WO2018139392A1

WO2018139392A1 - Polyimide-based film and laminate

Info

Publication number: WO2018139392A1
Application number: PCT/JP2018/001716
Authority: WO
Inventors: 真義唐澤; 未央安井; 桜井　孝至
Original assignee: 住友化学株式会社
Priority date: 2017-01-25
Filing date: 2018-01-22
Publication date: 2018-08-02
Also published as: JP2018119144A; CN110234687B; CN110234687A; KR20190109481A; TW201833184A; KR102475756B1; JP7164304B2

Abstract

The present invention addresses the problem in which the surface of an image display device in some cases appears tinted when viewed through polarized sunglasses. The purpose of the present invention is to provide a front panel for an image display device, in particular a front panel for a flexible display, which can suppress the tinting that occurs when the display is viewed through polarized sunglasses. The present invention provides a polyimide-based film having an in-plane retardation of at least 3,000 nm at a wavelength of 589.4 nm.

Description

Polyimide film and laminate

The present invention relates to a polyimide film and a laminate comprising the polyimide film and a hard coat layer.

Currently, image display devices such as liquid crystal display devices and organic EL display devices are widely used not only for televisions but also for various applications such as mobile phones and smart watches. With the expansion of such applications, image display devices (flexible displays) having flexible characteristics are demanded, and it is necessary to make each member flexible.

The image display device includes a display element such as a liquid crystal display element or an organic EL display element, a polarizing plate, a retardation plate, a front plate, and the like. In order to achieve a flexible display, all these members need to have flexible properties. When the member of the image display device is made of a polymer material having flexible characteristics (for example, Patent Document 1), the member is easy to bend, so that it is relatively easy to apply to a flexible display. However, glass that has been used as a front plate material for image display devices so far has high transparency and can exhibit high hardness depending on the type of glass, but it is very stiff and easy to break. Use as a material is difficult.

JP-A-8-327819

Therefore, the use of polymer materials as a material to replace glass is being studied. Since the front plate made of a polymer material is easy to exhibit flexible characteristics, it can be used for various applications. For example, when used in a mobile phone, a smart watch, a car navigation system, etc., the image display device can be made not only in a flat shape but also in various shapes by utilizing the flexible characteristic of the front plate.

Also, in the front plate, not only the flexible characteristics but also the visibility when incorporated in the image display device is important. When the light is strong or in the vehicle, the user may wear polarized sunglasses and watch the image display device. However, when the image display device is viewed through the polarized sunglasses, the surface of the image display device may be colored. When such a phenomenon occurs, the visibility decreases, and in the case of car navigation, for example, the driving of the car may be hindered.

Therefore, an object of the present invention is to provide a front plate for an image display device, particularly a front plate for a flexible display, which can suppress coloring through polarized sunglasses.

As a result of intensive studies to solve the above problems, the present inventors have completed the present invention.
That is, the present invention provides the following preferred embodiments.
[1] A polyimide film having an in-plane retardation at a wavelength of 589.4 nm of 3,000 nm or more.
[2] The polyimide film according to [1], wherein the total light transmittance is 85% or more.
[3] The polyimide film according to [1] to [2], wherein the polyimide polymer contained in the polyimide film contains a fluorine atom in the molecule.
[4] The polyimide film according to any one of [1] to [3], wherein the yellowness (YI) is 5 or less.
[5] A laminate comprising the polyimide film according to any one of [1] to [4] and a hard coat layer disposed on at least one surface of the polyimide film.
[6] An optical member comprising the polyimide film according to any one of [1] to [4] or the laminate according to [5].
[7] An image display device comprising the polyimide film according to [1] to [4], the laminate according to [5], or the optical member according to [6].
[8] A step of applying a hard coat layer composition on a polyimide film to form a coating film, a step of stretching the polyimide film uniaxially or biaxially, and irradiating the coating film with high energy rays, The manufacturing method of the laminated body containing the polyimide-type film and hard coat layer including the process of hardening a coating film and forming a hard-coat layer.
[9] It further includes a step of applying a liquid containing a polyimide polymer imidized with polyamic acid to a substrate to form a coating film, and a step of drying the applied liquid to form a polyimide film. The manufacturing method according to [8] above.

According to the present invention, it is possible to provide a front plate for an image display device, particularly a front plate for a flexible display, which can suppress coloring through polarized sunglasses.

It is a schematic sectional drawing which shows an example of a structure of the laminated body which is one embodiment of this invention. It is a schematic sectional drawing which shows an example of a structure of a flexible display provided with the laminated body which is one embodiment of this invention.

Hereinafter, embodiments of the present invention will be described in detail. Note that the scope of the present invention is not limited to the embodiment described here, and various modifications can be made without departing from the spirit of the present invention.

[Polyimide film]
In one embodiment of the present invention, a polyimide film having an in-plane retardation at a wavelength of 589.4 nm of 3,000 nm or more is provided. The polyimide film is a film comprising a polyimide polymer. Since the polyimide polymer is excellent in heat resistance, flexibility and rigidity, it is suitable as a front plate material for an image display device, particularly as a front plate (window film) material for a flexible display. The polyimide film may be a single layer or a multilayer. When a polyimide-type film is a multilayer, each layer may be the same composition and a different composition may be sufficient as it. The polyimide film includes at least one selected from the group consisting of polyimide and polyamideimide. That is, the polyimide film can contain polyimide or polyamideimide, and may contain both polyimide and polyamideimide.

(Polyimide polymer)
The polyimide polymer refers to polyimide and polyamideimide. Polyamideimide is a polymer containing a repeating structural unit containing both an imide group and an amide group, or a polymer containing both a repeating structural unit containing an imide group and a repeating structural unit containing an amide group. A polyimide is a polymer containing a repeating structural unit containing an imide group.

The polyimide polymer can be produced using, for example, a tetracarboxylic acid compound and a diamine compound described later as main raw materials. In one embodiment of the present invention, the polyimide polymer has a repeating structural unit represented by the formula (10). Here, G is a tetravalent organic group, and A is a divalent organic group. In the polyimide polymer, a structure represented by two or more formulas (10) in which G and / or A are different may be included.

The polyimide polymer includes one or more selected from the group consisting of structures represented by formula (11), formula (12), and formula (13) as long as various physical properties of the polyimide film are not impaired. You may go out.

G and G ¹ are each independently a tetravalent organic group, preferably an organic group that may be substituted with a hydrocarbon group or a fluorine-substituted hydrocarbon group. The organic group is preferably an organic group which may be substituted with a hydrocarbon group or a fluorine-substituted hydrocarbon group. The organic group is preferably a tetravalent organic group having 4 to 40 carbon atoms. The hydrocarbon group and the fluorine-substituted hydrocarbon group preferably have 1 to 8 carbon atoms. The G and ^{G 1,} equation (20), equation (21), equation (22), equation (23), equation (24), equation (25), equation (26), equation (27), formula (28 ) And a group represented by formula (29); a group in which a hydrogen atom in the groups represented by formula (20) to formula (29) is 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.

In formula (20) to formula (29),
* Represents a bond,
Z is a single _{_{_{bond, -O -, - CH 2 -}}} , - CH 2 -CH 2 -, - CH (CH 3) -, - C (CH 3) 2 -, - C (CF 3) 2 -, - _{Ar -, - SO 2 -,} - CO -, - O-Ar-O -, - Ar-O-Ar -, - Ar-CH 2 -Ar -, - Ar-C (CH 3) 2 -Ar- , or —Ar—SO ₂ —Ar— is represented. Ar represents an arylene group having 6 to 20 carbon atoms in which a hydrogen atom may be substituted with a fluorine atom, and specific examples thereof include a phenylene group.

As G and G ¹ , among the groups represented by the formulas (20) to (29), from the viewpoint of the surface hardness and flexibility of the polyimide film comprising the polyimide polymer, the formula (26) The groups represented by the formula (28) and the formula (29) are preferable, and the group represented by the formula (26) is more preferable because the yellowness of the obtained film is easily suppressed. Further, Z is, from the viewpoint of surface hardness and flexibility of the polyimide film comprising said polyimide polymer, independently, a single _{bond, -O -, - CH 2 -} , - CH 2 -CH 2 —, —CH (CH ₃ ) —, —C (CH ₃ ) ₂ — or —C (CF ₃ ) ₂ — is preferred, —O—, —CH ₂ —, —CH (CH ₃ ) —, -C _(CH _{3) 2} - or -C _(CF _{3) 2} -, more preferably, -C _(CH _{3) 2} - or -C _(CF _{3) 2} - is more preferably, -C (CF ₃ ) ₂ — is particularly preferred.

G ² is a trivalent organic group, and is preferably an organic group which may be substituted with a hydrocarbon group or a fluorine-substituted hydrocarbon group. The organic group is preferably a trivalent organic group having 4 to 40 carbon atoms. The hydrocarbon group and the fluorine-substituted hydrocarbon group preferably have 1 to 8 carbon atoms. The organic group preferably has 4 to 40 carbon atoms. The G ^2, equation (20), equation (21), equation (22), equation (23), equation (24), equation (25), equation (26), equation (27), equation (28) or Examples thereof include a group in which any one of the bonds of the group represented by formula (29) is replaced with a hydrogen atom, and a trivalent chain hydrocarbon group having 6 or less carbon atoms. The example of Z in the formula is the same as the example of Z in the description about G.

G ³ is a divalent organic group, preferably an organic group which may be substituted with a hydrocarbon group or a fluorine-substituted hydrocarbon group. The organic group is preferably a divalent organic group having 4 to 40 carbon atoms. The hydrocarbon group and the fluorine-substituted hydrocarbon group preferably have 1 to 8 carbon atoms. The organic group preferably has 4 to 40 carbon atoms. The G ^3, equation (20), equation (21), equation (22), equation (23), equation (24), equation (25), equation (26), equation (27), equation (28) or Examples of the bond of the group represented by formula (29) include a group in which two that are not adjacent to each other are replaced with hydrogen atoms, and a chain hydrocarbon group having 6 or less carbon atoms. The example of Z in the formula is the same as the example of Z in the description about G.

