Polyimide-based resin precursor

Abstract

To provide a polyimide-based resin precursor which enables formation of a polyimide-based film that has low Df and is excellent in bending resistance even at a low heat imidization temperature.SOLUTION: A polyimide-based resin precursor contains a structural unit (A) derived from a tetracarboxylic acid anhydride and a structural unit (B) derived from diamine, wherein the structural unit (A) contains a structural unit (A1) derived from an ester bond-containing tetracarboxylic acid anhydride and a structural unit (A2) derived from a biphenyl skeleton-containing tetracarboxylic acid anhydride, the structural unit (A) satisfies a relation of Expression (X): (content of structural unit (A3) derived from tetracarboxylic acid anhydride other than structural unit (A1) and structural unit (A2)) / (total amount of structural unit (A1) and structural unit (A2))<0.67, the structural unit (B) includes a structural unit (B1) derived from biphenyl skeleton-containing diamine, the content of the structural unit (B1) exceeds 30 mol% with respect to the total amount of the structural unit (B), and the weight average molecular weight of the polyimide-based resin precursor in terms of polystyrene is larger than 100,000.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This invention relates to a polyimide resin precursor that can be used as a substrate material for printed circuit boards and antenna boards for high-frequency band applications. [Background technology]

[0002] Flexible printed circuit boards (hereinafter sometimes referred to as FPCs) are thin, lightweight, and flexible, enabling three-dimensional, high-density mounting. They are used in many electronic devices such as mobile phones and hard drives, contributing to their miniaturization and weight reduction. Traditionally, polyimide resin, which has excellent heat resistance, mechanical properties, and electrical insulation properties, has been widely used for FPCs. In recent years, the fifth-generation mobile communication system, known as 5G, has been steadily gaining popularity. Conventional polyimide materials suffer from significant transmission loss when transmitting high-frequency signals used in 5G communication, resulting in problems such as electrical signal loss and long signal delays. Therefore, polyimide films with low dielectric loss tangent (hereinafter sometimes referred to as Df) and relative permittivity (hereinafter sometimes referred to as Dk) are being investigated to reduce transmission loss. Furthermore, the applications of FPCs are expanding to include wiring in the movable parts of electronic devices, as well as components such as cables and connectors. With the introduction of foldable devices, there is a growing demand for FPCs with higher bending resistance. Therefore, in addition to having low Df and Dk, there is a need for polyimide films with excellent bending resistance.

[0003] For example, Patent Document 1 discloses a polyimide resin precursor obtained by reacting an ester-containing tetracarboxylic anhydride and a tetracarboxylic anhydride component containing 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 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 residues including at least one of tetracarboxylic residues derived from 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA residue) and tetracarboxylic residues derived from 1,4-phenylenebis(trimellitic acid monoester) dianhydride (TAHQ residue), and diamine residues derived from a specific diamine compound. Furthermore, Patent Document 3 discloses a polyimide precursor resin composition containing a polyimide precursor resin obtained by condensation polymerization of an aromatic tetracarboxylic dianhydride and a diamine, wherein at least one of the aromatic tetracarboxylic dianhydride and the diamine has a biphenyl skeleton, the content of the biphenyl skeleton is 40 mol% or more relative to the total amount of the aromatic tetracarboxylic dianhydride and the diamine, and the aromatic tetracarboxylic dianhydride contains 5 mol% or more of p-phenylenebis(trimellitic acid monoester acid anhydride) relative to the total amount, and a polyimide resin film obtained from the composition. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2018-150544 [Patent Document 2] International Publication No. 2018 / 061727 [Patent Document 3] Japanese Patent Publication No. 2014-208793 [Overview of the project] [Problems that the invention aims to solve]

[0005] As metal-clad laminates such as copper-clad laminates (hereinafter sometimes referred to as CCL) used in FPCs, laminates having a single or multiple layers of polyimide resin with metal foil such as a copper foil layer on one or both sides are widely used. Metal-clad laminates such as CCL having a polyimide film may be manufactured by casting a polyimide resin precursor solution onto metal foil such as copper foil, and then thermally imidizing the coating film of the polyimide resin precursor. This thermal imidization is usually carried out by heating at a high temperature, for example, around 360°C. In high-frequency current transmission, 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, surface roughness and oxidation of metal foils such as copper foil tend to cause a decrease in transmission loss. For example, when copper foil is heated to high temperatures of 350°C or higher, surface roughness, increased grain size, and oxidation occur, and the interface tends to become rough. Furthermore, an increase in grain size on the copper foil surface reduces the bending resistance of the copper foil, and consequently, the bending resistance of CCL tends to decrease. Therefore, exposure of metal foils such as copper foils to high temperatures along with the polyimide resin during the thermal imidation process can lead to a decrease in transmission loss and a decrease in bending resistance.

[0006] According to the inventors' studies, conventional polyimide resins sometimes fail to sufficiently reduce the Df and Dk of the resulting polyimide film when thermal imidation is performed at low temperatures below 350°C. If metal-clad laminates such as CCL are produced by thermal imidation at high temperatures above 350°C to sufficiently reduce the Df and Dk of these polyimide resins and polyimide films, surface roughening of metal foils such as copper foil occurs, as described above. Therefore, it is difficult to achieve both suppression of metal foil surface roughening and oxidation and reduction of the Df of the polyimide layer, thereby forming metal-clad laminates such as CCL with low transmission loss when used in high-frequency circuits. Furthermore, conventional polyimide films sometimes lack sufficient bending resistance.

[0007] Therefore, the object of the present invention is to provide a polyimide resin precursor that can form a polyimide film with low Df and excellent bending resistance, even at low thermal imidation temperatures. [Means for solving the problem]

[0008] The present inventors, after diligent research to solve the above problems, arrived at the present invention. That is, the present invention provides the following preferred embodiments.

[0009] [1] A polyimide resin precursor comprising a constituent unit (A) derived from tetracarboxylic anhydride and a constituent unit (B) derived from diamine, The aforementioned constituent unit (A) includes a constituent unit (A1) derived from an ester bond-containing tetracarboxylic anhydride and a constituent unit (A2) derived from a biphenyl skeleton-containing tetracarboxylic anhydride. The aforementioned constituent unit (A) is given by formula (X): (Content of constituent units (A3) derived from tetracarboxylic anhydride other than the aforementioned constituent units (A1) and (A2)) / (Total amount of constituent units (A1) and (A2)) < 0.67 (X) Satisfying the relationship, The aforementioned constituent unit (B) includes a constituent unit (B1) derived from a biphenyl skeleton-containing diamine, and the content of the constituent unit (B1) exceeds 30 mol% of the total amount of the constituent unit (B). The polyimide resin precursor has a weight-average molecular weight on a polystyrene basis greater than 100,000. [2] The above-mentioned constituent unit (A1) is given by formula (a1): [ka] [In formula (a1), Z represents a divalent organic group, R a1 Each of these independently represents a halogen atom, or an alkyl group, alkoxy group, aryl group, or aryloxy group which may have a halogen atom. [s represents integers between 0 and 3, independently of each other.] A polyimide resin precursor as described in [1], which is a constituent unit (a1) derived from a tetracarboxylic anhydride represented by . [3] The aforementioned constituent unit (A2) is given by formula (a2): [ka] [In formula (a2), R a2 Each of these independently represents a halogen atom, or an alkyl group, alkoxy group, aryl group, or aryloxy group which may have a halogen atom. [t represents integers from 0 to 3, independently of each other.] A polyimide resin precursor according to [1] or [2], which is a constituent unit (a2) derived from a tetracarboxylic anhydride represented by . [4] The aforementioned constituent unit (B1) is given by formula (b1): [ka] [In formula (b1), R b1 Each of these independently represents a halogen atom, or an alkyl group, alkoxy group, aryl group, or aryloxy group which may have a halogen atom. [p represents an integer between 0 and 4] A polyimide resin precursor according to any of [1] to [3], which is a diamine-derived structural unit (b1) represented by [1]. [5] The constituent unit (B) is given by formula (b2): [ka] [In formula (b2), R b2 Each of these independently represents a halogen atom, or an alkyl group, alkoxy group, aryl group, or aryloxy group which may have a halogen atom. W is independent of each other and is -O-, -CH2-, -CH2-CH2-, -CH(CH3)-, -C(CH3)2-, -C(CF3)2-, -COO-, -OOC-, -SO2-, -S-, -CO-, or -N(R c )- represents R c This represents a monovalent hydrocarbon group having 1 to 12 carbon atoms, which may be substituted with hydrogen atoms or halogen atoms. m is an integer from 1 to 4. [q represents an integer between 0 and 4, independently of each other.] A polyimide resin precursor according to any one of [1] to [4], further comprising a diamine-derived structural unit (b2) represented by [1]. [6] The polyimide resin precursor according to [5], wherein in the constituent unit (b2), m is 3 and W is independently -O- or -C(CH3)2-. [7] A polyimide resin obtained from a polyimide resin precursor described in any of [1] to [6]. [8] The polyimide resin described in [7], wherein the glass transition temperature is 200-290°C. [9] Storage modulus at 280°C is 3 × 10⁻⁶ 8 A polyimide resin according to [7] or [8], wherein the Pa is less than Pa.

[10] A polyimide film containing a polyimide resin as described in any of [7] to [9].

[11] The polyimide film described in

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

[12] A laminated film comprising a metal foil layer on one or both sides of the polyimide film described in

[10] or

[11] .

[13] A flexible printed circuit board containing the polyimide film described in

[10] or

[11] . [Effects of the Invention]

[0010] According to the present invention, a polyimide resin precursor can be provided that can form a polyimide-based film with low Df and excellent bending resistance, even at low thermal imidation temperatures. [Modes for carrying out the invention]

[0011] The embodiments of the present invention will be described in detail below. However, the scope of the present invention is not limited to the embodiments described herein, and various modifications can be made without departing from the spirit of the invention.

[0012] [Polyimide resin precursor] The polyimide resin precursor of the present invention comprises a constituent unit (A) derived from a tetracarboxylic anhydride (hereinafter sometimes simply referred to as constituent unit (A)) and a constituent unit (B) derived from a diamine (hereinafter sometimes simply referred to as constituent unit (B)), wherein constituent unit (A) comprises a constituent unit (A1) derived from an ester bond-containing tetracarboxylic anhydride (hereinafter sometimes simply referred to as constituent unit (A1)) and a constituent unit (A2) derived from a biphenyl skeleton-containing tetracarboxylic anhydride (hereinafter sometimes simply referred to as constituent unit (A2)), and constituent unit (A) is given by formula (X):(constituent unit (A1 The relationship (content of constituent units (A3) derived from tetracarboxylic anhydride other than constituent unit (A2)) / (total amount of constituent units (A1) and constituent units (A2)) < 0.67(X) is satisfied, constituent unit (B) includes constituent unit (B1) derived from biphenyl skeleton-containing diamine (hereinafter sometimes simply referred to as constituent unit (B1)), the content of constituent unit (B1) exceeds 30 mol% of the total amount of constituent unit (B), and the weight-average molecular weight of the polyimide resin precursor of the present invention on a polystyrene basis (hereinafter sometimes referred to as Mw) is greater than 100,000. In this specification, polyimide may be referred to as PI. In the present invention, "derived constituent unit" means "derived constituent unit," and for example, "tetracarboxylic anhydride-derived constituent unit (A)" means "constituent unit (A) derived from tetracarboxylic anhydride."

[0013] The inventors have found that in a PI-based resin precursor, if the constituent unit (A) satisfies the relationship of formula (X), the content of constituent unit (B1) exceeds 30 mol%, and Mw is greater than 100,000, a PI-based resin precursor can be obtained that can form a PI-based film with low Df and excellent bending resistance, even at low thermal imidation temperatures. This is presumed to be because, when the constituent unit (A) satisfies the relationship of formula (X), the content of constituent unit (B1) is within the above range, and Mw is within the above range, when the PI-based resin precursor is thermally imidated to obtain a PI-based resin, even at low thermal imidation temperatures, the amic acid moiety and imide moiety move simultaneously to easily form a higher-order structure, and the resulting PI-based resin as a whole is more likely to form a desirable higher-order structure in which the rotation of molecular chains is suppressed. As a result, the rotation of polar groups in the PI-based resin is suppressed, and the loss of electrical energy as thermal motion is reduced. Therefore, the PI-based resin precursor of the present invention can form a PI-based film that reduces Df while maintaining excellent flexural resistance, even at low thermal imidation temperatures.

[0014] The constituent unit (A) contained in the PI resin precursor is given by formula (X): (Content of constituent units (A3) derived from tetracarboxylic anhydride other than constituent units (A1) and (A2)) / (Total amount of constituent units (A1) and (A2)) < 0.67 (X) The relationship is satisfied, that is, the value of the left side of equation (X) is less than 0.67. Therefore, the imide group concentration of the PI resin obtained from the PI resin precursor of the present invention tends to decrease, improving the moisture resistance of the obtained PI resin and making it easier to reduce the Df of the obtained PI film. As a result, even if the imidization temperature of the PI resin is low, it is easy to reduce the Df of the obtained PI film.

[0015] 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, even more preferably 0.3 or less, and particularly preferably 0.20 or less, from the viewpoint of easily reducing the Df of the PI-based film and improving its mechanical properties even at low imidation temperatures. Furthermore, the lower limit of the value of the left side of formula (X) is not particularly limited and may be 0 or greater.

[0016] The denominator on the left side of equation (X), that is, the total amount of constituent units (A1) and (A2) relative to the total amount of constituent unit (A), is not particularly limited as long as equation (X) is satisfied. However, from the viewpoint of easily reducing the Df of the PI-based film obtained even at low imidation temperatures and easily improving bending resistance, it is preferably 50 mol% or more, more preferably 60 mol% or more, even more preferably 70 mol% or more, even more preferably 80 mol% or more, and particularly preferably 90 mol% or more, relative to the total amount of constituent unit (A). Furthermore, there is no particular upper limit on the total amount of constituent units (A1) and (A2), and may be, for example, 100 mol% or less. The proportion of the constituent units is, for example, 1 It can be measured using 1H-NMR, or it can be calculated from the raw material charging ratio.

