JP2018123319A - Polyimide film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical film that can be used as a front plate material of a flexible display and improves the visibility of white printing of a bezel part.SOLUTION: A polyimide film contains at least one polyimide polymer and has a yellowness YI of 0<YI<1.0.SELECTED DRAWING: None

Description

  The present invention relates to a polyimide film.

  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 apparatus includes a polarizing plate, a retardation plate, a front plate, and the like in addition to a display element such as a liquid crystal display element or an organic EL display element. 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.

  In an image display device, for the purpose of protecting and supporting the display portion, there is usually an outer frame portion having a predetermined width on the periphery of the display substrate. This outer frame portion is referred to as a bezel portion or a frame portion. The bezel portion is usually printed with an arbitrary color tone, and the user visually recognizes the color tone of the bezel portion through the front plate located on the bezel portion.

Japanese Patent Laid-Open No. 2006-93992

  However, when a conventional polyimide film is used as a front plate material of an image display device having a bezel portion on which white printing is performed, the visibility of white printing on the bezel portion may not be good. For example, Patent Document 1 discloses a polyimide film having a yellowness of about 2; however, with such a yellowness polyimide film, the white hue of the bezel portion cannot be maintained, and white printing is not possible. It may be yellowish and visible.

  The present invention has been made in view of the above-described problems of the prior art, and can provide an optical film that can be used as a front plate material of a flexible display and has good visibility of white printing on a bezel portion. Objective.

In order to solve the above-mentioned problems, the present inventors diligently studied various characteristics of an optical film used as a front plate material. As a result, it has been found that the above problem can be solved by a polyimide film having a yellowness YI of 0 <YI <1.0, and the present invention has been completed. Conventionally, a polyimide film having a yellowness YI in the above range has not been noticed because it is difficult to achieve a thickness of 30 microns or more. However, the present inventors adjust the yellowness of the polyimide film to the above range and use it as a front plate material, thereby improving the visibility of white printing on the bezel part and the visibility of the display part. I found that it was not damaged.
That is, the present invention includes the following preferred embodiments.
[1] A polyimide film containing at least one polyimide polymer and having a yellowness YI of 0 <YI <1.0.
[2] The polyimide film according to [1], wherein the thickness is 20 to 200 μm.
[3] The polyimide film according to [1] or [2], wherein the total light transmittance is 88.0% or more.
[4] The polyimide film according to any one of [1] to [3], further containing at least one bluing agent.
[5] A single layer containing a bluing agent and a polyimide polymer, a laminate having at least a layer containing a bluing agent and a polyimide polymer, or a polyimide polymer The polyimide film according to any one of [1] to [4], which is a laminate having at least a hue adjusting layer containing a base material layer and a bluing agent.
[6] A layer containing at least one layer of the bluing agent, and in each layer containing the bluing agent, the amount of the bluing agent added based on the total mass of the layer is X (ppm). The product of X and Y calculated as the thickness of Y (μm) (X × Y) is calculated for all layers containing the bluing agent, and the total value is 300 to 4,500, The polyimide film according to any one of [1] to [5].
[7] The bluing agent is represented by the formula (6):
[In Formula (6), X ¹ represents OH, NHR ¹ or NR ¹ R ² , X ² represents NHR ³ or NR ³ R ⁴ , and R ¹ , R ² , R ³ and R ⁴ are independent of each other. And a phenyl group substituted with a linear or branched alkyl group having 1 to 6 carbon atoms or a linear or branched alkyl group having 1 to 6 carbon atoms. ]
The polyimide film according to any one of [4] to [6], wherein the polyimide film is a compound having a 1% thermal weight loss temperature of 220 ° C. or higher.
[8] The bluing agent is represented by the formulas (1) to (3):
The polyimide film according to [7], which is at least one selected from the group consisting of compounds represented by:
[9] The polyimide film according to any one of [1] to [8], further containing silica particles.

  Since the polyimide film of the present invention has a yellowness YI of 0 <YI <1.0 which is the above predetermined range, for example, when used as a front plate material of a flexible display having a bezel portion on which white printing is performed. Excellent visibility.

It is a figure which shows the part covered with the white bezel and polyimide film in an Example.

  Hereinafter, embodiments of the present invention will be described in detail.

[Polyimide film]
(Yellowness YI)
The polyimide film of the present invention is characterized in that the yellowness YI is 0 <YI <1.0. Yellowness YI is measured in accordance with JIS K 7373: 2006 by measuring transmittance for light of 300 to 800 nm with an ultraviolet-visible spectrophotometer (for example, spectrophotometer V-670 manufactured by JASCO Corporation). Is calculated from the following three stimulus values (x, y and z) by the following equation.

The yellowness YI of the polyimide film of the present invention is 0 <YI <1.0. A polyimide film having such yellowness looks bluish when viewed alone.
Therefore, when such a polyimide film having yellowness YI is used as a front plate material of a flexible display having a bezel portion on which white printing is performed, for example, the white printing on the bezel portion is considered to appear bluish. However, when YI is in the above range, the white color of the bezel portion is maintained while maintaining the visibility of the display portion when used as a front plate material, even though the film looks bluish when viewed by itself. I found out.

  If the yellowness of the polyimide film is 0 or less, the blueness of the film is too strong, and the white printing and display portion of the bezel portion is bluish and visually recognized. Moreover, since the total light transmittance of a film can also fall as blueness becomes strong, visibility falls. From the viewpoint of facilitating the visual recognition of the white hue of the bezel portion, the yellowness is preferably more than 0, and more preferably 0.01 or more.

  When the yellowness of the polyimide film is 1 or more, even when the film alone appears bluish, the bluishness is not sufficient when used as a front plate material for a flexible display having a bezel portion with white printing. For this reason, the white hue of the bezel portion is not maintained, and it is visually recognized as yellowish. From the viewpoint of making it easy to visually recognize the white hue of the bezel portion, the yellowness is preferably less than 1.0, and more preferably 0.99 or less.

  Examples of the method for adjusting the yellowness to the above range include a method of adding colorless and transparent inorganic particles to the polyimide resin to be used, a method of adding a bluing agent, and the like.

(Polyimide polymer)
The polyimide film of the present invention contains a polyimide polymer. In this specification, the polyimide polymer is a polymer (polyimide) containing a repeating structural unit containing an imide group, a polymer containing a repeating structural unit containing both an imide group and an amide group, and an imide group. One containing any one selected from a polymer containing both a repeating structural unit containing and a repeating structural unit containing an amide group is shown.

  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 following formula (10). Here, G is a tetravalent organic group, and A is a divalent organic group. The polyimide polymer may include a structure represented by two or more types of formula (10) in which G and / or A are different.

  In addition, 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. May be.

