JP2022117110A - Optical film and flexible display device provided with optical film - Google Patents

Abstract

To provide an optical film having excellent UV blocking properties and gas barrier properties, and a flexible display device having the optical film.SOLUTION: The present invention relates to an optical film which contains a polyimide resin having a structural unit derived from an aliphatic diamine, has a light transmittance of 10% or less at 350 nm, and has a photoelastic coefficient of 50×10-12 Pa-1 or less.SELECTED DRAWING: None

Description

TECHNICAL FIELD The present invention relates to an optical film and a flexible display device having the optical film.

Optical films are used in various applications such as display devices such as liquid crystal and organic EL, touch sensors, speakers, and semiconductors. For example, as a touch sensor substrate material, a polyimide film having dimensional stability is known (for example, Patent Documents 1 and 2).

In recent years, the development of flexible display devices has progressed rapidly, and when used for such cutting-edge display applications, in order to protect the display device not only from ultraviolet rays but also from oxygen and water vapor, There is a demand for optical films that are excellent in both gas barrier properties.

JP-A-2005-336243 International Publication No. 2019/156717 Pamphlet

However, according to the studies of the present inventors, the aromatic polyimide film described in Patent Document 1 does not necessarily have high gas barrier properties. In addition, the aliphatic polyimide film described in Patent Document 2 tends to have low UV-cutting properties and high water absorption, and it is difficult to achieve both high UV-cutting properties and gas barrier properties.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an optical film excellent in ultraviolet shielding properties and gas barrier properties, and a flexible display device comprising the optical film.

As a result of intensive studies to solve the above problems, the present inventors have found that the optical film contains a polyimide resin having a structural unit derived from an aliphatic diamine, and has a light transmittance at 350 nm of 10% or less and a photoelasticity. The inventors have found that the above problem can be solved by reducing the coefficient to 50×10 ⁻¹² Pa ⁻¹ or less, and have completed the present invention. That is, the present invention includes the following preferred aspects.

［式（１）中、Ｘは２価の有機基を表し、Ｙは４価の有機基を表し、＊は結合手を表す］
で表される構成単位を有し、式（１）で表される構成単位は、Ｘとして、２価の脂肪族基を含む、〔１〕～〔７〕のいずれかに記載の光学フィルム。
〔９〕前記式（１）で表される構成単位は、Ｙとして、式（２）：

［式（２）中、Ｒ^２～Ｒ^７は、互いに独立に、水素原子、炭素数１～６のアルキル基、炭素数１～６のアルコキシ基又は炭素数６～１２のアリール基を表し、Ｒ^２～Ｒ^７に含まれる水素原子は、互いに独立に、ハロゲン原子で置換されていてもよく、Ｖは、単結合、－Ｏ－、－ＣＨ_２－、－ＣＨ_２－ＣＨ_２－、－ＣＨ（ＣＨ_３）－、－Ｃ（ＣＨ_３）_２－、－Ｃ（ＣＦ_３）_２－、－ＳＯ_２－、－Ｓ－、－ＣＯ－又は－Ｎ（Ｒ^８）－を表し、Ｒ^８は、水素原子、又はハロゲン原子で置換されていてもよい炭素数１～１２の一価の炭化水素基を表し、＊は結合手を表す］
で表される構造を含む、〔８〕に記載の光学フィルム。
〔１０〕前記ポリイミド系樹脂はフッ素原子を含有する、〔８〕又は〔９〕に記載の光学フィルム。
〔１１〕〔１〕～〔１０〕のいずれかに記載の光学フィルムを備える、フレキシブル表示装置。
〔１２〕更に偏光板を備える、〔１１〕に記載のフレキシブル表示装置。
〔１３〕更にタッチセンサを備える、〔１１〕又は〔１２〕に記載のフレキシブル表示装置。 [1] An optical film comprising a polyimide resin having a structural unit derived from an aliphatic diamine, having a light transmittance at 350 nm of 10% or less and a photoelastic coefficient of 50×10 ⁻¹² Pa ⁻¹ or less.
[2] The optical film of [1], which has a humidity expansion coefficient of more than 10 ppm.
[3] The optical film of [1] or [2], which has a water absorption rate of 2.5% or less at 60°C.
[4] The optical film according to any one of [1] to [3], wherein the solvent content is 7.0% by mass or less based on the mass of the optical film.
[5] The optical film according to any one of [1] to [4], which has a light transmittance of 90% or more at 500 nm.
[6] The optical film according to any one of [1] to [5], which contains a filler.
[7] The optical film according to any one of [1] to [6], which has a thickness of 10 μm or more and 100 μm or less.
[8] The polyimide resin has the formula (1):

[In formula (1), X represents a divalent organic group, Y represents a tetravalent organic group, and * represents a bond]
The optical film according to any one of [1] to [7], wherein the structural unit represented by formula (1) contains a divalent aliphatic group as X.
[9] The structural unit represented by the formula (1) is represented by the formula (2) as Y:

[In formula (2), R ² to R ⁷ each independently represent a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms or an aryl group having 6 to 12 carbon atoms, The hydrogen atoms contained in R ² to R ⁷ may be independently substituted with halogen atoms, and V is a single bond, —O—, —CH ₂ —, —CH ₂ —CH ₂ —, — CH(CH ₃ )—, —C(CH ₃ ) ₂ —, —C(CF ₃ ) ₂ —, —SO ₂ —, —S—, —CO— or —N(R ⁸ )—, and R ⁸ represents a hydrogen atom or a monovalent hydrocarbon group having 1 to 12 carbon atoms which may be substituted with a halogen atom, * represents a bond]
The optical film of [8], comprising a structure represented by:
[10] The optical film of [8] or [9], wherein the polyimide resin contains a fluorine atom.
[11] A flexible display device comprising the optical film according to any one of [1] to [10].
[12] The flexible display device according to [11], further comprising a polarizing plate.
[13] The flexible display device according to [11] or [12], further comprising a touch sensor.

ADVANTAGE OF THE INVENTION According to this invention, the flexible display apparatus provided with the optical film excellent in ultraviolet-ray cut property and gas-barrier property, and this optical film can be provided.

The optical film of the present invention contains a polyimide resin having structural units derived from an aliphatic diamine, has a light transmittance at 350 nm of 10% or less, and a photoelastic coefficient of 50×10 ⁻¹² Pa ⁻¹ or less.

Surprisingly, the present inventors have found that an optical film containing a polyimide resin having a structural unit derived from an aliphatic diamine exhibits excellent gas barrier properties when the photoelastic coefficient is 50×10 ⁻¹² Pa ⁻¹ or less. found that can be achieved. In this specification, unless otherwise specified, "excellent gas barrier properties" or "high gas barrier properties" means that both the water vapor permeability and the oxygen permeability are low, and the water vapor permeability is preferably 100 g/m ² . /24 hours/0.1 mm or less, indicating that the oxygen permeability satisfies 1000 cc (NTP)/m ² /24 hours/0.1 mm/atm.

[Polyimide resin]
A polyimide resin means a polymer containing a repeating structural unit (also referred to as a structural unit) containing an imide group, and may further contain a repeating structural unit containing an amide group.

In the present invention, the polyimide resin contains structural units derived from an aliphatic diamine. An aliphatic diamine represents a diamine having an aliphatic group, and may contain other substituents in part of its structure, but does not have an aromatic ring. When the polyimide-based resin contains structural units derived from an aliphatic diamine, the photoelastic coefficient of the optical film tends to decrease, and as a result, the gas barrier properties of the optical film tend to increase. Aliphatic diamines include, for example, acyclic aliphatic diamines and cycloaliphatic diamines, and acyclic aliphatic diamines are preferred because they tend to increase the gas barrier properties of the optical film. Acyclic aliphatic diamines include, for example, 1,2-diaminoethane, 1,3-diaminopropane, 1,4-diaminobutane, 1,5-diaminopentane, 1,6-diaminohexane, 1,2 -Diaminopropane, 1,2-diaminobutane, 1,3-diaminobutane, 2-methyl-1,2-diaminopropane, 2-methyl-1,3-diaminopropane, and other linear chain having 2 to 10 carbon atoms or branched diaminoalkanes. Cycloaliphatic diamines include, for example, 1,3-bis(aminomethyl)cyclohexane, 1,4-bis(aminomethyl)cyclohexane, norbornanediamine and 4,4'-diaminodicyclohexylmethane. These can be used alone or in combination of two or more. Among these, 1,2-diaminoethane, 1,3-diaminopropane, 1,4-diaminobutane (sometimes referred to as 1,4-DAB), 1, 1, and 1,2-diaminoethane, 1,3-diaminopropane, 1,4-diaminobutane (sometimes referred to as 1,4-DAB), 1, 5-diaminopentane, 1,6-diaminohexane, 1,2-diaminopropane, 1,2-diaminobutane, 1,3-diaminobutane, 2-methyl-1,2-diaminopropane, 2-methyl-1, Diaminoalkanes having 2 to 10 carbon atoms such as 3-diaminopropane are preferred, diaminoalkanes having 2 to 6 carbon atoms are more preferred, and 1,4-diaminobutane is even more preferred.

The polyimide-based resin may contain a structural unit derived from an aromatic diamine in addition to a structural unit derived from an aliphatic diamine. An aromatic diamine represents a diamine having an aromatic ring, and may contain an aliphatic group or other substituents in part of its structure. This aromatic ring may be a single ring or a condensed ring, and examples include, but are not limited to, benzene ring, naphthalene ring, anthracene ring, and fluorene ring.

Examples of aromatic diamines include p-phenylenediamine, m-phenylenediamine, 2,4-toluenediamine, m-xylylenediamine, p-xylylenediamine, 1,5-diaminonaphthalene and 2,6-diaminonaphthalene. of, an aromatic diamine having one aromatic ring, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylpropane, 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 3,3'- Diaminodiphenyl ether, 4,4'-diaminodiphenylsulfone, 3,4'-diaminodiphenylsulfone, 3,3'-diaminodiphenylsulfone, 1,4-bis(4-aminophenoxy)benzene, 1,3-bis(4 -aminophenoxy)benzene, bis[4-(4-aminophenoxy)phenyl]sulfone, bis[4-(3-aminophenoxy)phenyl]sulfone, 2,2-bis[4-(4-aminophenoxy)phenyl] Propane, 2,2-bis[4-(3-aminophenoxy)phenyl]propane, 2,2′-dimethylbenzidine, 2,2′-bis(trifluoromethyl)-4,4′-diaminodiphenyl (TFMB) 4,4′-(Hexafluoropropylidene)dianiline, 4,4′-bis(4-aminophenoxy)biphenyl, 9,9-bis(4-aminophenyl)fluorene, 9,9-bis (4-amino-3-methylphenyl) fluorene, 9,9-bis(4-amino-3-chlorophenyl) fluorene, 9,9-bis(4-amino-3-fluorophenyl) fluorene, etc., aromatic rings Aromatic diamines having two or more are mentioned. These can be used singly or in combination of two or more.

