Method for manufacturing conductive member, and conductive member

Abstract

This method for manufacturing a conductive member includes: having a powder adhered to the surface of a metal member by an electrostatic coating method, the powder containing a thermoplastic polyimide that includes a structural unit represented by formula (1); and forming an insulating coating film by heating the adhered powder and melting the powder. With respect to the IR spectrum of the insulating coating film, the ratio I1487 / I1778 of the absorption intensity I1487 at 1487 cm- 1 to the absorption intensity I1778 at 1778 cm- 1 is 3.0 to 5.0 and / or the ratio I1232 / I1778 of the absorption intensity I1232 at 1232 cm- 1 to the absorption intensity I1778 at 1778 cm- 1 is 3.0 to 5.0.

Description

Conductive member manufacturing method and conductive member

[0001] The present disclosure relates to a method for manufacturing a conductive member and a conductive member.

[0002] Polyimide generally has excellent heat resistance and insulating properties at high temperatures, and therefore polyimide is being considered as a material for forming insulating layers of conductive members such as bus bars.

[0003] For example, Patent Document 1 discloses that a powder coating of a thermoplastic polyimide polymer is applied to a pipe using a fluidized bed method to form a coating having heat resistance, weather resistance, and corrosion resistance. Note that the fluidized bed method requires strict control of the particle shape and particle size of the powder coating.

[0004] Patent Document 1: Japanese Unexamined Patent Publication No. 4-339880

[0005] In addition to the fluidized bed coating method, electrostatic coating is also known as a method for forming coatings using powder paint. Electrostatic coating involves spraying charged powder particles onto a desired substrate, thereby adhering the powder to the substrate. After adhering the powder to form a powder layer on the substrate, the powder layer is heated to melt the particles contained in the powder layer, smoothing the powder layer and forming a coating (also referred to as a paint film). Electrostatic coating can form thin coatings with high thickness uniformity on substrates with complex shapes, such as curved shapes or shapes with variable thickness or width. However, in conventional electrostatic coating methods, after spraying the powder onto the substrate, the powder layer is heated (i.e., annealed) at a relatively high temperature for a long period of time to smooth or homogenize it. Therefore, depending on the powder components, heating may not produce a coating with the desired physical properties.

[0006] The present disclosure has been made in view of the above, and relates to a method for manufacturing a conductive member in which a decrease in breakdown voltage is suppressed, and a conductive member manufactured by the manufacturing method.

[0007] Specific means for solving the above problems include the following aspects: <1> A method for forming an insulating coating comprising: attaching a powder containing a thermoplastic polyimide having a structural unit represented by the following formula (1) to the surface of a metal member by electrostatic coating; and heating the attached powder to melt the powder and form an insulating coating, wherein the insulating coating has a peak at 1487 cm in the IR spectrum of the insulating coating. －１ Absorption intensity I １４８７ and 1778 cm －１ Absorption intensity I １７７８ Relative to I １４８７ / I １７７８ is 3.0 to 5.0 and 1232 cm －１ Absorption intensity I １２３２ and 1778 cm －１ Absorption intensity I １７７８ Relative to I １２３２ / I １７７８ and the value is 3.0 to 5.0.

[0008]

[0009]

[0010] In the formula (1), X represents a direct bond, —SO ２ -, -CO-, -C(CH ３ ) ２ -, -C(CF ３ ) ２ - or -S-. R1, R2, R3, and R4 each independently represent a hydrogen atom, an alkyl group, an alkoxy group, a halogenated alkyl group, a halogenated alkoxy group, or a halogen atom. In the formula (1), Y is a group represented by any of the formulas (2-1) to (2-4). In the formulas (2-1) to (2-4), * represents a bond, and the aromatic ring may have a substituent.

[0011] <2> The method for producing a conductive member according to <1>, wherein the heating temperature is 390°C to 430°C. <3> The method for producing a conductive member according to <1> or <2>, wherein the heating time is longer than 0 minutes and shorter than or equal to 30 minutes. <4> The method for producing a conductive member according to any one of <1> to <3>, wherein the powder satisfies at least one of a particle diameter d50 corresponding to 50% of the cumulative particle size distribution on a volume basis of 5 μm to 100 μm and a particle diameter d90 corresponding to 90% of the cumulative particle size distribution on a volume basis of 10 μm to 200 μm. <5> The method for producing a conductive member according to any one of <1> to <4>, wherein the material of the metal member is any one of copper, copper alloy, iron, iron alloy including steel, aluminum, and aluminum alloy. <6> The method for producing a conductive member according to any one of <1> to <5>, wherein the metal member is a surface-treated metal member. <7> The method for producing a conductive member according to any one of <1> to <6>, wherein the insulating coating has a thickness of 5 μm to 1000 μm. <8> A conductive member comprising a metal member and an insulating coating covering at least a part of a surface of the metal member, wherein the insulating coating contains a thermoplastic polyimide containing a structural unit represented by the following formula (1), and wherein the insulating coating has a peak at 1487 cm in an IR spectrum: －１ Absorption intensity I １４８７ and 1778 cm －１ Absorption intensity I １７７８ Relative to I １４８７ / I １７７８ is 3.0 to 5.0 and 1232 cm －１ Absorption intensity I １２３２ and 1778 cm －１ Absorption intensity I １７７８ Relative to I １２３２ / I １７７８ and a value of 3.0 to 5.0.

[0012]

[0013]

[0014] In the formula (1), X represents a direct bond, —SO ２ -, -CO-, -C(CH ３ ) ２ -, -C(CF ３ )２ - or -S-. R1, R2, R3, and R4 each independently represent a hydrogen atom, an alkyl group, an alkoxy group, a halogenated alkyl group, a halogenated alkoxy group, or a halogen atom. In the formula (1), Y represents a group represented by any one of the formulas (2-1) to (2-4). In the formulas (2-1) to (2-4), * represents a bond, and the aromatic ring may have a substituent. <9> The conductive member according to <8>, wherein the material of the metal member is any one of copper, a copper alloy, aluminum, and an aluminum alloy. <10> The conductive member according to <8>, wherein the material of the metal member is copper or a copper alloy. <11> The conductive member according to any one of <8> to <10>, wherein, when a cross-cut test in accordance with ISO 2409:1992 is performed, the proportion of the number of squares in which the insulating coating did not peel off from the metal member is 80% or more of the total number of squares.

[0015] According to the present disclosure, there are provided a method for manufacturing a conductive member in which a decrease in breakdown voltage is suppressed, and a conductive member manufactured by the manufacturing method.

[0016] An embodiment of the present disclosure will be described in detail below. However, the present disclosure is not limited to the following embodiment. In the following disclosure, components (including element steps, etc.) are not essential unless otherwise specified. The same applies to numerical values ​​and their ranges, and do not limit the present disclosure.

[0017] In the present disclosure, when a numerical range is indicated using "to", the numerical values ​​before and after "to" are included as the lower and upper limits, respectively. In the present disclosure, when a numerical range is described in stages, the upper or lower limit of one numerical range may be replaced with the upper or lower limit of another staged numerical range. Furthermore, in the present disclosure, the upper or lower limit of that numerical range may be replaced with a value shown in the examples. In the present disclosure, when multiple substances corresponding to each component are present in the composition, the content of each component refers to the total content of the multiple substances present in the composition, unless otherwise specified. In the present disclosure, when multiple elements are listed using "or", this does not exclude the combination of multiple elements unless a technical contradiction occurs, unless otherwise specified. In the present disclosure, when an element is described in the singular, this does not exclude the presence of multiple elements unless a technical contradiction occurs, unless otherwise specified. In the present disclosure, multiple exemplary embodiments described separately may be combined with each other to form a new embodiment, unless mutually contradictory.

[0018] <<Method for manufacturing conductive member>> A method for manufacturing a conductive member according to the present disclosure includes: attaching a powder containing a thermoplastic polyimide having a structural unit represented by the following formula (1) to a surface of a metal member by electrostatic coating; and heating the attached powder to melt the powder and form an insulating coating, wherein the insulating coating has a peak at 1487 cm in an IR spectrum thereof: －１ Absorption intensity I １４８７ and 1778 cm －１ Absorption intensity I １７７８ Relative to I １４８７ / I １７７８ is 3.0 to 5.0 and 1232 cm －１ Absorption intensity I １２３２ and 1778 cm －１ Absorption intensity I １７７８ Relative to I １２３２ / I １７７８ is 3.0 to 5.0.

