JP6695367B2 - Polyimide film - Google Patents

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, an image display device (flexible display) having a flexible property is required, and it is also 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 and a front plate. 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 a flexible property (for example, Patent Document 1), the member is likely to bend, so that the application to the flexible display is relatively easy to carry out. However, while glass that has been used as a front plate material for image display devices has high transparency and can exhibit high hardness depending on the type of glass, it is extremely rigid and easily broken, so the front plate of a flexible display. It is difficult to use as a material.

  In the image display device, for the purpose of protecting and supporting the display portion, an outer frame portion having a predetermined width is usually present at the peripheral edge of the display substrate. This outer frame portion is called a bezel portion or a frame portion. Usually, the bezel portion is printed in an arbitrary color tone, and the user visually recognizes the color tone of the bezel portion through the front plate located above the bezel portion.

JP, 2016-93992, A

  However, when the 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 degree of yellowness of about 2, but such a polyimide film having a degree of yellowness cannot maintain the white hue of the bezel portion, resulting in white printing. It may be yellowish and visible.

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

In order to solve the above problems, the present inventors have made extensive studies on various characteristics of an optical film used as a front plate material. As a result, they have surprisingly found that a polyimide film having a yellowness YI of 0 <YI <1.0 can solve the above-mentioned problems, and have completed the present invention. A polyimide film having a yellowness YI in the above range has not been conventionally focused because it is difficult to achieve a thickness of 30 microns or more. However, the present inventors have adjusted the yellowness of the polyimide film in the above range, and by using it as a front plate material, the visibility of white printing on the bezel portion is good, and the visibility of the display portion is 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 as described in [1] above, which has a thickness of 20 to 200 μm.
[3] The polyimide film as described in [1] or [2], which has a total light transmittance of 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-based polymer, a laminate having at least a layer containing a bluing agent and a polyimide-based polymer, or containing a polyimide-based polymer The polyimide film according to any one of [1] to [4] above, which is a laminate having at least a substrate layer and a hue adjusting layer containing a bluing agent.
[6] A layer containing at least one layer containing a bluing agent, wherein the addition amount of the bluing agent in each layer containing a bluing agent is X (ppm) based on the total mass of the layer, The product of X and Y (X × Y) calculated with the thickness of Y as (μm) for all layers containing the bluing agent is 300 to 4,500. The polyimide film according to any one of 1] to [5].
[7] The bluing agent has 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 represents a linear or branched alkyl group having 1 to 6 carbon atoms or a phenyl group substituted with a linear or branched alkyl group having 1 to 6 carbon atoms. ]
And the polyimide film according to any one of [4] to [6], which is a compound having a 1% thermal weight loss temperature of 220 ° C. or higher.
[8] The bluing agent is represented by the formula (1) to the formula (3):
The polyimide film according to the above [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-mentioned predetermined range, for example, when used as a front plate material of a flexible display having a bezel portion printed with white. Excellent visibility.

It is a figure which shows the part covered with the white bezel and the 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. The yellowness YI is measured according to JIS K 7373: 2006 by using a UV-visible spectrophotometer (for example, a spectrophotometer V-670 manufactured by JASCO Corporation) to measure transmittance for light of 300 to 800 nm. It is calculated from the following three stimulus values (x, y and z).

The yellow degree YI of the polyimide film of the present invention is 0 <YI <1.0. A polyimide film having such a degree of yellowness looks bluish when the film alone is visually recognized.
Therefore, when a polyimide film having such a yellowness YI is used as a front plate material of a flexible display having a bezel part printed with white, for example, it is considered that the white print of the bezel part looks bluish. However, when YI is set in the above range, when the film alone looks visually bluish, when it is used as the front plate material, the white hue of the bezel part is maintained while maintaining the visibility of the display part. I found out that

  When the degree of yellowness of the polyimide film is 0 or less, the bluishness of the film is too strong, and the white print and the display portion of the bezel portion are bluish and visible, which is not preferable. Further, as the bluish color becomes stronger, the total light transmittance of the film may decrease, and thus the visibility decreases. From the viewpoint of making it easier to visually recognize 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 if the film alone looks bluish, the bluishness is not sufficient when used as a front plate material for a flexible display having a bezel part printed with white. Therefore, the white hue of the bezel portion is not maintained, and the bezel 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 of adjusting the yellowness to the above range include a method of adding colorless and transparent inorganic particles to the polyimide resin 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 the present specification, the polyimide-based polymer refers to a polymer containing a repeating structural unit containing an imide group (polyimide), a polymer containing a repeating structural unit containing both an imide group and an amide group, and an imide group. A polymer containing any one selected from polymers containing both a repeating structural unit containing a repeating structural unit and a repeating structural unit containing an amide group is shown.

  The polyimide-based polymer can be produced, for example, by using a tetracarboxylic acid compound and a diamine compound described below as main raw materials. In one embodiment of the present invention, the polyimide-based 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-based polymer may include two or more types of structures represented by the formula (10) in which G and / or A are different.

  Further, the polyimide-based polymer contains one or more selected from the group consisting of structures represented by formula (11), formula (12) and formula (13) within a range not impairing various physical properties of the polyimide film. You may stay.

G and G ¹ are each independently a tetravalent organic group, preferably a hydrocarbon group or an organic group which may be substituted with 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. As G and G ¹ , formula (20), formula (21), formula (22), formula (23), formula (24), formula (25), formula (26), formula (27), formula (28) ) Or a group represented by the formula (29) and a chain hydrocarbon group having 4 or less carbon atoms and 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 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 a specific example thereof is a phenylene group. G and G ¹ are preferably represented by formula (20), formula (21), formula (22), formula (23), formula (24) and formula (25) because the yellowness of the obtained film is easily suppressed. Is a group represented by formula (26) or formula (27).

