CN116178713A

CN116178713A - Polyimide film

Info

Publication number: CN116178713A
Application number: CN202211483712.4A
Authority: CN
Inventors: 塚田洋行; 小沼勇辅; 高田敦弘; 桑崎直人
Original assignee: Sumitomo Chemical Co Ltd
Current assignee: Sumitomo Chemical Co Ltd
Priority date: 2021-11-26
Filing date: 2022-11-24
Publication date: 2023-05-30
Also published as: JP2023079201A; TW202337956A; KR20230078549A

Abstract

The present invention relates to a polyimide film. A polyimide film comprising a polyimide resin containing a structural unit (A) derived from a tetracarboxylic anhydride and a structural unit (B) derived from a diamine, wherein the polyimide film has an in-plane orientation index defined by formula 1 of 58 or more. In formula 1, FWHM represents a half-width of a peak appearing at an azimuth angle corresponding to the ND direction of the film in an azimuth angle distribution of 2θ=16°, the azimuth angle distribution being obtained by analysis of a two-dimensional diffraction image measured by transmission X-ray diffraction, the two-dimensional diffraction image being measured by X-ray incidence parallel to the TD direction of the film. In-plane orientation index= [ (180-FWHM)/180 ] ×100 (formula 1).

Description

Polyimide film

Technical Field

To a polyimide film that can be used for a printed circuit board, a substrate material for an antenna substrate, etc. that can cope with a high frequency band, a method for producing the polyimide film, and a laminate film and a flexible printed circuit board that include the polyimide film.

Background

Flexible printed circuit boards (hereinafter, sometimes referred to as FPCs) are thin and lightweight, and have flexibility, so that they can be mounted in a three-dimensional and high-density manner, and are used in many electronic devices such as mobile phones and hard disks, contributing to miniaturization and weight reduction. Conventionally, polyimide resins excellent in heat resistance, mechanical properties, and electrical insulation have been widely used in FPCs, and for example, as a metal-clad laminate such as a copper-clad laminate (hereinafter, abbreviated as CCL) used for FPCs, a laminate having a copper foil layer on one or both surfaces of a single-layer or multi-layer polyimide film has been known.

In recent years, a fifth generation mobile communication system called 5G has been widely used (for example, patent document 1).

Patent document 1: japanese patent laid-open No. 2021-161285

Disclosure of Invention

However, in the case of a metal-clad laminate using a polyimide material conventionally used, when a high-frequency signal for 5G communication is transmitted, there are disadvantages such as a large transmission loss, a loss of an electric signal, and a long delay time of the signal. Therefore, for the purpose of reducing the transmission loss, a polyimide film having a low dielectric loss tangent (hereinafter, may be referred to as Df) and a low relative dielectric constant (hereinafter, may be referred to as Dk) has been studied, but a polyimide film having a sufficiently low relative dielectric constant and low dielectric loss tangent has not been found.

It is therefore an object of the present invention to provide: a polyimide film having a low Df and capable of forming a metal-clad laminate such as CCL having a low transmission loss in a high-frequency band, and a method for producing the same; a laminated film comprising the polyimide film and a flexible printed circuit board.

As a result of intensive studies to solve the above problems, the inventors of the present application have found that a polyimide film having a reduced Df can be obtained by adjusting the higher order structure of a polyimide resin under specific conditions, and completed the present invention. That is, the present invention provides the following preferred embodiments.

[1] A polyimide film comprising a polyimide resin containing a structural unit (A) derived from a tetracarboxylic anhydride and a structural unit (B) derived from a diamine, wherein the polyimide film has an in-plane orientation index defined by formula 1 of 58 or more.

In-plane orientation index = [ (180-FWHM)/180 ] ×100 (formula 1)

In expression 1, FWHM represents a half-width of a peak appearing at an azimuth angle corresponding to the ND direction of the film in an azimuth angle distribution of 2θ=16°, the azimuth angle distribution being obtained by analysis of a two-dimensional diffraction image measured by transmission X-ray diffraction, the two-dimensional diffraction image being measured by X-ray incidence parallel to the TD direction of the film. ]

[2] The polyimide film according to [1], which has a molecular periodicity index represented by formula 2 of 7.0 or more.

Molecular periodicity index=i (16 °)/I (min) (formula 2)

In formula 2, I (16 °) represents 2θ in the diffraction intensity distribution obtained by reflection X-ray diffraction measurement ₁ Maximum value of diffraction intensity at=15.5 to 16.5°,

i (min) represents 2 [ theta ] in the diffraction intensity distribution obtained by reflection X-ray diffraction measurement ₁ Minimum value of diffraction intensity at=20 to 30°.]

[3] The polyimide-based film according to [1] or [2], wherein the in-plane anisotropy index A defined by the formula 3 is 0.8 to 1.2, and the in-plane anisotropy index B defined by the formula 4 is more than 1.1.

In-plane anisotropy index a=i (MD)/I (TD) (formula 3)

In-plane anisotropy index b=i (MAX)/I (MIN) (formula 4)

[ in formula 3 and

formula

4, 2. Theta ₂ In the azimuth distribution of =16°, I (MD) represents the diffraction intensity corresponding to the MD direction of the film, I (TD) represents the diffraction intensity corresponding to the TD direction, I (MAX) represents the maximum value of the diffraction intensity, and I (MIN) representsThe minimum value of the diffraction intensity is obtained by analyzing a two-dimensional diffraction image measured by transmission X-ray diffraction, the two-dimensional diffraction image being measured by injecting X-rays parallel to the ND direction of the film.]

[4] The polyimide film according to any one of [1] to [3], wherein the structural unit (A) comprises a structural unit (A1) derived from a tetracarboxylic anhydride containing an ester bond.

[5] The polyimide film according to any one of [1] to [4], wherein the structural unit (A) comprises a structural unit (A2) derived from a tetracarboxylic anhydride containing a biphenyl skeleton.

[6] The polyimide film according to the item [5], wherein the structural unit (A) satisfies the relation of the formula (X).

(content of structural units derived from tetracarboxylic anhydride other than the structural unit (A1) and the structural unit (A2)/(total amount of the structural unit (A1) and the structural unit (A2)) <1.1 (X)

[7] The polyimide film according to any one of [4] to [6], wherein the structural unit (A1) is a structural unit (A1) derived from a tetracarboxylic anhydride represented by the formula (A1).

[ in formula (a 1), Z represents a 2-valent organic group,

R ^a1 independently of one another, represents a halogen atom or an alkyl, alkoxy, aryl or aryloxy group which may have a halogen atom,

s independently of one another represent an integer from 0 to 3 ]

[8] The polyimide film according to any one of [5] to [7], wherein the structural unit (A2) is a structural unit (A2) derived from a tetracarboxylic anhydride represented by the formula (A2).

[ in formula (a 2), R ^a2 Independently of one another, represents a halogen atom or an alkyl, alkoxy, aryl or aryloxy group which may have a halogen atom,

t represents an integer of 0 to 3 independently of one another

[9] The polyimide film according to any one of [1] to [8], wherein the structural unit (B) comprises a structural unit (B1) derived from a diamine having a biphenyl skeleton.

[10] The polyimide film according to the item [9], wherein the structural unit (B1) is a structural unit (B1) derived from a diamine represented by the formula (B1).

[ in formula (b 1), R ^b1 Independently of one another, represents a halogen atom or an alkyl, alkoxy, aryl or aryloxy group which may have a halogen atom,

p represents an integer of 0 to 4]

[11] The polyimide film according to [9] or [10], wherein the content of the structural unit (B1) is more than 30 mol% based on the total amount of the structural units (B).

[12] The polyimide film according to any one of [1] to [11], wherein the structural unit (B) comprises a structural unit (B2) derived from a diamine represented by the formula (B2).

[ in formula (b 2), R ^b2 Independently of one another, represents a halogen atom or an alkyl, alkoxy, aryl or aryloxy group which may have a halogen atom, R ^b2 The hydrogen atoms contained in (a) may be substituted with halogen atoms independently of each other,

w independently of one another represents-O-, -CH ₂ -、-CH ₂ -CH ₂ -、-CH(CH ₃ )-、-C(CH ₃ ) ₂ -、-C(CF ₃ ) ₂ -、-COO-、-OOC-、-SO ₂ -, -S-, -CO-or-N (R) ^c )-，R ^c Represents a hydrogen atom, a monovalent hydrocarbon group having 1 to 12 carbon atoms which may be substituted with a halogen atom, m represents an integer of 0 to 4,

q represents an integer of 0 to 4 independently of each other

[13]Such as [12]]In the polyimide film, m in the structural unit (b 2) is 3,W, and independently of each other, represents-O-or-C (CH) ₃ ) ₂ -。

[14] The polyimide film according to any one of [1] to [13], which has a dielectric loss tangent of less than 0.004 at 10 GHz.

[15]Such as [1]]～[14]The polyimide film according to any one of the above, wherein the polyimide resin has a storage elastic modulus of less than 3X 10 at 280 ℃ ⁸ Pa。

[16] The polyimide film according to any one of [1] to [15], wherein the glass transition temperature of the polyimide resin is 200 to 290 ℃.

[17] The polyimide film according to any one of [1] to [16], which has a thickness of 5 to 100. Mu.m.

[18] A laminated film comprising a metal foil layer on one or both surfaces of the polyimide film of any one of [1] to [17 ].

[19] A flexible printed circuit board comprising the polyimide film according to any one of [1] to [17 ].

[20] The method for producing a polyimide-based film according to any one of [1] to [17], comprising the steps of:

a step of applying a polyimide resin precursor solution containing a structural unit derived from tetracarboxylic anhydride and a structural unit derived from diamine to a substrate; and

and imidizing the polyimide resin precursor by heat treatment at 200 ℃ to 500 ℃.

Effects of the invention

According to the present invention, a polyimide film having a low Df can be provided, which can form a metal-clad laminate such as CCL having a low transmission loss in a high frequency band.

Drawings

Fig. 1 is a schematic diagram for explaining a method of determining an in-plane orientation index by transmission X-ray diffraction measurement.

Fig. 2 is a graph showing an azimuthal distribution of the polyimide film of example 4 obtained by transmission X-ray diffraction measurement.

FIG. 3 is a schematic diagram for explaining a method of determining a molecular periodicity index by reflection X-ray diffraction measurement.

Fig. 4 is a graph showing a diffraction intensity distribution obtained by reflection X-ray diffraction measurement of the polyimide film of example 4.

Fig. 5 is a schematic diagram for explaining a method of determining an in-plane anisotropy index by transmission X-ray diffraction measurement.

Fig. 6 is a graph showing an azimuthal distribution of the polyimide-based film of example 4 obtained by transmission X-ray diffraction measurement.

Description of the reference numerals

1a, 1b, 1c test piece for measurement

2a, 2b, 2c X-ray source

3a, 3b, 3c detector

4. A position where the minimum intensity in the range of 180 to 360 DEG in azimuth is half the intensity of the peak intensity existing at 270 DEG based on the minimum intensity

5. 4. Position width of peak of (2)

6 sample holder

7A line connecting detection positions of 2b and 3b

8···2θ ₁ Maximum value of diffraction intensity in range of=15.5 to 16.5°

9···2θ ₁ Minimum value of diffraction intensity at=20° to 30 °

10. azimuth angle 0 DEG diffraction intensity

Diffraction intensity at azimuth angle 90 DEG

Diffraction intensity at 180 DEG at 12 DEG azimuth

13 azimuth angle of 0 to 360 DEG

Diffraction intensity at 14 azimuthal angle 270 DEG

15 azimuth angle of 0 to 360 DEG

16 azimuth 360 DEG diffraction intensity

Detailed Description

[ polyimide film ]

(in-plane orientation index)

The polyimide film of the present invention comprises a polyimide resin containing a structural unit (a) derived from a tetracarboxylic anhydride and a structural unit (B) derived from a diamine, and has an in-plane orientation index (also simply referred to as an in-plane orientation index) defined by the following formula 1 of 58 or more.

In-plane orientation index = [ (180-FWHM)/180 ] ×100 (formula 1)

The in-plane orientation index can be obtained by measuring the FWHM by transmission X-ray measurement and substituting the obtained value of the FWHM into formula 1.

The method of measuring FWHM will be described below with reference to fig. 1 and 2. Fig. 1 is a schematic diagram for explaining a method of determining an in-plane orientation index by transmission X-ray diffraction measurement. In fig. 1, the dimensions of the measurement test piece, for example, the aspect ratio, etc., are adjusted to facilitate understanding of the description, and are not limited thereto.

First, a film is cut and/or laminated to prepare a test piece for measurement. The size of the test piece for measurement is not limited as long as sufficient resolution and diffraction intensity can be obtained, but it is preferable that the width in the MD direction is 0.5 to 3cm, the width in the TD direction is 0.5 to 2mm, and the thickness in the ND direction is 100 μm or more. The upper limit of the thickness in the ND direction may be preferably 2mm or less. The thickness can be obtained by overlapping a plurality of films. Next, as shown in fig. 1, a measurement test piece 1a is set on the X-ray apparatus so that the irradiation direction of the X-rays is parallel to the TD direction of the film. Then, X-rays are irradiated from the X-ray source 2a to the measurement test piece 1a, and a two-dimensional diffraction image is obtained by the detector 3 a. The obtained two-dimensional diffraction image was corrected using a two-dimensional diffraction image (air space) obtained without providing the measurement test piece 1a. Further, from the two-dimensional diffraction image, an azimuth distribution of diffraction angles 2θ=16° was obtained such that 0 ° and 180 ° of the azimuth distribution correspond to the MD direction of the measurement test piece 1a, and 90 ° and 270 ° of the azimuth distribution correspond to the ND direction of the measurement test piece 1a. The diffraction intensity at each azimuth angle is an average value of diffraction intensities in a range of 2θ=15.5 to 16.5 °.

Half-peak widths of peaks existing at 90 ° and 270 ° in the obtained azimuth distribution (azimuth β=0 to 360°) were obtained, and an average value of 2 half-peak widths was used as FWHM. The half-width represents the peak width at the intensity position at the center between the peak intensity existing at 90 ° or 270 °, and the minimum intensity in the range of-90 ° to +90° of the azimuth angle of the peak intensity (i.e., the peak width at the position that becomes one half of the peak intensity existing at 90 ° or 270 ° with the minimum intensity as a reference). For example, in the azimuth distribution shown in fig. 2, the half-width of the peak present at 270 ° corresponding to the ND direction is: the width of the peak shown by 5 in fig. 2 at the position shown by 4 in fig. 2, which becomes one half intensity with reference to the minimum intensity in the range of 180 to 360 °.

In the present specification, the MD direction is a direction parallel to the machine direction of travel in the film surface during manufacturing, the TD direction is a direction perpendicular to the machine direction of travel, and the ND direction is a film thickness direction, that is, a direction perpendicular to the film surface. When the directions of the MD direction and the TD direction in the film surface are not clear, the following method is used for determination.

In the azimuth distribution of 2θ=16° measured by irradiating X-rays from the ND direction by transmission X-ray measurement, the azimuth with the strongest diffraction intensity is taken as the MD direction.

The X-ray apparatus may be set to the following measurement conditions.

X-ray source: cu-K alpha ray

Voltage: 40kV (kilovolt)

Current: 20mA

Camera length: 70mm of

Exposure time: for 10 minutes

Beam diameter: 0.25mm

In the azimuth distribution of 2θ=16°, the sharper the peak appearing in the ND direction, the smaller the value of FWHM, the larger the in-plane orientation index in the formula will be.

In the present specification, polyimide is sometimes referred to as PI.

The inventors of the present application have found that, in a PI-based film comprising a polyimide-based resin containing a structural unit (a) derived from a tetracarboxylic anhydride and a structural unit (B) derived from a diamine, the Df of the PI-based film can be unexpectedly reduced when the in-plane orientation index defined by formula 1 is 58 or more.

The diffraction peak in the X-ray diffraction measurement shows a periodic structure having a distance corresponding to the diffraction angle 2θ, and when the peak intensity is strong, the component having the periodic structure is more or the periodicity of the component has higher regularity. In addition, when the diffraction peak is strongly detected at a specific azimuth angle, it means that a periodic structure is formed along the azimuth direction or that the molecular main chain is oriented in a direction perpendicular to the azimuth angle.

It is known that various kinds of periodicity in the higher order structure of the molecular chain of PI-based resin are reflected in the X-ray measurement of PI-based films, and that many diffraction peaks such as those shown in fig. 4 are detected.

If the in-plane orientation index defined by formula 1 is 58 or more, PI-based resins oriented along the film plane are present to some extent, and they are distributed so as to maintain a distance corresponding to the diffraction angle 2θ=16° in the film vertical direction. It is estimated that if the PI-based resin has such a regular higher order structure, the rotational movement of the molecular chain of the resin is suppressed for some reason, and Df of the PI-based film is reduced.

On the other hand, if the in-plane orientation index defined by formula 1 is less than 58, the rotational movement of the molecular chain of the resin cannot be sufficiently suppressed, and Df of the PI-based film cannot be sufficiently reduced.

In the PI-based film of the present invention, the in-plane orientation index is preferably 60 or more, more preferably 62 or more, still more preferably 64 or more, still more preferably 66 or more, particularly preferably 68 or more, and particularly preferably 69 or more. If the in-plane orientation index is equal to or greater than the lower limit, df of the PI film is easily reduced. The upper limit of the in-plane orientation index is preferably 95 or less, more preferably 90 or less, further preferably 85 or less, further more preferably 80 or less. If the in-plane orientation index is equal to or less than the upper limit, the dielectric constant is kept low, and the anisotropy of the mechanical strength is easily suppressed, and in addition, the bending resistance is easily improved. The in-plane orientation index can be obtained by the method described above, and can be obtained by the method described in the examples.

The in-plane orientation index can be adjusted by appropriately adjusting the types of the constituent units constituting the PI-based resin and the constitution thereof, and the molecular weight of the PI-based resin, the coating and imidization conditions, and other manufacturing methods, and can be adjusted within the above-described range by, for example, adopting a preferable mode in the following description, particularly, a mode in which improvement of dielectric characteristics such as Df reduction is described. For example, the structural unit and the content thereof of the PI-based resin described later, the solvent contained in the PI-based resin precursor solution described later, the imidization conditions described later, and the like can be suitably adjusted. In addition, if an ester bond is contained in the PI-based resin, the in-plane orientation index tends to be high, and if a soft component is contained in the PI-based resin, the in-plane orientation index tends to be easily lowered.

(molecular periodicity index)

In one embodiment of the present invention, the PI-based film of the present invention preferably has a molecular periodicity index represented by the following formula 2 of 7.0 or more.

Molecular periodicity index=i (16 °)/I (min) (formula 2)

The molecular periodicity index was obtained by measuring I (16 °) and I (min) by reflection X-ray diffraction measurement and substituting the values into formula 2.

