JP2018115273A - Varnish, enamel wire, and coil and electric component including the enamel wire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a varnish that enables higher concentrations and lower viscosities, and prevents cracking in deposition to achieve a thickened film, and an enamel wire and a coil and an electric component including the enamel wire.SOLUTION: A varnish contains a polyamic acid having a structure in which: at least one of repeating units represented by predetermined structural formulae and a repeating unit represented by a predetermined structural formula are amide-bonded alternately for connection. There are also provided an enamel wire and a coil and an electric component including the enamel wire.SELECTED DRAWING: None

Description

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

  An enameled wire (enameled wire having an insulating coating) is widely used as an electric wire used for a coil provided in an electrical component such as a rotating electrical machine or a transformer. The enameled wire has a configuration in which an insulating coating is formed on the outer layer of a metal conductor wire formed in a cross-sectional shape (for example, a circular shape or a rectangular shape) that matches the application and shape of the coil provided. In recent years, from the viewpoint of improving energy efficiency, miniaturization, higher output, and higher efficiency of electric parts used in various electric devices (for example, home appliances, industrial electric machines, marine electric machines, railroads, automobile electric machines) have progressed. It is out.

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

  In an electrical component that is controlled by an inverter, a higher voltage such as an inverter surge voltage is applied to the coil in the electrical component, so that the insulating coating may be deteriorated or damaged due to the occurrence of partial discharge. Therefore, the 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 parts, it is effective to reduce the diameter and density of the windings in the coil and increase the space factor of the metal conductor wires. Therefore, the enameled wire is required to have a thin and uniform insulating coating. In order to obtain a thin and uniform insulating film, the insulating film is formed by forming a very thin film by one application and baking of varnish (insulating paint) and repeating it several times. Is called. For example, in order to form an insulating film having a thickness of 50 μm to 100 μm, currently, 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 have unevenness.

  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, improvement in productivity in the coating and baking process is required. 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 for thickening an insulating film by applying and baking with a small number of times using a varnish having a high concentration and a low viscosity has been studied. In relation to 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. Further, 0 mol to 0.95 mol of a specific diamine is reacted with 1 mol of a specific tetracarboxylic dianhydride in a solvent and then reacted with water or alcohol to obtain a carboxylic acid. A method for producing a polyimide precursor solution is described in which 0.95 mol to 1.05 mol of a specific diamine is added to 1 mol of acid. Furthermore, the polyimide coating film obtained from the said polyimide precursor solution is described. And the manufacturing method of the polyimide coating film which coats the said polyimide precursor solution on a base material and carries out the heating imidation is described.

JP 2001-31764 A (refer to [Abstract] in particular. Published Patent Gazette corresponding to Japanese Patent No. 4589471)

  When the present inventors examined, at the time of baking after apply | coating the polyimide precursor solution of patent document 1 to a core wire (metal conductor wire), for example, in the polyimide coating film (insulating film) formed on the surface of a core wire, It was found that cracking occurred. 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 in terms of perspective.

  When forming a thick insulating film, it is preferable to form the insulating film 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 problems, and the problem to be solved by the present invention is that it is possible to increase the concentration and decrease the viscosity, and to suppress the occurrence of cracks during film formation. It is to provide a varnish capable of being thickened, an enameled wire, a coil including the enameled wire, and an electric component.

  The present inventors have intensively studied to solve the above problems. As a result, the following knowledge was found and the present invention was solved. That is, the gist of the present invention will be described later in the embodiment for carrying out the invention and at least one of the repeating units represented by the formulas (1) to (4) described later in the embodiment for carrying out the invention. The present invention relates to a varnish characterized by containing a polyamic acid having a structure constituted by connecting repeating units represented by the formula (5) alternately by amide bonds. Other solutions will be described later in the embodiment for carrying out the invention.

  According to the present invention, a varnish capable of increasing the concentration and decreasing the viscosity and suppressing the generation of cracks during film formation to increase the thickness, the enameled wire, the coil including the enameled wire, and the electrical component Can be provided.

It is sectional drawing of the enamel wire in 1st embodiment. It is sectional drawing of the enamel wire in 2nd embodiment. It is sectional drawing of the enamel wire in 3rd embodiment. It is sectional drawing of the enamel wire in 4th embodiment. It is a figure which shows the structure of the stator vicinity provided to the rotary electric machine in 5th embodiment.

  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 in the first embodiment. The enameled wire 10 has a circular cross section as shown in FIG. And the enamel wire 10 is provided with the metal conductor wire 1 (core wire) comprised with the metal conductor with a small electrical resistivity, and the insulating film 2 formed in the surface. The insulating coating 2 is formed by applying the varnish of the present embodiment to the surface of the metal conductor wire 1 and then baking (drying) it. The insulating coating 2 contains polyimide.

  The material constituting the metal conductor wire 1 may be any material as long as it has a low electrical resistivity 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, for example, in the case of copper, tough pitch copper, deoxidized copper, oxygen-free copper and the like can be mentioned. These may be appropriately plated with tin, nickel, silver, aluminum or the like on the surface. Furthermore, for example, 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.

  The insulating coating 2 prevents the current flowing through the metal conductor wire 1 from leaking, that is, insulates. The insulating coating 2 includes polyimide as described above. And this polyimide is obtained by dehydrating and imidizing the polyamic acid contained in the varnish of this embodiment. Here, for convenience, the varnish of this embodiment capable of forming the insulating coating 2 will be described.

  The insulating coating 2 is formed by applying and baking (heating) the varnish of the present embodiment on the surface of the metal conductor wire 1. This varnish contains polyamic acid. Then, the polyamic acid is dehydrated by baking, and a polyimide having a structure of the following formula (12) is generated. Therefore, the polyamic acid contained in this varnish serves as a polyimide precursor. Hereinafter, the polyamic acid contained in the varnish of the present embodiment is appropriately referred to as “polyamic acid of the present embodiment”.

  The polyamic acid of this embodiment is obtained by polycondensation of 4,4′-oxydiphthalic dianhydride (hereinafter referred to as ODPA) and 4,4′-oxydiaminodiphenyl ether (hereinafter referred to as ODA). It is what That is, when ODPA is hydrolyzed and the carboxylic acid anhydride constituting ODPA is opened, a carboxyl group and an ester group are generated. Then, the produced carboxyl group and the amino group constituting ODA are polycondensed to form an amide bond to form a polymer, thereby producing a polyamic acid. The ester group generated during the hydrolysis of ODPA may generate a carboxyl group by binding a proton, or may bond to an arbitrary cation (for example, a methyl group) to form a methyl ester or the like.