G ² is a trivalent organic group, preferably a hydrocarbon group or an organic group which may be substituted with 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. As G ² , the formula (20), formula (21), formula (22), formula (23), formula (24), formula (25), formula (26), formula (27), formula (28) or Examples thereof include a group in which any one of the bonds of the group represented by the 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 a hydrocarbon group or an organic group which may be substituted with 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. As G ³ , the formula (20), the formula (21), the formula (22), the formula (23), the formula (24), the formula (25), the formula (26), the formula (27), the formula (28), or Among the bonds of the group represented by the formula (29), a group in which two nonadjacent bonds are replaced by hydrogen atoms and a chain hydrocarbon group having 6 or less carbon atoms are exemplified.

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 carbon number of the organic group is preferably 4 to 40. The hydrocarbon group or the fluorine-substituted hydrocarbon group preferably has 1 to 8 carbon atoms. 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 the 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) 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 -, - representing the or -CO- - SO _2.
One example is the ^{Z 1} and ^{Z 3} is -O-, and, ^{Z 2} is _{-CH 2 -, - C (CH} 3) 2 -, - C (CF 3) 2 - or -SO ₂ - in is there. The bonding position of each of Z ¹ and Z ² to each ring and the bonding position of each of Z ² and Z ³ to each ring are preferably 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 an amide group. The polyamide according to this embodiment is a polymer mainly composed of the repeating structural unit represented by the above formula (13). Preferable examples and specific examples are the same as the preferable examples of G ³ and A ³ in the polyimide-based polymer. It may include two or more types of structures represented by formula (13) in which G ³ and / or A ³ are different.

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

  Examples of the tetracarboxylic acid compound used in the synthesis of the polyimide include aromatic tetracarboxylic acid compounds such as aromatic tetracarboxylic dianhydride; and aliphatic tetracarboxylic acid compounds such as aliphatic tetracarboxylic dianhydride. .. The tetracarboxylic acid compounds may be used alone or in combination of two or more. 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 (sometimes referred to as OPDA), 3,3 ′, 4,4′-benzophenone tetracarboxylic dianhydride. 2,2 ', 3,3'-benzophenonetetracarboxylic dianhydride, 3,3', 4,4'-biphenyltetracarboxylic dianhydride (sometimes referred to as BPDA), 2,2 ', 3,3'-biphenyltetracarboxylic dianhydride, 3,3', 4,4'-diphenylsulfone tetracarboxylic dianhydride, 2,2-bis (3,4-dicarboxyphenyl) propane dianhydride Anhydride, 2,2-bis (2,3-dicarboxyphenyl) propane dianhydride, 2,2-bis (3,4-dicarboxyphenoxyphenyl) propane dianhydride, 4,4 '-(hexafluoro Isopropylidene) diphthalic acid dianhydride (sometimes 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 acid dianhydride, 4,4 ′-(m- Examples include phenylenedioxy) diphthalic acid dianhydride, 2,3,6,7-naphthalenetetracarboxylic acid dianhydride, and 1,2,4,5-benzenetetracarboxylic acid dianhydride.
Among these, 4,4'-oxydiphthalic acid dianhydride, 3,3 ', 4,4'-benzophenone tetracarboxylic acid dianhydride and 2,2', 3,3'-benzophenone tetracarboxylic acid dianhydride are preferable. 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 acid dianhydride (6FDA), 1,2-bis (2,3-dicarboxyphenyl) Ethane dianhydride, 1,1-bis (2,3-dicarboxyphenyl) ethane dianhydride, 1,2-bis (3,4-dicarboxyphenyl) ethane dianhydride, 1,1-bis (3 , 4-Dicarboxyphenyl) ethane dianhydride, bis (3,4-dicarboxyphenyl) methane dianhydride, bis (2,3-dicarboxyphenyl) methane dianhydride, 4,4 '-(p- Examples thereof include phenylenedioxy) diphthalic acid dianhydride and 4,4 ′-(m-phenylenedioxy) diphthalic acid dianhydride, and more preferably 4,4′-oxydiphthalic acid 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 dianhydride. These can be used alone or in combination of two or more.

  Examples of the aliphatic tetracarboxylic acid dianhydride include cyclic or acyclic aliphatic tetracarboxylic acid 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, 1,2,3,4-cyclopentanetetracarboxylic dianhydride, etc., cycloalkanetetracarboxylic dianhydride, bicyclo [2.2 .2] Oct-7-ene-2,3,5,6-tetracarboxylic dianhydride, dicyclohexyl 3,3′-4,4′-tetracarboxylic dianhydride and positional isomers thereof. .. These may be used alone or in combination of two or more. Specific examples of the acyclic aliphatic tetracarboxylic acid dianhydride include 1,2,3,4-butanetetracarboxylic acid dianhydride and 1,2,3,4-pentanetetracarboxylic acid dianhydride. These may be used alone or in combination of two or more. Moreover, you may use combining cycloaliphatic tetracarboxylic dianhydride and acyclic aliphatic tetracarboxylic dianhydride.

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

  Incidentally, the polyimide-based polymer according to the present embodiment, in the range that does not impair various physical properties of the polyimide film, in addition to the anhydride of tetracarboxylic acid used in the above polyimide synthesis, tetracarboxylic acid, tricarboxylic acid and dicarboxylic acid. In addition, it may be a product obtained by further reacting an anhydride or derivative thereof.

  Examples of the tetracarboxylic acid include a water adduct of an anhydride of the above tetracarboxylic acid compound.

Examples of the tricarboxylic acid compound include aromatic tricarboxylic acids, aliphatic tricarboxylic acids and their 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 anhydride of tricarboxylic acid; 2,3,6-naphthalene tricarboxylic acid-2,3-anhydride; and phthalic anhydride and benzoic acid is 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 their 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; dicarboxylic acid compounds of chain hydrocarbons having 8 or less carbon atoms and two single bond benzoic _{acid, -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 —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 There ^{-O -, - NR 9 -,} - C (= O) - is a compound linked by - or -SO _2. These may be used alone or in combination of two or more. Here, R < ⁹ > represents the C1-C12 hydrocarbon group which may be substituted by the halogen atom.

