Resin composition, insulated wire, and method for producing insulated wire

Abstract

Provided is a resin composition comprising: a polyimide precursor which is a reaction product of an aromatic tetracarboxylic dianhydride with an aromatic diamine; an organic solvent; and an amine compound. The pKa of a conjugate acid of the amine compound is 11 or less, and the molecular weight of the amine compound is 70 or more.

Description

Resin composition, insulated wire, and method for producing insulated wire

[0001] This disclosure relates to a resin composition, an insulated wire, and a method for producing an insulated wire. This application claims priority to Japanese Application No. 2024-019610, filed February 13, 2024, and incorporates by reference all of the contents of that application.

[0002] Patent Document 1 describes a polyimide resin varnish whose main component is a polyimide precursor resin obtained by reacting an aromatic diamine with an aromatic tetracarboxylic dianhydride, in which the imide group concentration after imidization of the polyimide precursor resin is greater than 35.0% and less than 36.0%.

[0003] JP 2013-253124 A

[0004] A resin composition according to one embodiment of the present disclosure includes a polyimide precursor that is a reaction product of an aromatic tetracarboxylic dianhydride and an aromatic diamine, an organic solvent, and an amine compound, wherein the pKa of a conjugated acid of the amine compound is 11 or less, and the molecular weight of the amine compound is 70 or more.

[0005] FIG. 1 is a schematic cross-sectional view showing an insulated wire according to one embodiment of the present disclosure.

[0006] [Problem to be Solved by the Present Disclosure] The problem to be solved by the present disclosure is to provide a resin composition that can form an insulating coating that is excellent in coating elongation and that exhibits little change in viscosity over time.

[0007] Effect of the Present Disclosure A resin composition according to one aspect of the present disclosure can form an insulating coating that has excellent coating elongation and exhibits little change in viscosity over time.

[0008] [Description of Embodiments of the Present Disclosure] First, embodiments of the present disclosure will be listed and described. Item 1. A resin composition comprising a polyimide precursor that is a reaction product of an aromatic tetracarboxylic dianhydride and an aromatic diamine, an organic solvent, and an amine compound, wherein the pKa of a conjugate acid of the amine compound is 11 or less and the molecular weight of the amine compound is 70 or more. Item 2. The resin composition according to Item 1, wherein the amine compound is an aromatic amine. Item 3. The resin composition according to Item 2, wherein the aromatic amine is an aromatic heterocyclic amine. Item 4. The resin composition according to Item 2, wherein the aromatic amine is an aromatic non-heterocyclic amine. Item 5. The resin composition according to Item 1, wherein the amine compound is an aliphatic amine. Item 6. The resin composition according to any one of Items 1 to 5, wherein the amine compound has a 5% mass loss temperature of 200°C or higher. Item 7. The resin composition according to any one of Items 1 to 6, wherein the content of the amine compound is 0.1 parts by mass or more and 3 parts by mass or less per 100 parts by mass of the polyimide precursor. Item 8. Viscosity η at 30 ° C ０ Viscosity η at 30 ° C. after storage at 40 ° C. for 7 days １ The ratio of η １ / η ０Item 10. An insulated electric wire comprising a conductor and an insulating coating covering the conductor, the insulating coating being formed from the resin composition according to any one of items 1 to 9. Item 11. The insulated electric wire according to item 10, wherein the insulating coating contains the amine compound or a decomposition product thereof, and the content of the amine compound or a decomposition product thereof in the insulating coating is 2.85 mass% or less relative to the mass of the insulating coating. Item 12. The insulated electric wire according to item 10 or 11, wherein the insulating coating contains a plurality of voids. Item 13. 10. A method for manufacturing an insulated wire including a conductor and an insulating coating covering the conductor, the method comprising: applying the resin composition according to any one of items 1 to 9 to an outer peripheral surface of the conductor; and heating the resin composition applied in the applying step.

[0009] [Details of Embodiment of Present Disclosure] Hereinafter, a resin composition, an insulated wire, and a method for producing an insulated wire according to one aspect of the present disclosure will be described.

[0010] <Resin Composition> The resin composition contains a polyimide precursor which is a reaction product of an aromatic tetracarboxylic dianhydride and an aromatic diamine, an organic solvent, and an amine compound described below.

[0011] The resin composition contains the amine compound, which enables the formation of an insulating coating that is excellent in film elongation and exhibits the effect of minimizing change in viscosity over time.

[0012] Although not wishing to be limited in any way, it is believed that the inclusion of a specific amine compound in the resin composition increases entanglement of polyimide molecular chains, improves intermolecular interactions, and increases the strength of the molecular chains themselves, making the composition less susceptible to breakage when stretched, thereby enabling the formation of an insulating coating with excellent elongation.

[0013] "Coating elongation" refers to the elongation at break (unit: %). Specifically, coating elongation is measured by the following method. A tubular insulating coating obtained by removing the conductor from an insulated electric wire is used as a sample. This sample is set in a tensile tester, and a tensile test is performed under the conditions of a chuck distance of 20 mm and a tensile speed of 10 mm / min, thereby measuring the elongation at break.

[0014] The present inventors have also found that if the pKa of the conjugate acid of the amine compound is too high, the viscosity of the resin composition may increase over time. Furthermore, the present inventors have found that there is a trade-off between improved film elongation and minimal change in viscosity over time. They have then discovered that a resin composition that achieves a good balance between film elongation and minimal change in viscosity over time can be obtained by using a specific amine compound that satisfies both of the following conditions 1 and 2: Condition 1: The pKa of the conjugate acid of the amine compound is 11 or less; Condition 2: The molecular weight of the amine compound is 70 or more.