  An ODPA skeleton derived from ODPA and an ODA skeleton derived from ODA constituting the polyamic acid contained in the varnish are represented by the following structural formulas. Among these, the skeleton represented by the following formulas (1) to (4) is an ODPA skeleton, and the skeleton represented by the following formula (5) is an ODA skeleton. Therefore, in the polyamic acid of this embodiment, at least one of the ODPA skeletons represented by the following formulas (1) to (4) and the ODA skeleton represented by the formula (5) are alternately formed by amide bonds. It has a linked polyamide structure. In addition, the kind of ODPA frame | skeleton contained in one polyamic acid may be only 1 type, and 2 or more types of ODPA frame | skeletons may be included in arbitrary combinations.

  In said formula (1)-(4), R represents a hydrogen atom or an alkyl group each independently. The alkyl group may be linear or cyclic, and may have a branch. The number of carbon atoms of the alkyl group is 3 or less, preferably 2 or less, particularly preferably 1 from the viewpoint of preventing suppression of the polyamidation reaction due to R steric hindrance.

  R is a hydrogen atom or an alkyl group as described above, but the content (modification rate) of the alkyl group is 2.5 mol% or more and 50 mol% or less with respect to the total amount of R contained in the polyamic acid. Is preferred. By setting the content of the alkyl group to 2.5 mol% or more, it is possible to enhance the effect of lowering the molecular weight and lowering the viscosity of the polyamic acid. In addition, when the content of the alkyl group is 50 mol% or less, the content of the acid anhydride with both ends opened can be reduced, a certain molecular weight can be maintained, and the film formability can be improved. The content of the alkyl group can be confirmed by, for example, NMR.

  In the above formulas (1) to (5), all have an ether bond capable of taking a flexible structure. Therefore, at least one of the ODPA skeletons represented by the above formulas (1) to (4) and the ODA skeleton represented by the above formula (5) are alternately linked by amide bonds. By using, a flexible structure as a whole molecule can be taken. Thereby, at the time of the polycondensation (imidation) which arises at the time of baking, breaking elongation can be improved and generation | occurrence | production of a crack can be prevented.

  Further, unlike polyimide contained in the insulating coating 2, polyamic acid has a relatively small molecular weight (the specific molecular weight will be described later). Therefore, the viscosity of the varnish can be reduced, and a high-density varnish can be obtained. And by using a varnish with a low viscosity and a high concentration, it can be easily applied in a small number of times, while reducing the number of times of application and baking, while preventing the occurrence of cracks, and thick film Can be achieved.

  Moreover, the polyamic acid of this embodiment is at least one of the following formulas (6) to (9) as a carboxy terminus and at least one of the following formulas (10) and (11) as an amino terminus. It is preferable to have.

  In the above formulas (6) to (11), X (bonded to the left end of the page in the formulas (6) to (9) and coupled to the right end of the page in the formulas (10) and (11)) is independent. Thus, it represents a polymerized structure in which ODPA skeletons and ODA skeletons are alternately bonded.

  When paying attention to one polyamic acid, at least one of the above formulas (6) to (9) is present at the carboxy terminus of the polyamic acid, or at the amino terminus of the polyamic acid, the above formula ( It is preferable that at least one of 10) and formula (11) is bonded. However, in the one polyamic acid, at least one of the above formulas (6) to (9) is bonded to the carboxy terminus of the polyamic acid, and the above formula is added to the amino terminus of the polyamic acid. It is particularly preferable that at least one of (10) and formula (11) is bonded.

  Any of the polymerization terminals represented by these formulas (6) to (11) has an ether bond capable of forming a flexible structure. Therefore, although details will be described later, even if the inside of the polyamic acid has a rigid structure by having a rigid skeleton in addition to the ODPA skeleton, the end thereof has a flexible structure. Thereby, at the time of baking, the carboxyl end and the amino end are likely to be close to each other, and polycondensation (polyimidization) easily proceeds. In addition, since the polycondensation proceeds while including a portion having a flexible structure, the occurrence of cracks is more reliably prevented.

  In addition, the polyamic acid of the present embodiment includes an aromatic tetramer having a rigid structure such as pyromellitic dianhydride and 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride together with the ODPA skeleton. A copolymer skeleton derived from carboxylic dianhydride (a copolymer skeleton having a rigid structure, a rigid skeleton) may be included. When a copolymer skeleton having such a rigid structure is included, the polyamic acid of the present embodiment includes at least one of repeating units represented by the above formulas (1) to (4) and the above formula ( In addition to the structure in which the repeating units represented by 5) are alternately linked by amide bonds, the copolymer skeleton having the rigid structure and the repeating units represented by the above formula (5) are alternately amides. It will include two types of structures linked together. By including a copolymer skeleton having such a rigid structure, the elastic modulus of the insulating coating 2 can be increased, and the elongation at break of the insulating coating 2 can be increased.

  The term “copolymer skeleton having a rigid structure” as used herein refers to “a repeating unit derived from a conjugated aromatic tetracarboxylic acid”. That is, in such a “conjugated aromatic ring tetracarboxylic acid” portion, the rotation and bending of the molecule are unlikely to occur. Therefore, in this specification, such a structure is referred to as a “copolymer skeleton having a rigid structure”.

  When the polyamic acid of the present embodiment includes a copolymer skeleton having a rigid structure together with the ODPA skeleton, the content of the ODPA skeleton is based on the entire aromatic tetracarboxylic acid skeleton (including the ODPA skeleton). The molar ratio is preferably greater than 0.25. In other words, when a copolymer skeleton having a rigid structure is included, the content of the copolymer skeleton having a rigid structure is based on the entire aromatic tetracarboxylic acid skeleton (including the ODPA skeleton). The molar ratio is preferably 0.75 or less. By setting it as such a range, the softness | flexibility of a polymerization terminal is maintained and the polycondensation reaction by the heating at the time of baking can be advanced especially favorable.