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

  Examples of the diamine used for synthesizing the polyimide include aliphatic diamine, aromatic diamine, and a mixture thereof. In addition, in this embodiment, an "aromatic diamine" represents a diamine in which an amino group is directly bonded to an aromatic ring, and may have an aliphatic group or another substituent in a part of its structure. The aromatic ring may be a single ring or a condensed ring, and examples thereof include a benzene ring, a naphthalene ring, an anthracene ring, and a fluorene ring, but are not limited thereto. Of 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 its structure.

  Examples of the aliphatic diamine include acyclic aliphatic diamines such as hexamethylenediamine and 1,3-bis (aminomethyl) cyclohexane, 1,4-bis (aminomethyl) cyclohexane, norbornanediamine, 4,4′- Examples thereof include cycloaliphatic diamines such as diaminodicyclohexylmethane. These may 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-diaminonaphthalene. Etc., aromatic diamine having one aromatic ring; 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) 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 (2,2'-bis (trifluoromethyl) -4,4'-diaminodiphenyl, also 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- Aromatic diamines having two or more aromatic rings such as amino-3-fluorophenyl) fluorene. These may 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'-diaminodiphenyl sulfone. , 3'-diaminodiphenyl sulfone, 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) and 4,4'-bis (4-aminophenoxy) biphenyl.
The aromatic diamine is 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 (trifluoromethyl) benzidine (TFMB), 4,4'-bis (4-aminophenoxy) biphenyl.

  Among the above diamines, from the viewpoint of high transparency and low coloring property, it is preferable to use at least one selected from the group consisting of aromatic diamines having a biphenyl structure. 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 one or more of the above compounds, and it is even more preferable to use 2,2′-bis (trifluoromethyl) benzidine (TFMB).

  The polyimide-based polymer and polyamide, which 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. (Acid chloride compound, tetracarboxylic acid compound analog such as tetracarboxylic acid dianhydride), tricarboxylic acid compound (acid chloride compound, tricarboxylic acid compound analog such as tricarboxylic acid anhydride) and dicarboxylic acid compound (acid chloride compound etc.) A dicarboxylic acid compound analog), which is a condensation-type polymer that is a polycondensation product with at least one compound contained in the group consisting of In addition to these, a dicarboxylic acid compound (including analogs such as acid chloride compounds) 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 formula (12) is usually derived from a diamine and a tricarboxylic acid compound. The repeating structural unit represented by formula (13) is usually derived from a diamine and a dicarboxylic acid compound. Specific examples of the diamine and tetracarboxylic acid compounds are as described above.

The molar ratio of the diamine and the carboxylic acid compound such as the tetracarboxylic acid compound can be appropriately adjusted within a range of 0.9 mol or more and 1.1 mol or less of the tetracarboxylic acid with respect to 1 mol of the diamine. Since the obtained polyimide-based polymer preferably has a high molecular weight in order to exhibit high folding endurance, it is more preferable that the tetracarboxylic acid is 0.98 mol or more and 1.02 mol per 1 mol of the diamine, and More preferably, it is 0.99 mol or more and 1.01 mol or less.
In addition, from the viewpoint of suppressing the yellowness of the obtained polyimide-based polymer film, it is preferable that the ratio of amino groups occupying the terminal of the obtained polymer is low, and carboxylic acid compounds such as tetracarboxylic acid compounds are used per 1 mol of diamine. It is preferably 1 mol or more.

  The weight average molecular weight of the polyimide-based polymer and the polyamide is preferably 10,000 to 500,000, more preferably 50,000 to 500,000, further preferably 70,000 to 450,000, and particularly preferably 100. 1,000 to 400,000. The larger the weight average molecular weight of the polyimide-based polymer and the polyamide, the more likely it is to exhibit high bending resistance when formed into a film. Therefore, from the viewpoint of easily increasing the bending resistance of the film, the weight average molecular weight is preferably the above lower limit or more. On the other hand, the smaller the weight average molecular weight of the polyimide-based polymer and the polyamide, the lower the viscosity of the varnish and the easier the processability of the varnish. Further, the stretchability of the polyimide film tends to be improved. 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 performing GPC measurement and converting into standard polystyrene.

  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, which can be introduced by the above-mentioned fluorine-containing substituent or the like. .. When the polyimide-based polymer and the 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, it is easy to suppress the occurrence of scratches and wrinkles in the polyimide film, 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 containing a fluorine atom in the polyimide-based polymer and polyamide include, for example, a fluoro group and a trifluoromethyl group.

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

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

  The reaction temperature of the diamine and the 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 48 hours. If necessary, the reaction may be performed under an inert atmosphere or reduced pressure. Further, the reaction may be carried out in a solvent, and examples of the solvent include the following solvents used for preparing a polyimide varnish.

  In one embodiment of the present invention, the content of the polyimide-based 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, and It is preferably 70% by mass or more. It is preferable that the content of the polyimide-based polymer is equal to or more than the above lower limit from the viewpoint of easily increasing the flexibility. The content of the polyimide-based polymer in the polyimide film is usually 100% by mass or less based on the total mass of the polyimide film.

(Bluing agent)
The polyimide film of the present invention preferably further contains a coloring agent, more preferably a bluing agent. The bluing agent is an additive (dye or pigment) that adjusts the hue by absorbing light in the visible light region, such as orange to yellow, and is, for example, ultramarine blue, dark blue, or cobalt blue. Inorganic dyes and pigments, for example, organic dyes and pigments such as phthalocyanine-based bluing agents and condensed polycyclic bluing 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 using thermogravimetry (TG) to measure the weight loss of the sample when heated at a constant rate. The 1% thermogravimetric reduction temperature can be determined as a temperature at which the weight reduction is 1% with respect to the charged weight. In the present specification, the 1% thermogravimetric reduction temperature is also referred to as "pyrolysis temperature".

