CN114556165A

CN114556165A - Optical film

Info

Publication number: CN114556165A
Application number: CN202080071669.3A
Authority: CN
Inventors: 宫本皓史; 江川贵将
Original assignee: Sumitomo Chemical Co Ltd
Current assignee: Sumitomo Chemical Co Ltd
Priority date: 2019-10-15
Filing date: 2020-10-12
Publication date: 2022-05-27
Also published as: KR20220084341A; TW202122463A; JP2021063212A; WO2021075395A1

Abstract

Provided is an optical film having excellent transparency and folding resistance. The optical film of the present invention includes a polyimide-based resin, which includes a structural unit represented by formula (1), includes a structure represented by formula (3) as Y in formula (1), and has a weight average molecular weight of 160000 or more.

Description

Optical film

Technical Field

The present invention relates to an optical film and a polyimide resin used for materials of a flexible display device and the like, and a flexible display device provided with the optical film.

Background

Display devices such as liquid crystal display devices and organic EL display devices are widely used in various applications such as mobile phones and smart watches. Glass is used as the front panel of such a display device, but glass is very rigid and easily broken, and thus it is difficult to use it as a front panel material of a flexible display device. As one of materials replacing glass, an optical film having high heat resistance and the like using a polymer such as a polyimide resin has been studied.

Patent document 1 discloses a polyimide resin containing, as monomer components, ester-type tetracarboxylic dianhydrides obtained by esterifying biphenyl-4, 4' diols with 2 trimellitic acids, and a polyimide film formed from the polyimide resin. A polyimide film formed from such a polyimide resin is advantageous in that it has high heat resistance and a low coefficient of linear thermal expansion.

Documents of the prior art

Patent document

Patent document 1: international publication No. 2014/046180

Disclosure of Invention

Problems to be solved by the invention

A film for a front panel, which is a material of a flexible display device, may also function to protect internal members of the flexible display device, and may be required to be thick in order to alleviate an impact from the outside. However, since the polyimide resin as in patent document 1 has a structure derived from a tetanic ester-type tetracarboxylic dianhydride, the transparency of the obtained polyimide film is insufficient, and particularly when the thickness is increased, the increase in haze and the decrease in transmittance become remarkable, and it is known that the transparency required for materials of flexible display devices and the like cannot be secured. In addition, an optical film used for a material of a flexible display device or the like is also required to have excellent folding resistance.

Accordingly, an object of the present invention is to provide an optical film and a polyimide-based resin which are excellent in transparency and folding resistance, and a flexible display device including the optical film.

Means for solving the problems

The present inventors have conducted intensive studies to solve the above problems, and as a result, have found that the above problems can be solved if a structure represented by formula (3) is contained as Y in formula (1) in an optical film containing a polyimide resin and the weight average molecular weight of the polyimide resin is adjusted, and have completed the present invention. That is, the present invention includes the following preferred embodiments.

[1] An optical film comprising a polyimide-based resin,

the polyimide resin comprises a structural unit represented by the formula (1),

[ chemical formula 1]

[ in the formula (1), X represents a divalent organic group,

y represents a tetravalent organic group,

denotes a bond

Y in the formula (1) has a structure represented by the formula (3), and the weight average molecular weight of the polyimide resin is 160000 or more,

[ chemical formula 2]

[ in the formula (3), R¹Independently of one another, a halogen atom, an alkyl group which may have a halogen atom, an alkoxy group, an aryl group or an aryloxy group,

R²～R⁵independently of each other, a hydrogen atom or a monovalent hydrocarbon group which may have a halogen atom,

m independently represents an integer of 0 to 3,

n represents an integer of 1 to 4,

denotes a bond wherein R is²～R⁵In at least 1 benzene ring of (2), R²～R⁵At least 1 of which is a monovalent hydrocarbon group which may have a halogen atom]。

[2] The optical film according to [1], wherein at least 1 of a divalent aromatic group, a divalent alicyclic group and a divalent aliphatic group is contained as X in the formula (1).

[3] The optical film according to [1] or [2], wherein the structure represented by formula (4) is contained as X in formula (1),

[ chemical formula 3]

[ in the formula (4), A represents a single bond, -O-, diphenylmethylene, a divalent hydrocarbon group which may have a halogen atom, -SO₂-、-S-、-CO-、-PO-、-PO₂-、-N(R^A1) -or-Si (R)^A2)₂-，

R^A1And R^A2Independently of each other, a hydrogen atom or an alkyl group which may have a halogen atom, R⁶Independently of one another, a halogen atom, an alkyl group which may have a halogen atom, an alkoxy group, an aryl group or an aryloxy group,

s independently represent an integer of 0 to 4,

denotes a bond ].

[4] The optical film according to any one of [1] to [3], which has a thickness of 35 μm or more.

[5] The optical film according to any one of [1] to [4], wherein the total light transmittance is 85% or more.

[6] The optical film according to any one of [1] to [5], which has a yellowness index of 3.0 or less.

[7] The optical film according to any one of [1] to [6], which has an elastic modulus of 3.5GPa or more.

[8] The optical film according to any one of [1] to [7], which is a film for a front panel of a flexible display device.

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

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

[11] The flexible display device according to [9] or [10], further comprising a polarizing plate.

[12] A polyimide resin comprising a structural unit represented by the formula (1),

[ chemical formula 4]

[ in the formula (1), X represents a divalent organic group,

y represents a tetravalent organic group,

denotes a bond

[ chemical formula 5]

m independently represents an integer of 0 to 3,

n represents an integer of 1 to 4,

Effects of the invention

The optical film of the present invention is excellent in transparency and folding resistance. Therefore, it can be suitably used for a material of a flexible display device or the like.

Detailed Description

[ optical film ]

The optical film of the present invention comprises a polyimide resin.

< polyimide-based resin >

The polyimide resin contained in the optical film of the present invention contains a structural unit represented by formula (1),

[ chemical formula 6]

[ in the formula (1), X represents a divalent organic group,

y represents a tetravalent organic group,

denotes a bond ].

In the formula (1), Y independently represents a tetravalent organic group, preferably a tetravalent organic group having 4 to 80 carbon atoms, and more preferably a tetravalent organic group having a cyclic structure and having 4 to 60 carbon atoms. Examples of the cyclic structure include alicyclic, aromatic ring, and heterocyclic structure. The organic group is an organic group in which a hydrogen atom in the organic group may be substituted with a substituent, and the substituent is preferably a halogen atom, a hydrocarbon group (for example, an alkyl group, an aryl group, or the like) which may have a halogen atom, an alkoxy group, or an aryloxy group, and in this case, the number of carbon atoms of the hydrocarbon group, the alkoxy group, or the aryloxy group which may have a halogen atom is preferably 1 to 8. The polyimide-based resin according to one embodiment of the present invention may contain a plurality of kinds of Y, and the plurality of kinds of Y may be the same or different from each other.

The polyimide resin of the present invention is characterized in that Y in formula (1) has a structure represented by formula (3), and the weight average molecular weight of the polyimide resin is 160000 or more,

[ chemical formula 7]

R²～R⁵independently of each other, a hydrogen atom or a monovalent hydrocarbon which may have a halogen atomThe base group is a group of a compound,

m independently represents an integer of 0 to 3,

n represents an integer of 1 to 4,

The present inventors have found that, in the case of a polyimide-based resin containing a structure represented by formula (3) as Y in formula (1) as described in patent document 1, the transparency of the obtained optical film is insufficient particularly if the thickness of the film is increased. It is also known that a reaction solution for polymerizing a polyimide resin having such a structure has a high viscosity and is difficult to polymerize, and therefore it is difficult to increase the molecular weight of the polyimide resin.

The present inventors have succeeded in increasing the weight average molecular weight of the polyimide-based resin to 160000 or more by optimizing the production conditions of the resin, and as a result, have unexpectedly found that the transparency of an optical film comprising the polyimide-based resin is significantly improved. In addition, it was found that the folding resistance of the optical film was improved.

Therefore, an optical film including the polyimide-based resin of the present invention can have excellent transparency and folding resistance. On the other hand, if the weight average molecular weight of the polyimide-based resin contained in the optical film is less than 160000, there is a tendency that an optical film having sufficient transparency and folding resistance cannot be obtained.

The polyimide resin in the present invention has a weight average molecular weight (hereinafter, abbreviated as Mw) of 160000 or more, preferably 180000 or more, more preferably 200000 or more, still more preferably 250000 or more, still more preferably 300000 or more, particularly preferably 350000 or more, preferably 1000000 or less, more preferably 800000 or less, still more preferably 700000 or less, and particularly preferably 600000 or less. When the Mw of the polyimide-based resin is not less than the lower limit, the transparency, elastic modulus and folding resistance of the obtained optical film can be easily further improved, and when the Mw is not more than the upper limit, gelation of the resin varnish can be easily suppressed, and the optical properties of the obtained optical film can be easily improved. The weight average molecular weight can be determined by, for example, gel permeation chromatography (hereinafter, sometimes referred to as GPC) measurement and conversion to standard polystyrene, and can be determined by, for example, the method described in examples.

In the formula (3), R¹Independently of one another, represents a halogen atom, an alkyl group which may have a halogen atom, an alkoxy group, an aryl group or an aryloxy group. Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom. Examples of the alkyl group include a methyl group, an ethyl group, a n-propyl group, an isopropyl group, a n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, a n-pentyl group, a 2-methyl-butyl group, a 3-methylbutyl group, a 2-ethyl-propyl group, and a n-hexyl group. Examples of the alkoxy group include a methoxy group, an ethoxy group, a propoxy group, an isopropoxy group, an n-butoxy group, an isobutoxy group, a sec-butoxy group, a tert-butoxy group, a pentyloxy group, a hexyloxy group, and a cyclohexyloxy group. Examples of the aryl group include a phenyl group, a tolyl group, a xylyl group, a naphthyl group, and a biphenyl group. Examples of the aryloxy group include a phenoxy group, a naphthoxy group, and a biphenyloxy group. R¹Independently of the others, it preferably represents a halogen atom, an alkyl group having 1 to 6 carbon atoms which may have a halogen atom, an alkoxy group having 1 to 6 carbon atoms, an aryl group having 6 to 12 carbon atoms, or an aryloxy group having 6 to 12 carbon atoms. From the viewpoint of easily improving the transparency, elastic modulus and folding resistance of the optical film, R¹The alkyl group or the alkoxy group may have a halogen atom, and the alkyl group or the alkoxy group may have 1 to 6 carbon atoms.

In the formula (3), m independently represents an integer of 0 to 3, preferably an integer of 0 to 2, more preferably 0 or 1, and even more preferably 0, from the viewpoint of easily improving the transparency, elastic modulus, and folding resistance of the optical film.

In the formula (3), R²、R³、R⁴And R⁵Independently represent a hydrogen atom or a monovalent hydrocarbon group which may have a halogen atom and has R²～R⁵In at least 1 benzene ring of (2), R²～R⁵At least 1 of them is a monovalent hydrocarbon group which may have a halogen atom. Examples of the hydrocarbon group include an aromatic hydrocarbon group, an alicyclic hydrocarbon group, and an aliphatic hydrocarbon group. Examples of the aromatic hydrocarbon group include aryl groups such as phenyl, tolyl, xylyl, naphthyl, and biphenyl. Examples of the alicyclic hydrocarbon group include a cycloalkyl group such as a cyclopentyl group and a cyclohexyl group. Examples of the aliphatic hydrocarbon group include alkyl groups such as a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, an n-pentyl group, a 2-methyl-butyl group, a 3-methylbutyl group, a 2-ethyl-propyl group, an n-hexyl group, an n-heptyl group, an n-octyl group, a tert-octyl group, an n-nonyl group, and an n-decyl group. Examples of the halogen atom include those described above. R²～R⁵Independently of each other, it preferably represents a hydrogen atom, an aryl group having 6 to 12 carbon atoms which may have a halogen atom, a cycloalkyl group having 4 to 8 carbon atoms, or an alkyl group having 1 to 6 carbon atoms. From the viewpoint of easily improving the solubility of the resin in the solvent and the transparency, elastic modulus and folding resistance of the optical film, R²～R⁵Independently of each other, a hydrogen atom or an alkyl group which may have a halogen atom is preferable, a hydrogen atom or an alkyl group which may have a halogen atom is more preferable, and a hydrogen atom or an alkyl group which may have a halogen atom is still more preferable, and 1 to 3. In addition, from the viewpoint of easily improving the solubility of the resin in the solvent and the transparency, elastic modulus and folding resistance of the optical film, the optical film has R²～R⁵Of at least 1 benzene ring, preferably R²～R⁵At least 2 of which are monovalent hydrocarbon groups which may have halogen atoms, more preferably R²～R⁵At least 3 of which are monovalent hydrocarbon groups that may have halogen atoms.

In the formula (3), n represents an integer of 1 to 4, and n is preferably an integer of 1 to 3, more preferably 2 or 3, and even more preferably 2, from the viewpoint of easily improving the transparency, elastic modulus, and folding resistance of the optical film. The structural unit represented by formula (1) may include 1 or more structures represented by formula (3) as Y.

In a preferred embodiment of the present invention, formula (3) is represented by formula (3').

[ chemical formula 8]

[ in formula (3'), a bond is represented ]

That is, at least a part of Y in formula (1) is represented by formula (3'). In such a form, the transparency, elastic modulus and folding resistance of the optical film are easily improved.

