TW202022020A - Optical film having the image to be visually recognized with high sharpness without distortion - Google Patents

Abstract

The present invention provides an optical film having excellent visibility in a wide-angle direction. An optical film of the present invention includes at least one resin selected from the group consisting of a polyimide-based resin and a polyamide-based resins, and satisfies formula (1): 0 ≤ Ts ≤ 0.35, wherein in formula (1), Ts represents the scattered light ratio (%) and 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 K-7136, respectively.

Description

Optical film

The present invention relates to an optical film used as a front panel of a flexible display device, etc., and a flexible display device provided with the optical film.

Previously, glass has been used as a material for display components such as solar cells or image display devices. However, for the recent requirements for miniaturization, thinning, weight reduction and flexibility, there are not enough materials. Therefore, as an alternative to glass, various films have been studied. As such a film, for example, there is an optical film containing a polyimide-based resin (for example, Patent Document 1). [Prior Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open No. 2009-215412

[Problems to be solved by the invention]

When an 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 where the image display surface is curved. Therefore, it is required to be superior in the wide-angle direction compared with a non-flexible image display surface The visibility. However, according to the research of the present inventors, it is known that the conventional optical film containing polyimide-based resin sometimes cannot sufficiently satisfy the visibility in the wide-angle direction.

Therefore, the object of the present invention is to provide an optical film having excellent visibility in a wide-angle direction, and a flexible display device provided with the optical film. [Technical means to solve the problem]

In order to solve the above-mentioned problems, the inventors conducted intensive research and found that in an optical film containing at least one resin selected from the group consisting of polyimide resins and polyimide resins, if the scattered light ratio In order to specify the range, the above-mentioned problems can be solved, thereby completing the present invention. That is, the present invention includes the following aspects.

[1] An optical film, which It contains at least one resin selected from the group consisting of polyimide resins and polyimide resins, and satisfies formula (1): 0≦Ts≦0.35 (1) [In formula (1), Ts represents the scattered light ratio (%), defined as Ts=Td/Tt×100, Td and Tt respectively represent the diffuse light transmittance (%) and total light transmittance measured according to JIS K 7136 rate(%)]. [2] The optical film as described in [1], which has a tensile modulus of elasticity at 80°C of 4,000 to 9,000 MPa. [3] The optical film as described in [1] or [2], wherein the absolute value ΔTs of the difference between the scattered light ratios before and after the bending resistance test according to JIS K 5600-5-1 is 0.15% or less. [4] The optical film as described in any one of [1] to [3], which has a thickness of 10 to 150 μm. [5] The optical film as described in any one of [1] to [4], wherein the content of the filler is 5% by mass or less relative 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 μm. [8] A flexible display device comprising the optical film as described in any one of [1] to [7]. [9] The flexible display device as described in [8], which further includes a touch sensor. [10] The flexible display device as described in [8] or [9], which further includes a polarizing plate. [Effect of invention]

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

[Optical Film] The optical film of the present invention contains at least one resin selected from the group consisting of transparent polyimide resins and polyamide resins, and satisfies formula (1): 0≦Ts≦0.35 (1) [In formula (1), Ts represents the scattered light ratio (%), defined as Ts=Td/Tt×100, Td and Tt respectively represent the diffuse light transmittance (%) and total light transmittance measured according to JIS K 7136 rate(%)]. Furthermore, the scattered light ratio may be the scattered light ratio within the thickness range of the following optical film.

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

The scattered light ratio of the optical film of the present invention is as small as 0-0.35%, so the visibility in the wide-angle direction is excellent. Therefore, when the optical film of the present invention is applied to an image display device, even if the optical film is viewed from an oblique direction, the image reflected on the display portion can be effectively prevented from being deformed or the image is blurred. Since the optical film of the present invention has such characteristics, when it is applied to a flexible display, even if an image is displayed in a state where the image display surface is curved, it can be visualized with higher definition. In this specification, the visibility refers to the ease of visibility when visually observing the display part of an image display device using an optical film, and for example, means the characteristic that can suppress the deformation of the image reflected on the display part or the phenomenon of blurring of the image. In addition, in this specification, the "wide-angle direction" refers to all angular directions with respect to the plane of the optical film, and particularly refers to the oblique direction with respect to the plane of the optical film.

In the formula (1), the diffuse light transmittance (Td) can be measured using a spectrophotometer in accordance with JIS K 7136, for example, it can be measured by the method described in the examples. In addition, the total light transmittance (Tt) can be measured using a haze meter in accordance with JIS K 7136, for example, it can be measured by the method described in the examples.

In the optical film of the present invention, the scattered light ratio is preferably 0.30% or less, more preferably 0.25% or less, further preferably 0.20% or less, particularly preferably 0.15% or less, and most preferably 0.10% or less. If the scattered light ratio is equal to or less than the above upper limit, the visibility in the wide-angle direction can be easily improved. The lower limit of the scattered light ratio is 0 or more. Furthermore, by appropriately adjusting the composition of the optical film, such as the type or composition ratio of the repetitive structure of the resin contained in the optical film, and the type or content of additives such as ultraviolet absorbers contained in the optical film, the optical film The thickness or the manufacturing conditions of the optical film, such as the type of varnish solvent, drying temperature, and drying time, can be adjusted to satisfy formula (1). Especially in the optical film forming step, if it is performed under the following drying conditions, it is easy to adjust 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. If the total light transmittance is more than the above lower limit, the transparency of the optical film becomes good, and it is easy to exhibit excellent visibility when applied to an image display device. In addition, the upper limit of the total light transmittance is usually 100% or less. Furthermore, the total light transmittance can be the total light transmittance (Tt) within the thickness range of the following optical film. If the total light transmittance is in the above range, for example, when incorporated into a display device, there is a tendency to obtain a bright display even if the amount of light from the backlight is reduced, which can contribute to energy saving.

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, still more preferably 0.25 or less, and particularly preferably 0.20 or less. If the diffused light transmittance (Td) is equal to or less than the above upper limit, the ratio of diffused light becomes smaller, and the visibility in the wide-angle direction is easily improved. In addition, the lower limit of the diffuse light transmittance (Td) is usually 0.01 or more. Furthermore, the diffuse light transmittance may be the diffuse light transmittance (Td) within the thickness range of the following optical film.

In a preferred embodiment of the present invention, the optical film of the present invention can also have an excellent tensile modulus in addition to excellent visibility in the wide-angle direction. The tensile elastic modulus of the optical film at 80° C. is preferably 4,000 MPa or more, more preferably 4,500 MPa or more, particularly preferably 5,000 MPa or more, and preferably 9,000 MPa or less, and more preferably 8,500 MPa or less. If the tensile modulus of elasticity is within the above range, the optical film tends to be less prone to dent defects and easily exhibit bending resistance. In addition, the tensile modulus of the optical film can be measured using a tensile tester in accordance with JIS K 7127, for example, it can be measured by the method described in the examples.

In a preferred embodiment of the present invention, the optical film of the present invention has excellent folding resistance. In the optical film of the present invention, the number of folds in the MIT flex fatigue test according to ASTM standard D2176-16 is preferably 200,000 or more, more preferably 300,000 or more, further preferably 500,000 or more, and more preferably 700,000 times or more. If the number of times of bending resistance is more than the above-mentioned lower limit, cracks, cracks, etc. are less likely to occur even when bent. Furthermore, the MIT flexural fatigue test can be measured by, for example, the method described in the examples.

In a preferred embodiment of the present invention, the optical film of the present invention has excellent bending resistance. Therefore, even if the bending is repeated, the optical characteristics can be maintained. In the optical film of the present invention, the absolute value ΔTs (%) of the difference in the scattered light ratio before and after the bending resistance test according to JIS K 5600-5-1 is preferably 1.4% or less, more preferably 1.2% or less, and further Preferably it is 1.0% or less, more preferably 0.5% or less, particularly preferably 0.1% or less, especially more preferably 0.05% or less, and most preferably 0.02% or less. If ΔTs is in the above range, when applied to an image display device such as a flexible display, it is easy to maintain excellent visibility in the wide-angle direction even if it is repeatedly bent. In addition, the bending resistance test can be measured by a bending tester in accordance with JIS K 5600-5-1, for example, it can be measured by the method described in the examples. In this specification, the so-called optical properties, for example, include scattered light ratio, diffuse light transmittance, total light transmittance, yellowness (YI), and haze that can be optically evaluated. The so-called "improvement of optical properties" means, for example, It means that the ratio of scattered light becomes lower, the diffuse light transmittance becomes lower, the total light transmittance becomes higher, the yellowness becomes lower, or the haze becomes lower.

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 Below 0.2%. If the haze of the optical film is less than or equal to the above upper limit, the transparency becomes good, and for example, when applied to an image display device, it is easy to exhibit excellent visibility. In addition, the lower limit of the haze is usually 0.01% or more. Furthermore, the haze can be measured using a haze computer in accordance with JIS K 7136:2000.

The yellowness (YI) of the optical film of the present invention is preferably 4.0 or less, more preferably 3.0 or less, still more preferably 2.5 or less, and particularly preferably 2.0 or less. If the yellowness of the optical film is less than the above upper limit, the transparency becomes good. For example, when it is applied to an image display device, it is easy to exhibit excellent visibility. In addition, the yellowness is usually -5 or higher, preferably -2 or higher. Furthermore, the yellowness (YI) can be measured in accordance with JIS K 7373: 2006, using an ultraviolet-visible-near-infrared spectrophotometer to measure the transmittance of light from 300 to 800 nm to obtain the tristimulus values (X, Y, Z), It is calculated based on the equation of YI=100×(1.2769X-1.0592Z)/Y.

The thickness of the optical film of the present invention is appropriately adjusted according to the application, and is preferably 10 μm or more, more preferably 20 μm or more, still more preferably 25 μm or more, particularly preferably 30 μm or more, and preferably 150 μm or less, It is more preferably 100 μm or less, and still more preferably 85 μm or less. If the thickness of the optical film is in the above range, it is advantageous from the viewpoint of bending resistance and visibility. The thickness of an optical film can be measured with a film thickness meter etc., for example, it can measure by the method described in an Example.

