JP2023132813A - Method for producing polyimide film - Google Patents

Abstract

To provide a method for producing a polyimide film that does not break even when tension is applied under heating.SOLUTION: A method for producing a polyimide film of the present invention includes a process of placing protective films with a melting point of 200°C or higher at an edge on at least one side of a polyimide-based raw material film in two or more opposing zones, and applying tension to the polyimide-based raw material film under heat, in a state in which the polyimide-based raw material film and the protective film are held by a holding member in the zones.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method for manufacturing a polyimide film used as a material for flexible display devices.

Image display devices such as liquid crystal display devices and organic EL display devices are widely used in various applications such as mobile phones and smart watches. Glass has been used as the front plate of such image display devices, but glass is very rigid and easily broken, so it is difficult to use it as a front plate material for, for example, flexible displays. As a polyimide film to replace glass, a polyimide film having transparency and mechanical strength, for example, is being considered (for example, Patent Document 1). It is known that such polyimide films are hard and difficult to stretch.

Special Publication No. 2014-528490

However, in order to verify the improvement of film properties, the present inventor applied tension to a polyimide film under heating and found that problems such as breakage may occur if tension is applied to a certain extent.

Therefore, an object of the present invention is to provide a method for producing a polyimide film that does not break even when tension is applied under heating.

As a result of intensive studies to solve the above problems, the present inventors have discovered that, in a method for producing a polyimide film, a protective film having a melting point of 200°C or higher is attached to an end portion of at least one surface of a polyimide raw material film. The above problem can be solved by applying tension to the polyimide raw material film under heating while the polyimide raw material film and the protective film are gripped by a gripping member in the area. Heading, we arrived at the present invention. That is, the present invention provides the following preferred embodiments.

[1] A protective film having a melting point of 200° C. or more is placed in two or more opposing areas at the end portion of at least one surface of the polyimide raw material film, and the polyimide raw material film and the protective film are arranged in two or more opposing areas. A method for producing a polyimide film, comprising the step of applying tension to the polyimide raw material film under heating while the polyimide film is held by a gripping member.
[2] The method according to [1], wherein the heating temperature is 200°C or higher.
[3] The method according to [1] or [2], wherein the protective film is disposed on both sides of the polyimide raw material film.
[4] The method according to any one of [1] to [3], wherein the protective film has a melting point of 250°C or higher.
[5] Any one of [1] to [4], wherein the protective film is at least one resin film selected from the group consisting of a polyimide-based protective film, a polytetrafluoroethylene-based protective film, and a polyester-based protective film. The method described in.
[6] The method according to any one of [1] to [5], wherein in the step, tension is applied by stretching.
[7] The length of one side of the polyimide film in the direction in which the tension is applied is 0.7 to 1.3 times the length of one side of the polyimide raw material film in the direction in which the tension is applied, [1] to [6] The method described in ].
[8] The method according to [6] or [7], wherein the stretching is performed using a uniaxial stretching machine or a biaxial stretching machine.
[9] The method according to any one of [1] to [8], wherein the gripping member includes at least one selected from the group consisting of a clip, a pin sheet, and a film chuck.

According to the present invention, it is possible to provide a method for producing a polyimide film that does not break even when tension is applied under heating.

1 is a schematic diagram schematically showing a preferred embodiment of a method for producing a polyimide film in an embodiment of the present invention. FIG. 2 is a schematic cross-sectional view showing a laminated state of the polyimide film and protective film of FIG. 1. FIG. FIG. 2 is a schematic cross-sectional view showing a state where the polyimide film and protective film of FIG. 1 are gripped by a gripping member. 1 is a schematic diagram schematically showing a preferred embodiment of a method for producing a polyimide film in an embodiment of the present invention.

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

[Production method of polyimide film]
In the method for producing a polyimide resin of the present invention, protective films having a melting point of 200° C. or more are placed in two or more opposing areas at the end of at least one surface of a polyimide raw material film, and the polyimide resin is The method includes a step (hereinafter sometimes referred to as step (X)) of applying tension to the polyimide-based raw material film under heating while the polyimide-based raw material film and the protective film are held by a gripping member. In this specification, a polyimide-based raw material film may be simply referred to as a "raw material film." Moreover, the raw material film and the polyimide film obtained by step (X) may be collectively referred to simply as a "film".

The present inventor investigated the relationship between tension on a polyimide raw material film, which is difficult to stretch, and film breakage, and found that in the process of applying tension to the raw material film under heating, the polyimide raw material film is held by a gripping member. When gripping, unexpectedly, if a protective film with a melting point of 200°C or more is placed in two or more opposing areas at the edges on one or both sides of the raw film and gripped together, the film will not break. We found that this does not occur. Although the reason is not clear, it is presumed that the protective film acts like a reinforcing material, and even if minute cracks or glaze occur at the edges of the raw film, they cannot propagate to the inside of the film. Therefore, in the manufacturing method of the present invention, the film can be stably transported, for example, even when tension is applied while transporting the film.

<Protective film>
The melting point of the protective film used in step (X) is 200°C or higher. The melting point of the protective film is preferably 220°C or higher, more preferably 250°C or higher, even more preferably 270°C or higher, even more preferably 290°C or higher, particularly preferably 300°C or higher, particularly preferably 320°C or higher, and extremely Preferably it is 340°C or higher. When the melting point of the protective film is equal to or higher than the above lower limit, problems such as breakage of the film and fusion (or adhesion) of the protective film to the gripping member are unlikely to occur. Further, the melting point of the protective film is preferably 450°C or lower, more preferably 400°C or lower. When the melting point of the protective film is below the above upper limit, the protective film tends to become flexible when heated, making it easy to grip the polyimide film and making it difficult for the film to break. Note that the upper limit and lower limit described in this specification can be arbitrarily combined.

The protective film is preferably one that does not fuse (or adhere) to the gripping member in step (X). The protective film is preferably a resin film, and specific examples of the resin film include polyester protective films such as polyethylene terephthalate (PET), polybutylene terephthalate, and polyethylene naphthalate; cellulose protective films such as diacetyl cellulose; and polycarbonate. Examples include protective films based on polyimide such as polyimide film and polyamideimide; protective films based on fluororesin such as polytetrafluoroethylene (PTFE); and the like. These protective films can be used alone or in combination of two or more. Among these, the protective film is selected from the group consisting of polyimide-based protective film, PTFE-based protective film, and polyester-based protective film, from the viewpoint that defects such as film breakage and fusion (or adhesion) to the gripping member are less likely to occur. At least one selected resin film is preferred, and a polyimide-based protective film and/or a PTFE-based protective film, particularly a PTFE-based protective film, is more preferred.

The thickness of the protective film is preferably 1 μm or more, more preferably 3 μm or more, still more preferably 5 μm or more, even more preferably 10 μm or more, particularly preferably 15 μm or more, particularly preferably 20 μm or more, and preferably 100 μm or less. , more preferably 90 μm or less, further preferably 80 μm or less, even more preferably 70 μm or less, particularly preferably 60 μm or less. When the thickness of the protective film is at least the above lower limit, breakage of the film can be easily suppressed and handleability can be easily improved. When the thickness of the protective film is equal to or less than the above upper limit, it is advantageous from the viewpoint of easy gripping with a gripping member. The thickness of the protective film can be measured using a film thickness meter or the like, for example, by the method described in Examples.

The protective film may be manufactured by a conventional method or a commercially available product may be used.

<Polyimide raw material film>
(Polyimide resin)
The polyimide raw material film used in step (X) contains a polyimide resin. Polyimide resins include polyimide resins and polyamideimide resins. A polyimide resin refers to a polymer containing a repeating structural unit containing an imide group, and a polyamide-imide resin refers to a polymer containing a repeating structural unit containing an imide group and a repeating structural unit containing an amide group.

In a preferred embodiment of the present invention, the polyimide resin contains a structural unit represented by formula (1) from the viewpoint of easily suppressing breakage of the film due to tension and easily improving the mechanical properties and optical properties of the film. It is preferable that the polyamide-imide resin contains a structural unit represented by formula (1) and a structural unit represented by formula (2).

The structural unit represented by formula (1) is preferably a structural unit formed by the reaction of a tetracarboxylic acid compound and a diamine compound, and the structural unit represented by formula (2) is preferably formed by a reaction between a dicarboxylic acid compound and a diamine compound. It is a structural unit formed by the reaction between a compound and a diamine compound.

Y in formula (1) independently represents a tetravalent organic group, preferably a tetravalent organic group having 4 to 40 carbon atoms. The organic group is an organic group in which a hydrogen atom in the organic group may be substituted with a hydrocarbon group or a fluorine-substituted hydrocarbon group; The number of carbon atoms is preferably 1 to 8. The polyimide resin in the present invention may contain multiple types of Y, and the multiple types of Y may be the same or different. Y is formula (20), formula (21), formula (22), formula (23), formula (24), formula (25), formula (26), formula (27), formula (28), or formula A group represented by (29); a group in which a hydrogen atom in the groups represented by formulas (20) to (29) is substituted with a methyl group, a fluoro group, a chloro group, or a trifluoromethyl group; and A tetravalent chain hydrocarbon group having 6 or less carbon atoms is exemplified.

［式（２０）～式（２９）中、＊は結合手を表し、
Ｗ^１は、単結合、－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－又は－Ａｒ－ＳＯ_２－Ａｒ－を表す。Ａｒは、水素原子がフッ素原子で置換されていてもよい炭素数６～２０のアリーレン基を表し、具体例としてはフェニレン基が挙げられる。］

[In formulas (20) to (29), * represents a bond,
W ¹ 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 represents -Ar-SO ₂ -Ar-. Ar represents an arylene group having 6 to 20 carbon atoms in which the hydrogen atom may be substituted with a fluorine atom, and a specific example thereof is a phenylene group. ]

In formula (20), formula (21), formula (22), formula (23), formula (24), formula (25), formula (26), formula (27), formula (28) and formula (29), Among the groups represented, groups represented by formula (26), formula (28), or formula (29) are preferred from the viewpoint of easily suppressing breakage of the film and easily improving the mechanical properties and optical properties of the film. , a group represented by formula (26) is more preferred. In addition, from the viewpoint of easily suppressing the breakage of the film due to tension and easily improving the mechanical properties and optical properties of the film, W ¹ independently includes a single bond, -O-, -CH ₂ -, -CH ₂ -CH ₂ -, -CH(CH ₃ )-, -C(CH ₃ ) ₂ - or -C(CF ₃ ) ₂ - is preferable, and a single bond, -O-, -CH ₂ -, -CH (CH ₃ )-, -C(CH ₃ ) ₂ - or -C(CF ₃ ) ₂ - is more preferable, and a single bond, -O-, -C(CH ₃ ) ₂ - or -C(CF ₃ ) ₂ - is more preferable, and -O- or -C(CF ₃ ) ₂ - is even more preferable.

In the above embodiment, at least some of the plurality of Y's in formula (1) are preferably structural units represented by formula (5). When at least some of the plurality of Y's in formula (1) are groups represented by formula (5), the resulting film tends to exhibit high transparency. In addition, due to the flexible skeleton of the methylene group, the solubility of polyimide resins in solvents can be improved, the viscosity of varnishes containing polyimide resins can be kept low, and the processing of films can be made easier. can do.

［式（５）中、Ｒ^１８～Ｒ^２５は、互いに独立に、水素原子、炭素数１～６のアルキル基又は炭素数６～１２のアリール基を表し、Ｒ^１８～Ｒ^２５に含まれる水素原子は、互いに独立に、ハロゲン原子で置換されていてもよく、
＊は結合手を表す。］

[In formula (5), R ¹⁸ to R ²⁵ independently represent a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, or an aryl group having 6 to 12 carbon atoms, and the hydrogen contained in R ¹⁸ to R ²⁵ The atoms may be substituted independently of each other with halogen atoms,
* represents a bond. ]

In formula (5), R ¹⁸ , R ¹⁹ , R ²⁰ , R ²¹ , R ²² , R ²³ , R ²⁴ , and R ²⁵ are each independently a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, or a C 6 alkyl group. -12 aryl group, preferably a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, more preferably a hydrogen atom or an alkyl group having 1 to 3 carbon atoms. Examples of the alkyl group having 1 to 6 carbon atoms, the alkoxy group having 1 to 6 carbon atoms, and the aryl group having 6 to 6 carbon atoms include the alkyl group having 1 to 6 carbon atoms and the alkoxy group having 1 to 6 carbon atoms in formula (3). Examples of the group or aryl group having 6 to 12 carbon atoms include those mentioned below. Here, the hydrogen atoms contained in R ¹⁸ to R ²⁵ may be independently substituted with halogen atoms. From the viewpoint of easily improving the mechanical properties and optical properties of the film, R ¹⁸ to R ²⁵ are more preferably a hydrogen atom, a methyl group, a fluoro group, a chloro group, or a trifluoromethyl group, and particularly preferably is a hydrogen atom or a trifluoromethyl group.

In a preferred embodiment of the present invention, the structural unit represented by formula (5) is a group represented by formula (5'), that is, at least a part of the plurality of Y's is a group represented by formula (5'). ). In this case, it is easy to improve the mechanical properties and optical properties of the film.

［式（５’）中、＊は結合手を表す］

[In formula (5'), * represents a bond]

In a preferred embodiment of the present invention, preferably 50 mol% or more, more preferably 60 mol% or more, and even more preferably 70 mol% or more of Y in the polyimide resin is represented by formula (5), particularly formula (5). '). When Y within the above range in the polyimide resin is represented by formula (5), especially formula (5'), the mechanical properties and optical properties of the film can be easily improved, and the skeleton containing a fluorine element can improve the polyimide resin. The solubility of the resin in the solvent is improved, and the viscosity of the varnish containing the polyimide resin can be suppressed to a low level. Furthermore, the film can be manufactured easily. Preferably, 100 mol% or less of Y in the polyimide resin is represented by formula (5), particularly formula (5'). Y in the polyimide resin may be represented by formula (5), particularly formula (5'). The content of the structural unit represented by the formula (5) of Y in the polyimide resin can be measured using, for example, ¹ H-NMR, or can be calculated from the charging ratio of raw materials.

