Insulated wire

Abstract

To provide an insulated wire having an insulating coating with a low dielectric constant and excellent adhesion, heat resistance, and mechanical strength. [Solution] An insulated electric wire comprising an electric wire and an insulating film provided on the electric wire, wherein at least one layer of the insulating film is a first insulating layer made of polyimide obtained by imidizing a first polyamic acid, the first polyamic acid is a polyamic acid obtained by a polyaddition reaction between (A) an acid dianhydride and (B) a diamine, and contains (B1) dimeramine in a molar ratio of 0.2 or more relative to the total diamine components, and contains a fluorine atom in one molecule of the raw material of the polyamic acid.

Description

Technical Field

[0001] The present invention relates to an insulated wire.

Background Art

[0002] In recent years, in addition to those using a conventional enameled wire having a circular cross-section (round enameled wire), those using an enameled wire having a rectangular cross-section (flat enameled wire) are used. Such flat enameled wires are required to have adhesion, heat resistance, and mechanical strength. For example, Patent Document 1 proposes an insulated wire having, in this order, a first layer made of polyimide not containing an adhesion improver, a second layer made of polyamideimide, and a third layer made of polyimide on a conductor.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] On the other hand, for the insulating film of an insulated wire, in order to cope with high frequencies, the demand for polyimide showing low dielectric characteristics is increasing. However, the polyimide described in Patent Document 1 was insufficient from the viewpoint of low dielectric characteristics. In addition, current polyimides tend to have impaired adhesion to a conductor when they have a low dielectric constant. On the other hand, when trying to improve adhesion and heat resistance, the dielectric constant increases and it becomes difficult to suppress partial discharge. Also, in the bending process of a flat wire, particularly in the process of edgewise bending, a larger load is applied to the coating resin than in the case of a normal round wire. Therefore, if the mechanical strength and elongation of the coating resin are not excellent, it will crack. Thus, a polyimide that satisfies all of low dielectric constant, adhesion, heat resistance, and mechanical strength has not been obtained.

[0005] The present invention aims to provide an insulated wire having an insulating coating with a low dielectric constant and excellent adhesion, heat resistance, and mechanical strength. [Means for solving the problem]

[0006] According to the present invention, the following insulated wire is provided. [1] An insulated electric wire comprising an electric wire and an insulating coating provided on the electric wire, At least one layer of the insulating film is a first insulating layer made of polyimide obtained by imidizing a first polyamic acid. The first polyamic acid is a polyamic acid obtained as a polyaddition reaction product of (A) an acidic dianhydride and (B) a diamine. The (B1) dimer amine is contained in a molar ratio of 0.2 or more relative to the total diamine components. The raw material for the polyamic acid contains a fluorine atom in one molecule. Insulated wire. [2] An insulated electric wire comprising an electric wire and an insulating coating provided on the electric wire, At least one layer of the insulating film is a second insulating layer made of polyimide obtained by imidizing a second polyamic acid. The aforementioned second polyamic acid is a polyamic acid obtained from a polyaddition reaction between (A1) an ester-type dianhydride and (B) a diamine. It contains (B1) dimer amine in a molar ratio of 0.3 or more relative to the total diamine components. Insulated wire. [3] In the insulated wire described in [1], The system comprises the electric wire, a second insulating layer provided on the electric wire, and the first insulating layer provided on the second insulating layer. The aforementioned second insulating layer is made of a polyimide obtained by imidizing a second polyamic acid. The aforementioned second polyamic acid is a polyamic acid obtained from a polyaddition reaction between (A1) an ester-type dianhydride and (B) a diamine. It contains (B1) dimer amine in a molar ratio of 0.3 or more relative to the total diamine components. Insulated wire. [Effects of the Invention]

[0007] According to one aspect of the present invention, an insulated wire can be provided having an insulating coating with a low dielectric constant and excellent adhesion, heat resistance, and mechanical strength. [Modes for carrying out the invention]

[0008] [Insulated wire] The first insulated wire according to this embodiment is an insulated wire comprising a wire and an insulating coating provided on the wire. At least one layer of the insulating coating is a first insulating layer made of polyimide obtained by imidizing a first polyamic acid. This first polyamic acid is a polyamic acid obtained as a polyaddition reaction product of (A) an acid dianhydride and (B) a diamine, and contains (B1) dimeramine in a molar ratio of 0.2 or more relative to the total diamine component, and contains a fluorine atom in one molecule of the raw material for the polyamic acid.

