JP7361479B2 - Optical film containing transparent polyimide polymer - Google Patents

Description

The present invention relates to an optical film containing a transparent polyimide polymer.

In recent years, optical films containing polyimide polymers have been used as functional films for imparting functions to image display devices such as televisions, personal computers, smartphones, tablets, and electronic paper. In particular, functional films used in display parts of electronic devices such as displays in image display devices and touch panels are required to have high transparency with little yellowing and high folding durability.
As a method for manufacturing such an optical film, a method is known in which a varnish containing a polyimide polymer and a solvent is applied onto a substrate to form a coating film, and the coating film is dried. For example, Patent Document 1 describes a method for manufacturing a film using a varnish containing a polyamideimide resin and butyl acetate.

Japanese Patent Application Publication No. 2015-174905

However, when the varnish is manufactured and then stored for a long period of time, or when the varnish is manufactured after the solvent used in the varnish is stored for a long period of time, the varnish itself becomes colored and the transparency of the resulting polyimide polymer film decreases. Something happened. As a countermeasure for restoring transparency, there is a method for purifying varnish, for example, a method in which a polyimide polymer is extracted from a colored varnish by precipitation and redissolved in a solvent, but this method is disadvantageous in terms of cost.
When using a varnish that has been stored for a long period of time or a varnish that is manufactured using a solvent that has been stored for a long period of time, it has been difficult to obtain an optical film with high transparency.

The present invention has been made in view of the above problems, and its purpose is to provide high transparency with little yellowing even when using a varnish that has been stored for a long time or a varnish that is manufactured using a solvent that has been stored for a long time. An object of the present invention is to provide an optical film having high bending durability.

The present inventor has completed the present invention as a result of intensive studies to solve the above problems. That is, the present invention includes the following aspects.
[1] An optical film containing a transparent polyimide polymer,
The ratio of the integral value A of the ¹ H-NMR signal derived from the terminal amino group of the transparent polyimide polymer to the integral value B of the ¹ H-NMR signal derived from the imide group in the chain of the transparent polyimide polymer. An optical film having an integral ratio A/B of 0.0001 or more and 0.001 or less.
[2] The optical film according to [1], wherein the transparent polyimide polymer has a polystyrene equivalent molecular weight of 250,000 to 500,000.
[3] The optical film according to [1] or [2], which has a thickness of 30 μm or more and 100 μm or less, and a total light transmittance of 85% or more.
[4] The optical film according to any one of [1] to [3], wherein the transparent polyimide polymer has a fluorine group.
[5] The optical film according to any one of [1] to [4], wherein the transparent polyimide polymer contains a repeating unit derived from a 2,2'-bis(trifluoromethyl)benzidine derivative.
[6] A method for producing an optical film comprising a step of casting a varnish containing a transparent polyimide polymer, the method comprising integrating ¹ H-NMR signals derived from imide groups in chains of the transparent polyimide polymer. The ratio of the integral value A of the ¹ H-NMR signal derived from the terminal amino group of the transparent polyimide polymer to the value B (integral ratio A/B) is 0.0001 or more and 0.001 or less, Production method.
[7] The method for producing an optical film according to [6], wherein the varnish contains an ester solvent.
[8] The optical film according to any one of [1] to [5] , which is a film for a front plate of a flexible display device.
[9] A flexible display device comprising the optical film according to [8].
[10] The flexible display device according to [9], further comprising a touch sensor.
[11] The flexible display device according to [9] or [10], further comprising a polarizing plate.

According to the present invention, there is provided an optical film having high transparency and high folding durability with little yellowing even when using a varnish that has been stored for a long time or a varnish that is manufactured using a solvent that has been stored for a long time. Can be done.

<Optical film>
The optical film of the present invention is
Contains transparent polyimide polymer,
The ratio of the integral value A of the ¹ H-NMR signal derived from the terminal amino group of the transparent polyimide polymer to the integral value B of the ¹ H-NMR signal derived from the imide group in the chain of the transparent polyimide polymer. (Integral ratio A/B) is 0.0001 or more and 0.001 or less.

[1. Integral ratio A/B]
When the integral ratio A/B is 0.0001 or more and 0.001 or less, the optical film has high transparency. This is thought to be because the terminal amino groups of the transparent polyimide polymer tend not to be oxidized by oxidizing agents such as peroxides because the proportion of terminal amino groups in the transparent polyimide polymer is sufficiently small. The integral ratio A/B of the transparent polyimide polymer is preferably 0.0002 or more and 0.0008 or less, more preferably 0.0003 or more and 0.0006 or less, from the viewpoint of further improving the transparency of the optical film. The method of calculating the integral ratio A/B in the molecular structure of the example of the present application will be explained in detail in the example. When the molecular structures are different, calculations can be made by appropriately selecting measurable peaks.
Examples of means for adjusting the integral ratio A/B include means for adjusting the degree of polymerization of the transparent polyimide polymer, and means for inhibiting the progress of the oxidation reaction by an oxidizing agent such as peroxide. Examples of means for adjusting the degree of polymerization include polymerization conditions (more specifically, polymerization time, polymerization temperature, use of catalyst, type of solvent, monomer concentration, etc.). As means for inhibiting the progress of the oxidation reaction, for example, means for reducing the concentration of peroxide in the varnish for producing an optical film (more specifically, means for inhibiting the production of peroxide in the varnish. means, etc.). The varnish contains a transparent polyimide polymer and a solvent. Peroxides in varnish are thought to be mainly generated by the reaction between solvent molecules in varnish and dissolved oxygen (oxidation reaction of solvent molecules). Therefore, as means for inhibiting the production of peroxide in the varnish, for example, means for reducing the dissolved oxygen concentration in the varnish, and selecting a type of solvent that does not easily react with oxygen to produce peroxide. Examples include means. As a means of reducing the dissolved oxygen concentration in the varnish, for example, bubbling treatment is performed on the solvent using an inert gas (more specifically, a rare gas such as argon gas and neon gas, nitrogen gas, etc.). Examples include means for replacing dissolved oxygen in the solvent with an inert gas, and means for reducing the oxygen concentration in the gas phase in contact with the solvent under a reduced pressure atmosphere or an inert gas atmosphere. The bubbling treatment time is preferably, for example, 10 minutes or more and 1 hour or less, from the viewpoint of sufficiently achieving replacement of dissolved oxygen and reducing costs. For example, when performing a bubbling process on a mixed solvent containing two types of esters, the bubbling process may be performed on at least one of the two solvents before mixing the two types of solvents. After mixing the two types of solvents, a bubbling process may be performed on the mixed solvent. Moreover, after preparing the varnish, a bubbling process may be performed on the varnish. The solvent will be described later.

In the present invention, the integral value B of the ¹ H-NMR signal derived from the imide groups of the transparent polyimide polymer is the integral value B of the ¹ H-NMR signal of the protons present corresponding to the number of imide groups of the transparent polyimide polymer. It may be an integral value. In addition, the integral value A of the ¹ H-NMR signal derived from the terminal amino group of the transparent polyimide polymer is the integral value A of the ¹ H-NMR signal of the protons present corresponding to the number of terminal amino groups of the transparent polyimide polymer. It may be an integral value.
The ¹ H-NMR signal derived from the terminal amino group is a signal derived from a proton near the terminal amino group, and a signal whose chemical shift does not overlap with other protons can be appropriately selected. As the ¹ H-NMR signal derived from the terminal amino group, ^{the 1} H-NMR signal derived from the proton of the amino group itself may be selected, but if the waveform changes due to the influence of moisture etc. and the accuracy decreases. or other peaks, it is preferable to select protons near the terminal amino group. As the ¹ H-NMR signals of protons present corresponding to the number of imide groups, ^{a 1} H-NMR peak of protons that has a strong correlation with the imide skeleton in the structure of the polymer may be selected. For example, to measure the integral value of the ¹ H-NMR signal derived from the terminal amino group, a specific proton A in a specific partial structure A near the terminal amino group is selected, and a proton in a similar partial structure is selected. Therefore, protons B having different chemical shifts can be used to measure the integral value of the ¹ H-NMR signal derived from the imide group. Based on the ratio of the integrated intensities of these ¹ H-NMR signals, the ¹ H-NMR signal originating from the terminal amino group of the transparent polyimide polymer to the integral value B of ^{the 1} H-NMR signal originating from the imide group. The ratio of integral values A (integral ratio A/B) can be determined. In this case, each proton is selected so that the number of protons A corresponds to the number of amino groups, and the number of protons B corresponds to the number of imide groups. As the partial structure A, a structure derived from diamine in the polymer can be mentioned.

[2. Polystyrene equivalent molecular weight]
The polystyrene equivalent molecular weight (polystyrene equivalent weight average molecular weight) of the transparent polyimide polymer is preferably 250,000 to 500,000, more preferably 270,000 to 450,000, and even more preferably 300,000 to 450,000. When the polystyrene equivalent molecular weight is 500,000 or less, the processability of the varnish for producing an optical film can be improved. When the polystyrene equivalent molecular weight is 250,000 or more, the folding durability of the optical film can be improved.
Therefore, when the polystyrene equivalent molecular weight is 250,000 or more and 500,000 or less, the folding durability of the optical film can be improved, and the processability of the varnish can be improved.
The polystyrene equivalent molecular weight of the transparent polyimide polymer is measured using gel permeation chromatography (GPC). The measurement method will be explained in detail in Examples.

Examples of means for adjusting the molecular weight in terms of polystyrene include means for adjusting the degree of polymerization of a transparent polyimide polymer. Examples of means for adjusting the degree of polymerization include polymerization conditions (more specifically, polymerization time, polymerization temperature, use of catalyst, type of solvent, monomer concentration, etc.).

[3. thickness]
The thickness of the optical film is preferably 30 μm or more and 100 μm or less, more preferably 30 μm or more and 90 μm or less, and still more preferably 30 μm or more and 85 μm or less . A thickness of 30 μm or more is advantageous in terms of internal protection when the optical film is used as a device, and a thickness of 100 μm or less is advantageous in terms of bending durability, cost, transparency, etc.