[0015] In this specification, the term "small change in viscosity over time" means that the viscosity η of the resin composition at 30°C is small. ０ Viscosity η at 30 ° C. after storage at 40 ° C. for 7 days １ The ratio of η １ / η ０ This means that the viscosity is not more than 20. The viscosity can be measured by the method described in the examples below.

[0016] In other words, the resin composition has a viscosity η ０ Viscosity η at 30 ° C. after storage at 40 ° C. for 7 days １ The ratio of η １ / η ０ It is preferable that the ratio η is 20 or less. １ / η ０ The upper limit of the ratio η may be 17, 16, 15, 12, 10, or 9. １ / η ０ The lower limit of is, for example, 1.

[0017] The resin composition can be suitably used as a resin composition (varnish) for forming an insulating coating for an insulated wire.

[0018] Each component contained in the resin composition will be described below.

[0019] (Polyimide Precursor) A polyimide precursor is a reaction product obtained by a condensation polymerization reaction between an aromatic tetracarboxylic dianhydride and an aromatic diamine. The polyimide precursor is a compound also called a polyamic acid (polyamic acid). The polyimide precursor undergoes a dehydration cyclization reaction (imidization reaction) to form a cyclic imide, thereby becoming a polyimide.

[0020] The aromatic tetracarboxylic dianhydride containing pyromellitic dianhydride (PMDA) can improve the heat resistance of the insulating coating. This is because PMDA has a rigid and linear molecular structure. The aromatic tetracarboxylic dianhydride may contain an aromatic tetracarboxylic dianhydride other than PMDA (hereinafter also referred to as "another aromatic tetracarboxylic dianhydride").

[0021] Examples of the other aromatic tetracarboxylic dianhydrides include 3,3',4,4'-biphenyltetracarboxylic dianhydride (s-BPDA), 2,3,3',4'-biphenyltetracarboxylic dianhydride (a-BPDA), 2,2',3,3'-biphenyltetracarboxylic dianhydride (i-BPDA), 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 4,4'-oxydiphthalic dianhydride, 2,2',3,3'-benzophenonetetracarboxylic dianhydride, 2,2-bis(3,4-dicarboxyphenyl)propane dianhydride, 2,2-bis(3,4-dicarboxyphenyl)propane dianhydride, and 2,2-bis(3,4-dicarboxyphenyl)propane dianhydride. Examples of other aromatic tetracarboxylic dianhydrides include bis(2,3-dicarboxyphenyl)propane dianhydride, 1,1-bis(3,4-dicarboxyphenyl)ethane dianhydride, 1,1-bis(2,3-dicarboxyphenyl)ethane dianhydride, bis(3,4-dicarboxyphenyl)methane dianhydride, bis(2,3-dicarboxyphenyl)methane dianhydride, bis(3,4-dicarboxyphenyl)sulfone dianhydride, bis(3,4-dicarboxyphenyl)ether dianhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, and 2,3,6,7-naphthalenetetracarboxylic dianhydride. These other aromatic tetracarboxylic dianhydrides may be used alone or in combination of two or more.

[0022] When biphenyltetracarboxylic dianhydride (BPDA) is used as the other aromatic tetracarboxylic dianhydride, the hydrolysis resistance of the polyimide precursor can be suitably improved.

[0023] The lower limit of the amount of PMDA relative to 100 mol% of the aromatic tetracarboxylic dianhydride may be 10 mol%, 20 mol%, or 30 mol%, and the upper limit of the amount of PMDA relative to 100 mol% of the aromatic tetracarboxylic dianhydride may be 100 mol%, 90 mol%, 80 mol%, or 70 mol%.

[0024] The content of the other aromatic tetracarboxylic dianhydride relative to 100 mol% of the aromatic tetracarboxylic dianhydride can be appropriately determined within a range that does not impair the effects of the present disclosure. The upper limit of the content of the other aromatic tetracarboxylic dianhydride may be 30 mol% or 20 mol%. The lower limit of the content of the other aromatic tetracarboxylic dianhydride may be 0 mol% or 10 mol%.

[0025] The aromatic diamine containing diaminodiphenyl ether (ODA) can improve the heat resistance of the insulating coating. This is because ODA has a rigid and linear molecular structure. Examples of ODA include 4,4'-diaminodiphenyl ether (4,4'-ODA), 3,4'-diaminodiphenyl ether (3,4'-ODA), 3,3'-diaminodiphenyl ether (3,3'-ODA), 2,4'-diaminodiphenyl ether (2,4'-ODA), and 2,2'-diaminodiphenyl ether (2,2'-ODA). Among these, the use of 4,4'-diaminodiphenyl ether (4,4'-ODA) can favorably improve the elongation of the insulating coating.

[0026] The lower limit of the ODA content relative to 100 mol% of the aromatic diamine may be 50 mol%, 60 mol%, or 70 mol%, and the upper limit of the ODA content relative to 100 mol% of the aromatic diamine may be 100 mol% or 90 mol%.

[0027] The aromatic diamine may further contain an aromatic diamine other than ODA (hereinafter also referred to as "other aromatic diamine"). Examples of the other aromatic diamine include 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP), 4,4'-bis(4-aminophenoxy)biphenyl (BAPB), 4,4'-diaminodiphenylmethane, 3,4'-diaminodiphenylmethane, 3,3'-diaminodiphenylmethane, 2,4'-diaminodiphenylmethane, 2,2'-diaminodiphenylmethane, 4,4'-diaminodiphenylsulfone, 3,4'-diaminodiphenylsulfone, 3,3'-diaminodiphenylsulfone, 2,4'-diaminodiphenylsulfone, 2,2'-diaminodiphenylsulfone, 4,4' Examples of the other aromatic diamines include 4,4'-dimethyl-4,4'-diaminodiphenylmethane, 4,4'-benzophenonediamine, 2,2'-dimethyl-4,4'-diaminodiphenylmethane ...

