Polyimide-based film

Abstract

To provide a polyimide-based film having low Df which enables formation of a metal-clad laminate such as CCL that suppresses roughness of a copper foil surface and has 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, wherein the polyimide-based resin has a storage elastic modulus at 280°C of less than 3×108 Pa and a glass transition temperature of 200-290°C.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This relates to a polyimide film that can be used as a substrate material for high-frequency printed circuit boards and antenna substrates. [Background technology]

[0002] Flexible printed circuits (hereinafter referred to as FPCs) are thin, lightweight, and flexible, allowing for three-dimensional, high-density mounting, and are used in many electronic devices such as mobile phones and hard disks, contributing to their miniaturization and weight reduction. Traditionally, polyimide resins, which have excellent heat resistance, mechanical properties, and electrical insulation, have been widely used for FPCs. In recent years, fifth-generation mobile communication systems, known as 5G, have become widely adopted. Conventionally used polyimide materials have significant transmission loss when transmitting the high-frequency signals used in 5G communications, resulting in problems such as electrical signal loss and long signal delay times. 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. For example, Patent Document 1 discloses a polyimide resin precursor obtained by reacting a tetracarboxylic anhydride component containing an ester-containing tetracarboxylic anhydride and biphenyltetracarboxylic anhydride with a diamine component containing 75 mol% or more of p-phenylenediamine, and a polyimide resin obtained by curing the polyimide resin precursor. Patent Document 2 also discloses a polyimide film having a non-thermoplastic polyimide layer containing a non-thermoplastic polyimide and a thermoplastic polyimide layer containing a thermoplastic polyimide, wherein the non-thermoplastic polyimide contains tetracarboxylic acid residues including at least one of tetracarboxylic acid residues derived from 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) (BPDA residue) and tetracarboxylic acid residues derived from 1,4-phenylenebis(trimellitic acid monoester) dianhydride (TAHQ) (TAHQ residue), and diamine residues derived from a specific diamine compound. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2018-150544 [Patent Document 2] International Publication No. 2018 / 061727 Summary of the Invention [Problem to be solved by the invention]

[0004] Copper-clad laminates (hereinafter sometimes referred to as CCLs) are widely used metal-clad laminates for FPCs, which are laminates having copper foil layers on one or both sides of a single or multiple polyimide resin layers. CCLs can be produced by casting a polyimide resin precursor solution onto copper foil to form a film, and then thermally imidizing the coating of the polyimide resin precursor. The thermal imidization is usually carried out by heating at a high temperature, for example, around 360°C. In the transmission of high-frequency current, the skin effect, a phenomenon in which current flows densely near the surface of the conductor, becomes prominent. Therefore, when metal-clad laminates such as CCL are used in high-frequency circuits, roughness and oxidation of the metal foil surface are likely to cause a decrease in transmission loss. For example, when copper foil is heated to temperatures above 350°C, the copper foil surface tends to become rough, the crystal grain size increases, oxidation occurs, and the interface tends to become rough. Therefore, exposure of metal foil such as copper foil to high temperatures together with polyimide resin during the thermal imidization process can cause a decrease in transmission loss. However, in conventional polyimide resin or polyimide film production, when thermal imidization is performed at a low temperature below 350°C, Df and Dk may not be sufficiently reduced. If thermal imidization is performed at a high temperature of 350°C or higher to produce a CCL in order to sufficiently reduce the Df and Dk of the polyimide resin or polyimide film, roughness of the copper foil surface occurs as described above. Therefore, it is difficult to suppress the roughness and oxidation of the copper foil surface while reducing the Df of the polyimide layer, and to form a CCL with low transmission loss when used in high-frequency circuits.

[0005] Therefore, an object of the present invention is to provide a polyimide film with low Df that can suppress roughening of the surface of metal foil such as copper foil and can form metal-clad laminates such as CCLs that have low transmission loss in the high-frequency band. [Means for solving the problem]

[0006] The present inventors have conducted extensive research to solve the above problems and have arrived at the present invention, which provides the following preferred embodiments.

[0007] [1] A polyimide resin containing a structural unit (A) derived from a tetracarboxylic acid anhydride and a structural unit (B) derived from a diamine, wherein the polyimide resin has a storage modulus of 3×10 at 280°C. 8 A polyimide film having a viscosity of less than 100 Pa and a glass transition temperature of 200 to 290°C. [2] The polyimide film according to [1], wherein the structural unit (A) includes a structural unit (A1) derived from an ester bond-containing tetracarboxylic acid anhydride. [3] The polyimide film according to [2], wherein the structural unit (A) further contains a structural unit (A2) derived from a biphenyl skeleton-containing tetracarboxylic acid anhydride. [4] The structural unit (A) is represented by the formula (X): (Content of the structural unit (A3) derived from a tetracarboxylic acid anhydride other than the structural unit (A1) and the structural unit (A2)) / (Total amount of the structural unit (A1) and the structural unit (A2))<1.1 (X) The polyimide film according to [3], which satisfies the following relationship: [5] The structural unit (A1) is represented by the formula (a1): [ka] [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's each independently represent an integer of 0 to 3. The polyimide film according to any one of [2] to [4], wherein the structural unit (a1) is derived from a tetracarboxylic acid anhydride represented by the following formula: [6] The structural unit (A2) is represented by the formula (a2): [ka] [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; and t's each independently represent an integer of 0 to 3. The polyimide film according to any one of [3] to [5], wherein the structural unit (a2) is derived from a tetracarboxylic acid anhydride represented by the following formula: [7] The polyimide film according to any one of [1] to [6], wherein the structural unit (B) includes a structural unit (B1) derived from a biphenyl skeleton-containing diamine. [8] The structural unit (B1) is represented by the formula (b1): [ka] [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 from 0 to 4. The polyimide film according to [7], wherein the structural unit (b1) is derived from a diamine represented by the formula: [9] The polyimide film according to [7] or [8], wherein the content of the structural unit (B1) exceeds 30 mol % based on the total amount of the structural unit (B).

[10] The structural unit (B) is represented by formula (b2): [ka] [In formula (b2), R b2each independently represents a halogen atom, or an alkyl group, alkoxy group, aryl group, or aryloxy group which may have a halogen atom; W is independently -O-, -CH2-, -CH2-CH2-, -CH(CH3)-, -C(CH3)2-, -C(CF3)2-, -COO-, -OOC-, -SO2-, -S-, -CO- or -N(R c )-, and 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 1 to 4; and q independently represents an integer of 0 to 4. The polyimide film according to any one of [1] to [9], which contains a structural unit (b2) derived from a diamine represented by the following formula:

[11] The polyimide film according to

[10] , wherein in the structural unit (b2), m is 3, and W each independently represents —O— or —C(CH 3 ) 2 —.

[12] A laminated film comprising a metal foil layer on one or both sides of the polyimide film according to any one of [1] to

[11] .

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

[11] .

[14] A step of applying a polyimide resin precursor solution containing a tetracarboxylic acid anhydride-derived structural unit (A) and a diamine-derived structural unit (B) onto a substrate; and A step of imidizing the polyimide resin precursor by heat treatment at 200°C or higher but lower than 350°C to form the polyimide film according to any one of [1] to

[11] on the substrate. A method for producing a laminated film, comprising:

[15] The method for producing a laminated film according to

[14] , wherein the substrate is a metal foil. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a polyimide film with low Df that can suppress roughening of the surface of a metal foil such as a copper foil and form a metal-clad laminate such as a CCL having low transmission loss in the high frequency band. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments of the present invention will be described in detail. Note that the scope of the present invention is not limited to the embodiments described here, and various modifications can be made without departing from the spirit of the present invention.

[0010] [Polyimide film] The polyimide film of the present invention comprises a polyimide resin containing a tetracarboxylic anhydride-derived structural unit (A) and a diamine-derived structural unit (B). In this specification, polyimide may be referred to as PI. In the present invention, the term "structural unit derived from" refers to a "structural unit derived from," for example, "tetracarboxylic anhydride-derived structural unit (A)" refers to a "tetracarboxylic anhydride-derived structural unit (A)."

[0011] <Polyimide resin> The storage modulus (hereinafter referred to as E') of PI resin at 280°C is 3 x 10 8 The viscosity is less than 10 Pa, and the glass transition temperature (hereinafter, sometimes referred to as Tg) is 200 to 290° C. The inventors have found that E′ at 280° C. is 3×10 8 They found that by using a PI resin having a modulus of elasticity less than 10 Pa and a Tg of 200 to 290°C, a PI film with low Df can be obtained even at a low thermal imidization temperature. This is presumably because, when the E' and Tg of the PI resin at 280°C are set within the above ranges, the PI resin is likely to form a preferred higher-order structure in which rotational motion is suppressed, thereby suppressing the rotation of polar groups in the PI resin and reducing the loss of electrical energy as thermal motion. Polyamic acid, a precursor of PI resin, begins to imidize at around 200°C. Generally, polyamic acid has a high degree of freedom in molecular structure, but after imidization, it becomes relatively rigid and the degree of freedom in molecular structure decreases. If the Tg of the PI resin is 200 to 290°C, even if the thermal imidization temperature is low, the thermal imidization temperature exceeds the Tg of the PI resin during the imidization process, so the amic acid moiety and the imide moiety move simultaneously to form a higher-order structure, which is thought to facilitate the formation of a desirable higher-order structure in which rotational movement of the resin as a whole is suppressed. Furthermore, it is believed that E' at 280°C is 3 x 10 8 When the viscosity is less than Pa, the imide moieties can move flexibly enough when forming a higher-order structure, which is thought to have the effect of making it easier for the resin as a whole to form a preferable higher-order structure in which rotational movement is suppressed.

[0012] The E' of the PI resin at 280°C is set to 3 × 10 8 Pa or less, preferably 2 x 10 8 Pa or less, preferably 1.5×10 8 Pa or less, more preferably 1×10 8 Pa or less, particularly preferably 0.8 × 10 8 In addition, the E' of the PI resin at 280°C is preferably 1 × 10 Pa or less, from the viewpoint of easily suppressing deformation of the PI film during processing. 4 Pa or more, preferably 1×10 5 Pa or more, more preferably 1×10 6 The E' of the PI resin can be measured by dynamic viscoelasticity measurement, for example, by the method described in the Examples.

[0013] The E' of the PI resin at 280°C can be adjusted by appropriately adjusting the type and composition of the structural units constituting the PI resin, as well as the molecular weight and production method of the PI resin, particularly the imidization conditions, etc. For example, the E' can be adjusted to fall within the above-mentioned range by adjusting the E' within the range described below as a preferred embodiment.

[0014] The Tg of the PI resin is 290°C or less, preferably less than 290°C, more preferably 280°C or less, even more preferably 275°C or less, still more preferably 260°C or less, particularly preferably 250°C or less, and especially preferably 240°C or less, from the viewpoint of easily reducing the Df of the resulting PI film even at a low thermal imidization temperature. Furthermore, the Tg of the PI resin is 200°C or more, more preferably 202°C or more, and even more preferably 205°C or more, from the viewpoint of easily reducing the Df of the PI film and easily increasing 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.

[0015] The Tg of the PI resin can be adjusted by appropriately adjusting the type and composition of the structural units constituting the PI resin, as well as the molecular weight and production method of the PI resin, particularly the imidization conditions, etc. For example, the Tg can be adjusted to fall within the above-mentioned range by adjusting the Tg within the range described below as a preferred embodiment.

[0016] (Structural Unit (A) Derived from Tetracarboxylic Acid Anhydride) The PI resin contains a structural unit (A) derived from a tetracarboxylic acid anhydride (hereinafter, sometimes simply referred to as structural unit (A)). The structural unit (A) is not particularly limited as long as the E′ and Tg of the PI resin at 280°C are within the above ranges. For example, the structural unit (A) may be a unit represented by the formula (1): [ka] [In formula (1), Y represents a tetravalent organic group] It is preferable that the structural unit is derived from a tetracarboxylic acid anhydride represented by the following formula:

[0017] In formula (1), Y's each independently represent 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 and a cyclic structure. Examples of the cyclic structure include alicyclic, aromatic, and heterocyclic structures. The organic group may have a hydrogen atom substituted with a halogen atom, a hydrocarbon group, an alkoxy group, or a halogenated hydrocarbon group. In such cases, 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's, which may be the same or different. Examples of Y's include groups or structures represented by formulas (31) to (40); groups in which a hydrogen atom in a group represented by formulas (31) to (40) is substituted with a methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, sec-butyl group, tert-butyl group, fluoro group, chloro group, or trifluoromethyl group; and tetravalent chain hydrocarbon groups having 1 to 8 carbon atoms.