The measurement methods of I (16 °) and I (min) will be described below with reference to fig. 3 and 4. Fig. 3 is a schematic diagram for explaining a method of determining a molecular periodicity index by reflection X-ray diffraction measurement. In fig. 3, the dimensions of the measurement test piece, for example, the aspect ratio, etc., are adjusted to facilitate understanding of the description, and are not limited thereto.

First, a film is cut and/or laminated to prepare a test piece for measurement. The size of the test piece for measurement is not limited as long as sufficient resolution and diffraction intensity can be obtained, but it is preferable that the width in the MD direction is 0.5cm to 5cm and the width in the TD direction is 0.5cm to 5cm. Next, as shown in fig. 3, the measurement sample 1b is attached to the sample holder 6 such that the ND direction of the film is parallel to the normal direction of the surface of the sample holder 6 (the direction perpendicular to the surface), and such that a line 7 connecting the detection positions of the X-ray source 2b and the detector 3b is parallel to the MD direction of the film when the sample holder 6 is set in the X-ray apparatus. Then, while maintaining the line 7 parallel to the MD direction, the diffraction angle 2θ is set ₁ Reflection measurement of the film surface was performed in the range of=5 to 30°, and diffraction distribution a of the film was obtained.

Further, the films were cut and/or laminated to obtain another test piece for measurement. Then, as shown in FIG. 3, the ND direction of the film is parallel to the normal direction of the surface of the sample holder 6 (the direction perpendicular to the surface)And when the sample holder 6 is set in the X-ray apparatus, the measurement sample 1b is attached to the sample holder 6 such that a line 7 connecting the detection positions of the X-ray source 2b and the detector 3b is parallel to the TD direction of the film. Next, at 2. Theta ₁ Reflection measurement of the film surface was performed in the range of=5 to 30°, and diffraction distribution B of the film was obtained. For each diffraction profile, the background was subtracted to perform blank correction. The average value of the diffraction distribution a and the diffraction distribution B corrected by the blank was taken as the diffraction intensity distribution of the film. Based on the diffraction intensity distribution of the film, 2 theta ₁ The maximum value of diffraction intensity in the range of=15.5 to 16.5° is I (16 °), and 2θ is set to ₁ The minimum value of diffraction intensity at=20 to 30° is regarded as I (min). For example, in the diffraction intensity distribution shown in fig. 4, I (16 °) is 2θ ₁ Maximum value of diffraction intensity in the range of=15.5 to 16.5° (8 in the figure), I (min) is 2θ ₁ Minimum value of diffraction intensity at=20 to 30° (9 in the figure).

The X-ray apparatus may be set to the following measurement conditions.

X-ray source: cu-K alpha ray

Guan Dianya: 40kV (kilovolt)

Guan Dianliu: 150mA

Divergent slit: 1 degree

Scattering slit: 1 degree

Light receiving slit: 0.15mm

Divergent longitudinal limiting slit: 10mm of

Measurement range: 2 theta ₁ ＝5～30°

Step size measurement: 0.02 degree

Scanning speed: 0.5 DEG/min

Sample holder: aluminum sample plate

If the molecular periodicity index represented by formula 2 is 7.0 or more, df of the PI-based film can be further reduced.

It is inferred that if the PI-based resin maintains the diffraction angle 2 theta ₁ Distributed at a distance of =16°, the rotational movement of the molecular chain of the resin is suppressed for some reason, the Df of the PI-based film is reduced, and ifWhen the molecular periodicity index is 7.0 or more, the number of components arranged at a constant distance becomes large, independent of the orientation of the molecular chain, and thus the Df becomes low.

In the PI-based film of the present invention, the molecular periodicity index is preferably 7.1 or more, more preferably 7.3 or more, still more preferably 7.5 or more, still more preferably 7.7 or more, and particularly preferably 7.8 or more. If the molecular periodicity index is not less than the lower limit, df of the PI-based film is likely to be reduced. The upper limit of the molecular periodicity index is preferably 20 or less, more preferably 15 or less, further preferably 12 or less, further more preferably 10 or less. If the molecular periodicity index is equal to or less than the upper limit, the bending resistance is easily improved. The molecular periodicity index can be obtained by the method described above, and can be obtained by the method described in examples, for example.

The molecular periodicity index can be adjusted by appropriately adjusting the types of the constituent units constituting the PI-based resin and their constitution, and the production methods such as the molecular weight of the PI-based resin and imidization conditions, and can be adjusted within the above-described range by, for example, adopting a preferable form in the following description, particularly, a form in which improvement of dielectric characteristics such as Df reduction is described. For example, the structural unit and the content thereof of the PI-based resin described later, the solvent contained in the PI-based resin precursor solution described later, the imidization conditions described later, and the like can be suitably adjusted. In addition, if an ester bond is contained in the PI-based resin, the molecular periodicity index tends to be high, and if a soft component in the PI-based resin is increased, the molecular periodicity index tends to be easily lowered.

(in-plane anisotropy index)

In one embodiment of the present invention, the PI-based film of the present invention preferably has an in-plane anisotropy index a defined by the following formula 3 of 0.8 to 1.2, and an in-plane anisotropy index B defined by the following formula 4 of more than 1.1.

In-plane anisotropy index a=i (MD)/I (TD) (formula 3)

In-plane anisotropy index b=i (MAX)/I (MIN) (formula 4)

[ in formula 3 and formula 4, the diffraction angle 2θ ₂ In the azimuth distribution of =16°, I (MD) represents the diffraction intensity corresponding to the MD direction of the film, I (TD) represents the diffraction intensity corresponding to the TD direction, I (MAX) represents the maximum value of the diffraction intensity, and I (MIN) represents the minimum value of the diffraction intensity, the azimuth distribution is obtained by analysis of a two-dimensional diffraction image measured by transmission X-ray diffraction, and the two-dimensional diffraction image is measured by injecting X-rays parallel to the ND direction of the film.]

The in-plane anisotropy indices a and B were obtained by measuring I (MD), I (TD), I (MAX), and I (MIN) by transmission X-ray diffraction measurement, and substituting them into

equations

3 and 4.

The measurement methods of I (MD), I (TD), I (MAX), and I (MIN) will be described below with reference to fig. 5 and 6. Fig. 5 is a schematic diagram for explaining a method of determining an in-plane anisotropy index by transmission X-ray diffraction measurement. In fig. 5, for example, the aspect ratio of the measurement test piece is adjusted to facilitate understanding of the description, and is not limited thereto.

First, a film is cut and/or laminated to prepare a test piece for measurement. The size of the test piece for measurement is not limited as long as sufficient resolution and diffraction intensity can be obtained, but it is preferable that the width in the MD direction is 0.5cm to 3cm and the width in the TD direction is 0.5cm to 3cm. The ND direction width can be preferably adjusted to 0.1mm to 2mm. Next, as shown in fig. 5, a measurement test piece 1c is set on the X-ray apparatus so that the irradiation direction of the X-rays is parallel to the ND direction of the film. Then, X-rays are irradiated from the X-ray source 2c to the measurement test piece 1c, and a two-dimensional diffraction image is obtained by the detector 3 c. The obtained two-dimensional diffraction image was corrected using a two-dimensional diffraction image (air space) obtained without providing the measurement test piece 1c. Further, 2 θ was obtained from the two-dimensional diffraction image so that 0 ° and 180 ° of the azimuth distribution corresponded to the MD direction of the test piece 1c for measurement and 90 ° and 270 ° of the azimuth distribution corresponded to the TD direction of the test piece 1c for measurement ₂ Azimuth distribution of =16°. Diffraction intensity at each azimuth angle is 2 theta ₂ Average value of diffraction intensity in the range of=15.5 to 16.5°.

In the resulting azimuth distribution (azimuth beta ₁ Of =0 to 360°, diffraction intensities of 0 ° and 180 ° were obtained, the average value thereof was defined as I (MD), and diffraction intensities of 90 ° and 270 ° were obtained, and the average value thereof was defined as I (TD). In addition, the azimuth distribution (. Beta.) obtained above ₁ In=0 to 360 °), the maximum value of the diffraction intensity in the range of 0 to 360 ° is defined as I (MAX), and the minimum value of the diffraction intensity is defined as I (MIN). For example, in the azimuth distribution shown in fig. 6, I (MD) is an average value of the diffraction intensity 10 at 0 ° and the diffraction intensity 12 at 180 °, I (TD) is an average value of the diffraction intensity 11 at 90 ° and the diffraction intensity 14 at 270 °, I (MAX) is a maximum value (15 in the drawing) in a range of 0 to 360 °, and I (MIN) is a minimum value (13 in the drawing) in a range of 0 to 360 °.

The X-ray apparatus may be set to the following measurement conditions.

X-ray source: cu-K alpha ray

Camera length: 70mm of

Exposure time: for 10 minutes

Voltage: 40kV (kilovolt)

Current: 20mA

Beam diameter: 0.25mm

The inventors of the present application have found that, in a PI-based film comprising a PI-based resin containing a structural unit (a) derived from a tetracarboxylic anhydride and a structural unit (B) derived from a diamine, the in-plane anisotropy index a defined by formula 3 is 0.8 to 1.2, and when the in-plane anisotropy index B defined by formula 4 is greater than 1.1, the Df of the PI-based film can be unexpectedly further reduced.

The in-plane anisotropy index a represents a ratio of the orientations of the molecular chains of the resin in the MD direction and the TD direction and the degree of regularity thereof, and the closer the in-plane anisotropy index a is to 1, the smaller the difference between the anisotropies of the MD and the TD is. When the in-plane anisotropy index a is 0.8 to 1.2, the film tends to have isotropic film properties in the plane of the film, and film properties which are isotropic thermally and mechanically tend to be easily formed asThe operation of processing the printed circuit board is easy. On the other hand, the in-plane anisotropy index B represents the ratio of the diffraction intensity in the direction of the strongest diffraction intensity to the direction of the weakest diffraction intensity in the azimuth distribution. The reason why the in-plane anisotropy index B is greater than 1.1 despite the in-plane anisotropy index A being 0.8 to 1.2 is considered to be that, as the properties of the PI-based resin itself, a film having a diffraction angle 2 theta equivalent to ₂ In the higher-order structure having a distance of =16°, it is assumed that the rotational movement of the molecular chain of the resin is easily suppressed in such a structure, and thus Df of the PI-based film is reduced.

In the PI-based film of the present invention, the in-plane anisotropy index a is preferably 0.8 or more, more preferably 0.83 or more, still more preferably 0.87 or more, still more preferably 0.9 or more, particularly preferably 0.93 or more, particularly preferably 0.97 or more, preferably 1.2 or less, more preferably 1.17 or less, still more preferably 1.13 or less, still more preferably 1.1 or less, particularly preferably 1.07 or less, and even more preferably 1.03 or less. When the in-plane anisotropy index a is within the above range, film properties that are isotropic thermally and mechanically are easily formed, and workability in processing as a printed circuit board is easily improved.

In the PI-based film of the present invention, the in-plane anisotropy index B is preferably 1.12 or more, more preferably 1.15 or more, still more preferably 1.17 or more, and still more preferably 1.2 or more. If the in-plane anisotropy index B is equal to or greater than the lower limit, df of the PI-based film is easily reduced. The upper limit of the in-plane anisotropy index B is preferably 3.0 or less, more preferably 2.5 or less, further preferably 2.0 or less, further more preferably 1.7 or less, and particularly preferably 1.5 or less. The in-plane anisotropy index can be obtained by the method described above, and can be obtained by the method described in examples, for example.

The in-plane anisotropy indices a and B can be adjusted by appropriately adjusting the types of the constituent units constituting the PI-based resin and the constitution thereof, and the molecular weight of the PI-based resin, the imidization conditions, and other production methods, and can be adjusted within the above-described range by, for example, adopting a preferable form in the following description, particularly, a form in which improvement of dielectric characteristics such as Df reduction is described. For example, the structural unit and the content thereof of the PI-based resin described later, the solvent contained in the PI-based resin precursor solution described later, the imidization conditions described later, and the like can be suitably adjusted. In addition, if the PI-based resin contains an ester bond, the in-plane anisotropy index B tends to be high, and if the PI-based resin contains a large amount of soft components, the in-plane anisotropy index B tends to be low.

In one embodiment of the present invention, the PI-based film of the present invention has a low linear expansion coefficient (hereinafter, may be referred to as CTE). The CTE of the PI-based film is preferably 50ppm/K or less, more preferably 40ppm/K or less, further preferably 30ppm/K or less, further more preferably 25ppm/K or less, particularly preferably 21ppm/K or less, preferably 0ppm/K or more, further preferably 5ppm/K or more, further preferably 8ppm/K or more, further more preferably 12ppm/K or more. By setting the range as described above, the CTE of the copper foil and PI layer is close, and thus peeling of the laminated film can be suppressed. The CTE may be measured by a thermo-mechanical analyzer (sometimes referred to as "TMA"), for example, and may be obtained by the method described in the examples.

For printed circuits, transmission loss is required to be small. The transmission loss is represented by the sum of dielectric loss, which is a loss due to an electric field generated by using a dielectric, and conductor loss, which is a loss due to a current flowing through a conductor. Further, it is known that the dielectric loss is approximately proportional to the index E represented by the formula (i).

E＝Df×(Dk) ^1/2 (i)

[ in formula (i), df represents the dielectric loss tangent and Dk represents the relative permittivity ]

In a high frequency region used for the 5G FPC, dielectric loss tends to increase, and therefore, a material that has a small value of the index E and can suppress dielectric loss is particularly required.

On the other hand, the current of the high-frequency signal concentrates on the outermost surface of the conductor. Therefore, the conductor loss is related to the dielectric properties of the connected dielectrics, which is known as (Dk) ^1/2 Approximately proportional.

As described above, the PI-based film of the present invention contains the PI-based resin containing the structural unit (a) derived from the tetracarboxylic anhydride and the structural unit (B) derived from the diamine, and the above-mentioned in-plane orientation index of the PI-based resin is 58 or more, so Df and Dk become small, and thus the index E of dielectric loss and conductor loss become small, and in a circuit containing the PI-based film, transmission loss can be reduced.

In one embodiment of the present invention, the index E of dielectric loss at 10GHz of the PI-based film is preferably 0.009 or less, more preferably 0.008 or less, still more preferably 0.007 or less, and particularly preferably 0.006 or less. The lower limit of the index E is not particularly limited, and may be, for example, 0 or more, since the lower limit of the index E is smaller as the transmission loss of an electronic circuit including the PI film is lower.

In one embodiment of the present invention, df at 10GHz of the PI film is preferably less than 0.004, more preferably not more than 0.0038, still more preferably not more than 0.0035, still more preferably not more than 0.0033, particularly preferably not more than 0.003, particularly preferably not more than 0.0027, particularly preferably not more than 0.0024, from the viewpoint of easily reducing the transmission loss of an electronic circuit including the PI film. The lower limit of Df is not particularly limited, and may be, for example, 0 or more, since the smaller Df is, the lower transmission loss of an electronic circuit including a PI film is reduced.

In one embodiment of the present invention, dk of the PI film at 10GHz is preferably less than 3.50, more preferably 3.45 or less, further preferably 3.40 or less, further more preferably 3.38 or less, and particularly preferably 3.36 or less.

The Df and Dk of the PI-based film can be measured using a vector network analyzer and a resonator, and can be measured by the method described in examples, for example.

In one embodiment of the present invention, the PI-based film of the present invention has a bending number to break of 15,000 or more, preferably 20,000 or more, more preferably 50,000 or more, still more preferably 100,000 or more, still more preferably 150,000 or more, and particularly preferably 200,000 or more in the MIT bending fatigue test according to ASTM standard D2176-16. If the number of bending times is equal to or greater than the lower limit, the occurrence of cracks, breaks, creases, and the like can be effectively suppressed even if the bending is repeated. The upper limit of the number of bending times is not particularly limited, and may be, for example, 10,000,000 times or less. The MIT bending fatigue test may be performed by using an MIT bending fatigue tester, and may be performed by the method described in examples, for example.

The thickness of the PI-based film of the present invention may be appropriately selected depending on the application, and is preferably 5 μm or more, more preferably 10 μm or more, further preferably 20 μm or more, preferably 500 μm or less, more preferably 300 μm or less, further preferably 100 μm or less, particularly preferably 80 μm or less, and particularly preferably 50 μm or less. The thickness of the film can be measured by a film thickness meter or the like. In the case where the film of the present invention is a multilayer film, the thickness refers to the thickness of the single layer portion. In addition, if the film thickness is reduced, the in-plane orientation index and the molecular periodicity index tend to be increased.

The PI-based film of the present invention may be subjected to surface treatments such as corona discharge treatment, plasma treatment, and ozone treatment by methods generally used in industry.

The PI-based film of the present invention has a low Df, and therefore can be suitably used for a printed circuit board, a substrate material for an antenna substrate, or the like which can cope with a high frequency band. A laminate having a copper foil layer on one or both sides of a PI-based resin in a single layer or multiple layers is widely used as CCL for FPC.

< polyimide resin >

The PI-based film of the present invention comprises a PI-based resin containing a structural unit (a) derived from a tetracarboxylic anhydride and a structural unit (B) derived from a diamine. In the present invention, "structural unit derived from …" means "structural unit derived from …", for example, "structural unit (a) derived from tetracarboxylic anhydride" means "structural unit (a) derived from tetracarboxylic anhydride".

(structural unit (A) derived from tetracarboxylic anhydride)

The PI-based resin contains a structural unit (a) derived from a tetracarboxylic anhydride (hereinafter, the structural unit (a) may be abbreviated as "structural unit"). The structural unit (a) is not particularly limited as long as the in-plane orientation index of the PI-based film is within the above-mentioned range, and for example, a structural unit derived from tetracarboxylic anhydride represented by the formula (1) is preferable.

[ in formula (1), Y represents a 4-valent organic group ]

In the formula (1), Y independently of each other represents a 4-valent organic group, preferably a 4-valent organic group having 4 to 40 carbon atoms, and more preferably a 4-valent organic group having 4 to 40 carbon atoms and having a cyclic structure. Examples of the cyclic structure include alicyclic, aromatic and heterocyclic structures. In the case of the aforementioned organic group, the hydrogen atom in the organic group may be substituted with a halogen atom, a hydrocarbon group, an alkoxy group or a halogenated hydrocarbon group, and in this case, the number of carbon atoms of these groups is preferably 1 to 8. The PI-based resin of the present invention may contain a plurality of kinds of Y, and the plurality of kinds of Y may be the same or different from each other. As Y, there may be mentioned: a group or structure represented by the formula (31) to the formula (40); a group in which a hydrogen atom in the group represented by the formula (31) to the formula (40) is substituted with a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, a fluoro group, a chloro group or a trifluoromethyl group; 4-valent hydrocarbon groups having 1 to 8 carbon atoms, and the like.