In one embodiment of the present invention, the proportion of the structural unit represented by formula (3) in Y in the structural unit represented by formula (1) is preferably 30 mol% or more, more preferably 50 mol% or more, and still more preferably 70 mol% or more, relative to the total molar amount (100 mol%) of the structural units represented by formula (1). When the ratio of the structural unit represented by formula (3) in Y is not less than the above lower limit, the transparency, elastic modulus and folding resistance of the optical film can be easily improved. The upper limit of the proportion of the structural unit represented by formula (3) in Y is 100 mol% or less. The ratio of the structural unit represented by the formula (3) of Y can be used, for example¹H-NMR was measured, or it was calculated from the charge ratio of the raw materials.

The polyimide-based resin of the present invention may further include, as Y in formula (1), structures represented by formula (20), formula (21), formula (22), formula (23), formula (24), formula (25), formula (26), formula (27), formula (28), and formula (29).

[ chemical formula 9]

In the formulae (20) to (29), W represents a bond¹Represents a single bond, -O-, diphenylmethylene, a divalent hydrocarbon group which may have a halogen atom, such as-CH₂-、-CH₂-CH₂-、-CH(CH₃)-、-C(CH₃)₂-、-C(CF₃)₂-、-Ar-、-SO₂-、-S-、-CO-、-PO-、-PO₂-、-N(R^W1) -or-Si (R)^W2)₂-、-O-Ar-O-、-Ar-O-Ar-、-Ar-CH₂-Ar-、-Ar-C(CH₃)₂-Ar-or Ar-SO₂-Ar-. Ar represents an arylene group having 6 to 20 carbon atoms which may have a fluorine atom, and a specific example thereof is a phenylene group. R^W1And R^W2Independently of each other, represents a hydrogen atom or an alkyl group which may have a halogen atom. The hydrogen atom in the group represented by the formula (20) to the formula (29) may be substituted with a methyl group, a fluoro group, a chloro group or a trifluoromethyl group; and a tetravalent chain hydrocarbon group having 6 or less carbon atoms. The hydrogen atom on the ring in the formulas (20) to (29) may be substituted by an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, or an aryl group having 6 to 12 carbon atoms. Examples of the alkyl group having 1 to 6 carbon atoms, the alkoxy group having 1 to 6 carbon atoms and the aryl group having 6 to 12 carbon atoms include R of the formula (3)¹And the groups exemplified above.

Among the groups represented by formulae (20) to (29), the group represented by formula (26), formula (28) or formula (29) is preferable, and the group represented by formula (26) is more preferable, from the viewpoint of easily improving the transparency, elastic modulus and folding resistance of the optical film. In addition, from the viewpoint of easily improving the transparency, elastic modulus and folding resistance of the optical film, W¹Preferably represents a single bond, -O-, -CH₂-、-CH₂-CH₂-、-CH(CH₃)-、-C(CH₃)₂-or C (CF)₃)₂-, more preferably represents a single bond, -O-, -CH₂-、-CH(CH₃)-、-C(CH₃)₂-or C (CF)₃)₂-, more preferably represents a single bond, -C (CH)₃)₂-or C (CF)₃)₂-, particularly preferably represents a single bond or C (CF)₃)₂-, most preferably-C (CF)₃)₂-。

In a preferred embodiment of the present invention, formula (26) is represented by formula (5),

[ chemical formula 10]

[ in the formula (5), B represents a single bond, -O-, diphenylmethylene, a divalent hydrocarbon group which may have a halogen atom, or-SO₂-、-S-、-CO-、-COO-、-PO-、-PO₂-、-N(R^B1) -or-Si (R)^B2)₂-，

R^B1And R^B2Independently of each other, represents a hydrogen atom or an alkyl group which may have a halogen atom,

R⁷independently of one another, a halogen atom, an alkyl group which may have a halogen atom, an alkoxy group, an aryl group or an aryloxy group,

t independently represents an integer of 0 to 3,

denotes a bond ].

If the polyimide-based resin further contains a structure represented by formula (5) as Y in formula (1), the solubility of the resin in a solvent, and the transparency, elastic modulus, and folding resistance of the optical film are easily improved.

In the formula (5), R⁷Independently of one another, represents a halogen atom, an alkyl group which may have a halogen atom, an alkoxy group, an aryl group or an aryloxy group. Examples of the halogen atom, the alkyl group which may have a halogen atom, the alkoxy group, the aryl group and the aryloxy group include R of the formula (3)¹And the groups exemplified above. From the viewpoint of transparency, elastic modulus and folding resistance of the optical film, R⁷Independently of each other, the alkyl group having 1 to 6 carbon atoms which may have a halogen atom is preferably represented, and the alkyl group having 1 to 3 carbon atoms which may have a halogen atom is more preferably represented.

In the formula (5), t represents an integer of 0 to 3, and preferably represents an integer of 0 to 2, more preferably 0 or 1, and even more preferably 0, from the viewpoint of easily improving the transparency, elastic modulus, and folding resistance of the optical film.

B in formula (5) independently represents a single bond, -O-, diphenylmethylene, a divalent hydrocarbon group which may have a halogen atom, -SO₂-、-S-、-CO-、-COO-、-PO-、-PO₂-、-N(R^B1) -or-Si (R)^B2)₂-，R^B1And R^B2Independently of each other, represents a hydrogen atom or an alkyl group which may have a halogen atom.

As the divalent hydrocarbon group which may have a halogen atom, R in the formula (3) may be mentioned²～R⁵The monovalent hydrocarbon group (2) may have a halogen atom, and 1 hydrogen atom may be further removed to obtain a divalent group. The divalent hydrocarbon group which may have a halogen atom may form a ring in place of 2 hydrogen atoms in the hydrogen atoms contained in the group, that is, the 2 hydrogen atoms may be replaced by a connecting bond to connect the 2 connecting bonds to form a ring, and examples of the ring include a cycloalkane ring having 3 to 12 carbon atoms. Further, the group represented by formula (5) is represented by-N (R) contained in B^B1) -and-Si (R)^B2)₂R in (A-C)^B1And R^B2Examples of the alkyl group which may have a halogen atom in (1) include R in the formula (3)¹The alkyl group in (1) may have a halogen atom and the groups exemplified above.

In the formula (5), B is preferably a single bond or a divalent hydrocarbon group which may have a halogen atom, and more preferably a single bond, -CH, from the viewpoint of easily improving the transparency, elastic modulus and folding resistance of the optical film₂-、-CH₂-CH₂-、-CH(CH₃)-、-C(CH₃)₂-or-C (CF)₃)₂-, further preferably a single bond, -C (CH)₃)₂-or-C (CF)₃)₂-, further more preferably a single bond or-C (CF)₃)₂-, particularly preferably-C (CF)₃)₂-。

In a preferred embodiment of the present invention, formula (5) is represented by formula (5').

[ chemical formula 11]

[ in formula (5') ]

That is, at least a part of Y in formula (1) is represented by formula (5'). In such a form, the transparency, elastic modulus and folding resistance of the optical film are easily improved.

In one embodiment of the present invention, when Y in formula (1) includes a structure represented by formula (5), the proportion of the structural unit represented by formula (5) in Y is preferably 5 mol% or more, more preferably 10 mol% or more, further preferably 15 mol% or more, further preferably 20 mol% or more, particularly preferably 25 mol% or more, more particularly preferably 30 mol%, preferably 80 mol% or less, more preferably 70 mol% or less, and further preferably 60 mol% or less, relative to the total molar amount of the structural units represented by formula (1). When the ratio of the structural unit represented by formula (5) in Y is in the above range, the transparency, elastic modulus and folding resistance of the optical film can be easily improved. The ratio of the structural unit represented by formula (5) in Y can be used, for example¹H-NMR was measured, or it was calculated from the charge ratio of the raw materials.

In one embodiment of the present invention, when Y in formula (1) includes a structure represented by formula (5), the total proportion of the structural unit represented by formula (3) in Y and the structural unit represented by formula (5) in Y is preferably 50 mol% or more, more preferably 70 mol% or more, further preferably 90 mol% or more, and preferably 100 mol% or less, relative to the total molar amount of the structural units represented by formula (1). When the total ratio is within the above range, the transparency, elastic modulus and folding resistance of the optical film are easily improved. The total ratio can be used, for example¹H-NMR was measured, or it was calculated from the charge ratio of the raw materials.

In the formula (1), X represents a divalent organic group, preferably a divalent organic group having 4 to 40 carbon atoms.

The polyimide-based resin in the present invention preferably contains at least 1 of a divalent aromatic group, a divalent alicyclic group, and a divalent aliphatic group, and more preferably contains a divalent aromatic group as X in formula (1) from the viewpoint of easily improving the transparency, elastic modulus, and folding resistance of the optical film. Examples of the divalent aromatic group include R in the formula (3)²～R⁵And the above exemplified arylA divalent aromatic hydrocarbon group in which 1 hydrogen atom of the hydrogen atoms in the aromatic hydrocarbon group is substituted with a connecting bond; at least 1 or more of the divalent aromatic hydrocarbon groups are bonded via a linking group, e.g., V described later¹And the like, to which the linking group is bonded. As the divalent alicyclic group, for example, there may be mentioned R in the formula (3)²～R⁵And 1 hydrogen atom of the hydrogen atoms in the alicyclic hydrocarbon groups exemplified hereinabove is substituted with a divalent alicyclic hydrocarbon group having a connecting bond; at least 1 or more of the divalent alicyclic hydrocarbon groups may be bonded via a linking group, e.g., V described later¹And the like, to which the linking group is bonded. Examples of the divalent aliphatic group include R in the formula (3)²～R⁵And 1 hydrogen atom of the hydrogen atoms in the aliphatic hydrocarbon groups exemplified hereinabove is substituted with a divalent aliphatic hydrocarbon group having a connecting bond; at least 1 or more of the divalent aliphatic hydrocarbon groups may be bonded via a linking group, e.g., V described later¹And the like, to which the linking group is bonded.

X in the formula (1) preferably represents a divalent organic group having 4 to 40 carbon atoms and having a cyclic structure such as an alicyclic ring, an aromatic ring, a heterocyclic ring structure, more preferably represents a divalent aromatic group having 4 to 40 carbon atoms and a divalent alicyclic group having 4 to 40 carbon atoms, and still more preferably represents a divalent aromatic group having 4 to 40 carbon atoms. The organic group may have a hydrogen atom substituted with a hydrocarbon group or a fluorine-substituted hydrocarbon group, and in this case, the number of carbon atoms in the hydrocarbon group and the fluorine-substituted hydrocarbon group is preferably 1 to 8. In one embodiment of the present invention, the polyimide-based resin of the present invention may contain a plurality of kinds of X, and the plurality of kinds of X may be the same or different from each other. Examples of X include groups represented by formula (10), formula (11), formula (12), formula (13), formula (14), formula (15), formula (16), formula (17), and formula (18); a group obtained by substituting a hydrogen atom in the groups represented by the formulae (10) to (18) 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.

[ chemical formula 12]

In the formulae (10) to (18),

the symbol denotes a bond of a bond,

V¹、V²and V³Independently of each other, represents a single bond, -O-, -S-, -CH₂-、-CH₂-CH₂-、-CH(CH₃)-、-C(CH₃)₂-、-C(CF₃)₂-、-SO₂-, -CO-or-N (Q) -. Wherein Q represents a monovalent hydrocarbon group having 1 to 12 carbon atoms which may have a halogen atom. Examples of the monovalent hydrocarbon group of 1 to 12 carbon atoms which may have a halogen atom include R of the formula (3)²～R⁵The monovalent hydrocarbon group which may have a halogen atom in (b) is exemplified above.

1 example is V¹And V³Is a single bond, -O-or-S-, and V²is-CH₂-、-C(CH₃)₂-、-C(CF₃)₂-or-SO₂-。V¹And V²Bonding position with respect to each ring, and V²And V³The bonding position to each ring is preferably meta-or para-position, and more preferably para-position, independently from each ring. The hydrogen atom on the ring in the formulae (10) to (18) may be substituted by an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, or an aryl group having 6 to 12 carbon atoms. Examples of the alkyl group having 1 to 6 carbon atoms, the alkoxy group having 1 to 6 carbon atoms and the aryl group having 6 to 12 carbon atoms include R of the formula (3)¹And the groups exemplified above.

In a preferred embodiment of the present invention, the polyimide-based resin in the present invention may further include a structure represented by formula (4) as X in formula (1).

[ chemical formula 13]

[ in the formula (4), A represents a single bond, -O-, diphenylmethylene, and may have a halogen atomA divalent hydrocarbon group of, -SO₂-、-S-、-CO-、-PO-、-PO₂-、-N(R^A1) -or-Si (R)^A2)₂-，

R^A1And R^A2Independently of each other, represents a hydrogen atom or an alkyl group which may have a halogen atom,

R⁶independently of one another, a halogen atom, an alkyl group which may have a halogen atom, an alkoxy group, an aryl group or an aryloxy group,

s independently represent an integer of 0 to 4,

denotes a bond

In such a form, the transparency, elastic modulus and folding resistance of the optical film are easily improved. In addition, the structural unit represented by formula (1) may contain 1 or more kinds of structures represented by formula (4) as X.

