JP2019174801A - Optical film containing transparent polyimide based polymer - Google Patents

Abstract

To provide an optical film having a high transparency of a low yellow coloration and a high folding resistance, even when a varnish after long-term storage or a varnish made of a solvent after long-term storage is used.SOLUTION: In an optical film containing a transparent polyimide based polymer, the ratio (integral ratio A/B) of the integrated value A ofH-NMR signal derived from a terminal amino group of the transparent polyimide based polymer to the integrated value B ofH-NMR signal derived from an imido group in a chain of the transparent polyimide based polymer is 0.0001 or more and 0.001 or less.SELECTED DRAWING: None

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, tab reds, and electronic paper. In particular, a functional film used for a display portion of an electronic device such as a display or a touch panel in the image display apparatus is required to have high transparency and small folding resistance with small yellow coloring.
As a method for producing 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 producing a film using a varnish containing a polyamideimide resin and butyl acetate.

JP2015-174905A

However, when the varnish is produced for a long period of time or when the varnish is produced after the solvent used for the varnish is preserved for a long period of time, the transparency of the polyimide polymer film obtained by coloring the varnish itself decreases. There was a thing. As a countermeasure for restoring transparency, there is a method of purifying varnish, for example, a method of taking out a polyimide polymer from a colored varnish by precipitation or the like and re-dissolving it in a solvent, which is disadvantageous in terms of cost.
Thus, when the varnish preserve | saved for a long term and the varnish manufactured with the solvent preserve | saved for a long term were used, it was difficult to obtain the optical film which has high transparency.

  The present invention has been made in view of the above problems, and the purpose thereof is high transparency that yellow coloring is small even when a varnish stored for a long time or a varnish manufactured with a solvent stored for a long time is used. An optical film having high folding resistance is provided.

As a result of intensive studies in order to solve the above problems, the present inventors have completed the present invention. That is, the present invention includes the following aspects.
[1] An optical film containing a transparent polyimide polymer,
Ratio of integrated value A of ¹ H-NMR signal derived from terminal amino group of transparent polyimide polymer to integrated value B of ¹ H-NMR signal derived from imide group in the chain of transparent polyimide polymer (Integral ratio A / B) is 0.0001 or more and 0.001 or less.
[2] The optical film according to [1], wherein the transparent polyimide polymer has a molecular weight in terms of polystyrene of 250,000 or more and 500,000 or less.
[3] The optical film according to [1] or [2], having a thickness of 30 μm to 100 μm 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 includes a repeating unit derived from a 2,2′-bis (trifluoromethyl) benzidine derivative.
[6] A method for producing an optical film having a step of casting a varnish containing a transparent polyimide polymer, and integrating the ¹ H-NMR signal derived from an imide group in the 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. 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 claims 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 including a touch sensor.
[11] The flexible display device according to [9] or [10], further including a polarizing plate.

  According to the present invention, even when a varnish stored for a long period of time or a varnish manufactured with a solvent stored for a long period of time is used, an optical film having high transparency and high folding resistance that yellow coloring is small is provided. Can do.

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

[1. Integration ratio A / B]
When the integration ratio A / B is 0.0001 or more and 0.001 or less, the transparency of the optical film is increased. This is probably because the terminal amino group present in the transparent polyimide polymer is sufficiently small and the terminal amino group of the transparent polyimide polymer tends not to be oxidized by an oxidizing agent such as a peroxide. 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 for calculating the integration ratio A / B in the molecular structure of the embodiment of the present application will be described in detail in the embodiment. When the molecular structures are different, a measurable peak can be appropriately selected and calculated.
Examples of means for adjusting the integration 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 with 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 a 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, inhibiting the formation of peroxide in the varnish) Means). The varnish contains a transparent polyimide polymer and a solvent. It is considered that the peroxide in the varnish is generated mainly by the reaction between the solvent molecules in the varnish and dissolved oxygen (oxidation reaction of the solvent molecules). For this reason, as means for inhibiting the generation of peroxide in the varnish, for example, a means for reducing the dissolved oxygen concentration in the varnish and a kind of solvent that does not easily generate peroxide by reacting with oxygen are selected. Means are mentioned. As a means for reducing the dissolved oxygen concentration in the varnish, for example, a bubbling process is performed on the solvent with an inert gas (more specifically, a rare gas such as argon gas and neon gas, and nitrogen gas). And means for substituting the 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 time for the bubbling treatment 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 the cost. For example, when performing a bubbling process with respect to the mixed solvent containing 2 types of ester, you may perform a bubbling process of at least one of those solvents, before mixing 2 types of solvents. After mixing the two solvents, a bubbling process may be performed on the mixed solvent. Moreover, you may perform a bubbling process with respect to a varnish after preparing a 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 group of the transparent polyimide polymer is the ¹ H-NMR signal of the proton present corresponding to the number of imide groups of the transparent polyimide polymer. It may be an integral value. The integral value A of the ¹ H-NMR signal derived from the terminal amino group of the transparent polyimide polymer is the ¹ H-NMR signal of the proton 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 in the vicinity of the terminal amino group, and a signal whose chemical shift does not overlap with other protons can be appropriately selected. As ^{1 H-NMR} signals derived from the terminal amino group, if may be selected ^{1 H-NMR} signals derived from the amino group itself protons, but the accuracy waveform by the influence of moisture or the like is changed lower When it overlaps with other peaks, it is preferable to select a proton in the vicinity of the terminal amino group. For the ¹ H-NMR signal of protons present corresponding to the number of imide groups, a ¹ H-NMR peak of a proton having a strong correlation with the imide skeleton may be selected in the polymer structure. For example, for measurement of the integrated value of the ¹ H-NMR signal derived from the terminal amino group, a specific proton A in a specific partial structure A in the vicinity of the terminal amino group is selected, and the proton in the similar partial structure is selected. Thus, 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 integrated intensity of these ¹ H-NMR signals, ¹ H-NMR signals derived for the integral value B of ¹ H-NMR signals derived from the imide groups, the terminal amino group of transparent polyimide polymer The ratio of the integral value A (integral ratio A / B) can be obtained. 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. Examples of the partial structure A include a structure derived from a diamine in a polymer.

[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 further preferably 300,000 to 450,000. When the molecular weight in terms of polystyrene is 500,000 or less, the processability of a varnish for producing an optical film can be improved. When the molecular weight in terms of polystyrene is 250,000 or more, the folding resistance of the optical film can be improved.
Therefore, when the molecular weight in terms of polystyrene is 250,000 or more and 500,000 or less, the folding resistance of the optical film can be improved and the workability of the varnish can be improved.
The measuring method of the polystyrene conversion molecular weight of a transparent polyimide polymer is measured using a gel permeation chromatography (GPC) method. The measuring method will be described 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 the 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 further preferably 30 μm or more and 85 μm. When the thickness is 30 μm or more, it is advantageous from the viewpoint of internal protection when the optical film is used as a device, and when the thickness is 100 μm or less, it is advantageous from the viewpoint of folding resistance, cost, transparency, and the like.

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

[5. Transparent polyimide polymer]
(Transparent polyimide polymer obtained by polymerization and imidization)
Examples of the transparent polyimide polymer include polyimide, and comprehensively include polyimide and derivatives thereof. In this specification, a polyimide means a polymer containing a repeating structural unit containing an imide group.

