JP2019026706A - Production method of varnish, production method of enamel wire, production method of coil and production method of electric component - Google Patents

Abstract

To provide a production method of a varnish, an enamel wire, a coil and an electric component capable of making high concentration and low viscosity, and capable of making a thick film by suppressing an occurrence of crack during film formation.SOLUTION: Connected oligomers obtained by amide bonding alternately a first repeating unit having an ester group and a second repeating unit having an amino group are polymerized to obtain polyamic acid, and a varnish containing the polyamic acid is produced. Then, this varnish is used to produce enamel wires, coils and electric components.SELECTED DRAWING: None

Description

  The present invention relates to a varnish manufacturing method, an enameled wire manufacturing method, a coil manufacturing method, and an electrical component manufacturing method.

  Enamelled wires (insulating coated enameled wires) are widely used as electric wires for coils of electric parts such as rotating electric machines and transformers. The enameled wire used here has a configuration in which an insulating film is formed on the outer layer of a metal conductor wire formed into a cross-sectional shape (for example, round shape, rectangular shape, etc.) that matches the application and shape of the coil. In recent years, from the viewpoint of improving energy efficiency, the efficiency, output, and size of electric parts used in home appliances, industrial electric machines, marine electric machines, railways, and automobile electric machines have been increasing.

  In order to achieve higher efficiency and higher output of electric parts, inverter control and higher voltage of electric parts are progressing. As a result, the temperature of the coil during the operation of the electrical component tends to be higher than before, and the coil enameled wire is required to have high heat resistance. Ensuring heat resistance in enameled wires is often achieved by using a resin composition having high heat resistance (for example, an imide resin) as an insulating coating material.

  In electrical parts that are inverter-controlled from the viewpoint of high efficiency, a high voltage is applied to the coil due to an inverter surge voltage or the like. For this reason, the insulating coating may deteriorate or be damaged due to the occurrence of partial discharge. Therefore, the coil enameled wire is also required to have excellent voltage resistance (pressure resistance). In order to improve the pressure resistance of the enameled wire, for example, a method using a resin composition having a low relative dielectric constant for the insulating coating, a method of increasing the thickness of the insulating coating, or the like can be considered.

  In order to reduce the size and increase the output of electrical equipment, it is effective to reduce the diameter and density of the enamel wire in the coil and increase the space factor of the metal conductor wire. Therefore, the coil enameled wire is required to have a thin and uniform insulating coating. The formation of the insulating film is preferably performed by forming an extremely thin film by one application and baking of varnish (insulating paint), and repeating this multiple times. Thereby, a thin and uniform insulating film can be obtained. For example, in order to form an insulating film having a thickness of 50 μm to 100 μm, application and baking are usually repeated about 10 to 20 times. However, if the number of times of application increases, irregularities are easily formed on the surface. Therefore, the coating is repeatedly performed so as not to be uneven.

  On the other hand, in recent years, for example, in order to cope with an increase in the amount of enameled wire used in the automobile field, an improvement in productivity in the coating and baking process has been demanded. That is, there is a need for a technique that can maintain or improve various performances of enameled wires (for example, heat resistance, pressure resistance, dimensional accuracy) while suppressing manufacturing costs. As one means for realizing this, a technique has been studied in which an insulating coating is thickened by applying and baking a small number of times using an insulating paint having a high concentration and a low viscosity. That is, there is a need for a technique for improving the ability to form a thick film by increasing the varnish concentration even if the coating film thickness is extremely thin in order to prevent unevenness of the insulating layer. Regarding such a technique, a technique described in Patent Document 1 is known.

  Patent Document 1 describes a polyimide precursor solution containing a salt composed of a specific carboxylic acid and a specific diamine as a solute. Moreover, after reacting 0 mol-0.95 mol of specific diamine with respect to 1 mol of specific tetracarboxylic dianhydrides in a solvent, and making it react with water or alcohol then, 1 mol of this carboxylic acid is obtained. The manufacturing method of the polyimide precursor solution which adds 0.95 mol-1.05 mol of specific diamine with respect to. The polyimide coating film obtained from the said polyimide precursor solution and the manufacturing method of the polyimide coating film which coats the said polyimide precursor solution on a base material, and heat-imidizes are described.

Japanese Patent Laid-Open No. 2001-31764 (see “Abstract” in particular. Published Patent Gazette corresponding to Japanese Patent No. 4589471)

  When the present inventors examined, the polyimide coating solution (insulating coating) formed on the core wire surface is cracked at the time of baking after applying the polyimide precursor solution of Patent Document 1 to the core wire (metal conductor wire), for example. (Crack) was found to occur. In particular, it has been found that such cracks are likely to occur when the film thickness is thick (that is, thick film). Therefore, in the technique described in Patent Document 1, when an enameled wire is manufactured by forming a thick insulating coating on the core wire, cracking occurs when attempting to form the thick film. There is room for improvement.

  Further, when forming a thick insulating film, it is preferable to form it by applying and baking as few times as possible from the viewpoint of productivity. That is, it is required to use a high-concentration varnish to increase the film thickness and to easily apply the varnish. And the ease of application | coating of this varnish can be achieved by the viscosity reduction of a varnish, for example.

  The present invention has been made in view of such a problem, and the problem to be solved by the present invention is that a high concentration and low viscosity can be achieved, and the generation of cracks during film formation is suppressed, and a thick film is formed. Varnish manufacturing method, enameled wire manufacturing method, coil manufacturing method, and electrical component manufacturing method are provided.

  As a result of intensive studies to solve the above problems, the present inventors have found the following knowledge and completed the present invention. That is, the gist of the present invention is an embodiment for carrying out the invention and at least one first repeating unit of structures represented by formula (1) to formula (4) described later in the embodiment for carrying out the invention. In which a polyamic acid is obtained by polymerizing oligomers linked by alternately repeating amide bonds with second repeating units represented by formula (5) described later, and a varnish containing the polyamic acid is produced. And a method for producing a varnish. The other means for solving will be described later in the mode for carrying out the invention.

  According to the present invention, a varnish manufacturing method, an enameled wire manufacturing method, a coil manufacturing method, and an electric machine capable of increasing the concentration and decreasing the viscosity and suppressing the occurrence of cracks during film formation to increase the film thickness. A method for manufacturing a component can be provided.

It is sectional drawing of the enamel wire manufactured by the manufacturing method of 1st embodiment. It is sectional drawing of the enamel wire manufactured by the manufacturing method of 2nd embodiment. It is sectional drawing of the enameled wire manufactured by the manufacturing method of 3rd embodiment. It is sectional drawing of the enameled wire manufactured by the manufacturing method of 4th embodiment. It is a figure which shows the structure of the stator vicinity with which the rotary electric machine manufactured by the manufacturing method of 5th embodiment was equipped.

  Hereinafter, a form (this embodiment) for carrying out the present invention will be described. However, the content described below is merely an example, and can be implemented with any changes without departing from the gist of the present invention. In addition, each drawing to be referred to may be appropriately enlarged or reduced for convenience of illustration, and the relative size of each member may be different from the actual one.

  FIG. 1 is a cross-sectional view of an enameled wire 10 manufactured by the manufacturing method of the first embodiment. The enameled wire 10 has a circular cross section as shown in FIG. The enameled wire 10 includes a metal conductor wire 1 (core wire) composed of a metal conductor having a small electrical resistance, and an insulating coating 2 formed on the surface thereof. In this embodiment, the insulating coating 2 is formed by applying varnish (including polyamic acid) to the surface of the metal conductor wire 1 and then baking (drying) it.