[0009] The polyimide formed using this first polyamic acid exhibits low dielectric properties due to its dimer skeleton, and the inclusion of a certain amount of dimeramine as a diamine component further reduces the dielectric constant and dielectric loss tangent, thereby achieving the desired low dielectric properties. Furthermore, it is possible to form a polyimide with excellent thermal decomposition resistance. In addition, by including a fluorine atom in one molecule of the polyamic acid raw material, the solubility of the polyimide in organic solvents can be improved.

[0010] The second insulated wire according to this embodiment is an insulated wire comprising a wire and an insulating coating provided on the wire. At least one layer of the insulating coating is a second insulating layer made of polyimide obtained by imidizing a second polyamic acid. This second polyamic acid is a polyamic acid obtained as a polyaddition reaction product of (A1) ester-type dianhydride and (B) diamine, and contains (B1) dimeramine in a molar ratio of 0.3 or more relative to the total diamine component.

[0011] The polyimide formed using this secondary polyamic acid has both an ester skeleton and a dimer skeleton. Low water absorption can be achieved due to the ester skeleton. Furthermore, low dielectric properties are exhibited due to the dimer skeleton, and the inclusion of a certain amount of dimeramine as a diamine component allows for even lower dielectric constant and dielectric loss tangent, thereby achieving the desired low dielectric properties. In addition, a polyimide with excellent thermal decomposition resistance can be formed.

[0012] (Electric wire) The electric wire used in this embodiment may be an electric wire with a circular cross-section, or an electric wire with a rectangular cross-section. In the case of a wire with a circular cross-section, its diameter is preferably, for example, 0.1 mm or more and 16 mm or less. For electric wires with a rectangular cross-section, the thickness (short side) is preferably between 0.1 mm and 3.5 mm. Furthermore, the width (long side) is preferably between 0.5 mm and 16 mm. Suitable materials for electric wires include copper, copper alloys, iron, silver, gold, aluminum, and aluminum alloys. Of these, copper or copper alloys are preferred from the viewpoint of mechanical strength and other factors.

[0013] (Insulating coating) At least one layer of the insulating film used in this embodiment must comprise at least one of the first insulating layer and the second insulating layer. Either of these first and second insulating layers can improve low dielectric properties and resistance to thermal decomposition. The first insulating layer is a layer made of polyimide obtained by imidizing the first polyamic acid. The second insulating layer is a layer made of polyimide obtained by imidizing the second polyamic acid. The first and second polyamic acids will be described later. The thickness of the insulating film is preferably 20 μm or more and 500 μm or less, more preferably 30 μm or more and 300 μm or less, and particularly preferably 40 μm or more and 150 μm or less. If the thickness is at least the lower limit, the heat resistance and mechanical strength can be further improved. On the other hand, if the thickness is at most the upper limit, coils and the like using the obtained insulated wire can be made sufficiently thin.

[0014] The insulating film used in this embodiment preferably includes a second insulating layer provided on the wire and a first insulating layer provided on the second insulating layer. With such a configuration, the following effects can be achieved. That is, the second insulating layer has better adhesion to the electrode than the first insulating layer. Therefore, by providing this second insulating layer between the first insulating layer and the wire, it is possible to improve the adhesion to the electrode while taking advantage of the high breakdown voltage, low dielectric constant, and heat resistance, which are the advantages of the first insulating layer.

[0015] (Polyamic acid) The first polyamic acid used in this embodiment is a polyamic acid that is a polyaddition reaction product of (A) an acid dianhydride and (B) a diamine, contains (B1) a dimer diamine at a molar ratio of 0.2 or more with respect to all diamine components, and contains a fluorine atom in one molecule of the raw material of the polyamic acid. The second polyamic acid used in this embodiment is a polyamic acid that is a polyaddition reaction product of (A1) an ester-type acid dianhydride and (B) a diamine, and contains (B1) a dimer diamine at a molar ratio of 0.3 or more with respect to all diamine components.