[0017] The content of the molecule on the left side of formula (X), i.e., the content of the tetracarboxylic anhydride-derived component (A3) other than component (A1) and component (A2) (hereinafter sometimes simply referred to as component (A3)) relative to the total amount of component (A), is not particularly limited as long as formula (X) is satisfied, but may be, for example, 0 to 40 mol%, preferably 40 mol% or less, more preferably 35 mol% or less, even more preferably 30 mol% or less, particularly preferably 25 mol% or less, particularly more preferably 20 mol% or less, and even more preferably 15% or less, and also preferably 0 mol% or more, more preferably 0.01 mol% or more, and even more preferably 10 mol% or more. When the content of component (A3) is within the above range, orientation of the resulting PI-based resin is likely to occur, so the Df of the resulting PI-based film is likely to be reduced and the bending resistance is likely to be improved. The ratio of the above-mentioned structural units can be measured using, for example, 1 H-NMR, or can also be calculated from the charging ratio of the raw materials. In the present specification, the "structural unit (A3) derived from a tetracarboxylic dianhydride other than the structural units (A1) and (A2)" means a structural unit derived from a tetracarboxylic dianhydride that does not correspond to either of the structural units (A1) and (A2), and the "content of the structural unit (A3)" means the total amount of the structural unit (A3) when there are a plurality of the structural units (A3).

[0018] The content of the structural unit (B1), preferably the structural unit (b1) described later, is more than 30 mol%, preferably 35 mol% or more, more preferably 40 mol% or more, still more preferably 60 mol% or more, still more preferably 70 mol% or more, particularly preferably 80 mol% or more, and particularly more preferably 90 mol% or more, based on the total amount of the structural unit (B), from the viewpoint of easily reducing the Df of the PI-based film and easily improving the bending resistance even at a low imidization temperature. Also, the upper limit of the content of the structural unit (B1), preferably the structural unit (b1) described later, is not particularly limited and may be 100 mol% or less based on the total amount of the structural unit (B). The ratio of the above-mentioned structural units can be measured using, for example, 1 H-NMR, or can also be calculated from the charging ratio of the raw materials.

[0019] The Mw of the PI-based resin precursor is greater than 100,000, preferably 110,000 or more, more preferably 120,000 or more, still more preferably 130,000 or more, and particularly preferably 140,000 or more in terms of polystyrene conversion, from the viewpoint of easily reducing the Df of the obtained PI-based film and easily improving the bending resistance. Also, from the viewpoint of the processability during film formation, it is preferably 1,000,000 or less, more preferably 700,000 or less, still more preferably 500,000 or less, still more preferably 400,000 or less, and particularly preferably 300,000 or less.

[0020] The ratio of Mw to the number-average molecular weight (hereinafter, the number-average molecular weight may be referred to as Mn) of the PI-based resin precursor (Mw / Mn) is preferably 3.5 or higher, more preferably 4.0 or higher, even more preferably 4.2 or higher, even more preferably 4.5 or higher, particularly preferably 4.7 or higher, preferably 8.0 or lower, more preferably 7.0 or lower, even more preferably 6.0 or lower, and particularly preferably 5.5 or lower, in terms of polystyrene, from the viewpoint of easily improving bending resistance. Furthermore, Mw and Mn can be determined by gel permeation chromatography (hereinafter sometimes referred to as GPC) and converted to standard polystyrene equivalents, for example, by the method described in the examples.

[0021] <Constituent unit (A) derived from tetracarboxylic anhydride> The PI-based resin precursor of the present invention contains a constituent unit (A) derived from tetracarboxylic anhydride.

[0022] (Constituent unit (A1) derived from ester-bonded tetracarboxylic anhydride) The constituent unit (A) includes the constituent unit (A1) derived from an ester bond-containing tetracarboxylic anhydride. When constituent unit (A) includes constituent unit (A1), the ester bond, which has molecular orientation properties, is incorporated into the PI resin precursor. This makes orientation easier during the process of coating the PI resin precursor solution onto a substrate and imidizing the coating film, and it is easier to reduce the Df of the resulting PI film even at low imidization temperatures. Furthermore, since the ester bond sites can rotate and maintain flexibility, it is easier to improve the bending resistance of the resulting PI film, and it is easier to reduce the coefficient of linear expansion (hereinafter sometimes referred to as CTE), thereby improving the dimensional stability of the PI film.

[0023] In one embodiment of the present invention, the constituent unit (A1) is not particularly limited as long as it contains an ester bond, and the constituent unit (A1) may contain one or two or more ester bonds. However, from the viewpoint of easily reducing the Df of the resulting PI-based film and easily improving its bending resistance, even at low imidation temperatures, formula (a1): [ka] [In formula (a1), Z represents a divalent organic group, R a1 Each of these independently represents a halogen atom, or an alkyl group, alkoxy group, aryl group, or aryloxy group which may have a halogen atom. [s represents integers between 0 and 3, independently of each other.] It is preferable that the constituent unit (a1) is derived from a tetracarboxylic anhydride represented by .

[0024] R in equation (a1) a1 Each of these independently represents a halogen atom, or an alkyl group, alkoxy group, aryl group, or aryloxy group which may have a halogen atom. From the viewpoint of easily reducing the Df of the resulting PI-based film even at low imidation temperatures, each of these preferably independently represents an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, or an aryl group having 6 to 12 carbon atoms. Examples of alkyl groups having 1 to 6 carbon atoms include methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, sec-butyl group, tert-butyl group, n-pentyl group, 2-methyl-butyl group, 3-methylbutyl group, 2-ethyl-propyl group, and n-hexyl group. Examples of alkoxy groups having 1 to 6 carbon atoms include methoxy, ethoxy, propyloxy, isopropyloxy, n-butoxy, isobutoxy, sec-butoxy, tert-butoxy, pentyloxy, hexyloxy, and cyclohexyloxy groups. Examples of aryl groups having 6 to 12 carbon atoms include phenyl, tolyl, xylyl, naphthyl, and biphenyl groups. R a1 The hydrogen atoms contained therein may be independently substituted with halogen atoms, and examples of such halogen atoms include fluorine atoms, chlorine atoms, bromine atoms, and iodine atoms. Among these, R is the most suitable because it can easily reduce the Df of PI-based films even at low imidation temperatures. a1Examples of these include alkyl groups having 1 to 6 carbon atoms, preferably alkyl groups having 1 to 3 carbon atoms, independently of each other. Furthermore, in formula (a1), s represents an integer between 0 and 3, independently of each other, preferably 0 or 1, and more preferably 0.

[0025] In formula (a1), Z represents a divalent organic group, preferably a divalent organic group having 4 to 40 carbon atoms, more preferably a divalent organic group having 4 to 40 carbon atoms having a cyclic structure, and even more preferably a divalent organic group having 4 to 40 carbon atoms having an aromatic ring. Among these, from the viewpoint of easily reducing the Df of the resulting PI-based film even at low imidation temperatures, Z is represented by formulas (z1), (z2), and (z3): [ka] [In formulas (z1) to (z3), R z11 ~R z14 Each of these independently represents a monovalent hydrocarbon group which may have a hydrogen atom or a halogen atom. R z2 These independently represent monovalent hydrocarbon groups that may have a halogen atom. n represents an integer from 1 to 4. j represents an integer between 0 and 3, independently of each other. [* represents a combination] It is preferable that the divalent organic group is represented by formula (z1), and more preferably that the divalent organic group is represented by formula (z1).

[0026] In one embodiment of the present invention, R in equation (z1) z11 ~R z14 Each of these independently represents a monovalent hydrocarbon group which may have a hydrogen atom or a halogen atom. Examples of monovalent hydrocarbon groups include aromatic hydrocarbon groups, alicyclic hydrocarbon groups, and aliphatic hydrocarbon groups. Examples of aromatic hydrocarbon groups include phenyl groups, tolyl groups, xylyl groups, naphthyl groups, and aryl groups such as biphenyl groups. Examples of alicyclic hydrocarbon groups include cyclopentyl groups, cyclohexyl groups, and other cycloalkyl groups. Examples of aliphatic hydrocarbon groups include alkyl groups such as methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, sec-butyl group, tert-butyl group, n-pentyl group, 2-methyl-butyl group, 3-methylbutyl group, 2-ethyl-propyl group, n-hexyl group, n-heptyl group, n-octyl group, tert-octyl group, n-nonyl group, and n-decyl group. Examples of halogen atoms include those listed above. R z11 ~R z14 From the viewpoint of easily reducing the Df of the PI-based film even at low imidation temperatures, each element independently preferably represents an alkyl group which may have a hydrogen atom or a halogen atom, more preferably an alkyl group having 1 to 6 carbon atoms which may have a hydrogen atom or a halogen atom, even more preferably an alkyl group having 1 to 3 carbon atoms which may have a hydrogen atom or a halogen atom, and particularly preferably a hydrogen atom.

[0027] In one embodiment of the present invention, from the viewpoint of easily reducing the Df of the PI-based film even at low imidation temperatures, R in formula (z1) z11 ~R z14 In a benzene ring having R z11 ~R z14 At least one of them may be a monovalent hydrocarbon group having a halogen atom, but R z11 ~R z14 It is preferable that all of them are hydrogen atoms.

[0028] In formula (z1), n ​​represents an integer from 1 to 4, and from the viewpoint of easily reducing the Df of the PI-based film even at low imidation temperatures, it preferably represents an integer from 1 to 3, more preferably 1 or 2, and particularly preferably 2.

[0029] In one embodiment of the present invention, R in equation (z2) z2R independently represents a monovalent hydrocarbon group which may have a halogen atom, and examples of monovalent hydrocarbon groups include those listed above. z2 From the viewpoint of easily reducing the Df of the PI-based film even at low imidation temperatures, these terms independently preferably represent 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.

[0030] In formula (z2), j represents 0 to 3 independently of each other. In one embodiment of the present invention, from the viewpoint of easily reducing the Df of the PI-based film even at low imidation temperatures, j is preferably 0 or 1, more preferably 0, and even more preferably all j are 0.

[0031] In one preferred embodiment of the present invention, formula (a1) is formula (a1') or formula (a1"): [ka] It is preferable that the PI resin precursor is represented by formula (a1), particularly formula (a1') or formula (a1"), as a constituent unit (A1). When the PI resin precursor contains a constituent unit derived from a tetracarboxylic anhydride represented by formula (a1), the Df of the resulting PI film is easily reduced and the bending resistance is easily improved, even at low imidation temperatures.

[0032] In one embodiment of the present invention, the content of constituent 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 particularly more preferably 40 mol% or more, relative to the total amount of constituent unit (A). Furthermore, the content of constituent unit (A1) is preferably 75 mol% or less, more preferably 70 mol% or less, even more preferably 65 mol% or less, and particularly preferably 60 mol% or less, relative to the total amount of constituent unit (A). When the content of constituent unit (A1) is within the above range, orientation of the resulting PI-based resin is more likely to occur, the Df of the resulting PI-based film is more likely to be reduced, and the bending resistance is more likely to be improved. The proportion of the constituent units is, for example, 1 It can be measured using 1H-NMR, or it can be calculated from the raw material charging ratio.

[0033] (Constituent unit (A2) derived from biphenyl skeleton-containing tetracarboxylic anhydride) The constituent unit (A) contains the constituent unit (A2) derived from a biphenyl skeleton-containing tetracarboxylic anhydride. When constituent unit (A) contains constituent unit (A2), it is easier to reduce the Df of the resulting PI-based film and improve its flexural resistance, even at low imidation temperatures.

[0034] In one embodiment of the present invention, the constituent unit (A2) is not particularly limited as long as it contains a biphenyl skeleton, and the constituent unit (A2) may contain one or more biphenyl skeletons. Furthermore, in one embodiment of the present invention, it is preferable that the constituent unit (A2) contains a biphenyl skeleton but does not contain an ester bond, and in this specification, a constituent unit derived from a tetracarboxylic anhydride that contains both an ester bond and a biphenyl skeleton is classified not as constituent unit (A2) but as a constituent unit (A1) derived from an ester bond-containing tetracarboxylic anhydride.

[0035] In one embodiment of the present invention, the constituent unit (A2) is given by formula (a2): [ka] [In formula (a2), R a2 Each of these independently represents a halogen atom, or an alkyl group, alkoxy group, aryl group, or aryloxy group which may have a halogen atom. [t represents integers from 0 to 3, independently of each other.] It is preferable that the constituent unit (a2) is derived from a tetracarboxylic anhydride represented by .

[0036] R in equation (a2) a2 Each of these independently represents a halogen atom, or an alkyl group, alkoxy group, aryl group, or aryloxy group which may have a halogen atom. From the viewpoint of easily reducing the Df of the resulting PI-based film and easily improving its flexural resistance, even at low imidation temperatures, each preferably independently represents a C1-C6 alkyl group, a C1-C6 alkoxy group, or a C6-C12 aryl group. Examples of C1-C6 alkyl groups, C1-C6 alkoxy groups, and C6-C12 aryl groups are those exemplified above. a2 The hydrogen atoms contained in may be independently substituted with halogen atoms, and examples of halogen atoms are those listed above. Among these, R is selected from the viewpoint of easily reducing the Df of the resulting PI-based film and improving its bending resistance, even at low imidation temperatures. a2 These are, independently of each other, preferably alkyl groups having 1 to 6 carbon atoms, and more preferably alkyl groups having 1 to 3 carbon atoms. Furthermore, in equation (a2), t represents an integer between 0 and 3, independently of each other, preferably 0 or 1, and more preferably 0.