[0018] [ka]

[0019] [In formulas (31) to (40), R 19 ~R 26 and R 23’ ~R 26’ each independently represents a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, or an aryl group having 6 to 12 carbon atoms; R 19 ~R 26 and R 23’ ~R 26’ The hydrogen atoms contained in may be substituted with halogen atoms, independently of one another, V 1 and V 2 are each independently a single bond (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 independently represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, D's each independently represent a single bond, -C(CH3)2- or -C(CF3)2-; i represents an integer of 1 to 3; * represents a bond) represents R j represents a hydrogen atom or a monovalent hydrocarbon group having 1 to 12 carbon atoms which may be substituted with a halogen atom, e and d each independently represent an integer of 0 to 2 (provided that e+d is not 0); f represents an integer of 0 to 3, g and h each independently represent an integer of 0 to 4; In formula (39), 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; s's each independently represent an integer of 0 to 3; In formula (40), 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; * represents a bond.

[0020] In order to facilitate the improvement of the mechanical and thermal properties of the PI resin of the present invention, Y in Formula (1) preferably contains at least one structure selected from the group consisting of structures represented by Formulas (31), (32), (33), (39), and (40), more preferably at least one structure selected from the group consisting of structures containing an ester bond and structures containing a biphenyl skeleton, and even more preferably at least one structure selected from the group consisting of structures represented by Formulas (39) and (40). In this specification, "mechanical properties" refers to mechanical properties including flex resistance, break resistance, and elastic modulus. "Improved mechanical properties" refers to, for example, increased flex resistance and / or elastic modulus. "Thermal properties" refers to thermal properties including Tg, coefficient of linear expansion (hereinafter sometimes referred to as CTE), reduced thermal denaturation and degradation, and reduced deformation after heating. "Improved thermal properties" refers to, for example, increased Tg and / or decreased CTE.

[0021] In formulas (31) to (33), R 19 ~R 26 and R 23’ ~R 26’ are each independently a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, or an aryl group having 6 to 12 carbon atoms. Examples of the alkyl group having 1 to 6 carbon atoms include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, an n-pentyl group, a 2-methylbutyl group, a 3-methylbutyl group, a 2-ethylpropyl group, and an n-hexyl group. Examples of the alkoxy group having 1 to 6 carbon atoms include a methoxy group, an ethoxy group, a propyloxy group, an isopropyloxy group, an n-butoxy group, an isobutoxy group, a sec-butoxy group, a tert-butoxy group, a pentyloxy group, a hexyloxy group, and a cyclohexyloxy group. Examples of the aryl group having 6 to 12 carbon atoms include a phenyl group, a tolyl group, a xylyl group, a naphthyl group, and a biphenyl group. 19 ~R26 and R 23’ ~R 26’ The hydrogen atoms contained in R may be substituted with halogen atoms, each independently of the other. Examples of the halogen atoms include fluorine, chlorine, bromine, and iodine atoms. Among these, R is particularly preferred from the viewpoint of improving the mechanical and thermal properties of the PI film. 19 ~R 26 and R 23’ ~R 26’ are each 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.

[0022] In equation (31), V 1 and V 2 are each independently a single bond (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), and from the viewpoint of easily improving the mechanical and thermal properties of the PI film, preferably represents a single bond (except when e+d=1), -O-, -CH2-, -C(CH3)2-, -C(CF3)2- or -CO-, more preferably represents a single bond (except when e+d=1), -O-, -C(CH3)2- or -C(CF3)2-. j represents a monovalent hydrocarbon group having 1 to 12 carbon atoms which may be substituted with a hydrogen atom or a halogen atom. Examples of the monovalent hydrocarbon group having 1 to 12 carbon atoms include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, 2-methylbutyl, 3-methylbutyl, 2-ethylpropyl, n-hexyl, n-heptyl, n-octyl, tert-octyl, n-nonyl, and n-decyl groups, which may be substituted with a halogen atom. Examples of the halogen atom include the same as those mentioned above.

[0023] In formula (31), e and d each independently represent an integer of 0 to 2 (provided that e+d is not 0), and preferably represent 0 or 1, from the viewpoint of easily reducing the Df of the PI film even at a low imidization temperature. Also, e+d preferably represents 1. In formula (31), when e is 0, the two benzene rings are V 1 When d is 0, the two benzene rings are V 2 indicates that there is no bond.

[0024] In formula (32) and formula (33), f represents an integer of 0 to 3, and preferably represents 0 or 1, more preferably 0, from the viewpoint that the Df of the PI film can be easily reduced even when the imidization temperature is low.

[0025] In formula (33), g and h each independently represent an integer of 0 to 4, and from the viewpoint of easily improving the mechanical properties and thermal properties of the PI film, preferably represent an integer of 0 to 2, more preferably 0 or 1. Furthermore, g+h preferably represents an integer of 0 to 2. Note that when f is 1 or greater, multiple g's and multiple h's may each independently be the same or different.

[0026] In formula (a), R 27 ~R 30 are each independently 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 27 ~R 30 are each independently preferably a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, and more preferably a hydrogen atom.

[0027] In formula (a), D represents a single bond, -C(CH3)2-, or -C(CF3)2-. When D has such a structure, the mechanical and thermal properties of the PI film are easily improved. i represents an integer of 1 to 3, and is preferably 1 or 2, from the viewpoint of easily improving the mechanical and thermal properties of the PI film. When i is 2 or more, a plurality of D and R27 ~R 30 may be the same or different, independently of each other.

[0028] In formula (39), Z represents a divalent organic group, and from the viewpoint of easily improving the mechanical properties and thermal properties of the PI film, Z preferably represents a divalent organic group having 4 to 40 carbon atoms, more preferably a divalent organic group having 4 to 40 carbon atoms and a cyclic structure, still more preferably a divalent organic group having 4 to 40 carbon atoms and an aromatic ring, and particularly preferably a group represented by formula (z1), formula (z2), or formula (z3): [ka] [In formulas (z1) to (z3), R z11 ~R z14 each independently represents a hydrogen atom or a monovalent hydrocarbon group which may have a halogen atom; R z2 each independently represents a monovalent hydrocarbon group which may have a halogen atom; n represents an integer of 1 to 4, j's each independently represent an integer of 0 to 3; * represents a bond. It particularly preferably represents a divalent organic group represented by formula (z1).

[0029] In formula (z1), R z11 ~R z14 represent, independently of each other, a hydrogen atom or a monovalent hydrocarbon group which may have a halogen atom. Examples of the monovalent hydrocarbon group include an aromatic hydrocarbon group, an alicyclic hydrocarbon group, and an aliphatic hydrocarbon group. Examples of the aromatic hydrocarbon group include aryl groups such as a phenyl group, a tolyl group, a xylyl group, a naphthyl group, and a biphenyl group. Examples of the alicyclic hydrocarbon group include cycloalkyl groups such as a cyclopentyl group and a cyclohexyl group. Examples of the aliphatic hydrocarbon group include alkyl groups such as methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, n-pentyl, 2-methylbutyl, 3-methylbutyl, 2-ethylpropyl, n-hexyl, n-heptyl, n-octyl, tert-octyl, n-nonyl, and n-decyl. Examples of the halogen atom include those described above. R z11 ~R z14 From the viewpoint of easily improving the mechanical properties and thermal properties of the PI film, each independently preferably represents a hydrogen atom or an alkyl group which may have a halogen atom, more preferably a hydrogen atom or an alkyl group having 1 to 6 carbon atoms which may have a halogen atom, even more preferably a hydrogen atom or an alkyl group having 1 to 3 carbon atoms which may have a halogen atom, and particularly preferably a hydrogen atom.

[0030] In formula (z1), n ​​represents an integer of 1 to 4, and is preferably an integer of 1 to 3, more preferably 1 or 2, and particularly preferably 2, from the viewpoint of easily reducing the Df of the PI film even when the imidization temperature is low.

[0031] In formula (z2), R z2 R each independently represent a monovalent hydrocarbon group which may have a halogen atom, and examples of the monovalent hydrocarbon group include those exemplified above. z2 From the viewpoint of easily improving the mechanical properties and thermal properties of the PI film, each 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.

[0032] In formula (z2), j's each independently represent an integer of 0 to 3, and are preferably 0 or 1, more preferably 0, from the viewpoint of easily reducing the Df of the PI film even when the imidization temperature is low.

[0033] In equation (39), Ra1 are each independently a halogen atom, or an alkyl group, alkoxy group, aryl group, or aryloxy group which may have a halogen atom, and preferably are each independently an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, or an aryl group having 6 to 12 carbon atoms, from the viewpoint of easily improving the mechanical properties and thermal properties of the PI film. Examples of the alkyl group having 1 to 6 carbon atoms, the alkoxy group having 1 to 6 carbon atoms, and the aryl group having 6 to 12 carbon atoms include those exemplified above. R a1 The hydrogen atoms contained in may be substituted with halogen atoms independently of one another, and examples of the halogen atoms include those exemplified above. Among these, from the viewpoint of easily reducing the Df of the PI film even at a low imidization temperature, R a1 are each independently an alkyl group preferably having 1 to 6 carbon atoms, more preferably an alkyl group having 1 to 3 carbon atoms.

[0034] In formula (39), s's each independently represent an integer of 0 to 3, and preferably represent an integer of 0 to 2, more preferably 0 or 1, from the viewpoint of easily improving the mechanical properties and thermal properties of the PI film.

[0035] In equation (40), R a2 are each independently a halogen atom, or an alkyl group, alkoxy group, aryl group, or aryloxy group which may have a halogen atom, and preferably are each independently an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, or an aryl group having 6 to 12 carbon atoms, from the viewpoint of easily improving the mechanical properties and thermal properties of the PI film. Examples of the alkyl group having 1 to 6 carbon atoms, the alkoxy group having 1 to 6 carbon atoms, and the aryl group having 6 to 12 carbon atoms include those exemplified above. R a2 The hydrogen atoms contained in may be substituted with halogen atoms independently of each other, and examples of halogen atoms include those exemplified above. Among these, from the viewpoint of easily improving the mechanical properties and thermal properties of the PI film, R a2are each independently preferably an alkyl group having 1 to 6 carbon atoms, more preferably an alkyl group having 1 to 3 carbon atoms.

[0036] In formula (40), t's each independently represent an integer of 0 to 3, and preferably represent an integer of 0 to 2, more preferably 0 or 1, from the viewpoint of easily improving the mechanical properties and thermal properties of the PI film.

[0037] Specific examples of the structures represented by formulas (31) to (33), (39) and (40) include structures represented by formulas (41) to (56). In these formulas, * represents a bond.

[0038] [ka]

[0039] In one embodiment of the present invention, when Y in formula (1) contains at least one structure selected from the group consisting of structures represented by formulas (31) to (33), (39), and (40), the proportion of structural units derived from tetracarboxylic acid anhydrides in which Y in formula (1) is at least one selected from the group consisting of structures represented by formulas (31) to (33), (39), and (40), particularly the proportion of structural units derived from tetracarboxylic acid anhydrides in which Y in formula (1) is at least one selected from the group consisting of structures represented by formulas (39) and (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 structural units (A). When this proportion is within the above range, the Df of the PI film is easily reduced. The proportion of these structural units is, for example, 1 It can be measured using H-NMR, or can be calculated from the ratio of raw materials used.

[0040] (Structural Unit (A1) Derived from Ester Bond-Containing Tetracarboxylic Acid Anhydride) In one embodiment of the present invention, the structural unit (A) preferably contains a structural unit (A1) derived from an ester bond-containing tetracarboxylic acid anhydride (hereinafter sometimes simply referred to as structural unit (A1)). When the structural unit (A) contains the structural unit (A1), an ester bond exhibiting molecular orientation is incorporated into the PI resin. This facilitates orientation during the process of applying a PI resin precursor solution to a substrate and imidizing the resulting coating, making it easy to reduce Df even at low imidization temperatures. For the same reasons, it also facilitates reducing the CTE and improving the dimensional stability of the PI film.

[0041] In one embodiment of the present invention, the structural unit (A1) is not particularly limited as long as it contains an ester bond, and the number of ester bonds contained in the structural unit (A1) may be one or two or more. However, from the standpoint of making it easy to reduce the Df of the PI film even when the imidization temperature is low, it is preferable that the structural unit (A1) be a structural unit represented by the formula (a1): [ka] [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's each independently represent an integer of 0 to 3. It is preferable that the structural unit (a1) is derived from a tetracarboxylic acid anhydride represented by the following formula:

[0042] R in formula (a1) a1 are each independently a halogen atom, or an alkyl group, alkoxy group, aryl group, or aryloxy group which may have a halogen atom, and preferably are each independently an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, or an aryl group having 6 to 12 carbon atoms, from the viewpoint of easily reducing the Df of the PI film even when the imidization temperature is low. Examples of the alkyl group having 1 to 6 carbon atoms, the alkoxy group having 1 to 6 carbon atoms, and the aryl group having 6 to 12 carbon atoms include those exemplified above. R a1The hydrogen atoms contained in may be substituted, independently of one another, with a halogen atom, and examples of the halogen atom include those exemplified above. Among these, R a1 are each independently preferably an alkyl group having 1 to 6 carbon atoms, more preferably an alkyl group having 1 to 3 carbon atoms. In addition, each s in formula (a1) independently represents an integer of 0 to 3, preferably 0 or 1, and more preferably 0.