[0016] (Component (A)) The first polyamic acid and the second polyamic acid used in this embodiment use (A) an acid dianhydride as one of the raw materials. Any known acid dianhydride can be used as appropriate. Examples of acid dianhydride components include 3,3',4,4'-biphenyltetracarboxylic acid dianhydride (BTDA), pyromellitic acid dianhydride (PMDA), 4,4'-(hexafluoroisopropylidene)diphthalic acid anhydride (6FDA), and ester-type acid dianhydrides having an ester bond in the molecule. Furthermore, from the viewpoint of including a fluorine atom in one molecule of at least one of the raw materials of the first polyamic acid, it is preferable to use a fluorine-containing acid dianhydride containing a fluorine atom in one molecule as (A) acid dianhydride, and it is preferable to use 4,4'-(hexafluoroisopropylidene)diphthalic acid anhydride (6FDA). When using this fluorine-containing acid dianhydride, it is preferable that the fluorine-containing acid dianhydride is included in a molar ratio of 0.2 or more (more preferably 0.5 or more) relative to the total acid dianhydride components. Furthermore, in this embodiment, it is preferable that the acid dianhydride component has structural units derived from (A1) ester-type acid dianhydride having ester bonds in the molecule. By having structural units derived from ester-type acid dianhydride in the polyamic acid, low water absorption can be imparted to the resulting polyimide. The acid dianhydride has two acid anhydride groups in one molecule, and is preferably a tetracarboxylic dianhydride, and more preferably an aromatic tetracarboxylic dianhydride. There may be one or more ester bonds in the molecule, preferably one to three, and more preferably one or two. The acid dianhydride may be used alone, or two or more may be used in combination.

[0017] Such (A1) ester-type dianhydride preferably has the structure shown in the following formula (1). In formula (1), Ar represents a substituted or unsubstituted arylene group, and a substituted arylene group means that the hydrogen atoms of an unsubstituted arylene group are substituted by any substituent. The number of carbon atoms in the substituted or unsubstituted arylene group (excluding the number of carbon atoms of the substituent) is preferably 6 or more and 20 or less, and more preferably 6 or more and 12 or less.

[0018] [ka]

[0019] In formula (1), examples of unsubstituted arylene groups in Ar include o-phenylene, m-phenylene, p-phenylene, 2,6-naphthylene, and 4,4'-biphenylylene. Among these, p-phenylene, 2,6-naphthylene, or 4,4'-biphenylylene are preferred.

[0020] Examples of substituents on the substituted arylene group include C1-C8 alkyl groups, halogen atoms (fluorine, chlorine, bromine, or iodine atoms), and halogenated alkyl groups in which the hydrogen atoms of the alkyl group are substituted with the halogen atoms. Among these substituents, C1-C8 alkyl groups are preferred, and methyl groups are more preferred. The number of substituents may be one or two or more. If there are two or more substituents, they may be the same or different. Specific examples of substituted arylene groups include the 2,2',3,3',5,5'-hexamethyl-4,4'-biphenylylene group.

[0021] Preferred examples of acid dianhydrides represented by formula (1) include the compound represented by formula (1-1) below (TAHQ) and the compound represented by formula (1-2) below (TMPBP-TME), with the compound represented by formula (1-2) below being more preferred.

[0022] [ka]

[0023] ((B) component) The first polyamic acid and the second polyamic acid used in this embodiment use (B) diamine as one of the raw materials. Any known diamine can be used as appropriate. The diamine component has structural units derived from a diamine, and one of the diamine components has structural units derived from (B1) dimer amine. Here, dimer amine refers to an aliphatic diamine in which two terminal carboxylic acid groups (-COOH) of a cyclic or acyclic dimer acid obtained as a dimer of an unsaturated fatty acid are substituted with a primary aminomethyl group (-CH2-NH2) or an amino group (-NH2). By having structural units derived from dimer amine in the polyamic acid, low dielectric properties can be imparted to the resulting polyimide. (B1) dimer amine may be used alone or two or more may be used in combination.