[4. Transmittance]
The total light transmittance of the optical film is preferably 85% or more, more preferably 88% or more, and still more preferably 90% or more.

[5. Transparent polyimide polymer]
(Transparent polyimide polymer obtained by polymerization and imidization)
Examples of the transparent polyimide polymer include polyimide, which comprehensively includes polyimide and its derivatives. As used herein, polyimide refers to a polymer containing repeating structural units containing imide groups.

It is preferable that the transparent polyimide polymer mainly contains repeating units represented by formula (10) from the viewpoint of transparency of the transparent polyimide polymer film. The ratio of the repeating unit represented by formula (10) is preferably 40 mol% or more, more preferably 50 mol% or more, even more preferably 70 mol% or more, based on the total of all repeating units of the transparent polyimide polymer. , even more preferably 90 mol% or more, particularly preferably 98 mol% or more. The repeating unit represented by formula (10) may be 100 mol%. Moreover, in formula (10), G is a tetravalent organic group, and A is a divalent organic group.
The transparent polyimide polymer may include two or more repeating units represented by formula (10) in which G and/or A are different.

The transparent polyimide polymer contains one or more repeating units represented by formula (11), formula (12), and formula (13) within a range that does not impair various physical properties of the transparent polyimide polymer film obtained. may further include.

In formulas (10) and (11), G and G ¹ represent a tetravalent organic group, preferably an organic group optionally substituted with a hydrocarbon group or a fluorine-substituted hydrocarbon group. As G and G ¹ , for example, formula (20), formula (21), formula (22), formula (23), formula (24), formula (25), formula (26), formula (27), formula Examples include groups represented by formula (28) and formula (29), and a tetravalent chain hydrocarbon group having 6 or less carbon atoms. * in formulas (20) to (29) represents a bond, and Z in formula (26) represents 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 (more specifically, a phenylene group, etc.) which may be substituted with a fluorine atom. From the viewpoint of suppressing the yellowness of the resulting film, G and G ¹ preferably represent groups represented by formulas (20) to (27).

In formula (12), G ² represents a trivalent organic group, preferably an organic group optionally substituted with a hydrocarbon group or a fluorine-substituted hydrocarbon group. Examples of the trivalent organic group represented by ^G2 include formula (20), formula (21), formula (22), formula (23), formula (24), formula (25), formula (26), and formula (27), a group in which one of the bonding hands of the group represented by formula (28) and formula (29) is replaced with a hydrogen atom, and a trivalent chain hydrocarbon group having 6 or less carbon atoms. It will be done.

In formula (13), G ³ represents a divalent organic group, preferably an organic group optionally substituted with a hydrocarbon group or a fluorine-substituted hydrocarbon group. Examples of the divalent organic group represented by ^G3 include formula (20), formula (21), formula (22), formula (23), formula (24), formula (25), formula (26), and formula (27), a group in which two non-adjacent bonds of the group represented by formula (28) and formula (29) are each replaced with a hydrogen atom, and a divalent chain hydrocarbon having 6 or less carbon atoms Examples include groups.

In formulas (10) to (13), A, A ¹ , A ² and A ³ each represent a divalent organic group, preferably substituted with a hydrocarbon group or a fluorine-substituted hydrocarbon group. Represents a good organic group. Examples of A, A ¹ , A ² , and A ³ include formula (30), formula (31), formula (32), formula (33), formula (34), formula (35), and formula (36). , a group represented by formula (37) and formula (38); a group substituted with a methyl group, a fluoro group, a chloro group, or a trifluoromethyl group; and a chain hydrocarbon group having 6 or less carbon atoms. can be mentioned.
* in formulas (30) to (38) represents a bond, and Z ¹ , Z ² and Z ³ in formulas (34) to (36) each independently represent a single bond, -O-, Represents -CH ₂ -, -CH ₂ -CH ₂ -, -CH(CH ₃ )-, -C(CH ₃ ) ₂ -, -C(CF ₃ ) ₂ -, -SO ₂ - or -CO-. One example is where Z ¹ and Z ³ are -O- and Z ² is -CH ₂ -, -C(CH ₃ ) ₂ -, -C(CF ₃ ) ₂ - or -SO ₂ -. represent. Z ¹ and Z ² and Z ² and Z ³ are each preferably at the meta or para position with respect to each ring.

The repeating units represented by formulas (10) and (11) are usually derived from diamines and tetracarboxylic acid compounds. The repeating unit represented by formula (12) is usually derived from a diamine and a tricarboxylic acid compound. The repeating unit represented by formula (13) is usually derived from a diamine and a dicarboxylic acid compound. These carboxylic acid compounds (tetracarboxylic acid compounds, tricarboxylic acid compounds, and dicarboxylic acid compounds) may be carboxylic acid compound analogs (more specifically, carboxylic acid anhydrides, halogenated alkanoyls, etc.).

It is preferable that the transparent polyimide polymer has a fluorine group. The transparent polyimide polymer preferably contains a repeating unit derived from a 2,2'-bis(trifluoromethyl)benzidine derivative. Note that in this specification, 2,2'-bis(trifluoromethyl)benzidine derivatives also include 2,2'-bis(trifluoromethyl)benzidine.

(Tetracarboxylic acid compound)
Examples of the tetracarboxylic acid compound include aromatic tetracarboxylic acid compounds such as aromatic tetracarboxylic dianhydride, and aliphatic tetracarboxylic acid compounds such as aliphatic tetracarboxylic dianhydride. These tetracarboxylic acid compounds may be used alone or in combination of two or more. The tetracarboxylic acid compound may be a tetracarboxylic acid compound analog such as a tetracarboxylic acid chloride compound in addition to a tetracarboxylic dianhydride.

Examples of aromatic tetracarboxylic dianhydrides include non-fused polycyclic aromatic tetracarboxylic dianhydrides, monocyclic aromatic tetracarboxylic dianhydrides, and fused polycyclic aromatic tetracarboxylic dianhydrides. Examples include carboxylic dianhydrides.
Examples of the non-fused polycyclic aromatic tetracarboxylic dianhydride include 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- dicarboxyphenyl)propane dianhydride, 2,2-bis(3,4-dicarboxyphenoxyphenyl)propane dianhydride, 4,4'-(hexafluoroisopropylidene)diphthalic dianhydride (hereinafter referred to as 6FDA) ), 1,2-bis(2,3-dicarboxyphenyl)ethane dianhydride, 1,1-bis(2,3-dicarboxyphenyl)ethane dianhydride, 1,2-bis (3,4-dicarboxyphenyl)ethane dianhydride, 1,1-bis(3,4-dicarboxyphenyl)ethane dianhydride, bis(3,4-dicarboxyphenyl)methane dianhydride, bis( 2,3-dicarboxyphenyl)methane dianhydride, 4,4'-(p-phenylenedioxy)diphthalic dianhydride and 4,4'-(m-phenylenedioxy)diphthalic dianhydride are mentioned. It will be done.

Furthermore, examples of the fused polycyclic aromatic tetracarboxylic dianhydride include 2,3,6,7-naphthalenetetracarboxylic dianhydride.
The aromatic tetracarboxylic dianhydride is preferably 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-dicarboxyphenyl)propane dianhydride Anhydride, 2,2-bis(3,4-dicarboxyphenoxyphenyl)propane dianhydride, 4,4'-(hexafluoroisopropylidene)diphthalic 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 and 4,4'-(m-phenylenedioxy)diphthalic dianhydride. These aromatic tetracarboxylic dianhydrides may be used alone or in combination of two or more.

Examples of the aliphatic tetracarboxylic dianhydride include cyclic or acyclic aliphatic tetracarboxylic dianhydride. In this specification, a cycloaliphatic tetracarboxylic dianhydride refers to a tetracarboxylic dianhydride having an alicyclic hydrocarbon structure. Examples of the cycloaliphatic tetracarboxylic dianhydride include 1,2,4,5-cyclohexanetetracarboxylic dianhydride, 1,2,3,4-cyclobutanetetracarboxylic dianhydride, and 1, Cycloalkanetetracarboxylic dianhydride such as 2,3,4-cyclopentanetetracarboxylic dianhydride, bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride Examples include acid dianhydride, dicyclohexyl-3,3',4,4'-tetracarboxylic dianhydride, and positional isomers thereof. These cycloaliphatic tetracarboxylic dianhydrides may be used alone or in combination of two or more. Examples of the acyclic aliphatic tetracarboxylic dianhydride include 1,2,3,4-butanetetracarboxylic dianhydride and 1,2,3,4-pentanetetracarboxylic dianhydride. . These acyclic aliphatic tetracarboxylic dianhydrides may be used alone or in combination of two or more.

From the viewpoint of further improving the transparency of the transparent polyimide polymer film, the tetracarboxylic acid compound is preferably an alicyclic tetracarboxylic dianhydride or a non-fused polycyclic aromatic tetracarboxylic dianhydride. 3,3',4,4'-biphenyltetracarboxylic dianhydride, 2,2',3,3'-biphenyltetracarboxylic dianhydride, 2,2-bis(3,4-dicarboxyphenyl) Propane dianhydride and 4,4'-(hexafluoroisopropylidene) diphthalic dianhydride (6FDA) are more preferred. These suitable tetracarboxylic acid compounds may be used alone or in combination of two or more.

(Tricarboxylic acid compounds and dicarboxylic acid compounds)
The raw material monomer can further contain a tricarboxylic acid compound and/or a dicarboxylic acid compound.
Examples of the tricarboxylic acid compound include aromatic tricarboxylic acids, aliphatic tricarboxylic acids, and their analogous acid chloride compounds and acid anhydrides. These tricarboxylic acid compounds may be used alone or in combination of two or more. Examples of tricarboxylic acid compounds include 1,2,4-benzenetricarboxylic anhydride; 2,3,6-naphthalenetricarboxylic acid-2,3-anhydride; phthalic anhydride and benzoic acid forming a single bond; Examples thereof include compounds linked by -CH ₂ -, -C(CH ₃ ) ₂ -, -C(CF ₃ ) ₂ -, -SO ₂ - or a phenylene group.