The transparent polyimide polymer preferably contains mainly a repeating unit represented by the formula (10) from the viewpoint of the transparency of the transparent polyimide polymer film. The ratio of the repeating unit represented by the formula (10) is preferably 40 mol% or more, more preferably 50 mol% or more, further preferably 70 mol% or more, based on the total of all repeating units of the transparent polyimide polymer. Even more preferably, it is 90 mol% or more, particularly preferably 98 mol% or more. 100 mol% may be sufficient as the repeating unit represented by Formula (10). 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 types of repeating units represented by the formula (10) in which G and / or A are different.

  The transparent polyimide polymer is one or more of repeating units represented by the formula (11), the formula (12) and the formula (13) as long as various physical properties of the obtained transparent polyimide polymer film are not impaired. May further be included.

In formula (10) and formula (11), G and G ¹ represent a tetravalent organic group, preferably an organic group which may be substituted with a hydrocarbon group or a fluorine-substituted hydrocarbon group. The G and ^{G 1,} for example, formula (20), equation (21), equation (22), equation (23), equation (24), equation (25), equation (26), equation (27), wherein And groups represented by (28) and formula (29), and chain hydrocarbon groups having 6 or less tetravalent carbon atoms. * The in formula (20) to (29) represents a bond, Z in the formula (26) is a single _{bond, -O -, - CH 2 -} , - CH 2 -CH 2 -, - CH ( _{CH 3) -, - C (} CH 3) 2 -, - C (CF 3) 2 -, - Ar -, - SO 2 -, - CO -, - O-Ar-O -, - Ar-O-Ar _{-, - Ar-CH 2 -Ar} -, - Ar-C (CH 3) represents a 2 -Ar- or _-Ar-SO 2 -Ar-. Ar represents an arylene group having 6 to 20 carbon atoms which may be substituted with a fluorine atom (more specifically, a phenylene group or the like). From the viewpoint of suppressing the yellowness of the resulting film, G and G ¹ preferably represent a group represented by Formula (20) to Formula (27).

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

In Formula (13), G ³ represents a divalent organic group, and preferably represents an organic group that may be substituted with a hydrocarbon group or a fluorine-substituted hydrocarbon group. Examples of the divalent organic group represented by G ³ 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 in the groups represented by formula (28) and formula (29) are each replaced by a hydrogen atom, and a divalent chain hydrocarbon having 6 or less carbon atoms Groups.

In the formulas (10) to (13), A, A ¹ , A ² and A ³ all represent a divalent organic group, preferably substituted with a hydrocarbon group or a fluorine-substituted hydrocarbon group. Represents a good organic group. As A, A ¹ , A ² , and A ³ , for example, Expression (30), Expression (31), Expression (32), Expression (33), Expression (34), Expression (35), Expression (36) Groups represented by formula (37) and formula (38); a group in which they are 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 Is mentioned.
* In Formula (30) to Formula (38) represents a bond, and Z ¹ , Z ² and Z ³ in Formula (34) to Formula (36) are each independently a single bond, —O—, _{-CH 2 -, - CH 2 -CH} 2 -, - CH (CH 3) -, - C (CH 3) 2 -, - C (CF 3) 2 -, - SO 2 - or an -CO-. One example is when Z ¹ and Z ³ are —O— and Z ² is —CH ₂ —, —C (CH ₃ ) ₂ —, —C (CF ₃ ) ₂ — or —SO ₂ —. To express. Z ¹ and Z ² , and Z ² and Z ³ are each preferably in a meta position or a para position with respect to each ring.

  The repeating unit represented by the formula (10) and the formula (11) is usually derived from a diamine and a tetracarboxylic acid compound. The repeating unit represented by the formula (12) is usually derived from a diamine and a tricarboxylic acid compound. The repeating unit represented by the 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, alkanoyl halides, and the like).

  The transparent polyimide polymer preferably has a fluorine group. The transparent polyimide polymer preferably includes a repeating unit derived from a 2,2′-bis (trifluoromethyl) benzidine derivative. In the present specification, the 2,2′-bis (trifluoromethyl) benzidine derivative also includes 2,2′-bis (trifluoromethyl) benzidine.

(Tetracarboxylic acid compound)
Examples of the tetracarboxylic acid compound include an aromatic tetracarboxylic acid compound such as an aromatic tetracarboxylic dianhydride and an aliphatic tetracarboxylic acid compound such as an aliphatic tetracarboxylic dianhydride. These tetracarboxylic acid compounds may be used individually by 1 type, and may be used in combination of 2 or more type. The tetracarboxylic acid compound may be a tetracarboxylic acid compound analog such as a tetracarboxylic acid chloride compound in addition to the tetracarboxylic dianhydride.

Examples of the aromatic tetracarboxylic dianhydride include non-condensed polycyclic aromatic tetracarboxylic dianhydride, monocyclic aromatic tetracarboxylic dianhydride, and condensed polycyclic aromatic tetra Carboxylic dianhydrides are mentioned.
Non-condensed polycyclic aromatic tetracarboxylic dianhydrides include, for example, 4,4′-oxydiphthalic dianhydride, 3,3 ′, 4,4′-benzophenone tetracarboxylic 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) To describe ), 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.

Examples of the condensed polycyclic aromatic tetracarboxylic dianhydride include 2,3,6,7-naphthalene tetracarboxylic dianhydride.
The aromatic tetracarboxylic dianhydride is preferably 4,4′-oxydiphthalic dianhydride, 3,3 ′, 4,4′-benzophenone tetracarboxylic 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 Anhydride, 2,2-bis (3,4-dicarboxyphenoxyphenyl) propane dianhydride, 4,4 '-(hexafluoroisopropylidene) diphthalic dianhydride, 1,2-bis (2,3- Dicarboxypheny ) 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. One of these aromatic tetracarboxylic dianhydrides may be used alone, or two or more thereof may be used in combination.

  Examples of the aliphatic tetracarboxylic dianhydride include a cyclic or acyclic aliphatic tetracarboxylic dianhydride. In this specification, the 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 dianhydrides such as 2,3,4-cyclopentanetetracarboxylic dianhydride, bicyclo [2.2.2] oct-7-ene-2,3,5,6-tetracarboxylic Examples thereof include acid dianhydride, dicyclohexyl-3,3 ′, 4,4′-tetracarboxylic dianhydride, and regioisomers thereof. One of these cycloaliphatic tetracarboxylic dianhydrides may be used alone, or two or more thereof may be used in combination. Examples of the acyclic aliphatic tetracarboxylic dianhydride include 1,2,3,4-butanetetracarboxylic dianhydride and 1,2,3,4-pentanetetracarboxylic dianhydride. . One of these acyclic aliphatic tetracarboxylic dianhydrides may be used alone, or two or more thereof may be used in combination.

  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-condensed polycyclic aromatic tetracarboxylic dianhydride, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride, 2,2 ′, 3,3′-biphenyltetracarboxylic dianhydride, 2,2-bis (3,4-dicarboxyphenyl) More preferred is propane dianhydride, 4,4 ′-(hexafluoroisopropylidene) diphthalic dianhydride (6FDA). These suitable tetracarboxylic acid compounds may be used singly or in combination of two or more.