The G ^2, attachment of the group in terms of surface hardness and flexibility of the polyimide film comprising said polyimide polymer, the above equation (26), of the formula (28) and (29) A group in which any one of the hands is replaced with a hydrogen atom is preferable, and a group in which any one of the bonding hands of the group represented by the formula (26) is replaced with a hydrogen atom is more preferable. Further, attachment of the group as a G ^3, from the viewpoint of surface hardness and flexibility of the polyimide film comprising said polyimide polymer, represented by the formula (26), equation (28) and (29) Among the hands, a group in which two non-adjacent ones are replaced with hydrogen atoms is preferable, and it is easy to suppress the yellowness of the resulting film. Therefore, two non-adjacent hands in the group represented by formula (26) are hydrogen. A group in which an atom is replaced is more preferable. Z, from the viewpoint of surface hardness and flexibility of the polyimide film comprising said polyimide polymer, independently, a single _{_{bond, -O -, - CH 2 -}} , - CH 2 -CH 2 -, —CH (CH ₃ ) —, —C (CH ₃ ) ₂ — or —C (CF ₃ ) ₂ — is preferable, —O—, —CH ₂ —, —CH (CH ₃ ) —, —C More preferably, it is (CH ₃ ) ₂ — or —C (CF ₃ ) ₂ —, more preferably —C (CH ₃ ) ₂ — or —C (CF ₃ ) ₂ —, and —C (CF ₃ ) ₂ − is particularly preferred.

A, A ¹ , A ² and A ³ are each independently a divalent organic group, preferably an organic group which may be substituted with a hydrocarbon group or a fluorine-substituted hydrocarbon group. The organic group preferably has 4 to 40 carbon atoms. The number of carbon atoms of the hydrocarbon group or the fluorine-substituted hydrocarbon group is preferably 1-8. As A, A ¹ , A ² and A ³ , Formula (30), Formula (31), Formula (32), Formula (33), Formula (34), Formula (35), Formula (36), Formula (37) and a group represented by formula (38); a hydrogen atom in the group represented by formula (30) to formula (38) is substituted with a methyl group, a fluoro group, a chloro group or a trifluoromethyl group. And a chain hydrocarbon group having 6 or less carbon atoms.

In formula (30) to formula (38), * represents a bond,
Z ^1, ^{Z 2} and ^{Z 3} are each independently a single _{_{_{bond, -O -, - CH 2 -}}} , - CH 2 -CH 2 -, - CH (CH 3) -, - C (CH 3) 2 —, —C (CF ₃ ) ₂ —, —SO ₂ — or —CO— is represented.
One example is when Z ¹ and Z ³ are —O— and Z ² is —CH ₂ —, —C (CH ₃ ) ₂ —, —C (CF ₃ ) ₂ — or —SO ₂ —. is there. It is preferable that the bonding position of each of Z ¹ and Z ² with respect to each ring and the bonding position of each of Z ² and Z ³ with respect to each ring is a meta position or a para position with respect to each ring.

Among the groups represented by formula (30) to formula (38), from the viewpoint of the surface hardness and flexibility of the polyimide film comprising the polyimide polymer, the groups represented by formula (33) to formula (37) are used. The group represented by formula (34) to formula (36) is more preferred, and the group represented by formula (34) is more preferred. Z ¹ , Z ² and Z ³ are preferably each independently a single bond or —O— from the viewpoint of the surface hardness and flexibility of the polyimide film comprising the polyimide polymer. More preferably, it is a single bond.

The polyimide film may contain polyamide. Polyamide is a polymer containing repeating structural units containing amide groups. The polyamide according to this embodiment is a polymer mainly composed of repeating structural units represented by the above formula (13). Preferred examples and specific examples of G ^3, and A ³ in the polyamides are respectively the same as G ^3, and A ³ in the polyimide polymer. G ³ and / or A ³ may contain different structures represented by two or more formulas (13).

The polyimide polymer can be obtained, for example, by polycondensation of a diamine and a tetracarboxylic acid compound (tetracarboxylic dianhydride or the like). For example, JP 2006-199945 A or JP 2008-163107 A Can be synthesized according to the method described in 1. Examples of commercially available polyimide products include Neoprim (registered trademark) manufactured by Mitsubishi Gas Chemical Co., Ltd., and KPI-MX300F manufactured by Kawamura Sangyo Co., Ltd.

Examples of tetracarboxylic acid compounds used for the synthesis of polyimide include aromatic tetracarboxylic acid compounds such as aromatic tetracarboxylic dianhydrides; and aliphatic tetracarboxylic acid compounds such as aliphatic tetracarboxylic dianhydrides. It is done. A tetracarboxylic acid compound may be used independently and may use 2 or more types together. The tetracarboxylic acid compound may be a tetracarboxylic acid compound analog such as a tetracarboxylic acid chloride compound in addition to the tetracarboxylic acid dianhydride.

Specific examples of the aromatic tetracarboxylic dianhydride include non-condensed polycyclic aromatic tetracarboxylic dianhydride, monocyclic aromatic tetracarboxylic dianhydride, and condensed polycyclic aromatic tetra Carboxylic dianhydrides are mentioned. Non-condensed polycyclic aromatic tetracarboxylic dianhydrides include 4,4'-oxydiphthalic dianhydride, 3,3 ', 4,4'-benzophenone tetracarboxylic dianhydride, 2,2' , 3,3′-benzophenonetetracarboxylic dianhydride, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride, 2,2 ′, 3,3′-biphenyltetracarboxylic dianhydride, 3,3 ′, 4,4′-diphenylsulfonetetracarboxylic dianhydride, 2,2-bis (3,4-dicarboxyphenyl) propane dianhydride, 2,2-bis (2,3-dicarboxy) Phenyl) propane dianhydride, 2,2-bis (3,4-dicarboxyphenoxyphenyl) propane dianhydride, 4,4 ′-(hexafluoroisopropylidene) diphthalic dianhydride (referred to as 6FDA) 1,2-bis (2,3-dicarboxyphenyl) ethane dianhydride, 1,1-bis (2,3-dicarboxyphenyl) ethane dianhydride, 1,2-bis (3, 4-dicarboxyphenyl) ethane dianhydride, 1,1-bis (3,4-dicarboxyphenyl) ethane dianhydride, bis (3,4-dicarboxyphenyl) methane dianhydride, bis (2,3 -Dicarboxyphenyl) methane dianhydride, 4,4 '-(p-phenylenedioxy) diphthalic dianhydride, and 4,4'-(m-phenylenedioxy) diphthalic dianhydride. Examples of the monocyclic aromatic tetracarboxylic dianhydride include 1,2,4,5-benzenetetracarboxylic dianhydride. Examples of the condensed polycyclic aromatic tetracarboxylic dianhydride include 2,3,6,7-naphthalene tetracarboxylic dianhydride. These can be used alone or in combination of two or more.

Among these, preferably 4,4′-oxydiphthalic dianhydride, 3,3 ′, 4,4′-benzophenone tetracarboxylic dianhydride, 2,2 ′, 3,3′-benzophenone tetracarboxylic dianhydride Anhydride, 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride, 2,2', 3,3'-biphenyltetracarboxylic dianhydride, 3,3 ', 4,4'-diphenyl Sulfonetetracarboxylic dianhydride, 2,2-bis (3,4-dicarboxyphenyl) propane dianhydride, 2,2-bis (2,3-dicarboxyphenyl) propane dianhydride, 2,2- Bis (3,4-dicarboxyphenoxyphenyl) propane dianhydride, 4,4 ′-(hexafluoroisopropylidene) diphthalic dianhydride (6FDA), 1,2-bis (2,3-dicarboxy) Enyl) ethane dianhydride, 1,1-bis (2,3-dicarboxyphenyl) ethane dianhydride, 1,2-bis (3,4-dicarboxyphenyl) ethane dianhydride, 1,1-bis (3,4-dicarboxyphenyl) ethane dianhydride, bis (3,4-dicarboxyphenyl) methane dianhydride, bis (2,3-dicarboxyphenyl) methane dianhydride, 4,4 ′-( and p-phenylenedioxy) diphthalic dianhydride and 4,4 ′-(m-phenylenedioxy) diphthalic dianhydride. More preferably 4,4′-oxydiphthalic dianhydride, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride, 2,2 ′, 3,3′-biphenyltetracarboxylic dianhydride, 4,4 ′-(Hexafluoroisopropylidene) diphthalic dianhydride (6FDA), bis (3,4-dicarboxyphenyl) methane dianhydride and 4,4 ′-(p-phenylenedioxy) diphthalic acid Anhydrides are mentioned. These can be used alone or in combination of two or more.

Examples of the aliphatic tetracarboxylic dianhydride include cyclic or acyclic aliphatic tetracarboxylic dianhydrides. The cycloaliphatic tetracarboxylic dianhydride is a tetracarboxylic dianhydride having an alicyclic hydrocarbon structure, and specific examples thereof include 1,2,4,5-cyclohexanetetracarboxylic dianhydride. 1, 2,3,4-cyclobutanetetracarboxylic dianhydride, cycloalkanetetracarboxylic dianhydride such as 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 their positional isomers . These can be used alone or in combination of two or more. Specific examples of the acyclic aliphatic tetracarboxylic dianhydride include 1,2,3,4-butanetetracarboxylic dianhydride, 1,2,3,4-pentanetetracarboxylic dianhydride, etc. These may be used alone or in combination of two or more. Further, a cycloaliphatic tetracarboxylic dianhydride and an acyclic aliphatic tetracarboxylic dianhydride may be used in combination.

Among the above tetracarboxylic dianhydrides, 4,4′-oxydiphthalic dianhydride, 3,3 ′, 4,4′-benzophenone tetracarboxylic dianhydride, from the viewpoint of high transparency and low colorability, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride, 2,2 ′, 3,3′-biphenyltetracarboxylic dianhydride, 3,3 ′, 4,4′-diphenylsulfonetetracarboxylic Preferred are acid dianhydride, 2,2-bis (3,4-dicarboxyphenyl) propane dianhydride, 4,4 ′-(hexafluoroisopropylidene) diphthalic dianhydride and mixtures thereof. ', 4,4'-biphenyltetracarboxylic dianhydride and 4,4'-(hexafluoroisopropylidene) diphthalic dianhydride and mixtures thereof are more preferred, and 4,4 '-( Hexafluorobutene isopropylidene) diphthalic acid dianhydride is more preferred.