  The material for forming the metal conductor wire 1 may be any material as long as it has a low electrical resistance and allows easy current flow. Specifically, for example, metal materials usually used for enameled wires, that is, copper and aluminum, various alloys, and the like can be given. More specifically, in the case of copper, tough pitch copper, deoxidized copper, oxygen-free copper and the like can be mentioned. In the case of various alloys, copper-tin alloy, copper-silver alloy, copper-zinc alloy, copper-chromium alloy, copper-zirconium alloy, aluminum-copper alloy, aluminum-silver alloy, aluminum-zinc alloy, aluminum -Iron alloy, No. 1 aluminum alloy (Aldrey Aluminum), etc. are mentioned. A metal film composed of tin, nickel, silver, aluminum, or the like may be appropriately formed on the surface of these metal materials.

  The insulating coating 2 prevents the current flowing through the metal conductor wire 1 from leaking, that is, insulates. The insulating coating 2 contains polyimide. And this polyimide is obtained by dehydrating and imidizing the polyamic acid contained in a varnish by heating. Therefore, this insulating coating 2 contains polyimide. Here, the varnish used when forming (manufacturing) the insulating coating 2 constituting the enameled wire 10 will be described.

  The varnish produced by the production method of the present embodiment is represented by at least one carboxyl unit (first repeating unit) of the structures represented by the following formulas (1) to (4) and the following formula (5). The polyamic acid obtained by polymerizing the oligomer (oligomer of this embodiment) connected by the amide bond alternately with the amino unit (second repeating unit) is included. Therefore, in this embodiment, a varnish is manufactured by superposing | polymerizing the oligomer of this embodiment and synthesizing a polyamic acid. In addition, the repeating unit which comprises the polyamic acid contained in a varnish, and the structural unit which comprises the oligomer used as the starting material of a polyamic acid are the same.

(In the formulas (1) to (4), each R independently represents a hydrogen atom or an alkyl group having 4 or less carbon atoms, and the alkyl group may be a chain or a ring, and has a branch. May be.)

  The carboxyl unit is a unit derived from the same component except that the bonding position with the amino unit is different. That is, the carboxyl unit is in an isomer relationship. Therefore, in this embodiment, the polyamic acid contained in the varnish and the oligomer that is the starting material thereof may be composed of only a single repeating unit among the carboxyl units, or may contain multiple types of carboxyl units. It may be configured.

  Here, as a monomer component (first component, hereinafter referred to as carboxyl component) capable of giving a carboxyl unit, for example, 4,4'-oxydiphthalic anhydride (ODPA) can be mentioned. Examples of the monomer component that can give an amino unit (second component, hereinafter referred to as amino component) include 4,4'-diaminodiphenyl ether (ODA).

  In the present embodiment, the polyamic acid contained in the varnish is obtained by polymerizing the oligomer (the oligomer of the present embodiment) as described above. Therefore, the polyamic acid is also formed by linking the carboxylic units and the amino units by alternately forming amide bonds.

  It is preferable that one of the structures represented by the following formulas (6) to (13) is arranged at the terminal of the polyamic acid. X represents a polycondensation structure of a carboxyl terminal and an amino terminal.

  (In the formulas (6) to (13), R is the same as R described in the formulas (1) to (4), and X is an amide bond between the carboxyl unit and the amino unit alternately. It has a linked structure.)

  In a polyamic acid, it is preferable that a carboxyl unit and an amino unit exist in the both terminal. That is, the polyamic acid preferably has both a carboxyl terminus and an amino terminus. Such a polyamic acid can be obtained, for example, by polymerizing an equal amount of a carboxyl component and an amino component in a molar ratio. However, in consideration of measurement errors and the like, a slight deviation (for example, about 5 mol% or less, preferably about 2 mol% or less) compared with the equivalent amount is allowed.

  In addition, in this specification, an oligomer means the polymer whose styrene conversion mass mean molecular weight is about 3000 or less normally. On the other hand, a polymer (polyamic acid) refers to a polymer having a styrene-equivalent mass average molecular weight usually exceeding 3000. However, the styrene-converted mass average molecular weight has a distribution. Therefore, the varnish containing polyamic acid may contain an oligomer having a styrene-converted mass average molecular weight of 3000 or less. Therefore, for example, when a varnish containing a polyamic acid is produced by polymerizing an oligomer having a styrene-converted mass average molecular weight of about 3000 or less (specifically, for example, about 1000), the produced varnish includes, for example, about 1000 to 2000 There is a possibility that an oligomer having a weight average molecular weight in terms of styrene is included. Thus, even the varnish containing the oligomer in addition to the polyamic acid is included in the category of the present invention.

  Hereinafter, as an example, a polyamic acid and an oligomer serving as a starting material thereof will be described using the structures of formulas (6) to (13). The above R is a hydrogen atom when the polymerization terminal is a carboxyl group. The carboxyl terminus of the oligomer is preferably any one of formulas (6) to (13). And in Formula (6)-(13), it is preferable that one of the two R contained is a hydrogen atom, and the other is an alkyl group. Among these alkyl groups, a chain alkyl group having 1 to 4 carbon atoms is preferable. Thereby, carboxylation and esterification of the acid anhydride structure at the polymerization terminal can be easily produced by selecting a hydrogen atom having a small steric hindrance and a chain alkyl group having 1 to 4 carbon atoms.

  Formula (14) shows an example of the amino terminal structure in the case where the raw material of the polyamic acid and its starting oligomer is only ODPA and ODA. In addition, description of an isomer is abbreviate | omitted.

  The polycondensation reaction does not proceed at normal temperature between the carboxyl terminal represented by the formulas (6) to (13) and the amino terminal (eg, represented by the formula (14)) present at the terminal of X. That is, the molecular weight of the polyamic acid starting from the oligomer is small. Therefore, the density | concentration of the varnish containing a polyamic acid can be increased, and a viscosity can be reduced. Furthermore, the storage stability can be improved by suppressing the polymerization reaction during storage.

  On the other hand, when the oligomer used as the starting material of the polyamic acid is heated to 200 ° C. or higher, the carboxyl terminal is ring-closed with the elimination of water or alcohol to form an acid anhydride structure. In particular, when ODPA is used as the carboxyl component, the acid anhydride structure is regenerated. Here, the chemical reaction formula in the case of having a methyl ester group (R is a methyl group) and a carboxyl group at the polymerization terminal is shown below.

  The acid anhydride regenerated at the polymerization end has high reactivity with the aromatic amino group present at the other polymerization end. In addition, the polycondensation structure consisting of a carboxyl unit and an amino unit contains many ether linkages, so it is flexible and has the property that the nearby acid anhydride and aromatic amino group are easily accessible at high temperatures. . Due to this effect, at a baking temperature exceeding 200 ° C., the polymerization of the low molecular weight polyamic acid proceeds with imidation of the polyamic acid contained in the varnish.

  That is, in the present invention, the polymerization of the low molecular weight polyamic acid proceeds during baking, so that the polyamic acid can be reduced in molecular weight while suppressing the deterioration of the heat and mechanical properties of the insulating coating. High concentration and low viscosity can be achieved. At the same time, a similar polycondensation reaction can proceed between oligomers that can be contained in the varnish to increase the molecular weight. As described above, according to the present invention in which the low molecular weight polyamic acid and its oligomer are increased in molecular weight during baking, the insulating coating 2 is given high elongation at break, and cracking of the insulating coating 2 during thick film formation is prevented. While having the effect of reducing the varnish viscosity and increasing its concentration.

  Next, a method for producing a varnish will be described by taking an example of production using ODPA and ODA while explaining an oligomer that is a starting material for polyamic acid contained in the varnish. For the sake of simplicity, the reaction amount ratio is expressed as a molar ratio.

  First, ODPA is dissolved in a solvent (for example, N-methyl-2-pyrrolidone, hereinafter referred to as NMP). The amount of ODPA used here is 1 mol for convenience. Then, ODA is dissolved in a solvent in which ODPA is dissolved (that is, ODPA solution). By dissolution of ODA, ODPA and ODA are polymerized to produce these oligomers.

