JP6439062B2 - Insulated wire manufacturing method - Google Patents

Description

  The present invention relates to a method for manufacturing an insulated wire.

  In recent years, with the miniaturization of electronic devices and electrical devices, there has been a demand for miniaturization of coils to be mounted on these devices. Miniaturization of the coil is realized by using an enameled wire having a rectangular cross section (flat angle enameled wire). The flat enameled wire can reduce the gap between enameled wires when coiled, and increase the space factor of the enameled wire, compared to the conventional enameled wire with a circular cross section (round enameled wire) Therefore, the coil can be reduced in size.

  A flat enameled wire has a flat conductor and an insulating film covering its periphery. The insulation film of the flat enameled wire used for the coil is required to have good flexibility, excellent heat resistance, and insulation. For example, an insulated wire (Patent Document 1) having a seizure layer of an emulsion type electrodeposition varnish containing an imide-based or amide-based polymer around a rectangular conductor, or a first polyamideimide around a rectangular conductor. An insulated wire having a first layer, a second layer made of a second polyamideimide, and a third layer made of polyimide has been proposed (Patent Document 2).

  These rectangular enamel wires can be usually obtained by coating the periphery of a rectangular conductor with an insulating film. However, in the enameled wire thus obtained, it is difficult to uniformly form the insulating film on the side portion and the flat portion of the cross section of the flat conductor, and in particular, the thickness of the side portion tends to be thin. On the other hand, it has been studied to roll a round conductor covered with an insulating layer and a self-bonding layer to obtain a flat enameled wire having a uniform thickness of the insulating film on the side portion and the flat portion (for example, Patent Documents). 3).

Japanese Patent Laid-Open No. 4-12407 JP-A-2015-135766 JP 54-37287 A

  Along with the demand for miniaturization, thinning of a rectangular conductor is required, and the thickness of the insulating film is also desired to be as thin as possible within the range in which insulation is maintained. However, in the case of a thin film according to miniaturization, when a flat enameled wire is wound in a coil shape, the side part is not fused by the self-bonding layer with respect to the flat part fused by the self-bonding layer. Since it is in an exposed state, when exposed to a severe use environment such as a high temperature, the insulating property tends to be insufficient. On the other hand, when the film thickness of the entire insulating film is increased in order to ensure the insulation of the side portion, the size of the entire coil becomes large. Therefore, it is necessary to roll the round conductor covered with the insulating film at a predetermined rolling ratio.

  However, when a round conductor covered with a conventional insulating film is rolled at a higher rolling ratio than conventional, there is a problem that cracks are generated in the flat portion of the insulating film. Such cracks tend to cause dielectric breakdown.

  Furthermore, the insulation film of the flat enameled wire is required to have high heat resistance that does not lose the insulation even in a high temperature use environment. However, since the insulated wire shown in Patent Document 3 mainly has a layer made of polyamideimide, the heat resistance is not sufficient. In addition, when the heat resistance of the insulating film is increased, the adhesion to the conductor is lowered, and in the insulating film obtained by applying the insulating coating a plurality of times, voids (in-layer peeling) are likely to occur in the layer. Thus, the heat resistance and the adhesion to the conductor or the in-layer adhesion are contradictory properties, and it has been difficult to achieve both.

  This invention is made | formed in view of the said subject, The crack of an insulating film is suppressed, and it provides the insulated wire which has high heat resistance, favorable adhesiveness with a conductor, and in-layer adhesiveness. With the goal.