[0028] When 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP) or 4,4'-bis(4-aminophenoxy)biphenyl (BAPB) is used as another aromatic diamine, the relative dielectric constant of the insulating film can be lowered.

[0029] The content of the other aromatic diamine relative to 100 mol% of the aromatic diamine can be appropriately determined within a range that does not impair the effects of the present disclosure. The upper limit of the content may be 40 mol% or 30 mol%. The lower limit of the content may be 0 mol% or 10 mol%.

[0030] The lower limit of the concentration of the polyimide precursor in the resin composition may be 10% by mass or 20% by mass. The upper limit of the concentration of the polyimide precursor in the varnish for rectangular insulated electric wire may be 50% by mass or 40% by mass. By setting the concentration of the polyimide precursor in the varnish for rectangular insulated electric wire at or above the lower limit, the amount of resin composition required in the entire manufacturing process to obtain an insulating coating of the desired thickness when forming an insulating coating using the resin composition can be reduced, thereby reducing the number of coating and heating steps. By setting the concentration at or below the upper limit, the viscosity of the resin composition can be appropriately adjusted while maintaining good coating properties, thereby improving coatability.

[0031] The molar ratio of the aromatic tetracarboxylic dianhydride to the aromatic diamine used as raw materials for the polyimide precursor (aromatic tetracarboxylic dianhydride:aromatic diamine) may be, for example, 95:105 or more and 105:95 or less, 97:103 or more and 103:97 or less, or 99:101 or more and 101:99 or less, from the viewpoint of ease of synthesis of the polyimide precursor. The aromatic tetracarboxylic dianhydride and the aromatic diamine may be substantially equimolar amounts. In this case, the molecular weight of the polyimide precursor can be increased. The term "substantially equimolar amount" refers to a molar ratio of the aromatic tetracarboxylic dianhydride to the aromatic diamine (aromatic tetracarboxylic dianhydride:aromatic diamine) in the range of 99:101 or more and 101:99 or less.

[0032] The lower limit of the weight-average molecular weight of the polyimide precursor may be 15,000 or 16,000. The upper limit of the weight-average molecular weight may be 100,000 or 50,000. When the weight-average molecular weight is equal to or greater than the lower limit, the film properties are improved. When the weight-average molecular weight is equal to or less than the upper limit, the coatability of the resin composition is improved.

[0033] (Method for synthesizing polyimide precursor) The polyimide precursor can be obtained by a condensation polymerization reaction between the aromatic tetracarboxylic dianhydride and the aromatic diamine described above. The condensation polymerization reaction can be carried out by the same method as the conventional method for synthesizing polyimide precursors. Specific examples of the condensation polymerization reaction include a method in which the aromatic tetracarboxylic dianhydride and the aromatic diamine are mixed in an organic solvent. This method allows the aromatic tetracarboxylic dianhydride and the aromatic diamine to polymerize, thereby obtaining a solution in which the polyimide precursor is dissolved in the organic solvent. For example, the degree of polymerization (weight average molecular weight) can be controlled by carrying out the condensation polymerization reaction in the presence of a reaction inhibitor.

[0034] The reaction inhibitor may be, for example, water (H ２ Examples of the alcohol having 1 to 15 carbon atoms include monohydric alcohols such as ethanol, methanol, propanol, butanol, and pentanol; and polyhydric alcohols such as ethylene glycol, propylene glycol, and glycerin. Examples of the acid anhydride include aliphatic acid anhydrides such as phthalic anhydride, maleic anhydride, and succinic anhydride; and aromatic acid anhydrides such as trimellitic acid.

[0035] The reaction conditions for the condensation polymerization can be appropriately set depending on the raw materials used, etc. For example, the reaction temperature can be set to 10° C. or higher and 100° C. or lower, and the reaction time can be set to 0.5 hours or higher and 24 hours or lower.

[0036] Examples of the organic solvent used in the condensation polymerization reaction include the same organic solvents as those described below.

[0037] (Organic Solvent) The organic solvent is not particularly limited as long as it is a solvent that can be used in synthesizing a polyimide precursor, and examples thereof include aprotic solvents. The term "aprotic solvent" refers to an organic solvent that does not have a group that releases a proton.

[0038] Examples of aprotic solvents include amide solvents such as N-methyl-2-pyrrolidone (NMP), N,N-dimethylacetamide (DMAc), and N,N-dimethylformamide (DMF); sulfur-containing solvents such as dimethyl sulfoxide; and lactone solvents such as γ-butyrolactone.

[0039] When the organic solvent is an amide solvent, the reaction can proceed efficiently. Furthermore, when the amide solvent is NMP or DMAc, the reaction can proceed more efficiently.

[0040] The organic solvents may be used alone or in combination of two or more.

[0041] The organic solvent may be a combination of the aprotic solvent and a low-dielectric-constant solvent. In this case, the dielectric constant of the insulating coating can be reduced. The term "low-dielectric-constant solvent" refers to an organic solvent having a dielectric constant of less than 15. Examples of low-dielectric-constant solvents include hydrocarbon solvents such as hexane, heptane, benzene, toluene, xylene, and naphtha; ester solvents such as methyl acetate, ethyl acetate, butyl acetate, and diethyl oxalate; ether solvents such as diethyl ether, ethylene glycol dimethyl ether, diethylene glycol monomethyl ether, ethylene glycol monobutyl ether (butyl cellosolve), diethylene glycol dimethyl ether, and tetrahydrofuran; halogen-based solvents such as dichloromethane and chlorobenzene; phenol-based solvents such as cresol and chlorophenol; and amine-based solvents such as pyridine.