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 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 ) Or a group represented by formula (29) and a tetravalent hydrocarbon group having 6 or less carbon atoms.

In formula (20)-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 It represents a _-Ar-SO 2 -Ar-. Ar represents an arylene group having 6 to 20 carbon atoms which may be substituted with a fluorine atom, and specific examples thereof include a phenylene group. G and G ¹ are preferably represented by the formula (20), the formula (21), the formula (22), the formula (23), the formula (24), and the formula (25) because the yellowness of the obtained film is easily suppressed. , A group represented by formula (26) or formula (27).

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 number of carbon atoms of the hydrocarbon group and the fluorine-substituted hydrocarbon group is preferably 1-8. 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.

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 carbon number of the hydrocarbon group and the fluorine-substituted hydrocarbon group is preferably 1-8. 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.

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) or a group represented by formula (38); a group in which they are substituted with a methyl group, a fluoro group, a chloro group or a trifluoromethyl group; and a chain hydrocarbon group having 6 or less carbon atoms.

In formula (30)-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 -, - representing the or -CO- - SO _2.
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.

The polyimide film of the present invention may contain polyamide. Polyamide is a polymer mainly containing repeating structural units containing amide groups. The polyamide according to this embodiment is a polymer mainly composed of the repeating structural unit represented by the above formula (13). Preferred examples and specific examples are the same as the preferred examples of G ³ and A ³ in the polyimide polymer. G ³ and / or A ³ may contain structures represented by two or more types of formula (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, in JP-A-2006-199945 or JP-A-2008-163107 It can be synthesized according to the methods described. Examples of commercially available polyimide products include Neoprim (registered trademark) manufactured by Mitsubishi Gas Chemical Co., Ltd., KPI-MX300F manufactured by Kawamura Sangyo Co., Ltd., and the like.

  Examples of the tetracarboxylic acid compound 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. . A tetracarboxylic acid compound may be used independently and may use 2 or more types together. The tetracarboxylic acid compound may be a dianhydride or a tetracarboxylic acid compound analog such as an acid chloride compound.

Specific examples of the aromatic tetracarboxylic dianhydride include 4,4′-oxydiphthalic dianhydride (may be described as OPDA), 3,3 ′, 4,4′-benzophenonetetracarboxylic dianhydride. 2,2 ′, 3,3′-benzophenonetetracarboxylic dianhydride, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride (may be referred to as BPDA), 2,2 ', 3,3'-biphenyltetracarboxylic dianhydride, 3,3', 4,4'-diphenylsulfonetetracarboxylic dianhydride, 2,2-bis (3,4-dicarboxyphenyl) propane Anhydride, 2,2-bis (2,3-dicarboxyphenyl) propane dianhydride, 2,2-bis (3,4-dicarboxyphenoxyphenyl) propane dianhydride, 4,4 ′-(hexafluoro Isopropylidene Diphthalic dianhydride (may be described as 6FDA), 1,2-bis (2,3-dicarboxyphenyl) ethane dianhydride, 1,1-bis (2,3-dicarboxyphenyl) ethane Anhydride, 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, 4,4 ′-(m-phenylenedioxy) ) Diphthalic dianhydride and 2,3,6,7-naphthalene tetracarboxylic dianhydride, 1,2,4,5-benzenetetracarboxylic dianhydride.
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-dicarboxyphenyl) Etani Water, 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-phenylenedi Oxy) 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-Dicarboki Ciphenyl) methane dianhydride and 4,4 ′-(p-phenylenedioxy) diphthalic dianhydride. These can be used alone or in combination of two or more.

  Examples of the aliphatic tetracarboxylic dianhydride include a cyclic or acyclic aliphatic tetracarboxylic dianhydride. 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, and the like. These may be used alone or in combination of two or more. Moreover, you may use combining a cycloaliphatic tetracarboxylic dianhydride and an acyclic aliphatic tetracarboxylic dianhydride.

  Among the above tetracarboxylic dianhydrides, 1,2,4,5-cyclohexanetetracarboxylic dianhydride, bicyclo [2.2.2] oct-7-ene are used from the viewpoint of high transparency and low colorability. -2,3,5,6-tetracarboxylic dianhydride and 4,4 '-(hexafluoroisopropylidene) diphthalic dianhydride, and mixtures thereof are preferred.

  In addition, in the range which does not impair the various physical properties of a polyimide film, in addition to the tetracarboxylic anhydride used for said polyimide synthesis | combination, the polyimide type polymer which concerns on this embodiment is tetracarboxylic acid, tricarboxylic acid, and dicarboxylic acid. Further, those obtained by further reacting anhydrides and derivatives thereof may be used.

  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, —CH _{2 -, - C (CH 3)} 2 -, - C (CF 3) 2 -, - SO 2 - or a compound linked phenylene group.

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 terephthalic acid; isophthalic acid; naphthalenedicarboxylic acid; 4,4′-biphenyldicarboxylic acid; 3,3′-biphenyldicarboxylic acid; a dicarboxylic acid compound of a chain hydrocarbon having 8 or less carbon atoms and two Benzoic acid is a single bond, —CH ₂ —, —S—, —C (CH ₃ ) ₂ —, —C (CF ₃ ) ₂ —, —O—, —NR ⁹ —, —C (═O) —, Examples thereof include compounds linked by —SO ₂ — or a phenylene group, and acid chloride compounds thereof.

The dicarboxylic acid compound is preferably terephthalic acid; isophthalic acid; 4,4′-biphenyldicarboxylic acid; 3,3′-biphenyldicarboxylic acid; and two benzoic acid-skeletons being —CH ₂ —, —C (═O ) -, - O -, ^- NR 9 -, - SO ₂ - is a compound which is linked by or a phenylene group, and more preferably, terephthalic acid, 4,4'-biphenyl dicarboxylic acid; and two benzoic acid - backbone Are compounds linked by —O—, —NR ⁹ —, —C (═O) — or —SO ₂ —. These can be used alone or in combination of two or more. Here, R ⁹ represents a hydrocarbon group having 1 to 12 carbon atoms which may be substituted with a halogen atom.

  The ratio of the tetracarboxylic acid compound to the total of the tetracarboxylic acid compound, tricarboxylic acid compound, and dicarboxylic acid compound is preferably 40 mol% or more, more preferably 50 mol% or more, and even more preferably 70 mol%. Or more, more preferably 90 mol% or more, and particularly preferably 98 mol% or more.

  As a diamine used for the synthesis | combination of a polyimide, an aliphatic diamine, aromatic diamine, or these mixtures are mentioned, for example. 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, the aromatic ring is preferably a benzene ring. 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, 4,4′- And cycloaliphatic diamines such as diaminodicyclohexylmethane. These can be used alone or in combination of two or more.

