WO2023101005A1

WO2023101005A1 - Film and polyimide-based resin

Info

Publication number: WO2023101005A1
Application number: PCT/JP2022/044523
Authority: WO
Inventors: 敏之横藤田; 康司石渡; 孝至桜井; 拓也森; ズームベルト，アーリヤン; マンチェスター，ショーン
Original assignee: 住友化学株式会社; ザイマージェンインコーポレイテッド
Priority date: 2021-12-03
Filing date: 2022-12-02
Publication date: 2023-06-08
Also published as: JP2023083147A

Abstract

The present invention relates to a film which comprises a polyimide-based resin having a structural unit derived from an aliphatic diamine and a fluorine atom, wherein the content of an oligomer having a molecular weight of at most 10,000 is 6.1 mass% or less with respect to the mass of the film.

Description

Film and polyimide resin

This patent application claims priority under the Paris Convention of Japanese Patent Application No. 2021-197339 (filing date: December 3, 2021), and is hereby incorporated by reference in its entirety. shall be incorporated into the book.

The present invention relates to a film used as a material for a flexible display device, a polyimide resin capable of forming the film, and a flexible display device comprising the film.

Films are used in a variety of applications, including display devices such as liquid crystal and organic EL, touch sensors, speakers, and semiconductors. For example, as touch sensor substrate materials, aromatic polyimide films and aliphatic polyimide films having dimensional stability are known (for example, Patent Documents 1 and 2). In recent years, with the spread of flexible display devices, touch sensor substrate materials used in such flexible display devices are also required to have a high degree of bending resistance.

JP-A-2005-336243 WO2019/156717

However, according to the study of the present inventor, it was found that the polyimide film containing structural units derived from an aliphatic diamine used as a touch sensor substrate material does not have sufficient bending resistance.

Accordingly, an object of the present invention is to provide a film having excellent bending resistance, a polyimide resin capable of forming the film, and a flexible display device comprising the film.

As a result of intensive studies to solve the above problems, the present inventors have found that, in a film containing a polyimide resin having a structural unit derived from an aliphatic diamine and a fluorine atom, the content of an oligomer having a molecular weight of 10,000 or less is reduced to 6 The inventors have found that the above problems can be solved by adjusting the concentration to 1% by mass or less, and have completed the present invention. That is, the present invention includes the following preferred aspects.

[1] A film containing a polyimide resin having a structural unit derived from an aliphatic diamine and a fluorine atom, and having a molecular weight of 10,000 or less and an oligomer content of 6.1% by mass or less based on the mass of the film. .
[2] The film according to [1], wherein the content of the oligomer having a molecular weight of 10,000 or less is 1.0% by mass or more relative to the mass of the film.
[3] The film according to [1] or [2], wherein the oligomer comprises a cyclic oligomer.
[4] The film according to any one of [1] to [3], wherein the oligomer has a molecular weight of 700 or more.
[5] The film according to any one of [1] to [4], wherein the weight average molecular weight (Mw) of the film is 150,000 or more.
[6] The film according to any one of [1] to [5], wherein the content of fluorine atoms in the polyimide resin is 10% by mass or more based on the mass of the polyimide resin.
[7] The film according to any one of [1] to [6], wherein the polyimide resin has an imidization rate of 99% or more.
[8] The polyimide resin has the formula (1):

[In the formula (1), X represents a divalent organic group, Y represents a tetravalent organic group, among the organic groups of X and Y, at least one contains a fluorine atom, * is a bond represents]
The 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 formula (1) is represented by 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, 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 )—, hydrogen atoms contained in R ² to R ⁷ and V are independently of each other optionally substituted with halogen atoms; 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 film according to [8], comprising the structure represented by
[10] A polyimide-based resin having a structural unit derived from an aliphatic diamine and a fluorine atom and having a molecular weight of 10,000 or less and an oligomer content of 5.5% by mass or less based on the mass of the polyimide-based resin. .
[11] The polyimide-based resin according to [10], wherein the content of the oligomer having a molecular weight of 10,000 or less is more than 0.7% by mass based on the mass of the polyimide-based resin.
[12] The polyimide resin according to [10] or [11], wherein the oligomer includes a cyclic oligomer.
[13] The polyimide resin according to any one of [10] to [12], wherein the oligomer has a molecular weight of 700 or more.
[14] The polyimide resin according to any one of [10] to [13], wherein the polyimide resin has a weight average molecular weight (Mw) of 170,000 or more.
[15] A flexible display device comprising the film according to any one of [1] to [9].
[16] The flexible display device according to [15], further comprising a polarizing plate.
[17] The flexible display device according to [15] or [16], further comprising a touch sensor.

The film of the present invention has excellent bending resistance. Therefore, it can be suitably used as a material for flexible display devices.

1 is a diagram showing the peaks of oligomers having a molecular weight of 10,000 or less in the GPC data of the film obtained in Example 1. FIG. 1 is a diagram showing the peaks of oligomers having a molecular weight of 10,000 or less in the GPC data of the polyimide resin obtained in Example 1. FIG. 2 is a diagram showing the results of MALDI-MS measurement of the polyimide resin obtained in Example 1. FIG.

[the film]
The film of the present invention contains a polyimide resin having a structural unit derived from an aliphatic diamine and a fluorine atom, and the content of an oligomer having a molecular weight of 10,000 or less is 6.1% by mass or less with respect to the mass of the film. be. In this specification, an oligomer having a molecular weight of 10,000 or less is sometimes referred to as an "oligomer having a molecular weight of 10,000 or less", and the content of the oligomer having a molecular weight of 10,000 or less is referred to as an "oligomer weight of 10,000 or less". Or it may simply be called "oligomer amount".

The present inventors have investigated the relationship between a film containing a polyimide resin having a structural unit derived from an aliphatic diamine and a fluorine atom and the flex resistance. Oligomers having a molecular weight of 10,000 or less are likely to be formed, and thus the film containing the polyimide resin has a relatively large amount of the oligomers, and it was found that the flex resistance of the film is lowered due to the influence of the oligomers. Accordingly, the present inventors found that when the amount of oligomers having a molecular weight of 10,000 or less in the film is adjusted to 6.1% by mass or less, the flex resistance is remarkably improved. Therefore, the film of the present invention has a molecular weight of 10,000 or less and an oligomer content of 6.1% by mass or less. When the amount of the oligomer having a molecular weight of 10,000 or less exceeds 6.1% by mass, the bending resistance tends to decrease.

Furthermore, the present inventors have investigated the film-forming properties of films containing polyimide resins, and found that polyimide resins having structural units and fluorine atoms derived from aliphatic diamines are difficult to dissolve in general-purpose solvents such as cyclohexanone. , agglomeration, etc. may occur, and it was found that the film formability of the film was not sufficient. Therefore, the present inventors focused on the relationship between the amount of oligomer and the film-forming property of the film, and conducted further studies. It has been found that the solubility of the polyimide resin in the solvent during film formation can be improved, that is, the film formability can be improved. It is presumed that this is because a predetermined amount or more of the oligomer having a molecular weight of 10,000 or less enters between the molecules of the polyimide resin, thereby effectively suppressing the stacking of the resins. In this specification, the solubility of a polyimide resin in a solvent may be simply referred to as "resin solubility".

<Polyimide resin>
The film of the present invention contains a polyimide resin having structural units derived from an aliphatic diamine and fluorine atoms. The 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. may contain.