[0024] Dimer acids are dibasic acids obtained by the intermolecular polymerization reaction of unsaturated fatty acids. Aliphatic diamines derived from dimer acids are obtained by polymerizing unsaturated fatty acids such as oleic acid, linoleic acid, or linolenic acid to form dimer acids, reducing them, and then aminating them. Such dimer amines are preferably diamine compounds obtained by substituting the terminal carboxylic acid group of a dibasic acid compound having 18 to 54 carbon atoms, preferably 22 to 44 carbon atoms, with a primary aminomethyl group or an amino group.

[0025] Commercially available dimeramines include "Versamin® 551" and "Versamin® 552" from Cognics Japan, and "PRIAMINE® 1073," "PRIAMINE® 1074," and "PRIAMINE® 1075" from Croda Japan.

[0026] Furthermore, in the first polyamic acid used in this embodiment, (B1) dimeramine is contained in a molar ratio of 0.2 or more relative to the total diamine components. In the second polyamic acid used in this embodiment, (B1) dimeramine is contained in a molar ratio of 0.3 or more relative to the total diamine components. By including dimeramine in a molar ratio above a certain level relative to the total diamine, the resulting polyimide can be given a lower dielectric constant and a lower dielectric loss tangent. The molar ratio of (B1) dimeramine to the total diamine components is preferably 0.3 or more, and more preferably 0.4 or more.

[0027] The first polyamic acid and the second polyamic acid used in this embodiment preferably contain (B2) aromatic diamine as another diamine component. Examples of (B2) aromatic diamines include p-phenylenediamine (PDA), m-phenylenediamine, 4,4'-oxydianiline (ODA), 3,3'-bistrifluoromethyl-4,4'-diaminobiphenyl (TFMB), 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenylmethane, 3,3'-dimethyl-4,4'-diaminodiphenylmethane, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, 1,2-bis(anilino)ethane, diaminodiphenylsulfone, Examples include diaminobenzanilide, diaminobenzoate, diaminodiphenyl sulfide, 2,2-bis(p-aminophenyl)propane, 2,2-bis(p-aminophenyl)hexafluoropropane, 1,5-diaminonaphthalene, diaminotoluene, diaminobenzotrifluoride, 1,4-bis(p-aminophenoxy)benzene, 4,4'-bis(p-aminophenoxy)biphenyl, diaminoanthraquinone, and 4,4'-bis(3-aminophenoxyphenyl)diphenylsulfone. Among these aromatic diamines, PDA, ODA, or TFMB are preferred, with ODA being more preferred. (B2) Aromatic diamines may be used alone or in combination of two or more. Furthermore, from the viewpoint of including a fluorine atom in one molecule of at least one of the raw materials of the first polyamic acid, it is preferable to use a fluorine-containing aromatic diamine (B21) containing fluorine in one molecule as the (B2) aromatic diamine, and it is preferable to use 3,3'-bistrifluoromethyl-4,4'-diaminobiphenyl (TFMB). When using this (B21) fluorine-containing aromatic diamine, it is preferable that the (B21) fluorine-containing aromatic diamine is included in a molar ratio of 0.2 or more (more preferably 0.5 or more) relative to the total diamine components.

[0028] The molar ratio of diamine to acidic dianhydride [(B) / (A)] is not particularly limited, but is preferably 0.90 to 1.10, more preferably 0.95 to 1.05, even more preferably 0.97 to 1.03, and particularly preferably 0.98 to 1.02.