＜Resin＞ The optical film of the present invention includes at least one resin selected from the group consisting of polyimide resins and polyimide resins. The so-called polyimide-based resin refers to a resin selected from the group consisting of a repeating structural unit containing an imine group (hereinafter, sometimes referred to as polyimide resin), and a resin containing both an imide group and an amido group At least one type of resin in the group consisting of the resin of the repeating structural unit (hereinafter, sometimes referred to as polyimide resin). In addition, the term "polyamide-based resin" means a resin containing a repeating structural unit containing an amide group.

The polyimide resin preferably has a repeating structural unit represented by formula (10). Here, G is a tetravalent organic group, and A is a divalent organic group. The polyimide-based resin may include two or more repeating structural units represented by formula (10) different in G and/or A. [Chem 1]

Polyimide-based resins can include at least one selected from the group consisting of repeating structural units represented by formula (11), formula (12) and formula (13) within the range of various physical properties of the non-destructive optical film. Repeating structural units.

[Chem 2]

In formula (10) and formula (11), G and G ¹ are each independently a tetravalent organic group, preferably an organic group that can be substituted with a hydrocarbon group or a fluorine-substituted hydrocarbon group. As G and G ¹ , formula (20), formula (21), formula (22), formula (23), formula (24), formula (25), formula (26), formula (27), formula ( 28) or a group represented by formula (29) and a tetravalent chain hydrocarbon group with 6 or less carbon atoms. In terms of easily suppressing the yellowness (YI value) of the optical film, the formula (20), formula (21), formula (22), formula (23), formula (24), and formula (25) are preferred among them , Formula (26) or Formula (27).

[Chemical 3]

In formulas (20) to (29), * represents a bonding 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 by a fluorine atom, and a specific example includes a phenylene group.

In the formula (12), G ² is a trivalent organic group, preferably an organic group that can be substituted with a hydrocarbon group or a fluorine-substituted hydrocarbon group. As G ² , formula (20), formula (21), formula (22), formula (23), formula (24), formula (25), formula (26), formula (27), and formula (28) can be exemplified Or any one of the bonding bonds of the group represented by formula (29) is substituted with a hydrogen atom group and a trivalent chain hydrocarbon group with 6 or less carbon atoms.

In the formula (13), G ³ is a divalent organic group, preferably an organic group that can be substituted with a hydrocarbon group or a fluorine-substituted hydrocarbon group. As G ³ , formula (20), formula (21), formula (22), formula (23), formula (24), formula (25), formula (26), formula (27), and formula (28) can be exemplified Or two non-adjacent bonding bonds of the group represented by the formula (29) are substituted with hydrogen atoms and a chain hydrocarbon group with 6 or less carbon atoms.

In formulas (10) to (13), A, A ¹ , A ² and A ³ are each independently a divalent organic group, preferably an organic group that can be substituted with a hydrocarbon group or a fluorine-substituted hydrocarbon group. Examples of A, A ¹ , A ² and A ^{3 include} : formula (30), formula (31), formula (32), formula (33), formula (34), formula (35), formula (36), A group represented by formula (37) or formula (38); a group substituted with a methyl group, a fluoro group, a chloro group, or a trifluoromethyl group; and a chain hydrocarbon group having 6 or less carbon atoms.

[Chem 4]

In formulas (30) to (38), * represents a bonding bond, Z ¹ , Z ² and Z ³ each independently represent 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-. An example is that Z ¹ and Z ³ are -O-, and Z ² is -CH ₂ -, -C(CH ₃ ) ₂ -, -C(CF ₃ ) ₂ -or -SO ₂ -. The bonding position of Z ¹ and Z ² to each ring, and the bonding position of Z ² and Z ³ to each ring are preferably meta or para with respect to each ring.

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

In one embodiment of the present invention, the polyimide-based resin is made of diamine and tetracarboxylic acid compounds (tetracarboxylic acid compound related products such as chlorine compounds and tetracarboxylic dianhydrides), and optionally dicarboxylic acid compounds Condensation-type polymers obtained by the reaction (condensation) of acid compounds (dicarboxylic acid compound related products such as chlorinated compounds), tricarboxylic acid compounds (tricarboxylic acid compound related products such as chlorinated chloride compounds and tricarboxylic anhydrides), etc. The repeating structural unit represented by formula (10) or formula (11) is usually derived from a diamine and a tetracarboxylic acid compound. The repeating structural unit represented by formula (12) is usually derived from diamine and tricarboxylic acid compounds. The repeating structural unit represented by the formula (13) is usually derived from a diamine and a dicarboxylic acid compound.

In one embodiment of the present invention, the polyamide resin is a condensation polymer obtained by reacting (condensation) a diamine and a dicarboxylic acid compound. That is, the repeating structural unit represented by formula (13) is usually 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 dianhydride. The tetracarboxylic acid compound may be used alone or in combination of two or more kinds. In addition to the dianhydride, the tetracarboxylic acid compound may also be a tetracarboxylic acid compound related product such as a chlorine compound.

Specific examples of aromatic tetracarboxylic dianhydrides include: 4,4'-oxydiphthalic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, 2 ,2',3,3'-benzophenonetetracarboxylic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 2,2',3,3'-biphenyltetracarboxylic dianhydride Carboxylic dianhydride, 3,3',4,4'-diphenyl tetracarboxylic dianhydride, 2,2-bis(3,4-dicarboxyphenyl)propane dianhydride, 2,2-bis( 2,3-Dicarboxyphenyl)propane dianhydride, 2,2-bis(3,4-dicarboxyphenoxyphenyl)propane dianhydride, 4,4'-(hexafluoroisopropylidene) dio Phthalic acid dianhydride (6FDA), 1,2-bis(2,3-dicarboxyphenyl)ethane dianhydride, 1,1-bis(2,3-dicarboxyphenyl)ethane dianhydride, 1 ,2-bis(3,4-dicarboxyphenyl)ethane dianhydride, 1,1-bis(3,4-dicarboxyphenyl)ethane dianhydride, bis(3,4-dicarboxyphenyl) Methane dianhydride, bis(2,3-dicarboxyphenyl) methane dianhydride and 4,4'-(terephthalic acid) diphthalic anhydride and 4,4'-(isophthalic acid) ) Diphthalic dianhydride. These can be used individually or in combination of 2 or more types.

Examples of the aliphatic tetracarboxylic dianhydride include cyclic or acyclic aliphatic tetracarboxylic dianhydrides. The so-called cyclic aliphatic tetracarboxylic dianhydride is a tetracarboxylic dianhydride having an alicyclic hydrocarbon structure. Specific examples include: 1,2,4,5-cyclohexane tetracarboxylic dianhydride, 1 , 2,3,4-cyclobutane tetracarboxylic dianhydride, 1,2,3,4-cyclopentane tetracarboxylic dianhydride and other cycloalkane tetracarboxylic dianhydrides, bicyclic [2.2.2]-7 -Octene-2,3,5,6-tetracarboxylic dianhydride, dicyclohexyl-3,3',4,4'-tetracarboxylic dianhydride and their positional isomers. These can be used individually or in combination of 2 or more types. Specific examples of acyclic aliphatic tetracarboxylic dianhydride include 1,2,3,4-butane tetracarboxylic dianhydride, 1,2,3,4-pentane tetracarboxylic dianhydride, etc. These can be used individually or in combination of 2 or more types. Moreover, it is also possible to use a combination of cyclic aliphatic tetracarboxylic dianhydride and acyclic aliphatic tetracarboxylic dianhydride.

Among the above-mentioned tetracarboxylic dianhydrides, 1,2,4,5-cyclohexanetetracarboxylic dianhydride is preferred from the viewpoint of easy improvement in visibility, elastic modulus, and bending resistance, and easy reduction in colorability. Anhydride, bicyclo[2.2.2]-7-octene-2,3,5,6-tetracarboxylic dianhydride and 4,4'-(hexafluoroisopropylidene)diphthalic dianhydride, And mixtures of these. Moreover, as the tetracarboxylic acid, the water adduct of the anhydride of the above-mentioned tetracarboxylic acid compound can also be used.

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

Examples of the dicarboxylic acid compound include aromatic dicarboxylic acids, aliphatic dicarboxylic acids, and related chlorinated compounds, acid anhydrides, and the like, and two or more of them may be used in combination. Specific examples thereof include: Terephthaloyl Chloride (TPC); Meta-phthaloyl Chloride; Naphthalene Dimethyl Chloride; 4,4'-Biphenyl Dimethyl Chloride; 3 ,3'-Biphenyl Dimethyl Chloride; 4,4'-Oxybis(Benzyl Chloride) (OBBC); Dicarboxylic acid compound of chain hydrocarbon with carbon number less than 8 and 2 benzoic acid with single bond , -CH ₂ -, -C(CH ₃ ) ₂ -, -C(CF ₃ ) ₂ -, -SO ₂ -or phenylene linking compound. If these dicarboxylic acid compounds are used, it is preferable from the viewpoint that visibility, elastic modulus, and bending resistance are easily improved, and colorability is easily reduced.

Examples of diamines include aliphatic diamines, aromatic diamines, or mixtures of these. Furthermore, in this embodiment, the so-called "aromatic diamine" means a diamine in which an amine group is directly bonded to an aromatic ring, and a part of its structure may include an aliphatic group or other substituents. The aromatic ring may be a monocyclic ring or a condensed ring, and a benzene ring, a naphthalene ring, an anthracene ring, and a sulphur ring may be exemplified, but it is not limited to these. Among them, the aromatic ring is preferably a benzene ring. In addition, the term "aliphatic diamine" refers to a diamine in which an amine group is directly bonded to an aliphatic group, and an aromatic ring or other substituents may be included in a part of the structure.

As aliphatic diamines, for example, acyclic aliphatic diamines such as hexamethylene diamine, 1,3-bis(aminomethyl)cyclohexane, 1,4-bis(aminomethyl)cyclohexane, etc. Cycloaliphatic diamines such as alkanes, noralkanediamines, 4,4'-diaminodicyclohexylmethane, etc. These can be used individually or in combination of 2 or more types.