  The amount of ODA (second component) used for oligomer formation is preferably 0.5 mol or less with respect to 1 mol of ODPA (first component). By doing in this way, the oligomer whose amino unit which is a unit derived from ODA is less than the carboxyl unit derived from ODPA is obtained. Moreover, although mentioned later for details, it becomes easy to obtain the oligomer which the carboxyl unit (unit corresponding to the acid anhydride group derived from ODPA) couple | bonded with the both terminal.

  In addition, with respect to the formation of the oligomer, with respect to the oligomer obtained by polymerizing ODA and ODPA, at least one of 0.025 mol to 0.5 mol monohydric alcohol and water (hereinafter referred to as “partial”) with respect to 1 mol of ODPA. It is preferable to act an esterifying agent). And it is preferable to polymerize the oligomer obtained by acting a partial esterifying agent, and to produce a polyamic acid.

  Due to the action of the partial esterifying agent, a part of the acid anhydride structure of ODPA present at the terminal of the oligomer changes to an ester group or a carboxyl group depending on the monovalent alcohol or water. Hereinafter, what was obtained by changing to a carboxyl group or an ester group is referred to as a “partially esterified product”. This reaction is referred to as “partial esterification reaction”.

  The production amount of the partially esterified product of ODPA is controlled by the addition amount (total amount) of monohydric alcohol and water, and the molecular weight of the polyamic acid (mass equivalent weight average molecular weight) is controlled by the production amount of the partially esterified product. For accurate control, it is preferable to carry out the partial esterification reaction in a homogeneous solution.

  And these polymerization advances by adding ODA with respect to the solution containing the oligomer manufactured in this way further. As the amount of ODA used, the remaining amount obtained by subtracting the amount used when the oligomer is used from the equivalent amount of ODPA used (for example, 1 mol) can be used. By the above operation, a polyamic acid containing an equal amount of a carboxyl unit derived from ODPA and an amino unit derived from ODA, and a varnish containing the polyamic acid are obtained.

  During the polyamic acid production reaction, a polycondensation reaction occurs between the acid anhydride group of ODPA and the amino group of ODA that remain without being affected by the partial esterification agent. On the other hand, the partially esterified product functions as a terminal blocking agent, and the molecular weight of the polyamic acid is reduced. In this low molecular weight polyamic acid, a partially esterified product used as a terminal blocking agent is disposed at one polymerization terminal, and an ODA-derived aromatic diamine is disposed at the other terminal. Therefore, if the amount of the partially esterifying agent used is large, the amount of partially esterified product increases, so that the polymerization does not proceed easily and the molecular weight of the polyamic acid becomes relatively small. On the other hand, if the amount of the partially esterifying agent used is small, the amount of the partially esterified product also decreases, so that the polymerization proceeds easily and the molecular weight of the polyamic acid becomes relatively large.

  The solubility of ODPA in NMP is low, and it is preferable to improve the solubility of ODPA in order to control the molecular weight of polyamic acid. Therefore, as a result of the study by the present inventors, in order to improve the solubility of ODPA during the production of the polyamic acid contained in the varnish, first, a predetermined amount of ODPA and ODA are reacted to form an oligomer. I found it effective. The oligomer preferably has ODPA-derived acid anhydride groups (carboxyl units) at both ends. And when the homogeneous solution of this oligomer is used as a starting material for the partial esterification reaction and polymerization condensation reaction, the viscosity of the varnish containing polyamic acid which is a polymer of the oligomer can be further reduced, and the concentration is, for example, about 50% by mass. A varnish can be obtained. This is an effect obtained when the partial esterification reaction proceeds efficiently by carrying out the partial esterification reaction in a homogeneous solution.

  In the polyamic acid, as described above, the carboxyl unit derived from ODPA and the amino unit derived from ODA are preferably equivalent. On the other hand, in the production of an oligomer that is a starting material for polyamic acid, the amount of ODA used is less than an equal amount of ODPA as described above (specifically, preferably 0.5 mol relative to 1 mol of ODPA). Or less). Therefore, first, the amount of ODA equivalent to ODPA was determined, and then an oligomer was prepared using a part of the determined amount of ODA and all of ODPA, and then manufactured by partial esterification. It is preferable to produce a polyamic acid by polymerizing the oligomer and the remainder of ODA.

  That is, when the oligomer is produced by polymerizing ODPA and a part of ODA equivalent in molar ratio with ODPA, the oligomer produced is polymerized to obtain the polyamic acid. It is preferable to polymerize the remaining ODA. Thereby, the polyamic acid in which the carboxyl unit derived from ODPA and the amino unit derived from ODA are contained in equal amounts as the whole polyamic acid is obtained while taking advantage of the oligomer.

  When the oligomer is polymerized to obtain a polyamic acid, the oligomer may be polymerized in the presence of a conjugated aromatic tetracarboxylic acid (which may be an anhydride). Thereby, the polyamic acid containing the unit derived from a conjugated aromatic tetracarboxylic acid is obtained. The conjugated aromatic tetracarboxylic acid here is a compound having a rigid and planar structure. By including the unit derived from the conjugated aromatic tetracarboxylic acid, the glass transition temperature of the polyamic acid is 40 ° C. or higher compared to the case where only ODPA and ODA are used as the constituent components while exhibiting the effects of the present invention. A high value of 300 ° C. or higher is shown. Examples of the conjugated aromatic tetracarboxylic acid include pyromellitic dianhydride and 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride.

  When the oligomer is polymerized in the presence of the conjugated aromatic tetracarboxylic acid, in the polyamic acid, the unit derived from ODPA is 12.5 mol% to 25 mol%, the unit derived from ODA is 50 mol%, and the balance It is preferable to determine the amount of conjugated aromatic tetracarboxylic acid used so that is a unit derived from the conjugated aromatic tetracarboxylic acid. This makes it possible to reduce the viscosity of the varnish, to increase the concentration, and to prevent cracking during thick film formation.

  Furthermore, other components may be used in addition to ODPA and ODA. Specifically, for example, aromatic diamines, fluorine-containing compounds (fluorene compounds, etc.) can be used. Among them, for example, fluorine-containing compounds such as 4,4 ′-(hexafluoroisopropylidene) diphthalic anhydride and 9,9-bis (3-methyl-4-aminophenyl) fluorene, compounds having bulky substituents, etc. By using it, the dielectric constant of the insulating film 2 can be reduced.

  The styrene-converted mass average molecular weight of the polyamic acid contained in the varnish is not particularly limited, but is preferably 3000 or more, more preferably 5000 or more, and still more preferably, from the viewpoint of lowering the viscosity of the varnish and film formability. 10,000 or more, particularly preferably 20000 or more, and the upper limit thereof is preferably 50000 or less, more preferably 45000 or less, and particularly preferably 40000 or less. By setting the styrene-converted mass average molecular weight within this range, the occurrence of cracks during baking can be sufficiently prevented, and both low viscosity and high concentration of the varnish can be easily achieved.

  The solid content concentration of the varnish is not particularly limited, but is preferably 30% by mass or more from the viewpoint of increasing the thickness of the insulating coating 2. In addition, solid content concentration can be calculated | required by measuring the dry mass which removed the solvent (for example, NMP) in a varnish completely.

  Further, the viscosity of the varnish is not particularly limited, but is preferably 50 Pa · s or less, more preferably 10 Pa · s or less, from the viewpoint of easy handling and application. In addition, a viscosity can be calculated | required according to the method as described in the Example mentioned later.

  Furthermore, in addition to the polyamic acid, the varnish may contain any material as long as the effects of the present invention are not significantly impaired. For example, the varnish may contain a low molecular weight substance such as a by-product of the polyamic acid or a polymerization residue. Specifically, a by-product (for example, esterified at both ends) at the time of the partial esterification reaction, a monomer or oligomer of a polymerization residue, and the like may be included. This is because these by-products and the like that can be contained in the varnish are also finally incorporated into the polymerization reaction during baking, and the decrease in elongation at break of the insulating coating 2 is suppressed. Therefore, the low molecular weight body can finally be made high molecular weight by the polymerization reaction that proceeds during baking.