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

Examples of the dicarboxylic acid compound include aromatic dicarboxylic acids, aliphatic dicarboxylic acids, and related acid chloride compounds and acid anhydrides. These dicarboxylic acid compounds may be used individually by 1 type, and may be used in combination of 2 or more type. Examples of the dicarboxylic acid compound include terephthalic acid; isophthalic acid; naphthalenedicarboxylic acid; 4,4′-biphenyldicarboxylic acid; 3,3′-biphenyldicarboxylic acid; dicarboxylic acid of a chain hydrocarbon having 8 or less carbon atoms. Examples include compounds in which a compound and 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, or mixtures thereof. In the present specification, the “aromatic diamine” refers to a diamine in which an amino group is directly bonded to an aromatic ring, and an aliphatic group or other substituent may be included in a part of the structure. The aromatic ring may be a single ring or a condensed ring. Examples of the aromatic ring include, but are not limited to, a benzene ring, a naphthalene ring, an anthracene ring, and a fluorene ring. Of the aromatic rings, a benzene ring is preferable. In the present specification, “aliphatic diamine” means a diamine in which an amino group is directly bonded to an aliphatic group, and an aromatic ring or other substituent may be included in a part of the structure. .

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

  Examples of the aromatic diamine include p-phenylenediamine, m-phenylenediamine, 2,4-toluenediamine, m-xylylenediamine, p-xylylenediamine, 1,5-diaminonaphthalene, and 2,6- Aromatic diamines 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′-diaminodiphenyl sulfone, 3,4′-diaminodiphenyl sulfone, 3,3′-diaminodiphenyl sulfone, 1,4-bis (4-aminophenoxy) benzene, 1,3- Bis (4-aminophenoxy) benzene, 4,4′-di Minodiphenylsulfone, bis [4- (4-aminophenoxy) phenyl] sulfone, bis [4- (3-aminophenoxy) phenyl] sulfone, 2,2-bis [4- (4-aminophenoxy) phenyl] propane, 2,2-bis [4- (3-aminophenoxy) phenyl] propane, 2,2′-dimethylbenzidine, 2,2′-bis (trifluoromethyl) -4,4′-diaminodiphenyl (2,2 ′ -Bis (trifluoromethyl) benzidine (TFMB)), 4,4'-bis (4-aminophenoxy) biphenyl, 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenylmethane 9,9-bis (4-aminophenyl) fluorene, 9,9-bis (4-amino-3-methylphenol) 2) Two or more aromatic rings such as fluorene, 9,9-bis (4-amino-3-chlorophenyl) fluorene, 9,9-bis (4-amino-3-fluorophenyl) fluorene, and derivatives thereof The aromatic diamine which has. These aromatic diamines may be used alone or in combination of two or more.

  The diamine can also have a fluorine-based substituent. As a fluorine-type substituent, they are a C1-C5 perfluoroalkyl group like a trifluoromethyl group, and a fluoro group, for example.

Among the diamines, from the viewpoint of high transparency and low colorability, 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. More preferably.
The diamine is preferably a diamine having a biphenyl structure and a fluorine-based substituent. Examples of the diamine having a biphenyl structure and a fluorine-based substituent include a 2,2′-bis (trifluoromethyl) benzidine (TFMB) derivative.

The molar ratio between the diamine in the raw material monomer and the carboxylic acid compound such as a tetracarboxylic acid compound is preferably within a range of 0.9 mol to 1.1 mol of the tetracarboxylic acid with respect to 1.00 mol of the diamine. Can be adjusted. In order to express high folding resistance, it is preferable that the obtained transparent polyimide-based polymer has a high molecular weight, so that tetracarboxylic acid is 0.98 mol or more and 1.02 mol or less with respect to 1.00 mol of diamine. More preferably, it is 0.99 mol or more and 1.01 mol or less.
In addition, from the viewpoint of suppressing the yellowness of the obtained transparent polyimide polymer film, it is preferable that the proportion of amino groups in the resulting polymer terminal is low, such as tetracarboxylic acid compound with respect to 1.00 mol of diamine. The carboxylic acid compound is preferably 1.00 mol or more.

  Adjusting the number of fluorines in the molecule of diamine and carboxylic acid compound (for example, 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 mass% or more, 10 mass% or more, or 20 mass% or more. Since the raw material cost tends to increase as the proportion of fluorine increases, the upper limit of the amount of fluorine is preferably 40% by mass or less. A fluorine-type substituent may exist in either diamine or a carboxylic acid compound, and may exist in both. By including a fluorine-based substituent, the YI value may be particularly reduced.

[6. Manufacturing method of optical film]
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 ¹ H-NMR signal derived from an imide group in the chain of the transparent polyimide polymer. The ratio (integral ratio A / B) 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 is 0.0001 or more and 0.001 or less. An example of a step of casting a varnish containing a transparent polyimide polymer will be described. A varnish is cast on the base material to form a coating film, and the solvent is removed from the coating film by means such as reduced pressure, drying, and heating, and then peeled off from the base material. Thereby, a transparent polyimide polymer film is obtained.

  Casting can be performed on a resin substrate, a stainless steel belt, or a glass substrate by a roll-to-roll or batch method. Examples of the resin base material include PET, PEN, polyimide, and polyamideimide. Of these resin substrates, PET is preferable from the viewpoints of adhesion to the film and cost.

  Even if the varnish obtained by the above production method is formed into a film without undergoing a purification step, a highly transparent transparent polyimide polymer film can be obtained. For this reason, a transparent polyimide polymer can be taken out from the varnish by precipitation or the like, and then formed into a film without undergoing a purification step in which it is redissolved in a solvent. This is a cost-effective process.

  In the method for producing an optical film of the present invention, a certain amount of an organic solvent is volatilized by passing the coating film through a drier that contacts a heated gas with the surface of the coating film, and the coating film is a self-supporting film. Or may be obtained by peeling from the support. The working temperature is adjusted depending on the substrate used, and when a resin substrate is used, it is generally carried out at or below the glass transition temperature thereof. Usually, it may be heated 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 added. It is also suitable to carry out under an inert atmosphere or under reduced pressure as appropriate.

  Moreover, you may heat the peeled transparent polyimide polymer film at 80-300 degreeC as needed.

  The varnish contains a transparent polyimide polymer and a solvent.

〔solvent〕
The solvent preferably has high transparency over a long period of time, while having basic characteristics as a composition of the varnish. The former is a characteristic in which a transparent polyimide polymer is dissolved or dispersed and the viscosity of the varnish is adjusted to a viscosity suitable for coating. The latter is, for example, a characteristic that a solvent molecule does not easily react with oxygen, or does not easily generate a peroxide having a high reaction activity even if it reacts with oxygen, and a characteristic that does not readily dissolve oxygen.
From the viewpoint of satisfying such characteristics, examples of the solvent include aprotic polar solvents (more specifically, N, N-dimethylacetamide (hereinafter sometimes referred to as DMAc), dimethyl sulfoxide, and the like). , Ketones (more specifically, cyclopentanone (hereinafter sometimes referred to as CP)), and carboxylic acid esters (more specifically, acetate esters and cyclic carboxylic acid esters) that are ester solvents. Etc.). Examples of the acetate ester 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 solvent may be used individually by 1 type, and may be used in combination of 2 or more type.