In addition to the tetracarboxylic acid compound used for said polyimide synthesis | combination in the range which does not impair the various physical properties of a polyimide-type film, the polyimide-type polymer which concerns on this embodiment is a tetracarboxylic acid compound, a tricarboxylic acid compound, and dicarboxylic acid. The acid compounds and their anhydrides and derivatives may be further reacted. As a derivative of the tetracarboxylic acid compound, tricarboxylic acid compound and dicarboxylic acid compound to be reacted, each acid chloride compound is given as a preferred example because of its high reaction activity.

Examples of the tetracarboxylic acid include anhydrous water adducts of the above tetracarboxylic acid compounds.

Examples of the tricarboxylic acid compound include aromatic tricarboxylic acid, aliphatic tricarboxylic acid and related acid chloride compounds, acid anhydrides, and the like, and two or more kinds may be used in combination. Specific examples include 1,2,4-benzenetricarboxylic acid anhydride; 2,3,6-naphthalenetricarboxylic acid-2,3-anhydride; phthalic acid anhydride and benzoic acid are a single bond, —O— , —CH ₂ —, —C (CH ₃ ) ₂ —, —C (CF ₃ ) ₂ —, —SO ₂ — or a phenylene group; and acid chloride compounds thereof.

Examples of the dicarboxylic acid compound include aromatic dicarboxylic acids, aliphatic dicarboxylic acids, and related acid chloride compounds, acid anhydrides, and the like, and two or more kinds may be used in combination. Specific examples include dicarboxylic acid compounds of terephthalic acid; isophthalic acid; naphthalenedicarboxylic acid; 4,4′-biphenyldicarboxylic acid; 3,3′-biphenyldicarboxylic acid; One benzoic acid skeleton is a single bond, —O—, —CH ₂ —, —C (CH ₃ ) ₂ —, —C (CF ₃ ) ₂ —, —SO ₂ —, —S—, —NR ⁹ —, — Examples thereof include compounds linked by C (═O) — or a phenylene group, and acid chloride compounds thereof. Here, R ⁹ is a hydrocarbon group having 1 to 12 carbon atoms which may be substituted with a halogen atom.

As the dicarboxylic acid compound, preferably terephthalic acid; isophthalic acid; 4,4′-biphenyldicarboxylic acid; 3,3′-biphenyldicarboxylic acid; and the two benzoic acid skeletons are —CH ₂ —, —C (═O) Compounds linked by —, —O—, —NR ⁹ —, —SO ₂ — or a phenylene group, and acid chloride compounds thereof, more preferably terephthalic acid; 4,4′-biphenyldicarboxylic acid; and 2 These are compounds in which two benzoic acid skeletons are linked by —O—, —NR ⁹ —, —C (═O) — or —SO ₂ — as well as their acid chloride compounds. Specific examples of the acid chloride compound include 4,4′-oxybis (benzoyl chloride) (sometimes referred to as OBBC) and terephthaloyl chloride (sometimes referred to as TPC). These can be used alone or in combination of two or more.

Examples of diamines used for the synthesis of polyimide polymers 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 an aliphatic group or other substituent may be included in a part of the structure. The aromatic ring may be a single ring or a condensed ring, and examples thereof include, but are not limited to, a benzene ring, a naphthalene ring, an anthracene ring, and a fluorene ring. Among these, a benzene ring is preferable. The “aliphatic diamine” refers to a diamine in which an amino group is directly bonded to an aliphatic group, and an aromatic ring or other substituent may be included in a part of the structure.

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

Examples of aromatic diamines include p-phenylenediamine, m-phenylenediamine, 2,4-toluenediamine, m-xylylenediamine, p-xylylenediamine, 1,5-diaminonaphthalene, and 2,6-diamino. An aromatic diamine having one aromatic ring, such as naphthalene; 4,4′-diaminodiphenylmethane, 4,4′-diaminodiphenylpropane, 4,4′-diaminodiphenyl ether, 3,4′-diaminodiphenyl ether, 3,3 '-Diaminodiphenyl ether, 4,4'-diaminodiphenyl sulfone, 3,4'-diaminodiphenyl sulfone, 3,3'-diaminodiphenyl sulfone, 1,4-bis (4-aminophenoxy) benzene, 1,3-bis (4-Aminophenoxy) benzene, 4,4'-diamino Phenylsulfone, bis [4- (4-aminophenoxy) phenyl] sulfone, bis [4- (3-aminophenoxy) phenyl] sulfone, 2,2-bis [4- (4-aminophenoxy) phenyl] propane, 2 , 2-bis [4- (3-aminophenoxy) phenyl] propane, 2,2′-dimethylbenzidine, 2,2′-bis (trifluoromethyl) benzidine (2,2′-bis (trifluoromethyl)- 4,4'-diaminodiphenyl (TFMB)), 4,4'-bis (4-aminophenoxy) biphenyl, 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 4, 4'-diaminodiphenylmethane, 9,9-bis (4-aminophenyl) fluorene, 9,9-bis (4-amino- Fragrances having two or more aromatic rings such as -methylphenyl) fluorene, 9,9-bis (4-amino-3-chlorophenyl) fluorene, and 9,9-bis (4-amino-3-fluorophenyl) fluorene Group diamines. These can be used alone or in combination of two or more.

As the aromatic diamine, preferably 4,4′-diaminodiphenylmethane, 4,4′-diaminodiphenylpropane, 4,4′-diaminodiphenyl ether, 3,3′-diaminodiphenyl ether, 4,4′-diaminodiphenyl sulfone, 3,3′-diaminodiphenylsulfone, 1,4-bis (4-aminophenoxy) benzene, bis [4- (4-aminophenoxy) phenyl] sulfone, bis [4- (3-aminophenoxy) phenyl] sulfone, 2,2-bis [4- (4-aminophenoxy) phenyl] propane, 2,2-bis [4- (3-aminophenoxy) phenyl] propane, 2,2′-dimethylbenzidine, 2,2′-bis (Trifluoromethyl) benzidine, 4,4'-bis (4-aminophenoxy) biphenyl More preferably 4,4′-diaminodiphenylmethane, 4,4′-diaminodiphenylpropane, 4,4′-diaminodiphenyl ether, 4,4′-diaminodiphenylsulfone, 1,4-bis (4-aminophenoxy) Benzene, bis [4- (4-aminophenoxy) phenyl] sulfone, 2,2-bis [4- (4-aminophenoxy) phenyl] propane, 2,2′-dimethylbenzidine, 2,2′-bis (tri Fluoromethyl) benzidine, 4,4′-bis (4-aminophenoxy) biphenyl. These can be used alone or in combination of two or more.

Among the diamines, from the viewpoint of high transparency and low colorability, it is preferable to use one or more selected from the group consisting of aromatic diamines having a biphenyl structure, specifically 2,2′-dimethylbenzidine. It is more preferable to use one or more selected from the group consisting of 2,2′-bis (trifluoromethyl) benzidine, 4,4′-bis (4-aminophenoxy) biphenyl, and 4,4′-diaminodiphenyl ether. More preferably, 2,2′-bis (trifluoromethyl) benzidine is used.

Polyimide polymers and polyamides, which are polymers containing at least one selected from the group consisting of repeating structural units represented by formula (10), formula (11), formula (12) and formula (13), are diamines. A tetracarboxylic acid compound (an acid chloride compound, an analog of a tetracarboxylic acid compound such as tetracarboxylic dianhydride), a tricarboxylic acid compound (an analog of a tricarboxylic acid compound such as an acid chloride compound or tricarboxylic acid anhydride), and a dicarboxylic acid It is a condensation polymer that is a polycondensation product with at least one compound selected from the group consisting of compounds (analogues of dicarboxylic acid compounds such as acid chloride compounds). In addition to these, a dicarboxylic acid compound (including analogs such as an acid chloride compound) may be used as a starting material. The repeating structural unit represented by the formula (11) is usually derived from diamines and tetracarboxylic acid compounds. The repeating structural unit represented by the formula (12) is usually derived from a diamine and a tricarboxylic acid compound. The repeating structural unit represented by the formula (13) is usually derived from a diamine and a dicarboxylic acid compound. Specific examples of the diamine and the tetracarboxylic acid compound are as described above. Further, a diisocyanate compound may be used in place of the diamine compound.

The molar ratio of the diamine to the carboxylic acid compound such as a tetracarboxylic acid compound can be appropriately adjusted within a range of 0.9 mol to 1.1 mol of the tetracarboxylic acid with respect to 1.00 mol of the diamine. In order to develop high folding resistance, it is preferable that the obtained polyimide polymer has a high molecular weight, so that tetracarboxylic acid is 0.98 mol or more and 1.02 mol with respect to 1.00 mol of diamine. More preferably, they are 0.99 mol% or more and 1.01 mol% or less.
Further, from the viewpoint of suppressing the yellowness of the obtained polyimide-based polymer film, it is preferable that the proportion of amino groups in the resulting polymer terminal is low, and carboxylic acids such as tetracarboxylic acid compounds with respect to 1.00 mol of diamine The compound is preferably 1.00 mol or more.

Adjusting the number of fluorine in the molecule of diamine and carboxylic acid compound (for example, tetracarboxylic acid compound), the fluorine content (fluorine atom content) in the resulting polyimide polymer is based on the mass of the polyimide polymer. 1 mass% or more, 5 mass% or more, 10 mass% or more, or 20 mass% or more. Since the raw material cost tends to increase as the proportion of fluorine increases, the upper limit of the amount of fluorine is preferably 40% by mass or less. A fluorine-type substituent may exist in either diamine or a carboxylic acid compound, and may exist in both. By including a fluorine-based substituent, the YI value may be particularly reduced.