Z in formula (2) independently represents a divalent organic group. In one embodiment of the present invention, the polyimide resin may contain multiple types of Z, and the multiple types of Z may be the same or different. The divalent organic group preferably represents a divalent organic group having 4 to 40 carbon atoms. The organic group may be substituted with a hydrocarbon group or a fluorine-substituted hydrocarbon group, and in that case, the number of carbon atoms in the hydrocarbon group and the fluorine-substituted hydrocarbon group is preferably 1 to 8. Examples of the organic group of Z include formula (20), formula (21), formula (22), formula (23), formula (24), formula (25), formula (26), formula (27), and formula (28). ) or a group in which two non-adjacent bonds of the group represented by formula (29) are replaced with hydrogen atoms, and a divalent chain hydrocarbon group having 6 or less carbon atoms are exemplified. From the viewpoint of improving the optical properties of the film, for example, easily reducing the YI value, formula (20), formula (21), formula (22), formula (23), formula (24), formula (25), formula (26) ), formula (27), formula (28) or formula (29), a group in which two non-adjacent bonds are replaced with hydrogen atoms is preferred. In one embodiment of the present invention, the polyimide resin may contain one type of organic group as Z, or may contain two or more types of organic groups.

Examples of the organic group of Z include formula (20'), formula (21'), formula (22'), formula (23'), formula (24'), formula (25'), formula (26'), and formula (27'), formula (28') and formula (29'):

［式（２０’）～式（２９’）中、Ｗ^１及び＊は、式（２０）～式（２９）において定義する通りである］
で表される２価の有機基がより好ましい。なお、式（２０）～式（２９）及び式（２０’）～式（２９’）における環上の水素原子は、炭素数１～８の炭化水素基、フッ素置換された炭素数１～８の炭化水素基、炭素数１～６のアルコキシ基、フッ素置換された炭素数１～６のアルコキシ基で置換されていてもよい。

[In formulas (20') to (29'), W ¹ and * are as defined in formulas (20) to (29)]
A divalent organic group represented by is more preferred. In addition, the hydrogen atom on the ring in formulas (20) to (29) and formulas (20') to (29') is a hydrocarbon group having 1 to 8 carbon atoms, or a fluorine-substituted group having 1 to 8 carbon atoms. may be substituted with a hydrocarbon group, an alkoxy group having 1 to 6 carbon atoms, or a fluorine-substituted alkoxy group having 1 to 6 carbon atoms.

［式（ｄ１）中、Ｒ^２４は、互いに独立に、水素原子、ハロゲン原子、炭素数１～６のアルキル基、炭素数１～６のアルコキシ基又は炭素数６～１２のアリール基を表し、Ｒ^２５は、Ｒ^２４又は－Ｃ（＝Ｏ）－＊を表し、＊は結合手を表す］
で表されるカルボン酸由来の構成単位をさらに有することが、ワニスの粘度を低くしやすく、ワニスの成膜性を高めやすく、得られるフィルムの均一性を高めやすい観点から好ましい。 When the polyimide resin has a structural unit in which Z in formula (2) is represented by any of the above formulas (20') to (29'), the polyimide resin has, in addition to the structural unit, , the following equation (d1):

[In formula (d1), R ²⁴ independently represents a hydrogen atom, a halogen atom, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, or an aryl group having 6 to 12 carbon atoms, R ²⁵ represents R ²⁴ or -C(=O)-*, * represents a bond]
It is preferable to further include a structural unit derived from a carboxylic acid represented by the following from the viewpoints of easily lowering the viscosity of the varnish, easily improving the film-forming properties of the varnish, and easily increasing the uniformity of the obtained film.

In R ²⁴ , the alkyl group having 1 to 6 carbon atoms, the alkoxy group having 1 to 6 carbon atoms, and the aryl group having 6 to 12 carbon atoms are exemplified with respect to R ¹ to R ⁸ in formula (3) described below, respectively. Examples include: Specifically, the structural unit (d1) includes a structural unit in which R ²⁴ and R ²⁵ are both hydrogen atoms (a structural unit derived from a dicarboxylic acid compound), a structural unit in which R ²⁴ is both a hydrogen atom, and R ²⁵ Examples include a structural unit in which -C(=O)-* (a structural unit derived from a tricarboxylic acid compound).

［式（３ａ）中、Ｒ^ｇ及びＲ^ｈは、互いに独立に、ハロゲン原子、炭素数１～６のアルキル基、炭素数１～６のアルコキシ基、又は炭素数６～１２のアリール基を表し、Ｒ^ｇ及びＲ^ｈに含まれる水素原子は、互いに独立に、ハロゲン原子で置換されていてもよく、
Ａ、ｍ及び＊は式（３）中のＡ、ｍ及び＊と同じであり、
ｔ及びｕは互いに独立に０～４の整数を表す］
で表されることが好ましく、式（３）：

［式（３）中、Ｒ^１～Ｒ^８は、互いに独立に、水素原子、炭素数１～６のアルキル基、炭素数１～６のアルコキシ基、又は炭素数６～１２のアリール基を表し、Ｒ^１～Ｒ^８に含まれる水素原子は、互いに独立に、ハロゲン原子で置換されていてもよく、
Ａは、互いに独立に、単結合、－Ｏ－、－ＣＨ_２－、－ＣＨ_２－ＣＨ_２－、－ＣＨ（ＣＨ_３）－、－Ｃ（ＣＨ_３）_２－、－Ｃ（ＣＦ_３）_２－、－ＳＯ_２－、－Ｓ－、－ＣＯ－又は－Ｎ（Ｒ^９）－を表し、Ｒ^９は水素原子又はハロゲン原子で置換されていてもよい炭素数１～１２の１価の炭化水素基を表し、
ｍは０～４の整数を表し、
＊は結合手を表す］
で表されることがより好ましい。 In one embodiment of the present invention, the polyimide resin may contain multiple types of Z, and the multiple types of Z may be the same or different. In particular, from the viewpoint of easily suppressing the breakage of the film due to tension and easily improving the mechanical properties and optical properties of the film, at least a part of Z is expressed by the formula (3a):

[In formula (3a), R ^g and R ^h independently represent a halogen atom, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, or an aryl group having 6 to 12 carbon atoms; , R ^g and R ^h may be independently substituted with a halogen atom,
A, m and * are the same as A, m and * in formula (3),
t and u independently represent integers from 0 to 4]
It is preferably represented by the formula (3):

[In formula (3), R ¹ to R ⁸ independently represent a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, or an aryl group having 6 to 12 carbon atoms. , the hydrogen atoms contained in R ¹ to R ⁸ may be independently substituted with halogen atoms,
A is, independently of each other, a single bond, -O-, -CH ₂ -, -CH ₂ -CH ₂ -, -CH(CH ₃ )-, -C(CH ₃ ) ₂ -, -C(CF ₃ ) ₂ -, -SO ₂ -, -S-, -CO- or -N(R ⁹ )-, where R ⁹ is a monovalent group having 1 to 12 carbon atoms which may be substituted with a hydrogen atom or a halogen atom. represents a hydrocarbon group,
m represents an integer from 0 to 4,
*represents a bond]
It is more preferable to express it as follows.

In formula (3) and formula (3a), A independently represents a single bond, -O-, -CH ₂ -, -CH ₂ -CH ₂ -, -CH(CH ₃ )-, -C(CH ₃ ) _2- , -C(CF ₃ ) ₂ -, -SO ₂ -, -S-, -CO- or -N(R ⁹ )-, easily suppresses film breakage due to tension, and is suitable for film machinery. From the viewpoint of easily improving optical properties and optical properties, it preferably represents -O- or -S-, and more preferably represents -O-.

R ¹ , R ² , R ³ , R ⁴ , R ⁵ , R ⁶ , R ⁷ and R ⁸ each independently represent a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, Or represents an aryl group having 6 to 12 carbon atoms. R ^g and R ^h each independently represent a halogen atom, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, or an aryl group having 6 to 12 carbon atoms. Examples of the alkyl group having 1 to 6 carbon atoms include methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, sec-butyl group, tert-butyl group, n-pentyl group, 2-methyl- Examples include butyl group, 3-methylbutyl group, 2-ethyl-propyl group, n-hexyl group, and the like. Examples of the alkoxy group having 1 to 6 carbon atoms include methoxy group, ethoxy group, propyloxy group, isopropyloxy group, butoxy group, isobutoxy group, tert-butoxy group, pentyloxy group, hexyloxy group, cyclohexyloxy group, etc. Can be mentioned. Examples of the aryl group having 6 to 12 carbon atoms include phenyl group, tolyl group, xylyl group, naphthyl group, and biphenyl group. From the viewpoint of easily suppressing the breakage of the film due to tension and easily improving the mechanical properties and optical properties of the film, R ^g and R ^h and R ¹ to R ⁸ are preferably hydrogen atoms or carbon atoms, independently of each other. It represents an alkyl group having 1 to 6 carbon atoms, more preferably a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, and even more preferably a hydrogen atom or a methyl group. Here, the hydrogen atoms contained in R ¹ to R ⁸ , R ^g and R ^h may be independently substituted with a halogen atom.

R ⁹ represents a hydrogen atom or a monovalent hydrocarbon group having 1 to 12 carbon atoms which may be substituted with a halogen atom. Examples of monovalent hydrocarbon groups having 1 to 12 carbon atoms include methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, sec-butyl group, tert-butyl group, n-pentyl group, Examples include 2-methyl-butyl group, 3-methylbutyl group, 2-ethyl-propyl group, n-hexyl, n-heptyl group, n-octyl group, tert-octyl group, n-nonyl group, n-decyl group, etc. and these may be substituted with a halogen atom. Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, and the like. The polyimide resin may contain multiple types of A, and the multiple types of A may be the same or different.

t and u in formula (3a) each independently represent an integer of 0 to 4, preferably an integer of 0 to 2, more preferably 0 or 1, and even more preferably 0.

In formula (3) and formula (3a), m is an integer in the range of 0 to 4, and when m is within this range, the stability of the varnish and the breakage of the film are easily suppressed, and the film is Mechanical properties tend to be good. Furthermore, in formula (3) and formula (3a), m is preferably an integer in the range of 0 to 3, more preferably an integer in the range of 0 to 2, still more preferably 0 or 1, and even more preferably 0. be. When m is within this range, breakage of the film can be easily suppressed and the mechanical properties of the film can be easily improved.

Z may contain one or more types of structural units represented by formula (3) or formula (3a), easily suppresses breakage of the film due to tension, and improves the mechanical properties and optical properties of the film. From the viewpoint of easy improvement, especially from the viewpoint of reducing the YI value and suppressing yellowing of the film over time, for example, two or more types of structural units with different m values, preferably two or three types of structural units with different m values. May include units. In that case, from the viewpoint of easily suppressing the breakage of the film due to tension and easily improving the mechanical properties and optical properties of the film, the resin is expressed by formula (3) or formula (3a) where m is 0 at Z. In addition to the structural unit, it is more preferable to further contain a structural unit represented by formula (3) or formula (3a) in which m is 1. Further, in addition to the structural unit represented by formula (2) having Z represented by formula (3) where m is 0, it is also preferable to further have a structural unit represented by formula (d1) above. .

で表される構成単位を有する。この場合、フィルムの機械的特性及び光学特性を向上しやすい。 In a preferred embodiment of the present invention, the resin has a structural unit represented by formula (3) in which m is 0 and R ⁵ to R ⁸ are a hydrogen atom or a methyl group. In a more preferred embodiment of the present invention, the resin includes a structural unit represented by formula (3) in which m is 0 and R ⁵ to R ⁸ are a hydrogen atom or a methyl group; (3'):

It has the structural unit represented by . In this case, it is easy to improve the mechanical properties and optical properties of the film.

In a preferred embodiment of the present invention, when the total of the structural units represented by formula (1) and formula (2) of the polyimide resin is 100 mol%, the formula (3) or The proportion of the structural unit represented by formula (3a) is preferably 20 mol% or more, more preferably 30 mol% or more, even more preferably 40 mol% or more, even more preferably 50 mol% or more, particularly preferably 60 mol% or more. It is mol% or more, preferably 90 mol% or less, more preferably 85 mol% or less, still more preferably 80 mol% or less. When the proportion of the structural units represented by formula (3) or formula (3a) is at least the above lower limit, it is easy to suppress breakage of the film due to tension, and it is easy to improve the mechanical properties and optical properties of the film. If the proportion of the structural units represented by formula (3) or formula (3a) is below the above upper limit, the viscosity of the resin-containing varnish will increase due to hydrogen bonding between amide bonds derived from formula (3) or formula (3a). It is easy to control and improve the processability of the film.

In addition, when the polyimide resin has a structural unit of formula (3) or formula (3a) where m is 1 to 4, the structural unit of the polyimide resin has a structural unit represented by formula (1) and a structural unit represented by formula (2). The proportion of the structural units of formula (3) or formula (3a) in which m is 1 to 4 is preferably 2 mol% or more, more preferably 4 mol%, when the total of the structural units is 100 mol%. % or more, more preferably 6 mol% or more, even more preferably 8 mol% or more, preferably 70 mol% or less, more preferably 50 mol% or less, still more preferably 30 mol% or less, even more preferably 15 mol% or more. The amount is not more than 12% by mole, particularly preferably not more than 12% by mole. When the proportion of the structural unit of formula (3) or formula (3a) in which m is 1 to 4 is equal to or higher than the above lower limit, it is easy to suppress the breakage of the film due to tension, and the mechanical properties and optical properties of the film are improved. It's easy to do. When the proportion of the structural units of formula (3) or formula (3a) in which m is 1 to 4 is below the above upper limit, resin-containing varnish due to hydrogen bonding between amide bonds derived from formula (3) or formula (3a) This suppresses the increase in viscosity and easily improves the processability of the film. The content of the structural unit represented by formula (1), formula (2), formula (3) or formula (3a) can be measured, for example, using ¹ H-NMR, or by It can also be calculated from the ratio.

