lower, and even more preferably 140°C. It is as follows. The heating time of the annealing step is, for example, 1 minute or more, preferably 5 minutes or more, more preferably 15 minutes or more, and, for example, 60 minutes or less, preferably 45 minutes or less.

As a result, a resin film is formed on the supporting base material. The thickness of the resin film is, for example, 70 μm or more and 200 μm or less. Next, the resin film is peeled off from the supporting base material.

E. Stretching Step Next, the resin film is stretched. Any suitable stretching method may be employed. Various stretching methods such as free-end stretching, fixed-end stretching, free-end shrinkage, and fixed-end shrinkage 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 angle θ (slow axis in the direction of angle θ) with respect to the longitudinal direction of the film can be obtained. Among such stretching methods, fixed end uniaxial stretching is preferably used.

In one embodiment, the resin film is preheated before stretching. The preheating temperature varies in relation to the Tg of the material included in the resin film, and is set by focusing on the Tg of the material having the lowest Tg: (Tg1). (Tg1) is, for example, the Tg of cellulose resin. 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 stretching temperature is also the same as the preheating temperature, 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 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 stretching ratio is, for example, 2.0 times or more, preferably 2.5 times or more, and, for example, 8.0 times or less, preferably 7.5 times or less.

F. Shrinking Step In one embodiment, the method for producing a retardation film further includes a step of heat-shrinking the resin film after the stretching step in the stretching direction (heat-shrinking step).
The heat shrinkage temperature is also set with respect to (Tg1) in the same way as the preheating and stretching temperatures, 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 less. 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.
Through the above steps, a retardation film is manufactured. In addition, the resin film after the stretching process can also be used as a retardation film without implementing the heat shrinking process.

G. Retardation Film A retardation film typically has a nanophase separation structure formed therein.
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 cellulose resin and the ester resin 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). An example of this is TEM observation of a cross section of a retardation film. When a nanophase separation structure is formed in a retardation film, two types of domains with different electron densities can be confirmed in TEM observation of a cross section of the retardation film, and the size (maximum length) of all domains is less than 100 nm. It can be confirmed that More specifically, the vicinity of the center in the thickness direction of the retardation film (an area of ±20% from the center in the thickness direction of the retardation film when the thickness of the retardation film is 100%) is sampled, and heavy metal staining is performed. A cross section of the retardation film is observed using a TEM (for example, HT7820, manufactured by Hitachi) using an ultra-thin section method including (cross-sectional TEM observation). This allows confirmation of the nanophase separation structure.

The retardation film contains a positive birefringent resin (the cellulose resin) and a negative birefringence resin (the ester resin). The wavelength dispersion characteristic of the retardation in the thickness direction of the retardation film can be understood as a combination of the wavelength dispersion characteristics of the retardation in the thickness direction of each of the positive birefringent resin and the negative birefringence resin. 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. .

A retardation film typically exhibits a refractive index characteristic of nx>ny≧nz. "ny=nz" includes not only the case where ny and nz are completely the same, but also the case where ny and nz are substantially the same. A retardation film having a refractive index characteristic of nx>ny=nz is sometimes referred to as a "positive A plate" or the like. A retardation film having a refractive index characteristic of nx>ny>nz is sometimes referred to as a "negative B plate" or the like.

The in-plane birefringence (Δn(550)) of the retardation film is, for example, 0.0015 to 0.01, for example, 0.0017 to 0.008, and for example, 0.002 to 0.007. .
The retardation film typically functions as a λ/4 plate. The Re(550) of the retardation film is, for example, 100 nm to 200 nm, for example 120 nm to 160 nm, and for example 130 nm to 150 nm.
The Nz coefficient of the retardation film is, for example, 0.9 to 3, and is, for example, 0.9 to 2.5, and is, for example, 0.9 to 1.5, and is, for example, 0.9 to 1.3. It is. 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 depending on the wavelength of measurement light with respect to in-plane retardation.
Re(450)/Re(550) of the retardation film is, for example, 0.8 to 1.0, for example, 0.60 to 0.90, and further, for example, 0.70 to 0.88.
Re(650)/Re(550) of the retardation film is, for example, 1.0 to 1.2, for example 1.0 to 1.15, and for example 1.0 to 1.1.
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 or more, preferably 20 μm or more, and, for example, 80 μm or less, preferably 60 μm or less.

