CN110967780B

CN110967780B - Optical film

Info

Publication number: CN110967780B
Application number: CN201910912901.0A
Authority: CN
Inventors: 大松一喜; 福井仁之; 唐泽真义
Original assignee: Sumitomo Chemical Co Ltd
Current assignee: Sumitomo Chemical Co Ltd
Priority date: 2018-09-28
Filing date: 2019-09-25
Publication date: 2023-05-26
Anticipated expiration: 2039-09-25
Also published as: TW202022020A; JP2020111750A; CN110967780A; KR20200037057A; JP6670967B1; KR102108371B1; KR20200051542A; JP2020056990A

Abstract

The invention aims to provide an optical film with excellent visibility in the wide-angle direction. The solution of the present invention is an optical film comprising at least 1 resin selected from the group consisting of polyimide-based resins and polyamide-based resins, the optical film satisfying formula (1). In the formula (1), ts represents a scattered light ratio (%), which is defined as ts=td/tt×100, and Td and Tt represent a diffuse light transmittance (%) and a total light transmittance (%) measured in accordance with JIS K-7136, respectively. Ts is more than or equal to 0 and less than or equal to 0.35 (1).

Description

Optical film

Technical Field

The present invention relates to an optical film that can be used as a front panel of a flexible display device or the like, and a flexible display device provided with the optical film.

Background

Conventionally, glass has been used as a material for display members such as solar cells and image display devices. However, these materials are not sufficiently made for the recent demands for downsizing, thinning, weight saving and flexibility. Therefore, as a substitute material for glass, various films have been studied. As such a film, for example, an optical film containing a polyimide resin is known (for example, patent document 1).

Prior art literature

Patent literature

Patent document 1: japanese patent laid-open No. 2009-215412

Disclosure of Invention

Problems to be solved by the invention

When the optical film is applied to a transparent member such as a front panel of a flexible display device, an image may be displayed in a state in which an image display surface is curved, and therefore excellent visibility in a wide-angle direction is required as compared with a non-curved image display surface. However, as a result of the studies by the present inventors, it has been found that the conventional optical film comprising a polyimide resin may not sufficiently satisfy the visibility in the wide-angle direction.

Accordingly, an object of the present invention is to provide an optical film excellent in visibility in a wide-angle direction and a flexible display device including the optical film.

Means for solving the problems

The present inventors have made intensive studies to solve the above problems, and as a result, have found that the above problems can be solved when the proportion of scattered light is within a predetermined range in an optical film containing at least 1 resin selected from the group consisting of polyimide-based resins and polyamide-based resins, and have completed the present invention. That is, the present invention includes the following means.

[1] An optical film comprising at least 1 resin selected from the group consisting of polyimide-based resins and polyamide-based resins, the optical film satisfying formula (1):

0≤Ts≤0.35 (1)

In the formula (1), ts represents a scattered light ratio (%), and is defined as ts=td/tt×100, and Td and Tt represent a diffuse light transmittance (%) and a total light transmittance (%) ] measured in accordance with JIS K7136, respectively.

[2] The optical film according to [1], wherein the optical film has a tensile elastic modulus at 80℃of 4,000 to 9,000MPa.

[3] The optical film according to [1] or [2], wherein an absolute value ΔTs of a difference between the ratios of the scattered light before and after the bending resistance test according to JIS K5600-5-1 is 0.15% or less.

[4] The optical film according to any one of [1] to [3], wherein the thickness of the optical film is 10 to 150. Mu.m.

[5] The optical film according to any one of [1] to [4], wherein the content of the filler is 5 mass% or less with respect to the mass of the optical film.

[6] The optical film according to any one of [1] to [5], which has a hard coat layer on at least one side.

[7] The optical film according to [6], wherein the thickness of the hard coat layer is 3 to 30. Mu.m.

[8] A flexible display device comprising the optical film of any one of [1] to [7 ].

[9] The flexible display device according to [8], further comprising a touch sensor.

[10] The flexible display device according to [8] or [9], which further comprises a polarizing plate.

ADVANTAGEOUS EFFECTS OF INVENTION

The optical film of the present invention is excellent in visibility in the wide-angle direction.

Detailed Description

[ optical film ]

The optical film of the present invention comprises at least 1 resin selected from the group consisting of a transparent polyimide-based resin and a polyamide-based resin, and satisfies the formula (1):

0≤Ts≤0.35 (1)

The scattered light ratio may be a scattered light ratio within a range of the thickness of an optical film described later.

As shown in the formula (1), the scattered light ratio (Ts) represents the ratio of the diffuse light transmittance (Td) to the total light transmittance (Tt), and the smaller the Ts is, the smaller the proportion of the diffuse light is, and the less likely the light is scattered on the surface and inside of the optical film.

The optical film of the present invention has a small proportion of scattered light (0 to 0.35%), and therefore has excellent visibility in the wide-angle direction. Therefore, when the optical film of the present invention is applied to an image display device, even when the optical film is observed from an oblique direction, the occurrence of distortion or blurring of an image projected on the display portion can be effectively suppressed. The optical film of the present invention has such characteristics, and therefore, even when applied to, for example, a flexible display, it can be viewed with high visibility, even if an image is displayed in a state in which the image display surface is curved. In the present specification, visibility means visibility when a display unit of an image display device to which an optical film is applied is visually observed, and for example, means a characteristic capable of suppressing distortion in an image projected by the display unit or a phenomenon in which the image is blurred. In the present specification, the wide-angle direction means all angular directions with respect to the plane of the optical film, and in particular, means an oblique direction with respect to the plane of the optical film.

In the formula (1), the diffuse light transmittance (Td) can be measured in accordance with JIS K7136 using a spectrocolorimeter, and can be measured, for example, by the method described in examples. The total light transmittance (Tt) may be measured in accordance with JIS K7136 using a haze meter, for example, by the method described in examples.

In the optical film of the present invention, the proportion of scattered light is preferably 0.30% or less, more preferably 0.25% or less, still more preferably 0.20% or less, particularly preferably 0.15% or less, and most preferably 0.10% or less. When the proportion of scattered light is equal to or less than the upper limit, visibility in the wide-angle direction is easily improved. The lower limit of the proportion of scattered light is 0 or more. The composition of the optical film, for example, the type and composition ratio of the repeating structure of the resin included in the optical film, the type and content of the additive such as the ultraviolet absorber included in the optical film, and the like are used; the thickness of the optical film; or the production conditions of the optical film, for example, the kind of varnish solvent, the drying temperature, the drying time, and the like, are appropriately adjusted so that the formula (1) can be satisfied. In particular, in the optical film forming step, when the step is performed under the drying condition described later, the step is easily adjusted so as to satisfy the formula (1).

In the optical film of the present invention, the total light transmittance (Tt) is preferably 80% or more, more preferably 85% or more, still more preferably 88% or more, and particularly preferably 90% or more. When the total light transmittance is not less than the lower limit, the optical film becomes excellent in transparency, and when applied to an image display device, excellent visibility is easily exhibited. The upper limit of the total light transmittance is usually 100% or less. The total light transmittance may be a total light transmittance (Tt) within a range of the thickness of the optical film described later. If the total light transmittance is within the above range, for example, when the backlight is mounted in a display device, a bright display tends to be obtained even if the light amount of the backlight is reduced, and energy saving can be contributed.

In the optical film of the present invention, the diffuse light transmittance (Td) is preferably 0.35 or less, more preferably 0.30 or less, further preferably 0.25 or less, and particularly preferably 0.20 or less. When the diffuse light transmittance (Td) is equal to or less than the upper limit, the proportion of diffuse light is small, and visibility in the wide-angle direction is easily improved. The lower limit of the diffuse light transmittance (Td) is usually 0.01 or more. The diffuse light transmittance may be a diffuse light transmittance (Td) within a range of the thickness of the optical film described later.

In a preferred embodiment of the present invention, the optical film of the present invention has excellent tensile elastic modulus in addition to excellent visibility in the wide-angle direction. The tensile elastic modulus of the optical film at 80℃is preferably 4,000MPa or more, more preferably 4,500MPa or more, particularly preferably 5,000MPa or more, preferably 9,000MPa or less, more preferably 8,500MPa or less. When the tensile elastic modulus is within the above range, there are the following tendencies: pit defects in the optical film become less likely to occur, and bending resistance becomes more likely to be exhibited. The tensile elastic modulus of the optical film can be measured according to JIS K7127 using a tensile tester, and can be measured, for example, by the method described in examples.

In a preferred embodiment of the present invention, the optical film of the present invention is excellent in folding endurance. The number of times of folding in the MIT folding endurance test according to ASTM standard D2176-16 is preferably 200,000 times or more, more preferably 300,000 times or more, still more preferably 500,000 times or more, particularly preferably 700,000 times or more, for the optical film of the present invention. When the number of times of folding is equal to or more than the lower limit, cracking, breakage, etc. are not easily generated even when folding is performed. The MIT folding endurance test can be measured by the method described in examples, for example.

In a preferred embodiment of the present invention, the optical film of the present invention is excellent in bending resistance. Therefore, even if repeatedly bent, the optical characteristics can be maintained. In the optical film of the present invention, the absolute value Δts (%) of the difference between the scattered light ratios before and after the bending resistance test according to JIS K5600-5-1 is preferably 1.4% or less, more preferably 1.2% or less, further preferably 1.0% or less, further preferably 0.5% or less, particularly preferably 0.1% or less, even more preferably 0.05% or less, and most preferably 0.02% or less. When Δts is within the above range, when applied to an image display device such as a flexible display, excellent visibility in the wide-angle direction is easily maintained even if the device is repeatedly bent. The bending resistance test can be carried out by a bending tester according to JIS K5600-5-1, and can be carried out by the method described in examples. In the present specification, the optical characteristics refer to characteristics that can be optically evaluated, including, for example, a ratio of scattered light, a diffuse light transmittance, a total light transmittance, a Yellowness (YI), and a haze, and the "optical characteristic improvement" refers to, for example: the diffuse light ratio becomes lower, the diffuse light transmittance becomes lower, the total light transmittance becomes higher, the yellowness becomes lower, or the haze becomes lower; etc.

In one embodiment of the present invention, the haze of the optical film of the present invention is preferably 1.0% or less, more preferably 0.5% or less, further preferably 0.4% or less, particularly preferably 0.3% or less, and most preferably 0.2% or less. When the haze of the optical film is equal to or less than the upper limit, the transparency becomes good, and for example, when the optical film is applied to an image display device, the optical film tends to exhibit excellent visibility. The lower limit of haze is usually 0.01% or more. The haze may be in accordance with JIS K7136: 2000, haze computer measurements were used.

The Yellowness (YI) of the optical film of the present invention is preferably 4.0 or less, more preferably 3.0 or less, further preferably 2.5 or less, and particularly preferably 2.0 or less. When the yellowness of the optical film is equal to or less than the upper limit, the transparency becomes good, and for example, when the optical film is applied to an image display device, excellent visibility is easily exhibited. The yellowness is usually-5 or more, preferably-2 or more. For the Yellowness (YI), the color may be defined in accordance with JIS K7373: 2006, the tristimulus value (X, Y, Z) is obtained by measuring the transmittance with respect to light of 300 to 800nm using an ultraviolet-visible near-infrared spectrophotometer, and calculated based on the formula yi=100× (1.2769X-1.0592Z)/Y.