In a preferred embodiment of the present invention, Z in the polyimide resin is preferably 30 mol% or more, more preferably 40 mol% or more, even more preferably 45 mol% or more, even more preferably 50 mol% or more, especially Preferably, 70 mol% or more is a structural unit represented by formula (3) or formula (3a), where m is 0 to 4. When the above lower limit or more of Z is a structural unit represented by formula (3) or formula (3a) where m is 0 to 4, it is easy to suppress the breakage of the film due to tension, and the mechanical properties of the film and Easy to improve optical properties. Further, it is sufficient that 100 mol% or less of Z in the polyimide resin is a structural unit represented by formula (3) or formula (3a) where m is 0 to 4. Note that the proportion of the structural unit represented by formula (3) or formula (3a), where m is 0 to 4, in the resin can be measured using, for example, ¹ H-NMR, or the proportion of It can also be calculated from the ratio.

In a preferred embodiment of the present invention, Z in the polyimide resin preferably contains 5 mol% or more, more preferably 8 mol% or more, still more preferably 10 mol% or more, and even more preferably 12 mol% or more. It is represented by formula (3) or formula (3a), where m is 1 to 4. When the above lower limit of Z of the polyimide resin is expressed by formula (3) or formula (3a) where m is 1 to 4, it is easy to suppress the breakage of the film due to tension, and the mechanical properties of the film and Easy to improve optical properties. Further, preferably 90 mol% or less, more preferably 70 mol% or less, still more preferably 50 mol% or less, and even more preferably 30 mol% or less of Z is a compound of formula (3) in which m is 1 to 4 or It is preferably represented by formula (3a). When below the above upper limit of Z is represented by formula (3) or formula (3a) where m is 1 to 4, an amide bond derived from formula (3) or formula (3a) where m is 1 to 4 This suppresses the increase in viscosity of resin-containing varnish due to inter-hydrogen bonding, making it easier to improve the processability of the film. Note that the proportion of the structural unit represented by formula (3) or formula (3a) in which m is 1 to 4 in the resin can be measured using, for example, ¹ H-NMR, or it can be determined from the charging ratio of raw materials. It can also be calculated.

In formula (1) and formula (2), X independently represents a divalent organic group, preferably a divalent organic group having 4 to 40 carbon atoms, more preferably a C4 organic group having a cyclic structure. Represents ~40 divalent organic groups. Examples of the cyclic structure include an alicyclic ring, an aromatic ring, and a heterocyclic structure. In the organic group, a hydrogen atom in the organic group may be substituted with a hydrocarbon group or a fluorine-substituted hydrocarbon group, and in that case, the number of carbon atoms in the hydrocarbon group and the fluorine-substituted hydrocarbon group is preferably is 1 to 8. In one embodiment of the present invention, the polyimide resin may contain multiple types of X, and the multiple types of X may be the same or different. X is expressed by formula (10), formula (11), formula (12), formula (13), formula (14), formula (15), formula (16), formula (17), and formula (18). groups in which the hydrogen atom in the groups represented by formulas (10) to (18) is substituted with a methyl group, fluoro group, chloro group or trifluoromethyl group; and groups having 6 or less carbon atoms; A chain hydrocarbon group is exemplified.

［式（１０）～式（１８）中、＊は結合手を表し、
Ｖ^１、Ｖ^２及びＶ^３は、互いに独立に、単結合、－Ｏ－、－Ｓ－、－ＣＨ_２－、－ＣＨ_２－ＣＨ_２－、－ＣＨ（ＣＨ_３）－、－Ｃ（ＣＨ_３）_２－、－Ｃ（ＣＦ_３）_２－、－ＳＯ_２－、－ＣＯ－又は－Ｎ（Ｑ）－を表す。ここで、Ｑはハロゲン原子で置換されていてもよい炭素数１～１２の１価の炭化水素基を表す。］

[In formulas (10) to (18), * represents a bond,
V ¹ , V ² and V ³ each independently represent a single bond, -O-, -S-, -CH ₂ -, -CH ₂ -CH ₂ -, -CH(CH ₃ )-, -C(CH ₃ ) represents _2- , -C(CF ₃ ) ₂ -, -SO ₂ -, -CO- or -N(Q)-. Here, Q represents a monovalent hydrocarbon group having 1 to 12 carbon atoms which may be substituted with a halogen atom. ]

Examples of the monovalent hydrocarbon group having 1 to 12 carbon atoms include the groups described above for R ⁹ .
One example is where V ¹ and V ³ are a single bond, -O- or -S-, and V ² is -CH ₂ -, -C(CH ₃ ) ₂ -, -C(CF ₃ ) ₂ - or -SO ₂ -. The bonding positions of V ¹ and V ² to each ring and the bonding positions of V ² and V ³ to each ring are independent of each other, preferably meta-position or para-position with respect to each ring, and more preferably is in para position.

Among the groups represented by formulas (10) to (18), formula (13) and formula (14 ), formula (15), formula (16) and formula (17) are preferable, and groups represented by formula (14), formula (15) and formula (16) are more preferable. Further, V ¹ , V ² and V ³ are each independently preferably a single bond, -O- or -S-, more preferably a single bond or -O-.

［式（４）中、Ｒ^１０～Ｒ^１７は、互いに独立に、水素原子、炭素数１～６のアルキル基、炭素数１～６のアルコキシ基又は炭素数６～１２のアリール基を表し、Ｒ^１０～Ｒ^１７に含まれる水素原子は、互いに独立に、ハロゲン原子で置換されていてもよく、＊は結合手を表す］
で表される構成単位である。式（１）及び式（２）中の複数のＸの少なくとも一部が式（４）で表される基であると、フィルムの機械的特性及び光学特性を向上しやすい。 In a preferred embodiment of the present invention, at least some of the plurality of Xs in formula (1) and formula (2) are represented by formula (4):

[In formula (4), R ¹⁰ to R ¹⁷ independently represent a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, or an aryl group having 6 to 12 carbon atoms, The hydrogen atoms contained in R ¹⁰ to R ¹⁷ may be independently substituted with halogen atoms, and * represents a bond]
It is a constituent unit expressed as . When at least some of the plurality of Xs in formulas (1) and (2) are groups represented by formula (4), the mechanical properties and optical properties of the film are likely to be improved.

In formula (4), R ¹⁰ , R ¹¹ , R ¹² , R ¹³ , R ¹⁴ , R ¹⁵ , R ¹⁶ and R ¹⁷ each independently represent a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, or a carbon number 1 ~6 alkoxy group or an aryl group having 6 to 12 carbon atoms. Examples of the alkyl group having 1 to 6 carbon atoms, the alkoxy group having 1 to 6 carbon atoms, or the aryl group having 6 to 12 carbon atoms include the alkyl group having 1 to 6 carbon atoms and the alkoxy group having 1 to 6 carbon atoms in formula (3). Examples of the group or aryl group having 6 to 12 carbon atoms include those exemplified. R ¹⁰ to R ¹⁷ independently of each other preferably represent a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, more preferably a ^hydrogen atom or an alkyl group having 1 to 3 carbon atoms; The hydrogen atoms contained in R ¹⁷ may be independently substituted with halogen atoms. Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom. From the viewpoint of easily improving the mechanical properties and optical properties of the film, R ¹⁰ to R ¹⁷ independently represent a hydrogen atom, a methyl group, a fluoro group, a chloro group, or a trifluoromethyl group, and even more preferably Preferably R ¹⁰ , R ¹² , R ¹³ , R ¹⁴ , R ¹⁵ and R ¹⁶ represent a hydrogen atom, and R ¹¹ and R ¹⁷ represent a hydrogen atom, a methyl group, a fluoro group, a chloro group or a trifluoromethyl group, particularly preferably R ¹¹ and R ¹⁷ represent a methyl group or a trifluoromethyl group.

で表される構成単位であり、すなわち、式（１）及び式（２）で表される複数の構成単位中の複数のＸの少なくとも一部は、式（４’）で表される構成単位である。この場合、フッ素元素を含有する骨格によりポリイミド系樹脂の溶媒への溶解性を高めやすい。また、ワニスの粘度を低減しやすく、フィルムの加工性を向上しやすい。また、フッ素元素を含有する骨格により、フィルムの機械的特性及び光学特性を向上しやすい。 In a preferred embodiment of the present invention, the structural unit represented by formula (4) is represented by formula (4'):

In other words, at least some of the plurality of X in the plurality of structural units represented by formula (1) and formula (2) are the structural units represented by formula (4'). It is. In this case, the solubility of the polyimide resin in the solvent can be easily increased due to the skeleton containing the fluorine element. In addition, it is easy to reduce the viscosity of the varnish and improve the processability of the film. Furthermore, the skeleton containing the fluorine element tends to improve the mechanical properties and optical properties of the film.

In a preferred embodiment of the present invention, preferably 30 mol% or more, more preferably 50 mol% or more, still more preferably 70 mol% or more of X in the polyimide resin is represented by formula (4), especially formula (4). '). When X within the above range in the polyimide resin is represented by formula (4), especially formula (4'), the solubility of the polyimide resin in a solvent can be easily improved due to the skeleton containing the fluorine element. Moreover, it is easy to reduce the viscosity of the varnish, and it is easy to improve the processability of the film obtained from the varnish. Furthermore, the skeleton containing the fluorine element tends to improve the mechanical properties and optical properties of the film. Preferably, 100 mol% or less of X in the polyimide resin is represented by formula (4), especially formula (4'). X in the polyimide resin may be the formula (4), especially the formula (4'). The proportion of the structural unit represented by the formula (4) of X in the resin can be measured using, for example, ¹ H-NMR, or can be calculated from the charging ratio of raw materials.

The polyimide resin can include a structural unit represented by formula (30) and/or a structural unit represented by formula (31), and the structural unit represented by formula (1) and formula (2) , the structural unit represented by formula (30) and/or the structural unit represented by formula (31).

In formula (30), Y ¹ is independently a tetravalent organic group, preferably an organic group in which the hydrogen atom in the organic group may be substituted with a hydrocarbon group or a fluorine-substituted hydrocarbon group. It is the basis. As Y ¹ , formula (20), formula (21), formula (22), formula (23), formula (24), formula (25), formula (26), formula (27), formula (28), and A group represented by formula (29), a group in which the hydrogen atom in the groups represented by formulas (20) to (29) is substituted with a methyl group, fluoro group, chloro group or trifluoromethyl group, Also, a tetravalent chain hydrocarbon group having 6 or less carbon atoms is exemplified. In one embodiment of the present invention, the polyimide resin may include multiple types of Y ¹ , and the multiple types of Y ¹ may be the same or different.

In formula (31), Y ² is a trivalent organic group, preferably an organic group in which a hydrogen atom in the organic group may be substituted with a hydrocarbon group or a fluorine-substituted hydrocarbon group. As ^Y2 , the above formula (20), formula (21), formula (22), formula (23), formula (24), formula (25), formula (26), formula (27), formula (28 ) and a group in which one of the bonding hands 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 are exemplified. In one embodiment of the present invention, the polyimide resin may include multiple types of Y ² , and the multiple types of Y ² may be the same or different.

In formulas (30) and (31), X ¹ and X ² are each independently a divalent organic group, preferably a hydrocarbon group in which the hydrogen atom in the organic group is a hydrocarbon group or a fluorine-substituted hydrocarbon group. is an organic group that may be substituted with As ^X1 and ^X2 , the above formula (10), formula (11), formula (12), formula (13), formula (14), formula (15), formula (16), formula (17) and A group represented by formula (18); a group in which the hydrogen atom in the groups represented by formulas (10) to (18) is substituted with a methyl group, fluoro group, chloro group or trifluoromethyl group; and A chain hydrocarbon group having 6 or less carbon atoms is exemplified.

In one embodiment of the present invention, the polyimide resin includes a structural unit represented by formula (1) and/or formula (2), and optionally a structure represented by formula (30) and/or formula (31). Consists of units. In addition, from the viewpoint of easily suppressing the breakage of the film due to tension and easily improving the mechanical properties and optical properties of the film, in the polyimide resin, the structural units represented by formulas (1) and (2) are Preferably 80 mol% or more, more preferably 90 mol% or more, even more preferably It is 95 mol% or more. In addition, in the polyimide resin, the structural units represented by formula (1) and formula (2) are represented by formula (1) and formula (2), and in some cases, formula (30) and/or formula (31). Based on all constituent units used, it is usually less than 100%. Note that the above ratio can be measured using, for example, ¹ H-NMR, or can also be calculated from the charging ratio of raw materials.

In one embodiment of the present invention, the content of the polyimide resin in the polyimide raw material film (or polyimide film) of the present invention is preferably 10 parts by mass or more, more preferably 10 parts by mass or more based on 100 parts by mass of the film. 30 parts by mass or more, more preferably 50 parts by mass or more, even more preferably 70 parts by mass or more, particularly preferably 80 parts by mass or more, preferably 100 parts by mass or less, 99.5 parts by mass or less, more preferably 95 parts by mass or less. Parts by mass or less. When the content of the polyimide resin is within the above range, it is easy to suppress breakage of the film due to tension, and it is easy to improve the mechanical properties and optical properties of the film.

In the polyimide resin, the content of the structural unit represented by formula (2) is preferably 0.1 mol or more, more preferably 0.5 mol per 1 mol of the structural unit represented by formula (1). mol or more, more preferably 1.0 mol or more, even more preferably 1.5 mol or more, preferably 6.0 mol or less, more preferably 5.0 mol or less, even more preferably 4.5 mol or less. be. When the content of the structural unit represented by formula (2) is at least the above lower limit, it is easy to suppress breakage of the film due to tension, and it is easy to improve the mechanical properties and optical properties of the film. In addition, when the content of the structural unit represented by formula (2) is below the above upper limit, thickening due to hydrogen bonding between amide bonds in formula (2) is suppressed, and the processability of the film is improved. Cheap.