  Among these solvents, from the viewpoint of further improving two properties, at least one solvent selected from the group consisting of GBL, DMAc, butyl acetate, amyl acetate, CP, and isoamyl acetate is preferable, and selected from the above solvents. More preferred are at least two kinds of esters. Examples of the at least one solvent include a combination of DMAc and GBL and CP and GBL. Examples of the combination of at least two kinds of 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, 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 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 And a combination of 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, amyl acetate and isoamyl acetate, GBL, butyl acetate, amyl acetate, GBL, butyl acetate, isoamyl acetate, GBL, amyl acetate, isoamyl acetate, butyl acetate, amyl acetate, isoamyl acetate, and combinations of GBL, butyl acetate, amyl acetate, and isoamyl acetate. More preferred 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 and amyl acetate and acetic acid A combination with isoamyl is mentioned.

In the case of a mixed solvent composed of two 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 composed of three 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 comprising 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 further preferably It is 40 mass% or more, and is 90 mass% or less normally, Preferably it is 80 mass% or less, More preferably, it is 70 mass% or less, More preferably, it is 60 mass% or less.

〔Additive〕
The varnish may further contain an additive as long as the transparency is not impaired. Examples of the additive include inorganic particles, ultraviolet absorbers, antioxidants, mold release agents, stabilizers, colorants, flame retardants, lubricants, thickeners, and leveling agents.

[7. Manufacturing method of varnish]
The method for producing the varnish includes, for example, a polymerization step in which a raw material monomer of a transparent polyimide polymer is polymerized in a solvent A to obtain a transparent polyimide polymer precursor, and a solvent containing a tertiary amine in a reduced pressure atmosphere. The imidization process which obtains a transparent polyimide polymer solution by imidating the transparent polyimide polymer precursor and the dilution process of preparing the varnish by diluting the transparent polyimide polymer solution with the solvent B. The manufacturing process of a varnish may further include the varnish extraction process which extracts a varnish from a reaction container.

(Polymerization process)
In the polymerization step, the raw material monomer of the transparent polyimide polymer is polymerized in the solvent A to obtain a transparent polyimide polymer precursor. The solvent A can be the same as those mentioned above. The quantity of the raw material monomer which occupies for the whole liquid containing a raw material monomer and the solvent A can be 10-60 mass%. When the amount of the raw material monomer is large, the polymerization rate tends to increase, and the molecular weight can be increased. Further, the polymerization time can be shortened, and the coloring of the transparent polyimide polymer tends to be suppressed. If the amount of the raw material monomer is too large, the viscosity of the polymer or the solution containing the polymer tends to increase, so that it becomes difficult to stir or the polymer adheres to the reaction vessel or stirring blade, resulting in a low yield. Sometimes it becomes. The solvent A can be the same as those mentioned above.

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

By sufficiently stirring the raw material monomer in the reaction mass, polymerization of the raw material monomer is promoted and a transparent polyimide polymer precursor is formed. If necessary, the reaction mass may be heated to about 40 to 90 ° C. The imidization process described later can also proceed in parallel with the progress of the raw material monomer polymerization process. In this case, the reaction mass may be heated to a higher temperature in accordance with the imidization conditions described later.
The polymerization reaction time 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 mixing the diamine and the solvent A, may be added after mixing, or may be added after mixing the diamine, the solvent, and the carboxylic acid compound.
Further, after diluting with a part of the solvent to be used, it may be added to the reaction mass.

[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 the tertiary amine include a tertiary amine represented by the formula (d) (hereinafter sometimes referred to as a tertiary amine 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 the 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, further preferably 170 ° C or higher, and particularly preferably 200 ° C or higher. Although the upper limit of the boiling point of the tertiary amine is not particularly defined, it is usually 350 ° C. or lower. When the boiling point of the tertiary amine is in the above range, it is preferable because the amount of catalyst removed outside the system tends to be suppressed when water is distilled off under reduced pressure.

(Imidization process)
Subsequently, in the imidization step, the transparent polyimide polymer precursor is imidized in a solvent A containing a tertiary amine in 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, the imidation of the transparent polyimide polymer precursor is promoted, and water generated as a by-product while producing polyimide is retained. Leave. It is preferable to imidize the transparent polyimide polymer precursor in the solvent A in the reaction vessel in which the above polymerization is performed. The tertiary amine may be added during or before the polymerization step for polymerizing the raw material monomer to produce a transparent polyimide polymer precursor as described above, but produces a transparent polyimide polymer precursor. It may be added after the process.

  The formation reaction of the transparent polyimide polymer precursor and the imidization reaction may proceed simultaneously. In that case, the bond of an amide group may be cut | disconnected by the water produced | generated by imidation reaction, and the molecular weight of the transparent polyimide type polymer obtained may become low. A film obtained from a varnish containing such a transparent polyimide polymer may have a low folding resistance. In the imidization step, the pressure in the reaction solution is reduced and water in the reaction solution is quickly removed, so that 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 and the imidation reaction of the transparent polyimide polymer precursor proceed simultaneously, the imidization process is performed in a reduced-pressure atmosphere, so that the transparent polyimide polymer is included without going through a purification process. Even if the film is produced directly from the varnish, the film tends to have high folding resistance.

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

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

The pressure in the imidization step is preferably 730 mmHg or less, more preferably 700 mmHg or less, and 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 perform the pressure at 400 mmHg or higher in order to increase the stability of the reaction. For the same reason, it may be more preferable to carry out at 600 mmHg or more.
If the pressure in the imidization step is set near the saturated vapor pressure of the solvent in the imidization step, YI tends to be suppressed. A pressure within 50 mmHg from the saturated vapor pressure is preferred.

The heating time is, for example, usually 1 to 24 hours, preferably 1 to 12 hours, more preferably 2 to 9 hours, further preferably 2 to 8 hours, still more preferably 2 to 6 hours, and particularly preferably 2 to 2 hours. 5 hours. It is preferable to stir during heating.
As the reaction time becomes longer, the molecular weight increases, but the yellowishness of the resin tends to increase. On the other hand, when 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 step is carried out under a reduced pressure atmosphere, the oxygen concentration in the gas phase contacting the liquid phase containing the solvent A in the reaction vessel is low, so that the dissolution of oxygen into the solvent A is reduced, and the transparent polyimide It is considered that the peroxide concentration in the polymer solution is reduced. In the production method, the imidization step by heating the reaction mass in 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 causes coloring in particular. For example, when the temperature of the reaction solution is 130 ° C. or higher, the oxygen concentration is preferably 0.02% or lower. In the synthesis of the precursor and the imidization of the precursor, oxygen is not substantially generated. For example, by reducing the oxygen concentration in the gas phase by replacing the inside of the reaction vessel with nitrogen gas before starting the raw material, The oxygen concentration in the gas phase in the conversion step can be reduced. The oxygen concentration in the imidization step can be grasped, 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 decompression, the oxygen concentration may be measured by sampling the gas phase before and after decompression. For the purpose of lowering the oxygen concentration as in the reduced pressure atmosphere, the imidization step may be performed in an inert gas atmosphere instead of the reduced pressure atmosphere.

  After heating, it 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 the 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. The solid content concentration in a suitable varnish is 10 to 25% by mass.
In addition, when producing a film from a varnish, if the varnish which contains 30 mass% or more of transparent polyimide type polymers with respect to the total amount of the solid content in a varnish is used, one of the main components mentioned later is a transparent polyimide type 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 in the reaction container, and can also be performed on the solution recovered from the reaction container.