The polyimide resin can further contain structural units derived from a tetracarboxylic acid compound. When a structural unit derived from a tetracarboxylic acid compound is contained, solvent resistance, heat resistance, optical properties and tensile strength are likely to be improved. Examples of tetracarboxylic acid compounds include aromatic tetracarboxylic acid compounds such as aromatic tetracarboxylic dianhydride; and aliphatic tetracarboxylic acid compounds such as aliphatic tetracarboxylic dianhydride. A tetracarboxylic acid compound may be used independently and may be used in combination of 2 or more type. The tetracarboxylic acid compound may be a dianhydride or a tetracarboxylic acid compound analog such as an acid chloride compound.

Specific examples of aromatic tetracarboxylic dianhydrides include non-condensed polycyclic aromatic tetracarboxylic dianhydrides, monocyclic aromatic tetracarboxylic dianhydrides and condensed polycyclic aromatic tetracarboxylic dianhydrides. Carboxylic acid dianhydrides are mentioned. Non-fused polycyclic aromatic tetracarboxylic dianhydrides include, for example, 4,4′-oxydiphthalic dianhydride, 3,3′,4,4′-benzophenonetetracarboxylic dianhydride, 2,2 ',3,3'-benzophenonetetracarboxylic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride (sometimes referred to as BPDA), 2,2',3,3 '-biphenyltetracarboxylic dianhydride, 3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride, 2,2-bis(3,4-dicarboxyphenyl)propane dianhydride, 2, 2-bis(2,3-dicarboxyphenyl)propane dianhydride, 2,2-bis(3,4-dicarboxyphenoxyphenyl)propane dianhydride, 4,4'-(hexafluoroisopropylidene)diphthalic acid Dianhydride (sometimes referred to as 6FDA), 1,2-bis(2,3-dicarboxyphenyl)ethane dianhydride, 1,1-bis(2,3-dicarboxyphenyl)ethane dianhydride , 1,2-bis(3,4-dicarboxyphenyl)ethane dianhydride, 1,1-bis(3,4-dicarboxyphenyl)ethane dianhydride, bis(3,4-dicarboxyphenyl)methane dianhydride, bis(2,3-dicarboxyphenyl)methane dianhydride, 4,4'-(p-phenylenedioxy)diphthalic dianhydride, 4,4'-(m-phenylenedioxy)diphthalic An acid dianhydride is mentioned. Further, the monocyclic aromatic tetracarboxylic dianhydrides include, for example, 1,2,4,5-benzenetetracarboxylic dianhydrides, and condensed polycyclic aromatic tetracarboxylic dianhydrides. Examples include 2,3,6,7-naphthalenetetracarboxylic dianhydride. These can be used singly or in combination of two or more.

Aliphatic tetracarboxylic dianhydrides include cyclic or acyclic aliphatic tetracarboxylic dianhydrides. The cyclic aliphatic tetracarboxylic dianhydride is a tetracarboxylic dianhydride having an alicyclic hydrocarbon structure, and specific examples thereof include 1,2,4,5-cyclohexanetetracarboxylic dianhydride. 1,2,3,4-cyclobutanetetracarboxylic dianhydride, cycloalkanetetracarboxylic dianhydride such as 1,2,3,4-cyclopentanetetracarboxylic dianhydride, bicyclo[2.2 .2] oct-7-ene-2,3,5,6-tetracarboxylic dianhydride, dicyclohexyl-3,3′,4,4′-tetracarboxylic dianhydride and positional isomers thereof be done. These can be used alone or in combination of two or more. Specific examples of the acyclic aliphatic tetracarboxylic dianhydride include 1,2,3,4-butanetetracarboxylic dianhydride and 1,2,3,4-pentanetetracarboxylic dianhydride. and these can be used alone or in combination of two or more. A cyclic aliphatic tetracarboxylic dianhydride and an acyclic aliphatic tetracarboxylic dianhydride may also be used in combination.

Among the tetracarboxylic dianhydrides, 4,4'-oxydiphthalic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 3,3′,4,4′-biphenyltetracarboxylic dianhydride, 2,2′,3,3′-biphenyltetracarboxylic dianhydride, 3,3′,4,4′-diphenylsulfonetetracarboxylic acid acid dianhydride, 2,2-bis(3,4-dicarboxyphenyl)propane dianhydride, 4,4′-(hexafluoroisopropylidene)diphthalic dianhydride, and mixtures thereof are preferred; 4'-(Hexafluoroisopropylidene)diphthalic dianhydride (6FDA) is more preferred.

In one embodiment of the present invention, the ratio of structural units derived from an aliphatic diamine is preferably 30 mol% or more, more preferably 50 mol% or more, relative to the total molar amount of all structural units constituting the polyimide resin. , more preferably 70 mol % or more, particularly preferably 90 mol % or more, and preferably 100 mol % or less. When the ratio of the structural unit derived from the aliphatic diamine is within the above range, the optical film tends to have high gas barrier properties. The ratio of the structural units can be measured using, for example, ¹ H-NMR, or can be calculated from the charging ratio of raw materials.

The polyimide resin, in addition to the structural units derived from the tetracarboxylic acid compound, other structural units derived from tetracarboxylic acid and structural units derived from tricarboxylic acid, as long as the various physical properties of the optical film are not impaired. It may further contain structural units derived from their anhydrides and derivatives.

Other tetracarboxylic acids include water adducts of the above tetracarboxylic acid compound anhydrides.

Examples of tricarboxylic acid compounds include aromatic tricarboxylic acids, aliphatic tricarboxylic acids, their analogous acid chloride compounds, acid anhydrides, and the like, and two or more of them may be used in combination. Specific examples include anhydride of 1,2,4-benzenetricarboxylic acid; 2,3,6-naphthalenetricarboxylic acid-2,3-anhydride; a single bond between phthalic anhydride and benzoic acid; , —CH ₂ —, —C(CH ₃ ) ₂ —, —C(CF ₃ ) ₂ —, —SO ₂ —, or compounds linked by a phenylene group.

［式（１）中、Ｘは２価の有機基を表し、Ｙは４価の有機基を表し、＊は結合手を表す］
で表される構成単位を有し、式（１）で表される構成単位は、Ｘとして、２価の脂肪族基を含むことが好ましい。このようなポリイミド系樹脂を含むと、光学フィルムのガスバリア性が高いものとなりやすい。 In the present invention, the polyimide resin has the formula (1):

[In formula (1), X represents a divalent organic group, Y represents a tetravalent organic group, and * represents a bond]
In the structural unit represented by formula (1), X preferably contains a divalent aliphatic group. When such a polyimide resin is included, the optical film tends to have high gas barrier properties.

Each X in formula (1) independently represents a divalent organic group, preferably a divalent organic group having 2 to 40 carbon atoms. Examples of divalent organic groups include divalent aromatic groups and divalent aliphatic groups. In this specification, a divalent aromatic group is a divalent organic group having an aromatic group, and may contain an aliphatic group or other substituents in part of its structure. A divalent aliphatic group is a divalent organic group having an aliphatic group, and may contain other substituents in part of its structure, but does not contain an aromatic group.

X in formula (1) includes a divalent aliphatic group, and examples of the divalent aliphatic group include a divalent acyclic aliphatic group and a divalent cycloaliphatic group. Among these, a divalent acyclic aliphatic group is preferable from the viewpoints of less stacking between molecules, a dense structure, and easy reduction of the photoelastic coefficient of the optical film.

In one embodiment of the present invention, the divalent acyclic aliphatic group for X in formula (1) includes, for example, ethylene group, trimethylene group, tetramethylene group, pentamethylene group, hexamethylene group and propylene group. , 1,2-butanediyl group, 1,3-butanediyl group, 2-methyl-1,2-propanediyl group, 2-methyl-1,3-propanediyl group, and other linear or branched alkylene groups are mentioned. A hydrogen atom in the divalent acyclic aliphatic group may be substituted with a halogen atom, and a carbon atom may be substituted with a heteroatom (eg, oxygen atom, nitrogen atom, etc.). The number of carbon atoms in the linear or branched alkylene group is preferably 2 or more, more preferably 3 or more, still more preferably 4 or more, and preferably 10 or less, from the viewpoint of easily increasing the gas barrier properties of the optical film. It is preferably 8 or less, more preferably 6 or less. Among the divalent acyclic aliphatic groups, alkylene groups having 2 to 6 carbon atoms such as ethylene group, trimethylene group, tetramethylene group, pentamethylene group and hexamethylene group are used from the viewpoint of easily increasing the gas barrier properties of the optical film. groups are preferred, and tetramethylene groups are more preferred.

In one embodiment of the present invention, the divalent aromatic group or divalent cycloaliphatic group for X in formula (1) includes formula (10), formula (11), formula (12), formula (13), a group represented by formula (14), formula (15), formula (16), formula (17) and formula (18); a group represented by those formulas (10) to (18) groups in which hydrogen atoms therein are substituted with methyl groups, fluoro groups, chloro groups or trifluoromethyl groups; and chain hydrocarbon groups having 6 or less carbon atoms.

In formulas (10) to (18),
* represents a bond,
V ¹ , V ² and V ³ are each independently a single bond, —O—, —S—, —CH ₂ —, —CH ₂ —CH ₂ —, —CH(CH ₃ )—, —C(CH ₃ ) represents _2- , -C(CF ₃ ) ₂ -, -SO ₂ -, -CO- or -N(Q)-; Here, Q represents a monovalent hydrocarbon group having 1 to 12 carbon atoms which may be substituted with a halogen atom. The monovalent hydrocarbon group having 1 to 12 carbon atoms which may be substituted with a halogen atom includes, for example, methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, sec-butyl group, tert -butyl group, n-pentyl group, 2-methyl-butyl group, 3-methylbutyl group, 2-ethyl-propyl group, n-hexyl group, n-heptyl group, n-octyl group, tert-octyl group, n- nonyl group, n-decyl group and the like. Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom and an iodine atom.
One example is V ¹ and V ³ are a single bond, -O- or -S- and V ² is -CH ₂ -, -C(CH ₃ ) ₂ -, -C(CF ₃ ) ₂ - or -SO ₂ -. The bonding positions of V ¹ and V ² to each ring and the bonding positions of V ² and V ³ to each ring independently of each other are preferably meta-position or para-position, more preferably para-position. rank. The hydrogen atoms on the rings in formulas (10) to (18) are substituted with an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, or an aryl group having 6 to 12 carbon atoms. good too. Examples of alkyl groups having 1 to 6 carbon atoms include methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, sec-butyl group, tert-butyl group, n-pentyl group, 2-methyl- butyl group, 3-methylbutyl group, 2-ethyl-propyl group, n-hexyl group and the like. Examples of alkoxy groups having 1 to 6 carbon atoms include methoxy, ethoxy, propyloxy, isopropyloxy, butoxy, isobutoxy, tert-butoxy, pentyloxy, hexyloxy and cyclohexyloxy groups. mentioned. Examples of the aryl group having 6 to 12 carbon atoms include phenyl group, tolyl group, xylyl group, naphthyl group and biphenyl group. These divalent cycloaliphatic groups or divalent aromatic groups can be used alone or in combination of two or more.