In a preferred embodiment of the present invention, the polyimide resin may contain a halogen atom such as a fluorine atom, which can be introduced, for example, by the above-mentioned fluorine-containing substituent. When the polyimide resin contains a halogen atom, the elastic modulus of the film containing the polyimide resin can be easily improved and the YI value can be easily reduced. When the elastic modulus of the film is high, it becomes easier to suppress the occurrence of scratches, wrinkles, etc. in the film when the film is used, for example, in a flexible display device. Moreover, when the YI value of the film is low, it becomes easier to improve the transparency and visibility of the film. The halogen atom is preferably a fluorine atom. Preferred fluorine-containing substituents for containing fluorine atoms in the polyimide resin include, for example, a fluoro group and a trifluoromethyl group.

The content of halogen atoms in the polyimide resin is preferably 1 to 40% by mass, more preferably 5 to 40% by mass, and even more preferably 5 to 30% by mass, based on the mass of the polyimide resin. When the content of halogen atoms is at least the above lower limit, the elastic modulus of the film containing polyimide resin can be further improved, the water absorption rate can be lowered, the YI value can be further reduced, and the transparency and visibility can be more easily improved. . When the content of halogen atoms is below the above upper limit, the resin can be easily synthesized.

In a preferred embodiment of the present invention, the imidization rate of the polyimide resin is preferably 90% or more, more preferably 93% or more, still more preferably 96% or more, and even more preferably 98% or more. From the viewpoint of easily improving the optical homogeneity of the film containing the polyimide resin, it is preferable that the imidization rate is equal to or higher than the above lower limit. Further, the upper limit of the imidization rate is 100% or less. The imidization rate indicates the ratio of the molar amount of imide bonds in the polyimide resin to twice the molar amount of the structural unit derived from the tetracarboxylic acid compound in the polyimide resin. In addition, when the polyimide resin contains a tricarboxylic acid compound, the value is twice the molar amount of the structural unit derived from the tetracarboxylic acid compound in the polyimide resin, and the molar amount of the structural unit derived from the tricarboxylic acid compound. It shows the ratio of the molar amount of imide bonds in the polyimide resin to the total of
Further, the imidization rate can be determined by an IR method, an NMR method, or the like. For example, in the NMR method, it can be measured by the method described in Examples. More specifically, when measuring the imidization rate of polyimide resin by ¹ H-NMR, in the obtained ¹ H-NMR spectrum, among the observed benzene protons, benzene derived from a structure that does not change before and after imidization is The integral value of proton A is IntA, and the integral value of amide protons derived from the amic acid structure remaining in the observed polyimide resin is IntB. From these integral values, the formula: imidization rate (%) = 100 × (1 -IntB/IntA), the imidization rate of the polyimide resin can be determined. When measuring the imidization rate of polyamide-imide resin by ¹ H-NMR, it can be measured by the method described in Examples.

The polyimide resin contained in the film of the present invention has a polystyrene-equivalent weight average molecular weight (hereinafter sometimes referred to as Mw) that easily suppresses breakage of the film due to tension and improves the mechanical and optical properties of the film. From a simple viewpoint, preferably 50,000 or more, more preferably 100,000 or more, still more preferably 150,000 or more, even more preferably 200,000 or more, particularly preferably 250,000 or more, particularly more preferably 280, 000 or more. The Mw of the polyimide resin in terms of polystyrene is preferably 800,000 or less, more preferably 600,000 or less, still more preferably 500,000 or less, from the viewpoint of ease of manufacturing varnish and film formability. More preferably, it is 450,000 or less. The above Mw is measured by gel permeation chromatography (hereinafter sometimes referred to as GPC). As the measurement conditions, the conditions described in Examples may be used.

The thickness of the polyimide raw material film in the present invention is preferably 5 μm or more, more preferably 10 μm or more, even more preferably 20 μm or more, particularly preferably 30 μm or more, particularly preferably 40 μm or more, and preferably 1,000 μm. The thickness is more preferably 500 μm or less, still more preferably 100 μm or less, even more preferably 80 μm or less, particularly preferably 70 μm or less, particularly preferably 60 μm or less. When the thickness of the raw material film is at least the above lower limit, it is easy to suppress breakage of the film due to tension, and it is easy to improve the mechanical properties of the obtained film. Moreover, when the thickness of the polyimide-based raw material film is below the above-mentioned upper limit, the optical properties of the obtained film are likely to be improved. The thickness of the raw material film can be measured using a film thickness meter or the like, for example, by the method described in Examples.

［式（３”）中、Ｒ^１～Ｒ^８は、互いに独立に、水素原子、炭素数１～６のアルキル基、炭素数１～６のアルコキシ基、又は炭素数６～１２のアリール基を表し、Ｒ^１～Ｒ^８に含まれる水素原子は、互いに独立に、ハロゲン原子で置換されていてもよく、
Ａは、単結合、－Ｏ－、－ＣＨ_２－、－ＣＨ_２－ＣＨ_２－、－ＣＨ（ＣＨ_３）－、－Ｃ（ＣＨ_３）_２－、－Ｃ（ＣＦ_３）_２－、－ＳＯ_２－、－Ｓ－、－ＣＯ－又は－Ｎ（Ｒ^９）－を表し、
Ｒ^９は水素原子、ハロゲン原子で置換されていてもよい炭素数１～１２の１価の炭化水素基を表し、
ｍは０～４の整数であり、
Ｒ^３１及びＲ^３２は、互いに独立に、ヒドロキシル基、メトキシ基、エトキシ基、ｎ－プロポキシ基、イソプロポキシ基、ｎ－ブトキシ基、ｓｅｃ－ブトキシ基、ｔｅｒｔ－ブトキシ基又は塩素原子を表す。］ (Production method of polyimide resin)
Polyimide resins can be produced, for example, using tetracarboxylic acid compounds and diamine compounds as main raw materials, and polyamide-imide resins can be produced, for example, using tetracarboxylic acid compounds, dicarboxylic acid compounds, and diamine compounds as main raw materials. Here, it is preferable that the dicarboxylic acid compound contains at least a compound represented by formula (3'').

[In formula (3''), R ¹ to R ⁸ independently represent a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, or an aryl group having 6 to 12 carbon atoms. and the hydrogen atoms contained in R ¹ to R ⁸ may be independently substituted with a halogen atom,
A is a single bond, -O-, -CH ₂ -, -CH ₂ -CH ₂ -, -CH(CH ₃ )-, -C(CH ₃ ) ₂ -, -C(CF ₃ ) ₂ -, - represents SO ₂ -, -S-, -CO- or -N(R ⁹ )-,
R ⁹ represents a monovalent hydrocarbon group having 1 to 12 carbon atoms which may be substituted with a hydrogen atom or a halogen atom,
m is an integer from 0 to 4,
R ³¹ and R ³² each independently represent a hydroxyl group, a methoxy group, an ethoxy group, an n-propoxy group, an isopropoxy group, an n-butoxy group, a sec-butoxy group, a tert-butoxy group, or a chlorine atom. ]

In a preferred embodiment of the present invention, the dicarboxylic acid compound is a compound represented by the formula (3'') where m is 0. The dicarboxylic acid compound is a compound represented by the formula (3'') where m is 0. It is more preferable to use a compound represented by formula (3'') in which A is an oxygen atom in addition to the compound represented by R ³¹ and This is a compound represented by formula (3'') in which R ³² is a chlorine atom. Further, a diisocyanate compound may be used instead of a diamine compound.

Examples of diamine compounds used in the production of polyimide resins include aliphatic diamines, aromatic diamines, and mixtures thereof. In addition, in this embodiment, "aromatic diamine" represents a diamine in which an amino group is directly bonded to an aromatic ring, and may include an aliphatic group or other substituent as part of its structure. This aromatic ring may be a single ring or a condensed ring, and examples thereof include, but are not limited to, a benzene ring, a naphthalene ring, an anthracene ring, and a fluorene ring. Among these, a benzene ring is preferred. Moreover, "aliphatic diamine" refers to a diamine in which an amino group is directly bonded to an aliphatic group, and may include an aromatic ring or other substituents as part of its structure.

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

Examples of aromatic diamines include p-phenylenediamine, m-phenylenediamine, 2,4-toluenediamine, m-xylylenediamine, p-xylylenediamine, 1,5-diaminonaphthalene, 2,6-diaminonaphthalene, etc. Aromatic diamine having one aromatic ring, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylpropane, 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 3,3'- Diaminodiphenyl ether, 4,4'-diaminodiphenylsulfone, 3,4'-diaminodiphenylsulfone, 3,3'-diaminodiphenylsulfone, 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)-4,4'-diaminodiphenyl (with 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, and 9,9-bis(4-amino-3-fluorophenyl)fluorene, which have two or more aromatic rings. These can be used alone or in combination of two or more.

Aromatic diamines are preferably 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylpropane, 4,4'-diaminodiphenyl ether, 3,3'-diaminodiphenyl ether, 4,4'-diaminodiphenyl sulfone, 3 , 3'-diaminodiphenylsulfone, 1,4-bis(4-aminophenoxy)benzene, bis[4-(4-aminophenoxy)phenyl]sulfone, bis[4-(3-aminophenoxy)phenyl]sulfone, 2 , 2-bis[4-(4-aminophenoxy)phenyl]propane, 2,2-bis[4-(3-aminophenoxy)phenyl]propane, 2,2'-dimethylbenzidine, TFMB, 4,4'- Bis(4-aminophenoxy)biphenyl, more preferably 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylpropane, 4,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl sulfone, 1, 4-bis(4-aminophenoxy)benzene, bis[4-(4-aminophenoxy)phenyl]sulfone, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, 2,2'-dimethylbenzidine , TFMB, 4,4'-bis(4-aminophenoxy)biphenyl. These can be used alone or in combination of two or more.

Among the above diamine compounds, it is preferable to use one or more selected from the group consisting of aromatic diamines having a biphenyl structure from the viewpoint of easily improving the mechanical properties and optical properties of the film. selected from the group consisting of TFMB, 2,2'-dimethylbenzidine, 2,2'-bis(trifluoromethyl)benzidine, 4,4'-bis(4-aminophenoxy)biphenyl and 4,4'-diaminodiphenyl ether It is more preferable to use one or more types, and it is even more preferable to use TFMB.

Examples of the tetracarboxylic acid compounds used in the production of polyimide resins include aromatic tetracarboxylic acid compounds such as aromatic tetracarboxylic dianhydride; and aliphatic tetracarboxylic acid compounds such as aliphatic tetracarboxylic dianhydride. can be mentioned. 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 aromatic tetracarboxylic dianhydrides include non-fused polycyclic aromatic tetracarboxylic dianhydrides, monocyclic aromatic tetracarboxylic dianhydrides, and fused polycyclic aromatic tetracarboxylic dianhydrides. Examples include carboxylic dianhydrides. Examples of the non-fused polycyclic aromatic tetracarboxylic dianhydride include 4,4'-oxydiphthalic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 2,2 ',3,3'-benzophenonetetracarboxylic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 2,2',3,3'-biphenyltetracarboxylic dianhydride , 3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride, 2,2-bis(3,4-dicarboxyphenyl)propane dianhydride, 2,2-bis(2,3-dicarboxylic dianhydride) carboxyphenyl)propane dianhydride, 2,2-bis(3,4-dicarboxyphenoxyphenyl)propane dianhydride, 4,4'-(hexafluoroisopropylidene)diphthalic dianhydride (described as 6FDA) ), 1,2-bis(2,3-dicarboxyphenyl)ethane dianhydride, 1,1-bis(2,3-dicarboxyphenyl)ethane dianhydride, 1,2-bis(3, 4-dicarboxyphenyl)ethane dianhydride, 1,1-bis(3,4-dicarboxyphenyl)ethane dianhydride, bis(3,4-dicarboxyphenyl)methane dianhydride, bis(2,3 -dicarboxyphenyl)methane dianhydride, 4,4'-(p-phenylenedioxy)diphthalic dianhydride, and 4,4'-(m-phenylenedioxy)diphthalic dianhydride. Furthermore, examples of the monocyclic aromatic tetracarboxylic dianhydride include 1,2,4,5-benzenetetracarboxylic dianhydride, and fused polycyclic aromatic tetracarboxylic dianhydride. Examples include 2,3,6,7-naphthalenetetracarboxylic dianhydride.

Among these, 4,4'-oxydiphthalic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, and 2,2',3,3'-benzophenonetetracarboxylic dianhydride are preferable. Anhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 2,2',3,3'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-diphenyl Sulfone tetracarboxylic dianhydride, 2,2-bis(3,4-dicarboxyphenyl)propane dianhydride, 2,2-bis(2,3-dicarboxyphenyl)propane dianhydride, 2,2- Bis(3,4-dicarboxyphenoxyphenyl)propane dianhydride, 6FDA, 1,2-bis(2,3-dicarboxyphenyl)ethane dianhydride, 1,1-bis(2,3-dicarboxyphenyl) ) Ethane dianhydride, 1,2-bis(3,4-dicarboxyphenyl)ethane dianhydride, 1,1-bis(3,4-dicarboxyphenyl)ethane dianhydride, bis(3,4- dicarboxyphenyl)methane dianhydride, bis(2,3-dicarboxyphenyl)methane dianhydride, 4,4'-(p-phenylenedioxy)diphthalic dianhydride and 4,4'-(m- (phenylenedioxy)diphthalic dianhydride, more preferably 4,4'-oxydiphthalic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 2,2', Examples include 3,3'-biphenyltetracarboxylic dianhydride, 6FDA, bis(3,4-dicarboxyphenyl)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 cyclic or acyclic aliphatic tetracarboxylic dianhydride. Cycloaliphatic tetracarboxylic dianhydride is a tetracarboxylic dianhydride having an alicyclic hydrocarbon structure, and specific examples include 1,2,4,5-cyclohexanetetracarboxylic dianhydride. dianhydride, cycloalkane tetracarboxylic dianhydride such as 1,2,3,4-cyclobutanetetracarboxylic dianhydride, 1,2,3,4-cyclopentane tetracarboxylic 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. It will be done. 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 and 1,2,3,4-pentanetetracarboxylic dianhydride. These can be used alone or in combination of two or more. Furthermore, a combination of a cycloaliphatic tetracarboxylic dianhydride and an acyclic aliphatic tetracarboxylic dianhydride may be used.