  The varnish may contain polyimide particles in addition to the polyamic acid. By containing the polyimide particles, the solid content concentration of the varnish can be increased while suppressing an excessive increase in the varnish viscosity. By increasing the concentration of the varnish, further thickening can be achieved. In addition, the polyimide particles have a higher affinity for polyamic acid and polyimide which is a cured product thereof than inorganic particles. Therefore, it is preferable in that it can suppress physical property deterioration of the insulating coating 2, particularly decrease in elongation at break, and is further preferable in that increase in dielectric constant can be suppressed low.

  The polyimide particles are preferably submicron (for example, about 0.5 μm to 0.7 μm) or more and 15 μm or less. By using submicron or larger polyimide particles, an excessive increase in the viscosity of the varnish can be suppressed. In addition, by using polyimide particles of 15 μm or less, the insulating coating 2 can be formed so as to be within a film thickness that can be formed by one application and baking. In addition, the particle diameter here means the diameter of the particles obtained by sieving so as to be in the above range.

  The amount of the polyimide particles used is preferably 10% by mass or more as the total solid content contained in the varnish, but from the viewpoint of the balance of the varnish viscosity, the solid content concentration, and the breaking elongation of the insulating coating. More preferably, the content is 20% by mass or more. The upper limit is preferably 50% by mass or less, but is 40% by mass or less from the balance of the viscosity and solid content of the varnish and the elongation at break of the insulating coating 2.

  Specific examples of usable polyimide particles can be obtained, for example, by reprecipitation and recovery of an oligomer which is a precursor of polyimide and heat treatment. Examples of commercially available products include UIP-R (particle diameter: 7 μm to 12 μm) and UIP-S (particle diameter: 10 μm to 15 μm) manufactured by Ube Industries, Ltd. Further, an insoluble thermosetting polyimide resin (for example, PETI-330 manufactured by Ube Industries, Ltd.) can be pulverized and used.

  The concentration of the varnish can also be increased by combining other organic fine particles, for example, organic fine particles such as acrylonitrile butadiene rubber particles, styrene butadiene rubber particles, and silicone rubber particles, in which case the insulating coating 2 It is preferable to take into consideration the heat resistance of the resin, especially the decrease in the thermal decomposition starting temperature.

  FIG. 2 is a cross-sectional view of the enameled wire 20 manufactured by the manufacturing method of the second embodiment. The enameled wire 20 shown in FIG. 2 can be manufactured using the varnish described with reference to FIG. Therefore, in the following description, the enameled wire 20 of the second embodiment will be described on the assumption that the varnish is used to manufacture the enameled wire 20 shown in FIG. The same applies to each embodiment shown in FIG.

  The enameled wire 10 shown in FIG. 1 has a circular cross section, but the enameled wire 20 shown in FIG. 2 has a substantially rectangular shape (chamfered rectangular shape). Since the varnish produced by the production method of the present embodiment has a high concentration and a low viscosity as described above, an efficient thickening is possible. Further, in the case of a rectangular shape as shown in FIG. 2, when used for a coil, it becomes possible to spread enamel wires densely, and there is an advantage that the coil can be easily reduced in size and increased in output.

  FIG. 3 is a cross-sectional view of an enameled wire manufactured by the manufacturing method of the third embodiment. An enameled wire 30 shown in FIG. 3 includes polyimide particles 4 in the insulating coating 2. That is, the enameled wire 30 shown in FIG. 3 is manufactured by applying and baking the varnish containing the polyimide particles 4 described above with reference to FIG. 1 to the metal conductor wire 1.

  Further, in the enameled wire 30 shown in FIG. 3, another insulating coating 3 is formed outside the insulating coating 2. That is, in the enameled wire 30, two layers of insulating coatings 2 and 3 are formed. The insulating coating 3 (second insulating coating, formed on the surface of the insulating coating 2) is composed of a repeating unit derived from a conjugated aromatic tetracarboxylic acid (such as PMDA) and ODA (4, 4 ′ -It is comprised including the polyimide which has a structure where the repeating unit derived from (diamino diphenyl ether) was alternately imidized and connected.

  The polyimide constituting the insulating coating 3 has high heat resistance and elastic modulus, and has a large elongation at break. Therefore, the durability of the enamel wire 30 can be enhanced while utilizing the advantages of the insulating coating 2 by forming another insulating coating 3 outside the insulating coating 2 formed by the varnish of the present embodiment. . The thickness of the insulating coating 3 is preferably 5% or more and 10% or less of the thickness of the insulating coating 2 from the viewpoint of reducing the number of coating and baking.

  FIG. 4 is a cross-sectional view of an enameled wire manufactured by the manufacturing method of the fourth embodiment. In the enameled wire 30 described with reference to FIG. 3, the cross-sectional shape is circular. However, in the enameled wire 40 shown in FIG. 4, the cross-section is almost rectangular (a chamfered rectangular shape). In the case of a rectangular shape as shown in FIG. 4, there is an advantage that enamel wires can be densely wound when used for a coil.

  FIG. 5 is a view showing a structure in the vicinity of a stator provided in a rotating electrical machine (a motor (not shown) or the like) manufactured by the manufacturing method of the fifth embodiment. In the stator 60, a coil 50 configured by winding the enameled wire 20 described with reference to FIG. 2 is incorporated in the slot 6 of the stator core 5. As described above, according to the varnish produced by the production method of the present embodiment, it is possible to increase the film thickness. Therefore, even when a current is passed at a high voltage, a high insulating property is maintained. Therefore, particularly in a rotating electric machine driven by a high voltage (only part of which is shown in FIG. 5), an enameled wire (for example, the enameled wire 20) obtained by using a varnish produced by the production method of the present embodiment is used. When applied, the effects of the present invention are suitably exhibited.

  As described above, the enamel wires 10, 20, 30, and 40 (enamel wires in the present embodiment) in each of the embodiments described above are not sacrificed for various performances (for example, heat resistance, pressure resistance, and dimensional accuracy). By using a varnish with a high concentration and a low viscosity, it can be produced with a small number of coating and baking. Moreover, even if the number of times of application and baking is small, a sufficient film thickness is secured, so that good insulation and heat resistance are exhibited. Therefore, according to the enameled wire of the present embodiment, it is possible to manufacture a coil that exhibits excellent effects while reducing manufacturing costs. The enameled wire according to the present embodiment can be applied to, for example, a rotating electric machine using the coil in addition to a coil applicable to an electric part such as a transformer. In addition, electrical parts using enameled wires are suitable for home appliances, industrial electrical machines, marine electrical machines, railways, automotive electrical machines, and the like.

  Hereinafter, the present invention will be described more specifically with reference to examples.

<Production and evaluation of varnish>
Example 1
The varnish of Example 1 is an example of a method for synthesizing a high-concentration low-viscosity varnish containing a polyamic acid starting from an oligomer of a flexible acid dianhydride ODPA and ODA having an ether group in the structure.

  In a 100 mL sample bottle, 15.4929 g (49.9117 mmol) of ODPA (manufactured by Wako Pure Chemical Industries, Ltd., hereinafter the same), 5.004 g (24.99 mmol) of ODA (manufactured by Wako Pure Chemical Industries, Ltd., hereinafter the same), NMP 48.2 g (manufactured by Wako Pure Chemical Industries, Ltd., hereinafter the same) was sampled, and the inside of the sample bottle was purged with nitrogen and sealed. ODPA was completely dissolved in NMP. This sample bottle was stirred at room temperature for 24 hours with a rotary mixer to prepare an ODPA-ODA-ODPA oligomer solution. This oligomer solution is a uniform solution having a concentration of 29.8% by mass, and the charge ratio of ODPA exceeds ODA, so that acid anhydride groups exist at both ends of the oligomer.