  In the reaction vessel, when the solvent B is added to the transparent polyimide polymer solution after imidization and the concentration of the transparent polyimide polymer in the reaction vessel is diluted, it remains in the reaction vessel in the next extraction step. The amount of the polymer can be reduced, and the yield of the polymer can be improved. Further, when the amount of the polymer remaining in the reaction vessel is reduced, the coloring (for example, yellow) of the obtained transparent polyimide polymer is improved in the subsequent polymerization and imidation repeating steps using this reaction vessel.

  The solvent B for dilution can be the same as those mentioned above. The solvent B and the solvent A may be the same type or different types. By appropriately selecting a solvent having high solubility in the polyimide resin as the solvent B for dilution, the recovery rate of the transparent polyimide polymer from the reaction vessel is increased.

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

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

Ratio of integrated value A of ¹ H-NMR signal derived from terminal amino group of transparent polyimide polymer to integrated value B of ¹ H-NMR signal derived from imide group in chain in transparent polyimide polymer ( In order to produce an optical film having an integration ratio A / B) of 0.0001 or more and 0.001 or less, the integration ratio A / B of the transparent polyimide polymer in the varnish at the time of cast film formation is 0.0001 or more. It is necessary to manage so that it is 0.001 or less.
The integration ratio A / B can be controlled by the molecular weight of the transparent polyimide polymer, the ratio of polymerization monomers, the order of preparation, and the like. When the molecular weight is high, the integration ratio A / B tends to decrease, and when the molecular weight is low, the integration ratio A / B tends to increase.
The integration ratio A / B may be reduced by storing the transparent polyimide polymer in a solution state (for example, polyimide varnish) for a long period of time. This is presumably because the terminal amino group of the transparent polyimide polymer changes due to oxidation during storage. The storage period depends on the type of solvent and storage conditions, but is preferably within 1 year, more preferably within 6 months, and even more preferably within 1 month. It is preferable that the storage temperature does not exceed 40 ° C., for example. From the viewpoint of suppressing oxidation of the terminal amino group, the amount of peroxide in the solvent is preferably small. From the viewpoint of suppressing the generation of peroxide, examples of the solvent include aprotic solvents (more specifically, DMAc and dimethyl sulfoxide), ketones (more specifically, CP, etc.), ester solvents, and the like. Carboxylic acid esters (more specifically, acetate esters, cyclic carboxylic acid esters, and the like) are preferable, and cyclic carboxylic acid esters (more specifically, γ-butyrolactone, etc.), acetate esters (more specifically, Butyl acetate, amyl acetate, etc.), N, N-dimethylacetamide, and mixtures thereof, more preferably γ-butyrolactone, butyl acetate, amyl acetate, N, N-dimethylacetamide, and their It is a mixture. By performing bubbling with an inert gas in the solvent before dilution, the dissolved oxygen in the solvent can be replaced with the inert gas, and the generation of peroxide can be suppressed. The oxidation of the terminal amino group can also be suppressed by filling the container with an inert gas and storing it.

  The transparent polyimide polymer film is used as an optical film, and is useful, for example, as a front plate of a display device, particularly as a front plate (window film) of a flexible display device. The 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 disposed on the viewing side on the flexible functional layer. This front plate has a function of protecting the flexible functional layer.

  Examples of the display device include a wearable device such as a television, a smartphone, a mobile phone, a car navigation, a tablet PC, a portable game machine, electronic paper, an indicator, a bulletin board, a clock, and a smart watch. Examples of the flexible display device include all display devices having flexible characteristics, and among them, a foldable display device and a rollable display device that are preferably foldable.

[Flexible display]
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 may be referred to as a window film. The flexible display device includes a flexible display device laminate and an organic EL display panel. The flexible display device laminate is arranged on the viewing side with respect to the organic EL display panel, and is configured to be bendable. 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 thereof is arbitrary, but the window film, the polarizing plate, It is preferable that the touch sensor or window film, the touch sensor, and the polarizing plate are laminated in this order. The presence of a polarizing plate on the viewing side of the touch sensor is preferable because the touch sensor pattern is less visible and the visibility of the display image is improved. Each member can be laminated | stacked using an adhesive agent, an adhesive, etc. Moreover, the light-shielding pattern formed in at least one surface of the any one layer of the said window film, a polarizing plate, and a touch sensor can be comprised.

[Polarizer]
The flexible display device of the present invention may further include a polarizing plate, preferably a circular polarizing plate. The circularly polarizing plate is a functional layer having a function of transmitting only a right or left circularly polarized component by laminating a λ / 4 retardation plate on a linearly polarizing plate. For example, external light is converted into right circularly polarized light, the external light reflected by the organic EL panel and turned into left circularly polarized light is blocked, and only the light emitting component of the organic EL is transmitted to suppress the influence of the reflected light and image Used to make it easier to see. In order to achieve the circular polarization function, the absorption axis of the linearly polarizing plate and the slow axis of the λ / 4 retardation plate need to be 45 ° theoretically, but practically 45 ± 10 °. The linearly polarizing plate and the λ / 4 retardation plate are not necessarily laminated 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 circular polarization at all wavelengths, the circular polarization plate in the present invention includes an elliptical polarization plate because it is not always necessary in practice. It is also preferable to further improve the visibility in a state where polarized sunglasses are applied by laminating a λ / 4 retardation film on the viewing side of the linearly polarizing plate and making the emitted light circularly polarized.

The linear polarizing plate is a functional layer having a function of blocking polarized light having a vibration component perpendicular to the light that is oscillating in the transmission axis direction. 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 linear polarizing plate may have a thickness of 200 μm or less, preferably 0.5 to 100 μm. When the thickness is in the above range, flexibility tends to be difficult 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 on a PVA-based film oriented by stretching or is stretched in a state of being adsorbed to PVA, whereby the dichroic dye is oriented and exhibits polarizing performance. In the production of the film-type polarizer, other processes such as swelling, crosslinking with boric acid, washing with an aqueous solution, and drying may be included. The stretching or dyeing process may be performed by a PVA film alone or in a state where it is laminated with another film such as polyethylene terephthalate. The thickness of the PVA film used is preferably 10 to 100 μm, and the draw ratio is preferably 2 to 10 times.
Furthermore, as another example of the polarizer, a liquid crystal-coated polarizer formed by coating a liquid crystal polarizing composition may be used. The liquid crystal polarizing composition may include a liquid crystal compound and a dichroic dye compound. The liquid crystalline compound only needs to have the property of exhibiting a liquid crystal state. In particular, the liquid crystalline compound preferably has a higher-order alignment state such as a smectic phase because it can exhibit high polarization performance. The liquid crystal compound preferably has a polymerizable functional group.

The dichroic dye is a dye that is aligned with the liquid crystal compound and exhibits dichroism, and the dichroic dye itself may have liquid crystallinity or have a polymerizable functional group. You can also Any compound in the liquid crystal polarizing composition has a polymerizable functional group.
The liquid crystal polarizing composition may further contain 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 applying 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 produced, for example, by applying an alignment film forming composition on a substrate and imparting alignment 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 and the like in addition to the aligning agent. Examples of the aligning agent include polyvinyl alcohols, polyacrylates, polyamic acids, and polyimides. When applying photo-alignment, it is preferable to use an aligning agent containing a cinnamate group. The polymer used as the aligning agent may have a weight average molecular weight of 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 the alignment regulating force. The liquid crystal polarizing layer can be peeled off from the base material, transferred and laminated, or the base material can be laminated as it is. It is also preferable that the base material plays a role as a transparent base material for a protective film, a retardation plate, or a window.