Examples of dicarboxylic acid compounds include aromatic dicarboxylic acids, aliphatic dicarboxylic acids, and their analogous acid chloride compounds and acid anhydrides. These dicarboxylic acid compounds may be used alone or in combination of two or more. Examples of dicarboxylic acid compounds include terephthalic acid; isophthalic acid; naphthalene dicarboxylic acid; 4,4'-biphenyldicarboxylic acid; 3,3'-biphenyldicarboxylic acid; chain hydrocarbon dicarboxylic acid having 8 or less carbon atoms. Examples include compounds in which two benzoic acids are linked by -CH ₂ -, -C(CH ₃ ) ₂ -, -C(CF ₃ ) ₂ -, -SO ₂ - or a phenylene group.

The ratio of the tetracarboxylic acid compound to the total of the tetracarboxylic acid compound, tricarboxylic acid compound, and dicarboxylic acid compound is preferably 40 mol% or more, more preferably 50 mol% or more, still more preferably 70 mol% or more, and even more preferably is 90 mol% or more, particularly preferably 98 mol% or more.

(diamine)
Examples of diamines include aliphatic diamines, aromatic diamines, and mixtures thereof. In this specification, the term "aromatic diamine" refers to a diamine in which an amino group is directly bonded to an aromatic ring, and may include an aliphatic group or other substituent as part of its structure. The aromatic ring may be a single ring or a fused ring. Examples of aromatic rings include, but are not limited to, benzene rings, naphthalene rings, anthracene rings, and fluorene rings. Among aromatic rings, a benzene ring is preferred. Furthermore, in this specification, "aliphatic diamine" refers to a diamine in which an amino group is directly bonded to an aliphatic group, and may include an aromatic ring or other substituents as part of its structure. .

Examples of aliphatic diamines include acyclic aliphatic diamines such as hexamethylene diamine, 1,3-bis(aminomethyl)cyclohexane, 1,4-bis(aminomethyl)cyclohexane, norbornanediamine, and 4, Examples include cycloaliphatic diamines such as 4'-diaminodicyclohexylmethane. These aliphatic diamines may be used alone or in combination of two or more.

Examples of aromatic diamines include p-phenylenediamine, m-phenylenediamine, 2,4-toluenediamine, m-xylylenediamine, p-xylylenediamine, and 1,5-diaminonaphthalene, and 2,6- Aromatic diamine having one aromatic ring such as diaminonaphthalene, 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-amino) phenoxy)phenyl]propane, 2,2-bis[4-(3-aminophenoxy)phenyl]propane, 2,2'-dimethylbenzidine, 2,2'-bis(trifluoromethyl)-4,4'-diamino Diphenyl (2,2'-bis(trifluoromethyl)benzidine (TFMB)), 4,4'-bis(4-aminophenoxy)biphenyl , 9,9 -bis(4-aminophenyl)fluorene, 9,9- Bis(4-amino-3-methylphenyl)fluorene, 9,9-bis(4-amino-3-chlorophenyl)fluorene, 9,9-bis(4-amino-3-fluorophenyl)fluorene, and derivatives thereof Examples include aromatic diamines having two or more aromatic rings. These aromatic diamines may be used alone or in combination of two or more.

The diamine can also have a fluorine substituent. Examples of the fluorine-based substituent include a perfluoroalkyl group having 1 to 5 carbon atoms, such as a trifluoromethyl group, and a fluoro group.

Among the above diamines, from the viewpoint of high transparency and low coloration, it is preferable to use one or more selected from the group consisting of aromatic diamines having a biphenyl structure. One or more selected from the group consisting of 2,2'-dimethylbenzidine, 2,2'-bis(trifluoromethyl)benzidine (TFMB) derivatives, and 4,4'-bis(4-aminophenoxy)biphenyl is used. It is even more preferable.
The diamine is preferably a diamine having a biphenyl structure and a fluorine substituent. Examples of diamines having a biphenyl structure and a fluorine substituent include 2,2'-bis(trifluoromethyl)benzidine (TFMB) derivatives.

The molar ratio of the diamine in the raw material monomer to the carboxylic acid compound such as a tetracarboxylic acid compound is preferably within the range of 0.9 mol or more and 1.1 mol or less of the tetracarboxylic acid per 1.00 mol of the diamine. Can be adjusted. In order to exhibit high bending durability, it is preferable that the obtained transparent polyimide polymer has a high molecular weight. It is more preferable that the amount is 0.99 mol or more and 1.01 mol or less.
In addition, from the viewpoint of suppressing the yellowness of the transparent polyimide polymer film obtained, it is preferable that the proportion of amino groups occupying the terminals of the obtained polymer is low, and The amount of carboxylic acid compound is preferably 1.00 mol or more.

By adjusting the number of fluorine in the molecule of diamine and carboxylic acid compound (e.g., tetracarboxylic acid compound), the amount of fluorine in the resulting transparent polyimide polymer is 1 mass based on the mass of the transparent polyimide polymer. % or more, 5% by mass or more, 10% by mass or more, or 20% by mass or more. Since raw material costs tend to increase as the proportion of fluorine increases, the upper limit of the amount of fluorine is preferably 40% by mass or less. The fluorine substituent may be present in either the diamine or the carboxylic acid compound, or in both. Including a fluorine substituent may particularly reduce the YI value.

[6. Optical film manufacturing method]
The method for producing an optical film of the present invention includes a step of casting a varnish containing a transparent polyimide polymer, and integrating ^{a 1} H-NMR signal derived from an imide group in a chain of the transparent polyimide polymer. The ratio of the integral value A of the ¹ H-NMR signal derived from the terminal amino group of the transparent polyimide polymer to the value B (integral ratio A/B) is 0.0001 or more and 0.001 or less. An example of a process of forming a film by casting a varnish containing a transparent polyimide polymer will be described. A coating film is formed by casting a varnish onto a substrate, and the solvent is removed from the coating film by means such as reduced pressure, drying, and heating, and the coating film is peeled off from the substrate. As a result, a transparent polyimide polymer film is obtained.

Casting can be done in a roll-to-roll or batch manner onto a resin substrate, a stainless steel belt, or a glass substrate. Examples of the resin base material include PET, PEN, polyimide, and polyamideimide. Among these resin base materials, PET is preferred from the viewpoint of adhesiveness with the film and cost.

Even if the varnish obtained by the above production method is made into a film without going through a purification step, a highly transparent transparent polyimide polymer film can be obtained. Therefore, the transparent polyimide polymer can be extracted from the varnish by precipitation or the like, and then formed into a film without going through a purification process in which it is redissolved in a solvent. This results in a cost-effective process.

In the method for producing an optical film of the present invention, a certain amount of organic solvent is volatilized by passing the coating film through a dryer that brings heated gas into contact with the surface of the coating film, and the coating film is transformed into a self-supporting film. It may also be obtained by peeling it off from the support. The temperature at which the process is carried out is adjusted depending on the base material used, and when a resin base material is used, it is generally carried out at a temperature below the glass transition temperature of the resin base material. Generally, it is sufficient to heat to an appropriate temperature of 50 to 300°C, and the heating temperature may be adjusted in multiple stages or a temperature gradient may be applied. It is also suitable to carry out the reaction under an inert atmosphere or under reduced pressure.

Further, if necessary, the peeled transparent polyimide polymer film may be further heated at 80 to 300°C.

The varnish contains a transparent polyimide polymer and a solvent.

〔solvent〕
It is preferable that the solvent has the basic properties as a varnish composition and also has high transparency for a long period of time. The former is a property of dissolving or dispersing the transparent polyimide polymer and adjusting the viscosity of the varnish to an appropriate viscosity for coating. The latter is, for example, a property in which the solvent molecules are difficult to react with oxygen, a property in which the solvent molecules are difficult to generate a highly reactive peroxide even if they react with oxygen, and a property in which oxygen is difficult to dissolve.
From the viewpoint of satisfying such characteristics, examples of solvents include, for example, aprotic polar solvents (more specifically, N,N-dimethylacetamide (hereinafter sometimes referred to as DMAc), dimethyl sulfoxide, etc.) , ketones (more specifically, cyclopentanone (hereinafter sometimes referred to as CP), etc.), and carboxylic acid esters that are ester solvents (more specifically, acetic acid esters, and cyclic carboxylic acid esters) etc.). Examples of acetic acid esters include butyl acetate, amyl acetate, and isoamyl acetate. Examples of the cyclic carboxylic acid ester include γ-butyrolactone (hereinafter sometimes referred to as GBL). These solvents may be used alone or in combination of two or more.

Among these solvents, from the viewpoint of further improving the two properties, at least one solvent selected from the group consisting of GBL, DMAc, butyl acetate, amyl acetate, CP, and isoamyl acetate is preferred; More preferably, at least two or more types of esters are used. Examples of the at least one solvent include combinations of DMAc and GBL, and CP and GBL. Examples of the combination of at least two or more esters include GBL and DMAc, GBL and butyl acetate, GBL and amyl acetate, GBL and isoamyl acetate, DMAc and butyl acetate, DMAc and amyl acetate, DMAc and isoamyl acetate, and butyl acetate. and amyl acetate, butyl acetate and isoamyl acetate, amyl acetate and isoamyl acetate, GBL and DMAc and butyl acetate, GBL and DMAc and amyl acetate, GBL and DMAc and isoamyl acetate, GBL and butyl acetate and amyl acetate, GBL and butyl acetate Isoamyl acetate, GBL and amyl acetate and isoamyl acetate, DMAc and butyl acetate and amyl acetate, DMAc and butyl acetate and isoamyl acetate, DMAc and amyl acetate and isoamyl acetate, butyl acetate and amyl acetate and isoamyl acetate, GBL and DMAc and butyl acetate and amyl acetate, GBL and DMAc and butyl acetate and isoamyl acetate, GBL and DMAc and amyl acetate and isoamyl acetate, GBL and butyl acetate and amyl acetate and isoamyl acetate, DMAc and butyl acetate and amyl acetate and isoamyl acetate, and GBL and DMAc and butyl acetate, amyl acetate, and isoamyl acetate, preferably GBL and butyl acetate, GBL and amyl acetate, GBL and isoamyl acetate, butyl acetate and amyl acetate, butyl acetate and isoamyl acetate, and amyl acetate and isoamyl acetate. , GBL and butyl acetate and amyl acetate, GBL and butyl acetate and isoamyl acetate, GBL and amyl acetate and isoamyl acetate, butyl acetate, amyl acetate and isoamyl acetate, and combinations of GBL, butyl acetate, amyl acetate and isoamyl acetate. more preferably GBL and butyl acetate, GBL and amyl acetate, GBL and isoamyl acetate, GBL and butyl acetate and amyl acetate, GBL and butyl acetate and isoamyl acetate, GBL and amyl acetate and isoamyl acetate, and GBL and butyl acetate. A combination of amyl acetate and isoamyl acetate may be mentioned.