In the present invention, the polyimide resin may contain multiple types of X, and the multiple types of X may be the same or different. For example, X in formula (1) may include a divalent acyclic aliphatic group, a divalent aromatic group and/or a divalent cycloaliphatic group.

In one embodiment of the present invention, the ratio of structural units in which X in formula (1) is a divalent aliphatic group, preferably a divalent acyclic aliphatic group, is represented by formula (1) It is preferably 30 mol% or more, more preferably 50 mol% or more, still more preferably 70 mol% or more, particularly preferably 90 mol% or more, and preferably 100 mol% or less based on the total molar amount of the structural units. be. When the ratio of structural units in which X in formula (1) is a divalent aliphatic group, preferably a divalent acyclic aliphatic group, is within the above range, the gas barrier properties of the optical film are likely to be enhanced. The ratio of the structural units can be measured using, for example, ¹ H-NMR, or can be calculated from the charging ratio of raw materials.

In formula (1), each Y independently represents a tetravalent organic group, preferably a tetravalent organic group having 4 to 40 carbon atoms, more preferably a tetravalent organic group having 4 to 40 carbon atoms and having a cyclic structure. represents a valent organic group. Cyclic structures include alicyclic, aromatic and heterocyclic structures. The organic group is an organic group in which a hydrogen atom may be substituted with a hydrocarbon group or a fluorine-substituted hydrocarbon group. The number of carbon atoms is preferably 1-8. The polyimide-based resin of the present invention may contain multiple types of Y, and the multiple types of Y may be the same or different. Y is represented by the following formula (20), formula (21), formula (22), formula (23), formula (24), formula (25), formula (26), formula (27), formula (28) and a group represented by the formula (29); a group in which the hydrogen atoms in the groups represented by the formulas (20) to (29) are substituted with a methyl group, a fluoro group, a chloro group or a trifluoromethyl group and a tetravalent chain hydrocarbon group having 6 or less carbon atoms.

In formulas (20) to (29),
* represents a bond,
W ¹ is a single bond, —O—, —CH ₂ —, —CH ₂ —CH ₂ —, —CH(CH ₃ )—, —C(CH ₃ ) ₂ —, —C(CF ₃ ) ₂ —, -Ar-, -SO ₂ -, -CO-, -O-Ar-O-, -Ar-O-Ar-, -Ar-CH ₂ -Ar-, -Ar-C(CH ₃ ) ₂ -Ar- or -Ar-SO ₂ -Ar-. Ar represents an arylene group having 6 to 20 carbon atoms in which a hydrogen atom may be substituted with a fluorine atom, and specific examples thereof include a phenylene group.

Among the groups represented by formulas (20) to (29), the groups represented by formula (26), (28), or (29) are preferable because they tend to increase the gas barrier properties of the optical film. A group represented by formula (26) is more preferred. In addition, since W ¹ tends to enhance the gas barrier properties of the optical film, W 1 is each independently a single bond, —O—, —CH ₂ —, —CH ₂ —CH ₂ —, —CH(CH ₃ )—, — preferably C(CH ₃ ) ₂ - or -C(CF ₃ ) ₂ -, a single bond, -O-, -CH ₂ -, -CH(CH ₃ )-, -C(CH ₃ ) ₂ - or -C(CF ₃ ) ₂ -, more preferably a single bond, -C(CH ₃ ) ₂ - or -C(CF ₃ ) ₂ -.

［式（２）中、Ｒ^２～Ｒ^７は、互いに独立に、水素原子、炭素数１～６のアルキル基、炭素数１～６のアルコキシ基又は炭素数６～１２のアリール基を表し、Ｒ^２～Ｒ^７に含まれる水素原子は、互いに独立に、ハロゲン原子で置換されていてもよく、Ｖは、単結合、－Ｏ－、－ＣＨ_２－、－ＣＨ_２－ＣＨ_２－、－ＣＨ（ＣＨ_３）－、－Ｃ（ＣＨ_３）_２－、－Ｃ（ＣＦ_３）_２－、－ＳＯ_２－、－Ｓ－、－ＣＯ－又は－Ｎ（Ｒ^８）－を表し、Ｒ^８は、水素原子、又はハロゲン原子で置換されていてもよい炭素数１～１２の一価の炭化水素基を表し、＊は結合手を表す］
で表される構造を含む。このような実施態様であると、光学フィルムのガスバリア性を高めやすい。なお、式（１）で表される構成単位は、Ｙとして、式（２）で表される構造を１種又は複数種含んでいてもよい。 In a preferred embodiment of the present invention, the structural unit represented by formula (1) is represented by Y as represented by formula (2):

[In formula (2), R ² to R ⁷ each independently represent a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms or an aryl group having 6 to 12 carbon atoms, The hydrogen atoms contained in R ² to R ⁷ may be independently substituted with halogen atoms, and V is a single bond, —O—, —CH ₂ —, —CH ₂ —CH ₂ —, — CH(CH ₃ )—, —C(CH ₃ ) ₂ —, —C(CF ₃ ) ₂ —, —SO ₂ —, —S—, —CO— or —N(R ⁸ )—, and R ⁸ represents a hydrogen atom or a monovalent hydrocarbon group having 1 to 12 carbon atoms which may be substituted with a halogen atom, * represents a bond]
Contains the structure represented by In such an embodiment, the gas barrier properties of the optical film are likely to be enhanced. The structural unit represented by formula (1) may contain, as Y, one or a plurality of structures represented by formula (2).

In formula (2), R ² , R ³ , R ⁴ , R ⁵ , R ⁶ and R ⁷ are each independently a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, or It represents an aryl group having 6 to 12 carbon atoms. The alkyl group having 1 to 6 carbon atoms, the alkoxy group having 1 to 6 carbon atoms, and the aryl group having 6 to 12 carbon atoms are respectively the alkyl group having 1 to 6 carbon atoms and the alkoxy group having 1 to 6 carbon atoms as exemplified above. and aryl groups having 6 to 12 carbon atoms. R ² to R ⁷ each independently represent preferably a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, more preferably a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, wherein R ² to Hydrogen atoms contained in ^R7 may be independently substituted with halogen atoms. Halogen atoms include fluorine, chlorine, bromine and iodine atoms. V is a single bond, -O-, -CH ₂ -, -CH ₂ -CH ₂ -, -CH(CH ₃ )-, -C(CH ₃ ) ₂ -, -C(CF ₃ ) ₂ -, - represents SO ₂ -, -S-, -CO- or -N(R ⁸ )-, where R ⁸ is a hydrogen atom or a monovalent hydrocarbon having 1 to 12 carbon atoms which may be substituted with a halogen atom; represents a group. As the monovalent hydrocarbon group having 1 to 12 carbon atoms which may be substituted with a halogen atom, the monovalent hydrocarbon group having 1 to 12 carbon atoms which may be substituted with a halogen atom is exemplified above. things are mentioned. Among these, V is a single bond, —O—, —CH ₂ —, —CH(CH ₃ )—, —C(CH ₃ ) ₂ — or —C( CF ₃ ) ₂ — is preferred, and a single bond, —C(CH ₃ ) ₂ — or —C(CF ₃ ) ₂ — is more preferred, and a single bond or —C(CF ₃ ) ₂ — It is even more preferable to have

［式（２’）中、＊は結合手を表す］
で表される。このような実施態様であると、光学フィルムのガスバリア性をより高めやすい。また、フッ素元素を含有する骨格により樹脂の溶媒への溶解性を向上し、ワニスの粘度を低く抑制することができ、光学フィルムの加工を容易にすることができる。 In a preferred embodiment of the present invention, formula (2) is represented by formula (2'):

[In formula (2′), * represents a bond]
is represented by In such an embodiment, the gas barrier properties of the optical film can be more easily improved. In addition, the fluorine element-containing skeleton improves the solubility of the resin in a solvent, suppresses the viscosity of the varnish, and facilitates the processing of the optical film.

In one embodiment of the present invention, when Y in formula (1) contains a structure represented by formula (2), Y in formula (1) is the proportion of structural units represented by formula (2) is preferably 30 mol% or more, more preferably 50 mol% or more, still more preferably 70 mol% or more, and particularly preferably 90 mol% or more, based on the total molar amount of the structural units represented by formula (1). and preferably 100 mol % or less. When the ratio of the structural unit represented by formula (2) for Y in formula (1) is within the above range, the gas barrier properties of the optical film are likely to be enhanced. The proportion of structural units in which Y in formula (1) is represented by formula (2) can be measured, for example, using ¹ H-NMR, or can be calculated from the charging ratio of raw materials.

In the present invention, the polyimide resin contains a structural unit represented by formula (30) and/or a structural unit represented by formula (31) in addition to the structural unit represented by formula (1). good too.

In formula (30), Y ¹ is a tetravalent organic group, preferably an organic group in which a hydrogen atom in the organic group may be substituted with a hydrocarbon group or a fluorine-substituted hydrocarbon group. Y ¹ is represented by formula (20), formula (21), formula (22), formula (23), formula (24), formula (25), formula (26), formula (27), formula (28) and a group represented by the formula (29), a group in which hydrogen atoms in the groups represented by the formulas (20) to (29) are substituted with a methyl group, a fluoro group, a chloro group or a trifluoromethyl group; and tetravalent chain hydrocarbon groups having 6 or less carbon atoms. In one embodiment of the present invention, the polyimide resin may contain multiple types of Y ¹ , and the multiple types of Y ¹ may be the same or different.

In formula (31), Y ² is a trivalent organic group, preferably an organic group in which a hydrogen atom in the organic group may be substituted with a hydrocarbon group or a fluorine-substituted hydrocarbon group. Y ² is represented by the above formula (20), formula (21), formula (22), formula (23), formula (24), formula (25), formula (26), formula (27), formula (28) ), a group in which one of the bonds of the group represented by formula (29) is replaced with a hydrogen atom, and a trivalent chain hydrocarbon group having 6 or less carbon atoms. In one embodiment of the present invention, the polyimide-based resin may contain multiple types of Y ² , and the multiple types of Y ² may be the same or different.

In formulas (30) and (31), X ¹ and X ² independently represent a divalent organic group, preferably a divalent organic group having 2 to 40 carbon atoms. Examples of the divalent organic group include a divalent aromatic group and a divalent aliphatic group. Examples of the divalent aliphatic group include a divalent acyclic aliphatic group and a divalent Cycloaliphatic groups are included. As the divalent cycloaliphatic group or divalent aromatic group for X ¹ and X ² , the above formula (10), formula (11), formula (12), formula (13), and formula (14) , groups represented by formula (15), formula (16), formula (17) and formula (18); hydrogen atoms in the groups represented by formulas (10) to (18) are methyl groups, a group substituted with a fluoro group, a chloro group or a trifluoromethyl group; and a chain hydrocarbon group having 6 or less carbon atoms. Examples of divalent acyclic aliphatic groups include ethylene, trimethylene, tetramethylene, pentamethylene, hexamethylene, propylene, 1,2-butanediyl, 1,3-butanediyl, 2 -Methyl-1,2-propanediyl group, 2-methyl-1,3-propanediyl group, and the like linear or branched alkylene groups having 2 to 10 carbon atoms.