[0043] In formula (a1), Z represents a divalent organic group, and examples of the divalent organic group include those exemplified above as the divalent organic group in formula (39). Among these, from the viewpoint of easily reducing the Df of the PI film even at a low imidization temperature, Z is preferably a group represented by formula (z1), formula (z2), or formula (z3): [ka] [In formulas (z1) to (z3), R z11 ~R z14 each independently represents a hydrogen atom or a monovalent hydrocarbon group which may have a halogen atom; R z2 each independently represents a monovalent hydrocarbon group which may have a halogen atom; n represents an integer of 1 to 4, j's each independently represent an integer of 0 to 3; * represents a bond. It is preferably a divalent organic group represented by formula (z1), and more preferably a divalent organic group represented by formula (z1).

[0044] In one embodiment of the present invention, R in formula (z1) z11 ~R z14 represent, independently of each other, a hydrogen atom or a monovalent hydrocarbon group which may have a halogen atom. Examples of the monovalent hydrocarbon group include those exemplified above. R z11 ~R z14From the viewpoint of easily reducing the Df of the PI film even when the imidization temperature is low, each independently preferably represents a hydrogen atom or an alkyl group which may have a halogen atom, more preferably a hydrogen atom or an alkyl group having 1 to 6 carbon atoms which may have a halogen atom, even more preferably a hydrogen atom or an alkyl group having 1 to 3 carbon atoms which may have a halogen atom, and particularly preferably a hydrogen atom.

[0045] In one embodiment of the present invention, R in formula (z2) z2 R each independently represent a monovalent hydrocarbon group which may have a halogen atom, and examples of the monovalent hydrocarbon group include those exemplified above. z2 From the viewpoint of easily improving the mechanical properties and thermal properties of the PI film, each 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.

[0046] In one embodiment of the present invention, from the viewpoint of easily reducing Df of the PI film even when the imidization temperature is low, R z11 ~R z14 In a benzene ring having R z11 ~R z14 At least one of R may be a monovalent hydrocarbon group which may have a halogen atom. z11 ~R z14 are preferably all hydrogen atoms.

[0047] In formula (z2), j's each independently represent an integer of 0 to 3. In one embodiment of the present invention, from the viewpoint of easily reducing the Df of the PI film even when the imidization temperature is low, j's each independently represent preferably 0 or 1, more preferably 0, and even more preferably all 0.

[0048] In formula (z1), n ​​represents an integer of 1 to 4, and is preferably an integer of 1 to 3, more preferably 1 or 2, and particularly preferably 2, from the viewpoint of easily reducing the Df of the PI film even when the imidization temperature is low.

[0049] In one preferred embodiment of the present invention, formula (a1) is represented by formula (a1′) or formula (a1″): [ka] When the PI resin contains a structural unit derived from a tetracarboxylic acid anhydride represented by formula (a1), particularly formula (a1') or (a1"), as the structural unit (A1), the Df of the resulting PI film is likely to be reduced even when the imidization temperature is low.

[0050] In one embodiment of the present invention, the content of the structural unit (A1) is preferably 10 mol% or more, more preferably 15 mol% or more, even more preferably 20 mol% or more, even more preferably 30 mol% or more, particularly preferably 35 mol% or more, and especially preferably 40 mol% or more, based on the total amount of the structural units (A). Furthermore, the content of the structural 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, based on the total amount of the structural units (A). When the content of the structural unit (A1) is within the above range, orientation of the PI resin is likely to occur, and the Df of the PI film is likely to decrease. The proportion of the structural unit may be, for example, 1 It can be measured using H-NMR, or can be calculated from the ratio of raw materials used.

[0051] (Structural unit (A2) derived from a biphenyl skeleton-containing tetracarboxylic acid anhydride) In one embodiment of the present invention, the structural unit (A) preferably contains a structural unit (A2) derived from a biphenyl skeleton-containing tetracarboxylic acid anhydride (hereinafter sometimes simply referred to as the structural unit (A2)). When the structural unit (A) contains the structural unit (A2), the Df of the resulting PI film is likely to be reduced even when the imidization temperature is low.

[0052] In one embodiment of the present invention, the structural unit (A2) is not particularly limited as long as it contains a biphenyl skeleton, and the structural unit (A2) may contain one or more biphenyl skeletons. Furthermore, in one embodiment of the present invention, the structural unit (A2) is preferably a structural unit that contains a biphenyl skeleton but does not contain an ester bond, and in this specification, a structural unit derived from a tetracarboxylic acid anhydride that contains both an ester bond and a biphenyl skeleton is classified as a structural unit (A1) derived from an ester bond-containing tetracarboxylic acid anhydride, rather than as a structural unit (A2).

[0053] In one embodiment of the present invention, the structural unit (A2) is represented by the formula (a2): [ka] [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; and t's each independently represent an integer of 0 to 3. Preferably, the structural unit (a2) is derived from a tetracarboxylic acid anhydride represented by the following formula:

[0054] R in formula (a2) a2 are each independently a halogen atom, or an alkyl group, alkoxy group, aryl group, or aryloxy group which may have a halogen atom, and preferably are each independently an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, or an aryl group having 6 to 12 carbon atoms, from the viewpoint of easily reducing the Df of the PI film even when the imidization temperature is low. Examples of the alkyl group having 1 to 6 carbon atoms, the alkoxy group having 1 to 6 carbon atoms, and the aryl group having 6 to 12 carbon atoms include those exemplified above. R a2 The hydrogen atoms contained in may be substituted with halogen atoms independently of one another, and examples of the halogen atoms include those exemplified above. Among these, from the viewpoint of easily reducing the Df of the PI film even at a low imidization temperature, Ra2 are each independently preferably an alkyl group having 1 to 6 carbon atoms, more preferably an alkyl group having 1 to 3 carbon atoms. In addition, t's in formula (a2) each independently represent an integer of 0 to 3, preferably 0 or 1, and more preferably 0.

[0055] The bonding positions of the two carboxylic acid anhydrides bonded to the benzene rings constituting the biphenyl skeleton in formula (a2) are not particularly limited, and may be 3,4- or 2,3-, independently of each other, based on the single bond bonding the two benzene rings. 3,4- is preferred from the viewpoint of facilitating a reduction in the Df of the PI film even at low imidization temperatures.

[0056] In one preferred embodiment of the present invention, formula (a2) is represented by formula (a2'): [ka] When the PI resin contains a structural unit derived from a tetracarboxylic acid anhydride represented by formula (a2), particularly formula (a2'), as the structural unit (A2), the Df of the resulting PI film can be easily reduced even if the imidization temperature is low.

[0057] In one embodiment of the present invention, the content of the structural unit (A2) is preferably 25 mol% or more, more preferably 30 mol% or more, even more preferably 35 mol% or more, and particularly preferably 40 mol% or more, based on the total amount of the structural units (A). Furthermore, the content of the structural unit (A2) is preferably 90 mol% or less, more preferably 85 mol% or less, even more preferably 80 mol% or less, even more preferably 70 mol% or less, and particularly preferably 60 mol% or less, based on the total amount of the structural units (A). When the content of the structural unit (A1) is within the above range, orientation of the PI resin is likely to occur, and the Df of the PI film is likely to decrease. The proportion of the structural units can be, for example, 1 It can be measured using H-NMR, or can be calculated from the ratio of raw materials used.

[0058] In one embodiment of the present invention, the total amount of the structural units (A1) and (A2) relative to the total amount of the structural units (A) is preferably 50 mol% or more, more preferably 60 mol% or more, even more preferably 70 mol% or more, still more preferably 80 mol% or more, and particularly preferably 90 mol% or more, relative to the total amount of the structural units (A), from the viewpoint of easily reducing the Df of the PI film even when the imidization temperature is low. Furthermore, there is no particular upper limit on the total amount of the structural units (A1) and (A2), and it may be, for example, 100 mol% or less. The ratio of the structural units may be, for example, 1 It can be measured using H-NMR, or can be calculated from the ratio of raw materials used.

[0059] (Structural unit (A3)) In one embodiment of the present invention, the structural unit (A) may contain a structural unit (A3) (hereinafter sometimes simply referred to as structural unit (A3)) derived from a tetracarboxylic acid anhydride other than the structural unit (A1) and the structural unit (A2). In this specification, the term "structural unit (A3) derived from a tetracarboxylic acid anhydride other than the structural unit (A1) and the structural unit (A2)" refers to a structural unit derived from a tetracarboxylic acid anhydride that does not fall under either the structural unit (A1) or the structural unit (A2), and the term "content of the structural unit (A3)" refers to the total amount of the structural unit (A3) when multiple structural units (A3) are present.

[0060] In one embodiment of the present invention, the structural unit (A3) is a structural unit derived from a tetracarboxylic acid anhydride that does not contain either an ester bond or a biphenyl skeleton, such as a structural unit derived from a tetracarboxylic acid anhydride in which Y in formula (1) is represented by any of formulas (31) to (38). From the viewpoint of easily reducing the Df of the PI film even at a low imidization temperature, the structural unit (A3) is preferably a structural unit derived from a tetracarboxylic acid anhydride in which Y in formula (1) is represented by any of formulas (42) to (49) or (53), and more preferably a structural unit derived from a tetracarboxylic acid anhydride in which Y in formula (1) is represented by formula (42), formula (46), formula (49), or formula (53).

[0061] In one embodiment of the present invention, when the structural unit (A3) is contained, the content thereof may be, for example, 0.01 to 55 mol %, or 0.01 to 40 mol %, relative to the total amount of the structural unit (A), and is preferably 40 mol % or less, more preferably 35 mol % or less, even more preferably 30 mol % or less, and particularly preferably 25 mol % or less, and is usually 0.01 mol % or more, preferably 10 mol % or more. When the content of the structural unit (A3) is within the above range, orientation of the PI resin is likely to occur, and the Df of the PI film is likely to decrease. The proportion of the structural unit may be, for example, 1 It can be measured using H-NMR, or can be calculated from the ratio of raw materials used.

[0062] In one embodiment of the present invention, when the structural unit (A3) is a structural unit derived from a tetracarboxylic acid anhydride represented by formula (32) in which Y in formula (1) is preferably Y in formula (32), more preferably a structural unit derived from a tetracarboxylic acid anhydride represented by formula (32) in which Y in formula (1) is f=0, its content relative to the total amount of structural unit (A) 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, and preferably 90 mol% or less, more preferably 80 mol% or less, even more preferably 70 mol% or less, particularly preferably 60 mol% or less. When the content is within the above range, the Df of the PI film is likely to be reduced. The proportion of the structural unit is, for example, 1 It can be measured using H-NMR, or can be calculated from the ratio of raw materials used.

[0063] In one embodiment of the present invention, when the structural unit (A) includes the structural units (A1) and (A2), the structural unit (A) is represented by the formula (X): (Content of structural unit (A3)) / (Total amount of structural unit (A1) and structural unit (A2))<1.1 (X) When the structural unit (A) satisfies the relationship of formula (X), that is, when the value of the left side of formula (X) is less than 1.1, particularly less than 0.67, the Df of the resulting PI film is likely to be reduced, and as a result, even if the imidization temperature of the PI resin is low, the Df of the resulting PI film is likely to be reduced, and a PI film with an excellent balance of mechanical properties can be obtained.

[0064] In one embodiment of the present invention, the value of the left side of formula (X) is preferably 0.6 or less, more preferably 0.5 or less, even more preferably 0.4 or less, still more preferably 0.3 or less, and particularly preferably 0.20 or less, from the viewpoint of easily reducing the Df of the PI film even at a low imidization temperature and easily improving the mechanical properties. There is no particular lower limit for the value of the left side of formula (X), and it may be 0 or more.

[0065] In one embodiment of the present invention, from the viewpoint of easily reducing the Df of the PI film, the structural unit (A) preferably contains a structural unit derived from a tetracarboxylic acid anhydride represented by formula (a2) and / or a structural unit derived from a tetracarboxylic acid anhydride represented by formula (32) in which 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 film, the structural unit (A) preferably contains at least one selected from the group consisting of a structural unit derived from a tetracarboxylic acid anhydride represented by formula (a1), a structural unit derived from a tetracarboxylic acid anhydride represented by formula (a2), and a structural unit derived from a tetracarboxylic acid anhydride represented by formula (32) in which Y in formula (1) is f = 0, and more preferably contains, in addition to the structural unit derived from a tetracarboxylic acid anhydride represented by formula (a1), a structural unit derived from a tetracarboxylic acid anhydride represented by formula (a2) and / or a structural unit derived from a tetracarboxylic acid anhydride represented by formula (32) in which Y in formula (1) is f = 0.