In the case of a mixed solvent consisting of two types of solvents, the mixing ratio (mass ratio) is preferably 1:9 to 9:1, more preferably 2:8 to 8:2. In the case of a mixed solvent consisting of three types of solvents, the mixing ratio (mass ratio) is preferably 1 to 8:1 to 8:1 to 8, more preferably 2 to 7:2 to 7:2 to 7. .
In the case of two or more solvents, the content of one of the two or more solvents is usually 10% by mass or more, preferably 20% by mass or more, more preferably 30% by mass or more, and even more preferably It is 40% by mass or more, and usually 90% by mass or less, preferably 80% by mass or less, more preferably 70% by mass or less, and still more preferably 60% by mass or less.

〔Additive〕
The varnish may further contain additives within a range that does not impair transparency. Examples of additives include inorganic particles, ultraviolet absorbers, antioxidants, mold release agents, stabilizers, colorants, flame retardants, lubricants, thickeners, and leveling agents.

[7. Varnish manufacturing method]
The method for producing varnish includes, for example, a polymerization step in which a raw material monomer for a transparent polyimide polymer is polymerized in a solvent A to obtain a transparent polyimide polymer precursor, and a polymerization step in which a transparent polyimide polymer precursor is obtained by polymerizing a raw material monomer for a transparent polyimide polymer in a solvent A containing a tertiary amine under a reduced pressure atmosphere. The method includes an imidization step of imidizing the transparent polyimide polymer precursor to obtain a transparent polyimide polymer solution, and a dilution step of diluting the transparent polyimide polymer solution with solvent B to prepare a varnish. The varnish manufacturing process may further include a varnish extraction step of extracting the varnish from the reaction vessel.

(Polymerization process)
In the polymerization step, a raw material monomer for a transparent polyimide polymer is polymerized in a solvent A to obtain a transparent polyimide polymer precursor. Solvent A can be the solvents listed above. The amount of the raw material monomer in the total liquid containing the raw material monomer and the solvent A can be 10 to 60% by mass. When the amount of raw material monomer is large, the polymerization rate tends to increase, and the molecular weight can be increased. Moreover, the polymerization time can be shortened, and coloring of the transparent polyimide polymer tends to be suppressed. If the amount of raw material monomer is too large, the viscosity of the polymer or the solution containing the polymer tends to increase, making it difficult to stir, or causing the polymer to adhere to the reaction vessel or stirring blade, resulting in a low yield. Sometimes it happens. Note that the solvent A can be any of the solvents mentioned above.

The order of mixing each component of the raw material monomer and the solvent A is not particularly limited, and they may be mixed all at the same time or separately, but after mixing at least a part of the diamine and the solvent. Preferably, a carboxylic acid compound is added. The diamine and carboxylic acid compound may be added in portions or may be added stepwise for each compound.

By thoroughly stirring the raw material monomers in the reaction mass, polymerization of the raw material monomers is promoted and a transparent polyimide polymer precursor is formed. If necessary, the reaction mass may be heated to about 40 to 90°C. Simultaneously with the progress of the polymerization step of the raw material monomers, the imidization step described below can also proceed. In this case, the reaction mass may be heated to a higher temperature in accordance with the imidization conditions described below.
The reaction time for polymerization can be, for example, 24 hours or less, 1 hour or less, or 1 to 24 hours.

The reaction mass may contain a tertiary amine during the polymerization process of the transparent polyimide polymer precursor. In this case, the tertiary amine may be added before or after mixing the diamine and solvent A, or may be added after mixing the diamine, solvent, and carboxylic acid compound.
Alternatively, it may be added to the reaction mass after being diluted with a portion of the solvent used.

[Tertiary amine]
The tertiary amine can function as a polymerization catalyst for the raw material monomer in the solvent A in the polymerization step, or as an imidization catalyst for the transparent polyimide polymer precursor in the solvent A in the imidization step.
Examples of tertiary amines include tertiary amines represented by formula (d) (hereinafter sometimes referred to as tertiary amines D).

式（ｄ）において、Ｒ_１Ｄは炭素原子数８～１５の三価の脂肪族炭化水素基である。

In formula (d), R _1D is a trivalent aliphatic hydrocarbon group having 8 to 15 carbon atoms.

Examples of the tertiary amine D include 2-methylpyridine, 3-methylpyridine, 4-methylpyridine, 2-ethylpyridine, 3-ethylpyridine, 4-ethylpyridine, 2,4-dimethylpyridine, 2,4 , 6-trimethylpyridine, 3,4-cyclopentenopyridine, 5,6,7,8-tetrahydroisoquinoline and isoquinoline.

The boiling point of the tertiary amine is preferably 120°C or higher, more preferably 140°C or higher, even more preferably 170°C or higher, particularly preferably 200°C or higher. The upper limit of the boiling point of the tertiary amine is not particularly defined, but is usually 350°C or lower. When the boiling point of the tertiary amine is within the above range, it is preferable because the amount of catalyst removed from the system tends to be suppressed when water is distilled off during reduced pressure.

(Imidization process)
Subsequently, in the imidization step, the transparent polyimide polymer precursor is imidized in a solvent A containing a tertiary amine under a reduced pressure atmosphere to obtain a transparent polyimide polymer solution. More specifically, by heating a reaction mass containing a tertiary amine in a reduced pressure atmosphere, imidization of a transparent polyimide polymer precursor is promoted, and while producing polyimide, by-products such as water are distilled off. leave It is preferable to imidize the transparent polyimide polymer precursor in solvent A in the reaction vessel in which the above polymerization was carried out. The tertiary amine may be added during or before the polymerization process of polymerizing raw material monomers to produce a transparent polyimide polymer precursor as described above; It may be added after the process.

The production reaction of the transparent polyimide polymer precursor and the imidization reaction may proceed simultaneously. In that case, the water produced in the imidization reaction may cleave the bonds of the amide groups, resulting in a lower molecular weight of the resulting transparent polyimide polymer. Films obtained from varnishes containing such transparent polyimide polymers may have reduced fold durability. During the imidization step, by quickly removing water in the reaction solution under reduced pressure, the cleavage reaction of the amide group can be suppressed and the molecular weight of the resulting transparent polyimide polymer can be increased. Therefore, especially when the production reaction of the transparent polyimide polymer precursor and the imidization reaction proceed simultaneously, by performing the imidization step under a reduced pressure atmosphere, the transparent polyimide polymer can be produced without going through the purification step. Producing film directly from varnish also tends to give the film high fold durability.

In the reaction mass, from the viewpoint of improving bending durability, the amount of tertiary amine added to 100 parts by mass of raw material monomer is preferably 0.05 parts by mass or more, more preferably 0.1 parts by mass or more, and even more preferably It is 0.2 parts by mass or more. On the other hand, for the purpose of suppressing coloring of the film, it is preferable that the amount of catalyst added is small. The amount of tertiary amine added is preferably 2 parts by mass or less, more preferably 1 part by mass or less, even more preferably 0.7 parts by mass or less, even more preferably 0.5 parts by mass or less, particularly preferably 0.3 parts by mass. Parts by mass or less.

The temperature of the imidization step is preferably 100°C or more and 250°C or less, more preferably 150°C or more and 210°C or less.

The pressure in the imidization step is preferably 730 mmHg or less, more preferably 700 mmHg or less, even more preferably 675 mmHg or less. The pressure in the imidization step can be, for example, 350 mmHg or more, and may be 500 mmHg or more. Depending on the vapor pressure of the solvent at the temperature of the imidization step, it may be preferable to carry out the reaction at a pressure of 400 mmHg or higher in order to improve the stability of the reaction. For the same reason, it may be more preferable to perform the treatment at 600 mmHg or higher.
If the pressure in the imidization step is set close to the saturated vapor pressure of the solvent in the imidization step, YI tends to be easily suppressed. The pressure is preferably within 50 mmHg from the saturated vapor pressure.

The heating time is, for example, usually 1 to 24 hours, preferably 1 to 12 hours, more preferably 2 to 9 hours, even more preferably 2 to 8 hours, even more preferably 2 to 6 hours, particularly preferably 2 to 12 hours. It is 5 hours. It is preferable to stir during heating.
As the reaction time increases, the molecular weight increases, but the resin tends to become more yellowish. On the other hand, if the reaction time is short, the molecular weight tends to be low and the yellow color tends to be weak.