  The protective film may be a transparent polymer film, and materials and additives used for the transparent substrate can be used. A cellulose film, an olefin film, an acrylic film, and a polyester film 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 an acrylate. If necessary, plasticizers, ultraviolet absorbers, infrared absorbers, colorants such as pigments and dyes, fluorescent brighteners, dispersants, thermal stabilizers, light stabilizers, antistatic agents, antioxidants, lubricants, solvents, etc. May be included. The protective film may have a thickness of 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 difficult to decrease. The protective film can also serve as a transparent substrate of the window.

The λ / 4 phase difference plate is a film that gives a phase difference of λ / 4 in a direction (in-plane direction of the film) orthogonal to the traveling direction of incident light. 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 adjusting agents, plasticizers, UV absorbers, infrared absorbers, colorants such as pigments and dyes, fluorescent brighteners, dispersants, heat stabilizers, light stabilizers, antistatic agents, antioxidants Further, it may contain a lubricant, a solvent and the like. The stretchable retardation plate may have a thickness of 200 μm or less, preferably 1 to 100 μm. When the thickness is in the above range, the flexibility of the film tends not to decrease.
Furthermore, as another example of the λ / 4 retardation plate, a liquid crystal coating type retardation plate formed by applying a liquid crystal composition may be used. The liquid crystal composition includes a liquid crystal compound having a property of exhibiting a liquid crystal state, such as nematic, cholesteric, and smectic. Any compound including a liquid crystal compound in the liquid crystal composition has a polymerizable functional group. The liquid crystal-coated retardation plate may further contain 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 coating type retardation plate can be produced by coating and curing a liquid crystal composition on an alignment film to form a liquid crystal retardation layer, as described for the liquid crystal polarizing layer. The liquid crystal coated retardation plate can be formed thinner than the stretched retardation plate. The thickness of the liquid crystal polarizing layer may be usually 0.5 to 10 μm, preferably 1 to 5 μm. The liquid crystal coating type retardation plate can be peeled off from the substrate, transferred, and laminated, or the substrate can be laminated as it is. It is also preferable that the base material plays a role as a transparent base material for a protective film, a retardation plate, or a window.

In general, there are many materials that exhibit higher birefringence as the wavelength is shorter and smaller birefringence as the wavelength is longer. In this case, since a phase difference of λ / 4 cannot be achieved in the entire visible light region, an in-plane phase difference of 100 to 180 nm, preferably 130, becomes λ / 4 with respect to the vicinity of 560 nm having high visibility. Often designed to be ˜150 nm. It is preferable to use a reverse dispersion λ / 4 phase difference plate using a material having birefringence wavelength dispersion characteristics opposite to that of normal, since the visibility can be improved. As such a material, those described in Japanese Patent Application Laid-Open No. 2007-232873 can be used in the case of a stretch-type phase difference plate, and those described in Japanese Patent Application Laid-Open No. 2010-30979 in the case of a liquid crystal coating type phase difference plate. preferable.
As another method, a technique for obtaining a broadband λ / 4 phase difference plate by combining with a λ / 2 phase difference plate is also known (Japanese Patent Laid-Open No. 10-90521). The λ / 2 phase difference plate is also manufactured by the same material method as the λ / 4 phase difference plate. Although the combination of the stretchable retardation plate and the liquid crystal coating type retardation plate is arbitrary, it is preferable to use the liquid crystal coating type retardation plate for both because the thickness can be reduced.
In order to improve the visibility in the oblique direction on the circularly polarizing plate, a method of laminating a positive C plate is also known (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. The touch sensor is used as input means. Various types of touch sensors such as a resistive film method, a surface acoustic wave method, an infrared method, an electromagnetic induction method, and a capacitance method have been proposed, and any method may be used. Of these, the electrostatic capacity method is preferable. The capacitive touch sensor is divided into an active region and a non-active region located in an outer portion of the active region. The active area is an area corresponding to an area (display unit) where a screen is displayed on the display panel, and is an area where a user's touch is sensed. This is a region corresponding to the display unit. The touch sensor includes a flexible substrate; a sensing pattern formed in an active region of the substrate; and formed in an inactive region 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 substrate having flexible characteristics, 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, the toughness is defined as a lower area of a curve up to a fracture point in a stress (MPa) -strain (%) curve (Stress-strain curve) obtained through a tensile test of a polymer material.

  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 in the same layer, and each pattern must be electrically connected in order to sense a touched point. The first pattern is a form in which each unit pattern is connected to each other via a joint, but the second pattern has a structure in which each unit pattern is separated from each other in an island form. A separate bridge electrode is required for connection. A 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-ethylenedithiothiophene)), carbon nanotube (CNT), graphene, metal wire, and the like. These can be used alone or in combination 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, telenium, and chromium. These can be used alone or in admixture of two or more.

The bridge electrode can be formed on the sensing pattern via the insulating layer and on the insulating layer. The bridge electrode is formed on the substrate, and the insulating layer and the sensing pattern can be formed thereon. The bridge electrode may be formed of the same material as the sensing pattern, and is 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 in a layer structure covering the sensing pattern. In the latter case, the bridge electrode can be connected to the second pattern via a contact hole formed in the insulating layer. The touch sensor has a transmittance difference between a pattern area where a pattern is formed and a non-pattern area where a pattern is not formed, specifically, a light transmittance induced by a difference in refractive index in these areas. As a means for appropriately compensating for the difference, an optical adjustment layer may be further included between the substrate and the electrode, 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 can include, for example, a copolymer of monomers such as an acrylate monomer, a styrene monomer, and a carboxylic acid monomer. The photocurable organic binder may be a copolymer including different repeating units such as an epoxy group-containing repeating unit, an acrylate repeating unit, and a carboxylic acid repeating unit.
Examples of the inorganic particles include zirconia particles, titania particles, and alumina particles. The photocurable composition may further contain additives such as a photopolymerization initiator, a polymerizable monomer, and a curing auxiliary agent.

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

  As the water-based solvent volatilization type adhesive, water-soluble polymers such as polyvinyl alcohol polymers and starches, water-dispersed polymers such as ethylene-vinyl acetate emulsions and styrene-butadiene emulsions 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, and the like may be blended. In the case of bonding with the water-based solvent volatile adhesive, the water-based solvent volatile adhesive can be injected between the layers to be bonded, and the adhesion layer can be bonded, and then dried to provide adhesion. The thickness of the adhesive layer in the case of using the aqueous solvent volatile adhesive may be usually 0.01 to 10 μm, preferably 0.1 to 1 μm. When the water-based solvent volatile adhesive is used for forming a plurality of layers, the thickness of each layer and the type of the 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 irradiates active energy rays to form an adhesive layer. The active energy ray-curable composition can contain at least one polymer of a radical polymerizable compound and a cationic polymerizable compound similar to the hard coat composition. The radical polymerizable compound is the same as the hard coat composition, and the same kind as the hard coat composition can be used. As the radical polymerizable compound used for the adhesive layer, a compound having an acryloyl group is preferable. It is also preferable to contain a monofunctional compound in order to lower the viscosity of the adhesive composition.