The aliphatic diamine in the structural unit derived from the aliphatic diamine constituting the polyimide resin represents a diamine having an aliphatic group, and may contain other substituents in part of its structure, but the aromatic ring is It does not have. When the polyimide-based resin contains structural units derived from aliphatic diamines, the optical properties of the obtained film can be improved, for example, retardation can be easily reduced. Aliphatic diamines include, for example, acyclic aliphatic diamines and cycloaliphatic diamines, and acyclic aliphatic diamines are preferable from the viewpoint of easily increasing the optical properties and heat resistance of the film. In addition, polyimide resins containing structural units derived from acyclic aliphatic diamines tend to have a relatively high content of oligomers with a molecular weight of 10,000 or less, such as cyclic oligomers, which can reduce bending resistance. Therefore, by reducing the content of the oligomer to a predetermined amount or less, the effect of the present invention relating to improvement in bending resistance is likely to be exhibited. Furthermore, polyimide resins containing structural units derived from acyclic aliphatic diamines tend to be difficult to dissolve in general-purpose solvents such as cyclohexanone. The effect of the present invention for improving the solubility of the resin is likely to be exhibited by adjusting the amount to a fixed amount or more. In the present specification, hereinafter, the meaning of "easy to improve bending resistance" is to obtain the effect of the present invention related to improving (or improving) bending resistance by adjusting the amount of oligomer to the upper limit or less. The meaning of "easy to improve the solubility of the resin" also includes the meaning of "easy to improve the solubility of the resin", and the effect of the present invention related to improving (or improving) the solubility of the resin by adjusting the amount of oligomer to the lower limit or more. It also includes the meaning of being easy to obtain. Acyclic aliphatic diamines include, for example, 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-1,3-diaminopropane linear or branched diaminoalkanes having 2 to 10 carbon atoms, and diamines in which at least some of the hydrogen atoms contained in these diamines are substituted with fluorine atoms. Cycloaliphatic diamines include, for example, 1,3-bis(aminomethyl)cyclohexane, 1,4-bis(aminomethyl)cyclohexane, norbornanediamine, 4,4'-diaminodicyclohexylmethane, and their diamines. Examples include diamines in which at least part of hydrogen atoms are substituted with fluorine atoms. These can be used alone or in combination of two or more. Among these, 1,2-diaminoethane, 1,3-diaminopropane, 1,4-diaminobutane, 1,4-diaminobutane, 1,2-diaminoethane, 1,3-diaminopropane, 1,4-diaminobutane, 1,4-diaminobutane, 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. These aliphatic diamines can be used singly or in combination of two or more. In this specification, optical properties mean optical properties possessed by the film, including retardation, transparency, and UV shielding properties. Unless otherwise specified, the retardation includes both thickness retardation and in-plane retardation.

The polyimide resin may contain structural units derived from aromatic diamines in addition to structural units derived from aliphatic diamines. 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 aromatic diamines 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, 4,4′-bis(4-aminophenoxy)biphenyl, 9,9-bis(4- Aromatics having two or more aromatic rings such as aminophenyl)fluorene, 9,9-bis(4-amino-3-methylphenyl)fluorene, 9,9-bis(4-amino-3-chlorophenyl)fluorene, etc. diamines; diamines in which at least part of the hydrogen atoms contained in these diamines are substituted with fluorine atoms; 2,2′-bis(trifluoromethyl)-4,4′-diaminodiphenyl (also referred to as TFMB); 4,4 '-(Hexafluoropropylidene)dianiline; 9,9-bis(4-amino-3-fluorophenyl)fluorene and the like. These aromatic diamines can be used singly or in combination of two or more.

The polyimide-based resin can further contain structural units derived from a tetracarboxylic acid compound. When a structural unit derived from a tetracarboxylic acid compound is contained, the optical properties, heat resistance, bending resistance, and solubility of the resin of the film are likely to be improved. Examples of tetracarboxylic acid compounds include aromatic tetracarboxylic acid compounds such as aromatic tetracarboxylic dianhydride; 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, 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-di Carboxyphenyl)propane dianhydride, 2,2-bis(3,4-dicarboxyphenoxyphenyl)propane dianhydride, 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 products, 4,4'-(m-phenylenedioxy) diphthalic dianhydride; tetracarboxylic dianhydrides in which at least part of the hydrogen atoms contained in these tetracarboxylic dianhydrides are substituted with fluorine atoms; 4,4'-(Hexafluoroisopropylidene)diphthalic dianhydride (sometimes referred to as 6FDA) and the like. Further, the monocyclic aromatic tetracarboxylic dianhydride includes, for example, 1,2,4,5-benzenetetracarboxylic dianhydride, and at least one hydrogen atom contained in the tetracarboxylic dianhydride. Examples include tetracarboxylic dianhydrides whose moieties are substituted with fluorine atoms, and the condensed polycyclic aromatic tetracarboxylic dianhydrides include, for example, 2,3,6,7-naphthalenetetracarboxylic dianhydride, and tetracarboxylic dianhydrides in which at least part of the hydrogen atoms contained in the tetracarboxylic dianhydrides are substituted with fluorine atoms. These can be used singly or in combination of two or more.

The 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; regioisomers thereof; tetracarboxylic dianhydride in which at least part of the hydrogen atoms contained in the tetracarboxylic dianhydride are substituted with fluorine atoms. These can be used singly or in combination of two or more. Specific examples of acyclic aliphatic tetracarboxylic dianhydrides include 1,2,3,4-butanetetracarboxylic dianhydride; 1,2,3,4-pentanetetracarboxylic dianhydride; tetracarboxylic dianhydride in which at least part of the hydrogen atoms contained in the tetracarboxylic dianhydride are substituted with fluorine atoms, 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 above tetracarboxylic acid compounds, 4,4'-oxydiphthalic dianhydride and 3,3',4,4' are preferred from the viewpoint of easily increasing the optical properties, heat resistance, flexibility and solubility of the resin of the film. -benzophenonetetracarboxylic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 2,2',3,3'-biphenyltetracarboxylic dianhydride, 3,3', 4,4′-diphenylsulfonetetracarboxylic dianhydride, 2,2-bis(3,4-dicarboxyphenyl)propane dianhydride, 6FDA, and mixtures thereof are preferred, with 6FDA being more preferred.

In one embodiment of the present invention, the ratio of structural units derived from aliphatic diamines is preferably 30 mol% or more, more preferably 50 mol%, relative to the total molar amount of all structural units derived from diamines constituting the polyimide resin. mol % or more, more preferably 70 mol % or more, particularly preferably 90 mol % or more, and preferably 100 mol % or less. When the proportion of the structural unit derived from the aliphatic diamine is within the above range, the optical properties, heat resistance, bending resistance and solubility of the resin of the film are likely to be improved. 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.

Incidentally, the polyimide-based resin, in addition to the structural units derived from the tetracarboxylic acid compound, other tetracarboxylic acid-derived structural units and tricarboxylic acid-derived structural units and their may further contain structural units derived from anhydrides and derivatives of.

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.

In a preferred embodiment of the present invention, the polyimide resin has the formula (1):

[In the formula (1), X represents a divalent organic group, Y represents a tetravalent organic group, among the organic groups of X and Y, at least one contains a fluorine atom, * is a bond represents]
In the structural unit represented by formula (1), X preferably contains a divalent aliphatic group. When such a polyimide-based resin is included, the optical properties, heat resistance, flex resistance, and resin solubility of the film are likely to be improved.

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.

In formula (1), at least one of the organic groups of X and Y contains a fluorine atom. That is, the fluorine atom may be contained in either one of X and Y, or may be contained in both. In one embodiment of the present invention, it is preferable that at least Y contains a fluorine atom, and X contains a fluorine atom, from the viewpoint of easily increasing the optical properties, heat resistance, flex resistance, and solubility of the resin of the film. and Y contains a fluorine atom. In addition, when Y has a plurality of types of organic groups, at least one organic group among the plurality of types may contain a fluorine atom. The same is true for X.