From the viewpoint of suppressing a decrease in transparency of the transparent polyimide polymer film, the imidization step is preferably performed in a reduced pressure atmosphere. When the imidization process is performed under a reduced pressure atmosphere, the oxygen concentration in the gas phase that comes into contact with the liquid phase containing solvent A in the reaction vessel is low, so the dissolution of oxygen into solvent A is reduced, and the transparent polyimide It is thought that the peroxide concentration in the system polymer solution is reduced. In the production method, the imidization step by heating the reaction mass under a reduced pressure atmosphere may be performed in a state where the oxygen concentration in the gas phase of the reaction vessel is low. The oxygen concentration may be low from the time of charging. The oxygen concentration is preferably 0.02% or less, more preferably 0.01% or less. If the oxygen concentration is high when heated to a high temperature, it will particularly cause coloring, so for example, when the temperature of the reaction solution is 130° C. or higher, it is preferable to keep the oxygen concentration at 0.02% or lower. Since virtually no oxygen is generated during the synthesis of the precursor and the imidization of the precursor, the imide The oxygen concentration in the gas phase in the oxidation step can be reduced. The oxygen concentration in the imidization step can be determined, for example, by analyzing the oxygen concentration in the gas removed from the reaction vessel when the pressure inside the reaction vessel is reduced. If it is difficult to measure the oxygen concentration during reduced pressure, the oxygen concentration may be measured by sampling the gas phase before and after the reduced pressure. For the purpose of lowering the oxygen concentration in the same way as under a reduced pressure atmosphere, the imidization step may be performed under an inert gas atmosphere instead of under a reduced pressure atmosphere.

After heating, the pressure is returned to atmospheric pressure and cooled to obtain a transparent polyimide polymer solution.

(dilution process)
In the subsequent dilution step, the transparent polyimide polymer solution is diluted with solvent B to prepare a varnish. More specifically, solvent B is further added to the obtained transparent polyimide polymer solution to adjust the concentration of the transparent polyimide polymer to obtain a varnish. A suitable solids concentration in the varnish is 10-25% by weight.
In addition, when producing a film from a varnish, if a varnish containing 30% by mass or more of a transparent polyimide polymer based on the total amount of solid content in the varnish is used, one of the main components described below will be a transparent polyimide polymer. A transparent polyimide polymer film can be easily obtained. The concentration of the transparent polyimide polymer is preferably 10% by mass or more, more preferably 13% by mass or more, based on the total mass of the varnish.

Dilution can be performed within the reaction vessel, or can be performed on the solution after it has been recovered from the reaction vessel.

If solvent B is added to the transparent polyimide polymer solution after imidization in the reaction container to dilute the concentration of the transparent polyimide polymer in the reaction container, it will remain in the reaction container during the next extraction process. The amount of polymer can be reduced and the yield of polymer can be improved. Furthermore, when the amount of polymer remaining in the reaction vessel is reduced, the coloring (for example, yellow) of the resulting transparent polyimide polymer is improved in the subsequent repeated steps of polymerization and imidization using this reaction vessel.

The diluting solvent B can be the solvents listed above. Solvent B and solvent A may be of the same type or may be of different types. By appropriately selecting a solvent with high solubility for the polyimide resin as the diluting solvent B, the recovery rate of the transparent polyimide polymer from the reaction vessel can be increased.

Dilution within the reaction vessel can also be performed multiple times using a plurality of different types of solvents B.

(Varnish extraction process)
Subsequently, in the varnish extraction step, varnish is extracted from the reaction vessel. The extracted varnish can be used in the film forming process described below.

The ratio of the integral value A of the ¹ H-NMR signal derived from the terminal amino group of the transparent polyimide polymer to the integral value B of the ¹ H-NMR signal derived from the imide group in the chain of the transparent polyimide polymer ( In order to produce an optical film with an integral ratio A/B) of 0.0001 or more and 0.001 or less, the integral ratio A/B of the transparent polyimide polymer in the varnish during cast film formation must be 0.0001 or more. It is necessary to manage it so that it is 0.001 or less.
The integral ratio A/B can be controlled by the molecular weight of the transparent polyimide polymer, the ratio of polymerization monomers, the order of charging, and the like. When the molecular weight is high, the integral ratio A/B tends to be small, and when the molecular weight is low, the integral ratio A/B tends to be large.
The integral ratio A/B may decrease when a transparent polyimide polymer is stored in a solution state (eg, polyimide varnish) for a long period of time. This is thought to be because the terminal amino groups of the transparent polyimide polymer change due to oxidation or the like during storage. The storage period depends on the type of solvent and storage conditions, but is preferably within one year, more preferably within six months, and still more preferably within one month. Preferably, the storage temperature does not exceed 40°C, for example. From the viewpoint of suppressing oxidation of terminal amino groups, the amount of peroxide in the solvent is preferably small. From the viewpoint of suppressing the generation of peroxides, examples of solvents include aprotic solvents (more specifically, DMAc and dimethyl sulfoxide, etc.), ketones (more specifically, CP, etc.), and ester solvents. Examples include carboxylic acid esters (more specifically, acetic acid esters, cyclic carboxylic esters, etc.), and preferably cyclic carboxylic acid esters (more specifically, γ-butyrolactone, etc.), acetic esters (more specifically, γ-butyrolactone, etc.). (butyl acetate, amyl acetate, etc.), N,N-dimethylacetamide, and mixtures thereof, more preferably γ-butyrolactone, butyl acetate, amyl acetate, N,N-dimethylacetamide, and their mixtures. It is a mixture. By bubbling an inert gas into the solvent before dilution, the dissolved oxygen in the solvent can be replaced with the inert gas, thereby suppressing the generation of peroxides. Oxidation of terminal amino groups can also be suppressed by filling the container with inert gas and storing it.

The transparent polyimide polymer film described above is used as an optical film, and is useful, for example, as a front plate of a display device, particularly a front plate (window film) of a flexible display device. A flexible display device includes, for example, a flexible functional layer and an optical film that is stacked on the flexible functional layer and functions as a front plate. That is, the front plate of the flexible display device is arranged on the viewing side above the flexible functional layer. This front plate has the function of protecting the flexible functional layer.

Examples of display devices include televisions, smartphones, mobile phones, car navigation systems, tablet PCs, portable game consoles, electronic paper, indicators, bulletin boards, watches, and wearable devices such as smart watches. Examples of flexible display devices include all display devices having flexible characteristics, preferably foldable display devices and rollable display devices.

[Flexible display device]
The present invention also provides a flexible display device comprising the optical film of the present invention. The optical film of the present invention is preferably used as a front plate in a flexible display device, and the front plate is sometimes referred to as a window film. The flexible display device is composed of a flexible display device laminate and an organic EL display panel, and the flexible display device laminate is arranged on the viewing side with respect to the organic EL display panel, and is configured to be foldable. The laminate for a flexible display device may contain a window film, a polarizing plate (preferably a circularly polarizing plate), and a touch sensor, and the order of stacking them is arbitrary, but from the viewing side the window film, polarizing plate, It is preferable that the touch sensor or window film, the touch sensor, and the polarizing plate are laminated in this order. It is preferable that a polarizing plate is present on the viewing side of the touch sensor because the pattern of the touch sensor becomes difficult to see and the visibility of the displayed image improves. Each member can be laminated using an adhesive, a pressure-sensitive adhesive, or the like. Further, a light shielding pattern may be provided on at least one surface of any one of the window film, polarizing plate, and touch sensor layer.

[Polarizer]
The flexible display device of the present invention may further include a polarizing plate, preferably a circularly polarizing plate. A circularly polarizing plate is a functional layer that has a function of transmitting only a right or left circularly polarized light component by laminating a λ/4 retardation plate on a linearly polarizing plate. For example, by converting external light into right-handed circularly polarized light, blocking the left-handed circularly polarized exterior light that is reflected by an organic EL panel, and transmitting only the organic EL light emitting component, the effect of reflected light is suppressed and images are created. Used to make it easier to see. In order to achieve the circular polarization function, the absorption axis of the linear polarizing plate and the slow axis of the λ/4 retardation plate should theoretically be 45°, but in practice they are 45±10°. The linear polarizing plate and the λ/4 retardation plate do not necessarily need to be stacked adjacent to each other, as long as the relationship between the absorption axis and the slow axis satisfies the above range. Although it is preferable to achieve complete circularly polarized light at all wavelengths, it is not necessary in practice, so the circularly polarizing plate in the present invention also includes an elliptically polarizing plate. It is also preferable to further laminate a λ/4 retardation film on the viewing side of the linearly polarizing plate to make the emitted light circularly polarized, thereby improving visibility when wearing polarized sunglasses.

The linear polarizing plate is a functional layer that allows light vibrating in the direction of the transmission axis to pass through, but has the function of blocking polarized light with a vibration component perpendicular to it. The linear polarizing plate may include a linear polarizer alone or a linear polarizer and a protective film attached to at least one surface thereof. The thickness of the linearly polarizing plate may be 200 μm or less, preferably 0.5 to 100 μm. When the thickness is within the above range, flexibility tends to be less likely to decrease.
The linear polarizer may be a film-type polarizer manufactured by dyeing and stretching a polyvinyl alcohol (PVA) film. A dichroic dye such as iodine is adsorbed to a PVA-based film that is oriented by stretching, or by being stretched while being adsorbed to PVA, the dichroic dye is oriented and exhibits polarizing performance. The production of the film-type polarizer may include other steps such as swelling, crosslinking with boric acid, washing with an aqueous solution, and drying. The stretching and dyeing steps may be performed on the PVA film alone, or may be performed on the PVA film laminated with another film such as polyethylene terephthalate. The thickness of the PVA film used is preferably 10 to 100 μm, and the stretching ratio is preferably 2 to 10 times.
Further, another example of the polarizer may be a liquid crystal coating type polarizer formed by applying a liquid crystal polarizing composition. The liquid crystal polarizing composition may include a liquid crystal compound and a dichroic dye compound. The liquid crystalline compound need only have the property of exhibiting a liquid crystal state, and it is particularly preferable that it has a high-order alignment state such as a smectic phase because it can exhibit high polarization performance. Moreover, it is also preferable that the liquid crystal compound has a polymerizable functional group.