In one embodiment of the present invention, the polyimide resin is a structural unit represented by the formula (1), and optionally a structural unit represented by the formula (30) and a structural unit represented by the formula (31) It consists of at least one selected structural unit. Further, since the gas barrier property of the optical film is easily improved, the ratio of the structural units represented by the formula (1) in the polyimide resin is the total structural units contained in the polyimide resin, for example, the ratio represented by the formula (1). and optionally at least one structural unit selected from structural units represented by formula (30) and structural units represented by formula (31), preferably 80 mol % or more, more preferably 90 mol % or more, and still more preferably 95 mol % or more. In addition, in polyimide resin, the upper limit of the ratio of the structural unit represented by Formula (1) is 100 mol%. The ratio can be measured, for example, using ¹ H-NMR, or can be calculated from the charging ratio of raw materials. Further, the polyimide-based resin in the present invention is preferably a polyimide resin because it easily enhances the gas barrier properties of the optical film.

In a preferred embodiment of the present invention, the polyimide resin may contain a halogen atom, preferably a fluorine atom, which can be introduced by, for example, the halogen-containing substituent group described above. When the polyimide resin contains a halogen atom, preferably a fluorine atom, the gas barrier property of the optical film tends to be enhanced. Preferred fluorine-containing substituents for allowing the polyimide resin to contain fluorine atoms include, for example, a fluoro group and a trifluoromethyl group.

The content of halogen atoms in the polyimide resin is preferably 1 to 40% by mass, more preferably 5 to 40% by mass, and still more preferably 5 to 30% by mass, based on the mass of the polyimide resin. When the halogen atom content is equal to or more than the lower limit and equal to or less than the upper limit, the gas barrier properties of the optical film tend to increase. In addition, synthesis tends to be easy.

The imidization rate of the polyimide resin is preferably 90% or higher, more preferably 93% or higher, and still more preferably 95% or higher. The imidization rate is preferably at least the above lower limit because it facilitates enhancing the gas barrier properties of the optical film. Moreover, the upper limit of the imidization rate is 100%. The imidization ratio indicates the ratio of the molar amount of imide bonds in the polyimide resin to twice the molar amount of the structural units derived from the tetracarboxylic acid compound in the polyimide resin. In the case where the polyimide resin contains a tricarboxylic acid compound, a value twice the molar amount of the structural units derived from the tetracarboxylic acid compound in the polyimide resin, and the molar amount of the structural units derived from the tricarboxylic acid compound It shows the ratio of the molar amount of imide bonds in the polyimide resin to the total of . Also, the imidization rate can be determined by IR method, NMR method, or the like.

In one embodiment of the present invention, the content of the polyimide resin contained in the optical film is preferably 40% by mass or more, more preferably 50% by mass or more, based on the mass of the optical film (100% by mass). It is preferably 60% by mass, particularly preferably 80% by mass or more, and preferably 100% by mass or less. When the content of the polyimide resin contained in the optical film is within the above range, the gas barrier properties of the optical film tend to increase.

[Method for producing polyimide resin]
A commercially available product may be used as the polyimide resin, or it may be produced by a conventional method. Although the method for producing the polyimide resin is not particularly limited, for example, the polyimide resin containing the structural unit represented by formula (1) is obtained by reacting a diamine compound and a tetracarboxylic acid compound to obtain a polyamic acid, and It can be produced by a method including a step of imidizing the polyamic acid. In addition to the tetracarboxylic acid compound, a tricarboxylic acid compound may be reacted.

The tetracarboxylic acid compound, the diamine compound and the tricarboxylic acid compound used in the synthesis of the polyimide resin are the same as the tetracarboxylic acid compound, the diamine compound and the tricarboxylic acid compound described in the [Polyimide resin] section, respectively. can be used.

In the production of the polyimide resin, the amounts of the diamine compound, the tetracarboxylic acid compound and the tricarboxylic acid compound to be used can be appropriately selected according to the desired ratio of each structural unit of the resin.
In a preferred embodiment of the present invention, the amount of the diamine compound used is preferably 0.94 mol or more, more preferably 0.96 mol or more, still more preferably 0.98 mol or more, per 1 mol of the tetracarboxylic acid compound. mol or more, particularly preferably 0.99 mol or more, preferably 1.20 mol or less, more preferably 1.10 mol or less, even more preferably 1.05 mol or less, particularly preferably 1.02 mol or less . When the amount of the diamine compound used relative to the tetracarboxylic acid compound is within the above range, the resulting optical film tends to have enhanced gas barrier properties.

The reaction temperature of the diamine compound and the tetracarboxylic acid compound is not particularly limited, and may be, for example, 5 to 200° C., and the reaction time is also not particularly limited, and may be, for example, about 30 minutes to 72 hours. In a preferred embodiment of the present invention, the reaction temperature is preferably 5 to 50°C, more preferably 5 to 40°C, still more preferably 5 to 25°C, the reaction time is preferably 3 to 24 hours, More preferably 5 to 20 hours. With such a reaction temperature and reaction time, the resulting optical film tends to have enhanced gas barrier properties.

The reaction between the diamine compound and the tetracarboxylic acid compound is preferably carried out in a solvent. The solvent is not particularly limited as long as it does not affect the reaction. Examples include water, methanol, ethanol, ethylene glycol, isopropyl alcohol, propylene glycol, ethylene glycol methyl ether, ethylene glycol butyl ether, 1-methoxy-2-propanol, Alcohol solvents such as 2-butoxyethanol and propylene glycol monomethyl ether; Phenol solvents such as phenol and cresol; Ethyl acetate, butyl acetate, ethylene glycol methyl ether acetate, γ-butyrolactone, γ-valerolactone, propylene glycol methyl ether acetate , ethyl lactate and other ester solvents; acetone, methyl ethyl ketone, cyclopentanone, cyclohexanone, 2-heptanone, methyl isobutyl ketone and other ketone solvents; pentane, hexane, heptane and other aliphatic hydrocarbon solvents; cyclic hydrocarbon solvents; aromatic hydrocarbon solvents such as toluene and xylene; nitrile solvents such as acetonitrile; ether solvents such as tetrahydrofuran and dimethoxyethane; chlorine-containing solvents such as chloroform and chlorobenzene; amide solvents such as N,N-dimethylformamide; sulfur-containing solvents such as dimethylsulfone, dimethylsulfoxide and sulfolane; carbonate solvents such as ethylene carbonate and propylene carbonate; and combinations thereof. Among these, phenol-based solvents and amide-based solvents can be preferably used from the viewpoint of solubility.
In a preferred embodiment of the present invention, the solvent used in the reaction is preferably a solvent that has been rigorously dehydrated to a water content of 700 ppm or less. The use of such a solvent tends to enhance the gas barrier properties of the resulting optical film.

The reaction between the diamine compound and the tetracarboxylic acid compound may be carried out under conditions of an inert atmosphere (nitrogen atmosphere, argon atmosphere, etc.) or reduced pressure, if necessary, and an inert atmosphere (nitrogen atmosphere, argon atmosphere, etc.). It is preferable to conduct the reaction in a strictly controlled dehydrated solvent while stirring. Under such conditions, the gas barrier properties of the resulting optical film tend to be enhanced.

In the imidization step, imidization may be performed using an imidization catalyst, imidization by heating, or a combination thereof. Examples of the imidization catalyst used in the imidization step include aliphatic amines such as tripropylamine, dibutylpropylamine and ethyldibutylamine; N-ethylpiperidine, N-propylpiperidine, N-butylpyrrolidine, N-butylpiperidine, and cycloaliphatic amines (monocyclic) such as N-propylhexahydroazepine; azabicyclo[2.2.1]heptane, azabicyclo[3.2.1]octane, azabicyclo[2.2.2]octane, and Alicyclic amines (polycyclic) such as azabicyclo[3.2.2]nonane; and pyridine, 2-methylpyridine (2-picoline), 3-methylpyridine (3-picoline), 4-methylpyridine (4 -picoline), 2-ethylpyridine, 3-ethylpyridine, 4-ethylpyridine, 2,4-dimethylpyridine, 2,4,6-trimethylpyridine, 3,4-cyclopentenopyridine, 5,6,7, Aromatic amines such as 8-tetrahydroisoquinoline and isoquinoline are included. Moreover, from the viewpoint of facilitating the imidization reaction, it is preferable to use an acid anhydride together with the imidization catalyst. Acid anhydrides include conventional acid anhydrides used in imidization reactions, and specific examples thereof include aliphatic acid anhydrides such as acetic anhydride, propionic anhydride and butyric anhydride, and aromatic acid anhydrides such as phthalic acid. and acid anhydrides.

In one embodiment of the present invention, when imidating, the reaction temperature is preferably 40°C or higher, more preferably 60°C or higher, still more preferably 80°C or higher, and preferably 190°C or lower, more preferably 170°C. 150° C. or less, more preferably 150° C. or less. The reaction time for the imidization step is preferably 30 minutes to 24 hours, more preferably 1 to 12 hours. When the reaction temperature and reaction time are within the above ranges, the resulting optical film tends to have enhanced gas barrier properties.

In one embodiment of the present invention, the weight average molecular weight (Mw) of the polyimide resin is preferably 50,000 or more, more preferably 100,000 or more, still more preferably 120,000 or more, and particularly preferably 150,000 or more. , very particularly preferably ≧200,000, preferably ≦800,000, more preferably ≦700,000, even more preferably ≦600,000. When the weight-average molecular weight (Mw) is at least the lower limit, the gas barrier properties of the resulting optical film tend to be enhanced, and when it is at most the upper limit, the workability of the film tends to be improved. The weight average molecular weight (Mw) can be obtained by performing gel permeation chromatography (GPC) measurement and converting to standard polystyrene, and can be calculated, for example, by the method described in Examples.

The polyimide resin may be isolated (separated and purified) by a conventional method such as filtration, concentration, extraction, crystallization, recrystallization, column chromatography or other separation means, or a combination of these separation means. In a preferred embodiment, the resin can be isolated by adding a large amount of alcohol such as methanol to the reaction solution containing the resin to precipitate the resin, followed by concentration, filtration, drying, and the like.