  The styrene-converted mass average molecular weight of the polyamic acid of the present embodiment is not particularly limited, but is preferably 3000 or more, more preferably 5000 or more, from the viewpoint of lowering the viscosity of the varnish and good film formability. More preferably, it is 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, it is possible to sufficiently prevent the occurrence of cracks during baking, and it is possible to make it easy to achieve both low viscosity and high concentration of varnish.

  The solid content concentration of the varnish of the present embodiment 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, N-methyl-2-pyrrolidone) in a varnish completely.

  Further, the viscosity of the varnish of the present embodiment is not particularly limited, but is preferably 50 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.

  In addition to the polyamic acid, the varnish of the present embodiment may contain any material as long as the effects of the present invention are not significantly impaired. For example, the varnish of this embodiment usually contains a solvent such as N-methyl-2-pyrrolidone. The amount of the solvent used is arbitrary, but if it is too large, the baking time may be prolonged or the concentration may be lowered. On the other hand, if the amount is too small, the viscosity may become excessively large and it may be difficult to apply. Therefore, it is preferable to determine the amount of solvent used in consideration of these points.

  Moreover, the varnish of this embodiment may contain the polyimide particle. By containing the polyimide particles, it is possible to increase the solid content concentration in the varnish while suppressing an excessive increase in the varnish viscosity. Thereby, 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 the physical properties of the insulating coating 2 can be suppressed, particularly the decrease in elongation at break, and further, the increase in dielectric constant can be suppressed low.

  The particle diameter of the polyimide particles is 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 range that can be formed by a single application and baking. Thereby, it can fully suppress that an unevenness | corrugation arises on the surface of the insulating film 2. FIG. 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 amount of the solid content contained in the varnish, but from the viewpoint of the balance of the viscosity and solid content concentration of the varnish and the breaking elongation of the insulating coating 2, More preferably, it is 20 mass% or more. Further, the upper limit is preferably 50% by mass or less, and more preferably 40% by mass or less from the viewpoint of the balance between 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 polyamic acid, which is a precursor of polyimide, and heat treatment. Examples of commercially available products include UIP-S (particle diameter: 7 μm to 12 μm) and UIP-R (particle diameter: 10 μm to 15 μm) manufactured by Ube Industries, Ltd. Furthermore, insoluble thermosetting polyimide or Ube Industries' PETI-330 resin may be crushed and used as polyimide particles.

  The insulating coating 2 obtained using the varnish of the present embodiment having the above components and physical properties contains polyimide as described above. The polyimide is an imidized polyamic acid obtained by polycondensation of the ODPA and the ODA. The skeleton (repeating unit) constituting this polyimide is represented by the following formula (12).

  When the varnish used includes the above-mentioned “copolymer skeleton having a rigid structure”, the insulating coating 2 includes a polyimide containing a skeleton derived from the “copolymer skeleton having a rigid structure”. Will be included.

  In addition, the styrene conversion mass mean molecular weight (measured by the same method as the molecular weight measurement method of the polyamic acid) of the polyimide contained in the insulating coating 2 is, for example, about several hundred thousand to several million. By appropriately changing the baking conditions according to the baking conditions and the thickness of the insulating coating 2, the styrene-converted mass average molecular weight can be controlled.

  FIG. 2 is a cross-sectional view of the enameled wire 20 in the second embodiment. The enameled wire 20 shown in FIG. 2 can be manufactured using the varnish of the present embodiment 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 of the present embodiment is used to manufacture the enameled wire 20 of the second embodiment 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). According to the varnish of the present embodiment, it is possible to increase the thickness as described above. Therefore, in the case of a rectangular shape as shown in FIG. Further, for example, when used for a coil, there is an advantage that it is easy to wind around the core.

  FIG. 3 is a cross-sectional view of the enameled wire 30 in 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 of this embodiment containing polyimide particles on the metal conductor wire 1 described with reference to FIG. is there.

  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 formed here (formed on the outermost side) has a structure obtained by polycondensation and imidization of 4,4′-diaminodiphenyl ether and an aromatic tetracarboxylic dianhydride having a rigid structure. It is comprised with the polyimide which has. That is, the insulating coating 3 is a polyimide having a structure in which repeating units derived from conjugated aromatic tetracarboxylic acids and repeating units derived from 4,4′-diaminodiphenyl ether are alternately imidized and connected. Is included.

  This polyimide 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% to 10% 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 the enameled wire 40 in the fourth embodiment. The enameled wire 30 described with reference to FIG. 3 has a circular cross section, but the enameled wire 40 shown in FIG. 4 has a substantially rectangular shape (chamfered rectangular shape). According to the varnish of the present embodiment, it is possible to increase the thickness as described above. Therefore, in the case of a rectangular shape as shown in FIG.

  FIG. 5 is a view showing the structure in the vicinity of the stator 60 provided for the rotating electrical machine (motor not shown) in 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 of the present embodiment, it is possible to increase the film thickness, and thus high insulation is exhibited even when a large current is passed. Therefore, when the enameled wire obtained by using the varnish of the present embodiment (for example, the enameled wire 20 described above) is applied to a rotating electric machine (only part of which is shown in FIG. 5) that allows a large current to flow. In particular, the effects of the present invention are particularly exhibited.

  As described above, the enameled wires 10, 20, 30, and 40 (the enameled wires of the present embodiment) of the above-described embodiments can be used without sacrificing 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 times. 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, a new effect is exhibited while reducing the manufacturing cost. And the enameled wire of this embodiment can be used suitably also as an electric wire for coils of electric parts, such as a transformer, besides a rotary electric machine. In addition, an electrical component using such an enameled wire is suitable as an electrical component used in various electrical devices (for example, home appliances, industrial electrical machinery, marine electrical machinery, railways, and automotive electrical machinery).

  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 a partially esterified product of a flexible acid anhydride 4,4′-oxydiphthalic dianhydride (ODPA) having an ether group in the structure and 4,4′-diaminodiphenyl ether (ODA). It is an example of the low viscosity varnish containing the polyamic acid which is a polycondensation product.

  In a 30 mL sample bottle, 1.8599 g (5.995 mmol) of ODPA manufactured by Wako Pure Chemical Industries, Ltd. and 17.35 g of ultra-dehydrated N-methyl-2-pyrrolidone (NMP) were collected, and the inside of the sample bottle was replaced with nitrogen. Sealed to dissolve ODPA. To this sample bottle, 0.0052 g (0.1623 mmol) of ultra-dehydrated methanol as an esterifying agent 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, 1.2007 g (5.996 mmol) of ODA was added, the inside of the sample bottle was purged with nitrogen, and the bottle was sealed. The sample bottle was stirred for 24 hours with a mix rotor to obtain the varnish of Example 1.