[0019]

[0020]

[0021] In the formula (1), X represents a direct bond, —SO ２ -, -CO-, -C(CH ３ ) ２ -, -C(CF ３ ) ２ - or -S-. R1, R2, R3, and R4 each independently represent a hydrogen atom, an alkyl group, an alkoxy group, a halogenated alkyl group, a halogenated alkoxy group, or a halogen atom. In the formula (1), Y is a group represented by any of the formulas (2-1) to (2-4). In the formulas (2-1) to (2-4), * represents a bond, and the aromatic ring may have a substituent.

[0022] According to the method for manufacturing a conductive member of the present disclosure, a method for manufacturing a conductive member in which a decrease in breakdown voltage is suppressed is provided. Although the effect of the method for manufacturing a conductive member of the present disclosure is not clear, it is presumed as follows.

[0023] As described above, when using electrostatic coating, a powder is sprayed onto a substrate, and then heated at a relatively high temperature for a long period of time to melt the powder, thereby forming a smooth coating. However, depending on the powder components, the components of the powder may change due to decomposition or the like upon heating, making it impossible to obtain a coating having the desired physical properties. In this situation, the present inventors have discovered a new problem that when an insulating coating is formed by electrostatic coating using a powder containing a thermoplastic polyimide having a structural unit represented by formula (1), the breakdown voltage of the formed coating decreases upon heating after electrostatic coating, and have discovered a method for producing a conductive member in which the decrease in breakdown voltage is suppressed.

[0024] In the method for producing a conductive member according to the present disclosure, electrostatic coating and subsequent heating are performed. －１ and the absorption intensity of 1778 cm －１ The ratio of the absorption intensity of １４８７ / I １７７８ is 3.0 to 5.0 and 1232 cm －１ and the absorption intensity of 1778 cm－１ The ratio of the absorption intensity of １２３２ / I １７７８ Since the heating is carried out so as to satisfy at least one of the above conditions: (a) the temperature is 3.0 to 5.0; and (b) the temperature is 3.0 to 5.0, the decrease in the breakdown voltage is suppressed.

[0025] In the IR spectrum, 1778 cm －１ The absorption peak appearing at 1487 cm is a peak derived from the imide group (O=C-N-C=O). －１ The absorption peak appearing at 1232 cm is a peak derived from the carbon-carbon double bond (C=C) in the aromatic ring. －１ The absorption peak appearing in the graph is a peak derived from an ether bond (—O—).

[0026] When a powder containing a thermoplastic polyimide having a structural unit represented by formula (1) is heated, decomposition of the thermoplastic polyimide may occur depending on heating conditions such as heating temperature and heating time. In this case, typically, among the structural units represented by formula (1), decomposition of the aromatic ring or cleavage of the ether bond is likely to occur. On the other hand, the imide group contained in the structural unit represented by formula (1) has higher thermal stability than the aromatic ring or the ether bond, and therefore is relatively resistant to decomposition or cleavage.

[0027] Therefore, the above ratio I １４８７ / I １７７８ It can be said that the ratio I is an index representing the degree of decomposition of the aromatic ring in the thermoplastic polyimide containing the structural unit represented by the above formula (1). １２３２ / I １７７８ It can be said that the ratio I is an index representing the degree of scission of ether bonds in a thermoplastic polyimide containing the structural unit represented by the above formula (1). １４８７ / I １７７８ is 3.0 to 5.0, and the ratio I １２３２ / I １７７８ is 3.0 to 5.0, this indicates that decomposition of the aromatic ring or cleavage of the ether bond is suppressed in the thermoplastic polyimide containing the structural unit represented by the above formula (1).

[0028] From the above, in the present disclosure, a coating film that is a melt of a thermoplastic polyimide containing a structural unit represented by formula (1) is suppressed from decreasing in breakdown voltage. Note that the present disclosure is not limited to the above-mentioned assumed mechanism.

[0029] <Electrostatic Coating Method> The method for producing a conductive member according to the present disclosure includes attaching a powder containing a thermoplastic polyimide having a structural unit represented by the above formula (1) to the surface of a metal member by an electrostatic coating method. In the present disclosure, the electrostatic coating method is not particularly limited as long as it can attach a powder containing a thermoplastic polyimide having a structural unit represented by the above formula (1) to the surface of the metal member.

[0030] [Powder] (Thermoplastic polyimide containing a structural unit represented by formula (1)) —Structural unit represented by formula (1)— The powder of the present disclosure contains a thermoplastic polyimide containing a structural unit represented by the following formula (1). The powder of the present disclosure preferably contains a plurality of particles containing a thermoplastic polyimide containing a structural unit represented by the following formula (1).

[0031]

[0032] In the formula (1), X represents a direct bond, —SO ２ -, -CO-, -C(CH ３ ) ２ -, -C(CF ３ ) ２ From the viewpoint of suppressing a decrease in the breakdown voltage, X is a direct bond, —C(CH ３ ) ２ -, or -C(CF ３ ) ２ Preferably, X is -, and more preferably a direct bond. A direct bond means that two aromatic rings adjacent to X are bonded by a carbon-carbon single bond. In other words, when X is a direct bond, it means that X does not exist.

[0033] In the formula (1), R1, R2, R3, and R4 each independently represent a hydrogen atom, an alkyl group, an alkoxy group, a halogenated alkyl group, a halogenated alkoxy group, or a halogen atom.

[0034] The alkyl group may be linear or branched. The number of carbon atoms in the alkyl group is preferably 1 to 40, and more preferably 1 to 10. Examples of the alkyl group include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a tert-butyl group, an n-pentyl group, an isoamyl group, a 2-ethylbutyl group, and an n-hexyl group.

[0035] The alkoxy group may be linear or branched. Examples of the alkoxy group include a methoxy group, an ethoxy group, an n-propyloxy group, an isopropyloxy group, an n-butyloxy group, an isobutyloxy group, a tert-butyloxy group, an n-pentyloxy group, and an n-hexyloxy group.

[0036] The halogenated alkyl group is preferably a group in which a hydrogen atom in the above-mentioned alkyl group is substituted with a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom. Examples of the halogenated alkyl group include a fluoromethyl group and a trifluoromethyl group.

[0037] The halogenated alkoxy group is preferably a group in which a hydrogen atom in the above-mentioned alkoxy group is substituted with a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom. Examples of the halogenated alkoxy group include a fluoromethoxy group.

[0038] Examples of halogen atoms include fluorine atoms, chlorine atoms, bromine atoms, and iodine atoms.

[0039] From the viewpoint of suppressing a decrease in breakdown voltage, R1, R2, R3, and R4 are each preferably independently a hydrogen atom or a methyl group, more preferably a hydrogen atom. R1, R2, R3, and R4 may be the same as or different from each other, but from the viewpoint of ease of synthesis, they are preferably the same as each other.

[0040] In the formula (1), Y is a group represented by any one of the following formulas (2-1) to (2-4): In the following formulas (2-1) to (2-4), * represents a bond, and the aromatic ring may have a substituent.

[0041]

[0042] From the viewpoint of suppressing a decrease in breakdown voltage, Y is preferably a group represented by formula (2-1) or formula (2-3), and more preferably represented by formula (2-1).

[0043] It should be noted that when Y in the formula (1) is a group represented by formula (2-1) among formulas (2-1) to (2-4), the melting point of the thermoplastic polyimide is likely to be highest. Therefore, when Y is a group represented by formula (2-1), the heating temperature required to form the coating is likely to be highest, and therefore, it can be said that it is likely to be decomposed when melted by heating to form the coating. Therefore, if a decrease in breakdown voltage is suppressed in an insulating coating of a conductive member produced using a thermoplastic polyimide that uses a group represented by formula (2-1), it can be said that a decrease in breakdown voltage is also sufficiently suppressed for thermoplastic polyimides that use groups represented by formulas (2-2) to (2-4).

[0044] The substituent that the aromatic ring in formula (2-1) to formula (2-4) may have is preferably a hydrogen atom, an alkyl group, an alkoxy group, a halogenated alkyl group, a halogenated alkoxy group, or a halogen atom. When the aromatic ring in formula (2-1) to formula (2-4) has multiple substituents, the substituents may be the same or different.

[0045] In the present disclosure, the term "thermoplastic polyimide" refers to a polyimide having thermoplastic properties. The thermoplastic polyimide is preferably a polyimide having a deflection temperature under load of 200°C or higher.