[0066] (Diamine-derived structural unit (B)) The PI resin contains a diamine-derived structural unit (B) (hereinafter, sometimes simply referred to as structural unit (B)). The structural unit (B) is not particularly limited as long as the E′ and Tg of the PI resin at 280°C are within the above ranges. For example, the structural unit (B) may be a unit represented by the formula (2): [ka] [In formula (2), X represents a divalent organic group] Preferably, the structural unit is derived from a diamine represented by the following formula:

[0067] 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 and a divalent aliphatic group. Examples of the divalent aliphatic group include a divalent acyclic aliphatic group or a divalent cyclic aliphatic group. Among these, from the viewpoint of easily improving the mechanical and thermal properties of the PI film, a divalent cyclic aliphatic group and a divalent aromatic group are preferred, and a divalent aromatic group is more preferred. The divalent organic group may have a hydrogen atom substituted with a halogen atom, a hydrocarbon group, an alkoxy group, or a halogenated hydrocarbon group. In such cases, the carbon number of these groups is preferably 1 to 8. In this specification, a divalent aromatic group refers to a divalent organic group having an aromatic group, and may include an aliphatic group or other substituent as part of its structure. Furthermore, a divalent aliphatic group is a divalent organic group having an aliphatic group, and may contain other substituents as part of its structure, but does not include an aromatic group.

[0068] In one embodiment of the present invention, the PI resin may contain multiple types of X, which may be the same or different from one another. Examples of X in formula (2) include groups (structures) represented by formulas (60) to (65), and groups in which a hydrogen atom in a group represented by formulas (60) to (65) is substituted with a methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, sec-butyl group, tert-butyl group, fluoro group, chloro group, or trifluoromethyl group.

[0069] [ka]

[0070] [In formula (60) and formula (61), R a and R b each independently represents a halogen atom, or an alkyl group, alkoxy group, aryl group, or aryloxy group which may have a halogen atom; W each independently represents a single bond, -O-, -CH2-, -CH2-CH2-, -CH(CH3)-, -C(CH3)2-, -C(CF3)2-, -COO-, -OOC-, -SO2-, -S-, -CO- or -N(R c )-, and 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, t represents an integer of 0 to 4, u represents an integer of 0 to 4, and n represents an integer of 0 to 4; In formula (62), ring A represents a cycloalkane ring having 3 to 8 carbon atoms. R d represents an alkyl group having 1 to 20 carbon atoms, r represents an integer of 0 or more and (the number of carbon atoms in ring A - 2) or less, S1 and S2 each independently represent an integer of 0 to 20; In formulas (60) to (65), * represents a bond.

[0071] Other examples of X in formula (2) include 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 and nitrogen atoms.

[0072] Among these, from the viewpoint of easily improving the mechanical and thermal properties of the PI film, the PI resin in the present invention preferably contains, as X in formula (2), a structure represented by formula (60) or formula (61), and more preferably contains a structure represented by formula (60).

[0073] In formula (60) and formula (61), the bond of each benzene ring or each cyclohexane ring may be bonded at any of the ortho-, meta-, or para-position, or the α-, β-, or γ-position, based on -W- or the single bond connecting each benzene ring or each cyclohexane ring. From the viewpoint of easily reducing the Df of the PI film even at a low imidization temperature and easily improving the dimensional stability, the bond is preferably at the meta- or para-position, or the β- or γ-position, and more preferably at the para- or γ-position. R a and R b are each independently 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, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, or an aryl group having 6 to 12 carbon atoms. Examples of the alkyl group having 1 to 6 carbon atoms, the alkoxy group having 1 to 6 carbon atoms, and the aryl group having 6 to 12 carbon atoms include those exemplified above. R a and R b The hydrogen atoms contained in R may be substituted, independently of one another, with halogen atoms, and examples of such halogen atoms include those exemplified above. From the viewpoint of easily reducing the Df of the PI film and easily improving the dimensional stability, R a and R b are each independently preferably an alkyl group having 1 to 6 carbon atoms or a fluorinated alkyl group having 1 to 6 carbon atoms, and from the viewpoint of easily improving adhesion to a substrate such as copper foil, are more preferably a fluorine-free alkyl group having 1 to 6 carbon atoms, even more preferably a fluorine-free alkyl group having 1 to 3 carbon atoms, and particularly preferably a methyl group.

[0074] In the formula (60) and the formula (61), t and u are each independently an integer of 0 to 4, and are preferably an integer of 0 to 2, more preferably 0 or 1, from the viewpoint of easily reducing the Df of the PI film and easily improving the dimensional stability.

[0075] In formula (60) and formula (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 )-, and from the viewpoint of easily reducing the Df of the PI film and easily improving the dimensional stability, preferably represents -O-, -CH2-, -C(CH3)2-, -C(CF3)2-, -COO-, -OOC- or -CO-, and further from the viewpoint of easily improving the adhesion to a substrate such as copper foil, more preferably represents a single bond, -O-, -CH2- or -C(CH3)2-, even more preferably -O- or -C(CH3)2-. c represents a monovalent hydrocarbon group having 1 to 12 carbon atoms which may be substituted with a hydrogen atom or a halogen atom. Examples of the monovalent hydrocarbon group having 1 to 12 carbon atoms include those exemplified above.

[0076] In the formulas (60) and (61), n ​​is an integer of 0 to 4, and from the viewpoint of easily reducing Df of the PI film and easily improving the dimensional stability, it is preferably an integer of 0 to 3, more preferably 1 to 3. When n is 2 or more, a plurality of W, R a and t may be the same or different, and the positions of the bonds of each benzene ring relative to -W- may be the same or different.

[0077] When the PI resin of the present invention contains two or more structures represented by formula (60) and formula (61) as X in formula (2), W, n, R in one of formulas (60) and (61) a , R b , t and u are independently of each other W, n, R in the other formulas (60) and (61). a , R b, t and u may be the same or different.

[0078] In formula (62), ring A represents a cycloalkane ring having 3 to 8 carbon atoms. Examples of the cycloalkane ring include a cyclopropane ring, a cyclobutane ring, a cyclopentane ring, a cyclohexane ring, a cycloheptane ring, and a cyclooctane ring, and preferably a cycloalkane ring having 4 to 6 carbon atoms. In ring A, the bonds may or may not be adjacent to each other. For example, when ring A is a cyclohexane ring, the two bonds may be in the α-position, β-position, or γ-position relationship, and preferably in the β-position or γ-position relationship.

[0079] R in equation (62) d represents an alkyl group having 1 to 20 carbon atoms, preferably an alkyl group having 1 to 10 carbon atoms, examples of which include those exemplified above. In formula (62), r represents an integer of 0 or more and not more than "the number of carbon atoms in ring A minus 2". r is preferably 0 or more and preferably 4 or less. In formula (62), S1 and S2 each independently represent an integer of 0 to 20. S1 and S2 each independently are preferably 0 or more, more preferably 2 or more, and preferably 15 or less.

[0080] Specific examples of the structures represented by formulas (60) to (62) include structures represented by formulas (71) to (92). In these formulas, * represents a bond.

[0081] [ka]

[0082] In a preferred embodiment of the present invention, when X in formula (2) contains at least one diamine-derived structural unit represented by formula (60) or formula (61), the proportion of the diamine-derived structural units represented by formula (60) or formula (61), particularly the proportion of diamine-derived structural units 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 units (B). When the proportion of diamine-derived structural units represented by formula (60) or formula (61) in formula (2), particularly the proportion of at least one diamine-derived structural unit in formula (60) where W represents a single bond, is within the above range, the Df of the PI film is easily reduced and the dimensional stability is easily improved. The proportion of the structural units can be, for example, 1 It can be measured using H-NMR, or can be calculated from the ratio of raw materials used.

[0083] (Structural unit (B1) derived from biphenyl skeleton-containing diamine) In one embodiment of the present invention, the structural unit (B) preferably contains a structural unit (B1) derived from a biphenyl skeleton-containing diamine (hereinafter, sometimes simply referred to as the structural unit (B1)). When the structural unit (B) contains the structural unit (B1), the Df of the resulting PI film is likely to be reduced even at a low imidization temperature. Therefore, an electrical circuit made of a PI film obtained at a low imidization temperature is likely to have reduced transmission loss.

[0084] In one embodiment of the present invention, the structural unit (B1) is not particularly limited as long as it contains a biphenyl skeleton, and the number of biphenyl skeletons contained in the structural unit (B1) may be one or more. In one embodiment of the present invention, from the viewpoint of easily reducing the Df of the PI film even when the imidization temperature is low, the structural unit (B1) is a unit represented by the formula (b1): [ka] [In formula (b1), Rb1 each independently represents a halogen atom, or an alkyl group, alkoxy group, aryl group, or aryloxy group which may have a halogen atom; p's each independently represent an integer of 0 to 4. Preferably, the structural unit (b1) is derived from a diamine and is represented by the following formula:

[0085] In formula (b1), R b1 are each independently 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, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, or an aryl group having 6 to 12 carbon atoms. Examples of the alkyl group having 1 to 6 carbon atoms, the alkoxy group having 1 to 6 carbon atoms, and the aryl group having 6 to 12 carbon atoms include those exemplified above. R b1 The hydrogen atoms contained in R may be substituted, independently of one another, with halogen atoms, and examples of such halogen atoms include those exemplified above. From the viewpoint of easily reducing the Df of the PI film and easily improving the dimensional stability, R b1 are each independently preferably an alkyl group having 1 to 6 carbon atoms or a fluorinated alkyl group having 1 to 6 carbon atoms, and from the viewpoint of easily improving adhesion to a substrate such as copper foil, are more preferably a fluorine-free alkyl group having 1 to 6 carbon atoms, even more preferably a fluorine-free alkyl group having 1 to 3 carbon atoms, and particularly preferably a methyl group.

[0086] In formula (b1), p's each independently represent an integer of 0 to 4, and are preferably an integer of 0 to 2, more preferably 0 or 1, from the viewpoint of easily reducing the Df of the PI film and easily improving the dimensional stability.

[0087] In formula (b1), the -NH2 group bonded to each benzene ring may be bonded at any of the ortho-, meta-, or para-positions, or the α-, β-, or γ-positions, based on the single bond connecting the benzene rings. From the viewpoint of easily reducing the Df of the PI film even at a low imidization temperature and easily improving the dimensional stability, the -NH2 group may be bonded preferably at the meta- or para-position, or the β- or γ-position, and more preferably at the para- or γ-position.

[0088] In one preferred embodiment of the present invention, formula (b1) is represented by formula (b1′): [ka] When the PI resin contains a diamine-derived structural unit represented by formula (b1), particularly formula (b1'), as the structural unit (B1), the Df of the resulting PI film is likely to be reduced even if the imidization temperature is low.

[0089] In one embodiment of the present invention, the content of the structural unit (B1), preferably the structural unit (b1), relative to the total amount of the structural units (B), is preferably 25 mol% or more, more preferably more than 30 mol%, even more preferably 35 mol% or more, even more preferably 40 mol% or more, particularly preferably 60 mol% or more, particularly preferably 70 mol% or more, especially more preferably 80 mol% or more, and especially more preferably 90 mol% or more. When the content of the structural unit (B1), preferably the structural unit (b1), is at or above the lower limit, Df is easily reduced even at low imidization temperatures. Furthermore, there is no particular upper limit for the content of the structural unit (B1), preferably the structural unit (b1), and it may be 100 mol% or less relative to the total amount of the structural units (B). The proportion of the structural units is, for example, 1 It can be measured using H-NMR, or can be calculated from the ratio of raw materials used.

[0090] (Structural unit (B2)) In one embodiment of the present invention, the structural unit (B) preferably includes a diamine-derived structural unit (B2) (hereinafter sometimes simply referred to as structural unit (B2)) having two or more aromatic rings, each of which is bonded via a divalent organic group. Examples of the divalent organic group in the structural unit (B2) include alkylene groups which may have a halogen atom, -O-, -COO-, -OOC-, -SO2-, -S-, -CO-, or -N(R c )-, etc., and 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. Among these, the divalent organic group in the structural unit (B2) is preferably -O-, -CH2-, -CH2-CH2-, -CH(CH3)-, -C(CH3)2-, -C(CF3)2-, -COO-, -OOC-, -SO2-, -S-, -CO-, or -N(R c )- is preferred.