[0042] The content of the organic solvent in the resin composition is not particularly limited as long as it is an amount that can uniformly dissolve or disperse the aromatic tetracarboxylic dianhydride and the aromatic diamine. However, if the amount is too large, a large amount of the organic solvent must be volatilized when forming the insulating coating, which may require a long time to form the insulating coating. Therefore, the content of the organic solvent can be, for example, 100 parts by mass or more and 1,000 parts by mass or less per 100 parts by mass of the aromatic tetracarboxylic dianhydride and the aromatic diamine combined.

[0043] (Amine Compound) The amine compound satisfies both of the following conditions 1 and 2. By using a specific amine compound that satisfies both of the following conditions 1 and 2, it is possible to obtain a resin composition that achieves a good balance between improved film elongation and minimal change in viscosity over time. Condition 1: The pKa of the conjugate acid of the amine compound is 11 or less. Condition 2: The molecular weight of the amine compound is 70 or more.

[0044] As used herein, "amine compounds" encompass primary amines, secondary amines, and tertiary amines. "Amine compounds" encompass "aromatic amines" and "aliphatic amines." "Aromatic amines" refer to amine compounds having an aromatic ring. "Aromatic amines" encompass "aromatic heterocyclic amines" and "aromatic non-heterocyclic amines." "Aromatic heterocyclic amines" refer to aromatic amine compounds having a heterocycle containing only nitrogen atoms as heteroatoms. "Aromatic non-heterocyclic amines" refer to aromatic amine compounds that do not have the heterocycle.

[0045] Examples of the aliphatic amine include chain amines such as triallylamine, N,N-dimethyldodecylamine, N,N,N,N-tetramethyl-1,6-hexamethylenediamine, and N,N-dimethylstearylamine; and amine compounds containing an aliphatic heterocycle such as a pyrrolidine ring, a piperidine ring, or a piperazine ring.

[0046] Examples of amine compounds containing an aliphatic heterocycle include bis(1,2,2,6,6-pentamethyl-4-piperidyl)sebacate, 1,2,2,6,6-pentamethyl-4-piperidyl methacrylate, tetrakis(1,2,2,6,6-pentamethyl-4-piperidyl)butane-1,2,3,4-tetracarboxylate, (2,2,6,6-tetramethyl-4-piperidyl)dodecyl succinimide, and N,N'-bis(2,2,6,6-tetramethyl-4-piperidyl)butanetetracarboxylate. Among these, bis(1,2,2,6,6-pentamethyl-4-piperidyl)sebacate is easy to handle because it is a liquid at room temperature and normal pressure.

[0047] Examples of aromatic heterocyclic amines include amine compounds containing a monocyclic aromatic heterocycle such as a pyrrole ring, an imidazole ring, a pyridine ring, a triazole ring, a pyrimidine ring, or a triazine ring, and amine compounds containing a polycyclic aromatic heterocycle such as an indole ring, a benzimidazole ring, an isoquinoline ring, or a phenanthroline ring. While not wishing to be restrictive, it is believed that when the amine compound is an aromatic heterocyclic amine, electrons are delocalized, resulting in an appropriate pKa value of the conjugate acid, and a better balance can be achieved between improved film elongation and minimal change in viscosity over time.

[0048] Examples of amine compounds containing a monocyclic aromatic heterocycle include 1,3,5-triazine-2,4,6-triamine, 1-benzyl-2-phenylimidazole, 2,4-diamino-6-[2'-undecylimidazolyl-(1')]ethyl-s-triazine, 1-cyanoethyl-2-undecylimidazole, 4-(3-phenylpropyl)pyridine, and 1-isobutyl-2-methylimidazole.

[0049] Examples of the amine compound containing a polycyclic aromatic heterocycle include benzimidazole, 1,10-phenanthroline, and isoquinoline.

[0050] Examples of aromatic non-heterocyclic amines include aniline derivatives such as 2,6-dimethylaniline, N,N-diethylaniline, and 2,6-diisopropylaniline; and dibenzylamine.

[0051] [Condition 1] Condition 1 is that the pKa of the conjugate acid of the amine compound is not more than 11. When the pKa of the conjugate acid of the amine compound is not more than 11, the change in viscosity of the resin composition over time can be reduced.

[0052] The lower limit of the pKa of the conjugate acid of the amine compound may be 4.0, 4.5, 5.0, 5.5, or 6.0. The upper limit of the pKa of the conjugate acid of the amine compound is 11. In this specification, the pKa of the conjugate acid of the amine compound is taken from the data published on the Chemical Book homepage (https: / / www.chemicalbook.com / ).

[0053] [Condition 2] Condition 2 is that the molecular weight of the amine compound is equal to or greater than 70. When the molecular weight of the amine compound is equal to or greater than 70, an appropriate amount of the amine compound remains in the insulating coating, thereby improving the elongation of the coating.

[0054] The lower limit of the molecular weight of the amine compound is 70, or may be 100, 120, or 130. The upper limit of the molecular weight of the amine compound may be 1,000, 700, or 600.

[0055] [Condition 3] The amine compound may further satisfy the following condition 3. In this case, a more appropriate amount of the amine compound remains in the insulating coating, thereby further improving the elongation of the coating. Condition 3: The 5% mass loss temperature of the amine compound is 200°C or higher.

[0056] The lower limit of the 5% mass loss temperature of the amine compound may be 200°C, 210°C, or 220°C. The upper limit of the 5% mass loss temperature of the amine compound may be 350°C, 300°C, 290°C, or 280°C. The 5% mass loss temperature of the amine compound can be measured using a thermogravimetric differential thermal analyzer (nitrogen atmosphere). That is, for example, using a thermogravimetric analyzer ("TGA4000" manufactured by PerkinElmer), the temperature at which the mass of a sample decreases by 5% by mass can be measured under conditions of a nitrogen atmosphere from room temperature at a heating rate of 20°C / min.