[0046] Examples of thermoplastic polyimides containing a structural unit represented by formula (1) include thermoplastic polyimides containing a structural unit represented by formula (3) below, thermoplastic polyimide copolymers containing structural units represented by formulas (4) and (5) below, and thermoplastic polyimide copolymers containing structural units represented by formulas (6) and (7) below.

[0047]

[0048]

[0049]

[0050] Here, m in the above formula (4) and n in the formula (5) represent the copolymerization ratio of the thermoplastic polyimide copolymer, and m / n (mol % / mol %) is preferably 4 to 99, more preferably 5 to 50, even more preferably 6 to 20, particularly preferably 7 to 15, and most preferably 9.

[0051]

[0052]

[0053] Here, p in the above formula (6) and q in the formula (7) represent the copolymerization ratio of the thermoplastic polyimide copolymer, and p / q (mol % / mol %) is preferably 0.01 to 100, more preferably 0.1 to 50, even more preferably 0.3 to 10, particularly preferably 0.5 to 3, and most preferably 1.

[0054] The thermoplastic polyimide containing the structural unit represented by formula (1) is preferably a thermoplastic polyimide resin composed of the structural unit represented by formula (1). A coating formed from the thermoplastic polyimide containing the structural unit represented by formula (1) has excellent electrical properties and heat resistance.

[0055] The thermoplastic polyimide containing the structural unit represented by formula (1) is preferably a thermoplastic polyimide containing the structural unit represented by formula (3), and more preferably a thermoplastic polyimide consisting of the structural unit represented by formula (3). A coating formed from a thermoplastic polyimide containing the structural unit represented by formula (3) has superior electrical properties and heat resistance.

[0056] The thermoplastic polyimide containing the structural unit represented by formula (1) is also preferably a thermoplastic polyimide copolymer containing structural units represented by formula (4) and formula (5), and more preferably a thermoplastic polyimide consisting of structural units represented by formula (4) and formula (5).

[0057] The thermoplastic polyimide containing the structural unit represented by formula (1) is also preferably a thermoplastic polyimide copolymer containing the structural units represented by formula (6) and formula (7), and more preferably a thermoplastic polyimide consisting of the structural units represented by formula (6) and formula (7).

[0058] In a thermoplastic polyimide containing a structural unit represented by formula (1), the structural unit represented by formula (1) may be one to ten types, one to five types, one or two types, or only one type.

[0059] —Structural Unit Represented by Other Than Formula (1)— The thermoplastic polyimide containing the structural unit represented by formula (1) may be a thermoplastic polyimide copolymer comprising the structural unit represented by formula (1) and a structural unit represented by a formula other than formula (1).

[0060] The structural unit other than that represented by formula (1) may be, for example, a structural unit derived from an aromatic hydrocarbon which may have a substituent, or a structural unit derived from an aliphatic hydrocarbon which may have a substituent. Examples of the substituent include a halogen atom, a carboxy group, a carbonyl group, an alkoxy group, an amino group, an amide group, an epoxy group, a (meth)acryloyl group, a vinyl group, and a sulfo group. The compound may have a plurality of substituents, and when a plurality of substituents are present, the substituents may be the same or different from each other.

[0061] -Number Average Molecular Weight of Thermoplastic Polyimide- The number average molecular weight of the thermoplastic polyimide containing the structural unit represented by formula (1) is preferably 3,000 to 100,000, more preferably 4,000 to 70,000, and even more preferably 5,000 to 40,000. In the present disclosure, the number average molecular weight is measured by gel permeation chromatography (GPC).

[0062] In the present disclosure, the number average molecular weight can be measured using gel permeation chromatography (GPC). Specifically, 1.5 mL of 4-chlorophenol was added to 5 mg of sample and gently stirred at 130-140°C. The resulting solution was air-cooled to room temperature, and 3.5 mL of chloroform was added. The solution was then filtered using a 0.2 μm filter to prepare a sample solution. Measurements were performed using the prepared sample solution under the following conditions: Detector: Differential Refractive Index Detector RI (RI-8020, manufactured by Tosoh Corporation) Columns: Two TSKgel GMHXL columns, one G2500HXL column (7.8 mm ID x 300 mm, manufactured by Tosoh Corporation) Column temperature: 23°C Solvent: 4-chlorophenol / chloroform (3 / 7) (volume / volume) Flow rate: 0.8 mL / min, sample concentration: 1 mg / ml, injection volume: 0.3 mL Standard sample: Monodisperse polystyrene manufactured by Tosoh Corporation

[0063] -Melt Index of Thermoplastic Polyimide- The melt index (hereinafter also referred to as "MI") of a thermoplastic polyimide containing a structural unit represented by formula (1) is not particularly limited, but is preferably 2 g / 10 min to 30 g / 10 min, more preferably 4 g / 10 min to 20 g / 10 min. In the present disclosure, MI can be measured using a melt indexer (manufactured by Toyo Seiki Seisaku-sho, Ltd., model number: A-371401705). Specifically, it can be measured in accordance with JIS K7210 (ISO 1133) under conditions of a cylinder temperature of 400°C and a load of 1.05 kg. The unit of MI is g / 10 min.

[0064] - Logarithmic Viscosity of Thermoplastic Polyimide - The logarithmic viscosity of the thermoplastic polyimide containing the structural unit represented by formula (1) is not particularly limited, but is preferably 0.1 dl / g to 3.0 dl / g, more preferably 0.2 dl / g to 2.0 dl / g, even more preferably 0.3 dl / g to 1.5 dl / g, and particularly preferably 0.4 dl / g to 1.0 dl / g. When the logarithmic viscosity is 0.1 dl / g to 3.0 dl / g, the molecular weight of the thermoplastic polyimide is more preferable, and the thermoplastic polyimide has excellent fluidity, making it easier to form a smoother coating, and the mechanical strength of the formed coating is also excellent.

[0065] The inherent viscosity is measured by heating a solution in a mixed solvent of parachlorophenol / phenol (90 / 10 weight ratio) at a concentration of 0.5 g / 100 ml to 200° C. and then cooling it to 35° C. The definition of inherent viscosity is given in "Polymer Handbook," published by Asakura Shoten and edited by the Japan Society for Analytical Chemistry, 1995, first edition, p. 58.

[0066] -Glass Transition Temperature Tg of Thermoplastic Polyimide- The lower limit of the glass transition temperature Tg of a thermoplastic polyimide containing a structural unit represented by formula (1) is not particularly limited, and from the viewpoint of heat resistance, it is preferably 200°C or higher, more preferably 210°C or higher, and even more preferably 220°C or higher. The upper limit of the glass transition temperature Tg is not particularly limited, and is preferably 300°C or lower, more preferably 290°C or lower, and even more preferably 280°C or lower. The upper limit of the glass transition temperature Tg may be 270°C or lower, 260°C or lower, 250°C or lower, or 240°C or lower.

[0067] In the present disclosure, the glass transition temperature Tg can be measured using a differential scanning calorimeter (DSC220C, manufactured by Seiko Instruments Inc.). Specifically, approximately 5 mg of material is sealed in a measurement aluminum pan and set in the differential scanning calorimeter. Then, it is heated from room temperature to 450°C at 10°C / min. To completely melt the substance to be measured, it is held at 450°C for 5 minutes, and then cooled to 30°C at 10°C / min. After leaving it at 30°C for 5 minutes, it is heated a second time to 450°C at 10°C / min. The inflection point corresponding to the glass transition is taken as the glass transition temperature (Tg).

[0068] -Melting Point of Thermoplastic Polyimide- The lower limit of the melting point of the thermoplastic polyimide containing the structural unit represented by formula (1) is not particularly limited, and from the viewpoint of heat resistance, it is preferably 340°C or higher, more preferably 350°C or higher, even more preferably 360°C or higher, still more preferably 370°C or higher, even more preferably 380°C or higher, and still more preferably 385°C or higher. The upper limit of the melting point of the thermoplastic polyimide resin is not particularly limited, and from the viewpoint of moldability, it is preferably 430°C or lower, more preferably 420°C or lower, even more preferably 410°C or lower, still more preferably 400°C or lower, even more preferably 395°C or lower, and still more preferably 390°C or lower. In the present disclosure, the melting point can be measured using a DSC (differential scanning calorimeter, DT-40 series, "DSC-41M", manufactured by Shimadzu Corporation).