[ in the formulae (31) to (33), R ¹⁹ ～R ²⁶ R is R ^23’ ～R ^26’ Independently of one another, represents 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, R ¹⁹ ～R ²⁶ R is R ^23’ ～R ^26’ The hydrogen atoms contained in (a) may be substituted with halogen atoms independently of each other,

V ¹ v (V) ² Independently of each other, represent a single bond (whereine+d=1), -O-, -CH ₂ -、-CH ₂ -CH ₂ -、-CH(CH ₃ )-、-C(CH ₃ ) ₂ -、-C(CF ₃ ) ₂ -、-SO ₂ -、-S-、-CO-、-N(R ^j ) -, a part of (a),

(in the formula (a), R ²⁷ ～R ³⁰ Independently of each other, represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms,

d independently of one another represents a single bond, -C (CH) ₃ ) ₂ -or-C (CF) ₃ ) ₂ ，

i represents an integer of 1 to 3,

indicating a connecting key

R ^j A monovalent hydrocarbon group having 1 to 12 carbon atoms which represents a hydrogen atom or a halogen atom,

e and d independently of one another represent an integer from 0 to 2 (where e+d is not 0),

f represents an integer of 0 to 3,

g and h independently of one another represent an integer from 0 to 4,

in the formula (39), Z represents a 2-valent organic group,

s independently of one another represent an integer from 0 to 3,

in the formula (40), R ^a2 Independently of one another, represents a halogen atom or an alkyl, alkoxy, aryl or aryloxy group which may have a halogen atom,

t independently of one another represents an integer from 0 to 3,

represents a bond.

In the PI-based resin in the present invention, Y in the formula (1) preferably contains at least 1 structure selected from the group consisting of structures represented by the formula (31), the formula (32), the formula (33), the formula (39) and the formula (40), more preferably contains at least 1 structure selected from the group consisting of structures containing an ester bond and structures containing a biphenyl skeleton, and even more preferably contains at least 1 structure selected from the group consisting of structures represented by the formula (39) and the formula (40), from the viewpoint of easy improvement of mechanical properties, thermal properties and dielectric characteristics of the PI-based film. In the present specification, the mechanical properties refer to mechanical properties including bending resistance, folding endurance, and elastic modulus, and the mechanical properties are improved, and for example, the bending resistance and/or elastic modulus are improved. The term "thermophysical properties" means thermophysical properties including glass transition temperature (Tg), CTE, little denaturation and deterioration due to heat, and little deformation after heating, and the term "thermophysical properties" means that Tg is high and/or CTE is low, for example. The dielectric characteristics refer to dielectric-related characteristics including Df and Dk, and an increase or an improvement in dielectric characteristics means a decrease in Df and/or Dk.

In the formulas (31) to (33), R ¹⁹ ～R ²⁶ R is R ^23’ ～R ^26’ Independently of each other, represents 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.

Examples of the alkyl group having 1 to 6 carbon atoms include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, 2-methylbutyl, 3-methylbutyl, 2-ethylpropyl, and n-hexyl.

Examples of the alkoxy group having 1 to 6 carbon atoms include methoxy group, ethoxy group, propyloxy group, isopropyloxy group, n-butoxy group, isobutoxy group, sec-butoxy group, t-butoxy group, pentyloxy group, hexyloxy group, cyclohexyloxy group and the like.

Examples of the aryl group having 6 to 12 carbon atoms include phenyl, tolyl, xylyl, naphthyl and biphenyl. R is R ¹⁹ ～R ²⁶ R is R ^23’ ～R ^26’ The hydrogen atoms included in (a) may be substituted with halogen atoms independently of each other, and examples of the halogen atoms include fluorine atoms, chlorine atoms, bromine atoms, and iodine atoms. Among them, R is from the viewpoint of easily improving mechanical properties and thermal properties of the PI-based film ¹⁹ ～R ²⁶ R is R ^23’ ～R ^26’ Independently of each other, a hydrogen atom or an alkyl group having 1 to 6 carbon atoms is preferable, a hydrogen atom or an alkyl group having 1 to 3 carbon atoms is more preferable, and a hydrogen atom is still more preferable.

In the formula (31), V ¹ V (V) ² Independently of one another, represents a single bond (where e+d=1 is excluded), -O-, -CH ₂ -、-CH ₂ -CH ₂ -、-CH(CH ₃ )-、-C(CH ₃ ) ₂ -、-C(CF ₃ ) ₂ -、-SO ₂ -、-S-、-CO-、-N(R ^j ) From the viewpoint of easiness of improvement of mechanical properties and thermal properties of the PI-based film, it is preferable that the formula (a) represents a single bond (excluding e+d=1), -O-, -CH ₂ -、-C(CH ₃ ) ₂ -、-C(CF ₃ ) ₂ -or-CO-, more preferably represents a single bond (wherein e+d=1 is excluded), -O-, -C (CH) ₃ ) ₂ -or-C (CF) ₃ ) ₂ -。R ^j A monovalent hydrocarbon group having 1 to 12 carbon atoms which may be substituted with a halogen atom. Examples of the 1-valent hydrocarbon group having 1 to 12 carbon atoms include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, 2-methylbutyl, 3-methylbutyl, 2-ethylpropyl, n-hexyl, n-heptyl, n-octyl, tert-octyl, n-nonyl, and n-decyl groups, which may be substituted with halogen atoms. The halogen atom may be the same as described above.

In the formula (31), e and d independently represent an integer of 0 to 2 (where e+d is not 0), and preferably represent 0 or 1 in view of easy reduction of Df of the PI-based film. In addition, e+d preferably represents 1. It should be noted that the number of the substrates,in the formula (31), when e is 0, the table ¹ ² When d is 0, it means that 2 benzene rings are not bonded by V.

In the formulas (32) and (33), f represents an integer of 0 to 3, and preferably represents 0 or 1, more preferably represents 0, from the viewpoint of easily lowering Df of the PI-based film.

In the formula (33), g and h independently represent an integer of 0 to 4, and from the viewpoint of easily improving the mechanical properties and thermal properties of the PI-based film, the integer is preferably 0 to 2, and more preferably 0 or 1. In addition, g+h preferably represents an integer of 0 to 2. When f is 1 or more, a plurality of g and h may be the same or different independently from each other.

In the formula (a), R ²⁷ ～R ³⁰ Independently of each other, represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms.

Examples of the alkyl group having 1 to 6 carbon atoms include the alkyl groups having 1 to 6 carbon atoms exemplified above. Among them, R is from the viewpoint of easily improving mechanical properties and thermal properties of the PI-based film ²⁷ ～R ³⁰ Independently of each other, preferably represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, more preferably represents a hydrogen atom.

In the formula (a), D represents a single bond, -C (CH) ₃ ) ₂ -or-C (CF) ₃ ) ₂ -. When D is such a structure, the mechanical properties and thermal properties of the PI-based film can be easily improved. i represents an integer of 1 to 3, and is preferably 1 or 2 in view of easiness in improving the mechanical properties and thermal properties of the PI-based film. When i is 2 or more, a plurality of D and R ²⁷ ～R ³⁰ Independently of each other, may be the same or different.

In the formula (39), Z represents a 2-valent organic group, preferably a 2-valent organic group having 4 to 40 carbon atoms, more preferably a 2-valent organic group having 4 to 40 carbon atoms and having a cyclic structure, even more preferably a 2-valent organic group having 4 to 40 carbon atoms and having an aromatic ring, particularly preferably a 2-valent organic group represented by the formula (Z1), the formula (Z2) or the formula (Z3), and even more preferably a 2-valent organic group represented by the formula (Z1), from the viewpoint of easiness in improving mechanical properties, thermal properties and dielectric properties of the PI-based film.

[ in the formulae (z 1) to (z 3), R ^z11 ～R ^z14 Independently of one another, represent a hydrogen atom, or a 1-valent hydrocarbon group which may have a halogen atom, R ^z2 Independent of each otherRepresents a 1-valent hydrocarbon group which may have a halogen atom, n represents an integer of 1 to 4, j represents an integer of 0 to 3 independently of one another, and x represents a bond]

In the formula (z 1), R ^z11 ～R ^z14 Independently of each other, represent a hydrogen atom, or a 1-valent hydrocarbon group which may have a halogen atom.

Examples of the 1-valent hydrocarbon group include an aromatic hydrocarbon group, an alicyclic hydrocarbon group, and an aliphatic hydrocarbon group.

Examples of the aromatic hydrocarbon group include aryl groups such as phenyl, tolyl, xylyl, naphthyl, and biphenyl.

Examples of the alicyclic hydrocarbon group include cycloalkyl groups such as cyclopentyl and cyclohexyl.

Examples of the aliphatic hydrocarbon group include alkyl groups such as methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, n-pentyl, 2-methylbutyl, 3-methylbutyl, 2-ethylpropyl, n-hexyl, n-heptyl, n-octyl, tert-octyl, n-nonyl, and n-decyl.

Examples of the halogen atom include those described above.

From the viewpoint of easily improving mechanical properties, thermal properties and dielectric characteristics of the PI-based film, R ^z11 ～R ^z14 Independently of each other, an alkyl group having a hydrogen atom or a halogen atom is preferable, an alkyl group having 1 to 6 carbon atoms which has a hydrogen atom or a halogen atom is more preferable, an alkyl group having 1 to 3 carbon atoms which has a hydrogen atom or a halogen atom is further preferable, and a hydrogen atom is particularly preferable.

In the formula (z 1), n represents an integer of 1 to 4, preferably an integer of 1 to 3, more preferably 1 or 2, and particularly preferably 2, from the viewpoint of easily lowering Df of the PI-based film.

In the formula (z 2), R ^z2 The 1-valent hydrocarbon groups which may have halogen atoms are represented independently of each other, and the 1-valent hydrocarbon groups exemplified above are exemplified as the 1-valent hydrocarbon groups. From the viewpoint of easily improving mechanical properties, thermal properties and dielectric characteristics of the PI-based film, R ^z2 Independently of each other, preferably represents an alkyl group which may have a halogen atom, more preferably represents a carbon atom which may have a halogen atomAlkyl having 1 to 6 sub-groups is more preferably an alkyl having 1 to 3 carbon atoms which may have a halogen atom.

In the formula (z 2), j is an integer of 0 to 3 independently of each other, and is preferably 0 or 1, more preferably 0, from the viewpoint of easily lowering Df of the PI-based film.

In the formula (39), R ^a1 Independently of each other, a halogen atom, or an alkyl group, an alkoxy group, an aryl group, or an aryloxy group which may have a halogen atom is preferably independently of each other, 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, from the viewpoint of easily improving the mechanical properties, thermal properties, and dielectric characteristics of the PI film.

Examples of the alkyl group having 1 to 6 carbon atoms, the alkoxy group having 1 to 6 carbon atoms, and the aryl group having 6 to 12 carbon atoms include those exemplified above.

R ^a1 The hydrogen atoms contained in (a) may be substituted with halogen atoms independently of each other, and examples of the halogen atoms include halogen atoms exemplified above. Among them, R is from the viewpoint of easily lowering Df of PI-based film ^a1 Independently of each other, alkyl groups having 1 to 6 carbon atoms are preferable, and alkyl groups having 1 to 3 carbon atoms are more preferable.

In the formula (39), s independently represents an integer of 0 to 3, preferably an integer of 0 to 2, more preferably 0 or 1, from the viewpoint of easily improving the mechanical properties, thermal properties and dielectric characteristics of the PI-based film.

In the formula (40), R ^a2 Independently of each other, a halogen atom, or an alkyl group, an alkoxy group, an aryl group, or an aryloxy group which may have a halogen atom is preferably independently of each other, 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, from the viewpoint of easily improving the mechanical properties, thermal properties, and dielectric characteristics of the PI film.

R ^a2 The hydrogen atoms contained in (a) may be substituted with halogen atoms independently of each other, asThe halogen atom may be exemplified by those exemplified above. Among them, R is from the viewpoint of easily improving mechanical properties, thermal properties and dielectric characteristics of the PI-based film ^a2 The alkyl groups having 1 to 6 carbon atoms are preferably used independently of each other, and the alkyl groups having 1 to 3 carbon atoms are more preferably used.

In the formula (40), t is an integer of 0 to 3 independently of each other, and is preferably an integer of 0 to 2, more preferably 0 or 1, from the viewpoint of improving mechanical properties, thermal properties and dielectric characteristics of the PI-based film.

Specific examples of the structures represented by the formulas (31) to (33), (39) and (40) include the structures represented by the formulas (41) to (56). In these formulae, the term "bond" means a bond.

In one embodiment of the present invention, when at least 1 selected from the group consisting of the structures represented by the formulas (31) to (33), the formulas (39) and the formulas (40) is included as Y in the formula (1), the proportion of the structural unit of the tetracarboxylic acid anhydride represented by at least 1 selected from the group consisting of the structures represented by the formulas (31) to (33), the formulas (39) and the formulas (40) in Y in the formula (1), particularly the proportion of the structural unit of the tetracarboxylic acid anhydride represented by at least 1 selected from the group consisting of the structures represented by the formulas (39) and the formulas (40) in Y in the formula (1), is preferably 30 mol% or more, more preferably 50 mol% or more, further preferably 70 mol% or more, particularly preferably 90 mol% or more, and preferably 100 mol% or less, relative to the total molar amount of the structural unit (a). If the ratio is within the above range, df of the PI-based film is easily reduced. The proportion of the aforementioned structural units can be used, for example ¹ H-NMR measurement may be performed or the ratio of raw materials may be calculated.

(structural unit (A1) derived from tetracarboxylic anhydride containing an ester bond)

In one embodiment of the present invention, the structural unit (a) preferably includes a structural unit (A1) derived from a tetracarboxylic anhydride containing an ester bond (hereinafter, the structural unit (A1) may be abbreviated). If the structural unit (a) contains the structural unit (A1), an ester bond having a molecular orientation is introduced into the PI-based resin, and therefore, in the step of applying the PI-based resin precursor solution to a substrate and imidizing the coating film, it is easy to adjust the X-ray parameters to the above-mentioned range, and it is easy to reduce Df. For the same reason, CTE is easily reduced and dimensional stability of PI-based films is easily improved. Further, even if the imidization temperature is low, for example, 350 ℃ or lower, df tends to be low, and therefore even if the CCL is produced by thermally imidizing a PI-based resin precursor coating film in a layered structure with a copper foil, deterioration of the copper foil surface is easily suppressed, and a CCL having excellent high frequency characteristics is easily obtained.

In the present specification, the in-plane orientation index, the molecular periodicity index, and the in-plane anisotropy index may be collectively referred to as X-ray parameters.

In one embodiment of the present invention, the structural unit (A1) is not particularly limited as long as it contains an ester bond, and the number of ester bonds contained in the structural unit (A1) may be 1 or 2 or more, and from the viewpoint of easily lowering Df of the PI-based film, the structural unit (A1) derived from the tetracarboxylic anhydride represented by the formula (A1) is preferable.

[ in formula (a 1), Z represents a 2-valent organic group,

s independently of one another represent an integer from 0 to 3 ]

R in formula (a 1) ^a1 Independently of each other, a halogen atom, or an alkyl group, an alkoxy group, an aryl group, or an aryloxy group which may have a halogen atom, and independently of each other, 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 is preferable from the viewpoint of easily lowering Df of the PI film.

R ^a1 The hydrogen atoms contained in (a) may be substituted with halogen atoms independently of each other, and examples of the halogen atoms include halogen atoms exemplified above.

Among them, R is from the viewpoint of easy reduction of Df of PI-based film ^a1 The alkyl groups having 1 to 6 carbon atoms are preferably used independently of each other, and the alkyl groups having 1 to 3 carbon atoms are more preferably used.

S in the formula (a 1) independently represents an integer of 0 to 3, preferably 0 or 1, and more preferably 0.

Z in the formula (a 1) represents a 2-valent organic group, and examples of the 2-valent organic group include the 2-valent organic groups exemplified above as the 2-valent organic groups in the formula (39). Among them, from the viewpoint of easily lowering Df of the PI-based film, Z is preferably a 2-valent organic group represented by the formula (Z1), the formula (Z2), or the formula (Z3), and more preferably a 2-valent organic group represented by the formula (Z1).

[ in the formula (z 1) and the formula (z 2), R ^z11 ～R ^z14 Independently of each other, represents a hydrogen atom, or a 1-valent hydrocarbon group which may have a halogen atom,

R ^z2 independently of each other, represents a 1-valent hydrocarbon group which may have a halogen atom,

n represents an integer of 1 to 4,

j independently of one another represents an integer from 0 to 3,

indicating a connection key

In one embodiment of the present invention, R in formula (z 1) ^z11 ～R ^z14 Independently of each other, represent a hydrogen atom, or a 1-valent hydrocarbon group which may have a halogen atom.

Examples of the 1-valent hydrocarbon group include the 1-valent hydrocarbon groups exemplified above.

From the viewpoint of easily lowering Df of PI film, R ^z11 ～R ^z14 Independently of each other, an alkyl group having a hydrogen atom or a halogen atom is preferable, an alkyl group having 1 to 6 carbon atoms having a hydrogen atom or a halogen atom is more preferable, an alkyl group having 1 to 3 carbon atoms having a hydrogen atom or a halogen atom is further preferable, and a hydrogen atom is particularly preferable.

In one embodiment of the present invention, R in formula (z 2) ^z2 The 1-valent hydrocarbon groups which may have halogen atoms are represented independently of each other, and the 1-valent hydrocarbon groups exemplified above are exemplified as the 1-valent hydrocarbon groups. From the viewpoint of easily improving mechanical properties, thermal properties and dielectric characteristics of the PI-based film, R ^z2 Independently of each other, an alkyl group which may have a halogen atom is preferably represented, an alkyl group having 1 to 6 carbon atoms which may have a halogen atom is more preferably represented, and an alkyl group having 1 to 3 carbon atoms which may have a halogen atom is further preferably represented.

In one embodiment of the present invention, R in the formula (z 1) is from the viewpoint of easily lowering Df of the PI film ^z11 ～R ^z14 R in the benzene ring of (C) ^z11 ～R ^z14 At least 1 of them may be a 1-valent hydrocarbon group which may have a halogen atom, but R is preferably ^z11 ～R ^z14 All hydrogen atoms.

J in the formula (z 2) independently represents 0 to 3. In one embodiment of the present invention, j is preferably 0 or 1, more preferably 0, and even more preferably all j are 0, independently of each other, from the viewpoint of easy reduction of Df of PI-based film.

In a preferred embodiment of the present invention, formula (a 1) is preferably represented by formula (a 1') or formula (a 1 ").

If the PI-based resin contains a structural unit derived from a tetracarboxylic anhydride represented by the formula (A1), in particular, the formula (A1 ') or the formula (A1') as the structural unit (A1), df of the obtained PI-based film is easily reduced. Further, even if the imidization temperature is low, for example, 350 ℃ or lower, df tends to be low, and therefore even if the CCL is produced by thermally imidizing a PI-based resin precursor coating film in a layered structure with a copper foil, deterioration of the copper foil surface is easily suppressed, and a CCL having excellent high frequency characteristics is easily obtained.