Examples of aromatic diamines include p-phenylenediamine, m-phenylenediamine, 2,4-toluenediamine, m-xylylenediamine, p-xylylenediamine, 1,5-diaminonaphthalene, 2 ,6-Diaminonaphthalene and other aromatic diamines with one aromatic ring; 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylpropane, 4,4'- Diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 3,3'-diaminodiphenyl ether, 4,4'-diaminodiphenyl ether, 3,4'-di Amino diphenyl benzene, 3,3'-diamino diphenyl benzene, 1,4-bis(4-aminophenoxy)benzene, 1,3-bis(4-aminophenoxy) Benzene, 4,4'-diaminodiphenyl ash, bis[4-(4-aminophenoxy)phenyl] ash, bis[4-(3-aminophenoxy)phenyl] ash , 2,2-bis[4-(4-aminophenoxy)phenyl]propane, 2,2-bis[4-(3-aminophenoxy)phenyl]propane, 2,2'- Dimethylbenzidine, 2,2'-bis(trifluoromethyl)benzidine (2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (TFMB)), 4 ,4'-bis(4-aminophenoxy)biphenyl, 9,9-bis(4-aminophenyl)pyridium, 9,9-bis(4-amino-3-methylphenyl) Tungsten, 9,9-bis(4-amino-3-chlorophenyl) tungsten, 9,9-bis(4-amino-3-fluorophenyl) tungsten, etc. with more than 2 aromatic rings amine. These can be used individually or in combination of 2 or more types.

Among the above-mentioned diamines, it is preferable to use one selected from the group consisting of aromatic diamines having a biphenyl structure from the viewpoint of easily improving visibility, elastic modulus, and bending resistance and easily reducing colorability. More than one kind. More preferably, it is selected from 2,2'-dimethylbenzidine, 2,2'-bis(trifluoromethyl)benzidine, 4,4'-bis(4-aminophenoxy)biphenyl And at least one of the group consisting of 4,4'-diaminodiphenyl ether, and it is more preferable to use 2,2'-bis(trifluoromethyl)benzidine.

The polyimide-based resin is obtained by mixing the above-mentioned diamine, tetracarboxylic acid compound, tricarboxylic acid compound, dicarboxylic acid compound and other raw materials by conventional methods, such as stirring, etc., to obtain an intermediate It is obtained by imidization in the presence of an imidization catalyst and optionally a dehydrating agent. The polyamide-based resin is obtained by mixing each raw material such as the diamine and the dicarboxylic acid compound by a conventional method, for example, a method such as stirring.

There are no particular limitations on the imidization catalyst used in the imidization step, and examples include aliphatic amines such as tripropylamine, dibutylpropylamine, and ethyldibutylamine; N-ethylpiperidine , N-propylpiperidine, N-butylpyrrolidine, N-butylpiperidine, and N-propyl hexahydroazepine and other alicyclic amines (monocyclic); azabicyclo[2.2.1] Alicyclic amines (polycyclic) such as heptane, azabicyclo[3.2.1]octane, azabicyclo[2.2.2]octane, and azabicyclo[3.2.2]nonane; and 2-methylpyridine, 3-methylpyridine, 4-methylpyridine, 2-ethylpyridine, 3-ethylpyridine, 4-ethylpyridine, 2,4-lutidine, 2,4,6 -Aromatic amines such as 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 steps of mixing the raw materials and the imidization, the reaction temperature is not particularly limited, and is, for example, 15 to 350°C, preferably 20 to 100°C. The reaction time is also not particularly limited, and is, for example, about 10 minutes to 10 hours. If necessary, the reaction can be carried out under an inert environment or under reduced pressure. In addition, the reaction can be carried out in a solvent, and examples of the solvent include those exemplified as a solvent for preparing a varnish. After the reaction, the polyimide resin or polyimide resin is refined. As a purification method, for example, a method of adding a poor solvent to the reaction solution, precipitating the resin by a reprecipitation method, drying, taking out the precipitate, and washing the precipitate with a solvent such as methanol and drying if necessary Wait. In addition, the production of the polyimide-based resin can also refer to, for example, the production method described in Japanese Patent Laid-Open No. 2006-199945 or Japanese Patent Laid-Open No. 2008-163107. In addition, a commercially available product may also be used for the polyimide-based resin, and specific examples thereof include Neopulim (registered trademark) manufactured by Mitsubishi Gas Chemical Co., Ltd., KPI-MX300F manufactured by Kawamura Sangyo Co., Ltd., and the like.

In one embodiment of the present invention, in the polyimide imine resin, the content of the structural unit represented by formula (13) relative to 1 mol of the structural unit represented by formula (10) 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, and preferably 6.0 mol or less, more preferably 5.0 mol or less, and still more preferably Below 4.5 mol. If the content of the structural unit represented by the formula (13) is in the above range, the visibility in the wide-angle direction, the elastic modulus, and the bending resistance are easily improved.

The weight average molecular weight of the polyimide resin or polyimide resin is preferably 200,000 or more, more preferably 250,000 or more, still more preferably 300,000 or more, preferably 600,000 or less, more preferably 550,000 or less, and more Best is 500,000. If the weight average molecular weight of the polyimide-based resin or the polyimide-based resin is more than the above lower limit, it is easy to improve the elastic modulus and the bending resistance of the optical film. In addition, if the weight average molecular weight is less than or equal to the above upper limit, the viscosity of the varnish is easily reduced, and the elongation and processability of the optical film are easily improved. In addition, the weight average molecular weight can be measured by gel permeation chromatography (GPC), can be obtained by standard polystyrene conversion, and can be calculated by, for example, the method described in the examples.

In a preferred embodiment of the present invention, the polyimide-based resin or polyimide-based resin contained in the optical film of the present invention may include, for example, halogen such as fluorine atoms that can be introduced by the above-mentioned fluorine-containing substituents. atom. When the polyimide resin or the polyimide resin contains halogen atoms, it is easy to increase the elastic modulus of the optical film and reduce the yellowness (YI value). If the elastic modulus of the optical film is high, it is easy to suppress the occurrence of damage and wrinkles of the film, and if the yellowness of the optical film is low, it is easy to improve the transparency and visibility of the film. The halogen atom is preferably a fluorine atom. As a preferable fluorine-containing substituent for making a polyimide resin or polyimide resin contain a fluorine atom, a fluorine group and a trifluoromethyl group are mentioned, for example.

The content of the halogen atom in the polyimide resin or polyimide resin is based on the mass of the polyimide resin or polyimide resin, preferably 1-40% by mass, more preferably 5~ 40% by mass, more preferably 5 to 30% by mass. If the content of halogen atoms is more than the above lower limit, the elastic modulus of the optical film is further increased, the water absorption rate is reduced, the yellowness (YI value) is further reduced, and transparency and visibility are easily improved. If the content of halogen atoms is equal to or less than the above upper limit, synthesis becomes easy.

The imidization rate of the polyimide resin in the optical film is preferably 90% or more, more preferably 95% or more, and still more preferably 98% or more. From the viewpoint of easy improvement of the flatness of the optical film and the visibility in the wide-angle direction, the imidization rate is preferably at least the above lower limit. In addition, the upper limit of the imidization rate is 100% or less. Furthermore, the imidization rate can be obtained by IR (Infrared Radiation) method, NMR (nuclear magnetic resonance) method, etc., for example, by the method described in the examples.

In one embodiment of the present invention, the content of the polyimide resin and/or polyimide resin in the optical film relative to the mass of the optical film is preferably 40% by mass or more, more preferably 50% by mass Above, it is more preferably 70% by mass or more, more preferably 80% by mass or more, and most preferably 90% by mass or more. The content of the polyimide-based resin and/or the polyimide-based resin is more than the above lower limit from the viewpoint of visibility in the wide-angle direction, elastic modulus, and bending resistance. Furthermore, the content of the polyimide resin and/or the polyimide resin in the optical film is usually 100% by mass or less with respect to the mass of the optical film.

As the resin contained in the optical film, two or more types of polyimide-based resins or two or more types of polyimide-based resins may be used, or a combination of polyimide-based resins and polyimide-based resins may be used. In order to obtain an optical film with a low scattered light ratio, it is preferable to coat a varnish with a specific solid content concentration and viscosity on the substrate in the following coating step to form a uniform coating film. In an embodiment of the present invention, it is preferable to use two or more types of polyimide resins or polyamide resins, for example, two or more types of polyimide resins, and two or more types of polyamide resins. Type resin, or a combination of one or more polyimide-based resins and one or more polyimide-based resins, etc. It is especially preferable to use two or more polyimides with different weight average molecular weights Series resin or polyamide resin. In the following coating steps, if this resin is included in the varnish, the solid content and viscosity of the varnish can be easily adjusted to a specific range, so a uniform coating film can be formed, and the obtained optical The film is adjusted to satisfy equation (1).

In a preferred embodiment of the present invention, two or more polyimide resins or polyimide resins having mutually different weight average molecular weights, and at least one polyimide resin or polyimide resin The weight average molecular weight of the amine resin is 250,000 to 500,000, and the weight average molecular weight of at least one polyimide resin or polyamide resin is 200,000 to 450,000. Furthermore, in a more preferable embodiment of the present invention, there are two kinds of polyimide resins or polyamide resins having mutually different weight average molecular weights, and one polyimide resin or polyamide resin The weight average molecular weight of the resin is 250,000 to 500,000, and the weight average molecular weight of another polyimide resin or polyamide resin is 200,000 to 450,000. In the following coating steps, if this resin is included in the varnish, the solid content and viscosity of the varnish can be easily adjusted to a specific range, so a uniform coating film can be formed, and the obtained optical The film is adjusted to satisfy equation (1). In addition, the mass ratio of a polyimide resin or polyimide resin to another polyimide resin or polyimide resin (the former/the latter) can be based on the type of resin or the solid state of the varnish required The concentration and viscosity of the substance components are appropriately selected, for example, 5/95 to 95/5.

＜Additives＞ The optical film of the present invention may further contain an ultraviolet absorber. For example, three-type ultraviolet absorbers, benzophenone-type ultraviolet absorbers, benzotriazole-type ultraviolet absorbers, benzoate-type ultraviolet absorbers, cyanoacrylate-type ultraviolet absorbers, and the like can be cited. These can be used individually or in combination of 2 or more types. As a preferable commercially available ultraviolet absorber, for example, Sumisorb (registered trademark) 340 manufactured by Sumika Chemtex Co., Ltd., Adekastab (registered trademark) LA-31 manufactured by ADEKA Co., Ltd., and BASF Japan Co., Ltd. The TINUVIN (registered trademark) 1577 and so on. If the ultraviolet absorber is contained, the deterioration of the resin in the optical film can be suppressed, so it is easy to improve the optical properties of the optical film. The content of the ultraviolet absorber is preferably 1-10% by mass, more preferably 3-6% by mass relative to the mass of the optical film of the present invention. If the content of the ultraviolet absorber is in the above range, it is easy to further improve the optical properties of the optical film.