[1] An insulated wire having a conductor, an insulating layer provided on the outer periphery thereof, and a self-bonding layer provided on the insulating layer and containing a resin having a softening temperature of 280 ° C. or less,
The insulated wire has a cross-sectional shape having a pair of long sides facing each other and a pair of short sides facing each other and curved outwardly, and the insulating layer is made of biphenyltetracarboxylic acid A tetracarboxylic acid component unit (a) containing 40 to 80 mol% anhydride units, 10 to 20 mol% benzophenonetetracarboxylic anhydride units, and 10 to 50 mol% pyromellitic anhydride units, and a diamine component The insulated wire containing the polyimide containing a unit (b).
[2] The ratio L / S between the length L of the long axis formed between the pair of short sides and the length S of the short axis formed between the pair of long sides is 5-15. The insulated wire according to [1].
[3] The polyimide comprises 40 to 80 mol% of 3,3 ′, 4,4′-biphenyltetracarboxylic anhydride units and 3,3 ′, 4,4′-benzophenonetetracarboxylic anhydride units 10 to 10. 20 mol%, a tetracarboxylic acid component unit (a1) containing 10-50 mol% pyromellitic anhydride units, and a diamine component unit (b1) containing 4,4′-diaminodiphenyl ether component units, The insulated wire according to [1] or [2].
[4] The polyimide comprises 3,3 ′, 4,4′-biphenyltetracarboxylic anhydride units 40-60 mol% and 3,3 ′, 4,4′-benzophenonetetracarboxylic anhydride units 10-10. A tetracarboxylic acid component unit (a2) composed of 20 mol% and pyromellitic anhydride units 25 to 50 mol%, and a diamine component unit (b1) containing a 4,4′-diaminodiphenyl ether component unit, The insulated wire according to any one of [1] to [3].
[5] The content ratio of the 3,3 ′, 4,4′-benzophenonetetracarboxylic anhydride unit to the 3,3 ′, 4,4′-biphenyltetracarboxylic anhydride unit is 26 mol% or more. The insulated wire according to [4].
[6] The insulated wire according to [2], wherein the ratio L / S is 8 to 10.
[7] The conductor has a cross-sectional shape having a pair of long sides facing each other and a pair of short sides facing each other and curved outwardly, and the cross-section of the conductor The length l of the long axis formed between the pair of short sides is 0.10 to 2.00 mm, and the length s of the short axis formed between the pair of short sides is 0.015 to 0.005. The insulated wire according to any one of [1] to [6], which is 50 mm.
[8] A method for producing an insulated wire according to any one of [1] to [7], comprising a conductor, 40-80 mol% of biphenyltetracarboxylic anhydride units provided on the outer periphery thereof, and benzophenone Insulation comprising a polyimide containing a tetracarboxylic acid component unit (a) containing 10 to 20 mol% of tetracarboxylic acid anhydride units and 10 to 50 mol% of pyromellitic anhydride units and a diamine component unit (b) The manufacturing method of an insulated wire including the process of obtaining the covering conductor which has a layer, and the process of rolling the said covering conductor.
[9] The method for manufacturing an insulated wire according to [8], further including a step of forming a self-bonding layer including a resin having a softening temperature of 280 ° C. or less on the outer periphery of the rolled coated conductor.

  ADVANTAGE OF THE INVENTION According to this invention, the insulated wire which the crack of an insulating film is suppressed, and has high heat resistance, and the favorable adhesiveness and in-layer adhesiveness with a conductor can be provided.

Sectional drawing which shows an example of a structure of the insulated wire of this invention

1. Insulated wire The insulated wire of the present invention includes a conductor, an insulating layer covering the outer periphery thereof, and a self-bonding layer covering the outer periphery thereof.

  FIG. 1 is a cross-sectional view showing an example of the configuration of an insulated wire. As shown in FIG. 1, the insulated wire 10 includes a conductor 11, an insulating layer 13 covering the outer periphery thereof, and a self-fusion layer 15 covering the outer periphery thereof.

  The insulated wire 10 has a substantially rectangular cross-sectional shape in which a pair of opposing short sides project in an arc shape; that is, “a pair of long sides facing each other” and “a pair facing each other, convex toward each other” It is preferable to have a cross-sectional shape having a “short side curved in the direction” (see FIG. 1). The long side portion is also called a flat portion, and the short side portion is also called a side portion.

  The ratio L / S (aspect ratio) between the length L of the long axis formed between the pair of short sides and the length S of the short axis formed between the pair of long sides in the cross section of the insulated wire 10 is: It is preferable that it is 5-15. When the ratio L / S is 5 or more, the thickness of the insulating layer 13 in the short side portion (side portion) can be sufficiently increased when rolled in one direction (direction orthogonal to the long side). The insulating property of the insulating layer 13 in the part (side part) is not easily impaired. When the ratio L / S is 15 or less, the thickness of the insulating layer 13 of the long side portion (flat portion) of the insulated wire 10 does not become too thin when rolled in one direction (direction orthogonal to the long side). Therefore, the long side portion (flat portion) is not easily cracked during rolling. Thereby, the insulation between the fused insulated wires can be sufficiently maintained, and conduction can be highly suppressed. The length L of the long axis formed between the pair of short sides corresponds to the maximum value of the distance between the pair of long sides. The length S of the short axis formed between the pair of long sides corresponds to the distance between the pair of short sides. The major axis and the minor axis are preferably orthogonal to each other. The ratio L / S is more preferably 5 to 15, and still more preferably 8 to 10. The length L of the major axis is preferably, for example, 0.10 to 2.00 mm, and more preferably 0.20 to 1.70 mm. The length S of the minor axis is preferably 0.015 to 0.50 mm, for example, and more preferably 0.02 to 0.20 mm.

  In order to obtain sufficient insulation, it is preferable that the thickness of the insulating layer 13 in the short side portion (side portion) is larger than the thickness of the insulating layer 13 in the long side portion (flat portion). Thereby, for example, even if the insulated wire 10 is wound in a coil shape and exposed to a severe use environment such as a high temperature, the short side portion (side portion) of the insulating layer 13 where the self-bonding layer is exposed ) Can be prevented from thermal degradation.