[0069] -Method of Obtaining Thermoplastic Polyimide- {Synthesis} A thermoplastic polyimide containing a structural unit represented by formula (1) can be synthesized by reacting an aromatic diamine compound (e.g., a compound represented by formula (8) below) with an aromatic tetracarboxylic dianhydride (e.g., a compound represented by formula (9) below) as raw materials in the presence or absence of an organic solvent, and imidizing the resulting polyamic acid. For production, conditions for known polyimide production methods can be utilized. At least one of the aromatic diamine compound and the aromatic tetracarboxylic dianhydride may be a biomass-derived compound, at least a portion of which is derived from biomass as a raw material. That is, the thermoplastic polyimide containing a structural unit represented by formula (1) of the present disclosure may be a biomass-derived thermoplastic polyimide.

[0070]

[0071] In the above formula (8), the definitions of X and R1 to R4 are the same as those of X and R1 to R4 in the above formula (1).

[0072]

[0073] In the above formula (9), the definition of Y is the same as the definition of Y in the above formula (1). When Y is formula (2-1) having no substituent on the aromatic ring, the aromatic tetracarboxylic dianhydride of formula (9) is formula (11) described later, and formula (11) is pyromellitic dianhydride.

[0074] More specifically, a thermoplastic polyimide containing a structural unit represented by formula (1) can be synthesized by the following method: A diamine (4,4'-bis(3-aminophenoxy)biphenyl (m-BP)) represented by the following formula (10) and a tetracarboxylic dianhydride (pyromellitic dianhydride (PMDA)) represented by the following formula (11) are subjected to dehydration co-condensation to obtain a thermoplastic polyimide containing a structural unit represented by formula (3).

[0075]

[0076]

[0077] The thermoplastic polyimide containing the structural unit represented by formula (1) can be synthesized by a known imidization reaction.

[0078] The amount of the raw material compound used is usually 0.90 to 0.99 equivalents of tetracarboxylic dianhydride per equivalent of diamine. The amount of the raw material compound used is preferably 0.93 to 0.985 equivalents, more preferably 0.95 to 0.98 equivalents. When the amount of the raw material compound used is 0.90 to 0.99 equivalents, the molecular weight of the thermoplastic polyimide becomes sufficiently high, and the thermoplastic polyimide has excellent fluidity, making it easier to form a smoother coating, and the mechanical strength of the formed coating is also excellent.

[0079] In the synthesis of thermoplastic polyimides, it is preferable to cap the reactive terminals of the molecules with phthalic anhydride, etc. By capping the reactive terminals, the thermal stability of the thermoplastic polyimide resin is significantly improved.

[0080] The reaction is particularly preferably carried out in an organic solvent. Examples of organic solvents include N,N-dimethylformamide, N,N-diethylacetamide, N,N-dimethoxyacetamide, N-methyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, N-methylcaprolactam, 1,2-dimethoxyethane, bis(2-methoxyethyl)ether, 1,2-bis(2-methoxyethoxy)ethane, bis[2-(2-methoxyethoxy)ethyl]ether, tetrahydrofuran, 1,3-dioxane, 1,4-dioxane, pyrroline, picoline, dimethyl sulfoxide, dimethyl sulfone, tetramethylurea hexamethylphosphoramide, phenol, o-cresol, m-cresol, p-cresol, p-chlorophenol, anisole, benzene, toluene, and xylene. The organic solvents may be used alone or in combination.

[0081] The reaction temperature is usually room temperature (e.g., 25°C) to 250°C, preferably 140°C to 200°C. The reaction pressure is not particularly limited, and normal pressure is sufficient. The reaction time varies depending on the type of solvent and the reaction temperature, but is usually preferably 4 to 24 hours. As for the imidization method, the precursor polyamic acid is heated to 100°C to 300°C for imidization, or chemically imidized using an imidizing agent such as acetic anhydride, to obtain the desired thermoplastic polyimide.

[0082] {Commercially Available Products} The thermoplastic polyimide containing the structural unit represented by formula (1) may be a commercially available product. Examples of commercially available thermoplastic polyimides containing the structural unit represented by formula (1) include AURUM (registered trademark) PD400, PD450, PD500A, and PD500M (all manufactured by Mitsui Chemicals, Inc.).

[0083] (Additives) The particles contained in the powder of the present disclosure may contain a component (i.e., an additive) other than the thermoplastic polyimide containing the structural unit represented by formula (1). The additive is not particularly limited, and may be, for example, at least one selected from the group consisting of carbon fiber, glass fiber, potassium titanate fiber, aluminum borate fiber, metal fiber, ceramic fiber, boron fiber, silicon carbide fiber, asbestos fiber, rock wool fiber, and aramid fiber.

[0084] The additives may optionally contain at least one of the following fillers, such as mica, synthetic mica, wollastonite, talc, silicone oil, fluorine-based oil, glass beads, molybdenum disulfide, clay, silica, alumina, diatomaceous earth, hydrated alumina, shirasu balloons, carbon nanotubes, calcium carbonate, hydrotalcite, fluorine, graphite (e.g., artificial graphite, natural graphite (e.g., flake graphite, scaly graphite, earthy graphite)), metal particles (e.g., metals, alloys), pigment particles (e.g., inorganic pigments, organic pigments), lubricants, release agents, stabilizers, colorants, crystal nucleating agents, ultraviolet absorbers, infrared reflectors, infrared absorbers, or antireflection agents, within the range that does not impair the properties of the thermoplastic polyimide.

[0085] The additive may contain, as needed, at least one of various liquid crystal polymers, thermoplastic resins (e.g., fluororesin, polyetherimide, polyethernitrile, polyetherketone, polyetheretherketone, polyetherketoneketone, polyetherketoneetherketoneketone, polyamideimide, polyethersulfone, polysulfone, polyarylate and / or polyphenylene sulfide), or thermosetting resins (e.g., epoxy resin, polybenzimidazole resin, polyimide resin, etc.) within a range that does not impair the properties of the thermoplastic polyimide.

[0086] When the particles contained in the powder of the present disclosure contain an additive, the content of the additive and the content of the thermoplastic polyimide are not particularly limited and are selected appropriately depending on the type of additive, etc.

[0087] The content of the thermoplastic polyimide containing the structural unit represented by formula (1) in the particles contained in the powder of the present disclosure is preferably 50% by mass to 100% by mass, more preferably 60% by mass to 100% by mass, even more preferably 70% by mass to 100% by mass, even more preferably 80% by mass to 100% by mass, and even more preferably 90% by mass to 100% by mass. That is, the content of the additive in the particles contained in the powder of the present disclosure is preferably 0% by mass to 50% by mass, more preferably 0% by mass to 40% by mass, even more preferably 0% by mass to 30% by mass, even more preferably 0% by mass to 20% by mass, and even more preferably 0% by mass (i.e., not contained) to 10% by mass, from the viewpoint of more excellent electrical properties and heat resistance.

[0088] (Particle diameter of powder) In the method for producing a conductive member of the present disclosure, the powder of the present disclosure preferably satisfies at least one of the following: a particle diameter d50 corresponding to 50% of the cumulative volume in the particle size distribution is 5 μm to 100 μm; and a particle diameter d90 corresponding to 90% of the cumulative volume in the particle size distribution is 10 μm to 200 μm. By making the particle diameter of the powder uniform, it becomes easier to produce a conductive member with uniform thickness and high surface smoothness. From the viewpoint of producing a conductive member with uniform thickness and high surface smoothness, it is more preferable that the powder of the present disclosure satisfies both the particle diameter d50 corresponding to 50% of the cumulative volume in the particle size distribution is 5 μm to 100 μm, and the particle diameter d90 corresponding to 90% of the cumulative volume in the particle size distribution is 10 μm to 200 μm.

[0089] In the present disclosure, the particle size at which the cumulative percentage in the volume-based particle size distribution is a given percentage is measured by a laser diffraction scattering method (wet). More specifically, the powder is mixed with distilled water (Fujifilm Wako Pure Chemical Industries, Ltd., refractive index 1.33) and dispersed for 2 minutes at an output of 25 W using an ultrasonic homogenizer built into the device. Then, the particle size is measured using a laser diffraction / scattering particle size distribution analyzer (Microtrac, model: Microtrac MT3300EXII) under the following particle conditions: transmittance: transparent, refractive index: 1.81, shape: aspherical

[0090] The particle diameter d50 at cumulative 50% in the volume-based particle size distribution is more preferably 5 μm to 100 μm, even more preferably 10 μm to 70 μm, and particularly preferably 20 μm to 40 μm.

[0091] The particle diameter d90 at 90% cumulative concentration in the volume-based particle size distribution is more preferably 10 μm to 200 μm, even more preferably 25 μm to 150 μm, and particularly preferably 40 μm to 100 μm.