Among the above tetracarboxylic dianhydrides, 4,4'-oxydiphthalic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic acid, and Dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 2,2',3,3'-biphenyltetracarboxylic dianhydride, 3,3',4,4'- Diphenylsulfone tetracarboxylic dianhydride, 2,2-bis(3,4-dicarboxyphenyl)propane dianhydride, 6FDA, and mixtures thereof are preferred, and 3,3',4,4'-biphenyltetracarboxylic dianhydride is preferred. Acid dianhydrides, 6FDA, and mixtures thereof are more preferred, and 6FDA is even more preferred.

As the dicarboxylic acid compound used for producing the polyimide resin, preferably terephthalic acid, 2-methoxyterephthalic acid, 4,4'-oxybisbenzoic acid, or acid chloride compounds thereof are used. In addition to terephthalic acid, 2-methoxyterephthalic acid, 4,4'-oxybisbenzoic acid or their acid chloride compounds, other dicarboxylic acid compounds may be used. Other dicarboxylic acid compounds include aromatic dicarboxylic acids, aliphatic dicarboxylic acids, and their analogous acid chloride compounds, acid anhydrides, etc., and two or more types may be used in combination. Specific examples include 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 benzoic acids. Examples include compounds in which are connected by a single bond, -CH ₂ -, -C(CH ₃ ) ₂ -, -C(CF ₃ ) ₂ -, -SO ₂ -, or a phenylene group, and acid chloride compounds thereof. As specific examples, 4,4'-oxybis(benzoyl chloride), terephthaloyl chloride, and 2-methoxyterephthalic acid chloride are preferred, and 4,4'-oxybis(benzoyl chloride) and terephthaloyl chloride or 2-methoxy More preferably, it is used in combination with terephthalic acid chloride.

The above polyimide resin may be one obtained by further reacting tetracarboxylic acid and tricarboxylic acid, as well as anhydrides and derivatives thereof, in addition to the above tetracarboxylic acid compound, as long as various physical properties of the film are not impaired. good.

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

Examples of the tricarboxylic acid compound include aromatic tricarboxylic acids, aliphatic tricarboxylic acids, and their analogous acid chloride compounds, acid anhydrides, etc., and two or more types may be used in combination. Specific examples include 1,2,4-benzenetricarboxylic acid anhydride; 1,3,5-benzenetricarboxylic acid chloride compound; 2,3,6-naphthalenetricarboxylic acid-2,3-anhydride; A compound in which an acid anhydride and benzoic acid are connected by a single bond, -O-, -CH ₂ -, -C(CH ₃ ) ₂ -, -C(CF ₃ ) ₂ -, -SO ₂ - or phenylene group can be mentioned.

In the production of polyimide resin, the amount of diamine compound, tetracarboxylic acid compound and/or dicarboxylic acid compound to be used can be appropriately selected depending on the desired ratio of each constituent unit of the resin.

In the production of polyimide resin, the reaction temperature of the diamine compound, tetracarboxylic acid compound and/or dicarboxylic acid compound is not particularly limited, but is, for example, 5 to 350°C, preferably 10 to 200°C, more preferably 20 to 100°C. It is. The reaction time is also not particularly limited, and is, for example, about 30 minutes to 10 hours. If necessary, the reaction may be carried out under an inert atmosphere or under reduced pressure. In a preferred form, the reaction is carried out with stirring under normal pressure and/or an inert gas atmosphere. Further, the reaction is preferably carried out in a solvent inert to the reaction. The solvent is not particularly limited as long as it does not affect the reaction, but examples include water, methanol, ethanol, ethylene glycol, isopropyl alcohol, propylene glycol, ethylene glycol methyl ether, ethylene glycol butyl ether, 1-methoxy-2-propanol, Alcohol solvents such as 2-butoxyethanol and propylene glycol monomethyl ether; ethyl acetate, butyl acetate, ethylene glycol methyl ether acetate, γ-butyrolactone (hereinafter sometimes referred to as GBL), γ-valerolactone, propylene glycol methyl Ester solvents such as ether acetate and ethyl lactate; ketone solvents such as acetone, methyl ethyl ketone, cyclopentanone, cyclohexanone, 2-heptanone, and methyl isobutyl ketone; aliphatic hydrocarbon solvents such as pentane, hexane, and heptane; ethyl cyclohexane, etc. alicyclic hydrocarbon solvents; aromatic hydrocarbon solvents such as toluene and xylene; nitrile solvents such as acetonitrile; ether solvents such as tetrahydrofuran and dimethoxyethane; chlorine-containing solvents such as chloroform and chlorobenzene; N,N-dimethyl Amide solvents such as acetamide (hereinafter sometimes referred to as DMAc) and N,N-dimethylformamide (hereinafter sometimes referred to as DMF); sulfur-containing solvents such as dimethylsulfone, dimethylsulfoxide, and sulfolane; Examples include carbonate solvents such as ethylene carbonate and propylene carbonate; and combinations thereof. Among these, amide solvents can be preferably used from the viewpoint of solubility.

In the imidization step in the production of polyimide resin, imidization can be carried out in the presence of an imidization catalyst. Examples of imidization catalysts include aliphatic amines such as tripropylamine, dibutylpropylamine, ethyldibutylamine, and diisopropylethylamine; N-ethylpiperidine, N-propylpiperidine, N-butylpyrrolidine, N-butylpiperidine, and N- Alicyclic amines (monocyclic) such as propylhexahydroazepine; azabicyclo[2.2.1]heptane, azabicyclo[3.2.1]octane, azabicyclo[2.2.2]octane, and azabicyclo[3 .2.2] Alicyclic amines (polycyclic) such as nonane; and pyridine, 2-methylpyridine (2-picoline), 3-methylpyridine (3-picoline), 4-methylpyridine (4-picoline) , 2-ethylpyridine, 3-ethylpyridine, 4-ethylpyridine, 2,4-dimethylpyridine, 2,4,6-trimethylpyridine, 3,4-cyclopentenopyridine, 5,6,7,8-tetrahydro Aromatic amines such as isoquinoline and isoquinoline are mentioned. Further, from the viewpoint of easily promoting the imidization reaction, it is preferable to use an acid anhydride together with the imidization catalyst. Examples of acid anhydrides include commonly used acid anhydrides used in imidization reactions. Specific examples thereof include aliphatic acid anhydrides such as acetic anhydride, propionic anhydride, and butyric anhydride, and aromatic acid anhydrides such as phthalic acid. Examples include acid anhydrides.

The polyimide resin may be isolated by separation and purification by a conventional method such as filtration, concentration, extraction, crystallization, recrystallization, column chromatography, or a combination of these methods, and is preferred. In the form, it can be isolated by adding a large amount of alcohol such as methanol to a reaction solution containing a polyimide resin to precipitate the resin, followed by concentration, filtration, drying, etc.

(filler)
The polyimide raw material film in the present invention may contain at least one filler. Examples of the filler include organic particles and inorganic particles, preferably inorganic particles. Inorganic particles include silica, zirconia, alumina, titania, clay, talc, zinc oxide, germanium oxide, indium oxide, tin oxide, indium tin oxide (sometimes referred to as ITO), antimony oxide, cerium oxide, and dioxide. Examples include metal oxide particles such as titanium and zirconium oxide, metal fluoride particles such as magnesium fluoride and sodium fluoride, calcium carbonate, magnesium carbonate, barium sulfate, and aluminum hydroxide. From the viewpoint of easily improving physical properties and optical properties, silica particles, zirconia particles, and alumina particles are preferred, and silica particles are more preferred. These fillers can be used alone or in combination of two or more.

The average primary particle diameter of the filler, preferably silica particles, is usually 1 nm or more, preferably 5 nm or more, more preferably 10 nm or more, even more preferably 15 nm or more, even more preferably 20 nm or more, and preferably 100 nm or less, more preferably is 90 nm or less, more preferably 80 nm or less, even more preferably 70 nm or less, particularly preferably 60 nm or less, particularly more preferably 50 nm or less, even more preferably 40 nm or less. When the average primary particle diameter of the filler, preferably silica particles, is within the above range, aggregation of the filler, preferably silica particles, is suppressed and the optical properties of the resulting film are likely to be improved. The average primary particle diameter of the filler can be measured by the BET method. Note that the average primary particle diameter may be measured by image analysis using a transmission electron microscope or a scanning electron microscope.

When the polyimide raw material film in the present invention contains a filler, preferably silica particles, the content of the filler, preferably silica particles, is usually 0.1% by mass or more, preferably 0.1% by mass or more, based on the total amount of the polyimide raw material film. 1% by mass or more, more preferably 5% by mass or more, still more preferably 10% by mass or more, even more preferably 15% by mass or more, preferably 60% by mass or less, more preferably 50% by mass or less, even more preferably It is 45% by mass or less. When the filler content is at least the above lower limit, the mechanical properties of the film are likely to be improved. Moreover, when the filler content is below the above upper limit, the storage stability of the varnish is improved, and the optical properties of the resulting film are likely to be improved.

(Ultraviolet absorber)
The polyimide raw material film in the present invention may contain an ultraviolet absorber. The ultraviolet absorber can be appropriately selected from those commonly used as ultraviolet absorbers in the field of resin materials. The ultraviolet absorber may include a compound that absorbs light with 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. When the polyimide-based raw material film in the present invention contains an ultraviolet absorber, deterioration of the resin is suppressed, so that the visibility of the film can be improved.
In addition, in this specification, a "system compound" refers to the derivative of the compound to which the said "system compound" is attached. For example, a "benzophenone compound" refers to a compound having benzophenone as a parent skeleton and a substituent bonded to benzophenone.

When the polyimide raw material film in the present invention contains a UV absorber, the content of the UV absorber is preferably 1% by mass or more, more preferably 2% by mass or more, based on the total amount of the polyimide raw material film. The content is preferably 3% by mass or more, even more preferably 4% by mass or more, preferably 10% by mass or less, more preferably 8% by mass or less, and still more preferably 6% by mass or less. The preferred content varies depending on the UV absorber used, but if the content of the UV absorber is adjusted so that the light transmittance at 400 nm is about 20 to 60%, the light resistance of the film will be increased and the transparency will be improved. You can get high quality film.

(Bluing agent)
The polyimide raw material film in the present invention may contain a bluing agent. A bluing agent is an additive such as a dye or pigment that absorbs light in a wavelength range from orange to yellow in the visible light range and adjusts the hue, such as ultramarine, deep blue, and cobalt blue. For example, organic dyes and pigments such as phthalocyanine blueing agents and condensed polycyclic blueing agents may be mentioned. 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. Examples of the condensed polycyclic bluing agent include anthraquinone bluing agents, indigo bluing agents, and phthalocyanine bluing agents.

When the polyimide raw material film in 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 preferably 100 ppm, based on the mass of the polyimide raw material film. The content is more preferably 80 ppm or less, and even more preferably 60 ppm or less. When the content of the bluing agent is at least the above-mentioned lower limit, it is easy to improve the optical properties of the film, and in particular, it is easy to reduce YI. Moreover, when the content of the bluing agent is below the above-mentioned upper limit, it is easy to improve the optical properties, and especially when applied to a display device, the visibility is easily improved without reducing the YI value too much.

(Additive)
The polyimide raw material film in the present invention may further contain additives other than fillers, ultraviolet absorbers, and bluing agents. Other additives include, for example, antioxidants, mold release agents, stabilizers, flame retardants, pH adjusters, silica dispersants, lubricants, thickeners, leveling agents, surfactants, antistatic agents, and lubricants. , antifouling agents, etc. When other additives are contained, their content is preferably 0.001 to 20% by mass, more preferably 0.01 to 15% by mass, and even more preferably 0.01% by mass, based on the mass of the polyimide raw material film. It may be 1 to 10% by weight.

<Production method of polyimide raw material film>
The method for producing the polyimide raw material film in the present invention is not particularly limited, but for example, the following steps:
(a) a varnish preparation step of preparing a resin composition containing at least a polyimide resin and a solvent;
The manufacturing method may include at least (b) a coating step of applying a varnish to a base material to form a coating film, and (c) a raw material film forming step of drying the coating film to form a polyimide-based raw material film. .

In the varnish preparation step, a varnish is prepared by dissolving a polyimide resin in a solvent, adding additives such as the filler, the ultraviolet absorber, and the bluing agent as needed, and stirring and mixing. In addition, when using silica particles as a filler, a silica sol dispersion containing silica particles is replaced with a solvent in which the polyimide resin can be dissolved, for example, the solvent used for preparing the varnish described below, and a silica sol is added to the resin. Good too.

The solvent used for preparing the varnish is not particularly limited as long as it can dissolve the polyimide resin. Examples of such solvents include amide solvents such as DMAc and DMF; lactone solvents such as GBL and γ-valerolactone; sulfur-containing solvents such as dimethylsulfone, dimethylsulfoxide, and sulfolane; carbonates such as ethylene carbonate and propylene carbonate. and combinations thereof. Among these, amide solvents or lactone solvents are preferred. These solvents can be used alone or in combination. Further, the varnish may contain water, an alcohol solvent, a ketone solvent, an acyclic ester solvent, an ether solvent, and the like. The solid content concentration of the varnish is preferably 1 to 25% by weight, more preferably 5 to 20% by weight, and still more preferably 5 to 15% by weight.