[0091] In one embodiment of the present invention, the structural unit (B) is represented by the formula (b2) as the structural unit (B2): [ka] [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; W is independently -O-, -CH2-, -CH2-CH2-, -CH(CH3)-, -C(CH3)2-, -C(CF3)2-, -COO-, -OOC-, -SO2-, -S-, -CO- or -N(R c )-, and 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 1 to 4; and q independently represents an integer of 0 to 4. When the structural unit (B) contains the structural unit (B2), particularly the structural unit (b2), the Df of the PI film obtained is likely to be reduced even at low imidization temperatures, and as a result, the transmission loss of an electronic circuit including the PI film obtained at low imidization temperatures is likely to be reduced.

[0092] In formula (b2), R b2 are each independently a halogen atom, or an alkyl group, alkoxy group, aryl group, or aryloxy group which may have a halogen atom, and preferably a halogen atom, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, or an aryl group having 6 to 12 carbon atoms. Examples of the alkyl group having 1 to 6 carbon atoms, the alkoxy group having 1 to 6 carbon atoms, and the aryl group having 6 to 12 carbon atoms include those exemplified above. R b2 The hydrogen atoms contained in R may be substituted, independently of one another, with halogen atoms, and examples of such halogen atoms include those exemplified above. From the viewpoint of easily reducing the Df of the PI film and easily improving the dimensional stability, R b2 are each independently preferably an alkyl group having 1 to 6 carbon atoms or a fluorinated alkyl group having 1 to 6 carbon atoms, and from the viewpoint of easily improving adhesion to a substrate such as copper foil, are more preferably a fluorine-free alkyl group having 1 to 6 carbon atoms, even more preferably a fluorine-free alkyl group having 1 to 3 carbon atoms, and particularly preferably a methyl group.

[0093] In formula (b2), q's each independently represent an integer of 0 to 4, and are preferably an integer of 0 to 2, more preferably 0 or 1, from the viewpoint of easily reducing the Df of the PI film and easily improving the dimensional stability.

[0094] In formula (b2), W is, independently of one another, -O-, -CH2-, -CH2-CH2-, -CH(CH3)-, -C(CH3)2-, -C(CF3)2-, -COO-, -OOC-, -SO2-, -S-, -CO- or -N(R c)-, and from the viewpoint of easily reducing the Df of the PI film and easily improving the dimensional stability, it preferably represents -O-, -CH2-, -C(CH3)2-, -C(CF3)2-, -COO-, -OOC- or -CO-, and from the viewpoint of easily improving the adhesion to a substrate such as copper foil, it more preferably represents -O-, -CH2- or -C(CH3)2-, and even more preferably represents -O- or -C(CH3)2-. c represents a monovalent hydrocarbon group having 1 to 12 carbon atoms which may be substituted with a hydrogen atom or a halogen atom. Examples of the monovalent hydrocarbon group having 1 to 12 carbon atoms include those exemplified above, which may be substituted with a halogen atom. Examples of the halogen atom include the same as those mentioned above.

[0095] In formula (b2), m is an integer of 1 to 4, and from the viewpoint of easily reducing Df of the PI film and easily improving the dimensional stability, it is preferably an integer of 1 to 3, more preferably 2 or 3. In formula (b2), multiple W, R b2 and q may be the same or different, and the position of -W- relative to -NH2 of each benzene ring may be the same or different.

[0096] In formula (b2), -W- may be bonded to any of the ortho-, meta-, or para-positions, or the α-, β-, or γ-positions, based on -NH2 of each benzene ring. From the viewpoint of easily reducing the Df of the PI film even at a low imidization temperature and easily improving the dimensional stability, -W- is preferably bonded to the meta- or para-position, or the β- or γ-position, and more preferably to the para- or γ-position.

[0097] In one embodiment of the present invention, from the viewpoint of easily reducing Df of the PI film even when the imidization temperature is low and easily improving the adhesion between the PI film and a substrate such as a copper foil, in formula (b2), it is preferable that m is 3 and each W independently represents —O— or —C(CH)—, and formula (b2) is represented by formula (b2′): [ka] When the PI resin contains the structural unit (b2), particularly a diamine-derived structural unit represented by formula (b2'), E' at 280°C tends to decrease, and as a result, the Df of the PI resin tends to decrease even when thermally imidized at low temperatures. This makes it easier to obtain a PI film that has a low Df even when the imidization temperature is low and that has excellent adhesion to copper foil.

[0098] In one embodiment of the present invention, the structural unit (b2) may contain, in addition to or instead of the diamine-derived structural unit represented by formula (b2'), a diamine-derived structural unit in which m is 1 and W is -O- in formula (b2).

[0099] In one embodiment of the present invention, the content of the structural unit (B2) is preferably 0 mol% or more, more preferably 0.3 mol% or more, even more preferably 0.5 mol% or more, even more preferably 0.8 mol% or more, particularly preferably 1 mol% or more, especially more preferably 5 mol% or more, and especially more preferably 8 mol% or more, relative to the total amount of the structural unit (B). When the content of the structural unit (B2) is at least the above-mentioned lower limit, the adhesion of the resulting PI film to a substrate such as copper foil is likely to be improved. Furthermore, the upper limit of the content of the structural 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 especially preferably 20 mol% or less, relative to the total amount of the structural unit (B). When the content of the structural unit (B2) is at most the above-mentioned upper limit, mechanical properties such as CTE tend to be easily improved. The proportion of the structural unit is, for example, 1 It can be measured using H-NMR, or can be calculated from the ratio of raw materials used.

[0100] (Structural unit (B3)) The PI resin may contain a diamine-derived structural unit (B3) (hereinafter sometimes simply referred to as structural unit (B3)) other than the structural units (B1) and (B2). Examples of the structural unit (B3) include a diamine-derived structural unit in which m in formula (b2) is 0, and a diamine-derived structural unit in which X in formula (2) is represented by formulas (61) to (64). Among these, diamine-derived structural units in which X in formula (2) is represented by formulas (71), (74), (77), (78), (89), and (90) are preferred, with the diamine-derived structural unit represented by formula (74) (p-phenylenediamine-derived structural unit) being more preferred. In this specification, "a diamine-derived structural unit (B3) other than the structural unit (B1) and the structural unit (B2)" refers to a diamine-derived structural unit that is different from both the structural unit (B1) and the structural unit (B2)."

[0101] In one embodiment of the present invention, when the structural unit (B) contains the structural unit (B3), the content of the structural 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 the structural unit (B).

[0102] In one embodiment of the present invention, the PI resin may contain halogen atoms, preferably fluorine atoms, which can be introduced, for example, by the above-mentioned halogen-containing substituents. When the PI resin contains fluorine atoms, the dielectric constant of the resulting PI film is likely to be reduced. Examples of fluorine-containing substituents suitable for incorporating fluorine atoms into the PI resin include a fluoro group and a trifluoromethyl group. In another embodiment of the present invention, the PI resin preferably 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. Furthermore, since fluorine in the PI resin tends to weaken the interaction between molecular chains, if the PI resin does not contain fluorine atoms, the PI resin is more likely to form a higher-order structure in which molecular rotation is suppressed, and as a result, the effects of the present invention tend to be more easily achieved.

[0103] 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 mass%, more preferably 0.1 to 30 mass%, even more preferably 0.1 to 20 mass%, and particularly preferably 0.1 to 10 mass%, based on the mass of the PI resin. When the halogen atom content is equal to or greater than the above-mentioned lower limit, the heat resistance and dielectric properties of the resulting PI film are likely to be improved. When the halogen atom content is equal to or less than the above-mentioned upper limit, it is advantageous in terms of cost, the CTE of the PI film is likely to be reduced, and the synthesis of the PI resin is facilitated. Dielectric properties refer to dielectric properties including the dielectric constant and dielectric loss tangent, and an increase or improvement in the dielectric properties refers to a decrease in the dielectric constant and / or dielectric loss tangent.

[0104] In one embodiment of the present invention, the imidization ratio of the PI resin is preferably 90% or more, more preferably 93% or more, and even more preferably 95% or more, and is usually 100% or less. From the viewpoint of easily improving mechanical properties, thermal properties, and dielectric characteristics, the imidization ratio is preferably equal to or greater than the above-mentioned lower limit. The imidization ratio indicates the ratio of the molar amount of imide bonds in the PI resin to twice the molar amount of structural units derived from tetracarboxylic acid compounds in the PI resin. When the PI resin contains a tricarboxylic acid compound, the imidization ratio indicates the ratio of the molar amount of imide bonds in the PI resin to the sum of twice the molar amount of structural units derived from tetracarboxylic acid compounds in the PI resin and the molar amount of structural units derived from tricarboxylic acid compounds. The imidization ratio can be determined by IR, NMR, or other methods.

[0105] In one embodiment of the present invention, the polystyrene-equivalent weight-average molecular weight (hereinafter, sometimes referred to as Mw) of the PI resin 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, and particularly preferably 130,000 or more, and is 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. Having an Mw equal to or greater than the above-mentioned lower limit facilitates improved mechanical properties such as break resistance. Having an Mw equal to or less than the above-mentioned upper limit is advantageous in terms of processability during film formation.

[0106] In one embodiment of the present invention, the ratio (Mw / Mn) of Mw to number average molecular weight (hereinafter, number average molecular weight may be referred to as Mn) of the PI resin, in terms of polystyrene, is preferably 3.5 or more, more preferably 4.0 or more, even more preferably 4.2 or more, still more preferably 4.5 or more, particularly preferably 4.7 or more, from the viewpoint of easily improving flex resistance, and is preferably 8.0 or less, more preferably 7.0 or less, even more preferably 6.0 or less, particularly preferably 5.5 or less. Note that Mw and Mn can be determined by gel permeation chromatography (hereinafter, sometimes referred to as GPC) measurement and converted into standard polystyrene.

[0107] In one embodiment of the present invention, the content of the 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, based on the mass of the PI film of the present invention. The upper limit of the PI resin content is not particularly limited, and is, for example, 100% by mass or less, preferably 99% by mass or less, and more preferably 95% by mass or less, based on the mass of the PI film. When the PI resin content is within the above range, the mechanical and thermal properties are likely to be improved.

[0108] The PI film of the present invention may contain a filler, if necessary. Examples of fillers include metal oxide particles such as silica and alumina, inorganic salts such as calcium carbonate, and polymer particles such as fluororesins and cycloolefin polymers. A single filler may be used, or two or more fillers may be used in combination. When a filler is contained, the content thereof is preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less, relative to the total mass of the PI film, and is preferably 0.01% by mass or more.

[0109] In one embodiment of the present invention, the PI film of the present invention may contain additives as needed. Examples of additives include antioxidants, flame retardants, crosslinking agents, surfactants, compatibilizers, imidization catalysts, weathering agents, lubricants, antiblocking agents, antistatic agents, antifogging agents, anti-dripping agents, and pigments. The additives may be used alone or in combination. The content of each additive may be appropriately selected within a range that does not impair the effects of the present invention. When various additives are included, the total content is preferably 7% by mass or less, more preferably 5% by mass or less, and even more preferably 4% by mass or less, relative to the total mass of the PI film, and is preferably 0.001% by mass or more.

[0110] <Polyimide film> The PI film of the present invention contains a PI resin containing a structural unit (A) derived from a tetracarboxylic acid anhydride and a structural unit (B) derived from a diamine, and the PI resin has an E' of 3×10 at 280° C. 8 Since the thermal imidization temperature is low, Df can be reduced, and the PI resin precursor has a Tg of 200 to 290°C. Therefore, the PI resin precursor can be suitably used for metal-clad laminates such as CCL, which are compatible with high frequencies. The present invention also encompasses a PI film containing a PI resin obtained by imidizing a PI resin precursor through a heat treatment at 200°C or higher but lower than 350°C.

[0111] In one embodiment of the present invention, the CTE of the PI film is preferably 50 ppm / K or less, more preferably 40 ppm / K or less, even more preferably 30 ppm / K or less, even more preferably 25 ppm / K or less, and is preferably 0 ppm / K or more, more preferably 5 ppm / K or more, even more preferably 8 ppm / K or more, and even more preferably 12 ppm / K or more. By setting the CTE within the above range, the CTE of the copper foil and the PI layer become close to each other, thereby suppressing peeling of the laminated film. Note that the CTE can be measured, for example, using a thermomechanical analyzer (sometimes referred to as "TMA") and is determined by the method described in the Examples.

[0112] Printed circuits are required to have low transmission loss. Transmission loss is expressed as the sum of dielectric loss, which is loss caused by the electric field generated in the dielectric, and conductor loss, which is loss caused by the current flowing through the conductor. Dielectric loss is known to be approximately proportional to the index E, which is expressed by formula (i).

[0113] E=Df×(Dk) 1 / 2 (i) [In formula (i), Df represents the dielectric loss tangent, and Dk represents the relative dielectric constant]

[0114] In the high frequency range used in 5G FPCs, dielectric loss tends to increase, so there is a particular demand for materials that have a small value of the index E and can suppress dielectric loss. On the other hand, high frequency signals concentrate current on the surface of the conductor. Therefore, conductor loss is related to the dielectric properties of the adjacent dielectric and is approximately (Dk) 1 / 2 is known to be proportional to

[0115] As described above, the PI film of the present invention contains a PI resin containing a tetracarboxylic anhydride-derived structural unit (A) and a diamine-derived structural unit (B), and the PI resin has an E' of 3×10 at 280° C. 8Since the dielectric constant is less than Pa and the Tg is 200 to 290°C, Df and Dk are small, which reduces the dielectric loss index E and conductor loss, and transmission loss can be reduced in circuits containing the PI film. In one embodiment of the present invention, the dielectric loss index E of the PI 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 an electronic circuit containing the PI film. Therefore, the lower limit of the index E is not particularly limited and may be, for example, 0 or more.

[0116] In one embodiment of the present invention, from the viewpoint of easily reducing transmission loss in an electronic circuit comprising a PI-based film, 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, especially preferably 0.0027 or less, and particularly preferably 0.0024 or less. The smaller the Df, the lower the transmission loss of an electronic circuit comprising a PI-based film, so the lower limit of Df is not particularly limited and may be, for example, 0 or more.

[0117] In one embodiment of the present invention, the Dk at 10 GHz of the PI-based film is preferably less than 3.50, more preferably 3.45 or less, even more preferably 3.40 or less, still more preferably 3.38 or less, particularly preferably 3.36 or less, especially more preferably 3.33 or less, especially more preferably 3.30 or less, particularly preferably 3.27 or less, and especially more preferably 3.22 or less.

[0118] The Df and Dk of the PI film can be measured using a vector network analyzer and a resonator, for example, by the method described in the Examples.

[0119] In one embodiment of the present invention, the PI film of the present invention can be bent at least 15,000 times, preferably at least 20,000 times, more preferably at least 50,000 times, even more preferably at least 100,000 times, even more preferably at least 150,000 times, and particularly preferably at least 200,000 times until breakage in an MIT folding fatigue test according to ASTM standard D2176-16. When the number of folding times is equal to or greater than the lower limit, the occurrence of cracks, breaks, creases, etc. can be effectively suppressed even when repeatedly folded. The upper limit of the number of folding times is not particularly limited, and may be, for example, 10,000,000 times or less. The MIT folding fatigue test can be measured using an MIT folding fatigue tester, for example, by the method described in the Examples.

[0120] In one embodiment of the present invention, from the viewpoint of easily reducing Df of a PI-based film and easily improving mechanical properties, E′ at 280°C of a PI-based resin and CTE of a PI-based film containing the PI resin are expressed by the formula (Y): (CTE of PI film) × (E' of PI resin at 280°C) 1 / 2 ≧30,000 It is preferable that the following relationship is satisfied.

[0121] In one embodiment of the present invention, from the viewpoint of easily reducing the Df of the PI film and easily increasing the flex resistance, the value of the left side of formula (Y) is preferably 40,000 or more, more preferably 50,000 or more, even more preferably 100,000 or more, still more preferably 120,000 or more, and particularly preferably 125,000 or more; and is preferably 1,500,000 or less, more preferably 1,000,000 or less, even more preferably 850,000 or less, still more preferably 700,000 or less, particularly preferably 500,000 or less, and particularly preferably 450,000 or less.

[0122] The thickness of the PI film of the present invention can be appropriately selected depending on the application, and is preferably 5 μm or more, more preferably 10 μm or more, and even more preferably 20 μm or more, and is 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 especially preferably 50 μm or less. The film thickness can be measured using a thickness meter or the like. When the film of the present invention is a multilayer film, the above thickness refers to the thickness of the single layer portion.

[0123] The PI film of the present invention may be subjected to a surface treatment such as corona discharge treatment, plasma treatment, or ozone treatment by a method generally employed industrially.

[0124] Because the PI film of the present invention has a low Df, it can be suitably used as a substrate material compatible with printed circuit boards and antenna substrates for high-frequency bands. Metal-clad laminates such as CCL used in FPCs are widely used laminates having a metal foil, such as a copper foil layer, on one or both sides of a single or multiple PI resin layers. When the PI film of the present invention is used as a resin layer, the PI film of the present invention can achieve a low Df even at a low imidization temperature. Therefore, even when a metal-clad laminate such as CCL is produced by thermally imidizing a PI resin precursor coating film on a metal foil such as copper foil, deterioration of the copper foil surface can be suppressed, and a metal-clad laminate such as CCL with excellent high-frequency properties can be obtained.

[0125] [Method for producing polyimide film] The method for producing the PI film of the present invention is not particularly limited, but may include, for example, the following steps: A step of applying a PI resin precursor solution containing a tetracarboxylic acid anhydride-derived structural unit (A) and a diamine-derived structural unit (B) onto a substrate; and A process of imidizing the PI resin precursor by heat treatment at 200°C or higher but lower than 350°C. It can be produced by a method comprising:

[0126] <Polyimide resin precursor solution coating process> (Preparation of PI resin precursor solution) The PI resin precursor solution contains a PI resin precursor containing a tetracarboxylic acid anhydride-derived structural unit (A) and a diamine-derived structural unit (B) and can be prepared by mixing the PI resin precursor with a solvent. In one embodiment of the present invention, the reaction solution containing the PI resin precursor obtained by the synthesis of the PI resin precursor may be appropriately diluted with a solvent as needed and used as a PI resin precursor solution.

[0127] The PI resin precursor of the present invention is obtained by reacting a tetracarboxylic acid anhydride with a diamine. In addition to the tetracarboxylic acid compound, a dicarboxylic acid compound or a tricarboxylic acid compound may also be reacted.

[0128] Examples of tetracarboxylic acid anhydrides used in the synthesis of PI resin precursors include aromatic tetracarboxylic acid compounds such as aromatic tetracarboxylic acid dianhydrides, and aliphatic tetracarboxylic acid compounds such as aliphatic tetracarboxylic acid dianhydrides. The tetracarboxylic acid compounds may be used alone or in combination of two or more. The tetracarboxylic acid compounds may be dianhydrides or tetracarboxylic acid compound analogs such as acid chloride compounds. Examples of the tetracarboxylic acid compound include tetracarboxylic acid anhydrides represented by the formula (1), and preferably tetracarboxylic acid anhydrides represented by the formula (a1), tetracarboxylic acid anhydrides represented by the formula (a2), and tetracarboxylic acid anhydrides in which Y in the formula (1) is represented by the formula (32).

[0129] Specific examples of tetracarboxylic acid compounds include pyromellitic anhydride (hereinafter sometimes referred to as PMDA), 4,4'-(4,4'-isopropylidenediphenoxy)diphthalic anhydride (hereinafter sometimes referred to as BPADA), 1,4,5,8-naphthalenetetracarboxylic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride (hereinafter sometimes referred to as BPDA), 4,4'-(hexafluoroisopropylidene)diphthalic dianhydride (hereinafter sometimes referred to as 6FDA), 4,4'-oxydiphthalic dianhydride, tetracarboxylic dianhydride (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 monoester dianhydride) (hereinafter sometimes referred to as TAHQ), ester of trimellitic anhydride with 2,2',3,3',5,5'-hexamethyl-4,4'-biphenol (hereinafter sometimes referred to as TMPBP), (sometimes referred to as BP-TME), 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 acid dianhydride, bis(2,3-dicarboxyphenyl) ether dianhydride, 3,3",4,4"-p-terphenyl tetracarboxylic acid dianhydride, 2,3,3",4"-p-terphenyl tetracarboxylic acid dianhydride, 2,2",3,3"-p-terphenyl tetracarboxylic acid 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 dianhydride (hereinafter sometimes referred to as HPMDA), 2,3,5,6-cyclohexanetetracarboxylic dianhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, cyclopentane-1,2,3,4-tetracarboxylic 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 carboxylic acid 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,Among these, BPDA, PMDA, TAHQ, and BP-TME are preferred, and BPDA, TAHQ, and BP-TME are more preferred, from the viewpoint of easily reducing the Df of the resulting PI film even at a low imidization temperature. These tetracarboxylic acid compounds can be used alone or in combination of two or more.

[0130] Examples of diamine compounds used in the synthesis of the PI resin precursor include aliphatic diamines, aromatic diamines, and mixtures thereof. The diamine compound includes, for example, a diamine compound represented by the formula (2), and preferably, a diamine compound represented by the formula (b1) or a diamine compound represented by the formula (b2). In this embodiment, "aromatic diamine" refers to a diamine having an aromatic ring, which may contain an aliphatic group or other substituents as part of its structure. The aromatic ring may be a single ring or a condensed ring, and examples thereof include a benzene ring, a naphthalene ring, an anthracene ring, and a fluorene ring, but are not limited to these. Among these, a benzene ring is preferable. Furthermore, "aliphatic diamine" refers to a diamine having an aliphatic group, which may contain other substituents as part of its structure, but does not have an aromatic ring.

[0131] 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), 1,4-bis(4-aminophenoxy)benzene (hereinafter sometimes referred to as TPE- Q), 1,3-bis(4-aminophenoxy)benzene (hereinafter sometimes referred to as TPE-R), 2,2-bis[4-(4-aminophenoxy)phenyl]propane (hereinafter sometimes referred to 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-amino phenoxy)]biphenyl, bis[1-(3-aminophenoxy)]biphenyl, bis[4-(4-aminophenoxy)phenyl]methane, bis[4-(3-aminophenoxy)phenyl]methane, bis[4-(4-aminophenoxy)phenyl]ether, bis[4-(3-aminophenoxy)phenyl]ether, bis[4-(4-aminophenoxy)]benzophenone, bis[4-(3-aminophenoxy)]benzophenone, 2,2-bis-[4-(4-aminophenoxy)phenyl]hexafluoropropane, 2,2-bis-[4-(3-aminophenoxy)] (aminophenoxy)phenyl]hexafluoropropane, 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-diaminodiphenylether, 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-aminocyclohexane) (xyl)methane, bis(p-β-amino-tert-butylphenyl) ether, bis(p-β-methyl-δ-aminopentyl)benzene, p-bis(2-methyl-4-aminopentyl)benzene, p-bis(1,1-dimethyl-5-aminopentyl)benzene, 1,5-diaminonaphthalene, 2,6-diaminonaphthalene, 2,4-bis(β-amino-tert-butyl)toluene, 2,4-diaminotoluene, m-xylene-2,5-diamine, p-xylene-2,5-diamine, m-xylylenediamine, p-xylylenediamine, piperazine, 4 ,4'-Diamino-2,2'-bis(trifluoromethyl)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'-(hexafluoropropylidene)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,Examples of the aromatic hydrocarbon radicals include 4'-diaminobenzanilide, 4,4'-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, BAPP, TPE-Q, TPE-R, etc. are preferred, and m-Tb, BAPP, etc. are more preferred, from the viewpoint of easily reducing the Df of the resulting PI film even at a low imidization temperature. The diamine compounds can be used alone or in combination of two or more.

[0132] The PI resin precursor may be obtained by further reacting the tetracarboxylic acid compound used in the synthesis of the PI resin precursor with other tetracarboxylic acids, dicarboxylic acids, tricarboxylic acids, and anhydrides and derivatives thereof, as long as the physical properties of the PI film are not impaired.

[0133] Other tetracarboxylic acids include water adducts of the anhydrides of the above tetracarboxylic acid compounds.

[0134] 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 of these may be used in combination. Specific examples include dicarboxylic acid compounds of terephthalic acid, isophthalic acid, naphthalenedicarboxylic acid, 4,4'-biphenyldicarboxylic acid, 3,3'-biphenyldicarboxylic acid, and chain hydrocarbons having 8 or less carbon atoms, as well as compounds in which two benzoic acids are linked by a single bond, -O-, -CH2-, -C(CH3)2-, -C(CF3)2-, -SO2-, or a phenylene group, and acid chloride compounds thereof.

[0135] Examples of tricarboxylic acid compounds include aromatic tricarboxylic acids, aliphatic tricarboxylic acids, and their analogous acid chloride compounds and acid anhydrides, and two or more of these may be used in combination. Specific examples include 1,2,4-benzenetricarboxylic acid anhydride; 2,3,6-naphthalenetricarboxylic acid-2,3-anhydride; and compounds in which phthalic anhydride and benzoic acid are linked via a single bond, -O-, -CH2-, -C(CH3)2-, -C(CF3)2-, -SO2-, or a phenylene group.