[0092] (Particle Shape of Powder) Examples of the particle shape of the powder include spherical, elliptical, needle-like, plate-like, rod-like, conical, cylindrical, cubic, rectangular, diamond-like, star-like, and irregular shapes. The powder particles may be solid particles, hollow particles, or perforated particles such as porous particles.

[0093] (Thermoplastic polyimide and additive in powder) In the present disclosure, the powder containing a thermoplastic polyimide having a structural unit represented by formula (1) may be a powder in which the thermoplastic polyimide having a structural unit represented by formula (1) and an additive are contained in the same particle. Alternatively, the powder containing a thermoplastic polyimide having a structural unit represented by formula (1) may be a mixed powder in which a powder of a thermoplastic polyimide having a structural unit represented by formula (1) and a powder of an additive are mixed.

[0094] [Metallic member] (Material) The material of the metallic member is not particularly limited. The material of the metallic member is preferably any of gold, gold alloy, silver, silver alloy, copper, copper alloy, iron, iron alloy including steel, aluminum, aluminum alloy, tungsten, or tungsten alloy. From the viewpoint of excellent conductivity and productivity, the material of the metallic member is more preferably any of copper, copper alloy, iron, iron alloy including steel, aluminum, or aluminum alloy, more preferably any of copper, copper alloy, aluminum, or aluminum alloy, and particularly preferably copper or copper alloy.

[0095] When a metal member is heated in air to approximately 400°C or higher, an oxide film is likely to form if the metal member is made of copper, a copper alloy, aluminum, or an aluminum alloy. However, the oxide film formed on copper, a copper alloy, aluminum, or an aluminum alloy is incompatible with thermoplastic polyimides containing the structural unit represented by formula (1). Therefore, if an insulating coating is formed after heating the metal member to approximately 400°C or higher, as in the conventional fluidized bed method, the insulating coating is formed on the oxide film, thereby reducing adhesion between the metal member and the insulating coating. On the other hand, in the electrostatic coating method, as in the manufacturing method of a conductive member disclosed herein, the surface of a metal member with almost no oxide film formed is covered with a powder of a thermoplastic polyimide containing the structural unit represented by formula (1), and then the metal member is heated to form an insulating coating. Therefore, even if the metal member is made of copper, a copper alloy, aluminum, or an aluminum alloy, an oxide film is unlikely to form, and adhesion between the insulating coating and the metal member can be sufficiently high.

[0096] Examples of gold alloys include alloys containing 40% or more by mass of gold, alloys containing 80% or more by mass, and alloys containing 99% or more by mass. Examples of silver alloys include alloys containing 40% or more by mass of silver, alloys containing 80% or more by mass, and alloys containing 99% or more by mass. Examples of copper alloys include alloys containing 40% or more by mass of copper, alloys containing 80% or more by mass, and alloys containing 99% or more by mass. Specific examples of copper alloys include beryllium copper, titanium copper, phosphor bronze, Corson alloy, red brass, brass, cupronickel, bronze, and nickel silver. Examples of iron alloys include alloys containing 40% or more by mass of iron, alloys containing 80% or more by mass, and alloys containing 99% or more by mass. Specific examples of iron alloys include stainless steel, mild steel, carbon steel, iron-nickel alloys, and steel. As the aluminum alloy, for example, the alloy that contains 40% by mass or more, the alloy that contains 80% by mass or more, and the alloy that contains 99% by mass or more of aluminum can be enumerated.As the tungsten alloy, for example, the alloy that contains 40% by mass or more, the alloy that contains 80% by mass or more, and the alloy that contains 99% by mass or more of tungsten can be enumerated.

[0097] The lower limit of the purity of the metal in the metal member is not particularly limited, and the purity of any of the metals gold, silver, copper, iron, aluminum, or tungsten is preferably 50.00 mass% or more, more preferably 60.00 mass% or more, even more preferably 70.00 mass% or more, particularly preferably 80.00 mass% or more, even more preferably 90.00 mass% or more, even more preferably 95.00 mass% or more, even more preferably 98.00 mass% or more, particularly more preferably 99.00 mass% or more, even more preferably 99.50 mass% or more, particularly preferably 99.90 mass% or more, and most preferably 99.95 mass% or more. The upper limit of the purity of the metal in the metal member is not particularly limited, and may be 100.00 mass%.

[0098] From the viewpoint of use as a conductive member, the copper is preferably pure copper (i.e., copper purity of 99.90% by mass or more). Examples of pure copper include oxygen-free copper (copper purity of 99.96% by mass or more), low-oxygen copper, tough pitch copper (copper purity of 99.90% by mass or more), and phosphorus-deoxidized copper (copper purity of 99.90% by mass or more). The oxygen content of low-oxygen copper is 30 ppm or less, preferably 20 ppm or less. From the viewpoint of excellent conductivity, oxygen-free copper is more preferred.

[0099] (Surface Treatment) The metal member of the present disclosure may be surface-treated to improve adhesion to the coating. The surface treatment method is not particularly limited, and examples include roughening treatment, buff polishing, UV ozone treatment, excimer treatment, alkali treatment, silane coupling agent treatment, and combinations thereof. As the surface treatment, roughening treatment is preferred to improve adhesion between the metal member and the coating. Examples of roughening treatment include dry roughening treatment and wet roughening treatment. Examples of dry roughening treatment include corona discharge treatment, plasma treatment, blasting treatment (e.g., sandblasting, blower blasting, or shot blasting), scrub polishing, and rolling treatment using an embossing roll. Examples of wet roughening treatment include etching treatment.

[0100] The arithmetic mean roughness Ra of the surface of the metal member of the present disclosure is preferably 0.01 μm to 100 μm, more preferably 0.05 μm to 50 μm, and even more preferably 0.1 μm to 30 μm. In the present disclosure, the arithmetic mean roughness Ra of the surface can be measured in accordance with JIS B 0601-1994 (ISO 4287:1997) using a surface roughness meter (Mitutoyo Corporation, Surftest SV-3200).

[0101] (Shape) The shape of the metal member is not particularly limited and may be, for example, a plate, a rod, a coil, a ring, an L-shape, a U-shape, or a T-shape. The size of the metal member is not particularly limited and may be appropriately set depending on the application, etc.

[0102] [Electrostatic Coating] (Apparatus) A known electrostatic coating apparatus can be used for electrostatic coating. Examples of the electrostatic coating apparatus include an electrostatic spray gun such as Encore XT manufactured by Nordson.

[0103] The method for charging the powder may be a friction charging method or a corona charging method. The friction charging method is a method in which powder is subjected to a friction charging treatment and then sprayed. The corona charging method is a method in which powder is subjected to a corona discharge treatment and then sprayed.

[0104] (Voltage) The voltage applied for electrostatic coating is preferably 10 kV to 300 kV, more preferably 20 kV to 200 kV, more preferably 30 kV to 100 kV, and more preferably 50 kV to 70 kV. By applying the above voltage to the powder, the powder is charged, which increases the adhesion efficiency to the metal member and makes the thickness of the powder that adheres uniform.

[0105] (Number of times electrostatic coating is performed) In the method for producing a conductive member of the present disclosure, the number of times electrostatic coating is performed on the metal member is not particularly limited. In order to obtain a coating of a desired thickness, electrostatic coating may be performed on the metal member 1 to 10 times, 1 to 5 times, 1 to 3 times, 1 or 2 times, or only 1 time. Note that when electrostatic coating is performed multiple times, it is preferable to perform heating (i.e., annealing) as described below after each electrostatic coating.

[0106] (Powder Thickness) The thickness of the powder (powder layer) to be adhered to the metal member is preferably 1 μm to 1500 μm, more preferably 5 μm to 1000 μm, even more preferably 5 μm to 500 μm, still more preferably 10 μm to 300 μm, and even more preferably 20 μm to 200 μm. The thickness of the powder to be adhered to the metal member was measured before and after adhesion, and the thickness was measured at three different locations and averaged.

[0107] [Formation of Insulating Coating] The method for manufacturing a conductive member according to the present disclosure includes heating (i.e., annealing) the attached powder to melt the powder and form an insulating coating. The heating of the attached powder may be performed by heating the entire metal member to which the powder is attached.