The thickness of the optical film of the present invention can be appropriately adjusted depending on the application, and is preferably 10 μm or more, more preferably 20 μm or more, further preferably 25 μm or more, particularly preferably 30 μm or more, preferably 150 μm or less, further preferably 100 μm or less, further preferably 85 μm or less. When the thickness of the optical film is in the above range, it is advantageous from the viewpoints of bending resistance and visibility. The thickness of the optical film can be measured by a film thickness meter or the like, and can be measured by the method described in examples, for example.

< resin >)

The optical film of the present invention comprises at least 1 resin selected from the group consisting of polyimide-based resins and polyamide-based resins. The polyimide-based resin means at least 1 resin selected from the group consisting of a resin containing a repeating structural unit including an imide group (hereinafter, sometimes referred to as a polyimide resin) and a resin containing a repeating structural unit including both an imide group and an amide group (hereinafter, sometimes referred to as a polyamideimide resin). The polyamide resin means a resin containing a repeating structural unit including an amide group.

The polyimide resin preferably has a repeating structural unit represented by the formula (10). Here, G is a 4-valent organic group, and a is a 2-valent organic group. The polyimide resin may contain 2 or more kinds of repeating structural units represented by the formula (10) different in G and/or a.

[ chemical formula 1]

The polyimide resin may contain 1 or more kinds of repeating structural units selected from the group consisting of the repeating structural units represented by the formulas (11), (12) and (13) within a range that does not impair various physical properties of the optical film.

[ chemical formula 2]

In the formula (10) and the formula (11), G and G ¹ Each independently is a 4-valent organic group, preferably an organic group that may be substituted with a hydrocarbon group or a hydrocarbon group substituted with fluorine. As G and G ¹ Examples of the "chain hydrocarbon" may include a group represented by formula (20), formula (21), formula (22), formula (23), formula (24), formula (25), formula (26), formula (27), formula (28) or formula (29) and a 4-valent hydrocarbon group having 6 or less carbon atoms. Among them, the group represented by formula (20), formula (21), formula (22), formula (23), formula (24), formula (25), formula (26) or formula (27) is preferable in terms of easy suppression of yellowness (YI value) of the optical film.

[ chemical formula 3]

In the formulas (20) to (29),

the term "a" means a chemical bond,

z represents a single bond, -O-, -CH ₂ -、-CH ₂ -CH ₂ -、-CH(CH ₃ )-、-C(CH ₃ ) ₂ -、-C(CF ₃ ) ₂ -、-Ar-、-SO ₂ -、-CO-、-O-Ar-O-、-Ar-O-Ar-、-Ar-CH ₂ -Ar-、-Ar-C(CH ₃ ) ₂ -Ar-or-Ar-SO ₂ Ar-. Ar represents an arylene group having 6 to 20 carbon atoms which may be substituted with a fluorine atom, and a specific example thereof is phenylene.

In the formula (12), G ² Organic groups of 3 valency are preferred, and organic groups which may be substituted with hydrocarbyl groups or with fluorine-substituted hydrocarbyl groups. As G ² Examples of the "chain hydrocarbon" may include a group in which 1 of the chemical bonds of the group represented by the formula (20), the formula (21), the formula (22), the formula (23), the formula (24), the formula (25), the formula (26), the formula (27), the formula (28) or the formula (29) is replaced with a hydrogen atom, and a 3-valent chain hydrocarbon group having 6 or less carbon atoms.

In the formula (13), G ³ The organic group having a valence of 2 is preferably an organic group which may be substituted with a hydrocarbon group or a hydrocarbon group substituted with fluorine. As G ³ Examples of the "compound" may include the formula (20), the formula (21), the formula (22), the formula (23), the formula (24), the formula (25) and the formula (26)) A chain hydrocarbon group having 6 or less carbon atoms, wherein 2 non-adjacent groups in the chemical bonds of the groups represented by the formulas (27), (28) and (29) are replaced with hydrogen atoms.

A, A in the formulae (10) to (13) ¹ 、A ² A is a ³ Each independently is a 2-valent organic group, preferably an organic group that may be substituted with a hydrocarbon group or a hydrocarbon group substituted with fluorine. As A, A ¹ 、A ² A is a ³ Examples of the "group" may include a group represented by formula (30), formula (31), formula (32), formula (33), formula (34), formula (35), formula (36), formula (37) or formula (38); groups obtained by substituting methyl, fluoro, chloro or trifluoromethyl; and a chain hydrocarbon group having 6 or less carbon atoms.

[ chemical formula 4]

In the formulas (30) to (38),

The term "a" means a chemical bond,

Z ¹ 、Z ² z is as follows ³ Each independently represents a single bond, -O-, -CH ₂ -、-CH ₂ -CH ₂ -、-CH(CH ₃ )-、-C(CH ₃ ) ₂ -、-C(CF ₃ ) ₂ -、-SO ₂ -or-CO-.

As 1 example, Z ¹ Z is as follows ³ is-O-, and Z ² is-CH ₂ -、-C(CH ₃ ) ₂ -、-C(CF ₃ ) ₂ -or-SO ₂ -。Z ¹ And Z ² Bonding position with respect to each ring, Z ² And Z ³ The bonding position with respect to each ring is preferably meta or para with respect to each ring.

From the viewpoint of improving visibility, the polyimide-based resin is preferably a polyamide-imide resin having at least a repeating structural unit represented by formula (10) and a repeating structural unit represented by formula (13). The polyamide resin preferably has at least a repeating structural unit represented by the formula (13).

In one embodiment of the present invention, the polyimide resin is a condensed polymer obtained by reacting (polycondensing) a diamine and a tetracarboxylic acid compound (a tetracarboxylic acid compound analogue such as an acid chloride compound or a tetracarboxylic acid dianhydride), and if necessary, a dicarboxylic acid compound (a dicarboxylic acid compound analogue such as an acid chloride compound) or a tricarboxylic acid compound (a tricarboxylic acid compound analogue such as an acid chloride compound or a tricarboxylic acid anhydride). The repeating structural unit represented by the formula (10) or (11) is generally derived from a diamine and a tetracarboxylic acid compound. The repeating structural unit represented by the formula (12) is generally derived from a diamine and tricarboxylic acid compound. The repeating structural unit represented by the formula (13) is generally derived from a diamine and a dicarboxylic acid compound.

In one embodiment of the present invention, the polyamide resin is a condensed polymer obtained by reacting (polycondensing) a diamine and a dicarboxylic acid compound. That is, the repeating structural unit represented by the formula (13) is generally derived from a diamine and a dicarboxylic acid compound.

Examples of the tetracarboxylic acid compound include aromatic tetracarboxylic acid compounds such as aromatic tetracarboxylic dianhydride; and aliphatic tetracarboxylic acid compounds such as aliphatic tetracarboxylic acid dianhydride. The tetracarboxylic acid compound may be used alone or in combination of 2 or more. The tetracarboxylic acid compound may be a tetracarboxylic acid compound analogue such as an acid chloride compound, in addition to the dianhydride.

Specific examples of the aromatic tetracarboxylic dianhydride include 4,4'-oxydiphthalic dianhydride (4, 4' -oxydiphthalic dianhydride), 3', 4' -benzophenone tetracarboxylic dianhydride, 2',3,3' -benzophenone tetracarboxylic dianhydride, 3', 4' -biphenyl tetracarboxylic dianhydride, 2', 3' -biphenyl tetracarboxylic dianhydride, 3',4,4' -diphenylsulfone tetracarboxylic dianhydride, 2-bis (3, 4-dicarboxyphenyl) propane dianhydride, 2-bis (2, 3-dicarboxyphenyl) propane dianhydride, 2-bis (3, 4-dicarboxyphenoxyphenyl) propane dianhydride, 4'- (hexafluoroisopropylidene) diphthalic dianhydride (4, 4' - (hexafluorooisopropylene) diphthalic dianhydride,6 FDA), 1, 2-bis (2, 3-dicarboxyphenyl) ethane dianhydride, 1-bis (2, 3-dicarboxyphenyl) ethane dianhydride, 1, 2-bis (3, 4-dicarboxyphenyl) ethane dianhydride, 1-bis (3, 4-dicarboxyphenyl) ethane dianhydride, bis (3, 4-dicarboxyphenyl) methane dianhydride, bis (2, 3-dicarboxyphenyl) methane dianhydride, and 4,4'- (p-phenylene) diphthalic dianhydride, and 4,4' - (m-phenylene) diphthalic dianhydride. They may be used alone or in combination of 2 or more.

Examples of the aliphatic tetracarboxylic dianhydride include cyclic or acyclic aliphatic tetracarboxylic dianhydrides. The cyclic aliphatic tetracarboxylic dianhydride means a tetracarboxylic dianhydride having an alicyclic hydrocarbon structure, and specific examples thereof include a cycloalkane tetracarboxylic dianhydride such as 1,2,4, 5-cyclohexane tetracarboxylic dianhydride, 1,2,3, 4-cyclobutane tetracarboxylic dianhydride, 1,2,3, 4-cyclopentane tetracarboxylic dianhydride, bicyclo [2.2.2] oct-7-ene-2, 3,5, 6-tetracarboxylic dianhydride, dicyclohexyl-3, 3', 4' -tetracarboxylic dianhydride, and positional isomers thereof. They may be used alone or in combination of 2 or more. Specific examples of the acyclic aliphatic tetracarboxylic dianhydride include 1,2,3, 4-butanetetracarboxylic dianhydride, 1,2,3, 4-pentanetetracarboxylic dianhydride, and the like, which may be used alone or in combination of 2 or more. In addition, cyclic aliphatic tetracarboxylic dianhydrides and acyclic aliphatic tetracarboxylic dianhydrides may be used in combination.

Among the above tetracarboxylic dianhydrides, 1,2,4, 5-cyclohexane tetracarboxylic dianhydride, bicyclo [2.2.2] oct-7-ene-2, 3,5, 6-tetracarboxylic dianhydride, 4' - (hexafluoroisopropylidene) diphthalic dianhydride, and mixtures thereof are preferred from the viewpoints of easy improvement of visibility, elastic modulus and bending resistance, and easy reduction of coloring. Further, as the tetracarboxylic acid, an aqueous adduct of an anhydride of the above-mentioned tetracarboxylic acid compound can be used.

Examples of the tricarboxylic acid compound include aromatic tricarboxylic acid, aliphatic tricarboxylic acid, and similar acid chloride compounds and acid anhydrides thereof, and 2 or more kinds thereof may be used in combination. Specific examples thereof include anhydrides of 1,2, 4-benzenetricarboxylic acid; 2,3, 6-naphthalene tricarboxylic acid-2, 3-anhydride; phthalic anhydride and benzoic acid via single bond, -CH ₂ -、-C(CH ₃ ) ₂ -、-C(CF ₃ ) ₂ -、-SO ₂ -or phenylene linked compounds.