R⁶Independently of one another, represents a halogen atom, an alkyl group which may have a halogen atom, an alkoxy group, an aryl group or an aryloxy group. Examples of the halogen atom, the alkyl group which may have a halogen atom, the alkoxy group, the aryl group and the aryloxy group include R of the formula (3)¹And the groups exemplified above.

Among them, R is from the viewpoint of easily improving the transparency, elastic modulus and folding resistance of the optical film⁶Independently of each other, the alkyl group has 1 to 6 carbon atoms or the haloalkyl group has 1 to 6 carbon atoms, more preferably the alkyl group has 1 to 6 carbon atoms or the fluoroalkyl group has 1 to 6 carbon atoms, and further preferably the perfluoroalkyl group. In a preferred embodiment, R⁶Independently of one another, methyl, chloro or trifluoromethyl. s independently represents an integer of 0 to 4, and preferably represents an integer of 1 to 3, more preferably 1 or 2, and even more preferably 1, from the viewpoint of facilitating improvement of transparency, elastic modulus, and folding resistance of the optical film.

In a preferred embodiment of the present invention, it is preferred that in each benzene ring, s is 1 and R is substituted at the ortho position based on-A-⁶And R is⁶Is methyl, fluoro, chloro or trifluoromethyl.

In the formula (4), the positions of the connecting bonds are preferably meta-position or para-position, and more preferably para-position, independently from each other, based on-a-, from the viewpoint of easily improving the transparency, elastic modulus and folding resistance of the optical film.

A in the formula (4) independently represents a single bond, -O-, diphenylmethylene, a divalent hydrocarbon group which may have a halogen atom, -SO₂-、-S-、-CO-、-PO-、-PO₂-、-N(R^A1) -or-Si (R)^A2)₂-，R^A1And R^A2Independently of each other, represents a hydrogen atom or an alkyl group which may have a halogen atom.

As the divalent hydrocarbon group which may have a halogen atom, R of the formula (3) may be mentioned²～R⁵The monovalent hydrocarbon group (2) may have a halogen atom, and 1 hydrogen atom may be further removed to obtain a divalent group. The divalent hydrocarbon group which may have a halogen atom may form a ring in place of 2 hydrogen atoms in the hydrogen atoms contained in the group, that is, the 2 hydrogen atoms may be replaced by a connecting bond to connect the 2 connecting bonds to form a ring, and examples of the ring include a cycloalkane ring having 3 to 12 carbon atoms. Further, the group represented by formula (4) is represented by-N (R) contained in A^A1) -and-Si (R)^A2)₂R of (A-C)^A1And R^A2Examples of the alkyl group which may have a halogen atom in (1) include R in the formula (3)¹The alkyl group which may have a halogen atom in (1) is exemplified above.

From the viewpoint of easily improving the transparency, elastic modulus and folding resistance of the optical film, A in the formula (3) is preferably a single bond, -CH₂-、-CH₂-CH₂-、-CH(CH₃)-、-C(CH₃)₂-or-C (CF)₃)₂-, more preferably a single bond, -C (CH)₃)₂-or-C (CF)₃)₂-, more preferably a single bond or-C (CF)₃)₂-, particularly preferably a single bond.

In a preferred embodiment of the present invention, in formula (4), R is represented by formula (4) from the viewpoint of facilitating improvement in transparency, elastic modulus and folding resistance of the optical film⁶Independently represents a C1-6 haloalkyl group, s represents 1 or 2, A represents a single bond, -C (CH)₃)₂-or-C (CF)₃)₂-。

In a preferred embodiment of the present invention, formula (4) is represented by formula (4').

[ chemical formula 14]

That is, at least a part of X in formula (1) is represented by formula (4'). In such a form, the transparency, elastic modulus and folding resistance of the optical film are easily improved. The structural unit represented by formula (1) may include 1 or more structures represented by formula (4') as X.

In one embodiment of the present invention, when X in formula (1) includes a structure represented by formula (4), the proportion of the structural unit represented by formula (4) in X is preferably 30 mol% or more, more preferably 50 mol% or more, further preferably 70 mol% or more, and preferably 100 mol% or less, relative to the total molar amount of the structural units represented by formula (1). When the ratio of the structural unit represented by formula (4) in X is in the above range, the transparency, elastic modulus and folding resistance of the optical film are easily improved. The proportion of the structural unit represented by the formula (4) in X can be used, for example¹H-NMR was measured, or it was calculated from the charge ratio of the raw materials.

The polyimide-based resin in the present invention may contain a structural unit represented by formula (30) and/or a structural unit represented by formula (31) in addition to the structural unit represented by formula (1).

[ chemical formula 15]

In the formula (30), Y¹Is a tetravalent organic group, preferably an organic group in which a hydrogen atom in the organic group may be substituted with a hydrocarbon group or a fluorine-substituted hydrocarbon group. As Y¹Examples thereof include formula (20), formula (21), formula (22), formula (23), formula (24), formula (25), formula (26) and formula (27)) A group represented by the formula (28) or the formula (29), a group obtained by substituting a hydrogen atom in the group represented by the formula (20) to the formula (29) with a methyl group, a fluoro group, a chloro group or a trifluoromethyl group, and a tetravalent chain hydrocarbon group having 6 or less carbon atoms. In one embodiment of the present invention, the polyimide-based resin may contain a plurality of kinds of Y¹Plural kinds of Y¹May be the same or different from each other.

In the formula (31), Y²Is a trivalent organic group, preferably an organic group in which a hydrogen atom in the organic group may be substituted with a hydrocarbon group or a hydrocarbon group substituted with fluorine. As Y²Examples thereof include a group in which any 1 of the connecting bonds of the groups represented by the above formulae (20), (21), (22), (23), (24), (25), (26), (27), (28) and (29) is substituted with a hydrogen atom, and a chain hydrocarbon group having 6 or less trivalent carbon atoms. In one embodiment of the present invention, the polyimide-based resin may contain a plurality of kinds of Y²Plural kinds of Y²May be the same or different from each other.

In formulae (30) and (31), X¹And X²Independently of one another, are divalent organic groups, preferably organic groups in which the hydrogen atoms of the organic group may be replaced by hydrocarbon groups or fluorine-substituted hydrocarbon groups. As X¹And X²Examples thereof include the groups represented by the above-mentioned formula (10), formula (11), formula (12), formula (13), formula (14), formula (15), formula (16), formula (17) and formula (18); a group obtained by substituting a hydrogen atom in the group represented by the formula (10) to the formula (18) 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.

In one embodiment of the present invention, the polyimide-based resin includes a structural unit represented by formula (1), and optionally at least 1 structural unit selected from the structural unit represented by formula (30) and the structural unit represented by formula (31). In addition, from the viewpoint of easily improving the transparency, elastic modulus and folding resistance of the optical film, the polyimide-based resin is based on all the structural units contained in the polyimide-based resin, for example, the structural unit represented by formula (1), and in some cases, the structural unit selected from the structural unit represented by formula (30) and the structural unit represented by formula (31)The total molar amount of at least 1 kind of structural unit in the structural units (2) is preferably 80 mol% or more, more preferably 90 mol% or more, and still more preferably 95 mol% or more, of the structural units represented by the formula (1). The upper limit of the proportion of the structural unit represented by formula (1) in the polyimide resin is 100 mol% or less. The above ratio can be used, for example¹H-NMR was measured, or it was calculated from the charge ratio of the raw materials. The polyimide resin in the present invention is preferably a polyimide resin from the viewpoint of easily improving the transparency, elastic modulus, and folding resistance of the optical film.

In a preferred embodiment of the present invention, the polyimide-based resin of the present invention may contain a halogen atom such as a fluorine atom which can be introduced through the above-mentioned fluorine-containing substituent or the like. When the polyimide resin contains a halogen atom, the yellowness (hereinafter, sometimes referred to as YI value) of the optical film is easily reduced, and the elastic modulus and the folding endurance are easily improved. In addition, if the elastic modulus of the optical film is high, the occurrence of scratches, wrinkles, and the like is easily suppressed. In addition, if the YI value of the optical film is low, the transparency and visibility of the film are easily improved. The halogen atom is preferably a fluorine atom. Examples of the preferable fluorine-containing substituent for making the polyimide resin contain a fluorine atom include a fluorine group and a trifluoromethyl group.

The content of the halogen atom in the polyimide resin is preferably 1 to 40% by mass, more preferably 5 to 40% by mass, and still more preferably 5 to 30% by mass, based on the mass of the polyimide resin. When the content of the halogen atom is not less than the lower limit, the YI value of the optical film is easily decreased, and the elastic modulus and the folding endurance are easily improved. If the content of the halogen atom is not more than the above upper limit, the synthesis becomes easy.

The imidization ratio of the polyimide resin is preferably 90% or more, more preferably 93% or more, and still more preferably 96% or more. The imidization ratio is preferably not less than the above-described lower limit from the viewpoint of easily improving the optical characteristics of the optical film. The upper limit of the imidization rate is 100% or less. The imidization ratio indicates a ratio of a molar amount of imide bonds in the polyimide-based resin to a value 2 times a molar amount of structural units derived from a tetracarboxylic acid compound in the polyimide-based resin. When the polyimide resin contains a tricarboxylic acid compound, the ratio of the molar amount of imide bonds in the polyimide resin to the total of a value 2 times the molar amount of structural units derived from a tetracarboxylic acid compound in the polyimide resin and the molar amount of structural units derived from a tricarboxylic acid compound is expressed. The imidization ratio can be determined by an IR method, an NMR method, or the like.

In one embodiment of the present invention, the polyimide-based resin contained in the optical film is preferably 40% by mass or more, more preferably 50% by mass or more, further preferably 60% by mass, particularly preferably 80% by mass or more, and preferably 100% by mass or less, based on 100% by mass of the optical film.

< method for producing polyimide resin >

The method for producing the polyimide-based resin contained in the optical film of the present invention is not particularly limited. In one embodiment of the present invention, the polyimide resin containing the structural unit represented by formula (1) can be produced by a method including a step of reacting a diamine compound with a tetracarboxylic acid compound to obtain a polyamic acid, and a step of imidizing the polyamic acid. In addition to the tetracarboxylic acid compound, a tricarboxylic acid compound may be reacted.

The tetracarboxylic acid compound used for producing the polyimide-based resin preferably contains at least a compound represented by the formula (X),

[ chemical formula 16]

[ in the formula (X), R¹～R⁵N and m are each independently of R in formula (3)¹～R⁵N and m are the same]。

In addition, in the formula (X)R¹～R⁵Preferred embodiments of n and m are also the same as R in formula (3)¹～R⁵N and m are the same.

The compound represented by the formula (X) can be obtained by a conventional method, for example, by reacting trimellitic anhydride or a derivative thereof with an aromatic diol, and a commercially available product can also be used.

The structural units represented by the formulae (1) and (30) are generally derived from a diamine compound and a tetracarboxylic acid compound. The structural unit represented by the formula (31) is usually derived from a diamine compound and a tricarboxylic acid compound.

Examples of the tetracarboxylic acid compound used for the synthesis of the polyimide-based resin 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 2 or more. The tetracarboxylic acid compound may be a tetracarboxylic acid compound analog such as an acid chloride compound, in addition to the dianhydride.

Specific examples of the aromatic tetracarboxylic dianhydride include non-condensed polycyclic aromatic tetracarboxylic dianhydrides, monocyclic aromatic tetracarboxylic dianhydrides, and condensed polycyclic aromatic tetracarboxylic dianhydrides. Examples of the non-condensed polycyclic aromatic tetracarboxylic acid dianhydride include an esterified product of trimellitic anhydride and 2,2 ', 3, 3', 5,5 '-hexamethyl-4, 4' -biphenol (hereinafter, may be referred to as "TAHMBP"), an esterified product of trimellitic anhydride and 2,2 ', 3, 3' -tetramethyl-4, 4 '-biphenol, an esterified product of trimellitic anhydride and 3, 3', 5,5 '-tetramethyl-4, 4' -biphenol, 4,4 '-oxydiphthalic dianhydride, 3, 3', 4,4 '-benzophenonetetracarboxylic acid dianhydride, 2', 3,3 '-benzophenonetetracarboxylic acid dianhydride, 3, 3', 4,4 '-biphenyltetracarboxylic acid dianhydride (hereinafter, may be referred to as "BPDA"), 2', 3,3 '-biphenyltetracarboxylic acid dianhydride, 2' -biphenyltetracarboxylic acid dianhydride, 3,3 ', 4,4 ' -diphenylsulfone tetracarboxylic dianhydride, 2-bis (3, 4-dicarboxyphenyl) propane dianhydride, 2-bis (2, 3-dicarboxyphenyl) propane dianhydride, 2-bis (3, 4-dicarboxyphenoxyphenyl) propane dianhydride, 4,4 ' - (hexafluoroisopropylidene) diphthalic dianhydride (hereinafter, sometimes referred to as 6FDA), 1, 2-bis (2, 3-dicarboxyphenyl) ethane dianhydride, 1-bis (2, 3-dicarboxyphenyl) ethane dianhydride, 1, 2-bis (3, 4-dicarboxyphenyl) ethane dianhydride, 1-bis (3, 4-dicarboxyphenyl) ethane dianhydride, bis (3, 4-dicarboxyphenyl) methane dianhydride, bis (2), 3-dicarboxyphenyl) methane dianhydride, 4 '- (p-phenylenedioxy) diphthalic dianhydride, and 4, 4' - (m-phenylenedioxy) diphthalic dianhydride. Examples of the monocyclic aromatic tetracarboxylic acid dianhydride include 1,2,4, 5-benzenetetracarboxylic acid dianhydride (also referred to as pyromellitic acid dianhydride, hereinafter sometimes referred to as PMDA), and examples of the condensed polycyclic aromatic tetracarboxylic acid dianhydride include 2,3,6, 7-naphthalenetetracarboxylic acid dianhydride.