  The solid content concentration (varnish concentration, the same applies hereinafter) of the obtained varnish was 15% by mass. Moreover, R in said Formula (1)-Formula (4) and Formula (6)-Formula (9) contained in the obtained varnish is either a hydrogen atom or a methyl group (1 carbon number).

  The molecular weight of the polyamic acid in this varnish was measured under the following conditions. The column is GelPak GL-S300MDT-5 × 2, the flow rate is 1 mL / min, the detector is UV (270 nm), the concentration is 5 mg / mL, the injection volume is 5 μL, the column temperature is 40 ° C., and the eluent is dimethylformamide and THF. Was mixed 1: 1 and further contained 0.06M phosphoric acid and 0.06M lithium bromide. The measured styrene conversion mass average molecular weight (hereinafter abbreviated as Mw) was 46000.

  Moreover, about this varnish, the viscosity in 30 degreeC by the Toki Sangyo company TV-25 type | mold viscosity meter was 0.28 Pa.s. This low viscosity is thought to be due to the lowering of molecular weight due to the use of partially esterified ODPA.

  Next, the film formability was evaluated. The varnish was coated on a 1 mm thick copper plate with a coating gap of 100 μm, placed on a 340 ° C. hot plate, held for 5 minutes and baked to form an insulating coating. As a result, an insulating film having a thickness of 10 μm was obtained. By visual observation, the insulating coating was not cracked and the appearance was good. Therefore, a sufficient film thickness was obtained even at a low concentration. In addition, the presence or absence of the crack in an insulating film was similarly evaluated by visual observation also in the following method. Next, the breaking elongation of the baked insulating film was evaluated 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 the conditions of the application | coating gap of 100 micrometers on this aluminum foil using the bar coater. The aluminum foil after varnish application is put together with the glass plate in a high-temperature bath and baked under conditions of 100 ° C / 60 minutes, 150 ° C / 30 minutes, 340 ° C / 5 minutes, and cooled to room temperature overnight, with aluminum foil An insulating coating was obtained.

  Next, the aluminum foil was removed with an 18% by mass hydrochloric acid aqueous solution to obtain an insulating film having a thickness of 10 μm. There was no crack in this insulating film, and the appearance was good. Therefore, a sufficient film thickness was obtained even at a low concentration. This is because the amount of dehydration at the time of polyimidization was reduced by adopting ODPA, which has a higher molecular weight than the monomer having a rigid structure such as pyromellitic dianhydride (PMDA), in tetracarboxylic dianhydride. It is considered that the low molecular weight and low viscosity are excellent in foam removal properties, and that foaming during drying is suppressed.

  The obtained insulating coating was punched out using a dumbbell SDK-500 type dumbbell carter to prepare a dumbbell-shaped sample. And about the breaking elongation (tensile ratio when a crack arises) of a dumbbell-shaped sample, Shimadzu Corporation AG-X type | mold autograph was used on the conditions of the distance between fulcrums of 50 mm, the tensile speed of 10 mm / min, and 25 degreeC. It was 60% when measured. This is a high value for an insulating film obtained from a low molecular weight substance. The reason for this is considered to be the effect that the low molecular weight substances are polymerized and made high in molecular weight during baking by including a highly flexible OPDA skeleton.

  Further, when a film was formed in the same manner with a coating gap of 150 μm, the thickness of the insulating coating was 15 μm, there were no cracks, and the appearance was good. Moreover, when the elongation at break was measured in the same manner, it was 60%. Therefore, even when the coating gap is increased, a thick insulating film can be formed, and the elongation at break is good.

  Thus, although the varnish of Example 1 had a low viscosity, the breaking elongation of the insulating film was large, and the effect of increasing the film thickness by increasing the coating gap was recognized. Therefore, this varnish is considered useful for increasing the thickness of the enameled wire insulation coating. In addition, since these effects can be achieved even with a small number of coatings and bakings, it is possible to reduce manufacturing costs and prevent unevenness from occurring in the insulating coating.

(Example 2)
The varnish of Example 2 is an example in which the partial esterification rate of ODPA (that is, the ratio of the methyl group as R in the above formulas (1) to (4)) is increased as compared with Example 1.

  The amount of ODPA used is 1.8237 g (5.879 mmol), the amount of NMP used is 17.80 g, the amount of ultra-dehydrated methanol used is 0.0932 g (2.909 mmol), and the amount of ODA used is 1.1768 g (5. The varnish of Example 2 was obtained in the same manner as Example 1 except that the amount was 877 mmol).

  The solid content concentration of the obtained varnish was 15% by mass. Moreover, R in said Formula (1)-Formula (4) and Formula (6)-Formula (9) contained in the obtained varnish is either a hydrogen atom or a methyl group (1 carbon number). However, since the amount of super-dehydrated methanol used (molar ratio to ODPA) is larger than that in Example 1, the amount of methyl groups in all R is larger than that in Example 1.

  And when Mw was measured like Example 1, Mw was 10,000. Therefore, the molecular weight was lower than that of Example 1 by adopting ODPA with an increased partial esterification rate. Moreover, when the viscosity was measured similarly to Example 1, it showed a very low value of 0.014 Pa · s.

  Further, the film formability was evaluated in the same manner as in Example 1. As a result, the insulating film thickness at the coating gap of 100 μm was 10 μm, and the insulating film thickness at the coating gap of 150 μm was 15 μm. In both the coating gaps of 100 μm and 150 μm, these insulating coatings were not cracked and their appearance was good.

  Further, the elongation at break of the insulating coating was measured in the same manner as in Example 1. As a result, the coating gap was 50% in both 100 μm and 150 μm, and the insulating coating obtained from the low molecular weight body showed a high value. . This is considered to be due to the effect of polymerizing low molecular weight substances at the time of baking to increase the molecular weight by including the OPDA skeleton.