[Optical film]
The optical film of the present invention contains a polyimide resin having structural units derived from an aliphatic diamine, has a light transmittance at 350 nm of 10% or less, and a photoelastic coefficient of 50×10 ⁻¹² Pa ⁻¹ or less. The optical film of the present invention contains a polyimide resin having a structural unit derived from an aliphatic diamine, has a light transmittance at 350 nm of 10% or less, and has a photoelastic coefficient of 50×10 ⁻¹² Pa ⁻¹ or less. , excellent UV protection and gas barrier properties. Therefore, since the optical film of the present invention has high barrier properties against ultraviolet rays, oxygen and water vapor, it is required to have high visibility under visible light, and is suitable for flexible display devices and the like whose performance tends to deteriorate due to water, oxygen, and the like. Available.

The optical film of the present invention has a photoelastic coefficient of 50×10 ⁻¹² Pa ⁻¹ or less. When the photoelastic coefficient is 50×10 ⁻¹² Pa ⁻¹ or less, the optical film has excellent gas barrier properties. If the photoelastic coefficient exceeds 50×10 ⁻¹² Pa ⁻¹ , it may be difficult to obtain high gas barrier properties. The photoelastic coefficient is preferably 45×10 ⁻¹² Pa ⁻¹ or less, more preferably 35×10 ⁻¹² Pa ⁻¹ or less, still more preferably 30×10 ⁻¹² Pa ⁻¹ or less, preferably 5×10 ⁻¹² Pa ⁻¹ or more, more preferably 7.5×10 ⁻¹² Pa ⁻¹ or more, still more preferably 10×10 ⁻¹² Pa ⁻¹ or more, still more preferably 12.5×10 ⁻¹² Pa ⁻¹ or more , particularly preferably 15×10 ⁻¹² Pa ⁻¹ or more, more preferably 17.5×10 ⁻¹² Pa ⁻¹ or more, still more preferably 20×10 ⁻¹² Pa ⁻¹ or more, still more preferably 22.5×10 −12 Pa −1 or more. It is at least 5×10 ⁻¹² Pa ⁻¹ , very particularly preferably at least 25×10 ⁻¹² Pa ⁻¹ . When the photoelastic coefficient is within the above range, the gas barrier properties, tensile strength, light transmittance at 500 nm, and glass transition temperature of the optical film tend to be within the desired ranges. It is easy to obtain an optical film that simultaneously satisfies The photoelastic coefficient is the type and composition ratio of the structural units that make up the resin contained in the optical film; the molecular weight of the resin; the solvent content of the optical film; the type and amount of additives; It can be adjusted within the above range by appropriately adjusting conditions, etc. In particular, the type and composition ratio of structural units constituting the resin contained in the optical film; the solvent content of the optical film; the manufacturing conditions of the optical film, etc. It can be adjusted within the above range by appropriate adjustment. The photoelastic coefficient can be measured using a phase difference measuring device, for example, by the method described in Examples below.

The optical film of the present invention has a light transmittance of 10% or less at 350 nm. When the light transmittance at 350 nm is 10% or less, the optical film is excellent in ultraviolet shielding properties. If the light transmittance at 350 nm exceeds 10%, the UV shielding property tends to be lowered. The light transmittance of the optical film of the present invention at 350 nm is preferably 8% or less, more preferably 5% or less. When the light transmittance at 350 nm is equal to or less than the upper limit, the ultraviolet shielding property can be improved. The lower limit of light transmittance at 350 nm is 0%. The light transmittance at 350 nm is preferably the light transmittance within the range of thickness (film thickness) of the optical film of the present invention. In addition, the light transmittance at 350 nm is based on the types and composition ratios of structural units that constitute the resin contained in the optical film; the thickness of the optical film; the solvent content of the optical film; the types and amounts of additives; The above range can be achieved by appropriately adjusting the conditions, the purity of the monomer, and the manufacturing conditions of the optical film. Cheap. The light transmittance at 350 nm can be measured using an ultraviolet-visible-near-infrared spectrophotometer, for example, by the method described in Examples.

The humidity expansion coefficient (hereinafter also referred to as “CME”) of the optical film of the present invention is preferably 5 ppm or more, more preferably 10 ppm or more, still more preferably 10 ppm or more, even more preferably 20 ppm or more, and very preferably It is 27 ppm or more, preferably 100 ppm or less, more preferably 80 ppm or less, and still more preferably 60 ppm or less. When the humidity expansion coefficient is within the above range, the gas barrier properties of the optical film are likely to be enhanced. In the present invention, the coefficient of humidity expansion refers to a value measured by the method described in Examples below under conditions of 60° C. and 90% RH. The humidity expansion coefficient is determined by adjusting the type and composition ratio of the structural units that make up the resin contained in the optical film; the solvent content of the optical film; the type and amount of additives; can be adjusted within the above range. The humidity expansion coefficient can be measured using a thermomechanical analyzer (TMA), for example, by the method described in Examples below.

Usually, when the humidity expansion coefficient is high, the gas barrier property tends to be lowered because it is easily affected by moisture. However, in a preferred embodiment of the present invention, the optical film of the present invention can exhibit excellent gas barrier properties even when the humidity expansion coefficient is relatively high, for example, over 10 ppm, preferably 20 ppm or more. Since the optical film of the present invention has such properties, when the optical film of the present invention is used in a display device or the like, the display device can be protected from water vapor and oxygen, and at the same time, it can be used in a normal (non-low-humidity environment) clean room. It is advantageous because it is possible to form a film at

The water absorption rate of the optical film of the present invention at 60° C. (hereinafter also simply referred to as “water absorption rate”) is preferably 2.5% or less, more preferably 2.1% or less, and still more preferably 1.9% or less. be. When the water absorption is equal to or less than the upper limit, the barrier properties against water vapor tend to be excellent. In addition, the lower limit of the water absorption is usually 0%. The water absorption rate is determined by appropriately adjusting the types and composition ratios of structural units that make up the resin contained in the optical film; the solvent content of the optical film; the types and amounts of additives; the manufacturing conditions for the resin; can be adjusted within the above range. The water absorption can be measured by using a thermal analyzer (TG/DTA6200) with specifications for high temperature and high humidity, and can be measured, for example, by the method described in Examples below.

In the optical film of the present invention, the solvent content (also referred to as residual solvent content) is preferably 7.0% by mass or less, more preferably 3.5% by mass or less, still more preferably 2% by mass, based on the mass of the optical film. 0.5% by mass or less, more preferably 1.4% by mass or less. When the solvent content is equal to or less than the upper limit, the gas barrier properties of the optical film are likely to be enhanced. In addition, the lower limit of the solvent content is usually 0.01% by mass. The solvent content can be adjusted within the above range by appropriately adjusting the type of solvent, the type of substrate, drying conditions (especially drying temperature, drying time, etc.), etc. in the optical film manufacturing process described below. The solvent content can be measured, for example, by the method described in Examples below.

The light transmittance of the optical film of the present invention at 500 nm is preferably 90.0% or higher, more preferably 90.2% or higher, even more preferably 90.3% or higher, and particularly preferably 90.4% or higher. When the light transmittance at 500 nm is equal to or higher than the lower limit, visibility can be easily improved when applied to a display device or the like. The upper limit of the light transmittance at 500 nm is 100% or less. Therefore, in a preferred embodiment of the present invention, the optical film can have good transmittance not only in the ultraviolet region but also in the visible light region. The light transmittance at 500 nm is preferably the light transmittance within the range of the thickness (film thickness) of the optical film of the present invention, and more preferably the light transmittance at 25 μm. The light transmittance at 500 nm is based on the types and composition ratios of structural units that constitute the resin contained in the optical film; the thickness of the optical film; the solvent content of the optical film; the types and amounts of additives; It can be adjusted within the above range by appropriately adjusting the conditions, the purity of the monomer, and the manufacturing conditions of the optical film. The light transmittance at 500 nm can be measured using an ultraviolet-visible-near-infrared spectrophotometer, for example, by the method described in Examples below.

The film thickness (also referred to as thickness) of the optical film of the present invention is preferably 10 μm or more, more preferably 20 μm or more, and preferably 100 μm or less, more preferably 80 μm or less. When the film thickness of the optical film is within the above range, it is easy to improve the optical properties and handleability of the optical film. The film thickness can be adjusted within the above range, for example, by appropriately adjusting the film forming conditions when producing the optical film. The film thickness of the optical film can be measured using a digital thickness gauge or the like, for example, by the method described in Examples below.

In a preferred embodiment of the present invention, the optical film of the present invention has a glass transition temperature (sometimes abbreviated as Tg) of preferably 165°C or higher, more preferably 170°C or higher, still more preferably 175°C or higher, and even more preferably 175°C or higher. It is preferably 180°C or higher, particularly preferably above 180°C, particularly more preferably 180.5°C or higher, even more preferably 181°C or higher, extremely preferably 182°C or higher, preferably 400°C or lower, more preferably 400°C or lower. 380° C. or lower, more preferably 350° C. or lower, particularly preferably 300° C. or lower. When the glass transition temperature is at least the above lower limit, the heat resistance and gas barrier properties are likely to be improved. When the glass transition temperature is equal to or lower than the above upper limit, secondary processing is facilitated. The glass transition temperature is the glass transition temperature by DSC (differential scanning calorimetry). The glass transition temperature is determined by the type and composition ratio of the structural units that make up the resin contained in the optical film; the solvent content of the optical film; the type and blending amount of additives; The above range can be achieved by appropriately adjusting the conditions. In particular, the type and composition ratio of the structural units constituting the resin are preferably selected as described above, and the solvent content of the optical film is adjusted. It may be adjusted to the above range by applying the drying conditions in the optical film manufacturing process. The glass transition temperature can be measured, for example, by DSC (differential scanning calorimetry) using a thermal analyzer under the following conditions: amount of sample measured: 5 mg; temperature range: room temperature to 400°C; temperature increase rate: 10°C/min. can.

In a preferred embodiment of the present invention, the optical film of the present invention has a tensile strength of preferably 70 MPa or higher, more preferably 80 MPa or higher, still more preferably 85 MPa or higher, even more preferably 86 MPa or higher, and particularly preferably 87 MPa or higher. More preferably 89 MPa or more, still more preferably 95 MPa or more, extremely preferably 100 MPa or more, preferably 200 MPa or less, more preferably 180 MPa or less. When the tensile strength is at least the above lower limit, it is easy to suppress damage to the optical film. The tensile strength can be measured using a tensile tester or the like under the conditions of a distance between chucks of 50 mm and a tensile speed of 20 mm/min. For example, it can be measured by the method described in Examples. In addition, the tensile strength is determined by the type and composition ratio of the structural units that make up the resin contained in the optical film; the solvent content of the optical film; the molecular weight of the resin; the type and amount of additives; it can be set within the above range by appropriately adjusting the manufacturing conditions of the optical film.