Among them, preferable examples thereof include an esterified product of trimellitic anhydride and 2,2 ', 3,3 ', 5,5 ' -hexamethyl-4, 4 ' -biphenol, an esterified product of trimellitic anhydride and 2,2 ', 3,3 ' -tetramethyl-4, 4 ' -biphenol, an esterified product of trimellitic anhydride and 3,3 ', 5,5 ' -tetramethyl-4, 4 ' -biphenol, PMDA, 4,4 ' -oxydiphthalic dianhydride, 3,3 ', 4,4 ' -benzophenone tetracarboxylic dianhydride, 2 ', 3,3 ' -benzophenone tetracarboxylic dianhydride, 3,3 ', 4,4 ' -biphenyl tetracarboxylic dianhydride, 2 ', 3,3 ' -biphenyl tetracarboxylic dianhydride, 3,3 ', 4,4 ' -diphenyl sulfone tetracarboxylic dianhydride, 2, 2-bis (3, 4-dicarboxyphenyl) propane dianhydride, 2-bis (2, 3-dicarboxyphenyl) propane dianhydride, 2-bis (3, 4-dicarboxyphenoxyphenyl) propane dianhydride, 6FDA, 1, 2-bis (2, 3-dicarboxyphenyl) ethane dianhydride, 1-bis (2, 3-dicarboxyphenyl) ethane dianhydride, 1, 2-bis (3, 4-dicarboxyphenyl) ethane dianhydride, 1-bis (3, 4-dicarboxyphenyl) ethane dianhydride, bis (3, 4-dicarboxyphenyl) methane dianhydride, bis (2, 3-dicarboxyphenyl) methane dianhydride, 4 '- (p-phenylenedioxy) diphthalic dianhydride and 4, 4' - (m-phenylenedioxy) diphthalic dianhydride, more preferable examples thereof include a esterified product of trimellitic anhydride and 2,2 ', 3, 3', 5,5 '-hexamethyl-4, 4' -biphenol, an esterified product of trimellitic anhydride and 2,2 ', 3, 3' -tetramethyl-4, 4 '-biphenol, an esterified product of trimellitic anhydride and 3, 3', 5,5 '-tetramethyl-4, 4' -biphenol, 4 '-oxydiphthalic dianhydride, BPDA, 2', 3,3 '-biphenyltetracarboxylic dianhydride, 6FDA, bis (3, 4-dicarboxyphenyl) methane dianhydride and 4, 4' - (p-phenylenedioxy) diphthalic dianhydride. These may be used alone or in combination of 2 or more.

Examples of the aliphatic tetracarboxylic dianhydride include cyclic and acyclic aliphatic tetracarboxylic dianhydrides. The cyclic aliphatic tetracarboxylic dianhydride is a tetracarboxylic dianhydride having an alicyclic hydrocarbon structure, and specific examples thereof include cycloalkanetetracarboxylic dianhydrides such as 1,2,4, 5-cyclohexanetetracarboxylic dianhydride, 1,2,3, 4-cyclobutanetetracarboxylic dianhydride and 1,2,3, 4-cyclopentanetetracarboxylic dianhydride, bicyclo [2.2.2] oct-7-ene-2, 3,5, 6-tetracarboxylic dianhydride, dicyclohexyl-3, 3 ', 4, 4' -tetracarboxylic dianhydride and positional isomers thereof. These may be used alone or in combination of 2 or more. Specific examples of the acyclic aliphatic tetracarboxylic acid dianhydride include 1,2,3, 4-butanetetracarboxylic acid dianhydride and 1,2,3, 4-pentanedicarboxylic acid dianhydride, and these can be used singly or in combination of 2 or more. In addition, a combination of a cyclic aliphatic tetracarboxylic dianhydride and an acyclic aliphatic tetracarboxylic dianhydride may be used.

Among the tetracarboxylic dianhydrides, preferred are esters of trimellitic anhydride and 2,2 ', 3,3 ', 5,5 ' -hexamethyl-4, 4 ' -biphenol, esters of trimellitic anhydride and 2,2 ', 3,3 ' -tetramethyl-4, 4 ' -biphenol, esters of trimellitic anhydride and 3,3 ', 5,5 ' -tetramethyl-4, 4 ' -biphenol, PMDA, 4,4 ' -oxydiphthalic dianhydride, 3,3 ', 4,4 ' -benzophenone tetracarboxylic dianhydride, 3,3 ', 4,4 ' -biphenyl tetracarboxylic dianhydride, 2 ', 3,3 ' -biphenyl tetracarboxylic dianhydride, 3,3 ', 4,4 ' -diphenylsulfone tetracarboxylic dianhydride, and the like, from the viewpoint of easily improving the transparency, elastic modulus and folding resistance of the optical film, 2, 2-bis (3, 4-dicarboxyphenyl) propane dianhydride, 6FDA, and mixtures thereof, more preferably a esterified product of trimellitic anhydride with 2,2 ', 3,3 ', 5,5 ' -hexamethyl-4, 4 ' -biphenol, a esterified product of trimellitic anhydride with 2,2 ', 3,3 ' -tetramethyl-4, 4 ' -biphenol, a esterified product of trimellitic anhydride with 3,3 ', 5,5 ' -tetramethyl-4, 4 ' -biphenol, 6FDA, and mixtures thereof, further preferably a esterified product of trimellitic anhydride with 2,2 ', 3,3 ', 5,5 ' -hexamethyl-4, 4 ' -biphenol, a esterified product of trimellitic anhydride with 2,2 ', 3,3 ' -tetramethyl-4, 4 ' -biphenol, and mixtures thereof, Esters of trimellitic anhydride with 3,3 ', 5,5 ' -tetramethyl-4, 4 ' -biphenol.

Examples of the diamine compound used for the synthesis of the polyimide-based resin include aliphatic diamines, aromatic diamines, and mixtures thereof. In the present embodiment, the "aromatic diamine" represents a diamine in which an amino group is directly bonded to an aromatic ring, and a part of the structure thereof may include an aliphatic group or another substituent. The aromatic ring may be a monocyclic ring or a condensed ring, and examples thereof include a benzene ring, a naphthalene ring, an anthracene ring, and a fluorene ring, but the aromatic ring is not limited thereto. Among them, benzene ring is preferable. The "aliphatic diamine" represents a diamine in which an amino group is directly bonded to an aliphatic group, and may have an aromatic ring or other substituent in a part of the structure.

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

Examples of the aromatic diamine include aromatic diamines having 1 aromatic ring such as p-phenylenediamine, m-phenylenediamine, 2, 4-toluenediamine, m-xylylenediamine, p-xylylenediamine, 1, 5-diaminonaphthalene, and 2, 6-diaminonaphthalene, 4 '-diaminodiphenylmethane, 4' -diaminodiphenylpropane, 4 '-diaminodiphenylether, 3' -diaminodiphenylether, 4 '-diaminodiphenylsulfone, 3' -diaminodiphenylsulfone, 1, 4-bis (4-aminophenoxy) benzene, 1, 3-bis (4-aminophenoxy) benzene, bis [4- (4-aminophenoxy) phenyl ] sulfone, and the like, Bis [4- (3-aminophenoxy) phenyl ] sulfone, 2-bis [4- (4-aminophenoxy) phenyl ] propane, 2-bis [4- (3-aminophenoxy) phenyl ] propane, 2 ' -dimethylbenzidine, 2 ' -bis (trifluoromethyl) -4,4 ' -diaminodiphenyl (hereinafter, may be referred to as TFMB), 4 ' - (hexafluoropropylidene) diphenylamine (hereinafter, may be referred to as 6FDAM), 4 ' -bis (4-aminophenoxy) biphenyl, 9-bis (4-aminophenyl) fluorene, 9-bis (4-amino-3-methylphenyl) fluorene, 9-bis (4-amino-3-chlorophenyl) fluorene, And aromatic diamines having 2 or more aromatic rings, such as 9, 9-bis (4-amino-3-fluorophenyl) fluorene. These may be used alone or in combination of 2 or more.

The aromatic diamine is preferably 4,4 '-diaminodiphenylmethane, 4' -diaminodiphenylpropane, 4 '-diaminodiphenylether, 3' -diaminodiphenylether, 4 '-diaminodiphenylsulfone, 3' -diaminodiphenylsulfone, 1, 4-bis (4-aminophenoxy) benzene, bis [4- (4-aminophenoxy) phenyl ] sulfone, bis [4- (3-aminophenoxy) phenyl ] sulfone, 2-bis [4- (4-aminophenoxy) phenyl ] propane, 2-bis [4- (3-aminophenoxy) phenyl ] propane, 2 '-dimethylbenzidine, TFMB, 4' -bis (4-aminophenoxy) biphenyl, more preferred are 4,4 '-diaminodiphenylmethane, 4' -diaminodiphenylpropane, 4 '-diaminodiphenyl ether, 4' -diaminodiphenylsulfone, 1, 4-bis (4-aminophenoxy) benzene, bis [4- (4-aminophenoxy) phenyl ] sulfone, 2-bis [4- (4-aminophenoxy) phenyl ] propane, 2 '-dimethylbenzidine, TFMB, 6FDAM and 4, 4' -bis (4-aminophenoxy) biphenyl. These may be used alone or in combination of 2 or more.

Among the diamine compounds, 1 or more selected from 2,2 ' -dimethylbenzidine, TFMB, 4 ' -bis (4-aminophenoxy) biphenyl, 6FDAM, and 4,4 ' -diaminodiphenyl ether are more preferably used, and TFMB and/or 6FDAM are still more preferably used, from the viewpoint of easily improving the transparency, elastic modulus, and folding resistance of the optical film.

The polyimide-based resin may be obtained by reacting a tetracarboxylic acid compound that can be used for the resin synthesis with other tetracarboxylic acids and tricarboxylic acids, and anhydrides and derivatives thereof, within a range that does not impair various physical properties of the optical film.

Examples of the other tetracarboxylic acid include water adducts of acid anhydrides of the above tetracarboxylic acid compounds.

Examples of the tricarboxylic acid compound include an aromatic tricarboxylic acid, an aliphatic tricarboxylic acid, and a similar acid chloride compound or acid anhydride thereof, and 2 or more species thereof may be used in combination. Specific examples thereof include acid anhydrides of 1,2, 4-benzenetricarboxylic acid; 2,3, 6-naphthalene tricarboxylic acid-2, 3-anhydride;phthalic anhydride and benzoic acid via a single bond, -O-, -CH₂-、-C(CH₃)₂-、-C(CF₃)₂-、-SO₂-or phenylene groups.

In the production of the polyimide-based resin, the amount of the diamine compound and the tetracarboxylic acid compound to be used may be appropriately selected depending on the ratio of each structural unit of the desired resin.

In a preferred embodiment of the present invention, the amount of the diamine compound used is preferably 0.94 mol or more, more preferably 0.96 mol or more, further preferably 0.98 mol or more, particularly preferably 0.99 mol or more, preferably 1.20 mol or less, more preferably 1.10 mol or less, further preferably 1.05 mol or less, and particularly preferably 1.02 mol or less based on 1mol of the tetracarboxylic acid compound. When the amount of the diamine compound used is within the above range relative to the tetracarboxylic acid compound, the weight average molecular weight of the polyimide resin can be easily adjusted to 160000 or more.

The reaction temperature of the diamine compound and the tetracarboxylic acid compound is not particularly limited, and may be, for example, 5 to 200 ℃ or the reaction time may be, for example, about 30 minutes to 72 hours. In a preferred embodiment of the present invention, the reaction temperature is preferably 5 to 50 ℃, more preferably 5 to 40 ℃, and still more preferably 5 to 25 ℃, and the reaction time is preferably 3 to 24 hours, and more preferably 5 to 20 hours, from the viewpoint of easily adjusting the weight average molecular weight of the polyimide resin to 160000 or more.

The reaction of the diamine compound with the tetracarboxylic acid compound is preferably carried out in a solvent. The solvent is not particularly limited as long as it does not affect the reaction, and examples thereof include alcohol solvents such as water, methanol, ethanol, ethylene glycol, isopropyl alcohol, propylene glycol, ethylene glycol methyl ether, ethylene glycol butyl ether, 1-methoxy-2-propanol, 2-butoxyethanol, and propylene glycol monomethyl ether; ester solvents such as ethyl acetate, butyl acetate, ethylene glycol methyl ether acetate, γ -butyrolactone, γ -valerolactone, propylene glycol methyl ether acetate, and ethyl lactate; ketone solvents such as acetone, methyl ethyl ketone, cyclopentanone, cyclohexanone, 2-heptanone, and methyl isobutyl ketone; aliphatic hydrocarbon solvents such as pentane, hexane, and heptane; alicyclic hydrocarbon solvents such as ethylcyclohexane; aromatic hydrocarbon solvents such as toluene and xylene; nitrile solvents such as acetonitrile; ether solvents such as tetrahydrofuran and dimethoxyethane; chlorine-containing solvents such as chloroform and chlorobenzene; amide solvents such as N, N-dimethylacetamide (hereinafter sometimes referred to as DMAc) and N, N-dimethylformamide (hereinafter sometimes referred to as DMF); sulfur-containing solvents such as dimethyl sulfone, dimethyl sulfoxide and sulfolane; carbonate solvents such as ethylene carbonate and propylene carbonate; and combinations thereof, and the like. Among them, an amide solvent can be preferably used from the viewpoint of solubility.