In the coating step, a varnish is applied onto the base material to form a coating film using a known coating method. Known coating methods include, for example, wire bar coating, reverse coating, roll coating such as gravure coating, die coating, comma coating, lip coating, spin coating, screen coating, fountain coating, and dipping. method, spray method, drool molding method, etc.

In the raw material film forming step, a polyimide raw material film can be formed by drying the coating film and peeling it off from the base material. Before peeling from the base material, a protection film may be laminated on the surface of the polyimide raw material film opposite to the base material, and then the base material may be peeled off. Drying of the coating film can usually be carried out at a temperature of 50 to 350°C. In a preferred embodiment of the present invention, the coating film is preferably dried over a relatively long period of time. The drying temperature is preferably 50 to 150°C, more preferably 60 to 130°C, even more preferably 70 to 120°C. The drying time is preferably 5 to 60 minutes, more preferably 10 to 40 minutes. Drying of the coating film may be carried out in one stage or in multiple stages. Multi-stage conditions can preferably be carried out with the same or different temperature conditions and/or drying times in each stage, for example drying may be carried out in 2 to 10 stages, preferably 3 to 8 stages. . From the viewpoint of easily improving the mechanical properties and optical properties of the polyimide film, it is preferable to carry out the process under multi-step conditions. In the case of multiple stages, the temperature profile preferably includes a temperature-lowering process, or a temperature-raising and temperature-falling process. Taking a three-stage temperature profile including a temperature cooling process as an example, the drying temperatures are 90 to 130°C (first temperature), 85 to 105°C (second temperature), and 75 to 95°C (third temperature). temperature). Here, the drying time may be, for example, 5 to 30 minutes at each stage. Drying of the coating film is preferably carried out such that the residual amount of solvent in the dried coating film is preferably 5 to 20% by mass, more preferably 6 to 15% by mass, based on the mass of the dried coating film. . When the residual amount of the solvent is within the above range, the peelability of the dried coating film from the substrate will be good, and the optical properties of the film will be easily improved. Furthermore, even when tension is applied under heating, the film is easily prevented from breaking, and even when gripped together with a protective film, the smoothness of the film is easily maintained. The coating film may be dried in an inert atmosphere or under reduced pressure, if necessary.

Examples of the base material include SUS plate if it is metal-based, PET film, PEN film if it is resin-based, other polyimide films other than the polyimide film in the present invention, polyamide-imide film, polyamide film, and cycloolefin film. Examples include polymer films and acrylic films. Among these, PET film, cycloolefin polymer film, etc. are preferred from the viewpoint of excellent smoothness and heat resistance, and PET film is more preferred from the viewpoint of adhesiveness with the film of the present invention and cost.

<Process (X)>
Step (X) includes the polyimide raw material film and the protective film having a melting point of 200° C. or higher, which is disposed in two or more opposing areas at the end on at least one surface of the polyimide raw material film. This is a step of applying tension to the polyimide raw material film under heating while being held by a holding member.

Since the method for producing a polyimide film of the present invention includes step (X), breakage of the film can be prevented. Furthermore, it is easy to suppress the fusion (or adhesion) of the protective film to the gripping member. Therefore, even if step (X) is carried out while being transported, for example, it is possible to transport it stably.

In a preferred embodiment of the present invention, the coating film drying step in the raw material film forming step is a preliminary drying step, and the polyimide raw material film is preferably a raw material film after the preliminary drying step. That is, it is preferable that the polyimide raw material film contains a certain amount of residual solvent from the viewpoint of suppressing breakage of the film, and the residual amount of the solvent is preferably 5% by mass or more, more preferably 6% by mass or more, Preferably it is 25% by mass or less, more preferably 20% by mass or less. Further, in a preferred embodiment of the present invention, step (X) is preferably a main drying step. In addition, in this specification, a polyimide-based raw material film (raw material film) means a film before being subjected to step (X) or while being subjected to step (X), and when performing step (X) multiple times, Refers to the film before the end of all tensioning steps.

The protective film is arranged in two or more opposing areas at the end portions of at least one surface of the polyimide raw material film, that is, one or both surfaces. From the viewpoint of easily suppressing breakage of the film, the protective film is preferably disposed on both sides of the polyimide raw material film. As described above, the protective film is held by the gripping member while being placed on at least one surface of the polyimide raw material film.

In one embodiment of the present invention, from the viewpoint of easily suppressing breakage of the film and facilitating efficient production, the area where the protective film is arranged on one side of the polyimide raw material film is Based on the total area, it is preferably 1% or more, more preferably 2% or more, even more preferably 5%, even more preferably 10% or more, preferably 40% or less, more preferably 35% or less, and even more preferably may be 30% or less.

In one embodiment of the present invention, the gripping member for gripping the raw material film and the protective film includes conventional gripping members such as a clip, a pin sheet, and a film chuck. From the viewpoint of easily suppressing breakage of the film and facilitating easy and efficient manufacturing, the gripping member preferably includes at least one selected from the group consisting of a clip, a pin sheet, and a film chuck, and the clip is more preferable. One or more gripping members can be used, and it is preferable to use more than one gripping member.

Step (X) may be performed while the raw material film is being transported or may be performed in a stationary state, but from the viewpoint of easily and efficiently producing a polyimide film, it is preferable to perform it while being transported. When carrying out step (X) while conveying, a uniaxial stretching machine (for example, a tenter dryer) or the like can be used. Moreover, when performing step (X) in a stationary state, for example, a biaxial stretching machine or the like can be used.

When step (X) is carried out while being transported, the polyimide raw material film is preferably a long polyimide raw material film, and the protective film is preferably a long protective film. In one embodiment of the present invention, the length of the raw material film in the width direction is generally 100 mm or more, preferably 300 mm or more, more preferably 500 mm or more, even more preferably 1000 mm or more, particularly preferably 1500 mm or more, and 2000 mm or more. It may be more than 5000 mm, and the upper limit is not particularly limited, but may be usually 5000 mm or less. The length in the longitudinal direction of the raw material film is preferably 100 mm or more, more preferably 100 m or more, still more preferably 500 m or more, even more preferably 1000 m or more, and the upper limit is not particularly limited. The length in the width direction of the protective film is preferably 1 mm or more, more preferably 5 mm or more, preferably 100 mm or less, more preferably 80 mm or less, even more preferably 60 mm or less, and 40 mm or less or 30 mm or less. good. The length of the protective film in the longitudinal direction is preferably 100 mm or more, more preferably 100 m or more, even more preferably 500 m or more, and even more preferably 1000 m or more, and although the upper limit is not particularly limited, it may usually be 5000 mm or less. . Note that the length in the width direction and the length in the longitudinal direction of the protective film respectively indicate the length of one protective film arranged in two or more opposing areas.

In step (X), the protective film is placed at least in two or more opposing areas at the end of the raw material film. Here, the "end" of the raw material film is preferably a range from one end (the end) of the raw material film in one direction to a portion corresponding to 1/5 of the length of the raw material film in the one direction. "Two or more opposing areas" means two opposing (or opposing) areas separated within the range of the edge, and "one direction" refers to the width direction of the film. Or, the longitudinal direction is shown, and if the film is square, the width direction is shown. From the viewpoint of easily suppressing breakage of the film, when carrying out step (X) while conveying, it is preferable that protective films are placed in two opposing areas at the end of the raw material film, and the width of the raw material film is It is more preferable that the protective film is disposed in two opposing areas at two ends in the direction (or along the longitudinal direction) (for example, the form shown in FIG. 1). When step (X) is carried out by standing still without being transported, it is preferable that a protective film is placed in each of the opposing areas of the four ends of the polyimide raw material film (for example, the form shown in FIG. 4). .

According to the manufacturing method according to a preferred embodiment of the present invention, even a polyimide film that is difficult to stretch can be stretched without breaking, etc., so that a stretched polyimide film can also be obtained. In addition, when the heating temperature when applying tension is relatively high and the tension ratio is increased, preferably when the stretching ratio is increased, the film is generally more likely to break, but in the production method of the present invention, Since a predetermined protective film is held together with the raw material film, breakage of the film can be effectively suppressed even if the heating temperature is relatively high and the tension is large.

The heating temperature in step (X) is preferably 200°C or higher, more preferably 220°C or higher, even more preferably 230°C or higher, even more preferably 240°C or higher, particularly preferably 250°C or higher, particularly more preferably 260°C. Above, particularly preferably 270°C or higher, preferably 400°C or lower, more preferably 380°C or lower, even more preferably 360°C or lower, even more preferably 340°C or lower, particularly preferably 320°C or lower, especially more preferably is below 300°C. When the heating temperature in step (X) is equal to or higher than the above lower limit, breakage of the film can be easily suppressed and residual solvent in the film can be easily removed. Moreover, it is easy to improve the optical properties and mechanical properties of the obtained film. When the heating temperature in step (X) is below the above upper limit, it is easy to suppress the fusion (or adhesion) of the protective film to the gripping member.

In one embodiment of the present invention, the length of one side of the polyimide film in the direction (sometimes referred to as the magnification of tension) relative to the length of one side of the polyimide raw material film in the direction in which tension is applied is preferably 0. .7 times or more, more preferably 0.8 times or more, even more preferably 0.9 times or more, even more preferably 1.00 times or more, particularly preferably more than 1.00 times, especially more preferably 1.01 times. Above, it is extremely preferably 1.03 times or more, extremely more preferably 1.05 times or more, preferably 1.30 times or less, more preferably 1.25 times or less, still more preferably 1.20 times or less, and More preferably, it is 1.15 times or less. When the tension magnification is at least the above lower limit, the mechanical properties and optical properties of the resulting polyimide film are likely to be improved. When the tension magnification is below the above upper limit, breakage of the film and fusion (or adhesion) of the protective film to the gripping member can be easily suppressed. Further, the length of one side is the length excluding the portion gripped by the gripping member (gripping portion). The magnification of tension indicates the magnification in the direction in which tension is applied, that is, usually the width direction or the longitudinal direction, but when step (X) is carried out while conveying, the tension magnification is preferably the magnification in the width direction. Note that heating the raw material film while gripping it causes shrinkage of the film, so the tension magnification can be adjusted to 1.00 times or less. Further, when the tension in the longitudinal direction is high, the film shrinks in the width direction, so that the magnification of the tension in the width direction may become 1.00 or less. When the tension in the width direction is high, the film shrinks in the longitudinal direction, so that the magnification of the tension in the longitudinal direction may become 1.00 or less.

In this specification, when the magnification of tension exceeds 1.00 times, applying the tension is referred to as "stretching", and the magnification of the tension is sometimes referred to as "stretching magnification".
In the production method of the present invention, surprisingly, a polyimide film that is normally difficult to stretch does not break even if it is stretched to some extent, so it is preferable to apply tension by stretching in step (X). The stretching is preferably carried out using a uniaxial stretching machine or a biaxial stretching machine from the viewpoint of easily suppressing breakage of the film and easily improving the mechanical strength and optical properties of the film.

FIG. 1 is a schematic view schematically showing a preferred embodiment of a method for producing a polyimide film according to an embodiment of the present invention. FIG. 2 is a schematic cross-sectional view showing a laminated state of the polyimide film and protective film of FIG. 1. FIG. 3 is a schematic cross-sectional view showing a state in which the polyimide film and protective film of FIG. 1 are gripped by a gripping member. Although FIGS. 1 to 3 will be described below, the present invention is not limited to these embodiments.

In the embodiment shown in FIG. 1, a long raw material film 1 is transported in the direction A in a tenter dryer, and then two A long protective film 2 is introduced from the dryer entrance so that the protective film 2 is placed in two opposing areas at the end. At the same time, a plurality of gripping members 3, which are fixed at appropriate positions on an endless chain 4 of a predetermined length and move in the direction B at the same speed as the raw material film, are arranged on the raw material film 1 and both sides thereof. After gripping the protective film 2 and applying tension while conveying it, the grip is released near the exit of the dryer, and the protective film is collected by winding or the like.

In the tenter dryer, the plurality of gripping members 3 are fixed to two endless chains 4 on both sides in the width direction of the raw material film 1 being transported, and move at the same speed as the transport speed. Both ends of the raw material film 1 are fixed by a plurality of gripping members 3 provided so as to face each other in the film width direction. After the process of applying tension under heating, the fixing of both ends of the film may be released at a suitable time, and this may be done within the dryer or after being conveyed from the dryer.

In the embodiment of FIG. 1, as shown in FIG. 2 (cross section along the width direction of the film not including the gripping member 3), two opposite sides of the raw material film 1 at two ends in the width direction of each surface A protective film is placed in one area. Further, as shown in FIG. 3 (a part of a cross section along the film width direction including the gripping member 3), the gripping member 3 is able to hold the raw material film 1 and the protective film 2 by the two gripping parts 3a located at the tip thereof. I have a grasp of this.

The shortest distance L (sometimes referred to as the gripping width L of the gripping member) from any gripping part located at one end of the raw material film to the one end (tip) of the raw material film is preferably 1 to 50 mm, more preferably Preferably it is 10 to 40 mm. When the gripping width L of the gripping member is within the above range, breakage of the film can be easily suppressed. In the measurement of the gripping width L, the reference point of the gripping portion is the end point of the gripping portion opposite to the one end of the raw material film.

The total area where the plurality of gripping members grip the raw material film and the protective film, that is, the total area of the gripping parts in contact with the protective film (sometimes referred to as gripping area) is preferably 5% of the total area of the protective film. ~95%, more preferably 10-80%. When the gripping area is within the above range, breakage of the film can be easily suppressed.

The temperature inside the dryer is preferably adjusted to, for example, the above heating temperature range. The heating time in the dryer is usually 60 seconds to 2 hours, preferably 5 minutes to 1 hour, and more preferably 5 to 40 minutes. The processing time may be adjusted as appropriate in consideration of conditions such as the temperature of the dryer, the moving speed, the speed and volume of hot air.