The dichroic dye is a dye that exhibits dichroism when aligned with the liquid crystal compound, and the dichroic dye itself may have liquid crystallinity or may have a polymerizable functional group. You can also do that. Any compound in the liquid crystal polarizing composition has a polymerizable functional group.
The liquid crystal polarizing composition may further include an initiator, a solvent, a dispersant, a leveling agent, a stabilizer, a surfactant, a crosslinking agent, a silane coupling agent, and the like.
The liquid crystal polarizing layer is manufactured by coating a liquid crystal polarizing composition on an alignment film to form a liquid crystal polarizing layer.
The liquid crystal polarizing layer can be formed thinner than a film-type polarizer. The thickness of the liquid crystal polarizing layer may be preferably 0.5 to 10 μm, more preferably 1 to 5 μm.
The alignment film can be manufactured, for example, by applying an alignment film-forming composition onto a base material and imparting alignment properties by rubbing, polarized light irradiation, or the like. The alignment film forming composition may contain a solvent, a crosslinking agent, an initiator, a dispersant, a leveling agent, a silane coupling agent, etc. in addition to the alignment agent. As the alignment agent, for example, polyvinyl alcohols, polyacrylates, polyamic acids, and polyimides can be used. When photoalignment is applied, it is preferable to use an alignment agent containing a cinnamate group. The weight average molecular weight of the polymer used as the alignment agent may be about 10,000 to 1,000,000. The thickness of the alignment film is preferably 5 to 10,000 nm, more preferably 10 to 500 nm, from the viewpoint of alignment regulating force. The liquid crystal polarizing layer can be peeled off from the base material and transferred and laminated, or the base material can be laminated as is. It is also preferable that the base material plays a role as a protective film, a retardation plate, or a transparent base material for a window.

The protective film may be any transparent polymer film, and materials and additives used for the transparent substrate can be used. Cellulose-based films, olefin-based films, acrylic films, and polyester-based films are preferred. It may be a coating type protective film obtained by applying and curing a cationic curing composition such as an epoxy resin or a radical curing composition such as acrylate. If necessary, plasticizers, ultraviolet absorbers, infrared absorbers, colorants such as pigments and dyes, optical brighteners, dispersants, heat stabilizers, light stabilizers, antistatic agents, antioxidants, lubricants, solvents, etc. May contain. The thickness of the protective film may be 200 μm or less, preferably 1 to 100 μm. When the thickness of the protective film is within the above range, the flexibility of the protective film is unlikely to decrease. The protective film can also serve as a transparent base material for the window.

The λ/4 retardation plate is a film that provides a retardation of λ/4 in a direction perpendicular to the traveling direction of incident light (in-plane direction of the film). The λ/4 retardation plate may be a stretched retardation plate manufactured by stretching a polymer film such as a cellulose film, an olefin film, or a polycarbonate film. If necessary, retardation adjusters, plasticizers, ultraviolet absorbers, infrared absorbers, colorants such as pigments and dyes, optical brighteners, dispersants, heat stabilizers, light stabilizers, antistatic agents, and antioxidants. , a lubricant, a solvent, etc. The thickness of the stretched retardation plate may be 200 μm or less, preferably 1 to 100 μm. When the thickness is within the above range, the flexibility of the film tends to be less likely to decrease.
Further, another example of the λ/4 retardation plate may be a liquid crystal coated retardation plate formed by applying a liquid crystal composition. The liquid crystal composition includes a liquid crystal compound that exhibits a liquid crystal state such as nematic, cholesteric, or smectic. Any compound containing a liquid crystal compound in the liquid crystal composition has a polymerizable functional group. The liquid crystal coated retardation plate may further include an initiator, a solvent, a dispersant, a leveling agent, a stabilizer, a surfactant, a crosslinking agent, a silane coupling agent, and the like. The liquid crystal coated retardation plate can be manufactured by coating and curing a liquid crystal composition on an alignment film to form a liquid crystal retardation layer in the same manner as described for the liquid crystal polarizing layer. A liquid crystal coated retardation plate can be formed thinner than a stretched retardation plate. The thickness of the liquid crystal polarizing layer may be generally 0.5 to 10 μm, preferably 1 to 5 μm. The liquid crystal coated retardation plate can be peeled off from the base material and transferred and laminated, or the base material can be laminated as is. It is also preferable that the base material plays a role as a protective film, a retardation plate, or a transparent base material for a window.

In general, many materials exhibit birefringence as the wavelength becomes shorter, and birefringence decreases as the wavelength increases. In this case, it is not possible to achieve a phase difference of λ/4 in the entire visible light region, so the in-plane phase difference is 100 to 180 nm, preferably 130 nm, which is λ/4 for the vicinity of 560 nm, where visibility is high. It is often designed to have a wavelength of ~150 nm. It is preferable to use an inverse dispersion λ/4 retardation plate made of a material having birefringence and wavelength dispersion characteristics opposite to those of normal ones because visibility can be improved. As such materials, those described in JP-A No. 2007-232873 for a stretched retardation plate, and those described in JP-A No. 2010-30979 for a liquid crystal coated retardation plate may be used. preferable.
Furthermore, as another method, a technique for obtaining a broadband λ/4 retardation plate by combining it with a λ/2 retardation plate is also known (Japanese Patent Laid-Open No. 10-90521). The λ/2 retardation plate is also manufactured using the same material method as the λ/4 retardation plate. Although the combination of the stretched type retardation plate and the liquid crystal coated type retardation plate is arbitrary, it is preferable to use a liquid crystal coated type retardation plate in both cases because the thickness can be reduced.
A method is also known in which a positive C plate is laminated on the circularly polarizing plate in order to improve visibility in an oblique direction (Japanese Patent Laid-Open No. 2014-224837). The positive C plate may also be a liquid crystal coated retardation plate or a stretched retardation plate. The retardation in the thickness direction is usually -200 to -20 nm, preferably -140 to -40 nm.

[Touch sensor]
The flexible display device of the present invention may further include a touch sensor. A touch sensor is used as an input means. Various types of touch sensors have been proposed, including a resistive film type, a surface acoustic wave type, an infrared type, an electromagnetic induction type, and a capacitance type, and any of these types may be used. Among these, the capacitive method is preferable. A capacitive touch sensor is divided into an active area and a non-active area located around the active area. The active area corresponds to the area where the screen is displayed on the display panel (display part) and is the area where the user's touch is sensed, and the inactive area is the area where the screen is not displayed on the display device (non-active area). This is the area corresponding to the display section). The touch sensor includes a substrate having flexible characteristics; a sensing pattern formed on an active area of the substrate; and a sensing pattern formed on a non-active area of the substrate and connected to an external driving circuit through the sensing pattern and a pad portion. Each sensing line can be included. As the flexible substrate, the same material as the transparent substrate of the window can be used. The substrate of the touch sensor preferably has a toughness of 2,000 MPa% or more from the viewpoint of suppressing cracks in the touch sensor. More preferably, the toughness may be 2,000 to 30,000 MPa%. Here, toughness is defined as the area under the stress-strain curve (MPa)-strain (%) obtained through a tensile experiment of the polymer material up to the breaking point.

The sensing pattern may include a first pattern formed in a first direction and a second pattern formed in a second direction. The first pattern and the second pattern are arranged in different directions. The first pattern and the second pattern are formed on the same layer and must be electrically connected to each other in order to sense a touched point. The first pattern has unit patterns connected to each other via joints, but the second pattern has a structure in which each unit pattern is isolated from each other in an island configuration, so the second pattern is electrically connected to the unit patterns. A separate bridge electrode is required for connection. A well-known transparent electrode material can be applied to the sensing pattern. For example, indium tin oxide (ITO), indium zinc oxide (IZO), zinc oxide (ZnO), indium zinc tin oxide (IZTO), indium gallium zinc oxide (IGZO), cadmium tin oxide (CTO) , PEDOT (poly(3,4-ethylenedioxythiophene)), carbon nanotubes (CNT), graphene, metal wires, etc., and these can be used alone or in a mixture of two or more. Preferably ITO can be used. The metal used for the metal wire is not particularly limited, and examples thereof include silver, gold, aluminum, copper, iron, nickel, titanium, terenium, and chromium. These can be used alone or in combination of two or more.

A bridge electrode may be formed on the sensing pattern through an insulating layer, and the bridge electrode may be formed on a substrate, and an insulating layer and a sensing pattern may be formed on the bridge electrode. The bridge electrode may be formed of the same material as the sensing pattern, and may be formed of a metal such as molybdenum, silver, aluminum, copper, palladium, gold, platinum, zinc, tin, titanium, or an alloy of two or more of these. You can also. Since the first pattern and the second pattern must be electrically insulated, an insulating layer is formed between the sensing pattern and the bridge electrode. The insulating layer may be formed only between the joint of the first pattern and the bridge electrode, or may be formed as a layer structure covering the sensing pattern. In the latter case, the bridge electrode can connect the second pattern through a contact hole formed in the insulating layer. The touch sensor detects the difference in transmittance between a patterned area and a non-patterned area, specifically, the difference in light transmittance induced by the difference in refractive index in these areas. An optical adjustment layer may be further included between the substrate and the electrode as a means for appropriately compensating for the difference, and the optical adjustment layer may include an inorganic insulating material or an organic insulating material. The optical adjustment layer can be formed by coating a photocurable composition containing a photocurable organic binder and a solvent on a substrate. The photocurable composition may further include inorganic particles. The inorganic particles can increase the refractive index of the optical adjustment layer.
The photocurable organic binder may include, for example, a copolymer of each monomer such as an acrylate monomer, a styrene monomer, or a carboxylic acid monomer. The photocurable organic binder may be a copolymer containing different repeating units such as epoxy group-containing repeating units, acrylate repeating units, and carboxylic acid repeating units.
The inorganic particles may include, for example, zirconia particles, titania particles, alumina particles, and the like. The photocurable composition may further contain additives such as a photopolymerization initiator, a polymerizable monomer, and a curing aid.

[Adhesive layer]
Each layer (window, polarizing plate, touch sensor) forming the laminate for a flexible display device and the film member (linear polarizing plate, λ/4 retardation plate, etc.) forming each layer can be bonded with an adhesive. Adhesives include water-based adhesives, organic solvent-based adhesives, solvent-free adhesives, solid adhesives, solvent-vaporizing adhesives, moisture-curing adhesives, heat-curing adhesives, anaerobic-curing adhesives, and activated adhesives. Commonly used adhesives such as energy ray curable adhesives, curing agent mixed adhesives, hot melt adhesives, pressure sensitive adhesives (adhesives), and rewet adhesives can be used. Among these, water-based solvent volatilization type adhesives, active energy ray curable adhesives, and adhesives are often used. The thickness of the adhesive layer can be adjusted as appropriate depending on the required adhesive strength, and is, for example, 0.01 to 500 μm, preferably 0.1 to 300 μm. A plurality of adhesive layers may be present in the flexible display device laminate, and the thickness of each adhesive layer and the type of adhesive used may be the same or different.

