JP2013253124A - Polyimide resin vanish, and insulated electric wire, electric coil and motor using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyimide resin vanish excellent in heat resistance and crazing resistance, and capable of forming an insulating layer having a low permittivity; and to provide an insulated electric wire excellent in heat resistance and crazing resistance, and capable of raising the corona discharge initiation.SOLUTION: A polyimide resin vanish has, as a main component, a polyimide precursor resin obtained by reacting an aromatic diamine with an aromatic tetracarboxylic anhydride, wherein the imide group concentration after the imidization of the polyimide precursor resin is >35.0% and <36.0%.

Description

  The present invention relates to a polyimide resin varnish that can be coated and baked on a conductor to form an insulating film, an insulated wire having an insulating layer formed using this polyimide resin varnish, an electric coil, and a motor.

  In an insulated wire used as a coil winding for a motor or the like, an insulating layer (insulating film) covering the conductor is required to have insulation, adhesion to the conductor, heat resistance, mechanical strength, and the like. Examples of the resin forming the insulating layer include polyimide resin, polyamideimide resin, and polyesterimide resin.

  In addition, in an electric device having a high applied voltage, for example, a motor used at a high voltage, a high voltage is applied to an insulated wire constituting the electric device, and partial discharge (corona discharge) is likely to occur on the surface of the insulating film. The generation of corona discharge tends to cause a local temperature rise and the generation of ozone and ions. As a result, the insulation coating of the insulated wire is deteriorated, resulting in early dielectric breakdown and shortening the life of the electrical equipment. Insulated wires used at high voltages are also required to improve the corona discharge starting voltage for the above reasons, and it is known that reducing the dielectric constant of the insulating layer is effective for this purpose.

  Polyimide resin is particularly excellent in heat resistance among resins widely used as insulating layers for insulated wires. Moreover, since it has a low dielectric constant and excellent mechanical properties, it is used as an insulating layer for insulated wires with high required properties. For example, Patent Document 1 discloses an enameled wire in which a polyimide resin enamel film layer is applied and baked directly on a conductor as an enameled wire having a heat resistance class C (class of 180 ° C. or higher).

  Patent Document 2 describes a polyimide resin having an aromatic ether structure. Specifically, a polyimide by reacting an acid anhydride having an aromatic ether structure such as 4,4′-oxydiphthalic dianhydride (ODPA) with a diamine having an aromatic ether structure and a diamine having a fluorene structure. The precursor is synthesized. The flexibility is improved by using an acid anhydride having an aromatic ether structure and a diamine. Further, it is described that the polyimide resin having such a structure has a low dielectric constant and can provide an insulating film excellent in suppressing corona generation.

JP-A-9-198932 JP 2010-67408 A

  As mentioned above, polyimide resin is a material that excels in heat resistance, mechanical properties, and electrical properties. However, the dielectric constant of polyimide resin, which is widely used as a coating layer for insulated wires, is 3.5, and corona discharge starts. In order to improve the voltage, it is required to further lower the dielectric constant. The present inventors pay attention to the imide group concentration of the polyimide resin and reduce the concentration of the highly polar imide group by using an aromatic diamine or aromatic tetracarboxylic dianhydride having a large molecular weight, and the dielectric constant of the polyimide resin. Has been filed as Japanese Patent Application No. 2011-091777.

  Moreover, when using an insulated wire for the coil used for the motor for motor vehicles etc., since the temperature of a use environment is high, long-term heat resistance is calculated | required by the insulated wire. In order to increase the insulation reliability of the insulated wire, a so-called varnish impregnation treatment in which a coil is formed by winding and then dip-coated with a thermosetting resin may be performed. Therefore, it is required that the coating of the insulated wire is free from cracking or cracking (crazing resistance) when it is brought into contact with the impregnated varnish (thermosetting resin liquid).

  According to the study by the present inventors, an insulated wire using a polyimide resin with a low imide group concentration and a low dielectric constant as a film has long-term heat resistance and crazing resistance compared to a general-purpose polyimide resin with a high imide group concentration. It turns out that it falls. Even if it is such an insulated wire, crazing resistance can be improved by performing a heat treatment (annealing treatment) at 180 ° C. for about 10 minutes after the production of the insulated wire, but the number of production processes is increased. Cost increases.