In one embodiment of the present invention, the content of the structural unit (A1) is preferably 10 mol% or more, more preferably 20 mol% or more, still more preferably 30 mol% or more, still more preferably 35 mol% or more, and particularly preferably 40 mol% or more, based on the total amount of the structural units (a). The content of the structural unit (A1) is preferably 75 mol% or less, more preferably 70 mol% or less, further preferably 65 mol% or less, and particularly preferably 60 mol% or less, based on the total amount of the structural units (a). When the content of the structural unit (A1) is within the above range, the X-ray parameter is easily adjusted to the above range, and Df of the PI-based film is easily reduced. The proportion of the aforementioned structural units can be used, for example ¹ H-NMR measurement may be performed or the ratio of raw materials may be calculated.

(structural unit (A2) derived from tetracarboxylic anhydride having a biphenyl skeleton)

In one embodiment of the present invention, the structural unit (a) preferably includes a structural unit (A2) derived from a tetracarboxylic anhydride containing a biphenyl skeleton (hereinafter, the structural unit (A2) may be abbreviated). If the structural unit (a) includes the structural unit (A2), df of the obtained PI-based film is easily reduced.

In one embodiment of the present invention, the structural unit (A2) is not particularly limited as long as it contains a biphenyl skeleton, and the number of biphenyl skeletons contained in the structural unit (A2) may be 1 or 2 or more. In one embodiment of the present invention, the structural unit (A2) is preferably a structural unit containing a biphenyl skeleton and not containing an ester bond, and in this specification, a structural unit derived from a tetracarboxylic anhydride containing both an ester bond and a biphenyl skeleton is not the structural unit (A2) but is classified as a structural unit (A1) derived from a tetracarboxylic anhydride containing an ester bond.

In one embodiment of the present invention, the structural unit (A2) is preferably a structural unit (A2) derived from a tetracarboxylic anhydride represented by the formula (A2).

t represents an integer of 0 to 3 independently of one another

R in formula (a 2) ^a2 Independently of each other, a halogen atom, or an alkyl group, an alkoxy group, an aryl group, or an aryloxy group which may have a halogen atom, and independently of each other, 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 is preferable from the viewpoint of easily lowering Df of the PI film. Examples of the alkyl group having 1 to 6 carbon atoms, the alkoxy group having 1 to 6 carbon atoms, and the aryl group having 6 to 12 carbon atoms include those exemplified above. R is R ^a2 The hydrogen atoms contained in (a) may be substituted with halogen atoms independently of each other, and examples of the halogen atoms include halogen atoms exemplified above. Among them, R is from the viewpoint of easily lowering Df of PI-based film ^a2 Independently of each other, an alkyl group having 1 to 6 carbon atoms is preferable, and an alkyl group having 1 to 3 carbon atoms is more preferable.

The bonding position of the 2 carboxylic acid anhydrides bonded to the benzene ring constituting the biphenyl skeleton in the formula (a 2) is not particularly limited, and may be 3,4-, or 2, 3-independently of each other based on the single bond bonding the 2 benzene rings, and is preferably 3, 4-from the viewpoint of easily lowering Df of the PI-based film.

In a preferred embodiment of the present invention, formula (a 2) is preferably represented by formula (a 2').

If the PI-based resin contains a structural unit derived from the tetracarboxylic anhydride represented by the formula (A2), in particular, by the formula (A2'), as the structural unit (A2), df of the obtained PI-based film tends to be reduced. Further, even if the imidization temperature is low, for example, 350 ℃ or lower, df tends to be low, and therefore even if the CCL is produced by thermally imidizing a PI-based resin precursor coating film in a layered structure with a copper foil, deterioration of the copper foil surface is easily suppressed, and a CCL having excellent high frequency characteristics is easily obtained.

In one embodiment of the present invention, the content of the structural unit (A2) is preferably 25 mol% or more, more preferably 30 mol% or more, further preferably 35 mol% or more, and particularly preferably 40 mol% or more, based on the total amount of the structural units (a). The content of the structural unit (A2) is preferably 90 mol% or less, more preferably 80 mol% or less, further preferably 70 mol% or less, and particularly preferably 60 mol% or less, based on the total amount of the structural units (a). When the content of the structural unit (A2) is within the above range, the X-ray parameter is easily adjusted to the above range, and Df of the PI-based film is easily reduced. The proportion of the aforementioned structural units can be used, for example ¹ H-NMR measurement may be performed or the ratio of raw materials may be calculated.

(structural unit (A3))

In one embodiment of the present invention, the structural unit (a) may include a structural unit (A3) derived from tetracarboxylic anhydride (hereinafter, may be abbreviated as a structural unit (A3)) other than the structural unit (A1) and the structural unit (A2).

In the present specification, "structural unit (A3) derived from tetracarboxylic anhydride other than structural unit (A1) and structural unit (A2)" refers to structural unit derived from tetracarboxylic anhydride which does not belong to either structural unit (A1) or structural unit (A2), and "content of structural unit (A3)" refers to the total amount of structural units (A3) when a plurality of structural units (A3) are present.

In one embodiment of the present invention, the structural unit (A3) is a structural unit derived from a tetracarboxylic anhydride not containing any one of an ester bond and a biphenyl skeleton, for example, a structural unit derived from a tetracarboxylic anhydride represented by the formula (31) to the formula (38) in the formula (1), and from the viewpoint of easily lowering Df of the PI-based film, a structural unit derived from a tetracarboxylic anhydride represented by the formula (42) to the formula (49) or the formula (53) in the formula (1) is preferable, and a structural unit derived from a tetracarboxylic anhydride represented by the formula (42), the formula (46), the formula (49), the formula (43) or the formula (53) in the formula (1) is more preferable, and a structural unit derived from a tetracarboxylic anhydride represented by the formula (42), the formula (46), the formula (49) or the formula (53) in the formula (1) is more preferable.

In one embodiment of the present invention, when the structural unit (A3) is included, the content thereof may be, for example, 0.01 to 55 mol%, or 0.01 to 40 mol%, preferably 40 mol% or less, more preferably 35 mol% or less, still more preferably 30 mol% or less, particularly preferably 25 mol% or less, and further, usually 0.01 mol% or more, preferably 10 mol% or more, with respect to the total amount of the structural unit (a). When the content of the structural unit (A3) is within the above range, the X-ray parameter is easily adjusted to the above range, and Df of the PI-based film is easily reduced. The proportion of the aforementioned structural units can be used, for example ¹ H-NMR measurement may be performed or the ratio of raw materials may be calculated.

In one embodiment of the present invention, when the structural unit (A3) is contained, preferably a structural unit derived from a tetracarboxylic anhydride represented by the formula (32) and Y in the formula (1), more preferably a structural unit derived from a tetracarboxylic anhydride represented by the formula (32) and Y in the formula (1) is f=0, the content thereof is preferably 10 mol% or more, more preferably 20 mol% or more, still more preferably 30 mol% or more, particularly preferably 40 mol% or more, preferably 90 mol% or less, still more preferably 80 mol% or less, still more preferably 70 mol% or less, and particularly preferably 60 mol% or less, relative to the total amount of the structural unit (a). If the content is within the above range, the X-ray parameters can be easily adjusted to the above range, and Df of the PI-based film can be easily reduced. The proportion of the aforementioned structural units can be used, for example ¹ H-NMR measurement may be performed or the ratio of raw materials may be calculated.

In one embodiment of the present invention, when the structural unit (a) includes the structural units (A1) and (A2), the structural unit (a) preferably satisfies the relationship of the formula (X).

(total amount of structural units (A3)/(total amount of structural units (A1) and structural units (A2)) <1.1 (X)

When the structural unit (a) satisfies the relation of the formula (X), that is, when the value on the left side of the formula (X) is less than 1.1, particularly less than 0.67, df of the obtained PI-based film is easily reduced, and a PI-based film excellent in balance with mechanical properties can be obtained.

In one embodiment of the present invention, the left-hand value of formula (X) is preferably 0.6 or less, more preferably 0.5 or less, even more preferably 0.4 or less, and particularly preferably 0.3 or less, from the viewpoint of easy reduction of Df of the PI-based film. The lower limit of the left value of the formula (X) is not particularly limited, and may be 0 or more.

In one embodiment of the present invention, the structural unit (a) preferably includes a structural unit derived from a tetracarboxylic anhydride represented by the formula (a 2) and/or a structural unit derived from a tetracarboxylic anhydride represented by the formula (32) in the formula (1) in which Y is f=0, from the viewpoint of easily lowering Df of the PI-based film. In one embodiment of the present invention, from the viewpoint of easy reduction of Df of PI-based film, the structural unit (a) preferably contains at least 1 selected from the group consisting of a structural unit derived from tetracarboxylic acid anhydride represented by formula (a 1), a structural unit derived from tetracarboxylic acid anhydride represented by formula (a 2), and a structural unit derived from tetracarboxylic acid anhydride represented by formula (32) in which Y in formula (1) is f=0, more preferably contains a structural unit derived from tetracarboxylic acid anhydride represented by formula (a 2) and/or a structural unit derived from tetracarboxylic acid anhydride represented by formula (32) in which Y in formula (1) is f=0, in addition to a structural unit derived from tetracarboxylic acid anhydride represented by formula (a 1).

(structural unit (B) derived from diamine)

The PI-based resin contains a structural unit (B) derived from a diamine (hereinafter, the structural unit (B) may be abbreviated). The structural unit (B) is not particularly limited as long as the in-plane orientation index of the PI-based film is within the above range, and for example, a structural unit derived from a diamine represented by the formula (2) is preferable.

H ₂ N-X-NH ₂ (2)

[ in formula (2), X represents a 2-valent organic group ]

In the formula (2), X represents a 2-valent organic group, preferably a 2-valent organic group having 2 to 100 carbon atoms. Examples of the 2-valent organic group include a 2-valent aromatic group and a 2-valent aliphatic group, and examples of the 2-valent aliphatic group include a 2-valent acyclic aliphatic group and a 2-valent cyclic aliphatic group. Among them, from the viewpoint of easiness in improving the mechanical properties and thermal properties of the PI-based film, a cyclic aliphatic group having a valence of 2 and an aromatic group having a valence of 2 are preferable, and an aromatic group having a valence of 2 is more preferable. In the case of a 2-valent organic group, the hydrogen atom in the organic group may be substituted with a halogen atom, a hydrocarbon group, an alkoxy group or a halogenated hydrocarbon group, and in this case, the number of carbon atoms of these groups is preferably 1 to 8. In the present specification, the 2-valent aromatic group is a 2-valent organic group having an aromatic group, and an aliphatic group or other substituent may be included in a part of the structure thereof. The aliphatic group having 2 valences is a 2-valent organic group having an aliphatic group, and may contain other substituents in a part of its structure, but may not contain an aromatic group.

In one embodiment of the present invention, the PI-based resin may contain a plurality of kinds of X, and the plurality of kinds of X may be the same as or different from each other. Examples of X in the formula (2) include: a group (structure) represented by the formula (60) to the formula (65); and a group in which a hydrogen atom in the group represented by the formula (60) to the formula (65) is substituted with a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, a fluoro group, a chloro group or a trifluoromethyl group.

[ in the formula (60) and the formula (61), R ^a R is R ^b Independently of one another, represents a halogen atom or an alkyl, alkoxy, aryl or aryloxy group which may have a halogen atom, R ^a R is R ^b The hydrogen atoms contained in (a) may be substituted with halogen atoms independently of each other,

w independently of one another represents a single bond, -O-, -CH ₂ -、-CH ₂ -CH ₂ -、-CH(CH ₃ )-、-C(CH ₃ ) ₂ -、-C(CF ₃ ) ₂ -、-COO-、-OOC-、-SO ₂ -, -S-, -CO-or-N (R) ^c )-，R ^c Represents a monovalent hydrocarbon group having 1 to 12 carbon atoms which may be substituted with a halogen atom,

t represents an integer of 0 to 4, u represents an integer of 0 to 4, n represents an integer of 0 to 4,

in the formula (62), the ring A represents a cycloalkane ring having 3 to 8 carbon atoms,

R ^d represents an alkyl group having 1 to 20 carbon atoms,

r represents an integer of 0 or more and (the number of carbon atoms of ring A is-2) or less,

s1 and S2 independently of each other represent an integer of 0 to 20,

In the formulae (60) to (65), the term "represents a bond". ]

Examples of the other X in the formula (2) include 2-valent acyclic aliphatic groups such as linear or branched alkylene groups, e.g., ethylene, 1, 3-propylene, 1, 4-butylene (tramethylene group), 1, 5-pentylene, 1, 6-hexylene, 1, 2-propylene, 1, 2-butanediyl, 1, 3-butanediyl, 1, 12-dodecanediyl, 2-methyl-1, 2-propanediyl, 2-methyl-1, 3-propanediyl, and the like. The hydrogen atom in the 2-valent acyclic aliphatic group may be substituted with a halogen atom, and the carbon atom may be replaced with a heteroatom, such as an oxygen atom, a nitrogen atom, or the like.

Among them, X in the formula (2) is preferably a structure represented by the formula (60) or the formula (61), and more preferably a structure represented by the formula (60) in view of easiness in improving mechanical properties, thermal properties and dielectric characteristics of the PI-based film.

In the formulae (60) and (61), the bond between each benzene ring and each cyclohexane ring may be bonded to any position of the ortho-, meta-or para-or alpha-, beta-or gamma-position based on-W-, or a single bond connecting each benzene ring and each cyclohexane ring, and may be preferably bonded to the meta-or para-or beta-or gamma-position, and may be more preferably bonded to the para-or gamma-position, from the viewpoint of easily lowering Df of the PI-based film and easily improving the dimensional stability.

R ^a R is R ^b Independently of each other, represents a halogen atom, or an alkyl group, an alkoxy group, an aryl group, or an aryloxy group which may have a halogen atom, preferably represents a halogen atom, or an alkyl group, an alkoxy group, or an aryl group which may have a halogen atom, more preferably represents 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, the alkoxy group having 1 to 6 carbon atoms, and the aryl group having 6 to 12 carbon atoms include those exemplified above. R is R ^a R is R ^b The hydrogen atoms included in (a) may be substituted with halogen atoms independently of each other, and examples of the halogen atoms include fluorine atoms, chlorine atoms, bromine atoms, and iodine atoms. R is from the viewpoint of easily lowering Df of PI film and easily improving dimensional stability ^a R is R ^b The alkyl group having 1 to 6 carbon atoms or the fluoroalkyl group having 1 to 6 carbon atoms is preferable independently of each other, and the alkyl group having 1 to 6 carbon atoms which does not contain fluorine is more preferable, the alkyl group having 1 to 3 carbon atoms which does not contain fluorine is still more preferable, and the methyl group is particularly preferable, from the viewpoint of improving the adhesion to a substrate such as copper foil.

In the formulae (60) and (61), t and u are each an integer of 0 to 4, and are preferably an integer of 0 to 2, more preferably 0 or 1, from the viewpoint of easy reduction of Df of the PI-based film and easy improvement of dimensional stability.

In the formula (60) and the formula (61), W independently represents a single bond, -O-, -CH ₂ -、-CH ₂ -CH ₂ -、-CH(CH ₃ )-、-C(CH ₃ ) ₂ -、-C(CF ₃ ) ₂ -、-COO-、-OOC-、-SO ₂ -, -S-, -CO-or-N (R) ^c ) In view of easy reduction of Df of PI film and easy improvement of dimensional stability, it preferably represents-O-, -CH ₂ -、-C(CH ₃ ) ₂ -、-C(CF ₃ ) ₂ -, -COO-, -OOC-or-CO-, from the viewpoint of facilitating further improvement of adhesion to a substrate such as copper foil, it is more preferable that the substrate represents a single bond or a-O-、-CH ₂ -or-C (CH) ₃ ) ₂ -, further preferably represents-O-or-C (CH) ₃ ) ₂ -。R ^c 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 monovalent hydrocarbon groups having 1 to 12 carbon atoms exemplified above.

In the formulas (60) and (61), n is an integer of 0 to 4, preferably an integer of 0 to 3, and more preferably 1 to 3, from the viewpoint of easy reduction of Df of the PI-based film and easy improvement of dimensional stability. When n is 2 or more, a plurality of W, R ^a And t may be the same or different from each other, and the positions of the connecting bonds of the benzene rings based on-W-may be the same or different.

In the case where the PI-based resin in the present invention contains 2 or more structures represented by the formulae (60) and (61) as X in the formula (2), W, n, and R in one of the formulae (60) and (61) ^a 、R ^b T and u independently of one another can be selected from W, n, R in the other formulae (60) and (61) ^a 、R ^b T and u are the same or different.

In the formula (62), the ring A represents a cycloalkane ring having 3 to 8 carbon atoms. Examples of the cycloalkane ring include a cyclopropane ring, a cyclobutane ring, a cyclopentane ring, a cyclohexane ring, a cycloheptane ring, and a cyclooctane ring, and preferred examples thereof include cycloalkane rings having 4 to 6 carbon atoms. In the ring a, the respective connection keys may or may not be adjacent to each other. For example, when the ring a is a cyclohexane ring, the 2 linkages may be in a positional relationship of α, β or γ, and may preferably be in a positional relationship of β or γ.

R in formula (62) ^d Represents an alkyl group having 1 to 20 carbon atoms. Examples of the alkyl group having 1 to 20 carbon atoms include R ⁷ ～R ¹⁸ The above-exemplified hydrocarbon group having 1 to 20 carbon atoms is preferably an alkyl group having 1 to 10 carbon atoms. R in the formula (62) represents an integer of 0 or more and "the number of carbon atoms of the ring A is 2 or less". r is preferably 0 or more, and preferably 4 or less. S1 and S2 in the formula (62) independently represent an integer of 0 to 20. S1 and S2 are each independently preferably 0 or more, more preferably 2 or more, preferably 15The following is given.

Specific examples of the structures represented by the formulas (60) to (62) include structures represented by the formulas (71) to (92). In these formulae, the term "bond" means a bond.

In a preferred embodiment of the present invention, when at least 1 structural unit derived from the diamine represented by the formula (60) and the diamine represented by the formula (61) is contained as X in the formula (2), the proportion of the structural units derived from the diamine represented by the formula (60) and the diamine represented by the formula (61) in X in the formula (2), particularly the proportion of the structural units derived from the diamine represented by the formula (60) in n being 1 and W representing a single bond, is preferably 25 mol% or more, more preferably more than 30 mol%, still more preferably 50 mol% or more, still more preferably 70 mol% or more, particularly preferably 90 mol% or more, and preferably 100 mol% or less, relative to the total molar amount of the structural units (B). If the ratio of the structural units derived from the diamine represented by the formula (60) and the formula (61) in X in the formula (2), particularly the ratio of the structural units derived from the diamine represented by the formula (60) in which at least 1W represents a single bond is within the above-mentioned range, df of the PI-based film is easily reduced and dimensional stability is easily improved. The proportion of the aforementioned structural units can be used, for example ¹ H-NMR measurement may be performed or the ratio of raw materials may be calculated.

(structural unit (B1) derived from diamine having a biphenyl skeleton)

In one embodiment of the present invention, the structural unit (B) preferably includes a structural unit (B1) derived from a diamine having a biphenyl skeleton (hereinafter, the structural unit (B1) may be abbreviated). In the PI-based resin having the structural unit (B) including the structural unit (B1), df of the obtained PI-based film is easily reduced, and thus transmission loss of a circuit including the obtained PI-based film is easily reduced.