[0029] ((C) component) The first and second polyamic acids used in this embodiment can be synthesized by known general methods. For example, a polyamic acid composition (polyamic acid solution) can be obtained by reacting (A) an acidic dianhydride and (B) a diamine in (C) an organic solvent. The organic solvent used for polymerization of polyamic acid is not particularly limited as long as it can dissolve the acidic dianhydride and diamine as monomer components and also dissolve the polyamic acid produced by the polyaddition reaction. Examples of such organic solvents include urea-based solvents such as tetramethylurea and N,N-dimethylethylurea; sulfone-based solvents such as dimethyl sulfoxide, diphenyl sulfone, and tetramethyl sulfone; amide-based solvents such as N,N-dimethylacetamide, N,N-dimethylformamide, N,N-diethylacetamide, N-methyl-2-pyrrolidone, and hexamethylphosphate triamide; ester-based solvents such as γ-butyrolactone; alkyl halide-based solvents such as chloroform and methylene chloride; aromatic hydrocarbon-based solvents such as benzene and toluene; phenol-based solvents such as phenol and cresol; ketone-based solvents such as cyclopentanone; and ether-based solvents such as tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane, dimethyl ether, diethyl ether, and p-cresol methyl ether. These organic solvents may be used individually or in combination of two or more. From the viewpoint of enhancing the solubility and reactivity of polyamic acids, the organic solvent is preferably selected from the group consisting of amide solvents, ketone solvents, ester solvents, and ether solvents, with amide solvents such as N,N-dimethylacetamide, N,N-dimethylformamide, N,N-diethylacetamide, and N-methyl-2-pyrrolidone being more preferred.

[0030] The molecular weight of polyamic acid can be adjusted by adjusting the molar ratio of the total number of moles of the acidic dianhydride component to the total number of moles of the diamine component. The molecular weight (weight-average molecular weight) of polyamic acid is not particularly limited, but from the viewpoint of solubility in organic solvents, it is more preferable to be between 10,000 and 100,000. The weight-average molecular weight of polyamic acid can be determined, for example, from the value converted to standard polystyrene by gel filtration chromatography (GPC) measurement.

[0031] The synthesis of polyamic acids by the polyaddition reaction of acidic dianhydrides and diamines is preferably carried out in an inert atmosphere such as argon or nitrogen. In an inert atmosphere, the polyaddition reaction proceeds by dissolving the acidic dianhydride and diamine in an organic solvent and mixing them. The order of addition of the acidic dianhydride and diamine is not particularly limited. For example, the diamine may be dissolved in an organic solvent or dispersed in a slurry to form a diamine solution, and the acidic dianhydride may be added to the diamine solution. The acidic dianhydride and diamine may be added directly to the organic solvent in a solid state, or they may be added separately dissolved in an organic solvent or dispersed in a slurry.

[0032] The temperature conditions for the polyaddition reaction are not particularly limited, but from the viewpoint of suppressing the decrease in molecular weight of the polyamic acid due to depolymerization, the reaction temperature is preferably 100°C or lower, and from the viewpoint of allowing the polyaddition reaction to proceed appropriately, the reaction temperature is more preferably 20°C to 80°C. The reaction time can be arbitrarily set within the range of 1 hour to 72 hours, and if necessary, it may be left overnight at room temperature.

[0033] When preparing the compositions of the first and second polyamic acids used in this embodiment, the viscosity of the solution is preferably 500 mPa·s or higher from the viewpoint of film-forming properties. Furthermore, the concentration of polyamic acid in the compositions of the first and second polyamic acids used in this embodiment is preferably 10% by mass or higher, more preferably 15% by mass or higher, and even more preferably 25% by mass or higher. In particular, if the concentration of polyamic acid is 15% by mass or higher, the productivity when forming polyimide coating films using polyamic acid can be increased. Furthermore, the upper limit of the concentration of polyamic acid is preferably 50% by mass or lower, and even more preferably 30% by mass or lower, from the viewpoint of sufficiently dissolving the polyamic acid in the organic solvent.

[0034] To impart processing properties or various functionalities to polyamic acid and polyimides formed using said polyamic acid, various organic or inorganic low-molecular-weight or high-molecular-weight compounds may be blended into the polyamic acid composition. For example, the polyamic acid composition may contain solvent-soluble polyimide resin, flame retardants, dyes, surfactants, leveling agents, plasticizers, fine particles, sensitizers, or silane coupling agents. The fine particles may be either organic or inorganic, and may have a porous or hollow structure. Furthermore, after polyimidization of the polyamic acid, some of the amino groups may be maleimidized.