In a preferred embodiment of the present invention, the solvent used in the reaction is preferably a solvent that is strictly dehydrated to a water content of 700ppm or less, from the viewpoint of easily adjusting the weight average molecular weight of the polyimide-based resin to 160000 or more.

The reaction between the diamine compound and the tetracarboxylic acid compound may be carried out in an inert atmosphere such as a nitrogen atmosphere or an argon atmosphere or under reduced pressure as necessary, and is preferably carried out in the inert atmosphere while stirring in a strictly controlled dehydration solvent from the viewpoint of easily adjusting the weight average molecular weight of the polyimide resin to 160000 or more.

Examples of the imidization catalyst used in the imidization step include aliphatic amines such as tripropylamine, dibutylpropylamine, and ethyldibutylamine; n-ethylpiperidine, N-propylpiperidine, N-butylpyrrolidine, N-butylpiperidine, and N-propylhexahydroazepine

Alicyclic amines (monocyclic); azabicyclo [2.2.1]Heptane, azabicyclo [3.2.1]Octane, azabicyclo [2.2.2]Octane, and azabicyclo [3.2.2]Alicyclic amines (polycyclic) such as nonane; and aromatic amines such as pyridine, 2-methylpyridine (2-picoline), 3-methylpyridine (3-picoline), 4-methylpyridine (4-picoline), 2-ethylpyridine, 3-ethylpyridine, 4-ethylpyridine, 2, 4-dimethylpyridine, 2,4, 6-trimethylpyridine, 3, 4-cyclopentenopyridine, 5,6,7, 8-tetrahydroisoquinoline, and isoquinoline. In addition, it is easyFrom the viewpoint of promoting the imidization reaction, it is preferable to use an acid anhydride together with an imidization catalyst. Examples of the acid anhydride include conventional acid anhydrides used in the imidization reaction, and specific examples thereof include aliphatic acid anhydrides such as acetic anhydride, propionic anhydride, and butyric anhydride, and aromatic acid anhydrides such as phthalic acid.

In a preferred embodiment of the present invention, the imidization step is preferably performed in stages, and the temperature is preferably raised to an optimum reaction temperature. By stepwise imidization, decomposition of the resin is suppressed, and the weight average molecular weight of the resulting polyimide resin can be easily adjusted to 160000 or more. The reaction temperature for raising the temperature in the stepwise imidization step is preferably 40 to 85 ℃, more preferably 45 to 80 ℃. When the reaction temperature is in the above range, the imidization reaction tends to proceed sufficiently, and the molecular weight tends not to decrease easily in the imidization of amic acid in the imidization step. The reaction time is preferably 30 minutes to 10 hours, more preferably 30 minutes to 5 hours. If the reaction time is within the above range, the resin may not be decomposed and the molecular weight may not be sufficiently increased, and the imidization ratio may be lowered and the molecular weight may not be lowered in the subsequent step. Thus, by controlling the imidization step in addition to the synthesis conditions described above, a resin having a large weight average molecular weight can be obtained.

The polyimide-based resin can be isolated by a conventional method, for example, by separation and purification by a separation method combining these separation methods such as filtration, concentration, extraction, crystallization, recrystallization, column chromatography, and the like, and in a preferred embodiment, the resin can be precipitated by adding a large amount of an alcohol such as methanol to the reaction solution containing the resin, and the separation can be performed by concentration, filtration, drying, and the like.

< additives >

The optical film of the present invention may further contain at least 1 kind of filler in addition to the polyimide-based resin. Examples of the filler include organic particles and inorganic particles, and inorganic particles are preferable. Examples of the inorganic particles include silica, zirconia, alumina, titania, zinc oxide, germanium oxide, indium oxide, tin oxide, Indium Tin Oxide (ITO), metal oxide particles such as antimony oxide and cerium oxide, and metal fluoride particles such as magnesium fluoride and sodium fluoride, among which silica particles, zirconia particles and alumina particles are preferable from the viewpoint of easily satisfying both the elastic modulus and the transparency of the optical film, and silica particles are more preferable. These fillers may be used alone or in combination of 2 or more.

The average primary particle diameter of the filler and preferably the silica particles is usually 1nm or more, preferably 5nm or more, more preferably 10nm or more, further preferably 15nm or more, particularly preferably 20nm or more, preferably 100nm or less, more preferably 90nm or less, further preferably 80nm or less, further preferably 70nm or less, particularly preferably 60nm or less, more particularly preferably 50nm or less, and most preferably 40nm or less. When the average primary particle diameter of the filler, preferably silica particles, is within the above range, both the elastic modulus and the transparency of the optical film can be easily achieved. Further, aggregation of the filler, preferably silica particles, is suppressed, and the transparency of the obtained optical film is easily improved. The average primary particle diameter of the filler can be measured by the BET method. The average primary particle size may be measured by image analysis using a transmission electron microscope or a scanning electron microscope.

When the optical film of the present invention contains a filler, preferably silica particles, the content of the filler is usually 0.1% by mass or more, preferably 1% by mass or more, more preferably 5% by mass or more, further preferably 10% by mass or more, further preferably 20% by mass or more, particularly preferably 30% by mass or more, and preferably 60% by mass or less, based on the mass of the optical film. When the content of the filler is not less than the above lower limit, the elastic modulus and the transparency of the obtained optical film can be easily achieved at the same time. In addition, if the content of the filler is not more than the above upper limit, the optical properties of the optical film are easily improved.

The optical film of the present invention may further contain an ultraviolet absorber. The ultraviolet absorber can be appropriately selected from ultraviolet absorbers generally used as ultraviolet absorbers in the field of resin materials. The ultraviolet absorber may contain a compound that absorbs light having a wavelength of 400nm or less. Examples of the ultraviolet absorber include at least 1 compound selected from benzophenone-based compounds, salicylate-based compounds, benzotriazole-based compounds, and triazine-based compounds. The ultraviolet absorbers may be used alone or in combination of two or more. Since the optical film contains the ultraviolet absorber, deterioration of the resin can be suppressed, and thus, visibility can be improved when the optical film is applied to an image display device or the like. In the present specification, the term "related compound" refers to a derivative of a compound having the "related compound". For example, the "benzophenone-based compound" refers to a compound having benzophenone as a parent skeleton and a substituent bonded to benzophenone.

When the optical film contains an ultraviolet absorber, the content of the ultraviolet absorber is preferably 1% by mass or more, more preferably 2% by mass or more, further preferably 3% by mass or more, preferably 10% by mass or less, more preferably 8% by mass or less, and further preferably 6% by mass or less with respect to the mass of the optical film. The preferable content varies depending on the ultraviolet absorber used, but if the content of the ultraviolet absorber is adjusted so that the light transmittance at 400nm becomes about 20 to 60%, the light resistance of the optical film can be improved and the transparency can be easily improved.

The optical film of the present invention may further contain other additives besides the filler and the ultraviolet absorber. Examples of the other additives include antioxidants, mold release agents, stabilizers, bluing agents, flame retardants, pH adjusters, silica dispersants, lubricants, thickeners, and leveling agents. When other additives are contained, the content thereof is preferably 0.001 to 20% by mass, more preferably 0.01 to 15% by mass, and still more preferably 0.1 to 10% by mass, based on the mass of the optical film.

< optical film >

In the optical film of the present invention, since the composition represented by formula (3) is contained as Y in formula (1) and the weight average molecular weight of the polyimide-based resin is adjusted to 160000 or more, excellent transparency and excellent folding resistance can be achieved at the same time. In addition, the optical film of the present invention is also excellent in elastic modulus. Therefore, the optical film of the present invention can be suitably used for a material of a flexible display device or the like. In the present specification, the transparency can be evaluated based on the total light transmittance, the haze and the like, and the improvement or increase of the transparency means that the total light transmittance is increased and the haze is decreased.

In a preferred embodiment of the present invention, the total light transmittance of the optical film of the present invention is preferably 85% or more, more preferably 88% or more, further preferably 89% or more, particularly preferably 90% or more, and most preferably 91% or more, in terms of the total light transmittance at a thickness of 50 μm. If the total light transmittance is not less than the lower limit, the transparency of the optical film can be improved, and high visibility can be exhibited when the optical film is used for a front panel of a display device or the like, for example. The upper limit of the total light transmittance is usually 100% or less. In addition, the total light transmittance may be in accordance with JIS K7105: 1981, the haze can be measured by using a haze computer, for example, by the method described in the examples. In the present specification, the total light transmittance may be a total light transmittance within a range of the thickness of the optical film of the present invention.

In a preferred embodiment of the present invention, the haze of the optical film of the present invention is preferably 2.0% or less, more preferably 1.5% or less, further preferably 1.0% or less, further preferably 0.8% or less, particularly preferably 0.5% or less, and most preferably 0.3% or less, when the thickness is 50 μm. When the haze of the optical film is not more than the above upper limit, the transparency of the optical film can be improved, and for example, when the optical film is used for a front panel of a display device, high visibility can be exhibited. The lower limit of the haze of the optical film is usually 0% or more. The haze may be measured according to JIS K7136: the measurement is carried out using a haze computer or the like, and can be carried out, for example, by the method described in examples. In the present description, the haze may be a haze within the range of the thickness of the optical film of the present invention.

In a preferred embodiment of the present invention, the YI value of the optical film of the present invention is preferably 3.0 or less, more preferably 2.8 or less, further preferably 2.5 or less, and usually-5 or more, preferably-2 or more. When the YI value of the optical film is not more than the above upper limit, the transparency of the optical film can be improved, and when the optical film is used for a front panel of a display device or the like, high visibility can be exhibited. The YI value can be calculated based on the formula of YI × (100 × (1.2769X-1.0592Z)/Y by measuring the transmittance of light of 300 to 800nm using an ultraviolet-visible near-infrared spectrophotometer to obtain the tristimulus value (X, Y, Z). For example, the calculation can be performed by the method described in the examples.

In a preferred embodiment of the present invention, the optical film of the present invention has excellent elastic modulus in addition to transparency and folding resistance. The elastic modulus of the optical film of the present invention is preferably 3.5GPa or more, more preferably 4.0GPa or more, and still more preferably 4.5GPa or more. When the elastic modulus is not less than the above lower limit, the deformation of the optical film is easily suppressed, and the durability is easily improved. The upper limit of the elastic modulus is not particularly limited, but is usually 15GPa or less. The modulus of elasticity can be measured using a tensile tester. More specifically, the elastic modulus can be measured by a tensile tester under the conditions of a chuck-to-chuck distance of 50mm and a tensile speed of 10 mm/min, and the stress-strain curve (S-S curve) can be used. The elastic modulus is a value at 25 ℃.

In a preferred embodiment of the present invention, the optical film of the present invention has excellent folding endurance. In the optical film of the present invention, the number of folding endurance tests in the MIT folding endurance test in accordance with ASTM standard D2176-16 is preferably 350000 or more, more preferably 400000 or more, and still more preferably 450000 or more. If the number of times of folding is not less than the above lower limit, the occurrence of cracks, fractures, and the like can be effectively suppressed even if the folding is repeated. The MIT bending fatigue test can be measured using an MIT bending fatigue tester, and can be measured, for example, by the method described in examples.

The total light transmittance and haze vary according to the thickness of the optical film, and the greater the thickness, the lower the total light transmittance, and the higher the haze. That is, it is difficult to produce an optical film having a high total light transmittance and a low haze in a film having a large thickness.

On the other hand, since the optical film of the present invention has a high level of transparency, it can exhibit high total light transmittance and low haze even if the thickness is large. Therefore, the thickness of the optical film of the present invention may be preferably 35 μm or more, more preferably 40 μm or more, and still more preferably 45 μm or more. The upper limit of the thickness of the optical film of the present invention is preferably 100 μm or less, more preferably 80 μm or less, and still more preferably 60 μm or less. The thickness of the optical film can be measured by a film thickness meter or the like, and can be measured, for example, by the method described in examples.

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

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

The thickness of the hard coat layer is not particularly limited, and may be, for example, 2 to 100 μm. When the thickness of the hard coat layer is within the above range, the impact resistance can be improved, the folding resistance is less likely to be lowered, and the problem of occurrence of curling due to curing shrinkage is less likely to occur. The hard coat layer may be formed by curing a hard coat composition containing a reactive material that can form a crosslinked structure by irradiation with active energy rays or thermal energy imparting, and the hard coat layer is preferably formed by irradiation with active energy rays. The active energy ray is defined as an energy ray capable of decomposing a compound generating an active species to generate an active species, and examples thereof include visible light, ultraviolet ray, infrared ray, X-ray, α -ray, β -ray, γ -ray, electron beam, and the like, and preferable examples thereof include ultraviolet ray. The hard coat composition contains at least 1 polymer of a radical polymerizable compound and a cation polymerizable compound.