In one embodiment of the present invention, the structural unit (B1) is not particularly limited as long as it contains a biphenyl skeleton, and the number of biphenyl skeletons contained in the structural unit (B1) may be 1 or 2 or more. In one embodiment of the present invention, the structural unit (B1) is preferably a structural unit (B1) derived from a diamine represented by the formula (B1) from the viewpoint of easily lowering Df of the PI-based film.

p represents an integer of 0 to 4 ]

In the formula (b 1), R ^b1 The halogen atom, or the alkyl group, alkoxy group, aryl group, or aryloxy group which may have a halogen atom is preferably independently represented by a halogen atom, or the alkyl group, alkoxy group, or aryl group which may have a halogen atom, more preferably by a halogen atom, alkyl group having 1 to 6 carbon atoms, alkoxy group having 1 to 6 carbon atoms, or aryl group having 6 to 12 carbon atoms, from the viewpoint of easiness in lowering Df of PI-based film and easiness in improving dimensional stability. Examples of the alkyl group having 1 to 6 carbon atoms, the alkoxy group having 1 to 6 carbon atoms, and the aryl group having 6 to 12 carbon atoms include those exemplified above. R is R ^b1 The hydrogen atoms included in (a) may be substituted with halogen atoms independently of each other, and examples of the halogen atoms include the same halogen atoms as described above. R is from the viewpoint of easily lowering Df of PI film and easily improving dimensional stability ^b1 The alkyl group having 1 to 6 carbon atoms or the fluoroalkyl group having 1 to 6 carbon atoms is preferable independently of each other, and the alkyl group having 1 to 6 carbon atoms which does not contain fluorine is more preferable, the alkyl group having 1 to 3 carbon atoms which does not contain fluorine is still more preferable, and the methyl group is particularly preferable, from the viewpoint of improving the adhesion to a substrate such as copper foil.

In the formula (b 1), p independently represents an integer of 0 to 4, and is preferably an integer of 0 to 2, more preferably 0 or 1, from the viewpoint of easy reduction of Df of the PI-based film and easy improvement of dimensional stability.

In the formula (b 1), the-NH groups bonded to the benzene rings ₂ The radicals being based on single bonds linking the benzene ringsAnd is bonded to any position among ortho-, meta-or para-or alpha-, beta-or gamma-positions, respectively, and may be bonded to meta-or para-or beta-or gamma-positions, or may be bonded to para-or gamma-positions, respectively, from the viewpoint of easy reduction of Df of PI-based films and easy improvement of dimensional stability.

In a preferred embodiment of the present invention, formula (b 1) is preferably represented by formula (b 1').

If the PI-based resin contains a structural unit derived from a diamine represented by the formula (B1), in particular, the formula (B1'), as the structural unit (B1), df of the obtained PI-based film tends to be lowered. Further, even if the imidization temperature is low, for example, 350 ℃ or lower, df tends to be low, and therefore even if the CCL is produced by thermally imidizing a PI-based resin precursor coating film in a layered structure with a copper foil, deterioration of the copper foil surface is easily suppressed, and a CCL having excellent high frequency characteristics is easily obtained.

In one embodiment of the present invention, the content of the structural unit (B1) (preferably the structural unit (B1)) is preferably 25 mol% or more, more preferably more than 30 mol%, further preferably 40 mol% or more, further more preferably 60 mol% or more, particularly preferably 70 mol% or more, particularly preferably 80 mol% or more, further particularly preferably 90 mol% or more, with respect to the total amount of the structural units (B). If the content of the structural unit (B1) (preferably the structural unit (B1)) is not less than the lower limit, df is easily lowered. The upper limit of the content of the structural unit (B1) (preferably the structural unit (B1)) is not particularly limited, and may be 100 mol% or less with respect to the total amount of the structural units (B). The proportion of the aforementioned structural units can be used, for example ¹ H-NMR measurement may be performed or the ratio of raw materials may be calculated.

(structural unit (B2))

In one embodiment of the present invention, the structural unit (B) preferably contains a structural unit derived from a compound having 2 or more aromatic rings,And each aromatic ring is bonded to a structural unit (B2) of a diamine (hereinafter, the structural unit (B2) may be abbreviated as "structural unit"). As the 2-valent organic group in the structural unit (B2), for example, examples thereof include alkylene groups which may have halogen atoms, -O-, -COO-, -OOC-, -SO ₂ -, -S-, -CO-or-N (R) ^c ) -etc., R ^c A monovalent hydrocarbon group having 1 to 12 carbon atoms which may be substituted with a halogen atom. Among them, the 2-valent organic group in the structural unit (B2) is preferably-O-, -CH ₂ -、-CH ₂ -CH ₂ -、-CH(CH ₃ )-、-C(CH ₃ ) ₂ -、-C(CF ₃ ) ₂ -、-COO-、-OOC-、-SO ₂ -, -S-, -CO-or-N (R) ^c )-。

In one embodiment of the present invention, the structural unit (B) preferably includes a structural unit (B2) (hereinafter, the structural unit (B2) may be abbreviated as "structural unit (B2)") derived from a diamine represented by the formula (B2) as the structural unit (B2).

[ in formula (b 2), R ^b2 Independently of one another, represents a halogen atom or an alkyl, alkoxy, aryl or aryloxy group which may have a halogen atom,

w independently of one another represents-O-, -CH ₂ -、-CH ₂ -CH ₂ -、-CH(CH ₃ )-、-C(CH ₃ ) ₂ -、-C(CF ₃ ) ₂ -、-COO-、-OOC-、-SO ₂ -, -S-, -CO-or-N (R) ^c )-，R ^c Represents a hydrogen atom, a monovalent hydrocarbon group having 1 to 12 carbon atoms which may be substituted with a halogen atom, m represents an integer of 1 to 4,

q represents an integer of 0 to 4 independently of each other

If the structural unit (B) includes the structural unit (B2), particularly the structural unit (B2), df of the obtained PI-based film is easily reduced, and as a result, transmission loss of an electronic circuit including the obtained PI-based film is easily reduced.

In the formula (b 2), R ^b2 Independent of each otherThe term "C1-C6 alkoxy" refers to a halogen atom, or an alkyl group, an alkoxy group, an aryl group or an aryloxy group which may have a halogen atom, and preferably refers to 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, the alkoxy group having 1 to 6 carbon atoms, and the aryl group having 6 to 12 carbon atoms include those exemplified above. R is R ^b2 The hydrogen atoms included in (a) may be substituted with halogen atoms independently of each other, and examples of the halogen atoms include the same halogen atoms as described above. R is from the viewpoint of easily lowering Df of PI film and easily improving dimensional stability ^b2 The alkyl group having 1 to 6 carbon atoms or the fluoroalkyl group having 1 to 6 carbon atoms is preferable independently of each other, and the alkyl group having 1 to 6 carbon atoms which does not contain fluorine is more preferable, the alkyl group having 1 to 3 carbon atoms which does not contain fluorine is still more preferable, and the methyl group is particularly preferable, from the viewpoint of improving the adhesion to a substrate such as copper foil.

In the formula (b 2), q independently represents an integer of 0 to 4, and is preferably an integer of 0 to 2, more preferably 0 or 1, from the viewpoint of easy reduction of Df of the PI-based film and easy improvement of dimensional stability.

In the formula (b 2), W independently of one another represents-O-, -CH ₂ -、-CH ₂ -CH ₂ -、-CH(CH ₃ )-、-C(CH ₃ ) ₂ -、-C(CF ₃ ) ₂ -、-COO-、-OOC-、-SO ₂ -, -S-, -CO-or-N (R) ^c ) In view of easy reduction of Df of PI film and easy improvement of dimensional stability, it preferably represents-O-, -CH ₂ -、-C(CH ₃ ) ₂ -、-C(CF ₃ ) ₂ -, -COO-, -OOC-or-CO-, from the viewpoint of facilitating further improvement of adhesion to a substrate such as copper foil, it is more preferable to represent-O-, -CH ₂ -or-C (CH) ₃ ) ₂ -, further preferably represents-O-or-C (CH) ₃ ) ₂ -。R ^c A monovalent hydrocarbon group having 1 to 12 carbon atoms which may be substituted with a halogen atom. Examples of the 1-valent hydrocarbon group having 1 to 12 carbon atoms include the 1-valent hydrocarbon groups having 1 to 12 carbon atoms exemplified above, which may be substituted with halogen atoms. As the halogen atom, a halogen atom is used,the same halogen atoms as described above can be used.

In the formula (b 2), m is an integer of 1 to 4, preferably an integer of 1 to 3, more preferably 2 or 3, from the viewpoint of easily lowering Df of the PI-based film and easily improving dimensional stability. In the formula (b 2), a plurality of W, R ^b2 And q may be the same or different from each other, by-NH of each benzene ring ₂ The positions of-W-as references may be the same or different.

In the formula (b 2), -W-may be represented by-NH of each benzene ring ₂ The bonding may be preferably at the ortho-or para-position, or at the beta-or gamma-position, or at any of the alpha-, beta-or gamma-positions, for the sake of easy reduction of Df of the PI-based film and easy improvement of dimensional stability.

In one embodiment of the present invention, from the viewpoint of easily lowering Df of the PI-based film and easily improving adhesion between the PI-based film and the copper foil, it is preferable that m in formula (b 2) is 3 and W independently represents-O-or-C (CH) ₃ ) ₂ More preferably, formula (b 2) is represented by formula (b 2').

If the PI-based resin contains the structural unit (b 2), particularly the structural unit derived from the diamine represented by the formula (b 2 '), the storage elastic modulus at 280 ℃ (hereinafter, sometimes referred to as E' at 280 ℃) tends to be easily reduced, and as a result, the Df of the PI-based film tends to be easily reduced, and a PI-based film excellent in adhesion to copper foil is easily obtained. Further, even if the imidization temperature is low, for example, 350 ℃ or lower, df tends to be low, and therefore even if the CCL is produced by thermally imidizing a PI-based resin precursor coating film in a layered structure with a copper foil, deterioration of the copper foil surface is easily suppressed, and a CCL having excellent high frequency characteristics is easily obtained.

In one embodiment of the present invention, the structural unit (b 2) may contain a structural unit derived from a diamine in which m is 1 and W represents-O-in the formula (b 2), in addition to or in place of the structural unit derived from a diamine in the formula (b 2').

In one embodiment of the present invention, the content of the structural unit (B2) is preferably 0 mol% or more, more preferably 0.3 mol% or more, still more preferably 0.5 mol% or more, still more preferably 0.8 mol% or more, particularly preferably 1 mol% or more, particularly preferably 5 mol% or more, and most preferably 8 mol% or more, based on the total amount of the structural units (B). When the content of the structural unit (B2) is not less than the lower limit, the adhesion between the obtained PI-based film and a base material such as copper foil is easily improved. The upper limit of the content of the structural unit (B2) is preferably 75 mol% or less, more preferably 60 mol% or less, still more preferably 40 mol% or less, still more preferably 30 mol% or less, and particularly preferably 20 mol% or less, based on the total amount of the structural units (B). When the content of the structural unit (B2) is not more than the upper limit, mechanical properties such as CTE tend to be easily improved. The proportion of the aforementioned structural units can be used, for example ¹ H-NMR measurement may be performed or the ratio of raw materials may be calculated.

(structural unit (B3))

The PI-based resin may contain a diamine-derived structural unit (B3) (hereinafter, the structural unit (B3) may be abbreviated as "structural unit (B3)") other than the structural unit (B1) and the structural unit (B2). Examples of the structural unit (B3) include a structural unit derived from a diamine having m of 0 in the formula (B2), a structural unit derived from a diamine represented by the formulae (61) to (64) in the formula (2), and the like, and among them, a structural unit derived from a diamine represented by the formula (74) in the formula (2) (a structural unit derived from p-phenylenediamine) is preferable. In the present specification, "the diamine-derived structural unit (B3) other than the structural unit (B1) and the structural unit (B2)" means a diamine-derived structural unit different from either the structural unit (B1) or the structural unit (B2).

In one embodiment of the present invention, when the structural unit (B) includes the structural unit (B3), the content of the structural unit (B3) is preferably 25 mol% or less, more preferably 20 mol% or less, still more preferably 10 mol% or less, and still more preferably 0.01 mol% or more, based on the total amount of the structural units (B).

In one embodiment of the present invention, the PI-based resin may contain a halogen atom, preferably a fluorine atom, which can be introduced by using the halogen atom-containing substituent described above, for example. When the PI-based resin contains fluorine atoms, the relative dielectric constant of the obtained PI-based film is easily reduced. Examples of the fluorine-containing substituent preferably used for containing a fluorine atom in the PI-based resin include a fluoro group and a trifluoromethyl group.

In another embodiment of the present invention, it is preferable that the PI-based resin does not contain fluorine atoms, in order to easily improve the adhesion between the PI-based film obtained and a substrate such as copper foil. Further, if the PI-based resin contains fluorine, the interaction between molecular chains tends to be weakened, and therefore if the PI-based resin does not contain fluorine atoms, the X-ray parameters tend to be easily adjusted to the above-described range, and Df of the obtained PI-based film tends to be easily reduced.

When the PI-based resin contains halogen atoms, the content of halogen atoms, particularly fluorine atoms, in the PI-based resin is preferably 0.1 to 35% by mass, more preferably 0.1 to 30% by mass, still more preferably 0.1 to 20% by mass, and particularly preferably 0.1 to 10% by mass, based on the mass of the PI-based resin. If the content of halogen atoms is not less than the lower limit, the heat resistance and dielectric characteristics of the obtained PI film can be easily improved. If the content of the halogen atom is not more than the upper limit, it is advantageous in terms of cost, and the CTE of the PI-based film is easily reduced, and the synthesis of the PI-based resin is easily performed.

In one embodiment of the present invention, the imidization ratio of the PI-based resin is preferably 90% or more, more preferably 93% or more, still more preferably 95% or more, and usually 100% or less. The imidization ratio is preferably not less than the lower limit described above from the viewpoint of easiness in improvement of mechanical properties, thermal properties, and dielectric characteristics. The imidization ratio represents a ratio of the molar amount of imide bonds in the PI-based resin to a value 2 times the molar amount of structural units derived from the tetracarboxylic acid compound in the PI-based resin. When the PI-based resin contains a tricarboxylic acid compound, the imidization rate represents a ratio of a molar amount of imide bonds in the PI-based resin to a total of a value 2 times a molar amount of structural units derived from the tetracarboxylic acid compound and a molar amount of structural units derived from the tricarboxylic acid compound in the PI-based resin. The imidization rate can be obtained by IR method, NMR method, or the like.

In one embodiment of the present invention, the weight average molecular weight (hereinafter, the weight average molecular weight may be referred to as Mw) of the PI-based resin in terms of polystyrene is preferably 100,000 or more, more preferably more than 100,000, further preferably 110,000 or more, further more preferably 120,000 or more, particularly preferably 130,000 or more, preferably 1,000,000 or less, more preferably 700,000 or less, further preferably 500,000 or less, and particularly preferably 300,000 or less. When Mw is not less than the lower limit, mechanical properties such as folding endurance can be easily improved. If the Mw is equal to or less than the upper limit, the film-forming property is advantageous from the viewpoint of the processability.

In one embodiment of the present invention, the ratio (Mw/Mn) of the Mw to the number average molecular weight (hereinafter, the number average molecular weight may be referred to as Mn) of the PI-based resin is preferably 3.5 or more, more preferably 4.0 or more, still more preferably 4.2 or more, particularly preferably 4.5 or more, still more preferably 4.7 or more, preferably 8.0 or less, more preferably 7.0 or less, still more preferably 6.0 or less, and particularly preferably 5.5 or less, in terms of polystyrene conversion, from the viewpoint of easiness in improvement of bending resistance. The Mw and Mn can be measured by gel permeation chromatography (hereinafter, may be referred to as GPC) and calculated as standard polystyrene.

In one embodiment of the present invention, the PI-based resin preferably has an E' at 280 ℃ of less than 3×10 from the viewpoint of easy reduction of Df of PI-based film ⁸ Pa, more preferably 3X 10 ⁸ Pa or less, more preferably 2X 10 ⁸ Pa or less, and more preferably 1.5X10 ⁸ Pa or less, particularly preferably 1×10 ⁸ Pa or less, particularly preferably 0.8X10 ⁸ Pa or below. In addition, from the viewpoint of easily suppressing deformation during processing of PI-based filmsThe E' of the PI-based resin at 280℃is preferably 1X 10 ⁴ Pa or more, more preferably 1×10 ⁵ Pa or more, more preferably 1×10 ⁶ Pa or more. The PI-based resin E' can be measured by dynamic viscoelasticity measurement, and can be measured by the method described in examples, for example.

The E' of the PI-based resin at 280℃can be adjusted by appropriately adjusting the types of the constituent units constituting the PI-based resin and their constitution, the molecular weight of the PI-based resin and the production method, particularly the imidization conditions, and the like, and can be adjusted within the ranges described as preferable in the present specification, for example.

In one embodiment of the present invention, the PI-based resin has a Tg of preferably 290 ℃ or less, more preferably less than 290 ℃, still more preferably 280 ℃ or less, still more preferably 275 ℃ or less, particularly preferably 260 ℃ or less, particularly preferably 250 ℃ or less, and still more preferably 240 ℃ or less, from the viewpoint of easy reduction of Df of the obtained PI-based film. Further, from the viewpoint of easily lowering Df of the PI-based film and easily improving heat resistance of the PI-based film, tg of the PI-based resin is preferably 200 ℃ or higher, more preferably 202 ℃ or higher, and even more preferably 205 ℃ or higher. The Tg of the PI-based resin can be measured by dynamic viscoelasticity measurement, and can be measured by the method described in examples, for example.

The Tg of the PI-based resin can be adjusted by appropriately adjusting the types of the structural units constituting the PI-based resin and the constitution thereof, and the molecular weight and the production method of the PI-based resin, particularly the imidization conditions, and the like, and can be adjusted to the ranges described as preferable modes in the following description, for example, so as to fall within the above ranges.

In one embodiment of the present invention, if the E' and Tg of the PI-based resin at 280 ℃ are in the above-described ranges, the PI-based resin is likely to have a desirable higher order structure in which the rotational movement is suppressed, and therefore, it is estimated that the rotation of the polar groups in the PI-based resin can be suppressed and the loss of electric energy by thermal movement can be reduced, thereby easily lowering Df of the PI-based film.