[0035] (Polyimide) The polyimide used in this embodiment is a polyimide obtained by imidizing at least one of the first polyamic acid and the second polyamic acid used in the above-described embodiment. The method for converting polyamic acid to polyimide is not particularly limited, but polyimide can be produced by dehydrating and cyclizing (imidizing) the polyamic acid obtained as described above. The dehydration and cyclization (imidization) method can be a known method such as thermal imidization, which involves dehydration and cyclization by heating, or chemical imidization, which involves chemical cyclization using a known dehydration and cyclization catalyst.

[0036] In the case of thermal imidation, the heating temperature is preferably 120°C to 350°C, and more preferably 150°C to 250°C. In the case of chemical imidation, for example, pyridine, triethylamine, or acetic anhydride can be used as the dehydration and ring-closing catalyst. In this case, the reaction temperature can be selected to any temperature between 20°C and 180°C, but it is preferably 150°C or lower. Imidation may be carried out in air, under reduced pressure, or in an inert gas such as nitrogen, but in order to obtain a highly transparent polyimide film, it is preferable to carry it out under reduced pressure or in an inert gas such as nitrogen.

[0037] The molecular weight (weight-average molecular weight) of the polyimide is not particularly limited, but it is preferably between 10,000 and 100,000 from the viewpoint of low dielectric properties, solubility in organic solvents, and film-forming properties of the resulting polyimide. The weight-average molecular weight of the polyimide can be determined, for example, from the value converted to standard polystyrene by gel filtration chromatography (GPC) measurement.

[0038] The method for forming an insulating film made of the polyimide on an electric wire is not particularly limited. For example, one method involves applying the above-mentioned polyamic acid composition in a film-like manner onto the electric wire, then drying and heating to remove the solvent and dehydrate and cyclize (imidize) the film, or applying a solution in which soluble polyimide obtained by converting polyamic acid to polyimide is dissolved in an organic solvent to the electric wire in a film-like manner, and then drying and removing the solvent. The method of application to the electric wire is not particularly limited, and conventionally known application methods can be applied.

[0039] The thickness of the insulating layer made of polyimide can be easily controlled by appropriately adjusting the solid content concentration of each component in the polyamic acid composition, the coating thickness, and the viscosity. [Examples]

[0040] Next, the present invention will be described in more detail with reference to examples and comparative examples, but the present invention is not limited in any way by these examples. The materials used in the examples and comparative examples are listed below. (Component A1) Ester-type acidic dianhydride: 2,2',3,3',5,5'-Hexamethyl[1,1'-biphenyl]-4,4'-diyl=bis(1,3-dioxo-1,3-dihydro-2-benzofuran-5-carboxylate) (TMPBP-TME) (Component A) Fluorine-containing dianhydride: 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6 FDA) Acidic dianhydride: 3,3',4,4'-biphenyltetracarboxylic acid dianhydride (BTDA) ((B1) component) Dimer amine: PRIAMINE 1075, manufactured by Croda Japan Co., Ltd. ((B2) component) Aromatic diamine: 4,4'-oxydianiline (ODA) (Component B21) Fluorine-containing aromatic diamine: 3,3'-bistrifluoromethyl-4,4'-diaminobiphenyl (TFMB) ((C) component) Organic solvent: N-methyl-2-pyrrolidone (NMP)

[0041] [Example 1] 4.0 parts by mass of dimer amine, 0.5 parts by mass of aromatic diamine, and 30 parts by mass of organic solvent were placed in a flask, and the diamine was dissolved. Next, 6.2 parts by mass of an ester-type dianhydride was added, and the mixture was stirred at 80°C for 24 hours to prepare a polyamic acid composition. Next, a rectangular cross-section wire (material: copper, thickness: 0.2 mm, width: 1 mm) was immersed in the obtained second polyamic acid composition, then removed, and once the dripping subsided, it was placed in an oven. A heat treatment was then performed at 160°C for 10 minutes, followed by 190°C for 20 minutes to produce an insulated wire (an insulated wire with a second insulating layer of 50 μm thickness).

[0042] [Example 2] 1.6 parts by mass of dimer amine, 2.3 parts by mass of fluorine-containing aromatic diamine, and 30 parts by mass of organic solvent were placed in a flask, and the diamine was dissolved. Next, 3.1 parts by mass of ester-type dianhydride and 1.6 parts by mass of dianhydride were added, and the mixture was stirred at 80°C for 5 hours to prepare the first polyamic acid composition. Next, an insulated wire (an insulated wire having a first insulating layer with a thickness of 50 μm) was fabricated in the same manner as in Example 1, except that the obtained first polyamic acid composition was used.