  Hereinafter, each layer which comprises the insulated wire 10 is demonstrated.

1-1. Conductor 11
The material of the conductor 11 may be copper, copper alloy, aluminum, iron, silver, or an alloy thereof, but is preferably copper or copper alloy from the viewpoint of mechanical strength, conductivity, and the like.

  The conductor 11 is a rolled conductor. Accordingly, the conductor 11 has a cross section having “a pair of long sides facing each other” and “a short side facing each other and curved outwardly,” similarly to the cross-sectional shape of the insulated wire 10 described above. It may have a shape (see FIG. 1).

  In the cross section of the conductor 11, the length l of the long axis formed between the pair of short sides is preferably 0.10 to 2.00 mm, and more preferably 0.20 to 1.70 mm. The length s of the short axis formed between the pair of long sides is preferably 0.015 to 0.50 mm, and more preferably 0.02 to 0.20 mm.

1-2. Insulating layer 13
The insulating layer 13 has a function of imparting heat resistance and insulation to the insulated wire 11. The insulating layer 13 includes polyimide.

  The polyimide has a tetracarboxylic acid component unit (a) and a diamine component unit (b).

  The tetracarboxylic acid component unit (a) constituting the polyimide includes a biphenyltetracarboxylic anhydride (BPDA) unit, a benzophenonetetracarboxylic anhydride (BTDA) unit, and a pyromellitic anhydride (PMDA) unit. It is preferable. Specifically, the tetracarboxylic acid component unit (a) is composed of 40 to 80 mol% biphenyltetracarboxylic anhydride (BPDA) unit, 10 to 20 mol% benzophenonetetracarboxylic anhydride (BTDA) unit, Preferably, it contains 10 to 50 mol% merit anhydride (PMDA) units; 40 to 60 mol% biphenyltetracarboxylic anhydride (BPDA) units and 10 to 20 benzophenonetetracarboxylic anhydride (BTDA) units. More preferably, it contains mol% and pyromellitic anhydride (BPDA) units of 25 to 50 mol%. However, the total (total number of moles) of tetracarboxylic acid component units is 100 mol%.

  Examples of biphenyltetracarboxylic anhydrides include 3,3 ′, 4,4′-biphenyltetracarboxylic anhydride, 2,2 ′, 3,3′-biphenyltetracarboxylic anhydride, 2,3,3 ', 4'-biphenyltetracarboxylic anhydride is included, and 3,3', 4,4'-biphenyltetracarboxylic anhydride is preferable.

  Examples of the benzophenone tetracarboxylic acid anhydride include 3,3 ′, 4,4′-benzophenone tetracarboxylic acid anhydride, 2,2 ′, 3,3′-benzophenone tetracarboxylic acid anhydride, and the like. Is 3,3 ′, 4,4′-benzophenonetetracarboxylic anhydride.

  Biphenyltetracarboxylic anhydride (BPDA) units tend to increase the oil resistance of polyimide. A benzophenone tetracarboxylic anhydride (BTDA) unit tends to improve the flexibility and fusing property of polyimide. The pyromellitic anhydride (PMDA) unit tends to increase the heat resistance of the polyimide.

  In order to increase the heat resistance of the insulating layer 13, it is preferable to increase the number of pyromellitic anhydride (PMDA) units contained in the polyimide. On the other hand, if the pyromellitic anhydride (PMDA) unit is excessively increased, the flexibility of the polyimide is likely to be impaired, and adhesion with the conductor 11 and in-layer peeling are likely to occur. Therefore, it is preferable to adjust the content ratio of the benzophenone tetracarboxylic anhydride (BTDA) unit capable of imparting flexibility and the biphenyltetracarboxylic anhydride (BPDA) unit capable of imparting appropriate heat resistance and flexibility. .

  That is, the content ratio (BTDA / BPDA) of the benzophenone tetracarboxylic anhydride (BTDA) unit to the biphenyltetracarboxylic anhydride (BPDA) unit is preferably 12.5 to 50 mol%, and 17 to 50 It is more preferable that it is mol%, and it is further more preferable that it is 26-35 mol%. The higher the content ratio (BTDA / BPDA), the less likely the flexibility and adhesion are impaired even if more pyromellitic anhydride (PMDA) units are included.

  The tetracarboxylic acid component unit (a) may further contain other aromatic tetracarboxylic acid units or aliphatic tetracarboxylic acid units as necessary.