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

The anthraquinone-based bluing agent has the formula (5):
Is a bluing agent containing an anthraquinone ring. The anthraquinone-based bluing agent preferably has 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 represents a linear or branched alkyl group having 1 to 6 carbon atoms or a phenyl group substituted with a linear or branched alkyl group having 1 to 6 carbon atoms. ]
And a compound having the general formula: X ¹ and X ^{2 in} formula (6) may be the same or different from each other. In the compound represented by the formula (6), at least one of X ¹ and X ^{2 in} the formula has a phenyl group substituted with a linear or branched alkyl group having 1 to 6 carbon atoms. It is more preferable that 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).

  The anthraquinone-based bluing agent is also available as a commercial product. Examples of commercially available products include Plast Blue 8510, Plast Blue 8514, Plast Blue 8516, Plast Blue 8520, Plast Blue 8540, Plast Blue 8580, Plast Blue 8590 (all of which are products of Arimoto Chemical Industry Co., Ltd.). For example, Macrolex Violet B, Macrolex Violet 3R, Macrolex Blue RR (all of which are manufactured by Bayer), etc. All are manufactured by Mitsubishi Chemical Co., Ltd., for example, Sumiplast Violet B, Sumiplast Blue OA, Sumiplast Blue GP, Sumiplast Turk Blue G, Sumiplast Blue S, Sumiplast Green G (all of which are Sumitomo Chemical (Manufactured by KK) and the like.

  The indigo-based bluing agent is a bluing agent containing indoxyl or thioindoxyl. The indigo-based bluing agent is also available as a commercial product. 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 bridged by 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 Dainichiseika Co., Ltd.), Pigment Blue 15, and Pigment Blue 16 (all of which are manufactured by Tokyo Chemical Industry Co., Ltd.). ..

  From the viewpoint of heat resistance, light resistance, and solubility, the polyimide film of the present invention preferably contains an anthraquinone-based bluing agent, and contains at least one bluing agent having a structure represented by formula (5). The group consisting of the compounds represented by the formulas (1) to (3) is more preferable, and it is further preferable that at least one bluing agent having the structure represented by the formula (6) is contained. It is particularly preferred to contain at least one bluing agent selected from The compounds represented by the formulas (1) to (3) are also available as commercial products. 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 (a compound represented by the formula (3), thermal decomposition temperature: 255 ° C.).

  The bluing agents may be used alone or in combination of two or more. 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 the kind of the bluing agent used is also 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, and more preferably 240 ° C. or higher, from the viewpoint of film moldability. 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, still more preferably 10 ppm or more, based on the total mass of the polyimide film. When the content of the bluing agent is at least the above lower limit, YI is sufficiently reduced, and the visibility of white printing on the bezel portion is easily improved, which is preferable. The above content is preferably 55 ppm or less, more preferably 50 ppm or less. When the content of the bluing agent is less than or equal to the above upper limit, the total light transmittance is not excessively lowered, and the visibility of white printing on the bezel portion and the overall visibility are easily compatible, which is preferable.

  When the polyimide film or laminate contains a bluing agent and at least one layer containing a bluing agent, for each layer containing a bluing agent, a bluing agent based on the total mass of the layer is used. The product of X and Y in each layer (X × Y), which is calculated by setting the added amount as X (ppm) and the thickness of the layer as Y (μm), was calculated for all layers containing the bluing agent. The total value is preferably 300 to 4,500, more preferably 400 to 4,250, and further preferably 500 to 4,000. When the total of the product 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-based polymer from the viewpoint of increasing 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 a 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 gas phase method may be used, but the silica sol is preferably used because it is easy to handle. preferable. Here, the inorganic particles may be bonded to each other by a molecule 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 further preferably 20 to 80 nm. It is preferable that the average primary particle size of the inorganic particles is equal to or less than the above upper limit from the viewpoint of easily increasing the transparency of the polyimide film. Further, it is preferable that the average primary particle diameter of the inorganic particles is equal to or more than the above lower limit, from the viewpoint of easy handling without the cohesive force of the inorganic particles being excessively increased. Here, the average primary particle diameter of the inorganic material that can be contained in the polyimide film can be determined by measuring the average value of 10 points of the unidirectional diameter with a transmission electron microscope. 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 or more and 90% by mass or less, more preferably 0% by mass or more and 60% by mass or less, based on the total mass of the polyimide film. Hereafter, it is more preferably 0% by mass or more and 40% by mass or less. When the content of the inorganic material is within the above range, the transparency and mechanical properties of the polyimide film tend to be compatible with each other.

  In one embodiment of the present invention, the polyimide film of the present invention contains silica particles. When the silica particles are contained, mechanical strength such as elastic modulus and flex resistance can be easily improved. 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, further preferably 60 nm or less. , Particularly preferably 40 nm or less. When the average primary particle diameter of the silica particles is in the above range, the aggregation of the silica particles can be suppressed, and the haze (Haze) and the yellowness (YI value) of the polyimide film can be reduced. The average primary particle diameter of silica particles can be measured, for example, by the BET method. The content of the silica particles is usually 0.1% by mass or more, preferably 1% by mass or more, more preferably 5% by mass or more, further preferably 10% by mass or more, particularly preferably 20% by mass based on 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 equal to or more than the above lower limit, the elastic modulus and bending resistance are easily improved, and when the content of the silica particles is less than or equal to the above upper limit, the haze and the yellowness (YI value). ) Is easier to reduce.

(UV absorber)
The polyimide film may contain one kind or two or more kinds 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 include 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 improved.

  In the present specification, the “system compound” refers to a compound to which the “system compound” is attached and a derivative thereof. For example, “benzophenone-based compound” refers to a compound having benzophenone, benzophenone as a base 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, further preferably 3% by mass or more, based on the total mass of the polyimide film. It is preferably 10% by mass or less, more preferably 8% by mass or less, still more preferably 6% by mass or less. When the ultraviolet absorber is in the above range, the weather resistance of the polyimide film can be enhanced particularly effectively, and a highly transparent polyimide film can be obtained.