As the water-based solvent volatilization type adhesive, a water-dispersed polymer such as a polyvinyl alcohol polymer, a water-soluble polymer such as starch, an ethylene-vinyl acetate emulsion, a styrene-butadiene emulsion, etc. can be used as the main polymer. In addition to water and the main polymer, a crosslinking agent, a silane compound, an ionic compound, a crosslinking catalyst, an antioxidant, a dye, a pigment, an inorganic filler, an organic solvent, etc. may be added. In the case of bonding with the aqueous solvent volatile adhesive, adhesiveness can be imparted by injecting the aqueous solvent volatile adhesive between the adherend layers, bonding the adherend layers, and then drying. The thickness of the adhesive layer when using the aqueous solvent volatile adhesive may be generally 0.01 to 10 μm, preferably 0.1 to 1 μm. When the aqueous solvent volatile adhesive is used to form multiple layers, the thickness of each layer and the type of adhesive may be the same or different.

The active energy ray curable adhesive can be formed by curing an active energy ray curable composition containing a reactive material that forms an adhesive layer by irradiation with active energy rays. The active energy ray-curable composition may contain at least one polymer of the same radical polymerizable compound and cationic polymerizable compound as the hard coat composition. The radically polymerizable compound is the same as the hard coat composition, and the same type of compound as the hard coat composition can be used. The radically polymerizable compound used in the adhesive layer is preferably a compound having an acryloyl group. It is also preferable to include a monofunctional compound in order to lower the viscosity of the adhesive composition.

The cationic polymerizable compound is the same as that in the hard coat composition, and the same type of compound as in the hard coat composition can be used. As the cationically polymerizable compound used in the active energy ray-curable composition, epoxy compounds are particularly preferred. It is also preferred to include a monofunctional compound as a reactive diluent to reduce the viscosity of the adhesive composition.
The active energy ray composition can further contain a polymerization initiator. Examples of the polymerization initiator include radical polymerization initiators, cationic polymerization initiators, radical and cationic polymerization initiators, and can be appropriately selected and used. These polymerization initiators are decomposed by at least one of active energy ray irradiation and heating to generate radicals or cations to advance radical polymerization and cationic polymerization. In the description of the hard coat composition, an initiator capable of initiating at least either radical polymerization or cationic polymerization by irradiation with active energy rays can be used.

The active energy ray-curable composition further contains an ion scavenger, an antioxidant, a chain transfer agent, an adhesion promoter, a thermoplastic resin, a filler, a flow viscosity modifier, a plasticizer, an antifoaming agent, an additive, and a solvent. can include. In the case of bonding with the active energy ray-curable adhesive, the active energy ray-curable composition is applied to one or both of the adhered layers and then laminated, and the active energy ray-curable composition is applied through either or both of the adhered layers. It can be bonded by irradiating it with energy rays and curing it. When using the active energy ray-curable adhesive, the thickness of the adhesive layer may be generally 0.01 to 20 μm, preferably 0.1 to 10 μm. When the active energy ray-curable adhesive is used to form multiple layers, the thickness of each layer and the type of adhesive used may be the same or different.

The adhesive may be classified into acrylic adhesives, urethane adhesives, rubber adhesives, silicone adhesives, etc. depending on the main polymer, and any of them can be used. In addition to the base polymer, the adhesive may contain a crosslinking agent, a silane compound, an ionic compound, a crosslinking catalyst, an antioxidant, a tackifier, a plasticizer, a dye, a pigment, an inorganic filler, and the like. A pressure-sensitive adhesive composition is obtained by dissolving and dispersing each component constituting the pressure-sensitive adhesive in a solvent, and the pressure-sensitive adhesive composition is applied onto a base material and then dried to form a pressure-sensitive adhesive layer (adhesive layer). be done. The adhesive layer may be formed directly or may be separately formed on a base material and transferred. It is also preferable to use a release film to cover the adhesive surface before adhesion. When using the above adhesive, the thickness of the adhesive layer may be generally 1 to 500 μm, preferably 2 to 300 μm. When the adhesive is used to form multiple layers, the thickness of each layer and the type of adhesive used may be the same or different.

[Shading pattern]
The light shielding pattern may be applied as at least a portion of a bezel or a housing of the flexible display device. The visibility of the image is improved by hiding the wiring arranged at the edge of the flexible display device by the light-shielding pattern and making it difficult to see. The light blocking pattern may have a single layer or a multilayer structure. The color of the light shielding pattern is not particularly limited, and may have various colors such as black, white, and metallic color. The light-shielding pattern can be formed using pigments for realizing colors and polymers such as acrylic resin, ester resin, epoxy resin, polyurethane, and silicone. These can be used alone or in a mixture of two or more. The light-shielding pattern can be formed by various methods such as printing, lithography, and inkjet. The thickness of the light shielding pattern is usually 1 to 100 μm, preferably 2 to 50 μm. Further, it is also preferable to provide a shape such as an inclination in the thickness direction of the light shielding pattern.

Hereinafter, the present invention will be explained in more detail with reference to Examples. "%" and "parts" in the examples mean % by mass and parts by mass unless otherwise specified. First, the evaluation method will be explained.

<1. Production of polyimide varnish and production of polyimide film>
(Example 1)
(1) Preparation of polyimide solution 0.5 parts by mass of isoquinoline as a catalyst (tertiary amine) was charged into a reaction vessel under a nitrogen atmosphere. The reaction vessel was connected to a vacuum pump equipped with a solvent trap and filter and placed in an oil bath. Next, 305.58 parts by mass of γ-butyrolactone (GBL) as solvent A and 104.43 parts by mass of 2,2'-bis(trifluoromethyl)benzidine (TFMB) as diamine were further charged into the reaction vessel. The contents in the reaction vessel were stirred to completely dissolve the contents. Furthermore, after 145.59 parts by mass of 4,4'-(hexafluoroisopropylidene) diphthalic dianhydride (6FDA) as a tetracarboxylic dianhydride was charged into the reaction vessel, the contents in the reaction vessel were stirred. At the same time, we started raising the temperature in an oil bath. The molar ratio of added TFMB and 6FDA (6FDA:TFMB) was 1.00:0.995, and the concentration of the raw material monomer was 45% by mass. The mass of the tertiary amine was 0.2 parts by mass based on 100 parts by mass of the raw material monomer. When the internal temperature inside the reaction vessel reached 120°C, the pressure inside the reaction vessel was reduced to 400 mmHg, and the internal temperature was subsequently raised to 180°C. After the internal temperature reached 180°C, the mixture was further heated and stirred for 5.5 hours, then the pressure was returned to atmospheric pressure, and the mixture was cooled to 170°C to obtain a polyimide solution. When the oxygen concentration in the reaction vessel was checked before and after the pressure reduction, it was found to be less than 0.01%. GBL was added at 170° C. to obtain a polyimide solution as a homogeneous solution having a polyimide solid content of 40% by mass.

(2) Manufacture of varnish N,N-dimethylacetamide (DMAc) as a diluting solvent (solvent B) was bubbled with nitrogen gas for 30 minutes. DMAc subjected to bubbling treatment was added to the polyimide solution obtained in the above (1) at 155°C to form a homogeneous solution having a polyimide solid content of 20% by mass, and the solution was taken out from the reaction vessel to obtain a varnish.

(3) Storage of polyimide varnish The varnish prepared in (2) above was stored for 5 months at a temperature of 25° C. and a humidity of 50%. The integral ratio A/B of polyimide in the varnish after storage was 0.00052, and the molecular weight in terms of polystyrene was 360,000.

(4) Formation of polyimide film DMAc prepared in (2) was added to 200.00 parts by mass of the polyimide varnish obtained in (3) above to prepare a 15% by mass solution, and it was mixed with PET (polyethylene terephthalate). ) After drooling on the film, it was heated at a temperature of 50°C for 30 minutes, and subsequently heated at a temperature of 140°C for 10 minutes to form a coating film on PET. The obtained coating film was peeled off from PET and further heated at 200° C. for 40 minutes to obtain a polyimide film. The thickness of the obtained polyimide film was 80 μm.

(Example 2)
(1) Preparation of varnish Example 1 except that the dilution solvent subjected to bubbling treatment was changed from DMAc to cyclopentanone (CP), and the temperature of the dilution solvent subjected to bubbling treatment was changed from 155°C to 130°C. A varnish was obtained in the same manner as in the method for producing varnish. The bubbling-treated CP was obtained by bubbling the CP with nitrogen gas for 40 minutes.

(2) Storage of polyimide varnish Example 1 except that the varnish to be stored was changed from the varnish of Example 1 (2) to the varnish of Example 2 (1), and the storage period was changed from 5 months to 2 weeks. The varnish was stored in the same manner as in (3). The integral ratio A/B of polyimide in the varnish after storage was 0.00035, and the molecular weight in terms of polystyrene was 300,000.

(3) Formation of polyimide film The varnish prepared in Example 1 (3) was changed to the varnish prepared in Example 2 (2), and the bubbling-treated DMAc prepared in Example 1 (2) was applied. A polyimide film was obtained in the same manner as in Example 1, except that the bubbling-treated CP prepared in Example 2 (1) was used. The thickness of the obtained polyimide film was 80 μm.

(Comparative example 1)
(1) Preparation of varnish Production of the varnish of Example 1 except that the dilution solvent was changed from bubbling-treated DMAc to non-bubbling-treated CP, and the temperature of the dilution solvent was changed from 155°C to 130°C. A varnish was obtained in the same manner as in the method.