  Examples of other aromatic tetracarboxylic acids include oxydiphthalic acid, 3-fluoropyromellitic anhydride, 3,6-difluoropyromellitic anhydride, 3,6-bis (trifluoromethyl) pyromellitic anhydride 1,2,3,4-benzenetetracarboxylic anhydride, 3oxy-4,4′-diphthalic anhydride, 2,2′-difluoro-3,3 ′, 4,4′-biphenyltetracarboxylic acid Anhydride, 5,5'-difluoro-3,3 ', 4,4'-biphenyltetracarboxylic anhydride, 6,6'-difluoro-3,3', 4,4'-biphenyltetracarboxylic anhydride 2,2 ′, 5,5 ′, 6,6′-hexafluoro-3,3 ′, 4,4′-biphenyltetracarboxylic anhydride, 2,2′-bis (trifluoromethyl) -3, 3 ', 4,4'-biphenyltetracarboxylic anhydride, 5,5'-bis (trifluoromethyl) -3,3', 4,4'-biphenyltetracarboxylic acid Acid anhydrides, 6,6′-bis (trifluoromethyl) -3,3 ′, 4,4′-biphenyltetracarboxylic acid anhydride and the like are included.

  Examples of aliphatic tetracarboxylic acids include ethane-1,1,2,2-tetracarboxylic dianhydride, cyclopentanetetracarboxylic anhydride, cyclohexane-1,2,3,4-tetracarboxylic anhydride Cyclohexane-1,2,4,5-tetracarboxylic anhydride, 3,3 ′, 4,4′-bicyclohexyltetracarboxylic anhydride, and the like.

  The diamine component unit (b) constituting the polyimide includes an aromatic diamine unit or an aliphatic diamine unit.

  The aromatic diamine unit is preferably an aromatic diamine unit having 6 to 30 carbon atoms. Examples of aromatic diamines include m-phenylenediamine, p-phenylenediamine, 2,4-diaminotoluene, 4,4′-diamino-3,3′-dimethyl-1,1′-biphenyl, 4,4 ′. -Diamino-3,3'-dihydroxy-1,1'-biphenyl, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl ether, 3,3'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl sulfone 4,4′-diaminodiphenyl sulfide, 2,2-bis (4-aminophenyl) propane, 2,2-bis (4-aminophenyl) hexafluoropropane, 1,3-bis (4-aminophenoxy) benzene 1,4-bis (4-aminophenoxy) benzene, 4,4′-bis (4-aminophenoxy) biphenyl, 2, -Bis [4- (4-aminophenoxy) phenyl] propane, 2,2-bis [4- (4-aminophenoxy) phenyl] hexafluoropropane, bis [4- (3-aminophenoxy) phenyl] sulfone, bis [4- (4-aminophenoxy) phenyl] sulfone and the like are included.

  The aliphatic diamine unit is preferably an aliphatic diamine unit having 4 to 20 carbon atoms. Examples of aliphatic diamines include 1,6-hexanediamine, 1,7-heptanediamine, 1,8-octanediamine, 1,9-nonanediamine, 1,10-decanediamine, 1,11-undecanediamine, , 12-dodecanediamine, 2-methyl-1,5-pentanediamine, 3-methyl-1,5-pentanediamine, 2,2,4-trimethyl-1,6-hexanediamine, 2,4,4-trimethyl -1,6-hexanediamine, 2-methyl-1,8-octanediamine, 5-methyl-1,9-nonanediamine and the like are included.

  Among them, an aromatic diamine unit is preferable because the heat resistance of polyimide can be improved, and a 4,4′-diaminodiphenyl ether unit is preferable because it has appropriate flexibility.

  The diamine component unit (b) preferably contains 80 mol% or more, preferably 90 mol% or more, more preferably 100 mol% of 4,4′-diaminodiphenyl ether unit. However, the total (total number of moles) of the diamine component unit (b) is 100 mol%.

The polyimide is composed of 40 to 80 mol% 3,3 ', 4,4'-biphenyltetracarboxylic anhydride units, 10 to 20 mol% 3,3', 4,4'-benzophenonetetracarboxylic anhydride units, It preferably contains a tetracarboxylic acid component unit (a1) containing 10 to 50 mol% of pyromellitic anhydride units and a diamine component unit (b1) containing 4,4′-diaminodiphenyl ether component units;
3,3 ′, 4,4′-biphenyltetracarboxylic anhydride units 40-60 mol%, 3,3 ′, 4,4′-benzophenone tetracarboxylic anhydride units 10-20 mol%, More preferably, it contains a tetracarboxylic acid component unit (a2) composed of 25 to 50 mol% of an acid anhydride unit and a diamine component unit (b1) containing a 4,4′-diaminodiphenyl ether component unit.

  The intrinsic viscosity of the polyimide is preferably 1 to 20 dl / g. When the intrinsic viscosity of polyimide is 20 dl / g or less, the viscosity of the polyimide varnish is appropriate, so that it is easy to form a uniform film thickness when applied to the outer periphery of the conductor 11.