[0108] (Heating) The heating condition of the attached powder is as follows: －１ Absorption intensity I １４８７ and 1778 cm －１ Absorption intensity I １７７８ Relative to I １４８７ / I １７７８ is 3.0 to 5.0 and 1232 cm －１ Absorption intensity I １２３２ and 1778 cm －１ Absorption intensity I １７７８ Relative to I １２３２ / I １７７８ The heating conditions are not particularly limited as long as they satisfy at least one of the following: and the ratio (I １４８７ / I １７７８ or I １２３２ / I １７７８ ) can be set to a desired numerical range.

[0109] From the viewpoint of suppressing a decrease in breakdown voltage, the temperature to which the adhered powder is heated is preferably 390°C to 430°C, more preferably 392°C to 420°C, even more preferably 393°C to 410°C, and particularly preferably 395°C to 405°C.

[0110] From the viewpoint of suppressing a decrease in breakdown voltage, the time for heating the adhered powder is preferably more than 0 minutes and not more than 30 minutes, more preferably 1 minute to 20 minutes, even more preferably 2 minutes to 15 minutes, and particularly preferably 3 minutes to 10 minutes.

[0111] -Melting- After the powder is attached to the surface of the metal member by electrostatic coating, a powder layer made of the powder is formed on the surface of the metal member, and by the heating, the particles containing the thermoplastic polyimide containing the structural unit represented by formula (1) melt and adjacent particles fuse together. This smoothes the powder layer and forms an insulating coating on the surface of the metal member. When the heating is carried out, the powder containing the thermoplastic polyimide containing the structural unit represented by formula (1) melts.

[0112] (Number of heating operations) In the method for producing a conductive member of the present disclosure, when electrostatic coating is performed on a metal member multiple times, as described above, it is preferable to perform heating once for each electrostatic coating operation. That is, when electrostatic coating is performed on a metal member multiple times, it is preferable to repeat electrostatic coating and heating. Since thermoplastic polyimides containing a structural unit represented by formula (1) are easily decomposed by high temperature and / or long-term heating, when heating is performed on a metal member multiple times, it is preferable that each of the multiple heating operations is within the above-mentioned preferred heating temperature range, and it is preferable that each of the multiple heating operations is within the above-mentioned preferred heating time range. It is even more preferable that the total time of the multiple heating operations is within the above-mentioned preferred heating time range.

[0113] (Insulating Coating) - Thickness of Insulating Coating - The thickness of the insulating coating is preferably 1 μm to 1500 μm, more preferably 5 μm to 1000 μm, even more preferably 5 μm to 500 μm, still more preferably 10 μm to 300 μm, and even more preferably 20 μm to 200 μm. The thickness of the insulating coating was measured by measuring the thickness of the metal before and after application, measuring the thickness at three different locations, and averaging the results. The thickness after powder application was measured by measuring the thickness of the metal member after heating.

[0114] -Arithmetic mean roughness of the insulating coating surface- The arithmetic mean roughness Ra of the insulating coating surface is preferably 0.1 μm to 100 μm, more preferably 0.3 μm to 50 μm, and even more preferably 0.5 μm to 30 μm. The arithmetic mean roughness Ra of the surface can be measured in accordance with JIS B0601-1994 (ISO 4287:1997) using a surface roughness meter (Mitutoyo Corporation, Surftest SV-3200). It is preferable to heat the adhered powder and smooth the powder layer so that the surface of the insulating coating falls within the above-mentioned arithmetic mean roughness Ra range.

[0115] -IR Spectrum of Insulation Coating- In the present disclosure, the IR spectrum can be measured by a microscopic transmission method using an infrared spectrophotometer.

[0116] In the IR spectrum of the insulating coating, from the viewpoint of suppressing a decrease in the breakdown voltage, －１ Absorption intensity I １４８７ and 1778 cm －１ Absorption intensity I １７７８ Relative to I １４８７ / I １７７８ is 3.0 to 5.0 and 1232 cm －１ Absorption intensity I １２３２ and 1778 cm －１ Absorption intensity I １７７８ Relative to I １２３２ / I １７７８ and the IR spectrum of the insulating coating is preferably 1487 cm from the viewpoint of suppressing a decrease in the breakdown voltage. －１ Absorption intensity I １４８７ and 1778 cm －１ Absorption intensity I １７７８ Relative to I １４８７ / I １７７８ is 3.0 to 5.0 and 1232 cm －１ Absorption intensity I １２３２ and 1778 cm －１ Absorption intensity I １７７８ Relative to I １２３２ / I １７７８ It is more preferable that both of the above conditions are satisfied.

[0117] Ratio I １４８７ / I １７７８ Compared to １２３２ / I １７７８ When both of the ratio I and the ratio I are less than 3.0, the ether bonds in the thermoplastic polyimide containing the structural unit represented by formula (1) are severely broken and the aromatic rings are severely decomposed, and the breakdown voltage drops to less than 50 kV / mm, resulting in poor electrical properties. １４８７ / I １７７８ Compared to １２３２ / I １７７８ If at least one of these is 3.0 or more, the chemical structure of the thermoplastic polyimide containing the structural unit represented by formula (1) is maintained to some extent, the breakdown voltage is 50 kV / mm or more, and the electrical properties can be said to be good.

[0118] In addition, I in the chemical structure of the thermoplastic polyimide containing the structural unit represented by formula (1) before heating １４８７ / I １７７８ The value of I is 5.0, １２３２ / I １７７８ is 5.0, which is derived from the abundance ratio of imide groups, carbon-carbon double bonds (C═C) derived from aromatic rings, and ether bonds in the chemical structure of the thermoplastic polyimide containing the structural unit represented by formula (1) before heating.

[0119] Ratio I １４８７ / I １７７８ is more preferably 3.1 to 5.0, even more preferably 3.1 to 4.5, and particularly preferably 3.2 to 4.0. １２３２ / I １７７８ is more preferably 3.1 to 5.0, even more preferably 3.1 to 4.5, and particularly preferably 3.1 to 4.0.

[0120] -Cross-cut test of insulating coating- When a cross-cut test conforming to ISO 2409:1992 (JIS K5600-5-6) is performed, the percentage of the number of squares in which the insulating coating did not peel off from the metal member is preferably 80% or more, more preferably 90% or more, and even more preferably 95% or more, relative to the total number of squares. The percentage of the number of squares in which the insulating coating did not peel off from the metal member is, for example, 100% or less, relative to the total number of squares. The details of the cross-cut test are as follows. More specifically, the insulating coating disposed on a planar region of the metal member is cut into a grid pattern with a width of 1 mm to form 25 squares. An adhesive tape (cellophane tape, manufactured by Nichiban Co., Ltd.) is applied to the area of ​​the insulating coating where the squares are formed, and the adhesive tape is then quickly pulled at an angle of approximately 60 degrees and peeled off. After the adhesive tape is peeled off, the squares are observed, and the percentage (%) of the number of squares in which the insulating coating has not been peeled off from the metal member is calculated relative to the total number of squares (25).

[0121] <Conductive Member> The conductive member of the present disclosure includes a metal member and an insulating coating covering at least a part of a surface of the metal member, wherein the insulating coating contains a thermoplastic polyimide containing a structural unit represented by the following formula (1), and the insulating coating has a structural unit represented by the following formula (1) in an IR spectrum of 1487 cm －１ Absorption intensity I １４８７ and 1778 cm －１ Absorption intensity I １７７８ Relative to I １４８７ / I １７７８ is 3.0 to 5.0 and 1232 cm －１ Absorption intensity I １２３２ and 1778 cm －１ Absorption intensity I １７７８ Relative to I １２３２ / I １７７８ is 3.0 to 5.0.

[0122]

[0123]

[0124] In the formula (1), X represents a direct bond, —SO ２ -, -CO-, -C(CH３ ) ２ -, -C(CF ３ ) ２ - or -S-. R1, R2, R3, and R4 each independently represent a hydrogen atom, an alkyl group, an alkoxy group, a halogenated alkyl group, a halogenated alkoxy group, or a halogen atom. In the formula (1), Y is a group represented by any of the formulas (2-1) to (2-4). In the formulas (2-1) to (2-4), * represents a bond, and the aromatic ring may have a substituent.

[0125] The definition, examples, and preferred aspects of formula (1) in the conductive member of the present disclosure are the same as the definition, examples, and preferred aspects of formula (1) described in the above-mentioned method for producing a conductive member of the present disclosure. Furthermore, the definition, examples, and preferred aspects of the conductive member in the conductive member of the present disclosure are also the same as the definition, examples, and preferred aspects of the conductive member described in the above-mentioned method for producing a conductive member of the present disclosure.