  Examples of the aromatic diamine include p-phenylenediamine, m-phenylenediamine, 2,4-toluenediamine, m-xylylenediamine, p-xylylenediamine, 1,5-diaminonaphthalene, and 2,6-diaminonaphthalene. An aromatic diamine having one aromatic ring, such as 4,4′-diaminodiphenylmethane, 4,4′-diaminodiphenylpropane, 4,4′-diaminodiphenyl ether (sometimes referred to as ODA), 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) ben 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, sometimes referred to as TFMB), 4,4′-bis (4-aminophenoxy) biphenyl, 9,9-bis (4-aminophenyl) fluorene, 9,9-bis (4-amino-3-methylphenyl) fluorene, 9,9-bis (4-amino-3-chlorophenyl) fluorene, 9,9-bis (4-amino-3- Ruorofeniru) of fluorene, aromatic diamine having two or more aromatic rings. These can be used alone or in combination of two or more.

The aromatic diamine is preferably 4,4′-diaminodiphenylmethane, 4,4′-diaminodiphenylpropane, 4,4′-diaminodiphenyl ether, 3,3′-diaminodiphenyl ether, 4,4′-diaminodiphenylsulfone, 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 (TFMB), 4,4′-bis (4-aminophenoxy) biphenyl.
More preferably, the aromatic diamine is 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 (trifluoromethyl) benzidine (TFMB), 4,4'-bis (4-aminophenoxy) biphenyl.

  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. Selected from the group consisting of 2,2'-dimethylbenzidine, 2,2'-bis (trifluoromethyl) benzidine (TFMB), 4,4'-bis (4-aminophenoxy) biphenyl and 4,4'-diaminodiphenyl ether It is more preferable to use at least one selected from the group consisting of 2,2′-bis (trifluoromethyl) benzidine (TFMB).

  Polyimide polymers and polyamides that are polymers containing at least one repeating structural unit represented by formula (10), formula (11), formula (12) or formula (13) are diamine and tetracarboxylic acid compound (Tetracarboxylic acid compound analogs such as acid chloride compounds and tetracarboxylic dianhydrides), tricarboxylic acid compounds (tricarboxylic acid compound analogs such as acid chloride compounds and tricarboxylic acid anhydrides) and dicarboxylic acid compounds (acid chloride compounds and the like) A polycondensation polymer that is a polycondensation product with at least one compound included in the group consisting of dicarboxylic acid compound analogs). 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.

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 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 0.98 mol or more and 1.02 mol of tetracarboxylic acid is more preferable with respect to 1 mol of diamine. More preferably, it is at least .99 mol and at most 1.01 mol.
In addition, from the viewpoint of suppressing the yellowness of the obtained polyimide polymer film, it is preferable that the proportion of amino groups in the resulting polymer terminal is low, and carboxylic acid compounds such as tetracarboxylic acid compounds with respect to 1 mol of diamine It is preferable that it is 1 mol or more.

  The weight average molecular weight of the polyimide polymer and polyamide is preferably 10,000 to 500,000, more preferably 50,000 to 500,000, still more preferably 70,000 to 450,000, and particularly preferably 100. , 400,000 to 400,000. As the weight average molecular weight of the polyimide polymer and the polyamide is larger, there is a tendency that high flex resistance is more easily developed when the film is formed. Therefore, from the viewpoint of easily improving the bending resistance of the film, the weight average molecular weight is preferably not less than the above lower limit. On the other hand, the smaller the weight average molecular weight of the polyimide polymer and polyamide, the easier it is to lower the viscosity of the varnish and the easier it is to improve processability. Moreover, there exists a tendency for the stretchability of a polyimide film to improve easily. Therefore, from the viewpoint of processability and stretchability, the weight average molecular weight is preferably not more than the above upper limit. The weight average molecular weight can be determined by standard polystyrene conversion by GPC measurement.

  In a preferred embodiment of the present invention, the polyimide-based polymer and polyamide contained in the polyimide film of the present invention may contain a halogen atom such as a fluorine atom that can be introduced by, for example, the above-mentioned fluorine-containing substituent. . When the polyimide polymer and polyamide contain a halogen atom, it is easy to improve the elastic modulus of the polyimide film and reduce the yellowness (YI value). When the elastic modulus of the polyimide film is high, generation of scratches and wrinkles in the polyimide film is easily suppressed, and when the yellowness of the polyimide film is low, the transparency of the film is easily improved. The halogen atom is preferably a fluorine atom. Preferred fluorine-containing substituents for incorporating a fluorine atom into the polyimide polymer and polyamide include, for example, a fluoro group and a trifluoromethyl group.

  The halogen atom content in the polyimide polymer or polyamide is preferably 1 to 40% by mass, more preferably 5 to 40% by mass, based on the mass of the polyimide polymer or polyamide. 10 mass% or more may be sufficient as the lower limit of content of a halogen atom, and 20 mass% or more may be sufficient as it. The range of preferable halogen atom content is 5 to 30% by mass. When the halogen atom content is 1% by mass or more, the elastic modulus when formed into a film is further improved, the water absorption is lowered, the YI value is further reduced, and the transparency is easily improved. If the halogen atom content exceeds 40% by mass, synthesis may be difficult. A fluorine-type substituent may exist in either diamine or a carboxylic acid compound, and may exist in both.

  In one embodiment of the present invention, the polyimide polymer can be generated by a polycondensation reaction between a diamine and a tetracarboxylic acid compound. In this polycondensation reaction, an imidization catalyst may be present. Examples of the imidation catalyst 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.

  Although the reaction temperature of a diamine and a tetracarboxylic acid compound is not specifically limited, For example, it is 50-350 degreeC. Although reaction time is not specifically limited, For example, it is about 30 minutes-48 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, based on the total mass of the polyimide film. Preferably it is 70 mass% or more. The content of the polyimide polymer is preferably equal to or more than the above lower limit from the viewpoint of easily improving the flexibility. In addition, content of the polyimide-type polymer in a polyimide film is 100 mass% or less normally on the basis of the total mass of a polyimide film.

(Bluing agent)
The polyimide film of the present invention preferably further contains a colorant, more preferably a bluing agent. The bluing agent is an additive (dye, pigment) that adjusts the hue by absorbing light in a wavelength region such as orange to yellow in the visible light region. For example, ultramarine, bitumen, cobalt blue, etc. And inorganic dyes and pigments such as organic dyes and pigments such as phthalocyanine blueing agents and condensed polycyclic blueing agents. The bluing agent is not particularly limited, but from the viewpoint of heat resistance, light resistance, and solubility, a condensed polycyclic bluing agent is preferable, and an anthraquinone bluing agent is more preferable. From the viewpoint of heat resistance, the bluing agent preferably has a 1% thermal weight loss temperature of 220 ° C. or higher. The thermogravimetric reduction temperature of the bluing agent can be obtained by measuring the weight loss of the sample when the temperature is raised at a constant rate using thermogravimetry (TG). The 1% thermal weight reduction temperature can be determined as the temperature at which the weight reduction is 1% with respect to the charged weight. In the present specification, the 1% thermogravimetric decrease temperature is also referred to as “thermal decomposition temperature”.