The polyamide acid, which is the PI-based resin precursor, starts imidization at about 200 ℃. In general, the degree of freedom of the molecular structure of the polyamic acid is high, but after imidization, the degree of freedom of the molecular structure is relatively rigid and is reduced. If the Tg of the PI-based resin is preferably 200 to 290 ℃, the thermal imidization temperature exceeds the Tg of the PI-based resin during the imidization, and therefore the amic acid moiety and the imide moiety move simultaneously to form a higher order structure, and therefore the resin as a whole tends to form a desirable higher order structure in which the rotational movement is suppressed. In addition, it is considered that E' is less than 3X 10 if it is preferable to use the catalyst at 280 ℃ ⁸ Pa, the imide moiety can be sufficiently flexibly moved when forming the higher order structure, and therefore, the resin as a whole is particularly easy to form an ideal higher order structure in which rotational movement is suppressed. As a result, even if the imidization temperature is low, for example, 350 ℃ or lower, df can be reduced, and therefore, even if the CCL is produced by thermally imidizing a PI-based resin precursor coating film in a laminated structure with a copper foil, degradation of the copper foil surface can be suppressed, and therefore, a CCL having excellent high frequency characteristics can be obtained.

In one embodiment of the present invention, the content of the PI-based resin in the PI-based film is preferably 60 mass% or more, more preferably 70 mass% or more, still more preferably 80 mass% or more, and particularly preferably 90 mass% or more, relative to the mass of the PI-based film of the present invention. The upper limit of the content of the PI-based resin is not particularly limited, but is, for example, 100 mass% or less, preferably 99 mass% or less, and more preferably 95 mass% or less, based on the mass of the PI-based film. When the content of the PI-based resin is within the above range, the mechanical properties, thermal properties and dielectric properties are easily improved.

The PI-based film of the present invention may contain a filler as needed. Examples of the filler include metal oxide particles such as silica and alumina, inorganic salt particles such as calcium carbonate, and polymer particles such as fluororesin and cycloolefin polymer. The filler may be used alone or in combination of 2 or more. When the filler is contained, the content thereof is preferably 50 mass% or less, more preferably 40 mass% or less, further preferably 30 mass% or less, and preferably 0.01 mass% or more, relative to the mass of the PI-based film.

In one embodiment of the present invention, the PI-based film of the present invention may contain an additive as required. Examples of the additives include antioxidants, flame retardants, crosslinking agents, surfactants, compatibilizers, imidization catalysts, weather-proofing agents, lubricants, antiblocking agents, antistatic agents, antihalation agents, dripless, pigments, and the like. The additives may be used singly or in combination of two or more. The content of each additive may be appropriately selected within a range that does not impair the effects of the present invention, and in the case where each additive is contained, the total content thereof is preferably 7 mass% or less, more preferably 5 mass% or less, further preferably 4 mass% or less, and still more preferably 0.001 mass% or more, relative to the mass of the PI-based film.

[ method for producing polyimide film ]

The method for producing the PI-based film of the present invention is not particularly limited, and for example, the PI-based film can be produced by a method comprising the following steps.

A step of applying a PI-based resin precursor solution containing a structural unit (a) derived from a tetracarboxylic anhydride and a structural unit (B) derived from a diamine to a substrate; and

and imidizing the PI-based resin precursor by heat treatment at 200 ℃ to 500 ℃.

< coating Process of polyimide-based resin precursor solution >

(preparation of PI-based resin precursor solution)

The PI-based resin precursor solution contains a PI-based resin precursor containing a structural unit (a) derived from a tetracarboxylic anhydride and a structural unit (B) derived from a diamine, and a solvent, and can be prepared by mixing the PI-based resin precursor with the solvent. In one embodiment of the present invention, the reaction solution containing the PI-based resin precursor obtained by synthesizing the PI-based resin precursor may be used as a PI-based resin precursor solution by appropriately diluting the reaction solution with a solvent as needed.

The PI-based resin precursor in the present invention can be obtained by reacting a tetracarboxylic anhydride with a diamine. In addition to the tetracarboxylic acid compound, a dicarboxylic acid compound and a tricarboxylic acid compound may be reacted.

Examples of the tetracarboxylic anhydride used for the synthesis of the PI-based resin precursor include: aromatic tetracarboxylic acid compounds such as aromatic tetracarboxylic acid dianhydride; aliphatic tetracarboxylic acid compounds such as aliphatic tetracarboxylic acid dianhydride, and the like. The tetracarboxylic acid compounds may be used alone or in combination of 2 or more. The tetracarboxylic acid compound may be a tetracarboxylic acid compound analogue such as an acyl chloride compound, in addition to the dianhydride.

Examples of the tetracarboxylic acid compound include tetracarboxylic acid anhydrides represented by the above formula (1), and preferably tetracarboxylic acid anhydrides represented by the formula (a 1), tetracarboxylic acid anhydrides represented by the formula (a 2), and tetracarboxylic acid anhydrides represented by the formula (32) in the formula (1) are given.

Specific examples of the tetracarboxylic acid compound include pyromellitic dianhydride (hereinafter, sometimes referred to as PMDA), 4' - (4, 4' -isopropylidenediphenoxy) diphthalic anhydride (hereinafter, sometimes referred to as BPADA), 1,4,5, 8-naphthalene tetracarboxylic acid dianhydride, 3',4' -biphenyl tetracarboxylic acid dianhydride (hereinafter, sometimes referred to as BPDA), 4' - (hexafluoroisopropylidene) diphthalic dianhydride (hereinafter sometimes referred to as 6 FDA), 4' -oxydiphthalic dianhydride (hereinafter, sometimes described as ODPA), 2', 3' -, 2,3', 4' -or 3,3',4' -benzophenone tetracarboxylic dianhydride, 2,3',3,4' -biphenyl tetracarboxylic dianhydride, 2',3,3' -biphenyltetracarboxylic dianhydride, p-phenylene bis (trimellitic acid monoester acid dianhydride) (hereinafter, sometimes referred to as TAHQ), an esterified product of trimellitic anhydride and 2,2', 3', 5' -hexamethyl-4, 4' -biphenol (hereinafter, sometimes referred to as TMPBP), 4' -bis (1, 3-dioxo-1, 3-dihydroisobenzofuran-5-ylcarbonyloxy) biphenyl (hereinafter, sometimes described as BP-TME), 2,3',3,4' -diphenyl ether tetracarboxylic dianhydride, bis (2, 3-dicarboxyphenyl) ether dianhydride, 3",4" -p-terphenyltetracarboxylic dianhydride, 2, 3",4" -p-terphenyltetracarboxylic dianhydride, 2", 3" -p-terphenyltetracarboxylic dianhydride, 2, 2-bis (2, 3-dicarboxyphenyl) -propane dianhydride, 2-bis (3, 4-dicarboxyphenyl) -propane dianhydride, bis (2, 3-dicarboxyphenyl) methane dianhydride, bis (3, 4-dicarboxyphenyl) methane dianhydride, 1-bis (2, 3-dicarboxyphenyl) ethane dianhydride, 1-bis (3, 4-dicarboxyphenyl) ethane dianhydride, 1,2,7,8-, 1,2,6, 7-phenanthrenetetracarboxylic acid dianhydride, 1,2,9,10-phenanthrenetetracarboxylic acid dianhydride, 2-bis (3, 4-dicarboxyphenyl) tetrafluoropropane dianhydride, 1,2,4, 5-cyclohexane tetracarboxylic acid dianhydride (hereinafter, sometimes referred to as HPMDA), 2,3,5, 6-cyclohexane tetracarboxylic dianhydride, 2,3,6, 7-naphthalene tetracarboxylic dianhydride, 1,2,5, 6-naphthalene tetracarboxylic dianhydride, cyclopentane-1, 2,3, 4-tetracarboxylic dianhydride, 4' -bis (2, 3-dicarboxyphenoxy) diphenylmethane dianhydride, 1,2,3, 4-cyclobutane tetracarboxylic dianhydride (hereinafter sometimes referred to as CBDA), norbornane-2-spiro-alpha ' -spiro-2 ' -norbornane-5, 5',6,6' -Tetracarboxylic acid anhydride, p-phenylene bis (trimellitic acid ester anhydride), 3',4' -diphenylsulfone tetracarboxylic acid dianhydride, 2,3,6, 7-anthracene tetracarboxylic acid dianhydride, 4, 8-dimethyl-1, 2,3,5,6, 7-hexahydronaphthalene-1, 2,5, 6-tetracarboxylic acid dianhydride, 2, 6-dichloronaphthalene-1, 4,5, 8-tetracarboxylic acid dianhydride, 2, 7-dichloronaphthalene-1, 4,5, 8-tetracarboxylic acid dianhydride, 2,3,6, 7-tetrachloronaphthalene-1, 4,5, 8-tetracarboxylic acid dianhydride, 2,3,6, 7-tetrachloronaphthalene-2, 3,6, 7-tetracarboxylic dianhydride, 1,4,5, 8-tetrachloronaphthalene-1, 4,5, 8-tetracarboxylic dianhydride, 1,4,5, 8-tetrachloronaphthalene-2, 3,6, 7-tetracarboxylic dianhydride, 2,3,8, 9-perylene tetracarboxylic dianhydride, 3,4,9, 10-perylene tetracarboxylic dianhydride, 4,5,10, 11-perylene tetracarboxylic dianhydride, 5,6,11, 12-perylene tetracarboxylic dianhydride, pyrazine-2, 3,5, 6-tetracarboxylic dianhydride, pyrrolidine-2, 3,4, 5-tetracarboxylic dianhydride, thiophene-2, 3,4, 5-tetracarboxylic dianhydride, bis (2, 3-dicarboxyphenyl) sulfone dianhydride, bis (3, 4-dicarboxyphenyl) sulfone dianhydride, and the like. Among them, BPDA, TAHQ, PMDA, BP-TME is preferable, and BPDA, TAHQ, BP-TME is more preferable, from the viewpoint that Df of the obtained PI film is easily lowered even if imidization temperature is low. These tetracarboxylic acid compounds may be used singly or in combination of two or more.

Examples of the diamine compound used for the synthesis of the PI-based resin precursor include aliphatic diamine, aromatic diamine, and a mixture thereof. In the present embodiment, the term "aromatic diamine" means a diamine having an aromatic ring, and may include an aliphatic group or other substituent in a part of its structure. The aromatic ring may be a single ring or a condensed ring, and examples thereof include a benzene ring, a naphthalene ring, an anthracene ring, and a fluorene ring, but is not limited thereto. Among them, benzene rings are preferable. The term "aliphatic diamine" means a diamine having an aliphatic group, and may include other substituents in a part of its structure, but does not have an aromatic ring.

Examples of the diamine compound include the diamine compound represented by the above formula (2), and preferably include the diamine compound represented by the formula (b 1) and the diamine compound represented by the formula (b 2).

Specific examples of the diamine compound include 1, 4-diaminocyclohexane, 4' -diamino-2, 2' -dimethylbiphenyl (hereinafter, sometimes referred to as m-Tb), 4' -diamino-3, 3' -dimethylbiphenyl, 2' -bis (trifluoromethyl) -4,4' -diaminobiphenyl (hereinafter, sometimes referred to as TFMB), 4' -diaminodiphenyl ether, 1, 3-bis (3-aminophenoxy) benzene (hereinafter, sometimes referred to as 1, 3-APB), 1, 4-bis (4-aminophenoxy) benzene (hereinafter, sometimes referred to as 1, 4-APB), 1, 3-bis (4-aminophenoxy) benzene, 2-bis [4- (4-aminophenoxy) phenyl ] propane (hereinafter sometimes referred to as BAPP), 2' -dimethyl-4, 4' -diaminobiphenyl, 3' -dihydroxy-4, 4' -diaminobiphenyl, 2-bis- [4- (3-aminophenoxy) phenyl ] propane, bis [4- (4-aminophenoxy) ] biphenyl, bis [4- (3-aminophenoxy) biphenyl, bis [1- (4-aminophenoxy) ] biphenyl, bis [1- (3-aminophenoxy) ] biphenyl, bis [4- (4-aminophenoxy) phenyl ] methane, bis [4- (3-aminophenoxy) phenyl ] methane, 3,3 '-methylenedianiline, 4' -diaminodiphenylpropane, 3 '-diaminodiphenylpropane, 4' -diaminodiphenylethane 3,3 '-diaminodiphenylethane, 4' -diaminodiphenylmethane, 3 '-diaminodiphenylmethane 3,3' -methylenedianiline, 4 '-diaminodiphenylpropane, 3' -diaminodiphenylpropane, 4 '-diaminodiphenylethane, 3' -diaminodiphenylethane, 4 '-diaminodiphenylmethane, 3' -diaminodiphenylmethane 3, 3-diaminodiphenyl ether, 3,4 '-diaminodiphenyl ether, benzidine, 3' -diaminobiphenyl, 3 '-dimethoxybenzidine, 4 "-diaminopara-terphenyl, 3" -diaminopara-terphenyl, m-phenylenediamine, p-phenylenediamine (hereinafter, sometimes described as p-PDA), resorcinol-bis (3-aminophenyl) ether, 4' - [1, 4-phenylenedi (1-methylethylidene) ] diphenylamine, 4,4' - [1, 3-phenylenebis (1-methylethylidene) ] dianiline, bis (p-aminocyclohexyl) methane, bis (p- β -amino-tert-butylphenyl) ether, bis (p- β -methyl- δ -aminopentyl) benzene, p-bis (2-methyl-4-aminopentyl) benzene, p-bis (1, 1-dimethyl-5-aminopentyl) benzene, 1, 5-diaminonaphthalene, 2, 6-diaminonaphthalene, 2, 4-bis (β -amino-tert-butyl) toluene, 2, 4-diaminotoluene, m-xylene-2, 5-diamine, p-xylene-2, 5-diamine, m-xylylenediamine, p-xylylenediamine, piperazine 4,4' -diamino-2, 2' -bis (trifluoromethyl) dicyclohexylmethane, 4' -diaminop-terphenyl, bis (4-aminophenyl) terephthalate, 1, 4-bis (4-aminophenoxy) -2, 5-di-tert-butylphenyl, 4' - (1, 3-phenylenediisopropylidene) diphenylamine, 1, 4-bis [2- (4-aminophenyl) -2-propyl ] benzene, 2, 4-diamino-3, 5-diethyltoluene, 2, 6-diamino-3, 5-diethyltoluene, 4' -bis (3-aminophenoxy) biphenyl, 4' - (hexafluoropropylene) diphenylamine, 1, 2-diaminoethane, 1, 3-diaminopropane, 1, 4-diaminobutane, 1, 5-diaminopentane, 1, 6-diaminohexane, 1, 2-diaminopropane, 1, 2-diaminobutane, 1, 3-diaminobutane, 2-methyl-1, 2-diaminopropane, 2-methyl-1, 3-diaminopropane, 1, 3-bis (aminomethyl) cyclohexane, 1, 4-bis (aminomethyl) cyclohexane, norbornanediamine, 2 '-methoxy-4, 4' -diaminobenzanilide, bis [4- (4-aminophenoxy) phenyl ] sulfone bis [4- (3-aminophenoxy) phenyl ] sulfone, 9-bis [4- (4-aminophenoxy) phenyl ] fluorene, 9-bis [4- (3-aminophenoxy) phenyl ] fluorene, 4 '-diaminodiphenyl sulfide, 3' -diaminodiphenyl sulfide, 4 '-diaminodiphenyl sulfone, 3,3' -diaminodiphenyl sulfone, 2, 5-diamino-1, 3, 4-oxadiazole, bis [4,4'- (4-aminophenoxy) ] anilide, bis [4,4' - (3-aminophenoxy) ] anilide, 2, 6-diaminopyridine, 2, 5-diaminopyridine, and the like. Among them, m-Tb, BAPP, and the like are preferable from the viewpoint that Df of the obtained PI-based film is easily reduced even if the imidization temperature is low. The diamine compound may be used singly or in combination of two or more.

The PI-based resin precursor may be a product obtained by reacting a tetracarboxylic acid, a dicarboxylic acid, a tricarboxylic acid, and an anhydride and a derivative thereof, in addition to the tetracarboxylic acid compound used for the synthesis of the resin precursor, within a range that does not impair the physical properties of the PI-based film.

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

Examples of the dicarboxylic acid compound include aromatic dicarboxylic acids, aliphatic dicarboxylic acids, and similar acid chloride compounds and acid anhydrides thereof, and 2 or more kinds of dicarboxylic acid compounds and acid anhydrides may be used in combination. Specific examples thereof include terephthalic acid; isophthalic acid; naphthalene dicarboxylic acid; 4,4' -biphenyl dicarboxylic acid; 3,3' -biphenyl dicarboxylic acid; dicarboxylic acid compound of chain hydrocarbon having 8 or less carbon atoms and 2 benzoic acids each having a single bond, -O-, -CH ₂ -、-C(CH ₃ ) ₂ -、-C(CF ₃ ) ₂ -、-SO ₂ -or phenylene-linked compounds, and acid chloride compounds thereof.

Examples of the tricarboxylic acid compound include aromatic tricarboxylic acid, aliphatic tricarboxylic acid, and similar acid chloride compounds and acid anhydrides thereof, and 2 or more kinds of tricarboxylic acid compounds and aliphatic tricarboxylic acid can be used in combination. Specific examples thereof include anhydrides of 1,2, 4-benzenetricarboxylic acid; 2,3, 6-naphthalene tricarboxylic acid-2, 3-anhydride; phthalic anhydride and benzoic acid through single bond, -O-, -CH ₂ -、-C(CH ₃ ) ₂ -、-C(CF ₃ ) ₂ -、-SO ₂ -or phenylene linked compounds.

In the production of the PI-based resin precursor, the amounts of diamine compound, tetracarboxylic acid compound, dicarboxylic acid compound, and tricarboxylic acid compound used may be appropriately selected according to the desired ratio of each structural unit of the PI-based resin.

In the present invention, the total number of moles of diamine compound used relative to 1 mole of the total amount of tetracarboxylic acid compound is defined as an amine ratio. In a preferred embodiment of the present invention, the amine ratio is preferably 0.90 mol or more, and preferably 0.999 mol or less, based on 1 mol of the total amount of the tetracarboxylic acid compounds. In another embodiment, the amine ratio is preferably 1.001 mol or more, and preferably 1.10 mol or less, based on 1 mol of the total amount of the tetracarboxylic acid compounds.

In one embodiment of the present invention, when the amine ratio is 1 or less, the amine ratio is preferably 0.90 to 0.999 mole, more preferably 0.95 to 0.997 mole, and still more preferably 0.97 to 0.995 mole.

In one embodiment of the present invention, when the amine ratio is 1 or more, the amine ratio is preferably 1.001 to 1.1 mol, more preferably 1.002 to 1.05 mol, and still more preferably 1.003 to 1.03 mol.

If the amine ratio is close to 1.0 mole, the molecular weight tends to be rapidly increased during synthesis, and if the amine ratio is greatly different from 1.0 mole, the molecular weight of the obtained PI-based resin tends to be easily decreased. If the molecular weight increases rapidly, the PI-based resin tends to grow unevenly in the synthetic material, and the physical properties of the PI-based resin tend to be difficult to stabilize. On the other hand, if the molecular weight is too low, the mechanical properties tend to be lowered.