[0136] In producing the PI resin precursor, the amounts of the diamine compound, tetracarboxylic acid compound, dicarboxylic acid compound, and tricarboxylic acid compound used can be appropriately selected depending on the ratio of each structural unit of the desired PI resin. In the present invention, the total number of moles of diamine compounds used per mole of the total amount of tetracarboxylic acid compounds is defined as the amine ratio. In a 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 the total amount of tetracarboxylic acid compounds. In another embodiment, the amine ratio is preferably 1.001 moles or more and preferably 1.10 moles or less per mole of the total amount of tetracarboxylic acid compounds. In one embodiment of the present invention, when the amine ratio is 1 or less, the amine ratio is preferably 0.90 mol or more and 0.999 mol or less, more preferably 0.95 mol or more and 0.997 mol or less, and even more preferably 0.97 mol or more and 0.995 mol or less. In one embodiment of the present invention, when the amine ratio is 1 or more, the amine ratio is preferably 1.001 mol or more and 1.1 mol or less, more preferably 1.002 mol or more and 1.05 mol or less, and even more preferably 1.003 mol or more and 1.03 mol or less. If the amine ratio is close to 1.0 moles, the molecular weight tends to increase rapidly during synthesis, but if it deviates significantly from 1.0 moles, the molecular weight of the resulting PI resin tends to decrease. If the molecular weight increases rapidly, it grows unevenly within the synthesis mass, making it difficult for the physical properties of the PI resin to stabilize. On the other hand, if the molecular weight is too low, the mechanical properties tend to decrease.

[0137] 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. If the reaction temperature is below the above upper limit, the Df of the resulting PI film is likely to be reduced, and this tendency is particularly pronounced in PI films containing a PI resin containing an ester bond, particularly a PI resin containing the structural 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. If the reaction temperature is above the above lower limit, the reaction rate is likely to be increased, and the polymerization time tends to be shortened. The reaction time is not particularly limited and may be, for example, about 0.5 to 72 hours, preferably 3 to 24 hours. When the reaction time is within the above range, the Df of the resulting PI film is likely to be reduced even if the imidization temperature is low.

[0138] The reaction between the diamine compound and the tetracarboxylic acid compound is preferably carried out in a solvent. The solvent is not particularly limited as long as it does not affect the reaction, and examples thereof include 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; ester solvents such as ethyl acetate, butyl acetate, ethylene glycol methyl ether acetate, propylene glycol methyl ether acetate, and ethyl lactate; lactone solvents such as γ-butyrolactone (hereinafter sometimes referred to as GBL) and γ-valerolactone; acetone, methyl ethyl ketone, cyclopentanone, cyclohexanone, 2-heptanone, methyl methyl ether ... Examples of suitable solvents include ketone solvents such as triisobutyl 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, phenol solvents, lactone solvents, amide solvents, and pyrrolidone solvents are preferred, and more preferably amide solvents.

[0139] 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 film even when the imidization temperature is low. Also, 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.

[0140] The reaction of the diamine compound with the tetracarboxylic acid compound may be carried out, as necessary, in an inert atmosphere such as a nitrogen atmosphere or an argon atmosphere or under reduced pressure. It is preferable to carry out the reaction in an inert atmosphere, such as a nitrogen atmosphere or an argon atmosphere, in a strictly controlled dehydrated solvent while stirring.

[0141] The solvent contained in the PI resin precursor solution can be any of the solvents exemplified for use in the reaction between a diamine compound and a tetracarboxylic acid compound. Examples of suitable solvents include lactone solvents, amide solvents, and pyrrolidone solvents, and more preferably amide solvents. 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 imidization temperatures. 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.

[0142] The content of the PI resin precursor in the PI 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, based on the total amount of the PI resin precursor solution, and 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. A PI resin precursor content within the above range provides excellent processability during film formation.

[0143] (Coating of polyimide resin precursor solution) The coating process of the PI resin precursor solution is a process in which the PI resin precursor solution is applied onto a substrate to form a coating film.

[0144] In the coating step, a coating film is formed by applying the composition to a substrate using a known coating or application method. Examples of known coating methods include roll coating methods such as wire bar coating, reverse coating, and gravure coating, die coating, comma coating, lip coating, spin coating, screen printing coating, fountain coating, dipping, spraying, curtain coating, slot coating, and drip molding. When applying a solution of a PI resin precursor to a substrate, a single layer of the PI resin precursor may be applied to the substrate, or multiple layers of the PI resin precursor may be applied to the substrate. When applying multiple layers of the PI resin precursor to the substrate, the application may be performed in multiple batches and dried, or multiple layers may be applied simultaneously.

[0145] Examples of the substrate include metal plates (e.g., copper plates) such as metal foils (e.g., copper foils), SUS plates such as SUS foils and SUS belts, glass substrates, PET films, PEN films, PI resin films other than the PI film of the present invention, polyamide resin films, etc. Among these, from the viewpoint of excellent heat resistance, copper plates, SUS plates, glass substrates, PET films, PEN films, etc. are preferred, and from the viewpoints of adhesion to the film and cost, copper plates, SUS plates, glass substrates, PET films, etc. are more preferred.

[0146] <Imidization process> The imidization step is a step in which the PI resin precursor coated on the substrate is imidized by heat treatment at 200°C or higher and lower than 350°C. In one embodiment of the present invention, the imidization step is preferably a step in which, prior to imidization of the PI resin precursor, the PI resin precursor solution coated on the substrate is dried by heating at a relatively low temperature, for example, below 200°C, and the resulting dried PI resin precursor film is imidized by heat treatment at a temperature of 200°C or higher but lower than 350°C. In one embodiment of the present invention, a PI film may be obtained by imidizing a dried film of a PI resin precursor on a substrate, or by peeling the dried film of a PI resin precursor from the substrate and then imidizing the dried film peeled from the substrate.

[0147] In one embodiment of the present invention, the drying temperature for the PI resin precursor coated on the substrate is not particularly limited as long as it is within a temperature range in which the solvent dries and solidifies. However, from the viewpoints of avoiding surface roughening due to rapid drying and suppressing wrinkles, creases, and the like that occur during processing, the drying temperature is preferably less than 300°C, more preferably 260°C or less, even more preferably 200°C or less, and even more preferably 180°C or less. From the viewpoint of productivity, the drying temperature is preferably 50°C or higher, more preferably 80°C or higher, and even more preferably 100°C or higher.

[0148] The PI resin precursor of the present invention can reduce the Df of the resulting PI film even when imidized at a low temperature. The heat treatment temperature in the imidization step, i.e., the imidization temperature, is preferably less than 350°C, more preferably 340°C or less, even more preferably 330°C or less, even more preferably 310°C or less, and particularly preferably 300°C or less. When the imidization temperature is below the above upper limit, even when a metal foil such as copper foil is used as the substrate, thermal degradation of the metal foil, particularly copper foil, can be suppressed, making it easier to obtain a 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, stepwise heating is preferred. For example, the solvent may be removed by heating at a relatively low temperature of 50 to 150°C, followed by stepwise heating to a temperature in the range of 200°C to less than 350°C for imidization.

[0149] In one embodiment of the present invention, the reaction time for imidization is preferably 0.5 to 24 hours, more preferably 1 to 12 hours. Furthermore, 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 easy to sufficiently improve the imidization rate, it is easy to prevent oxidative degradation of the resin, and it is easy to improve the dielectric properties and flex resistance of the resulting PI film.

[0150] After imidization, the coating film formed on the substrate can be peeled off from the substrate to obtain a PI film. In one embodiment of the present invention, when the substrate is a metal foil such as copper foil, the PI film can be formed without peeling off the coating film from the metal foil such as copper foil, and the resulting laminate film in which the PI film is laminated on the metal foil such as copper foil can be used for a metal-clad laminate such as CCL.

[0151] When the film of the present invention is a multilayer film, it can be produced by a multilayer film forming method such as coextrusion, extrusion lamination, thermal lamination, or dry lamination.

[0152] [Laminated film] The PI film of the present invention has a low Df and can therefore be suitably used to form metal-clad laminates for use in FPCs. Therefore, the present invention encompasses a laminate film that uses the PI film of the present invention as a PI layer and includes a PI layer and a metal foil layer. In one embodiment of the present invention, the laminate film of the present invention may include a metal foil layer on only one side or both sides of the PI layer.

[0153] In one embodiment of the present invention, examples of the metal foil include copper foil, SUS foil, and aluminum foil, with copper foil being preferred from the viewpoints of electrical conductivity and metal workability.

[0154] The PI film of the present invention has a low Df even when the thermal imidization temperature is low, and can be suitably used for forming a CCL having excellent high-frequency characteristics. Therefore, in a preferred embodiment of the present invention, the laminate film of the present invention is preferably a laminate film including a copper foil layer on one or both sides of the PI film of the present invention.

[0155] 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. Furthermore, from the viewpoint of facilitating circuit miniaturization and improving folding resistance, the thickness 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 meter or the like. When metal foil layers, particularly copper foil layers, are included on both sides of the PI film, the thicknesses of the metal foil layers, particularly the copper foil layers, may be the same or different.

[0156] 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, and is preferably 100 μm or less, more preferably 80 μm or less, even more preferably 60 μm or less. The thickness of the laminated film can be measured using a film thickness meter or the like.

[0157] The laminated film of the present invention may contain other layers such as functional layers in addition to the PI film and metal foil layer, particularly a copper foil layer. Examples of functional layers include the layers exemplified above, such as a thermoplastic PI resin layer containing a thermoplastic PI resin or an adhesive layer. The functional layers may be used alone or in combination of two or more.

[0158] In one embodiment of the present invention, the laminate film of the present invention may be a two-layer metal-clad laminate consisting of a metal foil layer and a PI layer, or a three-layer metal-clad laminate consisting of a metal foil layer, a PI layer, and an adhesive layer. From the viewpoints of heat resistance, dimensional stability, and weight reduction, however, a two-layer metal-clad laminate not including an adhesive layer is preferred. Furthermore, since the PI film of the present invention has a low Df even at a low imidization temperature, deterioration of the copper foil surface can be suppressed even when a laminate film using a copper foil as the metal foil is produced by thermally imidizing a PI resin precursor coating film on the copper foil. Therefore, the laminate film of the present invention has excellent high-frequency characteristics even without an adhesive layer.

[0159] In one embodiment of the present invention, the PI film of the present invention may be in direct contact with a metal foil layer, particularly a copper foil layer, or a functional layer may be inserted between the PI film and the metal foil layer, particularly the copper foil layer, so that they are in contact with each other via the functional layer. However, from the viewpoint of easily improving mechanical properties and thermal properties, it is preferable that the PI film be in direct contact with the metal foil layer, particularly the copper foil layer. The functional layer that may be inserted between the PI film of the present invention and the metal foil layer may be a thermoplastic PI layer. From the viewpoint of easily improving mechanical properties and thermal properties, the layer that is in direct contact with the metal foil layer, particularly the copper foil layer, is preferably the PI film of the present invention or a thermoplastic PI layer as a functional layer.

[0160] [Method for producing laminated film] The present invention relates to a method for producing a method for manufacturing a semiconductor device comprising the steps of: A step of applying a PI resin precursor solution containing a tetracarboxylic acid anhydride-derived structural unit (A) and a diamine-derived structural unit (B) onto a substrate; and A step of imidizing the PI resin precursor by heat treatment at 200°C or higher but lower than 350°C to form the PI film of the present invention on the substrate. The present invention also encompasses a method for producing a laminated film, which includes the steps of:

[0161] Regarding the "step of applying a PI resin precursor solution containing a tetracarboxylic acid anhydride-derived structural unit (A) and a diamine-derived structural unit (B) onto a substrate" and the "step of imidizing the PI resin precursor by heat treatment at 200°C or higher but lower than 350°C to form the PI film of the present invention on the substrate" in the method for producing a laminated film of the present invention, the explanations for each step described in the section [Method for producing a polyimide film] also apply.

[0162] In one embodiment of the present invention, the substrate is preferably a metal foil, particularly preferably a copper foil. The description of the metal foil, particularly the copper foil, in the section [Laminated Film] also applies.

[0163] The laminate film of the present invention may also be produced by methods other than those described above. For example, a PI resin precursor solution containing a tetracarboxylic acid anhydride-derived structural unit (A) and a diamine-derived structural unit (B) may be applied to a substrate other than the metal foil contained in the laminate film, followed by drying to obtain a dried PI resin precursor film, which is then peeled off from the substrate and laminated to a metal foil. The dried PI resin precursor film and the metal foil may be laminated by a press method, a lamination method using a heated roll, or other methods. The imidization of the PI resin precursor may be performed simultaneously during the lamination process. However, because the PI film of the present invention has a low Df even at low imidization temperatures, deterioration of the copper foil surface can be suppressed, even when a laminate film using a copper foil as the metal foil is produced by thermally imidizing a PI resin precursor coating on copper foil. Therefore, the laminate film of the present invention exhibits excellent high-frequency characteristics even when produced without the lamination process described above.