  To this sample bottle, 0.4 g (12.4844 mmol, 25 mol% with respect to ODAP) of ultra-dehydrated methanol (manufactured by Wako Pure Chemical Industries, Ltd., hereinafter the same) was added as a partial esterifying agent, and the bottle was sealed with nitrogen. The sample bottle was stirred with a rotary mixer for 24 hours at room temperature. In this step, a part of the acid anhydride group present at the end of the oligomer was carboxylated and esterified. Subsequently, the sample bottle was opened, 49995 g (24.9675 mmol) of ODA was added, and the molar ratio of ODPA and ODA was adjusted to 1: 1. Thereafter, the inside of the sample bottle was purged with nitrogen and sealed, and stirred for 24 hours with a rotary mixer to obtain a polyamic acid varnish having a concentration of 34.9% by mass.

  The styrene conversion weight average molecular weight (hereinafter abbreviated as Mw) of the polyamic acid in the varnish was observed under the following conditions. Two GelPak GL-S300MDT-5s were connected to the column, the eluent flow rate was adjusted to 1 mL / min, the detector was adjusted to UV (270 nm), the varnish concentration was adjusted to 5 mg / mL, the injection volume was 5 μL, and the column temperature was At 40 ° C., the eluent was prepared by mixing dimethylformamide and tetrahydrofuran in a 1: 1 volume ratio and further containing 0.06M phosphoric acid and 0.06M lithium bromide. The observed Mw was 21000.

  In a normal polyamic acid such as Comparative Example 1 described later, when an acid dianhydride and an aromatic diamine are charged in a 1: 1 molar ratio, a high molecular weight polyamic acid having an Mw of 100,000 or more is obtained. By increasing the molecular weight, film forming properties can be secured, and the breaking elongation of the insulating coating can be improved. In contrast, the polyamic acid in Example 1 was confirmed to have a low molecular weight due to the end-capping effect of the partially esterified product of the ODPA-ODA-ODPA oligomer. Further, when the viscosity at 30 ° C. was observed with a TV-25 viscometer manufactured by Toki Sangyo Co., Ltd., a very low value of 4.8 Pa · s was observed. This low viscosity is based on the effect of lowering the molecular weight of the polyamic acid.

  Next, the film formability was evaluated. The varnish was coated on a 1 mm thick copper plate with a coating gap of 150 μm, placed on a 340 ° C. hot plate, held for 5 minutes and baked to produce an insulating coating. As a result, an insulating film having a thickness of 37 μm was obtained. This insulating film had no cracks and had a good appearance. This polyamic acid varnish was capable of baking a thicker coating film than the polyamic acid varnish composed only of the rigid structure described in Comparative Example 1 described later.

  The elongation at break of the insulating coating was observed as follows. An aluminum foil having a thickness of 10 μm, a length of 180 mm, and a width of 150 mm was attached to a glass plate having a thickness of 5 mm and a length and width of 200 mm with a polyimide tape. And the varnish was apply | coated on this aluminum foil on the conditions of the application | coating gap of 50 micrometers using the bar coater. The aluminum foil after varnish application is placed in a high-temperature bath together with the glass plate, baked under conditions of 100 ° C./60 minutes, 150 ° C./30 minutes, 340 ° C./5 minutes, and cooled to room temperature over one night. An insulating coating was obtained. There was no crack in this insulating film, and the appearance was good.

  The aluminum foil was removed with an 18% by mass hydrochloric acid aqueous solution to obtain an insulating film having a thickness of 12 μm. The insulating coating was punched using a dumbbell SDK-500 type dumbbell cutter to prepare a dumbbell-shaped sample. The breaking elongation of the dumbbell-shaped sample was 50% when observed under the conditions of a distance between fulcrums of 50 mm, a tensile speed of 10 mm / min, and 25 ° C. using an AG-X type autograph manufactured by Shimadzu Corporation.

  The polyamic acid of Example 1 having a polycondensation structure of ODPA and ODA having a carboxyl group and an ester group at one end of the polyamic acid and an aromatic amino group derived from ODA at the other end is baked. Since polymerization between polyamic acids sometimes proceeds (hereinafter referred to as “in-situ polymerization”), a result was obtained that an insulating film having good thick film forming ability and high elongation at break was formed. The present polyamic acid, which can be applied and baked with a thick film and can form an insulating film having a high elongation at break, is considered effective for increasing the thickness of the insulating film of enameled wire.

(Example 2)
The polyamic acid varnish of Example 2 was an example in which the partial esterification rate of ODPA was increased in order to achieve a higher concentration than Example 1, that is, the synthesis of a high concentration low viscosity varnish to which a large amount of methanol as an esterifying agent was added. It is an example.

  In a 100 mL sample bottle, 15.5093 g (49.99945 mmol) of ODPA, 5.0054 g (24.9938 mmol) of ODA, and 48 g of NMP were collected, and the inside of the sample bottle was purged with nitrogen and sealed. ODPA was completely dissolved in NMP. This sample bottle was stirred at room temperature for 24 hours with a rotary mixer to prepare an ODPA-ODA-ODPA oligomer solution. This oligomer solution was a homogeneous solution having a concentration of 29.9% by mass.

  To this sample bottle, 0.8008 g (24.9938 mmol, about 50 mol% with respect to ODPA) of ultra-dehydrated methanol as a partial esterifying agent was added, and the bottle was sealed with nitrogen. The amount of methanol added was about twice that of Example 1. The sample bottle was stirred with a rotary mixer for 24 hours at room temperature. In this step, a part of the acid anhydride group present at the end of the oligomer was carboxylated and esterified. Next, the sample bottle was opened, and 5.0055 g (24.99975 mmol) of ODA was added to adjust the molar ratio of ODPA and ODA to 1: 1. Thereafter, the inside of the sample bottle was purged with nitrogen and sealed up, and stirred for 24 hours with a rotary mixer to obtain a varnish having a concentration of 35.4% by mass. Evaluation similar to Example 1 was performed with respect to this varnish.

  The Mw of this polyamic acid was 6000. It was confirmed that the molecular weight was lower than that of the polyamic acid of Example 1 by adding a large amount of the esterifying methanol to increase the partial esterification rate of ODPA. The varnish viscosity was 0.53 Pa · s, which was lower than the varnish of Example 1, due to the effect of lowering the molecular weight. Further, the insulation film thickness at a coating gap of 150 μm was 42 μm, and despite its low viscosity and low molecular weight, the insulation coating had no cracks and its appearance was good.

  The breaking elongation of the insulating film was 50%, and the insulating film obtained from the polyamic acid having a low molecular weight showed a high value. In the polyamic acid of Example 2 in which the esterifying agent was increased, that is, the ODPA-ODA-ODPA oligomer having a high partial esterification rate and the molecular weight was reduced, the breakage was caused by the effect of in situ polymerization during baking. It shows that an insulating film having high elongation can be obtained. The present polyamic acid is suitable for the formation of an enameled wire insulating film because it has the effect of reducing the viscosity of an extremely high varnish, the ability to form an insulating film, and the elongation at break of the insulating film.

(Example 3)
Example 3 is an example of a high-concentration low-viscosity varnish obtained by increasing the concentration of the varnish of Example 2.

  In a 100 mL sample bottle, 15.506 g (49.9839 mmol) of ODPA, 5.0044 g (24.992 mmol) of ODA, and 27.3 g of NMP were collected, and the sample bottle was purged with nitrogen and sealed. ODPA was completely dissolved in NMP. This sample bottle was stirred at room temperature for 24 hours with a rotary mixer to prepare an ODPA-ODA-ODPA oligomer solution. The oligomer solution had a concentration of 42.9% by mass and was a uniform solution.