The reaction temperature of the diamine compound and the tetracarboxylic acid compound is preferably 50℃or lower, more preferably 40℃or lower, and still more preferably 30℃or lower. If the reaction temperature is not higher than the upper limit, df of the obtained PI-based film tends to be easily lowered, and this tendency is particularly remarkable in PI-based films containing PI-based resins containing ester bonds, particularly PI-based resins containing the structural unit (A1). The reaction temperature of the diamine compound and the tetracarboxylic acid compound is preferably 5℃or higher, more preferably 10℃or higher, and still more preferably 15℃or higher. If the reaction temperature is not less than the lower limit, the reaction rate tends to be easily increased, and the polymerization time tends to be shortened.

The reaction time is not particularly limited, and may be, for example, about 0.5 to 72 hours, preferably 3 to 24 hours. If the reaction time is within the above range, df of the obtained PI film tends to be lowered even if the imidization temperature is low.

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

In one embodiment of the present invention, the boiling point of the solvent used for the reaction between the diamine compound and the tetracarboxylic acid compound is preferably 230 ℃ or less, more preferably 200 ℃ or less, and even more preferably 180 ℃ or less, from the viewpoint that Df of the obtained PI-based film is easily reduced even if the imidization temperature is low. In addition, the boiling point of the solvent is preferably 100 ℃ or higher, more preferably 120 ℃ or higher, from the viewpoint of easy reduction of Df of the obtained PI-based film.

The reaction of the diamine compound and the tetracarboxylic acid compound may be carried out under an inert atmosphere such as a nitrogen atmosphere or an argon atmosphere or under reduced pressure, as required, and is preferably carried out under an inert atmosphere such as a nitrogen atmosphere or an argon atmosphere while stirring in a strictly controlled dehydration solvent.

The solvent contained in the PI-based resin precursor solution may be exemplified by a solvent used for the reaction of the diamine compound and the tetracarboxylic acid compound, and is preferably a lactone-based solvent, an amide-based solvent, or a pyrrolidone-based solvent, and more preferably an amide-based solvent. In one embodiment of the present invention, the boiling point of the solvent contained in the PI-based resin precursor solution is preferably 230 ℃ or less, more preferably 200 ℃ or less, still more preferably 180 ℃ or less, and particularly preferably 170 ℃ or less, from the viewpoint that Df of the obtained PI-based film is easily reduced even if the imidization temperature is low. In addition, the boiling point of the solvent is preferably 100 ℃ or higher, more preferably 120 ℃ or higher, from the viewpoint of easy reduction of Df of the obtained PI-based film.

The content of the PI-based resin precursor contained in the PI-based resin precursor solution is preferably 8 mass% or more, more preferably 10 mass% or more, further preferably 12 mass% or more, particularly preferably 13 mass% or more, and further preferably 30 mass% or less, more preferably 25 mass% or less, further preferably 23 mass% or less, particularly preferably 20 mass% or less, relative to the total amount of the PI-based resin precursor solution. When the content of the PI-based resin precursor is within the above range, the processability in film formation is excellent.

(coating of polyimide-based resin precursor solution)

The PI-based resin precursor solution coating step is a step of forming a coating film by applying the PI-based resin precursor solution to a substrate.

In the coating step, a PI-based resin precursor solution is applied to a substrate by a known coating method or a known coating method to form a coating film. Examples of known coating methods include bar coating, reverse coating, roll coating such as gravure coating, die coating, comma coating, lip coating, spin coating, screen printing, spray coating, dip coating, spray coating, curtain coating, slit coating, and casting. When the PI-based resin precursor solution is applied or coated on the substrate, a single layer of PI-based resin precursor solution may be applied to the substrate, or a plurality of layers of PI-based resin precursor solution may be applied to the substrate. In the case of coating a plurality of layers of PI-based resin precursor solutions on a substrate, the coating may be performed in a plurality of times and dried, or a plurality of layers may be simultaneously coated.

Examples of the base material include a metal plate (e.g., copper plate) such as a metal foil (e.g., copper foil), a SUS plate such as a SUS foil or a SUS tape, a glass substrate, a PET film, a PEN film, a PI-based resin film other than the PI-based film of the present invention, a polyamide-based resin film, and the like. Among them, copper plates, SUS plates, glass substrates, PET films, PEN films, and the like are preferable from the viewpoint of excellent heat resistance, and copper plates, SUS plates, glass substrates, PET films, and the like are more preferable from the viewpoints of adhesion to films and cost.

< imidization Process >

The imidization step is a step of imidizing the PI-based resin precursor applied to the substrate by heat treatment at 200 ℃ to 500 ℃.

In one embodiment of the present invention, the imidization step is preferably the following step: before imidization of the PI-based resin precursor, the PI-based resin precursor solution applied to the substrate is heated and dried at a relatively low temperature, and the obtained PI-based resin precursor-containing dried film is imidized by heat treatment at 200 ℃ to 500 ℃.

In one embodiment of the present invention, the PI-based film may be obtained by imidizing a dried film of the PI-based resin precursor on the substrate, or the dried film of the PI-based resin precursor may be peeled off from the substrate, and the dried film peeled off from the substrate may be imidized to obtain the PI-based film.

In one embodiment of the present invention, the drying temperature of the PI-based resin precursor applied to the substrate is not particularly limited as long as it is in a temperature range where the solvent can be dried and solidified, and is preferably lower than 300 ℃, more preferably lower than 260 ℃, still more preferably lower than 200 ℃, still more preferably lower than 180 ℃, and further preferably higher than 50 ℃, more preferably higher than 80 ℃, still more preferably higher than 100 ℃ from the viewpoint of avoiding surface roughness due to rapid drying and suppressing wrinkles, kinks and the like generated during processing.

In one embodiment of the present invention, the PI-based resin precursor of the present invention can reduce Df of the obtained PI-based film even when imidized at a low temperature. The heat treatment temperature in the imidization step, that is, the imidization temperature is preferably 500 ℃ or less, more preferably 400 ℃ or less, further preferably 350 ℃ or less, further more preferably 340 ℃ or less, particularly preferably 330 ℃ or less, particularly preferably 310 ℃ or less, and most preferably 300 ℃ or less. When the imidization temperature is equal to or lower than the upper limit, oxidation degradation of the resin or the like is less likely to occur, and CCL having excellent high frequency characteristics is easily obtained. In addition, from the viewpoint of easily and sufficiently improving the imidization rate, the imidization temperature is preferably 200 ℃ or higher, more preferably 210 ℃ or higher, and further preferably 220 ℃ or higher. In addition, from the viewpoint of easy obtaining of a smooth film, it is preferable to heat stepwise. For example, the imidization may be performed by heating at a relatively low temperature of 50 to 300 ℃ to remove the solvent, and then heating the mixture to a temperature ranging from 200 ℃ to 500 ℃, preferably from 200 ℃ to 400 ℃, more preferably from 200 ℃ to 350 ℃. In one embodiment of the present invention, the PI-based film of the present invention preferably contains a PI-based resin obtained by imidizing a PI-based resin precursor by heat treatment at 200 ℃ to 500 ℃, preferably 200 ℃ to 400 ℃, more preferably 200 ℃ to 350 ℃.

In one embodiment of the present invention, the reaction time in imidization is preferably 30 minutes to 24 hours, more preferably 1 to 12 hours. In one embodiment of the present invention, the time for maintaining the temperature of 200 ℃ or higher is preferably 10 to 90 minutes, more preferably 15 to 70 minutes, and even more preferably 20 to 50 minutes. When the reaction time at 200 ℃ or higher in imidization is within the above range, the imidization rate is easily improved sufficiently, oxidation degradation of the resin is easily prevented, and the dielectric characteristics and bending resistance of the obtained PI-based film are easily improved.

After imidization, the coating film formed on the substrate is peeled off from the substrate, whereby a PI-based film can be obtained. In one embodiment of the present invention, in the case where the base material is copper foil, the PI-based film may be formed without peeling the coating film from the copper foil, and the obtained laminated film in which the PI-based film is laminated on the copper foil may be used for CCL.

When the film of the present invention is a multilayer film, it can be produced by a multilayer film forming method such as a coextrusion process, an extrusion lamination process, a thermal lamination process, or a dry lamination process.

[ laminated film ]

The PI film of the present invention has a low Df and can therefore be suitably used for forming a metal-clad laminate for FPC. Accordingly, a laminated film including a PI layer and a metal foil layer using the PI-based film of the present invention as a PI layer is included. In one embodiment of the present invention, the laminated film of the present invention may include a metal foil layer on only one side of the PI layer, or may include metal foil layers on both sides of the PI layer.

In one embodiment of the present invention, examples of the metal foil include copper foil, SUS foil, and aluminum foil, and copper foil is preferable from the viewpoints of conductivity and metalprocessability.

Since the PI-based film of the present invention has a low Df and can be suitably used for forming CCL having excellent high frequency characteristics, in a preferred embodiment of the present invention, the laminated film of the present invention is preferably a laminated film comprising a copper foil layer on one or both surfaces of the PI-based film of the present invention.

In one embodiment of the present invention, the thickness of the metal foil layer, particularly the copper foil layer, is preferably 1 μm or more, more preferably 5 μm or more, and is preferably 100 μm or less, more preferably 50 μm or less, still more preferably 30 μm or less, particularly preferably 20 μm or less, from the viewpoint of easiness in making the circuit finer and easiness in improving the folding endurance. The thickness of the metal foil layer, particularly the copper foil layer, can be measured using a film thickness meter or the like. In the case where the PI film includes metal foil layers, particularly copper foil layers, on both surfaces thereof, the thicknesses of the metal foil layers, particularly copper foil layers, may be the same or different from each other.

In one embodiment of the present invention, the thickness of the laminated film is preferably 5 μm or more, more preferably 10 μm or more, further preferably 15 μm or more, preferably 100 μm or less, more preferably 80 μm or less, further preferably 60 μm or less. The thickness of the laminated film can be measured by a film thickness meter or the like.

The laminated film of the present invention may include other layers such as a functional layer in addition to the PI-based film and the metal foil layer, particularly the copper foil layer. The functional layer may be a thermoplastic PI-based resin layer containing a thermoplastic PI-based resin, an adhesive layer, or the like. The functional layer may be used singly or in combination of two or more.

In one embodiment of the present invention, the laminate film of the present invention may be a double-layer metal-clad laminate comprising a metal foil layer and a PI layer, or may be a three-layer metal-clad laminate comprising a metal foil layer, a PI layer, and an adhesive layer, and is preferably a double-layer metal-clad laminate comprising no adhesive layer from the viewpoints of heat resistance, dimensional stability, and weight reduction.

In a preferred embodiment of the present invention, the PI-based film of the present invention has a low Df even when the imidization temperature is low, and therefore, even when a laminated film in which a metal foil is a copper foil is produced by thermal imidization of a PI-based resin precursor coating film on the copper foil, deterioration of the copper foil surface can be suppressed. Therefore, in a preferred embodiment of the present invention, the laminated film of the present invention has excellent high frequency characteristics even if it does not include an adhesive layer.

In one embodiment of the present invention, the PI-based film of the present invention may be directly in contact with the metal foil layer, particularly the copper foil layer, or may be interposed between the PI-based film and the metal foil layer, particularly the copper foil layer, and then the PI-based film and the metal foil layer, particularly the copper foil layer, may be directly in contact with each other from the viewpoint of improving mechanical properties and thermal properties.

The functional layer that can be interposed between the PI-based film of the present invention and the metal foil layer can be a thermoplastic PI layer. The PI film of the present invention or the thermoplastic PI layer as a functional layer is preferable from the viewpoint of easiness in improvement of mechanical properties and thermal properties, and a layer directly contacting a metal foil layer, particularly a copper foil layer.

[ method for producing laminated film ]

The present invention also includes a method for producing a laminated film, the method comprising the steps of:

imidizing the PI-based resin precursor by heat treatment at 200 ℃ to 500 ℃ inclusive, thereby forming the PI-based film of the present invention on the substrate.

In the method for producing a laminated film of the present invention, "the step of applying a PI-based resin precursor solution containing a structural unit (a) derived from a tetracarboxylic acid anhydride and a structural unit (B) derived from a diamine to a substrate" and "the step of imidizing a PI-based resin precursor by heat treatment at 200 ℃ to 500 ℃ inclusive to form a PI-based film of the present invention on a substrate" are applicable to the same description as that described in the item [ method for producing a polyimide-based film ] concerning each step.

In one embodiment of the present invention, the substrate is preferably a metal foil, and particularly preferably a copper foil. The same applies to the description relating to the metal foil, particularly the copper foil, as described in the item [ laminated film ].

The laminated film of the present invention can be produced by a method other than the above method, for example, the following method: a PI-based resin precursor solution containing a structural unit (a) derived from tetracarboxylic acid anhydride and a structural unit (B) derived from diamine is applied to a substrate other than the metal foil contained in the laminated film, and dried, and the dried film of PI-based resin precursor thus obtained is peeled off from the substrate, and the peeled dried film of PI-based resin precursor is bonded to the metal foil. As a method for bonding the dried film of the PI-based resin precursor to the metal foil, a method based on pressurization, a lamination method using a heat roller, or the like may be used, or imidization of the PI-based resin precursor may be performed simultaneously in the bonding step.

[ Flexible printed Circuit Board ]

The PI-based film of the present invention can reduce transmission loss of a circuit including the PI-based film, and can be suitably used as an FPC substrate material. Accordingly, the present invention also includes an FPC substrate comprising the PI-based film of the present invention.

Examples (example)

The present invention will be described more specifically with reference to examples and comparative examples, but the present invention is not limited to the examples.

Abbreviations used in the examples and comparative examples represent the following compounds.

BPDA:3,3', 4' -biphenyltetracarboxylic dianhydride

TAHQ: para-phenylene bis (trimellitic acid monoester acid dianhydride)

BP-TME:4,4' -bis (1, 3-dioxo-1, 3-dihydroisobenzofuran-5-ylcarbonyloxy) biphenyl

PMDA: pyromellitic dianhydride

m-Tb:4,4 '-diamino-2, 2' -dimethylbiphenyl

BAPP:2, 2-bis [4- (4-aminophenoxy) phenyl ] propane

[ Synthesis of polyimide resin precursor ]

Example 1

m-Tb 17.95g (84.5 mmol) and BAPP 0.35g (0.9 mmol) were dissolved in 284g of DMAc, followed by addition of 19.38g (42.3 mmol) of TAHQ and stirring at 20℃for 1 hour under nitrogen atmosphere. Then, 12.44g (42.3 mmol) of BPDA was added thereto and stirred at 20℃for 24 hours under a nitrogen atmosphere to obtain a PI resin precursor composition. The molar ratio of diamine monomer used relative to acid dianhydride monomer was 1.01.

Examples 2 to 8 and comparative example 1

PI resin precursor compositions were obtained in the same manner as in example 1, except that the types of monomers and the monomer compositions used were changed as shown in table 1. The order of addition of the monomers is not particularly described, and the diamines are added in the order of diamines derived from the structural units (B1), (B2) and (B3) and the acid dianhydrides are added in the order of acid dianhydrides derived from the structural units (A1), (A2) and (A3).

[ production of polyimide film ]

The PI resin precursor compositions obtained in examples 2 to 8 and comparative example 1 were diluted appropriately in a range where the content of PI resin precursor was 10 mass% or more, using a solvent used in the synthesis of PI resin precursor, and the viscosity was adjusted to 40,000cps or less, to prepare PI resin precursor solutions. The PI resin precursor solutions were subjected to film formation under any one of the following film formation conditions 1 to 4 as shown in table 1, respectively, to obtain PI films formed of PI resins. In example 4, the azimuthal distribution in the measurement of the in-plane orientation index is shown in fig. 2, the diffraction intensity distribution in the measurement of the molecular periodicity index is shown in fig. 4, and the azimuthal distribution in the measurement of the in-plane anisotropy index is shown in fig. 6.

< conditions for film formation 1>

The PI resin precursor solution was cast on a glass substrate, and a coating film of the PI resin precursor solution was molded at a linear speed of 0.4 m/min using an applicator. The coating film was heated at 120℃for 30 minutes, and the obtained film was peeled off from the glass substrate, followed by fixing the film to a metal frame. The film fixed to the metal frame was heated from 30 to 270 ℃ over 19 minutes in an atmosphere having an oxygen concentration of 7%, and then cooled to 200 ℃ over 35 minutes, thereby producing a PI film. The time for maintaining the temperature of 220 ℃ or higher was 23 minutes. The time for maintaining the temperature of 200℃or higher was 34 minutes.

< conditions for film formation 2>

The PI resin precursor solution was cast on a glass substrate, and a coating film of the PI resin precursor solution was molded at a linear speed of 0.4 m/min using an applicator. The coating film was heated at 120℃for 30 minutes, and the obtained film was peeled off from the glass substrate, followed by fixing the film to a metal frame. The film fixed to the metal frame was heated from 30 to 320 ℃ over 9 minutes in an atmosphere having an oxygen concentration of 1%, and then heated at 320 ℃ for 6 minutes, cooled to 200 ℃ over 15 minutes, to prepare a PI film. The time for maintaining the temperature of 220 ℃ or higher was 21 minutes. The time for maintaining the temperature of 200℃or higher was 25 minutes.

< conditions for film formation 3>

The PI resin precursor solution was cast on a glass substrate, and a coating film of the PI resin precursor solution was molded at a linear speed of 0.4 m/min using an applicator. The coating film was heated at 120℃for 30 minutes, and the obtained film was peeled off from the glass substrate, followed by fixing the film to a metal frame. The film fixed to the metal frame was heated from 30 to 320 ℃ over 5 minutes in an atmosphere having an oxygen concentration of 1%, and then heated at 320 ℃ for 5 minutes, cooled to 200 ℃ over 15 minutes, to prepare a PI film. The time for maintaining the temperature of 220 ℃ or higher was 17 minutes. The time for maintaining the temperature of 200℃or higher was 21 minutes.

< conditions for film formation 4>

The PI resin precursor solution was cast on the roughened surface side (surface roughness; rz=1.3 μm) of an electrolytic copper foil (JX metal, JXEFL-BHM thickness of 12 μm), and a coating film of the PI resin precursor solution was molded at a line speed of 0.4 m/min using an applicator. The coating film was heated at 120℃for 30 minutes and dried. Then, the laminated film of the copper foil and the precursor was fixed to a metal frame, and after 9 minutes of heating from 30 ℃ to 320 ℃ in an atmosphere having an oxygen concentration of 1%, heating was performed at 320 ℃ for 6 minutes, and cooling was performed to 200 ℃ for 15 minutes, thereby producing a laminated film of the PI film and the copper foil. The time for maintaining the temperature of 220 ℃ or higher was 21 minutes. The time for maintaining the temperature of 200℃or higher was 25 minutes.

The obtained laminated film of PI film and copper foil was immersed in a large volume of 40 mass% aqueous solution of ferric chloride at room temperature for 10 minutes, and after visual confirmation that no copper remained, it was dried at 80 ℃ for 1 hour to obtain an individual PI film.