  As described above, the varnish of Example 2 has a lower viscosity than that of Example 1, yet has a large elongation at break of the insulating coating, and also has the effect of increasing the thickness by increasing the coating gap. It was. Therefore, this varnish is considered useful for increasing the thickness of the enameled wire insulation coating. In addition, since these effects can be achieved even with a small number of coatings and bakings, it is possible to reduce manufacturing costs and prevent unevenness from occurring in the insulating coating.

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

  In a 100 mL sample bottle, 15.5.424 g (49.94 mmol) of ODPA and 48.83 g of NMP were collected, and the sample bottle was purged with nitrogen in the same manner as in Example 1 and sealed with a rotary mixer for 24 hours. In this solution, ODPA was not completely dissolved. Thereafter, the varnish of Example 3 was used in the same manner as in Example 1 except that the amount of super-dehydrated methanol used was 0.8 g (24.970 mmol) and the amount of ODA used was 10.02 g (49.950 mmol). Got.

  The solid content concentration of the obtained varnish was 35% by mass. Moreover, R in said Formula (1)-Formula (4) and Formula (6)-Formula (9) contained in the obtained varnish is either a hydrogen atom or a methyl group (1 carbon number). However, since the amount of super-dehydrated methanol used (molar ratio to ODPA) is larger than that in Example 1, the amount of methyl groups in all R is larger than that in Example 1.

  When Mw was measured in the same manner as in Example 1, Mw was 11000. Therefore, the molecular weight was lower than that of Example 1 by adopting ODPA with an increased partial esterification rate. Further, when the viscosity was measured in the same manner as in Example 1, the varnish viscosity was 1.35 Pa · s, which is an extremely low value as a high concentration varnish.

  Further, the film formability was evaluated in the same manner as in Example 1. As a result, the insulating film thickness at the coating gap of 100 μm was 25 μm, and the insulating film thickness at the coating gap of 150 μm was 38 μm. That is, an insulating film thicker than that of Example 2 could be obtained due to the effect of increasing the concentration. In both the coating gaps of 100 μm and 150 μm, these insulating coatings were not cracked and their appearance was good.

  Further, the elongation at break of the insulating coating was measured in the same manner as in Example 1. As a result, the coating gap was 50% in both 100 μm and 150 μm, and the insulating coating obtained from the low molecular weight body showed a high value. . This is considered to be due to the effect of polymerizing low molecular weight substances at the time of baking to increase the molecular weight by including the OPDA skeleton.

  As described above, the varnish of Example 3 has a large elongation at break and a thickening effect by increasing the coating gap while achieving both low viscosity and high concentration. It was. Therefore, this varnish is considered useful for increasing the thickness of the enameled wire insulation coating. In addition, since these effects can be achieved even with a small number of coatings and bakings, it is possible to reduce manufacturing costs and prevent unevenness from occurring in the insulating coating.

Example 4
The varnish of Example 4 has a structure derived from pyromellitic dianhydride (PMDA), which is an acid dianhydride having a rigid structure, in the polyamic acid structure of this embodiment (a copolymer skeleton having a rigid structure). It is an example of the varnish when it is contained.

  In a 100 mL sample bottle, 3.831 g (12.485 mmol) of ODPA and 41.20 g of NMP were collected, and the inside of the sample bottle was purged with nitrogen as in Example 1 and sealed with a rotary mixer to dissolve. To this sample bottle, 0.1238 g (3.746 mmol) of ultra-dehydrated methanol as an esterifying agent was added, purged with nitrogen in the same manner as in Example 1, sealed, and then stirred at room temperature for 24 hours with a rotary mixer. Next, the sample bottle was opened, 9.99 g (49.940 mmol) of ODA was added, the inside of the sample bottle was purged with nitrogen, and after sealing, the sample bottle was stirred with a mix rotor for 24 hours.

  The sample bottle was opened, and 8.1913 g of PMDA (37.450 mmol, 0.75 as the molar ratio of ODPA and PMDA to the whole) was added, and the inside of the sample bottle was purged with nitrogen and sealed. The sample bottle was stirred for 24 hours with a mix rotor to obtain the varnish of Example 4.

  The solid content concentration of the obtained varnish was 35% by mass. Moreover, R in said Formula (1)-Formula (4) and Formula (6)-Formula (9) contained in the obtained varnish is either a hydrogen atom or a methyl group (1 carbon number). However, since the amount of super-dehydrated methanol used (molar ratio to ODPA) is larger than that in Example 1, the amount of methyl groups in all R is larger than that in Example 1.

  When Mw was measured in the same manner as in Example 1, Mw was 37000. Therefore, the molecular weight was lower than that of Example 1 by adopting ODPA with an increased partial esterification rate. Moreover, when the viscosity was measured like Example 1, varnish viscosity also showed 37 Pa * s which is a very 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. This was larger than Example 1 and Example 2, and was similar to Example 3. Also, no cracking occurred during baking. In addition to the effect of polymerizing low molecular weight polymers during baking to increase the molecular weight by including an OPDA skeleton, the intermolecular structure due to the flat structure of the copolymerized PMDA skeleton (copolymer skeleton having a rigid structure) Based on the packing effect.

  Further, the breaking elongation of the insulating coating measured in the same manner as in Example 1 was 70%, which was a value larger than those in Examples 1 to 3. In addition to the effect that the low molecular weight polymers are polymerized by baking and contain high molecular weight by including the OPDA skeleton, the result is a molecule with a flat structure of the copolymerized PMDA skeleton (copolymer skeleton having a rigid structure). It is thought to be based on the packing effect between.

  As described above, the varnish of Example 4 was also found to have the effect of increasing the elongation at break of the insulating coating and increasing the film thickness with a large coating gap while achieving both low viscosity and high concentration. Therefore, this varnish is considered useful for increasing the thickness of the enameled wire insulation coating. In addition, since these effects can be achieved even with a small number of coatings and bakings, it is possible to reduce manufacturing costs and prevent unevenness from occurring in the insulating coating.

(Example 5)
The varnish of Example 5 is an example of a varnish obtained by mixing the varnish described in Example 3 and the varnish described in Example 4. Therefore, the polyimide contained in the insulating coating contains polyimide obtained by copolymerizing the polyamic acid of Example 3 and the polyamic acid of Example 4.

  In a 250 mL planetary stirring plastic container, 10 g of the varnish described in Example 3 and 90 g of the varnish described in Example 4 were collected. And the varnish of Example 5 was produced by mixing the varnish with the rotation / revolution mixer ARE-310 made by Shinky Corporation under the condition of 2000 rpm / 3 minutes. The solid content concentration of the obtained varnish was 35% by mass.