The intrinsic viscosity of polyimide can be measured by the following procedure. A polyimide is dissolved in concentrated sulfuric acid to obtain a sample solution. The flow down time of the obtained sample solution is measured under the condition of 25 ° C. ± 0.05 ° C. using an Ubbelohde viscometer, and is applied to the following formula to calculate the intrinsic viscosity [η].
[Η] = ηSP / [C (1 + kηSP)]
[Η]: Intrinsic viscosity (dl / g)
ηSP: specific viscosity C: sample concentration (g / dl)
t: Number of seconds that the sample solution flows (seconds)
t0: The number of seconds during which the solvent flows (seconds)
k: Constant (slope obtained by measuring the specific viscosity of samples having different solution concentrations (three or more points), plotting the solution concentration on the horizontal axis, and ηsp / C on the vertical axis)
ηSP = (t−t0) / t0

The present inventors made a plurality of insulated wires using polyimides having different softening temperatures while changing the temperature (wire temperature) during baking, and compared the presence or absence of delamination within the insulating layer. As a result, the relationship shown in Table 1 below was found.

  As shown in Table 1, when the softening temperature of polyimide is low, in-layer adhesion is easily obtained, but heat resistance is low. On the other hand, when the softening temperature of polyimide is high, the heat resistance is good, but the in-layer adhesion is difficult to obtain unless the linear temperature is increased. Increasing the wire temperature leads to a decrease in productivity. Accordingly, since both good heat resistance and in-layer adhesion can be achieved without increasing the linear temperature, the softening temperature of polyimide is preferably 350 to 500 ° C, more preferably 400 to 500 ° C. preferable.

  When the softening temperature of the polyimide is 350 ° C., preferably 400 ° C. or higher, the heat resistance is not easily impaired. When the softening temperature of the polyimide is 500 ° C. or lower, it is not necessary to excessively increase the linear temperature during baking, and thus productivity is unlikely to decrease. The softening temperature of polyimide can be measured according to JIS C32166-6.

  The polyimide content is preferably 50% by mass or more based on the total mass of the insulating layer 13. When the content of the polyimide is 50% by mass or more, sufficient heat resistance and insulating properties are easily obtained. The content of the polyimide is preferably 80% by mass or more, and more preferably 90% by mass or more with respect to the total mass of the insulating layer 13.

  The insulating layer 13 may further include other components as necessary. Examples of other components include an adhesion improver.

  The thickness of the long side portion (flat portion) of the insulating layer 13 is preferably 50 to 90% with respect to the total thickness of the long side portion (flat portion) of the insulating layer 13 and the self-bonding layer 15. When the thickness ratio of the insulating layer 13 is 50% or more, the heat resistance of the insulated wire 10 can be sufficiently increased. When the thickness ratio of the insulating layer 13 is 90% or less, an increase in the volume of the insulated wire 10 can be suppressed without impairing the fusibility. The thickness of the insulating layer 13 is more preferably 60 to 70% with respect to the total thickness of the insulating layer 13 and the self-bonding layer 15. The thickness of the insulating layer 13 can be set to, for example, 2.00 to 10.00 μm. The thickness of the insulating layer 13 is calculated from the average value of the thicknesses of the flat portions of the insulating layer 13 when the cross section of the insulated wire 10 is observed with a microscope.

  The insulating layer 13 is made of polyimide having pyromellitic anhydride (PMDA) units, benzophenonetetracarboxylic anhydride (BTDA) units, and biphenyltetracarboxylic anhydride (BPDA) units in a predetermined ratio as tetracarboxylic acid components. Since it contains, it has high heat resistance and a softness | flexibility (or adhesiveness). Therefore, even if the insulated wire is rolled at a high magnification, cracking of the insulating layer 13 (particularly, the long side portion (flat portion)), adhesion to the conductor 11, and delamination in the layer are highly suppressed. ing. Furthermore, since the insulated wire also has high heat resistance, even if it is exposed to a high temperature when it is incorporated in a product such as a coil, the insulation is not easily impaired.

1-3. Self-bonding layer 15
The self-bonding layer 15 is provided on the outermost surface of the insulated wire 10 and has a function of thermally fusing the plurality of insulated wires 10 together. Therefore, the self-bonding layer 15 preferably contains a resin having a softening temperature of 280 ° C. or lower, preferably 200 ° C. or lower. The softening temperature of the resin can be measured according to JIS C32166-6, as described above.

  Examples of such resins include polyvinyl acetal (eg, polyvinyl formal, polyvinyl butyral, etc.), polyurethane, phenoxy resin (eg, bisphenol A type phenoxy resin, bisphenol S type phenoxy resin), polyamide (eg, nylon 6, nylon 66, etc.) Aliphatic polyamide), polyamideimide, polyetherimide, polyester, polysulfone and the like. Among these, polyamide is preferable and aliphatic polyamide is more preferable because it can be fused at a low temperature without impairing heat resistance.