[0043] [Comparative Example 1] 2.0 parts by mass of aromatic diamine and 16.76 parts by mass of organic solvent were placed in a separable flask, and the temperature was raised to 70°C to dissolve the diamine. Next, 2.18 parts by mass of acidic dianhydride were added, the mixture was heated to 100°C, and stirred for 2 hours to prepare a polyamic acid composition. Next, an insulated wire (an insulated wire with an insulating coating 50 μm thick) was prepared in the same manner as in Example 1, except that the obtained polyamic acid composition was used.

[0044] [Comparative Example 2] A polyamic acid composition was prepared by placing 4.4 parts by mass of fluorine-containing dianhydride, 3.2 parts by mass of fluorine-containing aromatic diamine, and 30.5 parts by mass of organic solvent into a separable flask and stirring at room temperature for 96 hours. Next, an insulated wire (an insulated wire with an insulating coating 50 μm thick) was prepared in the same manner as in Example 1, except that the obtained polyamic acid composition was used.

[0045] [Evaluation of insulating coating] The insulating film was evaluated (dielectric constant, dielectric strength, elongation at break, heat resistance, and copper adhesion) using the following method. The results are shown in Table 1. Table 1 also shows the blending amounts of component (A) and component (B) in each example, the molar ratio of component (A), the molar ratio of component (B), the molar ratio of diamine to acidic dianhydride [(B) / (A)], and the presence or absence of fluorine atoms in one molecule of the raw material. (1) Dielectric constant First, test specimens were prepared as follows: A polyamic acid composition was applied to a substrate (PET film, thickness: 38 μm, with release treatment) using a bar coater, and then heat-treated at 160°C for 10 minutes, followed by 190°C for 20 minutes to produce test specimens of the specified size. The dielectric constant of the obtained test specimens (thickness: 20-40 μm, length: 50 mm, width: 2 mm) was measured using the cavity resonance method with a network analyzer and cavity resonator manufactured by Key Sight Technologies, under the conditions of a measurement temperature of 25°C, a measurement humidity of 50 RH%, and a frequency of 1 MHz. The dielectric constant was then evaluated according to the following criteria. ○: The dielectric constant is less than 3.0. ×: The dielectric constant is 3.0 or higher. (2) Withstand voltage Except for the size of the test specimen, (1) test specimens of the specified size were prepared in the same manner as those prepared for dielectric constant testing. For the obtained test specimens (thickness: 20-40 μm), the voltage was increased at 0.5 kV / sec in the thickness direction of the specimen, and the conductive voltage was measured using the "Ultra-High Voltage Withstand Voltage Tester Model 7472" manufactured by Keisoku Gijutsu Kenkyusho Co., Ltd., and the dielectric breakdown voltage was calculated. Then, the withstand voltage was evaluated according to the following criteria. ○: The dielectric breakdown voltage is greater than 200kV / mm. ×: The dielectric breakdown voltage is 200kV / mm or less. (3) Elongation at break Except for the size of the test specimen, (1) test specimens of the specified size were prepared in the same manner as those prepared for dielectric constant testing. The obtained test specimens (thickness: 20-40 μm) were measured for elongation using an Autograph machine manufactured by SHIMAZU Corporation at a tensile speed of 5 mm / min, in accordance with the method described in JIS C 3216-3 3.1. The elongation at break was then evaluated according to the following criteria. ○: The growth rate is 5% or more. ×: The growth rate is less than 5%. (4) Heat resistance Except for the size of the test specimen, (1) test specimens of the specified size were prepared in the same manner as those prepared for dielectric constant testing. The obtained test specimens (thickness: 20-40 μm) were subjected to thermogravimetric analysis using a thermogravimetric analyzer (STA7200RV, manufactured by Hitachi High-Tech Science Corporation). The thermogravimetric analysis conditions were a heating rate of 10°C / min and a nitrogen atmosphere (200 mL / min). The temperature at which a 5% weight reduction occurred was measured by thermogravimetric analysis. Then, the heat resistance was evaluated according to the following criteria. ◎: The temperature is 350℃ or higher when the weight decreases by 5%. ○: The temperature at which the weight decreases by 5% is between 250°C and 350°C. ×: The temperature at which the weight decreases by 5% is less than 250°C. (5) Copper adhesion The obtained insulated wires were used as test specimens, and their copper adhesion was evaluated according to the following criteria, in accordance with the method described in JIS C 3216-3 JA.5.2. ○: No peeling of the coating on the flat rectangular wire. ×: Coating peeling present.