  Examples of the condensed polycyclic bluing agent include anthraquinone bluing agents, indigo bluing agents, and phthalocyanine bluing agents.

The anthraquinone-based bluing agent has the formula (5):
It is a bluing agent containing the anthraquinone ring represented by these. As an anthraquinone-based bluing agent, preferably the formula (6):
[In Formula (6), X ¹ represents OH, NHR ¹ or NR ¹ R ² , X ² represents NHR ³ or NR ³ R ⁴ , and R ¹ , R ² , R ³ and R ⁴ are independent of each other. And a phenyl group substituted with a linear or branched alkyl group having 1 to 6 carbon atoms or a linear or branched alkyl group having 1 to 6 carbon atoms. ]
And a compound having a general formula represented by: X ¹ and X ² in the formula (6) may be the same as or different from each other. The compound represented by the formula (6) has a phenyl group in which at least one of X ¹ and X ^{2 in} the formula is substituted with a linear or branched alkyl group having 1 to 6 carbon atoms. Preferably, X ¹ or X ² has a phenyl group substituted with a linear or branched alkyl group having 1 to 6 carbon atoms.

More preferable examples of the anthraquinone-based bluing agent include compounds represented by formulas (1) to (3).

  Anthraquinone-based bluing agents are also available as commercial products. Examples of commercially available products include Plast Blue 8510, Plast Blue 8514, Plast Blue 8516, Plast Blue 8520, Plast Blue 8540, Plast Blue 8580, and Plast Blue 8590 (all of which are manufactured by Arimoto Chemical Industry Co., Ltd.). For example, Macrolex Violet B, Macrolex Violet 3R, Macrolex Blue RR (all of which are manufactured by Bayer), for example, Dial Resin Blue B, Dialresin Violet D, Dial Resin Blue J, Dialresin Blue N (above, Such as Sumiplast Violet B, Sumiplast Blue OA, Sumiplast Blue GP, Sumiplast Turk Blue G, Sumip Examples include Last Blue S and Sumiplast Green G (all of which are manufactured by Sumitomo Chemical Co., Ltd.).

  The indigo-based bluing agent is a bluing agent containing indoxyl or thioindoxyl. Indigo-based bluing agents are also available as commercial products. Examples of commercially available products include Dystar Indigo 4B Coll Liq, DyStar Indigo Coat, Dystar Indigo Vat (all of which are manufactured by Dystar).

  The phthalocyanine-based bluing agent is a bluing agent containing a cyclic structure in which four phthalimides are crosslinked with nitrogen atoms. The phthalocyanine-based bluing agent is also available as a commercial product. Examples of commercially available products include Chromofine Blue, Chromofine Green (all of which are manufactured by Dainichi Seika Co., Ltd.), Pigment Blue 15 and Pigment Blue 16 (all of which are manufactured by Tokyo Chemical Industry Co., Ltd.). .

  The polyimide film of the present invention preferably contains an anthraquinone-based bluing agent from the viewpoint of heat resistance, light resistance, and solubility, and includes at least one bluing agent having a structure represented by the formula (5). It is more preferable to contain, it is further more preferable to contain the at least 1 type of bluing agent which has a structure represented by Formula (6), The group which consists of a compound represented by Formula (1)-Formula (3) It is particularly preferred to contain at least one bluing agent selected from: In addition, the compound represented by Formula (1)-Formula (3) is also available as a commercial item. Commercially available products include Sumiplast Violet B (compound represented by formula (1), thermal decomposition temperature: 277 ° C.), Sumiplast Blue OA (compound represented by formula (2), thermal decomposition temperature: 248 ° C.) And Sumiplast Blue GP (compound represented by formula (3), thermal decomposition temperature: 255 ° C.).

  A blueing agent may be used individually by 1 type, and may use 2 or more types together. From the viewpoint of maintaining a high total light transmittance, it is preferable that the total amount (blending amount) of the bluing agent is relatively small, and it is preferable that the type of bluing agent to be used is small.

  When the polyimide film of the present invention contains a bluing agent, the 1% thermal weight loss temperature of the bluing agent is preferably 220 ° C. or higher, more preferably 240 ° C. or higher, from the viewpoint of film processability. The method for measuring the 1% thermal weight loss temperature of the bluing agent is as described above.

  When the polyimide film of the present invention contains a bluing agent, the content of the bluing agent is preferably 5 ppm or more, more preferably 8 ppm or more, and even more preferably 10 ppm or more, based on the total mass of the polyimide film. When the content of the bluing agent is not less than the above lower limit, it is preferable because YI is sufficiently lowered and the visibility of white printing on the bezel portion is easily improved. The content is preferably 55 ppm or less, more preferably 50 ppm or less. When the content of the bluing agent is not more than the above upper limit, the total light transmittance is not excessively lowered, and it is preferable because it is easy to achieve both the visibility of white printing on the bezel portion and the overall visibility.

  When the polyimide film or laminate contains a bluing agent and includes a layer containing at least one bluing agent, for each layer containing the bluing agent, the bluing agent based on the total mass of the layer Calculate the product of X and Y (X × Y) in each layer for all layers containing the bluing agent, where the amount added is X (ppm) and the thickness of the layer is Y (μm). The total value is preferably 300 to 4,500, more preferably 400 to 4,250, and even more preferably 500 to 4,000. When the sum of the products of X and Y (X × Y) is within the above range, it is easy to obtain a polyimide film having a desired yellowness YI.

(Inorganic particles)
The polyimide film of the present invention 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, and more preferably silica particles. As the silica particles, a silica sol in which silica particles are dispersed in an organic solvent or the like may be used, or a silica fine particle powder produced by a vapor phase method may be used. preferable. Here, the inorganic particles may be bonded by molecules having a siloxane bond.

  The average primary particle diameter of the inorganic particles is preferably 5 to 100 nm, more preferably 10 to 90 nm, and still more preferably 20 to 80 nm. The average primary particle diameter of the inorganic particles is preferably not more than the above upper limit from the viewpoint of easily increasing the transparency of the polyimide film. Moreover, it is preferable from the viewpoint that it is easy to handle that the average primary particle diameter of the inorganic particles is equal to or more than the above lower limit without excessively increasing the cohesive force of the inorganic particles. Here, the average primary particle diameter of the inorganic material that can be contained in the polyimide film can be determined by measuring an average value of 10 constant-direction diameters with a transmission electron microscope. In addition, the particle size distribution of the inorganic particles before forming the polyimide film can be measured using a commercially available laser diffraction particle size distribution meter.