The retardation film may be sheet-shaped or may be 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 retardation film can be wound into a roll.

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.

(1) Measurement of thickness Thickness was measured using a linear gauge (manufactured by Ozaki Seisakusho Co., Ltd., product name "D-10S").

(2) Measurement of retardation value The retardation values of the retardation layers used in Examples and Comparative Examples were automatically measured using Axoscan (manufactured by Axometrics). The measurement wavelength was 450 nm, 550 nm, or 650 nm, and the measurement temperature was 23°C.

(3) Calculation of in-plane birefringence Δn/draw ratio (stretch orientation) In-plane birefringence Δn (550) is calculated based on the retardation value measured in (1) above, and in-plane birefringence Δn ( In-plane birefringence Δn/stretching ratio was calculated by dividing 550) by the stretching ratio. The results are shown in Table 2. FIG. 1 shows the correlation between the Hansen solubility parameter distance (HSP distance ^{*positive birefringence resin} ) between the positive birefringence resin and the solvent and the stretching orientation (in-plane birefringence Δn/stretching ratio). FIG. 2 shows the correlation between the Hansen solubility parameter distance (HSP distance ^{*negative birefringence resin} ) between the negative birefringence resin and the solvent and the in-plane birefringence Δn/stretching ratio.

(4) Calculation of Δ dispersion (inverse dispersion) Δ dispersion was calculated using the following formula (A). Δdispersion is defined as an index of how much inverse dispersion is expressed per unit magnification. In other words, it is the absolute value of the slope when the effective magnification is plotted on the horizontal axis and the inverse variance value is plotted on the vertical axis. However, the initial dispersion value of the phase difference is defined as 1. The results are shown in Table 2. The correlation between {(HSP distance ^{*positive birefringence resin} )−(HSP distance ^{*negative birefringence resin} )} ² and Δ dispersion is shown in FIG.
Δdispersion=|1-inverse dispersion value after stretching|/effective magnification...(A)
(In formula (A), the inverse dispersion value after stretching is Re(450)/Re(550); the effective magnification is (stretching ratio-1).

<<Production Example 1; Synthesis of ester resin exhibiting negative birefringence (9-vinylcarbazole/α-cyano-4-hydroxyisobutyl cinnamate/isobutyl acrylate)>>
A glass ampoule with a capacity of 50 mL contains 12.20 g of 9-vinylcarbazole, 7.74 g of isobutyl α-cyano-4-hydroxycinnamate, 4.05 g of isobutyl acrylate, and 2,5-dimethyl-2,5 as a polymerization initiator. 0.453 g of -di(2-ethylhexanoylperoxy)hexane and 36.00 g of methyl ethyl ketone were added, and after repeated nitrogen substitution and depressurization, 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 (mass ratio 80/20) to precipitate. After filtration, the filtrate was It was washed five times with 110 g of methanol/water mixed solvent (mass 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 polymer was 50,000, and the ratio of residue units was 50 mol% of 9-vinylcarbazole residue units and 25 mol% of isobutyl α-cyano-4-hydroxycinnamate residue units. %, and the isobutyl acrylate residue unit was 25 mol%.