The cationic polymerizable compound is the same as that of the hard coat composition, and the same kind as that of the hard coat composition can be used. As the cationic polymerizable compound used in the active energy ray-curable composition, an epoxy compound is particularly preferable. It is also preferable to include a monofunctional compound as a reactive diluent in order to lower the viscosity of the adhesive composition.
The active energy ray composition may further contain a polymerization initiator. Examples of the polymerization initiator include radical polymerization initiators, cationic polymerization initiators, radicals and cationic polymerization initiators, which 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 one of radical polymerization or cationic polymerization by irradiation with active energy rays can be used.

  The active energy ray curable composition further includes 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 solvent, an additive, a solvent. Can be included. When adhering with the active energy ray curable adhesive, the active energy ray curable composition is applied to either or both of the adherend layers and then bonded, and the active energy ray curable composition is activated through either of the adhering layers or both of the adhering layers. It can be bonded by irradiating with energy rays and curing. When the active energy ray-curable adhesive is used, the thickness of the adhesive layer is usually 0.01 to 20 μm, preferably 0.1 to 10 μm. When the active energy ray-curable adhesive is used for forming a plurality of layers, the thickness of each layer and the type of adhesive used may be the same or different.

  The pressure-sensitive adhesive is classified into an acrylic pressure-sensitive adhesive, a urethane pressure-sensitive adhesive, a rubber pressure-sensitive adhesive, a silicone pressure-sensitive adhesive, and the like depending on the main polymer, and any of them can be used. In addition to the main 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. Each component constituting the pressure-sensitive adhesive is dissolved and dispersed in a solvent to obtain a pressure-sensitive adhesive composition, and the pressure-sensitive adhesive composition is applied onto a substrate and then dried to form a pressure-sensitive adhesive layer (adhesive layer). Is done. The pressure-sensitive adhesive layer may be directly formed, or a layer separately formed on the substrate can be transferred. In order to cover the adhesive surface before bonding, it is also preferred to use a release film. When the pressure-sensitive adhesive is used, the thickness of the adhesive layer is usually 1 to 500 μm, preferably 2 to 300 μm. When the pressure-sensitive adhesive is used for forming a plurality of layers, the thickness of each layer and the type of the pressure-sensitive adhesive used may be the same or different.

[Shading pattern]
The light shielding pattern can be applied as at least part of a bezel or a housing of the flexible display device. The visibility of the image is improved by concealing the wiring arranged at the edge of the flexible display device by the light-shielding pattern and making it difficult to see. The light shielding pattern may be a single layer or a multilayer. The color of the light-shielding pattern is not particularly limited, and can have various colors such as black, white, and metal color. The light shielding pattern can be formed of a pigment for embodying a color and a polymer such as an acrylic resin, an ester resin, an epoxy resin, polyurethane, or 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. It is also preferable to give a shape such as an inclination in the thickness direction of the light shielding pattern.

  Hereinafter, the present invention will be described in more detail with reference to examples. Unless otherwise specified, “%” and “parts” in the examples mean mass% and parts by mass. First, the evaluation method will be described.

<1. Manufacture of polyimide varnish and film formation of polyimide film>
Example 1
(1) Preparation of polyimide solution In a nitrogen atmosphere, 0.5 part by mass of isoquinoline as a catalyst (tertiary amine) was charged into a reaction vessel. The reaction vessel was connected to a vacuum pump equipped with a solvent trap and a filter, and was installed 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 added to the reaction vessel. The contents in the reaction vessel were stirred and completely dissolved. Furthermore, after putting 145.59 parts by mass of 4,4 ′-(hexafluoroisopropylidene) diphthalic dianhydride (6FDA) as tetracarboxylic dianhydride into the reaction vessel, the contents in the reaction vessel were stirred. Meanwhile, the temperature started to rise in the oil bath. The molar ratio of TFMB to 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 with respect to 100 parts by mass of the raw material monomer was 0.2 parts by mass. When the internal temperature in the reaction vessel reached 120 ° C, the pressure in the reaction vessel was reduced to 400 mmHg, and then the internal temperature was raised to 180 ° C. After the internal temperature reached 180 ° C., the mixture was further heated and stirred for 5.5 hours and then returned to atmospheric pressure and cooled to 170 ° C. to obtain a polyimide solution. When the oxygen concentration in the reaction vessel was confirmed before and after decompression, it was less than 0.01%. GBL was added at 170 degreeC, and the polyimide solution was obtained as a uniform solution whose solid content of a polyimide is 40 mass%.

(2) Manufacture of varnish N, N-dimethylacetamide (DMAc) as a diluting solvent (solvent B) was bubbled with nitrogen gas for 30 minutes. To the polyimide solution obtained in (1) above, DMAc subjected to bubbling treatment was added at 155 ° C. to obtain a uniform solution having a polyimide solid content of 20% by mass, and 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 in an environment of temperature 25 ° C. and humidity 50%. The integral ratio A / B of the polyimide in the varnish after storage was 0.00052, and the polystyrene equivalent molecular weight was 360,000.

(4) Polyimide film formation 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, which was then PET (polyethylene terephthalate). After flowing 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 from PET and further heated at 200 ° C. for 40 minutes to obtain a polyimide film. The resulting polyimide film had a thickness of 80 μm.

(Example 2)
(1) Preparation of Varnish Example 1 except that the diluted solvent subjected to the bubbling treatment was changed from DMAc to cyclopentanone (CP), and the temperature of the diluted solvent subjected to the bubbling treatment was changed from 155 ° C to 130 ° C. A varnish was obtained in the same manner as in the method for producing a varnish. CP subjected to bubbling treatment was obtained by bubbling 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 (3). The integral ratio A / B of the polyimide in the varnish after storage was 0.00035, and the molecular weight in terms of polystyrene was 300,000.

(3) Film formation of polyimide film The varnish prepared in Example 1 (3) was changed to the varnish prepared in Example 2 (2), and DMAc subjected to the bubbling treatment prepared in Example 1 (2) was performed. A polyimide film was obtained in the same manner as in the production method of Example 1, except that the CP was subjected to the bubbling treatment prepared in Example 2 (1). The resulting polyimide film had a thickness of 80 μm.

(Comparative Example 1)
(1) Preparation of varnish Production of varnish of Example 1 except that the dilution solvent was changed from DMAc subjected to bubbling treatment to CP without bubbling treatment, and the temperature of the dilution solvent was changed from 155 ° C to 130 ° C. A varnish was obtained in the same manner as described above.

(2) Storage of polyimide varnish Example except that 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 as in 1 (3). The integral ratio A / B of the polyimide in the varnish after storage was 0.00006, and the polystyrene equivalent molecular weight was 320,000.

(3) Polyimide film formation The varnish prepared in Example 1 (3) was changed to the varnish prepared in Comparative Example 1 (2), and the DMAc subjected to the bubbling treatment prepared in Example 1 (2) was compared. A polyimide film was obtained in the same manner as in the production method of Example 1, except that the CP prepared in Example 1 (1) was not subjected to the bubbling treatment. The resulting polyimide film had a thickness of 80 μm.

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

(2) Storage of polyimide varnish Example except that 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 as in 1 (3). The integral ratio A / B of the polyimide in the varnish after storage was 0.0062, and the molecular weight in terms of polystyrene was 190,000.