[0037] The bonding positions of the two carboxylic acid anhydrides attached to the benzene rings constituting the biphenyl skeleton in formula (a2) are not particularly limited. Based on the single bond connecting the two benzene rings, they may be 3,4- or 2,3-, independently of each other. However, from the viewpoint of easily reducing the Df of the resulting PI-based film and improving its flexural resistance, even at low imidation temperatures, the 3,4- bond is preferred.

[0038] In a preferred embodiment of the present invention, formula (a2) is formula (a2'): [ka] It is preferable that the PI resin precursor contains a constituent unit derived from a tetracarboxylic anhydride represented by formula (a2), particularly formula (a2'), as a constituent unit (A2). This makes it easier to reduce the Df of the resulting PI film and improve its bending resistance, even at low imidation temperatures.

[0039] In one embodiment of the present invention, the content of constituent unit (A2) is preferably 25 mol% or more, more preferably 30 mol% or more, even more preferably 35 mol% or more, and particularly preferably 40 mol% or more, relative to the total amount of constituent unit (A). Furthermore, the content of constituent unit (A2) is preferably 90 mol% or less, more preferably 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, relative to the total amount of constituent unit (A). When the content of constituent unit (A2) is within the above range, orientation of the PI-based resin is more likely to occur, and therefore the Df of the PI-based film is more likely to be reduced. The proportion of the constituent units is, for example, 1 It can be measured using 1H-NMR, or it can be calculated from the raw material charging ratio.

[0040] (Component unit (A3)) In one embodiment of the present invention, the constituent unit (A) may include constituent units (A3) derived from tetracarboxylic anhydride other than constituent units (A1) and (A2).

[0041] In one embodiment of the present invention, the constituent unit (A3) is a constituent unit derived from a tetracarboxylic anhydride that does not contain either an ester bond or a biphenyl skeleton, for example, formula (1): [ka] [In equation (1), Y is given by equations (31) to (38): [ka] [In formulas (31) to (38), R 19 ~R 26 and R 23’ ~R 26’ Each of these independently represents a hydrogen atom, a C1-C6 alkyl group, a C1-C6 alkoxy group, or a C6-C12 aryl group, and R 19 ~R 26 and R 23’ ~R 26’ The hydrogen atoms contained therein may be independently substituted by halogen atoms. V 1 and V 2 These are independent of each other, single bonds (except when e+d=1), -O-, -CH2-, -CH2-CH2-, -CH(CH3)-, -C(CH3)2-, -C(CF3)2-, -SO2-, -S-, -CO-, -N(R j )-, or formula (a) [ka] (In formula (a), R 27 ~R 30 Each of these independently represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms. D independently represents a single bond, -C(CH3)2-, or -C(CF3)2-. i represents an integer from 1 to 3. * represents a bond. R j This represents a monovalent hydrocarbon group having 1 to 12 carbon atoms, which may be substituted with a hydrogen atom or a halogen atom. e and d represent integers between 0 and 2, independently of each other (where e + d is not 0). f represents an integer between 0 and 3. g and h represent integers between 0 and 4, independently of each other. * indicates a bond. [Represents a tetravalent organic group represented by ] Examples of constituent units derived from tetracarboxylic anhydrides are shown.

[0042] In equations (31) to (33), R 19~R 26 and R 23’ ~R 26’ Each of these independently represents a hydrogen atom, a C1-C6 alkyl group, a C1-C6 alkoxy group, or a C6-C12 aryl group. Examples of C1-C6 alkyl groups, C1-C6 alkoxy groups, and C6-C12 aryl groups include those exemplified above. 19 ~R 26 and R 23’ ~R 26’ The hydrogen atoms contained in may be independently substituted with halogen atoms, and examples of halogen atoms include those listed above. Among these, R is chosen because it is easier to improve the mechanical and thermal properties of the resulting PI-based film. 19 ~R 26 and R 23’ ~R 26’ Independently of each other, hydrogen atoms or alkyl groups having 1 to 6 carbon atoms are preferred, hydrogen atoms or alkyl groups having 1 to 3 carbon atoms are more preferred, and hydrogen atoms are even more preferred. Mechanical properties refer to mechanical properties including bending resistance and elastic modulus, and improved mechanical properties indicate, for example, increased bending resistance and / or elastic modulus. Thermal properties refer to thermal properties including glass transition temperature (hereinafter sometimes referred to as Tg), CTE, low thermal deformation and degradation, and low deformation after heating, and improved thermal properties indicate, for example, increased Tg and / or decreased CTE.

[0043] In equation (31), V 1 and V 2 These are independent of each other, single bonds (except when e+d=1), -O-, -CH2-, -CH2-CH2-, -CH(CH3)-, -C(CH3)2-, -C(CF3)2-, -SO2-, -S-, -CO-, -N(R j)- or formula (a) represents, and from the viewpoint of easily improving the mechanical and thermal properties of PI-based films, preferably a single bond (except when e+d=1), -O-, -CH2-, -C(CH3)2-, -C(CF3)2- or -CO- represents, and more preferably a single bond (except when e+d=1), -O-, -C(CH3)2- or -C(CF3)2- represents. j The symbol represents a monovalent hydrocarbon group having 1 to 12 carbon atoms, which may be substituted with hydrogen atoms or halogen atoms. Examples of monovalent hydrocarbon groups having 1 to 12 carbon atoms include methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, sec-butyl group, tert-butyl group, n-pentyl group, 2-methyl-butyl group, 3-methyl-butyl group, 2-ethyl-propyl group, n-hexyl group, n-heptyl group, n-octyl group, tert-octyl group, n-nonyl group, and n-decyl group, which may be substituted with halogen atoms. Examples of halogen atoms are the same as those listed above.

[0044] In formula (31), e and d independently represent integers from 0 to 2 (where e + d is not 0), and preferably represent 0 or 1 from the viewpoint of easily reducing the Df of the PI-based film even at low imidation temperatures. Also, e + d preferably represents 1. Note that in formula (31), when e is 0, the two benzene rings are V 1 This indicates that they are not bonded, and when d is 0, the two benzene rings are V 2 This indicates that they are not joined together.

[0045] In formulas (32) and (33), f represents an integer from 0 to 3, and from the viewpoint of easily reducing the Df of the PI-based film even at low imidation temperatures, it preferably represents 0 or 1, more preferably 0.

[0046] In formula (33), g and h represent integers between 0 and 4, independently of each other, and preferably represent integers between 0 and 2, more preferably 0 or 1, from the viewpoint of easily improving the mechanical and thermal properties of the PI-based film. Also, g + h preferably represents an integer between 0 and 2. When f is 1 or greater, multiple g and h may be the same or different, independently of each other.

[0047] In equation (a), R 27 ~R 30 Each of these independently represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms. Examples of alkyl groups having 1 to 6 carbon atoms are those exemplified above. Among these, R is particularly important from the viewpoint of easily improving the mechanical and thermal properties of PI-based films. 27 ~R 30 Each of these elements independently represents, preferably, a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, and more preferably, a hydrogen atom.

[0048] In formula (a), D represents a single bond, -C(CH3)2-, or -C(CF3)2-. Having such a structure for D makes it easier to improve the mechanical and thermal properties of the PI-based film. i represents an integer from 1 to 3, and is preferably 1 or 2 from the viewpoint of easily improving the mechanical and thermal properties of the PI-based film. If i is 2 or greater, multiple D and R are present. 27 ~R 30 These elements may be identical or different, and may be independent of each other.

[0049] Among these, from the viewpoint of easily reducing the Df of the resulting PI-based film and improving its bending resistance, even at low imidation temperatures, it is preferable that Y in formula (1) is from formulas (42) to (49) or (53): [ka] The constituent units are derived from tetracarboxylic anhydrides represented by formula (1), more preferably the constituent units derived from tetracarboxylic anhydrides represented by formula (42), formula (43), formula (46), formula (49), or formula (53) in formula (1), and even more preferably the constituent units derived from tetracarboxylic anhydrides represented by formula (42), formula (46), formula (49), or formula (53) in formula (1). In these formulas, * represents a bond.

[0050] <Diamine-derived structural unit (B)> The PI-based resin precursor of the present invention contains a diamine-derived structural unit (B).

[0051] (Constituent unit (B1) derived from biphenyl skeleton-containing diamine) The constituent unit (B) contains the constituent unit (B1) derived from a biphenyl skeleton-containing diamine. A PI-based resin precursor in which constituent unit (B) contains constituent unit (B1) tends to reduce the Df of the resulting PI-based film even at low imidation temperatures, thus reducing transmission loss in electrical circuits made from this PI-based film. Furthermore, the inclusion of constituent unit (B1) in the constituent unit (B) tends to improve the bending resistance of the resulting PI-based film.

[0052] In one embodiment of the present invention, the constituent unit (B1) is not particularly limited as long as it contains a biphenyl skeleton, and the constituent unit (B1) may contain one or more biphenyl skeletons. In one embodiment of the present invention, the constituent unit (B1) is such that it is easy to reduce the Df of the PI-based film obtained even at a low imidation temperature and easy to improve the bending resistance, and formula (b1): [ka] [In formula (b1), R b1 Each of these independently represents a halogen atom, or an alkyl group, alkoxy group, aryl group, or aryloxy group which may have a halogen atom. [p represents an integer between 0 and 4] It is preferable that the constituent unit (b1) is derived from a diamine represented by .

[0053] In equation (b1), R b1 Each of these independently represents a halogen atom, or an alkyl group, alkoxy group, aryl group, or aryloxy group which may have a halogen atom, preferably a halogen atom, an alkyl group, alkoxy group, or aryl group which may have a halogen atom, more preferably a halogen atom, a C1-C6 alkyl group, a C1-C6 alkoxy group, or a C6-C12 aryl group. Examples of C1-C6 alkyl groups, C1-C6 alkoxy groups, and C6-C12 aryl groups are those exemplified above. b1 The hydrogen atoms contained therein may be independently substituted with halogen atoms, and examples of such halogen atoms include those exemplified above. From the viewpoint of easily reducing the Df of the resulting PI-based film and easily improving bending resistance and dimensional stability, R b1 These are preferably, independently of each other, an alkyl group having 1 to 6 carbon atoms or a fluorinated alkyl group having 1 to 6 carbon atoms. From the viewpoint of easily improving adhesion to substrates such as copper foil, it is more preferably an alkyl group having 1 to 6 carbon atoms that does not contain fluorine, even more preferably an alkyl group having 1 to 3 carbon atoms that does not contain fluorine, and particularly preferably a methyl group.

[0054] In formula (b1), p represents an integer between 0 and 4, independently of each other. From the viewpoint of easily reducing the Df of the PI-based film and easily improving bending resistance and dimensional stability, p is preferably an integer between 0 and 2, more preferably 0 or 1.

[0055] In formula (b1), the -NH2 group bonded to each benzene ring may be bonded to the ortho, meta, or para position, or to the α, β, or γ position, relative to the single bond connecting each benzene ring. From the viewpoint of easily reducing the Df of the PI-based film even at low imidation temperatures and easily improving dimensional stability, it is preferable that the bond be to the meta or para position, or to the β or γ position, more preferably to the para or γ position.

[0056] In a preferred embodiment of the present invention, formula (b1) is formula (b1'): [ka] It is preferable that it be represented as such. When the PI resin precursor contains a diamine-derived structural unit represented by formula (b1), particularly formula (b1'), as a structural unit (B1), the Df of the resulting PI film is easily reduced and the bending resistance is easily improved, even at low imidation temperatures.

[0057] (Component unit (B2)) In one embodiment of the present invention, it is preferable that the constituent unit (B) includes a diamine-derived constituent unit (B2) (hereinafter sometimes simply referred to as constituent unit (B2)) having two or more aromatic rings, each aromatic ring being bonded via a divalent organic group. The divalent organic group in constituent unit (B2) may be, for example, an alkylene group which may have a halogen atom, -O-, -COO-, -OOC-, -SO2-, -S-, -CO- or -N(R c )- and others are examples, R c - represents a monovalent hydrocarbon group with 1 to 12 carbon atoms, which may be substituted with hydrogen atoms or halogen atoms. Among these, the divalent organic groups in the constituent unit (B2) are -O-, -CH2-, -CH2-CH2-, -CH(CH3)-, -C(CH3)2-, -C(CF3)2-, -COO-, -OOC-, -SO2-, -S-, -CO-, or -N(R c )- is preferable.

[0058] The constituent unit (B2) is given by formula (b2): [ka] [In formula (b2), R b2 Each of these independently represents a halogen atom, or an alkyl group, alkoxy group, aryl group, or aryloxy group which may have a halogen atom. W is independent of each other and is -O-, -CH2-, -CH2-CH2-, -CH(CH3)-, -C(CH3)2-, -C(CF3)2-, -COO-, -OOC-, -SO2-, -S-, -CO-, or -N(Rc )- represents R c This represents a monovalent hydrocarbon group having 1 to 12 carbon atoms, which may be substituted with hydrogen atoms or halogen atoms. m represents an integer from 1 to 4. [q represents an integer between 0 and 4, independently of each other.] The diamine-derived constituent unit (b2) represented by (hereinafter sometimes simply referred to as constituent unit (b2)), formula (2): [ka] [In equation (2), X is given by equation (65): [ka] (In formula (65), * represents a bond) This represents a divalent organic group. Examples include diamine-derived structural units represented by . Among these, structural unit (B2) is preferably structural unit (b2) from the viewpoint that the Df of the obtained PI-based film is easily reduced even at low imidation temperatures and the bending resistance is easily improved. When structural unit (B) includes structural unit (B2), in particular structural unit (b2), the Df of the obtained PI-based film is easily reduced even at low imidation temperatures, as a result, the transmission loss of the electronic circuit containing the obtained PI-based film is easily reduced even at low imidation temperatures, and the bending resistance of the obtained PI-based film is easily improved.