[Examples 1 to 8 and Comparative Examples 1 to 5]
Ethyl cellulose (positive birefringence resin, manufactured by Dow Chemical Company, ETHOCEL standard 100, number average molecular weight Mn = 58,000, weight average molecular weight Mw = 180,000, Mw/Mn = 3.2, fully substituted Table 1 and It was dissolved in the solvent shown in Table 2 to obtain a resin solution with a solid content concentration of 16% by mass.
Table 1 shows the composition of the mixed solvent, the boiling point and sp value of each solvent, and the respective energies (intermolecular dispersion force energy δ _d , Intermolecular dipole interaction energy δ _p and intermolecular hydrogen bond energy δ _h ) are shown. Table 2 shows the composition of the mixed solvent, HSP distance ^{* positive birefringence resin} , HSP distance ^{* negative birefringence resin} , and {HSP distance ^{* positive birefringence resin} - HSP distance ^{* negative birefringence resin} } ² shows.
Next, the resin solution was stirred for 30 minutes using a disper mixer, and then left to stand for 2 hours to defoam. The defoamed resin solution was applied onto a polyethylene terephthalate (PET) film (supporting base material, Cosmoshine A4610 manufactured by Toyobo Co., Ltd.) using an applicator so that the wet thickness was approximately 810 μm to form a coating film. Formed.
Next, the coating film was dried in an oven in three stages at 65° C. for 6 minutes, 85° C. for 1 minute, and 110° C. for 2 minutes, and then allowed to stand at room temperature (23° C.) for 60 minutes. Thereafter, the dried coating film was again annealed in an oven at 130° C. for 60 minutes. As a result, a resin film was formed on the PET film.
Then, the resin film was peeled off from the PET film. The resin film after peeling was preheated at 165° C./1 minute, and then fixed-end transverse stretching was performed at the stretching ratio shown in Table 2 at a stretching temperature of 155° C. and a stretching speed of 2 mm/sec. Thereafter, the stretched resin film was shrunk by 2% in the width direction at a shrinkage temperature of 155° C. to obtain a retardation film. The refractive index characteristics of the retardation film showed nx>ny>nz. The retardation film was subjected to the thickness measurement described above. The thickness of the retardation film was 46 μm.

[evaluation]
As is clear from Figures 1 and ² , the Hansen solubility parameter distance (HSP ^* It has a greater effect on the stretch orientation (Δn/stretch ratio) than ^{the negative birefringence resin), and HSP *By setting the positive birefringence resin} to 11.15 or less, the stretch orientation can be significantly improved. Recognize.
As is clear from FIG. 3, it can be seen that when {HSP ^{*Positive birefringence resin} −HSP ^{*Negative birefringence resin} } ² is 60 or less, the inverse dispersion (Δ dispersion) can be improved.

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 (8)

a step of preparing a resin solution by dissolving a resin exhibiting positive birefringence and a resin exhibiting negative birefringence in a solvent;
a step of applying the resin solution onto a supporting base material to form a coating film on the supporting base material;
heating the coating film to form a resin film;
Stretching the resin film,
A method for producing a retardation film, wherein the Hansen solubility parameter distance between the resin exhibiting positive birefringence and the solvent is 11.15 or less. The method for producing a retardation film according to claim 1, wherein the resin solution satisfies the following formula (I):
{HSP distance ^{* Positive birefringence resin} - HSP distance ^{* Negative birefringence resin} } ² <60...(I)
(In formula (I), HSP distance ^{*positive birefringence resin} indicates the Hansen solubility parameter distance between the resin exhibiting positive birefringence and the solvent; HSP distance ^{*negative birefringence resin} exhibiting negative birefringence. The Hansen solubility parameter distance between the resin and solvent shown is shown). The method for producing a retardation film according to claim 1 or 2, wherein the solvent is a mixed solvent containing a first solvent and a second solvent. The method for producing a retardation film according to claim 3, wherein the mixed solvent contains dioxolane. A claim that produces a retardation film in which Re(450)/Re(550) is 0.8 to 1.0 and Re(650)/Re(550) is 1.0 to 1.2. 3. The method for producing a retardation film according to 1 or 2. The method for producing a retardation film according to claim 1 or 2, wherein the resin exhibiting positive birefringence includes a cellulose resin having a structural unit represented by the following formula (1):

(In formula (1), each of R ₁ to R ₃ represents a hydrogen atom or a substituent having 1 to 12 carbon atoms). 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 (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 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 7, 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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