The weight average molecular weight (Mw) of the polyimide polymer and polyamide is preferably 10,000 to 800,000. The lower limit of the weight average molecular weight is more preferably 50,000 or more, further preferably 70,000 or more, and particularly preferably 100,000 or more. The upper limit of the weight average molecular weight is more preferably 750,000 or less, further preferably 600,000 or less, and particularly preferably 500,000 or less. The weight average molecular weight of the polyimide-based polymer and polyamide may be smaller, for example, 480,000 or less, 450,000 or less, or 400,000 or less. The preferred range of this weight average molecular weight is preferably 100,000 to 800,000, more preferably 150,000 to 750,000, still more preferably 200,000 to 600,000, particularly preferably. 250,000-500,000. When the weight average molecular weight of the polyimide polymer and the polyamide is equal to or higher than the lower limit, the polyimide film can have high flexibility and can be stretched without breaking. When the weight average molecular weight of the polyimide polymer and polyamide is not more than the above upper limit, the viscosity of the polyimide varnish can be suppressed low, and the polyimide film can be easily stretched, so that the workability is good. In addition, a weight average molecular weight can be calculated | required by GPC measurement and standard polystyrene conversion, and can be specifically calculated | required by the method as described in an Example.

In a preferred embodiment of the present invention, the polyimide polymer and polyamide contained in the polyimide film may contain a fluorine atom that can be introduced by the above-described fluorine substituent or the like. Specific examples of the fluorine-containing substituent include a fluoro group and a trifluoromethyl group. Since the polyimide polymer and polyamide contain fluorine atoms, the elasticity of the polyimide film can be improved and the yellowness (YI value) can be reduced at the same time. Preferably it contains atoms. Moreover, when a polyimide-type polymer and polyamide contain a fluorine atom in a molecule | numerator, the water absorption rate of a polyimide-type film will reduce, and also the deformation | transformation of a polyimide-type film can be suppressed. In addition, when the polyimide polymer and polyamide contain fluorine atoms in the molecule, when the laminate film and the laminate described later are folded, the fold line is difficult to remain, and the flexible display is bent. The polyimide-based film and the laminate can be particularly usefully used.

The fluorine atom content (fluorine atom content) in the polyimide polymer and polyamide is improved in hardness, improved elastic modulus, reduced yellowness (improved transparency), reduced water absorption, and polyimide film. From the viewpoint of suppressing deformation, it is preferably 1% by mass to 40% by mass, more preferably 3% by mass to 35% by mass, and further preferably 5% by mass to 32% by mass, based on the mass of the polyimide polymer. When the fluorine atom content is 1% by mass or more, there is a tendency that the elastic modulus when formed into a film is further improved, the water absorption is decreased, the YI value is further reduced, and the transparency is further improved. . If the fluorine atom content is 40% by mass or less, it is easy to increase the molecular weight of the polyimide.

In one embodiment of the present invention, the polyimide polymer can be produced by a polycondensation reaction between a diamine and a tetracarboxylic acid compound. In this polycondensation reaction, an imidization catalyst may be present. Examples of imidation catalysts include aliphatic amines such as tripropylamine, dibutylpropylamine, and ethyldibutylamine; N-ethylpiperidine, N-propylpiperidine, N-butylpyrrolidine, N-butylpiperidine, and N-propylhexahydro Alicyclic amines (monocyclic) such as azepine; azabicyclo [2.2.1] heptane, azabicyclo [3.2.1] octane, azabicyclo [2.2.2] octane, and azabicyclo [3.2. 2] Cycloaliphatic amines such as nonane (polycyclic); and 2-methylpyridine, 3-methylpyridine, 4-methylpyridine, 2-ethylpyridine, 3-ethylpyridine, 4-ethylpyridine, 2,4- Dimethylpyridine, 2,4,6-trimethylpyridine, 3,4-cyclopentenopyridine, 5,6,7,8 Tetrahydroisoquinoline, and aromatic amines isoquinoline.

The reaction temperature of the diamine and tetracarboxylic acid compound is not particularly limited, but is, for example, 50 to 350 ° C. The reaction time is not particularly limited, but is, for example, about 30 minutes to 24 hours, preferably about 30 minutes to 10 hours. If necessary, the reaction may be carried out under an inert atmosphere or under reduced pressure. Moreover, reaction may be performed in a solvent and the following solvent used for preparation of a polyimide varnish is mentioned as a solvent, for example.

In one embodiment of the present invention, the content of the polyimide polymer in the polyimide film is preferably 40% by mass or more, more preferably 50% by mass or more, and still more preferably based on the total mass of the polyimide film. 70% by mass or more. When the content of the polyimide polymer is 40% by mass or more, the flexibility of the polyimide film is good. In addition, content of the polyimide-type polymer in a polyimide-type film is 100 mass% or less normally on the basis of the total mass of a polyimide-type film.

(Inorganic material)
The polyimide film may further contain an inorganic material such as inorganic particles in addition to the polyimide polymer from the viewpoint of increasing the strength. Examples of the inorganic material include inorganic particles such as titania particles, alumina particles, zirconia particles, and silica particles, and silicon compounds such as quaternary alkoxysilanes such as tetraethyl orthosilicate. From the viewpoint of the stability of the polyimide varnish for producing the polyimide film, the inorganic material is preferably inorganic particles, particularly silica particles. The inorganic particles may be bonded by molecules having a siloxane bond.

The average primary particle diameter of the inorganic particles is preferably 10 to 100 nm, more preferably 20 to 80 nm, from the viewpoint of transparency of the polyimide film, mechanical properties, and suppression of inorganic particle aggregation. In the present invention, the average primary particle diameter can be determined by measuring 10 points in a fixed direction diameter with a transmission electron microscope (TEM) and obtaining an average value thereof.

When the polyimide film contains an inorganic material, the content of the inorganic material in the polyimide film is preferably 0% by mass to 90% by mass, more preferably 0% by mass or more, based on the total mass of the polyimide film. It is 60 mass% or less, More preferably, it is 0 mass% or more and 40 mass% or less. If the content of the inorganic material is within the above range, the transparency and mechanical properties of the polyimide film tend to be compatible.

(UV absorber)
The polyimide film may contain one type or two or more types of ultraviolet absorbers. The ultraviolet absorber can be appropriately selected from those usually used as an ultraviolet absorber in the field of resin materials. The ultraviolet absorber may contain a compound that absorbs light having a wavelength of 400 nm or less. Examples of the ultraviolet absorber include at least one compound selected from the group consisting of benzophenone compounds, salicylate compounds, benzotriazole compounds, and triazine compounds. Since the polyimide film contains an ultraviolet absorber, deterioration of the polyimide polymer is suppressed, so that the visibility of the polyimide film can be improved.
In the present specification, the “system compound” refers to a compound to which the “system compound” is attached and derivatives thereof. For example, a “benzophenone compound” refers to a compound having benzophenone as a host skeleton and a substituent bonded to benzophenone.

When the polyimide 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, and further preferably 3% by mass with respect to the total mass of the polyimide film. % Or more, preferably 10% by mass or less, more preferably 8% by mass or less, and further preferably 6% by mass or less. When the ultraviolet absorber is within the above range, the weather resistance of the polyimide film can be particularly effectively enhanced, and a highly transparent polyimide film can be obtained.

(Other additives)
The polyimide film may further contain other additives as long as the transparency, flexibility and retardation are not impaired. Examples of other components include antioxidants, mold release agents, stabilizers, bluing agents, flame retardants, pH adjusters, silica dispersants, lubricants, thickeners, and leveling agents.

The content of other additives is preferably 0% by mass or more and 20% by mass or less, and more preferably 0% by mass or more and 10% by mass or less with respect to the mass of the polyimide film.

The thickness of the polyimide film is appropriately adjusted depending on the application, but is usually 10 to 1000 μm, preferably 20 to 500 μm, more preferably 25 to 400 μm, and further preferably 30 to 300 μm. In the present invention, the thickness can be measured by a contact-type digimatic indicator. When the thickness of the polyimide film is equal to or more than the above lower limit, the surface hardness of the laminate (polyimide film on which the hard coat layer is laminated), which will be described later, is improved, and the handling properties of the polyimide film are improved. Hard to break when stretched. When the thickness of the polyimide film is equal to or less than the above upper limit, the bending resistance of the polyimide film (difficult to attach a broken line when folded) is improved.

The polyimide film has a total light transmittance Tt based on JIS K 7105: 1981 of preferably 85% or more, more preferably 90% or more, and further preferably 92% or more. When the total light transmittance Tt of the polyimide film is equal to or higher than the lower limit, sufficient visibility can be secured when the polyimide film is incorporated into an image display device. In addition, the upper limit of the total light transmittance Tt of the polyimide film is usually 100% or less.

The polyimide film has a yellowness YI based on JIS K 7373: 2006, preferably 5 or less, more preferably 4 or less, and even more preferably 3 or less. The transparency of a polyimide film can be made high as YI of a polyimide film is below the said upper limit. In addition, the lower limit of YI of a polyimide-type film is 0 or more normally.

The polyimide film has an in-plane retardation (retardation) at a wavelength of 589.4 nm of 3,000 nm or more, preferably more than 3,000 nm, more preferably 3,200 nm or more, still more preferably 3,500 nm or more, particularly preferably 4. It is not less than 30,000 nm, preferably not more than 30,000 nm, more preferably not more than 25,000 nm, still more preferably not more than 20,000 nm, and particularly preferably not more than 17,000 nm. If the in-plane retardation of the polyimide film at a wavelength of 589.4 nm is less than 3,000 nm, coloring through polarized sunglasses cannot be sufficiently suppressed, resulting in a problem in visibility. When the in-plane retardation of the polyimide film at a wavelength of 589.4 nm is equal to or greater than the lower limit, coloring through the polarized sunglasses is suppressed when the polyimide film is used as a front plate (window film) of an image display device. be able to. When the in-plane retardation of the polyimide film at a wavelength of 589.4 nm is less than or equal to the above upper limit, coloring of the polyimide film can be suppressed, and the flexibility of the polyimide film can be increased. Useful as a display front plate.

The reason why the in-plane retardation at the wavelength of 589.4 nm is within the above range can suppress the coloring through the sunglasses is that the number of peaks in the transmission spectrum spectrum from the image display element increases, and the transmitted light is white light. Because it becomes.