X in formula (1) includes a divalent aliphatic group, and the divalent aliphatic group includes, for example, a divalent acyclic aliphatic group or a divalent cycloaliphatic group. Among these, a divalent acyclic aliphatic group is preferable from the viewpoint of easily improving the optical properties, heat resistance, flex resistance, and solubility of the resin of the 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 is mentioned. A hydrogen atom in the divalent acyclic aliphatic group may be substituted with a halogen atom, preferably a fluorine atom, and a carbon atom may be substituted with a heteroatom (e.g., oxygen atom, nitrogen atom, etc.) good. The number of carbon atoms in the linear or branched alkylene group is preferably 2 or more, more preferably 3 or more, and still more preferably 3 or more, from the viewpoint of easily improving the optical properties, heat resistance, flex resistance, and solubility of the resin of the film. is 4 or more, preferably 10 or less, more preferably 8 or less, still more preferably 6 or less. Among the divalent acyclic aliphatic groups, from the viewpoint of easily improving the optical properties, heat resistance, flex resistance and solubility of the resin of the film, ethylene group, trimethylene group, tetramethylene group, pentamethylene group, An alkylene group having 2 to 6 carbon atoms such as a hexamethylene group is preferred, and a tetramethylene group is 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, n-heptyl group, n-octyl group, tert-octyl group, n-nonyl group and n-decyl group. 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.

The polyimide resin in the present invention 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 optical properties, heat resistance, and resistance of the film are improved. It is easy to improve flexibility and resin solubility. 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 in the organic group may be substituted with a hydrocarbon group or a halogen-substituted hydrocarbon group. The number of carbon atoms is preferably 1-8. The polyimide resin in 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), from the viewpoint of easily increasing the optical properties, heat resistance, flex resistance and solubility of the resin of the film, formula (26), formula (28) or formula A group represented by (29) is preferred, and a group represented by formula (26) is more preferred. W ¹ is each independently a single bond, —O—, —CH ₂ —, —CH ₂ —CH ₂ from the viewpoint of easily increasing the optical properties, heat resistance, flex resistance, and solubility of the resin of the film. -, -CH(CH ₃ )-, -C(CH ₃ ) ₂ - or -C(CF ₃ ) ₂ -, preferably 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 - is more preferred.

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, 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 )—, hydrogen atoms contained in R ² to R ⁷ and V are independently of each other optionally substituted with halogen atoms; 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 film tends to exhibit excellent optical properties, heat resistance, bending resistance, and resin solubility. 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 above-exemplified alkyl groups having 1 to 6 carbon atoms and alkoxy groups having 1 to 6 carbon atoms. 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, 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 represents -, -CO- or -N(R ⁸ )-, where hydrogen atoms contained in R ² to R ⁷ and V may be independently substituted with halogen atoms. The halogen atom includes those exemplified above, and is preferably a fluorine atom. 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. As the monovalent hydrocarbon group having 1 to 12 carbon atoms which may be substituted with a halogen atom, the monovalent hydrocarbon groups having 1 to 12 carbon atoms which may be substituted with a halogen atom are 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 single bond, -C(CH ₃ ) ₂ - or -C(CF ₃ ) ₂ - is more preferred, and single More preferably, it is a bond or -C(CF ₃ ) ₂ -.

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 film tends to exhibit excellent optical properties, heat resistance and bending resistance. In addition, the skeleton containing elemental fluorine improves the solubility of the resin in a solvent, suppresses the viscosity of the varnish to a low level, and facilitates the enhancement of the film formability of the film.

In one embodiment of the present invention, when Y in formula (1) includes a structure represented by formula (2), Y in formula (1) is the ratio 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, relative to 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 optical properties, heat resistance, flex resistance, and resin solubility of the 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.

Polyimide resin in the present invention, in addition to the structural unit represented by the formula (1), even if it contains a structural unit represented by the formula (30) and / or a structural unit represented by the formula (31) good.

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. As Y ² , the above formulas (20), (21), (22), (23), (24), (25), (26), (27), (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 in X ¹ and X ² , the above formula (10), formula (11), formula (12), formula (13), 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. A hydrogen atom in the divalent acyclic aliphatic group may be substituted with a halogen atom, preferably a fluorine atom, and a carbon atom may be substituted with a heteroatom (e.g., oxygen atom, nitrogen atom, etc.) good.

In one embodiment of the present invention, the polyimide resin is a structural unit represented by formula (1), and optionally a structural unit represented by formula (30) and a structural unit represented by formula (31) It consists of at least one selected structural unit. In addition, from the viewpoint of easily improving the optical properties, heat resistance, flex resistance and solubility of the resin of the film, the proportion of the structural unit represented by the formula (1) in the polyimide resin is included in the polyimide resin. all structural units represented by formula (1), and optionally at least one structural unit selected from structural units represented by formula (30) and structural units represented by formula (31) It is preferably 80 mol % or more, more preferably 90 mol % or more, and still more preferably 95 mol % or more, based on the total molar amount of the units. In addition, in polyimide resin, the upper limit of the ratio of the structural unit represented by Formula (1) is 100 mol% or less. The above ratio can be measured, for example, using ¹ H-NMR, or can be calculated from the charging ratio of raw materials. Moreover, the polyimide-based resin in the present invention is preferably a polyimide resin from the viewpoint of easily improving the optical properties, heat resistance, flex resistance, and solubility of the resin of the film.

The polyimide resin in the present invention contains fluorine atoms. By including fluorine atoms in the polyimide resin, the optical properties, heat resistance, bending resistance, and resin solubility of the film can be easily improved. In the polyimide resin of the present invention, a fluorine atom may be present in the resin, and the form of introduction of the fluorine atom is not particularly limited, but the fluorine atom is introduced into the polyimide resin by a fluorine-containing substituent is preferred. The fluorine-containing substituent includes, for example, a fluoro group and a trifluoromethyl group, from the viewpoint of easily increasing the optical properties, heat resistance, flex resistance, and solubility of the resin of the film.

The content of fluorine atoms in the polyimide resin in the present invention is preferably 1% by mass or more, more preferably 5% by mass or more, still more preferably 10% by mass or more, and even more preferably, relative to the mass of the polyimide resin. is 15% by mass or more, particularly preferably 20% by mass or more, preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less. When the fluorine atom content is at least the above lower limit, the optical properties, heat resistance, flex resistance, and resin solubility of the film are likely to be enhanced. When the content of fluorine atoms is equal to or less than the above upper limit, synthesis becomes easier. The content of fluorine atoms can be determined, for example, by the method described in Examples.

The imidization rate of the polyimide resin is preferably 90% or higher, more preferably 93% or higher, still more preferably 95% or higher, even more preferably 97% or higher, and particularly preferably 99% or higher. When the imidization rate is at least the above lower limit, it is easy to improve the optical properties. The upper limit of the imidization rate is 100% or less. 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 an IR method, an NMR method, or the like, and can be determined, for example, by the method described in Examples.

In one embodiment of the present invention, the content of the polyimide resin is preferably 40% by mass or more, more preferably 50% by mass or more, still more preferably 60% by mass, particularly preferably 80% by mass, based on the mass of the film. % by mass or more, preferably 100% by mass or less. When the content of the polyimide-based resin is within the above range, it is easy to improve the optical properties, heat resistance, flex resistance, and solubility of the resin of the resulting film.

<Method for producing polyimide resin>
Although the method for producing the polyimide resin in the present invention is not particularly limited, for example, the polyimide resin containing the structural unit represented by the formula (1) is obtained by reacting a diamine compound and a tetracarboxylic acid compound to obtain a polyamic acid. and 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 for synthesizing 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, it is easy to improve the optical properties, heat resistance, flex resistance, and solubility of the resin of the film.

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 200°C, more preferably 50 to 190°C, still more preferably 100 to 180°C, and the reaction time is preferably 3 to 24 hours. More preferably 5 to 20 hours. With such a reaction temperature and reaction time, it is easy to improve the optical properties, heat resistance, flex resistance, and solubility of the resin of the film. The Mw and Mn of the polyimide resin are respectively reaction conditions such as reaction time and reaction temperature; types and amounts of diamine compound, tetracarboxylic acid compound, catalyst, and solvent; composition of good solvent and poor solvent in precipitation operation and can be adjusted by appropriately changing the composition of the cleaning solution.

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, but 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 improve the optical properties, heat resistance, flex resistance, and solubility of the resin of the 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, it is easy to improve the optical properties, heat resistance, flex resistance, and solubility of the resin of the film.

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. It is below. 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 optical properties, heat resistance, flex resistance and solubility of the resin of the film are likely to be improved. In the step of obtaining the polyamic acid, when the diamine compound and the tetracarboxylic acid compound are reacted, an imidization catalyst may be added in advance, and the step of obtaining the polyamic acid and the imidization step may be performed simultaneously. can.

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 method for purifying a resin according to a preferred embodiment, a large amount of an alcoholic solvent such as methanol, ethanol, n-propanol, isopropanol is added to a reaction solution containing a resin to precipitate the resin, followed by concentration, filtration, drying, and the like. can be isolated by

<Oligomer>
In the film of the present invention, the content of oligomers having a molecular weight of 10,000 or less is 6.1 mass % or less. As used herein, the term "oligomer" refers to a polymer in which monomers are combined, which is a dimer or more and has a molecular weight of 10,000 or less.

The content of the oligomer having a molecular weight of 10,000 or less is 6.1% by mass or less, preferably 6.0% by mass or less, more preferably 5.8% by mass or less, and still more preferably 5.5% by mass, relative to the mass of the film. % or less, more preferably 5.0 mass % or less, particularly preferably 4.5 mass % or less, and even more preferably 4.0 mass % or less. When the content of the oligomer having a molecular weight of 10,000 or less is equal to or less than the above upper limit, the flex resistance of the film is likely to be improved. In addition, the content of the oligomer having a molecular weight of 10,000 or less is preferably 1.0% by mass or more, more preferably 1.5% by mass or more, still more preferably 2.0% by mass or more, and still more preferably 1.0% by mass or more, based on the mass of the film. It is preferably 2.5% by mass or more, particularly preferably 3.0% by mass or more. When the content of the oligomer having a molecular weight of 10,000 or less is at least the above lower limit, the solubility of the polyimide resin in a solvent during film formation is likely to be improved. The content of oligomers having a molecular weight of 10,000 or less can be obtained by performing gel permeation chromatography (GPC) measurement and converting to standard polystyrene, for example, it can be calculated by the method described in Examples.

Although the lower limit of the molecular weight of the oligomer in the film is not particularly limited, it is preferably 700 or more, more preferably 800 or more, even more preferably 900 or more, and still more preferably 1,000 or more. When the molecular weight of the oligomer is at least the above lower limit, the flex resistance of the film and the solubility of the resin are likely to be improved. The lower limit of the molecular weight of the oligomer can be the molecular weight of the dimer. The film may contain 1 or 2 or more oligomers, preferably 2 or more, more preferably 4 or more, still more preferably 6 or more, preferably 20 or less, more preferably 15 or less. , and more preferably 10 or less. Here, the different types of oligomers means not only different types of monomer units constituting the oligomers, but also different monomer unit ratios, molecular weights, and the like.

Specifically, the type of oligomer is not particularly limited, and examples thereof include polyimide-based oligomers, polyamide-based oligomers, polyester-based oligomers, polyolefin-based oligomers, polycarbonate-based oligomers, polystyrene-based oligomers, and polyvinyl alcohol-based oligomers. Polyimide-based oligomers are preferred from the standpoint of facilitating the enhancement of flexibility and resin solubility. The polyimide-based oligomer means an oligomer containing an imide group and optionally an amide group, and from the viewpoint of easily improving the flexibility of the film and the solubility of the resin, the diamine compound described in the section <Polyimide-based resin> above. and the tetracarboxylic acid compound and optionally the tricarboxylic acid compound as monomer units (structural units), and more preferably an oligomer having a structural unit represented by formula (1). It is more preferable that the oligomer has a structural unit described as preferable among the structural units represented by formula (1). The oligomer may be intentionally added during the film manufacturing process, but in a preferred embodiment of the present invention, the polyimide resin manufacturing process and/or the film manufacturing process, particularly the polyimide resin manufacturing process The oligomer preferably comprises the same monomeric units as the polyimide-based resin in the film, since oligomers can be formed at .

Oligomers may be linear oligomers or cyclic oligomers. The oligomer preferably contains a cyclic oligomer from the viewpoint of easily improving the flexibility of the film and the solubility of the resin. In particular, when a cyclic oligomer is included, it is easy to effectively suppress stacking between resins and aggregation of the resins due to this, so that the solubility of the resin in a solvent can be easily improved. In addition, the cyclic oligomer is a cyclic multimer, such as a 2- to 20-mer, preferably a 2- to 15-mer, more preferably a 2- to 10-mer, from the viewpoint of easily improving the flexibility of the film and the solubility of the resin. , more preferably 2-8mers.
In a preferred embodiment of the invention, the cyclic oligomer has formula (A):

[In Formula (A), X and Y are the same as X and Y in Formula (1), respectively, and n represents an integer of 1 or more]
is a cyclic oligomer represented by When the cyclic oligomer is represented by the formula (A), the flex resistance of the film and the solubility of the resin are likely to be improved. The oligomer in the present invention preferably contains a plurality of cyclic oligomers represented by formula (A) from the viewpoint of improving flexibility and resin solubility.

From the viewpoint of easily improving the flexibility of the film and the solubility of the resin, preferred X and Y in formula (A) are respectively the same as preferred X and Y in formula (1). In formula (A), two or more X's may be the same or different, and two or more Y's may be the same or different. From the viewpoint of easily improving the flexibility of the film and the solubility of the resin, it is preferable that two or more Xs and two or more Ys in the formula (A) are the same.

In formula (A), n represents an integer of 1 or more. n is preferably an integer of 1 to 19, more preferably an integer of 1 to 14, still more preferably an integer of 1 to 9, still more preferably an integer from the viewpoint of easily improving the flex resistance of the film and the solubility of the resin. An integer from 1 to 7.

In a preferred embodiment of the invention, the cyclic oligomer has formula (B):

[n is synonymous with n in formula (A)]
It is preferably a cyclic oligomer represented by. When the cyclic oligomer is a cyclic oligomer represented by formula (B), it is easy to improve the flexibility of the film and the solubility of the resin. The oligomer in the present invention preferably contains a plurality of cyclic oligomers represented by formula (B) from the viewpoint of improving flexibility and resin solubility.

Oligomers with a molecular weight of 10,000 or less can be assigned using a matrix-assisted laser desorption/ionization time-of-flight mass spectrometer (MALDI-MS measurement), for example, by the method described in the Examples.

The content of the cyclic oligomer, preferably the cyclic oligomer represented by formula (A), is preferably 30% by mass or more, more preferably 50% by mass or more, still more preferably 70% by mass, based on the mass of the oligomer contained in the film. % by mass or more, more preferably 90% by mass or more, particularly preferably 95% by mass or more, and the upper limit is 100% by mass or less. When the content of the polyimide-based oligomer in the film is at least the above lower limit, it is easy to improve the flexibility of the film and the solubility of the resin.

Methods for adjusting the amount of oligomers in the film include, for example, a method by molecular weight fractionation; a method using the method for purifying the resin according to the preferred embodiment of the present invention; a method for adjusting the monomer concentration in the polymerization step of the polyimide resin; A method of adjusting the solvent ratio of a poor solvent and a good solvent (reaction solvent) in the purification (or precipitation) step; and a method of adjusting the polymer concentration in the resin purification (or precipitation) step. In the step of refining (or precipitating) the resin, the method of dropping a poor solvent such as an alcoholic solvent into the reaction solution tends to reduce the amount of oligomers more than the method of dropping the reaction solution into the poor solvent. Also, the amount of oligomer tends to be reduced as the monomer concentration in the resin polymerization step is increased. Furthermore, the smaller the ratio of the poor solvent to the good solvent (reaction solvent) in the resin purification (or precipitation) step, the more the oligomer content tends to be reduced. In addition, the amount of oligomer tends to decrease as the polymer concentration in the resin purification (or precipitation) step decreases.

<Film>
The film of the present invention contains a polyimide resin having a structural unit derived from an aliphatic diamine and a fluorine atom, and contains 6.1% by mass or less of an oligomer having a molecular weight of 10,000 or less. Therefore, bending resistance can be improved, and excellent bending resistance can be obtained. Furthermore, the film according to the preferred embodiment of the present invention, in which the content of the oligomer having a molecular weight of 10,000 or less is 1.0% by mass or more, can improve the solubility of the resin in a solvent, and thus has excellent flex resistance and , and excellent resin solubility can be compatible. Therefore, the film of the present invention can be suitably used as a material for flexible display devices and the like. Moreover, the film of the present invention is preferably an optical film, and the film has excellent optical properties.

In one embodiment of the present invention, the weight average molecular weight (Mw) of the film is preferably 50,000 or more, more preferably 70,000 or more, still more preferably 100,000 or more, still more preferably 150,000 or more, Particularly preferably 170,000 or more, particularly more preferably 180,000 or more, extremely preferably 197,000 or more, preferably 750,000 or less, more preferably 650,000 or less, further preferably 550,000 or less be. When the Mw of the film is at least the above lower limit, the heat resistance and bending resistance of the film are likely to be enhanced. Further, when the Mw is equal to or less than the above upper limit, it is easy to improve the thickness retardation of the film, workability and the solubility of the resin.

In one embodiment of the present invention, the number average molecular weight (sometimes abbreviated as Mn) of the film is preferably 10,000 or more, more preferably 15,000 or more, still more preferably 20,000 or more, still more preferably It is 25,000 or more, preferably 150,000 or less, more preferably 120,000 or less, still more preferably 100,000 or less, even more preferably 50,000 or less, and particularly preferably 40,000 or less. When the Mn of the film is at least the above lower limit, the heat resistance and flex resistance are likely to be enhanced. Further, when the Mn is equal to or less than the above upper limit, it is easy to improve the thickness retardation of the film, the workability and the solubility of the resin. Each of the Mw and Mn of the film 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 Mw and Mn of the film were measured by GPC after dissolving the film itself.

The ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of the film (Mw/Mn; also referred to as molecular weight distribution) is preferably 15 or less, more preferably 13 or less, still more preferably 10 or less, and preferably is 2.0 or more, more preferably 3.0 or more, and still more preferably 4.0 or more. When the molecular weight distribution (Mw/Mn) of the film is equal to or less than the above upper limit, it is easy to improve the thickness retardation of the film, the workability and the solubility of the resin, and the molecular weight distribution (Mw/Mn) of the film is equal to or lower than the above lower limit. It is easy to improve heat resistance and bending resistance as it is above.

In one embodiment of the present invention, in a bending endurance test, the number of times of bending at a bending radius of 1 mm is preferably 100,000 or more, more preferably 150,000 or more, and more preferably 200,000. times or more, more preferably 300,000 times or more, still more preferably 400,000 times or more. When the number of times of bending is equal to or more than the above lower limit, it is easy to effectively suppress breakage of the film even if the film is repeatedly bent. The upper limit of the number of bends is usually 5,000,000 or less. The number of bends of the film can be measured using a planar body no-load U-shaped stretch tester (tabletop durability tester) under the conditions of a test speed of 30 rpm and a bending radius R of 1 mm, for example, by the method described in Examples. can.

The thickness of the film of the present invention can be appropriately selected depending on the application, and is preferably 5 µm or more, more preferably 10 µm or more, still more preferably 15 µm or more, preferably 100 µm or less, more preferably 80 µm or less, and still more preferably 60 µm. Below, it is particularly preferably 50 μm or less. When the thickness of the film is within the above range, it is advantageous from the viewpoint of the bending resistance of the film. The thickness of the film can be measured using a thickness meter or the like, for example, by the method described in Examples.

In one embodiment of the present invention, the film of the present invention may contain an ultraviolet absorber. The film of the present invention contains the polyimide resin, and the content of the oligomer having a molecular weight of 10,000 or less is adjusted to the above upper limit or less. there is Moreover, in a preferred embodiment of the present invention, the content of the oligomer having a molecular weight of 10,000 or less is adjusted to the above lower limit or more. can be improved, that is, the film formability during film production can be improved. 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. 300 to 400 nm, preferably around 320 to 360 nm UV absorption, without reducing the transmittance in the visible light region, from the viewpoint of improving the UV cut properties of the film, a benzotriazole-based UV absorber and At least one selected from the group consisting of triazine-based ultraviolet absorbers is preferably used, and benzotriazole-based ultraviolet absorbers are more preferable.

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 the 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 ADEKA Corporation's product name: ADEKA STAB (registered trademark) LA-31 (2,2'-methylenebis[6-(2H-benzo triazol-2-yl)-4-(1,1,3,3-tetramethylbutyl)phenol]). The ultraviolet absorber is preferably the compound represented by formula (I) and Tinuvin 213 (methyl 3-[3-(2H-benzotriazol-2-yl) 5-tert-butyl-4-hydroxyphenyl]propionate It is a reaction product 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. product 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.

A triazine-based ultraviolet absorbent is used in a film containing a polyimide-based resin as an ultraviolet absorbent according to another preferred embodiment. 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 represented by 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 light absorption of 300 to 400 nm, more preferably 320 to 360 nm, and even more preferably around 350 nm.

When the 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. It is 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, it is easy to improve the UV cut property of the film, and when the content of the UV absorber is at most the above upper limit, the optical properties, heat resistance, and bending resistance of the film are improved. It is easy to improve properties and resin solubility.

The film of the present invention may contain at least one filler. When the filler is contained, the optical properties, heat resistance and bending resistance of the film are likely to be improved. 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, and among these, silica particles, zirconia particles, and alumina particles are preferable from the viewpoint that the film tends to have well-balanced optical properties, heat resistance, and flex resistance. and more preferably silica particles. 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 optical properties, heat resistance and flex resistance of the resulting 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 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 film. Above, more preferably 10% by mass or more, preferably 60% by mass or less, more preferably 50% by mass or less, still more preferably 40% by mass or less. When the content of the filler is within the above range, it is easy to improve the optical properties, heat resistance, and flex resistance of the film.

The film of the present invention may further contain additives other than ultraviolet absorbers and fillers. 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 is preferably 0.001 to 20% by mass, more preferably 0.01 to 15% by mass, more preferably 0.1 to 10% by mass, based on the mass of the film. % by mass.

Applications of the 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. may As described above, the film of the present invention may be a single layer or a laminate. The film of the present invention may be used as it is, or may be used as a laminate with another film. You may When the film is a laminate, the film includes all layers laminated on one side or both sides of the film.

When the film of the present invention is a laminate, it preferably has one or more functional layers on at least one surface of the 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 film of the present invention may have a protective film on at least one side (single side or both sides). For example, when the film of the present invention has a functional layer on one side, the protective film may be laminated on the film side surface or the functional layer side surface, or may be laminated on both the film side and the functional layer side. may When the film of the present invention 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 film or the functional layer, and is not particularly limited as long as it is a peelable film that can protect the surface of the 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 film of the present invention 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 film of the present invention has two protective films, the thickness of each protective film may be the same or different.

[Film manufacturing method]
The film of the present invention is not particularly limited, but for example the following steps:
(a) a step of preparing a liquid (also referred to as varnish) containing the polyimide resin (hereinafter referred to as a varnish preparation step);
(b) a step of applying a varnish to a substrate to form a coating film (hereinafter referred to as a coating step); and (c) a step of drying the applied liquid (coating film) to form a film (hereinafter referred to as film forming process)
It can be manufactured by a method comprising

In the varnish preparation process, the varnish is prepared by dissolving the polyimide resin in a solvent, adding the additives as necessary, and stirring and mixing.

The solvent used for preparing the varnish is not particularly limited as long as it can dissolve the polyimide 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 is mentioned. Among these, amide solvents, lactone solvents and ketone solvents are preferred. These solvents can be used alone or in combination of two or more. In addition, the varnish may contain water, alcohol solvents, acyclic ester solvents, ether solvents, and the like. In particular, in a preferred embodiment of the present invention, the amount of oligomer is adjusted to the above lower limit or more, so that the resin can be easily dissolved even when using a ketone-based solvent in which polyimide-based resins such as cyclohexanone are difficult to dissolve. A film having excellent optical properties, bending resistance, and the like can be formed.

The solid content concentration of the varnish is preferably 1-30% by mass, more preferably 5-25% by mass, and still more preferably 10-20% 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, it is easy to make the film uniform, and it is easy to obtain a film excellent in optical properties, heat resistance and bending resistance.

In the coating process, the varnish is applied to the substrate by a known coating method to form a coating film. 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 film forming process, the film can be formed by drying the coating film and peeling it off from the substrate. A drying step for drying the 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 of the invention, it is preferred to carry out the drying in stages. A varnish containing a high-molecular-weight resin tends to have a high viscosity, making it generally difficult to obtain a uniform film, and optical properties (especially transparency), bending resistance, and heat resistance may deteriorate. Therefore, by performing stepwise drying, it is possible to uniformly dry the varnish containing the high molecular weight resin, and it has excellent optical properties (especially transparency), a high Tg, and excellent heat resistance and bending resistance. you can get the film. 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 low temperature to high temperature within such a range, a film excellent in optical properties, heat resistance and flex resistance can be easily obtained. If desired, drying of the coating may be performed under inert atmospheric conditions. Further, if the film is dried under vacuum conditions, minute air bubbles may be generated and remain in the film, which may cause deterioration of transparency. Therefore, it is preferable to dry the film under atmospheric pressure.

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

The film of the present invention can be suitably used as a substrate for display devices, particularly touch sensors. 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 invention includes flexible displays comprising the films of the invention. Examples of the flexible display device include display devices having flexible characteristics, such as televisions, smartphones, mobile phones, and smart watches.
A flexible display device is a display device that is used with an operation such as repeatedly bending or winding the display device, and examples thereof include a rollable display and a foldable display. A rollable display is an image display device in which an image display portion is wound into a roll and is used in a state in which the image display portion is pulled out to form a flat or curved surface. is an image display device that is performed each time it is used. A foldable display is an image display device in which an image display portion is folded and used in a state where the image display portion is opened to form a flat surface or a curved surface. It is an image display device that can be used.

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. A touch sensor substrate (or a touch sensor film) used in such a flexible display device is required to have bending resistance, and the film of the present invention has excellent bending resistance. (or a 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.

[Polyimide resin]
The present invention is a polyimide resin having a structural unit derived from an aliphatic diamine and a fluorine atom, and having a content of an oligomer having a molecular weight of 10,000 or less is 5.5% by mass or less with respect to the mass of the polyimide resin. encompasses Since the content of the oligomer having a molecular weight of 10,000 or less is 5.5% by mass or less, the polyimide resin of the present invention can form a film having excellent bending resistance. When the content of the oligomer having a molecular weight of 10,000 or less in the polyimide resin exceeds 5.5% by mass, the flex resistance of the film tends to decrease.

In the polyimide resin of the present invention, the content of the oligomer having a molecular weight of 10,000 or less is 5.5% by mass or less, preferably 5.0% by mass or less, more preferably 4.5% by mass, based on the mass of the polyimide resin. % or less, more preferably 4.0 mass % or less, still more preferably 3.5 mass % or less. When the content of the oligomer having a molecular weight of 10,000 or less is equal to or less than the above upper limit, the bending resistance of the obtained film is likely to be improved.

In the polyimide resin of the present invention, the content of the oligomer having a molecular weight of 10,000 or less is preferably more than 0.7% by mass, more preferably 1.0% by mass or more, more preferably 1.0% by mass or more, and more preferably It is 1.5% by mass or more, more preferably 2.0% by mass or more, and particularly preferably 2.5% by mass or more. When the content of the oligomer having a molecular weight of 10,000 or less is at least the above lower limit, the solubility of the polyimide resin in a solvent during film formation is likely to be improved. In a preferred embodiment of the present invention, the polyimide resin has a content of oligomers with a molecular weight of 10,000 or less, which is adjusted to more than 0.7% by mass and 5.5% by mass or less, so that excellent flex resistance and excellent solubility. The content of oligomers having a molecular weight of 10,000 or less can be obtained by performing gel permeation chromatography (GPC) measurement and converting to standard polystyrene, for example, it can be calculated by the method described in Examples.

Because polyimide resins can be thermally decomposed during film formation, the oligomer content in the polyimide resin before film formation tends to be smaller than the oligomer content in the film. The oligomer in the polyimide resin of the present invention is the same as the oligomer described in the section <Oligomer> above, except for the content range.

In one embodiment of the present invention, the weight average molecular weight (Mw) of the polyimide resin is preferably 100,000 or more, more preferably 150,000 or more, still more preferably 170,000 or more, still more preferably 200,000. or more, particularly preferably 220,000 or more, particularly more preferably 230,000 or more, extremely preferably 250,000 or more, preferably 800,000 or less, more preferably 700,000 or less, further preferably 600,000 It is below. When the Mw of the polyimide resin is at least the above lower limit, the heat resistance and flex resistance of the film can be easily improved. Further, when the Mw of the polyimide-based resin is equal to or less than the above upper limit, it is easy to improve the thickness retardation of the film, the workability and the solubility of the resin.

In one embodiment of the present invention, the number average molecular weight (Mn) of the polyimide resin is preferably 15,000 or more, more preferably 20,000 or more, still more preferably 25,000 or more, still more preferably 35,000 above, particularly preferably 40,000 or more, particularly more preferably 45,000 or more, preferably 180,000 or less, more preferably 150,000 or less, still more preferably 130,000 or less, still more preferably 80, 000 or less, particularly preferably 70,000 or less. When the Mn of the polyimide resin is at least the above lower limit, the heat resistance and flex resistance of the film are likely to be improved. Further, when the Mn of the polyimide resin is equal to or less than the above upper limit, it is easy to improve the thickness retardation of the film, workability and the solubility of the resin. The Mw and Mn of the polyimide resin can each 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 ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of the polyimide resin (Mw/Mn; molecular weight distribution) is preferably 13 or less, more preferably 11 or less, and still more preferably 8.0 or less. , preferably 1.5 or more, more preferably 2.0 or more, and still more preferably 3.0 or more. When the molecular weight distribution (Mw/Mn) of the polyimide resin is the above upper limit or less, the thickness retardation of the film, the processability and the solubility of the resin are easily improved, and the molecular weight distribution (Mw/Mn) of the polyimide resin is at least the above lower limit, the heat resistance and flex resistance of the film tend to be enhanced.

The polyimide-based resin of the present invention is a resin composed of one or more polyimide-based resins, and includes a mixture of two or more polyimide-based resins (sometimes referred to as a polyimide-based resin blend). When the polyimide-based resin in the present invention is a polyimide-based resin blend, the above Mw of the polyimide-based resin blend can be determined by measuring the polyimide-based resin blend itself by GPC and converting it to standard polystyrene. Mn, molecular weight distribution (Mw/Mn), imidization rate, and fluorine atom content are similarly determined by measuring the polyimide resin blend itself.

　Since the polyimide resin can be thermally decomposed during film formation, the average molecular weight of the polyimide resin tends to be larger than the average molecular weight of the film. The polyimide-based resin of the present invention is the same as the polyimide-based resin described in the section <Polyimide-based resin> above, except for the range of Mw, Mn and molecular weight distribution. The method for producing the polyimide resin of the present invention is the same as the method described in <Method for producing polyimide resin> above.

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. First, the measurement method will be explained.

<Mw, Mn, Oligomer Amount of Resin and Film>
The weight-average molecular weight (Mw), number-average molecular weight (Mn), and content of oligomers having a molecular weight of 10,000 or less of the polyimide resins and films obtained in Examples and Comparative Examples were determined using GPC as follows. was measured under the conditions of
(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)

(analysis conditions)
Software: LabSolutions manufactured by Shimadzu Corporation
Algorithm: i-Peak Finder
Peak detection sensitivity: 5
Peak detection range: 0-12 min Baseline processing: Baseline length 10 min
Peak filter: minimum area: 10000 uV*sec
Minimum height: 10uV
Minimum height/width: 3000uV/min

<Assignment of Oligomer>
Oligomers having a molecular weight of 10,000 or less in polyimide resins and films obtained in Examples and Comparative Examples were attributed by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-MS measurement) shown below. carried out.
(MALDI-MS conditions)
Apparatus: JEOL Ltd. JMS-S3000
Mode: Spiral positive
Laser intensity: 35
Laser Mode: 250Hz
Delay time: 200ns
m/z: 250-5000
Detector: 55
Plate: μ-Focus-MALDI Plate (manufactured by HST)
Preprocessing:
The sample was dissolved in NMP, and 2,5-dihydroxybenzoic acid (DHB) was used as the matrix (MA), dissolved in methanol, and the sample solution and the matrix solution were dropped and dried in this order.

<Imidation rate>
The imidization ratios of the polyimide resins obtained in Examples and Comparative Examples were 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 1H 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 1H 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

<Content of fluorine atoms>
The content of fluorine atoms in the polyimide resins obtained in Examples and Comparative Examples was obtained by burning and decomposing the polyimide resin in a flask, absorbing the generated gas into an aqueous sodium hydroxide solution in the flask, and determining the fluorine content in the water. The ion concentration was obtained by measuring with ion chromatography (“ICS-5000”, manufactured by Thermo Fisher Scientific).

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

<Flexibility test>
The number of bending times of the films obtained in Examples and Comparative Examples was determined as follows. The film was cut into strips of width 10 mm×length 120 mm using a dumbbell cutter. The cut film is set on the main body with a planar body no-load U-shaped stretching test (desktop type durability test) machine ("model DMLHB-FS", Yuasa System Co., Ltd.), and the test speed is 30 rpm and the bending radius is R. = 1 mm, the number of times of bending until the film was broken was measured, and this was defined as the number of times of bending. Note that the evaluation was performed with 400,000 times as the upper limit.

<Evaluation of Solubility in Solvent>
Solubility in solvents of the polyimide resins obtained in Examples and Comparative Examples was evaluated as follows. When a resin having a solid content concentration of 13 to 17% by mass was stirred in cyclohexanone at 25° C. for 8 hours, the presence or absence of undissolved residue was visually confirmed.
In the solubility evaluation, cyclohexanone was used as an example of a solvent in which the polyimide resin is difficult to dissolve.

[Example 1]
(polyimide resin)
In a nitrogen gas atmosphere, m-cresol (manufactured by Honshu Chemical Industry Co., Ltd.) 893 kg, 1,4-DAB (manufactured by AnQore) 40 kg, 6FDA (manufactured by Hakko Tsusho Co., Ltd.) are placed in a reaction vessel equipped with a stirring blade. After adding 201 kg and 17 kg of isoquinoline (manufactured by C-Chem Co., Ltd.), the temperature was raised to 130°C, and after stirring for 8 hours, the obtained reaction solution was cooled to 40°C. While stirring, 1,680 kg of methanol (manufactured by Sumitomo Chemical Co., Ltd.) was added to precipitate, followed by filtration. The filtered precipitate was washed with methanol (706 kg) three times, and the washed precipitate was dried at 70° C. for 40 hours to obtain 209 kg of polyimide resin.
The obtained polyimide resin had a weight average molecular weight (Mw) of 249,000, a number average molecular weight (Mn) of 37,000, a molecular weight distribution (Mw/Mn) of 6.6, and a molecular weight of 10,000. The content of 000 or less oligomers was 4.6% by mass. The imidization rate of the polyimide resin was 99.6%, and the content of fluorine atoms was 22% by mass.

(the film)
A varnish was prepared by dissolving the polyimide resin obtained above in cyclohexanone and adding 2 phr (2 parts by mass to 100 parts by mass of the polyimide resin) of Sumisorb 340 as an ultraviolet absorber (UVA). Then, 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 a film with a thickness of 50 μm. The bending number of the obtained film was 400,000 times or more.
Further, according to the results of GPC when the obtained film was redissolved, the polyimide resin in the film had a weight average molecular weight (Mw) of 198,000 and a number average molecular weight (Mn) of 28,000. The molecular weight distribution (Mw/Mn) was 7.1, and the content of oligomers having a molecular weight of 10,000 or less was 5.8% by mass.

[Example 2]
(polyimide resin)
In a nitrogen gas atmosphere, 893 kg of m-cresol (Honshu Chemical Industry Co., Ltd.), 40 kg of 1,4-DAB (manufactured by AnQore), and 201 kg of 6FDA (manufactured by Hakko Tsusho Co., Ltd.) are placed in a reaction vessel equipped with a stirring blade. , and 17 kg of isoquinoline (manufactured by C-Chem Co., Ltd.) were added, the temperature was raised to 130°C, and after stirring for 8 hours, the resulting reaction solution was cooled to 40°C. While stirring, 1,680 kg of methanol (manufactured by Sumitomo Chemical Co., Ltd.) was added to precipitate, followed by filtration. The filtered precipitate was washed with methanol (706 kg) five times, and the washed precipitate was dried at 70° C. for 40 hours to obtain 210 kg of polyimide resin. The resulting polyimide resin had a weight average molecular weight (Mw) of 218,000, a number average molecular weight (Mn) of 34,000, a molecular weight distribution (Mw/Mn) of 6.5, and a molecular weight of 10,000. The content of 000 or less oligomers was 4.4% by mass. Also, the imidization rate of the polyimide resin was 99.7%.

(the film)
A film was obtained in the same manner as in Example 1 using the polyimide resin obtained above. In addition, the number of bending times of the obtained film was 150,000.
According to the results of GPC when the obtained film was redissolved, the polyimide resin in the film had a weight average molecular weight (Mw) of 176,000 and a number average molecular weight (Mn) of 30,000. The molecular weight distribution (Mw/Mn) was 5.8, and the content of oligomers having a molecular weight of 10,000 or less was 4.8% by mass.

[Example 3]
(polyimide resin)
In a nitrogen gas atmosphere, 104 g of m-cresol (Honshu Chemical Industry Co., Ltd.), 8 g of 1,4-DAB (manufactured by ThermoFisher), and 40 g of 6FDA (manufactured by Hakko Tsusho Co., Ltd.) were added to a reaction vessel equipped with a stirring blade. , and 3 g of isoquinoline (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) were added, the temperature was raised to 130° C., the mixture was stirred for 8 hours, and then diluted with m-cresol (75 g). Cooled to °C. While stirring, after adding 336 g of SOLMIX AP-1 (manufactured by Nippon Alcohol Sales Co., Ltd.; denatured alcohol (composition: 85.5% ethanol, 13.4% isopropanol, 1.1% methanol)) to precipitate. , filtered. The filtered precipitate was washed with SOLMIX AP-1 (141 g) five times, and the washed precipitate was dried at 70° C. for 12 hours to obtain 42 g of polyimide resin. The obtained polyimide resin had a weight average molecular weight (Mw) of 228,000, a number average molecular weight (Mn) of 52,000, a molecular weight distribution (Mw/Mn) of 4.4, and a molecular weight of 10,000. The content of 000 or less oligomers was 2.7% by mass.

(the film)
A film was obtained in the same manner as in Example 1 using the polyimide resin obtained above. In addition, the number of bending times of the obtained film was 350,000.
According to the results of GPC when the obtained film was redissolved, the polyimide resin in the film had a weight average molecular weight (Mw) of 196,000 and a number average molecular weight (Mn) of 20,000. The molecular weight distribution (Mw/Mn) was 9.7, and the content of oligomers having a molecular weight of 10,000 or less was 4.2% by mass.

[Example 4]
(polyimide resin)
In a nitrogen gas atmosphere, 134 g of m-cresol (Honshu Chemical Industry Co., Ltd.), 8 g of 1,4-DAB (manufactured by ThermoFisher), and 40 g of 6FDA (manufactured by Hakko Tsusho Co., Ltd.) were added to a reaction vessel equipped with a stirring blade. , and 3 g of isoquinoline (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) were added, the temperature was raised to 130° C., the mixture was stirred for 8 hours, and then diluted with m-cresol (119 g). Cooled to °C. While stirring, 476 g of SOLMIX AP-1 (manufactured by Nippon Alcohol Trading Co., Ltd.) was added to precipitate, followed by filtration. The filtered precipitate was washed with SOLMIX AP-1 (141 g) five times, and the washed precipitate was dried at 70° C. for 12 hours to obtain 38 g of a polyimide resin. The obtained polyimide resin had a weight average molecular weight (Mw) of 302,000, a number average molecular weight (Mn) of 50,000, a molecular weight distribution (Mw/Mn) of 6.0, and a molecular weight of 10,000. The content of 000 or less oligomers was 3.1 mass %.

(the film)
A film was obtained in the same manner as in Example 1 using the polyimide resin obtained above. In addition, the number of bending times of the obtained film was 400,000 times or more.
According to the results of GPC when the obtained film was redissolved, the polyimide resin in the film had a weight average molecular weight (Mw) of 196,000 and a number average molecular weight (Mn) of 20,000. The molecular weight distribution (Mw/Mn) was 9.7, and the content of oligomers having a molecular weight of 10,000 or less was 4.2% by mass.

[Comparative Example 1]
(polyimide resin)
A polyimide resin (A) (6FDA-DAB) consisting of 6FDA-derived structural units and 1,4-DAB-derived structural units was produced by the method described in International Publication No. 2019/156717. The resulting polyimide resin (A) has a weight average molecular weight (Mw) of 151,000, a number average molecular weight (Mn) of 26,000, and a molecular weight distribution (Mw/Mn) of 5.7. The content of oligomers having a molecular weight of 10,000 or less was 6.0% by mass.

Next, according to the method described in International Publication No. 2019/156717, a polyimide-based resin (B) (6FDA-DAB) consisting of 6FDA-derived structural units and 1,4-DAB-derived structural units was produced. The resulting polyimide resin (B) has a weight average molecular weight (Mw) of 280,000, a number average molecular weight (Mn) of 37,000, and a molecular weight distribution (Mw/Mn) of 8.3. The content of oligomers having a molecular weight of 10,000 or less was 5.5 mass %.

A polyimide resin was obtained by mixing the polyimide resin (A) and the polyimide resin (B) obtained above so that the weight ratio was 1:1. The resulting polyimide resin had a weight average molecular weight (Mw) of 216,000, a number average molecular weight (Mn) of 32,000, a molecular weight distribution (Mw/Mn) of 6.8, and a molecular weight of 10,000. The content of 000 or less oligomers was 5.8% by weight.

(the film)
A film was obtained in the same manner as in Example 1 by dissolving the polyimide resin obtained above in cyclohexanone. In addition, the bending number of the obtained film was 90,000 times.
According to the results of GPC when the obtained film was redissolved, the weight average molecular weight (Mw) was 190,000, the number average molecular weight (Mn) was 25,000, and the molecular weight distribution (Mw/ Mn) was 7.5, and the content of oligomers having a molecular weight of 10,000 or less was 6.2% by mass.

[Comparative Example 2]
(polyimide resin)
A polyimide resin (C) (6FDA-DAB) consisting of 6FDA-derived structural units and 1,4-DAB-derived structural units was produced by the method described in International Publication No. 2019/156717. The resulting polyimide resin (C) has a weight average molecular weight (Mw) of 183,000, a number average molecular weight (Mn) of 27,000, and a molecular weight distribution (Mw/Mn) of 6.8. The content of oligomers having a molecular weight of 10,000 or less was 6.3% by mass.

A polyimide resin was obtained by mixing the polyimide resin (C) obtained above and the polyimide resin (B) in a weight ratio of 1:2. The resulting polyimide resin had a weight average molecular weight (Mw) of 248,000, a number average molecular weight (Mn) of 34,000, a molecular weight distribution (Mw/Mn) of 7.8, and a molecular weight of 10,000. The content of 000 or less oligomers was 5.8% by mass.

(the film)
A film was obtained in the same manner as in Example 1 by dissolving the polyimide resin obtained above in cyclohexanone. In addition, the bending number of the obtained film was 30,000 times.
According to the results of GPC when the obtained film was redissolved, the polyimide resin in the film had a weight average molecular weight (Mw) of 205,000 and a number average molecular weight (Mn) of 21,000. The molecular weight distribution (Mw/Mn) was 9.8, and the content of oligomers having a molecular weight of 10,000 or less was 6.3% by mass.

Table 1 shows the results of the flexibility test of the films obtained in Examples and Comparative Examples and the solubility evaluation of the polyimide resin in solvents by the above method. Table 1 also shows the Mw and the amount of oligomer obtained by the GPC measurement of the film and the polyimide resin. 1 shows the peaks of oligomers with a molecular weight of 10,000 or less in the GPC data of the film obtained in Example 1, and FIG. Below 10,000 oligomer peaks are shown.

(Assignment of oligomers with a molecular weight of 10,000 or less)
By the above method, the films and polyimide resins obtained in Examples and Comparative Examples were subjected to MALDI-MS measurement, and the attribution of the components having a molecular weight of 10,000 or less was performed. A peak of a cyclic multimer formed by binding was detected. At least 2 to 7 cyclic cyclic multimers were included as cyclic multimers. Therefore, it was confirmed that the oligomer having a molecular weight of 10,000 or less was a cyclic oligomer. The results of MALDI-MS measurement of the polyimide resin obtained in Example 1 are shown in FIG.

Claims

A film containing a polyimide resin having a structural unit derived from an aliphatic diamine and a fluorine atom, and containing an oligomer having a molecular weight of 10,000 or less in an amount of 6.1% by mass or less relative to the mass of the film.
The film according to claim 1, wherein the content of the oligomer having a molecular weight of 10,000 or less is 1.0% by mass or more relative to the mass of the film.
The film according to claim 1 or 2, wherein the oligomer includes a cyclic oligomer.
The film according to any one of claims 1 to 3, wherein the oligomer has a molecular weight of 700 or more.
The film according to any one of claims 1 to 4, wherein the weight average molecular weight (Mw) of the film is 150,000 or more.
The film according to any one of claims 1 to 5, wherein the content of fluorine atoms in the polyimide resin is 10% by mass or more with respect to the mass of the polyimide resin.
The film according to any one of claims 1 to 6, wherein the polyimide resin has an imidization rate of 99% or more.
The polyimide resin has the formula (1):

[In the formula (1), X represents a divalent organic group, Y represents a tetravalent organic group, among the organic groups of X and Y, at least one contains a fluorine atom, * is a bond represents]
8. The film according to any one of claims 1 to 7, wherein the structural unit represented by formula (1) contains a divalent aliphatic group as X.
The structural unit represented by formula (1) is represented by 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, 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 )—, hydrogen atoms contained in R 2 to R 7 and V are independently of each other optionally substituted with halogen atoms; 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 film of claim 8, comprising a structure represented by:
A polyimide resin in which the content of an oligomer having a structural unit derived from an aliphatic diamine and a fluorine atom and having a molecular weight of 10,000 or less is 5.5% by mass or less relative to the mass of the polyimide resin.
The polyimide-based resin according to claim 10, wherein the content of the oligomer having a molecular weight of 10,000 or less is more than 0.7% by mass based on the mass of the polyimide-based resin.
The polyimide resin according to claim 10 or 11, wherein the oligomer includes a cyclic oligomer.
The polyimide resin according to any one of claims 10 to 12, wherein the oligomer has a molecular weight of 700 or more.
The polyimide resin according to any one of claims 10 to 13, wherein the polyimide resin has a weight average molecular weight (Mw) of 170,000 or more.
A flexible display device comprising the film according to any one of claims 1 to 9.
The flexible display device according to claim 15, further comprising a polarizing plate.
The flexible display device according to claim 15 or 16, further comprising a touch sensor.