[0059] In equation (b2), R b2 Each of these independently represents a halogen atom, or an alkyl group, alkoxy group, aryl group, or aryloxy group which may have a halogen atom, preferably a halogen atom, a C1-C6 alkyl group, a C1-C6 alkoxy group, or a C6-C12 aryl group. Examples of C1-C6 alkyl groups, C1-C6 alkoxy groups, and C6-C12 aryl groups are those exemplified above. b2The hydrogen atoms contained therein may be independently substituted with halogen atoms, and examples of such halogen atoms include those exemplified above. Even at low imidation temperatures, the Df of the resulting PI-based film can be easily reduced, and the bending resistance and dimensional stability can be easily improved, b2 These are preferably, independently of each other, an alkyl group having 1 to 6 carbon atoms or a fluorinated alkyl group having 1 to 6 carbon atoms. From the viewpoint of easily improving adhesion to substrates such as copper foil, it is more preferably an alkyl group having 1 to 6 carbon atoms that does not contain fluorine, even more preferably an alkyl group having 1 to 3 carbon atoms that does not contain fluorine, and particularly preferably a methyl group.

[0060] In formula (b2), q represents an integer between 0 and 4, independently of each other. From the viewpoint of easily reducing the Df of the resulting PI-based film even at low imidation temperatures and easily improving bending resistance and dimensional stability, q is preferably an integer between 0 and 2, more preferably 0 or 1.

[0061] In equation (b2), W is independently of each other -O-, -CH2-, -CH2-CH2-, -CH(CH3)-, -C(CH3)2-, -C(CF3)2-, -COO-, -OOC-, -SO2-, -S-, -CO-, or -N(R c )- represents -O-, -CH2-, -C(CH3)2-, -C(CF3)2-, -COO-, -OOC- or -CO-, and more preferably -O-, -CH2- or -C(CH3)2-, and even more preferably -O- or -C(CH3)2-, from the viewpoint of easily improving adhesion to substrates such as copper foil. c This represents a monovalent hydrocarbon group having 1 to 12 carbon atoms, which may be substituted with hydrogen atoms or halogen atoms. Examples of monovalent hydrocarbon groups having 1 to 12 carbon atoms are those exemplified above, which may be substituted with halogen atoms. Examples of halogen atoms are the same as those exemplified above.

[0062] In formula (b2), m is an integer from 1 to 4, and is preferably an integer from 1 to 3, more preferably 2 or 3, from the viewpoint of easily reducing the Df of the resulting PI-based film even at low imidation temperatures and easily improving bending resistance and dimensional stability. In formula (b2), multiple W, R b2 , and q may be the same or different from each other, and the positions of -W- relative to -NH2 on each benzene ring may be the same or different.

[0063] In formula (b2), -W- may be bonded to the ortho, meta, or para position, or to the α, β, or γ position, relative to the -NH2 of each benzene ring. From the viewpoint of easily reducing the Df of the resulting PI-based film even at low imidation temperatures and easily improving flexural resistance and dimensional stability, it is preferably bonded to the meta or para position, or to the β or γ position, more preferably to the para or γ position.

[0064] In one embodiment of the present invention, from the viewpoint of easily reducing the Df of the obtained PI-based film and improving its bending resistance, even at low imidation temperatures, and from the viewpoint of easily improving the adhesion between the obtained PI-based film and metal foils such as copper foil, it is preferable that in formula (b2), m is 3 and W independently represents -O- or -C(CH3)2-, and formula (b2) is formula (b2'): [ka] It is more preferable that it be represented as follows. When the PI resin precursor contains constituent unit (b2), in particular a constituent unit derived from a diamine represented by formula (b2'), it is easier to obtain a PI film that has a low Df and excellent adhesion to metal foils such as copper foil, even at low imidation temperatures.

[0065] In one embodiment of the present invention, the constituent unit (b2) may include, in addition to, a constituent unit derived from a diamine represented by formula (b2'), or in place of said constituent unit, a constituent unit derived from a diamine in formula (b2) where m is 1 and W represents -O-.

[0066] In one embodiment of the present invention, the content of the structural unit (B2) is preferably 0 mol% or more, more preferably 0.3 mol% or more, still more preferably 0.5 mol% or more, even more preferably 0.8 mol% or more, particularly preferably 1 mol% or more, particularly more preferably 5 mol% or more, and particularly still more preferably 8 mol% or more, based on the total amount of the structural unit (B). When the content of the structural unit (B2) is at least the above lower limit, it is easy to improve the adhesion of the obtained PI-based film to a substrate such as a copper foil. Further, the upper limit of the content of the structural unit (B2) is preferably 75 mol% or less, more preferably 60 mol% or less, still more preferably 40 mol% or less, even more preferably 30 mol% or less, particularly preferably 20 mol% or less, based on the total amount of the structural unit (B). When the content of the structural unit (B2) is at most the above upper limit, the mechanical properties such as the CTE of the obtained PI-based film tend to be easily improved. The ratio of the above structural units can be measured using, for example 1 H-NMR, or can also be calculated from the charging ratio of the raw materials.

[0067] (structural unit (B3)) The PI-based resin precursor may contain, as the structural unit (B), a structural unit (B3) derived from a diamine other than the structural unit (B1) and the structural unit (B2) (hereinafter, may be simply abbreviated as the structural unit (B3)). Examples of the structural unit (B3) include a structural unit derived from a diamine in which m in the formula (b2) is 0, and X in the formula (2) is one of the formulas (61) to (64): [Chemical formula] [In the formula (61), R a , R b , W, t, u and n are each independently the same as R a , R b , W, t, u and n in the formula (60), In the 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 is 0 or more and represents an integer less than or equal to (the number of carbon atoms of ring A - 2), S1 and S2 represent integers between 0 and 20, independently of each other. In equations (61) to (64), * represents a combination. Examples include diamine-derived structural units represented by [the formula shown]. In this specification, "constituent units (B3) derived from diamine other than constituent units (B1) and constituent units (B2)" means constituent units derived from diamine that are different from both constituent units (B1) and constituent units (B2).

[0068] In formula (62), ring A represents a cycloalkane ring having 3 to 8 carbon atoms. Examples of cycloalkane rings include cyclopropane, cyclobutane, cyclopentane, cyclohexane, cycloheptane, and cyclooctane rings, with cycloalkane rings having 4 to 6 carbon atoms being preferred. In ring A, each bond may or may not be adjacent to one another. For example, if ring A is a cyclohexane ring, the two bonds may be in an α, β, or γ positional relationship, preferably in a β or γ positional relationship.

[0069] 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, and examples thereof are those exemplified above. In formula (62), r is 0 or greater and represents an integer less than or equal to "the number of carbon atoms in ring A minus 2". r is preferably 0 or greater, and preferably 4 or less. In formula (62), S1 and S2 independently represent integers from 0 to 20. S1 and S2 independently are preferably 0 or greater, more preferably 2 or greater, and preferably 15 or less.

[0070] Specific examples of the constituent unit (B3) include the diamine-derived constituent units represented by formulas (71), (74), (77), (78), (89), and (90) in formula (2). Among these, the diamine-derived constituent unit represented by formula (74) in formula (2) (the p-phenylenediamine-derived constituent unit) is preferred. In these formulas, * represents a bond.

[0071] [ka]

[0072] In one embodiment of the present invention, when constituent unit (B) contains constituent unit (B3), the content of constituent unit (B3) is preferably 25 mol% or less, more preferably 20 mol% or less, even more preferably 10 mol% or less, and preferably 0.01 mol% or more, relative to the total amount of constituent unit (B).

[0073] In one embodiment of the present invention, the PI resin precursor may contain halogen atoms, preferably fluorine atoms, which can be introduced by, for example, the halogen-containing substituents described above. When the PI resin precursor contains fluorine atoms, the dielectric constant of the resulting PI film is easily reduced. Preferred fluorine-containing substituents for incorporating fluorine atoms into the PI resin precursor include, for example, fluoro groups and trifluoromethyl groups. Furthermore, in another embodiment of the present invention, it is preferable that the PI resin precursor 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. In addition, since the presence of fluorine in the PI resin precursor tends to weaken the interactions between molecular chains, the absence of fluorine atoms tends to suppress the rotation of the higher-order structure of the PI resin obtained from the PI resin precursor, making it easier to reduce the Df of the resulting PI film and improve its bending resistance.

[0074] When the PI resin precursor contains halogen atoms, the content of halogen atoms, particularly fluorine atoms, in the PI resin precursor is preferably 0.1 to 35% by mass, more preferably 0.1 to 30% by mass, even more preferably 0.1 to 20% by mass, and particularly preferably 0.1 to 10% by mass, based on the mass of the PI resin precursor. If the halogen atom content is above the lower limit, it is easier to improve the heat resistance and dielectric properties of the resulting PI film. If the halogen atom content is below the upper limit, it is advantageous in terms of cost, easier to reduce the CTE of the PI film, and easier to synthesize the PI resin. Dielectric properties refer to dielectric properties including relative permittivity and dielectric loss tangent, and an increase or improvement in dielectric properties indicates a decrease in relative permittivity and / or dielectric loss tangent.

[0075] [Method for producing polyimide resin precursors] The PI-based resin precursor of the present invention is obtained by reacting a tetracarboxylic anhydride with a diamine. In addition to the tetracarboxylic acid compound, dicarboxylic acid compounds and tricarboxylic acid compounds may also be reacted.

[0076] Examples of tetracarboxylic anhydrides used in the synthesis of PI-based resin precursors include aromatic tetracarboxylic acid compounds such as aromatic tetracarboxylic dianhydrides, and aliphatic tetracarboxylic acid compounds such as aliphatic tetracarboxylic dianhydrides. Tetracarboxylic acid compounds may be used individually or in combination of two or more. In addition to dianhydrides, tetracarboxylic acid compounds may also be tetracarboxylic acid compound analogs such as acid chloride compounds. Examples of tetracarboxylic acid compounds include tetracarboxylic anhydrides represented by formula (1) above, and preferably, tetracarboxylic anhydrides represented by formula (a1) or tetracarboxylic anhydrides represented by formula (a2).

[0077] Specific examples of tetracarboxylic acid compounds include pyromellitic anhydride (sometimes referred to as PMDA), 4,4'-(4,4'-isopropylidene diphenoxy)diphthalic anhydride (sometimes referred to as BPADA), 1,4,5,8-naphthalenetetracarboxylic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride (sometimes referred to as BPDA), 4,4'-(hexafluoroisopropylidene)diphthalic dianhydride (sometimes referred to as 6FDA), and 4,4'-oxydiphthalic dianhydride. Aqueous compounds (hereinafter sometimes referred to as ODPA), 2,2',3,3'-, 2,3,3',4'- or 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 2,3',3,4'-biphenyltetracarboxylic dianhydride, 2,2',3,3'-biphenyltetracarboxylic dianhydride, p-phenylenebis(trimellitic acid monoesteric acid dianhydride) (hereinafter sometimes referred to as TAHQ), esterified products of trimellitic anhydride and 2,2',3,3',5,5'-hexamethyl-4,4'-biphenol (hereinafter referred to as TMPBP) (may be), 4,4'-bis(1,3-dioxo-1,3-dihydroisobenzofuran-5-ylcarbonyloxy)biphenyl (hereinafter sometimes referred to as BP-TME), 2,3',3,4'-diphenyl ether tetracarboxylic dianhydride, bis(2,3-dicarboxyphenyl) ether dianhydride, 3,3”,4,4”-p-terphenyl tetracarboxylic dianhydride, 2,3,3”,4”-p-terphenyl tetracarboxylic dianhydride, 2,2”,3,3”-p-terphenyl tetracarboxylic dianhydride, 2,2-bis(2, 3-Dicarboxyphenyl)-propane dianhydride, 2,2-bis(3,4-dicarboxyphenyl)-propane dianhydride, bis(2,3-dicarboxyphenyl)methane dianhydride, bis(3,4-dicarboxyphenyl)methane dianhydride, 1,1-bis(2,3-dicarboxyphenyl)ethane dianhydride, 1,1-bis(3,4-dicarboxyphenyl)ethane dianhydride, 1,2,7,8-,1,2,6,7-phenanthrene-tetracarboxylic acid dianhydride, 1,2,9,10-phenanthrene-tetracarboxylic acid dianhydride, 2,2-bis(3,4-Dicarboxyphenyl)tetrafluoropropane dianhydride, 1,2,4,5-cyclohexanetetracarboxylic acid dianhydride (hereinafter sometimes referred to as HPMDA), 2,3,5,6-cyclohexanetetracarboxylic acid dianhydride, 2,3,6,7-naphthalenetetracarboxylic acid dianhydride, 1,2,5,6-naphthalenetetracarboxylic acid dianhydride, cyclopentane-1,2,3,4-tetracarboxylic acid dianhydride, 4,4'-bis(2,3-dicarboxyphenoxy)diphenylmethane dianhydride, 1,2, 3,4-Cyclobutanetetracarboxylic dianhydride (hereinafter sometimes referred to as CBDA), norbornane-2-spiro-α'-spiro-2”-norbornane-5,5',6,6'-tetracarboxylic anhydride, p-phenylenebis(trimellitate anhydride), 3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride, 2,3,6,7-anthracenetetracarboxylic dianhydride, 4,8-dimethyl-1,2,3,5,6,7-hexahydronaphthalene-1,2,5,6-tetracarboxylic dianhydride , 2,6-dichloronaphthalene-1,4,5,8-tetracarboxylic dianhydride, 2,7-dichloronaphthalene-1,4,5,8-tetracarboxylic dianhydride, 2,3,6,7-tetrachloronaphthalene-1,4,5,8-tetracarboxylic dianhydride, 2,3,6,7-tetrachloronaphthalene-2,3,6,7-tetracarboxylic dianhydride, 1,4,5,8-tetrachloronaphthalene-1,4,5,8-tetracarboxylic dianhydride, 1,4,5,8-tetrachloronaphthalene-2,3,6,7-tetracarboxylic dianhydride Dianhydride, 2,3,8,9-perylene-tetracarboxylic acid dianhydride, 3,4,9,10-perylene-tetracarboxylic acid dianhydride, 4,5,10,11-perylene-tetracarboxylic acid dianhydride, 5,6,11,12-perylene-tetracarboxylic acid dianhydride, pyrazine-2,3,5,6-tetracarboxylic acid dianhydride, pyrrolidine-2,3,4,5-tetracarboxylic acid dianhydride, thiophene-2,3,4,5-tetracarboxylic acid dianhydride, bis(2,3-dicarboxyphenyl)sulfone dianhydride, bis(3,Examples include 4-dicarboxyphenyl)sulfone dianhydride. Among these, BPDA, TAHQ, and BP-TME are preferred from the viewpoint of easily reducing the Df of the PI-based film obtained even at low imidation temperatures and improving flexural resistance. These tetracarboxylic acid compounds can be used individually or in combination of two or more.