[ Synthesis of polyimide resin precursor and production of polyimide film ]

Comparative example 2

m-Tb 70.33g (331 mmol) was dissolved in 720g of NMP, followed by adding 73.06g (248 mmol) of BPDA73.94 g (83 mmol) of TAHQ and stirring at room temperature under nitrogen atmosphere for 1 hour. Then, the mixture was stirred at 60℃for 20 hours to obtain a PI resin precursor composition. Further, the Mw of the PI resin precursor in terms of polystyrene was 91,000, and the Mn was 27,000. The PI resin precursor composition was diluted with NMP as appropriate to adjust the viscosity, thereby preparing a PI resin precursor solution, and the PI resin precursor solution was subjected to film formation under the aforementioned film formation condition 1, to obtain a PI film.

The resulting PI film had a thickness of 30 μm, dk of 3.45, df of 0.0040, index E of 0.0074, and CTE of 38.2ppm. In addition, the Tg of the PI resin was 255℃and E' at 280℃was 5.53X 10 ⁸ Pa。

Further, tg was found from the storage elastic modulus curve using the tangent method to be 230 ℃. The in-plane orientation index of the obtained PI film was 57.3, the molecular periodicity index was 7.55, the in-plane anisotropy index a was 1.0, and the in-plane anisotropy index B was 1.1.

The PI films obtained in examples and comparative examples were measured and evaluated. The measurement and evaluation methods are described below.

< determination of glass transition temperature Tg >

The Tg of the PI resins obtained in examples and comparative examples was determined by measuring PI films as follows.

The measurement was performed under the following test samples and conditions using a dynamic viscoelasticity measuring apparatus (IT Keisoku Seigyo co., ltd., DVA-220) to obtain a tan δ curve as a ratio of a value of Storage modulus (E') to a value of Loss modulus (E "). The peak of the tan delta curve was taken as the highest point of the Tg.

Test piece: rectangular parallelepiped having a length of 40mm, a width of 5mm, and a thickness of 30 μm (the thickness varies depending on the film used)

Experimental mode: single frequency, constant speed heating

The experimental mode is as follows: stretching

Sample holding interval length: 15mm of

Determination of the onset temperature: room temperature to 342 DEG C

Heating rate: 5 ℃/min

Frequency: 10Hz

Static/dynamic stress ratio: 1.8

The main collected data:

(1) Storage modulus of elasticity (E')

(2) Loss modulus of elasticity (Loss modulus, E')

(3)tanδ(E”/E’)

< measurement of storage elastic modulus (E') >

E' at 280℃of the PI resins obtained in examples and comparative examples was obtained by measuring dynamic viscoelasticity in the same manner as the Tg.

< measurement of X-ray >

(1) In-plane orientation index

The PI films obtained in examples and comparative examples were subjected to transmission wide-angle X-ray diffraction measurement under the following conditions.

Device name: nanover of Rigaku small-angle and wide-angle X-ray scattering/diffracting device

Detector: pichatus 100k

X-ray source: cu-K alpha ray

Voltage: 40kV (kilovolt)

Current: 20mA

Camera length: 70mm of

Exposure time: for 10 minutes

Beam diameter: 0.25mm

Specifically, 4 sheets of film are overlapped in the ND direction so that the MD direction coincides. The overlapping films were cut with a trimming knife (trimming knife) so that the width in the MD direction was 1cm and the width in the TD direction was 1mm, to obtain test pieces for measurement. Next, as shown in fig. 1, a measurement test piece 1a is set in the X-ray apparatus so that the irradiation direction of the X-rays is parallel to the TD direction of the film, and X-rays are irradiated from the X-ray source 2a to the measurement test piece 1a, whereby a two-dimensional diffraction image is obtained by the detector 3 a. The obtained two-dimensional diffraction image was corrected using a two-dimensional diffraction image (air space) obtained without providing the measurement test piece 1 a. Further, from the two-dimensional diffraction image, an azimuth distribution of 2θ=16° was obtained such that 0 ° and 180 ° of the azimuth distribution corresponded to the MD direction of the measurement test piece 1a, and 90 ° and 270 ° of the azimuth distribution corresponded to the ND direction of the measurement test piece 1 a. The diffraction intensity at each azimuth angle is an average value of diffraction intensities in a range of 2θ=15.5 to 16.5 °. Half-width of peaks existing at 90 ° and 270 ° in the obtained azimuth distribution (β=0 to 360°) was obtained, and the average value of 2 half-widths was substituted as FWHM into expression 1 to obtain an in-plane orientation index. The half-width of the peak present at 90 ° is the peak width at the intensity position at the center between the peak intensity present at 90 ° and the minimum intensity in the range of 0 to 180 ° (i.e., the peak width at the position that becomes the half intensity of the peak intensity present at 90 ° when the minimum intensity is taken as a reference), and the half-width of the peak present at 270 ° is the peak width at the intensity position at the center between the peak intensity present at 270 ° and the minimum intensity in the range of 180 to 360 ° (i.e., the peak width at the position that becomes the half intensity of the peak intensity present at 270 ° when the minimum intensity is taken as a reference).

(2) Index of molecular periodicity

The PI films obtained in examples and comparative examples were subjected to reflection wide-angle X-ray diffraction measurement under the following conditions.

Device name: RINT-2000 as X-ray diffraction apparatus manufactured by Rigaku corporation

X-ray source: cu-K alpha ray

Guan Dianya: 40kV (kilovolt)

Guan Dianliu: 150mA

Divergent slit: 1 degree

Scattering slit: 1 degree

Light receiving slit: 0.15mm

Divergent longitudinal limiting slit: 10mm of

Measurement range: 2 theta ₁ ＝5～30°

Step size measurement: 0.02 degree

Scanning speed: 0.5 DEG/min

Sample holder: sample plate (bottomless) made of Rigaku

Detector: scintillation counter manufactured by Rigaku corporation

Specifically, the film was cut so that the MD direction was 3cm and the TD direction was 2.5cm, to obtain a measurement sample 1b. Next, as shown in fig. 3, the measurement sample 1b is attached to the sample holder 6 such that the ND direction of the film is parallel to the normal direction of the surface of the sample holder 6 (i.e., the direction perpendicular to the surface), and such that a line 7 connecting the detection positions of the X-ray source 2b and the detector 3b is parallel to the MD direction of the film when the sample holder 6 is set in the X-ray apparatus. Next, while maintaining the line 7 parallel to the MD direction, at 2θ ₁ Reflection measurement of the film surface was performed in the range of=5 to 30°, and diffraction distribution a of the film was obtained.

Further, the film was cut so that the MD direction was 2.5cm and the TD direction was 3cm, to obtain a measurement sample 1b. Next, as shown in fig. 3, the measurement sample 1b is attached to the sample holder 6 such that the ND direction of the film is parallel to the normal direction of the surface of the sample holder 6 (i.e., the direction perpendicular to the surface), and such that a line 7 connecting the detection positions of the X-ray source 2b and the detector 3b is parallel to the TD direction of the film when the sample holder 6 is set in the X-ray apparatus. Next, while maintaining the line 7 parallel to the TD direction, the line is aligned with the line in 2θ ₁ Reflection measurement of the film surface was performed in the range of=5 to 30°, and diffraction distribution B of the film was obtained.

For each diffraction profile, the background was subtracted to perform blank correction. The average value of the diffraction distribution a and the diffraction distribution B corrected by the blank was taken as the diffraction intensity distribution of the film. Based on the diffraction intensity distribution of the film, 2 theta ₁ The maximum value of diffraction intensity in the range of=15.5 to 16.5° is I (16 °), and 2θ is set to ₁ The minimum value of diffraction intensity at=20 to 30° is regarded as I (min), and substituted intoThe molecular periodicity index was obtained by the method described in formula 2.

(3) In-plane anisotropy index A, B

Detector: pichatus 100k

X-ray source: cu-K alpha ray

Camera length: 70mm of

Exposure time: for 10 minutes

Voltage: 40kV (kilovolt)

Current: 20mA

Beam diameter: 0.25mm

Specifically, 4 sheets of film are overlapped in the ND direction so that the MD direction coincides. The overlapping films were cut with a trimming knife (trimming knife) so that the width in the MD direction became 2cm and the width in the TD direction became 2cm, to obtain test pieces for measurement. Next, as shown in fig. 5, a measurement test piece 1c is set on the X-ray apparatus so that the irradiation direction of the X-rays is parallel to the ND direction of the film. Then, X-rays are irradiated from the X-ray source 2c to the measurement test piece 1c, and a two-dimensional diffraction image is obtained by the detector 3 c. The obtained two-dimensional diffraction image was corrected using an air gap as the two-dimensional diffraction image obtained without providing the measurement test piece 1c. Further, 2 θ was obtained from the two-dimensional diffraction image so that 0 ° and 180 ° of the azimuth distribution corresponded to the MD direction of the test piece 1c for measurement and 90 ° and 270 ° of the azimuth distribution corresponded to the TD direction of the test piece 1c for measurement ₂ Azimuth distribution of =16°. Diffraction intensity at each azimuth angle is 2 theta ₂ Average value of diffraction intensity in the range of=15.5 to 16.5°.

In the resulting azimuth distribution (. Beta ₁ Of =0 to 360°, diffraction intensities of 0 ° and 180 ° were obtained, the average value thereof was defined as I (MD), and diffraction intensities of 90 ° and 270 ° were obtained, and the average value thereof was defined as I (TD). In addition, the azimuth angle obtained aboveDistribution (beta) ₁ In=0 to 360 °), the maximum value of the diffraction intensity in the range of 0 to 360 ° is defined as I (MAX), and the minimum value of the diffraction intensity is defined as I (MIN). Finally, the in-plane anisotropy index a and the in-plane anisotropy index B are obtained by substituting the values into the

above formulas

3 and 4.

< measurement of weight average molecular weight Mw and number average molecular weight Mn >

Mw and Mn in terms of polystyrene of the synthesized PI resin precursor were measured by GPC. GPC measurement was performed under the following conditions.

(1) Pretreatment method

After the sample was diluted with DMF, the solution was filtered through a 0.45 μm membrane filter to obtain a measurement solution.

(2) Measurement conditions

Column: 2 TSKgel SuperAWM-H (inner diameter of 6.0mm, length of 150 mm) were joined

Eluent: DMF (10 mmol/L lithium bromide added, 30mmol/L phosphoric acid added)

Flow rate: 0.6 mL/min

A detector: RI detector

Column temperature: 40 DEG C

Injection amount: 20 mu L

Molecular weight standard: standard polystyrene

< measurement of coefficient of Linear thermal expansion (CTE) >)

The CTE of the PI films obtained in examples and comparative examples was measured using TMA under the following conditions, and the CTE was calculated at 50 ℃ to 100 ℃.

The device comprises: TMA/SS7100 manufactured by Hitachi High-Tech Science Corporation

Load: 50.0mN

Temperature program: heating from 20 ℃ to 130 ℃ at a speed of 5 ℃ per minute

< evaluation of index E of dielectric loss >

The index E of dielectric loss of the PI films obtained in examples and comparative examples was calculated from the following formula.

E＝Df×(Dk) ^1/2 (i)

Df: dielectric loss tangent

Dk: relative dielectric constant

(measurement of Df and Dk)

Measurement samples of 50 mm. Times.50 mm were cut out from the PI films obtained in examples and comparative examples, and Df and Dk were measured under the following conditions. The samples were conditioned at 25 ℃/55% RH for 24 hours and then assayed.

The device comprises: anritsu Corporation compact USB vector network analyzer (product name: MS 46122B)

AET Inc. cavity resonator (TE mode 10GHz type)

Measuring frequency: 10GHz (10 GHz)

Measuring atmosphere: 23 ℃/50% RH

< evaluation of bending resistance >

The bending resistance of the PI films obtained in examples 3, 6 and 8 was evaluated by measuring the number of times of bending the films under the following conditions. The film was cut into rectangles of 100mm length and 10mm width using a dumbbell cutter. The cut film was set in an MIT folding endurance tester (MIT-DA manufactured by eastern chemical industry) in accordance with ASTM standard D2176-16, and the film was alternately folded in both the front and back directions under the conditions of a test speed of 175cpm, a folding angle of 135 °, a load of 750g, and r=1.0 mm of a folding jig, and the number of folds until breakage occurred was measured. The greater the number of bending times, the more excellent the bending resistance.

The PI films obtained in examples 3, 6 and 8 were bent 24 ten thousand times, 16 ten thousand times and 2 ten thousand times, respectively.

The measurement and evaluation results of the PI films obtained in examples and comparative examples are shown in table 1.

TABLE 1

As shown in table 1, it was confirmed that: the PI films obtained in examples 1 to 8 have lower Df and lower index E of dielectric loss than those obtained in comparative examples 1 and 2. Therefore, the PI film of the present invention can be suitably used for a metal-clad laminate such as CCL which can cope with a high frequency band and has a small transmission loss.

Claims

1. A polyimide film comprising a polyimide resin containing a structural unit (A) derived from a tetracarboxylic anhydride and a structural unit (B) derived from a diamine, wherein the polyimide film has an in-plane orientation index defined by formula 1 of 58 or more,

in-plane orientation index = [ (180-FWHM)/180 ] ×100 (formula 1)

In formula 1, FWHM represents a half-width of a peak appearing at an azimuth angle corresponding to the ND direction of the film in an azimuth angle distribution of 2θ=16°, the azimuth angle distribution being obtained by analysis of a two-dimensional diffraction image measured by transmission X-ray diffraction, the two-dimensional diffraction image being measured by X-ray incidence parallel to the TD direction of the film.

2. The polyimide-based film according to claim 1, wherein the polyimide-based film has a molecular periodicity index represented by formula 2 of 7.0 or more,

molecular periodicity index=i (16 °)/I (min) (formula 2)

In formula 2, I (16 DEG) represents 2 theta in the diffraction intensity distribution obtained by the reflection method X-ray diffraction measurement ₁ Maximum value of diffraction intensity at=15.5 to 16.5°,

i (min) represents 2 [ theta ] in the diffraction intensity distribution obtained by reflection X-ray diffraction measurement ₁ Minimum value of diffraction intensity at=20 to 30°.

3. The polyimide-based film according to claim 1 or 2, wherein the in-plane anisotropy index A defined by formula 3 is 0.8 to 1.2, the in-plane anisotropy index B defined by formula 4 is greater than 1.1,

In-plane anisotropy index a=i (MD)/I (TD) (formula 3)

In-plane anisotropy index b=i (MAX)/I (MIN) (formula 4)

In the formulas 3 and 4, 2 theta ₂ In the azimuth distribution of =16°, I (MD) represents the diffraction intensity corresponding to the MD direction of the film, I (TD) represents the diffraction intensity corresponding to the TD direction, I (MAX) represents the maximum value of the diffraction intensity, and I (MIN) represents the minimum value of the diffraction intensity, the azimuth distribution is obtained by analysis of a two-dimensional diffraction image measured by transmission X-ray diffraction, and the two-dimensional diffraction image is measured by injecting X-rays parallel to the ND direction of the film.

4. The polyimide-based film according to any one of claims 1 to 3, wherein the structural unit (A) comprises a structural unit (A1) derived from a tetracarboxylic anhydride containing an ester bond.

5. The polyimide-based film according to any one of claims 1 to 4, wherein the structural unit (A) comprises a structural unit (A2) derived from a tetracarboxylic anhydride containing a biphenyl skeleton.

6. The polyimide-based film according to claim 5, wherein the structural unit (A) satisfies the relationship of formula (X),

(content of structural units derived from tetracarboxylic anhydride other than the structural unit (A1) and the structural unit (A2)/(total amount of the structural unit (A1) and the structural unit (A2)) <1.1 (X).

7. The polyimide-based film according to any one of claims 4 to 6, wherein the structural unit (A1) is a structural unit (A1) derived from a tetracarboxylic anhydride represented by the formula (A1),

in the formula (a 1), Z represents a 2-valent organic group,

R ^a1 independently of one another, represents a halogen atom, or an alkyl, alkoxy, aryl or aryl group which may have a halogen atomAn oxygen group, an oxygen group and a nitrogen atom,

s independently of one another represent an integer from 0 to 3.

8. The polyimide-based film according to any one of claims 5 to 7, wherein the structural unit (A2) is a structural unit (A2) derived from a tetracarboxylic anhydride represented by the formula (A2),

in the formula (a 2), R ^a2 Independently of one another, represents a halogen atom or an alkyl, alkoxy, aryl or aryloxy group which may have a halogen atom,

t independently of one another represents an integer from 0 to 3.

9. The polyimide-based film according to any one of claims 1 to 8, wherein the structural unit (B) comprises a structural unit (B1) derived from a diamine having a biphenyl skeleton.

10. The polyimide-based film according to claim 9, wherein the structural unit (B1) is a structural unit (B1) derived from a diamine represented by the formula (B1),

in the formula (b 1), R ^b1 Independently of one another, represents a halogen atom or an alkyl, alkoxy, aryl or aryloxy group which may have a halogen atom,

p represents an integer of 0 to 4.

11. The polyimide-based film according to claim 9 or 10, wherein the content of the structural unit (B1) is more than 30 mol% with respect to the total amount of the structural units (B).

12. The polyimide-based film according to any one of claims 1 to 11, wherein the structural unit (B) comprises a structural unit (B2) derived from a diamine represented by the formula (B2),

in the formula (b 2), R ^b2 Independently of one another, represents a halogen atom or an alkyl, alkoxy, aryl or aryloxy group which may have a halogen atom, R ^b2 The hydrogen atoms contained in (a) may be substituted with halogen atoms independently of each other,

w independently of one another represents-O-, -CH ₂ -、-CH ₂ -CH ₂ -、-CH(CH ₃ )-、-C(CH ₃ ) ₂ -、-C(CF ₃ ) ₂ -、-COO-、-OOC-、-SO ₂ -, -S-, -CO-or-N (R) ^c )-，R ^c Represents a monovalent hydrocarbon group having 1 to 12 carbon atoms which may be substituted with a halogen atom,

m represents an integer of 0 to 4,

q independently of one another represents an integer from 0 to 4.

13. The polyimide-based film according to claim 12, wherein m in the structural unit (b 2) is 3,W, independently of each other, represents-O-or-C (CH ₃ ) ₂ -。

14. The polyimide film according to any one of claims 1 to 13, which has a dielectric loss tangent of less than 0.004 at 10 GHz.

15. The polyimide-based film according to any one of claims 1 to 14, wherein the polyimide-based resin has a storage elastic modulus at 280 ℃ of less than 3X 10 ⁸ Pa。

16. The polyimide-based film according to any one of claims 1 to 15, wherein the polyimide-based resin has a glass transition temperature of 200 to 290 ℃.

17. The polyimide film according to any one of claims 1 to 16, which has a thickness of 5 to 100 μm.

18. A laminated film comprising a metal foil layer on one or both surfaces of the polyimide film according to any one of claims 1 to 17.

19. A flexible printed circuit board comprising the polyimide film according to any one of claims 1 to 17.

20. The method for producing a polyimide-based film according to any one of claims 1 to 17, comprising the steps of: