Polyimide-based film

Abstract

To provide a polyimide-based film having low Df which enables formation of a metal-clad laminate such as CCL having a low transmission loss in a high frequency band.SOLUTION: A polyimide-based film contains a polyimide-based resin containing a structural unit (A) derived from a tetracarboxylic acid anhydride and a structural unit (B) derived from diamine, and has an in-plane orientation index defined by Expression 1 of 58 or more. Expression (1): In-plane orientation index=[(180-FWHW) / 180]×100. In Expression 1, FWHM represents a half-value width of a peak appearing at an azimuth angle corresponding to an ND direction of the film in an azimuth angle profile at 2θ=16°, which is measured by making X rays incident parallel to a TD direction of the film and is obtained by analysis of a two-dimensional diffraction image in X-ray diffraction measurement with a transmission method.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This invention relates to a polyimide-based film that can be used as a substrate material for high-frequency band printed circuit boards and antenna boards, a method for manufacturing the same, and a laminated film and a flexible printed circuit board containing the polyimide-based film. [Background technology]

[0002] Flexible printed circuit boards (hereinafter sometimes referred to as FPCs) are thin, lightweight, and flexible, enabling three-dimensional, high-density mounting. They are used in many electronic devices such as mobile phones and hard drives, contributing to their miniaturization and weight reduction. Conventionally, polyimide resin, which has excellent heat resistance, mechanical properties, and electrical insulation properties, has been widely used for FPCs. For example, as a metal-clad laminate used in FPCs, such as copper-clad laminates (hereinafter sometimes abbreviated as CCLs), laminates having copper foil layers on one or both sides of a single or multiple layers of polyimide film are known. In recent years, the fifth-generation mobile communication system, known as 5G, has been steadily gaining popularity (see, for example, Patent Document 1).

[0003] [Patent Document 1] Japanese Patent Publication No. 2021-161285 [Overview of the project] [Problems that the invention aims to solve]

[0004] However, conventional metal-clad laminates using polyimide materials suffer from significant transmission loss when transmitting high-frequency signals used in 5G communication, resulting in drawbacks such as electrical signal loss and long signal delays. Therefore, polyimide films with low dielectric loss tangent (hereinafter sometimes referred to as Df) and relative permittivity (hereinafter sometimes referred to as Dk) are being investigated to reduce transmission loss, but polyimide films with sufficiently low relative permittivity and dielectric loss tangent have not yet been found.

[0005] Therefore, the object of the present invention is to provide a polyimide-based film with low Df that can form metal-clad laminates such as CCL with low transmission loss in the high-frequency band, a method for manufacturing the same, and a laminated film and a flexible printed circuit board containing the polyimide-based film. [Means for solving the problem]

[0006] As a result of diligent research to solve the above problems, the present inventors have discovered that a polyimide-based film with reduced Df can be obtained by adjusting the higher-order structure of the polyimide-based resin to specific conditions, and have arrived at the present invention. That is, the present invention provides the following preferred embodiments.

[0007] [1] A polyimide film comprising a polyimide resin containing a constituent unit (A) derived from tetracarboxylic anhydride and a constituent unit (B) derived from diamine, wherein the in-plane orientation index defined by formula 1 is 58 or higher. In-plane orientation index = [(180-FWHM) / 180]×100 (Equation 1) [In Equation 1, FWHM represents the full width at half maximum of the peak appearing at the azimuth angle corresponding to the ND direction of the film, in the azimuth profile at 2θ = 16°, obtained by analyzing the two-dimensional diffraction pattern of a transmission X-ray diffraction measurement performed by incidenting X-rays parallel to the TD direction of the film.] [2] The polyimide film described in [1], wherein the molecular periodicity index represented by Equation 2 is 7.0 or greater. Molecular periodicity index = I(16°) / I(min) (Equation 2) [In Equation 2, I(16°) represents the maximum diffraction intensity in the diffraction intensity profile obtained by reflection X-ray diffraction measurement at 2θ1 = 15.5 to 16.5°.] I(min) represents the minimum diffraction intensity in the diffraction intensity profile obtained by reflection X-ray diffraction measurement at 2θ1 = 20~30°. [3] A polyimide film according to [1] or [2], wherein the in-plane anisotropy index A defined by formula 3 is 0.8 or more and 1.2 or less, and the in-plane anisotropy index B defined by formula 4 is greater than 1.1. In-plane anisotropy index A = I(MD) / I(TD) (Equation 3) In-plane anisotropy index B = I(MAX) / I(MIN) (Equation 4) [In equations 3 and 4, in the azimuth angle profile at 2θ² = 16° obtained by analyzing the two-dimensional diffraction pattern of a transmission X-ray diffraction measurement performed by incidenting X-rays parallel to the ND direction of the film, 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.] [4] The polyimide film according to any one of [1] to [3], wherein the constituent unit (A) comprises a constituent unit (A1) derived from an ester bond-containing tetracarboxylic anhydride. [5] The polyimide film according to any one of [1] to [4], wherein the constituent unit (A) comprises a constituent unit (A2) derived from a biphenyl skeleton-containing tetracarboxylic anhydride. [6] The constituent unit (A) is given by formula (X): (Content of constituent units derived from tetracarboxylic anhydride other than the aforementioned constituent units (A1) and (A2)) / (Total amount of the aforementioned constituent units (A1) and (A2)) < 1.1 (X) A polyimide film according to [5] that satisfies the relationship. [7] The constituent unit (A1) is given by formula (a1): [ka] [In formula (a1), Z represents a divalent organic group, R a1 Each of these independently represents a halogen atom, or an alkyl group, alkoxy group, aryl group, or aryloxy group which may have a halogen atom. [s represents integers between 0 and 3, independently of each other.] A polyimide film according to any one of [4] to [6], wherein the constituent unit (a1) is derived from a tetracarboxylic anhydride represented by [a1]. [8] The constituent unit (A2) is given by formula (a2): [ka] [In formula (a2), R a2 Each of these independently represents a halogen atom, or an alkyl group, alkoxy group, aryl group, or aryloxy group which may have a halogen atom. [t represents integers from 0 to 3, independently of each other.] A polyimide film according to any one of [5] to [7], wherein the constituent unit (a2) is derived from a tetracarboxylic anhydride represented by [a2]. [9] The polyimide film according to any one of [1] to [8], wherein the constituent unit (B) comprises a constituent unit (B1) derived from a biphenyl skeleton-containing diamine.

[10] The constituent unit (B1) is given by formula (b1): [ka] [In formula (b1), R b1 Each of these independently represents a halogen atom, or an alkyl group, alkoxy group, aryl group, or aryloxy group which may have a halogen atom. [p represents an integer between 0 and 4] A polyimide film as described in [9], wherein the constituent unit (b1) is derived from a diamine represented by [9].

[11] The polyimide film according to [9] or

[10] , wherein the content of the constituent unit (B1) exceeds 30 mol% of the total amount of the constituent unit (B).

[12] The constituent unit (B) is given by formula (b2): [ka] [In formula (b2), R b2 Each of these independently represents a halogen atom, or an alkyl group, alkoxy group, aryl group, or aryloxy group which may have a halogen atom, and R b2 The hydrogen atoms contained therein may be independently substituted by halogen atoms. W is independent of each other and is -O-, -CH2-, -CH2-CH2-, -CH(CH3)-, -C(CH3)2-, -C(CF3)2-, -COO-, -OOC-, -SO2-, -S-, -CO-, or -N(Rc )- represents R c This represents a monovalent hydrocarbon group having 1 to 12 carbon atoms, which may be substituted with hydrogen atoms or halogen atoms. m represents an integer from 0 to 4. [q represents an integer between 0 and 4, independently of each other.] A polyimide film according to any one of [1] to

[11] , comprising a diamine-derived structural unit (b2) represented by [1].

[13] The polyimide film according to

[12] , wherein in the constituent unit (b2), m is 3 and W independently represents -O- or -C(CH3)2-.

[14] A polyimide film according to any of [1] to

[13] , wherein the dielectric loss tangent at 10 GHz is less than 0.004.

[15] The storage modulus of the polyimide resin at 280°C is 3 × 10⁻⁶ 8 A polyimide film according to any of [1] to

[14] , having a Pa of less than [1].

[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°C.

[17] A polyimide film according to any of [1] to

[16] , having a thickness of 5 to 100 μm. A laminated film comprising a metal foil layer on one or both sides of a polyimide film as described in any of

[18] [1] to

[17] . A flexible printed circuit board containing a polyimide film as described in any of

[19] [1] to

[17] .

[20] A step of coating a polyimide resin precursor solution containing constituent units derived from tetracarboxylic anhydride and constituent units derived from diamine onto a substrate, and A method for producing a polyimide film according to any one of [1] to

[17] , comprising the step of imidizing a polyimide resin precursor by heat treatment at a temperature of 200°C or higher and 500°C or lower. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a polyimide-based film with low Df that can form metal-clad laminates such as CCL with low transmission loss in the high-frequency band. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 is a schematic diagram illustrating the method for determining the in-plane orientation index by transmission X-ray diffraction measurement. [Figure 2] Figure 2 shows the azimuth angle profile obtained by transmission X-ray diffraction measurement of the polyimide film of Example 4. [Figure 3] Figure 3 is a schematic diagram illustrating the method for determining molecular periodicity indices using reflection X-ray diffraction measurements. [Figure 4] Figure 4 shows the diffraction intensity profile obtained by reflection X-ray diffraction measurement of the polyimide film of Example 4. [Figure 5] Figure 5 is a schematic diagram illustrating the method for determining the in-plane anisotropy index by transmission X-ray diffraction measurement. [Figure 6] Figure 6 shows the azimuth angle profile obtained by transmission X-ray diffraction measurement of the polyimide film of Example 4. [Modes for carrying out the invention]

[0010] [Polyimide film] (In-plane orientation index) The polyimide film of the present invention comprises a polyimide resin containing a constituent unit (A) derived from tetracarboxylic anhydride and a constituent unit (B) derived from diamine, and has an in-plane orientation index (also simply called the in-plane orientation index) of 58 or higher, as defined by the following formula 1.

[0011] In-plane orientation index = [(180-FWHM) / 180]×100 (Equation 1) [In Equation 1, FWHM represents the full width at half maximum of the peak appearing at the azimuth angle corresponding to the ND direction of the film, in the azimuth profile at 2θ = 16°, obtained by analyzing the two-dimensional diffraction pattern of a transmission X-ray diffraction measurement performed by incidenting X-rays parallel to the TD direction of the film.]

[0012] The in-plane orientation index can be determined by measuring the FWHM using transmission X-ray measurement and substituting the obtained FWHM value into Equation 1.

[0013] The measurement method for FWHM will be explained below using Figures 1 and 2. Figure 1 is a schematic diagram illustrating the method for determining the in-plane orientation index by transmission X-ray diffraction measurement. Note that in Figure 1, the size of the test specimen, such as the aspect ratio, has been adjusted for clarity of explanation and is not limited to this.

[0014] First, a test specimen for measurement is prepared by cutting and / or stacking films. The size of the test specimen is not limited as long as it is large enough to obtain sufficient resolution and diffraction intensity, but preferably, the width in the MD direction is 0.5 to 3 cm, the width in the TD direction is 0.5 to 2 mm, and the thickness in the ND direction is 100 μm or more. The upper limit of the thickness in the ND direction is preferably 2 mm or less. This thickness can be obtained by stacking multiple films. Next, as shown in Figure 1, the test specimen 1a is set in the X-ray apparatus so that the direction of X-ray irradiation is parallel to the TD direction of the film. Then, X-rays are incident on the test specimen 1a from the X-ray source 2a, and a two-dimensional diffraction pattern is obtained by the detector 3a. The obtained two-dimensional diffraction pattern is corrected using a two-dimensional diffraction pattern (air blank) obtained without setting up the test specimen 1a. Furthermore, from the two-dimensional diffraction pattern, an azimuth profile at a diffraction angle of 2θ = 16° is obtained such that the azimuth profiles of 0° and 180° correspond to the MD direction of the test specimen 1a, and the azimuth profiles of 90° and 270° correspond to the ND direction of the test specimen 1a. The diffraction intensity for each azimuth angle is the average value of the diffraction intensity in the range of 2θ = 15.5 to 16.5°.

[0015] In the resulting azimuth profile (azimuth angle β = 0 to 360°), the full width at half maximum (FWHM) of the peaks at 90° and 270° is determined, and the average of the two FWHMs is defined as FWHM. The FWHM represents the peak width at the midpoint between the peak intensity at 90° or 270° and the minimum intensity in the azimuth angle range of -90° to +90° of that peak intensity (i.e., the peak width at the position where the intensity is half that of the peak intensity at 90° or 270°, relative to the minimum intensity). For example, in the azimuth profile shown in Figure 2, the FWHM of the peak at 270°, corresponding to the ND direction, is the peak width shown as 5 in Figure 2, at the position shown as 4 in Figure 2, where the intensity is half that of the minimum intensity in the range of 180 to 360°. In this specification, the MD direction is the direction parallel to the machine flow direction during manufacturing within the film plane, the TD direction is the direction perpendicular to the machine flow direction, and the ND direction is the thickness direction of the film, i.e., the direction perpendicular to the film plane. If the direction of the MD direction and TD direction within the film plane is unknown, it shall be determined by the following method. In the azimuth angle profile at 2θ=16°, measured by irradiating with X-rays from the ND direction using transmission X-ray measurement, the azimuth angle with the strongest diffraction intensity is defined as the MD direction.

[0016] Furthermore, the above X-ray apparatus can be set to the following measurement conditions. ·X-ray source: Cu-Kα ray Voltage: 40kV ·Current: 20mA • Camera length: 70mm • Exposure time: 10 minutes • Beam diameter: 0.25 mm

[0017] In the azimuth profile at 2θ=16°, the sharper the peak appearing in the ND direction, the smaller the FWHM value becomes, and the larger the in-plane orientation index in the equation can be.

[0018] In this specification, polyimide may be referred to as PI. The inventors have discovered that, in a PI-based film containing a polyimide resin containing a constituent unit (A) derived from tetracarboxylic anhydride and a constituent unit (B) derived from diamine, if the in-plane orientation index defined by Formula 1 is 58 or higher, the Df of the PI-based film can be reduced, which is unexpected. In X-ray diffraction measurements, diffraction peaks indicate a periodic structure at a distance corresponding to the diffraction angle 2θ. A strong peak intensity indicates a large number of components with a periodic structure, or that the periodicity of those components is highly regular. Furthermore, if the diffraction peak is strongly detected at a specific azimuth angle, it indicates that a periodic structure is formed in the direction of that azimuth angle, or that the molecular backbone is oriented perpendicular to the azimuth angle. In X-ray measurements of PI-based films, it is known that many diffraction peaks are detected, such as those shown in Figure 4, reflecting multiple periodicities in the higher-order structure of the molecular chains of the PI-based resin. If the in-plane orientation index defined in Equation 1 is 58 or higher, it means that a certain amount of PI-based resin is oriented along the film plane, and that these are distributed perpendicular to the film at a distance corresponding to the diffraction angle 2θ = 16°. When PI-based resin forms such a regular higher-order structure, it is presumed that the rotational motion of the resin's molecular chains is suppressed for some reason, and the Df of the PI-based film is reduced. On the other hand, if the in-plane orientation index defined in Equation 1 is less than 58, the rotational motion of the resin's molecular chains is not sufficiently suppressed, and the Df of the PI-based film cannot be sufficiently reduced.

[0019] In the PI-based film of the present invention, the in-plane orientation index is preferably 60 or higher, more preferably 62 or higher, even more preferably 64 or higher, even more preferably 66 or higher, particularly preferably 68 or higher, and particularly more preferably 69 or higher. When the in-plane orientation index is above the lower limit of the above, it is easier to reduce the Df of the PI film. The upper limit of the in-plane orientation index is preferably 95 or lower, more preferably 90 or lower, even more preferably 85 or lower, and even more preferably 80 or lower. When the in-plane orientation index is below the upper limit of the above, it is easier to keep the dielectric constant low, suppress extreme anisotropy of mechanical strength, and improve bending resistance. The in-plane orientation index can be determined by the above method, or for example, by the method described in the examples.

[0020] The in-plane orientation index can be adjusted by appropriately adjusting the type and composition of the constituent units of the PI resin, the molecular weight of the PI resin, and the manufacturing method such as coating and imidization conditions. For example, it may be adjusted to the above range by adopting preferred embodiments described later, particularly embodiments that improve dielectric properties such as Df reduction. For example, it may be adjusted by using preferred constituent units of the PI resin and their content described later, the solvent contained in the preferred PI resin precursor solution described later, and the preferred imidization conditions described later. Furthermore, the in-plane orientation index tends to increase when ester bonds are included in the PI resin, and tends to decrease when there are many flexible components in the PI resin.

[0021] (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 higher. Molecular periodicity index = I(16°) / I(min) (Equation 2) [In Equation 2, I(16°) represents the maximum diffraction intensity in the diffraction intensity profile obtained by reflection X-ray diffraction measurement at 2θ1 = 15.5 to 16.5°.] I(min) represents the minimum diffraction intensity in the diffraction intensity profile obtained by reflection X-ray diffraction measurement at 2θ1 = 20~30°.

[0022] The molecular periodicity index is determined by measuring I(16°) and I(min) using reflection X-ray diffraction and substituting them into Equation 2.

[0023] The measurement methods for I(16°) and I(min) will be explained below using Figures 3 and 4. Figure 3 is a schematic diagram illustrating the method for determining the molecular periodicity index by reflection X-ray diffraction measurement. Note that in Figure 3, the dimensions of the test specimen, such as the aspect ratio, have been adjusted for clarity of explanation and are not limited to these dimensions.

[0024] First, a test specimen for measurement is prepared by cutting and / or stacking the film. The size of the test specimen is not limited as long as it is large enough to obtain sufficient resolution and diffraction intensity, but preferably the width in the MD direction is 0.5 cm to 5 cm and the width in the TD direction is 0.5 cm to 5 cm. Next, as shown in Figure 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 when the sample holder 6 is installed in the X-ray apparatus, the MD direction of the film is parallel to the line 7 connecting the detection position of the X-ray source 2b and the detector 3b. Next, while maintaining the parallelism between line 7 and the MD direction, the reflectance measurement of the film surface is performed in the diffraction angle range 2θ1 = 5 to 30° to obtain the diffraction profile A of the film. Next, the film is cut and / or stacked to obtain another test piece for measurement. Then, as shown in Figure 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 when the sample holder 6 is installed in the X-ray apparatus, the TD direction of the film is parallel to the line 7 connecting the detection position of the X-ray source 2b and the detection position of the detector 3b. Next, the reflectance measurement of the film surface is performed in the range of 2θ1 = 5 to 30° to obtain the diffraction profile B of the film. Each diffraction profile is blank-corrected by subtracting the background. The average value of the blank-corrected diffraction profile A and diffraction profile B is taken as the diffraction intensity profile of the film. From the diffraction intensity profile of the film, the maximum diffraction intensity in the range of 2θ1 = 15.5 to 16.5° is taken as I(16°), and the minimum diffraction intensity in the range of 2θ1 = 20 to 30° is taken as I(min). For example, in the diffraction intensity profile shown in Figure 4, I(16°) is the maximum diffraction intensity in the range of 2θ1 = 15.5 to 16.5° (8 in the figure), and I(min) is the minimum diffraction intensity in the range of 2θ1 = 20 to 30° (9 in the figure). Furthermore, the above X-ray apparatus can be set to the following measurement conditions. ·X-ray source: Cu-Kα ray • Tube voltage: 40kV ·Tube current: 150mA • Divergent slit: 1° • Scattering slit: 1° • Light-receiving slit: 0.15mm • Divergence vertical limiting slit: 10mm • Measurement range: 2θ1 = 5~30° • Measurement step: 0.02° • Scan speed: 0.5° / min • Sample holder: Aluminum sample plate

[0025] If the molecular periodicity index expressed in Equation 2 is 7.0 or higher, the Df of the PI-based film can be further reduced. It is estimated that if PI resins are distributed while maintaining a distance corresponding to a diffraction angle 2θ1 = 16°, the rotational motion of the resin's molecular chains is suppressed for some reason, and the Df of the PI film is reduced. However, if the molecular periodicity index is 7.0 or higher, it is estimated that a lower Df will result because there will be more components that are arranged at such a constant distance regardless of the orientation of the molecular chains.

[0026] In the PI-based film of the present invention, the molecular periodicity index is preferably 7.1 or higher, more preferably 7.3 or higher, even more preferably 7.5 or higher, even more preferably 7.7 or higher, and particularly preferably 7.8 or higher. When the molecular periodicity index is above the lower limit of the above, it is easier to reduce the Df of the PI-based film. The upper limit of the molecular periodicity index is preferably 20 or lower, more preferably 15 or lower, even more preferably 12 or lower, and even more preferably 10 or lower. When the molecular periodicity index is below the upper limit of the above, it is easier to improve the bending resistance. The molecular periodicity index can be determined by the above method, and may also be determined by the method described in the examples, for example.

[0027] The molecular periodicity index can be adjusted by appropriately adjusting the types and composition of the constituent units of the PI resin, the molecular weight of the PI resin, and the manufacturing method such as the imidation conditions. For example, it may be adjusted to the above range by adopting preferred embodiments described later, particularly embodiments that improve dielectric properties such as Df reduction. For example, it may be adjusted by using the preferred constituent units of the PI resin and their content described later, the solvent contained in the preferred PI resin precursor solution described later, and the preferred imidation conditions described later. Furthermore, the molecular periodicity index tends to increase when ester bonds are included in the PI resin, and tends to decrease when there are many flexible components in the PI resin.

[0028] (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 that is 0.8 or more and 1.2 or less, and an in-plane anisotropy index B defined by the following formula 4 that is greater than 1.1.

[0029] In-plane anisotropy index A = I(MD) / I(TD) (Equation 3) In-plane anisotropy index B = I(MAX) / I(MIN) (Equation 4) [In equations 3 and 4, in the azimuth profile at a diffraction angle of 2θ² = 16° obtained by analyzing the two-dimensional diffraction pattern of a transmission X-ray diffraction measurement performed by incidenting X-rays parallel to the ND direction of the film, 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.]

[0030] The in-plane anisotropy indices A and B are determined by measuring I(MD), I(TD), I(MAX), and I(MIN) by transmission X-ray diffraction and substituting them into equations 3 and 4.

[0031] The measurement methods for I(MD), I(TD), I(MAX), and I(MIN) will be explained below using Figures 5 and 6. Figure 5 is a schematic diagram illustrating the method for determining the in-plane anisotropy index by transmission X-ray diffraction measurement. Note that in Figure 5, the aspect ratio of the test specimen used for measurement has been adjusted for clarity of explanation and is not limited to it.

[0032] First, a test specimen for measurement is prepared by cutting and / or stacking the film. The size of the test specimen is not limited as long as it is large enough to obtain sufficient resolution and diffraction intensity, but preferably the width in the MD direction is 0.5 cm to 3 cm and the width in the TD direction is 0.5 cm to 3 cm. The width in the ND direction is preferably adjusted to 0.1 mm to 2 mm. Next, as shown in Figure 5, the test specimen 1c is set in the X-ray apparatus so that the direction of X-ray irradiation is parallel to the ND direction of the film. Then, X-rays are incident on the test specimen 1c from the X-ray source 2c, and a two-dimensional diffraction pattern is obtained by the detector 3c. The obtained two-dimensional diffraction pattern is corrected using a two-dimensional diffraction pattern (air blank) obtained without setting up the test specimen 1c. Furthermore, from the two-dimensional diffraction pattern, an azimuth profile at 2θ2 = 16° is obtained such that the azimuth profiles at 0° and 180° correspond to the MD direction of the test specimen 1c, and the azimuth profiles at 90° and 270° correspond to the TD direction of the test specimen 1c. The diffraction intensity for each azimuth angle is the average value of the diffraction intensity in the range of 2θ2 = 15.5 to 16.5°. In the obtained azimuth profile (azimuth angle β1 = 0 to 360°), the diffraction intensities at 0° and 180° are determined, and their average value is defined as I(MD). The diffraction intensities at 90° and 270° are determined, and their average value is defined as I(TD). Furthermore, in the above-mentioned azimuth profile (β1 = 0 to 360°), the maximum diffraction intensity in the range of 0 to 360° is defined as I(MAX), and the minimum diffraction intensity is defined as I(MIN). For example, in the azimuth profile shown in Figure 6, I(MD) is the average of the diffraction intensity 10 at 0° and the diffraction intensity 12 at 180°, I(TD) is the average of the diffraction intensity 11 at 90° and the diffraction intensity 14 at 270°, I(MAX) is the maximum value in the range of 0 to 360° (15 in the figure), and I(MIN) is the minimum value in the range of 0 to 360° (13 in the figure). Furthermore, the above X-ray apparatus can be set to the following measurement conditions. ·X-ray source: Cu-Kα ray • Camera length: 70mm • Exposure time: 10 minutes Voltage: 40kV ·Current: 20mA • Beam diameter: 0.25 mm

[0033] The inventors have discovered that, in a PI-based film containing a PI-based resin containing a constituent unit (A) derived from tetracarboxylic anhydride and a constituent unit (B) derived from diamine, if the in-plane anisotropy index A defined by formula 3 is 0.8 or more and 1.2 or less, and the in-plane anisotropy index B defined by formula 4 is greater than 1.1, the Df of the PI-based film can be reduced, which is surprising.

[0034] The in-plane anisotropy index A represents the ratio of the orientation and degree of regularity of the resin's molecular chains in the MD direction and the TD direction. A value closer to 1 indicates a smaller difference in anisotropy between MD and TD. When the in-plane anisotropy index A is between 0.8 and 1.2, the film has isotropic properties within its plane and tends to have isotropic thermal and mechanical properties, making it easier to handle when processed into printed circuit boards. On the other hand, the in-plane anisotropy index B represents the ratio of the diffraction intensity in the direction with the strongest diffraction intensity to the direction with the weakest diffraction intensity in the azimuthal angle profile. If the in-plane anisotropy index B is greater than 1.1 despite the in-plane anisotropy index A being between 0.8 and 1.2, it is thought that the PI resin itself forms a higher-order structure with a distance corresponding to the diffraction angle 2θ² = 16°. In such a structure, the rotational motion of the resin's molecular chains is easily suppressed, and it is estimated that the Df of the PI film is reduced.

[0035] In the PI-based film of the present invention, the in-plane anisotropy index A is preferably 0.8 or higher, more preferably 0.83 or higher, even more preferably 0.87 or higher, even more preferably 0.9 or higher, particularly preferably 0.93 or higher, particularly more preferably 0.97 or higher, preferably 1.2 or lower, more preferably 1.17 or lower, even more preferably 1.13 or lower, even more preferably 1.1 or lower, particularly preferably 1.07 or lower, and particularly more preferably 1.03 or lower. When the in-plane anisotropy index A is within the above range, the film tends to have thermally and mechanically isotropic properties, making it easier to handle when processing it as a printed circuit board.

[0036] In the PI-based film of the present invention, the in-plane anisotropy index B is preferably 1.12 or higher, more preferably 1.15 or higher, even more preferably 1.17 or higher, and still more preferably 1.2 or higher. When the in-plane anisotropy index B is above the lower limit of the above, it is easier to reduce the Df of the PI-based film. The upper limit of the in-plane anisotropy index B is preferably 3.0 or lower, more preferably 2.5 or lower, even more preferably 2.0 or lower, still more preferably 1.7 or lower, and particularly preferably 1.5 or lower. The in-plane anisotropy index can be determined by the above method, or for example, by the method described in the examples.

[0037] The in-plane anisotropy indices A and B can be adjusted by appropriately adjusting the types and composition of the constituent units of the PI resin, the molecular weight of the PI resin, and the manufacturing method such as the imidation conditions. For example, they may be adjusted to the above range by adopting preferred embodiments described later, particularly embodiments that improve dielectric properties such as Df reduction. For example, they may be adjusted by using the preferred constituent units of the PI resin and their content described later, the solvent contained in the preferred PI resin precursor solution described later, and the preferred imidation conditions described later. Furthermore, the in-plane anisotropy index B tends to increase when ester bonds are included in the PI resin, and tends to decrease when there are many flexible components in the PI resin.

[0038] In one embodiment of the present invention, the PI-based film of the present invention has a low coefficient of thermal expansion (hereinafter sometimes referred to as CTE). The CTE of the PI-based film is preferably 50 ppm / K or less, more preferably 40 ppm / K or less, still more preferably 30 ppm / K or less, even more preferably 25 ppm / K or less, particularly preferably 21 ppm / K or less, and is preferably 0 ppm / K or more, more preferably 5 ppm / K or more, still more preferably 8 ppm / K or more, even more preferably 12 ppm / K or more. By setting it within the above range, the CTEs of the copper foil and the PI layer become close, so that peeling of the laminated film can be suppressed. The CTE can be measured, for example, by a thermomechanical analyzer (sometimes referred to as "TMA") and is determined by the method described in the examples.

[0039] For printed circuits, it is required that the transmission loss be reduced. The transmission loss is represented by the sum of the dielectric loss, which is the loss generated by the electric field generated in the dielectric, and the conductor loss, which is the loss caused by the current flowing through the conductor. And it is known that the dielectric loss is approximately proportional to the index E expressed by formula (i).

[0040] E = Df × (Dk) 1 / 2 (i) [In formula (i), Df represents the dielectric tangent and Dk represents the relative dielectric constant]

[0041] In the high-frequency range used in 5G FPCs, since the dielectric loss tends to increase, the value of the index E is small, and a material that can suppress the dielectric loss is particularly required. On the other hand, in a high-frequency signal, the current concentrates on the very surface of the conductor. Therefore, the conductor loss is related to the dielectric characteristics of the contacting dielectric and is known to be approximately proportional to (Dk). 1 / 2

[0042] As described above, the PI-based film of the present invention contains a PI-based resin containing a constituent unit (A) derived from tetracarboxylic anhydride and a constituent unit (B) derived from diamine. Since the in-plane orientation index of the PI-based resin is 58 or higher, Df and Dk become smaller, which in turn reduces the dielectric loss index E and conductor loss. Therefore, transmission loss can be reduced in circuits containing the PI-based film. In one embodiment of the present invention, the dielectric loss index E of the PI-based film at 10 GHz is preferably 0.009 or less, more preferably 0.008 or less, even more preferably 0.007 or less, and particularly preferably 0.006 or less. The smaller the index E, the lower the transmission loss of the electronic circuit including the PI-based film; therefore, the lower limit of the index E is not particularly limited and may be, for example, 0 or greater.

[0043] In one embodiment of the present invention, the Df of the PI-based film at 10 GHz is preferably less than 0.004, more preferably 0.0038 or less, even more preferably 0.0035 or less, even more preferably 0.0033 or less, particularly preferably 0.003 or less, particularly more preferably 0.0027 or less, and especially preferably 0.0024 or less, from the viewpoint of easily reducing the transmission loss of the electronic circuit including the PI-based film. The smaller the Df, the lower the transmission loss of the electronic circuit including the PI-based film; therefore, the lower limit of the Df is not particularly limited and may be, for example, 0 or more.

[0044] In one embodiment of the present invention, the Dk of the PI-based film at 10 GHz is preferably less than 3.50, more preferably 3.45 or less, even more preferably 3.40 or less, even more preferably 3.38 or less, and particularly preferably 3.36 or less.

[0045] The Df and Dk of a PI-based film can be measured using a vector network analyzer and a resonator, for example, by the method described in the examples.

[0046] In one embodiment of the present invention, the number of folds until fracture in the MIT fold fatigue test of the PI-based film of the present invention in accordance with ASTM standard D2176-16 is 15,000 or more, preferably 20,000 or more, more preferably 50,000 or more, even more preferably 100,000 or more, even more preferably 150,000 or more, and particularly preferably 200,000 or more. When the number of folds is above the lower limit of the above, the occurrence of cracks, breaks, creases, etc. can be effectively suppressed even with repeated bending. Furthermore, the upper limit of the number of folds is not particularly limited and may be, for example, 10,000,000 or less. The MIT fold fatigue test can be measured using an MIT fold fatigue tester, and can be measured, for example, by the method described in the examples.

[0047] The thickness of the PI-based film of the present invention can be appropriately selected depending on the application, preferably 5 μm or more, more preferably 10 μm or more, even more preferably 20 μm or more, preferably 500 μm or less, more preferably 300 μm or less, even more preferably 100 μm or less, particularly preferably 80 μm or less, and particularly more preferably 50 μm or less. The film thickness can be measured using a film thickness gauge or the like. Note that if the film of the present invention is a multilayer film, the above thickness represents the thickness of the single layer portion. Furthermore, reducing the film thickness tends to increase the in-plane orientation index and molecular periodicity index.

[0048] The PI-based film of the present invention may be subjected to surface treatments such as corona discharge treatment, plasma treatment, or ozone treatment by methods commonly used in industry.

[0049] Because the PI-based film of the present invention has a low Df, it can be suitably used as a substrate material for high-frequency band printed circuit boards and antenna boards. For FPCs, laminates of copper foil have copper foil layers on one or both sides of a single or multiple layers of PI-based resin, and these are widely used as CCLs.

[0050] <Polyimide resin> The PI-based film of the present invention comprises a PI-based resin containing a constituent unit (A) derived from tetracarboxylic anhydride and a constituent unit (B) derived from diamine. In the present invention, "derived constituent unit" means "derived constituent unit," and for example, "tetracarboxylic anhydride-derived constituent unit (A)" means "constituent unit (A) derived from tetracarboxylic anhydride."

[0051] (Constituent unit (A) derived from tetracarboxylic anhydride) PI-based resins contain constituent units (A) derived from tetracarboxylic anhydride (hereinafter sometimes simply referred to as constituent unit (A)). Constituent unit (A) is not particularly limited as long as the in-plane orientation index of the PI-based film is within the above range, but for example, formula (1): [ka] [In formula (1), Y represents a tetravalent organic group.] Preferably, the constituent units are derived from tetracarboxylic anhydrides represented by [formula].

[0052] In formula (1), Y independently represents a tetravalent organic group, preferably a tetravalent organic group having 4 to 40 carbon atoms, and more preferably a tetravalent organic group having 4 to 40 carbon atoms having a cyclic structure. Examples of cyclic structures include alicyclic, aromatic, and heterocyclic structures. The hydrogen atoms in the organic group may be substituted with halogen atoms, hydrocarbon groups, alkoxy groups, or halogenated hydrocarbon groups, in which case the number of carbon atoms in these groups is preferably 1 to 8. The PI resin of the present invention may contain multiple types of Y, and the multiple types of Y may be the same or different from each other. Examples of Y include groups or structures represented by formulas (31) to (40); groups in which the hydrogen atoms in the groups represented by formulas (31) to (40) are substituted with methyl groups, ethyl groups, n-propyl groups, isopropyl groups, n-butyl groups, isobutyl groups, sec-butyl groups, tert-butyl groups, fluoro groups, chloro groups, or trifluoromethyl groups; and tetravalent chain hydrocarbon groups having 1 to 8 carbon atoms.

[0053] [ka] [In formulas (31) to (33), R 19 ~R 26 and R 23’ ~R 26’ Each of these independently represents a hydrogen atom, a C1-C6 alkyl group, a C1-C6 alkoxy group, or a C6-C12 aryl group, and R 19 ~R 26 and R 23’ ~R 26’ The hydrogen atoms contained therein may be independently substituted by halogen atoms. V 1 and V 2 These are independent of each other, single bonds (except when e+d=1), -O-, -CH2-, -CH2-CH2-, -CH(CH3)-, -C(CH3)2-, -C(CF3)2-, -SO2-, -S-, -CO-, -N(R j )-, or formula (a) [ka] (In formula (a), R 27 ~R 30 Each of these independently represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms. D independently represents a single bond, -C(CH3)2-, or -C(CF3)2. i represents an integer from 1 to 3. (* represents a connection) This represents, R j This represents a monovalent hydrocarbon group having 1 to 12 carbon atoms, which may be substituted with a hydrogen atom or a halogen atom. e and d represent integers between 0 and 2, independently of each other (where e + d is not 0). f represents an integer between 0 and 3. g and h represent integers between 0 and 4, independently of each other. In formula (39), Z represents a divalent organic group, R a1 Each of these independently represents a halogen atom, or an alkyl group, alkoxy group, aryl group, or aryloxy group which may have a halogen atom. s represents an integer between 0 and 3, independently of each other. In formula (40), R a2 Each of these independently represents a halogen atom, or an alkyl group, alkoxy group, aryl group, or aryloxy group which may have a halogen atom. t represents an integer between 0 and 3, independently of each other. * represents a bond.

[0054] In the present invention, the PI resin preferably includes, as Y in formula (1), at least one structure selected from the group consisting of structures represented by formulas (31), (32), (33), (39), and (40), from the viewpoint of easily improving the mechanical properties, thermal properties, and dielectric properties of the PI film, more preferably includes at least one structure selected from the group consisting of structures containing ester bonds and structures containing biphenyl skeletons, and even more preferably includes at least one structure selected from the group consisting of structures represented by formulas (39) and (40). In this specification, mechanical properties include flexural resistance, bending resistance, and elastic modulus, and improved mechanical properties indicate, for example, increased flexural resistance and / or increased elastic modulus. Furthermore, thermal properties include glass transition temperature (Tg), CTE, low thermal deformation and degradation, and low deformation after heating, and improved thermal properties indicate, for example, increased Tg and / or decreased CTE. Furthermore, dielectric properties refer to characteristics related to dielectric properties, including Df and Dk, and an increase or improvement in dielectric properties indicates a decrease in Df and / or Dk.

[0055] In equations (31) to (33), R 19 ~R 26 and R 23’ ~R 26’ Each of these independently represents a hydrogen atom, a C1-C6 alkyl group, a C1-C6 alkoxy group, or a C6-C12 aryl group. Examples of alkyl groups having 1 to 6 carbon atoms include methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, sec-butyl group, tert-butyl group, n-pentyl group, 2-methyl-butyl group, 3-methylbutyl group, 2-ethyl-propyl group, and n-hexyl group. Examples of alkoxy groups having 1 to 6 carbon atoms include methoxy, ethoxy, propyloxy, isopropyloxy, n-butoxy, isobutoxy, sec-butoxy, tert-butoxy, pentyloxy, hexyloxy, and cyclohexyloxy groups. Examples of aryl groups having 6 to 12 carbon atoms include phenyl, tolyl, xylyl, naphthyl, and biphenyl groups. 19 ~R 26 and R 23’ ~R 26’ The hydrogen atoms contained therein may be independently substituted with halogen atoms, and examples of such halogen atoms include fluorine atoms, chlorine atoms, bromine atoms, and iodine atoms. Among these, R is preferred from the viewpoint of easily improving the mechanical and thermal properties of the PI film. 19 ~R 26 and R 23’ ~R 26’ Each of these is independently preferably a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, more preferably a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, and even more preferably a hydrogen atom.

[0056] In equation (31), V 1 and V 2 These are independent of each other, single bonds (except when e+d=1), -O-, -CH2-, -CH2-CH2-, -CH(CH3)-, -C(CH3)2-, -C(CF3)2-, -SO2-, -S-, -CO-, -N(R j )- or formula (a) represents, and from the viewpoint of easily improving the mechanical and thermal properties of PI-based films, preferably a single bond (except when e+d=1), -O-, -CH2-, -C(CH3)2-, -C(CF3)2- or -CO- represents, and more preferably a single bond (except when e+d=1), -O-, -C(CH3)2- or -C(CF3)2- represents.j The symbol represents a monovalent hydrocarbon group having 1 to 12 carbon atoms, which may be substituted with hydrogen atoms or halogen atoms. Examples of monovalent hydrocarbon groups having 1 to 12 carbon atoms include methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, sec-butyl group, tert-butyl group, n-pentyl group, 2-methyl-butyl group, 3-methyl-butyl group, 2-ethyl-propyl group, n-hexyl group, n-heptyl group, n-octyl group, tert-octyl group, n-nonyl group, and n-decyl group, which may be substituted with halogen atoms. Examples of halogen atoms are the same as those listed above.

[0057] In formula (31), e and d independently represent integers from 0 to 2 (where e + d is not 0), and preferably represent 0 or 1 from the viewpoint of easily reducing the Df of the PI-based film. Also, e + d preferably represents 1. Note that in formula (31), when e is 0, the two benzene rings are V 1 This indicates that they are not bonded, and when d is 0, the two benzene rings are V 2 This indicates that they are not joined together.

[0058] In formulas (32) and (33), f represents an integer between 0 and 3, and from the viewpoint of easily reducing the Df of the PI-based film, it preferably represents 0 or 1, more preferably 0.

[0059] In formula (33), g and h represent integers between 0 and 4, independently of each other, and preferably represent integers between 0 and 2, more preferably 0 or 1, from the viewpoint of easily improving the mechanical and thermal properties of the PI-based film. Also, g + h preferably represents an integer between 0 and 2. When f is 1 or greater, multiple g and h may be the same or different, independently of each other.

[0060] In equation (a), R 27 ~R 30 Each of these independently represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms. Examples of alkyl groups having 1 to 6 carbon atoms include those exemplified above. Among these, R is considered to be the most effective in improving the mechanical and thermal properties of PI films. 27 ~R 30 Each of these elements independently represents, preferably, a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, and more preferably, a hydrogen atom.

[0061] In formula (a), D represents a single bond, -C(CH3)2-, or -C(CF3)2-. Having such a structure for D makes it easier to improve the mechanical and thermal properties of the PI-based film. i represents an integer from 1 to 3, and is preferably 1 or 2 from the viewpoint of easily improving the mechanical and thermal properties of the PI-based film. If i is 2 or greater, multiple D and R are present. 27 ~R 30 These elements may be identical or different, and may be independent of each other.

[0062] In formula (39), Z represents a divalent organic group, and from the viewpoint of easily improving the mechanical properties, thermal properties, and dielectric properties of the PI-based film, it preferably represents a divalent organic group having 4 to 40 carbon atoms, more preferably a divalent organic group having 4 to 40 carbon atoms having a cyclic structure, and even more preferably a divalent organic group having 4 to 40 carbon atoms having an aromatic ring, and particularly preferably formulas (z1), (z2), or (z3): [ka] [In formulas (z1) to (z3), R z11 ~R z14 R represents a monovalent hydrocarbon group which may have a hydrogen atom or a halogen atom, independently of each other. z2 [where n represents a monovalent hydrocarbon group which may have a halogen atom independently, n represents an integer from 1 to 4, j represents an integer from 0 to 3 independently, and * represents a bond] This represents a divalent organic group represented by formula (z1), and more preferably a divalent organic group represented by formula (z1).

[0063] In equation (z1), R z11 ~R z14Each of these independently represents a monovalent hydrocarbon group which may have a hydrogen atom or a halogen atom. Examples of monovalent hydrocarbon groups include aromatic hydrocarbon groups, alicyclic hydrocarbon groups, and aliphatic hydrocarbon groups. Examples of aromatic hydrocarbon groups include aryl groups such as phenyl, tolyl, xylyl, naphthyl, and biphenyl groups. Examples of alicyclic hydrocarbon groups include cycloalkyl groups such as cyclopentyl groups and cyclohexyl groups. Examples of aliphatic hydrocarbon groups include alkyl groups such as methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, sec-butyl group, tert-butyl group, n-pentyl group, 2-methyl-butyl group, 3-methylbutyl group, 2-ethyl-propyl group, n-hexyl group, n-heptyl group, n-octyl group, tert-octyl group, n-nonyl group, and n-decyl group. Examples of halogen atoms include those listed above. R z11 ~R z14 From the viewpoint of easily improving the mechanical properties, thermal properties, and dielectric properties of PI-based films, each element independently preferably represents an alkyl group which may have a hydrogen atom or a halogen atom, more preferably an alkyl group having 1 to 6 carbon atoms which may have a hydrogen atom or a halogen atom, even more preferably an alkyl group having 1 to 3 carbon atoms which may have a hydrogen atom or a halogen atom, and particularly preferably a hydrogen atom.

[0064] In formula (z1), n ​​represents an integer from 1 to 4, and from the viewpoint of easily reducing the Df of the PI-based film, it preferably represents an integer from 1 to 3, more preferably 1 or 2, and particularly preferably 2.

[0065] In equation (z2), R z2 R independently represents a monovalent hydrocarbon group which may have a halogen atom, and examples of monovalent hydrocarbon groups include those listed above. z2From the viewpoint of easily improving the mechanical properties, thermal properties, and dielectric properties of PI-based films, each element independently preferably represents an alkyl group which may have a halogen atom, more preferably an alkyl group having 1 to 6 carbon atoms which may have a halogen atom, and even more preferably an alkyl group having 1 to 3 carbon atoms which may have a halogen atom.

[0066] In equation (z2), j represents an integer between 0 and 3, independently of each other, and is preferably 0 or 1, more preferably 0, from the viewpoint of easily reducing the Df of the PI-based film.

[0067] In equation (39), R a1 Each of these independently represents a halogen atom, or an alkyl group, alkoxy group, aryl group, or aryloxy group which may have a halogen atom. From the viewpoint of easily improving the mechanical properties, thermal properties, and dielectric properties of the PI-based film, each of these preferably independently represents 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 alkyl groups having 1 to 6 carbon atoms, alkoxy groups having 1 to 6 carbon atoms, and aryl groups having 6 to 12 carbon atoms include those exemplified above. R a1 The hydrogen atoms contained therein may be independently substituted with halogen atoms, and examples of halogen atoms include those listed above. Among these, R is preferred from the viewpoint of easily reducing the Df of the PI film. a1 Each of these independently represents an alkyl group, preferably having 1 to 6 carbon atoms, and more preferably having 1 to 3 carbon atoms.

[0068] In formula (39), s represents an integer between 0 and 3, independently of each other, and preferably represents an integer between 0 and 2, more preferably 0 or 1, from the viewpoint of easily improving the mechanical properties, thermal properties, and dielectric properties of the PI-based film.

[0069] In equation (40), R a2Each of these independently represents a halogen atom, or an alkyl group, alkoxy group, aryl group, or aryloxy group which may have a halogen atom. From the viewpoint of easily improving the mechanical properties, thermal properties, and dielectric properties of the PI-based film, each of these preferably independently represents 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 alkyl groups having 1 to 6 carbon atoms, alkoxy groups having 1 to 6 carbon atoms, and aryl groups having 6 to 12 carbon atoms include those exemplified above. R a2 The hydrogen atoms contained in may be independently substituted with halogen atoms, and examples of halogen atoms include those listed above. Among these, R is chosen from the viewpoint of easily improving the mechanical, thermal, and dielectric properties of the PI film. a2 Examples include alkyl groups having 1 to 6 carbon atoms, preferably alkyl groups having 1 to 3 carbon atoms, independently of each other.

[0070] In formula (40), t represents an integer between 0 and 3, independently of each other, and preferably represents an integer between 0 and 2, more preferably 0 or 1, from the viewpoint of easily improving the mechanical properties, thermal properties, and dielectric properties of the PI-based film.

[0071] Specific examples of the structures represented by equations (31) to (33), (39), and (40) include the structures represented by equations (41) to (56). In these equations, * represents a coupling.

[0072] [ka]

[0073] In one embodiment of the present invention, when Y in formula (1) includes at least one selected from the group consisting of structures represented by formulas (31) to (33), formula (39), and formula (40), the proportion of constituent units derived from tetracarboxylic anhydride, in particular the proportion of constituent units derived from tetracarboxylic anhydride, in which Y in formula (1) is at least one selected from the group consisting of structures represented by formulas (31) to (33), formula (39), and formula (40), is preferably 30 mol% or more, more preferably 50 mol% or more, even 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 constituent units (A). When the proportion is within the above range, the Df of the PI-based film is easily reduced. The proportion of the constituent units is, for example, 1 It can be measured using 1H-NMR, or it can be calculated from the raw material charging ratio.

[0074] (Constituent unit (A1) derived from ester-bonded tetracarboxylic anhydride) In one embodiment of the present invention, it is preferable that the constituent unit (A) includes a constituent unit (A1) derived from an ester bond-containing tetracarboxylic anhydride (hereinafter sometimes simply referred to as constituent unit (A1)). When constituent unit (A) includes the constituent unit (A1), molecularly oriented ester bonds are incorporated into the PI-based resin, making it easier to adjust the X-ray parameters to the above range and reduce Df in the step of coating the PI-based resin precursor solution onto a substrate and imidizing the coating film. Also, for the same reason, it is easier to reduce CTE and improve the dimensional stability of the PI-based film. Furthermore, even at low temperatures such as 350°C or below, Df tends to be low, so even when the CCL is produced by thermal imidizing the PI-based resin precursor coating film in a laminated configuration with copper foil, it is easier to suppress the deterioration of the copper foil surface and obtain a CCL with excellent high-frequency characteristics. In this specification, the in-plane orientation index, molecular periodicity index, and in-plane anisotropy index are collectively referred to as X-ray parameters.

[0075] In one embodiment of the present invention, the constituent unit (A1) is not particularly limited as long as it contains an ester bond, and the constituent unit (A1) may contain one or two or more ester bonds, but from the viewpoint of easily reducing the Df of the PI-based film, formula (a1): [ka] [In formula (a1), Z represents a divalent organic group, R a1 Each of these independently represents a halogen atom, or an alkyl group, alkoxy group, aryl group, or aryloxy group which may have a halogen atom. [s represents integers between 0 and 3, independently of each other.] It is preferable that the constituent unit (a1) is derived from a tetracarboxylic anhydride represented by .

[0076] R in equation (a1) a1 Each of these independently represents a halogen atom, or an alkyl group, alkoxy group, aryl group, or aryloxy group which may have a halogen atom. From the viewpoint of easily reducing the Df of the PI-based film, each of these preferably independently represents 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 alkyl groups having 1 to 6 carbon atoms, alkoxy groups having 1 to 6 carbon atoms, and aryl groups having 6 to 12 carbon atoms include those exemplified above. R a1 The hydrogen atoms contained therein may be independently substituted with halogen atoms, and examples of halogen atoms include those listed above. Among these, R is the most suitable for reducing the Df of PI-type films. a1 Examples of these include alkyl groups having 1 to 6 carbon atoms, preferably alkyl groups having 1 to 3 carbon atoms, independently of each other. Furthermore, in formula (a1), s represents an integer between 0 and 3, independently of each other, preferably 0 or 1, more preferably 0.

[0077] In formula (a1), Z represents a divalent organic group, and examples of divalent organic groups include those exemplified above as divalent organic groups in formula (39). Among these, from the viewpoint of easily reducing the Df of PI-based films, Z is represented by formulas (z1), (z2), and (z3): [ka] [In equations (z1) and (z2), R z11 ~R z14 Each of these independently represents a monovalent hydrocarbon group which may have a hydrogen atom or a halogen atom. R z2 These independently represent monovalent hydrocarbon groups which may have a halogen atom. n represents an integer from 1 to 4. j represents an integer between 0 and 3, independently of each other. * represents a combination. It is preferable that the divalent organic group is represented by formula (z1), and more preferably that the divalent organic group is represented by formula (z1).

[0078] In one embodiment of the present invention, R in equation (z1) z11 ~R z14 Each of these independently represents a monovalent hydrocarbon group which may have a hydrogen atom or a halogen atom. Examples of monovalent hydrocarbon groups include those exemplified above. R z11 ~R z14 From the viewpoint of easily reducing the Df of PI-based films, each element independently preferably represents an alkyl group which may have a hydrogen atom or a halogen atom, more preferably an alkyl group having 1 to 6 carbon atoms which may have a hydrogen atom or a halogen atom, even more preferably an alkyl group having 1 to 3 carbon atoms which may have a hydrogen atom or a halogen atom, and particularly preferably a hydrogen atom.

[0079] In one embodiment of the present invention, R in equation (z2) z2 R independently represents a monovalent hydrocarbon group which may have a halogen atom, and examples of monovalent hydrocarbon groups include those listed above. z2From the viewpoint of easily improving the mechanical properties, thermal properties, and dielectric properties of PI-based films, each element independently preferably represents an alkyl group which may have a halogen atom, more preferably an alkyl group having 1 to 6 carbon atoms which may have a halogen atom, and even more preferably an alkyl group having 1 to 3 carbon atoms which may have a halogen atom.

[0080] In one embodiment of the present invention, from the viewpoint of easily reducing the Df of the PI-based film, R in formula (z1) z11 ~R z14 In a benzene ring having R z11 ~R z14 At least one of them may be a monovalent hydrocarbon group having a halogen atom, but R z11 ~R z14 It is preferable that all of them are hydrogen atoms.

[0081] In formula (z2), j represents 0 to 3 independently of each other. In one embodiment of the present invention, from the viewpoint of easily reducing the Df of the PI-based film, j is preferably 0 or 1, more preferably 0, and even more preferably all j are 0.

[0082] In formula (z1), n ​​represents an integer from 1 to 4, and from the viewpoint of easily reducing the Df of the PI-based film, it preferably represents an integer from 1 to 3, more preferably 1 or 2, and particularly preferably 2.

[0083] In a preferred embodiment of the present invention, formula (a1) is formula (a1') or formula (a1"): [ka] It is preferable that the PI resin is represented by the formula (a1), particularly formula (a1') or formula (a1"), as a constituent unit (A1). When the PI resin contains a constituent unit derived from a tetracarboxylic anhydride represented by formula (a1), particularly formula (a1') or formula (a1"), the Df of the resulting PI film is easily reduced. Furthermore, even at low temperatures such as 350°C or below, the Df tends to be low, so even when the CCL is produced by thermal imidizing a PI resin precursor coating film in a laminated configuration with copper foil, the deterioration of the copper foil surface is easily suppressed, and a CCL with excellent high-frequency characteristics is easily obtained.

[0084] In one embodiment of the present invention, the content of constituent unit (A1) is preferably 10 mol% or more, more preferably 20 mol% or more, even more preferably 30 mol% or more, even more preferably 35 mol% or more, and particularly preferably 40 mol% or more, relative to the total amount of constituent unit (A). Furthermore, the content of constituent unit (A1) is preferably 75 mol% or less, more preferably 70 mol% or less, even more preferably 65 mol% or less, and particularly preferably 60 mol% or less, relative to the total amount of constituent unit (A). When the content of constituent unit (A1) is within the above range, it is easier to adjust the X-ray parameters to the above range, and the Df of the PI-based film is easily reduced. The proportion of the constituent units is, for example, 1 It can be measured using 1H-NMR, or it can be calculated from the raw material charging ratio.

[0085] (Constituent unit (A2) derived from biphenyl skeleton-containing tetracarboxylic anhydride) In one embodiment of the present invention, it is preferable that the constituent unit (A) includes a constituent unit (A2) derived from a biphenyl skeleton-containing tetracarboxylic anhydride (hereinafter sometimes simply referred to as constituent unit (A2)). When constituent unit (A) includes the constituent unit (A2), the Df of the resulting PI-based film is easily reduced.

[0086] In one embodiment of the present invention, the constitutional unit (A2) is not particularly limited as long as it contains a biphenyl skeleton, and the number of biphenyl skeletons contained in the constitutional unit (A2) may be one or two or more. Further, in one embodiment of the present invention, the constitutional unit (A2) preferably contains a biphenyl skeleton and does not contain an ester bond. In the present specification, a constitutional unit derived from a tetracarboxylic dianhydride containing both an ester bond and a biphenyl skeleton is not the constitutional unit (A2), but is classified as the constitutional unit (A1) derived from an ester bond-containing tetracarboxylic dianhydride.

[0087] In one embodiment of the present invention, the constitutional unit (A2) has the formula (a2):

Chemical formula

[0088] R a2 in formula (a2) each independently represents a halogen atom, or an alkyl group, an alkoxy group, an aryl group or an aryloxy group which may have a halogen atom. From the viewpoint of easily reducing the Df of the PI-based film, preferably each independently represents 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. The hydrogen atoms contained in R a2 may each independently be substituted with a halogen atom, and examples of the halogen atom include those exemplified above. Among these, from the viewpoint of easily reducing the Df of the PI-based film, R a2 is preferably an alkyl group having 1 to 6 carbon atoms, more preferably an alkyl group having 1 to 3 carbon atoms, each independently.

[0089] The bonding positions of the two carboxylic acid anhydrides attached to the benzene rings constituting the biphenyl skeleton in formula (a2) are not particularly limited. Based on the single bond connecting the two benzene rings, they may be 3,4- or 2,3-, independently of each other. From the viewpoint of easily reducing the Df of the PI-based film, 3,4- is preferred.

[0090] In a preferred embodiment of the present invention, formula (a2) is formula (a2'): [ka] It is preferable that it be represented as such. When the PI resin contains a constituent unit derived from a tetracarboxylic anhydride represented by formula (a2), particularly formula (a2'), as a constituent unit (A2), the Df of the resulting PI film is easily reduced. Furthermore, even at low temperatures such as 350°C or below, the Df tends to be low, so even when the CCL is produced by thermal imidizing a PI resin precursor coating film in a laminated configuration with copper foil, the deterioration of the copper foil surface is easily suppressed, and CCL with excellent high-frequency characteristics is easily obtained.

[0091] In one embodiment of the present invention, the content of constituent unit (A2) is preferably 25 mol% or more, more preferably 30 mol% or more, even more preferably 35 mol% or more, and particularly preferably 40 mol% or more, relative to the total amount of constituent unit (A). Furthermore, the content of constituent unit (A2) is preferably 90 mol% or less, more preferably 80 mol% or less, even more preferably 70 mol% or less, and particularly preferably 60 mol% or less, relative to the total amount of constituent unit (A). When the content of constituent unit (A2) is within the above range, it is easier to adjust the X-ray parameters to the above range, and the Df of the PI-based film is easily reduced. The proportion of the constituent units is, for example, 1 It can be measured using 1H-NMR, or it can be calculated from the raw material charging ratio.

[0092] (Component unit (A3)) In one embodiment of the present invention, the constituent unit (A) may include a constituent unit (A3) derived from a tetracarboxylic anhydride other than constituent units (A1) and (A2) (hereinafter sometimes simply referred to as constituent unit (A3)). In this specification, "constituent units (A3) derived from tetracarboxylic anhydride other than constituent units (A1) and constituent units (A2)" means constituent units derived from tetracarboxylic anhydride that do not fall under either constituent unit (A1) or constituent unit (A2), and "constituent unit (A3) content" means the total amount of constituent unit (A3) if there are multiple constituent units (A3).

[0093] In one embodiment of the present invention, the constituent unit (A3) is a constituent unit derived from a tetracarboxylic anhydride that does not contain either an ester bond or a biphenyl skeleton, for example, a constituent unit derived from a tetracarboxylic anhydride represented by formulas (31) to (38) in formula (1). From the viewpoint of easily reducing the Df of the PI-based film, it is preferable that the constituent unit derived from a tetracarboxylic anhydride represented by formulas (42) to (49) or (53) in formula (1), more preferably that the constituent unit derived from a tetracarboxylic anhydride represented by formulas (42), (46), (49), (43), or (53) in formula (1), and even more preferably that the constituent unit derived from a tetracarboxylic anhydride represented by formulas (42), (46), (49), or (53) in formula (1).

[0094] In one embodiment of the present invention, if a constituent unit (A3) is included, its content may be, for example, 0.01 to 55 mol%, or 0.01 to 40 mol%, relative to the total amount of constituent units (A), preferably 40 mol% or less, more preferably 35 mol% or less, even more preferably 30 mol% or less, particularly preferably 25 mol% or less, and usually 0.01 mol% or more, preferably 10 mol% or more. When the content of constituent unit (A3) is within the above range, it is easy to adjust the X-ray parameters to the above range, and the Df of the PI-based film is easily reduced. The proportion of the constituent units is, for example 1 It can be measured using 1H-NMR, or it can be calculated from the raw material charging ratio.

[0095] In one embodiment of the present invention, when the constituent unit (A3), preferably a constituent unit derived from a tetracarboxylic anhydride represented by formula (32) where Y in formula (1) is f=0, more preferably a constituent unit derived from a tetracarboxylic anhydride represented by formula (32) where Y in formula (1) is f=0, is included, the content is preferably 10 mol% or more, more preferably 20 mol% or more, even more preferably 30 mol% or more, particularly preferably 40 mol% or more, preferably 90 mol% or less, more preferably 80 mol% or less, even more preferably 70 mol% or less, particularly preferably 60 mol% or less, with respect to the total amount of constituent unit (A). When the content is within the above range, it is easy to adjust the X-ray parameters to the above range and the Df of the PI-based film is easily reduced. The proportion of the constituent unit is, for example 1 It can be measured using 1H-NMR, or it can be calculated from the raw material charging ratio.

[0096] In one embodiment of the present invention, if a constituent unit (A) includes constituent units (A1) and (A2), then constituent unit (A) is given by formula (X): (Total amount of component unit (A3)) / (Total amount of component units (A1) and (A2)) < 1.1 (X) It is preferable that the following relationship is satisfied. When the constituent unit (A) satisfies the relationship of equation (X), that is, when the value of the left side of equation (X) is less than 1.1, and especially less than 0.67, it is easier to reduce the Df of the resulting PI-based film and obtain a PI-based film with an excellent balance of mechanical properties.

[0097] In one embodiment of the present invention, the value on the left side of equation (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 easily reducing the Df of the PI-based film. Furthermore, the lower limit of the value on the left side of equation (X) is not particularly limited and may be 0 or greater.

[0098] In one embodiment of the present invention, from the viewpoint of easily reducing the Df of the PI-based film, the constituent unit (A) preferably includes a constituent unit derived from a tetracarboxylic anhydride represented by formula (a2), and / or a constituent unit derived from a tetracarboxylic anhydride represented by formula (32), where Y in formula (1) is f=0. In one embodiment of the present invention, from the viewpoint of easily reducing the Df of the PI-based film, the constituent unit (A) preferably includes at least one selected from the group consisting of a constituent unit derived from a tetracarboxylic anhydride represented by formula (a1), a constituent unit derived from a tetracarboxylic anhydride represented by formula (a2), and a constituent unit derived from a tetracarboxylic anhydride represented by formula (32), where Y in formula (1) is f=0, and more preferably includes a constituent unit derived from a tetracarboxylic anhydride represented by formula (a1), a constituent unit derived from a tetracarboxylic anhydride represented by formula (a2), and / or a constituent unit derived from a tetracarboxylic anhydride represented by formula (32), where Y in formula (1) is f=0.

[0099] (Diamine-derived structural unit (B)) PI-based resins contain diamine-derived constituent units (B) (hereinafter sometimes simply referred to as constituent units (B)). Constituent units (B) are not particularly limited as long as the in-plane orientation index of the PI-based film is within the above range, but for example, formula (2): [ka] [In formula (2), X represents a divalent organic group.] Preferably, the constituent unit is derived from a diamine represented by .

[0100] In formula (2), X represents a divalent organic group, preferably a divalent organic group having 2 to 100 carbon atoms. Examples of the divalent organic group include a divalent aromatic group, a divalent aliphatic group, etc. Examples of the divalent aliphatic group include a divalent acyclic aliphatic group or a divalent cyclic aliphatic group. Among these groups, from the viewpoint of easily improving the mechanical properties and thermal properties of the PI-based film, a divalent cyclic aliphatic group and a divalent aromatic group are preferable, and a divalent aromatic group is more preferable. The hydrogen atoms in the divalent organic group may be substituted with halogen atoms, hydrocarbon groups, alkoxy groups or halogenated hydrocarbon groups. In that case, the carbon number of these groups is preferably 1 to 8. In the present specification, the divalent aromatic group is a divalent organic group having an aromatic group, and may contain an aliphatic group or other substituents in a part of its structure. Further, the divalent aliphatic group is a divalent organic group having an aliphatic group, and may contain other substituents in a part of its structure, but does not contain an aromatic group.

[0101] In one embodiment of the present invention, the PI-based resin may contain a plurality of types of X, and the plurality of types of X may be the same as or different from each other. Examples of X in formula (2) include groups (structures) represented by formulas (60) to (65); groups in which hydrogen atoms in the groups represented by formulas (60) to (65) are substituted with methyl groups, ethyl groups, n-propyl groups, isopropyl groups, n-butyl groups, isobutyl groups, sec-butyl groups, tert-butyl groups, fluoro groups, chloro groups or trifluoromethyl groups, etc.

[0102] [Chemical formula] [In formulas (60) and (61), R a [[ID=I5]]and R b each independently represent a halogen atom, or an alkyl group, an alkoxy group, an aryl group or an aryloxy group which may have a halogen atom. Hydrogen atoms contained in R a and R b may be independently substituted with halogen atoms, W is independent of each other, consisting of single bonds, -O-, -CH2-, -CH2-CH2-, -CH(CH3)-, -C(CH3)2-, -C(CF3)2-, -COO-, -OOC-, -SO2-, -S-, -CO-, or -N(R c )- represents R c This represents a monovalent hydrocarbon group having 1 to 12 carbon atoms, which may be substituted with hydrogen atoms or halogen atoms. t represents an integer between 0 and 4, u represents an integer between 0 and 4, and n represents an integer between 0 and 4. In formula (62), ring A represents a cycloalkane ring having 3 to 8 carbon atoms. R d This represents an alkyl group with 1 to 20 carbon atoms. r represents an integer greater than or equal to 0 and less than or equal to (the number of carbon atoms in ring A - 2). S1 and S2 represent integers between 0 and 20, independently of each other. In equations (60) to (65), * represents a combination.

[0103] Other examples of X in formula (2) include, for example, divalent acyclic aliphatic groups such as linear or branched alkylene groups such as ethylene, trimethylene, tetramethylene, pentamethylene, hexamethylene, propylene, 1,2-butanediyl, 1,3-butanediyl, 1,12-dodecanediyl, 2-methyl-1,2-propanediyl, and 2-methyl-1,3-propanediyl. Hydrogen atoms in the divalent acyclic aliphatic groups may be substituted with halogen atoms, and carbon atoms may be substituted with heteroatoms, such as oxygen or nitrogen atoms.

[0104] Among these, from the viewpoint of easily improving the mechanical properties, thermal properties, and dielectric properties of the PI-based film, the PI-based resin in the present invention preferably includes the structures represented by formulas (60) and (61) as X in formula (2), and more preferably includes the structure represented by formula (60).

[0105] In formulas (60) and (61), the bonds of each benzene ring or each cyclohexane ring may be bonded to the ortho, meta, or para position, or to the α, β, or γ position, respectively, with reference to the -W- or the single bond connecting each benzene ring or each cyclohexane ring. From the viewpoint of easily reducing the Df of the PI-based film and easily improving dimensional stability, the bonds may preferably be to the meta or para position, or to the β or γ position, more preferably to the para or γ position. R a and R b Each of these independently represents a halogen atom, or an alkyl group, alkoxy group, aryl group, or aryloxy group which may have a halogen atom, preferably a halogen atom, or an alkyl group, alkoxy group, or aryl group which may have a halogen atom, more preferably a halogen atom, a C1-C6 alkyl group, a C1-C6 alkoxy group, or a C6-C12 aryl group. Examples of C1-C6 alkyl groups, C1-C6 alkoxy groups, and C6-C12 aryl groups are those exemplified above. a and R b The hydrogen atoms contained therein may be independently substituted with halogen atoms, and examples of such halogen atoms include fluorine atoms, chlorine atoms, bromine atoms, and iodine atoms. From the viewpoint of easily reducing the Df of the PI-based film and easily improving dimensional stability, R a and R b These are preferably, independently of each other, an alkyl group having 1 to 6 carbon atoms or a fluorinated alkyl group having 1 to 6 carbon atoms. From the viewpoint of easily improving adhesion to substrates such as copper foil, it is more preferably an alkyl group having 1 to 6 carbon atoms that does not contain fluorine, even more preferably an alkyl group having 1 to 3 carbon atoms that does not contain fluorine, and particularly preferably a methyl group.

[0106] In formulas (60) and (61), t and u are integers between 0 and 4, independently of each other, and are preferably integers between 0 and 2, more preferably 0 or 1, from the viewpoint of easily reducing the Df of the PI-based film and easily improving dimensional stability.

[0107] In equations (60) and (61), W is independently of each other: a single bond, -O-, -CH2-, -CH2-CH2-, -CH(CH3)-, -C(CH3)2-, -C(CF3)2-, -COO-, -OOC-, -SO2-, -S-, -CO-, or -N(R c From the viewpoint of reducing the Df of the PI-based film and improving dimensional stability, it is preferable to represent -O-, -CH2-, -C(CH3)2-, -C(CF3)2-, -COO-, -OOC-, or -CO-, and from the viewpoint of further improving adhesion to substrates such as copper foil, it is more preferable to represent a single bond, -O-, -CH2-, or -C(CH3)2-, and even more preferably -O- or -C(CH3)2-. c This represents a monovalent hydrocarbon group having 1 to 12 carbon atoms, which may be substituted with hydrogen atoms or halogen atoms. Examples of monovalent hydrocarbon groups having 1 to 12 carbon atoms are those exemplified above.

[0108] In formulas (60) and (61), n ​​is an integer from 0 to 4, and is preferably an integer from 0 to 3, more preferably 1 to 3, from the viewpoint of easily reducing the Df of the PI-based film and easily improving dimensional stability. When n is 2 or more, multiple W, R a , and t may be the same or different from each other, and the positions of the bonds of each benzene ring relative to -W- may also be the same or different.

[0109] In the present invention, if the PI resin contains two or more structures represented by formulas (60) and (61) as X in formula (2), then W, n, and R in one of the formulas (60) and (61) are... a , R b t and u are independent of each other, and W, n, and R in the other equations (60) and (61). a , R b t and u may be the same or different.

[0110] In formula (62), ring A represents a cycloalkane ring having 3 to 8 carbon atoms. Examples of cycloalkane rings include cyclopropane, cyclobutane, cyclopentane, cyclohexane, cycloheptane, and cyclooctane rings, with cycloalkane rings having 4 to 6 carbon atoms being preferred. In ring A, each bond may or may not be adjacent to one another. For example, if ring A is a cyclohexane ring, the two bonds may be in an α, β, or γ positional relationship, preferably in a β or γ positional relationship.

[0111] R in equation (62) d R represents an alkyl group having 1 to 20 carbon atoms. Examples of alkyl groups having 1 to 20 carbon atoms include R 7 ~R 18 Examples of hydrocarbon groups having 1 to 20 carbon atoms in are those exemplified above, and preferably represent alkyl groups having 1 to 10 carbon atoms. In formula (62), r is 0 or greater and represents an integer less than or equal to "the number of carbon atoms in ring A minus 2". r is preferably 0 or greater, and preferably 4 or less. In formula (62), S1 and S2 independently represent integers from 0 to 20. S1 and S2 independently are preferably 0 or greater, more preferably 2 or greater, and preferably 15 or less.

[0112] Specific examples of the structures represented by equations (60) to (62) include those represented by equations (71) to (92). In these equations, * represents a bond.

[0113] [ka]

[0114] In a preferred embodiment of the present invention, when X in formula (2) includes at least one diamine-derived structural unit represented by formulas (60) and (61), the proportion of diamine-derived structural units represented by formulas (60) and (61), particularly in formula (60) where n is 1 and W represents a single bond, is preferably 25 mol% or more, more preferably more than 30 mol%, even more preferably 50 mol% or more, even 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 structural unit (B). When the proportion of diamine-derived structural units represented by formulas (60) and (61), particularly in formula (60) where at least one W represents a single bond, is within the above range, it is easier to reduce the Df of the PI-based film and improve its dimensional stability. The proportion of the structural units is, for example, 1 It can be measured using 1H-NMR, or it can be calculated from the raw material charging ratio.

[0115] (Constituent unit (B1) derived from biphenyl skeleton-containing diamine) In one embodiment of the present invention, it is preferable that the constituent unit (B) includes a constituent unit (B1) derived from a biphenyl skeleton-containing diamine (hereinafter sometimes simply referred to as constituent unit (B1)). Since the Df of the resulting PI-based film is easily reduced when the constituent unit (B) is a PI-based resin containing the constituent unit (B1), the electrical circuit made of the resulting PI-based film is easily able to reduce transmission loss.

[0116] In one embodiment of the present invention, the constituent unit (B1) is not particularly limited as long as it contains a biphenyl skeleton, and the constituent unit (B1) may contain one or more biphenyl skeletons. In one embodiment of the present invention, from the viewpoint of easily reducing the Df of the PI-based film, the constituent unit (B1) is given by formula (b1): [ka] [In formula (b1), R b1Each of these independently represents a halogen atom, or an alkyl group, alkoxy group, aryl group, or aryloxy group which may have a halogen atom. [p represents an integer between 0 and 4] It is preferable that the constituent unit (b1) is derived from a diamine represented by .

[0117] In equation (b1), R b1 Each of these independently represents a halogen atom, or an alkyl group, alkoxy group, aryl group, or aryloxy group which may have a halogen atom. From the viewpoint of easily reducing the Df of the PI-based film and easily improving dimensional stability, each of these preferably independently represents a halogen atom, or an alkyl group, alkoxy group, or aryl group which may have a halogen atom. More preferably, it represents a halogen atom, a C1-C6 alkyl group, a C1-C6 alkoxy group, or a C6-C12 aryl group. Examples of C1-C6 alkyl groups, C1-C6 alkoxy groups, and C6-C12 aryl groups are those exemplified above. b1 The hydrogen atoms contained therein may be independently substituted with halogen atoms, and examples of such halogen atoms are the same as those described above. From the viewpoint of easily reducing the Df of the PI film and easily improving dimensional stability, R b1 These are preferably, independently of each other, an alkyl group having 1 to 6 carbon atoms or a fluorinated alkyl group having 1 to 6 carbon atoms. From the viewpoint of easily improving adhesion to substrates such as copper foil, it is more preferably an alkyl group having 1 to 6 carbon atoms that does not contain fluorine, even more preferably an alkyl group having 1 to 3 carbon atoms that does not contain fluorine, and particularly preferably a methyl group.

[0118] In formula (b1), p represents an integer between 0 and 4, independently of each other, and is preferably an integer between 0 and 2, more preferably 0 or 1, from the viewpoint of easily reducing the Df of the PI-based film and easily improving dimensional stability.

[0119] In formula (b1), the -NH2 group bonded to each benzene ring may be bonded to the ortho, meta, or para position, or to the α, β, or γ position, relative to the single bond connecting each benzene ring. From the viewpoint of easily reducing the Df of the PI-based film and easily improving dimensional stability, it is preferable that the bond be to the meta or para position, or to the β or γ position, more preferably to the para or γ position.

[0120] In a preferred embodiment of the present invention, formula (b1) is formula (b1'): [ka] It is preferable that it be represented as such. When the PI resin contains a diamine-derived constituent unit represented by formula (b1), particularly formula (b1'), as a constituent unit (B1), the Df of the resulting PI film tends to be reduced. Furthermore, even at low temperatures such as 350°C or below, the Df tends to be low, so even when the CCL is produced by thermal imidizing a PI resin precursor coating film in a laminated configuration with copper foil, the deterioration of the copper foil surface is easily suppressed, and a CCL with excellent high-frequency characteristics is easily obtained.

[0121] In one embodiment of the present invention, the content of constituent unit (B1), preferably constituent unit (b1), is preferably 25 mol% or more, more preferably more than 30 mol%, even more preferably 40 mol% or more, even more preferably 60 mol% or more, particularly preferably 70 mol% or more, particularly more preferably 80 mol% or more, and most even more preferably 90 mol% or more, relative to the total amount of constituent unit (B). When the content of constituent unit (B1), preferably constituent unit (b1), is above the above lower limit, Df is easily reduced. Furthermore, there is no particular upper limit to the content of constituent unit (B1), preferably constituent unit (b1), and it may be 100 mol% or less relative to the total amount of constituent unit (B). The proportion of the constituent units is, for example, 1 It can be measured using 1H-NMR, or it can be calculated from the raw material charging ratio.

[0122] (Component unit (B2)) In one embodiment of the present invention, it is preferable that the constituent unit (B) includes a diamine-derived constituent unit (B2) (hereinafter sometimes simply referred to as constituent unit (B2)) having two or more aromatic rings, each aromatic ring being bonded via a divalent organic group. The divalent organic group in constituent unit (B2) may be, for example, an alkylene group which may have a halogen atom, -O-, -COO-, -OOC-, -SO2-, -S-, -CO- or -N(R c )- and others are examples, R c - represents a monovalent hydrocarbon group having 1 to 12 carbon atoms, which may be substituted with hydrogen atoms or halogen atoms. Among these, the divalent organic groups in the constituent unit (B2) are -O-, -CH2-, -CH2-CH2-, -CH(CH3)-, -C(CH3)2-, -C(CF3)2-, -COO-, -OOC-, -SO2-, -S-, -CO-, or -N(R c )- is preferable.

[0123] In one embodiment of the present invention, the constituent unit (B) is defined as constituent unit (B2) by formula (b2): [ka] [In formula (b2), R b2 Each of these independently represents a halogen atom, or an alkyl group, alkoxy group, aryl group, or aryloxy group which may have a halogen atom. W is independent of each other and is -O-, -CH2-, -CH2-CH2-, -CH(CH3)-, -C(CH3)2-, -C(CF3)2-, -COO-, -OOC-, -SO2-, -S-, -CO-, or -N(R c )- represents R c This represents a monovalent hydrocarbon group having 1 to 12 carbon atoms, which may be substituted with hydrogen atoms or halogen atoms. m represents an integer from 1 to 4. [q represents an integer between 0 and 4, independently of each other.] It is preferable that the constituent unit (b2) derived from the diamine represented by (b2) (hereinafter sometimes simply referred to as constituent unit (b2)) is included. When constituent unit (B) includes the constituent unit (B2), in particular constituent unit (b2), the Df of the resulting PI-based film is easily reduced, and as a result, the transmission loss of the electronic circuit containing the resulting PI-based film is easily reduced.

[0124] In equation (b2), R b2 Each of these independently represents a halogen atom, or an alkyl group, alkoxy group, aryl group, or aryloxy group which may have a halogen atom, preferably a halogen atom, a C1-C6 alkyl group, a C1-C6 alkoxy group, or a C6-C12 aryl group. Examples of C1-C6 alkyl groups, C1-C6 alkoxy groups, and C6-C12 aryl groups are those exemplified above. b2 The hydrogen atoms contained therein may be independently substituted with halogen atoms, and examples of such halogen atoms are the same as those described above. From the viewpoint of easily reducing the Df of the PI film and easily improving dimensional stability, R b2 These are preferably, independently of each other, an alkyl group having 1 to 6 carbon atoms or a fluorinated alkyl group having 1 to 6 carbon atoms. From the viewpoint of easily improving adhesion to substrates such as copper foil, it is more preferably an alkyl group having 1 to 6 carbon atoms that does not contain fluorine, even more preferably an alkyl group having 1 to 3 carbon atoms that does not contain fluorine, and particularly preferably a methyl group.

[0125] In formula (b2), q represents an integer between 0 and 4, independently of each other, and is preferably an integer between 0 and 2, more preferably 0 or 1, from the viewpoint of easily reducing the Df of the PI-based film and easily improving dimensional stability.

[0126] In equation (b2), W is independently of each other -O-, -CH2-, -CH2-CH2-, -CH(CH3)-, -C(CH3)2-, -C(CF3)2-, -COO-, -OOC-, -SO2-, -S-, -CO-, or -N(R cFrom the viewpoint of reducing the Df of the PI-based film and improving dimensional stability, it is preferable to represent -O-, -CH2-, -C(CH3)2-, -C(CF3)2-, -COO-, -OOC-, or -CO-, and from the viewpoint of further improving adhesion to substrates such as copper foil, it is more preferable to represent -O-, -CH2-, or -C(CH3)2-, and even more preferably -O- or -C(CH3)2-. c This represents a monovalent hydrocarbon group having 1 to 12 carbon atoms, which may be substituted with hydrogen atoms or halogen atoms. Examples of monovalent hydrocarbon groups having 1 to 12 carbon atoms are those exemplified above, which may be substituted with halogen atoms. Examples of halogen atoms are the same as those exemplified above.

[0127] In formula (b2), m is an integer from 1 to 4, and is preferably an integer from 1 to 3, more preferably 2 or 3, from the viewpoint of easily reducing the Df of the PI-based film and easily improving dimensional stability. In formula (b2), multiple W, R b2 , and q may be the same or different from each other, and the positions of -W- relative to -NH2 on each benzene ring may be the same or different.

[0128] In formula (b2), -W- may be bonded to the ortho, meta, or para position, or to the α, β, or γ position, relative to the -NH2 of each benzene ring. From the viewpoint of easily reducing the Df of the PI-based film and easily improving dimensional stability, it is preferably bonded to the meta or para position, or to the β or γ position, more preferably to the para or γ position.

[0129] In one embodiment of the present invention, from the viewpoint of easily reducing the Df of the PI-based film and easily improving the adhesion between the PI-based film and the copper foil, it is preferable that in formula (b2), m is 3 and W independently represents -O- or -C(CH3)2-, and formula (b2) is formula (b2'): [ka] It is more preferable that it be represented as follows. When the PI resin contains the constituent unit (b2), in particular the diamine-derived constituent unit represented by formula (b2'), the storage modulus at 280°C (hereinafter sometimes referred to as E' at 280°C) tends to decrease, and as a result, the Df of the PI film tends to decrease, and it is easier to obtain a PI film with excellent adhesion to copper foil. Furthermore, even at low temperatures such as 350°C or below, the Df tends to decrease, so even when the CCL is produced by thermal imidizing a PI resin precursor coating film in a laminated configuration with copper foil, it is easier to suppress the deterioration of the copper foil surface and easier to obtain a CCL with excellent high-frequency characteristics.

[0130] In one embodiment of the present invention, the constituent unit (b2) may include, in addition to, a constituent unit derived from a diamine represented by formula (b2'), or in place of said constituent unit, a constituent unit derived from a diamine in formula (b2) where m is 1 and W represents -O-.

[0131] In one embodiment of the present invention, the content of constituent unit (B2) is preferably 0 mol% or more, more preferably 0.3 mol% or more, even more preferably 0.5 mol% or more, even more preferably 0.8 mol% or more, particularly preferably 1 mol% or more, particularly more preferably 5 mol% or more, and extremely preferably 8 mol% or more, relative to the total amount of constituent unit (B). When the content of constituent unit (B2) is above the lower limit, the adhesion of the resulting PI-based film to a substrate such as copper foil tends to improve. Furthermore, the upper limit of the content of constituent unit (B2) is preferably 75 mol% or less, more preferably 60 mol% or less, even more preferably 40 mol% or less, even more preferably 30 mol% or less, and particularly preferably 20 mol% or less, relative to the total amount of constituent unit (B). When the content of constituent unit (B2) is below the upper limit, there is a tendency for mechanical properties such as CTE and dielectric properties to improve. The proportion of the constituent units is, for example 1 It can be measured using 1H-NMR, or it can be calculated from the raw material charging ratio.

[0132] (Component unit (B3)) PI resins may contain diamine-derived constituent units (B3) other than constituent units (B1) and (B2) (hereinafter sometimes simply referred to as constituent unit (B3)). Examples of constituent unit (B3) include diamine-derived constituent units in formula (b2) where m is 0, and diamine-derived constituent units in formula (2) where X is represented by formulas (61) to (64). Among these, diamine-derived constituent units in formula (2) where X is represented by formula (74) (p-phenylenediamine-derived constituent units) are preferred. In this specification, "diamine-derived constituent units (B3) other than constituent units (B1) and (B2)" means diamine-derived constituent units that are different from both constituent units (B1) and (B2).

[0133] In one embodiment of the present invention, when constituent unit (B) contains constituent unit (B3), the content of constituent unit (B3) is preferably 25 mol% or less, more preferably 20 mol% or less, even more preferably 10 mol% or less, and preferably 0.01 mol% or more, relative to the total amount of constituent unit (B).

[0134] In one embodiment of the present invention, the PI resin may contain halogen atoms, preferably fluorine atoms, which can be introduced by, for example, the halogen-containing substituents described above. When the PI resin contains fluorine atoms, the dielectric constant of the resulting PI film is easily reduced. Preferred fluorine-containing substituents for incorporating fluorine atoms into the PI resin include, for example, fluoro groups and trifluoromethyl groups. Furthermore, in another embodiment of the present invention, it is preferable that the PI resin does not contain fluorine atoms, from the viewpoint of easily improving the adhesion of the resulting PI film to a substrate such as copper foil. Also, since the presence of fluorine in the PI resin tends to weaken the interactions between molecular chains, the absence of fluorine atoms makes it easier to adjust the X-ray parameters to the above range and tends to reduce the Df of the resulting PI film.

[0135] When the PI resin contains halogen atoms, the content of halogen atoms, particularly fluorine atoms, in the PI resin is preferably 0.1 to 35% by mass, more preferably 0.1 to 30% by mass, even more preferably 0.1 to 20% by mass, and most preferably 0.1 to 10% by mass, based on the mass of the PI resin. If the halogen atom content is above the lower limit, it is easier to improve the heat resistance and dielectric properties of the resulting PI film. If the halogen atom content is below the upper limit, it is advantageous in terms of cost, makes it easier to reduce the CTE of the PI film, and facilitates the synthesis of the PI resin.

[0136] In one embodiment of the present invention, the imidation rate of the PI resin is preferably 90% or more, more preferably 93% or more, even more preferably 95% or more, and usually 100% or less. From the viewpoint of easily improving mechanical properties, thermal properties, and dielectric properties, it is preferable that the imidation rate is above the lower limit mentioned above. The imidation rate represents the ratio of the molar amount of imide bonds in the PI resin to twice the molar amount of constituent units derived from the tetracarboxylic acid compound in the PI resin. If the PI resin contains a tricarboxylic acid compound, the imidation rate represents the ratio of the molar amount of imide bonds in the PI resin to the sum of twice the molar amount of constituent units derived from the tetracarboxylic acid compound and the molar amount of constituent units derived from the tricarboxylic acid compound. The imidation rate can be determined by methods such as IR or NMR.

[0137] In one embodiment of the present invention, the weight-average molecular weight of the PI resin on a polystyrene basis (hereinafter, the weight-average molecular weight may be referred to as Mw) is preferably 100,000 or more, more preferably greater than 100,000, even more preferably 110,000 or more, even more preferably 120,000 or more, particularly preferably 130,000 or more, preferably 1,000,000 or less, more preferably 700,000 or less, even more preferably 500,000 or less, and particularly preferably 300,000 or less. When Mw is above the lower limit above, it is easier to improve mechanical properties such as bending resistance. When Mw is below the upper limit above, it is advantageous in terms of processability during film formation.

[0138] In one embodiment of the present invention, the ratio (Mw / Mn) of the Mw of the PI resin to the number average molecular weight (hereinafter, the number average molecular weight may be referred to as Mn) is preferably 3.5 or higher, more preferably 4.0 or higher, even more preferably 4.2 or higher, even more preferably 4.5 or higher, particularly preferably 4.7 or higher, preferably 8.0 or lower, more preferably 7.0 or lower, even more preferably 6.0 or lower, and particularly preferably 5.5 or lower, in terms of polystyrene equivalent, from the viewpoint of easily improving bending resistance. Mw and Mn can be determined by gel permeation chromatography (hereinafter, sometimes referred to as GPC) measurement and converted to standard polystyrene equivalent.

[0139] In one embodiment of the present invention, the E' of the PI resin at 280°C is preferably 3 × 10 from the viewpoint of easily reducing the Df of the PI film. 8 Less than Pa, more comfortable 3 × 10 8 Pa or less, more preferably 2 × 10⁻⁶ 8 Pa or less, more preferably 1.5 × 10 8 Pa or less, particularly preferably 1 × 10⁻⁶ 8 Pa or less, especially more preferably 0.8 × 10 8 It is less than or equal to Pa. Furthermore, the E' of the PI resin at 280°C is preferably 1 × 10⁻¹⁰ from the viewpoint of easily suppressing deformation during processing of the PI film. 4 Pa or higher, comfort level 1 x 10 5 Pa or higher, more preferably 1 × 10⁻⁶ 6 It is Pa or higher. The E' of PI resin can be measured by dynamic viscoelasticity measurement, for example, by the method described in the examples.

[0140] The E' of the PI resin at 280°C can be adjusted by appropriately adjusting the types and compositions of the constituent units of the PI resin, as well as the molecular weight and manufacturing method of the PI resin, particularly the imidation conditions. For example, it can be adjusted to the range described as a preferred embodiment in this specification.

[0141] In one embodiment of the present invention, the Tg of the PI resin is preferably 290°C or lower, more preferably less than 290°C, even more preferably 280°C or lower, even more preferably 275°C or lower, particularly preferably 260°C or lower, particularly more preferably 250°C or lower, and particularly still more preferably 240°C or lower, from the viewpoint of easily reducing the Df of the resulting PI film. Furthermore, the Tg of the PI resin is preferably 200°C or higher, more preferably 202°C or higher, and even more preferably 205°C or higher, from the viewpoint of easily reducing the Df of the PI film and easily improving the heat resistance of the PI film. The Tg of the PI resin can be measured by dynamic viscoelasticity measurement, for example, by the method described in the examples.

[0142] The Tg of the PI resin can be adjusted by appropriately adjusting the types and composition of the constituent units that make up the PI resin, as well as the molecular weight and manufacturing method of the PI resin, particularly the imidation conditions. For example, it can be adjusted to the range described as a preferred embodiment in the description below.

[0143] In one embodiment of the present invention, if the E' and Tg of the PI resin at 280°C are within the above range, the PI resin is more likely to form a desirable higher-order structure in which rotational motion is suppressed. This is presumed to suppress the rotation of polar groups in the PI resin, reducing the loss of electrical energy as thermal motion, and thereby making it easier to reduce the Df of the PI film. Furthermore, polyamic acid, a precursor of PI-based resins, begins imidation at around 200°C. Generally, polyamic acid has a high degree of freedom in its molecular structure, but after imidation, it becomes relatively rigid, and the degree of freedom in its molecular structure decreases. If the Tg of the PI-based resin is preferably 200-290°C, the thermal imidation temperature exceeds the Tg of the PI-based resin during the progression of imidation. As a result, the amic acid moiety and the imide moiety move simultaneously to form a higher-order structure, making it easier for a desirable higher-order structure to be formed in which the rotational motion of the resin as a whole is suppressed. Also, preferably, E' at 280°C is 3 × 10⁻⁶ 8When the Pa is less than a certain value, the imide moieties can move sufficiently flexibly when forming the higher-order structure, making it easier for the resin as a whole to form a desirable higher-order structure with suppressed rotational motion. As a result, even at low temperatures such as 350°C or below, the Df can be kept low. Therefore, even when the CCL is manufactured by thermal imidizing a PI-based resin precursor coating film in a laminated configuration with copper foil, degradation of the copper foil surface can be suppressed, and a CCL with excellent high-frequency characteristics can be obtained.

[0144] In one embodiment of the present invention, the content of PI resin in the PI film is preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, and particularly preferably 90% by mass or more, relative to the mass of the PI film of the present invention. Furthermore, there is no particular upper limit to the content of PI resin, and it is, for example, 100% by mass or less, preferably 99% by mass or less, and more preferably 95% by mass or less, relative to the mass of the PI film. When the content of PI resin is within the above range, it is easy to improve the mechanical properties, thermal properties and dielectric properties.

[0145] The PI-based film of the present invention may optionally contain fillers. Examples of fillers include metal oxide particles such as silica and alumina, inorganic salt particles such as calcium carbonate, and polymer particles such as fluororesins and cycloolefin polymers. Fillers can be used alone or in combination of two or more types. When fillers are included, their content is preferably 50% by mass or less, more preferably 40% by mass or less, even more preferably 30% by mass or less, and preferably 0.01% by mass or more, based on the mass of the PI-based film.

[0146] Furthermore, in one embodiment of the present invention, the PI-based film of the present invention may contain additives as needed. Examples of additives include antioxidants, flame retardants, crosslinking agents, surfactants, compatibilizers, imidation catalysts, weathering agents, lubricants, antiblocking agents, antistatic agents, antifogging agents, anti-drip agents, and pigments. Additives can be used individually or in combination of two or more. The content of each additive can be appropriately selected within a range that does not impair the effects of the present invention, and when various additives are included, their total content is preferably 7% by mass or less, more preferably 5% by mass or less, even more preferably 4% by mass or less, and preferably 0.001% by mass or more, based on the mass of the PI-based film.

[0147] [Method for manufacturing polyimide films] The method for producing the PI-based film of the present invention is not particularly limited, but for example, the following steps: A step of coating a substrate with a PI-based resin precursor solution containing a constituent unit (A) derived from tetracarboxylic anhydride and a constituent unit (B) derived from diamine, and A process of imidizing a PI-based resin precursor by heat treatment at a temperature between 200°C and 500°C. It can be manufactured by a method that includes [a specific component].

[0148] <Coating process for polyimide resin precursor solution> (Preparation of PI resin precursor solution) The PI-based resin precursor solution comprises a PI-based resin precursor containing a constituent unit (A) derived from tetracarboxylic anhydride and a constituent unit (B) derived from diamine, and a solvent, and can be prepared by mixing the PI-based resin precursor and the solvent. In addition, in one embodiment of the present invention, the reaction solution containing the PI-based resin precursor obtained by the synthesis of the PI-based resin precursor may be appropriately diluted with a solvent as needed and used as the PI-based resin precursor solution.

[0149] The PI-based resin precursor in this invention is obtained by reacting a tetracarboxylic anhydride with a diamine. In addition to the tetracarboxylic acid compound, dicarboxylic acid compounds and tricarboxylic acid compounds may also be reacted.

[0150] Examples of the tetracarboxylic acid anhydride used for synthesizing the PI resin precursor include aromatic tetracarboxylic acid compounds such as aromatic tetracarboxylic dianhydrides; and aliphatic tetracarboxylic acid compounds such as aliphatic tetracarboxylic dianhydrides. The tetracarboxylic acid compound may be used alone or in combination of two or more. The tetracarboxylic acid compound may be an analog of a tetracarboxylic acid compound such as an acid chloride compound in addition to the dianhydride. Examples of the tetracarboxylic acid compound include, for example, the tetracarboxylic acid anhydride represented by the above formula (1), preferably, the tetracarboxylic acid anhydride represented by the formula (a1), the tetracarboxylic acid anhydride represented by the formula (a2), and the tetracarboxylic acid anhydride in which Y in the formula (1) is represented by the formula (32).

[0151] Specific examples of tetracarboxylic acid compounds include pyromellitic anhydride (sometimes referred to as PMDA), 4,4'-(4,4'-isopropylidene diphenoxy)diphthalic anhydride (sometimes referred to as BPADA), 1,4,5,8-naphthalenetetracarboxylic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride (sometimes referred to as BPDA), 4,4'-(hexafluoroisopropylidene)diphthalic dianhydride (sometimes referred to as 6FDA), and 4,4'-oxydiphthalic dianhydride. Aqueous compounds (hereinafter sometimes referred to as ODPA), 2,2',3,3'-, 2,3,3',4'- or 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 2,3',3,4'-biphenyltetracarboxylic dianhydride, 2,2',3,3'-biphenyltetracarboxylic dianhydride, p-phenylenebis(trimellitic acid monoesteric acid dianhydride) (hereinafter sometimes referred to as TAHQ), esterified products of trimellitic anhydride and 2,2',3,3',5,5'-hexamethyl-4,4'-biphenol (hereinafter referred to as TMPBP) (may be), 4,4'-bis(1,3-dioxo-1,3-dihydroisobenzofuran-5-ylcarbonyloxy)biphenyl (hereinafter sometimes referred to as BP-TME), 2,3',3,4'-diphenyl ether tetracarboxylic dianhydride, bis(2,3-dicarboxyphenyl) ether dianhydride, 3,3”,4,4”-p-terphenyl tetracarboxylic dianhydride, 2,3,3”,4”-p-terphenyl tetracarboxylic dianhydride, 2,2”,3,3”-p-terphenyl tetracarboxylic dianhydride, 2,2-bis(2, 3-Dicarboxyphenyl)-propane dianhydride, 2,2-bis(3,4-dicarboxyphenyl)-propane dianhydride, bis(2,3-dicarboxyphenyl)methane dianhydride, bis(3,4-dicarboxyphenyl)methane dianhydride, 1,1-bis(2,3-dicarboxyphenyl)ethane dianhydride, 1,1-bis(3,4-dicarboxyphenyl)ethane dianhydride, 1,2,7,8-,1,2,6,7-phenanthrene-tetracarboxylic acid dianhydride, 1,2,9,10-phenanthrene-tetracarboxylic acid dianhydride, 2,2-bis(3,4-Dicarboxyphenyl)tetrafluoropropane dianhydride, 1,2,4,5-cyclohexanetetracarboxylic acid dianhydride (hereinafter sometimes referred to as HPMDA), 2,3,5,6-cyclohexanetetracarboxylic acid dianhydride, 2,3,6,7-naphthalenetetracarboxylic acid dianhydride, 1,2,5,6-naphthalenetetracarboxylic acid dianhydride, cyclopentane-1,2,3,4-tetracarboxylic acid dianhydride, 4,4'-bis(2,3-dicarboxyphenoxy)diphenylmethane dianhydride, 1,2, 3,4-Cyclobutanetetracarboxylic dianhydride (hereinafter sometimes referred to as CBDA), norbornane-2-spiro-α'-spiro-2”-norbornane-5,5',6,6'-tetracarboxylic anhydride, p-phenylenebis(trimellitate anhydride), 3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride, 2,3,6,7-anthracenetetracarboxylic dianhydride, 4,8-dimethyl-1,2,3,5,6,7-hexahydronaphthalene-1,2,5,6-tetracarboxylic dianhydride , 2,6-dichloronaphthalene-1,4,5,8-tetracarboxylic dianhydride, 2,7-dichloronaphthalene-1,4,5,8-tetracarboxylic dianhydride, 2,3,6,7-tetrachloronaphthalene-1,4,5,8-tetracarboxylic 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 Dianhydride, 2,3,8,9-perylene-tetracarboxylic acid dianhydride, 3,4,9,10-perylene-tetracarboxylic acid dianhydride, 4,5,10,11-perylene-tetracarboxylic acid dianhydride, 5,6,11,12-perylene-tetracarboxylic acid dianhydride, pyrazine-2,3,5,6-tetracarboxylic acid dianhydride, pyrrolidine-2,3,4,5-tetracarboxylic acid dianhydride, thiophene-2,3,4,5-tetracarboxylic acid dianhydride, bis(2,3-dicarboxyphenyl)sulfone dianhydride, bis(3,Examples thereof include 4-dicarboxyphenyl)sulfone dianhydride and the like. Among these, from the viewpoint of easily reducing Df of the PI-based film obtained even at a low imidization temperature, BPDA, PMDA, TAHQ, and BP-TME are preferable, and BPDA, TAHQ, and BP-TME are more preferable. These tetracarboxylic acid compounds can be used alone or in combination of two or more.

[0152] Examples of the diamine compound used for synthesizing the PI-based resin precursor include aliphatic diamines, aromatic diamines, and mixtures thereof. In the present embodiment, the "aromatic diamine" represents a diamine having an aromatic ring, and may contain an aliphatic group or other substituents in a part of its structure. This aromatic ring may be a monocyclic ring or a condensed ring, and examples thereof include a benzene ring, a naphthalene ring, an anthracene ring, and a fluorene ring, but are not limited thereto. Among these, a benzene ring is preferable. The "aliphatic diamine" represents a diamine having an aliphatic group, and may contain other substituents in a part of its structure, but does not have an aromatic ring. Examples of the diamine compound include, for example, the diamine compound represented by the above formula (2), and preferably, the diamine compound represented by the formula (b1) and the diamine compound represented by the formula (b2).

[0153] Specific examples of diamine compounds include 1,4-diaminocyclohexane, 4,4'-diamino-2,2'-dimethylbiphenyl (hereinafter sometimes referred to as m-TB), 4,4'-diamino-3,3'-dimethylbiphenyl, 2,2'-bis(trifluoromethyl)-4,4'-diaminodiphenyl (hereinafter sometimes referred to as TFMB), 4,4'-diaminodiphenyl ether, 1,3-bis(3-aminophenoxy)benzene (hereinafter sometimes referred to as 1,3-APB), and 1,4-bis(4-aminophenoxy)benzene (hereinafter referred to as 1,4-A (Sometimes abbreviated as PB), 1,3-bis(4-aminophenoxy)benzene, 2,2-bis[4-(4-aminophenoxy)phenyl]propane (hereinafter sometimes abbreviated as BAPP), 2,2'-dimethyl-4,4'-diaminobiphenyl, 3,3'-dihydroxy-4,4'-diaminobiphenyl, 2,2-bis-[4-(3-aminophenoxy)phenyl]propane, bis[4-(4-aminophenoxy)]biphenyl, bis[4-(3-aminophenoxy)biphenyl, bis[1-(4-aminophenoxy)]biphenyl, bis[1-(3- 2,2-bis-[4-(4-aminophenoxy)phenyl]hexafluoropropane, 2,2-bis-[4-(3-aminophenoxy)phenyl]hexafluoropropane N, 4,4'-methylenedi-o-toluidine, 4,4'-methylenedi-2,6-xylidine, 4,4'-methylene-2,6-diethylaniline, 4,4'-methylenedianiline, 3,3'-methylenedianiline, 4,4'-diaminodiphenylpropane, 3,3'-diaminodiphenylpropane, 4,4'-diaminodiphenylethane, 3,3'-diaminodiphenylethane, 4,4'-diaminodiphenylmethane, 3,3'-diaminodiphenylmethane, 3,3-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, benzidine, 3,3'-Diaminobiphenyl, 3,3'-Dimethoxybenzidine, 4,4"-Diamino-p-terphenyl, 3,3"-Diamino-p-terphenyl, m-Phenylenediamine, p-Phenylenediamine (hereinafter sometimes referred to as p-PDA), Resorcinol-bis(3-aminophenyl) ether, 4,4'-[1,4-Phenylenebis(1-methylethylidene)]bisaniline, 4,4'-[1,3-Phenylenebis(1-methylethylidene)]bisaniline, 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(triflu) Oromethyl)bicyclohexane, 4,4'-diaminodicyclohexylmethane, 4,4"-diamino-p-terphenyl, bis(4-aminophenyl)terephthalate, 1,4-bis(4-aminophenoxy)-2,5-di-tert-butylbenzene, 4,4'-(1,3-phenylenediisopropylidene)bisaniline, 1,4-bis[2-(4-aminophenyl)-2-propyl]benzene, 2,4-diamino-3,5-diethyltoluene, 2,6-diamino-3,5-diethyltoluene, 4,4'-bis(3-aminophenoxy)biphenyl , 4,4'-(hexafluoropropyridene)dianiline, 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, 4,Examples include 4'-diaminobenzanilide, bis[4-(4-aminophenoxy)phenyl]sulfone, bis[4-(3-aminophenoxy)phenyl]sulfone, 9,9-bis[4-(4-aminophenoxy)phenyl]fluorene, 9,9-bis[4-(3-aminophenoxy)phenyl]fluorene, 4,4'-diaminodiphenyl sulfide, 3,3'-diaminodiphenyl sulfide, 4,4'-diaminodiphenyl sulfone, 3,3'-diaminodiphenyl sulfone, 2,5-diamino-1,3,4-oxadiazole, bis[4,4'-(4-aminophenoxy)]benzanilide, bis[4,4'-(3-aminophenoxy)]benzanilide, 2,6-diaminopyridine, and 2,5-diaminopyridine. Among these, m-TB and BAPP are preferred from the viewpoint of easily reducing the Df of the PI-based film obtained even at low imidation temperatures. The diamine compounds can be used alone or in combination of two or more.

[0154] Furthermore, the above-mentioned PI-based resin precursor may be obtained by further reacting other tetracarboxylic acids, dicarboxylic acids, and tricarboxylic acids, as well as their anhydrides and derivatives, in addition to the tetracarboxylic acid compound used in the synthesis of the above-mentioned resin precursor, to the extent that it does not impair the various physical properties of the PI-based film.

[0155] Other tetracarboxylic acids include the hydrate adducts of the anhydrides of the above-mentioned tetracarboxylic acid compounds.

[0156] Examples of dicarboxylic acid compounds include aromatic dicarboxylic acids, aliphatic dicarboxylic acids and their related acid chloride compounds, acid anhydrides, etc., and two or more may be used in combination. Specific examples include terephthalic acid; isophthalic acid; naphthalenedicarboxylic acid; 4,4'-biphenyldicarboxylic acid; 3,3'-biphenyldicarboxylic acid; dicarboxylic acid compounds of chain hydrocarbons having 8 or fewer carbon atoms; compounds in which two benzoic acids are linked by a single bond, -O-, -CH2-, -C(CH3)2-, -C(CF3)2-, -SO2-, or phenylene group; and acid chloride compounds thereof.

[0157] Examples of tricarboxylic acid compounds include aromatic tricarboxylic acids, aliphatic tricarboxylic acids and their related acid chloride compounds, acid anhydrides, etc., and two or more may be used in combination. Specific examples include 1,2,4-benzenetricarboxylic acid anhydride; 2,3,6-naphthalentricarboxylic acid-2,3-anhydride; and compounds in which phthalic anhydride and benzoic acid are linked by a single bond, -O-, -CH2-, -C(CH3)2-, -C(CF3)2-, -SO2-, or phenylene group.

[0158] In the production of PI-based resin precursors, the amounts used of diamine compounds, tetracarboxylic acid compounds, dicarboxylic acid compounds, and tricarboxylic acid compounds can be appropriately selected according to the ratio of each constituent unit of the desired PI-based resin. In the present invention, the total number of moles of diamine compound used per mole of total tetracarboxylic acid compound is defined as the amine ratio. In one preferred embodiment of the present invention, the amine ratio is preferably 0.90 moles or more and preferably 0.999 moles or less per mole of total tetracarboxylic acid compound. In another embodiment, the amine ratio is preferably 1.001 moles or more and preferably 1.10 moles or less per mole of total tetracarboxylic acid compound. In one embodiment of the present invention, when the amine ratio is 1 or less, the amine ratio is preferably 0.90 moles or more and 0.999 moles or less, more preferably 0.95 moles or more and 0.997 moles or less, and even more preferably 0.97 moles or more and 0.995 moles or less. In one embodiment of the present invention, when the amine ratio is 1 or more, the amine ratio is preferably 1.001 moles or more and 1.1 moles or less, more preferably 1.002 moles or more and 1.05 moles or less, and even more preferably 1.003 moles or more and 1.03 moles or less. When the amine ratio is close to 1.0 mole, the molecular weight tends to increase rapidly during synthesis, while when it deviates significantly from 1.0 mole, the molecular weight of the resulting PI-based resin tends to decrease. When the molecular weight increases rapidly, it tends to grow unevenly within the synthesized mass, making it difficult to stabilize the physical properties of the PI-based resin. On the other hand, if the molecular weight is too low, the mechanical properties tend to deteriorate.

[0159] The reaction temperature between the diamine compound and the tetracarboxylic acid compound is preferably 50°C or lower, more preferably 40°C or lower, and even more preferably 30°C or lower. When the reaction temperature is below the above upper limit, the Df of the resulting PI-based film is easily reduced, and this tendency is particularly pronounced in PI-based resins containing ester bonds, especially in PI-based films containing PI-based resins containing constituent unit (A1). Furthermore, the reaction temperature between the diamine compound and the tetracarboxylic acid compound is preferably 5°C or higher, more preferably 10°C or higher, and even more preferably 15°C or higher. When the reaction temperature is above the above lower limit, the reaction rate is easily increased, and the polymerization time tends to be shortened. The reaction time is not particularly limited and may be, for example, 0.5 to 72 hours, preferably 3 to 24 hours. When the reaction time is within the above range, the Df of the resulting PI-based film is easily reduced even at low imidation temperatures.

[0160] The reaction between a diamine compound and a 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, but examples include alcoholic solvents such as water, methanol, ethanol, ethylene glycol, isopropyl alcohol, propylene glycol, ethylene glycol methyl ether, ethylene glycol butyl ether, 1-methoxy-2-propanol, 2-butoxyethanol, and propylene glycol monomethyl ether; phenolic solvents such as phenol and cresol; esteric solvents such as ethyl acetate, butyl acetate, ethylene glycol methyl ether acetate, propylene glycol methyl ether acetate, and ethyl lactate; lactoneic solvents such as γ-butyrolactone (hereinafter sometimes referred to as GBL) and γ-valerolactone; acetone, methyl ethyl ketone, cyclopentanone, cyclohexanone, 2-heptanone, and methyl ethyl ether. Examples of solvents include ketone solvents such as 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 sometimes referred to as NMP); and combinations thereof. Among these, from the viewpoint of solubility, phenolic solvents, lactone solvents, amide solvents, pyrrolidone solvents, and more preferably amide solvents can be suitably used.

[0161] In one embodiment of the present invention, the boiling point of the solvent used in the reaction between the diamine compound and the tetracarboxylic acid compound is preferably 230°C or lower, more preferably 200°C or lower, and even more preferably 180°C or lower, from the viewpoint of easily reducing the Df of the resulting PI-based film, even at low imidation temperatures. Furthermore, the boiling point of the solvent is preferably 100°C or higher, more preferably 120°C or higher, from the viewpoint of easily reducing the Df of the resulting PI-based film.

[0162] The reaction between 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 needed. Preferably, the reaction is carried out under an inert atmosphere, such as a nitrogen atmosphere or an argon atmosphere, while stirring in a strictly controlled dehydrated solvent.

[0163] The solvent contained in the PI resin precursor solution is one of the solvents exemplified for use in the reaction between the diamine compound and the tetracarboxylic acid compound, and is preferably a lactone-based solvent, an amide-based solvent, a pyrrolidone-based solvent, and more preferably an amide-based solvent. Furthermore, in one embodiment of the present invention, the boiling point of the solvent contained in the PI resin precursor solution is preferably 230°C or lower, more preferably 200°C or lower, even more preferably 180°C or lower, and particularly preferably 170°C or lower, from the viewpoint of easily reducing the Df of the resulting PI film, even at low imidation temperatures. Furthermore, the boiling point of the solvent is preferably 100°C or higher, more preferably 120°C or higher, from the viewpoint of easily reducing the Df of the resulting PI film.

[0164] The content of the PI-based resin precursor in the PI-based resin precursor solution is preferably 8% by mass or more, more preferably 10% by mass or more, even more preferably 12% by mass or more, and particularly preferably 13% by mass or more, relative to the total amount of the PI-based resin precursor solution. Furthermore, it is preferably 30% by mass or less, more preferably 25% by mass or less, even more preferably 23% by mass or less, and particularly preferably 20% by mass or less. When the content of the PI-based resin precursor is within the above range, the processability during film formation is excellent.

[0165] (Coating of polyimide resin precursor solution) The coating process for PI-based resin precursor solution involves coating the substrate with the PI-based resin precursor solution to form a coating film.

[0166] In the coating process, a PI-based resin precursor solution is applied to the substrate by a known coating or application method to form a coating film. Known coating methods include, for example, wire bar coating, reverse coating, gravure coating and other roll coating methods, die coating, comma coating, lip coating, spin coating, screen printing coating, fountain coating, dipping, spraying, curtain coating, slot coating, and flow molding. When applying or coating the PI-based resin precursor solution to the substrate, a single layer of the PI-based resin precursor solution may be applied to the substrate, or multiple layers of the PI-based resin precursor solution may be applied to the substrate. When applying multiple layers of the PI-based resin precursor solution to the substrate, the application may be done in multiple stages and dried, or multiple layers may be applied simultaneously.

[0167] Examples of substrates include metal plates such as metal foil (e.g., copper foil), SUS plates such as SUS foil and SUS belts, glass substrates, PET films, PEN films, other PI resin films other than the PI film of the present invention, and polyamide resin films. Among these, copper plates, SUS plates, glass substrates, PET films, and PEN films are preferred from the viewpoint of excellent heat resistance, and copper plates, SUS plates, glass substrates, or PET films are more preferred from the viewpoint of adhesion to the film and cost.

[0168] <Imidification Process> The imidization process is a process of imidizing a PI-based resin precursor coated on a substrate by heat treatment at a temperature between 200°C and 500°C. In one embodiment of the present invention, in the imidization step, before the imidization of the PI-based resin precursor, the PI-based resin precursor solution coated on the substrate is heated and dried at a relatively low temperature, and the obtained dry film containing the PI-based resin precursor is imidized by heat treatment at 200°C or higher and 500°C or lower. This is preferably the case. Also, in one embodiment of the present invention, a dry film of the PI-based resin precursor on the substrate may be imidized to obtain a PI-based film, or the dry film of the PI-based resin precursor may be peeled from the substrate, and the dry film peeled from the substrate may be imidized to obtain a PI-based film.

[0169] In one embodiment of the present invention, the drying temperature of the PI-based resin precursor coated on the substrate is not particularly limited as long as it is within the temperature range in which the solvent dries and solidifies. However, from the perspective of avoiding surface roughness caused by rapid drying and suppressing wrinkles and warping generated during processing, it is preferably less than 300°C, more preferably 260°C or lower, even more preferably 200°C or lower, and even more preferably 180°C or lower. Also, from the perspective of productivity, it is preferably 50°C or higher, more preferably 80°C or higher, and even more preferably 100°C or higher.

[0170] In one embodiment of the present invention, the PI-based resin precursor can reduce the Df of the resulting PI-based film even when imidized at a low temperature. The heat treatment temperature in the imidization process, i.e., the imidization temperature, is preferably 500°C or lower, more preferably 400°C or lower, even more preferably less than 350°C, even more preferably 340°C or lower, particularly preferably 330°C or lower, particularly more preferably 310°C or lower, and most preferably 300°C or lower. When the imidization temperature is below the above upper limit, oxidative degradation of the resin is less likely to occur, and it is easier to obtain CCL with excellent high-frequency characteristics. Furthermore, from the viewpoint of easily improving the imidization rate, the imidization temperature is preferably 200°C or higher, more preferably 210°C or higher, and even more preferably 220°C or higher. Furthermore, from the viewpoint of easily obtaining a smooth film, it is preferable to perform heating in stages. For example, the solvent may be removed by heating at a relatively low temperature of 50 to 300°C, and then imidization may be carried out by stepwise heating to a temperature in the range of 200°C to 500°C, preferably 200°C to 400°C, and more preferably 200°C to less than 350°C. 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°C to 500°C, preferably 200°C to 400°C, and more preferably 200°C to less than 350°C.

[0171] In one embodiment of the present invention, the reaction time for imidization is preferably 30 minutes to 24 hours, more preferably 1 to 12 hours. Also in one embodiment of the present invention, the time for maintaining a temperature of 200°C 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 for imidization at 200°C or higher is within the above range, it is easier to sufficiently improve the imidization rate, easier to prevent oxidative degradation of the resin, and easier to improve the dielectric properties and flexural resistance of the resulting PI-based film.

[0172] After imidization, a PI-based film can be obtained by peeling off the coating film formed on the substrate from the substrate. In one embodiment of the present invention, if the substrate is copper foil, a PI-based film can be formed without peeling off the coating film from the copper foil, and the resulting laminated film, in which the PI-based film is laminated on the copper foil, can be used as CCL.

[0173] If the film of the present invention is a multilayer film, it can be manufactured by a multilayer film formation method such as co-extrusion, extrusion lamination, heat lamination, or dry lamination.

[0174] [Laminated film] Because the PI-based film of the present invention has a low Df, it can be suitably used for forming metal-clad laminates used in FPCs. Therefore, the present invention includes a laminated film that includes a PI layer and a metal foil layer, using the PI-based film of the present invention as the PI layer. In one embodiment of the present invention, the laminated film of the present invention may include the metal foil layer on only one side of the PI layer or on both sides.

[0175] In one embodiment of the present invention, examples of metal foils include copper foil, SUS foil, and aluminum foil, but copper foil is preferred from the viewpoint of conductivity and metalworkability.

[0176] Since the PI-based film of the present invention has a low Df and can be suitably used for forming CCLs with excellent high-frequency characteristics, in a preferred embodiment of the present invention, the laminated film of the present invention is preferably a laminated film that includes a copper foil layer on one or both sides of the PI-based film of the present invention.

[0177] 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 from the viewpoint of facilitating circuit miniaturization and improving bending resistance, it is preferably 100 μm or less, more preferably 50 μm or less, even more preferably 30 μm or less, and particularly preferably 20 μm or less. The thickness of the metal foil layer, particularly the copper foil layer, can be measured using a film thickness gauge or the like. When the PI-based film contains metal foil layers, particularly copper foil layers, on both sides, the thicknesses of each metal foil layer, particularly each copper foil layer, may be the same or different from each other.

[0178] 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, even more preferably 15 μm or more, preferably 100 μm or less, more preferably 80 μm or less, and even more preferably 60 μm or less. The thickness of the laminated film can be measured using a film thickness gauge or the like.

[0179] The laminated film of the present invention may include other layers, such as functional layers, in addition to the PI-based film and metal foil layer, particularly the copper foil layer. Examples of functional layers include the layers described above, such as a thermoplastic PI-based resin layer containing a thermoplastic PI-based resin or an adhesive layer. Functional layers can be used alone or in combination of two or more types.

[0180] In one embodiment of the present invention, the laminated film of the present invention may be a two-layer metal-clad laminate composed of a metal foil layer and a PI layer, or a three-layer metal-clad laminate composed of a metal foil layer, a PI layer and an adhesive layer. However, from the viewpoint of heat resistance, dimensional stability and weight reduction, a two-layer metal-clad laminate without an adhesive layer is preferred. In a preferred embodiment of the present invention, the PI-based film of the present invention has a low Df even at low imidation temperatures. Therefore, even when a laminated film in which the metal foil is copper foil is manufactured by thermal imidation of a PI-based resin precursor coating on copper foil, deterioration of the copper foil surface can be suppressed. Accordingly, in a preferred embodiment of the present invention, the laminated film of the present invention has excellent high-frequency characteristics even without including an adhesive layer.

[0181] Furthermore, in one embodiment of the present invention, the PI-based film and the metal foil layer, particularly the copper foil layer, may be in direct contact, or a functional layer may be inserted between the PI-based film and the metal foil layer, particularly the copper foil layer, and they may be in contact via the functional layer. However, from the viewpoint of easily improving mechanical and thermal properties, it is preferable that the PI-based film and the metal foil layer, particularly the copper foil layer, are in direct contact. The functional layer that may be inserted between the PI-based film and the metal foil layer of the present invention may be a thermoplastic PI layer. From the viewpoint of easily improving mechanical and thermal properties, it is preferable that the layer in direct contact with the metal foil layer, particularly the copper foil layer, is the PI film or a thermoplastic PI layer as a functional layer of the present invention.

[0182] [Method for manufacturing laminated film] The present invention involves the following steps: A step of coating a substrate with a PI-based resin precursor solution containing a constituent unit (A) derived from tetracarboxylic anhydride and a constituent unit (B) derived from diamine, and A process of imidizing a PI-based resin precursor by heat treatment at a temperature of 200°C to 500°C to form the PI-based film of the present invention on a substrate. This also includes methods for manufacturing laminated films.

[0183] In the method for manufacturing the laminated film of the present invention, the steps of "coating a PI-based resin precursor solution containing a constituent unit (A) derived from tetracarboxylic anhydride and a constituent unit (B) derived from diamine onto a substrate" and "imidizing the PI-based resin precursor by heat treatment at 200°C to 500°C to form the PI-based film of the present invention on a substrate" are similarly governed by the descriptions of each step described in the section on "Method for Manufacturing Polyimide Films."

[0184] In one embodiment of the present invention, the substrate is preferably a metal foil, and particularly preferably a copper foil. The description regarding the metal foil, and especially the copper foil, is similar to the description regarding the metal foil in the [Laminated Film] section.

[0185] The laminated film of the present invention may also be manufactured by a method other than the above method, for example, by coating and drying a PI-based resin precursor solution containing constituent units (A) derived from tetracarboxylic anhydride and constituent units (B) derived from diamine onto a substrate other than the metal foil contained in the laminated film, peeling off the dried film of the PI-based resin precursor from the substrate, and laminating the peeled dried film of the PI-based resin precursor onto the metal foil. The method for laminating the dried film of the PI-based resin precursor and the metal foil may be a pressing method, a lamination method using a hot roll, etc., and imidization of the PI-based resin precursor may be performed simultaneously in the lamination process.

[0186] [Flexible Printed Circuit Board] Because the PI-based film of the present invention has a low Df, it can reduce the transmission loss of electrical circuits made of the PI-based film and can be suitably used as an FPC substrate material. Therefore, the present invention also includes FPC substrates containing the PI-based film of the present invention. [Examples]

[0187] The present invention will be described more specifically below based on examples and comparative examples, but the present invention is not limited to the following examples.

[0188] The abbreviations used in the examples and comparative examples refer to the following compounds. BPDA: 3,3',4,4'-biphenyltetracarboxylic acid dianhydride TAHQ: p-phenylenebis(trimellitic acid monoesteric acid dianhydride) BP-TME:4,4'-bis(1,3-dioxo-1,3-dihydroisobenzofuran-5-ylcarbonyloxy)biphenyl PMDA: Pyromellitic anhydride m-TB: 4,4'-diamino-2,2'-dimethylbiphenyl BAPP: 2,2-Bis[4-(4-aminophenoxy)phenyl]propane

[0189] [Synthesis of polyimide resin precursors] (Example 1) 17.95 g (84.5 mmol) of m-TB and 0.35 g (0.9 mmol) of BAPP were dissolved in 284 g of DMAc, and then 19.38 g (42.3 mmol) of TAHQ was added and the mixture was stirred at 20°C under a nitrogen atmosphere for 1 hour. Subsequently, 12.44 g (42.3 mmol) of BPDA was added and the mixture was stirred at 20°C under a nitrogen atmosphere for 24 hours to obtain a PI resin precursor composition. The molar ratio of diamine monomer to acid dianhydride monomer used was 1.01.

[0190] (Examples 2-8 and Comparative Example 1) A PI resin precursor composition was obtained in the same manner as in Example 1, except that the types and compositions of monomers used were changed as shown in Table 1. Unless otherwise specified, the order in which monomers were added was diamine followed by acidic dianhydride. The diamines were added in the order of the diamines that derive constituent units (B1), (B2), and (B3), and the acidic dianhydrides were added in the order of the acidic dianhydrides that derive constituent units (A1), (A2), and (A3).

[0191] [Manufacturing of polyimide film] Using the solvent used in the synthesis of the PI resin precursor, the PI resin precursor compositions obtained in Examples 2-8 and Comparative Example 1 were appropriately diluted to a viscosity of 40,000 cps or less, within a range where the PI resin precursor content was 10% by mass or more, to prepare PI resin precursor solutions. The PI resin precursor solutions were each fabricated under one of the following film formation conditions 1-4, as shown in Table 1, to obtain PI films made of PI resin. In Example 4, the azimuth angle profile in the measurement of the in-plane orientation index is shown in Figure 2, the diffraction intensity profile in the measurement of the molecular periodicity index is shown in Figure 4, and the azimuth angle profile in the measurement of the in-plane anisotropy index is shown in Figure 6.

[0192] <Film forming conditions 1> A PI resin precursor solution was poured onto a glass substrate, and a coating film of the PI resin precursor solution was formed using an applicator at a linear velocity of 0.4 m / min. The coating film was heated at 120°C for 30 minutes, and after peeling the resulting film from the glass substrate, the film was fixed to a metal frame. The film fixed to the metal frame was heated from 30°C to 270°C over 19 minutes in a 7% oxygen atmosphere, and then cooled to 200°C over 35 minutes to produce a PI film. The time at which a temperature of 220°C or higher was maintained was 23 minutes. The time at which a temperature of 200°C or higher was maintained was 34 minutes.

[0193] <Film forming conditions 2> A PI resin precursor solution was poured onto a glass substrate, and a coating film of the PI resin precursor solution was formed using an applicator at a linear velocity of 0.4 m / min. The coating film was heated at 120°C for 30 minutes, and after peeling the resulting film from the glass substrate, the film was fixed to a metal frame. The film fixed to the metal frame was heated in a 1% oxygen atmosphere from 30°C to 320°C over 9 minutes, then heated at 320°C for 6 minutes, and cooled to 200°C over 15 minutes to produce a PI film. The time at which a temperature of 220°C or higher was maintained was 21 minutes. The time at which a temperature of 200°C or higher was maintained was 25 minutes.

[0194] <Film forming conditions 3> A PI resin precursor solution was poured onto a glass substrate, and a coating film of the PI resin precursor solution was formed using an applicator at a linear velocity of 0.4 m / min. The coating film was heated at 120°C for 30 minutes, and after peeling the resulting film from the glass substrate, the film was fixed to a metal frame. The film fixed to the metal frame was heated from 30°C to 320°C over 5 minutes in a 1% oxygen atmosphere, then heated at 320°C for 5 minutes, and cooled to 200°C over 15 minutes to produce a PI film. The time at which a temperature of 220°C or higher was maintained was 17 minutes. The time at which a temperature of 200°C or higher was maintained was 21 minutes.

[0195] <Film forming conditions 4> A PI resin precursor solution was poured onto the roughened side (surface roughness; Rz = 1.3 μm) of an electrolytic copper foil (manufactured by JX Metals Corporation, JXEFL-BHM, 12 μm thick), and a coating film of the PI resin precursor solution was formed using an applicator at a linear velocity of 0.4 m / min. The coating film was heated at 120°C for 30 minutes to dry. Then, the laminated film of copper foil and precursor was fixed to a gold frame, and the temperature was raised from 30°C to 320°C over 9 minutes in a 1% oxygen atmosphere, followed by heating at 320°C for 6 minutes, and then cooling to 200°C over 15 minutes to produce a laminated film of PI film and copper foil. The time at which the temperature was maintained above 220°C was 21 minutes. The time at which the temperature was maintained above 200°C was 25 minutes. The resulting laminated film of PI film and copper foil was immersed in a large volume of 40% by mass ferric chloride aqueous solution at room temperature for 10 minutes. After visually confirming that no copper remained, it was dried at 80°C for 1 hour to obtain a single PI film.

[0196] [Synthesis of polyimide resin precursors and production of polyimide films] (Comparative Example 2) 70.33 g (331 mmol) of m-TB was dissolved in 720 g of NMP, then 73.06 g (248 mmol) of BPDA and 37.94 g (83 mmol) of TAHQ were added, and the mixture was stirred at room temperature under a nitrogen atmosphere for 1 hour. The mixture was then stirred at 60°C for 20 hours to obtain a PI resin precursor composition. The polystyrene equivalent Mw of the PI resin precursor was 91,000, and the Mn was 27,000. The PI resin precursor composition was appropriately diluted with NMP to adjust the viscosity and prepare a PI resin precursor solution. The obtained PI resin precursor solution was then fabricated under the aforementioned film-forming conditions 1 to obtain a PI film. The obtained PI film had a thickness of 30 μm, a Dk of 3.45, a Df of 0.0040, an index E of 0.0074, and a CTE of 38.2 ppm. The Tg of the PI resin was 255°C, and the E' at 280°C was 5.53 × 10⁻⁶. 8 It was Pa. Also, from the storage elastic modulus curve, the Tg obtained using the tangent method was 230°C. 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.

[0197] For the PI films obtained in the examples and comparative examples, various measurements and evaluations were performed. The measurement and evaluation methods are described below.

[0198] <Measurement of Glass Transition Temperature Tg> The Tg of the PI resins obtained in the examples and comparative examples was determined by measuring the PI film as follows. Using a dynamic viscoelasticity measuring device (manufactured by IT Measurement Control Co., Ltd., DVA-220), measurements were carried out under the following samples and conditions to obtain a tanδ curve, which is the ratio of the values of the storage elastic modulus (Storage modulus, E’) and the loss elastic modulus (Loss modulus, E”). The apex of the peak of the tanδ curve was taken as Tg. Test piece: A rectangular parallelepiped with a length of 40 mm, a width of 5 mm, and a thickness of 30 μm (the thickness varies depending on the film used). Experimental mode: Single frequency, constant rate of temperature increase Experimental pattern: Tensile Length between sample grips: 15 mm Measurement start temperature: Room temperature to 342°C Rate of temperature increase: 5°C / min Frequency: 10 Hz Static / dynamic stress ratio: 1.8 Main collected data: (1) Storage elastic modulus (Storage modulus, E’) (2) Loss elastic modulus (Loss modulus, E”) (3) tanδ (E” / E’)

[0199] <Measurement of Storage Elastic Modulus (E’)> The E’ of the PI resins obtained in the examples and comparative examples at 280°C was determined by performing dynamic viscoelasticity measurement in the same manner as the measurement of Tg.

[0200] <X-ray Measurement> (1) In-plane orientation index The PI films obtained in the examples and comparative examples were subjected to transmission wide-angle X-ray diffraction measurements under the following conditions. • Equipment name: Nanoviewer, a small-angle / wide-angle X-ray scattering / diffraction device manufactured by Rigaku Corporation. • Detector: Pilatus 100k ·X-ray source: Cu-Kα ray Voltage: 40kV ·Current: 20mA • Camera length: 70mm • Exposure time: 10 minutes • Beam diameter: 0.25 mm

[0201] Specifically, four films were stacked in the ND direction so that the MD direction was aligned. A trimming knife was used to cut the stacked films so that the width in the MD direction was 1 cm and the width in the TD direction was 1 mm to obtain a test specimen for measurement. Next, as shown in Figure 1, the test specimen 1a was set in the X-ray apparatus so that the direction of X-ray irradiation was parallel to the TD direction of the film, and X-rays were incident on the test specimen 1a from the X-ray source 2a, and a two-dimensional diffraction pattern was obtained by the detector 3a. The obtained two-dimensional diffraction pattern was corrected using a two-dimensional diffraction pattern (air blank) obtained without setting up the test specimen 1a. Furthermore, from the two-dimensional diffraction pattern, an azimuth profile at 2θ=16° was obtained such that the azimuth profile of 0° and 180° corresponds to the MD direction of the test specimen 1a, and the azimuth profile of 90° and 270° corresponds to the ND direction of the test specimen 1a. The diffraction intensity for each azimuth angle was the average value of the diffraction intensity in the range of 2θ=15.5~16.5°. In the obtained azimuthal angle profiles (β = 0 to 360°), the full width at half maximum (FWHM) of the peaks at 90° and 270° was determined, and the average of the two FWHMs was taken as FWHM. This was then substituted into Equation 1 to determine the in-plane orientation index. The FWHM of the peak at 90° is the peak width at the midpoint between the peak intensity at 90° and the minimum intensity in the range of 0 to 180° (i.e., the peak width at the position where the intensity is half that of the peak intensity at 90°, relative to the minimum intensity). The FWHM of the peak at 270° is the peak width at the midpoint between the peak intensity at 270° and the minimum intensity in the range of 180 to 360° (i.e., the peak width at the position where the intensity is half that of the peak intensity at 270°, relative to the minimum intensity).

[0202] (2) Molecular periodicity index The PI films obtained in the examples and comparative examples were subjected to reflection-type wide-angle X-ray diffraction measurements under the following conditions. • Equipment name: RIGAK Corporation X-ray diffractometer RINT-2000 ·X-ray source: Cu-Kα ray • Tube voltage: 40kV ·Tube current: 150mA • Divergent slit: 1° • Scattering slit: 1° • Light-receiving slit: 0.15mm • Divergence vertical limiting slit: 10mm • Measurement range: 2θ1 = 5~30° • Measurement step: 0.02° • Scan speed: 0.5° / min • Sample holder: Aluminum sample plate (without bottom) manufactured by Rigaku Corporation • Detector: Rigaku Corporation, scintillation counter

[0203] Specifically, the film was cut to a length of 3 cm in the MD direction and 2.5 cm in the TD direction to obtain a sample 1b for measurement. Next, as shown in Figure 3, the sample 1b for measurement was attached to the sample holder 6 such that the ND direction of the film was parallel to the normal direction of the surface of the sample holder 6, i.e., the direction perpendicular to the surface, and that when the sample holder 6 was installed in the X-ray apparatus, the line 7 connecting the detection positions of the X-ray source 2b and the detector 3b was parallel to the MD direction of the film. Then, while maintaining the parallelism between line 7 and the MD direction, reflection measurements of the film surface were performed in the range of 2θ1 = 5 to 30° to obtain the diffraction profile A of the film. Next, the film was cut into sections of 2.5 cm in the MD direction and 3 cm in the TD direction to obtain a sample 1b for measurement. Then, as shown in Figure 3, the sample 1b for measurement was attached to the sample holder 6 such that the ND direction of the film was parallel to the normal direction of the surface of the sample holder 6, i.e., perpendicular to the surface, and that the TD direction of the film was parallel to the line 7 connecting the detection positions of the X-ray source 2b and the detector 3b when the sample holder 6 was installed in the X-ray apparatus. Then, while maintaining the parallelism between line 7 and the TD direction, the reflectance measurement of the film surface was performed in the range of 2θ1 = 5 to 30° to obtain the diffraction profile B of the film. Each diffraction profile was blank-corrected by subtracting the background. The average of the blank-corrected diffraction profile A and diffraction profile B was used as the diffraction intensity profile of the film. From the diffraction intensity profile of the film, the maximum diffraction intensity in the range of 2θ1 = 15.5 to 16.5° was defined as I(16°), and the minimum diffraction intensity in the range of 2θ1 = 20 to 30° was defined as I(min). These values ​​were substituted into Equation 2 to obtain the molecular periodicity index.

[0204] (3) In-plane anisotropy indices A, B The PI films obtained in the examples and comparative examples were subjected to transmission wide-angle X-ray diffraction measurements under the following conditions. • Equipment name: Nanoviewer, a small-angle / wide-angle X-ray scattering / diffraction device manufactured by Rigaku Corporation. • Detector: Pilatus 100k ·X-ray source: Cu-Kα ray • Camera length: 70mm • Exposure time: 10 minutes Voltage: 40kV ·Current: 20mA • Beam diameter: 0.25 mm

[0205] Specifically, four films were stacked in the ND direction so that their MD directions coincided. A trimming knife was used to cut the stacked films so that their width in the MD direction was 2 cm and their width in the TD direction was 2 cm, thereby obtaining a test specimen for measurement. Next, as shown in Figure 5, the test specimen 1c was set in the X-ray apparatus so that the direction of X-ray irradiation was parallel to the ND direction of the film. Then, X-rays were incident on the test specimen 1c from the X-ray source 2c, and a two-dimensional diffraction pattern was obtained by the detector 3c. The obtained two-dimensional diffraction pattern was corrected using an air blank, which is a two-dimensional diffraction pattern obtained without setting up the test specimen 1c. Furthermore, from the two-dimensional diffraction pattern, an azimuth angle profile at 2θ2 = 16° was obtained such that the azimuth angle profiles of 0° and 180° correspond to the MD direction of the test specimen 1c, and the azimuth angle profiles of 90° and 270° correspond to the TD direction of the test specimen 1c. The diffraction intensity for each azimuth angle was calculated using the average value of the diffraction intensity in the range of 2θ² = 15.5 to 16.5°. In the obtained azimuth profile (β1 = 0 to 360°), the diffraction intensities at 0° and 180° were determined, and their average value was defined as I(MD). The diffraction intensities at 90° and 270° were also determined, and their average value was defined as I(TD). Furthermore, in the above obtained azimuth profile (β1 = 0 to 360°), the maximum diffraction intensity in the range of 0 to 360° was defined as I(MAX), and the minimum diffraction intensity was defined as I(MIN). Finally, these values ​​were substituted into equations 3 and 4 to determine the in-plane anisotropy index A and the in-plane anisotropy index B.

[0206] <Measurement of weight-average molecular weight Mw and number-average molecular weight Mn> The polystyrene-based Mw and Mn of the PI resin precursor obtained through synthesis were measured using GPC. The GPC measurements were performed under the following conditions. (1) Pretreatment method The sample was diluted with DMF and then filtered through a 0.45 μm membrane filter to obtain the measurement solution. (2) Measurement conditions Column: Two TSKgel SuperAWM-H columns (6.0mm inner diameter, 150mm length) connected together. Eluent: DMF (with 10 mmol / L lithium bromide added, and 30 mmol / L phosphoric acid added) Flow rate: 0.6mL / min Detector: RI detector Column temperature: 40℃ Injection volume: 20μL Molecular weight standard: Standard polystyrene

[0207] <Measurement of linear thermal expansion coefficient (CTE)> The CTE of the PI films obtained in the examples and comparative examples was measured using a TMA under the following conditions, and the CTE at temperatures from 50°C to 100°C was calculated. Equipment: Hitachi High-Tech Science Co., Ltd. TMA / SS7100 Load: 50.0 mN Temperature program: Heats up from 20°C to 130°C at a rate of 5°C / minute. Test specimen: A rectangular parallelepiped measuring 40 mm in length, 5 mm in width, and 30 μm in thickness (thickness may vary depending on the film used).

[0208] <Evaluation of the dielectric loss index E> The dielectric loss index E of the PI films obtained in the examples and comparative examples was calculated using the following formula. E = Df × (Dk) 1 / 2 (i) Df: Dielectric loss tangent Dk: relative permittivity

[0209] (Measurement of Df and Dk) Measurement samples measuring 50 mm x 50 mm were cut from the PI films obtained in the examples and comparative examples, and Df and Dk were measured under the following conditions. The samples were conditioned at 25°C / 55%RH for 24 hours before measurement. Equipment: Compact USB Vector Network Analyzer manufactured by Anritsu Corporation (Product name: MS46122B) Cavity resonator manufactured by AET Co., Ltd. (TE mode, 10GHz type) Measurement frequency: 10GHz Measurement environment: 23℃ / 50%RH

[0210] <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 folds of the film under the following conditions. The film was cut into strips 100 mm long and 10 mm wide using a dumbbell cutter. The cut film was placed in an MIT bending fatigue tester (MIT-DA, manufactured by Toyo Seiki Seisakusho Co., Ltd.) compliant with ASTM standard D2176-16, and the film was alternately folded in both directions under the conditions of a test speed of 175 cpm, a bending angle of 135°, a load of 750 g, and a bending clamp radius of R=1.0 mm. The number of folds until breakage was measured. A higher number of folds indicates better bending resistance. The number of folds for the PI films obtained in Examples 3, 6, and 8 was 240,000, 160,000, and 20,000, respectively.

[0211] Table 1 shows the measurement and evaluation results for the PI films obtained in the examples and comparative examples.

[0212] [Table 1]

[0213] As shown in Table 1, the PI films obtained in Examples 1 to 8 were found to have lower Df and lower dielectric loss index E compared to Comparative Examples 1 and 2. Therefore, the PI film of the present invention can be suitably used in metal-clad laminates such as CCL that have low transmission loss and can handle high-frequency bands. [Explanation of Symbols]

[0214] 1a, 1b, 1c... Test specimens for measurement 2a, 2b, 2c...X-ray source 3a, 3b, 3c...detector 4. The position where the intensity is half of the peak intensity at 270°, based on the minimum intensity in the azimuth angle range of 180-360°. Width of the peak at position 5...4 6. Sample holder 7....Line connecting the detection positions of 2b and 3b 8. Maximum diffraction intensity in the range of 2θ1 = 15.5~16.5° 9···2θ1=20°~30° Minimum value of diffraction intensity 10. Diffraction intensity at an azimuth angle of 0° 11. Diffraction intensity at an azimuth angle of 90° 12. Diffraction intensity at an azimuth angle of 180° 13. Minimum value in the range of azimuth angle from 0 to 360° 14. Diffraction intensity at an azimuth angle of 270° 15. Maximum value in the azimuth angle range of 0 to 360° 16. Diffraction intensity at an azimuth angle of 360°

Claims

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

2. 2. The polyimide film according to claim 1, wherein the molecular periodicity index represented by formula 2 is 7.0 or more. Molecular periodicity index = I (16°) / I (min) (Formula 2) [In formula 2, I(16°) represents the 2θ １ represents the maximum value of the diffraction intensity at 15.5 to 16.5°, I (min) is the value of 2θ in the diffraction intensity profile obtained by reflection X-ray diffraction measurement. １ = represents the minimum value of the diffraction intensity at 20 to 30 degrees.]

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

1. In-plane anisotropy index A = I(MD) / I(TD) (Equation 3) In-plane anisotropy index B = I(MAX) / I(MIN) (Equation 4) [In Equation 3 and Equation 4, 2θ is obtained by analyzing a two-dimensional diffraction image of a transmission X-ray diffraction measurement measured by irradiating X-rays parallel to the ND direction of the film.] ２ In the azimuth angle profile at θ = 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.]

4. 2. The polyimide film according to claim 1, wherein the structural unit (A) comprises a structural unit (A1) derived from an ester bond-containing tetracarboxylic acid anhydride.

5. 2. The polyimide film according to claim 1, wherein the structural unit (A) includes a structural unit (A2) derived from a biphenyl skeleton-containing tetracarboxylic acid anhydride.

6. The structural unit (A) is represented by the formula (X): (Content of structural units derived from tetracarboxylic acid anhydrides 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) The polyimide film according to claim 5 , which satisfies the following relationship:

7. The structural unit (A1) is represented by the formula (a1): 【Chemical 1】 [In formula (a1), Z represents a divalent organic group, R ａ１ each independently represents a halogen atom, or an alkyl group, alkoxy group, aryl group, or aryloxy group which may have a halogen atom; and s each independently represents an integer of 0 to 3. The polyimide film according to claim 4 , wherein the structural unit (a1) is derived from a tetracarboxylic acid anhydride represented by the formula:

8. The structural unit (A2) is represented by the formula (a2): 【Chemistry 2】 [In formula (a2), R ａ２ each independently represents a halogen atom, or an alkyl group, alkoxy group, aryl group, or aryloxy group which may have a halogen atom; t's each independently represent an integer of 0 to 3. The polyimide film according to claim 5 , wherein the structural unit (a2) is derived from a tetracarboxylic acid anhydride represented by the following formula:

9. 2. The polyimide film according to claim 1, wherein the structural unit (B) includes a structural unit (B1) derived from a biphenyl skeleton-containing diamine.

10. The structural unit (B1) is represented by the formula (b1): 【Chemistry 3】 [In formula (b1), R ｂ１ each independently represents a halogen atom, or an alkyl group, alkoxy group, aryl group, or aryloxy group which may have a halogen atom; p represents an integer of 0 to 4. The polyimide film according to claim 9 , wherein the structural unit (b1) is derived from a diamine represented by the formula:

11. 10. The polyimide film according to claim 9, wherein the content of the structural unit (B1) exceeds 30 mol% based on the total amount of the structural unit (B).

12. The structural unit (B) is represented by formula (b2): 【Chemistry 4】 [In formula (b2), R ｂ２ each independently represents a halogen atom, or an alkyl group, alkoxy group, aryl group, or aryloxy group which may have a halogen atom; R ｂ２ The hydrogen atoms contained in may be substituted with halogen atoms, independently of one another, W is independently —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 hydrogen atom or a halogen atom, m represents an integer of 0 to 4; and q each independently represents an integer of 0 to 4. The polyimide film according to claim 1, comprising a structural unit (b2) derived from a diamine represented by the following formula:

13. In the structural unit (b2), m is 3, and each W is independently —O— or —C(CH ３ ) ２ The polyimide film according to claim 12, wherein

14. 2. The polyimide film according to claim 1, wherein the polyimide film has a dielectric loss tangent at 10 GHz of less than 0.

004.

15. The storage modulus of the polyimide resin at 280°C is 3 × 10 ８ The polyimide-based film according to claim 1 , wherein the modulus of elasticity is less than 100 Pa.

16. 2. The polyimide film according to claim 1, wherein the polyimide resin has a glass transition temperature of 200 to 290°C.

17. 2. The polyimide film according to claim 1, which has a thickness of 5 to 100 μm.

18. A laminated film comprising a metal foil layer on one or both sides 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. A step of applying a polyimide resin precursor solution containing a tetracarboxylic acid anhydride-derived structural unit and a diamine-derived structural unit onto a substrate; and The method for producing a polyimide film according to any one of claims 1 to 17, comprising a step of imidizing a polyimide resin precursor by heat treatment at 200°C or higher and 500°C or lower.

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