In addition, compared with other polymer materials such as PET film, polyimide film tends to exhibit in-plane retardation due to a low draw ratio, and there is little dimensional change even in high temperature environment of 100 ° C. or higher. Application to image display elements such as car navigation used in the environment is suitable.

In addition, since the said polyimide-type film and the laminated body mentioned later have the in-plane phase difference of the said range, it can be used as a phase difference film. That is, it can be used as a front plate (window film) of an image display device, and at the same time, can exhibit a function as a retardation film. Therefore, the polyimide-based film and laminate according to an embodiment of the present invention can contribute to simplification of the image display device, which is advantageous in terms of cost of the image display device and contributes to thinning of the image display device. obtain.

The method for controlling the retardation of the polyimide film is not particularly limited. For example, the selection of the type of polyimide polymer contained in the polyimide film, the stretching process of the polyimide film, and / or the thickness of the polyimide film. Adjustment and the like. When the polyimide film is a stretched film, it is preferable because the retardation can be adjusted by selecting the stretching ratio, and the retardation can be easily adjusted. When selecting the thickness of the polyimide film, the thickness may be adjusted by laminating a plurality of polyimide films. By selecting a polyimide-based polymer that easily develops a phase difference, it is easy to produce a polyimide-based film having a phase difference within the above range. Moreover, in order to suppress the fracture | rupture of a polyimide-type film when extending | stretching a polyimide-type film, you may enlarge the thickness of a polyimide-type film. The polyimide film may be a single layer or a multilayer.

[Laminate]
In one embodiment of the present invention, there is also provided a laminate (also referred to as “laminate of the present invention”) comprising the polyimide film and a hard coat layer disposed on at least one surface of the polyimide film. Is done. The laminate includes a polyimide film containing a polyimide polymer, a hard coat layer disposed on at least one surface of the polyimide film, and a functional layer and / or a primer layer as necessary. . The laminate is excellent in mechanical properties such as surface hardness and tear strength. In particular, when the polyimide film contained in the laminate is a stretched film, the ease with which the fold line remains is greatly different between when folded horizontally in the stretching direction and when folded vertically in the stretching direction. Absent. Therefore, the laminated body can be used for flexible displays having various shapes and flexible displays having deformed shapes.

The structure in one embodiment of the laminate of the present invention will be described with reference to FIG. 1. The laminate (10) has a hard coat layer (2) laminated on one surface of a polyimide film (1). Another hard coat layer (not shown) that is the same as or different from the hard coat layer (2) may be laminated on the other surface of the polyimide film (1). A primer layer (not shown) described later is provided between the polyimide film (1) and the hard coat layer (2) and / or between the polyimide film (1) and another hard coat layer. Also good. Furthermore, the laminated body may contain a functional layer (not shown) described later. The location where the functional layer is disposed is not limited, and the functional layer may be disposed on the polyimide film, may be disposed on the hard coat layer (2), or may be disposed on another hard coat layer. .

[Hard coat layer]
In the laminate which is one embodiment of the present invention, a hard coat layer is disposed on one or both surfaces of the polyimide film. In a preferred embodiment of the present invention, the hard coat layer is disposed at least on the viewing side surface of the polyimide film. Each hard coat layer may have a single layer structure or a multilayer structure.

The surface hardness of the hard coat layer is preferably F or more, more preferably H or more, and further preferably 2H or more. When the surface hardness of the hard coat layer is not less than the above lower limit value, scratches on the surface of the image display device can be advantageously suppressed when the laminate is used as a front plate (window film) of the image display device. This can contribute to prevention of shrinkage and expansion of the polyimide film. The surface hardness of the hard coat layer is usually 9H or less. In the present invention, the surface hardness can be measured according to JIS K5600-5-4: 1999.

The hard coat layer comprises a hard coat layer resin. Examples of the hard coat layer resin include acrylic resins, epoxy resins, urethane resins, benzyl chloride resins, vinyl resins, silicone resins, or a mixture thereof. Examples thereof include ultraviolet curable resins such as resins, electron beam curable resins, and thermosetting resins. In particular, the hard coat layer preferably contains an acrylic resin from the viewpoint of mechanical properties such as surface hardness and from an industrial viewpoint.

Examples of the acrylic resin include urethane acrylate, urethane methacrylate (hereinafter, acrylate and / or methacrylate are described as (meth) acrylate), alkyl (meth) acrylate, ester (meth) acrylate, epoxy (meth) acrylate, and A polymer, a copolymer, etc. are mentioned. Specifically, methyl (meth) acrylate, butyl (meth) acrylate, methoxyethyl (meth) acrylate, butoxyethyl (meth) acrylate, phenyl (meth) acrylate, ethylene glycol di (meth) acrylate, propylene glycol di (meth) ) Acrylate, neopentyl glycol di (meth) acrylate, dipropylene glycol di (meth) acrylate, ethylene glycol di (meth) acrylate, propylene glycol di (meth) acrylate, pentaerythritol tri (meth) acrylate, and polymers thereof And copolymers.

The hard coat layer may contain a photopolymerization initiator and / or an organic solvent, and may contain inorganic oxides such as silica particles, alumina, and polyorganosiloxane. In a preferred embodiment of the present invention, the hard coat layer comprises an acrylic resin and silica particles from the viewpoint of mechanical properties such as surface hardness and an industrial viewpoint.

The thickness of the hard coat layer is appropriately adjusted according to the use of the image display device to which the laminate is applied, and may be, for example, 1 to 50 μm, particularly 2 to 30 μm. In the present invention, the thickness of the hard coat layer can be calculated from the difference from the base material thickness using, for example, a contact-type digimatic indicator.

In a preferred embodiment of the present invention, the hard coat layer may be a stretched film. The hard coat layer which is a stretched film can be prepared by drying a coating film of the following hard coat layer composition, performing a stretching treatment, and irradiating with a high energy ray.

[Primer layer]
In the laminate which is an embodiment of the present invention, a primer layer may be disposed between the polyimide film and the hard coat layer. When hard coat layers are arranged on both surfaces of the polyimide film, a primer layer may be arranged only between the polyimide film and one hard coat layer, and the polyimide film and one hard coat layer A primer layer may be disposed both between and between the polyimide film and the other hard coat layer.

The primer layer is a layer formed from a primer agent, and can improve the adhesion between the polyimide film and the hard coat layer. The compound contained in the primer layer may be chemically bonded to the polyimide polymer or the like contained in the polyimide film at the interface.

Examples of the primer agent include a primer agent of an epoxy compound of an ultraviolet curing type, a thermosetting type, or a two-component curing type. The primer agent may be a polyamic acid. These are suitable for enhancing the adhesion between the polyimide film and the hard coat layer.

The primer agent may contain a silane coupling agent. The silane coupling agent may be chemically bonded to a silicon compound that can be included in the polyimide film by a condensation reaction. The silane coupling agent can be suitably used particularly when the compounding ratio of the silicon compound that can be contained in the polyimide film is high.

The silane coupling agent is a compound having an alkoxysilyl group having a silicon atom and 1 to 3 alkoxy groups covalently bonded to the silicon atom. A compound having a structure in which two or more alkoxy groups are covalently bonded to a silicon atom is preferable, and a compound having a structure in which three alkoxy groups are covalently bonded to a silicon atom is more preferable. Examples of the alkoxy group include a methoxy group, an ethoxy group, an isopropoxy group, an n-butoxy group, and a t-butoxy group. Of these, a methoxy group or an ethoxy group is preferable because of its high reactivity with silicon materials.

The silane coupling agent preferably has a substituent having high affinity with the polyimide film and the hard coat layer. From the viewpoint of affinity with the polyimide polymer contained in the polyimide film, the substituent of the silane coupling agent is preferably an epoxy group, an amino group, a ureido group or an isocyanate group. When the hard coat layer contains (meth) acrylates, the affinity increases when the silane coupling agent that can be used in the primer layer has an epoxy group, a methacryl group, an acrylic group, an amino group, or a styryl group. Therefore, it is preferable. Among these, a silane coupling agent having a substituent selected from a methacryl group, an acryl group, and an amino group is preferable because it tends to be excellent in affinity between the polyimide film and the hard coat layer.

The thickness of the primer layer is appropriately adjusted according to the hard coat layer, and is, for example, 0.01 nm to 20 μm. When using an epoxy compound primer, the thickness of the primer layer 25 is preferably 0.01 to 20 μm, more preferably 0.1 to 10 μm. When a silane coupling agent is used, the thickness of the primer layer is preferably 0.1 nm to 1 μm, more preferably 0.5 nm to 0.1 μm.

[Functional layer]
The laminate which is one embodiment of the present invention may further include a functional layer in addition to the polyimide film and the hard coat layer. Examples of the functional layer include layers having various functions such as an ultraviolet absorbing layer, an adhesive layer, a hue adjusting layer, and a refractive index adjusting layer. The laminate may include one or more functional layers. One functional layer may have a plurality of functions.

The ultraviolet absorbing layer is a layer having an ultraviolet absorbing function. For example, a main material selected from an ultraviolet curable transparent resin, an electron beam curable transparent resin, and a thermosetting transparent resin, It is composed of dispersed UV absorbers. By providing the ultraviolet absorbing layer as the functional layer, a change in yellowness due to light irradiation can be easily suppressed.

The adhesive layer is a layer having an adhesive function, and has a function of adhering a polyimide film or a laminate to other members. As the material for forming the adhesive layer, a conventionally known material can be used. For example, a thermosetting resin composition or a photocurable resin composition can be used.

The adhesive layer may be composed of a resin composition containing a component having a polymerizable functional group. In this case, strong adhesion can be achieved by further polymerizing the resin composition constituting the adhesive layer after the polyimide-based film or laminate is adhered to another member. The adhesive strength between the polyimide film or laminate and the adhesive layer may be 0.1 N / cm or more, or 0.5 N / cm or more.

The adhesive layer may contain a thermosetting resin composition or a photocurable resin composition as a material. In this case, the resin composition can be polymerized and cured by supplying energy afterwards.