(Other additives)
The polyimide film may further contain other additives as long as 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 the other additive is preferably 0% by mass or more and 20% by mass or less, 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 only needs to have a yellowness YI in the range of 0 <YI <1.0, and can be appropriately adjusted according to the application. The thickness of the polyimide film is preferably 20 to 200 μm, more preferably 25 to 150 μm, further 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 and the like are easily increased. Further, it is preferable that the thickness is less than or equal to the above upper limit because the bending resistance of the film is easily increased.

(Total light transmittance)
The polyimide film of the present invention 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. It is 0.5% or more, and most preferably 90.0% or more. When the total light transmittance of the polyimide film is at least the above lower limit, sufficient visibility can be secured when the polyimide film is incorporated into an image display device. The upper limit of the total light transmittance of the polyimide film is usually 100% or less. The total light transmittance is preferably 88.0% or more in the thickness range of the above film, and more preferably shows the above numerical value when measured at a thickness of 50 to 100 μm.

(Visibility)
Since the yellowness YI of the present invention is 0 <YI <1.0, the polyimide film of the present invention has excellent visibility when used as a front plate material of a flexible display having a bezel portion printed with white. 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, the film. When the product is installed on a commercially available white bezel-printed display, the white bezel looks white, and the characters tend to be recognized correctly when visually observed. Furthermore, a polyimide film having a thickness of 50 to 100 μm, a yellowness YI of 0.01 or more, and a total light transmittance of 90.0% or more, the film is a commercially available white film. When visually observing the color tones when the display is printed on a bezel, the white bezel looks white, and letters tend to be more 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 visually observing the colors when installed, the white bezel tends to be visible as yellowish white or bluish white. The visibility can be evaluated by the method described in Examples, 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 viewpoints of thinning the image display device and economical efficiency, it is preferable to contain the bluing agent and the polyimide-based polymer in one layer, and specifically, the bluing agent and the polyimide-based polymer are contained. More preferably, it is a single layer or a laminate having at least a layer containing a bluing agent and a polyimide-based polymer. Further, 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-based polymer, or More preferably, it is a laminate having at least a base material layer containing a polyimide-based 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-based polymer. Is more preferable. 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. Then, the film is formed. Here, an ordinary bluing agent is often accompanied by deterioration such as thermal decomposition during film formation for drying the solvent from the varnish. Therefore, from the viewpoint of easily incorporating the bluing agent and the polyimide-based polymer in one layer to achieve the function of the hue adjusting layer in a single layer, a bluing agent having a thermal decomposition temperature of at least 200 ° C. or higher is used. Preferably. A polyimide film containing a bluing agent and a polyimide-based polymer in one layer is preferable from the viewpoints of thinning the 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 layer structure. In the present specification, when simply referred to as “polyimide film”, it may be either the polyimide film or the polyimide laminate having the above layer structure, 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. Further, one functional layer may have a plurality of functions. For example, when the polyimide film of the present invention has a single-layer structure, the functional layer may be formed on a single-layer polyimide film to obtain a multilayer polyimide laminate. When the polyimide film of the present invention has at least the substrate layer and the hue adjusting layer, the functional layer having various functions such as the hard coat layer, the ultraviolet absorbing layer, the adhesive layer, the refractive index adjusting layer, and the primer layer. A bluing agent may be added to these to make these functional layers a hue adjusting layer. When the polyimide film of the present invention has at least the above-mentioned base material layer and hue adjustment layer, a functional layer may be further laminated thereon.

  The hard coat layer is preferably arranged on the surface of the polyimide film on the viewing side. The thickness of the hard coat layer may be, for example, 2 μm to 20 μm. The hard coat layer may have a single-layer structure or a multi-layer structure. The hard coat layer contains a hard coat layer resin, and examples of the hard coat layer resin include acrylic resin, epoxy resin, urethane resin, benzyl chloride resin, vinyl resin or silicone resin, or a mixture thereof. Examples thereof include ultraviolet curable resins, electron beam curable resins, and thermosetting resins such as resins. In particular, the hard coat layer preferably contains an acrylic resin from the viewpoint of mechanical properties such as surface hardness and industrial viewpoint.

  Examples of the acrylic resin include urethane acrylate, urethane methacrylate (hereinafter, acrylate and / or methacrylate are referred to as (meth) acrylate), alkyl (meth) acrylate, ester (meth) acrylate, and epoxy (meth) acrylate, and the like. Examples thereof include polymers and copolymers. 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). ) Crylate, neopentyl glycol di (meth) acrylate, dipropylene glycol di (meth) acrylate, pentaerythritol tri (meth) acrylate, and their polymers and copolymers.

  The ultraviolet absorbing layer is a layer having a function of absorbing ultraviolet rays, for example, a main material selected from a transparent resin of an ultraviolet curable type, a transparent resin of an electron beam curable type, and a transparent resin of a thermosetting type, and the main material It is composed of dispersed ultraviolet absorbers. By providing the ultraviolet absorbing layer as the functional layer, it is possible to easily suppress the change in yellowness due to light irradiation. The thickness of the ultraviolet absorbing layer may be, for example, 2 μm to 20 μm.

  The adhesive layer is a layer having an adhesive function, and has a function of adhering the polyimide film or the polyimide laminate to another member. A commonly known material can be used as the material for forming the adhesive layer. 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 realized by further adhering the polyimide film or the polyimide laminate to another member and then further polymerizing the resin composition forming the adhesive layer. The adhesive strength between the polyimide film or the polyimide 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 a pressure sensitive adhesive (Pressure Sensitive Adhesive, PSA) that is attached to an object by pressing. The pressure-sensitive adhesive may be an adhesive that is "a substance that has adhesiveness at room temperature and that adheres to an adherend with a light pressure" (JIS K6800), "a protective film (microcapsule) for a specific component". And a capsule-type adhesive which is "adhesive capable of maintaining stability until the coating is broken by an 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 the polyimide laminate having the refractive index. The refractive index adjusting layer may be, for example, a resin layer containing an appropriately selected resin and optionally a pigment, or a metal thin film.

  Examples of the pigment for adjusting the refractive index include silicon oxide, aluminum oxide, antimony oxide, tin oxide, titanium oxide, zirconium oxide and tantalum oxide. The average particle size of the pigment may be 0.1 μm or less. By setting the average particle diameter of the pigment to 0.1 μm or less, diffuse reflection of light passing 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. An oxide or a metal nitride is mentioned.

  The primer layer may be arranged between the polyimide film and the functional layer for the purpose of enhancing the adhesion between these layers. When the functional layer is arranged on both surfaces of the polyimide film, the primer layer may be arranged only between the polyimide film and one of the functional layers, and between the polyimide film and one of the functional layers and the polyimide film. A primer layer may be arranged both between the other functional layer and the other functional layer. The thickness of the primer layer can be 0.05 μm to 5 μm.

  The primer layer is a layer formed of a primer agent and can enhance 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-based polymer contained in the polyimide film at the interface.

  Examples of the primer agent include an ultraviolet-curable, heat-curable or two-component curable epoxy compound primer agent. The primer agent may be a polyamic acid. These are suitable for increasing 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 the silicon compound that may be contained in the polyimide film by a condensation reaction.
The silane coupling agent can be suitably used especially 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 containing a structure in which two or more alkoxy groups are covalently bonded to a silicon atom is preferable, and a compound containing 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. Of these, a methoxy group and an ethoxy group are preferable because they can enhance the reactivity with a silicon material.

  The silane coupling agent preferably has a substituent having a high affinity with the polyimide film and the hard coat layer. From the viewpoint of affinity with the polyimide-based 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 acryl 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 have excellent 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 above-mentioned functional layer, 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 the other components described for the hard coat layer and / or the primer layer, and the resin and the 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 substrate layer and a hue adjusting layer, the content of the bluing agent contained in the hue adjusting layer is a resin component contained in the hue adjusting layer, preferably a hard component. The amount is preferably 100 ppm or more, more preferably 300 ppm or more, still more preferably 500 ppm or more, based on the coat forming component, more preferably the acrylic resin. When the content of the bluing agent is at least the above lower limit, the thickness of the hard coat layer can be set within an appropriate range, which is preferable. Further, the content is preferably 4,000 ppm or less, more preferably 3,000 ppm or less, further preferably 2,500 ppm or less. When the content of the bluing agent is at most the above upper limit, high transmittance can be maintained, which is preferable.

[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 containing a polyimide-based polymer (polyimide varnish) to a substrate to form a coating film (application step), and (b) drying the applied liquid (polyimide varnish) to form a polyimide film Forming process (film forming process)
Can be manufactured by a manufacturing method including. Steps (a) and (b) may usually be performed in this order.

  In the coating step, first, a liquid containing a polyimide-based polymer (polyimide varnish) is prepared. For the preparation of the polyimide varnish, the tetracarboxylic acid compound, the diamine, and, if necessary, other components are mixed and reacted to prepare a polyimide mixed solution. A solvent and, if necessary, the above-mentioned bluing agent, ultraviolet absorber and other additives are added to this polyimide mixed solution and stirred to prepare a solution (polyimide varnish) containing a polyimide-based polymer. Instead of the polyimide mixed liquid, a solution of the purchased polyimide-based polymer or the like, or a purchased solution of the solid polyimide-based polymer or the like 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 the solvent include amide solvents such as N, N-dimethylacetamide and N, N-dimethylformamide; lactone solvents such as γ-butyrolactone and γ-valerolactone; sulfur-containing dimethyl sulfone, dimethyl sulfoxide, sulfolane and the like. Examples of the solvent 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. Water may be contained in the polyimide varnish.

  Next, a coating film is formed on the base material such as a resin base material, a SUS belt, or a glass base material by a well-known roll-to-roll method or a batch method by using a polyimide varnish by spout 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 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 the resin base material include PET film, PEN film, polyimide film, and polyamide-imide film. Among them, the PET film, the PEN film, the polyimide film, and the polyamide-imide film are preferable from the viewpoint of excellent heat resistance. Furthermore, a PET film is more preferable from the viewpoint of adhesion to a polyimide film and cost.

  When the polyimide film of the present invention is a single layer containing a polyimide-based polymer and a bluing agent, at least one bluing agent is added to the liquid (polyimide varnish) containing the polyimide-based polymer. By using the polyimide varnish obtained in this way, it can be manufactured in the same manner as above. Here, an ordinary bluing agent is often accompanied by deterioration such as thermal decomposition during film formation for drying a solvent from a varnish. Therefore, in a preferred embodiment of the present invention in which one layer contains a bluing agent and a polyimide-based polymer, 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 has, for example, at least 1 in a liquid containing the polyimide-based polymer (polyimide varnish). A polyimide varnish obtained by adding a seed bluing agent may be applied onto the above substrate to produce a laminate, or the polyimide-based polymer and bluing obtained as described above. You may manufacture by adhering the single layer containing an agent to another layer, or providing the functional layer mentioned above in this single layer.
Also in this embodiment, since a bluing agent and a polyimide-based 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 base material layer containing a polyimide-based polymer and a hue adjusting layer containing a bluing agent, such a laminate has, for example, the following steps:
(C) Manufacturing by a step of forming a coating film by coating a composition containing a bluing agent (hereinafter also referred to as "bluing agent composition") on a polyimide film (coating film forming step) You can

  In the coating film forming step, first, a bluing agent composition is prepared. For example, the bluing agent composition may contain the above-mentioned hard coat layer resin, and optionally 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; pentane and the like. Aliphatic hydrocarbon solvents; and aromatic hydrocarbon solvents such as toluene and xylene. The photopolymerization initiator and / or the organic solvent may be used alone or in combination of two or more kinds. Further, the hard coat layer composition may contain other additives than the above.

  Next, the bluing 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, and after forming the coating film by coating the bluing agent composition on the substrate, the coating film of the polyimide film may be formed on the coating film. .. Alternatively, the polyimide film may be attached using a known adhesive and / or 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 150 ° C., and the drying time is usually 30 to 180 seconds. It may be dried in the air, in an inert atmosphere, or under reduced pressure.

In the curing step, the coating film (resin composition) is irradiated with high energy rays (active energy rays) to cure the coating film to form a hue adjusting 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, but the integrated light quantity represented by 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 even more preferably 80 to 500 mJ / cm ² . When the integrated light amount is within the above range, a sufficient amount of active species derived from the photopolymerization initiator can be generated to allow the curing reaction to proceed more reliably, and the irradiation time does not become too long, resulting in good production. You can maintain sex. Further, it is useful because the hardness of the hue adjusting layer can be further increased by passing through the irradiation step in this range.

  When the photocurable adhesive is cured by irradiation with high-energy rays, it is preferable to perform the curing under the condition that the optical functions such as retardation and transparency of the polyimide film are not deteriorated.

[Image display device]
INDUSTRIAL APPLICABILITY 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, particularly a flexible display, provided with the polyimide film of the present invention is also provided. The flexible display according to the present embodiment has, for example, a flexible functional layer and the above-mentioned polyimide film that is superposed on the flexible functional layer and functions as a front plate. That is, the front plate of the flexible display is arranged on the visible side above the flexible functional layer. This front plate has a function of protecting the flexible functional layer.

  Examples of the image display device include TVs, smartphones, mobile phones, car navigations, tablet PCs, portable game machines, electronic paper, indicators, bulletin boards, watches, and wearable devices such as smart watches. The flexible display includes 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 smart phone, 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 a flexible property and also has a yellowness YI within a predetermined range, the image display device has a good visibility when used as a front plate material of a flexible display having a bezel part printed with white, for example. Excel.

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

<Measurement of total light transmittance>
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 prepare a 20 mass% solution, which was then diluted 100 times with a DMF eluent to obtain a 0.45 μm membrane filter. The filtered solution was used as a measurement solution.
(2) Measurement condition column: TSKgel SuperAWM-H × 2 + SuperAW 2500 × 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 yellow index (YI index) of the sample was measured using an ultraviolet-visible near-infrared spectrophotometer V-670 manufactured by JASCO Corporation in accordance with JIS K7373: 2006. After performing the background measurement in the absence of the sample, the sample was set in the sample holder, the transmittance for light of 300 to 800 nm was measured, and the tristimulus values (x, y, z) were obtained. The YI value was calculated based on the following formula.

<Visibility evaluation of white hue>
Regarding the produced film, as shown in FIG. 1, Table 1 shows the visibility when the color of the film was visually observed when the film was placed on a commercially available white bezel-printed display. The visibility was evaluated by the viewer observing the sample from the viewing distance of 1 m and 2 m under the irradiation intensity of 1000 to 2000 lx, and the white hue of the bezel portion was evaluated according to the following four grades. The visibility of the character is "very good" when the character is clearly visible, "good" when it is not clear than "very good" but the character can be correctly recognized, and the character cannot be correctly recognized or recognized. When it is difficult to do so, it is said to be "bad".
⊚: The white bezel looks white, and the visibility of the characters displayed on the display is very good.
◯: The white bezel looks white, and the visibility of the characters displayed on the display is good.
Δ: The white bezel is clearly colored and cannot be said to be white, but the visibility of characters is good.
X: The white bezel is clearly colored and cannot be said to be white, and the visibility of the characters is poor.

[Production Example 1] Production of polyimide varnish (1) containing polyimide-based polymer (1) In a nitrogen atmosphere, 1.25 g of isoquinoline was placed in 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) were put into a reaction vessel, and the mixture was stirred. Dissolved. Furthermore, 145.88 g of 4,4 ′-(hexafluoroisopropylidene) diphthalic acid dianhydride (6FDA) was added to the reaction vessel, and then the temperature was started in an oil bath while stirring the mixture.
The molar ratio of TFMB and 6FDA added was 1.00: 0.99, and the monomer concentration in the mixture was 40% by mass. 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. Then, 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) which was a uniform solution was taken out from the reaction vessel. When the GPC measurement was performed on the polyimide in the obtained polyimide varnish, the weight average molecular weight was 360,000. The fluorine atom content of the polyimide was 31.3% by mass.

[Production Example 2] Polyimide varnish (2) containing a polyimide-based polymer (2)
As the polyimide varnish (2), "Neoprim (registered trademark) C6A20" manufactured by Mitsubishi Gas Chemical Co., Inc. was used. “Neoprim C6A20” contains 22% by mass of the 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 under a nitrogen atmosphere, 2,2'-bis (trifluoromethyl) -4 was added. , 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 while stirring at room temperature. Next, 16.78 g (37.77 mmol) of 4,4 ′-(hexafluoroisopropylidene) diphthalic acid dianhydride (6FDA) was added to the flask, and the mixture was stirred at room temperature for 3 hours. Then, 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, and after stirring at room temperature for 30 minutes, the temperature was raised to 70 ° C using an oil bath, The mixture was further stirred for 3 hours to obtain a polyimide varnish (3) containing the polyimide polymer (3).
The obtained polyimide varnish (3) was cooled to room temperature, put into a large amount of methanol in a thread form, the deposited precipitate was taken out, immersed in methanol for 6 hours, and then washed with methanol. Next, the precipitate was dried under reduced pressure at 100 ° C. to obtain a polyimide 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]
To 200.00 g of the polyimide varnish (1) obtained in Production Example 1, 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 with 0.50 mg (31 ppm relative 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 spout molding. Then, the coating film was dried by heating at 50 ° C. for 30 minutes and 140 ° C. for 10 minutes, and the coating film was peeled off from the PET film. Then, the coating film was heated at 200 ° C. for 40 minutes to obtain a polyimide film having a thickness of 80 μm.