Examples of the dicarboxylic acid compound include aromatic dicarboxylic acids, aliphatic dicarboxylic acids, and similar acid chloride compounds and acid anhydrides thereof, and 2 or more of them may be used in combination. Specific examples thereof include terephthaloyl dichloride (terephthaloyl chloride (TPC)); isophthaloyl dichloride; naphthalene dicarboxylic acid dichloride; 4,4' -biphenyldicarboxylic acid dichloride; 3,3' -biphenyl dicarboxylic acid dichloride; 4,4'-oxybis (benzoyl chloride) (OBBC, 4' -oxybis (benzoyl chloride)); dicarboxylic acid compound of chain hydrocarbon having 8 or less carbon atoms and 2 benzoic acids via single bond, -CH ₂ -、-C(CH ₃ ) ₂ -、-C(CF ₃ ) ₂ -、-SO ₂ -or phenylene linked compounds. When these dicarboxylic acid compounds are used, the visibility, elastic modulus and bending resistance are easily improved, and the colorability is easily reduced, which is preferable.

Examples of the diamine include aliphatic diamine, aromatic diamine, and a mixture thereof. In the present embodiment, the term "aromatic diamine" means a diamine in which an amino group is directly bonded to an aromatic ring, and a part of the structure thereof may include an aliphatic group or other substituent. The aromatic ring may be a single ring or a condensed ring, and examples thereof include a benzene ring, a naphthalene ring, an anthracene ring, and a fluorene ring, but are not limited thereto. Among these, the aromatic ring is preferably a benzene ring. The term "aliphatic diamine" means a diamine in which an amino group is directly bonded to an aliphatic group, and a part of the structure thereof may include an aromatic ring and other substituents.

Examples of the aliphatic diamine include acyclic aliphatic diamines such as 1, 6-hexamethylenediamine and cyclic aliphatic diamines such as 1, 3-bis (aminomethyl) cyclohexane, 1, 4-bis (aminomethyl) cyclohexane, norbornanediamine, 4' -diaminodicyclohexylmethane, and the like. They may be used alone or in combination of 2 or more.

Examples of the aromatic diamine include aromatic diamines having 1 aromatic ring such as p-phenylenediamine, m-phenylenediamine, 2, 4-toluenediamine, m-xylylenediamine, p-xylylenediamine, 1, 5-diaminonaphthalene, and 2, 6-diaminonaphthalene; 4,4 '-diaminodiphenylmethane, 4' -diaminodiphenylpropane, 4 '-diaminodiphenylether, 3,4' -diaminodiphenylether 3,3 '-diaminodiphenyl ether, 4' -diaminodiphenyl sulfone, 3,4 '-diaminodiphenyl sulfone 3,3' -diaminodiphenyl sulfone, 1, 4-bis (4-aminophenoxy) benzene, 1, 3-bis (4-aminophenoxy) benzene, 4 '-diaminodiphenyl sulfone, bis [4- (4-aminophenoxy) phenyl ] sulfone, bis [4- (3-aminophenoxy) phenyl ] sulfone, a 2, 2-bis [4- (4-aminophenoxy) phenyl ] propane, 2-bis [4- (3-aminophenoxy) phenyl ] propane, 2' -dimethylbenzidine, 2 '-bis (trifluoromethyl) benzidine (2, 2' -bis (trifluoromethyl) -4,4 '-diaminobiphenyl (TFMB)); aromatic diamines having 2 or more aromatic rings, such as 4,4' -bis (4-aminophenoxy) biphenyl, 9-bis (4-aminophenyl) fluorene, 9-bis (4-amino-3-methylphenyl) fluorene, 9-bis (4-amino-3-chlorophenyl) fluorene, and 9, 9-bis (4-amino-3-fluorophenyl) fluorene. They may be used alone or in combination of 2 or more.

Among the diamines, 1 or more selected from the group consisting of aromatic diamines having a biphenyl structure is preferably used from the viewpoints of easy improvement of visibility, elastic modulus and bending resistance, and easy reduction of coloring. More preferably, 1 or more selected from the group consisting of 2,2' -dimethylbenzidine, 2' -bis (trifluoromethyl) benzidine, 4' -bis (4-aminophenoxy) biphenyl and 4,4' -diaminodiphenyl ether is used, and still more preferably, 2' -bis (trifluoromethyl) benzidine is used.

The polyimide-based resin can be obtained by: the above-mentioned raw materials such as diamine, tetracarboxylic acid compound, tricarboxylic acid compound, dicarboxylic acid compound and the like are mixed by a conventional method such as stirring, and then the obtained intermediate is imidized in the presence of an imidization catalyst and, if necessary, a dehydrating agent. The polyamide resin can be obtained by mixing the above-mentioned respective raw materials such as diamine and dicarboxylic acid compound by a conventional method, for example, stirring.

The imidization catalyst used in the imidization step is not particularly limited, and examples thereof include tripropylamine, dibutylpropylamine, and ethyl Aliphatic amines such as dibutylamine; n-ethylpiperidine, N-propylpiperidine, N-butylpyrrolidine, N-butylpiperidine, and N-propylhexahydroazepine

Iso-alicyclic amines (monocyclic); azabicyclo [2.2.1]Heptane, azabicyclo [3.2.1]Octane, azabicyclo [2.2.2]Octane and azabicyclo [3.2.2]Alicyclic amines (polycyclic) such as nonane; and aromatic amines such as 2-methylpyridine, 3-methylpyridine, 4-methylpyridine, 2-ethylpyridine, 3-ethylpyridine, 4-ethylpyridine, 2, 4-lutidine, 2,4, 6-trimethylpyridine, 3, 4-cyclopentenopyridine, 5,6,7, 8-tetrahydroisoquinoline, and isoquinoline.

The dehydrating agent used in the imidization step is not particularly limited, and examples thereof include acetic anhydride, propionic anhydride, isobutyric anhydride, pivalic anhydride, butyric anhydride, and isovaleric anhydride.

In the mixing and imidization steps of the raw materials, the reaction temperature is not particularly limited, and is, for example, 15 to 350 ℃, preferably 20 to 100 ℃. The reaction time is also not particularly limited, and is, for example, about 10 minutes to 10 hours. The reaction may be carried out under an inert atmosphere or under reduced pressure, as required. The reaction may be carried out in a solvent, and examples of the solvent include solvents that can be used for the preparation of a varnish. After the reaction, the polyimide-based resin or the polyamide-based resin is purified. Examples of the purification method include the following methods: the poor solvent is added to the reaction solution, the resin is precipitated by reprecipitation, and the precipitate is taken out after drying, and if necessary, the precipitate is washed with a solvent such as methanol and dried. The polyimide resin can be produced by, for example, the production method described in Japanese patent application laid-open No. 2006-199945 or Japanese patent application laid-open No. 2008-163107. As the polyimide resin, commercially available ones can be used, and specific examples thereof include Neopulim (registered trademark) manufactured by Mitsubishi gas chemical corporation, KPI-MX300F manufactured by Hecun industries, ltd.

In one embodiment of the present invention, the content of the structural unit represented by the formula (13) in the polyamideimide resin is preferably 0.1 mol or more, more preferably 0.5 mol or more, still more preferably 1.0 mol or more, particularly preferably 1.5 mol or more, preferably 6.0 mol or less, more preferably 5.0 mol or less, and still more preferably 4.5 mol or less, based on 1 mol of the structural unit represented by the formula (10). When the content of the structural unit represented by the formula (13) is within the above range, visibility in the wide-angle direction, elastic modulus, and bending resistance are easily improved.

The weight average molecular weight of the polyimide-based resin or the polyamide-based resin is preferably 200,000 or more, more preferably 250,000 or more, further preferably 300,000 or more, preferably 600,000 or less, more preferably 550,000 or less, further preferably 500,000. When the weight average molecular weight of the polyimide-based resin or the polyamide-based resin is not less than the lower limit, the elastic modulus and the bending resistance of the optical film can be easily improved. When the weight average molecular weight is not more than the upper limit, the viscosity of the varnish is easily reduced, and the stretchability and processability of the optical film are easily improved. The weight average molecular weight can be obtained by performing Gel Permeation Chromatography (GPC) measurement and converting it into standard polystyrene, and can be calculated by the method described in examples, for example.

In a preferred embodiment of the present invention, the polyimide-based resin or polyamide-based resin contained in the optical film of the present invention may contain a halogen atom such as a fluorine atom which can be introduced by using the fluorine-containing substituent or the like described above. When the polyimide-based resin or the polyamide-based resin contains a halogen atom, the elastic modulus of the optical film is easily increased, and the yellowness (YI value) is easily reduced. When the elastic modulus of the optical film is high, the occurrence of scratches, wrinkles, and the like in the film is easily suppressed, and when the yellowness of the optical film is low, the transparency and visibility of the film are easily improved. The halogen atom is preferably a fluorine atom. Examples of the fluorine-containing substituent that is preferable for containing a fluorine atom in the polyimide-based resin or the polyamide-based resin include a fluorine group and a trifluoromethyl group.

The content of the halogen atom in the polyimide-based resin or the polyamide-based resin is preferably 1 to 40% by mass, more preferably 5 to 40% by mass, and still more preferably 5 to 30% by mass, based on the mass of the polyimide-based resin or the polyamide-based resin. When the content of halogen atoms is not less than the lower limit, the elastic modulus of the optical film is easily further improved, the water absorption is reduced, the yellowness (YI value) is further reduced, and the transparency and visibility are further improved. When the content of halogen atoms is not more than the upper limit, the synthesis becomes easy.

The imidization ratio of the polyimide resin in the optical film is preferably 90% or more, more preferably 95% or more, and even more preferably 98% or more. The imidization ratio is preferably not less than the lower limit described above from the viewpoint of easiness in improving the flatness and visibility in the wide-angle direction of the optical film. The upper limit of the imidization ratio is 100% or less. The imidization rate may be obtained by IR method, NMR method, or the like, and may be obtained by the method described in examples, for example.

In one embodiment of the present invention, the content of the polyimide-based resin and/or the polyamide-based resin in the optical film is preferably 40 mass% or more, more preferably 50 mass% or more, further preferably 70 mass% or more, particularly preferably 80 mass% or more, and most preferably 90 mass% or more, based on the mass of the optical film. When the content of the polyimide-based resin and/or polyamide-based resin is not less than the lower limit, the polyimide-based resin and/or polyamide-based resin are advantageous from the viewpoints of visibility in the wide-angle direction, elastic modulus and bending resistance. The content of the polyimide resin and/or the polyamide resin in the optical film is usually 100 mass% or less with respect to the mass of the optical film.

As the resin contained in the optical film, 2 or more polyimide-based resins or 2 or more polyamide-based resins may be used, or a polyimide-based resin and a polyamide-based resin may be used in combination.

In order to obtain an optical film having a low proportion of scattered light, a varnish having a specific solid content concentration and viscosity is preferably applied to a substrate in a coating step described later to form a uniform coating film. In one embodiment of the present invention, it is preferable to use 2 or more polyimide-based resins or polyamide-based resins, for example, 2 or more polyimide-based resins, 2 or more polyamide-based resins, or a combination of 1 or more polyimide-based resins and 1 or more polyamide-based resins, and it is particularly preferable to use 2 or more polyimide-based resins or polyamide-based resins having mutually different weight average molecular weights. In the coating step described later, when such a resin is contained in the varnish, the solid content concentration and viscosity of the varnish can be easily adjusted to a specific range, and therefore a uniform coating film can be formed, and the obtained optical film can be easily adjusted to satisfy the formula (1).