  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 to 60% by mass, based on the total mass of the polyimide film. Hereinafter, it is more preferably 0% by mass or more and 40% by 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.

  In one embodiment of the present invention, the polyimide film of the present invention contains silica particles. When silica particles are contained, it is easy to improve mechanical strength such as elastic modulus and bending resistance. The average primary particle diameter of the silica particles is preferably 5 nm or more, more preferably 10 nm or more, further preferably 15 nm or more, particularly preferably 20 nm or more, preferably 100 nm or less, more preferably 80 nm or less, and further preferably 60 nm or less. Especially preferably, it is 40 nm or less. When the average primary particle size of the silica particles is within the above range, aggregation of the silica particles can be suppressed, and the haze (Haze) and yellowness (YI value) of the polyimide film can be reduced. In addition, the average primary particle diameter of a silica particle can be measured by BET method, for example. The content of silica particles is usually 0.1% by mass or more, preferably 1% by mass or more, more preferably 5% by mass or more, still more preferably 10% by mass or more, and particularly preferably 20% by mass with respect to the mass of the polyimide film. It is at least mass%, preferably at most 60 mass%, more preferably at most 50 mass%. When the content of the silica particles is at least the above lower limit, the elastic modulus and the bending resistance are easily improved, and when the content of the silica particles is at most the above upper limit, the haze and yellowness (YI value) ) Is easier to reduce.

(UV absorber)
The polyimide film may contain 1 type, or 2 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 the ultraviolet absorber, the deterioration of the polyimide resin is suppressed, so that the visibility of the polyimide film can be enhanced.

  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-based compound” refers to a compound having benzophenone and benzophenone as a parent 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 or more with respect to the total mass of the polyimide film. Preferably, it is 10 mass% or less, More preferably, it is 8 mass% or less, More preferably, it is 6 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 additives 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.

(thickness)
The thickness of the polyimide film of the present invention may be adjusted as appropriate depending on the application, as long as the yellowness YI is in the range of 0 <YI <1.0. The thickness of the polyimide film is preferably 20 to 200 μm, more preferably 25 to 150 μm, still more preferably 30 to 100 μm, and particularly preferably 50 to 100 μm. In the present invention, the thickness can be measured with a contact-type digimatic indicator. It is preferable that the thickness is equal to or more than the above lower limit because the handleability as a film is easily improved and the pencil hardness is easily increased. Moreover, since it is easy to raise the bending tolerance of a film, it is preferable that thickness is below the said upper limit.

(Total light transmittance)
The polyimide film of the present invention preferably has a total light transmittance according to JIS K 7105: 1981 of preferably 88.0% or more, more preferably 88.5% or more, still more preferably 89.0% or more, and particularly preferably 89. .5% or more, very preferably 90.0% or more. When the total light transmittance of the polyimide film is not less than the above 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 of a polyimide film is 100% or less normally. The total light transmittance is preferably 88.0% or more in the thickness range of the above film, and more preferably the above numerical value when measured at a thickness of 50 to 100 μm.

(Visibility)
Since the degree of yellowness YI is 0 <YI <1.0, the polyimide film of the present invention has excellent visibility when used as a front plate material for a flexible display having a bezel portion on which white printing has been performed. The visibility of the polyimide film is a polyimide film having a thickness of 50 to 100 μm, the yellowness YI is 0.01 or more, and the total light transmittance is 89.0% or more. When the eye is visually observed when it is installed on a commercially available white bezel-printed display, the white bezel looks white and the characters tend to be recognized correctly. Furthermore, it is a polyimide film having a thickness of 50 to 100 μm, and when the yellowness YI is 0.01 or more and the total light transmittance is 90.0% or more, the film is made commercially available white. When visually observing the color when placed on a bezel-printed display, the white bezel looks white and the characters tend to be clearly recognized.
When the yellowness YI of the polyimide film is 1 or more, or 0 or less, even if the total light transmittance is 89.0% or more, the film is applied to a commercially available white bezel-printed display. When the color when installed is visually observed, the white bezel tends to be visually recognized as yellowish white or bluish white. In addition, visibility can be evaluated by the method as described in an Example, for example.

(Layer structure)
The layer structure of the polyimide film of the present invention is not particularly limited, and may be a single layer or a multilayer of two or more layers. When the polyimide film has a multilayer structure, two or more layers containing a bluing agent may be included. From the viewpoint of thinning the image display device and economical efficiency, it is preferable to contain the bluing agent and the polyimide polymer in one layer. Specifically, the bluing agent and the polyimide polymer are contained. It is more preferably a single layer or a laminate having at least a layer containing a bluing agent and a polyimide polymer. From the viewpoint of impact resistance, the polyimide film of the present invention preferably has a multilayer structure of two or more layers, and is a laminate having at least a layer containing a bluing agent and a polyimide polymer, or More preferably, it is a laminate having at least a base layer containing a polyimide polymer and a hue adjusting layer containing a bluing agent, and a laminate having at least a layer containing a bluing agent and a polyimide polymer. More preferably. When forming a layer containing a bluing agent and a polyimide polymer, add a bluing agent to a solvent containing a polyimide polymer to prepare a varnish, apply the varnish, and dry the solvent contained in the varnish. To form a film. Here, the usual bluing agent is often accompanied by degradation such as thermal decomposition during film formation for drying the solvent from the varnish. Therefore, a bluing agent having a thermal decomposition temperature of at least 200 ° C. or more is used from the viewpoint of including a bluing agent and a polyimide-based polymer in one layer and easily achieving the function of the hue adjustment layer in a single layer. It is preferable. A polyimide film containing a bluing agent and a polyimide-based polymer in one layer is preferable from the viewpoint of reducing the thickness of an image display device and economy.

[Polyimide laminate]
The polyimide film of the present invention may be a polyimide laminate in which one or more functional layers are further laminated on the polyimide film having the above-described layer configuration. In this specification, when it is simply referred to as “polyimide film”, it may be either a polyimide film having the above-described layer structure or a polyimide laminate, and both are applicable. Examples of the functional layer include layers having various functions such as a hard coat layer, an ultraviolet absorbing layer, an adhesive layer, a refractive index adjusting layer, and a primer layer. The thickness of the functional layer can be adjusted to an appropriate thickness depending on the type of the functional layer laminated on the polyimide film. The polyimide film may have one or more functional layers. One functional layer may have a plurality of functions. For example, when the polyimide film of the present invention has a single-layer configuration, the functional layer may be formed on a single-layer polyimide film to obtain a multilayer polyimide laminate. In addition, when the polyimide film of the present invention has at least the base layer and the hue adjustment layer, functional layers having various functions such as the hard coat layer, the ultraviolet absorption layer, the adhesive layer, the refractive index adjustment layer, and the primer layer. The functional layer may be used as a hue adjusting layer by adding a bluing agent. Moreover, when the polyimide film of this invention has the said base material layer and a hue adjustment layer at least, you may laminate | stack a functional layer further on this.