[0164] [Flexible Printed Circuit Board] The PI film of the present invention has a low Df, which can reduce transmission loss in electric circuits made of the PI film, making it suitable for use as an FPC substrate material. The present invention also encompasses FPC substrates containing the above-mentioned PI film. [Example]

[0165] The present invention will be described in more detail below based on examples and comparative examples, but the present invention is not limited to the following examples.

[0166] The abbreviations used in the Examples, Comparative Examples and Reference Examples represent the following compounds.

[0167] BPDA: 3,3',4,4'-biphenyltetracarboxylic dianhydride TAHQ: p-phenylenebis(trimellitic acid monoester dianhydride) PMDA: Pyromellitic dianhydride BP-TME: 4,4'-bis(1,3-dioxo-1,3-dihydroisobenzofuran-5-ylcarbonyloxy)biphenyl OPDA: 4,4'-oxydiphthalic dianhydride BPADA: 4,4'-(4,4'-isopropylidenediphenoxy)diphthalic anhydride m-Tb: 4,4'-diamino-2,2'-dimethylbiphenyl BAPP: 2,2-bis[4-(4-aminophenoxy)phenyl]propane TPE-R: 1,3-bis(4-aminophenoxy)benzene TPE-Q: 1,4-bis(4-aminophenoxy)benzene PDA: p-phenylenediamine

[0168] [Synthesis of polyimide resin precursor] Example 1 17.93 g (84.4 mmol) of m-Tb and 0.35 g (0.9 mmol) of BAPP were dissolved in 284 g of DMAc, followed by the addition of 19.35 g (42.2 mmol) of TAHQ and stirring under a nitrogen atmosphere at 20°C for 1 hour. 12.42 g (42.2 mmol) of BPDA was then added and the mixture was stirred under a nitrogen atmosphere at 20°C for 24 hours to obtain a PI resin precursor composition. The molar ratio of diamine monomer to acid dianhydride monomer used was 1.01.

[0169] (Examples 2 to 16 and Comparative Examples 1 to 5) A PI resin precursor composition was obtained in the same manner as in Example 1, except that the type and composition of the monomers used were changed as shown in Table 1. Unless otherwise specified, the order of addition of the monomers was diamine, followed by acid dianhydride, with the diamines being added in the order of diamines deriving structural units (B1), (B2), and (B3), and the acid dianhydrides being added in the order of acid dianhydrides deriving structural units (A1), (A2), and (A3).

[0170] [Production of polyimide film] The PI resin precursor compositions obtained in Examples 1 to 16 and Comparative Examples 1 to 5 were diluted with the solvent used in synthesizing the PI resin precursor to a viscosity of 40,000 cps or less, using the same solvent as used in synthesizing the PI resin precursor. The PI resin precursor solutions were then formed into films under any of the following film-forming conditions 1 to 4, as shown in Table 1, to obtain PI films made of PI resin.

[0171] <Film forming conditions 1> The PI resin precursor solution was cast onto a glass substrate by drip casting, and a coating film of the PI resin precursor solution was formed using an applicator at a linear speed of 0.4 m / min. The coating film was heated at 120°C for 30 minutes, and the resulting film was peeled off from the glass substrate and then fixed to a metal frame. The film fixed to the metal frame was heated from 30°C to 270°C over 19 minutes in an atmosphere with an oxygen concentration of 7%, and then cooled to 200°C over 35 minutes to produce a PI film. The temperature was maintained at 220°C or higher for 23 minutes. The temperature was also maintained at 200°C or higher for 34 minutes.

[0172] <Film forming conditions 2> The PI resin precursor solution was applied by drip casting to the roughened surface (surface roughness: Rz = 1.3 μm) of electrolytic copper foil (JX Metals, JXEFL-BHM, 12 μm thick). A coating film of the PI resin precursor solution was formed using an applicator at a linear speed of 0.4 m / min. The coating film was then heated to 120°C for 30 minutes and dried. The copper foil and precursor laminate film was then fixed to a metal frame and heated from 30°C to 320°C over 9 minutes in an oxygen atmosphere of 1%, then heated at 320°C for 6 minutes, and cooled to 200°C over 15 minutes to produce a PI film and copper foil laminate film. The temperature was maintained at 220°C or higher for 21 minutes. The temperature was also maintained at 200°C or higher for 25 minutes. The resulting laminated film of PI film and copper foil was immersed in a large volume of a 40% by mass aqueous solution of ferric chloride at room temperature for 10 minutes. After visually confirming that no copper remained, the film was dried at 80°C for 1 hour to obtain a single PI film.

[0173] <Film forming conditions 3> The PI resin precursor solution was cast onto a glass substrate by drip casting, and a coating film of the resin precursor solution was formed using an applicator at a linear speed of 0.4 m / min. The coating film was heated at 120°C for 30 minutes, and the resulting film was peeled off from the glass substrate and then fixed to a metal frame. The film fixed to the metal frame was heated from 30°C to 320°C over 9 minutes in an atmosphere with an oxygen concentration of 1%, then heated at 320°C for 6 minutes, and cooled to 200°C over 15 minutes to produce a PI film. The temperature was maintained at 220°C or higher for 21 minutes. The temperature was also maintained at 200°C or higher for 25 minutes.

[0174] <Film forming conditions 4> The PI resin precursor solution was cast onto a glass substrate by drip casting, and a coating film of the PI resin precursor solution was formed using an applicator at a linear speed of 0.4 m / min. The coating film was heated at 120°C for 30 minutes, and the resulting film was peeled off from the glass substrate and then fixed to a metal frame. The film fixed to the metal frame was heated from 30°C to 320°C over 5 minutes in an atmosphere with an oxygen concentration of 1%, then heated at 320°C for 5 minutes, and cooled to 200°C over 15 minutes to produce a PI film. The temperature was maintained at 220°C or higher for 17 minutes. The temperature was also maintained at 200°C or higher for 21 minutes.

[0175] [Synthesis of polyimide resin precursor and production of polyimide film] (Comparative Example 6) 70.33 g (331 mmol) of m-Tb was dissolved in 720 g of NMP, followed by the addition of 73.06 g (248 mmol) of BPDA and 37.94 g (83 mmol) of TAHQ. The mixture was stirred at room temperature for 1 hour under a nitrogen atmosphere. 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 Mn was 27,000. The PI resin precursor composition was diluted with NMP to adjust the viscosity, preparing a PI resin precursor solution. The resulting PI resin precursor solution was then formed into a film under the film formation condition 1 described above, yielding 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 E' at 280°C was 5.53 × 10 8 It was Pa. The Tg was determined from the storage modulus curve using the tangent method and was found to be 230°C.

[0176] The PI films obtained in the examples and comparative examples were subjected to various measurements and evaluations. The measurement and evaluation methods are explained below.

[0177] <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. Measurements were performed using a dynamic viscoelasticity measuring device (IT Measurement Control Co., Ltd., DVA-220) under the following sample and conditions to obtain a tanδ curve, which is the ratio of the storage modulus (E') to the loss modulus (E"). The highest point of the peak of the tanδ curve was taken as Tg. Test piece: rectangular parallelepiped with a length of 40 mm, a width of 5 mm, and a thickness of 50 μm (the thickness varies depending on the film used) Experimental mode: Single frequency, constant temperature rise Experimental method: Tensile Sample grip length: 15 mm Measurement start temperature: Room temperature ~ 342℃ Heating rate: 5°C / min Frequency: 10Hz Static / dynamic stress ratio: 1.8 Main data collected: (1) Storage modulus (E') (2) Loss modulus (E”) (3) tanδ(E” / E')

[0178] <Measurement of storage modulus (E')> The E' at 280°C of the PI resins obtained in the examples and comparative examples was determined by dynamic viscoelasticity measurement in the same manner as in the measurement of Tg.

[0179] <Measurement of weight average molecular weight Mw and number average molecular weight Mn> The polystyrene-equivalent Mw and Mn of the synthesized PI resin precursor were measured using GPC under the following conditions. (1) Pretreatment method The sample was diluted with DMF and filtered through a 0.45 μm membrane filter to prepare a measurement solution. (2) Measurement conditions Column: Two TSKgel SuperAWM-H columns (inner diameter 6.0 mm, length 150 mm) connected together Eluent: DMF (10 mmol / L lithium bromide added, 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

[0180] <Measurement of coefficient of linear thermal expansion (CTE)> The CTE of the PI films obtained in the examples and comparative examples was measured using TMA under the following conditions, and the CTE at 50°C to 100°C was calculated. Equipment: Hitachi High-Tech Science TMA / SS7100 Load: 50.0mN Temperature program: 20°C to 130°C at a rate of 5°C / min Test piece: rectangular parallelepiped with a length of 40 mm, a width of 5 mm, and a thickness of 50 μm (thickness may vary depending on the film used)

[0181] <Evaluation of dielectric loss index E> The dielectric loss index E of the film was calculated using the following formula. E=Df×(Dk) 1 / 2 (i) Df: Dielectric loss tangent Dk: relative permittivity

[0182] (Measurement of Df and Dk) Measurement samples of 50 mm x 50 mm were cut out 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, and then the measurements were carried out. Equipment: Anritsu Corporation Compact USB Vector Network Analyzer (Product name: MS46122B) AET Corporation Cavity Resonator (TE mode 10GHz type) Measurement frequency: 10GHz Measurement atmosphere: 23°C / 50%RH

[0183] <Bending resistance evaluation> The flex resistance of the PI films obtained in Examples 4, 10, 13, 14, and 15 was evaluated by measuring the number of times the film could be folded 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 folding fatigue tester (MIT-DA, manufactured by Toyo Seiki Seisakusho Co., Ltd.) conforming to ASTM standard D2176-16. The film was folded alternately in both directions at a test speed of 175 cpm, a bending angle of 135°, a load of 750 g, and a bending clamp radius of 1.0 mm. The number of folds required until the film broke was measured. A higher number of folds indicates better flex resistance. The number of folds of the PI films obtained in Examples 4, 10, 13, 14, and 15 was 240,000 times, 15,000 times, 160,000 times, 130,000 times, and 20,000 times, respectively. For the PI films obtained in Examples 4, 10, 13, 14, and 15, the CTE of the PI film × E' of the PI resin at 280°C was calculated. 1 / 2 The values ​​were 136141, 115683, 141751, 121951, and 116579, respectively.

[0184] Table 1 shows the measurement and evaluation results and the amine ratio for the PI films obtained in the examples and comparative examples.

[0185] [Table 1]

[0186] As shown in Table 1, the PI films obtained in Examples 1 to 16 were confirmed to have lower Df and a lower dielectric loss index E than the comparative examples, even when the maximum imidization temperature was as low as 270°C or 320°C. Therefore, even when the PI film of the present invention is produced by casting a PI resin precursor solution onto copper foil and then thermally imidizing the coated film of the PI resin precursor solution on a metal foil such as copper foil, thermal degradation such as surface roughening of the metal foil such as copper foil can be suppressed, and the film can be suitably used for metal-clad laminates such as CCLs that are compatible with high frequency bands and have low transmission loss.

Claims

1. The polyimide resin contains a structural unit (A) derived from a tetracarboxylic acid anhydride and a structural unit (B) derived from a diamine, and the polyimide resin has a storage modulus at 280°C of 3 x 10 ８ A polyimide film having a modulus of less than 100 Pa and a glass transition temperature of 200 to 290°C.

2. 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.

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

4. The structural unit (A) is represented by the formula (X): (Content of the structural unit (A3) derived from a tetracarboxylic acid anhydride other than the structural unit (A1) and the structural unit (A2)) / (Total amount of the structural unit (A1) and the structural unit (A2))<1.1 (X) The polyimide film according to claim 3 , which satisfies the following relationship:

5. 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.

3. The polyimide film according to claim 2, wherein the structural unit (a1) is derived from a tetracarboxylic acid anhydride represented by the following formula:

6. 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 3 , wherein the structural unit (a2) is derived from a tetracarboxylic acid anhydride represented by the following formula:

7. 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.

8. 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 7, wherein the structural unit (b1) is derived from a diamine represented by the formula:

9. 8. The polyimide film according to claim 7, wherein the content of the structural unit (B1) exceeds 30 mol% based on the total amount of the structural unit (B).

10. 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; 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 1 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:

11. 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 10, wherein

12. 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 11.

13. A flexible printed circuit board comprising the polyimide film according to any one of claims 1 to 11.

14. A step of applying a polyimide resin precursor solution containing a tetracarboxylic acid anhydride-derived structural unit (A) and a diamine-derived structural unit (B) onto a substrate; and A step of imidizing the polyimide resin precursor by heat treatment at 200°C or higher but lower than 350°C to form the polyimide film according to any one of claims 1 to 11 on the substrate. A method for producing a laminated film, comprising:

15. The method for producing a laminated film according to claim 14, wherein the substrate is a metal foil.

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