  The self-bonding layer 15 may further include other components as necessary. Examples of other components include an antioxidant and a lubricant.

  The antioxidant may have a function of preventing thermal deterioration of the thermoplastic resin contained in the self-bonding layer 15. Examples of the antioxidant include phenol-based antioxidants, sulfur-based antioxidants, phosphorus-based antioxidants, amine-based antioxidants, and the like.

  Examples of the lubricant include synthetic lubricants such as polyethylene wax, silicone resin and fluororesin, and natural lubricants such as beeswax, carnauba wax and candelilla wax.

  The thickness of the long side portion (flat portion) of the self-bonding layer 15 is preferably 10 to 50% with respect to the total thickness of the long side portion (flat portion) of the insulating layer 13 and the self-bonding layer 15. . When the thickness ratio of the self-bonding layer 15 is 10% or more, sufficient fusing property is easily obtained. When the thickness ratio of the self-bonding layer 15 is 50% or less, an increase in the volume of the insulated wire 10 can be suppressed without impairing the insulating properties. The thickness of the self-bonding layer 15 is more preferably 30 to 40% with respect to the thickness of the entire layer covering the conductor 11. The thickness of the self-bonding layer 15 can be set to, for example, 1.0 to 10.0 μm.

  The insulated wire 10 of the present invention may further include other layers as necessary.

  The insulated wire 10 of the present invention can be preferably used as a winding of an electric coil that requires heat resistance, such as industrial and automobile motors and generators.

2. Method for Producing Insulated Wire The method for producing an insulated wire of the present invention includes at least 1) a step of obtaining a coated conductor in which the outer periphery of the conductor is covered with the above-described insulating layer containing polyimide, and 2) a step of rolling the coated conductor, including. If necessary, 3) a step of further forming a self-bonding layer on the outer periphery of the rolled coated conductor may be further performed.

Step 1) An insulating layer containing the aforementioned polyimide is formed on the outer periphery of the conductor to obtain a coated conductor.

  The insulating layer can be formed by baking after applying a polyimide precursor varnish or a polyimide varnish to the outer periphery of a conductor as a raw material. The conductor as the raw material may be a round conductor or a flat conductor.

  The application of the polyimide precursor varnish or the polyimide varnish can be performed by, for example, a coating method, a dipping method, or an electrodeposition method.

  After applying the polyimide precursor varnish or the polyimide varnish, the baking operation may be performed only once or a plurality of times. When the above operation is performed a plurality of times, adhesion failure may occur between the (n-1) th coating layer and the nth coating layer. However, such poor adhesion can be satisfactorily suppressed by using the aforementioned polyimide.

  The baking temperature may be at least a temperature at which the solvent in the varnish can be removed (when the polyimide precursor varnish is used, the temperature at which the polyimide precursor can be cured), for example, 200 to 500 ° C., preferably 300 to 400 ° C. .

  The polyimide precursor varnish or polyimide varnish is obtained by dissolving a polyimide precursor or polyimide in a solvent. These varnishes can be obtained by reacting the aforementioned tetracarboxylic acid component (a) with the diamine component (b) in a solvent. Examples of the solvent used include aprotic polar solvents such as 2-pyrrolidone, N-methyl-2-pyrrolidone (NMP) and N, N-dimethylacetamide, and phenolic solvents such as phenol, cresol and xylenol. It is.

  In this step, a self-bonding layer may be further formed on the insulating layer, or a self-bonding layer may be further formed after the step 2) (the above-mentioned step 3)).

  The self-bonding layer can be formed by baking after applying the composition for self-bonding layer, as described above. The composition for self-bonding layers may contain the above-mentioned thermoplastic resin and a solvent. The solvent is the same as the solvent contained in the polyimide precursor varnish or the polyimide varnish.

About the process of 2) The obtained coated conductor is rolled so that the cross-sectional shape of the insulated wire obtained may become a predetermined shape. Specifically, in the rolling of the coated conductor, the insulated wire 10 to be obtained has a cross-sectional shape as shown in FIG. 1, and the major axis length L and the minor axis length S of the cross section of the insulated wire 10 are obtained. The ratio L / S is preferably 1.5 to 15, preferably 5 to 15, more preferably 8 to 10.

  The coated conductor to be rolled includes an insulating layer containing the aforementioned polyimide. The insulating layer containing polyimide described above has good heat resistance and flexibility (or adhesion). Therefore, the crack (especially the crack of a long side part (flat part)) of the insulating layer at the time of rolling can be suppressed.

Step 3) When the self-bonding layer is not formed in the step 1), a self-bonding layer may be further formed on the outer periphery of the coated conductor rolled in the step 2).

  In the following, the invention will be described in more detail with reference to examples. These examples do not limit the scope of the present invention.

1. Preparation of polyimide varnish (Preparation Example 1)
In a flask equipped with a stirrer, a nitrogen inflow tube and a heating / cooling device, 3,7 ′, 4,4′-biphenyltetracarboxylic dianhydride (BPDA) 0.47 mol, 3,3 ′ as a tetracarboxylic acid component. , 4,4'-benzophenonetetracarboxylic dianhydride (BTDA) 0.15 mol, pyromellitic anhydride (PMDA) 0.33 mol, 4,4'-diaminodiphenyl ether (DDE) 1.02 as the diamine component Mole was charged. As a solvent, 400 parts by mass of N-methyl-2-pyrrolidone was added to 100 parts by mass of the total of the tetracarboxylic acid component and the diamine component, and reacted for 2 hours while stirring in a nitrogen atmosphere. Thereby, a polyimide varnish (C-1) having a resin content of 20% by mass was obtained.

(Preparation Example 2)
In a flask equipped with a stirrer, a nitrogen inflow pipe and a heating / cooling device, 1.00 mol of pyromellitic anhydride (PMDA) as a tetracarboxylic acid component and 1.02 mol of 4,4′-diaminodiphenyl ether (DDE) as a diamine component Was introduced. As a solvent, 400 parts by mass of N-methyl-2-pyrrolidone was added to 100 parts by mass of the total of the tetracarboxylic acid component and the diamine component, and reacted for 2 hours while stirring in a nitrogen atmosphere. Thereby, a polyimide varnish (C-2) having a resin content of 20% by mass was obtained.

(Adjustment Example 3)
In a flask equipped with a stirrer, a nitrogen inflow pipe and a heating / cooling device, 0.59 mol of 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride (BPDA) as a tetracarboxylic acid component, 3,3 ′ , 4,4'-benzophenonetetracarboxylic dianhydride (BTDA) 0.16 mol and pyromellitic anhydride (PMDA) 0.25 mol, 4,4'-diaminodiphenyl ether (DDE) 1.02 as the diamine component Mole was charged. As a solvent, 400 parts by mass of N-methyl-2-pyrrolidone was added to 100 parts by mass of the total of the tetracarboxylic acid component and the diamine component, and reacted for 2 hours while stirring in a nitrogen atmosphere. Thereby, a polyimide varnish (C-3) having a resin content of 20% by mass was obtained.

(Adjustment example 4)
In a flask equipped with a stirrer, a nitrogen inflow pipe and a heating / cooling device, 0.70 mol of 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride (BPDA) as a tetracarboxylic acid component, 3,3 ′ , 4,4'-benzophenonetetracarboxylic dianhydride (BTDA) 0.10 mol, pyromellitic anhydride (PMDA) 0.20 mol, 4,4'-diaminodiphenyl ether (DDE) 1.02 as the diamine component Mole was charged. As a solvent, 400 parts by mass of N-methyl-2-pyrrolidone was added to 100 parts by mass of the total of the tetracarboxylic acid component and the diamine component, and reacted for 2 hours while stirring in a nitrogen atmosphere. Thereby, a polyimide varnish (C-4) having a resin content of 20% by mass was obtained.

Table 2 shows the monomer compositions of the polyimides prepared in Preparation Examples 1 to 4.

2. Production and evaluation of insulated wires (Example 1)
After applying the polyimide varnish (C-1) prepared in Preparation Example 1 around a round copper conductor having a diameter of 0.25 mm, an insulating layer made of polyimide having a thickness of 4.5 μm is baked at a predetermined temperature. Obtained. The obtained round conductor was rolled only in one direction.
On this rolled polyimide layer of the coated conductor, TCV V1-14 modified B (manufactured by Tohoku Paint Co., Ltd., aliphatic polyamide) was further applied and dried to form a self-bonding layer having a thickness of 3.0 μm. The insulated wire 1 was obtained.
The length L of the major axis of the cross section of the insulated wire is 1.2 mm, the length S of the minor axis is 0.20 mm, and the ratio of the length L of the major axis to the length S of the minor axis L / S was 6.
In the same way as described above, the cross section of the conducting wire constituting the insulated wire also had a major axis length l of 1141 μm and a minor axis length s of 192.7 μm.

(Examples 2-3)
Insulated wires 2 to 3 were obtained in the same manner as in Example 1 except that the rolling conditions were changed so that the ratio L / S of the cross section of the obtained insulated wires was a value shown in Table 3.

(Examples 4 to 5)
Insulated wires 4 to 5 were obtained in the same manner as in Example 1 except that the type of polyimide varnish was changed as shown in Table 3.

(Comparative Examples 1-3)
Insulated wires 6 to 8 were obtained in the same manner as in Example 1 except that the ratio L / S of the cross section of the polyimide varnish and the insulated wire was changed as shown in Table 4.

  The softening temperature of the obtained insulating layer of the coated conductor and the self-bonding layer of the insulated wire was measured according to JIS C3216-6 (circular crossing method).

(Softening temperature)
The coated conductor was cut 30 cm each to obtain two test pieces. The two test pieces were each made into a ring and crossed, the weight was hung, and placed in a thermostatic bath. Then, an AC voltage of 100 V was applied to the test piece, the temperature was increased at a rate of 2 ° C. per minute, and the temperature at which the short circuit occurred was measured with a thermocouple fixed to the part closest to the test piece, and the softening temperature of the insulating layer It was. The short circuit current was 5 to 20 mA.
The same measurement was performed on the insulated wire, and the softening temperature of the self-bonding layer was measured.

  Furthermore, the following methods evaluated the presence or absence of the crack of the insulating layer of a covering conductor, and the peeling in a layer.

(crack)
On the cut surface of the coated conductor after rolling, the presence or absence of cracks in the long side portion (flat portion) of the insulating layer (cracks entered in a direction substantially perpendicular to the conductor) was observed with an SEM. And based on the following criteria, the crack was evaluated.
◎: No cracks ○: Slight cracks are observed, but there is no substantial problem ×: Many cracks are observed, which is a substantial problem ◎ and ○ are insulated because there are few cracks Means good fracture characteristics.

(In-layer peeling)
On the cut surface of the coated conductor, the presence or absence of in-layer peeling (gap) of the insulating layer was observed with an SEM. And it evaluated on the following references | standards.
A: There is no delamination in the layer. O: There is a slight delamination within the layer, but there is no substantial problem.

The overall evaluation of the softening temperature (heat resistance), cracking, and delamination of the insulating layer was performed based on the following criteria.
A: All of softening temperature, cracks, and delamination
B: One of softening temperature, crack, and delamination is ○, the rest is ◎
C: Two or more of softening temperature, cracking, and delamination are ○
D: One or more of softening temperature, cracking, and delamination in the layer
The softening temperature (heat resistance) was evaluated as ４００ when 400 ° C or higher, ◯ when 350 ° C or higher and lower than 400 ° C, and x when lower than 350 ° C.

Table 3 shows the evaluation results of Examples 1 to 5, and Table 4 shows the evaluation results of Comparative Examples 1 to 3.

  As shown in Table 3, in the coated conductors of Examples 1 to 5, there was no crack in the insulating layer, and no delamination was observed. In particular, the coated conductor of Example 4 using polyimide C-3 having a BTDA / BPDA ratio of 27 mol% is the coated conductor of Example 5 using polyimide C-4 having a BTDA / BPDA ratio of 15 mol%. It can be seen that cracking during rolling can be reduced without lowering the softening temperature. This is presumably because the polyimide C-3 insulating layer is more flexible and tougher than the polyimide C-4 insulating layer.

  On the other hand, the coated conductors of Comparative Examples 1 to 3 show that although the heat resistance of the insulating layer is high, delamination occurs, and the rectangular wires cannot be fused when coiled.

  INDUSTRIAL APPLICABILITY The present invention can provide an insulated wire in which cracking of an insulating layer is suppressed, and has high heat resistance, good adhesion to a conductor, and in-layer adhesion.

10 Insulated wire 11 Conductor 13 Insulating layer 15 Self-bonding layer

Claims (3)

An insulated wire having a conductor, an insulating layer provided on an outer periphery thereof, and a self-bonding layer provided on the insulating layer and including a resin having a softening temperature of 280 ° C. or less,
The insulated wire has a cross-sectional shape having a pair of long sides facing each other and a pair of short sides facing each other and curved outwardly,
The insulating layer includes tetracarboxylic acid containing 40 to 80 mol% biphenyltetracarboxylic anhydride units, 10 to 20 mol% benzophenonetetracarboxylic anhydride units, and 10 to 50 mol% pyromellitic anhydride units. It is a manufacturing method of the insulated wire containing the polyimide containing a component unit (a) and a diamine component unit (b),
Conductor, provided on the outer periphery thereof, 40-80 mol% biphenyltetracarboxylic anhydride units, 10-20 mol% benzophenonetetracarboxylic anhydride units, 10-50 mol% pyromellitic anhydride units, Obtaining a coated conductor having a tetracarboxylic acid component unit containing (a) and an insulating layer containing polyimide containing a diamine component unit (b);
A method for producing an insulated wire, comprising a step of rolling the coated conductor.   The manufacturing method of the insulated wire of Claim 1 which further includes the process of forming the self-fusion layer containing resin with a softening temperature of 280 degrees C or less on the outer periphery of the rolled said covered conductor.   The ratio L / S between the length L of the long axis formed between the pair of short sides and the length S of the short axis formed between the pair of long sides is 5 to 15. Item 3. A method for producing an insulated wire according to Item 1 or 2.

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