The optical film of the invention may contain an ultraviolet absorber. By containing an ultraviolet absorber, the light absorption in the ultraviolet region can be easily reduced. Therefore, in the optical film of the present invention having a photoelastic coefficient of 50×10 ⁻¹² Pa ⁻¹ or less, both UV cut property and gas barrier property can be enhanced. Examples of ultraviolet absorbers include benzotriazole derivatives (benzotriazole-based ultraviolet absorbers), triazine derivatives (triazine-based ultraviolet absorbers) such as 1,3,5-triphenyltriazine derivatives (triazine-based ultraviolet absorbers), benzophenone derivatives (benzophenone-based ultraviolet absorbers ), and salicylate derivatives (salicylate-based ultraviolet absorbers), and at least one selected from the group consisting of these can be used. Benzotriazole-based UV absorbers have UV absorbency in the vicinity of 300 to 400 nm, preferably 320 to 360 nm, and can improve the UV cut property of optical films without reducing the transmittance in the visible light region. and triazine-based UV absorbers, preferably benzotriazole-based UV absorbers.

Specific examples of benzotriazole-based UV absorbers include the compound represented by formula (I), trade name of Sumitomo Chemical Co., Ltd.: Sumisorb (registered trademark) 250 (2-[2-hydroxy-3-(3 ,4,5,6-tetrahydrophthalimido-methodiyl)-5-methylphenyl]benzotriazole), trade name manufactured by BASF Japan Ltd.: Tinuvin (registered trademark) 360 (2,2′-methylenebis[6-(2H -benzotriazol-2-yl)-4-tert-octylphenol]) and Tinuvin 213 (methyl 3-[3-(2H-benzotriazol-2-yl)5-tert-butyl-4-hydroxyphenyl]propionate with PEG300 and reaction products), which can be used alone or in combination of two or more. Specific examples of the compound represented by formula (I) include trade names manufactured by Sumitomo Chemical Co., Ltd.: Sumisorb 200 (2-(2-hydroxy-5-methylphenyl)benzotriazole), Sumisorb 300 (2-(3 -tert-butyl-2-hydroxy-5-methylphenyl)-5-chlorobenzotriazole), Sumisorb 340 (2-(2-hydroxy-5-tert-octylphenyl)benzotriazole), Sumisorb 350 (2-(2 -Hydroxy 3,5-di-tert-pentylphenyl)benzotriazole) and BASF Japan Ltd. trade name: Tinuvin 327 (2-(2'-hydroxy-3',5'-di-tert-butyl phenyl)-5-chlorobenzotriazole), Tinuvin 571 (2-(2H-benzotriazol-2-yl)-6-dodecyl-4-methyl-phenol) and Tinuvin 234 (2-(2H-benzotriazol-2-yl )-4,6-bis(1-methyl-1-phenylethyl)phenol) and product name of ADEKA Corporation: ADEKA STAB (registered trademark) LA-31 (2,2′-methylenebis[6-(2H-benzo triazol-2-yl)-4-(1,1,3,3-tetramethylbutyl)phenol]). The UV absorber is preferably a compound represented by formula (I) and Tinuvin 213 (methyl 3-[3-(2H-benzotriazol-2-yl) 5-tert-butyl-4-hydroxyphenyl]propionate Reaction products with PEG300, more preferably trade names manufactured by Sumitomo Chemical Co., Ltd.: Sumisorb 200 (2-(2-hydroxy-5-methylphenyl)benzotriazole), Sumisorb 300 (2-(3-tert -butyl-2-hydroxy-5-methylphenyl)-5-chlorobenzotriazole), Sumisorb 340 (2-(2-hydroxy-5-tert-octylphenyl)benzotriazole), Sumisorb 350 (2-(2-hydroxy 3,5-di-tert-pentylphenyl)benzotriazole), product name of ADEKA Corporation: ADEKA STAB LA-31 (2,2′-methylenebis[6-(2H-benzotriazol-2-yl)-4- (1,1,3,3-tetramethylbutyl)phenol]) and BASF Japan Ltd. trade name: Tinuvin 327 (2-(2′-hydroxy-3′,5′-di-tert-butylphenyl )-5-chlorobenzotriazole) and Tinuvin 571 (2-(2H-benzotriazol-2-yl)-6-dodecyl-4-methyl-phenol), most preferably manufactured by Sumitomo Chemical Co., Ltd. under the trade name: Sumisorb 340 (2-(2-hydroxy-5-tert-octylphenyl)benzotriazole), Sumisorb 350 (2-(2-hydroxy-3,5-di-tert-pentylphenyl)benzotriazole), and ADEKA Corporation Product name: Adekastab LA-31 (2,2′-methylenebis[6-(2H-benzotriazol-2-yl)-4-(1,1,3,3-tetramethylbutyl)phenol]).

In formula (I), X ^I is a hydrogen atom, a fluorine atom, a chlorine atom, an alkyl group having 1 to 5 carbon atoms or an alkoxy group having 1 to 5 carbon atoms, and R ^I1 and R ^I2 are each independently a hydrogen atom. or a hydrocarbon group having 1 to 20 carbon atoms, and at ^least one of R ¹¹ and R 12 is a hydrocarbon group having 1 to 20 carbon atoms.

The alkyl group having 1 to 5 carbon atoms in X ^I includes methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, sec-butyl group, tert-butyl group, n-pentyl group, 2- Examples include methyl-butyl group, 3-methylbutyl group, 2-ethyl-propyl group and the like.
The alkoxy group having 1 to 5 carbon atoms in X ^I includes a methoxy group, ethoxy group, n-propoxy group, isopropoxy group, n-butoxy group, sec-butoxy group, tert-butoxy group, n-pentyloxy group, 2-methyl-butoxy group, 3-methylbutoxy group, 2-ethyl-propoxy group and the like.
X ^I is preferably a hydrogen atom, a fluorine atom, a chlorine atom or a methyl group, more preferably a hydrogen atom, a fluorine atom or a chlorine atom.

R ¹¹ and R ¹² each independently represent a hydrogen atom or a hydrocarbon group having 1 to 20 carbon atoms, and at ^least one of R ¹¹ and R 12 is a hydrocarbon group. When each of R ^I1 and R ^I2 is a hydrocarbon group, it is preferably a hydrocarbon group having 1 to 12 carbon atoms, more preferably a hydrocarbon group having 1 to 8 carbon atoms. Specific examples include methyl group, tert-butyl group, tert-pentyl group and tert-octyl group.

As an ultraviolet absorber according to another preferred embodiment, a triazine-based ultraviolet absorber is used in an optical film containing a polyimide resin. Triazine-based UV absorbers include compounds represented by the following formula (II). A specific example thereof is the product name of ADEKA Corporation: ADEKA STAB LA-46 (2-(4,6-diphenyl-1,3,5-triazin-2-yl)-5-[2-(2-ethyl hexanoyloxy)ethoxy]phenol), trade name manufactured by BASF Japan Ltd.: Tinuvin 400 (2-[4-[2-hydroxy-3-tridecyloxypropyl]oxy]-2-hydroxyphenyl]-4,6 -bis(2,4-dimethylphenyl)-1,3,5-triazine), 2-[4-[2-hydroxy-3-didecyloxypropyl]oxy]-2-hydroxyphenyl]-4,6-bis (2,4-dimethylphenyl)-1,3,5-triazine), Tinuvin 405 (2-[4(2-hydroxy-3-(2′-ethyl)hexyl)oxy]-2-hydroxyphenyl]-4 ,6-bis(2,4-dimethylphenyl)-1,3,5-triazine), Tinuvin 460 (2,4-bis(2-hydroxy-4-butyloxyphenyl)-6-(2,4-bis -Butyroxyphenyl)-1,3,5-triazine), Tinuvin 479 (hydroxyphenyltriazine-based UV absorber), and Chemipro Kasei Co., Ltd. product name: KEMISORB (registered trademark) 102 (2-[4,6 -Bis(2,4-dimethylphenyl)-1,3,5-triazin-2-yl]-5-(n-octyloxy)phenol) and the like, which may be used alone or in combination of two or more. can be done. The compound of formula (II) is preferably Adekastab LA-46(2-(4,6-diphenyl-1,3,5-triazin-2-yl)-5-[2-(2-ethyl hexanoyloxy)ethoxy]phenol).

In formula (II), Y ^I1 to Y ^I4 are each independently a hydrogen atom, a fluorine atom, a chlorine atom, a hydroxy group, an alkyl group having 1 to 20 carbon atoms or an alkoxy group having 1 to 20 carbon atoms, preferably is a hydrogen atom, an alkyl group having 1 to 12 carbon atoms or an alkoxy group having 1 to 12 carbon atoms, more preferably a hydrogen atom.

In formula (II), R ^I3 is a hydrogen atom, a hydrocarbon group having 1 to 20 carbon atoms, an alkoxy group having 1 to 20 carbon atoms containing one oxygen atom, or an alkylketooxy having 1 to 12 carbon atoms. an alkoxy group having 1 to 4 carbon atoms substituted with a group, preferably substituted with an alkoxy group having 1 to 12 carbon atoms containing one oxygen atom or an alkylketooxy group having 8 to 12 carbon atoms. It is an alkoxy group having 2 to 4 carbon atoms, more preferably an alkoxy group having 2 to 4 carbon atoms substituted with an alkylketooxy group having 8 to 12 carbon atoms.

Examples of alkyl groups having 1 to 20 carbon atoms as Y ^I1 to Y ^I4 include methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, sec-butyl group, tert-butyl group, n -pentyl group, n-hexyl group, n-heptyl group, n-octyl group, n-nonyl group, n-decyl group, n-dodecyl group and n-undecyl group. Examples of alkoxy groups having 1 to 20 carbon atoms include methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, sec-butoxy, tert-butoxy, n-pentyloxy, n -hexyloxy group, n-heptyloxy group, n-octyloxy group, n-nonyloxy group, n-decyloxy group, n-dodecyloxy group and n-undecyloxy group.

The ultraviolet absorber preferably has a light absorption of 300 to 400 nm, more preferably a light absorption of 320 to 360 nm, and even more preferably a light absorption of around 350 nm.

When the optical film of the present invention contains ultraviolet absorption, the content of the ultraviolet absorber is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, with respect to 100 parts by mass of the polyimide resin. More preferably 0.8 parts by mass or more, particularly preferably 1 part by mass or more, preferably 10 parts by mass or less, more preferably 8 parts by mass or less, and even more preferably 5 parts by mass or less. When the content of the UV absorber is at least the above lower limit, the UV blocking property of the optical film is likely to be improved, and when the content of the UV absorber is below the above upper limit, the transparency and mechanical properties of the optical film are improved. Easy to raise.

The optical film of the present invention may contain at least one filler. When the optical film contains a filler, the gas barrier properties of the optical film, particularly the oxygen permeability, are likely to be reduced. Examples of the filler include organic particles and inorganic particles, preferably inorganic particles. Examples of inorganic particles include metal oxide particles such as silica, zirconia, alumina, titania, zinc oxide, germanium oxide, indium oxide, tin oxide, indium tin oxide (ITO), antimony oxide, and cerium oxide; Examples include metal fluoride particles such as sodium chloride. Among these, silica particles, zirconia particles, and alumina particles are preferred from the viewpoint of easily increasing the gas barrier properties of the optical film, and silica particles are more preferred. . These fillers can be used singly or in combination of two or more.