In a preferred embodiment of the present invention, the polyimide-based resin or polyamide-based resin has at least 2 kinds of different weight average molecular weights, and the weight average molecular weight of at least 1 kind of polyimide-based resin or polyamide-based resin is 250,000 ～ 500,000, and the weight average molecular weight of at least 1 kind of polyimide-based resin or polyamide-based resin is 200,000 ～ 450,000. In a more preferred embodiment of the present invention, the polyimide-based resin or polyamide-based resin is 2 kinds of polyimide-based resins or polyamide-based resins having different weight average molecular weights, and the weight average molecular weight of one of the polyimide-based resins or polyamide-based resins is 250,000 ～ 500,000 and the weight average molecular weight of the other polyimide-based resin or polyamide-based resin is 200,000 ～ 450,000. In the coating step described later, when such a resin is contained in the varnish, the solid content concentration and viscosity of the varnish can be easily adjusted to a specific range, and therefore a uniform coating film can be formed, and the obtained optical film can be easily adjusted to satisfy the formula (1).

The mass ratio of one polyimide-based resin or polyamide-based resin to the other polyimide-based resin or polyamide-based resin (the former/the latter) may be appropriately selected depending on the kind of resin, the desired solid content concentration and viscosity of the varnish, and may be, for example, 5/95 to 95/5.

< additive >)

The optical film of the present invention may further comprise an ultraviolet absorber. Examples thereof include triazine-based ultraviolet absorbers, benzophenone-based ultraviolet absorbers, benzotriazole-based ultraviolet absorbers, benzoate-based ultraviolet absorbers, and cyanoacrylate-based ultraviolet absorbers. These may be used alone or in combination of 2 or more. Preferred commercially available ultraviolet absorbers include, for example, sumika Chemtex Company, sumisorb (registered trademark) 340 manufactured by Limited, (ADK STAB (registered trademark) LA-31 manufactured by ADEKA, and TINUVIN (registered trademark) 1577 manufactured by BASF Japan (Inc.). When the ultraviolet absorber is contained, deterioration of the resin in the optical film is suppressed, and therefore, the optical properties of the optical film are easily improved. The content of the ultraviolet absorber is preferably 1 to 10 mass%, more preferably 3 to 6 mass%, relative to the mass of the optical film of the present invention. When the content of the ultraviolet absorber is within the above range, the optical properties of the optical film can be easily further improved.

The optical film of the present invention may further contain additives other than the ultraviolet absorber. Examples of such other additives include fillers, brighteners, antioxidants, pH adjusters, and leveling agents. However, the optical film of the present invention is preferably substantially free of filler (e.g., silica particles). Specifically, the content of the filler is preferably 5 mass% or less, more preferably 3 mass% or less, further preferably 1 mass% or less, particularly preferably 0.5 mass% or less, and most preferably 0.1 mass% or less, relative to the mass of the optical film.

The use of the optical film of the present invention is not particularly limited, and can be used for various purposes. The optical film of the present invention may be a single layer or a laminate as described above, and the optical film of the present invention may be used as it is, or may be used as a laminate with other films. When the optical film is a laminate, the optical film is referred to as an optical film including all layers laminated on one or both surfaces of the optical film.

When the optical film of the present invention is a laminate, it is preferable that at least one surface of the optical film has 1 or more functional layers. Examples of the functional layer include an ultraviolet absorbing layer, a hard coat layer, a primer layer, a gas barrier layer, an adhesive layer, a hue adjusting layer, and a refractive index adjusting layer. The functional layer may be used alone or in combination of two or more.

The ultraviolet absorbing layer is a layer having an ultraviolet absorbing function, and is composed of a main material selected from the group consisting of ultraviolet curable transparent resins, electron beam curable transparent resins, and thermosetting transparent resins, and an ultraviolet absorber dispersed in the main material.

The adhesive layer is a layer having an adhesive function, and has a function of adhering the optical film to other members. As a material for forming the adhesive layer, a conventionally known material can be used. For example, a thermosetting resin composition or a photocurable resin composition may be used. In this case, the thermosetting resin composition or the photocurable resin composition can be cured by supplying energy afterwards to form a polymer.

The adhesive layer may be a layer called a pressure-sensitive adhesive (Pressure Sensitive Adhesive, PSA) that is bonded to the object by pressing. The pressure-sensitive adhesive may be an adhesive which is "a substance which adheres to an adherend at ordinary temperature by a low pressure" (JIS K6800), or may be a capsule-type adhesive which is "an adhesive which can maintain stability before the film is broken by an appropriate means (pressure, heat, etc.) (JIS K6800) by containing a specific component in a protective film (microcapsule).

The hue control layer is a layer having a hue control function, and is a layer capable of controlling the optical laminate to a target hue. The hue control layer is, for example, a layer containing a resin and a colorant. Examples of the colorant include inorganic pigments such as titanium oxide, zinc oxide, iron oxide red, titanium oxide-based calcined pigments, ultramarine blue, cobalt aluminate, and carbon black; organic pigments such as azo-based compounds, quinacridone-based compounds, anthraquinone-based compounds, perylene-based compounds, isoindolinone-based compounds, phthalocyanine-based compounds, quinophthalone-based compounds, petrolatum (threne) -based compounds, and diketopyrrolopyrrole-based compounds; such pigments as barium sulfate and calcium carbonate; and dyes such as basic dyes, acid dyes, and mordant dyes.

The refractive index adjusting layer is a layer having a function of adjusting a refractive index, and is, for example, a layer having a refractive index different from that of a single-layer optical film and capable of imparting a predetermined refractive index to the optical film. The refractive index adjusting layer may be, for example, a resin layer which is appropriately selected and which further contains a pigment according to circumstances, or a metal thin film. Examples of the pigment for adjusting the refractive index include silicon oxide, aluminum oxide, antimony oxide, tin oxide, titanium oxide, zirconium oxide, and tantalum oxide. The pigment may have an average primary particle diameter of 0.1 μm or less. By setting the average primary particle diameter of the pigment to 0.1 μm or less, diffuse reflection of light transmitted through the refractive index adjusting layer can be prevented, and deterioration of transparency can be prevented. Examples of the metal that can be used for the refractive index adjustment layer include metal oxides or metal nitrides such as titanium oxide, tantalum oxide, zirconium oxide, zinc oxide, tin oxide, silicon oxide, indium oxide, titanium oxynitride, titanium nitride, silicon oxynitride, and silicon nitride.

In a preferred embodiment of the present invention, the optical film has a hard coating on at least one side (one or both sides). In the case where the hard coat layer is provided on both sides, the components contained in the 2 hard coat layers may be the same or different from each other.

Examples of the hard coat layer include known hard coat layers such as acrylic, epoxy, urethane, benzyl chloride, and vinyl. Among these, from the viewpoint of suppressing a decrease in visibility in the wide-angle direction of the optical film and improving the bending resistance, it is preferable to use a hard coat layer of acrylic, urethane, or a combination thereof. The hard coat layer is preferably a cured product of a curable composition containing a curable compound, and is formed by polymerizing the curable compound by irradiation with active energy rays. Examples of the curable compound include polyfunctional (meth) acrylate compounds. The polyfunctional (meth) acrylate compound is a compound having at least 2 (meth) acryloyl groups in a molecule.

Examples of the polyfunctional (meth) acrylate compound include ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, 1, 6-hexanediol di (meth) acrylate, neopentyl glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, trimethylolethane tri (meth) acrylate, tetramethylolmethane tetra (meth) acrylate, pentaglycerol (pentaglycerol) tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, glycerol tri (meth) acrylate, dipentaerythritol tetra (meth) acrylate, dipentaerythritol penta (meth) acrylate, dipentaerythritol hexa (meth) acrylate, and tri ((meth) acryloxyethyl) isocyanurate; a phosphazene (meth) acrylate compound obtained by introducing a (meth) acryloyl group into a phosphazene ring of a phosphazene compound; a urethane (meth) acrylate compound obtained by reacting a polyisocyanate having at least 2 isocyanate groups in the molecule with a polyol compound having at least 1 (meth) acryloyl group and hydroxyl group; a polyester (meth) acrylate compound obtained by reacting a carboxylic acid halide having at least 2 functional groups in the molecule with a polyol compound having at least 1 (meth) acryloyl group and hydroxyl group; and oligomers such as dimers, trimers, etc. of the above-mentioned respective compounds. These compounds may be used alone or in combination of 2 or more kinds.

The curable compound may contain a monofunctional (meth) acrylate compound in addition to the polyfunctional (meth) acrylate compound. Examples of the monofunctional (meth) acrylate compound include hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate, 2-hydroxy-3-phenoxypropyl (meth) acrylate, and glycidyl (meth) acrylate. These compounds may be used alone or in combination of 2 or more. The content of the monofunctional (meth) acrylate compound is preferably 10 mass% or less, based on 100 mass% of the solid content of the compound contained in the curable composition. In the present specification, the solid content refers to all components except the solvent contained in the curable composition.

The curable compound may contain a polymerizable oligomer. By containing the polymerizable oligomer, the hardness of the hard coat layer can be adjusted. Examples of the polymerizable oligomer include macromers such as terminal (meth) acrylate polymethyl methacrylate, terminal styryl poly (meth) acrylate, terminal (meth) acrylate polystyrene, terminal (meth) acrylate polyethylene glycol, terminal (meth) acrylate acrylonitrile-styrene copolymer, terminal (meth) acrylate styrene- (meth) acrylate methyl copolymer, and the like. The content of the polymerizable oligomer is preferably 5 to 50% by mass based on 100% by mass of the solid content of the compound contained in the curable composition.

The curable composition for forming a hard coat layer may contain an additive in addition to the polyfunctional (meth) acrylate compound and the polymerizable oligomer. Examples of the additive include a polymerization initiator, silica, a leveling agent, and a solvent. Examples of the solvent include methyl ethyl ketone and polypropylene glycol monomethyl ether.

The thickness of the hard coat layer is preferably 3 to 30 μm, more preferably 5 to 25 μm, and even more preferably 5 to 20 μm, from the viewpoint of improving the hardness, bending resistance and visibility of the optical film.

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

The thickness of the protective film is not particularly limited, and is usually 10 to 120. Mu.m, preferably 15 to 110. Mu.m, more preferably 20 to 100. Mu.m. In the case where the optical film has two protective films, the thickness of each protective film may be the same or different.

[ method for producing optical film ]

The optical film of the present invention is not particularly limited, and can be produced, for example, by a method comprising the following steps.

(a) A step of preparing a liquid containing the resin (hereinafter, may be referred to as a varnish) (varnish preparation step),

(b) A step of forming a coating film by applying a varnish to a substrate (coating step), and

(c) A step of forming an optical film by drying the applied liquid (coating film) (optical film forming step)

In the varnish preparation step, the resin is dissolved in a solvent, and the ultraviolet absorber and the other additives are added as necessary, followed by stirring and mixing, thereby preparing a varnish.

The solvent used for preparing the varnish is not particularly limited as long as the aforementioned resin can be dissolved. Examples of such solvents include amide solvents such as N, N-dimethylacetamide (DMAc) and N, N-dimethylformamide; lactone solvents such as gamma-butyrolactone (GBL) and gamma-valerolactone; sulfur-containing solvents such as dimethyl sulfone, dimethyl sulfoxide, and sulfolane; carbonate solvents such as ethylene carbonate and propylene carbonate; and combinations thereof (mixed solvents). Among these, an amide-based solvent or a lactone-based solvent is preferable. These solvents may be used singly or in combination of two or more. The varnish may contain water, an alcohol-based solvent, a ketone-based solvent, an acyclic ester-based solvent, an ether-based solvent, or the like. The solid content concentration of the varnish is preferably 1 to 25% by mass, more preferably 5 to 20% by mass.