The radical polymerizable compound is a compound having a radical polymerizable group. The radical polymerizable group of the radical polymerizable compound may be any functional group capable of undergoing a radical polymerization reaction, and examples thereof include a group containing a carbon-carbon unsaturated double bond, specifically, a vinyl group and a (meth) acryloyl group. When the radical polymerizable compound has 2 or more radical polymerizable groups, the radical polymerizable groups may be the same or different. The number of the radical polymerizable groups in 1 molecule of the radical polymerizable compound is preferably 2 or more in order to increase the hardness of the hard coat layer. The radical polymerizable compound preferably includes a compound having a (meth) acryloyl group in view of high reactivity, specifically, a compound called a multifunctional acrylate monomer having 2 to 6 (meth) acryloyl groups in 1 molecule, an epoxy (meth) acrylate, a urethane (meth) acrylate, an oligomer called a polyester (meth) acrylate having a plurality of (meth) acryloyl groups in a molecule and having a molecular weight of several hundred to several thousand, and preferably 1 or more selected from the group consisting of an epoxy (meth) acrylate, a urethane (meth) acrylate, and a polyester (meth) acrylate.

The cationically polymerizable compound is a compound having a cationically polymerizable group such as an epoxy group, an oxetane group, or a vinyloxy group. The number of the cationically polymerizable groups contained in 1 molecule of the cationically polymerizable compound is preferably 2 or more, and more preferably 3 or more, from the viewpoint of improving the hardness of the hard coat layer.

Among the above cationically polymerizable compounds, preferred are compounds having at least 1 of an epoxy group and an oxetane group as a cationically polymerizable group. From the viewpoint of reducing shrinkage accompanying the polymerization reaction, a cyclic ether group such as an epoxy group or an oxetane group is preferable. In addition, the compound having an epoxy group in a cyclic ether group has the following advantages: it is easy to obtain compounds having various structures, to exert no adverse effect on the durability of the obtained hard coat layer, and to control the compatibility with the radical polymerizable compound. In addition, the oxetanyl group in the cyclic ether group has advantages that the polymerization degree is easily increased, the toxicity is low, the network formation rate of the cationically polymerizable compound in the obtained hard coat layer is increased, and an independent network is formed even in a region where the radically polymerizable compound is mixed with the epoxy group without leaving an unreacted monomer in the film.

Examples of the cationically polymerizable compound having an epoxy group include polyglycidyl ethers of polyhydric alcohols having an alicyclic ring, and alicyclic epoxy resins obtained by epoxidizing compounds containing a cyclohexene ring or a cyclopentene ring with an appropriate oxidizing agent such as hydrogen peroxide or a peracid; aliphatic epoxy resins such as polyglycidyl ethers of aliphatic polyhydric alcohols or alkylene oxide adducts thereof, polyglycidyl esters of aliphatic long-chain polybasic acids, homopolymers and copolymers of glycidyl (meth) acrylate; glycidyl ethers produced by the reaction of epichlorohydrin with bisphenols such as bisphenol a, bisphenol F, and hydrogenated bisphenol a, or derivatives thereof such as alkylene oxide adducts and caprolactone adducts, and glycidyl ether type epoxy resins derived from bisphenols such as phenol novolac epoxy resins.

The above hard coat composition may further comprise a polymerization initiator. Examples of the polymerization initiator include a radical polymerization initiator, a cationic polymerization initiator, and the like, and can be appropriately selected and used. These polymerization initiators are decomposed by at least one of irradiation with active energy rays and heating to generate radicals or cations to perform radical polymerization and cationic polymerization.

The radical polymerization initiator may be any one that can release a substance that initiates radical polymerization by at least one of irradiation with active energy rays and heating. Examples of the thermal radical polymerization initiator include organic peroxides such as hydrogen peroxide and perbenzoic acid, and azo compounds such as azobisbutyronitrile.

The active energy ray radical polymerization initiator includes a Type1 radical polymerization initiator which generates radicals by decomposition of molecules and a Type2 radical polymerization initiator which generates radicals by hydrogen abstraction reaction in the coexistence of a tertiary amine, and they can be used alone or in combination.

The cationic polymerization initiator may be a cationic polymerization initiator that can release a substance that initiates cationic polymerization by at least either irradiation with active energy rays or heating. As the cationic polymerization initiator, aromatic iodonium salts, aromatic sulfonium salts, cyclopentadienyl iron (II) complexes, and the like can be used. They may initiate cationic polymerization by either or both of irradiation with active energy rays or heating depending on the structure.

The polymerization initiator may be preferably contained in an amount of 0.1 to 10% by mass based on 100% by mass of the entire hard coat composition. When the content of the polymerization initiator is within the above range, the curing can be sufficiently advanced, the mechanical properties and the adhesion of the finally obtained coating film can be in a favorable range, and poor adhesion, cracking, and curling due to curing shrinkage tend to be less likely to occur.

The above hard coating composition may further comprise one or more selected from solvents and additives.

The solvent can dissolve or disperse the polymerizable compound and the polymerization initiator, and any solvent known as a solvent for a hard coat composition in the art can be used within a range not to impair the effect of the present invention.

The above additives may further contain inorganic particles, leveling agents, stabilizers, surfactants, antistatic agents, lubricants, antifouling agents, and the like.

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

The pressure-sensitive adhesive layer is a layer having a pressure-sensitive adhesive function, and has a function of bonding the optical film to another member. As a material for forming the adhesive layer, a generally known material can be used. For example, a thermosetting resin composition or a photocurable 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 after the end of the curing process.

The Pressure-Sensitive Adhesive layer may be a layer called a Pressure-Sensitive Adhesive (PSA) that is pressed and attached to an object. The pressure-sensitive adhesive may be a capsule type adhesive which is an "adhesive having adhesiveness at normal temperature and adhering to an adherend under light pressure" (JIS K6800) or an "adhesive capable of holding stability until a protective coating (microcapsule) contains a specific component and the coating is broken by an appropriate means (pressure, heat, etc.)" (JIS K6800).

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

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

In one embodiment of the present invention, the optical film may have a protective film on at least one side, i.e., one side or both sides. For example, when the optical film has a functional layer on one surface thereof, the protective film may be laminated on the surface of the optical film or the surface of the functional layer, or may be laminated on both the optical film and the functional layer. When the optical film has functional layers on both surfaces, the protective film may be laminated on the surface on one functional layer side or may be laminated on the surfaces on both functional layer sides. The protective film is a film for temporarily protecting the surface of the optical film or the functional layer, and is not particularly limited as long as it is a peelable film capable of protecting the surface of the optical film or the functional layer. Examples of the protective film include polyester resin films such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate; polyolefin resin films such as polyethylene and polypropylene films, and acrylic resin films, and are preferably selected from the group consisting of polyolefin resin films, polyethylene terephthalate resin films, and acrylic resin films. In the case where the optical film has 2 protective films, the respective protective films may be the same or different.

The thickness of the protective film is not particularly limited, but is usually 10 to 120 μm, preferably 15 to 110 μm, and more preferably 20 to 100 μm. In the case where the optical film has 2 protective films, the thicknesses of the respective protective films may be the same or different.

[ method for producing optical film ]

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

(a) A step (varnish preparation step) of preparing a liquid (sometimes referred to as a resin varnish) containing the polyimide-based resin;

(b) a step (coating step) of applying a resin varnish to a base material to form a coating film; and

(c) and a step of drying the applied liquid (coating film) to form an optical film (optical film forming step).

In the varnish preparation step, the resin varnish is prepared by dissolving the polyimide resin in a solvent, adding the additive as needed, and stirring and mixing the mixture.

The solvent used in the preparation of the resin varnish is not particularly limited as long as it can dissolve the resin. Examples of the solvent include amide solvents such as DMAc and DMF; lactone solvents such as γ -butyrolactone (hereinafter, sometimes referred to as GBL) and γ -valerolactone; sulfur-containing solvents such as dimethyl sulfone, dimethyl sulfoxide and sulfolane; carbonate solvents such as ethylene carbonate and propylene carbonate; and combinations thereof. Among them, an amide solvent or a lactone solvent is preferable. These solvents may be used alone or in combination of two or more. The resin varnish may contain water, an alcohol solvent, a ketone solvent, an acyclic ester solvent, an ether solvent, and the like. The solid content concentration of the varnish is preferably 1 to 25% by mass, and more preferably 5 to 15% by mass. In the present specification, the solid content of the varnish indicates the total amount of components obtained by removing the solvent from the varnish.

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

In the optical film forming step, the coating film is dried and peeled from the substrate, whereby an optical film can be formed. After the peeling, a drying step of drying the optical film may be further performed. The drying of the coating film can be carried out at a temperature of usually 50 to 350 ℃ and preferably 50 to 230 ℃. In a preferred embodiment of the present invention, the drying is preferably performed in stages. A varnish containing a high molecular weight resin tends to have a high viscosity, and it is generally difficult to obtain a uniform film, and a film having excellent transparency may not be obtained. Therefore, by performing the drying step by step, the varnish containing the high molecular weight resin can be uniformly dried, and the transparency can be improved. If necessary, the coating film may be dried under an inert atmosphere. Further, if the optical film is dried under vacuum conditions, fine bubbles may be generated or remain in the film, which may cause deterioration of transparency, and therefore, it is preferable to perform the drying under atmospheric pressure.

Examples of the substrate include a PET film, a PEN film, another polyimide resin, a polyamide resin film, and the like. Among them, a PET film, a PEN film, and the like are preferable from the viewpoint of excellent heat resistance, and a PET film is more preferable from the viewpoint of adhesion to an optical film and cost.

The optical film of the present invention can be suitably used as a front panel (sometimes referred to as a window film) of a display device, particularly a flexible display device, particularly a front panel of a rollable display, a foldable display. That is, the optical film of the present invention is preferably a film for a front panel of a flexible display device. The front panel has a function of protecting the display elements of the flexible display device. The flexible display device is a display device used in association with operations such as repeated bending and repeated winding of the image display device. The front panel of such a flexible display device used with repeated bending operations is required to have high folding endurance. In addition, high visibility is also required for the front panel. In comparison with a film for a substrate of an image display device used inside an image display device, a film for a front panel of an image display device, particularly a front panel of a flexible display device, is required to have high visibility and high folding resistance. For example, the film of the present invention preferably has the above-described total light transmittance, haze and/or YI value from the viewpoint of easily improving the visibility when used for a front panel of a flexible display device, and preferably satisfies the above-described folding endurance in the folding endurance test from the viewpoint of easily improving the folding endurance when used as a front panel of a flexible display device.

Examples of the display device include wearable devices such as televisions, smartphones, mobile phones, car navigation systems, tablet PCs, portable game machines, electronic papers, indicators, bulletin boards, clocks, and smartwatches. Examples of the flexible display include display devices having flexible characteristics, such as televisions, smartphones, mobile phones, and smartwatches. Examples of the flexible display device include all image display devices having a flexible property, such as the above-described rollable display and foldable display. A rollable display is an image display device used in a state where an image display portion including a front panel is rolled in a roll shape and the image display portion is drawn out to be flat or curved, and is an image display device that performs an operation such as rolling in a roll shape every time it is used. The foldable display is an image display device used in a state where an image display portion including a front panel is folded and the image display portion is opened to be flat or curved, and is an image display device which performs an operation such as folding every time it is used. Such an image display device in which operations such as winding and bending are repeated is referred to as a flexible display device.

[ Flexible display device ]

The present invention includes a flexible display device provided with the optical film of the present invention. The optical film of the present invention is preferably used as a front panel in a flexible display device, which is sometimes referred to as a window film. The flexible display device includes a laminate for flexible display device and an organic EL display panel, and the laminate for flexible display device is arranged on the viewing side of the organic EL display panel and is configured to be bendable. The laminate for a flexible display device may further contain a polarizing plate and a touch sensor, and the order of lamination is arbitrary, and preferably, the laminate is laminated in the order of a window film, a polarizing plate, a touch sensor or a window film, a touch sensor, and a polarizing plate from the viewing side. If the polarizing plate is present at a position closer to the viewing side than the touch sensor, the pattern of the touch sensor is not easily viewed, and the visibility of the display image is improved, which is preferable. The respective members may be laminated using an adhesive, or the like. Further, the light-shielding film may include a light-shielding pattern formed on at least one surface of any one of the window film, the polarizing plate, and the touch sensor.

[ polarizing plate ]

As described above, the flexible display device of the present invention preferably further includes a polarizing plate, and particularly, preferably further includes a circularly polarizing plate. The circularly polarizing plate is a functional layer having a function of transmitting only right-or left-handed circularly polarized light components by laminating a λ/4 phase difference plate on a linearly polarizing plate. For example, the present invention is used to convert external light into right-circularly polarized light, block external light reflected by the organic EL panel and turned into left-circularly polarized light, and transmit only light emitting components of the organic EL panel, thereby suppressing the influence of reflected light and facilitating the observation of an image. In order to realize the circularly polarized light function, the absorption axis of the linearly polarizing plate and the slow axis of the λ/4 phase difference plate need to be 45 ° in theory, but in practical use, 45 ± 10 °. The linear polarizing plate and the λ/4 phase difference plate do not necessarily have to be stacked adjacent to each other as long as the relationship between the absorption axis and the slow axis satisfies the above range. It is preferable to realize completely circularly polarized light at all wavelengths, but this is not necessarily the case in practical applications, and therefore the circularly polarizing plate in the present invention also includes an elliptically polarizing plate. It is also preferable that a λ/4 retardation film is further laminated on the viewing side of the linear polarizing plate to convert the emitted light into circularly polarized light, thereby improving the viewing ability in a state where the polarized sunglasses are worn.