The average primary particle size of the filler, preferably silica particles, is usually 1 nm or more, preferably 5 nm or more, more preferably 10 nm or more, still more preferably 15 nm or more, particularly preferably 20 nm or more, and preferably 100 nm or less, more preferably It is 80 nm or less, more preferably 60 nm or less, still more preferably 40 nm or less. When the average primary particle size of the silica particles is within the above range, aggregation of the silica particles is suppressed, and the gas barrier properties of the resulting optical film are likely to be improved. The average primary particle size of the filler can be measured by the BET method. The average primary particle size may be measured by image analysis using a transmission electron microscope or a scanning electron microscope.

When the optical film of the present invention contains a filler, preferably silica particles, the content of the filler is usually 0.1% by mass or more, preferably 1% by mass or more, more preferably 5% by mass, based on the mass of the optical film. % by mass or more, more preferably 10% by mass or more, preferably 60% by mass or less, more preferably 50% by mass or less, and even more preferably 40% by mass or less. When the content of the filler is within the above range, it is easy to improve the gas barrier property while maintaining the transparency of the optical film.

The optical film of the present invention may further contain additives other than the ultraviolet absorber and filler. Other additives include, for example, antioxidants, release agents, stabilizers, bluing agents, flame retardants, pH adjusters, silica dispersants, lubricants, thickeners, and leveling agents. When other additives are contained, the content thereof is preferably 0.001 to 20% by mass, more preferably 0.01 to 15% by mass, and still more preferably 0.1 to 20% by mass, based on the mass of the optical film. It may be 10% by mass.

Applications of the optical film of the present invention are not particularly limited, and various applications such as substrates for touch sensors, materials for flexible display devices, protective films, films for bezel printing, semiconductor applications, speaker diaphragms, IR cut filters, etc. You may The optical film of the present invention may be a single layer or a laminate. The optical film of the present invention may be used as it is, or may be used as a laminate with another film. . When the optical film is a laminate, the optical film includes all layers laminated on one side or both sides of the optical film.

When the optical film of the present invention is a laminate, it preferably has one or more functional layers on at least one surface of the optical film. Examples of functional layers include a hard coat layer, a primer layer, a gas barrier layer, an ultraviolet absorption layer, an adhesive layer, a hue adjustment layer, a refractive index adjustment layer and the like. A functional layer can be used individually or in combination of 2 or more types.

In one embodiment of the present invention, the optical film may have a protective film on at least one side (single side or both sides). For example, when the optical film has a functional layer on one side, the protective film may be laminated on the optical film side surface or the functional layer side surface, or may be laminated on both the optical film side and the functional layer side. may When the optical film has functional layers on both sides, the protective film may be laminated on one functional layer side surface, or may be laminated on both functional layer side surfaces. The protective film is a film for temporarily protecting the surface of the optical film or the functional layer, and is not particularly limited as long as it is a peelable film capable of protecting the surface of the optical film or the functional layer. Examples of protective films include polyester resin films such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate; polyolefin resin films such as polyethylene and polypropylene films; acrylic resin films; It is preferably selected from the group consisting of a terephthalate resin film and an acrylic resin film. When the optical film has two protective films, each protective film may be the same or different.

The thickness of the protective film is not particularly limited, but is usually 10-120 μm, preferably 15-110 μm, more preferably 20-100 μm. When the optical film has two protective films, the thickness of each protective film may be the same or different.

[Method for producing optical film]
In the present invention, the optical film is not particularly limited, but for example the following steps:
(a) a step of preparing a liquid (which may be referred to as varnish) containing a polyimide resin (varnish preparation step);
(b) a step of applying a varnish to a substrate to form a coating film (coating step); and (c) a step of drying the applied liquid (coating film) to form an optical film (optical film forming step). )
It can be manufactured by a method comprising

In the varnish preparation step, the varnish is prepared by dissolving the polyimide-based resin in a solvent, adding additives described below as necessary, and stirring and mixing.

The solvent used for preparing the varnish is not particularly limited as long as it can dissolve the resin. Examples of such solvents include amide solvents such as N,N-dimethylacetamide (DMAc) and N,N-dimethylformamide (DMF); lactone solvents such as γ-butyrolactone (GBL) and γ-valerolactone; ketone solvents such as methyl ethyl ketone, cyclopentanone, cyclohexanone, 2-heptanone and methyl isobutyl ketone; sulfur-containing solvents such as dimethylsulfone, dimethylsulfoxide and sulfolane; carbonate solvents such as ethylene carbonate and propylene carbonate; and combinations thereof are mentioned. Among these, amide-based solvents, lactone-based solvents, and ketone-based solvents are preferred from the viewpoint of resin solubility. These solvents can be used alone or in combination of two or more. The varnish may also contain water, alcoholic solvents, acyclic ester solvents, etheric solvents, and the like.

The solid content concentration of the varnish is preferably 1 to 30% by mass, more preferably 5 to 25% by mass, still more preferably 10 to 20% by mass. In addition, in this specification, the solid content of the varnish indicates the total amount of the components of the varnish excluding the solvent. Also, the viscosity of the varnish is preferably 5 to 100 Pa·s, more preferably 10 to 50 Pa·s. When the viscosity of the varnish is within the above range, the optical film can be easily made uniform, and an optical film having a uniform thickness can be easily obtained. The viscosity of the varnish can be measured using a viscometer, for example, by the method described in Examples.

In the application step, a coating film is formed by applying the varnish onto the substrate by a known application method. Known coating methods include, for example, wire bar coating, reverse coating, roll coating such as gravure coating, die coating, comma coating, lip coating, spin coating, screen coating, fountain coating, dipping, Examples include a spray method and a casting method.

In the optical film forming step, the optical film can be formed by drying the coating film and peeling it off from the substrate. A drying process for drying the optical film may be performed after the peeling. Drying of the coating film can be carried out at a temperature of usually 50 to 350°C, preferably 50 to 220°C. In a preferred embodiment, the drying is preferably done in stages. Varnishes containing high molecular weight resins tend to have high viscosities, and optical films obtained from such varnishes tend to have non-uniform thicknesses. Such an optical film tends to locally deteriorate in gas barrier properties. Therefore, by performing stepwise drying, the varnish containing the high-molecular-weight resin can be dried uniformly, making it easier to obtain an optical film having excellent gas barrier properties. In a more preferred embodiment of the present invention, after heating at a relatively low temperature of 100-170°C, heating can be performed at 185-220°C. Drying (or heating time) is preferably 5 minutes to 5 hours, more preferably 10 minutes to 1 hour. By stepwise heating from a low temperature to a high temperature within such a range, an optical film having a uniform thickness can be obtained, and an optical film having a higher gas barrier property can be easily obtained. Also, the appearance of the optical film tends to be better. If desired, drying of the coating may be performed under inert atmospheric conditions. Further, if the optical film is dried under vacuum conditions, fine air bubbles may be generated and remain in the film, which may cause deterioration of transparency. Therefore, it is preferable to dry the optical film under atmospheric pressure.

Examples of substrates include glass substrates, PET films, PEN films, and other polyimide resin or polyamide resin films. Among them, glass, PET film, PEN film and the like are preferred from the viewpoint of excellent heat resistance, and glass substrates and PET films are more preferred from the viewpoint of adhesion to polyimide films and cost.

The optical film of the present invention can be suitably used as a display device, particularly as a touch sensor substrate. Examples of display devices include wearable devices such as televisions, smartphones, mobile phones, car navigation systems, tablet PCs, mobile game machines, electronic paper, indicators, bulletin boards, watches, and smart watches.

[Flexible display device]
The present invention includes flexible display devices comprising the optical film of the present invention. Examples of the flexible display device include display devices having flexible characteristics, such as televisions, smartphones, mobile phones, and smart watches. A specific configuration of the flexible display device is not particularly limited, but includes, for example, a configuration including a laminate for a flexible display device and an organic EL display panel. Such a flexible display device of the present invention preferably further includes a polarizing plate and/or a touch sensor. Commonly used polarizing plates or touch sensors may be used, and these may be included in the laminate for a flexible display device. Polarizing plates include, for example, circularly polarizing plates, and touch sensors include various modes such as a resistive film system, a surface acoustic wave system, an infrared system, an electromagnetic induction system, and a capacitance system. In a preferred embodiment of the present invention, the optical film of the present invention can be used as the touch sensor substrate (or touch sensor film).
In one embodiment of the present invention, the laminate for a flexible display device preferably further includes a window film on the viewing side. The sensor and the polarizing plate may be laminated in this order. These members may be laminated using an adhesive or pressure-sensitive adhesive, and other members other than these members may be included.

EXAMPLES The present invention will be described in more detail below based on examples and comparative examples, but the present invention is not limited to the following examples.

[Photoelastic coefficient]
The photoelastic coefficients of the optical films obtained in Examples and Comparative Examples were determined using an in-plane retardation measurement mode (using a wavelength of 590 nm) of a retardation measurement device (KOBRA-WRP manufactured by Oji Scientific Instruments Co., Ltd.). . Place the attached sample tensioning jig at the sample measurement site, measure the phase difference change due to the load change for the 15 mm × 150 mm test piece, linearly approximate the result to obtain the slope, then use the following formula asked.
Photoelastic coefficient=Slope×1.5×10 ⁻⁹ /9.8 (cm ² /dyn)

[Coefficient of humidity expansion (CME)]
The humidity expansion coefficients of the optical films obtained in Examples and Comparative Examples were measured using a thermomechanical analyzer (TMA) having a constant temperature and humidity chamber. The test piece is held with a constant load (20 mN) applied to a pair of clamps, and the temperature in the constant temperature and humidity chamber is changed from 60 ° C. and 0% RH to 60 ° C. and 90% RH by the temperature program, The clamp-to-clamp distance that changed between 0% and 90% RH was measured, and the amount of change was calculated as the coefficient of humidity expansion.

[Water absorption]
For the water absorption of the optical films obtained in Examples and Comparative Examples, the weight of the sample was measured in an AIR atmosphere with controlled temperature and humidity, and the weight change rate was obtained from the amount of change from the weight before humidification. For the measurement, a thermal analyzer (TG/DTA6200 manufactured by Seiko Electronics Industries Co., Ltd.) with specifications for high temperature and high humidity was used. Two sample plates were placed on the balance beam, and a test piece (approximately 15 mm×15 mm) was set on one of the sample plates. The sample temperature was adjusted in a circulation constant temperature bath for sample temperature control, and the humidity was adjusted by circulating dry air at 100 mL/min in a warm water circulation furnace. The measurement temperature was controlled stepwise from 25° C. to 60° C., then the humidity was changed from 0% RH to 90% RH, and after standing until the sample weight stabilized under each temperature and humidity condition, the sample weight was measured. was measured. The water absorption (weight change) % was calculated from the following formula.
Water absorption (mg) = sample weight (mg) at each humidity - sample weight (mg) without humidification
Water absorption rate (%) = water absorption amount (mg) / sample weight without humidification (mg) x 100
The water absorption rate at 60° C. and 90% RH was obtained from the above formula.