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

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 as described above, or may be a laminate, and the optical film of the present invention may be used directly, or may be further used as a laminate with other films. In addition, when the optical film is a laminate, all layers including all layers laminated on one or both sides of the optical film are called optical films.

When the optical film of the present invention is a laminate, it is preferable to have one or more functional layers on at least one surface of the optical film. As the functional layer, for example, an ultraviolet absorbing layer, a hard coat layer, an undercoat layer, a gas barrier layer, an adhesion layer, a hue adjustment layer, a refractive index adjustment layer, etc. can be cited. The functional layer can be used alone or in combination of two or more.

The ultraviolet absorbing layer is a layer having ultraviolet absorbing function, and includes, for example, a main material selected from ultraviolet curable transparent resin, electron beam curable transparent resin, and thermosetting transparent resin, and an ultraviolet absorber dispersed in the main material.

The adhesive layer is a layer with adhesive function, and has the function of bonding the optical film to other components. As the forming material of the adhesive layer, generally known ones can be used. For example, a thermosetting resin composition or a photocuring resin composition can be used. In this case, the thermosetting resin composition or the photocurable resin composition can be polymerized and cured by supplying energy afterwards.

The adhesive layer may be a layer called Pressure Sensitive Adhesive (PSA) that adheres to an object by pressing. Pressure-sensitive adhesives can be used as "substances that have adhesiveness at room temperature and adhere to the material to be adhered with a lighter pressure" (JIS K 6800), and can also be used as an "incorporating specific ingredients into the protection The film (microcapsule) is a capsule-type adhesive agent that can maintain stability before breaking the film by an appropriate method (pressure, heat, etc.)" (JIS K 6800).

The hue adjustment layer is a layer having a hue adjustment function, and is a layer that can adjust the optical laminate to the target hue. The hue adjusting layer is, for example, a layer containing resin and coloring agent. Examples of the colorant include inorganic pigments such as titanium oxide, zinc oxide, red lead, titanyl calcined pigments, ultramarine blue, cobalt aluminate, and carbon black; azo compounds, quinacridone compounds, anthracene Organic pigments such as quinone compounds, perylene compounds, isoindolinone compounds, phthalocyanine compounds, quinophthalone compounds, Shihlin compounds, and diketopyrrolopyrrole compounds; barium sulfate, and calcium carbonate Extender pigments; and dyes such as basic dyes, acid dyes, and mordant dyes.

The refractive index adjustment layer is a layer having a refractive index adjustment function, and is a layer that has a refractive index different from, for example, a single-layer optical film and can give a predetermined refractive index to the optical film. The refractive index adjustment layer may be, for example, a resin layer containing appropriately selected resin and further containing a pigment as appropriate, or a metal thin film. Examples of pigments for adjusting the refractive index include silica, alumina, antimony oxide, tin oxide, titanium oxide, zirconium oxide, and tantalum oxide. The average primary particle size of the pigment may be 0.1 μm or less. By setting the average primary particle size of the pigment to 0.1 μm or less, the random reflection of the light passing through the refractive index adjustment layer can be prevented, and the decrease in transparency can be prevented. Examples of metals used for the refractive index adjustment layer include titanium oxide, tantalum oxide, zirconium oxide, zinc oxide, tin oxide, silicon oxide, indium oxide, titanium oxynitride, titanium nitride, silicon oxynitride, silicon nitride, etc. Metal oxide or metal nitride.

In a preferred embodiment of the present invention, the optical film has a hard coating on at least one side (single side or both sides). In the case of having hard coats on both sides, the components contained in the two hard coats 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 them, from the viewpoint of suppressing the decrease in the visibility of the optical film in the wide-angle direction and improving the bending resistance, a hard coat of acrylic, urethane, and combinations thereof can be preferably used Floor. 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. As a curable compound, a polyfunctional (meth)acrylate type compound is mentioned, for example. The so-called polyfunctional (meth)acrylate compound refers to a compound having at least two (meth)acrylic groups in the molecule.

As the polyfunctional (meth)acrylate-based compound, for example, ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylic acid Ester, neopentyl glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, trimethylolethane tri(meth)acrylate, tetramethylolmethane tri(meth)acrylate ) Acrylate, tetramethylolmethane tetra(meth)acrylate, pentaglycerol tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, glycerol tri(meth)acrylate ) Acrylate, dipentaerythritol tri(meth)acrylate, dipentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, isocyanurate tri(( (Meth) acryloxyethyl) ester; a phosphazene-based (meth)acrylate compound with a (meth)acryloyl group introduced into the phosphazene ring of the phosphazene compound; by having at least 2 isoforms in the molecule A (meth)acrylate urethane compound obtained by the reaction of a polyisocyanate of a cyanate group and a polyol compound having at least one (meth)acrylic acid group and a hydroxyl group; by having at least two carboxylic acids in the molecule A polyester (meth)acrylate compound obtained by the reaction of a halide and a polyol compound having at least one (meth)acrylic acid group and a hydroxyl group; and the dimers, trimers, etc. of the above-mentioned compounds的oligomers and so on. These compounds are used individually or in mixture of two or more types.

In addition to the above-mentioned polyfunctional (meth)acrylate-based compound, the curable compound may contain a monofunctional (meth)acrylate-based compound. As the monofunctional (meth)acrylate compound, for example, hydroxyethyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, (methyl) ) Hydroxybutyl acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, glycidyl (meth)acrylate, etc. These compounds can be used alone or in mixture of two or more kinds. The content of the monofunctional (meth)acrylate compound is preferably 10% by mass or less when the solid content of the compound contained in the curable composition is 100% by mass. In addition, in this specification, the so-called solid content means all the components other than the solvent contained in the curable composition.

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

In addition to the polyfunctional (meth)acrylate compound and polymerizable oligomer, the curable composition forming the hard coat layer may also contain additives. Examples of additives include polymerization initiators, silica, leveling agents, and solvents. As a solvent, methyl ethyl ketone, polypropylene glycol monomethyl ether, etc. are mentioned, for example.

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

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

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

[Method of manufacturing optical film] The optical film of the present invention is not particularly limited. For example, it can be manufactured by a method including the following steps: (a) A step of preparing a liquid containing the above resin (hereinafter, sometimes referred to as a varnish) (a varnish preparation step); (b) The step of applying varnish to the substrate to form a coating film (coating step); and (c) The step of drying the applied liquid (coating film) to form an optical film (optical film forming step).

In the varnish preparation step, the varnish is prepared by dissolving the above-mentioned resin in a solvent, adding the above-mentioned ultraviolet absorber and the above-mentioned other additives as necessary, and stirring and mixing them to prepare a varnish.

The solvent used to prepare the varnish is not particularly limited as long as it can dissolve the above-mentioned resin. Examples of the solvent include: amide-based solvents such as N,N-dimethylacetamide (DMAc) and N,N-dimethylformamide; γ-butyrolactone (GBL), γ-pentyl Lactone-based solvents such as lactone; sulfur-containing solvents such as dimethyl sulfene, dimethyl sulfide, and cyclobutane; carbonate-based solvents such as ethylene carbonate and propylene carbonate; and combinations thereof (mixed Solvent). Among these, an amide-based solvent or a lactone-based solvent is preferable. These solvents can be used alone or in combination of two or more. In addition, the varnish may contain water, alcohol solvents, ketone solvents, acyclic ester solvents, ether solvents, and 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 coated on the substrate by a known coating method to form a coating film. As well-known coating methods, for example, roll coating methods such as wire bar coating, reverse coating, and gravure coating, die nozzle coating methods, comma coating methods, and die lip coating methods are mentioned. , Spin coating method, screen coating method, spray coating method, dipping method, spray method, casting method, etc.

As an example of the base material, SUS (Steel Use Stainless, stainless steel) plate can be cited for metal, and PET (polyethylene terephthalate) film, PEN (polyethylene naphthalate, polyethylene naphthalate) for resin Diester) film, other polyimide resin or polyamide resin film, cycloolefin polymer (COP) film, acrylic film, etc. Among them, from the viewpoint of excellent smoothness and heat resistance, a PET film, a COP film, etc. are preferred, and further, from the viewpoint of adhesion to an optical film and cost, a PET film is more preferred.

In the optical film forming step, the coating film is dried (referred to as the first drying), and after peeling from the substrate, the dried coating film is further dried (referred to as the second drying or post-baking treatment), thereby forming an optical membrane. The first drying may be carried out in an inert environment or under reduced pressure as needed. The first drying is preferably performed at a relatively low temperature and takes time. If it takes time to perform the first drying at a relatively low temperature, it is easy to make the scattered light ratio of the obtained optical film satisfy the formula (1).

Here, when the optical film of the present invention is manufactured industrially, compared with a laboratory-level manufacturing environment, the actual manufacturing environment is not conducive to obtaining a lower scattered light ratio Ts in most cases. As a result, it is difficult to improve The wide-angle visibility of the optical film. As mentioned above, it is better to spend time for the first drying at a relatively low temperature. However, when the first drying is performed at a laboratory level, the drying can be carried out in a closed dryer, so it is relatively difficult to cause external factors. The surface of the optical film is rough. On the other hand, when an optical film is manufactured industrially, for example, it is necessary to heat a wide area in the first drying. Therefore, an air blower may also be used during heating. As a result, the surface condition of the optical film tends to become rough, and it is difficult to reduce the scattered light ratio Ts of the optical film.