  To this sample bottle, 0.8006 g (24.9938 mmol, approximately 50 mol% with respect to ODPA) of ultra-dehydrated methanol as a partial esterifying agent was added, and the air was replaced with nitrogen, followed by sealing. The sample bottle was stirred with a rotary mixer for 24 hours at room temperature. In this step, a part of the acid anhydride group present at the end of the oligomer was carboxylated and esterified. Next, the sample bottle was opened, and 5.0044 g (24.99975 mmol) of ODA was added to adjust the molar ratio of ODPA and ODA to 1: 1. Thereafter, the inside of the sample bottle was replaced with nitrogen and sealed up, and stirred for 24 hours with a rotary mixer to obtain a polyamic acid varnish having a concentration of 49.1% by mass. Evaluation similar to Example 1 was performed with respect to this varnish.

  The Mw of this polyamic acid was 6000. By using more methanol as an esterifying agent than in Example 1 and increasing the partial esterification rate of the ODPA-ODA-ODPA oligomer, it was confirmed that the molecular weight was lower than in Example 1. The varnish viscosity was 6 Pa · s, which is an extremely low value for a high concentration varnish.

  The insulating film thickness at the coating gap of 150 μm was 53 μm, and an insulating film thicker than that of Example 2 could be obtained due to the effect of increasing the concentration. The insulating coating had no cracks and had a good appearance.

  The breaking elongation of the insulating coating was 50% as measured in the same manner as in the Examples, and the insulating coating obtained from the low molecular weight body showed a high value. This is considered to be an effect of polymerizing low molecular weight polyamic acids during baking to increase the molecular weight. This polyamic acid varnish corresponds to the improvement of workability by lowering the viscosity and increasing the film thickness by increasing the concentration, and is considered useful for increasing the thickness of the enameled insulating film.

Example 4
The polyamic acid varnish of Example 4 is a synthesis of a high-concentration low-viscosity varnish containing a polyamic acid having a copolymer structure of a partially esterified product of ODPA-ODA-ODPA oligomer and PMDA, which is an acid dianhydride having a rigid structure. It is an example.

  In a 100 mL sample bottle, 7.75 g (24.9823 mmol) of ODPA, 1.6688 g (8.334 mmol) of ODA, and 43.6 g of NMP were collected, and the inside of the sample bottle was purged with nitrogen and sealed. ODPA was completely dissolved in NMP. This sample bottle was immersed in an oil bath at 90 ° C. and stirred with a magnetic stirrer for 30 minutes to obtain a uniform solution. Then, it stirred at room temperature for 24 hours with the rotary mixer, and produced the ODPA-ODA-ODPA oligomer solution. The concentration of the oligomer solution was 17.8% by mass and was a uniform solution.

  To this sample bottle, 0.3997 g (12.475 mmol, about 50 mol% with respect to ODPA) of ultra-dehydrated methanol as a partial esterifying agent was added, and the air was replaced with nitrogen, and the bottle was sealed. The sample bottle was stirred with a rotary mixer for 24 hours at room temperature. In this step, a part of the acid anhydride group present at the end of the oligomer was carboxylated and esterified. Next, the sample bottle was opened, and 8.372 g (41.636 mmol) of ODA was added, and the inside of the sample bottle was purged with nitrogen and sealed. The sample bottle was stirred with a rotary mixer at room temperature for 24 hours.

  The sample bottle was opened, 5.4642 g (24.9826 mmol) of PMDA (manufactured by Wako Pure Chemical Industries, Ltd., hereinafter the same) was added, the inside of the sample bottle was replaced with nitrogen, and the bottle was sealed. The sample bottle was immersed in an oil bath at 100 ° C. and stirred with a magnetic stirrer for 3 hours to obtain a uniform solution. Then, it stirred at room temperature for 24 hours with the rotary mixer at room temperature, and the varnish of Example 4 was obtained. The obtained varnish was a uniform solution and the concentration was 35.1% by mass. Evaluation similar to Example 1 was performed with respect to this varnish.

  Mw was 24000. Due to the effect of partial esterification of the ODPA-ODA-ODPA oligomer, it was confirmed that the molecular weight of the ternary copolymer of ODPA, ODA and PMDA can be reduced. The varnish viscosity was 6.4 Pa · s, which was a low value as a high concentration varnish.

  Furthermore, when the film formability was evaluated in the same manner as in Example 1, the insulation film thickness at a coating gap of 150 μm was 37 μm. In spite of introducing PMDA having a rigid structure into the insulating film, the insulating film had no cracks during baking and had a good appearance. In the present polyamic acid, even when a rigid structure such as PMDA is introduced, in-situ polymerization between low molecular weight polyamic acids occurs during baking, and it is considered that cracking of the insulating coating could be prevented.

  Furthermore, the elongation at break of the insulating coating measured in the same manner as in Example 1 was 65%, which was a larger value than in Examples 1 to 3. This is considered to be due to the intermolecular packing effect due to the rigid and flat structure of the copolymerized PMDA in addition to the effect of in situ polymerization during baking.

  As described above, the varnish of Example 4 was found to have the effect of increasing the elongation at break and increasing the thickness of the insulating coating while achieving both low viscosity and high concentration. Therefore, this varnish can contribute to the thickening and high performance of the insulating coating while suppressing the manufacturing cost of the insulating coating.

(Example 5)
Example 5 is a synthesis example of a high-concentration low-viscosity varnish in which the blending amount of ODPA is increased as compared with Example 4.

  A magnetic stirrer is placed in a 100 mL sample bottle, and then 10.743 g (32.4747 mmol) of ODPA, 2.168 g (10.825 mmol) of ODA and 45.2 g of NMP are collected, and nitrogen is added to the sample bottle. Replaced and sealed. ODPA was completely dissolved in NMP. This sample bottle was immersed in an oil bath at 90 ° C. and stirred with a magnetic stirrer for 30 minutes to obtain a uniform solution. Then, it stirred at room temperature for 24 hours with the rotary mixer, and produced the ODPA-ODA-ODPA oligomer solution. The concentration of the oligomer solution was 21.3% by mass and was a uniform solution.

  To this sample bottle, 0.5188 g (16.923 mmol, 49.8612 mol% with respect to ODPA) of ultra-dehydrated methanol as a partial esterifying agent was added, and the bottle was purged with nitrogen and sealed. The sample bottle was stirred with a rotary mixer for 24 hours at room temperature. In this step, a part of the acid anhydride group present at the end of the oligomer was carboxylated and esterified. Next, the sample bottle was opened, 7.8366 g (39.136 mmol) of ODA was added, the inside of the sample bottle was replaced with nitrogen, and the bottle was sealed. The sample bottle was stirred with a rotary mixer at room temperature for 24 hours.

  The sample bottle was opened, 3.8251 g (17.4886 mmol) of PMDA was added, the inside of the sample bottle was replaced with nitrogen, and the bottle was sealed. The sample bottle was immersed in an oil bath at 100 ° C. and stirred with a magnetic stirrer for 3 hours to obtain a uniform solution. Then, it stirred at room temperature with the rotary mixer for 24 hours under room temperature. The obtained varnish was a uniform solution and the concentration was 35.1% by mass. Evaluation similar to Example 1 was performed with respect to this varnish.

  Mw was 18000, which was smaller than that in Example 4. This is considered to be the effect of increasing the amount of ODPA which is a component of the terminal structure to be partially esterified. Further, a varnish viscosity of 3.4 Pa · s lower than that of Example 4 was observed due to the effect of lowering the molecular weight.

  Furthermore, when the film formability was evaluated in the same manner as in Example 1, the insulation film thickness at a coating gap of 150 μm was 37 μm. Further, the insulating coating had a good appearance without cracking during baking, despite the introduction of PMDA having a rigid structure into the structure. In this polyamic acid, even when a rigid structure such as PMDA is introduced, in-situ polymerization in which polycondensation of low molecular weight polyamic acids proceeds during baking, and cracking of the insulating coating could be prevented. Conceivable.