[0078] Examples of diamine compounds used in the synthesis of PI-based resin precursors include aliphatic diamines, aromatic diamines, and mixtures thereof. In this embodiment, "aromatic diamine" refers to a diamine having an aromatic ring, and its structure may include an aliphatic group or other substituents. This aromatic ring may be a monoring or a fused ring, and examples include, but are not limited to, a benzene ring, a naphthalene ring, anthracene ring, and a fluorene ring. Among these, a benzene ring is preferred. "Aliphatic diamine" refers to a diamine having an aliphatic group, and its structure may include other substituents, but it does not have an aromatic ring. Examples of diamine compounds include the diamine compound represented by formula (2) above, and preferably, the diamine compound represented by formula (b1) or the diamine compound represented by formula (b2).

[0079] Specific examples of diamine compounds include 1,4-diaminocyclohexane, 4,4'-diamino-2,2'-dimethylbiphenyl (hereinafter sometimes referred to as m-Tb), 4,4'-diamino-3,3'-dimethylbiphenyl, 2,2'-bis(trifluoromethyl)-4,4'-diaminodiphenyl (hereinafter sometimes referred to as TFMB), 4,4'-diaminodiphenyl ether, 1,3-bis(3-aminophenoxy)benzene (hereinafter sometimes referred to as 1,3-APB), and 1,4-bis(4-aminophenoxy)benzene (hereinafter referred to as TPE- (Sometimes abbreviated as Q), 1,3-bis(4-aminophenoxy)benzene, 2,2-bis[4-(4-aminophenoxy)phenyl]propane (sometimes abbreviated as BAPP), 2,2'-dimethyl-4,4'-diaminobiphenyl, 3,3'-dihydroxy-4,4'-diaminobiphenyl, 2,2-bis-[4-(3-aminophenoxy)phenyl]propane, bis[4-(4-aminophenoxy)]biphenyl, bis[4-(3-aminophenoxy)biphenyl, bis[1-(4-aminophenoxy)]biphenyl, bis[1-(3-amino Phenoxy)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)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-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, benzidine, 3,3'-Diaminobiphenyl, 3,3'-Dimethoxybenzidine, 4,4"-Diamino-p-terphenyl, 3,3"-Diamino-p-terphenyl, m-Phenylenediamine, p-Phenylenediamine (sometimes written as p-PDA), Resorcinol-bis(3-aminophenyl) ether, 4,4'-[1,4-Phenylenebis(1-methylethylidene)]bisaniline, 4,4'-[1,3-Phenylenebis(1-methylethylidene)]bisaniline, Bis(p-aminocyclohexyl)methane, Bis(p-β-amino-tert-buty Biphenyl 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(trifluoro Methyl)bicyclohexane, 4,4'-diaminodicyclohexylmethane, 4,4"-diamino-p-terphenyl, bis(4-aminophenyl)terephthalate, 1,4-bis(4-aminophenoxy)-2,5-di-tert-butylbenzene, 4,4'-(1,3-phenylenediisopropylidene)bisaniline, 1,4-bis[2-(4-aminophenyl)-2-propyl]benzene, 2,4-diamino-3,5-diethyltoluene, 2,6-diamino-3,5-diethyltoluene, 4,4'-bis(3-aminophenoxy)biphenyl, 4,4'-(hexafluoropropyridene)dianiline, 1,2-diaminoethane, 1,3-diaminopropane, 1,4-diaminobutane, 1,5-diaminopentane, 1,6-diaminohexane, 1,2-diaminopropane, 1,2-diaminobutane, 1,3-diaminobutane, 2-methyl-1,2-diaminopropane, 2-methyl-1,3-diaminopropane, 1,3-bis(aminomethyl)cyclohexane, 1,4-bis(aminomethyl)cyclohexane, norbornanediamine, 2'-methoxy-4,4'-diaminobenzanilide, 4,Examples include 4'-diaminobenzanilide, bis[4-(4-aminophenoxy)phenyl]sulfone, bis[4-(3-aminophenoxy)phenyl]sulfone, 9,9-bis[4-(4-aminophenoxy)phenyl]fluorene, 9,9-bis[4-(3-aminophenoxy)phenyl]fluorene, 4,4'-diaminodiphenyl sulfide, 3,3'-diaminodiphenyl sulfide, 4,4'-diaminodiphenyl sulfone, 3,3'-diaminodiphenyl sulfone, 2,5-diamino-1,3,4-oxadiazole, bis[4,4'-(4-aminophenoxy)]benzanilide, bis[4,4'-(3-aminophenoxy)]benzanilide, 2,6-diaminopyridine, and 2,5-diaminopyridine. Among these, m-Tb, BAPP, TPE-Q, and 1,3-bis(4-aminophenoxy)benzene are preferred, and m-Tb, BAPP, etc. are more preferred, from the viewpoint of easily reducing the Df of the PI-based film obtained even at low imidation temperatures and easily improving flexural resistance. The diamine compounds can be used alone or in combination of two or more.

[0080] Furthermore, the PI-based resin precursor of the present invention may be obtained by further reacting other tetracarboxylic acids, dicarboxylic acids, and tricarboxylic acids, as well as their anhydrides and derivatives, in addition to the tetracarboxylic acid compound used in the synthesis of the PI-based resin precursor, to the extent that it does not impair the various physical properties of the resulting PI-based film.

[0081] Other tetracarboxylic acids include the hydrate adducts of the anhydrides of the above-mentioned tetracarboxylic acid compounds.

[0082] Examples of dicarboxylic acid compounds include aromatic dicarboxylic acids, aliphatic dicarboxylic acids and their related acid chloride compounds, acid anhydrides, etc., and two or more may be used in combination. Specific examples include dicarboxylic acid compounds of terephthalic acid, isophthalic acid, naphthalenedicarboxylic acid, 4,4'-biphenyldicarboxylic acid, 3,3'-biphenyldicarboxylic acid, and chain hydrocarbons having 8 or fewer 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 phenylene group, and their acid chloride compounds.

[0083] Examples of tricarboxylic acid compounds include aromatic tricarboxylic acids, aliphatic tricarboxylic acids and their related acid chloride compounds, acid anhydrides, etc., and two or more may be used in combination. Specific examples include 1,2,4-benzenetricarboxylic acid anhydride; 2,3,6-naphthalentricarboxylic acid-2,3-anhydride; and compounds in which phthalic anhydride and benzoic acid are linked by a single bond, -O-, -CH2-, -C(CH3)2-, -C(CF3)2-, -SO2-, or phenylene group.

[0084] In the production of PI-based resin precursors, the amounts of diamine compounds, tetracarboxylic acid compounds, dicarboxylic acid compounds, and tricarboxylic acid compounds used can be appropriately selected according to the desired ratio of each constituent unit of the PI-based resin precursor. In the present invention, the total number of moles of diamine compound used per mole of total tetracarboxylic acid compound is defined as the amine ratio. In one preferred embodiment of the present invention, the amine ratio is preferably 0.90 moles or more and preferably 0.999 moles or less per mole of total tetracarboxylic acid compound. In another embodiment, the amine ratio is preferably 1.001 moles or more and preferably 1.10 moles or less per mole of total tetracarboxylic acid compound. In one embodiment of the present invention, when the amine ratio is 1 or less, the amine ratio is preferably 0.90 moles or more and 0.999 moles or less, more preferably 0.95 moles or more and 0.997 moles or less, and even more preferably 0.97 moles or more and 0.995 moles or less. In one embodiment of the present invention, when the amine ratio is 1 or more, the amine ratio is preferably 1.001 moles or more and 1.1 moles or less, more preferably 1.002 moles or more and 1.05 moles or less, and even more preferably 1.003 moles or more and 1.03 moles or less. When the amine ratio is close to 1.0 mole, the molecular weight tends to increase rapidly during synthesis, while when it deviates significantly from 1.0 mole, the molecular weight of the resulting PI-based resin tends to decrease. When the molecular weight increases rapidly, it grows non-uniformly within the synthesis mass, and the physical properties of the PI-based resin obtained from the PI-based resin precursor tend to be unstable. On the other hand, if the molecular weight is too low, the mechanical properties tend to deteriorate.

[0085] The reaction temperature between the diamine compound and the tetracarboxylic acid compound is preferably 50°C or lower, more preferably 40°C or lower, and even more preferably 30°C or lower. When the reaction temperature is below the above upper limit, the Df of the resulting PI-based film is easily reduced and the bending resistance is easily improved. This tendency is particularly pronounced in PI-based resins obtained from PI-based resin precursors containing ester bonds, and especially in PI-based films containing PI-based resins obtained from PI-based resin precursors containing constituent unit (A1). Furthermore, the reaction temperature between the diamine compound and the tetracarboxylic acid compound is preferably 5°C or higher, more preferably 10°C or higher, and even more preferably 15°C or higher. When the reaction temperature is above the above lower limit, the reaction rate is easily increased and the polymerization time tends to be shortened. The reaction time is not particularly limited and may be, for example, 0.5 to 72 hours, preferably 3 to 24 hours. When the reaction time is within the above range, the Df of the resulting PI-based film is easily reduced even at low imidation temperatures.

[0086] The reaction between a diamine compound and a tetracarboxylic acid compound is preferably carried out in a solvent. The solvent is not particularly limited as long as it does not affect the reaction, but examples include alcoholic solvents such as water, methanol, ethanol, ethylene glycol, isopropyl alcohol, propylene glycol, ethylene glycol methyl ether, ethylene glycol butyl ether, 1-methoxy-2-propanol, 2-butoxyethanol, and propylene glycol monomethyl ether; phenolic solvents such as phenol and cresol; esteric solvents such as ethyl acetate, butyl acetate, ethylene glycol methyl ether acetate, propylene glycol methyl ether acetate, and ethyl lactate; lactoneic solvents such as γ-butyrolactone (hereinafter sometimes referred to as GBL) and γ-valerolactone; acetone, methyl ethyl ketone, cyclopentanone, cyclohexanone, 2-heptanone, and methyl ethyl ether. Examples of solvents include ketone solvents such as isobutyl ketone; aliphatic hydrocarbon solvents such as pentane, hexane, and heptane; alicyclic hydrocarbon solvents such as ethylcyclohexane; aromatic hydrocarbon solvents such as toluene and xylene; nitrile solvents such as acetonitrile; ether solvents such as tetrahydrofuran and dimethoxyethane; chlorine-containing solvents such as chloroform and chlorobenzene; amide solvents such as N,N-dimethylacetamide (hereinafter sometimes referred to as DMAc) and N,N-dimethylformamide (hereinafter sometimes referred to as DMF); sulfur-containing solvents such as dimethyl sulfone, dimethyl sulfoxide, and sulfolane; carbonate solvents such as ethylene carbonate and propylene carbonate; pyrrolidone solvents such as N-methylpyrrolidone (hereinafter sometimes referred to as NMP); and combinations thereof. Among these, from the viewpoint of solubility, phenolic solvents, lactone solvents, amide solvents, pyrrolidone solvents, and more preferably amide solvents can be suitably used.

[0087] In one embodiment of the present invention, the boiling point of the solvent used in the reaction between the diamine compound and the tetracarboxylic acid compound is preferably 230°C or lower, more preferably 200°C or lower, and even more preferably 180°C or lower, from the viewpoint of easily reducing the Df of the resulting PI-based film and improving its bending resistance, even at a low imidation temperature. Furthermore, the boiling point of the solvent is preferably 100°C or higher, more preferably 120°C or higher, from the viewpoint of easily reducing the Df of the resulting PI-based film, even at a low imidation temperature.

[0088] The reaction between the diamine compound and the tetracarboxylic acid compound may be carried out under an inert atmosphere such as a nitrogen atmosphere or an argon atmosphere, or under reduced pressure, as needed. Preferably, the reaction is carried out under an inert atmosphere, such as a nitrogen atmosphere or an argon atmosphere, while stirring in a strictly controlled dehydrated solvent.

[0089] The PI-based resin precursor may be separated and purified and isolated by conventional methods, such as filtration, concentration, extraction, crystallization, recrystallization, column chromatography, or a combination thereof. Alternatively, the reaction solution containing the PI-based resin precursor obtained by the synthesis of the PI-based resin precursor may be used in the production of the PI-based resin without isolation.

[0090] [Polyimide resin] The present invention also includes PI-based resins obtained from the PI-based resin precursor of the present invention. As described below, the PI-based resin of the present invention is a PI-based resin obtained by imidizing the above-mentioned PI-based resin precursor.

[0091] Since the PI-based resin of the present invention is obtained from the PI-based resin precursor of the present invention, it contains the same constituent units as those contained in the PI-based resin precursor of the present invention, such as constituent unit (A1), constituent unit (A2), constituent unit (B1), etc., in the same amounts. Therefore, the descriptions regarding the types and content of constituent units contained in the PI-based resin are the same as those described in the section on [Polyimide Resin Precursor].