[Solvent content]
(Thermogravimetric-differential thermal (TG-DTA) measurement)
Using a TG-DTA measuring device (“TG/DTA6300” manufactured by Hitachi High-Tech Science), the amount of residual solvent (solvent content) in the optical films obtained in Examples and Comparative Examples was measured.
About 20 mg of sample was obtained from the optical film. This sample was heated from room temperature to 120° C. at a temperature increase rate of 10° C./minute, held at 120° C. for 5 minutes, and then heated (heated) to 400° C. at a temperature increase rate of 10° C./minute. , measured the mass change of the sample.
From the TG-DTA measurement results, the mass reduction rate S (mass%) from 120 ° C to 250 ° C
was calculated according to the following formula (1).
S (% by mass) = 100 - (W1/W0) x 100 (1)
[In formula (1), W0 is the mass of the sample after being held at 120 ° C. for 5 minutes, and W1 is 250
is the mass of the sample in ° C]
The calculated mass reduction rate S was defined as the residual solvent amount S (% by mass) in the optical film.

[Light transmittance at 350 nm and 500 nm]
The light transmittance at 350 nm and 500 nm in the optical films obtained in Examples and Comparative Examples was measured using an ultraviolet-visible-near-infrared spectrophotometer V-670 manufactured by JASCO Corporation. obtained by measuring the rate.

[Measurement of glass transition temperature]
The glass transition temperatures (Tg) of the optical films obtained in Examples and Comparative Examples were measured by DSC (differential scanning calorimetry) using a thermal analyzer (“DSC Q200”, manufactured by TA Instruments). The measurement conditions were as follows: amount of sample to be measured: 5 mg; temperature range: room temperature to 400°C; heating rate: 10°C/min.

[Measurement of tensile strength]
The tensile strength of the optical films obtained in Examples and Comparative Examples was measured using a precision universal tester (“Autograph AG-IS” manufactured by Shimadzu Corporation) as follows.
The optical film was cut into a width of 10 mm and a length of 100 mm to prepare a strip-shaped test piece. Next, using the precision universal testing machine, a tensile test was performed under the conditions of a distance between chucks of 50 mm and a tensile speed of 20 mm/min to measure the tensile strength of the optical film.

[Thickness]
The film thickness of the optical films obtained in Examples and Comparative Examples was measured three times using a contact-type digital thickness gauge (manufactured by Mitutoyo Co., Ltd.), and the average value of the three measured values was taken as the film thickness of the optical film. and

[Weight average molecular weight (Mw)]
The weight average molecular weight (Mw) of the synthesized polyimide resin was measured using GPC under the following conditions.
(GPC conditions)
Apparatus: Shimadzu LC-20A
Column: TSKgel GMHHR-M (mix column, exclusion limit molecular weight: 4 million)
Guard column: TSKgel guard column HHR-H
Mobile phase: N-methyl-2-pyrrolidinone (NMP), 10 mM LiBr added * NMP is HPLC grade, LiBr is reagent first grade (anhydride) Flow rate: 1 mL/min Measurement time: 20 minutes Column oven: 40°C
Detection: UV 275nm
Wash solvent: NMP
Sample concentration: 1 mg/mL (20 wt% reaction mass diluted to 5 mg/mL with mobile phase for analysis)
Molecular weight calibration: Standard polystyrene manufactured by Polymer Laboratories (17 molecular weights with a molecular weight of 5-4 million)

[Imidation rate]
The imidization rate of the synthesized polyimide resin was measured using NMR under the following conditions.
(NMR conditions)
10 mg of polyimide resin was weighed, and after adding 0.75 ml of heavy DMSO, the resin was dissolved by heating at 120° C. for 20 minutes. The solution was transferred to an NMR tube and ¹ H NMR measurements were performed at 100° C. using a Bruker AV600 instrument. Protons derived from the imide group and protons derived from the amide group were assigned from the ¹ H NMR spectrum, and the imidization rate was determined using the following equation.
Imidation rate = {imido group integral ratio/(imido group integral ratio + amide group integral ratio)} × 100

[viscosity]
The viscosity of the varnish was measured using an E-type viscometer (“HBDV-II + P CP”, manufactured by Brook Field) using 0.6 cc of varnish as a sample under the conditions of 25° C. and 3 rpm.

[Water vapor permeability]
Using a Lyssy L80 series water vapor permeability meter, the water vapor permeability of the optical films obtained in Examples and Comparative Examples was evaluated. Measurement conditions are as follows.
Test method: Moisture sensitive sensor method Temperature/humidity conditions: 25°C, 90% RH
Measurement area: 1.3×10 ⁻⁵ m ²

[Oxygen permeability]
Using a differential pressure type gas permeability measuring device (GTR-30AS type) manufactured by GTR Tech Co., Ltd., the optical films obtained in Examples and Comparative Examples were measured in accordance with JIS K 7126-1 (differential pressure method). Oxygen permeability was evaluated. Measurement conditions are as follows.
Measurement temperature: 30°C
Transmission area: 15.2 cm ² (φ44 mm)
Permeable gas: Oxygen (ultra-high purity)
Supply gas pressure: 2 kgf/cm ² (differential pressure: 223 cmHg)

[Synthesis Example 1]
In a nitrogen gas atmosphere, m-cresol (manufactured by Honshu Chemical Industry Co., Ltd.) 178.78 kg, 1,4-DAB (manufactured by ThermoFisher) 7.940 kg, and 6FDA (Hakko Tsusho) were added to a reaction vessel equipped with a stirring blade. Co., Ltd.) was added, then 3.428 kg of isoquinoline (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added, the temperature was raised to 158 ° C., and after stirring for 5 hours, m-cresol was added. 74.49 kg was added, and the resulting reaction liquid was cooled to 50°C. While stirring, 118.97 kg of Solmix AP-1 (manufactured by Nippon Alcohol Trading Co., Ltd.) was added, and 356.91 kg of Solmix AP-1 was further added, followed by filtration. The filtered precipitate was washed with Solmix AP-1 (70.62 kg), suspended and filtered four times with Solmix AP-1 (141.23 kg), and the precipitate was dried in a dryer at 70°C for 96 hours. 39.97 kg of polyimide-based resin was obtained. The weight average molecular weight (Mw) of the produced polyimide resin was 252,000, and the imidization rate was 99.9%.

(Example 1)
A varnish was prepared by dissolving the polyimide resin obtained in Synthesis Example 1 in cyclohexanone so that the solid content concentration was 15% by mass, and adding 2 phr of Sumisorb 340 as an ultraviolet absorber (UVA). The viscosity of the varnish was 26 Pa·s. Next, the obtained varnish was applied to a glass substrate, heated at 140° C. for 10 minutes, further heated at 200° C. for 30 minutes, and peeled off from the glass substrate to obtain an optical film with a thickness of 25 μm. The amount of residual solvent in the obtained optical film was 1.2% by mass.

(Example 2)
The polyimide resin obtained in Synthesis Example 1 was dissolved in cyclohexanone so that the solid content concentration was 15% by mass, and 2 phr of Sumisorb 340 was added as an ultraviolet absorber (UVA). Next, silica (product name: CHO-ST-M, manufacturer name: Nissan Chemical Industries, Ltd., average primary particle size: 22 nm) was added to 20% by mass relative to the polyimide resin to prepare a varnish. The viscosity of the varnish was 10 Pa·s. The obtained varnish was applied to a glass substrate, heated at 140° C. for 10 minutes, further heated at 200° C. for 30 minutes, and peeled off from the glass substrate to obtain an optical film with a thickness of 25 μm. The amount of residual solvent in the obtained optical film was 1.5% by mass. The content of silica was 16.4% by mass with respect to the mass of the optical film.

(Comparative example 1)
Polyimide resin (hereinafter also referred to as PI) ("KPI-MX300F", manufactured by Kawamura Sangyo Co., Ltd.) was dissolved in DMAc so that the solid content concentration was 12% by mass to prepare a varnish. The varnish was applied to a glass substrate, heated at 140° C. for 10 minutes, further heated at 200° C. for 20 minutes, and peeled off from the glass substrate to obtain an optical film with a thickness of 30 μm. The amount of residual solvent in the obtained optical film was 1.5% by mass.

Table 1 shows the evaluation results of the physical properties and gas barrier properties of the optical films obtained in Examples and Comparative Examples.

As shown in Table 1, the optical films of Examples 1 and 2 having small photoelastic coefficients had low water vapor permeability and low oxygen permeability, and had excellent gas barrier properties. In addition, the light transmittance at 350 nm was low, and the ultraviolet shielding property was also excellent. Therefore, it was found that the optical films of Examples 1 and 2 are excellent in both ultraviolet shielding properties and gas barrier properties.

Claims (13)

An optical film comprising a polyimide resin having structural units derived from an aliphatic diamine, having a light transmittance at 350 nm of 10% or less and a photoelastic coefficient of 50×10 ⁻¹² Pa ⁻¹ or less. 2. The optical film of claim 1, wherein the humidity expansion coefficient is greater than 10 ppm. The optical film according to claim 1 or 2, wherein the water absorption at 60°C is 2.5% or less. The optical film according to any one of claims 1 to 3, wherein the solvent content is 7.0% by mass or less with respect to the mass of the optical film. 5. The optical film according to claim 1, which has a light transmittance of 90% or more at 500 nm. 6. The optical film according to any one of claims 1 to 5, which contains a filler. 7. The optical film according to any one of claims 1 to 6, having a film thickness of 10 µm or more and 100 µm or less. The polyimide resin has the formula (1):

[In formula (1), X represents a divalent organic group, Y represents a tetravalent organic group, and * represents a bond]
8. The optical film according to claim 1, wherein the structural unit represented by formula (1) contains a divalent aliphatic group as X. The structural unit represented by the formula (1) is represented by Y as the formula (2):

[In formula (2), R ² to R ⁷ each independently represent a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms or an aryl group having 6 to 12 carbon atoms, The hydrogen atoms contained in R ² to R ⁷ may be independently substituted with halogen atoms, and V is a single bond, —O—, —CH ₂ —, —CH ₂ —CH ₂ —, — CH(CH ₃ )—, —C(CH ₃ ) ₂ —, —C(CF ₃ ) ₂ —, —SO ₂ —, —S—, —CO— or —N(R ⁸ )—, and R ⁸ represents a hydrogen atom or a monovalent hydrocarbon group having 1 to 12 carbon atoms which may be substituted with a halogen atom, * represents a bond]
9. The optical film of claim 8, comprising a structure represented by: 10. The optical film according to claim 8, wherein the polyimide resin contains fluorine atoms. A flexible display device comprising the optical film according to any one of claims 1 to 10. 12. The flexible display of Claim 11, further comprising a polarizer. 13. A flexible display device according to claim 11 or 12, further comprising a touch sensor.