[0046] [Table 1]

[0047] As is clear from the results shown in Table 1, the insulated wires of the present invention (Examples 1 and 2) were confirmed to have good results in all aspects, including dielectric constant, dielectric strength, elongation at break, heat resistance, and copper adhesion. Therefore, it was confirmed that the insulated wire of the present invention has an insulating coating with a low dielectric constant and excellent adhesion, heat resistance, and mechanical strength. Furthermore, it was found that the insulated wire obtained in Example 2 (an insulated wire having a first insulating layer) had superior heat resistance compared to the insulated wire obtained in Example 1 (an insulated wire having a second insulating layer).

[0048] [Example 3] First, a second polyamic acid composition was obtained in the same manner as in Example 1. Then, a first polyamic acid composition was obtained in the same manner as in Example 2. Next, a rectangular cross-section wire (material: copper, thickness: 0.2 mm, width: 1 mm) was immersed in the obtained second polyamic acid composition, then removed, and once the dripping subsided, it was placed in an oven. A heat treatment was then performed at 160°C for 10 minutes, followed by 190°C for 20 minutes to produce an insulated wire (an insulated wire with a second insulating layer of 50 μm thickness). Furthermore, this insulated wire was immersed in the obtained first polyamic acid composition, then removed, and once the dripping subsided, it was placed in an oven. A heat treatment was then performed at 160°C for 10 minutes, followed by 190°C for 20 minutes to produce an insulated wire (an insulated wire with a first insulating layer of 50 μm thickness on top of a second insulating layer of 50 μm thickness).

[0049] The obtained insulated wires were evaluated for dielectric constant, dielectric strength, elongation at break, heat resistance, and copper adhesion. As a result, the evaluation results for dielectric constant, dielectric strength, elongation at break, and copper adhesion were "○", and the evaluation result for heat resistance was "◎". From this, it was found that the insulated wire of Example 3 can improve heat resistance compared to the insulated wire of Example 1 while maintaining various physical properties such as copper adhesion.

Claims

1. An insulated electric wire comprising an electric wire and an insulating coating provided on the electric wire, At least one layer of the insulating film is a first insulating layer made of polyimide obtained by imidizing a first polyamic acid. The first polyamic acid is a polyamic acid obtained as a polyaddition reaction product of (A) an acidic dianhydride and (B) a diamine. The (B1) dimer amine is contained in a molar ratio of 0.2 or more relative to the total diamine components. The raw material for the polyamic acid contains a fluorine atom in one molecule. Insulated wire.

2. An insulated electric wire comprising an electric wire and an insulating coating provided on the electric wire, At least one layer of the insulating film is a second insulating layer made of polyimide obtained by imidizing a second polyamic acid. The aforementioned second polyamic acid is a polyamic acid obtained as a polyaddition reaction product of (A1) an ester-type dianhydride and (B) a diamine. (B1) dimer amine is contained in a molar ratio of 0.3 or more relative to the total diamine components. Insulated wire.

3. In the insulated wire according to claim 1, The system comprises the electric wire, a second insulating layer provided on the electric wire, and the first insulating layer provided on the second insulating layer. The aforementioned second insulating layer is made of a polyimide obtained by imidizing a second polyamic acid. The aforementioned second polyamic acid is a polyamic acid obtained as a polyaddition reaction product of (A1) an ester-type dianhydride and (B) a diamine. (B1) dimer amine is contained in a molar ratio of 0.3 or more relative to the total diamine components. Insulated wire.

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