[0092] In one embodiment of the present invention, the PI resin may contain halogen atoms, preferably fluorine atoms, which can be introduced by, for example, the halogen-containing substituents described above. When the PI resin contains fluorine atoms, the dielectric constant of the resulting PI film is easily reduced. Preferred fluorine-containing substituents for incorporating fluorine atoms into the PI resin include, for example, fluoro groups and trifluoromethyl groups. Furthermore, in another embodiment of the present invention, it is preferable that the PI resin does not contain fluorine atoms, from the viewpoint of easily improving the adhesion of the resulting PI film to a substrate such as copper foil. Also, since the presence of fluorine in the PI resin tends to weaken the interactions between molecular chains, the absence of fluorine atoms makes it easier to form a higher-order structure in which molecular rotation of the PI resin is suppressed, and as a result, it is easier to obtain the effects of the present invention.

[0093] When the PI resin contains halogen atoms, the content of halogen atoms, particularly fluorine atoms, in the PI resin is preferably 0.1 to 35% by mass, more preferably 0.1 to 30% by mass, even more preferably 0.1 to 20% by mass, and most preferably 0.1 to 10% by mass, based on the mass of the PI resin. If the halogen atom content is above the lower limit, it is easier to improve the heat resistance and dielectric properties of the resulting PI film. If the halogen atom content is below the upper limit, it is advantageous in terms of cost, makes it easier to reduce the CTE of the PI film, and facilitates the synthesis of the PI resin.

[0094] In one embodiment of the present invention, the imidation rate of the PI resin is preferably 90% or more, more preferably 93% or more, even more preferably 95% or more, and usually 100% or less. From the viewpoint of easily improving mechanical properties, thermal properties, and dielectric properties, it is preferable that the imidation rate is above the lower limit mentioned above. The imidation rate represents the ratio of the molar amount of imide bonds in the PI resin to twice the molar amount of constituent units derived from the tetracarboxylic acid compound in the PI resin. If the PI resin contains a tricarboxylic acid compound, the imidation rate represents the ratio of the molar amount of imide bonds in the PI resin to the sum of twice the molar amount of constituent units derived from the tetracarboxylic acid compound and the molar amount of constituent units derived from the tricarboxylic acid compound. The imidation rate can be determined by methods such as IR or NMR.

[0095] In one embodiment of the present invention, the polystyrene equivalent Mw of the PI resin is preferably greater than 100,000, more preferably 110,000 or more, even more preferably 120,000 or more, particularly preferably 130,000 or more, preferably 1,000,000 or less, more preferably 700,000 or less, even more preferably 500,000 or less, and particularly preferably 300,000 or less. When Mw is above the lower limit, it is easier to improve mechanical properties such as bending resistance. When Mw is below the upper limit, it is advantageous in terms of processability during film formation.

[0096] In one embodiment of the present invention, the ratio of Mw to Mn (Mw / Mn) of the PI resin is preferably 3.5 or higher, more preferably 4.0 or higher, even more preferably 4.2 or higher, even more preferably 4.5 or higher, particularly preferably 4.7 or higher, preferably 8.0 or lower, more preferably 7.0 or lower, even more preferably 6.0 or lower, and particularly preferably 5.5 or lower, based on polystyrene equivalent. Mw and Mn can be determined by gel permeation chromatography (hereinafter sometimes referred to as GPC) measurement and converted to standard polystyrene equivalent.

[0097] In one embodiment of the present invention, from the viewpoint that even when the thermal imidization temperature is low, the Tg of the PI-based resin is likely to reduce the Df of the obtained PI-based film and is likely to improve the bending resistance, it is preferably 290 °C or lower, more preferably less than 290 °C, still more preferably 280 °C or lower, even more preferably 275 °C or lower, particularly preferably 260 °C or lower, especially preferably 250 °C or lower, and particularly more preferably 240 °C or lower. From the viewpoint of being likely to reduce the Df of the PI-based film and being likely to enhance the heat resistance of the PI-based film, it is preferably 200 °C or higher, more preferably 202 °C or higher, and still more preferably 205 °C or higher. The Tg of the PI-based resin can be measured by dynamic viscoelasticity measurement, for example, by the method described in the examples.

[0098] The Tg of the PI-based resin can be adjusted by appropriately adjusting the types and structures of the constituent units constituting the PI-based resin, as well as the molecular weight and manufacturing method of the PI-based resin, particularly the imidization conditions, etc. For example, it can be adjusted within the above range by adjusting within the range described as a preferred embodiment in the above description.

[0099] In one embodiment of the present invention, the storage elastic modulus (hereinafter sometimes referred to as E') of the PI-based resin at 280 °C is preferably 3×10 8 Pa or less, more preferably 2×10 8 Pa or less, still more preferably 1.5×10 8 Pa or less, even more preferably 1×10 8 Pa or less, particularly preferably 0.8×10 8 Pa or less from the viewpoint of being likely to reduce the Df of the obtained PI-based film and being likely to improve the bending resistance. From the viewpoint of being likely to suppress deformation during processing of the PI-based film, it is preferably 1×10 4 Pa or more, more preferably 1×10 5 Pa or more, still more preferably 1×10 6 Pa or more. The E' of the PI-based resin can be measured by dynamic viscoelasticity measurement, for example, by the method described in the examples.

[0100] The E' of the PI resin at 280°C can be adjusted by appropriately adjusting the types and compositions of the constituent units of the PI resin, as well as the molecular weight and manufacturing method of the PI resin, particularly the imidation conditions. For example, it can be adjusted to the range described as a preferred embodiment in the above description.

[0101] [Method for producing polyimide resins] The PI-based resin of the present invention can be produced by imidizing the PI-based resin precursor of the present invention, and it is preferable to produce it by imidizing the PI-based resin precursor by heat treatment at 200°C or higher and less than 350°C.

[0102] In the present invention, even when imidizing the PI resin precursor at a low temperature, the Df of the resulting PI-based film containing the PI resin can be reduced and the flexural resistance can be improved. Therefore, the imidization temperature is preferably less than 350°C, more preferably 340°C or lower, even more preferably 330°C or lower, even more preferably 310°C or lower, and particularly preferably 300°C or lower. 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. Heating may also be carried out in stages. For example, the solvent may be removed by heating at a relatively low temperature of 50 to 150°C, and then imidization may be carried out by gradually heating to a temperature in the range of 200°C or higher and less than 350°C.

[0103] In one embodiment of the present invention, the reaction time for imidization is preferably 30 minutes to 24 hours, more preferably 1 to 12 hours. Also in one embodiment of the present invention, the time for maintaining a temperature of 200°C or higher is preferably 5 to 90 minutes, more preferably 15 to 70 minutes, and even more preferably 20 to 50 minutes. When the reaction time for imidization at 200°C or higher is within the above range, it is easier to sufficiently improve the imidization rate, prevent oxidative degradation of the resin, and improve dielectric properties and bending resistance.

[0104] PI resins can be separated, purified, and isolated by conventional methods, such as filtration, concentration, extraction, crystallization, recrystallization, column chromatography, or combinations thereof.

[0105] [Polyimide film] The PI-based film of the present invention contains a PI-based resin obtained from the PI-based resin precursor of the present invention. The PI-based film of the present invention has a low Df and excellent flexural resistance even at low imidation temperatures. Therefore, the present invention also includes PI-based films containing the PI-based resin of the present invention. Furthermore, the present invention also includes PI-based films containing a PI-based resin obtained by imidizing the PI-based resin precursor by heat treatment at a temperature of 200°C or higher and less than 350°C.

[0106] In one embodiment of the present invention, the content of PI resin in the PI film is preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, and particularly preferably 90% by mass or more, relative to the mass of the PI film of the present invention. Furthermore, there is no particular upper limit to the content of PI resin, and it is, for example, 100% by mass or less, preferably 99% by mass or less, and more preferably 95% by mass or less, relative to the mass of the PI film. When the content of PI resin is within the above range, it is easy to improve the mechanical properties and thermal properties.

[0107] The PI-based film of the present invention may optionally contain fillers. Examples of fillers include metal oxide particles such as silica and alumina, inorganic salts such as calcium carbonate, and polymer particles such as fluororesins and cycloolefin polymers. Fillers can be used alone or in combination of two or more types. When fillers are included, their content is preferably 50% by mass or less, more preferably 40% by mass or less, even more preferably 30% by mass or less, and preferably 0.01% by mass or more, based on the total mass of the PI-based film.

[0108] Furthermore, in one embodiment of the present invention, the PI-based film of the present invention may contain additives as needed. Examples of additives include antioxidants, flame retardants, crosslinking agents, surfactants, compatibilizers, imidation catalysts, weathering agents, lubricants, antiblocking agents, antistatic agents, antifogging agents, anti-drip agents, and pigments. Additives can be used individually or in combination of two or more. The content of each additive can be appropriately selected within a range that does not impair the effects of the present invention, and when various additives are included, their total content is preferably 7% by mass or less, more preferably 5% by mass or less, even more preferably 4% by mass or less, and preferably 0.001% by mass or more, based on the mass of the PI-based film.

[0109] In one embodiment of the present invention, the CTE of the PI-based 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, 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, so that peeling of the laminated film can be suppressed. The CTE can be measured, for example, by a thermomechanical analyzer (hereinafter sometimes referred to as "TMA") and can be determined by the method described in the examples.

[0110] Printed circuits require low transmission loss. Transmission loss is expressed as the sum of dielectric loss, which is the loss caused by the electric field generated in the dielectric, and conductor loss, which is the loss caused by the current flowing through the conductor. It is known that dielectric loss is approximately proportional to the index E, which is expressed by equation (i).

[0111] E = Df × (Dk) 1 / 2 (i) [In equation (i), Df represents the dielectric loss tangent and Dk represents the relative permittivity.]

[0112] In the high-frequency range used in 5G FPCs, dielectric loss tends to increase, so there is a particular need for materials with a small value of the aforementioned index E that can suppress dielectric loss. On the other hand, high-frequency signals concentrate current at the very surface of the conductor. Therefore, conductor loss is related to the dielectric properties of the contacting dielectric and is approximately (Dk) 1 / 2 It is known to be proportional to [something].

[0113] As described above, the PI-based film obtained from the PI-based resin precursor of the present invention satisfies the relationship of formula (X) in the PI-based resin precursor, the content of constituent unit (B1) exceeds 30 mol%, and Mw is greater than 100,000. As a result, Df and Dk become smaller, the dielectric loss index E and conductor loss also become smaller, and transmission loss can be reduced in circuits containing the PI-based film.

[0114] In one embodiment of the present invention, the dielectric loss index E of the PI-based film at 10 GHz is preferably 0.01 or less, more preferably 0.009 or less, even more preferably 0.008 or less, even more preferably 0.007 or less, and particularly preferably 0.006 or less. The smaller the index E, the lower the transmission loss of the electronic circuit including the PI-based film; therefore, the lower limit of the index E is not particularly limited and may be, for example, 0 or more.

[0115] In one embodiment of the present invention, the Df of the PI-based film at 10 GHz is preferably less than 0.004, more preferably 0.0038 or less, even more preferably 0.0035 or less, even more preferably 0.0033 or less, particularly preferably 0.0030 or less, particularly more preferably 0.0027 or less, and especially preferably 0.0024 or less, from the viewpoint of easily reducing the transmission loss of the electronic circuit including the PI-based film. The smaller the Df, the lower the transmission loss of the electronic circuit including the PI-based film; therefore, the lower limit of the Df is not particularly limited and may be, for example, 0 or more.

[0116] In one embodiment of the present invention, the Dk of the PI-based film at 10 GHz is preferably less than 3.50, more preferably 3.45 or less, even more preferably 3.40 or less, even more preferably 3.38 or less, particularly preferably 3.36 or less, particularly more preferably 3.33 or less, particularly more preferably 3.30 or less, particularly preferably 3.27 or less, and particularly more preferably 3.22 or less.

[0117] The Df and Dk of a PI-based film can be measured using a vector network analyzer and a resonator, for example, by the method described in the examples.

[0118] As described above, the PI-based film of the present invention obtained from the PI-based resin precursor of the present invention has excellent bending resistance, particularly bending resistance, because in the PI-based resin precursor, the constituent unit (A) satisfies the relationship of formula (X), the content of constituent unit (B1) exceeds 30 mol%, and Mw is greater than 100,000. The number of folds until fracture in the MIT fold fatigue test of the PI-based film of the present invention in accordance with ASTM standard D2176-16 is preferably 20,000 or more, more preferably 30,000 or more, even more preferably 50,000 or more, even more preferably 100,000 or more, particularly preferably 150,000 or more, and particularly more preferably 200,000 or more. When the number of folds is above the lower limit above, the occurrence of cracks, breaks, creases, etc. can be effectively suppressed even with repeated bending. Furthermore, the upper limit of the number of folds is not particularly limited and may be, for example, 10,000,000 or less. Furthermore, the MIT fracture fatigue test can be performed using the MIT fracture fatigue testing machine, and can be performed, for example, by the method described in the examples.

[0119] In one embodiment of the present invention, from the viewpoint of easily reducing the Df of the PI-based film and easily improving its bending resistance, the E' of the PI-based resin at 280°C and the CTE of the PI-based film containing the PI resin are given by formula (Y): 120,000 ≤ (CTE of PI film) × (E' of PI resin at 280°C) 1 / 2 ≤850,000 It is preferable that the relationship is satisfied.

[0120] In one embodiment of the present invention, the value of formula (Y) is preferably greater than 120,000, more preferably 125,000 or more, even more preferably 135,000 or more, preferably 750,000 or less, more preferably 500,000 or less, even more preferably 450,000 or less, even more preferably 400,000 or less, particularly preferably 300,000 or less, particularly more preferably 200,000 or less, and especially still more preferably 190,000 or less, from the viewpoint of easily reducing the Df of the PI-based film and easily improving its bending resistance.