  When the viscosity was measured in the same manner as in Example 1, it was 25 Pa · s lower than in Example 4. The insulating film thickness at a coating gap of 150 μm was 37 μm. And the formed insulation film did not have a crack, and the external appearance was favorable. Mw is not measured.

  Furthermore, the breaking elongation of the insulating coating measured in the same manner as in Example 1 was 70%, and the insulating coating obtained from the low molecular weight body showed a high value. By mixing the varnish of Example 4 having a low viscosity with the varnish of Example 3 having a slightly high viscosity, the viscosity of the varnish could be reduced. Moreover, it was confirmed that even when the viscosity was lowered in this way, the high elongation at break of the insulating coating was maintained. Therefore, this varnish is considered useful for increasing the thickness of the enameled wire insulation coating. In addition, since these effects can be achieved even with a small number of coatings and bakings, it is possible to reduce manufacturing costs and prevent unevenness from occurring in the insulating coating.

(Example 6)
The varnish of Example 6 is an example of a varnish obtained by mixing polyimide particles (PI particles) with the varnish of Example 5. Therefore, an insulating coating in which the polyimide imidized with the polyamic acid contained in Example 5 and the PI particles are integrated is formed.

  In a 250 mL planetary stirring vessel, 10 g of the varnish described in Example 3, 90 g of the varnish described in Example 4, and 8.25 g of PI particles (UIP-R average particle size: 7.3 μm manufactured by Ube Industries) Each was collected. The varnish of Example 6 was prepared by mixing this polycontainer with a rotation / revolution mixer ARE-310 manufactured by Sinky Corporation under the condition of 2000 rpm / 30 minutes. The solid content concentration of the obtained varnish could be increased to 40% by mass by adding PI particles.

  Further, when the viscosity was measured in the same manner as in Example 1, the viscosity of the varnish was 50 Pa · s. Therefore, even with a high concentration varnish such as 40% by mass, the viscosity could be kept low. Further, the insulating film thickness at the coating gap of 150 μm was 42 μm, and an insulating film thicker than that of Example 5 could be formed by increasing the concentration. And the formed insulation film did not have a crack, and the external appearance was favorable.

  Furthermore, the breaking elongation of the insulating coating measured in the same manner as in Example 1 was 60%, and the insulating coating obtained from the low molecular weight body showed a high value. It was confirmed that by using PI particles, the film thickness was increased while increasing the concentration, and the high elongation at break of the insulating coating was maintained. Therefore, this varnish is considered useful for increasing the thickness of the enameled wire insulation coating. In addition, since these effects can be achieved even with a small number of coatings and bakings, it is possible to reduce manufacturing costs and prevent unevenness from occurring in the insulating coating.

(Example 7)
The varnish of Example 7 is a varnish adjusted to the same varnish concentration as Example 5 by adjusting the concentration with NMP while adding PI particles to the varnish of Example 5. In other words, the varnish of Example 6 containing PI particles was adjusted to the same varnish concentration as that of Example 5 using NMP.

  In a 250 mL planetary stirring vessel, 10 g of the varnish described in Example 3, 90 g of the varnish described in Example 4, and 8.25 g of PI particles (UIP-R average particle size: 7.3 μm manufactured by Ube Industries) 16.25 g of NMP was collected. The varnish of Example 7 was prepared by mixing this polycontainer with a rotation / revolution mixer ARE-310 manufactured by Shinky Corporation under the condition of 2000 rpm / 30 minutes. The solid content concentration of the obtained varnish was 35% by mass.

  Further, when the viscosity was measured in the same manner as in Example 1, the viscosity of the varnish was 16 Pa · s, which was significantly lower than that in Example 5 or Example 6. This is presumably because the ratio of polyamic acid to the total amount of NMP in the varnish was reduced by the addition of NMP. Further, the insulation film thickness at a coating gap of 150 μm was 37 μm.

  Further, the breaking elongation of the insulating coating measured in the same manner as in Example 1 was 60%, and the insulating coating obtained from the low molecular weight body showed a high value. This is presumably because the addition of NMP decreased the polyamic acid ratio as described above, but PI particles were used to compensate for the decrease in the ratio.

  As described above, the varnish of Example 7 was also effective in increasing the breaking strength of the insulating coating and increasing the film thickness with a large coating gap while achieving both low viscosity and high concentration. Therefore, this varnish is considered useful for increasing the thickness of the enameled wire insulation coating. In addition, since these effects can be achieved even with a small number of coatings and bakings, it is possible to reduce manufacturing costs and prevent unevenness from occurring in the insulating coating.

(Example 8)
In the varnish of Example 8, R in the ODPA skeleton represented by the above formulas (1) to (4) and the carboxy terminal structure represented by the formulas (6) to (9) are all hydrogen atoms. This is a varnish taking the case of

  In a 100 mL sample bottle, 15.5.424 g (49.94 mmol) of ODPA and 48.83 g of NMP were collected, and the sample bottle was purged with nitrogen in the same manner as in Example 1 and sealed with a rotary mixer for 24 hours. In this solution, ODPA was not completely dissolved. To this sample bottle, 0.44 g (24.444 mmol) of distilled water as a carboxyl agent was added, and after replacing with nitrogen in the same manner as in Example 1, the vessel was sealed and stirred at room temperature for 24 hours with a rotary mixer. Next, the sample bottle was opened, and 10.000 g (49.940 mmol) of ODA was added, and the inside of the sample bottle was purged with nitrogen and sealed, and then the sample bottle was placed in a mix rotor for 24 hours in the same manner as in Example 1. The varnish of Example 8 was obtained by stirring. The solid content concentration of the obtained varnish was 35% by mass.

  When Mw was measured in the same manner as in Example 1, Mw was 10,000. By making all R hydrogen atoms, the molecular weight was lower than in Example 1. Moreover, when the viscosity was measured like Example 1, varnish viscosity also showed 1.2 Pa.s which is a very low value as a high concentration varnish.

  Further, the film formability was evaluated in the same manner as in Example 1. As a result, the insulating film thickness at the coating gap of 100 μm was 25 μm, and the insulating film thickness at the coating gap of 150 μm was 38 μm. In both the coating gaps of 100 μm and 150 μm, these insulating coatings were not cracked and their appearance was good.