  This invention is made | formed in view of said problem, and makes it a subject to provide the polyimide resin varnish which can form an insulating layer of a low dielectric constant, without raise | generating the heat resistance and a crazing-proof characteristic. The present invention also provides an insulated wire having an insulating layer formed using the above polyimide resin varnish and capable of improving heat resistance, crazing resistance and corona discharge starting voltage, and an electric coil and motor using the same. This is the issue.

The present invention is a polyimide resin varnish mainly composed of a polyimide precursor resin obtained by reacting an aromatic diamine and an aromatic tetracarboxylic dianhydride,
A polyimide resin varnish having an imide group concentration after imidization of the polyimide precursor resin of greater than 35.0% and less than 36.0% (Claim 1). By setting the imide group concentration in the above range, the dielectric constant can be reduced without lowering the heat resistance and crazing resistance.

The imide group concentration is the polyimide resin after imidizing the polyimide precursor. (Molecular weight of imide group part) / (Molecular weight of all polymers) × 100 (%)
It is a value calculated by. Since the polyimide precursor is obtained by reacting an aromatic diamine and an aromatic tetracarboxylic dianhydride, the imide group concentration is increased when the molecular weight of each monomer (aromatic diamine or aromatic tetracarboxylic dianhydride) increases. Lower. In addition, the general polyimide resin generally used for the film of an insulated wire is obtained by imidizing a polyimide precursor (polyamic acid) obtained by polymerizing pyromellitic dianhydride and 4,4'-diaminodiphenyl ether. The imide group concentration is 36.6%.

  If the imide group concentration is lowered, the dielectric constant can be lowered. However, if the imide group concentration is too low, the heat resistance and crazing resistance deteriorate. By setting the imide group concentration in the range of 35.0% to 36.0%, the dielectric constant can be reduced without lowering the heat resistance and crazing resistance. The imide group concentration is adjusted by arbitrarily selecting the aromatic diamine and the aromatic tetracarboxylic dianhydride constituting the polyimide precursor so that the imide group concentration falls within the above range.

  The group consisting of 2,2-bis [4- (aminophenoxy) phenyl] propane, 1,3-bis (4-aminophenoxy) benzene, and 1,4-bis (4-aminophenoxy) benzene as the aromatic diamine It is preferable to contain 1 or more types selected from (Claim 2). These aromatic diamines have a large molecular weight and can reduce the imide group concentration. In particular, when PMDA is selected as the aromatic tetracarboxylic dianhydride, heat resistance, crazing resistance and dielectric constant are balanced, which is preferable. A plurality of aromatic diamines may be used in combination. In this case, it is preferable to adjust the imide group concentration by combining the aromatic diamine having a large molecular weight with an aromatic dian having a small molecular weight such as 4,4'-diaminodiphenyl ether (ODA).

  The aromatic tetracarboxylic dianhydride is preferably pyromellitic dianhydride (PMDA) (Claim 3). Pyromellitic dianhydride has a relatively small molecular weight and a rigid structure. In order to adjust the imide group concentration, it is considered that either aromatic diamine or aromatic tetracarboxylic acid has a large molecular weight, but if an aromatic tetracarboxylic acid having a large molecular weight is used, the heat resistance is lowered. Therefore, it is preferable that PMDA having a low molecular weight is selected as the acid component and the imide group concentration is adjusted using an aromatic diamine having a high molecular weight because the heat resistance is improved.

  Invention of Claim 4 is an insulated wire which has a conductor and the insulating layer which coat | covers this conductor directly or through another layer, Comprising: The said insulating layer is formed by apply | coating and baking said polyimide resin varnish It is the insulated wire which is made. Since the dielectric constant of the insulating layer is low, an insulated wire having a high corona discharge starting voltage can be obtained. Moreover, since it is excellent also in heat resistance and crazing resistance, it can be used suitably especially as an insulated wire used by varnish impregnation treatment.

  The invention according to claim 5 is an electric coil formed by winding the insulated wire. A sixth aspect of the present invention is a motor having the electric coil according to the fifth aspect. Since an insulated wire excellent in heat resistance and crazing resistance is used, it can be used in a high temperature environment, and the insulating layer is not easily cracked during the varnish impregnation treatment. Further, even when a high voltage is applied, the insulating film is hardly deteriorated, so that the life can be extended.

  According to the present invention, it is possible to provide a polyimide resin varnish capable of forming an insulating layer having a low dielectric constant without causing deterioration of heat resistance and crazing resistance. Moreover, the insulated wire of this invention can improve heat resistance, crazing resistance, and a corona discharge start voltage.

It is a cross-sectional schematic diagram which shows an example of the insulated wire of this invention. It is a schematic diagram which shows an example of the coil of this invention. It is a schematic diagram which shows an example of the motor of this invention. It is a schematic diagram explaining the measuring method of a dielectric constant.

  The polyimide precursor resin (polyamic acid) which is the main component of the polyimide resin varnish of the present invention is obtained by condensation polymerization of an aromatic tetracarboxylic dianhydride and an aromatic diamine. This condensation polymerization reaction can be performed under the same conditions as in the conventional synthesis of a polyimide precursor.

  As aromatic tetracarboxylic dianhydrides, pyromellitic dianhydride (PMDA), 4,4′-oxydiphthalic dianhydride (ODPA), 3,4,3 ′, 4′-biphenyltetracarboxylic dianhydride Anhydride (BPDA), 3,3 ′, 4,4′-benzophenone tetracarboxylic dianhydride (BTDA), 3,3 ′, 4,4′-diphenylsulfone tetracarboxylic dianhydride, bicyclo (2, 2,2) -Oct-7-ene-2,3,5,6-tetracarboxylic dianhydride, 1,2,4,5-cyclohexanetetracarboxylic dianhydride, 2,2-bis (3 Examples include 4-dicarboxyxyphenyl) hexafluoropropane dianhydride, 5- (2,5-dioxotetrahydrofuryl) -3-methyl-3-cyclohexene-1,2-dicarboxylic dianhydride, and the like.

  Among these, pyromellitic dianhydride (PMDA) is preferable because it has a low molecular weight and a rigid structure and can improve the heat resistance of the polyimide resin.

  Aromatic diamines include 4,4′-diaminodiphenyl ether (ODA), 4,4′-methylenedianiline (MDA), 2,2-bis [4- (aminophenoxy) phenyl] propane (BAPP), 1, 4-bis (4-aminophenoxy) benzene (TPE-Q), 1,3-bis (4-aminophenoxy) benzene (TPE-R), 1,1-bis [4- (4-aminophenoxy) phenyl] Examples include cyclohexane (4-APBZ), 1,3-bis (3-aminophenoxy) benzene (3-APB), 1,5-bis (3-aminophenoxy) naphthalene (1,5-BAPN), and the like.

  Among these, 2,2-bis [4- (aminophenoxy) phenyl] propane (BAPP), 1,3-bis (4-aminophenoxy) benzene (TPE-R), 1,4-bis (4-aminophenoxy) Benzene (TPE-Q) can be preferably used because it has a large molecular weight and can reduce the imide group concentration. The imide group concentration can be adjusted by using these aromatic diamines in combination with an aromatic diamine having a small molecular weight such as ODA and MDA.

The aromatic tetracarboxylic dianhydride and the aromatic diamine are selected so that the imide group concentration after imidization is 28.0% or more and 33.0% or less. In the polyimide resin after imidizing the polyimide precursor, the imide group concentration is
(Molecular weight of imide group) / (Molecular weight of all polymers) × 100
It is a value calculated by. Specifically, the imide group concentration is calculated by the following method.

The imide group density | concentration in a unit unit is calculated from the molecular weight of aromatic tetracarboxylic dianhydride and aromatic diamine. For example, in the case of polyimide represented by the following formula (1), the imide group concentration is imide group molecular weight = 70.03 x 2 = 140.06.
Since unit molecular weight = 894.96,
Imide group concentration (%) = (140.06) / (894.96) × 100 = 15.6%
It becomes.

  The above aromatic tetracarboxylic dianhydride and aromatic diamine are mixed and reacted. When the total amount (equivalent) of aromatic diamine and the total amount (equivalent) of aromatic tetracarboxylic dianhydride is about 1: 1, the reaction proceeds favorably, which is preferable. Each material is mixed and heated to react in an organic solvent to obtain a polyimide precursor resin.

  As the organic solvent, an aprotic polar organic solvent such as N-methyl-2-pyrrolidone, N, N-dimethylformamide, N, N-dimethylacetamide, dimethyl sulfoxide, and γ-butyrolactone can be used. These organic solvents may be used alone or in combination of two or more.

  The amount of the organic solvent is not particularly limited as long as it is an amount capable of uniformly dispersing the aromatic tetracarboxylic dianhydride and the aromatic diamine, but usually 100 parts by mass per 100 parts by mass of the total amount of these components. ˜1000 parts by mass (so that the resin concentration is about 10% to 50%). If the amount of the organic solvent is reduced, the amount of the solid content of the polyimide resin varnish obtained is increased, which is effective for cost reduction.

  Various additives such as pigments, dyes, inorganic or organic fillers, lubricants, adhesion improvers, reactive low molecules, compatibilizers, and the like may be added to the polyimide resin varnish. When melamine, a triazole compound, a tetrazole compound, a thiol compound, or the like is added as an adhesion improver, adhesion with the conductor can be improved. Furthermore, other resins can be mixed and used within a range not impairing the gist of the present invention.

  The insulating layer is formed by applying and baking a polyimide resin varnish directly on the conductor or through another layer. In the baking step, the polyimide precursor resin is imidized to become polyimide. Application and baking can be performed in the same manner as in the production of a normal insulated wire. For example, after the resin varnish is applied to the conductor, an insulating layer is formed by repeating a baking operation by passing the inside of a furnace having a set temperature of 350 to 500 ° C. for 5 to 10 seconds per pass several times. The insulating layer has a thickness of 10 μm to 150 μm.

  As the conductor, copper, copper alloy, aluminum or the like can be used. The size of the conductor and the cross-sectional shape thereof are not particularly limited, but in the case of a round wire, a conductor diameter of 100 μm to 5 mm is generally used, and in the case of a flat wire, one having a side length of 500 μm to 5 mm is generally used.

  The insulating layer may be a single layer or a multilayer. When the insulating layer is a single layer, only the insulating layer formed by applying and baking the above polyimide resin varnish becomes the insulating layer. When the insulating layer has a multilayer structure, another insulating layer is formed before or after the formation of the insulating layer made of polyimide. As the resin for forming the other insulating layer, any resin such as general-purpose polyimide, polyamideimide, polyesterimide, polyurethane, and polyetherimide can be used.

  Furthermore, it is preferable to have a surface lubricating layer as the outermost layer as the insulating layer because the workability is further improved. Moreover, you may apply | coat surface lubricating oil to the outer side of an insulated wire. In this case, insertability and workability are further improved.

  FIG. 1 is a schematic cross-sectional view showing an example of the insulated wire of the present invention. A multi-layer insulating layer is provided outside the conductor 3, and the insulating layers are a first insulating layer 1 and a second insulating layer 2 from the conductor side. When the first insulating layer 1 and the second insulating layer 2 are all formed by applying and baking the polyimide resin varnish of the present invention, an insulated wire having an insulating layer with excellent heat resistance and crazing resistance and a low dielectric constant is obtained. It is done. In order to improve the adhesion with the conductor, the first insulating layer 1 may be made of other resin having excellent adhesion with the conductor, such as polyamideimide. The insulated wire of the present invention is not limited to this shape.

  FIG. 3A is a schematic diagram illustrating an example of the electric coil of the present invention, and FIG. 3B is a cross-sectional view taken along the line A-A ′ of FIG. The electric wire 12 is formed by winding the insulated wire 11 outside the core 13 made of a magnetic material. A member composed of a core and an electric coil is used as a rotor or a stator of a motor. For example, as shown in FIG. 4, a stator 15 in which a plurality of divided stators 14 including a core 13 and an electric coil 12 are combined and arranged in an annular shape is used as a constituent member of a motor.

  In order to increase the insulation reliability of the electric coil wound as described above, the electric coil after the winding is subjected to varnish impregnation treatment. Specifically, the electric coil is immersed in a thermosetting resin liquid such as an epoxy resin or a xylene resin to attach the thermosetting resin around the coil, and then heat-treated to cure the thermosetting resin. The curing temperature of the thermosetting resin is about 100 ° C to 180 ° C. Thus, an electric coil impregnated with varnish is obtained.

  Next, the present invention will be described in more detail based on examples. The scope of the present invention is not limited to this example.

(Examples 1-3, Comparative Examples 1-6)
(Preparation of polyimide precursor resin)
After dissolving the types and amounts of aromatic diamines (ODA, BAPP) shown in Table 1 in N-methylpyrrolidone, the types and amounts of aromatic tetracarboxylic acid anhydrides (PMDA) shown in Table 1 are added to form a nitrogen atmosphere. The mixture was stirred at room temperature for 1 hour. Thereafter, the mixture was stirred at 60 ° C. for 20 hours to finish the reaction, and cooled to room temperature to obtain a polyimide resin varnish. In addition, the numerical value of the compounding amount described in Table 1 is a molar ratio. The imide group concentration calculated from the molecular weight of each component is shown in Table 1.

(Production of insulated wires)
A process of applying and baking a polyimide resin varnish produced on the surface of a flat conductor having a thickness of 1.5 mm and a width of 3.0 mm by a conventional method is repeated a plurality of times to form an insulating layer having a thickness of about 40 μm. Comparative Example 1-6 The insulated wire was produced.

(Measurement of dielectric constant)
About each obtained insulated wire, the dielectric constant of the insulating layer was measured. As shown in FIG. 4, a silver paste was applied to three places on the surface of the insulated wire to prepare a measurement sample (the width of application is 10 mm at both ends and 100 mm at the center). The capacitance between the conductor and the silver paste was measured with an LCR meter, and the dielectric constant was calculated from the measured capacitance value and the thickness of the insulating layer. The measurement was performed under conditions of a temperature of 30 ° C. and a humidity of 50%.

(Evaluation of thermal durability)
Each obtained insulated wire 1 m was left in a thermostatic bath at a temperature of 280 ° C., and the time until the insulation layer was cracked was measured. An acceptance criterion was that no cracking occurred for 48 hours or more.

(Evaluation of crazing resistance)
Each obtained insulated wire was stretched 10%, 10 m was immersed in xylene monomer for about 30 seconds and then taken out, the insulating layer was observed, and the number of cracks generated per 1 m of the insulated wire was measured. The acceptance criterion was that the number of cracks generated per 1 m was 0. The results are shown in Table 1.

  In Examples 1 to 3 and Comparative Examples 1 to 6, ODA having a low molecular weight and BAPP having a high molecular weight are used in combination as an aromatic diamine, and the imide group concentration is adjusted by changing the ratio of BAPP from 0% to 50%. . The dielectric constant decreases as the BAPP ratio increases and the imide group concentration decreases. However, the lower the imide group concentration, the lower the heat resistance and the worse the crazing resistance. The crazing resistance satisfies the acceptance criteria in Example 3 where the imide group concentration exceeds 35.0%, and the dielectric constant is lower than 3.5 of the general-purpose polyimide (Comparative Example 1) because the imide group concentration is Example 1 with less than 36.0%. From the above, it can be seen that the imide group concentration capable of achieving both heat resistance, crazing resistance and low dielectric constant is more than 35.0% and less than 36.0%.

DESCRIPTION OF SYMBOLS 1 1st insulating layer 2 2nd insulating layer 3 Conductor 11 Insulated electric wire 12 Electric coil 13 Core 14 Split stator 15 Stator

Claims (6)

A polyimide resin varnish mainly composed of a polyimide precursor resin obtained by reacting an aromatic diamine and an aromatic tetracarboxylic dianhydride,
A polyimide resin varnish having an imide group concentration after imidation of the polyimide precursor resin of greater than 35.0% and less than 36.0%.   The aromatic diamine is 2,2-bis [4- (aminophenoxy) phenyl] propane (BAPP), 1,3-bis (4-aminophenoxy) benzene, and 1,4-bis (4-aminophenoxy). The polyimide resin varnish of Claim 1 containing 1 or more types selected from the group which consists of benzene.   The polyimide resin varnish according to claim 1, wherein the aromatic tetracarboxylic dianhydride is pyromellitic dianhydride.   It is an insulated wire which has an insulating layer which coat | covers a conductor and this conductor directly or through another layer, Comprising: The said insulating layer apply | coats and bakes the polyimide resin varnish of any one of Claims 1-3 An insulated wire that is formed as a result.   An electric coil formed by winding the insulated wire according to claim 4.   A motor having the electric coil according to claim 5.

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