In the coating step, a varnish is applied to the substrate by a known coating method to form a coating film. Examples of known coating methods include roll coating methods such as bar coating, reverse coating and gravure coating, die coating, comma coating, lip coating, spin coating, screen coating, spray coating, dip coating, spray coating and casting.

Examples of the substrate include SUS plates when the substrate is a metal type, and PET films, PEN films, other polyimide-based resins, polyamide-based resin films, cycloolefin polymer (COP) films, acrylic films, and the like when the substrate is a resin type. Among them, PET films, COP films, and the like are preferable from the viewpoint of excellent smoothness and heat resistance, and PET films are more preferable from the viewpoint of adhesion to optical films and cost.

In the optical film forming step, the coating film is dried (referred to as the 1 st drying), and after being peeled off from the base material, the dried coating film is further dried (referred to as the 2 nd drying or post baking treatment), whereby an optical film is formed. The 1 st drying may be performed under an inert atmosphere or under reduced pressure, as required. Drying 1 is preferably carried out at a lower temperature and takes time. If the 1 st drying is performed at a relatively low temperature, the proportion of scattered light of the obtained optical film can easily be made to satisfy the formula (1).

Here, in the case of industrially producing the optical film of the present invention, the actual production environment is often unfavorable to obtain a low scattered light ratio Ts as compared with the laboratory-level production environment, and as a result, it may be difficult to improve the wide-angle visibility of the optical film. Although it takes time to perform the 1 st drying at a lower temperature as described above, in the laboratory grade, the drying may be performed in a sealed dryer at the time of the 1 st drying, and thus, roughness of the surface of the optical film due to external factors is less likely to occur. In contrast, in the case of industrially producing an optical film, for example, since a large area needs to be heated in the 1 st drying, an air blowing device may be used in the heating. As a result, the surface state of the optical film tends to be rough, and it is difficult to reduce the scattered light ratio Ts of the optical film.

In the case of drying by heating, particularly in view of the external factors as described above in the case of industrially producing an optical film, the 1 st drying temperature is preferably 60 to 150 ℃, more preferably 60 to 140 ℃, still more preferably 70 to 140 ℃. The time for the 1 st drying is preferably 1 to 60 minutes, more preferably 5 to 40 minutes. In particular, in consideration of the above external factors in the case of industrially producing an optical film, it is preferable to conduct the film production under a drying temperature condition of 3 stages or more. The multi-stage conditions may be carried out under the same or different temperature conditions and/or drying times in each stage, and for example, drying may be carried out in 3 to 10 stages, preferably 3 to 8 stages. When the 1 st drying is performed under a multistage condition of 3 stages or more, the obtained optical film easily satisfies the formula (1). In the case of the multi-stage condition of 3 or more stages, the 1 st drying temperature distribution (temperature profile) preferably includes a temperature rise and a temperature drop. That is, the 1 st drying condition in the optical film forming step is more preferably a heating temperature condition in which the temperature distribution includes 3 or more stages of temperature increase and temperature decrease. When the temperature distribution is exemplified by 4 stages, the 1 st drying temperature is 70 to 90 ℃ (1 st temperature), 90 to 120 ℃ (2 nd temperature), 80 to 120 ℃ (3 rd temperature) and 80 to 100 ℃ (4 th temperature) in this order. In this example, the 1 st drying temperature is raised from the 1 st temperature to the 2 nd temperature, then lowered from the 2 nd temperature to the 3 rd temperature, and then lowered from the 3 rd temperature to the 4 th temperature. The 1 st drying time is, for example, 5 to 15 minutes in each stage. The 1 st drying is preferably performed so that the solvent remaining amount of the dried coating film is preferably 5 to 15% by mass, more preferably 6 to 12% by mass, based on the mass of the dried coating film. When the solvent residual amount is within the above range, the peeling of the dried coating film from the substrate becomes good, and the obtained optical film easily satisfies the formula (1).

The temperature of the 2 nd drying is preferably 150 to 300 ℃, more preferably 180 to 250 ℃, still more preferably 180 to 230 ℃. The time for the 2 nd drying is preferably 10 to 60 minutes, more preferably 30 to 50 minutes.

The 2 nd drying may be performed in a monolithic manner, but in the case of industrial production, it is preferable to perform in a roll-to-roll (roll-to-roll) manner from the viewpoint of production efficiency. In the case of the monolithic system, it is preferable to dry the substrate in a state in which the substrate is uniformly elongated in the in-plane direction.

In the roll-to-roll system, the dried coating film is preferably dried in a state of being elongated in the transport direction, and the transport speed is preferably 0.1 to 5 m/min, more preferably 0.5 to 3 m/min, and even more preferably 0.7 to 1.5 m/min, from the viewpoint that the optical film easily satisfies the formula (1). The 2 nd drying may be performed under 1 stage or multistage conditions, and is preferably performed under multistage conditions, from the viewpoint that the optical film easily satisfies the formula (1). In the multistage conditions, it is preferable that the drying be performed in at least 1 selected from the same or different temperature conditions, drying time, and wind speed of hot air in each stage, and for example, the drying be performed in 2 to 10 stages, preferably 3 to 8 stages. In each stage, the wind speed of the hot air is preferably 5 to 20 m/min, more preferably 10 to 15 m/min, and even more preferably 11 to 14 m/min, from the viewpoint that the obtained optical film easily satisfies the formula (1).

In the case where the optical film of the present invention includes a hard coat layer, the hard coat layer may be formed, for example, as follows: the curable composition is applied to at least one surface of the optical film to form a coating film, and the coating film is irradiated with high-energy rays to cure the coating film.

The coating method includes known coating methods exemplified above. The irradiation intensity of the high-energy ray (for example, active energy ray) at the time of curing is appropriately determined depending on the composition of the curable composition, and is not particularly limited, but irradiation in a wavelength region effective for activation of the polymerization initiator is preferable. The irradiation intensity is preferably 0.1 to 6,000mW/cm ² More preferably 10 to 1,000mW/cm ² More preferably 20 to 500mW/cm ² . When the irradiation intensity is within the above range, an appropriate reaction time can be ensured, and yellowing and deterioration of the resin due to heat radiated from the light source and heat release at the time of curing reaction can be suppressed. The irradiation time is appropriately selected depending on the composition of the curable composition, and is not particularly limited, and may be represented by the product of the irradiation intensity and the irradiation timeThe cumulative light quantity of (C) is preferably 10 to 10,000mJ/cm ² More preferably 50 to 1,000mJ/cm ² Further preferably 80 to 500mJ/cm ² Is set by the mode of (2). When the cumulative amount of light is within the above range, a sufficient amount of active species derived from the polymerization initiator can be generated, so that the curing reaction can be performed more reliably, and the irradiation time does not become excessively long, thereby maintaining good productivity. Further, the hardness of the hard coat layer can be further improved by the irradiation step in this range, and therefore, it is useful. From the viewpoints of improving the smoothness of the hard coat layer and further improving the visibility in the wide-angle direction of the optical film, the type of solvent, the composition ratio, the optimization of the solid content concentration, the addition of a leveling agent, and the like can be cited.

Flexible image display device

The present invention includes a flexible display device provided with the aforementioned optical film. The optical film of the present invention is preferably used as a front panel, sometimes referred to as a window film, in a flexible image display device. The flexible image display device is formed of a laminate for a flexible image display device and an organic EL display panel, and the laminate for a flexible image display device is disposed on the viewing side with respect to the organic EL display panel so as to be bendable. The laminate for a flexible image display device may further include a polarizing plate (preferably a circular polarizing plate) and a touch sensor, and the lamination order thereof is arbitrary, but it is preferable that the laminate is laminated in order of a window film, a polarizing plate, a touch sensor, or a window film, a touch sensor, and a polarizing plate from the viewing side. When the polarizing plate is present on the viewing side of the touch sensor, the pattern of the touch sensor is less likely to be viewed, and the visibility of the display image is improved, which is preferable. The components may be laminated using an adhesive, a binder, or the like. The touch panel may further include a light shielding pattern formed on at least one surface of any one of the window film, the polarizing plate, and the touch sensor.

[ polarizing plate ]

As described above, the flexible display device of the present invention is preferably provided with a polarizing plate, and among them, a circular polarizing plate is preferable. The circular polarizing plate is a functional layer having a function of transmitting only a right-handed or left-handed circularly polarized light component by laminating a λ/4 retardation plate on a linear polarizing plate. For example, can be used to: the external light is converted into right circularly polarized light, and the external light reflected by the organic EL panel into left circularly polarized light is blocked, and only the light-emitting component of the organic EL is transmitted, thereby suppressing the influence of the reflected light, and making it easy to view an image. In order to realize the circularly polarized light function, the absorption axis of the linear polarizing plate and the slow axis of the λ/4 retardation plate should be 45 ° in theory, but in practical application, 45±10°. The linear polarizing plate and the λ/4 retardation plate do not necessarily have to be stacked adjacently, as long as the relationship between the absorption axis and the slow axis satisfies the aforementioned range. It is preferable to achieve complete circularly polarized light at full wavelength, but this is not necessarily the case in practical applications, and thus circular polarizing plates in the present invention also include elliptical polarizing plates. It is also preferable to further laminate a lambda/4 phase difference film on the viewing side of the linear polarizing plate to convert the outgoing light into circularly polarized light, thereby improving visibility in a state where polarized sunglasses are worn.

The linear polarizing plate is a functional layer having the following functions: light vibrating in the transmission axis direction passes through but blocks polarized light of a vibrating component perpendicular thereto. The linear polarizing plate may be a single linear polarizer, or may have a structure including a linear polarizer and a protective film attached to at least one surface thereof. The thickness of the linear polarizing plate may be 200 μm or less, and preferably 0.5 to 100 μm. When the thickness of the linear polarizing plate is within the above range, the flexibility of the linear polarizing plate tends to be less likely to be lowered.

The linear polarizer may be a film type polarizer manufactured by dyeing and stretching a polyvinyl alcohol (hereinafter, may be abbreviated as PVA) film. Polarizing performance can be exhibited by adsorbing a dichroic dye such as iodine to a PVA film oriented by stretching or by stretching the film in a state of being adsorbed to PVA to orient the dichroic dye. In the production of the film polarizer, the film polarizer may further include swelling, crosslinking by boric acid, washing by an aqueous solution, drying, and the like. The stretching and dyeing steps may be performed as a PVA-based film alone or in a laminate with another film such as polyethylene terephthalate. The thickness of the PVA film used is preferably 10 to 100. Mu.m, and the stretching ratio is preferably 2 to 10 times.

In addition, as another example of the polarizer, a liquid crystal coated polarizer formed by coating a liquid crystal polarizing composition may be mentioned. The liquid crystal polarizing composition may contain a liquid crystal compound and a dichroic dye compound. The liquid crystalline compound is preferable because it has a property of exhibiting a liquid crystal state, and particularly, it can exhibit a high polarizing performance when it has a high-order alignment state such as smectic state. In addition, it is preferable that the liquid crystalline compound has a polymerizable functional group.