  It is preferable that the hard coat layer is disposed on the viewing side surface of the polyimide film. The thickness of the hard coat layer can be set to 2 μm to 20 μm, for example. The hard coat layer may have a single layer structure or a multilayer structure. The hard coat layer includes a hard coat layer resin, and examples of the hard coat layer resin include acrylic resins, epoxy resins, urethane resins, benzyl chloride resins, vinyl resins, silicone resins, and mixtures 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, pentaerythritol tri (meth) acrylate, and polymers and copolymers thereof.

  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 thickness of the ultraviolet absorbing layer can be set to 2 μm to 20 μm, for example.

  The adhesive layer is a layer having an adhesive function, and has a function of bonding a polyimide film or a polyimide 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 adhesion layer may be comprised from the resin composition containing the component which has a polymerizable functional group. In this case, strong adhesion can be realized by further polymerizing the resin composition constituting the adhesive layer after the polyimide film or the polyimide laminate is adhered to another member. The adhesive strength between the polyimide film or polyimide laminate and the adhesive layer may be 0.1 N / cm or more, or 0.5 N / cm or more.

  The pressure-sensitive 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 (Pressure Sensitive Adhesive, PSA), which is attached to an object by pressing, may be used as the pressure-sensitive adhesive layer. The pressure-sensitive adhesive may be a pressure-sensitive adhesive that is “a substance that is sticky at room 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 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 is a layer capable of imparting a predetermined refractive index to a polyimide laminate having the refractive index. 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 particle diameter of the pigment may be 0.1 μm or less. By setting the average particle size 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 for the purpose of improving the adhesion between these layers. When functional layers are disposed on both surfaces of the polyimide film, a primer layer may be disposed only between the polyimide film and one functional layer, and between the polyimide film and one functional layer and the polyimide film. A primer layer may be disposed both between the other functional layer. The thickness of the primer layer can be 0.05 μm to 5 μm.

  A primer layer is a layer formed from the primer agent, and can improve the adhesiveness of a polyimide film and a hard-coat layer. The compound contained in the primer layer may be chemically bonded to the polyimide polymer contained in the polyimide film at the interface.

  Examples of the primer agent include an ultraviolet curable, thermosetting, or two-component curable epoxy compound primer agent. The primer agent may be a polyamic acid. These are suitable for improving 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 tert-butoxy group. Among these, a methoxy group and an ethoxy group are preferable because reactivity with a silicon material can be increased.

  It is preferable that a silane coupling agent has a substituent with high affinity with a polyimide film and a 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 for 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.

  From the viewpoint of production, it is preferable to add a bluing agent to the functional layer described above, preferably the hard coat layer and / or the primer layer, to make these functional layers a hue adjusting layer. Therefore, in this embodiment, the hue adjustment layer preferably contains the resin and other components described for the hard coat layer and / or primer layer, and contains the resin and other components described for the hard coat layer. Is more preferable. In one embodiment of the present invention in which the polyimide film of the present invention has at least a base layer and a hue adjustment layer, the content of the bluing agent contained in the hue adjustment layer is a resin component, preferably hard, contained in the hue adjustment layer. It is preferably 100 ppm or more, more preferably 300 ppm or more, and even more preferably 500 ppm or more, based on the coat forming component, more preferably acrylic resin. When the content of the bluing agent is not less than the above lower limit, it is preferable because the thickness of the hard coat layer can be within an appropriate range. Further, the content is preferably 4,000 ppm or less, more preferably 3,000 ppm or less, and further preferably 2,500 ppm or less. When the content of the bluing agent is not more than the above upper limit, it is preferable because high transmittance can be maintained.

[Production method]
An example of the method for producing the polyimide film of the present invention will be described.

In one embodiment of the present invention, the polyimide film has, for example, the following steps:
(A) A step of applying a liquid (polyimide varnish) containing a polyimide polymer to a substrate to form a coating film (application step), and (b) drying the applied liquid (polyimide varnish) to obtain a polyimide film. Forming process (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 step, 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 bluing agent, 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; sulfur-containing solvents such as dimethylsulfone, dimethylsulfoxide, and sulfolane. Examples thereof include carbonate solvents such as ethylene carbonate and propylene carbonate; and combinations (mixed solvents) thereof. 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 base material such as a resin base material, a SUS belt, or a glass base material using a polyimide varnish by fluency molding or the like.

In the film forming step, the 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 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.

  You may perform the surface treatment process which surface-treats to the at least one surface of a polyimide film. Examples of the surface treatment include UV ozone treatment, plasma treatment, and corona discharge treatment.

  Examples of the resin substrate include a PET film, a PEN film, a polyimide film, and a polyamideimide film. 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 from the viewpoint of adhesion to the polyimide film and cost.

  When the polyimide film of the present invention is a single layer containing a polyimide polymer and a bluing agent, the layer is further added with at least one bluing agent to the liquid containing the polyimide polymer (polyimide varnish). By using the polyimide varnish obtained as described above, it can be produced in the same manner as described above. Here, the usual bluing agent is often accompanied by degradation such as thermal decomposition during film formation for drying the solvent from the varnish. Therefore, in a preferred embodiment of the present invention in which a bluing agent and a polyimide polymer are contained in one layer, it is preferable to use a bluing agent having a thermal decomposition temperature of at least 220 ° C. or higher.

When the polyimide film of the present invention is a laminate having at least a layer containing a polyimide-based polymer and a bluing agent, the laminate is, for example, at least 1 in addition to a liquid (polyimide varnish) containing the polyimide-based polymer. A polyimide varnish obtained by adding a seed bluing agent may be coated on the substrate to produce a laminate, or the polyimide polymer and bluing obtained as described above. You may manufacture by bonding the single layer containing an agent to another layer, or providing the functional layer described above in this single layer.
Also in this embodiment, since the bluing agent and the polyimide polymer are contained in one layer, it is preferable to use a bluing agent having a thermal decomposition temperature of at least 220 ° C. or more.

When the polyimide film of the present invention is a laminate having at least a base material layer containing a polyimide-based polymer and a hue adjusting layer containing a bluing agent, such a laminate is, for example, the following steps:
(C) Manufacture by a process of forming a coating film (coating film forming process) by applying a composition containing a blueing agent (hereinafter also referred to as “blueing agent composition”) on a polyimide film. Can do.