The pressure-sensitive adhesive layer may be a layer called pressure sensitive adhesive (Pressure Sensitive Adhesive, PSA) that is adhered to an object by pressing. The pressure-sensitive adhesive may be a pressure-sensitive adhesive that is “a substance that is sticky at normal temperature and adheres to an adherend with light pressure” (JIS K6800). And an adhesive that can maintain stability until the coating is broken by appropriate means (pressure, heat, etc.) (JIS K6800).

The hue adjustment layer is a layer having a function of hue adjustment, and is a layer capable of adjusting the laminated body to a target hue. A hue adjustment layer is a layer containing resin and a coloring agent, for example. Examples of the colorant include inorganic pigments such as titanium oxide, zinc oxide, dial, titanium oxide-based fired pigment, ultramarine, cobalt aluminate, and carbon black; azo-based compounds, quinacridone-based compounds, anthraquinone-based compounds, Organic pigments such as perylene compounds, isoindolinone compounds, phthalocyanine compounds, quinophthalone compounds, selenium compounds, and diketopyrrolopyrrole compounds; extender pigments such as barium sulfate and calcium carbonate; and basic dyes, Examples include acid dyes and mordant dyes.

The refractive index adjusting layer is a layer having a function of adjusting the refractive index, has a refractive index different from that of the polyimide film, and can give a predetermined refractive index to the laminate. The refractive index adjustment layer may be, for example, an appropriately selected resin, and optionally a resin layer further containing a pigment, or may be a metal thin film.

Examples of the pigment for adjusting the refractive index include silicon oxide, aluminum oxide, antimony oxide, tin oxide, titanium oxide, zirconium oxide and tantalum oxide. The 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, irregular reflection of light transmitted through the refractive index adjusting layer can be prevented, and a decrease in transparency can be prevented.

Examples of the metal used for the refractive index adjustment layer include metals 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. Oxides or metal nitrides may be mentioned.

The primer layer may be disposed between the polyimide film and the functional layer.

The laminate preferably has an in-plane retardation at a wavelength of 589.4 nm of 3,000 nm or more, more preferably 3,500 nm or more, still more preferably 4,000 nm or more, preferably 30,000 nm or less, more preferably 25. 17,000 nm or less, more preferably 20,000 nm or less, and particularly preferably 17,000 nm or less. When the phase difference of the laminate is equal to or more than the lower limit, coloring through the polarized sunglasses can be suppressed when the laminate is used as a front plate of an image display device. When the retardation of the laminate is not more than the above upper limit value, the flexibility of the laminate can be increased and it is useful as a front plate of a flexible display.

The laminate has a total light transmittance Tt based on JIS K 7105: 1981 of preferably 85% or more, more preferably 90% or more, and still more preferably 92% or more. When the total light transmittance of the laminate is not less than the above lower limit, sufficient visibility can be secured when the laminate is incorporated in an image display device. In addition, the upper limit of the total light transmittance of a laminated body is 100% or less normally.

The laminate has a yellowness (YI) based on JIS K 7373: 2006, preferably 5 or less, more preferably 4 or less, and even more preferably 3 or less. The transparency of a laminated body can be made high as YI of a laminated body is below the said upper limit. In addition, the lower limit of YI of a laminated body is 0 or more normally.

The thickness of the laminate is appropriately adjusted depending on the application, but is usually 10 to 1,000 μm, preferably 15 to 500 μm, more preferably 20 to 400 μm, and further preferably 25 to 300 μm. When the thickness of the laminate is within the above range, the flexibility is good, and at the same time, it can contribute to the thinning of the image display device.

[Production method]
The manufacturing method of a polyimide-type film and a laminated body is not specifically limited. Below, an example of the manufacturing method of a polyimide-type film and a laminated body is demonstrated.

(Production method of polyimide film)
In one embodiment of the present invention, the polyimide film, for example, includes the following steps:
(A) Applying a liquid (polyimide varnish) containing a polyimide-based polymer to a substrate to form a coating film (application process), and (b) drying the applied liquid (polyimide varnish) to obtain a polyimide system Process for forming a film (film forming process)
It can manufacture with the manufacturing method containing. Steps (a) and (b) may usually be performed in this order.

In the coating process, first, a liquid containing a polyimide polymer (polyimide varnish) is prepared. In order to prepare a polyimide varnish, the tetracarboxylic acid compound, the diamine, and other components as necessary are mixed and reacted to prepare a polyimide mixed solution. A solvent (polyimide varnish) containing a polyimide-based polymer is prepared by adding a solvent, and, if necessary, the ultraviolet absorber and other additives to the polyimide mixed solution and stirring. Instead of the polyimide mixed solution, a solution such as a purchased polyimide polymer or a solution such as a purchased solid polyimide polymer may be used.

The solvent used for preparing the polyimide varnish is not particularly limited as long as it can dissolve the polyimide polymer. Examples of such solvents include amide solvents such as N, N-dimethylacetamide and N, N-dimethylformamide; lactone solvents such as γ-butyrolactone and γ-valerolactone; and sulfur-containing solvents such as dimethylsulfone, dimethylsulfoxide, and sulfolane. Examples thereof include carbonate solvents such as ethylene carbonate and propylene carbonate; and combinations thereof (mixed solvents). Among these solvents, amide solvents or lactone solvents are preferable. The polyimide varnish may contain water.

Next, for example, by a known roll-to-roll or batch method, a coating film is formed on a substrate such as a resin substrate, a SUS belt, or a glass substrate by using a polyimide varnish by fluency molding or the like. Can do.

In the film forming step, a polyimide film can be formed by drying the coating film and peeling it from the substrate. You may perform the drying process which dries a polyimide-type film further after peeling. The coating film can be dried usually at a temperature of 50 to 350 ° C. If necessary, the coating film may be dried under an inert atmosphere or under reduced pressure.

A surface treatment step of performing a surface treatment on at least one surface of the polyimide film may be performed. Examples of the surface treatment include UV ozone treatment, plasma treatment, and corona discharge treatment.

Examples of resin base materials include PET films, PEN films, and polyimide films. Among these, from the viewpoint of excellent heat resistance, a PET film, a PEN film, a polyimide film, and a polyamideimide film are preferable. Furthermore, a PET film is more preferable as the resin base material from the viewpoint of adhesion to the polyimide film as the front plate and cost. Further, the thickness of the resin substrate is not particularly limited, and is, for example, 10 to 500 μm, preferably 50 to 300 μm. In addition, the polyimide-type film as a resin base material is synonymous with the polyimide-type film of Paragraph 0014.

The method for producing a polyimide film may include (c) a step of stretching the polyimide film uniaxially or biaxially (film stretching step). In the film stretching step, the stretching may be uniaxial stretching or biaxial stretching, but it is preferable to stretch the polyimide film by uniaxial stretching from the viewpoint of the in-plane retardation distribution uniformity. In the case of performing biaxial stretching, the biaxial stretching may be simultaneous biaxial stretching or sequential biaxial stretching. The draw ratio is not particularly limited, but is preferably 1.05 to 5.0 times, more preferably 1.1 to 4.0 times, and still more preferably 1.3 to 3.0 times. When the draw ratio is in the above range, there are few breaks due to the drawing process, and the desired phase difference can be obtained. You may perform a film extending process during drying of a coating film. The film stretching step may be performed under heating, and the temperature (stretching temperature) is, for example, 150 to 350 ° C. When the stretching temperature is 150 to 350 ° C., the polyimide and polyamideimide are easily stretched without causing breakage. After stretching, the polyimide film may be relaxed and heat-set. In addition, you may extend | stretch a polyimide-type film, drying a coating film.

(Laminate manufacturing method)
Next, manufacture of a laminated body is demonstrated. In one embodiment of the present invention, a laminate comprising a polyimide film and a hard coat layer disposed on at least one surface of the polyimide film, that is, a laminate comprising a polyimide film and a hard coat layer is, for example, The following steps:
(D) A process of applying a hard coat layer composition on a polyimide film to form a coating film (coating film forming process), and (e) irradiating the coating film with high energy rays to cure the coating film. Step to form a hard coat layer (curing step)
It can manufacture with the manufacturing method containing. The order of the steps may be the order of steps (d) and (e). Normally, the steps (d) and (e) can be performed after the steps (a) and (b) and optionally (c).

In the coating film forming step, a hard coat layer composition is first prepared. The hard coat layer composition contains the above hard coat layer resin and, if necessary, a photopolymerization initiator, an organic solvent and / or an inorganic oxide, and can be prepared by mixing these components. it can. Examples of the photopolymerization initiator include benzoin compounds, benzophenone compounds, alkylphenone compounds, acylphosphine oxide compounds, triazine compounds, iodonium salts, and sulfonium salts. Examples of the organic solvent include alcohol solvents such as ethanol, ethylene glycol, isopropyl alcohol, and propylene glycol; ester solvents such as ethyl acetate and γ-butyrolactone; ketone solvents such as acetone, methyl ethyl ketone, and cyclopentanone; Aliphatic hydrocarbon solvents; and aromatic hydrocarbon solvents such as toluene and xylene. A photoinitiator and / or an organic solvent may be individual, and may be used in combination of 2 or more type. Further, the hard coat layer composition may contain the other additives.

Next, a hard coat layer composition is applied onto the polyimide film to form a coating film. The formation order of the polyimide film and the coating film may be reversed. After forming the coating film by applying the hard coat layer composition on the substrate, the coating film of the polyimide film is formed on the coating film. Also good. Moreover, you may bond to a polyimide-type film using a well-known adhesive agent and / or an adhesive.

The coating film formed on the polyimide film may be dried. The coating film can be dried by evaporating the solvent at a temperature of 50 to 350 ° C., and the drying time is usually 30 to 180 seconds. You may dry in air | atmosphere, inert atmosphere, or the conditions of pressure reduction.