The inside of a tenter dryer may be one space or divided into a plurality of spaces, but in one embodiment of the present invention, the inside of the dryer is divided into a plurality of spaces. It is preferable that The space may be a space whose temperature conditions, wind speed conditions, etc. can be controlled, and may not have a physical boundary such as a partition plate. When the inside of the dryer is divided into a plurality of spaces, the space may be divided into a plurality of spaces perpendicularly or parallel to the film transport direction. The number of spaces is usually 2 to 20, preferably 3 to 18, more preferably 4 to 15, and still more preferably 5 to 10. Regardless of the internal structure of the dryer, the entire dryer may serve as a heating zone, or a portion of the interior thereof may serve as a heating zone. In addition to the dryer, an oven may also be used as another device. The temperature settings for each space may be the same or different.

Heating in the tenter dryer may be performed by a hot air treatment method and/or a radiation treatment method, but it is preferable to perform at least a hot air treatment method. The speed of hot air in each space (or room) is preferably 5 to 20 m/sec, more preferably 8 to 15 m/sec, and even more preferably 11 to 14 m/sec.

The transport speed of the film is preferably 0.1 to 10 m/sec, more preferably 0.5 to 5 m/sec.

The tension magnification (or stretching magnification) can be adjusted by appropriately adjusting the distance N between the gripping portions in the width direction and changing the tension applied to the film during the transportation process in the dryer. For example, when stretching, the ratio of the distance N2 between the grips inside the dryer to the distance N1 between the grips at the entrance of the dryer (referred to as ratio Z) may be set to a predetermined value exceeding 1.00 times. When the tension magnification is set to 1.00 times or less, the ratio Z may be set to a predetermined value of 1.00 times or less. The ratio Z can be selected from the same range as the tension magnification described above.

When the polyimide film that has undergone step (X) exits the dryer, it is rapidly cooled and shrinks, which may cause cracks. Therefore, the distance between the grips at the dryer outlet N3 (ratio Q ) is preferably set small.

It is preferable to slit the edges of the polyimide film immediately after it comes out of the dryer. By performing slitting, the cracks that tend to occur between the gripping part and the ungripped part at the edge of the film can be removed from the film. The spread of cracks can be prevented in advance.

The polyimide film obtained in step (X) may be wound up into a roll. When wound up into a roll, another resin film or the like may be laminated and wound up. The thickness of the other resin film is usually 10 to 100 μm, preferably 10 to 80 μm.

FIG. 4 is a schematic view schematically showing a preferred embodiment of a method for producing a polyimide film in one embodiment of the present invention. The embodiment of FIG. 4 shows a method of carrying out step (X) in a stationary state, and tension is applied to the raw material film under heating in a stationary state. Specifically, protective films 2' are disposed on both sides of the sheet-shaped raw material film 1' in opposing areas of the four ends of each surface. The plurality of gripping members 3' grip the sheet-shaped raw material film 1' and the protective film 2' by gripping portions 3' as shown in FIG.

In step (X), after performing the step of applying tension using the tenter dryer or the like, further uniaxial stretching may be performed, from the viewpoint of easily improving the mechanical strength of the film, preferably the dent resistance described below. , uniaxial stretching or biaxial stretching may be performed. The stretching can be performed using, for example, a uniaxial stretching machine or a biaxial stretching machine. When biaxial stretching is performed, sequential stretching or simultaneous biaxial stretching may be performed. The stretching temperature can be selected from the range of heating temperatures mentioned above, and the stretching ratio can also be selected from the range of stretching ratios described above.

<Polyimide film>
The polyimide film obtained by the production method of the present invention does not cause film breakage and can suppress the fusion (or adhesion) of the protective film to the gripping member, so it has a good appearance and has good optical and mechanical properties. Excellent. Note that since the polyimide film is obtained by applying a predetermined tension to the polyimide raw material film, the contained components and their ratios are the same as those of the polyimide raw material film.

As mentioned above, polyimide films are hard and difficult to stretch, so they are usually not stretched. However, since the present inventor attempted to stretch such a polyimide film, he conducted a thorough study on the relationship between tension and breakage, and developed a new method for producing a tensioned (preferably stretched) polyimide film. I found a way. Furthermore, it has been found that the resulting polyimide film has particularly improved dent resistance.

The dent resistance can be evaluated by dent resistance pencil hardness. Measurement of dent resistance pencil hardness is performed by forming a dent on the film with a pencil having a predetermined hardness, and then determining whether or not there is a dent after 24 hours in an environment of 23°C and 50% RH. The hardness when the dents do not disappear and remain can be defined as the dent resistance pencil hardness of the film. Specifically, for example, a test sample is prepared by laminating a polyimide film using OCA having a storage elastic modulus of 0.1 MPa and a thickness of 25 μm at 25° C. on a 165 μm resin film having a polyimide base material. Next, the pencil was placed on a 0.7 mm thick glass with the polyimide film side facing up at a 45° angle in an environment of 23°C and 50% RH, and the pencil speed was adjusted while applying a constant load (300 g). It can be measured at 300 mm/min using a pencil hardness tester. Judgment can be made by conducting a 15 mm test and visually observing whether there is a dent or not after 24 hours in a 23° C. 50% RH environment. In one embodiment of the present invention, the dent resistance pencil hardness of the polyimide film is preferably 5B or more, more preferably 4B or more. When the dent resistance pencil hardness is at least the above lower limit, scratches and dents on the surface of the display device can be easily suppressed when the polyimide film is used as a front plate of the display device. Further, the dent resistance pencil hardness of the polyimide film is usually 9H or less.

In one embodiment of the present invention, the solvent content (or residual amount) of the polyimide film is preferably 0.001% by mass or more, more preferably 0.01% by mass or more, and even more preferably is 0.1% by mass or more, preferably 3% by mass or less, more preferably 2% by mass or less, even more preferably 1.5% by mass or less, even more preferably 1.3% by mass or less, particularly preferably 1 .0% by mass or less. When the solvent content of the polyimide film is within the above range, the mechanical properties, optical properties, and appearance of the film tend to be good.

In one embodiment of the present invention, the thickness of the polyimide film is preferably 5 μm or more, more preferably 10 μm or more, even more preferably 20 μm or more, particularly preferably 30 μm or more, particularly preferably 40 μm or more, and preferably is 1,000 μm or less, more preferably 500 μm or less, even more preferably 100 μm or less, even more preferably 80 μm or less, particularly preferably 70 μm or less, particularly preferably 60 μm or less. When the thickness of the polyimide film is at least the above-mentioned lower limit, mechanical properties are easily improved, and when it is at most the above-mentioned upper limit, optical properties are easily improved. The thickness of the polyimide film can be measured using a film thickness meter or the like, for example, by the method described in Examples.
In this specification, optical properties mean properties that can be evaluated optically, such as total light transmittance, YI value, haze, etc., and improving or increasing optical properties means, for example, total light transmittance, YI value, haze, etc. This indicates that the ratio is higher, the YI value is lower, the haze is lower, etc. In addition, mechanical properties mean mechanical properties such as dent resistance, bending resistance, and elastic modulus, and improving or increasing mechanical properties means, for example, dent resistance, bending resistance, Indicates that the modulus of elasticity, etc. increases.

Since the polyimide film obtained by the production method of the present invention has excellent optical properties, it is preferably an optical film. In the production method of the present invention, even if the raw material film is an optical film, a polyimide film can be produced without reducing optical properties such as total light transmittance and YI. The optical film preferably means a film having at least a high total light transmittance, and the total light transmittance is preferably 80% or more, more preferably 85% or more, still more preferably 90% or more, and usually It is 100% or less. When the total light transmittance of the polyimide film is equal to or higher than the above lower limit, the polyimide film has good transparency, and can contribute to high visibility when used for a front panel of a display device, for example. Note that the total light transmittance may be the total light transmittance in the above thickness range of the polyimide film. Further, the total light transmittance can be measured using a haze computer in accordance with JIS K 7105:1981, for example, by the method described in Examples.

In one embodiment of the present invention, the haze of the polyimide film is preferably 3.0% or less, more preferably 2.0% or less, even more preferably 1.0% or less, even more preferably 0.5% or less. , particularly preferably 0.3% or less, and usually 0.01% or more. When the haze of the polyimide film is less than or equal to the above upper limit, the polyimide film has good transparency, and can contribute to high visibility when used for a front panel of a display device, for example. Note that haze can be measured using a haze computer in accordance with JIS K 7136:2000, for example.

In one embodiment of the present invention, the YI value (yellowness) of the polyimide film is preferably 8 or less, more preferably 5 or less, even more preferably 4 or less, even more preferably 3 or less, particularly preferably 2 or less, It is particularly preferably 1.7 or less, usually -5 or more, and preferably -2 or more. When the YI value of the polyimide film is less than or equal to the above upper limit, transparency will be good and, for example, when used for a front panel of a display device, it can contribute to high visibility. The YI value is determined by measuring the transmittance of light in the range of 300 to 800 nm using an ultraviolet-visible near-infrared spectrophotometer in accordance with JIS K 7373:2006, and calculating the tristimulus value (X, Y, Z). ) can be calculated based on the formula YI=100×(1.2769X−1.0592Z)/Y, and can be measured, for example, by the method described in Examples.

The use of the polyimide film obtained by the production method of the present invention is not particularly limited, and may be used for various purposes. As mentioned above, the polyimide film may be a single layer or a laminate, and the polyimide film may be used as it is, or it may be laminated with other films. It may also be used as a laminate. Note that when the polyimide film is a laminate, all layers laminated on one or both sides of the polyimide film are referred to as the polyimide film.

When the polyimide film is a laminate, it is preferable to have one or more functional layers on at least one surface of the polyimide film. Examples of the functional layer include an ultraviolet absorbing layer, a hard coat layer, a primer layer, a gas barrier layer, an adhesive layer, a hue adjusting layer, and a refractive index adjusting layer. The functional layers can be used alone or in combination.

[Flexible display device]
The polyimide film obtained by the production method of the present invention may be used for flexible display devices. The polyimide film in the present invention is preferably used as a front plate in a flexible display device, and the front plate is sometimes referred to as a window film. The flexible display device is composed of a flexible display device laminate and an organic EL display panel, and the flexible display device laminate is arranged on the viewing side with respect to the organic EL display panel, and is configured to be foldable. The laminate for a flexible display device may further contain a polarizing plate and a touch sensor, and the order of stacking them is arbitrary. , a polarizing plate are preferably laminated in this order. It is preferable that the polarizing plate is present on the viewing side of the touch sensor because the pattern of the touch sensor becomes less visible and the visibility of the displayed image improves. Each member can be laminated using an adhesive, a pressure-sensitive adhesive, or the like. Further, a light shielding pattern may be provided on at least one surface of any one of the window film, polarizing plate, and touch sensor layer.

〔Polarizer〕
As described above, the flexible display device preferably further includes a polarizing plate, particularly a circularly polarizing plate. A circularly polarizing plate is a functional layer that has a function of transmitting only a right circularly polarized light component or a left circularly polarized light component by laminating a λ/4 retardation plate on a linearly polarizing plate. For example, by converting external light into right-handed circularly polarized light, blocking the left-handed circularly polarized external light that is reflected by the organic EL panel, and transmitting only the organic EL light emitting component, the effect of reflected light is suppressed and the image is imaged. Used to make it easier to see. In order to achieve the circular polarization function, the absorption axis of the linear polarizing plate and the slow axis of the λ/4 retardation plate should theoretically be 45°, but in practice they are 45±10°. The linear polarizing plate and the λ/4 retardation plate do not necessarily need to be stacked adjacent to each other, as long as the relationship between the absorption axis and the slow axis satisfies the above range. Although it is preferable to achieve complete circularly polarized light at all wavelengths, it is not necessary in practice, so the circularly polarizing plate in the present invention also includes an elliptically polarizing plate. It is also preferable to further laminate a λ/4 retardation film on the viewing side of the linearly polarizing plate to make the emitted light circularly polarized, thereby improving visibility when wearing polarized sunglasses.

[Touch sensor]
As described above, the flexible display device preferably further includes a touch sensor. A touch sensor is used as an input means. As the touch sensor, there are various types such as a resistive film type, a surface acoustic wave type, an infrared type, an electromagnetic induction type, and a capacitance type, and preferably a capacitance type is used.
A capacitive touch sensor is divided into an active area and a non-active area located around the active area. The active area corresponds to the area of the display panel where the screen is displayed, and is the area where the user's touch is sensed, and the inactive area is the non-display area where the screen is not displayed on the display device. This is an area corresponding to an area. The touch sensor includes a flexible substrate, a sensing pattern formed in an active area of the substrate, and a sensing pattern formed in an inactive area of the substrate, and connected to an external driving circuit through the sensing pattern and a pad. Each sensing line can be included. As the flexible substrate, the same material as the transparent substrate of the window film can be used.

[Adhesive layer]
Each layer such as a window film, a circularly polarizing plate, and a touch sensor forming the laminate for a flexible display device, and film members such as a linearly polarizing plate and a λ/4 retardation plate constituting each layer can be bonded with an adhesive. can. The adhesives include water-based adhesives, organic solvent-based adhesives, solvent-free adhesives, solid adhesives, solvent-vaporizing adhesives, water-based solvent-vaporizing adhesives, moisture-curing adhesives, heat-curing adhesives, and anaerobic adhesives. Commonly used adhesives such as hardening type, active energy ray hardening type adhesive, curing agent mixed type adhesive, hot melt type adhesive, pressure sensitive type adhesive, pressure sensitive adhesive, rewetting type adhesive, etc. Preferably, a water-based solvent volatilization adhesive, an active energy ray curable adhesive, or a pressure-sensitive adhesive can be used. The thickness of the adhesive layer can be adjusted as appropriate depending on the required adhesive strength, and is preferably 0.01 to 500 μm, more preferably 0.1 to 300 μm. A plurality of adhesive layers are present in the laminate for a flexible display device, and the thickness and type of each adhesive layer may be the same or different.

Hereinafter, the present invention will be explained in more detail with reference to Examples. "%" and "parts" in the examples mean % by mass and parts by mass, respectively, unless otherwise specified. First, a method for measuring physical property values will be explained.