In the case of drying by heating, the temperature of the first drying is preferably 60-150°C, more preferably 60-140°C, and particularly considering the external factors described above when manufacturing optical films in industry. It is preferably 70 to 140°C. The first drying time is preferably 1 to 60 minutes, more preferably 5 to 40 minutes. In particular, in consideration of the above-mentioned external factors when manufacturing optical films industrially, it is preferable to implement it under the drying temperature condition of three stages or more. Multi-stage conditions can be implemented in each stage under the same or different temperature conditions and/or drying time. For example, drying can be carried out in 3-10 stages, preferably 3-8 stages. If the first drying is performed under a multi-stage condition of three or more stages, the obtained optical film easily satisfies the formula (1). In the case of a multi-stage condition with three or more stages, it is preferable that the temperature distribution of the first drying includes heating and cooling. That is, the first drying condition in the optical film forming step is more preferably a heating temperature condition in which the temperature distribution includes three or more stages of temperature increase and temperature decrease. As such a temperature distribution, if a four-stage case is taken as an example, the temperature of the first drying is 70 to 90°C (first temperature), 90 to 120°C (second temperature), and 80 to 120°C (second temperature). 3 temperature) and 80 to 100°C (the fourth temperature). In this example, the temperature of the first drying is increased from the first temperature to the second temperature, then the temperature is decreased from the second temperature to the third temperature, and then the temperature is decreased from the third temperature to the fourth temperature. Here, the time for the first drying is, for example, 5 to 15 minutes in each stage. It is preferable to perform the first drying with the residual amount of the solvent of the dried coating film relative to the mass of the dried coating film, preferably 5 to 15% by mass, more preferably 6 to 12% by mass. If the residual amount of the solvent is in the above range, the peelability of the dry coating film from the substrate becomes good, and the obtained optical film easily satisfies the formula (1).

The temperature of the second drying is preferably 150 to 300°C, more preferably 180 to 250°C, and still more preferably 180 to 230°C. The time for the second drying is preferably 10 to 60 minutes, more preferably 30 to 50 minutes.

The second drying may be performed in a single-piece type. In the case of industrial production, it is preferably performed by a roll-to-roll method from the viewpoint of production efficiency. In the single-piece type, it is preferable to perform drying in a state uniformly elongated in the in-plane direction. In the roll-to-roll method, from the viewpoint that the optical film easily satisfies the formula (1), it is preferable to dry the dry coating film in a state stretched in the conveying direction, and the conveying speed is preferably 0.1 to 5 m/min , More preferably 0.5 to 3 m/min, still more preferably 0.7 to 1.5 m/min. The second drying can be carried out under one-stage or multi-stage conditions. From the viewpoint that the optical film easily satisfies the formula (1), it is preferably carried out under multi-stage conditions. Multi-stage conditions are preferably implemented in each stage, which can be selected from at least one of the same or different temperature conditions, drying time and hot air speed. For example, drying can be carried out in 2-10 stages, preferably 3-8 stages. . In addition, in each stage, the wind speed of the hot air is preferably 5-20 m/min, more preferably 10-15 m/min, and still more preferably, from the viewpoint that the obtained optical film easily satisfies formula (1) It is 11～14 m/min.

When the optical film of the present invention has a hard coat layer, the hard coat layer can be formed by applying a curable composition on at least one side of the optical film to form a coating film, and irradiating the coating film with high energy rays to harden the coating film. .

Examples of the coating method include the well-known coating methods exemplified above. The irradiation intensity of high energy rays (for example, active energy rays) during curing is appropriately determined according to the composition of the curable composition, and is not particularly limited. It is preferably irradiation in a wavelength region effective for activation of the polymerization initiator. The irradiation intensity is preferably 0.1 to 6,000 mW/cm ² , more preferably 10 to 1,000 mW/cm ² , and still more preferably 20 to 500 mW/cm ² . If the irradiation intensity is within the above range, an appropriate reaction time can be ensured, and yellowing or deterioration of the resin due to the heat radiated from the light source and the exothermic heat during the curing reaction can be suppressed. The irradiation time may be appropriately selected according to the composition of the curable composition and is not particularly limited. The cumulative light quantity expressed as the product of the irradiation intensity and the irradiation time is preferably 10 to 10,000 mJ/cm ² , more preferably 50 to 1,000 mJ/cm ² , and more preferably 80-500 mJ/cm ² . If the cumulative amount of light is within the above range, a sufficient amount of active species derived from the polymerization initiator can be generated and the curing reaction can proceed more reliably, and the irradiation time is not too long and good productivity can be maintained. In addition, by going through the irradiation step within this range, the hardness of the hard coat layer can be further increased, which is useful. From the viewpoint of improving the smoothness of the hard coat layer and further improving the visibility of the optical film in the wide-angle direction, the type of solvent, the ratio of components, the optimization of the solid content concentration, and the addition of leveling agents can be cited.

[Flexible Image Display Device] The present invention includes a flexible display device provided with the above-mentioned optical film. The optical film of the present invention is preferably used as a front panel in a flexible image display device, and the front panel is sometimes called a window film. The flexible image display device includes a laminate for a flexible image display device and an organic EL (Electroluminescence) display panel, and is configured such that the organic EL display panel is configured to be flexible on the viewing side A laminate for an image display device and can be bent. As a laminated body for a flexible image display device, it may further contain a polarizing plate, preferably a circular polarizing plate, and a touch sensor. The order of the layers is arbitrary, but it is preferable that windows are laminated in order from the viewing side Film, polarizing plate, touch sensor or window film, touch sensor, polarizing plate. If there is a polarizing plate on the side that is more visible than the touch sensor, the pattern of the touch sensor is not easily visible, and the visibility of the displayed image becomes better, which is better. Each member can be laminated using adhesives, adhesives, etc. In addition, it may be provided with a light-shielding pattern formed on at least one surface of any one of the above-mentioned window film, polarizer, and touch sensor.

[Polarizer] As described above, the flexible display device of the present invention preferably includes a polarizing plate, especially a circular polarizing plate. The circular polarizing plate is a functional layer that has the function of transmitting only the right or left circularly polarized light component by laminating a λ/4 phase difference plate on the linear polarizing plate. For example, it is used to convert external light into right circular polarized light and block the outer boundary light reflected by the organic EL panel to become left circular polarized light, and only transmit the luminous components of the organic EL, thereby suppressing the influence of reflected light and making it easier to see the image . In order to achieve the circular polarization function, the absorption axis of the linear polarizer and the late axis of the λ/4 retardation plate must theoretically be 45°, but in actual applications it is 45±10°. The linear polarizing plate and the λ/4 retardation plate do not necessarily have to be laminated adjacently, as long as the relationship between the absorption axis and the slow phase axis satisfies the above range. Although it is preferable to achieve complete circular polarization at all wavelengths, this is not necessarily the case in practical applications. Therefore, the circular polarization plate of the present invention also includes an elliptical polarization plate. It is also preferable to laminate a λ/4 retardation film on the visibility side of the linear polarizer to make the emitted light circularly polarized, thereby improving the visibility when wearing polarized sunglasses.

The linear polarizer is a functional layer that transmits light that vibrates in the direction of the transmission axis, but blocks the polarization of the vibration component perpendicular to it. The above-mentioned linear polarizing plate may be provided with a single linear polarizing element or with a linear polarizing element and a protective film attached to at least one surface thereof. The thickness of the linear polarizer may be 200 μm or less, preferably 0.5-100 μm. If the thickness of the linear polarizer is in the above range, the flexibility of the linear polarizer tends not to be easily reduced.

The above-mentioned linear polarizing element may be a film-type polarizing element manufactured by dyeing and stretching a polyvinyl alcohol (hereinafter sometimes referred to as PVA) film. The dichroic dye such as iodine is adsorbed on the PVA-based film aligned by stretching, or stretched while adsorbing on the PVA, thereby aligning the dichroic dye and exhibiting polarization performance. In the manufacture of the above-mentioned film-type polarizing element, there may be additional steps such as swelling, cross-linking with boric acid, washing with aqueous solution, and drying. The stretching or dyeing step can be carried out with a PVA-based film alone or in the state of being laminated with other films such as polyethylene terephthalate. The thickness of the PVA-based film used is preferably 10-100 μm, and the above-mentioned stretching ratio is preferably 2-10 times. Furthermore, as another example of the above-mentioned polarizing element, a liquid crystal coating type polarizing element formed by applying a liquid crystal polarizing composition can be cited. The liquid crystal polarizing composition may contain a liquid crystal compound and a dichroic dye compound. The above-mentioned liquid crystalline compound only needs to have the property of displaying a liquid crystal state, especially if it has an alignment state of the order of the order of smectic alignment, it can exhibit higher polarization performance, so it is preferable. Moreover, it is preferable that the liquid crystal compound has a polymerizable functional group. The dichroic dye compound is a dye that is aligned with the liquid crystal compound to exhibit dichroism, and may have a polymerizable functional group, and the dichroic dye itself may have liquid crystallinity. Any of the compounds contained in the liquid crystal polarizing composition has a polymerizable functional group. The liquid crystal polarizing composition may further include a starter, a solvent, a dispersant, a leveling agent, a stabilizer, a surfactant, a crosslinking agent, a silane coupling agent, and the like. The above-mentioned liquid crystal polarizing layer is manufactured by coating a liquid crystal polarizing composition on an alignment film to form a liquid crystal polarizing layer. The liquid crystal polarizing layer can be formed to be thinner than the film-type polarizing element, and its thickness is preferably 0.5-10 μm, more preferably 1-5 μm.

The above-mentioned alignment film is produced by, for example, coating an alignment film forming composition on a substrate and imparting alignment properties by rubbing, polarized light irradiation, or the like. The alignment film forming composition described above includes an alignment agent, and may further include a solvent, a crosslinking agent, an initiator, a dispersant, a leveling agent, a silane coupling agent, and the like. Examples of the aforementioned alignment agent include polyvinyl alcohols, polyacrylates, polyamides, and polyimines. In the case of using an alignment agent that imparts alignment properties by polarized light irradiation, it is preferable to use an alignment agent containing a cinnamate group. The weight average molecular weight of the polymer used as the above-mentioned alignment agent is, for example, about 10,000 to 1,000,000. The thickness of the alignment film is preferably 5 to 10,000 nm, and more preferably 10 to 500 nm in terms of sufficiently exhibiting the alignment restriction force. The liquid crystal polarizing layer may be peeled from the base material and then transferred and laminated, or the base material may be laminated directly. The above-mentioned base material is also preferably used as a transparent base material for protective film, phase difference plate, and window film.

The protective film may be a transparent polymer film, and the same materials or additives used for the transparent substrate of the window film can be used. In addition, it may be a coating type protective film obtained by applying and curing a cationic curing composition such as epoxy resin or a radical curing composition such as acrylate. The protective film may optionally contain plasticizers, ultraviolet absorbers, infrared absorbers, coloring agents such as pigments or dyes, fluorescent brighteners, dispersants, heat stabilizers, light stabilizers, antistatic agents, and antioxidants. , Lubricants, solvents, etc. The thickness of the protective film is preferably 200 μm or less, more preferably 1-100 μm. If the thickness of the protective film is in the above range, there is a tendency that the flexibility of the film is not easily reduced.