The linear polarizing plate is a functional layer having the following functions: light vibrating in the direction of the transmission axis is allowed to pass through, and polarized light of a vibration component perpendicular to the light is blocked. The linear polarizing plate may be a single linear polarizer or a linear polarizer and a protective film attached to at least one surface of the linear polarizer. The thickness of the linear polarizer may be 200 μm or less, and preferably 0.5 to 100 μm. If the thickness of the linear polarizing plate is in the above range, the flexibility of the linear polarizing plate tends not to be easily reduced.

The linear polarizer may be a film-type polarizer produced by dyeing and stretching a polyvinyl alcohol (hereinafter, abbreviated as PVA) film. The polarizing film exhibits polarization performance by orienting a dichroic dye such as iodine by adsorbing the dichroic dye to a PVA-based film that has been oriented by stretching or stretching the film in a state of being adsorbed to PVA. The production of the film-type polarizing plate may further include steps such as swelling, crosslinking with boric acid, washing with an aqueous solution, and drying. The stretching and dyeing step may be performed as a PVA film alone or in a state of being laminated with another film such as polyethylene terephthalate. The thickness of the PVA film to be used is preferably 10 to 100 μm, and the stretching ratio is preferably 2 to 10 times.

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

The dichroic dye compound may have a polymerizable functional group, and may have liquid crystal properties by itself.

Any one of the compounds contained in the liquid crystal polarizing composition has a polymerizable functional group. The liquid crystal polarizing composition may further include an initiator, a solvent, a dispersant, a leveling agent, a stabilizer, a surfactant, a crosslinking agent, a silane coupling agent, and the like.

The liquid crystal polarizing layer is produced by applying a liquid crystal polarizing composition to an alignment film to form a liquid crystal polarizing layer. The liquid crystal polarizing layer can be formed thinner than the film-type polarizing plate, and the thickness thereof is preferably 0.5 to 10 μm, more preferably 1 to 5 μm.

The alignment film is produced by, for example, applying an alignment film-forming composition to a base material and imparting alignment properties by rubbing, polarized light irradiation, or the like. The alignment film-forming composition may contain an alignment agent, and may further contain a solvent, a crosslinking agent, an initiator, a dispersant, a leveling agent, a silane coupling agent, and the like. Examples of the orientation agent include polyvinyl alcohols, polyacrylates, polyamide acids, and polyimides. In the case of using an aligning agent which imparts alignment properties by polarized light irradiation, it is preferable to use an aligning agent containing a cinnamate group. The weight average molecular weight of the polymer used as the orientation agent is, for example, about 10000 to 1000000. The thickness of the alignment film is preferably 5 to 10000nm, and more preferably 10 to 500nm in view of sufficiently expressing an alignment controlling force.

The liquid crystal polarizing layer may be formed by peeling off the substrate and then transferring the resultant, or the substrate may be directly formed. The substrate preferably functions as a transparent substrate for a protective film, a retardation plate, and a window film.

The protective film may be a transparent polymer film, and may be made of the same material or additive as that used for the transparent base material of the window film. The protective film may be a coating type protective film obtained by coating and curing a cationically curable composition such as an epoxy resin or a radically curable composition such as an acrylate. The protective film may contain a plasticizer, an ultraviolet absorber, an infrared absorber, a pigment, a colorant such as a dye, a fluorescent brightener, a dispersant, a heat stabilizer, a light stabilizer, an antistatic agent, an antioxidant, a lubricant, a solvent, and the like as required. The thickness of the protective film is preferably 200 μm or less, and more preferably 1 to 100 μm. If the thickness of the protective film is within the above range, the flexibility of the film tends not to be easily lowered.

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

The thickness of the stretched phase difference plate is preferably 200 μm or less, and more preferably 1 to 100 μm. If the thickness of the stretched retardation film is within the above range, the flexibility of the stretched retardation film tends not to be easily lowered.

Further, another example of the λ/4 retardation plate is a liquid crystal coating type retardation plate formed by coating a liquid crystal composition.

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

The liquid crystal composition may further include an initiator, a solvent, a dispersant, a leveling agent, a stabilizer, a surfactant, a crosslinking agent, a silane coupling agent, and the like.

The liquid crystal coating type retardation plate can be produced by coating a liquid crystal composition on a substrate and curing the coating to form a liquid crystal retardation layer, similarly to the liquid crystal polarizing layer. The liquid crystal coating type retardation plate can be formed thinner than the stretching type retardation plate. The thickness of the liquid crystal polarizing layer is preferably 0.5 to 10 μm, and more preferably 1 to 5 μm.

The liquid crystal-coated retardation film may be laminated by being peeled off from a substrate and then transferred, or the substrate may be directly laminated. The substrate preferably functions as a transparent substrate for a protective film, a retardation plate, and a window film.

In general, the birefringence is larger as the wavelength is shorter, and more materials exhibit smaller birefringence as the wavelength is longer. In this case, since a retardation of λ/4 cannot be realized in all visible light regions, the in-plane retardation can be designed to be preferably 100 to 180nm, more preferably 130 to 150nm, so as to be λ/4 in the vicinity of 560nm, which has high visibility. The inverse dispersion λ/4 phase difference plate using a material having a birefringence wavelength dispersion characteristic opposite to that of the usual one is preferable in view of good visibility. As such a material, for example, a material described in japanese patent application laid-open No. 2007-232873 and the like can be used for the stretching type retardation plate, and a liquid crystal coating type retardation plate described in japanese patent application laid-open No. 2010-30979 and the like can be used for the liquid crystal coating type retardation plate.

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

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

[ touch sensor ]

As described above, the flexible display device of the present invention preferably further includes a touch sensor. A touch sensor may be used as an input mechanism. The touch sensor includes various types such as a resistive film type, a surface acoustic wave type, an infrared ray type, an electromagnetic induction type, and a capacitance type, and preferably includes a capacitance type.

The electrostatic capacitive touch sensor may be divided into an active region and a non-active region located at a peripheral portion of the active region. The active area is an area corresponding to an area of a display portion on the display panel where a screen is displayed, and is an area where a touch of a user is sensed, and the inactive area is an area corresponding to an area of the display portion on the display device where the screen is not displayed. The touch sensor may include: a substrate having flexible properties; a sensing pattern formed in an active region of the substrate; and sensing lines formed in the non-active region of the substrate and connected to an external driving circuit via the sensing patterns and the pad portions. As the substrate having the flexible property, the same material as the transparent substrate of the window film can be used.

The sensing pattern may include a 1 st pattern formed along a 1 st direction and a 2 nd pattern formed along a 2 nd direction. The 1 st pattern and the 2 nd pattern are arranged in different directions from each other. The 1 st pattern and the 2 nd pattern are formed in the same layer, and in order to sense a touched position, the patterns must be electrically connected. The 1 st pattern is a configuration in which a plurality of unit patterns are connected to each other via a terminal, and the 2 nd pattern is a configuration in which a plurality of unit patterns are separated from each other in an island form, and therefore, in order to electrically connect the 2 nd pattern, an additional bridge electrode is required. As the electrode for connecting the 2 nd pattern, a known transparent electrode can be applied. Examples of the material of the transparent electrode include Indium Tin Oxide (ITO), Indium Zinc Oxide (IZO), zinc oxide (ZnO), Indium Zinc Tin Oxide (IZTO), Indium Gallium Zinc Oxide (IGZO), Cadmium Tin Oxide (CTO), PEDOT (poly (3,4-ethylenedioxythiophene)), Carbon Nanotubes (CNTs), graphene, and a metal wire, and ITO is preferably used. These may be used alone or in combination of 2 or more. The metal used in the metal wire is not particularly limited, and examples thereof include silver, gold, aluminum, copper, iron, nickel, titanium, selenium, chromium, and the like, and these may be used singly or in combination of 2 or more.

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

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

With the above touch sensor, as means for appropriately compensating for a difference in transmittance between a pattern region where a sensing pattern is formed and a non-pattern region where no sensing pattern is formed, specifically, a difference in transmittance caused by a difference in refractive index in these regions, an optical adjustment layer may be further included between the substrate and the electrode. The optical adjustment layer may contain an inorganic insulating substance or an organic insulating substance. The optical adjustment layer may be formed by applying a photocurable composition including a photocurable organic binder and a solvent onto a substrate. The above-mentioned photocurable composition may further comprise inorganic particles. The refractive index of the optical adjustment layer can be increased by the inorganic particles.

The photocurable organic binder may contain a copolymer of monomers such as an acrylate monomer, a styrene monomer, and a carboxylic acid monomer within a range not to impair the effects of the present invention. The photocurable organic binder may be, for example, a copolymer containing repeating units different from each other, such as repeating units containing an epoxy group, repeating units containing an acrylate, repeating units containing a carboxylic acid, and the like.

Examples of the inorganic particles include zirconia particles, titania particles, and alumina particles.

The photocurable composition may further contain various additives such as a photopolymerization initiator, a polymerizable monomer, and a curing assistant.

[ adhesive layer ]

The layers such as the window film, circularly polarizing plate, and touch sensor, and the film members such as the linearly polarizing plate and the λ/4 retardation plate constituting each layer, which form the laminate for a flexible display device, may be bonded to each other with an adhesive. As the adhesive, a commonly used adhesive such as an aqueous adhesive, an organic solvent adhesive, a solventless adhesive, a solid adhesive, a solvent volatile adhesive, an aqueous solvent volatile adhesive, a moisture curable adhesive, a heat curable adhesive, an anaerobic curable adhesive, an active energy ray curable adhesive, a curing agent hybrid adhesive, a hot melt adhesive, a pressure sensitive adhesive, a remoistenable adhesive, or the like can be used, and an aqueous solvent volatile adhesive, an active energy ray curable adhesive, or a pressure sensitive adhesive can be preferably used. The thickness of the adhesive layer can be adjusted as appropriate in accordance with the required adhesive strength and the like, and is preferably 0.01 to 500 μm, more preferably 0.1 to 300 μm. The laminate for a flexible display device has a plurality of adhesive layers, and the thickness and type of each layer may be the same or different.

The aqueous solvent-volatile adhesive may be a polyvinyl alcohol polymer, a water-soluble polymer such as starch, or a water-dispersed polymer such as an ethylene-vinyl acetate emulsion or a styrene-butadiene emulsion. In addition to the above-mentioned main agent polymer and water, a crosslinking agent, a silane compound, an ionic compound, a crosslinking catalyst, an antioxidant, a dye, a pigment, an inorganic filler, an organic solvent, and the like may be blended. In the case of bonding with the aqueous solvent volatile adhesive, adhesiveness may be imparted by injecting the aqueous solvent volatile adhesive between the layers to be bonded, bonding the layers to be bonded, and then drying. When the aqueous solvent-volatile adhesive is used, the thickness of the adhesive layer is preferably 0.01 to 10 μm, more preferably 0.1 to 1 μm. When the aqueous solvent volatile adhesive is used in a plurality of layers, the thickness and type of each layer may be the same or different.

The active energy ray-curable adhesive may be formed by curing an active energy ray-curable composition containing a reactive material that forms an adhesive layer by irradiation with an active energy ray. The active energy ray-curable composition may contain at least 1 polymer of the radical polymerizable compound and the cationic polymerizable compound, which are the same as the polymers contained in the hard coat composition. The radical polymerizable compound may be the same as the radical polymerizable compound in the hard coat composition.

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

As the cationically polymerizable compound which can be used in the active energy ray-curable composition, an epoxy compound is particularly preferable. In order to reduce the viscosity as an 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 contain a monofunctional compound. Examples of the monofunctional compound include an acrylate monomer having 1 (meth) acryloyl group in 1 molecule, and a compound having 1 epoxy group or oxetanyl group in 1 molecule, for example, glycidyl (meth) acrylate.

The active energy ray composition may further include a polymerization initiator. Examples of the polymerization initiator include a radical polymerization initiator, a cationic polymerization initiator, and the like, and they can be appropriately selected and used. These polymerization initiators are decomposed by at least one of irradiation with active energy rays and heating, and radical polymerization and cationic polymerization are carried out by generating radicals or cations. At least one initiator capable of initiating radical polymerization or cationic polymerization by irradiation with active energy rays described in the description of the hard coat composition may be used.

The active energy ray-curable composition may further contain an ion scavenger, an antioxidant, a chain transfer agent, an adhesion-imparting agent, a thermoplastic resin, a filler, a flow viscosity modifier, a plasticizer, a defoaming agent solvent, an additive, and a solvent. When 2 layers to be bonded are bonded by the active energy ray-curable adhesive, the bonding can be performed by: the active energy ray-curable composition is applied to either or both of the adhesive layers and then bonded to each other, and the adhesive layers are cured by irradiation with active energy rays. When the active energy ray-curable adhesive is used, the thickness of the adhesive layer is preferably 0.01 to 20 μm, more preferably 0.1 to 10 μm. When the active energy ray-curable adhesive is used to form a plurality of adhesive layers, the thickness and type of each layer may be the same or different.