<Measurement of weight average molecular weight>
The weight average molecular weights of the polyimide resins used in Examples and Comparative Examples were measured as follows.
Gel permeation chromatography (GPC) measurement (1) Pretreatment method Add the following eluent to polyimide resin so that the polyimide resin concentration is 2 mg/mL, heat at 80 ° C. with stirring for 30 minutes, and after cooling. The solution was filtered through a 0.45 μm membrane filter and used as a measurement solution.
(2) Measurement conditions Column: Tosoh Corporation TSKgel α-2500 ((7) 7.8 mm diameter x 300 mm) x 1, α-M ((13) 7.8 mm diameter x 300 mm) x 2 Eluent : Dimethylformamide DMF (contains 10 mmol/L lithium bromide)
Flow rate: 1.0 mL/min Detector: RI detector Column temperature: 40°C
Injection volume: 100μL
Molecular weight standard: standard polystyrene

<Measurement of imidization rate>
The imidization rate of the polyimide resin used in Examples and Comparative Examples was determined by ¹ H-NMR measurement as follows.
(1) Pretreatment method A polyimide film was dissolved in deuterated dimethyl sulfoxide (DMSO-d6) to form a solution with a polyimide resin concentration of 2% by mass, which was used as a measurement sample.
(2) Measurement conditions Measuring device: JEOL 400MHz NMR device JNM-ECZ400S/L1
Standard substance: DMSO-d6 (2.5ppm)
Sample temperature: room temperature Accumulation number: 256 times Relaxation time: 5 seconds (3) Imidization rate analysis method (imidization rate of polyimide resin)
In the ¹ H-NMR spectrum obtained by the above measurement, the observed benzene protons originate from a structure that does not change before and after imidization, and are not affected by the structure derived from the amic acid structure remaining in the polyimide resin. The integral value of benzene proton C was defined as IntC. Furthermore, among the observed benzene protons, the integral value of benzene proton D, which originates from a structure that does not change before and after imidization and is influenced by the structure derived from the amic acid structure remaining in the polyimide resin, was defined as IntD. The β value was determined from the obtained IntC and IntD using the following formula.
β=IntD/IntC
Next, the β value of the above formula was determined for a plurality of polyimide resins, and the following correlation formula was obtained from these results.
Imidization rate (%)=k×β+100
In the above correlation equation, k is a constant.
By substituting β into the correlation equation, the imidization rate (%) of the polyimide resin was obtained.

<Thickness>
The thickness of the protective film used in the Examples and Comparative Examples and the thickness of the obtained polyimide film were measured using an ABS Digimatic Indicator (manufactured by Mitutoyo Co., Ltd., "ID-C112BS").

<Melting point of protective film>
The melting points of the protective films used in Examples and Comparative Examples were measured in accordance with JIS K7121 using a differential scanning calorimeter.

<Viscosity of varnish>
The viscosity of the varnishes in Examples and Comparative Examples was measured using an E-type viscometer DV-II+Pro manufactured by Brookfield Co., Ltd. in accordance with JIS K 8803:2011. The measurement temperature was 25°C.

<Residual solvent amount of polyimide film>
The solvent content (residual solvent amount) of the raw material films and polyimide films in Examples and Comparative Examples was measured by thermogravimetric-differential thermal (TG-DTA) measurement using the following procedure. The mass reduction rate S (mass %) at 250° C. was calculated according to the following formula. The calculated mass reduction rate S was defined as the residual solvent amount S (mass %) in the polyimide film.
TG-DTA measuring device: TG/DTA6300 manufactured by Hitachi High-Tech Science Co., Ltd.
Measurement conditions: Approximately 20 mg of sample was heated from room temperature to 120°C at a heating rate of 10°C/min, held at 120°C for 5 minutes, and then heated to 400°C at a heating rate of 10°C/min. (heating) while measuring the change in mass of the sample.
S (mass%) = 100 - (W1/W0) x 100
[In the formula, W0 is the mass of the sample after being held at 120°C for 5 minutes, and W1 is the mass of the sample at 250°C].
In addition, when the protect film was laminated|stacked on the side opposite to the support body of a polyimide film, the protect film and support body were peeled, and the residual solvent amount was measured.

<Measurement of total light transmittance>
In accordance with JIS K 7105:1981, the total light transmittance of the polyimide film in the example was measured using a fully automatic direct reading haze computer HGM-2DP manufactured by Suga Test Instruments Co., Ltd.

<Measurement of YI value>
The YI value (Yellow Index) of the polyimide film in the example was measured in accordance with JIS K 7373:2006 using an ultraviolet-visible-near-infrared spectrophotometer "V-670" manufactured by JASCO Corporation. . After performing background measurement without a sample, set the film on the sample holder and measure the transmittance for light in the range of 300 to 800 nm, calculate the tristimulus values (X, Y, Z), and use the following formula. The YI value was calculated based on this.
YI=100×(1.2769X-1.0592Z)/Y

<Production Example 1: Preparation of polyimide resin>
In a nitrogen gas atmosphere, 313.57 g of DMAc was added to a 1 L separable flask equipped with a stirring blade, and the required amount of ion-exchanged water was added so that the water content was 700 ppm. Then, 18.53 g (57.86 mmol) of TFMB was added, and TFMB was dissolved in DMAc with stirring at room temperature. Next, 7.64 g (17.19 mmol) of 6FDA was added to the flask, cooled to 10° C., and stirred for 16 hours. Thereafter, 1.69 g (5.73 mmol) of OBBC and then 6.28 g (30.93 mmol) of TPC were added to the flask and stirred at 10° C. for 30 minutes. Next, 313.57 g of DMAc adjusted to a moisture content of 700 ppm was added, and after stirring for 10 minutes, 0.70 g (3.45 mmol) of TPC was added to the flask, and after stirring at 10°C for 30 minutes, 0.0367 g of TFMB was added. (0.115 mmol) was added and stirred for 2 hours. Next, 5.18 g (40.11) of diisopropylethylamine, 3.74 g (40.11 mmol) of 4-methylpyridine, and 12.29 g (120.30 mmol) of acetic anhydride were added to the flask, and the mixture was stirred at 10° C. for 30 minutes. Then, using an oil bath, the temperature was raised from 10°C to 50°C for 30 minutes, from 50°C to 60°C for 10 minutes, from 60°C to 65°C for 10 minutes, and then from 65°C to 70°C for 10 minutes. The temperature was raised stepwise from 70°C to 75°C over 10 minutes, and the mixture was further stirred while keeping the temperature at 70°C for 3 hours to obtain a reaction solution. The resulting reaction solution was cooled to room temperature, poured into a large excess of methanol in the form of a thread, and the deposited precipitate was filtered and taken out as a solid, which was immersed in methanol for 6 hours. Thereafter, solid matter was filtered out again and washed with a large excess amount of methanol. Next, the solid material was dried under reduced pressure at 80° C. for 24 hours to obtain polyimide resin (1). The weight average molecular weight Mw of the obtained polyimide resin (1) was 295,000, and the imidization rate was 98.1%.

<Production Example 2: Preparation of varnish>
Polyimide resin (1) was added to GBL and completely dissolved by stirring at room temperature for 24 hours to obtain varnish (1) with a viscosity of 40,000 cps at 25° C. and a solid content of 8.5%.

<Example 1>
(Manufacture of polyimide film)
A polyethylene terephthalate film base material (manufactured by Toyobo Co., Ltd.: Cosmoshine (registered trademark) A4100, hereinafter referred to as PET base material) with a thickness of 188 μm is unwound, and the PET is transported at a linear speed of 0.30 m/min. Varnish (1) placed in a tank was applied onto the substrate from a nozzle by drooling to a width of 500 mm. Then, while conveying at the same linear speed, the applied varnish is heated in a dryer at 120°C for 20 minutes, 95°C for 10 minutes, and 85°C for 10 minutes to dry the applied varnish and form a raw material film (dry coating film). Obtained. Next, a protect film (manufactured by San-A Kaken Co., Ltd.; NSA-33T) is unwound from the roll and pasted on the surface of the raw material film opposite to the surface that contacts the PET base material, and then The PET base material was peeled off and wound up as a PET base material roll, and the remaining laminate film (I) was obtained as a laminate roll (I) with a length of 100 m. The length of the raw material film in the width direction was 40 cm, and the length in the longitudinal direction was 100 m. Further, the amount of residual solvent in the raw material film was 15% by mass.
Next, the laminated film (I) is unwound from the obtained laminated body roll (I) at a conveyance speed of 2.0 m/sec, and the protective film is peeled off from the laminated film (I) and wound up as a protective film roll. As shown in FIGS. 1 and 2, the remaining raw material film was dried in a tenter dryer as shown below while applying tension to a laminate consisting of raw material film 1 and protective film 2 under the following conditions. Note that, as shown in FIG. 1, the tenter dryer is equipped with a mechanism for gripping both ends of the film using clips. Further, the interior is divided into a first chamber to a sixth chamber in order from the film entrance side (not shown). At that time, as shown in FIG. 3, a protective film 2 is placed between the clip 3 (gripping member 3) and the raw material film 1 (on both sides of the raw material film) using Kapton (melting point ≧350°C, 50 μm ) was put into the dryer from the inlet, and the protective film 2 was rolled up and collected at the dryer outlet, and then a polyimide film was obtained. As shown in FIG. 1, the protective films 2 are arranged in two opposing areas at two ends in the width direction (or along the longitudinal direction) on both sides of the raw material film. The obtained polyimide film had a thickness of 50 μm, a residual solvent amount of 0.5% by mass, a total light transmittance of 90.0%, and a YI value (yellowness) of 1.5. Further, the length of the protective film in the width direction was 50 mm, and the length in the longitudinal direction was 100 m.

<Tenter type dryer>
・Clip grip width (shortest distance from the grip located at one end of the raw material film to that one end (tip) of the raw material film): 25 mm
・Ratio Z of the distance N2 between the gripping parts at both ends of the film in the dryer to the distance N1 between the gripping parts at both ends of the film at the entrance of the dryer: 1.1
- Ratio of the distance N3 between the grips at both ends of the film at the dryer outlet to the distance N1 between the grips at both ends of the film at the dryer entrance: Q: 0.98
・Temperature inside the dryer: 280℃
・Wind speed in each chamber in the dryer: 13.5 m/sec in the 1st chamber, 13 m/sec in the 2nd chamber, 11 m/sec in the 3rd to 6th chambers

<Example 2>
A polyimide film was obtained in the same manner as in Example 1, except that the thickness of the polyimide film used as the protective film was changed to 25 μm. The obtained polyimide film 2 had a thickness of 50 μm and a residual solvent amount of 0.5% by mass.

<Example 3>
A polyimide film was obtained in the same manner as in Example 1, except that the protective film was changed from polyimide film to polytetrafluoroethylene (Nitflon manufactured by Nitto Denko, melting point ≧327°C, thickness 50 μm). The obtained polyimide film 3 had a thickness of 50 μm and a residual solvent amount of 0.5% by mass.

<Example 4>
Same as Example 1 except that the protective film was changed from polyimide film to PET (Polyester film "E5000" manufactured by Toyobo, melting point 260 ° C., thickness 50 μm) and the temperature of the dryer was changed to 260 ° C. A polyimide film 4 was obtained by the method. The obtained polyimide film had a thickness of 50 μm and a residual solvent amount of 1.0% by mass.

<Comparative example 1>
A polyimide film was produced in the same manner as in Example 1 except that a protective film was not used.

<Comparative example 2>
A polyimide film was produced in the same manner as in Example 1, except that a polyethylene film ("Toretec 7332" manufactured by Toray Film Co., Ltd., melting point ≦150°C, thickness 30 μm) was used as the protective film.

<Comparative example 3>
A polyimide film was produced in the same manner as in Example 1, except that polypropylene (Toray Fan, manufactured by Toray Industries, Ltd., melting point ≦170°C, thickness 30 μm) was used as the protective film.

Table 1 shows the results of manufacturing polyimide films in Examples 1 to 4 and Comparative Examples 1 to 3.

As shown in Table 1, it was confirmed that in the production methods of Examples 1 to 4, polyimide films were stably obtained without breaking. On the other hand, it was confirmed that in the manufacturing method of Comparative Example 1, the polyimide film broke, and in the manufacturing methods of Comparative Examples 2 and 3, resin adhesion to the clip and breakage of the film occurred, resulting in poor conveyance.

1, 1'...Raw material film 2,2'...Protective film 3,3'...Gripping member 3a...Gripping part 4...Endless chain A...Transportation direction B...Movement direction of the gripping member N...Distance between the gripping parts in the width direction L ...Gripping width of gripping member

Claims (9)

A protective film having a melting point of 200° C. or more is arranged in two or more opposing areas at an end portion on at least one surface of the polyimide raw material film, and in the area, the polyimide raw material film and the protective film are held together by a gripping member. A method for producing a polyimide film, the method comprising the step of applying tension to the polyimide raw material film under heating while being held by the polyimide film. The method according to claim 1, wherein the heating temperature is 200°C or higher. The method according to claim 1 or 2, wherein the protective film is placed on both sides of the polyimide raw material film. The method according to any one of claims 1 to 3, wherein the protective film has a melting point of 250°C or higher. The method according to any one of claims 1 to 4, wherein the protective film is at least one resin film selected from the group consisting of a polyimide-based protective film, a polytetrafluoroethylene-based protective film, and a polyester-based protective film. The method according to any one of claims 1 to 5, wherein in the step, tension is applied by stretching. Any one of claims 1 to 6, wherein the length of one side of the polyimide film in the direction is 0.7 to 1.3 times the length of one side of the polyimide raw material film in the direction in which the tension is applied. Method described. The method according to claim 6 or 7, wherein the stretching is performed using a uniaxial stretching machine or a biaxial stretching machine. The method according to any one of claims 1 to 8, wherein the gripping member includes at least one selected from the group consisting of a clip, a pin sheet, and a film chuck.

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