[0121] The thickness of the PI-based film of the present invention can be appropriately selected depending on the application, preferably 5 μm or more, more preferably 10 μm or more, even more preferably 20 μm or more, preferably 500 μm or less, more preferably 300 μm or less, even more preferably 100 μm or less, particularly preferably 80 μm or less, and particularly more preferably 50 μm or less. The film thickness can be measured using a film thickness gauge or the like. Note that if the film of the present invention is a multilayer film, the above thickness represents the thickness of the single layer portion.

[0122] The PI-based film of the present invention may be subjected to surface treatments such as corona discharge treatment, plasma treatment, or ozone treatment by methods commonly used in industry.

[0123] The PI-based film of the present invention has a low Df and excellent bending resistance, making it suitable for use as a substrate material for high-frequency printed circuit boards and antenna boards. Metal-clad laminates such as CCL used in FPCs are widely used, which have a single or multiple layers of PI-based resin with a thin metal layer such as a copper foil layer on one or both sides. When the PI-based film of the present invention is used as a resin layer, the PI-based film of the present invention can have a low Df even at low imidation temperatures. Therefore, even when metal-clad laminates such as CCL are manufactured by thermal imidation of a PI-based resin precursor coating on a metal foil such as copper foil, deterioration of the metal foil surface can be suppressed, and CCL with excellent high-frequency characteristics can be obtained.

[0124] [Method for manufacturing polyimide films] The PI-based film of the present invention is produced by, for example, the following process: A step of coating a PI-based resin precursor solution containing the PI-based resin precursor of the present invention onto a substrate, and A process of imidizing a PI-based resin precursor by heat treatment at a temperature between 200°C and 350°C. It can be manufactured by a method that includes [a specific component].

[0125] <Coating process for polyimide resin precursor solution> (Preparation of PI resin precursor solution) The PI-based resin precursor solution comprises the PI-based resin precursor of the present invention and a solvent, and can be prepared by mixing the PI-based resin precursor of the present invention with the solvent. In addition, in one embodiment of the present invention, a reaction solution containing the PI-based resin precursor obtained by the synthesis of the PI-based resin precursor may be appropriately diluted with a solvent as needed and used as the PI-based resin precursor solution.

[0126] The solvent contained in the PI resin precursor solution is one of the solvents exemplified for use in the reaction between the diamine compound and the tetracarboxylic acid compound in the production of the PI resin precursor, and is preferably a lactone solvent, an amide solvent, a pyrrolidone solvent, and more preferably an amide solvent. Furthermore, in one embodiment of the present invention, the boiling point of the solvent contained in the PI resin precursor solution is preferably 230°C or lower, more preferably 200°C or lower, even more preferably 180°C or lower, and particularly preferably 170°C or lower, from the viewpoint of easily reducing the Df of the obtained PI film and easily improving its bending resistance, even at low imidation temperatures. Furthermore, the boiling point of the solvent is preferably 100°C or higher, more preferably 120°C or higher, from the viewpoint of easily reducing the Df of the obtained PI film and easily improving its bending resistance.

[0127] The content of the PI-based resin precursor in the PI-based resin precursor solution is preferably 8% by mass or more, more preferably 10% by mass or more, even more preferably 12% by mass or more, and particularly preferably 13% by mass or more, relative to the total amount of the PI-based resin precursor solution. Furthermore, it is preferably 30% by mass or less, more preferably 25% by mass or less, even more preferably 23% by mass or less, and particularly preferably 20% by mass or less. When the content of the PI-based resin precursor is within the above range, the processability during film formation is excellent.

[0128] (Coating of polyimide resin precursor solution) The coating process for PI-based resin precursor solution involves coating the substrate with the PI-based resin precursor solution to form a coating film.

[0129] In the coating process, a coating film is formed by coating the substrate with the composition using a known coating or application method. Known coating methods include, for example, wire bar coating, reverse coating, roll coating methods such as gravure coating, die coating, comma coating, lip coating, spin coating, screen printing coating, fountain coating, dipping, spraying, curtain coating, slot coating, and flow molding. When coating or applying a solution of PI-based resin precursor onto a substrate, a single layer of PI-based resin precursor may be coated onto the substrate, or multiple layers of PI-based resin precursor may be coated onto the substrate. When coating multiple layers of PI-based resin precursor onto a substrate, the coating may be applied in multiple stages and dried, or multiple layers may be applied simultaneously.

[0130] Examples of substrates include copper plates such as copper foil, SUS plates such as SUS foil and SUS belts, glass substrates, PET films, PEN films, other PI resin films other than the PI film of the present invention, and polyamide resin films. Among these, copper plates, SUS plates, glass substrates, PET films, and PEN films are preferred from the viewpoint of excellent heat resistance, and copper plates, SUS plates, glass substrates, or PET films are more preferred from the viewpoint of adhesion to the film and cost.

[0131] <Imidification Process> The imidization process involves imidizing the PI-based resin precursor coated on the substrate by heat treatment at a temperature between 200°C and 350°C. In one embodiment of the present invention, the imidation step is preferably a step in which, before imidizing the PI-based resin precursor, a PI-based resin precursor solution coated on a substrate is heated and dried at a relatively low temperature of, for example, less than 200°C, and the resulting dried film of the PI-based resin precursor is imidized by heat treatment at a temperature of 200°C or higher and less than 350°C. Furthermore, in one embodiment of the present invention, a PI-based film may be obtained by imidizing the dried film of the PI-based resin precursor on the substrate, or a PI-based film may be obtained by peeling the dried film of the PI-based resin precursor from the substrate and imidizing the dried film peeled from the substrate.

[0132] In one embodiment of the present invention, the drying temperature of the PI-based resin precursor coated on the substrate is not particularly limited as long as it is within the temperature range in which the solvent dries and solidifies. However, from the viewpoint of avoiding surface roughness due to rapid drying and suppressing wrinkles and distortions that occur during processing, it 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. Furthermore, from the viewpoint of productivity, it is preferably 50°C or higher, more preferably 80°C or higher, and even more preferably 100°C or higher.

[0133] The PI-based resin precursor in this invention can reduce the Df of the resulting PI-based film and improve its flexural resistance, even when imidized at low temperatures. The heat treatment temperature in the imidization process, 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, especially the copper foil, can be suppressed, making it easier to obtain CCL with excellent high-frequency characteristics and flexural resistance. Furthermore, from the viewpoint of easily improving the imidization rate, the imidization temperature is preferably 200°C or higher, more preferably 210°C or higher, and even more preferably 220°C or higher. Furthermore, from the viewpoint of easily obtaining a smooth film, it is preferable to perform heating in stages. For example, after heating at a relatively low temperature of 50 to 150°C to remove the solvent, imidization may be performed by heating in stages to a temperature in the range of 200°C to less than 350°C.

[0134] In one embodiment of the present invention, the reaction time for imidization is preferably 30 minutes to 24 hours, more preferably 1 to 12 hours. Also in one embodiment of the present invention, the time for maintaining a temperature of 200°C or higher is preferably 10 minutes to 90 minutes, more preferably 15 minutes to 70 minutes, and even more preferably 20 minutes to 50 minutes.

[0135] After imidization, a PI-based film can be obtained by peeling off the coating film formed on the substrate from the substrate. In one embodiment of the present invention, if the substrate is a metal foil such as copper foil, a PI-based film can be formed without peeling off the coating film from the metal foil such as copper foil, and the resulting laminated film in which the PI-based film is laminated on the metal foil such as copper foil can be used as CCL.

[0136] If the film of the present invention is a multilayer film, it can be manufactured by a multilayer film formation method such as co-extrusion, extrusion lamination, heat lamination, or dry lamination.

[0137] [Laminated film] The PI-based film of the present invention has a low Df and excellent bending resistance, making it suitable for use in forming metal-clad laminates used in FPCs. Therefore, the present invention includes a laminated film that includes a PI layer and a metal foil layer, using the PI-based film of the present invention as the PI layer. In one embodiment of the present invention, the laminated film of the present invention may include the metal foil layer on only one side of the PI layer or on both sides.

[0138] In one embodiment of the present invention, examples of metal foils include copper foil, SUS foil, and aluminum foil, but copper foil is preferred from the viewpoint of conductivity and metalworkability.

[0139] The PI-based film of the present invention can be suitably used for forming CCLs that have a low Df, excellent high-frequency characteristics and bending resistance, even at low thermal imidation temperatures. Therefore, in a preferred embodiment of the present invention, the laminated film of the present invention is preferably a laminated film that includes a copper foil layer on one or both sides of the PI-based film of the present invention.

[0140] In one embodiment of the present invention, the thickness of the metal foil layer, particularly the copper foil layer, is preferably 1 μm or more, more preferably 5 μm or more, and from the viewpoint of facilitating circuit miniaturization and improving bending resistance, it is preferably 100 μm or less, more preferably 50 μm or less, even more preferably 30 μm or less, and particularly preferably 20 μm or less. The thickness of the metal foil layer, particularly the copper foil layer, can be measured using a film thickness gauge or the like. When the PI-based film contains metal foil layers, particularly copper foil layers, on both sides, the thicknesses of each metal foil layer, particularly each copper foil layer, may be the same or different from each other.

[0141] In one embodiment of the present invention, the thickness of the laminated film is preferably 5 μm or more, more preferably 10 μm or more, even more preferably 15 μm or more, preferably 100 μm or less, more preferably 80 μm or less, and even more preferably 60 μm or less. The thickness of the laminated film can be measured using a film thickness gauge or the like.

[0142] The laminated film of the present invention may include other layers, such as functional layers, in addition to the PI-based film and metal foil layer, particularly the copper foil layer. Examples of functional layers include the layers described above, such as a thermoplastic PI-based resin layer containing a thermoplastic PI-based resin or an adhesive layer. Functional layers can be used alone or in combination of two or more types.

[0143] In one embodiment of the present invention, the laminated film of the present invention may be a two-layer metal-clad laminate composed of a metal foil layer and a PI layer, or a three-layer metal-clad laminate composed of a metal foil layer, a PI layer and an adhesive layer. However, from the viewpoint of heat resistance, dimensional stability and weight reduction, a two-layer metal-clad laminate without an adhesive layer is preferred. Furthermore, the PI-based film of the present invention has a low Df even at low imidation temperatures and exhibits excellent bending resistance. Therefore, even when a laminated film in which the metal foil is copper foil is manufactured by thermal imidation of a PI-based resin precursor coating on copper foil, deterioration of the copper foil surface can be suppressed. Accordingly, the laminated film of the present invention has excellent high-frequency characteristics even without including an adhesive layer.

[0144] Furthermore, in one embodiment of the present invention, the PI-based film and the metal foil layer, particularly the copper foil layer, may be in direct contact, or a functional layer may be inserted between the PI-based film and the metal foil layer, particularly the copper foil layer, and they may be in contact via the functional layer. However, from the viewpoint of easily improving mechanical and thermal properties, it is preferable that the PI-based film and the metal foil layer, particularly the copper foil layer, are in direct contact. The functional layer that may be inserted between the PI-based film and the metal foil layer of the present invention may be a thermoplastic PI layer. From the viewpoint of easily improving mechanical and thermal properties, it is preferable that the layer in direct contact with the metal foil layer, particularly the copper foil layer, is the PI film or a thermoplastic PI layer as a functional layer of the present invention.

[0145] [Method for manufacturing laminated film] The laminated film of the present invention is formed by, for example, the following steps: A step of coating a PI-based resin precursor solution containing the PI-based resin precursor of the present invention onto a substrate, and A process of imidizing a PI-based resin precursor by heat treatment at 200°C or higher and less than 350°C to form the PI-based film of the present invention on a substrate. It can be manufactured by a method that includes [a specific component].

[0146] In the method for manufacturing the laminated film of the present invention, the steps of "coating a PI-based resin precursor solution containing the PI-based resin precursor of the present invention onto a substrate" and "imidizing the PI-based resin precursor by heat treatment at 200°C or higher and less than 350°C to form the PI-based film of the present invention on a substrate" are similarly governed by the descriptions of each step described in the section on "Method for Manufacturing Polyimide Films."

[0147] In one embodiment of the present invention, the substrate is preferably a metal foil, and particularly preferably a copper foil. The description regarding the metal foil, and especially the copper foil, is similar to the description regarding the metal foil in the [Laminated Film] section.

[0148] The laminated film of the present invention may also be manufactured by a method other than the above-described method, for example, by coating a PI-based resin precursor solution containing the PI-based resin precursor of the present invention onto a substrate other than the metal foil included in the laminated film, drying the resulting dried film of the PI-based resin precursor, peeling it off the substrate, and laminating the peeled dried film of the PI-based resin precursor onto the metal foil. Methods for laminating the dried film of the PI-based resin precursor with the metal foil may include pressing, lamination using a hot roll, etc., and the imidization of the PI-based resin precursor may be performed simultaneously during the lamination process. However, since the PI-based film of the present invention has a low Df and excellent flexural resistance even at low imidization temperatures, for example, even if a laminated film is manufactured where the metal foil is copper foil by thermal imidization of the PI-based resin precursor coating on copper foil, deterioration of the copper foil surface can be suppressed. Therefore, the laminated film of the present invention has excellent high-frequency characteristics and flexural resistance even when manufactured without going through the above-described lamination process.

[0149] [Flexible Printed Circuit Board] The PI-based film obtained from the PI-based resin precursor of the present invention has a low Df and excellent bending resistance, making it suitable for use as an FPC substrate material, particularly for FPC substrates for foldable devices. The present invention also encompasses FPC substrates containing the above-mentioned PI-based film. [Examples]

[0150] The present invention will be described more specifically below based on examples and comparative examples, but the present invention is not limited to the following examples.