  Moreover, the breaking elongation of the insulating film measured in the same manner as in Example 1 was 50% in both cases where the coating gap was 100 μm and 150 μm, and the insulating film obtained from the low molecular weight body showed a high value. In particular, from comparison with Example 3, it was confirmed that even when R is a hydrogen atom or an alkyl group, high elongation at break was exhibited.

  Thus, in the varnish of Example 8, even when R is a hydrogen atom, the elongation at break of the insulating coating is increased and the coating gap is increased while achieving both low viscosity and high concentration. The effect of increasing the film thickness was also observed. Therefore, this varnish is considered useful for increasing the thickness of the enameled wire insulation coating. In addition, since these effects can be achieved even with a small number of coatings and bakings, it is possible to reduce manufacturing costs and prevent unevenness from occurring in the insulating coating.

Example 9
The varnish of Example 9 is an example of a varnish obtained by mixing the varnish described in Example 4 and the varnish described in Example 8. Therefore, the polyimide contained in the insulating coating contains polyimide obtained by copolymerizing the polyamic acid of Example 4 and the polyamic acid of Example 8.

  In a 250 mL planetary stirring plastic container, 90 g of the varnish described in Example 4 and 10 g of the varnish described in Example 8 were collected. And the varnish of the poly container was mixed with the rotation / revolution mixer ARE-310 made by Shinky Corporation under the condition of 2000 rpm / 3 minutes, and the varnish of Example 9 was produced.

  When the viscosity was measured in the same manner as in Example 1, it was 23 Pa · s lower than that in Example 4. Further, when the insulation film thickness at the coating gap of 150 μm was measured in the same manner as in Example 1, it was 37 μm. Furthermore, the insulation coating had no cracks and the appearance was good. And the breaking elongation measured like Example 1 was 70%, and showed a high value as an insulating film obtained from the low molecular weight body.

  As described above, the varnish of Example 9 has the effect of increasing the breaking strength of the insulating film and increasing the film thickness with a large coating gap while achieving both low viscosity and high concentration as in Example 5. Was also recognized. Therefore, this varnish is considered useful for increasing the thickness of the enameled wire insulation coating. In addition, since these effects can be achieved even with a small number of coatings and bakings, it is possible to reduce manufacturing costs and prevent unevenness from occurring in the insulating coating.

(Comparative Example 1)
The varnish of Comparative Example 1 is an example of a varnish containing a polyamic acid having a structure in which a copolymer skeleton having a rigid structure and an ODA skeleton are alternately linked by an amide bond. Therefore, Comparative Example 1 is an example of a polyamic acid that does not include the structures represented by the above formulas (1) to (4). The “copolymer skeleton having a rigid structure” used in Comparative Example 1 is a skeleton derived from pyromellitic dianhydride (PMDA).

  In a 30 mL sample bottle, 1.4338 g (7.16 mmol) of ODA manufactured by Wako Pure Chemical Industries, Ltd. and 17 g of NMP were respectively collected, 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 manufactured by Wako Pure Chemical Industries, Ltd. was added, purged with nitrogen in the same manner as in Example 1, sealed, and then stirred at room temperature for 24 hours with a rotary mixer. The varnish of Comparative Example 1 was obtained. The solid content concentration of the obtained varnish was 15% by mass.

  When Mw was measured in the same manner as in Example 1, Mw was 120,000. Further, when the viscosity was measured in the same manner as in Example 1, the viscosity was 6.8 Pa · s. Furthermore, when the film formability was evaluated in the same manner as in Example 1, the insulating film thickness at the coating gap of 100 μm was 10 μm. The insulating coating formed here had no cracks and the appearance was good. Further, the elongation at break of the formed insulating coating was measured in the same manner as in Example 1 and found to be 65%.

  However, in the coating gap of 150 μm, an attempt was made to increase the thickness of the insulating coating by applying a thick coating, but foaming occurred during baking, and the insulating coating could not be formed. Therefore, in order to increase the film thickness, it is considered necessary to repeatedly apply as thinly as possible in order to suppress foaming. Specifically, in order to form a thick film having a thickness of 150 μm using the varnish of Comparative Example 1, it is estimated that at least 15 coatings are necessary.

  In the varnish of Comparative Example 1, due to the large molecular weight of the polyamic acid, an insulating film having a large elongation at break was obtained at a coating gap of 100 μm. However, although the solid concentration was as low as 15% by mass, the viscosity was 6.8 Pa · s, which was extremely large compared to Examples 1 and 2 having the same concentration. The film thickness of the insulating coating was as small as 10 μm. For this reason, it is considered that it is difficult to achieve both high varnish concentration and low viscosity. Further, foaming occurs when the coating gap becomes large (for example, 150 μm). For this reason, it has been found that if an attempt is made to increase the film thickness, a large number of coating steps are required, which takes a lot of labor.

(Comparative Example 2)
The varnish of Comparative Example 2 was obtained by obtaining a polyamic acid having a structure in which a copolymer skeleton having a rigid structure and an ODA skeleton are alternately linked by amide bonds, and then adding ODA, whereby a copolymer having a rigid structure is added. It is an example of the varnish which adjusted the equivalence ratio of a polymerization frame | skeleton and ODA frame | skeleton as 1: 1 molar ratio. The “copolymer skeleton having a rigid structure” used in Comparative Example 2 is a skeleton derived from pyromellitic dianhydride (PMDA).

  In a 50 mL sample bottle, 2.0040 g (10.008 mmol) of ODA manufactured by Wako Pure Chemical Industries, Ltd. and 30.5 g of NMP were collected, 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 manufactured by Wako Pure Chemical Industries, Ltd. was added, and after replacing with nitrogen in the same manner as in Example 1, the mixture was sealed and stirred at room temperature for 24 hours with a rotary mixer. .

  After opening the sample bottle, 0.3189 g (9.958 mmol) of ultra-dehydrated methanol manufactured by Wako Pure Chemical Industries, Ltd. was added as an esterifying agent, and the inside of the sample bottle was replaced with nitrogen in the same manner as in Example 4, and then sealed. The mixture was stirred for 24 hours with a mix rotor. After stirring, 0.9965 g (4.976 mmol) of ODA was further added to obtain a varnish of Comparative Example 2. The solid content concentration of the obtained varnish was 17.8% by mass.