  In the coating film forming step, a bluing agent composition is first prepared. For example, the bluing agent composition may contain the hard coat layer resin and, if necessary, a photopolymerization initiator, an organic solvent and / or an inorganic oxide, and is prepared by mixing these components. Good. In this case, the hue adjusting layer containing the bluing agent also has the function of a hard coat layer. In this embodiment, 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 blueing agent 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 bluing agent composition on the substrate, the coating film of the polyimide film may be formed on the coating film. . Moreover, you may affix on a polyimide film using a well-known adhesive agent and / or an adhesive.

  You may dry the coating film formed on the polyimide film. The coating film can be dried by evaporating the solvent at a temperature of 50 to 150 ° 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.

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 hue adjustment layer. The irradiation intensity is appropriately determined depending on the composition of the bluing agent 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 from 20 to 500 mW / 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 , and 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 hue adjusting layer can be further increased by passing through 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 of a polyimide film and transparency, do not fall, for example.

[Image display device]
The polyimide film of the present invention is useful as a front plate of an image display device, particularly as a front plate (window film) of a flexible display. In another embodiment of the present invention, an image display device comprising the polyimide film of the present invention, particularly a flexible display, is also provided. The flexible display according to the present embodiment includes, for example, a flexible functional layer and the polyimide film that is superimposed 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.

  Examples of the image display device include wearable devices 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. The flexible display is all image display devices having flexible characteristics.

  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. Since this image display device has flexible characteristics and at the same time has a yellowness YI within a predetermined range, for example, when used as a front plate material of a flexible display having a bezel portion on which white printing has been performed, the image display device is highly visible. Excellent.

  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.

<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 weight average molecular weight>
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 × 2 + SuperAW2500 × 1 (6.0 mm ID × 150 mm × 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

<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 based on JIS K 7373: 2006. After performing background measurement in the absence of a sample, the sample was set on a sample holder, and transmittance measurement for light of 300 to 800 nm was performed to obtain tristimulus values (x, y, z). The YI value was calculated based on the following formula.

<Visibility evaluation of white hue>
About the produced film, as shown in FIG. 1, visibility is shown in Table 1 when the film is visually observed when the film is placed on a commercially available white bezel-printed display. Visibility was determined by evaluating the white hue of the bezel portion in the following four stages, when the viewer viewed the sample from a viewing distance of 1 m and 2 m under an irradiation intensity of 1000 to 2000 lx. Character visibility is “very good” when the character looks clear, “good” when the character can be recognized correctly although it is not clear than “very good”, and the character cannot be recognized or recognized correctly The case where it is difficult to do is regarded as “bad”.
A: The white bezel looks white and the visibility of characters displayed on the display is very good.
○: The white bezel looks white, and the visibility of characters displayed on the display is good.
Δ: The white bezel is clearly colored and cannot be said to be white, but the character visibility is good.
X: The white bezel is clearly colored and cannot be said to be white, and the visibility of characters is poor.

[Production Example 1] Production of polyimide varnish (1) containing polyimide polymer (1) In 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. did. 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., heating and stirring were further performed for 4 hours. Thereafter, the pressure was restored to atmospheric pressure, and the internal temperature was cooled to 155 ° C. to obtain a polyimide solution. 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 (1) as 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 360,000. Moreover, the fluorine atom content of the polyimide was 31.3% by mass.

[Production Example 2] Polyimide varnish (2) containing polyimide polymer (2)
As the polyimide varnish (2), “Neoprim (registered trademark) C6A20” manufactured by Mitsubishi Gas Chemical Co., Ltd. was used. “Neoprim C6A20” contains 22% by mass of a polyimide-based polymer (2) in a γ-butyrolactone solvent.

[Production Example 3] Production of polyimide varnish (3) containing polyimide polymer (3) In a 1 L separable flask equipped with a stirring blade in a nitrogen atmosphere, 2,2'-bis (trifluoromethyl) -4 4,4'-diaminodiphenyl (TFMB) 40.00 g (124.91 mmol) and N, N-dimethylacetamide (DMAc) 682.51 g were added, and TFMB was dissolved in DMAc with stirring at room temperature. Next, 16.78 g (37.77 mmol) of 4,4 ′-(hexafluoroisopropylidene) diphthalic dianhydride (6FDA) was added to the flask and stirred at room temperature for 3 hours. Thereafter, 3.72 g (12.59 mmol) of 4,4′-oxybis (benzoyl chloride) (OBBC) and then 15.34 g (75.55 mmol) of terephthaloyl chloride (TPC) were added to the flask and stirred at room temperature for 1 hour. did. Next, 8.21 g (88.14 mmol) of 4-methylpyridine and 15.43 g (151.10 mmol) of acetic anhydride were added to the flask, stirred at room temperature for 30 minutes, then heated to 70 ° C. using an oil bath, The mixture was further stirred for 3 hours to obtain a polyimide varnish (3) containing a polyimide polymer (3).
The obtained polyimide varnish (3) was cooled to room temperature, poured into a large amount of methanol in a string form, 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 a polyimide polymer (3) having a weight average molecular weight Mw of 430,000. The weight average molecular weight was measured in the same manner as in Example 1. The fluorine atom content of the polyimide was 26% by mass.

[Example 1]
200.00 g of the polyimide varnish (1) obtained in Production Example 1 was added to 18.40 g of GBL and 11.82 g of N, N-dimethylacetamide (DMAc), Sumiplast Violet B (compound represented by the formula (1)) 1 Further diluted by adding 50 mg (31 ppm with respect to the solid content in the polyimide varnish). 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, and the coating film was peeled off from the PET film. Then, the polyimide film which has a thickness of 80 micrometers was obtained by heating a coating film for 40 minutes at 200 degreeC.

[Example 2]
A polyimide film was obtained in the same manner as in Example 1 except that the addition amount of the bluing agent was 0 ppm. Then, 12.0 mg (500 ppm with respect to solid content in Z-624) of Sumiplast Violet B (compound represented by Formula (1)) was added to 24.0 g of Z-624 made by AICA on the polyimide film. Then, coating was performed using a wire bar so that the thickness after drying was 5 μm to form 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.

[Comparative Example 1]
A polyimide film was obtained in the same manner as in Example 1 except that the addition amount of the bluing agent was 0.63 ppm.

[Comparative Example 2]
A polyimide film was obtained in the same manner as in Example 2 except that the addition amount of the bluing agent was 10 ppm.

[Example 3]
A polyimide film was prepared in the same manner as in Example 1 except that Sumiplast Blue OA (compound represented by the formula (2)) was used instead of Sumiplast Violet B, and the addition amount of the bluing agent was 50 ppm. Obtained. The polyimide film thus obtained was heated at 200 ° C. for 40 minutes to obtain a polyimide film having a thickness of 50 μm.