  Furthermore, the breaking elongation of the insulating coating measured in the same manner as in Example 1 was 65%, and the insulating coating obtained from the low molecular weight body showed a high value. This is considered to be due to the intermolecular packing effect due to the rigid and flat structure of the copolymerized PMDA in addition to the effect of in situ polymerization during baking.

  As described above, the varnish of Example 5 was found to have the effect of increasing the elongation at break and increasing the thickness of the insulating coating while achieving both low viscosity and high concentration. Therefore, this varnish can contribute to the thickening and high performance of the insulating coating while suppressing the manufacturing cost of the insulating coating.

(Reference Example 1)
Reference Example 1 is a production example in which ODPA is directly partially esterified according to a method (Japanese Patent Application No. 2017-007318) already filed by the same applicant as the present applicant without using the oligomer in Example 2.

  A magnetic stirrer was placed in a 100 mL sample bottle, and then 15.424 g (49.94 mmol) of ODPA and 48.8 g of NMP were collected, and the sample bottle was purged with nitrogen and sealed. Thereafter, the mixture was stirred for 24 hours with a rotary mixer at room temperature. In this solution, ODPA was not completely dissolved, and ODPA insoluble matter was present. The concentration was 24.1% by mass.

  Next, the sample bottle was opened, 0.8 g (24.97 mmol, 50 mol% with respect to ODPA) of ultra-dehydrated methanol was added as a partial esterifying agent, and the atmosphere was replaced with nitrogen, followed by sealing. The sample bottle was stirred with a rotary mixer for 24 hours at room temperature. In this step, a part of the acid anhydride group present at the end of the oligomer was carboxylated and esterified.

  The sample bottle was opened, and 10.02 g (49.95 mmol) of ODA was added, and the inside of the sample bottle was purged with nitrogen and sealed. The sample bottle was stirred with a rotary mixer at room temperature for 24 hours. The obtained varnish was a uniform solution and the concentration was 35% by mass. Evaluation similar to Example 1 was performed with respect to this varnish.

  Mw was 11000, and a higher molecular weight than Example 2 was observed. Despite the use of an esterifying agent in the same amount as in Example 2, the polyamic acid in this example had a higher molecular weight than the polyamic acid in Example 2. This was because ODPA having low solubility was directly esterified, so that the insoluble component was insufficiently esterified and thus the molecular weight was increased. In addition, a varnish viscosity of 1.4 Pa · s higher than that of Example 2 was observed due to the increase in the molecular weight.

  Further, when the film formability was evaluated in the same manner as in Example 1, the insulating film thickness at the coating gap of 150 μm was 38 μm, the insulating film had no cracks, and the breaking elongation of the insulating film was 50%. The insulating film obtained from the molecular weight body showed a high value. Since the polyamic acid of Reference Example 1 also has in-situ polymerizability, it has excellent film-forming properties and gives an insulating coating with high elongation at break, but has a higher viscosity than the polyamic acid varnish of Example 2 of the same composition. For further higher concentration, it can be said that it is preferable to reduce the varnish viscosity by lowering the molecular weight.

(Reference Example 2)
Reference Example 2 is a production example in which ODPA is directly partially esterified according to a method (Japanese Patent Application No. 2017-007318) already filed by the same applicant as the present applicant without using the oligomer in Example 5.

  A magnetic stirrer was placed in a 100 mL sample bottle, then 10.0743 g (32.4747 mmol) of ODPA and 45.2 g of NMP were collected, and the inside of the sample bottle was purged with nitrogen and sealed. Thereafter, the mixture was stirred for 24 hours with a rotary mixer at room temperature. In this solution, ODPA was not completely dissolved, and ODPA insoluble matter was present. The concentration was 18.2% by mass.

  Next, the sample bottle was opened, 0.5188 g (16.923 mmol, 49.8612 mol% with respect to ODPA) of ultra-dehydrated methanol was added as a partial esterifying agent, and the atmosphere was replaced with nitrogen, followed by sealing. The sample bottle was stirred with a rotary mixer for 24 hours at room temperature. In this step, a part of the acid anhydride group present at the end of the oligomer was carboxylated and esterified.

  The sample bottle was opened, and 10.0046 g (49.963 mmol) of ODA was added. The inside of the sample bottle was purged with nitrogen and sealed. The sample bottle was stirred with a rotary mixer at room temperature for 24 hours. The obtained varnish was a uniform solution. Next, the sample bottle was opened, and 3.8251 g (17.4886 mmol) of PMDA was added to replace the inside of the sample bottle with nitrogen. The sample bottle was immersed in an oil bath at 100 ° C. and stirred with a magnetic stirrer for 3 hours to obtain a uniform solution. Thereafter, the mixture was stirred for 24 hours with a rotary mixer at room temperature. The obtained varnish was a uniform solution, and the solid content concentration was 35.1% by mass. Evaluation similar to Example 1 was performed with respect to this varnish.

  Mw was 23000, which was larger than that in Example 5. Despite the use of an esterifying agent in an amount equivalent to that in Example 5, the polyamic acid in this example was made higher in molecular weight than the polyamic acid in Example 5. This was because ODPA having low solubility was directly esterified, so that the insoluble component was insufficiently esterified and thus the molecular weight was increased. Further, a varnish viscosity of 6.3 Pa · s higher than that of Example 5 was observed due to the increase in the molecular weight.

  Furthermore, when the film formability was evaluated in the same manner as in Example 1, the insulation film thickness at a coating gap of 150 μm was 37 μm. Further, the insulating coating had a good appearance without cracking during baking, despite the introduction of PMDA having a rigid structure into the structure. Even in the case of the present polyamic acid, in-situ polymerization in which polycondensation of low molecular weight polyamic acids proceeds at the time of baking appears, and it is considered that cracking of the insulating coating could be prevented.

  However, the breaking elongation of the insulating coating decreased to 35%. As described above, in this reference example, it is considered that ODPA is directly partially esterified, and the insoluble component is not esterified but has a high molecular weight. That is, it is considered that an esterifying agent that did not contribute to esterification remains in the system. When PMDA is added to this system, PMDA may also be esterified during the polymerization process. PMDA has a rigid structure and is considered to have low in-situ polymerizability. In this system, although the film-forming property is good due to the effect of polyamic acid containing high molecular weight ODPA, esterification and carboxylation products of polyamic acid containing PMDA with low in-situ polymerizability are generated, and the insulating coating is broken. We believe that the growth has declined.

  The results of Examples 1 to 5 and Reference Examples 1 and 2 are summarized in Table 1. The “solid content concentration” of “oligomer production conditions and physical properties” in Reference Examples 1 and 2 indicates the solid content concentration of the NMP solution of ODPA because no oligomer was produced.

(Comparative Example 1)
Comparative Example 1 is a synthesis example of a polyamic acid varnish containing a polyamic acid composed of PMDA having a rigid structure and ODA having an ether bond. The structure terminal of Comparative Example 1 does not include a polycondensation structure of ODPA and ODA having a carboxyl group and an ester group.

  1.4338 g (7.16 mmol) of ODA and 17 g of NMP were collected in a 30 mL sample bottle, and the inside of the sample bottle was purged with nitrogen and sealed to dissolve ODA. To this sample bottle, 1.5647 g (7.15 mmol) of PMDA was added, purged with nitrogen, and sealed. The sample bottle was stirred with a rotary mixer for 24 hours at room temperature to obtain a varnish of Comparative Example 1. The concentration of the varnish was 15% by mass. Evaluation similar to Example 1 was performed using this varnish.