The method for producing a laminate may include (f) a step of stretching a polyimide film including a coating film uniaxially or biaxially (laminate stretching step) after the coating film forming step. The stretching may be uniaxial stretching or biaxial stretching, but from the viewpoint of in-plane retardation distribution uniformity, it is preferable to stretch the polyimide film including the coating film by uniaxial stretching. In the case of performing biaxial stretching, the biaxial stretching may be simultaneous biaxial stretching or sequential biaxial stretching. The draw ratio depends on the draw ratio in the film stretching step, but is preferably 1.05 to 5.0 times, more preferably 1.1 to 4.0 times, and still more preferably 1.3 to 3.0 times. . When the draw ratio is in the above range, there are few breaks due to the drawing process, and the desired phase difference can be obtained. The stretching step may be performed during drying of the coating film. The stretching step may be performed under heating, and the temperature is, for example, 150 to 350 ° C. After stretching, the polyimide film may be relaxed and heat-set. In addition, you may extend | stretch a polyimide-type film, drying a coating film.

When the laminate stretching step is performed after the coating film forming step, drying of the coating and stretching of the laminate can be performed at the same time, which is advantageous from the viewpoint of process design. Moreover, when performing a extending process after the said coating-film formation process, it is not necessary to perform a film extending process in the manufacturing method of a polyimide-type film. In addition, when performing a laminated body extending process after a coating-film formation process, the coating film arrange | positioned on a polyimide-type film is also extended simultaneously with extending | stretching of a polyimide-type film.

In the curing step, the coating film (resin composition) is irradiated with high energy rays (active energy rays), and the coating film is cured to form a hard coat layer. The irradiation intensity is appropriately determined depending on the composition of the hard coat layer composition and is not particularly limited, but irradiation in a wavelength region effective for activating the photopolymerization initiator is preferable. The irradiation intensity is preferably 0.1 ~ 6,000mW / cm ^2, more preferably 10 ~ 1,000mW / cm ^2, more preferably 20 ~ 500mW / cm ^2. When the irradiation intensity is within the above range, an appropriate reaction time can be secured, and yellowing and deterioration of the resin due to heat radiated from the light source and heat generated during the curing reaction can be suppressed. The irradiation time may be appropriately selected depending on the composition of the hard coat layer composition and is not particularly limited. However, the integrated light amount expressed as the product of the irradiation intensity and the irradiation time is preferably 10 to 10,000 mJ. / Cm ² , more preferably 50 to 1,000 mJ / cm ² , still more preferably 80 to 500 mJ / cm ² . When the integrated light quantity is within the above range, a sufficient amount of active species derived from the photopolymerization initiator can be generated, and the curing reaction can proceed more reliably, and the irradiation time is not too long, and the production is good. Can maintain sex. Moreover, it is useful because the hardness of the hard coat layer can be further increased by performing the irradiation step in this range.

In addition, when hardening a photocurable adhesive agent by irradiation of a high energy ray, it is preferable to harden | cure on conditions that optical functions, such as a phase difference and transparency of a polyimide-type film, for example are not reduced.

[Optical member and image display device]
In one embodiment of the present invention, an optical member comprising the above polyimide film or laminate is provided. Examples of the optical member include a front plate of an image display device, particularly a front plate (window film) of a flexible display. In another embodiment of the present invention, an image display device including such an optical member, particularly a flexible display is also provided. The flexible display according to the present embodiment includes, for example, a flexible functional layer and the optical member that is stacked on the flexible functional layer and functions as a front plate. That is, the front plate of the flexible display is arranged on the viewing side on the flexible functional layer. This front plate has a function of protecting the flexible functional layer. And since this front board has a high phase difference, it is not necessary to arrange | position a phase difference plate in an image display apparatus, especially a flexible display. Therefore, the components of the image display device can be simplified, which is advantageous in terms of manufacturing and can contribute to the thinness of the image display device. From such a viewpoint, in a preferred embodiment of the present invention, an image display device including the optical member, particularly a flexible display, does not have a retardation film. The retardation film is an optical film exhibiting optical anisotropy. For example, the retardation film according to the purpose of use, such as for the purpose of compensating for coloring or viewing angle due to birefringence of various wave plates and liquid crystal layers, etc. It is what you have.

Examples of the image display device include wearable devices such as a television, a smartphone, a mobile phone, a car navigation system, a tablet PC, a portable game machine, electronic paper, an indicator, a bulletin board, a clock, and a smart watch. The flexible display is all image display devices having flexible characteristics.

An example of a flexible display is shown in FIG. This flexible display 100 has a configuration of front plate 110 / polarizing film 120 / touch sensor film 130 / organic EL element layer 140 / TFT substrate 150 in order from the surface side (viewing side). A layer other than the front plate 110 in the flexible display 100 is the flexible functional layer 200. An adhesive layer or the like may be included between the surface of each layer and each layer. As the front plate 110, the optical member such as the laminate 10 according to an embodiment of the present invention can be used.

Further, although an organic EL element is exemplified as the light source, the light source is not limited to this in the present embodiment. For example, it may be a liquid crystal display device, a plasma display panel, an inorganic EL display, a cathode ray tube display device, a surface electric field display, or the like, and this embodiment can be suitably used as a front plate of these display elements.

Such an image display device, particularly a flexible display, is advantageously used as a wearable device such as a television, a smartphone, a mobile phone, a car navigation, a tablet PC, a portable game machine, electronic paper, an indicator, a bulletin board, a clock, and a smart watch. be able to. An image display device including the polyimide film has flexible characteristics and can further suppress coloring through polarized sunglasses. In addition, the image display device including the laminate has flexible characteristics, can suppress coloring through polarized sunglasses, and at the same time has high surface hardness, so that the surface is hardly damaged.

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

<Surface hardness measurement>
As the surface hardness of the sample hard coat layer, the pencil hardness of the sample hard coat layer surface was adopted in accordance with JIS K5600-5-4: 1999. The load was 750 g.

<Total light transmittance measurement>
The total light transmittance of the sample was measured by a fully automatic direct reading haze computer HGM-2DP manufactured by Suga Test Instruments Co., Ltd. according to JIS K7105: 1981.

<Measurement of yellowness (YI value)>
The yellowness (Yellow Index: YI value) of the sample was measured using an ultraviolet-visible near-infrared spectrophotometer V-670 manufactured by JASCO Corporation in accordance with JIS K 7373: 2006. After performing background measurement in the absence of a sample, the sample was set in a sample holder, and the transmittance for light of 300 to 800 nm was measured to obtain tristimulus values (X, Y, Z). The YI value was calculated based on the following formula.
YI = 100 × (1.2769X−1.0592Z) / Y

<Phase difference (retardation) measurement>
In-plane retardation of the sample was measured using a phase difference measuring device KOBRA-WPR manufactured by Oji Scientific Instruments. A sample cut out at 4 cm × 5 cm was placed in the apparatus, the retardation at a wavelength of 589.6 nm at an incident angle of 0 ° was measured, and the measured value was taken as the in-plane retardation Re. Moreover, the sample used for the measurement cut out the center part of the width direction of a film, and made the film width direction the slow axis.

<Weight average molecular weight measurement>
Gel Permeation Chromatography (GPC) Measurement (1) Pretreatment Method A sample was dissolved in γ-butyrolactone (GBL) to make a 20 mass% solution, then diluted 100 times with DMF eluent, and a 0.45 μm membrane filter The filtered solution was used as a measurement solution.
(2) Measurement condition column: TSKgel SuperAWM-H x 2 + SuperAW 2500 x 1 (6.0 mm ID x 150 mm x 3)
Eluent: DMF (10 mM lithium bromide added)
Flow rate: 0.6 mL / min.
Detector: RI detector Column temperature: 40 ° C
Injection volume: 20 μL
Molecular weight standard: Standard polystyrene

[Synthesis Example 1]
[Preparation of polyimide film]
Under a nitrogen atmosphere, 1.25 g of isoquinoline was charged into a reaction vessel connected to a vacuum pump equipped with a solvent trap and a filter. Next, 375.00 g of γ-butyrolactone (GBL) and 104.12 g of 2,2′-bis (trifluoromethyl) -4,4′-diaminodiphenyl (TFMB) are added to the reaction vessel, and the mixture is stirred. And dissolved. Further, 145.88 g of 4,4 ′-(hexafluoroisopropylidene) diphthalic dianhydride (6FDA) was added to the reaction vessel, and then the temperature was raised in an oil bath while stirring the mixture. The added TFMB to 6FDA molar ratio was 1.00: 0.99, and the monomer concentration in the mixture was 40% by weight. When the internal temperature of the reaction vessel reached 80 ° C., the pressure was reduced to 650 mmHg, and then the internal temperature was raised to 180 ° C. After the internal temperature reached 180 ° C., the mixture was further heated for 4 hours under stirring. Thereafter, the pressure was restored to atmospheric pressure, the internal temperature was cooled to 155 ° C., and a polyimide solution was obtained. GBL was added at 155 ° C. to prepare a uniform solution having a polyimide solid content of 24% by mass, and then the polyimide varnish, which was a uniform solution, was taken out of the reaction vessel. When the GPC measurement was performed about the polyimide in the obtained polyimide varnish, the weight average molecular weight was 360000. Moreover, the fluorine atom content of the polyimide polymer was 31.3% by mass.

GPL38.31 g and N, N-dimethylacetamide (DMAc) 11.82 g were added to 200.00 g of the polyimide varnish to further dilute. Using the diluted polyimide varnish, a coating film was formed on a PET (polyethylene terephthalate) film by fluent casting. Then, the coating film was dried by heating at 50 ° C. for 30 minutes and at 140 ° C. for 10 minutes to obtain a polyimide film.

[Synthesis Example 2]
[Preparation of polyimide film]
Under a nitrogen gas atmosphere, TFMB 50 g (156.13 mmol) and DMAc 642.07 g were added to a 1 L separable flask equipped with a stirring blade, and TFMB was dissolved in DMAc while stirring at room temperature. Next, 20.84 g (46.91 mmol) of 6FDA was added to the flask and stirred at room temperature for 3 hours. Thereafter, 9.23 g (31.27 mmol) of 4,4′-oxybis (benzoyl chloride) (OBBC) and then 15.87 g (78.18 mmol) of terephthaloyl chloride (TPC) were added to the flask and stirred at room temperature for 1 hour. did. Next, 9.89 g (106.17 mmol) of 4-methylpyridine and 14.37 g (140.73 mmol) of acetic anhydride were added to the flask. After stirring for 30 minutes at room temperature, the temperature was raised to 70 ° C. using an oil bath, The mixture was further stirred for 3 hours to obtain a reaction solution.
The resulting reaction solution was cooled to room temperature, poured into a large amount of methanol in the form of a thread, the deposited precipitate was taken out, immersed in methanol for 6 hours, and washed with methanol. Next, the precipitate was dried under reduced pressure at 100 ° C. to obtain polyamideimide. When the obtained polyamideimide was subjected to GPC measurement, the weight average molecular weight was 420,000.