[Example 4]
A polyimide film was prepared in the same manner as in Example 1 except that Sumiplast Blue GP (compound represented by the formula (3)) was used instead of Sumiplast Violet B and the amount of the blueing agent was 50 ppm. Obtained. The polyimide film thus obtained was heated at 200 ° C. for 40 minutes to obtain a polyimide film having a thickness of 50 μm.

[Example 5]
A polyimide film was obtained in the same manner as in Example 1 except that the amount of the blueing agent added was 10 ppm. The polyimide film thus obtained was heated at 200 ° C. for 40 minutes to obtain a polyimide film having a thickness of 50 μm.

[Example 6]
A polyimide film was prepared in the same manner as in Example 1 except that the amount of the blueing agent added was 47 ppm and the polyimide polymer obtained in Production Example 2 was used instead of the polyimide polymer obtained in Production Example 1. Obtained.

[Comparative Example 3]
A polyimide film was obtained in the same manner as in Example 6 except that the amount of the blueing agent added was 63 ppm.

[Comparative Example 4]
A polyimide film was obtained in the same manner as in Example 6 except that the addition amount of the bluing agent was 0.63 ppm.

[Example 7]
Polyimide varnish (2) “Neoprim C6A20” (γ-butyrolactone solvent, 22% by mass) manufactured by Mitsubishi Gas Chemical Co., Ltd. 38 ppm of the dispersed solution and Sumiplast Violet B were mixed and stirred for 30 minutes to obtain a polyimide varnish (2 ′). Here, the mass ratio of the solid content of the silica particles and the solid content of the polyimide polymer was set to 30:70.
Next, it was cast into a base material to obtain a polyimide-based polymer film original fabric having a thickness of 50 μm. Next, a coating film was formed on the 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, and the coating film was peeled off from the PET film. Then, the polyimide film which has a thickness of 80 micrometers was obtained by heating a coating film for 40 minutes at 200 degreeC.

[Example 8]
A polyimide film was obtained in the same manner as in Example 7 except that the amount of the blueing agent added was 50 ppm.

[Example 9]
20 g of the polyimide polymer (3) powder obtained in Production Example 3 was 272.093 g of γ-butyrolactone, and the mass ratio of the solid content of silica particles (average primary particle diameter 27 nm) and the solid content of the polyimide polymer was 50: 50. Dissolved in a mixed solution of 66.534 g of silica particles dispersed in γ-butyrolactone at a solid content concentration of 30% by mass and 2.00 mg of Sumiplast Violet B (50 ppm relative to the solid content in the polyimide varnish). And the polyimide varnish (3 ') was obtained by stirring for 3 hours. Using a diluted polyimide varnish, a coating film was formed by fluent casting on a PET (polyethylene terephthalate) film. Then, the coating film was dried by heating at 50 ° C. for 30 minutes and at 140 ° C. for 10 minutes, and the coating film was peeled off from the PET film. Then, the polyimide film which has a thickness of 50 micrometers was obtained by heating a coating film for 40 minutes at 200 degreeC.

[Comparative Example 5]
A polyimide film was obtained in the same manner as in Example 7 except that the addition amount of the bluing agent was 0.63 ppm.

[Reference Example 1]
The same procedure as in Example 9 was performed except that 1.417 mg (50 ppm based on the solid content in the polyimide varnish) of copper phthalocyanine (manufactured by DIC Corporation, product name FASTOGEN Blue CA5380) was used instead of Sumiplast Violet B. A polyimide film having a thickness of 50 μm was obtained.

The polyimide films of Examples 1 to 9, Comparative Examples 1 to 5, and Reference Example 1 obtained as described above were measured for total light transmittance and yellowness (YI value). Furthermore, the addition amount of the bluing agent based on the total mass of the layer containing the bluing agent is X (ppm), the thickness of the layer containing the bluing agent is Y (μm), and the product of X and Y (X × Y) was calculated. In this example and the comparative example, since the layer containing the bluing agent is one layer, the product of X and Y is the same as that of X and Y for all the layers containing the bluing agent. This is the sum of products. The obtained results are shown in Table 1 below. In addition, the thickness of the film in Table 1 is the thickness of the film (single layer or laminate) of the present invention, and the thickness of the bluing layer is the thickness of the layer containing the bluing agent in the film of the present invention (Y μm). ). In the column of the type of bluing agent in Table 1, Sumiplast Violet B is “B”, Sumiplast Blue OA is “OA”, Sumiplast Blue GP is “GP”, and Copper Phthalocyanine is “Cu”. Respectively.

The polyimide films of Examples 1 to 9 having yellowness YI in the predetermined range have good visibility of white hue, and are suitable as a front plate material for a flexible display having a bezel portion on which white printing has been performed. It can be used.
From the above, it has been found that when an anthraquinone-based bluing agent is preferably contained as a bluing agent, a desired YI value can be obtained with a small amount of use, and a film having a high total light transmittance tends to be obtained. .

1 White bezel 2 Polyimide film cover part 3 Polyimide film uncovered part

Claims (9)

  A polyimide film containing at least one polyimide polymer and having a yellowness degree YI of 0 <YI <1.0.   The polyimide film of Claim 1 whose thickness is 20-200 micrometers.   The polyimide film of Claim 1 or 2 whose total light transmittance is 88.0% or more.   The polyimide film according to claim 1, further comprising at least one bluing agent.   It is a single layer containing a bluing agent and a polyimide polymer, or a laminate having at least a layer containing a bluing agent and a polyimide polymer, or a substrate layer containing a polyimide polymer The polyimide film according to claim 1, which is a laminate having at least a hue adjusting layer containing a bluing agent.   Including each layer containing at least one bluing agent, the amount of bluing agent added to each layer containing the bluing agent based on the total mass of the layer is X (ppm), and the thickness of the layer is The product of X and Y calculated as Y (μm) (X × Y) is calculated for all layers containing the bluing agent, and the total value is 300 to 4,500. The polyimide film according to any one of the above. The bluing agent is of formula (6):
[In Formula (6), X ¹ represents OH, NHR ¹ or NR ¹ R ² , X ² represents NHR ³ or NR ³ R ⁴ , and R ¹ , R ² , R ³ and R ⁴ are independent of each other. And a phenyl group substituted with a linear or branched alkyl group having 1 to 6 carbon atoms or a linear or branched alkyl group having 1 to 6 carbon atoms. ]
The polyimide film according to claim 4, wherein the polyimide film is a compound having a 1% thermal weight loss temperature of 220 ° C. or higher. The bluing agent is represented by the formulas (1) to (3):
The polyimide film according to claim 7, which is at least one selected from the group consisting of compounds represented by:   Furthermore, the polyimide film in any one of Claims 1-8 containing a silica particle.