  Mw was as large as 120,000, and its viscosity was 6.8 Pa · s, which was a high value as a low concentration varnish. The coating gap was 100 μm and the thickness of the insulating film was 10 μm. Although an attempt was made to increase the film thickness by setting the coating gap to 150 μm, foaming occurred during baking, and an insulating film could not be obtained.

  The appearance of the insulating film having a thickness of 10 μm was good and its elongation at break was as high as 65%. However, in order to increase the thickness of the insulating film using the varnish of Comparative Example 1, many coatings were used. Repeat baking.

(Comparative Example 2)
In Comparative Example 2, a predetermined amount of ODA monomer was mixed with a low molecular weight polyamic acid composed of PMDA and ODA having a carboxyl group and a carboxylic acid ester group at both ends, and the equivalent ratio of PMDA and ODA was 1: 1. It is an example of the varnish adjusted as molar ratio. Both polymerization terminals of the polyamic acid have a polycondensation structure of PMDA and ODA having a carboxyl group and an ester group.

  2.0040 g (10.008 mmol) of ODA and 30.5 g of NMP were collected in a 50 mL sample bottle, and the inside of the sample bottle was purged with nitrogen and sealed to dissolve ODA. To this sample bottle, 3.2684 g (14.984 mmol) of PMDA was added, purged with nitrogen, and sealed. The sample bottle was stirred with a rotary mixer for 24 hours at room temperature.

  The sample bottle was opened, 0.3189 g (9.958 mmol) of ultra-dehydrated methanol was added as an esterifying agent, the inside of the sample bottle was replaced with nitrogen, and the bottle was sealed. The sample bottle was stirred with a rotary mixer at room temperature for 24 hours. To this varnish, 0.9965 g (4.976 mmol) of ODA was added to obtain a varnish having a concentration of 17.8% by mass. Evaluation similar to Example 1 was performed using this varnish.

  Mw was as small as 43,000. Therefore, the varnish viscosity was as low as 0.2 Pa · s. The formation thickness of the insulating film at a coating gap of 100 μm was 10 μm. Although the appearance of this insulating film was good, the elongation at break was lowered to 25% due to the effect of lower molecular weight, and the elongation at break was reduced. Further, although an attempt was made to form a film with a coating gap of 150 μm, foaming occurred and the film could not be formed, and an insulating film could not be obtained.

(Comparative Example 3)
Comparative Example 3 is an example in which the concentration of the polyamic acid varnish of Comparative Example 2 is increased.

  1.0019 grams (5.003 mmol) of ODA and 15.13 g of NMP were collected in a 50 mL sample bottle, and the inside of the sample bottle was purged with nitrogen and sealed to dissolve ODA. To this sample bottle, 1.6377 grams (7.508 mmol) of PMDA was added, purged with nitrogen, and sealed. The sample bottle was stirred with a rotary mixer for 24 hours at room temperature.

  The sample bottle was opened, 0.1633 g (5.097 mmol) of ultra-dehydrated methanol was added as an esterifying agent, and the inside of the sample bottle was purged with nitrogen and sealed. The sample bottle was stirred with a rotary mixer at room temperature for 24 hours. Next, the same operation was repeated as follows to increase the concentration.

  To this sample bottle, 1.0007 g (4.998 mmol) of ODA and 1.6369 g (7.505 mmol) of PMDA were added, purged with nitrogen, sealed, and stirred with a rotary mixer at room temperature for 24 hours. Next, 0.1594 g (4.975 mmol) of ultra-dehydrated methanol was added, the inside of the sample bottle was purged with nitrogen, and the bottle was sealed, and the sample bottle was stirred for 24 hours at room temperature with a rotary mixer.

  Further, 1.0017 g (5.002 mmol) of ODA and 1.6258 g (7.454 mmol) of PMDA were added to the sample bottle, purged with nitrogen, sealed, and stirred at room temperature for 24 hours with a rotary mixer. Next, 0.1576 g (4.919 mmol) of ultra-dehydrated methanol was added, the inside of the sample bottle was purged with nitrogen, sealed, and the sample bottle was stirred for 24 hours at room temperature with a rotary mixer.

  Finally, in order to make the equivalent ratio of PMDA and ODA coincide, 1.4929 g (7.456 mmol) of ODA was added to this varnish and dissolved to obtain a varnish having a concentration of 39.5% by mass. Evaluation similar to Example 1 was performed using this varnish.

  The molecular weight of the polyamic acid of Comparative Example 3 was 43000. The varnish viscosity increased to 42.5 Pa · s due to the effect of higher concentration than in Example 2. In both coating gaps of 100 μm and 150 μm, when the coating was baked, many cracks were generated in the insulating film, and no insulating film was obtained.

  From this result, polyamic acid consisting only of PMDA, which is tetracarboxylic dianhydride having a rigid structure with ODA, can achieve high concentration and low viscosity due to low molecular weight, but it has a low molecular weight, so it is used as an insulating coating. It was found that cracks are likely to occur and are not suitable for thick film coating processes.

  The results of Comparative Examples 1 to 3 are summarized in Table 2.

DESCRIPTION OF SYMBOLS 1 Metal conductor wire 2 Insulation film 3 Insulation film 4 Polyimide particle 10 Enamel wire 20 Enamel wire 30 Enamel wire 40 Enamel wire 50 Coil 60 Rotor

Claims (10)

At least one first repeating unit of structures represented by the following formulas (1) to (4) and a second repeating unit represented by the following formula (5) are linked by alternately amide bonds. A method for producing a varnish comprising obtaining a polyamic acid by polymerizing an oligomer and producing a varnish containing the polyamic acid.

(In the formulas (1) to (4), each R independently represents a hydrogen atom or an alkyl group having 4 or less carbon atoms, and the alkyl group may be a chain or a ring, and has a branch. May be.) Generating the oligomer by polymerizing the first component constituting the first repeating unit and the second component constituting the second repeating unit;
The method for producing a varnish according to claim 1, wherein when the oligomer is produced, the amount of the second component used is 0.5 mol or less with respect to 1 mol of the first component.   After polymerizing the first component constituting the first repeating unit and the second component constituting the second repeating unit, the amount used is 0.025 mol to 0.5 mol with respect to 1 mol of the first component. The method for producing a varnish according to claim 1 or 2, wherein the oligomer is produced by reacting at least one of a monohydric alcohol and water. In the production of the oligomer, the first component constituting the first repeating unit, the second component constituting the second repeating unit in a part of an amount equivalent to the first component in a molar ratio with the first component; To produce the oligomer by polymerizing
When the produced oligomer is polymerized to obtain the polyamic acid, the oligomer and the remaining second component in an amount equivalent to the first component in a molar ratio are polymerized to obtain the polyamic acid. The method for producing a varnish according to claim 1, wherein the varnish is obtained.   The method for producing a varnish according to claim 1 or 2, wherein the polyamic acid is obtained by polymerizing the oligomer in the presence of a conjugated aromatic tetracarboxylic acid.   In the polyamic acid, the first repeating unit is 12.5 mol% to 25 mol%, the second repeating unit is 50 mol%, and the remainder is a unit derived from the conjugated aromatic tetracarboxylic acid. The method for producing a varnish according to claim 5, wherein:   An enameled wire having an insulating coating containing polyimide is produced by applying and baking the varnish produced by the method for producing a varnish according to claim 1 or 2 onto a metal conductor wire. Method.   A polyimide having a structure in which a repeating unit derived from a conjugated aromatic tetracarboxylic acid and a repeating unit derived from 4,4′-diaminodiphenyl ether are alternately imidized and connected to the surface of the insulating coating; The method for producing an enameled wire according to claim 7, wherein a second insulating film is formed.   A coil manufacturing method using the enameled wire manufactured using the enameled wire manufacturing method according to claim 7 or 8. A method for manufacturing an electrical component, comprising: manufacturing an electrical component using a coil manufactured using the method for manufacturing a coil according to claim 9.

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