The above-mentioned λ/4 retardation plate is a film that provides a λ/4 retardation in a direction orthogonal to the traveling direction of incident light (in-plane direction of the film). The above-mentioned λ/4 retardation plate is a stretched retardation plate manufactured by stretching a polymer film such as a cellulose-based film, an olefin-based film, and a polycarbonate-based film. The above-mentioned λ/4 retardation plate may optionally contain retardation adjusters, plasticizers, ultraviolet absorbers, infrared absorbers, coloring agents such as pigments or dyes, fluorescent brighteners, dispersants, heat stabilizers, light Stabilizers, antistatic agents, antioxidants, lubricants, solvents, etc. The thickness of the extended phase difference plate is preferably 200 μm or less, more preferably 1-100 μm. If the thickness of the extended phase difference plate is in the above range, the flexibility of the extended phase difference plate tends to be less likely to decrease. Furthermore, as another example of the aforementioned λ/4 retardation plate, a liquid crystal coating type retardation plate formed by applying a liquid crystal composition can be cited. The above-mentioned liquid crystal composition includes a liquid crystal compound showing a liquid crystal state such as nematic, cholesteric, and smectic. The above-mentioned liquid crystal compound has a polymerizable functional group. The above-mentioned liquid crystal composition may further include a starter, a solvent, a dispersant, a leveling agent, a stabilizer, a surfactant, a crosslinking agent, a silane coupling agent, and the like. The liquid crystal coating type retardation plate can be manufactured by applying a liquid crystal composition on a base and curing the liquid crystal retardation layer in the same manner as the liquid crystal polarizing layer. The liquid crystal coating type retardation plate can be formed to be thinner than the extension type retardation plate. The thickness of the liquid crystal polarizing layer is preferably 0.5 to 10 μm, more preferably 1 to 5 μm. The liquid crystal coating type retardation plate may be peeled from the base material and then transferred and laminated, or the base material may be directly laminated. The above-mentioned base material is also preferably used as a transparent base material for protective film, phase difference plate, and window film.

Generally speaking, most materials show birefringence that the shorter the wavelength, the greater the birefringence, and the longer the wavelength, the smaller the birefringence. In this case, the phase difference of λ/4 cannot be achieved in the entire visible light region. Therefore, the in-plane phase difference is preferably designed to be 100 to 180 in such a way that it becomes λ/4 in the vicinity of 560 nm, which has a higher visual sensitivity. nm, more preferably 130 to 150 nm. A reverse dispersion λ/4 retardation plate using a material having birefringence wavelength dispersion characteristics opposite to that of usual is preferable in terms of good visibility. As such a material, for example, the extension type retardation plate can use what is described in Japanese Patent Laid-Open No. 2007-232873, and the liquid crystal coating type retardation plate can use what is described in Japanese Patent Laid-Open No. 2010-30979. In addition, as another method, a technique of obtaining a wide-band λ/4 retardation plate by combining with a λ/2 retardation plate is also known (for example, Japanese Patent Laid-Open No. 10-90521 etc.). The λ/2 retardation plate is also manufactured by the same material method as the λ/4 retardation plate. The combination of the extension type retardation plate and the liquid crystal coating type retardation plate is arbitrary, but any of them can be thinned by using the liquid crystal coating type retardation plate. For the above circular polarizing plate, in order to improve the visibility in the oblique direction, a method of laminating positive C plates is known (for example, Japanese Patent Laid-Open No. 2014-224837 etc.). The positive C plate can be a liquid crystal coating type retardation plate or an extended 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] The flexible display device of the present invention preferably has a touch sensor as described above. The touch sensor is used as an input mechanism. As the touch sensor, various types such as a resistive film method, a surface acoustic wave method, an infrared method, an electromagnetic induction method, and an electrostatic capacitance method can be cited, and the electrostatic capacitance method is preferred. The capacitive touch sensor is divided into an active area and an inactive area located outside the active area. The active area is the area corresponding to the area on the display panel (display part) that senses the user's touch, and the inactive area corresponds to the area (non-display part) of the display device that does not display the picture area. The touch sensor may include: a substrate with flexible characteristics, a sensing pattern formed on the active area of the substrate, and an inactive area formed on the substrate and used to communicate with each other through the sensing pattern and the bonding pad. Each sensing line connected to the external drive circuit. As a substrate with flexible characteristics, the same material as the transparent substrate of the above-mentioned window film can be used.

The aforementioned sensing pattern may include a first pattern formed in the first direction and a second pattern formed in the second direction. The first pattern and the second pattern are arranged in different directions. The first pattern and the second pattern are formed on the same layer. In order to sense the touched location, each pattern must be electrically connected. The first pattern is a form in which a plurality of unit patterns are connected to each other via a joint, and the second pattern is a structure in which a plurality of unit patterns are separated from each other in an island form. Therefore, in order to electrically connect the second pattern, another bridge electrode is required. The electrode used for the connection of the second pattern can be a well-known transparent electrode. Examples of materials for the transparent electrode include indium tin oxide (ITO), indium zinc oxide (IZO), zinc oxide (ZnO), indium zinc tin oxide (IZTO), and indium gallium zinc oxide (IGZO) , Cadmium tin oxide (CTO), PEDOT (poly(3,4-ethylenedioxythiophene), poly(3,4-ethylenedioxythiophene)), carbon nanotube (CNT), graphene, metal wire, etc. A good example is ITO. These can be used individually or in mixture of 2 or more types. The metal used for the metal wire is not particularly limited, and examples include silver, gold, aluminum, copper, iron, nickel, titanium, tellurium, chromium, etc., and these can be used alone or in combination of two or more. The bridge electrode can be formed on the upper part of the insulating layer via the insulating layer on the upper part of the sensing pattern, and the bridge electrode can be formed on the substrate, and the insulating layer and the sensing pattern can be formed thereon. The above-mentioned bridge electrode may also 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 two or more of these. The first pattern and the second pattern must be electrically insulated, so an insulating layer is formed between the sensing pattern and the bridge electrode. The insulating layer can also be formed only between the joints of the first pattern and the bridging electrodes, or as a layer covering the entire sensing pattern. In the case of covering the whole layer of the sensing pattern, the bridge electrode may be connected to the second pattern through the contact hole formed in the insulating layer.

The above-mentioned touch sensor may further include an optical adjustment layer between the substrate and the electrode to appropriately compensate for the difference in transmittance between the pattern area where the sensing pattern is formed and the non-pattern area where the sensing pattern is not formed. It is the mechanism of the difference in light transmittance induced by the difference in refractive index of these areas. The optical adjustment layer may include an inorganic insulating material or an organic insulating material. The optical adjustment layer can be formed by coating a photocuring composition containing a photocuring organic adhesive and a solvent on a substrate. The aforementioned photocurable composition may further include inorganic particles. The above-mentioned inorganic particles can increase the refractive index of the optical adjustment layer. The above-mentioned photocurable organic adhesive may include copolymers of monomers such as acrylic ester monomers, styrene monomers, and carboxylic acid monomers within a range that does not impair the effects of the present invention. The above-mentioned photocurable organic adhesive may also be a copolymer containing different repeating units such as epoxy-containing repeating units, acrylate repeating units, carboxylic acid repeating units, and the like. Examples of the above-mentioned inorganic particles include zirconium oxide particles, titanium oxide particles, and aluminum oxide particles. The photocurable composition may further include various additives such as a photopolymerization initiator, a polymerizable monomer, and a curing auxiliary agent.

[Next layer] The layers (window film, circular polarizing plate, touch sensor) and the film members (linear polarizing plate, λ/4 phase difference plate, etc.) constituting each layer of the laminated body for the flexible image display device can be formed by Adhesive for bonding. As the adhesive, water-based adhesives, water-based solvent-volatile adhesives, organic solvents, solvent-free adhesives, solid adhesives, solvent-volatile adhesives, moisture-curing adhesives, and heat-curing adhesives can be used , Anaerobic curing type, active energy ray curing type adhesive, curing agent mixed type adhesive, hot melt type adhesive, pressure sensitive type adhesive (adhesive), rewetting type adhesive and other commonly used adhesives, etc., Preferably, a water-based solvent volatile adhesive, an active energy ray hardening adhesive, and an adhesive can be used. The thickness of the adhesive layer can be appropriately adjusted according to the required adhesive force, etc., preferably 0.01 to 500 μm, more preferably 0.1 to 300 μm. There are a plurality of adhesive layers in the above-mentioned laminate for flexible image display devices, and the thickness or type of each may be the same or different.

As the above-mentioned aqueous solvent volatile adhesive, water-dispersed polymers such as polyvinyl alcohol-based polymers, starches, etc., ethylene-vinyl acetate emulsions, styrene-butadiene emulsions, and other water-dispersed polymers can be used as main components. Agent polymer. In addition to the above-mentioned main agent polymer and water, crosslinking agents, silane-based compounds, ionic compounds, crosslinking catalysts, antioxidants, dyes, pigments, inorganic fillers, organic solvents, etc. can also be formulated. In the case of bonding by the above-mentioned water-based solvent-volatile adhesive, the above-mentioned water-based solvent-volatile adhesive may be injected between layers to be bonded to bond the adhered layer, and then dried to impart adhesiveness. In the case of using the above-mentioned aqueous solvent volatile adhesive, the thickness of the adhesive layer is preferably 0.01-10 μm, more preferably 0.1-1 μm. When the above-mentioned water-based solvent-volatile adhesive is used for multiple layers, the thickness or type of each layer may be the same or different.

The active energy ray curable adhesive can be formed by curing an active energy ray curable composition containing a reactive material that forms an adhesive layer by irradiating active energy rays. The active energy ray hardening composition may contain at least one polymer of the same radical polymerizable compound and cation polymerizable compound as those contained in the hard coat composition. The radical polymerizable compound can be the same as the radical polymerizable compound in the hard coat composition. The above-mentioned cationically polymerizable compound can use the same compound as the cationically polymerizable compound in the hard coat composition. As the cationic polymerizable compound used in the active energy ray hardening composition, an epoxy compound is particularly preferred. In order to reduce the viscosity of the adhesive composition, it is also preferable to include a monofunctional compound as a reactive diluent.