  When Mw was measured in the same manner as in Example 1, Mw was 43,000. Further, when the viscosity was measured in the same manner as in Example 1, the viscosity was 0.2 Pa · s. Furthermore, when the film formability was evaluated in the same manner as in Example 1, the insulating film thickness at the coating gap of 100 μm was 10 μm. The insulating coating formed here had no cracks and the appearance was good.

  However, the elongation at break of the formed insulating coating was measured in the same manner as in Example 1 and found to be 25%. Although this varnish has a low viscosity, there is a problem in that the breaking elongation of the formed insulating coating is as small as 25% and the film thickness is as small as 10 μm. The reason for this result is thought to be due to the lower molecular weight of the polyamic acid. That is, in the varnish of Comparative Example 2 using only the PMDA-derived skeleton, which is a copolymer skeleton having a rigid structure, the entire polyamic acid molecule including both ends is rigid, and the elongation at break is reduced due to the effect of low molecular weight. It is thought that it fell.

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

  The amount of ODA used is 1.0019 g (5.003 mmol), the amount of NMP used is 15.13 g, the amount of PMDA used is 1.6377 g (7.508 mmol), and the amount of ultra-dehydrated methanol used is 0.1633 g (5. 097 mmol), and a varnish was obtained in the same manner as in Comparative Example 2 except that stirring by the mix rotor was not performed.

  Next, 1.0007 g (4.998 mmol) of ODA and 1.6369 g (7.505 mmol) of PMDA and 1.6369 g (7.505 mmol) of PMDA were added to the sample bottle containing the varnish obtained here. Stir for hours. Next, 0.1594 g (4.975 mmol) of ultra-dehydrated methanol was added, the inside of the sample bottle was purged with nitrogen, sealed, and the sample bottle was stirred with a mix rotor for 24 hours.

  Further, 1.0017 g (5.002 mmol) of ODA and 1.6258 g (7.454 mmol) of PMDA were further added to the sample bottle after stirring, purged with nitrogen, sealed, and stirred with a rotary mixer for 24 hours. 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 with a mix rotor for 24 hours. Finally, in order to match the equivalent ratio of PMDA and ODA, 1.4929 g (7.456 mmol) of ODA was added to the sample bottle and dissolved to obtain a varnish of Comparative Example 3 having a solid content concentration of 39.5% by mass. .

  The resulting polyamic acid of Comparative Example 3 is increased in concentration by repeating the polymerization procedure of Comparative Example 2 above, so the molecular weight measured in the same manner as in Example 1 is estimated to be about 43,000. Further, the varnish viscosity was measured in the same manner as in Example 1. As a result, the varnish viscosity was increased to 42.5 Pa · s due to the effect of increasing the concentration, but it was in a viscosity range in which application was possible.

  However, when the film was applied and baked with a coating gap of 100 μm, many cracks were generated in the insulating film, and it could not be said that the appearance was good, and the film thickness could not be measured. From this result, even if the polyamic acid consisting only of a copolymer skeleton and an ODA skeleton having a rigid structure has a rigid structure at both ends even if the concentration is increased, the insulating film is likely to be cracked. It was found that the film cannot be thickened.

  The above results are summarized in Table 1 below. In Table 1, “-” indicates that measurement is not performed or measurement is not possible.

<Production and evaluation of multilayer insulation coating>
An insulating film with aluminum foil prepared in Example 7 (see Example 1 as appropriate) was adhered to a glass substrate with a polyimide tape, and the varnish prepared in Comparative Example 1 was applied on the insulating film with a coating gap of 50 μm. In the same manner as in No. 1, a dumbbell-shaped sample was produced. This dumbbell-shaped sample includes an insulating film obtained by applying the varnish of the present embodiment, and an insulating film (second insulating film) obtained by applying the varnish produced in Comparative Example 1 thereon. Are stacked. That is, here, it is an evaluation of a model of the enameled wire shown in FIGS.

  Regarding the thickness of the insulating coating, the insulating coating of Example 7 was 37 μm, the insulating coating of Comparative Example 1 (second insulating coating) was 5 μm, and the thickness was 42 μm as a whole. Due to the two-layered insulating coating, the elongation at break measured by the same method as in Example 1 increased to 65% compared to Example 7 and Comparative Example 1. Therefore, it was found that the physical properties of the insulating coating can be improved by installing the insulating coating of Comparative Example 1 using the PMDA skeleton having a rigid structure on the insulating coating of Example 7 containing PI particles. .

1 Metal conductor wire 2 Insulating film 3 Insulating film (second insulating film)
4 Polyimide particles 10 Enamel wire 20 Enamel wire 30 Enamel wire 40 Enamel wire 50 Coil 60 Stator (Electric parts)

Claims (9)

It has a polyamide structure in which at least one of the repeating units represented by the following formulas (1) to (4) and the repeating unit represented by the following formula (5) are linked by alternately amide bonds. Varnish characterized by containing polyamic acid.

In the formulas (1) to (4), each R independently represents a hydrogen atom or an alkyl group having 3 or less carbon atoms, and the alkyl group may be a chain or a ring, and has a branch. Also good. The polyamic acid is
Having at least one of the structures represented by the following formulas (6) to (9) at the carboxy terminus;
The varnish according to claim 1, having at least one of the following formulas (10) and (11) at an amino terminus.

In the formulas (6) to (11), X represents the polyamide structure.   The varnish according to claim 1 or 2, wherein the polyamic acid contains a repeating unit derived from a conjugated aromatic tetracarboxylic acid.   The varnish according to claim 1 or 2, wherein the polyamic acid has a styrene-converted mass average molecular weight of 3,000 to 50,000.   The varnish according to claim 1, comprising polyimide particles. A metal conductor wire and an insulating film formed on the surface of the metal conductor wire;
The said insulating film contains the polyimide which has a repeating unit represented by following formula (12), The enamel wire characterized by the above-mentioned.

  A polyimide having a structure in which repeating units derived from a conjugated aromatic tetracarboxylic acid and repeating units derived from 4,4′-diaminodiphenyl ether are alternately imidized and connected to the surface of the insulating coating. The enameled wire according to claim 6, wherein a second insulating film is formed.   A coil comprising the enameled wire according to claim 6 or 7.   An electrical component comprising the coil according to claim 8.

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