[Example 2]
A polyimide film was obtained in the same manner as in Example 1 except that the amount of bluing agent added was 0 ppm. Then, on the polyimide film, 22.0 g of Z-624 manufactured by AICA was added with 12.0 mg of Sumiplast Violet B (a compound represented by the formula (1)) (500 ppm with respect to the solid content in Z-624). Then, coating was performed using a wire bar so that the thickness after drying was 5 μm to form a coating film. The obtained coating film was dried at 120 ° C. for 1 minute and then irradiated with ultraviolet rays at an ultraviolet irradiation amount of 500 mJ / cm ² to cure the coating film 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 amount of the bluing agent added was 0.63 ppm.

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

[Example 3]
A polyimide film was prepared in the same manner as in Example 1 except that Sumiplast Blue OA (a compound represented by the formula (2)) was used instead of Sumiplast Violet B, and the amount of the bluing agent added 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 (a compound represented by the formula (3)) was used instead of Sumiplast Violet B, and the amount of the bluing agent added 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 bluing 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 bluing agent added was 47 ppm and the polyimide-based polymer obtained in Production Example 1 was used instead of the polyimide-based 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 bluing agent added was 63 ppm.

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

[Example 7]
Polyimide varnish (2) manufactured by Mitsubishi Gas Chemical Co., Inc. "Neoprim C6A20" (γ-butyrolactone solvent, 22% by mass), γ-butyrolactone with silica particles (average primary particle diameter 23 nm) having a solid content concentration of 30% by mass. 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-based polymer was set to 30:70.
Next, it was cast on a substrate to form a film of a polyimide-based polymer film having a thickness of 50 μm. Next, a coating film was formed on the PET (polyethylene terephthalate) film by the casting method. Then, the coating film was dried by heating at 50 ° C. for 30 minutes and 140 ° C. for 10 minutes, and the coating film was peeled off from the PET film. Then, the coating film was heated at 200 ° C. for 40 minutes to obtain a polyimide film having a thickness of 80 μm.

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

[Example 9]
20 g of the polyimide-based polymer (3) powder obtained in Production Example 3 was mixed with 272.093 g of γ-butyrolactone, the solid content of silica particles (average primary particle diameter 27 nm) and the solid content of the polyimide-based polymer were 50:50. Dissolved in a solution in which 66.534 g of silica particles dispersed in γ-butyrolactone at a solid concentration of 30 mass% and Sumiplast Violet B (2.00 mg) (50 ppm based on the solid content in the polyimide varnish) were mixed so that the concentration became 50. Then, the polyimide varnish (3 ′) was obtained by stirring for 3 hours. Using a diluted polyimide varnish, a coating film was formed on a PET (polyethylene terephthalate) film by spout molding. Then, the coating film was dried by heating at 50 ° C. for 30 minutes and 140 ° C. for 10 minutes, and the coating film was peeled off from the PET film. Then, the coating film was heated at 200 ° C. for 40 minutes to obtain a polyimide film having a thickness of 50 μm.

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

With respect to the polyimide films of Examples 1 to 9, Comparative Examples 1 to 5 and Reference Example 1 obtained as described above, total light transmittance and yellowness (YI value) were measured. Further, 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 layers containing the bluing agent. It is the sum of the products. The results obtained are shown in Table 1 below. 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 (Y μm in the film of the present invention. ). In addition, 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". And respectively.

The polyimide films of Examples 1 to 9 having the yellowness YI in the predetermined range have good visibility of white hues, and are suitable as a front plate material for a flexible display having a bezel portion printed with white. It can be used.
Further, 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 (10)

Contains at least one polyimide polymer, Ri yellowness YI is 0 <YI <1.0 der, the polyimide polymer of the formula (10):
[In the formula, G is a tetravalent organic group, and A is a divalent organic group]
And a repeating structural unit represented by the formula (13):
[In the formula, G ³ and A ³ are divalent organic groups]
A polyimide film having a repeating structural unit represented by: and the weight average molecular weight of the polyimide polymer is 70,000 or more .   The polyimide film according to claim 1, having a thickness of 20 to 200 μm.   The polyimide film according to claim 1, which has a total light transmittance of 88.0% or more.   The polyimide film according to claim 1, which has a total light transmittance of 88.5% or more. Further comprising at least one bluing agent, a polyimide film according to any one of claims 1-4. It is a single layer containing a bluing agent and a polyimide-based polymer, a laminate having at least a layer containing a bluing agent and a polyimide-based polymer, or a base material layer containing a polyimide-based polymer. polyimide film described as having at least laminate the hue adjustment layer containing a bluing agent, in any one of claims 1-5. At least one layer containing a bluing agent is added, and in each layer containing a bluing agent, the addition amount of the bluing agent based on the total mass of the layer is X (ppm), and the thickness of the layer is Y a ([mu] m) X and Y of the product calculated as (X × Y), the value obtained by the sum is calculated for all of the layer containing the bluing agent is 300～4,500 claim 1-6 The polyimide film according to any one of 1. The bluing agent has 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 represents a linear or branched alkyl group having 1 to 6 carbon atoms or a phenyl group substituted with a linear or branched alkyl group having 1 to 6 carbon atoms. ]
The polyimide film according to any one of claims 5 to 7 , which is a compound having a 1% thermal weight loss temperature of 220 ° C or higher. The bluing agent is represented by the formula (1) to the formula (3):
The polyimide film according to claim 8 , which is at least one selected from the group consisting of compounds represented by: Further containing silica particles, polyimide film according to any one of claims 1-9.