In order to reduce the viscosity, the active energy ray composition may include a monofunctional compound. Examples of the monofunctional compound include acrylate monomers having one (meth)acrylic acid group in one molecule, or compounds having one epoxy group or oxetanyl group in one molecule, such as (Meth) glycidyl acrylate and the like. The active energy ray composition may further include a polymerization initiator. Examples of the polymerization initiator include radical polymerization initiators, cationic polymerization initiators, radical and cationic polymerization initiators, and the like, and these can be appropriately selected and used. These polymerization initiators are decomposed by at least one of active energy ray irradiation and heating to generate free radicals or cations to cause radical polymerization and cationic polymerization to proceed. In the description of the hard coating composition, an initiator capable of starting at least one of radical polymerization and cationic polymerization by active energy ray irradiation can be used. The active energy ray hardening composition may further include an ion scavenger, an antioxidant, a chain transfer agent, an adhesion imparting agent, a thermoplastic resin, a filler, a fluid viscosity adjuster, a plasticizer, a defoamer solvent, an additive, and a solvent. In the case where two adhesive layers are bonded by the active energy ray-curable adhesive, the active energy ray curing composition can be applied to either or both of the adhesive layers and then bonded , Irradiating active energy rays to any one of the adhered layers or two of the adhered layers to harden and adhere. In the case of using the active energy ray-curable adhesive, the thickness of the adhesive layer is preferably 0.01-20 μm, more preferably 0.1-10 μm. When the above-mentioned active energy ray-curable adhesive is used for the formation of a plurality of adhesive layers, the thickness or type of each layer may be the same or different.

The above-mentioned adhesives are classified into acrylic adhesives, urethane-based adhesives, rubber-based adhesives, silicone-based adhesives, etc. corresponding to the main agent polymer, and any of them can be used. In addition to the main agent polymer, the adhesive can also be formulated with cross-linking agents, silane-based compounds, ionic compounds, cross-linking catalysts, antioxidants, adhesion imparting agents, plasticizers, dyes, pigments, inorganic fillers, etc. The adhesive composition is obtained by dissolving and dispersing the components constituting the adhesive in a solvent, and the adhesive composition is applied on a substrate and then dried to form an adhesive layer followed by a layer. The adhesive layer can be formed directly, or it can be transferred on the substrate. In order to cover the adhesive surface before bonding, it is also preferable to use a release film. In the case of using the above-mentioned active energy ray-curable adhesive, the thickness of the adhesive layer is preferably 0.1 to 500 μm, more preferably 1 to 300 μm. When using multiple layers of the above-mentioned adhesive, the thickness or type of each layer may be the same or different.

[Shading Pattern] The light-shielding pattern can be used as at least a part of the frame or housing of the flexible image display device. By shielding the wiring arranged at the edge of the flexible image display device with the light-shielding pattern so that it is not easily visible, the visibility of the image is improved. The aforementioned light-shielding pattern may be in the form of a single layer or multiple layers. The color of the shading pattern is not particularly limited, and can be black, white, metallic and other colors. The light-shielding pattern can be formed by polymers such as pigments, acrylic resins, ester resins, epoxy resins, polyurethanes, and silicones for color realization. These can also be used alone or in a mixture of two or more. The light-shielding pattern can be formed by various methods such as printing, lithography, and inkjet. The thickness of the light shielding pattern is preferably 1-100 μm, more preferably 2-50 μm. Furthermore, it is also preferable to give a shape such as an inclination to the thickness direction of the light shielding pattern. [Example]

Hereinafter, the present invention will be explained in more detail with examples. Unless otherwise specified, the "%" and "parts" in the examples mean mass% and mass parts. First, the evaluation method is explained.

＜Weight average molecular weight＞ The gel permeation chromatography (GPC) measurement was performed using a liquid chromatograph LC-10ATvp manufactured by Shimadzu Corporation. (1) Pretreatment method After dissolving the polyimide resin obtained in Production Examples 1 to 4 in γ-butyrolactone (GBL) to make a 20% by mass solution, it was diluted 100 times with DMF eluent to 0.45 μm The membrane filter is filtered, and the obtained is used as the measurement solution. (2) Measurement conditions Column: TSKgel SuperAWM-H×2＋SuperAW2500×1 (6.0 mm I.D.×150 mm×3) Eluent: DMF (add 10 mmol of lithium bromide) Flow rate: 0.6 mL/min Detector: RI detector Column temperature: 40℃ Injection volume: 20 μL Molecular weight standard: standard polystyrene

<The imidization rate> The imidization rate is determined by ¹ H-NMR measurement as follows. (1) Pretreatment method The polyimide resin obtained in Production Examples 1 to 4 was dissolved in deuterated dimethyl sulfide (DMSO-d ₆ ) to prepare a 2% by mass solution, which was used as the measurement Sample. (2) Measurement condition measuring device: 400 MHz NMR device JNM-ECZ400S/L1 manufactured by JEOL Standard material: DMSO-d ₆ (2.5 ppm) Sample temperature: Room temperature Accumulated times: 256 times Relaxation time: 5 seconds (3) 醯Analysis method of imidization rate (Imidation rate of polyimide resin) In the ¹ H-NMR spectrum obtained from a measurement sample containing polyimide resin, the observed benzene protons are derived from The integral value of the benzene proton A of the unchanged structure before and after imidization is set as Int _A. In addition, the observed integral value of the amide proton derived from the amide acid structure remaining in the polyimide resin is set to Int _B. From these integral values, the imidization rate of the polyimide resin was calculated based on the following formula. The imidization rate (%)=100×(1－Int _B /Int _A )

(The imidization rate of polyamide imide resin) In the ¹ H-NMR spectrum obtained from a measurement sample containing polyamide imide resin, the observed benzene protons are derived from acetamide The integral value of the benzene proton C, which has the unchanged structure before and after imidization and is not affected by the structure derived from the residual acid structure in the polyamide imide resin, is set to Int _C. In addition, among the observed benzene protons, the benzene proton D is derived from the structure unchanged before and after the imidization and is affected by the structure derived from the residual acid structure in the polyimide resin. The integral value is set to Int _D. From the obtained Int _C and Int _D , the β value is calculated by the following formula. β=Int _D /Int _C Next, for a plurality of polyimide resins, the β value of the above formula and the imidization rate of the polyimide resin of the above formula are obtained, and the following are obtained from the results The correlation formula. The imidization rate (%)=k×β+100 In the above correlation formula, k is a constant. Substitute β into the correlation formula to obtain the imidization rate (%) of the polyimide resin.

＜Scattered light ratio (Ts)＞ With respect to the optical films obtained in the Examples and Comparative Examples, the diffuse light transmittance (Td) (%) was determined by a spectrophotometer CM3700A manufactured by Konica Minolta Co., Ltd. according to JIS K 7136. In addition, according to JIS K 7136, the total light transmittance (Tt) (%) is obtained by the haze meter NDH5000 manufactured by Nippon Denshoku Industries Co., Ltd. Substitute the obtained Td and Tt into the equation of scattered light ratio (Ts)=Td/Tt×100 to calculate the scattered light ratio (Ts) (%) of the optical film.

＜Tensile elastic modulus＞ The tensile elastic modulus of the optical films obtained in the examples and comparative examples is based on JIS K 7127, using an electromechanical universal testing machine (manufactured by Instron) at a temperature of 80°C and a test speed of 5 m/min And the load element is 5 kN to carry on the tensile test and measured. The optical film system was allowed to stand for 5 minutes in an environment of 80°C and then the measurement was started.

＜Bending resistance test＞ According to JIS K 5600-5-1, the bending resistance test (bending radius R = 1 mm, bending times 100 times) was carried out with a small desktop bending tester manufactured by Yuasa System Co., Ltd. For the optical film after the bending resistance test, the scattered light ratio after the bending resistance test is measured in the same way as the measurement method of the above-mentioned <scattered light ratio (Ts)>, and the difference between the scattered light ratio before and after the bending resistance test is calculated The absolute value of ΔTs.

＜Folding resistance＞ According to ASTM standard D2176-16, the number of bending times of the optical films in the examples and comparative examples was calculated as follows. Use a dumbbell cutter to cut the optical film into short strips of 15 mm×100 mm. Set the cut optical film on the body of the MIT flexural fatigue testing machine ("Model 0530", manufactured by Toyo Seiki Seisakusho Co., Ltd.) at a test speed of 175 cpm, a bending angle of 135°, a load of 0.75 kgf, and a bending jig. Under the condition of radius R=1 mm, the number of reciprocating bending in the front and back direction before the optical film is broken is measured, and this is the number of bending.

＜Yellowness (YI value)＞ The yellowness (Yellow Index: YI value) of the optical films obtained in the Examples and Comparative Examples was measured using an ultraviolet-visible-near-infrared spectrophotometer "V-670" manufactured by JASCO Corporation. After the background measurement is performed without the sample, the optical film is set in the sample holder, and the transmittance of light from 300 to 800 nm is measured to obtain the tristimulus value (X, Y, Z) based on the following formula Calculate the YI value. YI=100×(1.2769X－1.0592Z)/Y

＜Thickness＞ With respect to the optical films obtained in the examples and comparative examples, the thickness of the optical film at 10 points or more was measured using a micrometer ("ID-C112XBS" manufactured by Mitutoyo Co., Ltd.), and the average value was calculated. The average value is taken as the thickness of the optical film.

＜Visibility evaluation＞ The optical films obtained in the examples and comparative examples were cut into 10 cm squares. Align the MD direction of the polarizer with the adhesive layer of the same size (10 cm square) with the MD direction of the cut optical film, and paste the polarizer with the adhesive layer on the cut optical film to make an evaluation sample . For the optical films of 1 Example and Comparative Example, two evaluation samples were prepared respectively. One of the two evaluation samples is fixed to the table in such a way that the fluorescent lamp is located in the vertical direction of the evaluation sample plane and the length direction of the fluorescent lamp is relative to the evaluation sample The MD direction becomes horizontal. The observer visually observes the fluorescent lamp image reflected on the surface of the evaluation sample from an angle of 30° inclined from the vertical direction to the plane of the evaluation sample. The length direction of the fluorescent lamp was changed from horizontal to vertical, except for this, another evaluation sample was fixed to the table in the same manner, and the fluorescent lamp image was observed. The visibility is evaluated based on the observation results and based on the following evaluation criteria.