The polyamideimide was added to the DMAc solvent and dissolved at a concentration of 10% to obtain a resin varnish. Using the diluted polyimide varnish, the coating film was dried in the same manner as in Synthesis Example 1 to obtain a polyimide film.

[Example 1]
The polyimide film obtained in Synthesis Example 1 was peeled from the PET film. The obtained polyimide-based film was uniaxially stretched at a stretching temperature of 200 ° C. and a stretching ratio of 1.35 times to obtain a stretched polyimide-based film having a thickness of 60 μm. When the center part of the stretched polyimide film was cut out and the in-plane retardation was measured, it was 4,000 nm.

On the stretched polyimide film, Z-624 manufactured by AICA was applied using a Mayer bar so that the thickness after drying was 5 μm, thereby forming a coating film. After drying the obtained coating film at 120 ° C. for 1 minute, the coating film was cured by irradiating with ultraviolet rays at an ultraviolet irradiation amount of 500 mJ / cm ² to form a hard coat layer having a thickness of 5 μm. This obtained the laminated body (1) provided with a stretched polyimide-type film (thickness: 60 micrometers) and a hard-coat layer (thickness: 5 micrometers). Next, when the pencil hardness was measured using the laminate (1), it was 3H. Moreover, total light transmittance measurement and yellowness measurement were performed. The results are shown in Table 1.

[Example 2]
The polyimide film obtained in Synthesis Example 1 was peeled from the PET film. On the obtained polyimide film, Z-624 manufactured by AICA was applied using a Mayer bar so that the thickness after drying was 6 μm, thereby forming a coating film. The obtained coating film was dried at 120 ° C. for 1 minute.

The polyimide film provided with the coating film was uniaxially stretched at a stretching temperature of 200 ° C. and a stretching ratio of 1.35 times to obtain a stretched polyimide film having a thickness of 65 μm. Thereafter, the coating film was cured by irradiating with ultraviolet rays at an ultraviolet irradiation amount of 500 mJ / cm ² to form a hard coat layer. This obtained the laminated body (2) provided with a polyimide-type film (thickness: 60 micrometers) and a hard-coat layer (thickness: 5 micrometers). When the center part of the laminated body (2) was cut out and the in-plane retardation was measured, it was 4,100 nm. Next, when the pencil hardness was measured using the laminate (2), it was 3H. Moreover, total light transmittance measurement and yellowness measurement were performed. The results are shown in Table 1.

[Example 3]
The polyimide film obtained in Synthesis Example 1 was peeled from the PET film. Then, after forming a coating film on the obtained polyimide film in the same manner as in Example 2, uniaxially stretching at a stretching temperature of 200 ° C. and a stretching ratio of 1.50, and then performing ultraviolet irradiation, A polyimide laminate (3) provided with a stretched polyimide film (thickness: 60 μm) and a hard coat layer (thickness: 5 μm) was obtained. When the center part of the laminated body (3) was cut out and the in-plane retardation was measured, it was 15,160 nm. Next, when the pencil hardness was measured using the laminate (3), it was 3H. Moreover, total light transmittance measurement and yellowness measurement were performed. The results are shown in Table 1.

[Example 4]
The polyimide film obtained in Synthesis Example 2 was peeled from the PET film. Then, after forming a coating film on the obtained laminated polyimide film in the same manner as in Example 2, the film was uniaxially stretched at a stretching temperature of 200 ° C. and a stretching ratio of 1.30, and then irradiated with ultraviolet rays. A laminate comprising a stretched polyimide film (thickness: 60 μm) and a hard coat layer (thickness: 5 μm) was obtained. When the center part of the laminate was cut out and the in-plane retardation was measured, it was 5,000 nm. Next, when the pencil hardness was measured using the laminate (3), it was 2H. Moreover, total light transmittance measurement and yellowness measurement were performed. The results are shown in Table 1.

[Comparative Example 1]
The polyimide-based film obtained in Synthesis Example 1 was peeled from the PET film and uniaxially stretched at a stretching temperature of 200 ° C. and a stretching ratio of 1.25 times to obtain a stretched polyimide-based film having a thickness of 60 μm. When the center part of the stretched polyimide film was cut out and the in-plane retardation was measured, it was 2,010 nm.

On the stretched polyimide film, Z-624 manufactured by AICA was applied using a Mayer bar so that the thickness after drying was 5 μm, thereby forming a coating film. After drying the obtained coating film at 120 ° C. for 1 minute, the coating film was cured by irradiating with ultraviolet rays at an ultraviolet irradiation amount of 500 mJ / cm ² to form a hard coat layer having a thickness of 5 μm. This obtained the laminated body (4) provided with a polyimide-type film (thickness: 65 micrometers) and a hard-coat layer (thickness: 5 micrometers). Next, when the pencil hardness was measured using the laminate (4), it was 3H. Moreover, total light transmittance measurement and yellowness measurement were performed. The results are shown in Table 1.

[Comparative Example 2]
The polyimide film obtained in Synthesis Example 2 was peeled from the PET film. Thereafter, the film was fixed to a metal frame and heated at a drying temperature of 200 ° C. to obtain an unstretched polyimide film having a thickness of 60 μm. The center part of the unstretched polyimide film was cut out, and when this in-plane retardation was measured, it was 210 nm, and then a laminate provided with a hard coat layer (thickness: 5 μm) in the same manner as in Example 1. Obtained. Next, when the pencil hardness was measured using the laminate, it was 2H. Moreover, total light transmittance measurement and yellowness measurement were performed. The results are shown in Table 1.

<Visibility evaluation>
Liquid crystal display elements were produced using the laminates (1) to (4) obtained in the respective examples and comparative examples. A manufacturing method of the liquid crystal display element is as follows.

[Production Method of Polarizing Plate (1)]
A polyvinyl alcohol film (trade name “Kuraray Vinylon VF-PS # 7500” manufactured by Kuraray Co., Ltd.) having an average polymerization degree of about 2400 and a saponification degree of 99.9 mol% and a thickness of 75 μm is immersed in pure water at 30 ° C. Then, the iodine dyeing process was performed by immersing at 30 ° C. in an aqueous solution having a weight ratio of iodine / potassium iodide / water of 0.02 / 1.5 / 100. Thereafter, the boric acid treatment step was performed by immersing the polyvinyl alcohol film in an aqueous solution having a weight ratio of potassium iodide / boric acid / water of 20/3/100 at 30 ° C. Subsequently, the polyvinyl alcohol film was washed with pure water and then dried to obtain a polarizing film in which iodine was adsorbed and oriented on polyvinyl alcohol. Stretching was mainly performed in the iodine staining and boric acid treatment steps, and the total stretching ratio was 5.9 times.

A polarizing plate (1) was obtained by laminating a cellulose triacetate resin (trade name “Fujitac TD40UZ” manufactured by Fuji Film Co., Ltd.) having a thickness of 40 μm on one side of the obtained polarizing film.

[Method of manufacturing liquid crystal display]
The polarizing plate on the upper surface of the liquid crystal panel (Diamondcrysta RDT196LM) manufactured by Mitsubishi Electric Corporation is peeled off. And pasted together to go straight. In addition, the polarizing plate (1) and the laminate were bonded so that the angle formed by the slow axis of the stretched polyimide film with respect to the absorption axis of the polarizing plate was 45 °. In this way, liquid crystal displays (1) to (4) were produced.

[Visibility evaluation method]
The visibility of the liquid crystal displays (1) to (4) was confirmed as follows.
The produced liquid crystal displays (1) to (4) were each displayed in white, and an observer wore polarized sunglasses manufactured by FERRY, and evaluated the visibility through polarized sunglasses. The observer observed the colored state of the display while changing the observation angle with respect to the image display element in the range of 45 ° to 135 °. The results are shown in Table 1. In addition, the evaluation criteria of visibility are as follows.
○: Coloring is not visually recognized at all.
X: Rainbow unevenness and coloring are confirmed.

As described above, in the laminates of Examples 1 to 4 according to the present invention, the visibility through polarized sunglasses could be improved. On the other hand, in Comparative Examples 1 and 2, coloring occurred, causing a problem in visibility.

DESCRIPTION OF SYMBOLS 1 Polyimide-type film 2 Hard-coat layer 10 Laminated body 110 Front plate 120 Polarizing film 130 Touch sensor film 140 Organic EL element 150 TFT substrate 200 Flexible functional layer

Claims

A polyimide film having an in-plane retardation at a wavelength of 589.4 nm of 3,000 nm or more.
The polyimide film according to claim 1, wherein the total light transmittance is 85% or more.
The polyimide film according to claim 1 or 2, wherein the polyimide polymer contained in the polyimide film contains a fluorine atom in the molecule.
The polyimide film according to any one of claims 1 to 3, having a yellowness index (YI) of 5 or less.
A laminate comprising the polyimide film according to any one of claims 1 to 4 and a hard coat layer disposed on at least one surface of the polyimide film.
An optical member comprising the polyimide film according to any one of claims 1 to 4 or the laminate according to claim 5.
An image display device comprising the polyimide film according to claims 1 to 4, the laminate according to claim 5, or the optical member according to claim 6.
A process of forming a coating film by applying a hard coat layer composition on a polyimide film,
Includes a polyimide film and a hard coat layer, including a step of stretching the polyimide film uniaxially or biaxially, and a step of irradiating the coating film with high energy rays to cure the coating film to form a hard coat layer A manufacturing method of a layered product.
The production according to claim 8, further comprising a step of applying a liquid containing a polyimide polymer to a substrate to form a coating film, and a step of drying the applied liquid to form a polyimide film. Method.