[0126] In the conductive member of the present disclosure, the insulating coating covers at least a portion of the surface of the metal member, preferably 50% or more, more preferably 70% or more, even more preferably 90% or more, and even more preferably the entire surface of the metal member.

[0127] Hereinafter, the present disclosure will be described more specifically with reference to examples, but the present disclosure is not limited to the following examples as long as it does not deviate from the gist of the disclosure.

[0128] <Synthesis of Thermoplastic Polyimide> Thermoplastic polyimides were synthesized according to the following procedure. The chemical formula of 4,4'-bis(3-aminophenoxy)biphenyl (m-BP) is shown in formula (10) above. The chemical formula of pyromellitic dianhydride (PMDA) is shown in formula (11) above. 4,4'-oxydianiline (ODA) is shown in formula (12) below. The chemical formula of biphenyltetracarboxylic dianhydride (BPDA) is shown in formula (13) below.

[0129]

[0130]

[0131] [Synthesis of Thermoplastic Polyimide Comprising Structural Units Represented by Formula (3) (1)] A vessel equipped with a stirrer, reflux condenser, water separator, and nitrogen inlet tube was prepared. 3.680 kg (10 mol) of 4,4'-bis(3-aminophenoxy)biphenyl, 2.071 kg (9.5 mol) of pyromellitic dianhydride, 0.148 kg (1.0 mol) of phthalic anhydride, and 21.53 kg of m-cresol were added to the vessel. The mixture was then heated to 200°C with stirring under a nitrogen atmosphere. During this time, approximately 350 ml of water was confirmed to be distilled off. The reaction was continued at 200°C for an additional 6 hours. The mixture was then cooled to room temperature, and 10.8 kg of toluene was added. The mixture was then filtered to obtain a yellow polyimide powder. The polyimide powder was washed with toluene and dried at 180°C for 24 hours to obtain 5.46 kg (yield: 98.5% by mass) of polyimide powder. The polyimide powder was further sieved through a sieve with a mesh size of 90 μm and dried at 200° C. for 8 hours to obtain a polyimide powder (a thermoplastic polyimide having a structural unit represented by formula (3), hereinafter also referred to as “PI-1”).

[0132] The physical properties of the obtained PI-1 (number average molecular weight, melt index, glass transition temperature Tg, melting point, and particle size) are shown in Table 1. The methods for measuring the physical properties are as described above.

[0133] [Synthesis of Thermoplastic Polyimide Comprising Structural Units Represented by Formula (3) (2)] A vessel equipped with a stirrer, reflux condenser, water separator, and nitrogen inlet tube was prepared. 2.873 kg (7.8 mol) of 4,4'-bis(3-aminophenoxy)biphenyl, 1.570 kg (7.25 mol) of pyromellitic dianhydride, 0.148 kg (1.0 mol) of phthalic anhydride, and 21.53 kg of m-cresol were added to the vessel. The mixture was then heated to 200°C with stirring under a nitrogen atmosphere. During this time, approximately 350 ml of water was confirmed to be distilled off. The reaction was continued for another 6 hours at 200°C. The mixture was then cooled to room temperature, and 10.8 kg of toluene was added. The mixture was then filtered to obtain a yellow polyimide powder. The polyimide powder was washed with toluene and dried at 180°C for 24 hours to obtain 5.46 kg (yield: 98.5% by mass) of polyimide powder. The polyimide powder was further sieved through a sieve with a mesh size of 90 μm and dried at 200° C. for 8 hours to obtain a polyimide powder (thermoplastic polyimide composed of a structural unit represented by formula (3), hereinafter also referred to as “PI-2”).

[0134] The physical properties of the obtained PI-2 (number average molecular weight, melt index, glass transition temperature Tg, melting point, and particle size) are shown in Table 1.

[0135] [Synthesis of Thermoplastic Polyimide Comprising Structural Units Represented by Formula (4) and Formula (5)] A vessel equipped with a stirrer, reflux condenser, water separator, and nitrogen inlet tube was prepared. 3.312 kg (9.0 mol) of 4,4'-bis(3-aminophenoxy)biphenyl, 0.2 kg (1.0 mol) of 4,4'-oxydianiline, 2.071 kg (9.5 mol) of pyromellitic dianhydride, 0.148 kg (1.0 mol) of phthalic anhydride, and 21.53 kg of m-cresol were added to the vessel. The mixture was then heated to 200°C with stirring under a nitrogen atmosphere. During this time, approximately 350 ml of water was confirmed to be distilled off. The reaction was continued for another 6 hours at 200°C. The mixture was then cooled to room temperature, and 10.8 kg of methanol was added. This was then filtered to obtain a yellow polyimide powder. This polyimide powder was washed with methanol and then dried at 180°C for 24 hours to obtain 5.26 kg (yield: 98% by mass) of polyimide powder. The polyimide powder was further sieved through a sieve with a mesh size of 90 μm and dried at 200°C for 8 hours to obtain polyimide powder (thermoplastic polyimide (m / n=9 / 1) composed of structural units represented by the above formulas (4) and (5), hereinafter also referred to as "PI-3").

[0136] The physical properties of the obtained PI-3 (number average molecular weight, melt index, glass transition temperature Tg, melting point, and particle size) are shown in Table 1.

[0137] [Synthesis of Thermoplastic Polyimide Comprising Structural Units Represented by Formula (6) and Formula (7)] A vessel equipped with a stirrer, reflux condenser, water separator, and nitrogen inlet tube was prepared. 3.684 kg (10.0 mol) of 4,4'-bis(3-aminophenoxy)biphenyl, 1.081 kg (4.96 mol) of pyromellitic dianhydride, 1.459 kg (4.86 mol) of biphenyltetracarboxylic dianhydride, 0.148 kg (1.0 mol) of phthalic anhydride, and 21.53 kg of m-cresol were added to the vessel. The mixture was then heated to 200°C with stirring under a nitrogen atmosphere. During this time, approximately 350 ml of water was confirmed to be distilled off. The reaction was continued for another 6 hours at 200°C. The mixture was then cooled to room temperature, and 10.8 kg of methanol was added. This was followed by filtration to obtain a yellow polyimide powder. This polyimide powder was washed with methanol and then dried at 180°C for 24 hours to obtain 5.46 kg (yield 98.5% by mass) of polyimide powder. The polyimide powder was further sieved through a sieve with a mesh size of 90 μm and dried at 200°C for 8 hours to obtain a polyimide powder (thermoplastic polyimide (p / q=1 / 1) composed of structural units represented by the above formulas (6) and (7), hereinafter referred to as "PI-4").

[0138] The physical properties of the obtained PI-4 (number average molecular weight, melt index, glass transition temperature Tg, melting point, and particle size) are shown in Table 1.

[0139]

[0140] <Metal Member> An oxygen-free copper plate (100 mm x 200 mm x 1 mm, C1020) was prepared as the metal member. The arithmetic mean roughness Ra of the surface of the metal member was 0.1 μm.

[0141] <Production of Conductive Member> [Example 1] Using an electrostatic coating device (Encore XT, manufactured by Nordson), a powder of thermoplastic polyimide PI-1 was electrostatically coated onto a metal member at a voltage of 60 kV, and the powder was adhered to the metal member. Subsequently, the metal member with the powder adhered thereto was heated (annealed) at 400°C for 7 minutes using an electric furnace (FO810, manufactured by Yamato Scientific Co., Ltd.). Further, electrostatic coating was similarly performed and heated at 400°C for 4 minutes. Further, electrostatic coating was similarly performed and heated at 400°C for 3 minutes to obtain an insulating coating. That is, electrostatic coating and heating were repeated three times. The powder was adhered to the metal member so that the thickness of the formed insulating coating was 0.2 mm. The arithmetic mean roughness Ra of the surface of the insulating coating was 0.5 μm.

[0142] Example 2 Using an electrostatic coating device (Nordson Encore XT), a powder of thermoplastic polyimide PI-2 was electrostatically coated onto a metal member at a voltage of 60 kV, and the powder was adhered to the metal member. The powder was adhered to the metal member so that the thickness of the insulating coating formed would be 0.05 mm. Subsequently, the metal member with the powder adhered thereto was heated at 400°C for 2.5 minutes using an electric furnace (Yamato Scientific FO810) to obtain an insulating coating.