(2) Storage of polyimide varnish The varnish to be stored was changed from the varnish of Example 1 (2) to the varnish of Comparative Example 1 (1), and the storage period was changed from 5 months to 4 months. The varnish was stored in the same manner as in 1(3). The integral ratio A/B of polyimide in the varnish after storage was 0.00006, and the molecular weight in terms of polystyrene was 320,000.

(3) Formation of polyimide film The varnish prepared in Example 1 (3) was changed to the varnish prepared in Comparative Example 1 (2), and the bubbling-treated DMAc prepared in Example 1 (2) was compared. A polyimide film was obtained in the same manner as in Example 1, except that the CP prepared in Example 1 (1) was used, which was not subjected to the bubbling treatment. The thickness of the obtained polyimide film was 80 μm.

(Comparative example 2)
(1) Preparation of varnish A varnish was obtained in the same manner as in Example 1, except that the dilution solvent was changed from DMAc subjected to bubbling treatment to GBL not subjected to bubbling treatment.

(2) Storage of polyimide varnish The varnish to be stored was changed from the varnish of Example 1 (2) to the varnish of Comparative Example 2 (1), and the storage period was changed from 5 months to 2 months. The varnish was stored in the same manner as in 1(3). The integral ratio A/B of polyimide in the varnish after storage was 0.0062, and the molecular weight in terms of polystyrene was 190,000.

(3) Formation of polyimide film The varnish prepared in Example 1 (3) was changed to the varnish prepared in Comparative Example 2 (2), and the bubbling-treated DMAc prepared in Example 1 (2) was compared. A polyimide film was obtained in the same manner as in Example 1, except that GBL prepared in Example 1 (1) and not subjected to bubbling treatment was used. The thickness of the obtained polyimide film was 80 μm.

<2. Measurement method and calculation method>

(1) Measurement of integral value The integral value of the polyimide resin used in Examples and Comparative Examples was measured by NMR and obtained from signals derived from the partial structures represented by formulas (40) and (41). The method of calculating the integral ratio from the measurement conditions and the obtained results is as follows. Note that formulas (40) and (41) are some of the structural units derived from TFMB that constitutes polyimide. In formula (40), one side represents a bond bonded to the nitrogen atom of an adjacent imide bond, and the other side represents a bond bonded to a carbon atom of an adjacent benzene ring. * in formula (41) represents a bond bonded to an adjacent benzene ring. In this example, the number of protons A corresponds to the number of terminal amino groups, and the number of protons B corresponds to the number of imide groups.

(Preparation method of measurement sample)
A large excess of methanol as a poor solvent was added to the stored varnishes prepared in Examples and Comparative Examples, and the polyimide resin was precipitated and dried by a reprecipitation method. The measurement sample was prepared by dissolving it in Note that the measurement sample can also be prepared from an optical film. Specifically, examples include a method in which the optical film is directly dissolved in a deuterated solvent, a method in which the optical film is dissolved in a soluble solvent, and the resulting solution is mixed with a deuterated solvent. If it is difficult to dissolve, it may be dissolved by ultrasonication or heating.

(NMR measurement conditions)
Measuring device: NMR device (Bruker “AVANCE600”)
Detector: “TCI Cryo Probe” manufactured by Bruker
Sample temperature: 303K
Sample concentration: 15mg/0.75mL
Solvent type: DMSO-d6
Pulse sequence: Uses Barker standard pulse sequence zg Cumulative number of times: 256 times Waiting time: 10 seconds

(Method for calculating integral ratio A/B of transparent polyimide polymer)
In the ¹ H-NMR spectrum obtained using a solution containing a polyimide resin as a measurement sample, B is the integral value of the signal derived from the proton (B) in formula (40), and B is the integral value of the signal derived from the proton (A). was designated as A. The integral range of integral value B was 7.65 to 7.75 ppm, and the integral range of integral value A was 6.78 to 6.83 ppm. The integral ratio A/B was determined from the obtained A and B. In addition, when signals originating from protons (A) and protons (B) overlap with signals originating from different structures, the intensity of the non-overlapping part of the signal is integrated, and the original signal is determined from the area ratio of that part. The signal intensity was determined and the integral ratio A/B was calculated.

(2) Measurement of polystyrene equivalent molecular weight Gel permeation chromatography (GPC) measurement (2-1) Pretreatment method Dissolve the stored varnishes prepared in Examples and Comparative Examples in γ-butyrolactone (GBL) to make a 20% solution. After that, the solution was diluted 100 times with DMF eluent and filtered through a 0.45 μm membrane filter, which was used as a measurement solution. Note that the measurement sample can also be prepared from an optical film. Specifically, the measurement is performed by dissolving the optical film in a mixed solution of DMF and GBL. If there is a peak due to an additive, etc., it may be ignored in the analysis, or the mixture may be removed by an appropriate method before GPC measurement.
(2-2) Measurement conditions Column: TSKgel SuperAWM-H x 2 + SuperAW2500 x 1 (6.0mm I.D. x 150mm x 3)
Eluent: DMF (added with 10 mmol of lithium bromide)
Flow rate: 0.6 mL/min Detector: RI detector Column temperature: 40°C
Injection volume: 20μL
Molecular weight standard: standard polystyrene

(3) Thickness measurement The thickness of the polyimide film was measured using a Digimatic Thickness Gauge (product number 547-401, manufactured by Mitutoyo Co., Ltd.).

<3. Evaluation method>
(1) Transparency evaluation method: Calculation method of film yellowness (YI value) The yellowness (Yellow Index: YI value) of each transparent polyimide polymer film obtained in Examples and Comparative Examples was Measurement was performed using a visible and near-infrared spectrophotometer (“V-670” manufactured by JASCO Corporation). After background measurement was performed without a sample, the polyimide film was set on a sample holder, transmittance measurement was performed for light with a wavelength of 300 to 800 nm, and tristimulus values (X, Y, Z) were determined. . The YI value was calculated from the tristimulus values based on the following formula. The YI value indicates that the smaller the absolute value of the YI value, the better the transparency.
YI value=100×(1.2769X-1.0592Z)/Y

(2) Evaluation method for folding durability: Method for measuring the number of times of MIT bending The folding durability of the transparent polyimide polymer films obtained in Examples and Comparative Examples was evaluated based on the following criteria. The film was cut into strips of 10 mm x 100 mm using a dumbbell cutter. The cut film was set in the MIT-DA MIT folding fatigue testing machine manufactured by Toyo Seiki Seisakusho Co., Ltd., and tested at a test speed of 175 cpm, a bending angle of 135°, a load of 750 g, and a bending clamp R of 1.0 mm. The film was alternately folded in both front and back directions, and the number of folds until breakage was measured. The greater the number of bends, the better the folding durability.

(3) Transparency evaluation method: Measuring method of total light transmittance (Tt) The total light transmittance (Tt: unit %) of the transparent polyimide polymer films obtained in Examples and Comparative Examples was measured according to JIS K 7105. :1981, it was measured using a fully automatic direct reading haze computer HGM-2DP manufactured by Suga Test Instruments Co., Ltd. The larger the total light transmittance, the more excellent the transparency.

The optical films of Examples 1 and 2 contained transparent polyimide polymers. The integral ratio A/B of the transparent polyimide polymer was 0.0001 or more and 0.001 or less.
The YI values of the optical films of Examples 1 and 2 were 1.9 and 2.0, respectively. The number of MIT bending times of the optical films of Examples 1 and 2 was 85,000 times and 78,000 times, respectively.

The optical films of Comparative Examples 1 and 2 contained transparent polyimide polymers. The integral ratio A/B of the transparent polyimide polymer contained in the optical films of Comparative Examples 1 and 2 was not within the range of 0.0001 or more and 0.001 or less.
The YI values of the optical films of Comparative Examples 1 and 2 were 3.8 and 1.9, respectively. Further, the number of MIT bending times of the optical films of Comparative Examples 1 and 2 was 80,000 times and 8,000 times, respectively.

From the above, it is clear that the optical films of Examples 1 and 2 have less yellow coloration, higher transparency, and higher folding durability than the optical films of Comparative Examples 1 and 2.

Claims (10)

An optical film containing a transparent polyimide polymer,
The ratio of the integral value A of the ¹ H-NMR signal derived from the terminal amino group of the transparent polyimide polymer to the integral value B of the ¹ H-NMR signal derived from the imide group in the chain of the transparent polyimide polymer. (Integral ratio A/B) is 0.0001 or more and 0.001 or less, and the polystyrene equivalent molecular weight of the transparent polyimide polymer is 250,000 or more and 500,000 or less. The optical film according to claim 1, having a thickness of 30 μm or more and 100 μm or less, and a total light transmittance of 85% or more. The optical film according to claim 1 or 2, wherein the transparent polyimide polymer has a fluorine group. The optical film according to any one of claims 1 to 3, wherein the transparent polyimide polymer contains a repeating unit derived from a 2,2'-bis(trifluoromethyl)benzidine derivative. An imidization step in which a transparent polyimide polymer precursor is imidized in a reduced pressure atmosphere to obtain a transparent polyimide polymer solution; a dilution step in which a varnish is prepared by diluting the transparent polyimide polymer solution with a diluting solvent; A method for producing an optical film comprising the step of casting the varnish into a film, the oxygen concentration in the gas phase of the reaction vessel in which the imidization step is performed is 0.02% or less, and the transparent polyimide polymer The integral value of the ¹ H-NMR signal derived from the terminal amino group of the transparent polyimide polymer contained in the solution , relative to the integral value B of the ¹ H-NMR signal derived from the imide group in the chain of the transparent polyimide polymer contained in the solution. A method for producing an optical film, wherein the ratio of A (integral ratio A/B) is 0.0001 or more and 0.001 or less, and the polystyrene equivalent molecular weight of the transparent polyimide polymer is 250,000 or more and 500,000 or less. The method for producing an optical film according to claim 5, wherein the varnish contains an ester solvent. The optical film according to any one of claims 1 to 4, which is a film for a front plate of a flexible display device. A flexible display device comprising the optical film according to claim 7. The flexible display device according to claim 8, further comprising a touch sensor. The flexible display device according to claim 8 or 9, further comprising a polarizing plate.