(3) Polyimide film formation The DMAc prepared in Example 1 (2) was compared with the DMAc prepared by changing the varnish prepared in Example 1 (3) to the varnish prepared in Comparative Example 2 (2). A polyimide film was obtained in the same manner as in the production method of Example 1, except that the GBL prepared in Example 1 (1) was not subjected to the bubbling treatment. The resulting polyimide film had a thickness of 80 μm.

<2. Measurement method and calculation method>

(1) Measurement of integral value The integral value of the polyimide resin used by the Example and the comparative example was measured by NMR, and was obtained from the signal derived from the partial structure represented by Formula (40) and Formula (41). The method for calculating the integration ratio from the measurement conditions and the obtained results is as follows. In addition, Formula (40) and (41) are some structural units derived from TFMB which comprises a polyimide. * In the formula (40) represents a bond bonded to the nitrogen atom of one adjacent imide bond, and the bond bonded to the carbon atom of the adjacent benzene ring. * In the 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.

(Measurement sample preparation method)
A polyimide resin obtained by adding a large excess amount of methanol as a poor solvent to the varnish after storage prepared in Examples and Comparative Examples and precipitating and drying by reprecipitation method is obtained as deuterated dimethyl sulfoxide (DMSO-d6). The sample dissolved in was used as a measurement sample. The measurement sample can also be prepared from an optical film. Specifically, a method of directly dissolving an optical film in a deuterated solvent, a method of dissolving an optical film in a soluble solvent, and mixing the resulting solution with a deuterated solvent are included. If it is difficult to dissolve, it may be dissolved by sonication or heating.

(NMR measurement conditions)
Measuring apparatus: NMR apparatus (“AVANCE600” manufactured by Bruker)
Detector: “TCI Cryo Probe” manufactured by Bruker
Sample temperature: 303K
Sample concentration: 15 mg / 0.75 mL
Solvent type: DMSO-d6
Pulse sequence: Burker standard pulse sequence zg is used. Number of integrations: 256. Wait time: 10 seconds.

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

(2) Measurement of molecular weight in terms of polystyrene Gel permeation chromatography (GPC) measurement (2-1) Pretreatment method The varnish after storage prepared in Examples and Comparative Examples was dissolved in γ-butyrolactone (GBL) to form a 20% solution. Then, the solution was diluted 100-fold with DMF eluent and filtered through a 0.45 μm membrane filter to obtain a measurement solution. The measurement sample can also be prepared from an optical film. Specifically, measurement is performed by dissolving the optical film in a mixed solution of DMF and GBL. If there is a peak such as an additive, it may be ignored and analyzed, or the mixture may be removed by an appropriate method before GPC measurement.
(2-2) Measurement condition column: TSKgel SuperAWM-H × 2 + SuperAW2500 × 1 (6.0 mm ID × 150 mm × 3)
Eluent: DMF (10 mmol of lithium bromide added)
Flow rate: 0.6 mL / min Detector: RI detector Column temperature: 40 ° C
Injection volume: 20 μL
Molecular weight standard: Standard polystyrene

(3) Thickness measurement The thickness of the polyimide film was measured using a Digimatic Thickness Gauge ("Part No. 547-401" manufactured by Mitutoyo Corporation).

<3. Evaluation method>
(1) Transparency evaluation method: Calculation method of yellowness (YI value) of film The yellowness (Yellow Index: YI value) of each of the transparent polyimide polymer films obtained in Examples and Comparative Examples is measured in ultraviolet. It measured using the visible near-infrared spectrophotometer ("V-670" by JASCO Corporation). After performing background measurement in the absence of a sample, a polyimide film was set on a sample holder, transmittance was measured for light having a wavelength of 300 to 800 nm, and tristimulus values (X, Y, Z) were obtained. . 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) Folding resistance evaluation method: MIT folding frequency measurement method The folding resistance of the transparent polyimide polymer films obtained in Examples and Comparative Examples was evaluated according to the following criteria. The film was cut into a 10 mm × 100 mm strip using a dumbbell cutter. The cut film was set in a MIT-DA MIT folding fatigue tester manufactured by Toyo Seiki Seisakusho Co., Ltd. under the conditions of a test speed of 175 cpm, a bending angle of 135 °, a load of 750 g, and a bending clamp of R = 1.0 mm. The film was alternately folded in both directions, and the number of times until the film was broken was measured. The greater the number of bendings, the better the folding resistance.

(3) Transparency evaluation method: Method for measuring total light transmittance (Tt) The total light transmittance (Tt: unit%) of the transparent polyimide polymer films obtained in the examples and comparative examples was measured according to JIS K 7105. : Measured with a fully automatic direct reading haze computer HGM-2DP manufactured by Suga Test Instruments Co., Ltd. according to 1981. It shows that it is excellent in transparency, so that the total light transmittance is large.

The optical films of Examples 1 and 2 contained a transparent polyimide polymer. 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 MIT folding times of the optical films of Examples 1 and 2 were 85,000 times and 78,000 times, respectively.

The optical films of Comparative Examples 1 and 2 contained a transparent polyimide polymer. The integral ratio A / B of the transparent polyimide polymer contained in the optical films of Comparative Examples 1 and 2 was not included in the range of 0.0001 to 0.001.
The YI values of the optical films of Comparative Examples 1 and 2 were 3.8 and 1.9, respectively. In addition, the MIT folding times of the optical films of Comparative Examples 1 and 2 were 80,000 times and 8,000 times, respectively.

  From the above, it is clear that the optical films of Examples 1 and 2 are smaller in yellow coloration than the optical films of Comparative Examples 1 and 2, and have high transparency and high folding resistance.

Claims (11)

An optical film containing a transparent polyimide polymer,
Ratio of integrated value A of ¹ H-NMR signal derived from terminal amino group of transparent polyimide polymer to integrated value B of ¹ H-NMR signal derived from imide group in the chain of transparent polyimide polymer (Integral ratio A / B) is 0.0001 or more and 0.001 or less.   The optical film according to claim 1, wherein the transparent polyimide polymer has a polystyrene-equivalent molecular weight of 250,000 to 500,000.   3. The optical film according to claim 1, wherein the optical film has a thickness of 30 μm to 100 μm and a total light transmittance of 85% or more.   The optical film according to claim 1, wherein the transparent polyimide polymer has a fluorine group.   The optical film according to any one of claims 1 to 4, wherein the transparent polyimide polymer comprises a repeating unit derived from a 2,2'-bis (trifluoromethyl) benzidine derivative. A method for producing an optical film comprising a step of casting a varnish containing a transparent polyimide polymer, wherein the integrated value B of the ¹ H-NMR signal is derived from an imide group in the chain of the transparent polyimide polymer. The method for producing an optical film, wherein the ratio of the integral value A (integral ratio A / B) of the ¹ H-NMR signal derived from the terminal amino group of the transparent polyimide polymer is 0.0001 or more and 0.001 or less.   The method for producing an optical film according to claim 6, wherein the varnish contains an ester solvent.   The optical film according to claim 1, which is a film for a front plate of a flexible display device.   A flexible display device comprising the optical film according to claim 8.   The flexible display device according to claim 9, further comprising a touch sensor.   The flexible display device according to claim 9, further comprising a polarizing plate.