[0151] The abbreviations used in the examples, comparative examples, and reference examples refer to the following compounds. BPDA: 3,3',4,4'-biphenyltetracarboxylic acid dianhydride TAHQ: p-phenylenebis(trimellitic acid monoesteric acid dianhydride) PMDA: Pyromellitic anhydride BP-TME: 4,4'-Bis(1,3-dioxo-1,3-dihydroisobenzofuran-5-ylcarbonyloxy)biphenyl m-Tb: 4,4'-diamino-2,2'-dimethylbiphenyl BAPP: 2,2-Bis[4-(4-aminophenoxy)phenyl]propane TPE-Q: 1,4-bis(4-aminophenoxy)benzene

[0152] [Synthesis of polyimide resin precursors] (Example 1) 27.00 g (127.2 mmol) of m-Tb was dissolved in 421 g of DMAc, and then 28.86 g (63.0 mmol) of TAHQ was added and the mixture was stirred at 20°C under a nitrogen atmosphere for 1 hour. Subsequently, 18.52 g (63.0 mmol) of BPDA was added and the mixture was stirred at 20°C under a nitrogen atmosphere for 24 hours to obtain a PI resin precursor composition. The molar ratio of diamine monomer to acid dianhydride monomer used was 1.01. The obtained PI resin precursor had a polystyrene-based molecular weight of Mn of 35,000 and a polystyrene-based molecular weight of 170,000.

[0153] (Examples 2-11, Comparative Examples 2, 3) A PI resin precursor composition was obtained in the same manner as in Example 1, except that the types and compositions of monomers used were changed as shown in Table 1. Unless otherwise specified, the order in which monomers were added was diamine followed by acidic dianhydride. The diamines were added in the order of the diamines that derive constituent units (B1), (B2), and (B3), and the acidic dianhydrides were added in the order of the acidic dianhydrides that derive constituent units (A1), (A2), and (A3).

[0154] [Manufacturing of polyimide film] Using the solvent used in the synthesis of the PI resin precursor, the PI resin precursor compositions obtained in Examples 1-11 and Comparative Examples 2 and 3 were appropriately diluted to a viscosity of 40,000 cps or less, within a range where the PI resin precursor content was 10% by mass or more, to prepare PI resin precursor solutions. Each of the PI resin precursor solutions was then used to form films under one of the following film formation conditions 1-4, as shown in Table 1, to obtain PI films made of PI resin.

[0155] <Film forming conditions 1> A PI resin precursor solution was poured onto a glass substrate, and a coating film of the PI resin precursor solution was formed using an applicator at a linear velocity of 0.4 m / min. The coating film was heated at 120°C for 30 minutes, and after peeling the resulting film from the glass substrate, the film was fixed to a metal frame. The film fixed to the metal frame was heated from 30°C to 270°C over 19 minutes in a 7% oxygen atmosphere, and then cooled to 200°C over 35 minutes to produce a PI film. The time at which a temperature of 220°C or higher was maintained was 23 minutes. The time at which a temperature of 200°C or higher was maintained was 34 minutes.

[0156] <Film forming conditions 2> A PI resin precursor solution was poured onto the roughened side (surface roughness; Rz = 1.3 μm) of an electrolytic copper foil (manufactured by JX Metals Corporation, JXEFL-BHM, 12 μm thick), and a coating film of the PI resin precursor solution was formed using an applicator at a linear velocity of 0.4 m / min. The coating film was heated at 120°C for 30 minutes to dry. Then, the laminated film of copper foil and precursor was fixed to a gold frame, and the temperature was raised from 30°C to 320°C over 9 minutes in a 1% oxygen atmosphere, followed by heating at 320°C for 6 minutes, and then cooling to 200°C over 15 minutes to produce a laminated film of PI film and copper foil. The time at which the temperature was maintained above 220°C was 21 minutes. The time at which the temperature was maintained above 200°C was 25 minutes. The resulting laminated film of PI film and copper foil was immersed in a large volume of 40% by mass ferric chloride aqueous solution at room temperature for 10 minutes. After visually confirming that no copper remained, it was dried at 80°C for 1 hour to obtain a single PI film.

[0157] <Film forming conditions 3> A PI resin precursor solution was poured onto a glass substrate, and a coating film of the resin precursor solution was formed using an applicator at a linear velocity of 0.4 m / min. The coating film was heated at 120°C for 30 minutes, and after peeling the resulting film from the glass substrate, the film was fixed to a metal frame. The film fixed to the metal frame was heated from 30°C to 320°C over 9 minutes in a 1% oxygen atmosphere, then heated at 320°C for 6 minutes, and cooled to 200°C over 15 minutes to produce a PI film. The time at which a temperature of 220°C or higher was maintained was 21 minutes. The time at which a temperature of 200°C or higher was maintained was 25 minutes.

[0158] <Film forming conditions 4> A PI resin precursor solution was poured onto a glass substrate, and a coating film of the PI resin precursor solution was formed using an applicator at a linear velocity of 0.4 m / min. The coating film was heated at 120°C for 30 minutes, and after peeling the resulting film from the glass substrate, the film was fixed to a metal frame. The film fixed to the metal frame was heated from 30°C to 320°C over 5 minutes in a 1% oxygen atmosphere, then heated at 320°C for 5 minutes, and cooled to 200°C over 15 minutes to produce a PI film. The time at which a temperature of 220°C or higher was maintained was 17 minutes. The time at which a temperature of 200°C or higher was maintained was 21 minutes.

[0159] [Synthesis of polyimide resin precursors and production of polyimide films] (Comparative Example 1) 70.33 g (331 mmol) of m-Tb was dissolved in 720 g of NMP, then 73.06 g (248 mmol) of BPDA and 37.94 g (83 mmol) of TAHQ were added, and the mixture was stirred at room temperature under a nitrogen atmosphere for 1 hour. The mixture was then stirred at 60°C for 20 hours to obtain a PI resin precursor composition. The polystyrene equivalent Mw of the PI resin precursor was 91,000, and the Mn was 27,000. The PI resin precursor composition was appropriately diluted with NMP to adjust the viscosity and prepare a PI resin precursor solution. The obtained PI resin precursor solution was then fabricated under the aforementioned film-forming conditions 1 to obtain a PI film. The obtained PI film had a thickness of 30 μm, a Dk of 3.45, a Df of 0.0040, an index E of 0.0074, 886 folds to breakage, and a CTE of 38.2 ppm. The Tg of the PI resin was 255°C, and the E' at 280°C was 5.53 × 10⁻⁶. 8 Pa is CTE×(E'). 1 / 2 is 8.98 × 10 5 That was the case. Furthermore, the Tg value, determined using the tangent method from the storage modulus curve, was 230°C.

[0160] The PI resin precursors and PI films obtained in the examples and comparative examples were subjected to various measurements and evaluations. The measurement and evaluation methods are described below.

[0161] <Measurement of Weight-Average Molecular Weight and Number-Average Molecular Weight> The Mw and Mn in terms of polystyrene of the PI resin precursor obtained by synthesis were measured using GPC. The GPC measurement was carried out under the following conditions. (1) Pretreatment Method The sample was diluted with DMF and then filtered through a 0.45 μm membrane filter to obtain a measurement solution. (2) Measurement Conditions Column: Two TSKgel SuperAWM-H (inner diameter 6.0 mm, length 150 mm) columns were connected in series. Eluent: DMF (added with 10 mmol / L lithium bromide and 30 mmol / L phosphoric acid) Flow rate: 0.6 mL / min Detector: RI detector Column temperature: 40 °C Injection volume: 20 μL Molecular weight standard: Standard polystyrene

[0162] <Measurement of Glass Transition Temperature (Tg)> The Tg of the PI resins obtained in the examples and comparative examples was determined by measuring the PI film as follows. Using a dynamic viscoelasticity measuring device (manufactured by IT Measurement & Control Co., Ltd., DVA-220), measurements were carried out under the following samples and conditions to obtain a tanδ curve, which is the ratio of the values of the storage modulus (E') and the loss modulus (E"). The apex of the peak of the tanδ curve was taken as Tg. Test piece: A rectangular parallelepiped with a length of 40 mm, a width of 5 mm, and a thickness of 50 μm (the thickness varies depending on the film used). Experimental mode: Single frequency, constant rate heating Experimental pattern: Tensile Sample grip length: 15 mm Measurement start temperature: Room temperature to 342 °C Heating rate: 5 °C / min Frequency: 10 Hz Static / dynamic stress ratio: 1.8 Main collected data: (1) Storage modulus (E') (2) Loss modulus (E”) (3) tanδ (E” / E’)

[0163] <Measurement of storage modulus (E’)> The E’ of the PI resins obtained in the examples and comparative examples at 280 °C was determined by performing dynamic viscoelasticity measurement in the same manner as the measurement of Tg.

[0164] <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 from 50 °C to 100 °C was calculated. Apparatus: TMA / SS7100 manufactured by Hitachi High-Technologies Corporation Load: 50.0 mN Temperature program: Heating from 20 °C to 130 °C at a rate of 5 °C / min Test piece: Cuboid with a length of 40 mm, a width of 5 mm, and a thickness of 50 μm (note that the thickness varies depending on the film used)

[0165] <Evaluation of the index E of dielectric loss> The index E of the dielectric loss of the film was calculated by the following formula.

[0166] E = Df × (Dk) 1 / 2 (i)

[0167] Df: Dielectric tangent Dk: Relative permittivity

[0168] (Measurement of Df and Dk) Measurement samples of 50 mm × 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. After conditioning the measurement samples at 25 °C / 55% RH for 24 hours, the measurement was performed. Apparatus: Compact USB Vector Network Analyzer (product name: MS46122B) manufactured by Anritsu Corporation Cavity resonator (TE mode 10 GHz type) manufactured by A&T Co., Ltd. Measurement frequency: 10 GHz Measurement environment: 23℃ / 50%RH

[0169] <Evaluation of bending resistance> The bending resistance of the PI films obtained in the examples and comparative examples was evaluated by measuring the number of times the film was 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 set in an MIT bending fatigue tester (MIT-DA, manufactured by Toyo Seiki Seisakusho Co., Ltd.) compliant with ASTM standard D2176-16, and the film was folded alternately in both directions under the conditions of a test speed of 175 cpm, a bending angle of 135°, a load of 750 g, and a bending clamp radius of R=1.0 mm, and the number of folds until breakage was measured. A higher number of folds indicates better bending resistance.

[0170] Table 1 shows the measurement and evaluation results, as well as the amine ratios, for the PI resin precursor, PI resin, and PI film obtained in the examples and comparative examples. In Table 1, CTE × (E') 1 / 2 This is the CTE of the PI film × (E' of the PI resin at 280°C) 1 / 2 This indicates.

[0171] [Table 1]

[0172] As shown in Table 1, the PI films obtained from the PI resin precursors of Examples 1 to 11 were found to have lower Df and superior flexural resistance compared to the comparative examples, even when the maximum imidization temperature was as low as 270°C or 320°C. Therefore, even when the PI-based film obtained from the PI-based resin precursor of the present invention is manufactured by casting a PI resin precursor solution onto a metal foil such as copper foil and then thermally imidizing the PI resin precursor solution coating on the metal foil, thermal degradation such as surface roughening of the metal foil can be suppressed. As a result, it can be suitably used in CCLs that are compatible with high-frequency bands, have low transmission loss and excellent flexural resistance, and are applicable to foldable devices. Consequently, an FPC with low dielectric loss can be provided. In addition, by using the PI resin precursor of the present invention, even if imidation is performed in a laminated configuration with metal foil such as copper foil, it becomes possible to manufacture FPC without exposing the metal foil to high temperatures. This suppresses surface roughness and oxidation of the metal foil, and reduces conductor loss, thus providing an FPC with suppressed transmission loss, which is the sum of dielectric loss and conductor loss. Furthermore, since the metal foil such as copper foil is not exposed to high temperatures, the decrease in bending resistance due to the increase in crystal grain size of the metal foil caused by heating can be suppressed, and an FPC with excellent bending resistance can be provided in which both the PI film and the metal foil can withstand continuous bending.

Claims

1. A polyimide resin precursor comprising a tetracarboxylic acid anhydride-derived structural unit (A) and a diamine-derived structural unit (B), the structural unit (A) includes a structural unit (A1) derived from an ester bond-containing tetracarboxylic acid anhydride and a structural unit (A2) derived from a biphenyl skeleton-containing tetracarboxylic acid anhydride, The structural unit (A) has 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))<0.67 (X) Fulfilling the relationship, the structural unit (B) includes a structural unit (B1) derived from a biphenyl skeleton-containing diamine, and the content of the structural unit (B1) exceeds 30 mol% with respect to the total amount of the structural unit (B); The polyimide resin precursor has a weight average molecular weight in terms of polystyrene of more than 100,000.

2. 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.

2. The polyimide resin precursor according to claim 1, wherein the structural unit (a1) is derived from a tetracarboxylic acid anhydride represented by the following formula:

3. 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.

2. The polyimide resin precursor according to claim 1, wherein the structural unit (a2) is derived from a tetracarboxylic acid anhydride represented by the following formula:

4. 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.

2. The polyimide resin precursor according to claim 1, wherein the structural unit (b1) is derived from a diamine represented by the following formula:

5. 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 is an integer from 1 to 4, and q each independently represents an integer of 0 to 4. The polyimide resin precursor according to claim 1, further comprising a structural unit (b2) derived from a diamine represented by the following formula:

6. In the structural unit (b2), m is 3, and each W is independently —O— or —C(CH ３ ) ２ The polyimide resin precursor according to claim 5, wherein

7. A polyimide resin obtained from the polyimide resin precursor according to claim 1.

8. The polyimide resin according to claim 7, which has a glass transition temperature of 200 to 290°C.

9. The storage modulus at 280°C is 3 x 10 ８ The polyimide resin according to claim 7, wherein the viscosity is less than 100 Pa.

10. A polyimide film comprising the polyimide resin according to claim 7.

11. The polyimide film according to claim 10, which has a dielectric loss tangent at 10 GHz of 0.004 or less.

12. A laminated film comprising the polyimide film according to claim 10 or 11 and a metal foil layer on one or both sides thereof.

13. A flexible printed circuit board comprising the polyimide film according to claim 10 or 11.

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