[0057] The lower limit of the content of the amine compound in the resin composition may be 0.1 parts by mass, 0.5 parts by mass, or 1 part by mass per 100 parts by mass of the polyimide precursor. The upper limit of the content of the amine compound may be 4 parts by mass or 3 parts by mass per 100 parts by mass of the polyimide precursor. When the content of the amine compound is within the above range, a better balance can be achieved between improved film elongation and minimal change in viscosity over time. Furthermore, when the content of the amine compound is 0.1 parts by mass or more and 3 parts by mass or less, film elongation can be further improved.

[0058] The amine compound may be blended directly into the resin composition, or may be blended after being dissolved or dispersed in an organic solvent.

[0059] (Pore-forming agent) The resin composition may contain a pore-forming agent. When the resin composition contains a pore-forming agent, an insulating coating having a plurality of pores can be formed.

[0060] The pore-forming agent is not particularly limited as long as it is an additive known to be used for forming an insulating coating having pores, and examples of the pore-forming agent include chemical foaming agents, thermally expandable microcapsules, particles containing thermally decomposable resins, high-boiling point solvents, hollow fillers, and aliphatic polycarboxylic acid esters.

[0061] When the pore-forming agent is a thermally decomposable resin-containing particle, an insulating coating having a good appearance can be formed even when the porosity is high. The thermally decomposable resin-containing particle is gasified by thermal decomposition, and pores are formed in the insulating coating in the area where the thermally decomposable resin-containing particle was present. In this case, an island phase of fine particles can be uniformly distributed in the resin portion (the sea phase of the resin matrix) that constitutes the insulating coating, and independent pores can be formed.

[0062] The thermally decomposable resin contained in the thermally decomposable resin-containing particles may be a resin that thermally decomposes at a temperature lower than the baking temperature of the polyimide that constitutes the insulating coating. The baking temperature of the polyimide is set appropriately depending on the type of material that constitutes the polyimide precursor, but is usually about 200°C or higher and 600°C or lower. The "thermal decomposition temperature" refers to the temperature at which the mass loss rate reaches 50% when the temperature is increased from room temperature at a rate of 10°C / min in an air atmosphere. The thermal decomposition temperature can be measured by measuring the thermogravimetry using a thermogravimetry-differential thermal analyzer ("TG / DTA" manufactured by SII NanoTechnology, Inc.).

[0063] Examples of the thermally decomposable resin contained in the thermally decomposable resin-containing particles include compounds in which one, both, or a portion of one or both ends of polyethylene glycol, polypropylene glycol, etc. are alkylated, (meth)acrylated, or epoxidized; polymers of (meth)acrylic acid esters having an alkyl group of 1 to 6 carbon atoms, such as polymethyl(meth)acrylate, polyethyl(meth)acrylate, polypropyl(meth)acrylate, and polybutyl(meth)acrylate; urethane oligomers, urethane polymers, polymers of modified (meth)acrylates, such as urethane(meth)acrylate, epoxy(meth)acrylate, and ε-caprolactone(meth)acrylate; poly(meth)acrylic acid; crosslinked products thereof; polystyrene; and crosslinked polystyrene. Polymers of (meth)acrylic acid esters having an alkyl group of 1 to 6 carbon atoms are prone to thermal decomposition at the baking temperature of the polyimide, easily forming voids in the insulating coating. Examples of the (meth)acrylic acid ester polymers include polymethyl methacrylate (PMMA). The term "(meth)acrylic acid" is a general term for "acrylic acid" and "methacrylic acid," and refers to either one or both of them. Furthermore, the term "(meth)acrylate" is a general term for "acrylate" and "methacrylate," and refers to either one or both of them.

[0064] The thermally decomposable resin-containing particles may be particles consisting solely of the thermally decomposable resin, or may be particles with a core-shell structure having a core primarily composed of the thermally decomposable resin and a shell primarily composed of a resin having a thermal decomposition temperature higher than that of the thermally decomposable resin. When a varnish containing particles with a core-shell structure is heated, only the core is thermally decomposed to form pores, with the shell remaining on the outer periphery of these pores. Particles with a core-shell structure can reduce the interconnection of pores and reduce the variation in pore size.

[0065] The main component of the shell is not particularly limited as long as it has a higher thermal decomposition temperature than the core, and may be a synthetic resin with a low dielectric constant and high heat resistance. Examples include polystyrene, silicone, fluororesin, and polyimide. Silicone, in particular, tends to increase elasticity, which results in good dispersion of pores in the insulating coating. This reduces interconnection of pores and reduces variability in pore size, resulting in excellent insulation and heat resistance.

[0066] The content of the pore-forming agent in the resin composition can be determined appropriately depending on, for example, the type of pore-forming agent, the target porosity of the insulating coating, and the like.

[0067] Examples of aliphatic polycarboxylic acid esters include aliphatic dicarboxylic acid esters such as dibutyl fumarate, dibutyl succinate, diethyl sebacate, diisobutyl adipate, dibutyl adipate, dibutyl sebacate, and bis(2-butoxyethyl) adipate, and citric acid esters such as triethyl citrate, triethyl O-acetylcitrate, tributyl citrate, and tributyl O-acetylcitrate. While not intended to be limiting, it is believed that when an insulating coating is formed, pores can be formed by phase separation between the resin matrix and the aliphatic polycarboxylic acid ester that constitute the insulating coating.

[0068] (Other Components) The resin composition may contain other components in addition to the above-described components. The other components are not particularly limited as long as they are blended into a varnish for forming an insulating coating for an insulated wire. Examples of other components include an antioxidant, a filler, a leveling agent, a curing agent, and an adhesion promoter.

[0069] <Insulated Wire> An insulated wire 1 shown in FIG. 1 includes a conductor 2 and an insulating coating 3 that covers the conductor 2 .

[0070] The cross-sectional shape of the insulated wire 1 is not particularly limited, and examples thereof include a circular shape (round wire), an elliptical shape, a square shape (rectangular wire), and a rectangular shape (flat wire). It is preferable that the cross-sectional shape of the insulated wire 1 is a rectangular shape, in other words, a flat wire. In this case, the insulated wire 1 can be wound at a high density during coil processing. It is also preferable that the cross-sectional shape of the insulated wire 1 and the cross-sectional shape of the conductor 2, which will be described later, are the same type of shape.

[0071] The insulated wire 1 can be suitably used as a coil winding wire (magnet wire).

[0072] (Conductor) Examples of the cross-sectional shape of the conductor 2 include a circular shape (round wire), an elliptical shape, a square shape, and a rectangular shape. When the insulated wire 1 is a rectangular wire, the cross-sectional shape of the conductor 2 is preferably a rectangular shape.

[0073] The conductor 2 may be made of a metal having high electrical conductivity and high mechanical strength. Examples of such metals include copper, copper alloys, aluminum, nickel, silver, mild steel, steel, and stainless steel. The conductor 2 may be made of a wire-shaped material or a multilayer structure in which a wire-shaped material is further coated with another metal, such as nickel-coated copper, silver-coated copper, copper-coated aluminum, or copper-coated steel.

[0074] The lower limit of the average cross-sectional area of ​​the conductor 2 is 0.01 mm ２ 0.1 mm ２ In this case, the volume of the insulating coating 3 relative to the conductor 2 in the insulated wire can be made appropriate, and the volume efficiency of a coil or the like formed using the insulated wire can be improved. The upper limit of the average cross-sectional area of ​​the conductor 2 is 20 mm ２10 mm ２ In this case, it is possible to reduce the need to form the insulating coating 3 thick enough to sufficiently reduce the relative dielectric constant, and it is possible to avoid an unnecessary increase in the diameter of the insulated wire.

[0075] (Insulating Coating) The insulating coating 3 is laminated on the outer peripheral surface of the conductor 2 so as to cover the conductor 2. The insulating coating 3 is composed of one or more layers. For example, when the insulating coating 3 is formed by the method described below (a method in which varnish application and baking are repeated multiple times), the insulating coating 3 has a laminated structure composed of multiple layers formed using varnish.

[0076] The insulating film 3 contains a resin matrix. The insulating film 3 is formed from the above-mentioned resin composition. Therefore, the resin matrix contains polyimide as a main component.

[0077] The average thickness of the insulating coating 3 is not particularly limited, and can usually be set to 2 μm or more and 300 μm or less.

[0078] The insulating coating 3 may contain a plurality of pores. In this case, it is possible to reduce the dielectric constant of the insulating coating 3. When the insulating coating 3 contains a plurality of pores, the plurality of pores in the insulating coating 3 are dispersed in the resin matrix.

[0079] When the insulating coating 3 contains multiple pores, the porosity of the insulating coating 3 is preferably 20% by volume or more and 60% by volume or less. If the porosity of the insulating coating 3 is 20% by volume or more, the dielectric constant of the insulating coating can be further reduced. Furthermore, since the insulating coating 3 is formed from the resin composition described above, even if the insulating coating has a high porosity of 20% by volume or more, the coating has excellent elongation. The porosity of the insulating coating 3 may be 40% by volume or more. The upper limit of the porosity of the insulating coating 3 may be 60% by volume or 50% by volume. "Porosity" refers to the percentage (unit: vol%) of the volume of the pores relative to the volume of the resin matrix and the insulating coating having the pores. Specifically, the porosity is measured by the following method. The porosity is calculated from the formula (W1-W2) x 100 / W1 using the mass W1 of the insulating coating without pores, which is calculated by multiplying the apparent volume V1 calculated from the outer diameter of the insulating coating by the density ρ1 of the material of the insulating coating, and the actual mass W2 of the insulating coating.

[0080] (Pores) The voids may be derived from thermally decomposable resin-containing particles. The thermally decomposable resin-containing particles are gasified by thermal decomposition, and voids are formed in the areas of the insulating coating 3 where the thermally decomposable resin-containing particles were present. In this case, the fine particles can be uniformly distributed as an island phase in the sea phase of the resin matrix that constitutes the insulating coating 3, forming independent voids.

[0081] If the lower limit of the average diameter of the plurality of pores is 0.1 μm, the mechanical properties of the insulating coating 3 can be improved. If the upper limit of the average diameter is 10 μm, the insulating properties of the insulating coating 3 can be improved. The average diameter is a value obtained by measuring a cross section of the insulated wire 1 using a pore diameter distribution measurement device (for example, the "Porous Material Automated Pore Size Distribution Measurement System" manufactured by Porous Materials).

[0082] The insulating coating may contain the amine compound or a decomposition product thereof.

[0083] When the insulating coating contains the amine compound or its decomposition products, the content of the amine compound or its decomposition products in the insulating coating is preferably 2.85 mass % or less relative to the mass of the insulating coating, in which case the amine compound or its decomposition products remain in a more appropriate amount in the insulating coating, thereby improving the adhesion of the insulating coating and reducing the dielectric constant of the insulating coating.

[0084] The upper limit of the content of the amine compound or its decomposition products is 2.85 mass%, or may be 2.80 mass%, or 2.70 mass%, and the lower limit of the content of the amine compound or its decomposition products is, for example, 0.01 mass%.

[0085] The content of the amine compound or its decomposition products in the insulating coating can be determined, for example, by using a pyrolysis gas chromatography mass spectrometer (Py-GC / MS, product name: "6890N / 5973Network", manufactured by Agilent Technologies). In this case, the atmosphere is He gas, and the flow rate is 1 mL / min. Furthermore, the pyrolysis temperature is set to 500°C for 1 min, which is sufficient to volatilize all of the amine compound.

[0086] The insulated wire may have a configuration other than the above. For example, the insulated wire may have an adhesion layer containing an additive such as an adhesion improver between the conductor 2 and the insulating coating 3. Examples of the adhesion improver include mercaptans such as 2-mercaptoimidazole and 5-amino-1,3,4-thiadiazole-2-thiol.

[0087] The insulated wire may have a surface friction adjusting layer as its outermost layer. Examples of the surface friction adjusting layer include a polyamide-imide, self-lubricating amide-imide, polyimide, and self-lubricating polyimide layer. The "outermost layer" refers to the layer located outermost in the laminate structure constituting the insulated wire, with the conductor side positioned inside.

[0088] The insulated wire may have an outermost adhesive layer containing an additive such as a foaming agent. Examples of the foaming agent include azo-based foaming agents such as azodicarbonamide and azobisisobutyronitrile, nitroso-based foaming agents such as dinitrosopentamethylenetetramine and N,N'-dinitroso-N,N'-dimethylterephthalamide, hydrazide-based foaming agents such as p-toluenesulfonylhydrazide, p,p'-oxybisbenzenesulfonylhydrazide and benzenesulfonylhydrazide, and trihydrazinotriazine.

[0089] The insulated wire may have an anti-surge layer containing an inorganic filler as its outermost layer. Examples of inorganic fillers include silica, alumina, magnesia, beryllium oxide, silicon carbide, titanium carbide, boron carbide, tungsten carbide, boron nitride, and silicon nitride. The inorganic filler may be surface-treated. Examples of surface treatment agents include silane coupling agents.

[0090] <Method for manufacturing insulated wire> A method for manufacturing an insulated wire includes a step of applying the resin composition to an outer peripheral surface of a conductor (coating step), and a step of heating the resin composition applied in the coating step (heating step).

[0091] In the coating step, the resin composition is applied to the outer peripheral surface of the conductor. Examples of methods for applying the resin composition to the outer peripheral surface of the conductor include a method using a coating device equipped with a liquid composition tank that stores the resin composition and a coating die. With this coating device, the resin composition adheres to the outer peripheral surface of the conductor as the conductor passes through the liquid composition tank, and then the resin composition is applied to a uniform thickness as the conductor passes through the coating die.

[0092] In the heating step, the resin composition applied to the conductor in the application step is heated to volatilize the organic solvent in the resin composition and cure the polyimide precursor to form a polyimide.

[0093] The heating step may be carried out by any known method, such as hot air heating, infrared heating, or high-frequency heating.

[0094] The heating temperature in the heating step can be, for example, 300° C. or more and 800° C. or less. The heating time in the heating step can be, for example, 5 seconds or more and 1 minute or less.

[0095] The coating step and the heating step are usually repeated multiple times. By repeating the steps multiple times, the thickness of the insulating coating can be increased. The hole diameter of the coating die can be adjusted appropriately depending on the number of repetitions.

[0096] The present invention will be described in more detail below with reference to experimental examples, but the present invention is not limited to these experimental examples.

[0097] <Preparation of resin composition and production of insulated wire> The names of the various components used in preparing the resin composition are shown below. When abbreviations are used, the name is also shown. (Aromatic tetracarboxylic dianhydride) PMDA: pyromellitic dianhydride (Aromatic diamine) ODA: 4,4'-diaminodiphenyl ether (Organic solvent) NMP: N-methyl-2-pyrrolidone DMAc: N,N-dimethylacetamide (Amine compounds) X-1 to X-14 and CX-1 to CX-2 shown in Tables 1 and 2 below were used. In Tables 1 and 2 below, "pKa" indicates the pKa of the conjugate acid of the corresponding amine compound.

[0098]

[0099]

[0100] [No. 1] (Preparation of Resin Composition) ODA as an aromatic diamine was dissolved in NMP. PMDA as an aromatic tetracarboxylic dianhydride was added so that the mixing ratio (molar ratio) of the aromatic tetracarboxylic dianhydride to the aromatic diamine was 100:100. The mixture was allowed to react at 30°C for 3 hours with stirring under a nitrogen atmosphere to synthesize a polyimide precursor, and a polyimide precursor solution containing NMP as a solvent (solids concentration: 28% by mass) was obtained. 2.0 parts by mass of amine compound X-1 was added to 100 parts by mass of the polyimide precursor to prepare Resin Composition No. 1.

[0101] (Preparation of Insulated Wire) A round copper wire having an average diameter of 1 mm was used as the conductor. Resin composition No. 1 was applied to the surface of the conductor, and the conductor coated with resin composition No. 1 was heated in a heating furnace at an inlet temperature of 400°C, an outlet temperature of 500°C, and a wire speed of 6.0 m / min. This process was repeated 13 times to form an insulating coating having an average thickness of 40 μm, thereby producing insulated wire No. 1.

[0102] [Nos. 2 to 34] Resin compositions No. 2 to No. 34 were prepared in the same manner as No. 1, except that the types and amounts of each component shown in Table 3 below were used, and insulated wires No. 2 to No. 9 and No. 12 to No. 34 were produced. Note that, because gelation was confirmed in resin compositions No. 10 and No. 11 in the evaluation of viscosity change over time, which will be described later, insulated wires No. 10 and No. 11 were not produced.

[0103] <Evaluation> The prepared resin compositions No. 1 to No. 34 were evaluated for change in viscosity over time according to the following method. Furthermore, the prepared insulated wires No. 1 to No. 9 and No. 12 to No. 34 were evaluated for coating elongation and measured for the content of the amine compound or its decomposition products according to the following methods.

[0104] [Change in Viscosity Over Time] The viscosity of each of the prepared resin compositions No. 1 to No. 34 at 30°C at the time of preparation (initial viscosity η ０Thereafter, the resin composition was sealed and stored at 40°C for 7 days, and the viscosity at 30°C after 7 days (viscosity after storage η １ The initial viscosity η ０ Viscosity after storage η １ The ratio of η １ / η ０ The ratio η １ / η ０ When the viscosity change over time was 20 or less, it was evaluated that the change in viscosity over time was small. The results are shown in the "Change in viscosity over time" column in Table 3 below. "Gelation" in the "Change in viscosity over time" column means that gelation was confirmed after 7 days, and the viscosity η after storage １ This indicates that the measurement was not possible.

[0105] [Coating Elongation] For the insulated wires No. 1 to No. 9 and No. 12 to No. 34 prepared above, the conductors were removed from the insulated wires to form tubular insulating coatings. The elongation at break (unit: %) was measured when the coatings were pulled using a tensile tester (Shimadzu Corporation's "Autograph AGS-X") at 25°C under conditions of a chuck distance of 20 mm and a pulling rate of 10 mm / min. The coating elongation measurement was performed five times, and the average value was calculated. The results are shown in the "Coating Elongation (%)" column in Table 3 below. A "-" in the "Coating Elongation (%)" column indicates that no insulated wire was prepared.

[0106] [Amine Compound Content] The content of amine compounds or their decomposition products (hereinafter also referred to as "amine compounds") in the prepared insulating coatings No. 1 to No. 9 and No. 12 to No. 34 was measured. The content of the amine compounds or their decomposition products in the insulating coatings was measured using a pyrolysis gas chromatography mass spectrometer (Py-GC / MS, product name: "6890N / 5973Network", manufactured by Agilent Technologies). The atmosphere was He gas, the flow rate was 1 mL / min, and the pyrolysis temperature was 500°C for 1 min, which was sufficient to completely volatilize the amine compounds. The insulating coatings were evaluated as "A" when the content of amine compounds in the insulating coating was 2.85 mass% or less relative to the mass of the insulating coating, and as "B" when the content was more than 2.85 mass%. "-" in the column "Amine compound content" indicates that no insulated wire was produced.

[0107] In Table 3 below, "acid anhydride" means "aromatic tetracarboxylic dianhydride." "Diamine" means "aromatic diamine." "-" in the "organic solvent" column indicates a single solvent. "-" in the "amine compound" column indicates that no amine compound is used. "Content (parts by mass)" in the "amine compound" column indicates the number of parts by mass of the amine compound per 100 parts by mass of the polyimide precursor.

[0108]

[0109] Table 3 shows that, compared to Nos. 9 to 11, 26, and 32, Samples No. 1 to 8, No. 12 to 25, No. 27 to 31, No. 33, and No. 34 showed less change in viscosity over time and were able to form insulating coatings with excellent coating elongation.

[0110] [Other Embodiments] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is not limited to the configurations of the above-described embodiments, but is defined by the claims, and is intended to include all modifications within the meaning and scope of the claims.

[0111] 1 insulated wire 2 conductor 3 insulating coating

Claims

1. A resin composition comprising: a polyimide precursor which is a reaction product of an aromatic tetracarboxylic dianhydride and an aromatic diamine; an organic solvent; and an amine compound, wherein the pKa of a conjugate acid of the amine compound is 11 or less; and the molecular weight of the amine compound is 70 or more.

2. The resin composition according to claim 1, wherein the amine compound is an aromatic amine.

3. The resin composition according to claim 2, wherein the aromatic amine is an aromatic heterocyclic amine.

4. The resin composition according to claim 2, wherein the aromatic amine is an aromatic non-heterocyclic amine.

5. The resin composition according to claim 1, wherein the amine compound is an aliphatic amine.

6. A resin composition according to any one of claims 1 to 5, wherein the 5% mass loss temperature of the amine compound is 200°C or higher.

7. A resin composition according to any one of claims 1 to 6, wherein the content of the amine compound is 0.1 parts by mass or more and 3 parts by mass or less per 100 parts by mass of the polyimide precursor.

8. Viscosity η at 30°C ０ Viscosity η at 30 ° C. after storage at 40 ° C. for 7 days １ The ratio of η １ / η ０ The resin composition according to any one of claims 1 to 7, wherein the σ is 20 or less.

9. The resin composition according to any one of claims 1 to 8, which is used to form an insulating coating for an insulated wire.

10. An insulated wire comprising: a conductor; and an insulating coating covering the conductor, wherein the insulating coating is formed from the resin composition according to any one of claims 1 to 9.

11. The insulated wire according to claim 10, wherein the insulating coating contains the amine compound or its decomposition product, and the content of the amine compound or its decomposition product in the insulating coating is 2.85 mass % or less relative to the mass of the insulating coating.

12. An insulated wire according to claim 10 or 11, wherein the insulating coating contains a plurality of pores.

13. A method for manufacturing an insulated wire comprising a conductor and an insulating coating covering the conductor, the method comprising the steps of: applying a resin composition according to any one of claims 1 to 9 to the outer peripheral surface of the conductor; and heating the resin composition applied in the application step.

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