(Assessment criteria for visibility) ◎: The deformation of the fluorescent lamp image was hardly recognized. ○: Visually recognize the distortion of the fluorescent lamp image. △: Distortion of the fluorescent lamp image is visually recognized. ×: Deformation of the fluorescent lamp image is clearly recognized.

The optical films obtained in the examples and comparative examples have a protective film on one side, but the above-mentioned measurement and evaluation are performed using the optical film in a state where the protective film has been peeled off.

[Production example 1: Production of polyimide resin (1)] Prepare a separable flask and oil bath equipped with silica gel tube, stirring device and thermometer. Put 4,4'-(hexafluoroisopropylidene) diphthalic anhydride (6FDA) 75.6 g, and 2,2'-bis(trifluoromethyl)-4,4'-di in the flask Aminodiphenyl (TFMB) 54.5 g. While stirring at 400 rpm, 530 g of N,N-dimethylacetamide (DMAc) was added, and stirring was continued until the contents of the flask became a homogeneous solution. Then, while adjusting the temperature in the container to a range of 20 to 30°C using an oil bath, stirring was continued for a further 20 hours, and the reaction proceeded to produce polyamide acid. After 30 minutes, the stirring speed was changed to 100 rpm. After stirring for 20 hours, the temperature of the reaction system was returned to room temperature, and 650 g of DMAc was added to adjust the polymer concentration to 10% by mass. Furthermore, 32.3 g of pyridine and 41.7 g of acetic anhydride were added, and the mixture was stirred at room temperature for 10 hours to carry out imidization. Take out the polyimide varnish from the reaction vessel. The obtained polyimide varnish was dropped into methanol for reprecipitation, and the obtained powder was heated and dried to remove the solvent to obtain a polyimide resin (1) as a solid component. GPC measurement of the obtained polyimide resin (1) showed that the weight average molecular weight was 350,000. In addition, the polyimide resin (1) had an imidization rate of 98.8%.

[Production Example 2: Production of Polyimide Resin (2)] Except that the reaction time was changed to 16 hours, a polyimide resin (2) was produced in the same manner as in Production Example 1. 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 Polyimide Resin (3)] In a nitrogen environment, add 45 g (140.52 mmol) of TFMB and 768.55 g of DMAc to a 1 L separable flask equipped with a stirring blade. While stirring at room temperature, dissolve TFMB in DMAc. Next, 18.92 g (42.58 mmol) of 6FDA was added to the flask, and the mixture was stirred at room temperature for 3 hours. Thereafter, 4.19 g (14.19 mmol) of 4,4'-oxybis(benzyl chloride) (OBBC), and then 17.29 g (85.16 mmol) of terephthalic acid chloride (TPC) were added to the flask, Stir at room temperature for 1 hour. Then, 4.63 g (49.68 mmol) of 4-picoline and 13.04 g (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°C using an oil bath, and then stirred for 3 hours to obtain The reaction solution. The obtained reaction solution was cooled to room temperature, and poured into a large amount of methanol in a linear fashion, and the deposited 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°C to obtain a polyimide resin (1). The weight average molecular weight of the polyimide resin (1) is 400,000, and the imidization rate is 98.1%.

[Production Example 4: Production of polyimide resin (4)] In a nitrogen environment, add 45 g (140.52 mmol) of TFMB and 768.55 g of DMAc to a 1 L separable flask equipped with a stirring blade. While stirring at room temperature, dissolve TFMB in DMAc. Next, 19.01 g (42.79 mmol) of 6FDA was added to the flask and stirred at room temperature for 3 hours. Thereafter, 4.21 g (14.26 mmol) of OBBC, and 17.30 g (85.59 mmol) of TPC were added to the flask, and the mixture was stirred at room temperature for 1 hour. Then, 4.63 g (49.68 mmol) of 4-picoline and 13.04 g (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°C using an oil bath, and then stirred for 3 hours to obtain The reaction solution. The obtained reaction solution was cooled to room temperature, and poured into a large amount of methanol in a linear fashion, and the deposited 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°C to obtain a polyamide imide resin (2). The weight average molecular weight of the obtained polyimide resin (2) was 365,000, and the imidization rate was 98.3%.

[Production Example 5: Production of varnish (1)-varnish (3)] The polyimide-based resin was dissolved in the solvent with the composition shown in Table 1, and Sumisorb 340 (UVA) manufactured by Sumika Chemtex Co., Ltd. was added at 5.7% by mass relative to the mass of the resin [2-(2 -Hydroxy-5-tertiary octylphenyl) benzotriazole] was used as an ultraviolet absorber, and stirred until it became uniform to obtain varnish (1) to varnish (3). Furthermore, in Table 1, the value in the "solvent" column represents the ratio (mass %) of the mass of the specific solvent to the total mass of all solvents. The value in the "polyimide resin" column represents the ratio (mass %) of the mass of a specific polyimide resin to the total mass of all polyimide resins. PI-1, PI-2, PAI-1, and PAI-2 in the "polyimide resin" column respectively represent polyimide resin (1), polyimide resin (2), polyimide resin Amine resin (1) and polyimide resin (2). The value in the "Additive" column represents the ratio (mass%) of the mass of the additive to the mass of the resin. The value in the "solid content concentration" column represents the ratio (mass%) of all components other than the solvent to the mass of the varnish.

[Table 1]

[Example 1: Manufacturing of optical film (1)] The varnish (1) is formed into a coating film on a PET (polyethylene terephthalate) film ("A4100" manufactured by Toyobo Co., Ltd., thickness 188 μm, thickness distribution ±2 μm) by casting. The line speed is 0.4 m/min. By heating at 70°C for 8 minutes, heating at 100°C for 10 minutes, heating at 90°C for 8 minutes, and heating at 80°C for 8 minutes, the coating film is dried and peeled from the PET film. For the obtained raw film 1 (width 700 mm), a tenter dryer (consisting of 1 to 6 chambers) using a clip as a holding member was used to remove the solvent, and then PET was laminated on one side of the dried film The protective film is used to obtain optical film 1 with a thickness of 79 μm. In more detail, drying of the raw film 1 is performed as follows. Set the temperature in the dryer to 200°C, the clamp holding width is 25 mm, the film transport speed is 1.0 m/min, and the ratio of the film width at the entrance of the dryer (the distance between the clamps) to the film width at the exit of the drying oven is 1.0 Adjust the wind speed in each chamber of the tenter dryer to 13.5 m/sec in 1 chamber, 13 m/sec in 2 chambers, and 11 m/sec in 3-6 chambers Adjustment. After the film is detached from the clip, cut the clip part, attach a PET-based protective film to one side of the film, and roll it up in ABS (acrylonitrile-butadiene-styrene, acrylonitrile-butadiene-styrene) 6 inches Core, and the optical film 1 is obtained.

[Example 2: Manufacturing of optical film (2)] Change the varnish (1) to varnish (2), change the line speed from 0.4 m/min to 0.3 m/min, and for the heating conditions of the coating film, follow the order of 8 minutes at 70°C and 10 at 100°C. Minutes, 8 minutes at 90°C and 8 minutes at 80°C changed to 10 minutes at 80°C, 10 minutes at 100°C, 10 minutes at 90°C, and 10 minutes at 80°C, except for that , The optical film 2 with a thickness of 49 μm is manufactured in the same manner as the manufacturing method of the optical film 1.

[Example 3: Manufacturing of optical film (3)] The varnish (1) was changed to varnish (3), and the line speed was changed from 0.4 m/min to 0.2 m/min. Otherwise, the optical film 3 with a thickness of 79 μm was obtained in the same manner as the manufacturing method of the optical film 1 .

[Example 4: Manufacturing of optical film (4)] Change varnish (1) to varnish (4), change the line speed from 0.4 m/min to 0.2 m/min, and change the heating conditions of the coating film to the following, that is, at 90°C for 8 minutes and at 100 Except for 10 minutes at °C, 8 minutes at 90 °C, and 8 minutes at 80 °C, an optical film 4 with a thickness of 79 μm was obtained in the same manner as the manufacturing method of the optical film 1.

[Comparative Example 1] A polyimide film ("UPILEX" manufactured by Ube Industries Co., Ltd., thickness 50 μm) was prepared as the optical film 5.

The total light transmittance Tt (%), diffuse light transmittance Td (%), scattered light ratio Ts (%), and tensile modulus (MPa) of the optical films obtained in Examples 1 to 4 and Comparative Example 1 ), the absolute value of the difference of the scattered light ratio before and after the bending resistance test ΔTs (%), YI, folding resistance (times) and the results of the visibility evaluation 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 compared with the optical film of Comparative Example 1 in which the scattered light ratio exceeded 0.35%. The result is relatively good. In addition, it was also confirmed that the optical films of Examples 1 to 4 had excellent tensile modulus of elasticity, folding resistance, and low yellowness. Therefore, the optical films of Examples 1 to 4 have excellent visibility in the wide-angle direction, and also have excellent tensile modulus and the like.

Claims (10)

An optical film, which It contains at least one resin selected from the group consisting of polyimide resins and polyimide resins, and satisfies formula (1): 0≦Ts≦0.35 (1) [In formula (1), Ts represents the scattered light ratio (%), defined as Ts=Td/Tt×100, Td and Tt respectively represent the diffuse light transmittance (%) and total light transmittance measured according to JIS K 7136 rate(%)]. For the optical film of claim 1, its tensile modulus of elasticity at 80°C is 4,000-9,000 MPa. For the optical film of claim 1 or 2, the absolute value ΔTs of the difference between the aforementioned scattered light ratios before and after the bending resistance test according to JIS K 5600-5-1 is 0.15% or less. For example, the optical film of claim 1 or 2 has a thickness of 10 to 150 μm. The optical film of claim 1 or 2, wherein the content of the filler is 5% by mass or less relative to the mass of the optical film. The optical film of claim 1 or 2, which has a hard coating on at least one side. The optical film of claim 6, wherein the thickness of the hard coat layer is 3-30 μm. A flexible display device provided with the optical film according to any one of claims 1 to 7. Such as the flexible display device of claim 8, which further includes a touch sensor. Such as the flexible display device of claim 8 or 9, which further includes a polarizing plate.