[0143] Example 3 Using an electrostatic coating device (Nordson Encore XT), a powder of thermoplastic polyimide PI-1 was electrostatically coated onto a metal member at a voltage of 60 kV, and the powder was adhered to the metal member. The powder was adhered to the metal member so that the thickness of the insulating coating formed would be 0.03 mm. Subsequently, the metal member with the powder adhered thereto was heated at 400°C for 3 minutes using an electric furnace (Yamato Scientific FO810) to obtain an insulating coating.

[0144] Example 4 Using an electrostatic coating device (Nordson Encore XT), a powder of thermoplastic polyimide PI-1 was electrostatically coated onto a metal member at a voltage of 60 kV, and the powder was adhered to the metal member. The powder was adhered to the metal member so that the thickness of the insulating coating formed would be 0.05 mm. Subsequently, the metal member with the powder adhered thereto was heated at 400°C for 10 minutes using an electric furnace (Yamato Scientific FO810) to obtain an insulating coating.

[0145] Example 5 An insulating coating was obtained in the same manner as in Example 4, except that the powder was adhered to the metal member so that the thickness of the insulating coating formed was 0.2 mm.

[0146] Example 6 An insulating coating was obtained in the same manner as in Example 4, except that electrostatic coating was performed using powder of thermoplastic polyimide PI-3.

[0147] Example 7 An insulating coating was obtained in the same manner as in Example 4, except that electrostatic coating was performed using powder of thermoplastic polyimide PI-4.

[0148] Example 8 An insulating coating was obtained in the same manner as in Example 4, except that heating was performed at 420°C.

[0149] Example 9 An insulating coating was obtained in the same manner as in Example 8, except that heating was carried out for 20 minutes.

[0150] Comparative Example 1 An insulating coating was obtained in the same manner as in Example 4, except that heating was performed at 450° C. for 5 minutes.

[0151] Comparative Example 2 An insulating coating was obtained in the same manner as in Example 4, except that heating was performed at 450° C. for 30 minutes.

[0152] Comparative Example 3 An insulating coating was obtained in the same manner as in Example 4, except that heating was performed at 450° C. for 60 minutes.

[0153] <Evaluation of Conductive Member> [IR Spectrum] Using an infrared spectrophotometer (Agilent, Cary 620 / 670), the IR spectrum of the insulating coating provided on the conductive member was measured by a microscopic transmission method. The detailed measurement conditions are as follows: Measurement area: 4000 cm －１ ~600cm －１ ・Resolution: 4cm －１ ・Number of times accumulated: 128 times

[0154] From the IR spectrum measured from the insulating coating provided on each conductive member, －１ and the absorption intensity of 1778 cm －１ The ratio of the absorption intensity of １４８７ / I １７７８ , and 1232 cm －１ and the absorption intensity of 1778 cm－１ The ratio of the absorption intensity of １２３２ / I １７７８ was calculated. －１ is a peak derived from the imide group, and 1487 cm －１ is a peak due to a carbon-carbon double bond (C═C) derived from an aromatic ring, and 1232 cm －１ is a peak derived from an ether bond (—O—). The results are shown in Table 2.

[0155] [Breakdown Voltage] The breakdown voltage (BDV) of the insulating coating provided on the conductive member was measured using a breakdown tester in accordance with IEC 60243-1 by a short-time breakdown method (measurement environment: 23°C, 50% RH). The measured value was the average of three tests. Furthermore, the breakdown voltage per mm of thickness of the insulating coating (kV / mm) was calculated from the measured breakdown voltage (kV). The results are shown in Table 2.

[0156] [Cross-Cut Test] The insulating coating was subjected to a cross-cut test in accordance with ISO 2409:1992 (JIS K5600-5-6). More specifically, the insulating coating disposed on a planar region of a metal member was cut into a grid pattern with a width of 1 mm to form 25 squares. An adhesive tape (cellophane tape, manufactured by Nichiban Co., Ltd.) was applied to the area of ​​the insulating coating where the squares were formed, and the adhesive tape was quickly pulled at an angle of approximately 60 degrees and peeled off. After peeling off the adhesive tape, the squares were observed, and the percentage (%) of the number of squares where the insulating coating was not peeled off from the metal member relative to the total number of squares (25) was calculated. The results are shown in Table 2.

[0157]

[0158] As shown in Table 2, the breakdown voltage was high in all of the conductive members obtained in Examples 1 to 9. From the above, a conductive member in which a decrease in breakdown voltage was suppressed was obtained by the method for producing a conductive member according to the present disclosure.

[0159] The disclosure of Japanese Patent Application No. 2023-219957, filed on December 26, 2023, is incorporated herein by reference in its entirety. All publications, patent applications, and technical standards mentioned herein are incorporated herein by reference to the same extent as if each individual publication, patent application, and technical standard was specifically and individually indicated to be incorporated by reference.

Claims

1. A method for producing an insulating coating comprising the steps of: attaching a powder containing a thermoplastic polyimide having a structural unit represented by the following formula (1) to the surface of a metal member by electrostatic coating; and heating the attached powder to melt the powder and form an insulating coating, wherein the insulating coating has an IR spectrum of 1487 cm －１ Absorption intensity I １４８７ and 1778 cm －１ Absorption intensity I １７７８ Comparison with I １４８７ / I １７７８ is 3.0 to 5.0 and 1232 cm －１ Absorption intensity I １２３２ and 1778 cm －１ Absorption intensity I １７７８ Comparison with I １２３２ / I １７７８ and wherein the conductive member manufacturing method satisfies at least one of the above. In the formula (1), X is a direct bond, -SO ２ -, -CO-, -C(CH ３ ) ２ -, -C(CF ３ ) ２ -, or -S-. R1, R2, R3, and R4 each independently represent a hydrogen atom, an alkyl group, an alkoxy group, a halogenated alkyl group, a halogenated alkoxy group, or a halogen atom. In the formula (1), Y is a group represented by any one of the formulas (2-1) to (2-4). In the formulas (2-1) to (2-4), * represents a bond, and the aromatic ring may have a substituent.

2. The manufacturing method of the conductive member according to claim 1, wherein the temperature of the heating is 390°C to 430°C.

3. The manufacturing method of the conductive member according to claim 1 or claim 2, wherein the time of the heating is more than 0 minutes and 30 minutes or less.

4. The manufacturing method of the conductive member according to claim 1 or claim 2, wherein the powder satisfies at least one of the following conditions: the particle diameter d50 at which the cumulative percentage is 50% in the volume-based particle size distribution is 5 μm to 100 μm, and the particle diameter d90 at which the cumulative percentage is 90% in the volume-based particle size distribution is 10 μm to 200 μm.

5. The manufacturing method of the conductive member according to claim 1 or claim 2, wherein the material of the metal member is any one of copper, copper alloy, iron, iron alloy containing steel, aluminum, or aluminum alloy.

6. The manufacturing method of the conductive member according to claim 1 or claim 2, wherein the metal member is a surface-treated metal member.

7. The manufacturing method of the conductive member according to claim 1 or claim 2, wherein the thickness of the insulating coating is 5 μm to 1000 μm.

8. A conductive member comprising a metal member and an insulating film covering at least a part of the surface of the metal member, wherein the insulating film contains a thermoplastic polyimide containing a structural unit represented by the following formula (1), and in the IR spectrum, the absorption intensity I －１ at 1487 cm １４８７ and the absorption intensity I －１ at 1778 cm １７７８ have a ratio I １４８７ / I １７７８ of 3.0 to 5.0, and the absorption intensity I －１ at 1232 cm １２３２ and the absorption intensity I －１ at 1778 cm １７７８ have a ratio I １２３２ / I １７７８ of 3.0 to 5.0, satisfying at least one of them. In the formula (1), X is a direct bond, -SO ２ -, -CO-, -C(CH ３ ) ２ -, -C(CF ３ ) ２ -, or -S-. R1, R2, R3, and R4 are each independently a hydrogen atom, an alkyl group, an alkoxy group, a halogenated alkyl group, a halogenated alkoxy group, or a halogen atom. In the formula (1), Y is a group represented by any one of the following formulas (2-1) to (2-4). In the following formulas (2-1) to (2-4), * represents a bond, and the aromatic ring may have a substituent.

9. The conductive member according to claim 8, wherein the material of the metal member is any one of copper, copper alloy, aluminum, or aluminum alloy.

10. The conductive member according to claim 8, wherein the material of the metal member is copper or copper alloy.

11. The conductive member according to any one of claims 8 to 10, wherein the ratio of the number of squares where the insulating coating does not peel off from the metal member when a cross-cut test conforming to ISO 2409:1992 is performed is 80% or more with respect to the total number of squares.

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