The dichroic dye compound is a dye which exhibits dichroism in conjunction with alignment of the liquid crystal compound, and may have a polymerizable functional group, and the dichroic dye itself may have liquid crystallinity.

Any one of the compounds contained 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 produced by: the liquid crystal polarizing composition is coated on the alignment film to form a liquid crystal polarizing layer. The liquid crystal polarizing layer can be formed to a thin thickness, preferably 0.5 to 10 μm, more preferably 1 to 5 μm, as compared with the film type polarizer.

The alignment film can be produced, for example, by: the alignment film-forming composition is applied to a substrate, and alignment is imparted by rubbing, polarized light irradiation, or the like. The orientation 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 orientation agent. Examples of the orientation agent include polyvinyl alcohols, polyacrylates, polyamide acids, and polyimides. In the case of using an alignment agent which imparts alignment properties by polarized light irradiation, an alignment agent containing a cinnamate group (cinnamate group) is preferably used. The weight average molecular weight of the polymer used as the alignment agent is, for example, about 10,000 ～ 1,000,000. The thickness of the alignment film is preferably 5 to 10,000nm, and more preferably 10 to 500nm from the viewpoint of sufficiently exhibiting an alignment controlling force.

The liquid crystal polarizing layer may be laminated by being peeled from a substrate and transferred, or the substrate may be directly laminated. The base material also preferably functions as a transparent base material for a protective film, a retardation film, and a window film.

The protective film may be a transparent polymer film, and the same materials and additives as those used for the transparent substrate of the window film may be used. The protective film may be a coated protective film obtained by coating and curing a cationic curing composition such as an epoxy resin or a radical curing composition such as an acrylate. The protective film may contain plasticizers, ultraviolet absorbers, infrared absorbers, colorants (pigments, dyes, and the like), fluorescent brighteners, dispersants, heat stabilizers, light stabilizers, antistatic agents, antioxidants, lubricants, solvents, and the like as necessary. The thickness of the protective film is preferably 200 μm or less, more preferably 1 to 100 μm. When the thickness of the protective film is within the above range, the flexibility of the film tends to be less likely to decrease.

The λ/4 retardation plate is a film that imparts a phase difference of λ/4 in a direction (in-plane direction of the film) orthogonal to the traveling direction of the incident light. The lambda/4 retardation plate may be a stretched retardation plate produced by stretching a polymer film such as a cellulose film, an olefin film, or a polycarbonate film. The lambda/4 phase difference plate may contain a phase difference regulator, a plasticizer, an ultraviolet absorber, an infrared absorber, a colorant (pigment, dye, or the like), an optical brightening agent, a dispersant, a heat stabilizer, a light stabilizer, an antistatic agent, an antioxidant, a lubricant, a solvent, or the like, as required.

The thickness of the stretched phase difference plate is preferably 200 μm or less, more preferably 1 to 100 μm. When the thickness of the stretched phase difference plate is within the above range, the flexibility of the stretched phase difference plate tends to be less likely to be lowered.

Another example of the λ/4 retardation plate is a liquid crystal coated retardation plate formed by coating a liquid crystal composition.

The liquid crystal composition contains a liquid crystalline compound which exhibits a liquid crystalline state such as nematic, cholesteric, smectic, or the like. The liquid crystalline compound has a polymerizable functional group.

The liquid crystal 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 coated retardation plate can be produced by: in the same manner as the liquid crystal polarizing layer, the liquid crystal composition is coated on a substrate and cured to form a liquid crystal retardation layer. The liquid crystal coating type retardation plate can be formed to have a smaller thickness than the stretching type retardation plate. The thickness of the liquid crystal polarizing layer is preferably 0.5 to 10. Mu.m, more preferably 1 to 5. Mu.m.

The liquid crystal coated retardation plate may be laminated by peeling from a substrate and then transferring, or may be laminated directly on the substrate. The base material also preferably functions as a transparent base material for a protective film, a retardation film, and a window film.

In general, the following materials are more: the shorter the wavelength, the greater the birefringence; the longer the wavelength, the smaller the birefringence is exhibited. In this case, since the phase difference of λ/4 cannot be achieved in the entire visible light region, the design is performed in the following manner: the in-plane retardation is preferably 100 to 180nm, more preferably 130 to 150nm, at about 560nm where the visibility is high. The inversely dispersed λ/4 retardation plate using a material having a wavelength dispersion characteristic of a birefringence opposite to that of the material is preferable in that the visibility is good. As such a material, for example, a material described in japanese patent application laid-open No. 2007-232873 or the like can be used for the stretched phase difference plate, and a material described in japanese patent application laid-open No. 2010-30979 can be used for the liquid crystal coated phase difference plate.

As another method, a technique of obtaining a wide-band lambda/4 phase difference plate by combining it with a lambda/2 phase difference plate is also known (for example, japanese unexamined patent publication No. 10-90521). The lambda/2 phase difference plate is also manufactured by the same material and method as the lambda/4 phase difference plate. The combination of the stretching type retardation plate and the liquid crystal coating type retardation plate is arbitrary, and the thickness can be reduced by using the liquid crystal coating type retardation plate.

For the circularly polarizing plate, a method of laminating a positive C plate is known in order to improve visibility in an oblique direction (for example, japanese patent application laid-open No. 2014-224837 and the like). The positive C plate may be a liquid crystal coated type retardation plate or a stretched type retardation plate. The retardation in the thickness direction of the retardation plate is preferably-200 to-20 nm, more preferably-140 to-40 nm.

[ touch sensor ]

As described above, the flexible display device of the present invention is preferably provided with a touch sensor. The touch sensor serves as an input mechanism. The touch sensor may be of various types such as a resistive film type, a surface elastic wave type, an infrared type, an electromagnetic induction type, and a capacitance type, and preferably of a capacitance type.

The capacitive touch sensor is divided into an active region and an inactive region located at an outer contour portion of the active region. The active region is a region corresponding to a region (display portion) on the display panel where a screen is displayed, and the inactive region is a region corresponding to a region (non-display portion) in the display device where a screen is not displayed, in response to a touch by a user. The touch sensor may include: a substrate having a flexible characteristic; a sensing pattern formed in an active region of the substrate; and each sensing line formed in the inactive region of the substrate and connecting the sensing pattern to an external driving circuit via a pad (pad) portion. As the substrate having the flexible characteristic, the same material as the transparent substrate of the window film can be used.

The sensing pattern may include a 1 st pattern formed in the 1 st direction and a 2 nd pattern formed in the 2 nd direction. The 1 st pattern and the 2 nd pattern are arranged in different directions from each other. The 1 st pattern and the 2 nd pattern are formed in the same layer, and each pattern must be electrically connected in order to sense the touched position. The 1 st pattern is a form in which a plurality of cell patterns are connected to each other via a joint, but the 2 nd pattern is a structure in which a plurality of cell patterns are separated from each other in an island form, and thus, in order to electrically connect the 2 nd pattern, a separate bridge electrode is required. For the electrode for connecting the 2 nd pattern, a known transparent electrode can be applied. Examples of the material of the transparent electrode include Indium Tin Oxide (ITO), indium Zinc Oxide (IZO), zinc oxide (ZnO), indium Zinc Tin Oxide (IZTO), indium Gallium Zinc Oxide (IGZO), cadmium Tin Oxide (CTO), PEDOT (poly (3, 4-ethylenedioxythiophene)), carbon Nanotubes (CNT), graphene, and metal wires, and ITO is preferable. These may be used alone or in combination of 2 or more. The metal used for the metal wire is not particularly limited, and examples thereof include silver, gold, aluminum, copper, iron, nickel, titanium, selenium, chromium, and the like, and they may be used alone or in combination of 2 or more.

The bridge electrode may be formed on the upper portion of the insulating layer through the insulating layer on the upper portion of the sensing pattern, and the bridge electrode may be formed on the substrate, and the insulating layer and the sensing pattern may be formed thereon. The bridge electrode may be formed of the same material as the sensing pattern, or may be formed of molybdenum, silver, aluminum, copper, palladium, gold, platinum, zinc, tin, titanium, or an alloy of 2 or more thereof.

Since the 1 st pattern and the 2 nd pattern must be electrically insulated, an insulating layer is formed between the sensing pattern and the bridging electrode. The insulating layer may be formed only between the 1 st pattern tab and the bridge electrode, or may be formed as a layer covering the entire sensing pattern. In the case of a layer covering the entire sensing pattern, the bridge electrode may be connected to the 2 nd pattern via a contact hole formed in the insulating layer.

In the touch sensor, an optical adjustment layer may be further included between the substrate and the electrode as means for appropriately compensating for the difference in transmittance between the pattern region where the sensing pattern is formed and the non-pattern region where the sensing pattern is not formed (specifically, the difference in transmittance due to the difference in refractive index in these regions). The optical adjustment layer may contain an inorganic insulating substance or an organic insulating substance. The optical adjustment layer may be formed by applying a photocurable composition containing a photocurable organic binder and a solvent to a substrate. The aforementioned photocurable composition may further comprise inorganic particles. The refractive index of the optical adjustment layer can be increased by the inorganic particles.

The photocurable organic binder may contain, for example, a copolymer of each monomer such as an acrylic monomer, a styrene monomer, and a carboxylic acid monomer, within a range that does not impair the effects of the present invention. The photocurable organic binder may be a copolymer containing, for example, repeating units that are different from each other, 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 various additives such as a photopolymerization initiator, a polymerizable monomer, and a curing auxiliary agent.

[ adhesive layer ]

The layers (window film, circular polarizing plate, touch sensor) forming the laminate for a flexible image display device may be bonded by an adhesive. As the adhesive, a conventionally used adhesive such as an aqueous adhesive, an aqueous solvent-volatile adhesive, an organic solvent-based adhesive, a solvent-free adhesive, a solid adhesive, a solvent-volatile adhesive, a moisture-curable adhesive, a heat-curable adhesive, an anaerobic-curable adhesive, an active energy ray-curable adhesive, a curing agent-mixed adhesive, a hot-melt adhesive, a pressure-sensitive adhesive (adhesive), a rewet adhesive, and the like can be used, and an aqueous solvent-volatile adhesive, an active energy ray-curable adhesive, and an adhesive can be preferably used. The thickness of the adhesive layer can be appropriately adjusted according to the required adhesive force or the like, and is preferably 0.01 to 500. Mu.m, more preferably 0.1 to 300. Mu.m. The laminate for a flexible image display device may have a plurality of adhesive layers, and the thickness and the type of each adhesive layer may be the same or different.

As the aqueous solvent-volatile adhesive, a polyvinyl alcohol polymer, a water-soluble polymer such as starch, a polymer in a water-dispersed state such as an ethylene-vinyl acetate emulsion or a styrene-butadiene emulsion can be used as a main polymer. In addition to the above-mentioned main agent polymer and water, a crosslinking agent, a silane-based 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 by using the aqueous solvent-volatile adhesive, the aqueous solvent-volatile adhesive is injected into the bonding interlayer, bonded to the bonding interlayer, and then dried to impart the bonding property. When the aqueous solvent-volatile adhesive is used, the thickness of the adhesive layer is preferably 0.01 to 10. Mu.m, more preferably 0.1 to 1. Mu.m. When the aqueous solvent-volatile adhesive is used in a plurality of layers, the thickness and type of each layer may be the same or different.