The adhesive may be classified into an acrylic adhesive, a urethane adhesive, a rubber adhesive, a silicone adhesive, and the like according to the base polymer, and may be used. The pressure-sensitive adhesive may contain a crosslinking agent, a silane compound, an ionic compound, a crosslinking catalyst, an antioxidant, a tackifier, a plasticizer, a dye, a pigment, an inorganic filler, and the like in addition to the main polymer. The adhesive layer-bonding layer is formed by dissolving and dispersing the components constituting the adhesive in a solvent to obtain an adhesive composition, applying the adhesive composition onto a substrate, and then drying the adhesive composition. The adhesive layer may be formed directly or a separate adhesive layer formed on the substrate may be transferred. A release film is also preferably used to cover the pressure-sensitive adhesive surface before bonding. When the active energy ray-curable adhesive is used, the thickness of the adhesive layer is preferably 0.1 to 500 μm, more preferably 1 to 300 μm. When a plurality of layers of the above-mentioned adhesive are used, the thickness and type of each layer may be the same or different.

[ light-shielding pattern ]

The light blocking pattern may be applied as at least a portion of a bezel or a housing of the flexible display device. The wiring disposed at the edge of the flexible display device is hidden by the light-shielding pattern, so that the wiring is not easily visible, thereby improving the visibility of the image. The light-shielding pattern may be in the form of a single layer or a plurality of layers. The color of the light-shielding pattern is not particularly limited, and may be various colors such as black, white, and metallic colors. The light-shielding pattern may be formed of a pigment for color development and polymers such as acrylic resin, ester resin, epoxy resin, polyurethane, silicone, and the like. They may be used alone or in the form of a mixture of 2 or more. The light-shielding pattern can be formed by various methods such as printing, photolithography, and inkjet. The thickness of the light-shielding pattern is preferably 1 to 100 μm, and more preferably 2 to 50 μm. Further, it is preferable to provide a shape such as an inclination in the thickness direction of the light-shielding pattern.

[ polyimide resin ]

The present invention includes a polyimide-based resin that includes a structural unit represented by formula (1), includes a structure represented by formula (3) as Y in formula (1), and has a weight average molecular weight of 160000 or more. The polyimide resin of the present invention has a structure represented by formula (3) as Y in formula (1), and the weight average molecular weight of the polyimide resin is 160000 or more, so that an optical film including the polyimide resin is excellent in transparency and folding resistance. In addition, an optical film including the polyimide-based resin of the present invention may have an excellent elastic modulus. Therefore, an optical film including the polyimide-based resin of the present invention can be suitably used for a material of a flexible display device or the like. The polyimide resin of the present invention is preferably the same as the polyimide resin described in the above item < polyimide resin >.

Examples

The present invention will be described more specifically below with reference to examples and comparative examples, but the present invention is not limited to the following examples. First, the measurement and evaluation method will be explained.

< Total light transmittance >

According to JIS K7105: 1981, the total light transmittance (Tt) of the optical films obtained in examples and comparative examples was measured by a fully automatic direct haze computer HGM-2DP manufactured by Suga Test Instruments.

< Haze (Haze) >

According to JIS K7136: the optical films obtained in examples and comparative examples were cut to a size of 30mm × 30mm, and the haze (%) was measured using a haze computer ("HGM-2 DP", manufactured by Suga Test Instruments).

< YI value >

The optical films obtained in examples and comparative examples were subjected to tristimulus values (X, Y, Z) obtained using an ultraviolet-visible near-infrared spectrophotometer (V-670, manufactured by Nippon spectral Co., Ltd.), and the YI value was calculated by substituting the tristimulus values into the following equation.

YI＝100×(1.2769X-1.0592Z)/Y

< evaluation of folding endurance >

The number of times of bending of the optical films in examples and comparative examples was determined as follows according to ASTM standard D2176-16. The optical film was cut into a 15mm × 100mm long strip shape using a dumbbell cutter. The cut optical film was set in a body of an MIT folding fatigue tester ("model 0530", manufactured by seiko corporation), and the number of times of reciprocal folding in the front and back directions until the optical film broke was measured as the number of times of folding (also referred to as the folding resistance number) under conditions of a test speed of 175cpm, a folding angle of 135 °, a load of 0.75kgf, and a radius R of a folding jig of 1 mm.

< modulus of elasticity >

The elastic modulus of the optical films obtained in examples and comparative examples was measured by using "Autograph AG-IS" manufactured by Shimadzu corporation. A film having a width of 10mm was produced, and a stress-strain curve (S-S curve) was measured under conditions of a chuck spacing of 50mm and a stretching speed of 10 mm/min, and the elastic modulus was calculated from the slope.

< determination of weight average molecular weight >

GPC measurement

(1) Pretreatment method

To the polyimide resins obtained in examples and comparative examples, a DMF eluent (a solution to which 10mmol/L lithium bromide was added) was added so that the concentration became 2mg/mL, and the resulting solution was filtered through a 0.45 μm membrane filter after heating at 80 ℃ for 30 minutes with stirring and cooling, to obtain a measurement solution.

(2) Measurement conditions

Column: TSKgel α -2500 (7)7.8mm diameter. times.300 mm. times.1, and α -M ((13)7.8mm diameter. times.300 mm). times.2, manufactured by Tosoh corporation

Eluent: DMF (adding 10mmol/L lithium bromide)

Flow rate: 1.0 mL/min

A detector: RI detector

Column temperature: 40 deg.C

Injection amount: 100 μ L

Molecular weight standard: standard polystyrene

< thickness of optical film >

The thickness of the optical films obtained in examples and comparative examples was measured using an ABS digital indicator ("ID-C112 BS", Mitutoyo Co., Ltd.).

< example 1 >

[ preparation of polyimide resin (1) ]

In a nitrogen atmosphere, TFMB and DMAc, which had been dehydrated strictly to a water content of 700ppm or less, were charged into a separable flask equipped with a stirring blade so that the solid content of TFMB became 7.81 mass%, and TFMB was dissolved in DMAc with stirring at room temperature. Subsequently, TAHMBP was added to the flask so as to be 101.01 mol% to TFMB, and the mixture was stirred at room temperature for 16 hours. Then, 4-methylpyridine (60.61 mol% relative to TFMB) and acetic anhydride (707.07 mol% relative to TFMB) were added thereto, and the mixture was stirred for 30 minutes, and then the internal temperature was increased stepwise to 50 ℃ for 20 minutes, stepwise to 60 ℃ for 20 minutes, stepwise to 70 ℃ for 20 minutes, and further stirred for 3 hours to obtain a reaction solution.

The obtained reaction solution was cooled to room temperature, put into a large amount of methanol in a filamentous form, and the precipitated precipitate was taken out, immersed in methanol for 6 hours, and then washed with methanol. Then, the precipitate was dried under reduced pressure at 60 ℃ to obtain a polyimide resin (1). The weight average molecular weight was 484000.

[ production of optical film (1) ]

DMAc was added to the obtained polyimide resin (1) so that the solid content concentration became 10 mass%, thereby producing a polyimide varnish (1). The obtained polyimide varnish (1) was applied to a smooth surface of a polyester substrate (product of Toyo chemical Co., Ltd., trade name "A4100") using an applicator so that the thickness of the self-supporting film became 55 μm, and was dried at 50 ℃ for 30 minutes and then at 140 ℃ for 15 minutes to obtain a self-supporting film. The free-standing film was fixed to a metal frame, and further dried at 200 ℃ for 60 minutes to obtain an optical film (1) having a thickness of 50 μm.

< comparative example 1 >

[ preparation of polyimide resin (2) ]

In a nitrogen atmosphere, TFMB and DMAc, which had been dehydrated strictly to a water content of 700ppm or less, were charged into a separable flask equipped with a stirring blade so that the solid content of TFMB became 9.43 mass%, and TFMB was dissolved in DMAc with stirring at room temperature. Then, 6FDA was added to the flask so that it was 101.01 mol% to TFMB, and the mixture was stirred at room temperature for 16 hours. Then, 4-methylpyridine (60.61 mol% relative to TFMB) and acetic anhydride (707.07 mol% relative to TFMB) were added thereto, and the mixture was stirred for 30 minutes, then the internal temperature was increased to 70 ℃ and further stirred for 3 hours, thereby obtaining a reaction solution.

The obtained reaction solution was cooled to room temperature, put into a large amount of methanol in a filamentous form, and the precipitated precipitate was taken out, immersed in methanol for 6 hours, and then washed with methanol. Then, the precipitate was dried under reduced pressure at 60 ℃ to obtain a polyimide resin (2). The weight average molecular weight is 255000.

[ production of optical film (2) ]

DMAc was added to the obtained polyimide resin (2) so that the solid content concentration became 10 mass%, thereby producing a polyimide varnish (2). The obtained polyimide varnish (2) was applied to a smooth surface of a polyester substrate (product of Toyo chemical Co., Ltd., trade name "A4100") using an applicator so that the thickness of the self-supporting film became 55 μm, and was dried at 50 ℃ for 30 minutes and then at 140 ℃ for 15 minutes to obtain a self-supporting film. The free-standing film was fixed to a metal frame, and further dried at 200 ℃ for 60 minutes to obtain an optical film (2) having a thickness of 50 μm.

< comparative example 2 >

[ preparation of polyimide resin (3) ]

In a nitrogen atmosphere, TFMB and DMAc, which had been dehydrated strictly to a water content of 700ppm or less, were charged into a separable flask equipped with a stirring blade so that the solid content of TFMB became 11.48 mass%, and TFMB was dissolved in DMAc with stirring at room temperature. Next, BPDA was added to the flask in an amount of 101.01 mol% based on TFMB, and stirring was performed at room temperature, but the viscosity increased with the passage of time, and the mixture became solid after 16 hours, and stirring became poor, so that the preparation was abandoned.

< comparative example 3 >

[ preparation of polyimide resin (4) ]

In a nitrogen atmosphere, TFMB and DMAc, which had been dehydrated strictly to a water content of 700ppm or less, were charged into a separable flask equipped with a stirring blade so that the solid content of TFMB became 8.52 mass%, and TFMB was dissolved in DMAc with stirring at room temperature. Next, an ester of trimellitic anhydride and 4, 4' -biphenol was added to the flask in an amount of 101.01 mol% based on TFMB, and stirring was carried out at room temperature, but the viscosity increased with time, and the mixture became a solid after 16 hours, and stirring became poor, so that the production was abandoned.

The optical films obtained in example 1 and comparative example 1 were measured for total light transmittance, haze, YI value, and elastic modulus, and evaluated for folding resistance, and the results are shown in table 1. In comparative examples 2 and 3, as described above, the solution state could not be maintained during the synthesis of the polyimide resin, and the polyimide resin could not be taken out, and thus evaluation as an optical film was not possible.

[ Table 1]

As shown in table 1, the optical film of example 1 was found to have a high folding times, a high total light transmittance, and a low haze.

Therefore, it is found that the optical film of the present invention is excellent in transparency and folding resistance.

Claims

1. An optical film comprising a polyimide-based resin,

the polyimide resin comprises a structural unit represented by the formula (1),

in the formula (1), X represents a divalent organic group,

y represents a tetravalent organic group,

the symbol denotes a bond of a bond,

in the formula (3), R¹Independently of one another, represents a halogen atom, an alkyl group, an alkoxy group, an aryl group or an aryloxy group, optionally having a halogen atom,

R²～R⁵independently of each other, a hydrogen atom or a monovalent hydrocarbon group optionally having a halogen atom, m independently of each other, an integer of 0 to 3,

n represents an integer of 1 to 4,

denotes a bond wherein R is²～R⁵In at least 1 benzene ring of (2), R²～R⁵At least 1 of which is a monovalent hydrocarbon group optionally having a halogen atom.

2. The optical film according to claim 1, wherein at least 1 of a divalent aromatic group, a divalent alicyclic group, and a divalent aliphatic group is contained as X in formula (1).

3. The optical film according to claim 1 or 2, wherein X in formula (1) includes a structure represented by formula (4),

in the formula (4), A represents a single bond, -O-, diphenylmethylene, a divalent hydrocarbon group optionally having a halogen atom, -SO₂-、-S-、-CO-、-PO-、-PO₂-、-N(R^A1) -or-Si (R)^A2)₂-，

R^A1And R^A2Independently of each other, a hydrogen atom or an alkyl group optionally having a halogen atom, R⁶Independently of each otherRepresents a halogen atom, an alkyl group optionally having a halogen atom, an alkoxy group, an aryl group or an aryloxy group,

s independently represent an integer of 0 to 4,

denotes a bond.

4. The optical film according to any one of claims 1 to 3, which has a thickness of 35 μm or more.

5. The optical film according to any one of claims 1 to 4, having a total light transmittance of 85% or more.

6. The optical film according to any one of claims 1 to 5, which has a yellowness index of 3.0 or less.

7. The optical film according to any one of claims 1 to 6, which has an elastic modulus of 3.5GPa or more.

8. The optical film according to any one of claims 1 to 7, which is a film for a front panel of a flexible display device.

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

10. The flexible display device of claim 9, further provided with a touch sensor.

11. The flexible display device according to claim 9 or 10, further provided with a polarizing plate.

12. A polyimide resin comprising a structural unit represented by the formula (1),

in the formula (1), X represents a divalent organic group,

y represents a tetravalent organic group,

a-represents a bond-linkage of the bond,

R²～R⁵independently of each other, a hydrogen atom or a monovalent hydrocarbon group optionally having a halogen atom,

m independently represents an integer of 0 to 3,

n represents an integer of 1 to 4,