The active energy ray-curable adhesive may be formed by curing an active energy ray-curable composition containing a reactive material capable of forming an adhesive layer by irradiation with active energy rays. The active energy ray-curable composition may contain at least one polymer selected from the group consisting of a radical polymerizable compound and a cation polymerizable compound, which are the same as those contained in the hard coat composition. The radical polymerizable compound may be the same as the radical polymerizable compound in the hard coat composition.

The cation polymerizable compound may be the same as that in the hard coat composition.

As the cationically polymerizable compound used in the active energy ray-curable composition, an epoxy compound is particularly preferable. In order to reduce the viscosity of the adhesive composition, it is also preferable to include a monofunctional compound as a reactive diluent.

To reduce the viscosity, the active energy ray composition may contain a monofunctional compound. Examples of the monofunctional compound include an acrylate monomer having 1 (meth) acryloyl group in 1 molecule and a compound having 1 epoxy group or oxetanyl group in 1 molecule, and examples thereof include glycidyl (meth) acrylate.

The active energy ray composition may further contain a polymerization initiator. Examples of the polymerization initiator include radical polymerization initiators, cationic polymerization initiators, radical polymerization initiators, and cationic polymerization initiators, which can be appropriately selected and used. These polymerization initiators are decomposed by at least one of irradiation with active energy rays and heating to generate radicals or cations, and the radical polymerization and the cationic polymerization are performed. An initiator capable of initiating at least either radical polymerization or cationic polymerization by irradiation with active energy rays as in the description of the hard coat composition may be used.

The active energy ray-curable composition may further contain an ion scavenger, an antioxidant, a chain transfer agent, a blocking agent, a thermoplastic resin, a filler, a flow viscosity regulator, a plasticizer, an antifoaming agent, an additive, and a solvent. In the case where 2 adherend layers are bonded by the active energy ray-curable adhesive, the adhesion can be achieved as follows: the active energy ray-curable composition is applied to one or both of the adherend layers, and then bonded thereto, and either one or both of the adherend layers is irradiated with active energy rays to cure the same. When the active energy ray-curable adhesive is used, the thickness of the adhesive layer is preferably 0.01 to 20. Mu.m, more preferably 0.1 to 10. Mu.m. When the active energy ray-curable adhesive is used for forming a plurality of adhesive layers, the thickness and type of each layer may be the same or different.

The binder may be classified into an acrylic binder, a urethane binder, a rubber binder, a silicone binder, and the like, depending on the main polymer. The adhesive may contain, in addition to the main polymer, a crosslinking agent, a silane compound, an ionic compound, a crosslinking catalyst, an antioxidant, an adhesion imparting agent, a plasticizer, a dye, a pigment, an inorganic filler, and the like. The adhesive layer (adhesive layer) is formed by dissolving and dispersing the components constituting the adhesive in a solvent to obtain an adhesive composition, and applying the adhesive composition to a substrate and then drying the substrate. The adhesive layer may be formed directly or may be transferred to another substrate. In order to cover the adhesive surface before bonding, a release film is also preferably used. When the active energy ray-curable adhesive is used, the thickness of the adhesive layer is preferably 0.1 to 500. Mu.m, more preferably 1 to 300. Mu.m. When the adhesive is used for a plurality of layers, the thickness and type of each layer may be the same or different.

[ shading Pattern ]

The light shielding pattern may be applied as at least a part of a bezel (bezel) or a case of the flexible image display device. The wiring arranged at the edge of the flexible image display device is shielded by a light shielding pattern, so that the wiring is not easily seen, thereby improving the visibility of the image. The light shielding pattern may be in the form of a single layer or a plurality of layers. The color of the light shielding pattern is not particularly limited, and may be various colors such as black, white, metallic color, and the like. The light shielding pattern may be formed of a pigment for color development, and a polymer such as an acrylic resin, an ester resin, an epoxy resin, polyurethane, or silicone. They may be used alone or in the form of a mixture of 2 or more. The light shielding pattern may be formed by various methods such as printing, photolithography, and ink-jet. The thickness of the light shielding pattern is preferably 1 to 100. Mu.m, more preferably 2 to 50. Mu.m. In addition, it is also preferable to impart a shape such as an inclination in the thickness direction of the light shielding pattern.

Examples

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

< weight average molecular weight >

Gel Permeation Chromatography (GPC) was performed using a liquid chromatograph LC-10ATvp manufactured by Shimadzu corporation.

(1) Pretreatment method

The polyimide-based resins obtained in production examples 1 to 4 were dissolved in gamma-butyrolactone (GBL) to prepare a 20 mass% solution, which was diluted 100 times with DMF eluent, and filtered through a 0.45 μm membrane filter to obtain a measurement solution.

(2) Measurement conditions

Column: TSKgel SuperAWM-H2+SuperAW2500×1 (6.0 mm I.D.×150mm×3 roots)

Eluent: DMF (10 mmol of lithium bromide added)

Flow rate: 0.6 mL/min

A detector: RI detector

Column temperature: 40 DEG C

Sample injection amount: 20 mu L

Molecular weight standard: standard polystyrene

< imidization Rate >)

Imidization utilization ¹ H-NMR measurement was performed in the following manner.

(1) Pretreatment method

The polyimide-based resins obtained in production examples 1 to 4 were dissolved in deuterated dimethyl sulfoxide (DMSO-d ₆ ) In the above, a 2 mass% solution was prepared, and the obtained solution was used as a measurement sample.

(2) Measurement conditions

Measurement device: JEOL 400MHz NMR apparatus JNM-ECZ400S/L1

Standard substance: DMSO-d ₆ (2.5ppm)

Sample temperature: room temperature

Cumulative number of times: 256 times

Relaxation time: 5 seconds

(3) Imidization rate analysis method

(imidization Rate of polyimide resin)

Obtained from a measurement sample containing polyimide resin ¹ In the H-NMR spectrum, the integral value of benzene proton A from the structure unchanged before and after imidization was set as Int _A . The integral value of the amide proton derived from the amic acid structure remaining in the polyimide resin was set to Int _B . From these integrated values, the polyamide is obtained based on the following formulaImidization ratio of the imine resin.

Imidization ratio (%) =100× (1-Int) _B /Int _A )

(imidization Rate of Polyamide imide resin)

Obtained from a measurement sample containing a polyamideimide resin ¹ In the H-NMR spectrum, the integral value of benzene proton C derived from the structure which does not change before and after imidization and is not affected by the structure derived from the amic acid structure remaining in the polyamideimide resin among the observed benzene protons was set to Int _C . Further, the integral value of benzene proton D, which is derived from the structure unchanged before and after imidization and is affected by the structure derived from the amic acid structure remaining in the polyamideimide resin, among the observed benzene protons is set to Int _D . According to the obtained Int _C Int _D The beta value was obtained by the following equation.

β＝Int _D /Int _C

Next, the β value of the above formula and the imidization rate of the polyimide resin of the above formula were obtained for a plurality of polyamide imide resins, and the following relational expression was obtained from these results.

Imidization ratio (%) =k×β+100

In the above-described correlation equation, k is a constant.

Substituting β into the correlation formula gives the imidization ratio (%) of the polyamideimide resin.

< scattered light proportion (Ts) >)

The optical films obtained in examples and comparative examples were subjected to determination of diffuse light transmittance (Td) (%) according to JIS K7136 using a spectrocolorimeter CM3700A manufactured by KONICA MINOLTA (ltd). Further, total light transmittance (Tt) (%) was obtained by using a haze meter NDH5000 manufactured by japan electric color industry (ltd) according to JIS K7136. The obtained Td and Tt are substituted into a formula of scattered light ratio (Ts) =td/tt×100, and the scattered light ratio (Ts) (%) of the optical film is calculated.

< tensile elastic modulus >)

The tensile elastic moduli of the optical films obtained in the examples and comparative examples were measured by performing a tensile test in accordance with JIS K7127 using an electromechanical universal tester (manufactured by INSTRON Co., ltd.) at a temperature of 80℃and a test speed of 5 m/min and a load cell of 5 kN. The optical film was allowed to stand in an environment of 80℃for 5 minutes and then measurement was started.

< test for bending resistance >

The bending resistance test (bending radius r=1 mm, number of times of bending 100) was performed in accordance with JIS K5600-5-1 using a YUASA SYSTEM co. The optical film after the bending resistance test was subjected to the same operation as the above-described measurement method for < scattered light ratio (Ts) > to measure the scattered light ratio after the bending resistance test, and the absolute value Δts of the difference between the scattered light ratios before and after the bending resistance test was calculated.

< folding endurance >)

The number of times of bending the optical films in examples and comparative examples was determined in accordance with ASTM standard D2176-16 as follows. The optical film was cut into 15mm by 100mm long strips using a dumbbell cutter. The cut optical film was set in a MIT bending fatigue tester ("model 0530", manufactured by eastern chemical Co., ltd.) and the number of times of reciprocal bending in the front-back direction until the optical film was broken was measured as the number of times of bending under the conditions of a test speed of 175cpm, a bending angle of 135 °, a load of 0.75kgf, and a radius r=1 mm of a bending jig (clamp).

< yellowness (YI value) >, and

the yellowness (Yellow Index): YI value) of the optical films obtained in examples and comparative examples was measured using an ultraviolet-visible near-infrared spectrophotometer "V-670" manufactured by Japan Specification (Co., ltd.). After background measurement is performed in a state where no sample is present, an optical film is set in a sample holder, and the light transmittance with respect to 300 to 800nm is measured to obtain a tristimulus value (X, Y, Z), and the YI value is calculated based on the following formula.

YI＝100×(1.2769X-1.0592Z)/Y

< thickness >

The optical films obtained in examples and comparative examples were measured for thickness at 10 or more by using a micrometer (Mitutoyo "ID-C112 XBS"), and the average value was calculated. The average value was taken as the thickness of the optical film.

< evaluation of visibility >)

The optical films obtained in examples and comparative examples were cut into 10cm squares. The MD direction of the polarizing plate with an adhesive layer of the same size (10 cm square) was aligned with the MD direction of the optical film obtained by dicing, and the polarizing plate with an adhesive layer was bonded to the optical film obtained by dicing, to prepare a sample for evaluation. For 1 optical film of each of examples and comparative examples, 2 evaluation samples were prepared.

One of the 2 samples for evaluation was fixed to a stage such that the fluorescent lamp was positioned in a direction perpendicular to the plane of the sample for evaluation and the longitudinal direction of the fluorescent lamp was horizontal to the MD direction of the sample for evaluation.

The fluorescent lamp image reflected on the surface of the sample for evaluation was visually observed by the observer from an angle inclined by 30 ° with respect to the vertical direction of the sample plane for evaluation.

The same procedure was performed except that the longitudinal direction of the fluorescent lamp was changed from horizontal to vertical, and another sample for evaluation was fixed to the stage, and the fluorescent lamp image was observed.

Based on the observation result, visibility was evaluated based on the following evaluation criteria.

(evaluation criterion for visibility)

And (3) the following materials: little distortion of the fluorescent lamp image was observed.

O: distortion of the fluorescent lamp image is slightly observed.

Delta: distortion of the fluorescent lamp image is observed.

X: distortion of the fluorescent lamp image is clearly observed.

The optical films obtained in examples and comparative examples have a protective film on one surface, but the measurement and evaluation described above were performed using an optical film in which the protective film was peeled off.

Production example 1: production of polyimide resin (1)

A separable flask equipped with a silicone tube, a stirring device, and a thermometer, and an oil bath were prepared. Into the flask, 75.6g of 4,4' - (hexafluoroisopropylidene) diphthalic dianhydride (6 FDA) and 54.5g of 2,2' -bis (trifluoromethyl) -4,4' -diaminobiphenyl (TFMB) were charged. 530g of N, N-dimethylacetamide (DMAc) was added while stirring at 400rpm, and stirring was continued until the contents of the flask became a uniform solution. Then, the temperature in the container was adjusted to be in the range of 20 to 30 ℃ by using an oil bath, and stirring was continued for further 20 hours to react the resultant mixture, thereby producing a polyamic acid. After 30 minutes, the stirring speed was changed to 100rpm. After stirring for 20 hours, the reaction system was returned to room temperature, 650g of DMAc was added thereto, and the concentration of the polymer was adjusted to 10 mass%. Further, 32.3g of pyridine and 41.7g of acetic anhydride were added thereto, and the mixture was stirred at room temperature for 10 hours to effect imidization. The polyimide varnish was taken out of the reaction vessel. The obtained polyimide varnish was added dropwise to methanol, reprecipitated, and the obtained powder was dried under heating to remove the solvent, thereby obtaining a polyimide resin (1) as a solid component. GPC measurement showed that weight average molecular weight of the obtained polyimide resin (1) was 350,000. The imidization ratio of the polyimide resin (1) was 98.8%.

Production example 2: production of polyimide resin (2)

A polyimide resin (2) was produced in the same manner as in production example 1, except that the reaction time was changed to 16 hours. The weight average molecular weight of the obtained polyimide resin (2) was 280,000, and the imidization rate was 98.3%.

Production example 3: production of polyamideimide resin (3)

To a 1L separable flask equipped with a stirring blade, 45g (140.52 mmol) of TFMB and 768.55g of DMAc were charged under a nitrogen atmosphere, and the TFMB was dissolved in the DMAc while stirring at room temperature. Next, to the flask was added 6FDA 18.92g (42.58 mmol), and the mixture was stirred at room temperature for 3 hours. Thereafter, 4.19g (14.19 mmol) of 4,4' -oxybis (benzoyl chloride) (OBBC) was added to the flask, followed by 17.29g (85.16 mmol) of terephthaloyl chloride (TPC) and stirred at room temperature for 1 hour. Next, 4.63g (49.68 mmol) of 4-methylpyridine and 13.04g (127.75 mmol) of acetic anhydride were added to the flask, and after stirring at room temperature for 30 minutes, the temperature was raised to 70℃using an oil bath, and further stirring was performed for 3 hours, to obtain a reaction solution.

The reaction solution obtained was cooled to room temperature, poured into a large amount of methanol in a linear manner, and the precipitate was taken out, immersed in methanol for 6 hours, and then washed with methanol. Next, the precipitate was dried under reduced pressure at 100 ℃ to obtain a polyamideimide resin (1). The weight average molecular weight of the polyamide-imide resin (1) was 400,000, and the imidization rate was 98.1%.

Production example 4: production of polyamideimide resin (4)

To a 1L separable flask equipped with a stirring blade, 45g (140.52 mmol) of TFMB and 768.55g of DMAc were charged under a nitrogen atmosphere, and the TFMB was dissolved in the DMAc while stirring at room temperature. Next, to the flask was added 6FDA 19.01g (42.79 mmol), and the mixture was stirred at room temperature for 3 hours. Thereafter, 4.21g (14.26 mmol) of OBBC was added to the flask, followed by 17.30g (85.59 mmol) of TPC, and the mixture was stirred at room temperature for 1 hour. Next, 4.63g (49.68 mmol) of 4-methylpyridine and 13.04g (127.75 mmol) of acetic anhydride were added to the flask, and after stirring at room temperature for 30 minutes, the temperature was raised to 70℃using an oil bath, and further stirring was performed for 3 hours, to obtain a reaction solution.

The reaction solution obtained was cooled to room temperature, poured into a large amount of methanol in a linear manner, and the precipitate was taken out, immersed in methanol for 6 hours, and then washed with methanol. Next, the precipitate was dried under reduced pressure at 100 ℃ to obtain a polyamideimide resin (2). The weight average molecular weight of the obtained polyamide-imide resin (2) was 365,000, and the imidization rate was 98.3%.

Production example 5: production of varnishes (1) to (3)

According to the compositions shown in Table 1, polyimide-based resins were dissolved in a solvent, and Sumisorb 340 (UVA) [2- (2-hydroxy-5-tert-octylphenyl) benzotriazole ] produced by Limited was added as an ultraviolet absorber so as to be 5.7 mass% with respect to the mass of the resins, and stirred until the mixture became uniform, to obtain varnishes (1) to (3).

In table 1, the value in the column "solvent" indicates the ratio (mass%) of the mass of the specific solvent to the total mass of all solvents. The value in the column "polyimide-based resin" indicates the ratio (mass%) of the mass of the specific polyimide-based resin relative to the total mass of all polyimide-based resins. PI-1, PI-2, PAI-1 and PAI-2 in the column of "polyimide-based resin" represent polyimide resin (1), polyimide resin (2), polyamideimide resin (1) and polyamideimide resin (2), respectively. The value in the column "additive" indicates the proportion of the mass of the additive relative to the mass of the resin (mass%). The value in the column "solid content concentration" indicates the proportion (mass%) of all components except the solvent with respect to the mass of the varnish.

TABLE 1

Example 1: production of optical film (1)

The varnish (1) was molded into a coating film by casting on a PET (polyethylene terephthalate) film (A4100, manufactured by Toyobo Co., ltd., thickness 188 μm, thickness distribution.+ -. 2 μm). The line speed was 0.4 m/min. The coating film was dried by heating at 70℃for 8 minutes, at 100℃for 10 minutes, at 90℃for 8 minutes, and at 80℃for 8 minutes, and the coating film was peeled from the PET film. For the obtained raw material film 1 (width 700 mm), a tenter dryer (composed of 1 to 6 chambers) using a clip (clip) as a gripper was used, the solvent was removed, and then a PET-based protective film was attached to one surface of the dried film, to obtain an optical film 1 having a thickness of 79 μm. The drying of the raw material film 1 is performed in more detail as follows. The temperature in the dryer was set to 200 ℃, the regulation was made so that the clip holding width was 25mm, the film conveying speed was 1.0 m/min, the ratio of the film width at the inlet of the dryer (distance between clips) to the film width at the outlet of the drying furnace was 1.0, and the wind speeds in the respective chambers of the tenter dryer were regulated so that 13.5 m/sec in the 1 st chamber, 13 m/sec in the 2 nd chamber, and 11 m/sec in the 3 rd to 6 th chambers. After the film was detached from the clip, the clip portion was cut (slit), a PET-based protective film was attached to one surface of the film, and the film was wound around an ABS 6-inch core, to obtain an optical film 1.

Example 2: production of optical film (2)

The same procedure as in the production method of the optical film 1 was conducted except that the varnish (1) was changed to the varnish (2), the line speed was changed from 0.4 m/min to 0.3 m/min, and the heating conditions of the coating film were changed from 8 minutes at 70 ℃, 10 minutes at 100 ℃, 8 minutes at 90 ℃ and 8 minutes at 80 ℃ to 10 minutes at 80 ℃, 10 minutes at 100 ℃, 10 minutes at 90 ℃, 10 minutes and 10 minutes at 80 ℃ in this order, to produce the optical film 2 having a thickness of 49 μm.

Example 3: production of optical film (3)

The same procedure as in the case of the method for producing the optical film 1 was conducted except that the line speed was changed from 0.4 m/min to 0.2 m/min by changing the varnish (1) to the varnish (3), and an optical film 3 having a thickness of 79 μm was obtained.

Example 4: production of optical film (4)

An optical film 4 having a thickness of 79 μm was obtained in the same manner as in the method for producing an optical film 1 except that the varnish (1) was changed to the varnish (4), the linear velocity was changed from 0.4 m/min to 0.2 m/min, and the heating conditions of the coating film were changed to 8 minutes at 90 ℃, 10 minutes at 100 ℃, 8 minutes at 90 ℃ and 8 minutes at 80 ℃ in this order.

Comparative example 1

As the optical film 5, a polyimide film (UPILEX, manufactured by Yu Xingzhi Co., ltd., thickness: 50 μm) was prepared.

The total light transmittance Tt (%), the diffuse light transmittance Td (%), the scattered light ratio Ts (%), the tensile elastic modulus (MPa), the absolute values Δts (%) of the differences between the scattered light ratios before and after the bending resistance test, YI, the folding endurance (secondary) and the visibility evaluation results of the optical films obtained in examples 1 to 4 and comparative example 1 are shown in table 2.

TABLE 2

As shown in table 2, it was confirmed that the optical films of examples 1 to 4, in which the scattered light ratio (Ts) was in the range of 0 to 0.35%, were excellent in the visibility evaluation as compared with the optical film of comparative example 1 in which the scattered light ratio was more than 0.35%. In addition, it was also confirmed that the optical films of examples 1 to 4 had excellent tensile elastic modulus and folding endurance, and low yellowness. Therefore, the optical films of examples 1 to 4 were excellent in visibility in the wide-angle direction, and also had excellent tensile elastic modulus and the like.

Claims

1. An optical film comprising a polyamideimide resin, the optical film satisfying formula (1):

0≤Ts≤0.35 (1)

in the formula (1), ts represents a scattered light ratio (%), which is defined as ts=td/tt×100, td and Tt represent a diffuse light transmittance (%) and a total light transmittance (%) measured in accordance with JIS K7136, respectively,

the polyamide-imide resin has at least a repeating structural unit represented by the formula (10) and a repeating structural unit represented by the formula (13),

The content of the repeating structural unit represented by the formula (13) is 0.1 to 6.0 mol based on 1 mol of the repeating structural unit represented by the formula (10),

in the formula (10), G is a 4-valent organic group, A is a 2-valent organic group,

in the formula (13), G ³ An organic group having a valence of 2, A ³ An organic group having a valence of 2.

2. The optical film according to claim 1, having a tensile elastic modulus at 80 ℃ of 4,000 to 9,000mpa.

3. The optical film according to claim 1 or 2, wherein an absolute value Δts of a difference between the scattered light ratios before and after the bending resistance test according to JIS K5600-5-1 is 0.15% or less.

4. The optical film according to claim 1 or 2, which has a thickness of 10 to 150 μm.

5. The optical film according to claim 1 or 2, wherein the content of the filler is 5 mass% or less with respect to the mass of the optical film.

6. The optical film according to claim 1 or 2, having a hard coating layer on at least one side.

7. The optical film according to claim 6, wherein the hard coat layer has a thickness of 3 to 30 μm.

8. A flexible display device comprising the optical film according to any one of claims 1 to 7.

9. The flexible display device of claim 8, further comprising a touch sensor.

10. The flexible display device according to claim 8 or 9, further comprising a polarizing plate.